Detection of organic vapors on sputtered and annealed thin Au films

NASA Astrophysics Data System (ADS)

Kvitek, O.; Kopacek, V.; Reznickova, A.; Svorcik, V.

2018-03-01

Unique optical properties of metal nanostructures enable construction of new types of chemical sensors. Nanostructures composed of Au on glass substrate were prepared by annealing of 2-20 nm thick sputtered Au films at 300 °C for 1 h. The annealing leads to transformation of the as sputtered continuous Au layers to a nanoisland structure. The forming nanostructure shows a strong, well defined surface plasmon resonance absorption band in UV-Vis spectrum, which is useful for construction of a chemical sensor. The samples were used to detect vapors of acetone and water in an experimental testing apparatus. The achieved signal-to-noise ratio was 583 and 386 for acetone and water vapors, respectively on the nanostructure prepared from 4 nm thick Au layer. The nanostructured sensitive layers, however, showed poor signal stability; therefore a polymer overlayer was introduced to protect it. The employed polystyrene film prepared by spin-coating improved sensitivity and selectivity of the sensor, while the dynamic properties of the sensing influenced only slightly.

Structure determination of a multilayer with an island-like overlayer using hard x-ray photoelectron spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Isomura, N., E-mail: isomura@mosk.tytlabs.co.jp; Kataoka, K.; Horibuchi, K.

We use hard X-ray photoelectron spectroscopy (HAXPES) to obtain the surface structure of a multilayer Au/SiO{sub 2}/Si substrate sample with an island-like overlayer. Photoelectron intensities are measured as a function of incident photon energy (PE) and take-off angle (TOA, measured from the sample surface). The Au layer coverage and Au and SiO{sub 2} layer thicknesses are obtained by the PE dependence, and are used for the following TOA analysis. The Au island lateral width in the cross section is obtained by the TOA dependence, including information about surface roughness, in consideration of the island shadowing at small TOAs. In bothmore » cases, curve-fitting analysis is conducted. The surface structure, which consists of layer thicknesses, overlayer coverage and island width, is determined nondestructively by a combination of PE and TOA dependent HAXPES measurements.« less

Simulation and Modeling of Self-Assembled Monolayers of Carboxylic Acid Thiols on Flat and Nanoparticle Gold Surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Techane, Sirnegeda D.; Baer, Donald R.; Castner, David G.

2011-09-01

Quantitative analysis of the 16-mercaptohexadecanoic acid self-assembled monolayer (C16 COOH-SAM) layer thickness on gold nanoparticles (AuNPs) was performed using simulation of electron spectra for surface analysis (SESSA) and x-ray photoelectron spectroscopy (XPS). XPS measurements of C16 COOH SAMs on flat gold surfaces were made at 9 different photoelectron take-off angles (5o to 85o in 5o increments), corrected using geometric weighting factors and then summed together to approximate spherical AuNPs. The SAM thickness and relative surface roughness (RSA) in SESSA were optimized to determine the best agreement between simulated and experimental surface composition. Based on the glancing angle results, it wasmore » found that inclusion of a hydrocarbon contamination layer on top the C16 COOH-SAM was necessary to improve the agreement between the SESSA and XPS results. For the 16 COOH-SAMs on flat Au surfaces, using a SAM thickness of 1.1Å/CH2 group, an RSA of 1.05 and a 1.5Å CH2-contamination overlayer (total film thickness = 21.5Å) for the SESSA calculations provided the best agreement with the experimental XPS data. After applying the appropriate geometric corrections and summing the SESSA flat surface compositions, the best fit results for the 16 COOH-SAM thickness and surface roughness on the AuNPs were determined to be 0.9Å/CH2 group and 1.06 RSA with a 1.5Å CH2-contamination overlayer (total film thickness = 18.5Å). The three angstrom difference in SAM thickness between the flat Au and AuNP surfaces suggests the alkyl chains of the SAM are slightly more tilted or disordered on the AuNP surfaces.« less

Color-tunable mixed photoluminescence emission from Alq3 organic layer in metal-Alq3-metal surface plasmon structure.

PubMed

Chen, Nai-Chuan; Liao, Chung-Chi; Chen, Cheng-Chang; Fan, Wan-Ting; Wu, Jin-Han; Li, Jung-Yu; Chen, Shih-Pu; Huang, Bohr-Ran; Lee, Li-Ling

2014-01-01

This work reports the color-tunable mixed photoluminescence (PL) emission from an Alq3 organic layer in an Au-Alq3-Au plasmonic structure through the combination of organic fluorescence emission and another form of emission that is enabled by the surface plasmons in the plasmonic structure. The emission wavelength of the latter depends on the Alq3 thickness and can be tuned within the Alq3 fluorescent spectra. Therefore, a two-color broadband, color-tunable mixed PL structure was obtained. Obvious changes in the Commission Internationale d'Eclairage (CIE) coordinates and the corresponding emission colors of Au-Alq3-Au samples clearly varied with the Alq3 thickness (90, 130, and 156 nm).

Color-tunable mixed photoluminescence emission from Alq3 organic layer in metal-Alq3-metal surface plasmon structure

PubMed Central

2014-01-01

This work reports the color-tunable mixed photoluminescence (PL) emission from an Alq3 organic layer in an Au-Alq3-Au plasmonic structure through the combination of organic fluorescence emission and another form of emission that is enabled by the surface plasmons in the plasmonic structure. The emission wavelength of the latter depends on the Alq3 thickness and can be tuned within the Alq3 fluorescent spectra. Therefore, a two-color broadband, color-tunable mixed PL structure was obtained. Obvious changes in the Commission Internationale d’Eclairage (CIE) coordinates and the corresponding emission colors of Au-Alq3-Au samples clearly varied with the Alq3 thickness (90, 130, and 156 nm). PMID:25328506

Interface effects in ultra-thin films: Magnetic and chemical properties

NASA Astrophysics Data System (ADS)

Park, Sungkyun

When the thickness of a magnetic layer is comparable to (or smaller than) the electron mean free path, the interface between magnetic and non-magnetic layers becomes very important factor to determine magnetic properties of the ultra-thin films. The quality of interface can enhance (or reduce) the desired properties. Several interesting physical phenomena were studied using these interface effects. The magnetic anisotropy of ultra-thin Co films is studied as function of non-magnetic underlayer thickness and non- magnetic overlayer materials using ex situ Brillouin light scattering (BLS). I observed that perpendicular magnetic anisotropy (PMA) increases with underlayer thickness and saturates after 5 ML. This saturation can be understood as a relaxation of the in-plane lattice parameter of Au(111) on top of Cu(111) to its bulk value. For the overlayer study, Cu, Al, and Au are used. An Au overlayer gives the largest PMA due to the largest in-plane lattice mismatch between Co and Au. An unusual effect was found by adding an additional layer on top of the Au overlayer. An additional Al capping layer on top of the Au overlayer reduces the PMA significantly. The possible explanation is that the misfit strain at the interface between the Al and the Au can be propagated through the Au layer to affect the magnetic properties of Co even though the in- plane lattice mismatch is less than 1%. Another interesting problem in interface interdiffusion and thermal stability in magnetic tunnel junction (MTJ) structures is studied using X-ray photoelectron spectroscopy (XPS). Since XPS is a very chemically sensitive technique, it allows us to monitor interface interdiffusion of the MTJ structures as-deposited and during post-deposition processing. For the plasma- oxidized samples, Fe only participates in the oxidation reduction process. In contrast to plasma-oxidized samples, there were no noticeable chemical shifts as- deposited and during post-deposition processing in air- oxidized samples. However, peak intensity variations were observed due to interface interdiffusion.

Photo-induced wettability of TiO{sub 2} film with Au buffer layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Purkayastha, Debarun Dhar; Sangani, L. D. Varma; Krishna, M. Ghanashyam

2014-04-24

The effect of thickness of Au buffer layer (15-25 nm) between TiO{sub 2} film and substrate on the wettability of TiO{sub 2} films is reported. TiO{sub 2} films grown on Au buffer layer have a higher contact angle of 96-;100° as compared to 47.6o for the film grown without buffer layer. The transition from hydrophobicity to hydrophilicity under UV irradiation occurs within 10 min. for the buffer layered films whereas it is almost 30 min. for the film grown without buffer layer. The enhanced photo induced hydrophilicity is shown to be surface energy driven.

Magnetic-plasmonic multilayered nanorods

NASA Astrophysics Data System (ADS)

Thumthan, Orathai

Multilayered nanorods which consist of alternating magnetic layers separated by Au layers combine two distinctive properties, magnetic properties and surface plasmonic resonance (SPR) properties into one nano-entity. Their magnetic properties are tunable by changing the layer thickness, varying from single domain to superparamagnetic state. Superparamagnetic is a key requirement for magnetic nanoparticles for bioapplications. Superparamagnetic nanoparticles exhibit high magnetic moments at low applied magnetic field while retain no magnetic moments when magnetic field is removed preventing them from aggregation due to magnetic attraction. Au layers in the nanorods provide anchorage sites for functional group attachment. Also, Au nanodisks exhibit SPR properties. The SPR peak can be tuned from 540 nm to 820 nm by controlling the thickness of magnetic segments while keeping Au thickness constant. In this research, there are three types of multilayered nanorod have been fabricated: Au/NiFe nanorods, Au/Fe nanorods, and Au/Co nanorods. These magnetic nanorods were fabricated by templated electrodeposition into the channels in Anodic Aluminum Oxide (AAO) membrane. The setup for AAO fabrication was developed as a part of this research. Our fabricated AAO membrane has channels with a diameter ranging from 40nm to 80 nm and a thickness of 10um to 12um. Magnetic properties of nanorods such as saturation field, saturation moment, coercivity and remanence are able to manipulate through their shape anisotropy. The magnetization will be easier in long axis rather than short axis of particle. In addition, Au nanodisks in the nanorod structure are not only serving as anchorage sites for functional groups but also provide SPR properties. Under irradiation of light Au nanodisks strongly absorb light at SPR frequency which ranging from 540 nm to 820 nm by controlling the thickness of magnetic segments while keeping Au thickness constant. The SPR tunability of nanorods in near-infrared region can be used in in-vivo biomedical applications such as photo thermal therapy because tissue has an absorption maximum in the infrared range. The magnetic nanorods were explored for the following two applications: 1) as active component orientation-tunable ferrogel for cell culture matrix, 2) as MRI contrast agent. The results show that Au/NiFe magnetic nanorods can be aligned along applied magnetic field. Using MTT assay for 3T3 fibroblast cells, the biocompatibility of Au/Co nanorods was investigated. It shows that cell proliferation after 72 hours of incubation with nanorods decreases as the concentration of nanorods increases. However, cell viability quantified by counting dead cell/live cell reveals that only few cells died after three days of incubation. Au/Co multilayered nanorods were tested as T2 MRI-contrast agent, and a very large relaxivity was observed. In summary, we have successfully fabricated multilayered nanorods with tunability in both magnetic and SPR properties. These nanorods can potentially be used in biological and biomedical fields.

Multi-technique characterization of gold electroplating on silver substrates for cultural heritage applications

NASA Astrophysics Data System (ADS)

Ortega-Feliu, I.; Ager, F. J.; Roldán, C.; Ferretti, M.; Juanes, D.; Scrivano, S.; Respaldiza, M. A.; Ferrazza, L.; Traver, I.; Grilli, M. L.

2017-09-01

This work presents a detailed study of a series of silver plates gilded via electroplating techniques in which the characteristics of the coating gold layers are investigated as a function of the electroplating variables (voltage, time, anode surface and temperature). Some reference samples were coated by radio frequency sputtering in order to compare gold layer homogeneity and effective density. Surface analysis was performed by means of atomic and nuclear techniques (SEM-EDX, EDXRF, PIXE and RBS) to obtain information about thickness, homogeneity, effective density, profile concentration of the gold layers and Au-Ag diffusion profiles. The gold layer thickness obtained by PIXE and EDXRF is consistent with the thickness obtained by means of RBS depth profiling. Electroplated gold mass thickness increases with electroplating time, anode area and voltage. However, electrodeposited samples present rough interfaces and gold layer effective densities lower than the nominal density of Au (19.3 g/cm3), whereas sputtering produces uniform layers with nominal density. These analyses provide valuable information to historians and curators and can help the restoration process of gold-plated silver objects.

Study of the Au-Cr bilayer system using X-ray reflectivity, GDOES, and ToF-SIMS

DOE PAGES

Jonnard, Philippe; Modi, Mohammed H.; Le Guen, Karine; ...

2018-04-17

Here, we study a Au (25 nm)/Cr (10 nm) bilayer system as a model of mirror for the soft X–ray energy range. The Au and Cr thin films are a few nanometer thick and are deposited on a float glass substrate. The sample is characterized by using 3 complementary techniques: soft X–ray reflectivity, glow discharge optical emission spectrometry (GDOES), and time–of–flight secondary ion mass spectroscopy (ToF–SIMS). Soft X–ray reflectivity provides information about the thickness and roughness of the different layers, while GDOES is used to obtain the elemental depth profile of the stack and ToF–SIMS to obtain the elemental andmore » chemical depth profiles. GDOES and ToF–SIMS have both a nanometer depth resolution. A coherent description of the bilayer stack is obtained through the combination of these techniques. It consists in 5 layers namely a surface contamination layer, a principal gold layer, a Au–Cr mixed layer, a Cr layer, and another contamination layer at the top of the substrate.« less

Study of the Au-Cr bilayer system using X-ray reflectivity, GDOES, and ToF-SIMS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jonnard, Philippe; Modi, Mohammed H.; Le Guen, Karine

Here, we study a Au (25 nm)/Cr (10 nm) bilayer system as a model of mirror for the soft X–ray energy range. The Au and Cr thin films are a few nanometer thick and are deposited on a float glass substrate. The sample is characterized by using 3 complementary techniques: soft X–ray reflectivity, glow discharge optical emission spectrometry (GDOES), and time–of–flight secondary ion mass spectroscopy (ToF–SIMS). Soft X–ray reflectivity provides information about the thickness and roughness of the different layers, while GDOES is used to obtain the elemental depth profile of the stack and ToF–SIMS to obtain the elemental andmore » chemical depth profiles. GDOES and ToF–SIMS have both a nanometer depth resolution. A coherent description of the bilayer stack is obtained through the combination of these techniques. It consists in 5 layers namely a surface contamination layer, a principal gold layer, a Au–Cr mixed layer, a Cr layer, and another contamination layer at the top of the substrate.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uribe, Fernando; Vianco, Paul Thomas; Zender, Gary L.

A study was performed that examined the microstructure and mechanical properties of 63Sn-37Pb (wt.%, Sn-Pb) solder joints made to thick film layers on low-temperature co-fired (LTCC) substrates. The thick film layers were combinations of the Dupont{trademark} 4596 (Au-Pt-Pd) conductor and Dupont{trademark} 5742 (Au) conductor, the latter having been deposited between the 4596 layer and LTCC substrate. Single (1x) and triple (3x) thicknesses of the 4596 layer were evaluated. Three footprint sizes were evaluated of the 5742 thick film. The solder joints exhibited excellent solderability of both the copper (Cu) lead and thick film surface. In all test sample configurations, themore » 5742 thick film prevented side wall cracking of the vias. The pull strengths were in the range of 3.4-4.0 lbs, which were only slightly lower than historical values for alumina (Al{sub 2}O{sub 3}) substrates. General (qualitative) observations: (a) The pull strength was maximized when the total number of thick film layers was between two and three. Fewer that two layers did not develop as strong of a bond at the thick film/LTCC interface; more than three layers and of increased footprint area, developed higher residual stresses at the thick film/LTCC interface and in the underlying LTCC material that weakened the joint. (b) Minimizing the area of the weaker 4596/LTCC interface (e.g., larger 5742 area) improved pull strength. Specific observations: (a) In the presence of vias and the need for the 3x 4596 thick film, the preferred 4596:5742 ratio was 1.0:0.5. (b) For those LTCC components that require the 3x 4596 layer, but do not have vias, it is preferred to refrain from using the 5742 layer. (c) In the absence of vias, the highest strength was realized with a 1x thick 5742 layer, a 1x thick 4596 layer, and a footprint ratio of 1.0:1.0.« less

Surface plasmon resonance in electrodynamically coupled Au NPs monolayer/dielectric spacer/Al film nanostructure: tuning by variation of spacer thickness

NASA Astrophysics Data System (ADS)

Yeshchenko, Oleg A.; Kozachenko, Viktor V.; Liakhov, Yuriy F.; Tomchuk, Anastasiya V.; Haftel, Michael; Pinchuk, Anatoliy O.

2017-10-01

Effects of plasmonic coupling between metal nanoparticles and thin metal films separated by thin dielectric film-spacers have been studied by means of light extinction in three-layer planar Au NPs monolayer/dielectric (shellac) film/Al film nanostructure. The influence of coupling on the spectral characteristics of the Au NPs SPR extinction peak has been analyzed with spacer thickness, varied from 3 to 200 nm. The main observed features are a strong red shift (160 nm), and non-monotonical behavior of the magnitude and width of Au NPs SPR, as the spacer thickness decreased. The appearance of an intensive gap mode peak was observed at a spacer thickness smaller than approximately 30 nm, caused by the hybridization of the Au NPs SPR mode and gap mode in the presence of the Al film. Additionally, the appreciable enhancement (5.6 times) of light extinction by the Au NPs monolayer in the presence of Al film has been observed. A certain value of dielectric spacer thickness (70 nm) exists at which such enhancement is maximal.

Modulation of Morphology and Optical Property of Multi-Metallic PdAuAg and PdAg Alloy Nanostructures.

PubMed

Pandey, Puran; Kunwar, Sundar; Sui, Mao; Bastola, Sushil; Lee, Jihoon

2018-05-16

In this work, the evolution of PdAg and PdAuAg alloy nanostructures is demonstrated on sapphire (0001) via the solid-state dewetting of multi-metallic thin films. Various surface configurations, size, and arrangements of bi- and tri-metallic alloy nanostructures are fabricated as a function of annealing temperature, annealing duration, film thickness, and deposition arrangements such as bi-layers (Pd/Ag), tri-layers (Pd/Au/Ag), and multi-layers (Pd/Au/Ag × 5). Specifically, the tri-layers film shows the gradual evolution of over-grown NPs, voids, wiggly nanostructures, and isolated PdAuAg alloy nanoparticles (NPs) along with the increased annealing temperature. In contrast, the multi-layers film with same thickness show the enhanced dewetting rate, which results in the formation of voids at relatively lower temperature, wider spacing, and structural regularity of alloy NPs at higher temperature. The dewetting enhancement is attributed to the increased number of interfaces and reduced individual layer thickness, which aid the inter-diffusion process at the initial stage. In addition, the time evolution of the Pd 150 nm /Ag 80 nm bi-layer films at constant temperature show the wiggly-connected and isolated PdAg alloy NPs. The overall evolution of alloy NPs is discussed based on the solid-state dewetting mechanism in conjunction with the diffusion, inter-diffusion, alloying, sublimation, Rayleigh instability, and surface energy minimization. Depending upon their surface morphologies, the bi- and tri-metallic alloy nanostructures exhibit the dynamic reflectance spectra, which show the formation of dipolar (above 700 nm) and quadrupolar resonance peaks (~ 380 nm) and wide dips in the visible region as correlated to the localized surface plasmon resonance (LSPR) effect. An absorption dip is readily shifted from ~ 510 to ~ 475 nm along with the decreased average size of alloy nanostructures.

Modulation of Morphology and Optical Property of Multi-Metallic PdAuAg and PdAg Alloy Nanostructures

NASA Astrophysics Data System (ADS)

Pandey, Puran; Kunwar, Sundar; Sui, Mao; Bastola, Sushil; Lee, Jihoon

2018-05-01

In this work, the evolution of PdAg and PdAuAg alloy nanostructures is demonstrated on sapphire (0001) via the solid-state dewetting of multi-metallic thin films. Various surface configurations, size, and arrangements of bi- and tri-metallic alloy nanostructures are fabricated as a function of annealing temperature, annealing duration, film thickness, and deposition arrangements such as bi-layers (Pd/Ag), tri-layers (Pd/Au/Ag), and multi-layers (Pd/Au/Ag × 5). Specifically, the tri-layers film shows the gradual evolution of over-grown NPs, voids, wiggly nanostructures, and isolated PdAuAg alloy nanoparticles (NPs) along with the increased annealing temperature. In contrast, the multi-layers film with same thickness show the enhanced dewetting rate, which results in the formation of voids at relatively lower temperature, wider spacing, and structural regularity of alloy NPs at higher temperature. The dewetting enhancement is attributed to the increased number of interfaces and reduced individual layer thickness, which aid the inter-diffusion process at the initial stage. In addition, the time evolution of the Pd150 nm/Ag80 nm bi-layer films at constant temperature show the wiggly-connected and isolated PdAg alloy NPs. The overall evolution of alloy NPs is discussed based on the solid-state dewetting mechanism in conjunction with the diffusion, inter-diffusion, alloying, sublimation, Rayleigh instability, and surface energy minimization. Depending upon their surface morphologies, the bi- and tri-metallic alloy nanostructures exhibit the dynamic reflectance spectra, which show the formation of dipolar (above 700 nm) and quadrupolar resonance peaks ( 380 nm) and wide dips in the visible region as correlated to the localized surface plasmon resonance (LSPR) effect. An absorption dip is readily shifted from 510 to 475 nm along with the decreased average size of alloy nanostructures.

Tailoring the charge carrier in few layers MoS2 field-effect transistors by Au metal adsorbate

NASA Astrophysics Data System (ADS)

Singh, Arun Kumar; Pandey, Rajiv K.; Prakash, Rajiv; Eom, Jonghwa

2018-04-01

It is an essential to tune the charge carrier concentrations in semiconductor in order to approach high-performance of the electronic and optoelectronic devices. Here, we report the effect of thin layer of gold (Au) metal on few layer (FL) molybdenum disulfide (MoS2) by atomic force microscopy (AFM), Raman spectroscopy and electrical charge transport measurements. The Raman spectra and charge transport measurements show that Au thin layer affect the electronic properties of the FL MoS2. After deposition of Au thin layer, the threshold voltages of FL MoS2 field-effect transistors (FETs) shift towards positive gate voltages, this reveal the p-doping in FL MoS2 nanosheets. The shift of peak frequencies of the Raman bands are also analyzed after the deposition of Au metal films of different thickness on FL MoS2 nanosheets. The surface morphology of Au metal on FL MoS2 is characterized by AFM and shows the smoother and denser film in comparison to Au metal on SiO2.

The effect of noble metal additives on the optimum operating temperature of SnO2 gas sensors

NASA Astrophysics Data System (ADS)

Mohammad-Yousefi, S.; Rahbarpour, S.; Ghafoorifard, H.

2017-12-01

The effect of Pd and Au additives on gas sensing properties of SnO2 was investigated. SnO2 pallets were fabricated and sintered at 900 °C for 90 minutes. Several nanometer layers of Pd and Au were deposited on separate SnO2 pallets and were intentionally dispersed into the SnO2 pallets by long heat treatment (400 °C for 1 Day). All metal loaded samples showed significant enhancement in response level and optimum operating temperature compare to pure SnO2 gas sensors. The amount of enhancement was strongly dependent on the material and the thickness of deposited metal layer. Studying butanol response showed that increasing the thickness of metal causes the response level to increase. Further thickness increase caused contrary effect and decreased the performance of sensors. Best results were achieved at 10 nm-thick Au and 7 nm-thick Pd. Generally, Pd-SnO2 samples demonstrated better performance than Au-SnO2 ones, however, Au-SnO2 samples were proved to be good candidate to sense reducing gases with lower hydrogen atoms in their formula. Given experimental results were also good evidence of chemical activity of gold and simply confirms the relation between chemical activity and gold particle size. Results were qualitatively described by gas diffusion theory and surface reactions take place on metal particles.The first section in your paper

Radiation dose enhancement in skin therapy with nanoparticle addition: A Monte Carlo study on kilovoltage photon and megavoltage electron beams

PubMed Central

Zheng, Xiao J; Chow, James C L

2017-01-01

AIM To investigated the dose enhancement due to the incorporation of nanoparticles in skin therapy using the kilovoltage (kV) photon and megavoltage (MV) electron beams. Monte Carlo simulations were used to predict the dose enhancement when different types and concentrations of nanoparticles were added to skin target layers of varying thickness. METHODS Clinical kV photon beams (105 and 220 kVp) and MV electron beams (4 and 6 MeV), produced by a Gulmay D3225 orthovoltage unit and a Varian 21 EX linear accelerator, were simulated using the EGSnrc Monte Carlo code. Doses at skin target layers with thicknesses ranging from 0.5 to 5 mm for the photon beams and 0.5 to 10 mm for the electron beams were determined. The skin target layer was added with the Au, Pt, I, Ag and Fe2O3 nanoparticles with concentrations ranging from 3 to 40 mg/mL. The dose enhancement ratio (DER), defined as the dose at the target layer with nanoparticle addition divided by the dose at the layer without nanoparticle addition, was calculated for each nanoparticle type, nanoparticle concentration and target layer thickness. RESULTS It was found that among all nanoparticles, Au had the highest DER (5.2-6.3) when irradiated with kV photon beams. Dependence of the DER on the target layer thickness was not significant for the 220 kVp photon beam but it was for 105 kVp beam for Au nanoparticle concentrations higher than 18 mg/mL. For other nanoparticles, the DER was dependent on the atomic number of the nanoparticle and energy spectrum of the photon beams. All nanoparticles showed an increase of DER with nanoparticle concentration during the photon beam irradiations regardless of thickness. For electron beams, the Au nanoparticles were found to have the highest DER (1.01-1.08) when the beam energy was equal to 4 MeV, but this was drastically lower than the DER values found using photon beams. The DER was also found affected by the depth of maximum dose of the electron beam and target thickness. For other nanoparticles with lower atomic number, DERs in the range of 0.99-1.02 were found using the 4 and 6 MeV electron beams. CONCLUSION In nanoparticle-enhanced skin therapy, Au nanoparticle addition can achieve the highest dose enhancement with 105 kVp photon beams. Electron beams, while popular for skin therapy, did not produce as high dose enhancements as kV photon beams. Additionally, the DER is dependent on nanoparticle type, nanoparticle concentration, skin target thickness and energies of the photon and electron beams. PMID:28298966

Direct electrochemistry of Shewanella loihica PV-4 on gold nanoparticles-modified boron-doped diamond electrodes fabricated by layer-by-layer technique.

PubMed

Wu, Wenguo; Xie, Ronggang; Bai, Linling; Tang, Zuming; Gu, Zhongze

2012-05-01

Microbial Fuel Cells (MFCs) are robust devices capable of taping biological energy, converting pollutants into electricity through renewable biomass. The fabrication of nanostructured electrodes with good bio- and electrochemical activity, play a profound role in promoting power generation of MFCs. Au nanoparticles (AuNPs)-modified Boron-Doped Diamond (BDD) electrodes are fabricated by layer-by-layer (LBL) self-assembly technique and used for the direct electrochemistry of Shewanella loihica PV-4 in an electrochemical cell. Experimental results show that the peak current densities generated on the Au/PAH multilayer-modified BDD electrodes increased from 1.25 to 2.93 microA/cm(-2) as the layer increased from 0 to 6. Different cell morphologies of S. loihica PV-4 were also observed on the electrodes and the highest density of cells was attached on the (Au/PAH)6/BDD electrode with well-formed three-dimensional nanostructure. The electrochemistry of S. loihica PV-4 was enhanced on the (Au/PAH)4/BDD electrode due to the appropriate amount of AuNPsand thickness of PAH layer.

Influence of SiO2 shell thickness on power conversion efficiency in plasmonic polymer solar cells with Au nanorod@SiO2 core-shell structures

PubMed Central

Zhang, Ran; Zhou, Yongfang; Peng, Ling; Li, Xue; Chen, Shufen; Feng, Xiaomiao; Guan, Yuqiao; Huang, Wei

2016-01-01

Locating core-shell metal nanoparticles into a photoactive layer or at the interface of photoactive layer/hole extraction layer is beneficial for fully employing surface plasmon energy, thus enhancing power conversion efficiency (PCE) in plasmonic organic photovoltaic devices (OPVs). Herein, we first investigated the influence of silica shell thickness in Au nanorods (NRs)@SiO2 core-shell structures on OPV performances by inserting them into poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) and thieno[3,4-b]thiophene/benzodithiophene (PTB7) interface, and amazedly found that a 2–3 nm silica shell onto Au NRs induces a highest short-circuit current density of 21.2 mA cm−2 and PCE of 9.55%. This is primarily due to an extremely strong local field and a much slower attenuation of localized surface plasmon resonance around ultrathin silica-coated Au NRs, with which the field intensity remains a high value in the active layer, thus sufficiently improves the absorption of PTB7. Our work provides a clear design concept on precise control of the shell of metal nanoparticles to realize high performances in plasmonic OPVs. PMID:27125309

Influence of SiO2 shell thickness on power conversion efficiency in plasmonic polymer solar cells with Au nanorod@SiO2 core-shell structures.

PubMed

Zhang, Ran; Zhou, Yongfang; Peng, Ling; Li, Xue; Chen, Shufen; Feng, Xiaomiao; Guan, Yuqiao; Huang, Wei

2016-04-29

Locating core-shell metal nanoparticles into a photoactive layer or at the interface of photoactive layer/hole extraction layer is beneficial for fully employing surface plasmon energy, thus enhancing power conversion efficiency (PCE) in plasmonic organic photovoltaic devices (OPVs). Herein, we first investigated the influence of silica shell thickness in Au nanorods (NRs)@SiO2 core-shell structures on OPV performances by inserting them into poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) and thieno[3,4-b]thiophene/benzodithiophene (PTB7) interface, and amazedly found that a 2-3 nm silica shell onto Au NRs induces a highest short-circuit current density of 21.2 mA cm(-2) and PCE of 9.55%. This is primarily due to an extremely strong local field and a much slower attenuation of localized surface plasmon resonance around ultrathin silica-coated Au NRs, with which the field intensity remains a high value in the active layer, thus sufficiently improves the absorption of PTB7. Our work provides a clear design concept on precise control of the shell of metal nanoparticles to realize high performances in plasmonic OPVs.

Magnetoresistance of layered structures with alternating in-plane and perpendicular anisotropies

NASA Astrophysics Data System (ADS)

Stobiecki, F.; Szymański, B.; Luciński, T.; Dubowik, J.; Urbaniak, M.; Röll, K.

2004-11-01

The magnetic properties of (Ni83Fe17/Au/Co/Au) multilayers with different thickness of Au (0.5⩽tAu⩽3 nm) and Co (0.2⩽tCo⩽1.5 nm) layers were characterized. For tAu⩾1.5 nm independent magnetization reversal of Ni-Fe and Co was found. Increase of tCo for (Ni83Fe17-2 nm/Au-3 nm/Co-tCo/Au-3 nm)15 multilayers results in a sequence of transformations in the magnetic properties due to changes in Co microstructure: from superparamagnetic to ferromagnetic clusters at tCo≈0.3 nm, from discontinuous to continuous layers at tCo≈0.6 nm and from perpendicular to in-plane anisotropy at tCo≈1.2 nm.

Stress engineering of high-quality single crystal diamond by heteroepitaxial lateral overgrowth

DOE PAGES

Tang, Y. -H.; Golding, B.

2016-02-02

Here, we describe a method for lateral overgrowth of low-stress single crystal diamond by chemical vapor deposition (CVD). The process is initiated by deposition of a thin (550 nm) (001) diamond layer on Ir-buffered a-plane sapphire. The diamond is partially masked by periodic thermally evaporated Au stripes using photolithography. Lateral overgrowth of the Au occurs with extremely effective filtering of threading dislocations. Thermal stress resulting from mismatch of the low thermal expansion diamond and the sapphire substrate is largely accommodated by the ductile Au layer. The stress state of the diamond is investigated by Raman spectroscopy for two thicknesses: atmore » 10 μm where the film has just overgrown the Au mask and at 180 μm where the film thickness greatly exceeds the scale of the masking. For the 10-μm film, the Raman linewidth shows spatial oscillations with the period of the Au stripes with a factor of 2 to 3 reduction relative to the unmasked region. In a 180-μm thick diamond film, the overall surface stress was extremely low, 0.00 ± 0.16 GPa, obtained from the Raman shift averaged over the 7.5mm diameter of the crystal at its surface. We conclude that the metal mask protects the overgrown diamond layer from substrate-induced thermal stress and cracking. Lastly, it is also responsible for low internal stress by reducing dislocation density by several orders of magnitude.« less

Facile Synthesis of Thick Films of Poly(methyl methacrylate), Poly(styrene), and Poly(vinyl pyridine) from Au Surfaces

PubMed Central

Saha, Sampa

2011-01-01

Atom transfer radical polymerization (ATRP) is commonly used to grow polymer brushes from Au surfaces, but the resulting film thicknesses are usually significantly less than with ATRP from SiO2 substrates. On Au, growth of poly(methyl methacrylate) (PMMA) blocks from poly(tert-butyl acrylate) brushes occurs more rapidly than growth of PMMA from initiator monolayers, suggesting that the disparity between growth rates from Au and SiO2 stems from the Au surface. Radical quenching by electron transfer from Au is probably not the termination mechanism because polymerization from thin, cross-linked initiators gives film thicknesses that are essentially the same as the thicknesses of films grown from SiO2 under the same polymerization conditions. However, this result is consistent with termination through desorption of thiols from non-cross-linked films, and reaction of these thiols with growing polymer chains. The enhanced stability of cross-linked initiators allows ATRP at temperatures up to ~100 °C and enables the growth of thick films of PMMA (350 nm), polystyrene (120 nm) and poly(vinyl pyridine) (200 nm) from Au surfaces in 1 hour. At temperatures >100 °C, the polymer brush layers delaminate as large area films. PMID:21728374

Growth of germanium on Au(111): formation of germanene or intermixing of Au and Ge atoms?

PubMed

Cantero, Esteban D; Solis, Lara M; Tong, Yongfeng; Fuhr, Javier D; Martiarena, María Luz; Grizzi, Oscar; Sánchez, Esteban A

2017-07-19

We studied the growth of Ge layers on Au(111) under ultra-high vacuum conditions from the submonolayer regime up to a few layers with Scanning Tunneling Microscopy (STM), Direct Recoiling Spectroscopy (DRS) and Low Energy Electron Diffraction (LEED). Most STM images for the thicker layers are consistent with a commensurate 5 × 8 arrangement. The high surface sensitivity of TOF-DRS allows us to confirm the coexistence of Au and Ge atoms in the top layer for all stages of growth. An estimation of the Au to Ge ratio at the surface of the thick layer gives about 1 Au atom per 2 Ge ones. When the growth is carried out at sample temperatures higher than about 420 K, a fraction of the deposited Ge atoms migrate into the bulk of Au. This incorporation of Ge into the bulk reduces the growth rate of the Ge films, making it more difficult to obtain films thicker than a few layers. After sputtering the Ge/Au surface, the segregation of bulk Ge atoms to the surface occurs for temperatures ≥600 K. The surface obtained after segregation of Ge reaches a stable condition (saturation) with an n × n symmetry with n on the order of 14.

Effects of nanoscale coatings on reliability of MEMS ohmic contact switches

NASA Astrophysics Data System (ADS)

Tremper, Amber Leigh

This thesis examines how the electrical and mechanical behavior of Au thin films is altered by the presence of ultra-thin metallic coatings. To examine the mechanical behavior, nanoindentation, nano-scratch, and atomic force microscopy (AFM) testing was performed. The electrical behavior was evaluated through Kelvin probe contact resistance measurements. This thesis shows that ultra-thin, hard, ductile coatings on a softer, ductile underlying layer (such as Ru or Pt on Au) had a significant effect on mechanical behavior of the system, and can be tailored to control the deformation resistance of the thin film system. Despite Ru and Pt having a higher hardness and plane strain modulus than Au, the Ru and Pt coatings decreased both the hardness and plane strain modulus of the layered system when the indentation depth was on the order of the coating thickness. Alternately, when the indentation depth was several times the coating thickness, the ductile, plastically hard, elastically stiff layer significantly hardened the contact response. These results correlate well with membrane stress theoretical predictions, and demonstrate that membrane theory can be applied even when the ratio of indentation depth, h, to coating thickness, t, is very large ( h/t<10). The transition from film-substrate models to membrane models occurs when the indent penetration depth to coating thickness ratio is less than ˜0.5. When the electrical behavior of the Ru-coated Au films was examined, it was found that all the measured resistances of the Au-only film and Ru-coated systems were several orders of magnitude larger than those predicted by Holm's law, but were still in good agreement with previously reported values in the literature. Previous studies attributed the high contact resistances to a variety of causes, including the buildup of an insulating contamination layer. This thesis determined the cause of the deviations to be large sheet resistance contributions to the total measured resistance. Further, studies on aged samples (with thicker contamination layers) conclusively showed that, while contamination increases the contact resistance, it also increases the dependence on force. This thesis also details that the relative contribution of contact resistance to the total measured resistance can be maximized by decreasing the probe spacing and tip radius. AFM testing of the layered systems showed that the coated samples had larger predicted plane strain moduli than the Au sample, in contrast to the nanoindentation testing. Thus, when the contact depth was kept sufficiently small, the contact stiffness increased as predicted by substrate models. When the contact depth was on the order of the coating thickness, the contact stiffness actually decreased. Additionally, the forceseparation plots showed that the Ru and Pt surfaces either accumulated large amounts of contamination or were less susceptible to being wiped clean than the Au film. Further, scratch testing of the Au film and Ru and Pt coatings show that the hard surface coatings reduce material removal and contact wear. Ultra-thin Ru and Pt surface coatings on Au films are shown to be improved material systems for ohmic contact switches. The wear is reduced for coated materials, while the resistance and power consumption through the coating are not significantly affected.

Irradiation effects on multilayered W/ZrO2 film under 4 MeV Au ions

NASA Astrophysics Data System (ADS)

Wang, Hongwei; Gao, Yuan; Fu, Engang; Yang, Tengfei; Xue, Jianming; Yan, Sha; Chu, Paul K.; Wang, Yugang

2014-12-01

Irradiation induced structural changes in multilayered W/ZrO2 nanocomposites with periodic bilayer thicknesses of (7/14 nm) and (70/140 nm) were investigated following Au+ ion irradiation. The samples were irradiated by 4 MeV Au ions with fluences ranging from 6 × 1014 to 1 × 1016 ions/cm2. The immiscible W/ZrO2 interfaces remained unchanged without intermixing of the layers upon the irradiation. No voids were observed in the samples with different periodic layer thicknesses. The XRD and XTEM studies reveal thickness dependent microstructural changes in the samples. W and ZrO2 grains in the thinner (7/14 nm) bilayer sample exhibit significant resistance to grain growth compared to the thicker (70/140 nm) bilayer sample as well as a W monolayer film. The high fraction of flat interfaces as well as grain boundaries in multilayer films plays a role in suppressing ion irradiation-induced grain growth and void formation.

Quantification of elemental area densities in multiple metal layers (Au/Ni/Cu) on a Cr-coated quartz glass substrate for certification of NMIJ CRM 5208-a.

PubMed

Ariga, Tomoko; Zhu, Yanbei; Ito, Mika; Takatsuka, Toshiko; Terauchi, Shinya; Kurokawa, Akira; Inagaki, Kazumi

2018-04-01

Area densities of Au/Ni/Cu layers on a Cr-coated quartz substrate were characterized to certify a multiple-metal-layer certified reference material (NMIJ CRM5208-a) that is intended for use in the analysis of the layer area density and the thickness by an X-ray fluorescence spectrometer. The area densities of Au/Ni/Cu layers were calculated from layer mass amounts and area. The layer mass amounts were determined by using wet chemical analyses, namely inductively coupled plasma mass spectrometry (ICP-MS), isotope-dilution (ID-) ICP-MS, and inductively coupled plasma optical emission spectrometry (ICP-OES) after dissolving the layers with diluted mixture of HCl and HNO 3 (1:1, v/v). Analytical results of the layer mass amounts obtained by the methods agreed well with each another within their uncertainty ranges. The area of the layer was determined by using a high-resolution optical scanner calibrated by Japan Calibration Service System (JCSS) standard scales. The property values of area density were 1.84 ± 0.05 μg/mm 2 for Au, 8.69 ± 0.17 μg/mm 2 for Ni, and 8.80 ± 0.14 μg/mm 2 for Cu (mean ± expanded uncertainty, coverage factor k = 2). In order to assess the reliability of these values, the density of each metal layer calculated from the property values of the area density and layer thickness measured by using a scanning electron microscope were compared with available literature values and good agreement between the observed values and values obtained in previous studies.

Enhanced middle-infrared light transmission through Au/SiO(x)N(y)/Au aperture arrays.

PubMed

Xiao, Gongli; Yao, Xiang; Ji, Xinming; Zhou, Jia; Bao, Zongming; Huang, Yiping

2011-12-01

The enhanced middle-infrared light transmission through Au/SiO(x)N(y)/Au aperture arrays by changing the refractive index and the thickness of a dielectric layer was studied experimentally. The results indicated that the transmission spectra was highly dependent on the refractive index and the thickness of SiO(x)N(y). We found that the transmission peaks redshifted regularly along with the refractive index from 1.6 to 1.8, owing to the role of surface plasmon polaritons (SPP) coupling in the Au/SiO(x)N(y)/Au cascaded metallic structure. Simultaneously, a higher transmission efficiency and narrower transmission peak was obtained in Au/SiO2.1N0.3/Au cascaded metallic structure with small refractive index (1.6) than in Au/SiO0.6N1/Au cascaded metallic structure with large refractive index (1.8). When the thickness of SiO(x)N(y) changes from 0.2 to 0.4 microm, the shape of transmission spectra exhibits a large change. It was found that a higher transmission efficiency and narrower transmission peak was obtained in Au/SiO(x)N(y)/Au cascaded metallic structure with a thin dielectric film (0.2 microm), with the increase of SiO(x)N(y) film's thickness, the transmission peak gradually widened and disappeared finally. This effect is useful in applications of biochemical sensing and tunable integrated plasmonic devices in the middle-infrared region.

Nanometer-thick gold on silicon as a proxy for single-crystal gold for the electrodeposition of epitaxial cuprous oxide thin films

DOE PAGES

Switzer, Jay A.; Hill, James C.; Mahenderkar, Naveen K.; ...

2016-05-27

Here, single-crystal Au is an excellent substrate for electrochemical epitaxial growth due to its chemical inertness, but the high cost of bulk Au single crystals prohibits their use in practical applications. Here, we show that ultrathin epitaxial films of Au electrodeposited onto Si(111), Si(100), and Si(110) wafers can serve as an inexpensive proxy for bulk single-crystal Au for the deposition of epitaxial films of cuprous oxide (Cu 2O). The Au films range in thickness from 7.7 nm for a film deposited for 5 min to 28.3 nm for a film deposited for 30 min. The film thicknesses are measured bymore » low-angle X-ray reflectivity and X-ray Laue oscillations. High-resolution TEM shows that there is not an interfacial SiO x layer between the Si and Au. The Au films deposited on the Si(111) substrates are smoother and have lower mosaic spread than those deposited onto Si(100) and Si(110). The mosaic spread of the Au(111) layer on Si(111) is only 0.15° for a 28.3 nm thick film. Au films deposited onto degenerate Si(111) exhibit ohmic behavior, whereas Au films deposited onto n-type Si(111) with a resistivity of 1.15 Ω·cm are rectifying with a barrier height of 0.85 eV. The Au and the Cu 2O follow the out-of-plane and in-plane orientations of the Si substrates, as determined by X-ray pole figures. The Au and Cu 2O films deposited on Si(100) and Si(110) are both twinned. The films grown on Si(100) have twins with a [221] orientation, and the films grown on Si(110) have twins with a [411] orientation. An interface model is proposed for all Si orientations, in which the –24.9% mismatch for the Au/Si system is reduced to only +0.13% by a coincident site lattice in which 4 unit meshes of Au coincide with 3 unit meshes of Si. Although this study only considers the deposition of epitaxial Cu 2O films on electrodeposited Au/Si, the thin Au films should serve as high-quality substrates for the deposition of a wide variety of epitaxial materials.« less

Thin noble metal films on Si (111) investigated by optical second-harmonic generation and photoemission

NASA Astrophysics Data System (ADS)

Pedersen, K.; Kristensen, T. B.; Pedersen, T. G.; Morgen, P.; Li, Z.; Hoffmann, S. V.

2002-05-01

Thin noble metal films (Ag, Au and Cu) on Si (111) have been investigated by optical second-harmonic generation (SHG) in combination with synchrotron radiation photoemission spectroscopy. The valence band spectra of Ag films show a quantization of the sp-band in the 4-eV energy range from the Fermi level down to the onset of the d-bands. For Cu and Au the corresponding energy range is much narrower and quantization effects are less visible. Quantization effects in SHG are observed as oscillations in the signal as a function of film thickness. The oscillations are strongest for Ag and less pronounced for Cu, in agreement with valence band photoemission spectra. In the case of Au, a reacted layer floating on top of the Au film masks the observation of quantum well levels by photoemission. However, SHG shows a well-developed quantization of levels in the Au film below the reacted layer. For Ag films, the relation between film thickness and photon energy of the SHG resonances indicates different types of resonances, some of which involve both quantum well and substrate states.

Transport in ultrathin gold films decorated with magnetic Gd atoms

NASA Astrophysics Data System (ADS)

Alemani, Micol; Helgren, Erik; Hugel, Addison; Hellman, Frances

2008-03-01

We have performed four-probe transport measurements of ultrathin Au films decorated with Gd ad-atoms. The samples were prepared by quench condensation, i.e., sequential evaporation on a cryogenically cooled substrate under UHV conditions while monitoring the film thickness and resistance. Electrically continuous Au films at thickness of about 2 mono-layers of material are grown on an amorphous Ge wetting layer. The quench condensation method provides a sensitive control on the sample growth process, allowing us to tune the morphological and electrical configuration of the system. The ultrathin gold films develop from an insulating to a metallic state as a function of film thickness. The temperature dependence of the Au conductivity for different thickness is studied. It evolves from hopping transport for the insulating films, to a ln T dependence for thicker films. For gold films in the insulating regime we found a decreasing resistance by adding Gd. This is in agreement with a decreasing tunneling barrier height between metallic atoms. The Gd magnetic moments are randomly oriented for isolated atoms. This magnetic disorder leads to scattering of the charge carriers and a reduced conductivity compared to nonmagnetic materials.

Cascaded Ga1-xAlxAs/GaAs solar cell with graded i-region

NASA Astrophysics Data System (ADS)

Mil'shtein, Sam; Halilov, Samed

2018-02-01

In current study we designed p-i-n junction with extended intrinsic layer, where linearly graded Alx Ga1-x As presents variable energy gap so needed for effective harvesting of sun radiation. The design realization involves two regions of compositional structure in the stacking direction. The top AlxGa1-xAs layer of 1 um total thickness has stoichiometric structure x=0.3-0.2d, where depth d runs from 0 to 1 um, topmost 200 nm of which is Be-doped. Bottom AlxGa1-xAs layer of 3 um total thickness has a variable composition of x=0.133-0.033d, d runs from 1 to 4 um, the very bottom of which with 10 nm thickness is Si-doped. On the top surface, there is a 50 nm layer of p+ doped GaAs as a spacer for growing AuGe/Ni anode electrode of 20% surface area, the bottom is coated with AuGe/Ni cathode electrode. The designed cell demonstrates 89% fill factor and 30% conversion efficiency without anti-reflection coating.

Effect of Pd Interlayer on Electrochemical Properties of ENIG Surface Finish in 3.5 wt.% NaCl Solution

NASA Astrophysics Data System (ADS)

Nam, N. D.; Bui, Q. V.; Nhan, H. T.; Phuong, D. V.; Bian, M. Z.

2014-09-01

The corrosion resistance of a multilayered (NiP-Pd-Au) coating with various thicknesses of palladium (Pd) interlayer deposited on copper by an electroless method was investigated using electrochemical techniques including potentiodynamic polarization and electrochemical impedance spectroscopy. In addition, the surface finish was examined by x-ray diffraction analysis and scanning electron microscopy, and the contact angle of the liquid-solid interface was recorded. The corrosion resistance of the copper substrate was considerably improved by Pd interlayer addition. Increase of the thickness of the Pd interlayer enhanced the performance of the Cu-NiP-Pd-Au coating due to low porosity, high protective efficiency, high charge-transfer resistance, and contact angle. These are attributed to the diffusion of layers in the Cu-NiP-Pd-Au coating acting as a physical barrier layer, leading to the protection provided by the coating.

Investigation of transparent zinc oxide-based contacts for high performance III-nitride light emitting diodes

NASA Astrophysics Data System (ADS)

Jung, Sungpyo

In this dissertation, we investigate Al-doped ZnO(AZO) contact structure to a variety of GaN LED structures. Our results show that ZnO is a potentially viable transparent contact for GaN-based LEDs. We began our investigation by depositing AZO and Ni/AZO contacts to p-GaN. However, these contacts are highly resistive. Next, we deposited thin Ni/Au layer, oxidized the Ni/Au layer to form a good ohmic contact to p-GaN, and then followed by the deposition of thick AZO layer. However, the electrical resistance of oxidized Ni/Au-AZO contacts is higher than that of the conventional Ni/Au contacts. We solve the high contact resistance problem by using a two-step thermal annealing process. In this method, Ni/Au layer is deposited first followed by the AZO layer without any annealing step. After finishing the device fabrication, the samples are annealed in air first to achieve low contact resistance with Ni/Au/AZO and p-GaN and then annealed in nitrogen to achieve low sheet resistance for the AZO layer. The improved electrical and optical characteristics of this scheme compared to conventional Ni/Au contact scheme are demonstrated on a variety of GaN LEDs: blue, green, small area, large area and bottom emitting LEDs. The benefits of ZnO-based contacts are more significant in large area LEDs that include lower forward voltage, and higher optical emission, better emission uniformity and reliability. The advantages of ZnO-based contact in terms of lower contact resistance and higher optical emission on LED fabricated on roughened GaN wafers are also demonstrated. For bottom emitting LED structure intended for flip chip applications, our original oxidized Ni/Au layer over coated with either Al or Ag contacts have shown to simultaneously yield superior I-V characteristics and greatly enhanced optical performance compared to conventional LEDs using a thick Ni/Au contact in the flip-chip configuration. However, the contact is unstable at operating temperatures > 100°C due to close proximity of Ag and Al with p-GaN. Here, the ZnO layer probably can be interdiffusion barrier layer of Al into GaN. We have demonstrated low contact resistance and higher light emission by using ZnO as a barrier material between oxidize Ni/Au and Al reflecting layer. In summary, our investigation demonstrates the applicability of ZnO-based transparent contacts for high performance LEDs that will be larger in size and are expected to be operating at higher current for solid-state lighting of the future. (Abstract shortened by UMI.)

Modification of the Near Surface Region Metastable Phases and Ion Induced Reactions

DTIC Science & Technology

1984-02-03

cell Si Dave Lilienfeld - amorphous Si layer thickness Au diffusion in metallic glasses Dave Lilienfeld & - low temperature Cu diffusion in Si Tim...Sullivan Fritz Stafford - defect characterization in implanted & annealed silicon-on-sapphire Peter Zielinski - Composition of CuZr metallic glass...ribbons 5. Prof. Johnson Dave Kuhn - measurement of Pd layer thickness Alexandra Elve - hydrogen profiles in metals Lauren Heitner - hydrogen diffusion in

Simulation and analysis of Au-MgF2 structure in plasmonic sensor in near infrared spectral region

NASA Astrophysics Data System (ADS)

Sharma, Anuj K.

2018-05-01

Plasmonic sensor based on metal-dielectric combination of gold and MgF2 layers is studied in near infrared (NIR) spectral region. An emphasis is given on the effect of variable thickness of MgF2 layer in combination with operating wavelength and gold layer thickness on the sensor's performance in NIR. It is established that the variation in MgF2 thickness in connection with plasmon penetration depth leads to significant variation in sensor's performance. The analysis leads to a conclusion that taking smaller values of MgF2 layer thickness and operating at longer NIR wavelength leads to enhanced sensing performance. Also, fluoride glass can provide better sensing performance than chalcogenide glass and silicon substrate.

Ultrathin Au film on polymer surface for surface plasmon polariton waveguide application

NASA Astrophysics Data System (ADS)

Liu, Tong; Ji, Lanting; He, Guobing; Sun, Xiaoqiang; Wang, Fei; Zhang, Daming

2017-11-01

Formation of laterally continuous ultrathin gold films on polymer substrates is a technological challenge. In this work, the vacuum thermal evaporation method is adopted to form continuous Au films in the thickness range of 7-17 nm on polymers of Poly(methyl-methacrylate-glycidly-methacrylate) and SU-8 film surface without using the adhesion or metallic seeding layers. Absorption spectrum, scanning electron microscope and atomic force microscope images are used to characterize the Au film thickness, roughness and optical loss. The result shows that molecular-scale structure, surface energy and electronegativity have impacts on the Au film morphology on polymers. Wet chemical etching is used to fabricate 7-nm thick Au stripes embedded in polymer claddings. These long-range surface plasmon polariton waveguides demonstrate the favorable morphological configurations and cross-sectional states. Through the end-fire excitation method, propagation losses of 6-μm wide Au stripes are compared to theoretical values and analyzed from practical film status. The smooth, patternable gold films on polymer provide potential applications to plasmonic waveguides, biosensing, metamaterials and optical antennas.

Molecular layers of ZnPc and FePc on Au(111) surface: Charge transfer and chemical interaction

NASA Astrophysics Data System (ADS)

Ahmadi, Sareh; Shariati, M. Nina; Yu, Shun; Göthelid, Mats

2012-08-01

We have studied zinc phthalocyanine (ZnPc) and iron phthalocyanine (FePc) thick films and monolayers on Au(111) using photoelectron spectroscopy and x-ray absorption spectroscopy. Both molecules are adsorbed flat on the surface at monolayer. ZnPc keeps this orientation in all investigated coverages, whereas FePc molecules stand up in the thick film. The stronger inter-molecular interaction of FePc molecules leads to change of orientation, as well as higher conductivity in FePc layer in comparison with ZnPc, which is reflected in thickness-dependent differences in core-level shifts. Work function changes indicate that both molecules donate charge to Au; through the π-system. However, the Fe3d derived lowest unoccupied molecular orbital receives charge from the substrate when forming an interface state at the Fermi level. Thus, the central atom plays an important role in mediating the charge, but the charge transfer as a whole is a balance between the two different charge transfer channels; π-system and the central atom.

The significant effect of the thickness of Ni film on the performance of the Ni/Au Ohmic contact to p-GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, X. J.; Zhao, D. G., E-mail: dgzhao@red.semi.ac.cn; Jiang, D. S.

2014-10-28

The significant effect of the thickness of Ni film on the performance of the Ohmic contact of Ni/Au to p-GaN is studied. The Ni/Au metal films with thickness of 15/50 nm on p-GaN led to better electrical characteristics, showing a lower specific contact resistivity after annealing in the presence of oxygen. Both the formation of a NiO layer and the evolution of metal structure on the sample surface and at the interface with p-GaN were checked by transmission electron microscopy and energy-dispersive x-ray spectroscopy. The experimental results indicate that a too thin Ni film cannot form enough NiO to decrease themore » barrier height and get Ohmic contact to p-GaN, while a too thick Ni film will transform into too thick NiO cover on the sample surface and thus will also deteriorate the electrical conductivity of sample.« less

Etching-dependent fluorescence quenching of Ag-dielectric-Au three-layered nanoshells: The effect of inner Ag nanosphere

NASA Astrophysics Data System (ADS)

Zhu, Jian; Xu, Zai-jie; Weng, Guo-jun; Zhao, Jing; Li, Jian-jun; Zhao, Jun-wu

2018-07-01

In this report, Ag-dielectric-Au three-layered nanoshells with controlled inner core size were synthesized. The fluorescence emission of the rhodamine 6G (R6G) could be quenched by the three-layered nanoshells distinctly. What's more, the fluorescence quenching efficiency could be further improved by tuning the etching of inner Ag nanosphere. The maximum fluorescence quenching efficiency is obtained when the separate layer just appears between the inner Ag core and the outer Au shell. Whereas the fluorescence quenching efficiency is weakened when no gaps take place around the inner Ag core or the separate layer is too thick and greater than 13 nm. The fluorescence quenching properties of the Ag-dielectric-Au three-layered nanoshells with different initial sizes of the Ag nanoparticles are also studied. The maximum fluorescence quenching efficiency is obtained when the three-layered nanoshells are synthesized based on the Ag nanoparticles with 60 nm, which is better than others two sizes (42 and 79 nm). Thus we believe that the size of initial Ag nanospheres also greatly affects the optimized fluorescence quenching efficiency. These results about fluorescence quenching properties of Ag-dielectric-Au three-layered nanoshells present a potential for design and fabrication of fluorescence nanosensors based on tuning the geometry of the inner core and the separate layer.

Connected Au network in annealed Ni/Au thin films on p-GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, S. P.; Jang, H. W.; Noh, D. Y.

2007-11-12

We report the formation of a connected Au network in annealed Ni/Au thin films on p-GaN, which was studied by scanning electron microscopy, transmission electron microscopy, and synchrotron x-ray diffraction. As the Ni was oxidized into NiO upon annealing at 530 deg. C in air, the Au layer was transformed to an interconnected network with an increased thickness. During annealing, Ni atoms diffuse out onto the Au through defects to form NiO, while Au atoms replace the Ni positions. The Au network grows downward until it reaches the p-GaN substrate, and NiO columns fill the space between the Au network.

Thickness-dependent electron mobility of single and few-layer MoS{sub 2} thin-film transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Ji Heon; Kim, Tae Ho; Lee, Hyunjea

We investigated the dependence of electron mobility on the thickness of MoS{sub 2} nanosheets by fabricating bottom-gate single and few-layer MoS{sub 2} thin-film transistors with SiO{sub 2} gate dielectrics and Au electrodes. All the fabricated MoS{sub 2} transistors showed on/off-current ratio of ∼10{sup 7} and saturated output characteristics without high-k capping layers. As the MoS{sub 2} thickness increased from 1 to 6 layers, the field-effect mobility of the fabricated MoS{sub 2} transistors increased from ∼10 to ∼18 cm{sup 2}V{sup −1}s{sup −1}. The increased subthreshold swing of the fabricated transistors with MoS{sub 2} thickness suggests that the increase of MoS{sub 2}more » mobility with thickness may be related to the dependence of the contact resistance and the dielectric constant of MoS{sub 2} layer on its thickness.« less

Multi-Layer SnSe Nanoflake Field-Effect Transistors with Low-Resistance Au Ohmic Contacts

NASA Astrophysics Data System (ADS)

Cho, Sang-Hyeok; Cho, Kwanghee; Park, No-Won; Park, Soonyong; Koh, Jung-Hyuk; Lee, Sang-Kwon

2017-05-01

We report p-type tin monoselenide (SnSe) single crystals, grown in double-sealed quartz ampoules using a modified Bridgman technique at 920 °C. X-ray powder diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) measurements clearly confirm that the grown SnSe consists of single-crystal SnSe. Electrical transport of multi-layer SnSe nanoflakes, which were prepared by exfoliation from bulk single crystals, was conducted using back-gated field-effect transistor (FET) structures with Au and Ti contacts on SiO2/Si substrates, revealing that multi-layer SnSe nanoflakes exhibit p-type semiconductor characteristics owing to the Sn vacancies on the surfaces of SnSe nanoflakes. In addition, a strong carrier screening effect was observed in 70-90-nm-thick SnSe nanoflake FETs. Furthermore, the effect of the metal contacts to multi-layer SnSe nanoflake-based FETs is also discussed with two different metals, such as Ti/Au and Au contacts.

Electron-lattice energy relaxation in laser-excited thin-film Au-insulator heterostructures studied by ultrafast MeV electron diffraction.

PubMed

Sokolowski-Tinten, K; Shen, X; Zheng, Q; Chase, T; Coffee, R; Jerman, M; Li, R K; Ligges, M; Makasyuk, I; Mo, M; Reid, A H; Rethfeld, B; Vecchione, T; Weathersby, S P; Dürr, H A; Wang, X J

2017-09-01

We apply time-resolved MeV electron diffraction to study the electron-lattice energy relaxation in thin film Au-insulator heterostructures. Through precise measurements of the transient Debye-Waller-factor, the mean-square atomic displacement is directly determined, which allows to quantitatively follow the temporal evolution of the lattice temperature after short pulse laser excitation. Data obtained over an extended range of laser fluences reveal an increased relaxation rate when the film thickness is reduced or the Au-film is capped with an additional insulator top-layer. This behavior is attributed to a cross-interfacial coupling of excited electrons in the Au film to phonons in the adjacent insulator layer(s). Analysis of the data using the two-temperature-model taking explicitly into account the additional energy loss at the interface(s) allows to deduce the relative strength of the two relaxation channels.

Electron-lattice energy relaxation in laser-excited thin-film Au-insulator heterostructures studied by ultrafast MeV electron diffraction

PubMed Central

Sokolowski-Tinten, K.; Shen, X.; Zheng, Q.; Chase, T.; Coffee, R.; Jerman, M.; Li, R. K.; Ligges, M.; Makasyuk, I.; Mo, M.; Reid, A. H.; Rethfeld, B.; Vecchione, T.; Weathersby, S. P.; Dürr, H. A.; Wang, X. J.

2017-01-01

We apply time-resolved MeV electron diffraction to study the electron-lattice energy relaxation in thin film Au-insulator heterostructures. Through precise measurements of the transient Debye-Waller-factor, the mean-square atomic displacement is directly determined, which allows to quantitatively follow the temporal evolution of the lattice temperature after short pulse laser excitation. Data obtained over an extended range of laser fluences reveal an increased relaxation rate when the film thickness is reduced or the Au-film is capped with an additional insulator top-layer. This behavior is attributed to a cross-interfacial coupling of excited electrons in the Au film to phonons in the adjacent insulator layer(s). Analysis of the data using the two-temperature-model taking explicitly into account the additional energy loss at the interface(s) allows to deduce the relative strength of the two relaxation channels. PMID:28795080

Novel Manufacturing Technologies for GHZ/THz Integrated Circuits on Synthetic Diamond Substrates

DTIC Science & Technology

2010-11-15

silicon form palladium silicide Pd2Si at a temperature of 400 ºС, thus ensuring high reliability of the contacts. All the above metallization layers were...indicate possibility of realization of ICs on diamond substrates. In the course of our studies it was found that the Ti-Pd-Au metallization system...thickness of 2-3 um) can be applied when forming the topology of IC elements on synthetic diamond layers, while the Cr–Cu–Ni–Au metallization system with

Z-scan studies of the nonlinear optical properties of gold nanoparticles prepared by electron beam deposition.

PubMed

Mezher, M H; Nady, A; Penny, R; Chong, W Y; Zakaria, R

2015-11-20

This paper details the fabrication process for placing single-layer gold (Au) nanoparticles on a planar substrate, and investigation of the resulting optical properties that can be exploited for nonlinear optics applications. Preparation of Au nanoparticles on the substrate involved electron beam deposition and subsequent thermal dewetting. The obtained thin films of Au had a variation in thicknesses related to the controllable deposition time during the electron beam deposition process. These samples were then subjected to thermal annealing at 600°C to produce a randomly distributed layer of Au nanoparticles. Observation from field-effect scanning electron microscope (FESEM) images indicated the size of Au nanoparticles ranges from ∼13 to ∼48  nm. Details of the optical properties related to peak absorption of localized surface plasmon resonance (LSPR) of the nanoparticle were revealed by use of UV-Vis spectroscopy. The Z-scan technique was used to measure the nonlinear effects on the fabricated Au nanoparticle layers where it strongly relates LSPR and nonlinear optical properties.

Dissociative adsorption of water on Au/MgO/Ag(001) from first principles calculations

NASA Astrophysics Data System (ADS)

Nevalaita, J.; Häkkinen, H.; Honkala, K.

2015-10-01

The molecular and dissociative adsorption of water on a Ag-supported 1 ML, 2 ML and 3 ML-a six atomic layer-thick MgO films with a single Au adatom is investigated using density functional theory calculations. The obtained results are compared to a bulk MgO(001) surface with an Au atom. On thin films the negatively charged Au strengthens the binding of the polar water molecule due to the attractive Au-H interaction. The adsorption energy trends of OH and H with respect to the film thickness depend on an adsorption site. In the case OH or H binds atop Au on MgO/Ag(001), the adsorption becomes more exothermic with the increasing film thickness, while the reverse trend is seen when the adsorption takes place on bare MgO/Ag(001). This behavior can be explained by different bonding mechanisms identified with the Bader analysis. Interestingly, we find that the rumpling of the MgO film and the MgO-Ag interface distance correlate with the charge transfer over the thin film and the interface charge, respectively. Moreover, we employ a modified Born-Haber-cycle to analyze the effect of film thickness to the adsorption energy of isolated Au and OH species on MgO/Ag(001). The analysis shows that the attractive Coulomb interaction between the negatively charged adsorbate and the positive MgO-Ag-interface does not completely account for the weaker binding with increasing film thickness. The redox energy associated with the charge transfer from the interface to the adsorbate is more exothermic with the increasing film thickness and partly compensates the decrease in the attractive Coulomb interaction.

Highly efficient phosphorescent organic light-emitting diode with a nanometer-thick Ni silicide/polycrystalline p-Si composite anode.

PubMed

Li, Y Z; Wang, Z L; Luo, H; Wang, Y Z; Xu, W J; Ran, G Z; Qin, G G; Zhao, W Q; Liu, H

2010-07-19

A phosphorescent organic light-emitting diode (PhOLED) with a nanometer-thick (approximately 10 nm) Ni silicide/ polycrystalline p-Si composite anode is reported. The structure of the PhOLED is Al mirror/ glass substrate / Si isolation layer / Ni silicide / polycrystalline p-Si/ V(2)O(5)/ NPB/ CBP: (ppy)(2)Ir(acac)/ Bphen/ Bphen: Cs(2)CO(3)/ Sm/ Au/ BCP. In the composite anode, the Ni-induced polycrystalline p-Si layer injects holes into the V(2)O(5)/ NPB, and the Ni silicide layer reduces the sheet resistance of the composite anode and thus the series resistance of the PhOLED. By adopting various measures for specially optimizing the thickness of the Ni layer, which induces Si crystallization and forms a Ni silicide layer of appropriate thickness, the highest external quantum efficiency and power conversion efficiency have been raised to 26% and 11%, respectively.

The effect of Au nanoparticles on the strain-dependent electrical properties of CVD graphene

NASA Astrophysics Data System (ADS)

Bai, Jing; Nan, Haiyan; Qi, Han; Bing, Dan; Du, Ruxia

2018-03-01

We conducted an experimental study of the effect of Au nanoparticles (NPs) on the strain-dependent electrical properties in chemical vapor deposition grown graphene. We used 5-nm thick Au NPs as an effective cover (and doping) layer for graphene, and found that Au NPs decrease electrical resistance by two orders of magnitude. In addition, the Au NPs suppress the effect of strain on resistance because the intrinsic topological cracks and grain boundaries in graphene are filled with Au nanoparticles. This method has a big potential to advance industrial production of large-area, high-quality electronic devices and graphene-based transparent electrodes.

Gate Tunable Transport in Graphene/MoS₂/(Cr/Au) Vertical Field-Effect Transistors.

PubMed

Nazir, Ghazanfar; Khan, Muhammad Farooq; Aftab, Sikandar; Afzal, Amir Muhammad; Dastgeer, Ghulam; Rehman, Malik Abdul; Seo, Yongho; Eom, Jonghwa

2017-12-28

Two-dimensional materials based vertical field-effect transistors have been widely studied due to their useful applications in industry. In the present study, we fabricate graphene/MoS₂/(Cr/Au) vertical transistor based on the mechanical exfoliation and dry transfer method. Since the bottom electrode was made of monolayer graphene (Gr), the electrical transport in our Gr/MoS₂/(Cr/Au) vertical transistors can be significantly modified by using back-gate voltage. Schottky barrier height at the interface between Gr and MoS₂ can be modified by back-gate voltage and the current bias. Vertical resistance (R vert ) of a Gr/MoS₂/(Cr/Au) transistor is compared with planar resistance (R planar ) of a conventional lateral MoS₂ field-effect transistor. We have also studied electrical properties for various thicknesses of MoS₂ channels in both vertical and lateral transistors. As the thickness of MoS₂ increases, R vert increases, but R planar decreases. The increase of R vert in the thicker MoS₂ film is attributed to the interlayer resistance in the vertical direction. However, R planar shows a lower value for a thicker MoS₂ film because of an excess of charge carriers available in upper layers connected directly to source/drain contacts that limits the conduction through layers closed to source/drain electrodes. Hence, interlayer resistance associated with these layers contributes to planer resistance in contrast to vertical devices in which all layers contribute interlayer resistance.

Electron Emission Observations from As-Grown and Vacuum-Coated Chemical Vapor Deposited Diamond

NASA Technical Reports Server (NTRS)

Lamouri, A.; Wang, Yaxin; Mearini, G. T.; Krainsky, I. L.; Dayton, J. A., Jr.; Mueller,W.

1996-01-01

Field emission has been observed from chemical vapor deposited diamond grown on Mo and Si substrates. Emission was observed at fields as low as 20 kV/cm. The samples were tested in the as-grown form, and after coating with thin films of Au, CsI, and Ni. The emission current was typically maximum at the onset of the applied field, but was unstable, and decreased rapidly with time from the as-grown films. Thin Au layers, approximately 15 nm thick, vacuum deposited onto the diamond samples significantly improved the stability of the emission current at values approximately equal to those from uncoated samples at the onset of the applied field. Thin layers of CsI, approximately 5 nm thick, were also observed to improve the stability of the emission current but at values less than those from the uncoated samples at the onset of the applied field. While Au and CsI improved the stability of the emission, Ni was observed to have no effect.

Performance enhancement of pentacene-based organic thin-film transistors using 6,13-pentacenequinone as a carrier injection interlayer

NASA Astrophysics Data System (ADS)

Fan, Ching-Lin; Lin, Wei-Chun; Chen, Hao-Wei

2018-06-01

This work demonstrates pentacene-based organic thin-film transistors (OTFTs) fabricated by inserting a 6,13-pentacenequinone (PQ) carrier injection layer between the source/drain (S/D) metal Au electrodes and pentacene channel layer. Compared to devices without a PQ layer, the performance characteristics including field-effect mobility, threshold voltage, and On/Off current ratio were significantly improved for the device with a 5-nm-thick PQ interlayer. These improvements are attributed to significant reduction of hole barrier height at the Au/pentacene channel interfaces. Therefore, it is believed that using PQ as the carrier injection layer is a good candidate to improve the pentacene-based OTFTs electrical performance.

Nanostructured GaAs solar cells via metal-assisted chemical etching of emitter layers.

PubMed

Song, Yunwon; Choi, Keorock; Jun, Dong-Hwan; Oh, Jungwoo

2017-10-02

GaAs solar cells with nanostructured emitter layers were fabricated via metal-assisted chemical etching. Au nanoparticles produced via thermal treatment of Au thin films were used as etch catalysts to texture an emitter surface with nanohole structures. Epi-wafers with emitter layers 0.5, 1.0, and 1.5 um in thickness were directly textured and a window layer removal process was performed before metal catalyst deposition. A nanohole-textured emitter layer provides effective light trapping capabilities, reducing the surface reflection of a textured solar cell by 11.0%. However, because the nanostructures have high surface area to volume ratios and large numbers of defects, various photovoltaic properties were diminished by high recombination losses. Thus, we have studied the application of nanohole structures to GaAs emitter solar cells and investigated the cells' antireflection and photovoltaic properties as a function of the nanohole structure and emitter thickness. Due to decreased surface reflection and improved shunt resistance, the solar cell efficiency increased from 4.25% for non-textured solar cells to 7.15% for solar cells textured for 5 min.

Investigation of graphene-on-metal substrates for SPR-based sensor using finite-difference time domain.

PubMed

Said, Fairus Atida; Menon, Pulliyaseri Susthitha; Rajendran, Venkatachalam; Shaari, Sahbudin; Majlis, Burhanuddin Y

2017-12-01

In this study, the authors investigated the effects of a single layer graphene as a coating layer on top of metal thin films such as silver, gold, aluminum and copper using finite-difference time domain method. To enhance the resolution of surface plasmon resonance (SPR) sensor, it is necessary to increase the SPR reflectivity and decrease the full-width-half maximum (FWHM) of the SPR curve so that there is minimum uncertainty in the determination of the resonance dip. Numerical data was verified with analytical and experimental data where all the data were in good agreement with resonance angle differing in <10% due to noise present in components such as humidity and temperature. In further analysis, reflectivity and FWHM were compared among four types of metal with various thin film thicknesses where graphene was applied on top of the metal layers, and data was compared against pure conventional metal thin films. A 60 nm-thick Au thin film results in higher performance with reflectivity of 92.4% and FWHM of 0.88° whereas single layer graphene-on-60 nm-thick Au gave reflectivity of 91.7% and FWHM of 1.32°. However, a graphene-on-40 nm-thick Ag also gave good performance with narrower FWHM of 0.88° and reflection spectra of 89.2%.

Deposition of gold nano-particles and nano-layers on polyethylene modified by plasma discharge and chemical treatment

NASA Astrophysics Data System (ADS)

Švorčík, V.; Chaloupka, A.; Záruba, K.; Král, V.; Bláhová, O.; Macková, A.; Hnatowicz, V.

2009-08-01

Polyethylene (PE) was treated in Ar plasma discharge and then grafted from methanol solution of 1,2-ethanedithiol to enhance adhesion of gold nano-particles or sputtered gold layers. The modified PE samples were either immersed into freshly prepared colloid solution of Au nano-particles or covered by sputtered, 50 nm thick gold nano-layer. Properties of the plasma modified, dithiol grafted and gold coated PE were studied using XPS, UV-VIS, AFM, EPR, RBS methods and nanoindentation. It was shown that the plasma treatment results in degradation of polymer chain, creation of excessive free radicals and conjugated double bonds. After grafting with 1,2-ethanedithiol the concentration of free radicals declined but the concentration of double bonds remained unchanged. Plasma treatment changes PE surface morphology and increases surface roughness too. Another significant change in the surface morphology and roughness was observed after deposition of Au nano-particles. The presence of Au on the sample surface after the coating with Au nano-particles was proved by XPS and RBS methods. Nanoindentation measurements shown that the grafting of plasma activated PE surface with dithiol increases significantly adhesion of sputtered Au nano-layer.

Localized surface plasmon resonance modulation of totally encapsulated VO2/Au/VO2 composite structure

NASA Astrophysics Data System (ADS)

Liang, Jiran; Guo, Jinbang; Zhao, Yirui; Zhang, Ying; Su, Tianyu

2018-07-01

We design and fabricate a totally encapsulated VO2/Au/VO2 composite structure which is aimed to improve the tunability of the localized surface plasmon resonance (LSPR) peak. In this work, the structure will ensure all the Au NPs’ resonant electric field area is filled with VO2. The modulation range of the totally encapsulated structure is larger than that of the semi-coated structure. To further improve the modulation range, we also explore the VO2 thickness dependence of the structure’s LSPR modulation. With the increase of the top layer VO2 thin film thickness, the modulation range becomes larger. When the thickness is about 80 nm, the absorption peak achieves a largest shift of 112 nm. FDTD solution and equivalent model of series capacitor are used to explain the phenomenon. These results will contribute to the area of metamaterial electromagnetic wave absorber and other fields.

Localized surface plasmon resonance modulation of totally encapsulated VO2/Au/VO2 composite structure.

PubMed

Liang, Jiran; Guo, Jinbang; Zhao, Yirui; Zhang, Ying; Su, Tianyu

2018-07-06

We design and fabricate a totally encapsulated VO 2 /Au/VO 2 composite structure which is aimed to improve the tunability of the localized surface plasmon resonance (LSPR) peak. In this work, the structure will ensure all the Au NPs' resonant electric field area is filled with VO 2 . The modulation range of the totally encapsulated structure is larger than that of the semi-coated structure. To further improve the modulation range, we also explore the VO 2 thickness dependence of the structure's LSPR modulation. With the increase of the top layer VO 2 thin film thickness, the modulation range becomes larger. When the thickness is about 80 nm, the absorption peak achieves a largest shift of 112 nm. FDTD solution and equivalent model of series capacitor are used to explain the phenomenon. These results will contribute to the area of metamaterial electromagnetic wave absorber and other fields.

Laser induced nanostructures created from Au layer on polyhydroxybutyrate

NASA Astrophysics Data System (ADS)

Michaljaničová, I.; Slepička, P.; Juřík, P.; Švorčík, V.

2017-11-01

Nanostructures as well as composite materials expand the range of materials properties and allow use of these materials in new and highly specific applications. In this paper, we described laser modification of polyhydroxybutyrate films covered with thin gold layer, which led to the formation of various composite structures. The crucial for the composite structures creation was setting of appropriate laser parameters; 15 mJ cm-2 laser fluence and 6 000 pulses were recognized as the best. The morphology of structures was determined by the thickness of the Au layer. The most interesting formations, very porous with the biggest roughness, were observed after treatment of foils covered with 10 nm of Au. The morphology was observed by atomic force microscopy. The influence on roughness and the difference between projected area and surface area was also determined.

A novel surface plasmon resonance biosensor based on the PDA-AgNPs-PDA-Au film sensing platform for horse IgG detection

NASA Astrophysics Data System (ADS)

Wang, Ning; Zhang, Di; Deng, Xinyu; Sun, Ying; Wang, Xinghua; Ma, Pinyi; Song, Daqian

2018-02-01

Herein we report a novel polydopamine-silver nanoparticle-polydopamine-gold (PDA-AgNPs-PDA-Au) film based surface plasmon resonance (SPR) biosensor for horse IgG detection. The PDA-AgNPs-PDA-Au film sensing platform was built on Au-film via layer-by-layer self-assembly. Ag ion was reduced in situ to AgNPs in presence of PDA. The top PDA layer can prevent AgNPs from being oxidized and connect with antibody via Schiff alkali reaction directly. The morphology and thickness of the modified gold film were characterized using scanning electron microscope and Talystep. Experimental results show that the PDA-AgNPs-PDA-Au film sensing platform is stable, regenerative and sensitive for horse IgG detection. The detection limit of horse IgG obtained with the present biosensor is 0.625 μg mL- 1, which is 2-fold and 4-fold lower than that obtained with biosensor based on PDA modified Au film and conventional biosensor based on MPA, respectively. Furthermore, when challenged to real serum samples, our sensor exhibited excellent specificity to horse IgG, suggesting its potential for industrial application.

Microstructural analysis of Ti/Al/Ti/Au ohmic contacts to n-AlGaN/GaN

NASA Astrophysics Data System (ADS)

Chen, J.; Ivey, D. G.; Bardwell, J.; Liu, Y.; Tang, H.; Webb, J. B.

2002-05-01

To develop high quality AlGaN/GaN heterostructure field effect transistors for use in high power, high frequency, and high temperature applications, low resistance, thermal stable ohmic contacts with good surface morphology are essential. Low specific contact resistances have been achieved using an Au/Ti/Al/Ti contact: a minimum value of 6.33×10-6 Ω cm2 was attained after annealing at 700 °C for 30 s. Microstructural analysis using transmission electron microscopy indicated that there is significant interaction between the metallization components and the semiconductor during annealing. The optimum electrical properties correspond to a microstructure that consists of Au2Ti and TiAl layers as well as of a thin Ti-rich layer (~10 nm thick) at the metallization/AlGaN interface. Degradation of the contact occurred for annealing temperatures in excess of 750 °C, and was accompanied by decomposition of the AlGaN layer and formation of a Au-Ti-Al-Ga quaternary phase.

Electrophoretic deposition of fluorescent Cu and Au sheets for light-emitting diodes

NASA Astrophysics Data System (ADS)

Liu, Jiale; Wu, Zhennan; Li, Tingting; Zhou, Ding; Zhang, Kai; Sheng, Yu; Cui, Jianli; Zhang, Hao; Yang, Bai

2015-12-01

Electrophoretic deposition (EPD) is a conventional method for fabricating film materials from nanometer-sized building blocks, and exhibits the advantages of low-cost, high-efficiency, wide-range thickness adjustment, and uniform deposition. Inspired by the interest in the application of two-dimensional (2D) nanomaterials, the EPD technique has been recently extended to building blocks with 2D features. However, the studies are mainly focused on simplex building blocks. The utilization of multiplex building blocks is rarely reported. In this work, we demonstrate a controlled EPD of Cu and Au sheets, which are 2D assemblies of luminescent Cu and Au nanoclusters. Systematic investigations reveal that both the deposition efficiency and the thickness are determined by the lateral size of the sheets. For Cu sheets with a large lateral size, a high ζ-potential and strong face-to-face van der Waals interactions facilitate the deposition with high efficiency. However, for Au sheets, the small lateral size and ζ-potential limit the formation of a thick film. To solve this problem, the deposition dynamics are controlled by increasing the concentration of the Au sheets and adding acetone. This understanding permits the fabrication of a binary EPD film by the stepwise deposition of Cu and Au sheets, thus producing a luminescent film with both Cu green emission and Au red emission. A white light-emitting diode prototype with color coordinates (x, y) = (0.31, 0.36) is fabricated by employing the EPD film as a color conversion layer on a 365 nm GaN clip and further tuning the amount of deposited Cu and Au sheets.Electrophoretic deposition (EPD) is a conventional method for fabricating film materials from nanometer-sized building blocks, and exhibits the advantages of low-cost, high-efficiency, wide-range thickness adjustment, and uniform deposition. Inspired by the interest in the application of two-dimensional (2D) nanomaterials, the EPD technique has been recently extended to building blocks with 2D features. However, the studies are mainly focused on simplex building blocks. The utilization of multiplex building blocks is rarely reported. In this work, we demonstrate a controlled EPD of Cu and Au sheets, which are 2D assemblies of luminescent Cu and Au nanoclusters. Systematic investigations reveal that both the deposition efficiency and the thickness are determined by the lateral size of the sheets. For Cu sheets with a large lateral size, a high ζ-potential and strong face-to-face van der Waals interactions facilitate the deposition with high efficiency. However, for Au sheets, the small lateral size and ζ-potential limit the formation of a thick film. To solve this problem, the deposition dynamics are controlled by increasing the concentration of the Au sheets and adding acetone. This understanding permits the fabrication of a binary EPD film by the stepwise deposition of Cu and Au sheets, thus producing a luminescent film with both Cu green emission and Au red emission. A white light-emitting diode prototype with color coordinates (x, y) = (0.31, 0.36) is fabricated by employing the EPD film as a color conversion layer on a 365 nm GaN clip and further tuning the amount of deposited Cu and Au sheets. Electronic supplementary information (ESI) available: Additional experimental information, and SEM images of Cu EPD films. See DOI: 10.1039/c5nr06599b

X-ray Fluorescence Spectroscopy Study of Coating Thickness and Base Metal Composition

NASA Technical Reports Server (NTRS)

Rolin, T. D.; Leszczuk, Y.

2008-01-01

For electrical, electronic, and electromechanical (EEE) parts to be approved for space use, they must be able to meet safety standards approved by NASA. A fast, reliable, and precise method is needed to make sure these standards are met. Many EEE parts are coated in gold (Au) and nickel (Ni), and the thickness coating is crucial to a part s performance. A nondestructive method that is efficient in measuring coating thickness is x-ray fluorescence (XRF) spectroscopy. The XRF spectrometer is a machine designed to measure layer thickness and composition of single or multilayered samples. By understanding the limitations in the collection of the data by this method, accurate composition and thickness measurements can be obtained for samples with Au and Ni coatings. To understand the limitations of data found, measurements were taken with the XRF spectrometer and compared to true values of standard reference materials (SRM) that were National Institute of Standards and Technology (NIST) traceable. For every sample, six different parameters were varied to understand measurement error: coating/substrate combination, number of layers, counting interval, collimator size, coating thickness, and test area location. Each measurement was taken in accordance with standards set by the American Society for Testing and Materials (ASTM) International Standard B 568.

Optical coating design for the annular mirrors of the Alpha I HF laser

NASA Astrophysics Data System (ADS)

Shellan, Jeffrey B.

The dielectric-coating design for the annular mirrors of the Alpha I HF laser is described along with the numerous other designs that were considered. The coatings were required to produce a 0-deg phase shift after one round trip, which involved reflections from six surfaces. Although novel high-reflectivity multilayer dielectric coatings satisfied this requirement, single-layer phase control coatings were preferred because the use of these greatly reduced coating layer-thickness control and thus resulted in significant program savings. Among the single-layer designs investigated, a coating consisting of a 0.06-micron-thick SiO layer was found to be sufficient for all surfaces except those of the rear cone, for which a 0.515-micron thick SiO layer was recommended. The metallic substrate selected was Au. These coatings were found to have a high damage threshold, provide the necessary polarization phase control, and to be quite forgiving to thickness deposition errors that were anticipated using existing chambers.

Photoacoustic emission from Au nanoparticles arrayed on thermal insulation layer.

PubMed

Namura, Kyoko; Suzuki, Motofumi; Nakajima, Kaoru; Kimura, Kenji

2013-04-08

Efficient photoacoustic emission from Au nanoparticles on a porous SiO(2) layer was investigated experimentally and theoretically. The Au nanoparticle arrays/porous SiO(2)/SiO(2)/Ag mirror sandwiches, namely, local plasmon resonators, were prepared by dynamic oblique deposition (DOD). Photoacoustic measurements were performed on the local plasmon resonators, whose optical absorption was varied from 0.03 (3%) to 0.95 by varying the thickness of the dielectric SiO(2) layer. The sample with high absorption (0.95) emitted a sound that was eight times stronger than that emitted by graphite (0.94) and three times stronger than that emitted by the sample without the porous SiO(2) layer (0.93). The contribution of the porous SiO(2) layer to the efficient photoacoustic emission was analyzed by means of a numerical method based on a one-dimensional heat transfer model. The result suggested that the low thermal conductivity of the underlying porous layer reduces the amount of heat escaping from the substrate and contributes to the efficient photoacoustic emission from Au nanoparticle arrays. Because both the thermal conductivity and the spatial distribution of the heat generation can be controlled by DOD, the local plasmon resonators produced by DOD are suitable for the spatio-temporal modulation of the local temperature.

Plasmon enhanced power conversion efficiency in inverted bulk heterojunction organic solar cell

NASA Astrophysics Data System (ADS)

Mohan, Minu; Ramkumar, S.; Namboothiry, Manoj A. G.

2017-08-01

P3HT:PCBM is one of the most studied polymer-fullerene system. However the reported power conversion efficiency (PCE) values falls within the range of 4% to 5%. The thin film architecture in OPVs exhibits low PCE compared to inorganic photovoltaic cells. This is mainly due to the low exciton diffusion length that limits the active layer thickness which in turn reduces the absorption of incident light. Several strategies are adapted in order to increase the absorption in the active layer without increasing the film thickness. Inclusion of metal nanoparticles into the polymer layer of bulk heterojunction (BHJ) solar cells is one of the promising methods. Incorporation of metal nanostructures increases the absorption of organic materials due to the high electromagnetic field strength in the vicinity of the excited surface plasmons. In this work, we used 60 nm Au plasmonic structures to improve the efficiency of organic solar cell. The prepared metal nano structures were characterized through scanning electron microscopy (SEM), and UV-Visible spectroscopy techniques. These prepared metallic nanoparticles can be incorporated either into the electron transport layer (ETL) or into the active P3HT:PC71BM layer. The effect of incorporation of plasmonic gold (Au) nanoparticle in the inverted bulk heterojunction organic photovoltaic cells (OPVs) of P3HT:PC71BM fabricated in ambient air condition is in progress. Initial studies shows an 8.5% enhancement in the PCE with the incorporation of Au nanoparticles under AM1.5G light of intensity 1 Sun.

A novel evaluation strategy for fatigue reliability of flexible nanoscale films

NASA Astrophysics Data System (ADS)

Zheng, Si-Xue; Luo, Xue-Mei; Wang, Dong; Zhang, Guang-Ping

2018-03-01

In order to evaluate fatigue reliability of nanoscale metal films on flexible substrates, here we proposed an effective evaluation way to obtain critical fatigue cracking strain based on the direct observation of fatigue damage sites through conventional dynamic bending testing technique. By this method, fatigue properties and damage behaviors of 930 nm-thick Au films and 600 nm-thick Mo-W multilayers with individual layer thickness 100 nm on flexible polyimide substrates were investigated. Coffin-Manson relationship between the fatigue life and the applied strain range was obtained for the Au films and Mo-W multilayers. The characterization of fatigue damage behaviors verifies the feasibility of this method, which seems easier and more effective comparing with the other testing methods.

Electron transport in ultra-thin films and ballistic electron emission microscopy

NASA Astrophysics Data System (ADS)

Claveau, Y.; Di Matteo, S.; de Andres, P. L.; Flores, F.

2017-03-01

We have developed a calculation scheme for the elastic electron current in ultra-thin epitaxial heterostructures. Our model uses a Keldysh’s non-equilibrium Green’s function formalism and a layer-by-layer construction of the epitaxial film. Such an approach is appropriate to describe the current in a ballistic electron emission microscope (BEEM) where the metal base layer is ultra-thin and generalizes a previous one based on a decimation technique appropriated for thick slabs. This formalism allows a full quantum mechanical description of the transmission across the epitaxial heterostructure interface, including multiple scattering via the Dyson equation, which is deemed a crucial ingredient to describe interfaces of ultra-thin layers properly in the future. We introduce a theoretical formulation needed for ultra-thin layers and we compare with results obtained for thick Au(1 1 1) metal layers. An interesting effect takes place for a width of about ten layers: a BEEM current can propagate via the center of the reciprocal space (\\overlineΓ ) along the Au(1 1 1) direction. We associate this current to a coherent interference finite-width effect that cannot be found using a decimation technique. Finally, we have tested the validity of the handy semiclassical formalism to describe the BEEM current.

Growth and sacrificial oxidation of transition metal nanolayers

NASA Astrophysics Data System (ADS)

Tsarfati, Tim; Zoethout, Erwin; van de Kruijs, Robbert; Bijkerk, Fred

2009-04-01

Growth and oxidation of Au, Pt, Pd, Rh, Cu, Ru, Ni and Co layers of 0.3-4.3 nm thickness on Mo have been investigated with ARPES and AFM. Co and Ni layers oxidize while the Mo remains metallic. For nobler metals, the on top O and oxidation state of subsurface Mo increase, suggesting sacrificial e - donation by Mo. Au and Cu, in spite of their significantly lower surface free energy, grow in islands on Mo and actually promote Mo oxidation. Applications of the sacrificial oxidation in nanometer thin layers exist in a range of nanoscopic devices, such as nano-electronics and protection of e.g. multilayer X-ray optics for astronomy, medicine and lithography.

Electrophoretic build-up of alternately multilayered films and micropatterns based on graphene sheets and nanoparticles and their applications in flexible supercapacitors.

PubMed

Niu, Zhiqiang; Du, Jianjun; Cao, Xuebo; Sun, Yinghui; Zhou, Weiya; Hng, Huey Hoon; Ma, Jan; Chen, Xiaodong; Xie, Sishen

2012-10-22

Graphene nanosheets and metal nanoparticles (NPs) have been used as nano-building-blocks for assembly into macroscale hybrid structures with promising performance in electrical devices. However, in most graphene and metal NP hybrid structures, the graphene sheets and metal NPs (e.g., AuNPs) do not enable control of the reaction process, orientation of building blocks, and organization at the nanoscale. Here, an electrophoretic layer-by-layer assembly for constructing multilayered reduced graphene oxide (RGO)/AuNP films and lateral micropatterns is presented. This assembly method allows easy control of the nano-architecture of building blocks along the normal direction of the film, including the number and thickness of RGO and AuNP layers, in addition to control of the lateral orientation of the resultant multilayered structures. Conductivity of multilayered RGO/AuNP hybrid nano-architecture shows great improvement caused by a bridging effect of the AuNPs along the out-of-plane direction between the upper and lower RGO layers. The results clearly show the potential of electrophoretic build-up in the fabrication of graphene-based alternately multilayered films and patterns. Finally, flexible supercapacitors based on multilayered RGO/AuNP hybrid films are fabricated, and excellent performance, such as high energy and power densities, are achieved. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Self-assembling of 2,3-phenyl/thienyl-substituted acrylic acids over polycrystalline gold

NASA Astrophysics Data System (ADS)

Csankó, K.; Kozma, G.; Valkai, L.; Kukovecz, Á.; Kónya, Z.; Sipos, P.; Pálinkó, I.

2013-07-01

Self-assembling layers were formed from sulfur-containing cinnamic acid analogues over polycrystalline Au surface. The horizontal organising forces were strong O-H⋯O and weaker C-H⋯S hydrogen bonds (the former interaction kept together the acid dimers serving as the fundamental unit, while the latter was crucial in the construction of the 2D layers), while the vertical organisation forces were provided by Au-S covalent bonds. Measurements by atomic force, scanning electron, infrared and Raman microscopies attested that the dimers were situated in a nearly perpendicular fashion to the Au surface providing a ˜30-40 nm thick organic "carpet" and out of this layer occasionally, peaks with height of ˜100-120 nm grew out. The outgrowth of these surface structures were most probably governed by the defects of the polycrystalline metal surface.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fischer, C G; Denison, A B; Weber, M H

We employed the two detector coincident Doppler Broadening Technique (coPAS) to investigate Ag, Au and Ag/Au alloy quantum dots of varying sizes which were deposited in thin layers on glass slides. The Ag quantum dots range from 2 to 3 nm in diameter, while the Ag/Au alloy quantum dots exhibit Ag cores of 2 nm and 3 nm and Au shells of varying thickness. We investigate the possibility of positron confinement in the Ag core due to positron affinity differences between Ag and Au. We describe the results and their significance to resolving the issue of whether positrons annihilate withinmore » the quantum dot itself or whether surface and positron escape effects play an important role.« less

Architecture of Pd-Au bimetallic nanoparticles in sodium bis(2-ethylhexyl)sulfosuccinate reverse micelles as investigated by X-ray absorption spectroscopy.

PubMed

Chen, Ching-Hsiang; Sarma, Loka Subramanyam; Chen, Jium-Ming; Shih, Shou-Chu; Wang, Guo-Rung; Liu, Din-Goa; Tang, Mau-Tsu; Lee, Jyh-Fu; Hwang, Bing-Joe

2007-09-01

In this study, we demonstrate the unique application of X-ray absorption spectroscopy (XAS) as a fundamental characterization tool to help in designing and controlling the architecture of Pd-Au bimetallic nanoparticles within a water-in-oil microemulsion system of water/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/n-heptane. Structural insights obtained from the in situ XAS measurements recorded at each step during the formation process revealed that Pd-Au bimetallic clusters with various Pd-Au atomic stackings are formed by properly performing hydrazine reduction and redox transmetalation reactions sequentially within water-in-oil microemulsions. A structural model is provided to explain reasonably each reaction step and to give detailed insight into the nucleation and growth mechanism of Pd-Au bimetallic clusters. The combination of in situ XAS analysis at both the Pd K-edge and the Au L(III)-edge and UV-vis absorption spectral features confirms that the formation of Pd-Au bimetallic clusters follows a (Pd(nuclei)-Au(stack))-Pd(surf) stacking. This result further implies that the thickness of Au(stack) and Pd(surf) layers may be modulated by varying the dosage of the Au precursor and hydrazine, respectively. In addition, a bimetallic (Pd-Au)(alloy) nanocluster with a (Pd(nuclei)-Au(stack))-(Pd-Au(alloy))(surf) stacking was also designed and synthesized in order to check the feasibility of Pd(surf) layer modification. The result reveals that the Pd(surf) layer of the stacked (Pd(nuclei)-Au)(stack) bimetallic clusters can be successfully modified to form a (Au-Pd alloy)(surf) layer by a co-reduction of Pd and Au ions by hydrazine. Further, we demonstrate the alloying extent or atomic distribution of Pd and Au in Pd-Au bimetallic nanoparticles from the derived XAS structural parameters. The complete XAS-based methodology, demonstrated here on the Pd-Au bimetallic system, can easily be extended to design and control the alloying extent or atomic distribution, atomic stacking, and electronic structure to construct many other types of bimetallic systems for interesting applications.

Localized surface plasmon resonance properties of Ag nanorod arrays on graphene-coated Au substrate

NASA Astrophysics Data System (ADS)

Mu, Haiwei; Lv, Jingwei; Liu, Chao; Sun, Tao; Chu, Paul K.; Zhang, Jingping

2017-11-01

Localized surface plasmon resonance (LSPR) on silver nanorod (SNR) arrays deposited on a graphene-coated Au substrate is investigated by the discrete dipole approximation (DDA) method. The resonance peaks in the extinction spectra of the SNR/graphene/Au structure show significantly different profiles as SNR height, and refractive index of the surrounding medium are varied gradually. Numerical simulation reveals that the shifts in the resonance peaks arise from hybridization of multiple plasmon modes as a result of coupling between the SNR arrays and graphene-coated Au substrate. Moreover, the LSPR modes blue-shifts from 800 nm to 700 nm when the thickness of the graphene layer in the metal nanoparticle (NP) - graphene hybrid nanostructure increases from 1 nm to 5 nm, which attribute to charge transfer between the graphene layer and SNR arrays. The results provide insights into metal NP-graphene hybrid nanostructures which have potential applications in plasmonics.

Analysis of the metal layer thickness influence on the dispersion characteristics of acoustic waves propagating in the layered piezoelectric structure "Me/AlN/Me/diamond".

PubMed

Burkov, S I; Zolotova, O P; Sorokin, B P

2018-02-01

The paper presents the results of computer simulation of the acoustic waves propagation in piezoelectric layered structures based on diamond substrate under the influence of various metal film deposition. It has been observed that the maximum phase velocity change Δv/v is achieved with an "Au/(001) AlN/Au/(100) diamond" PLS configuration. However, if the acoustic impedance of the metal layer is greater than the acoustic impedance of the substrate, an elastic wave reflection can be observed, reducing the Δv/v quantities. Obtained results may be useful in the development of resonant and sensor acousto-electronic devices based on the Rayleigh and Love waves. Copyright © 2017 Elsevier B.V. All rights reserved.

SERS Taper-Fiber Nanoprobe Modified by Gold Nanoparticles Wrapped with Ultrathin Alumina Film by Atomic Layer Deposition

PubMed Central

Xu, Wenjie; Chen, Zhenyi; Chen, Na; Zhang, Heng; Liu, Shupeng; Hu, Xinmao; Wen, Jianxiang; Wang, Tingyun

2017-01-01

A taper-fiber SERS nanoprobe modified by gold nanoparticles (Au-NPs) with ultrathin alumina layers was fabricated and its ability to perform remote Raman detection was demonstrated. The taper-fiber nanoprobe (TFNP) with a nanoscale tip size under 80 nm was made by heated pulling combined with the chemical etching method. The Au-NPs were deposited on the TFNP surface with the electrostatic self-assembly technology, and then the TFNP was wrapped with ultrathin alumina layers by the atomic layer deposition (ALD) technique. The results told us that with the increasing thickness of the alumina film, the Raman signals decreased. With approximately 1 nm alumina film, the remote detection limit for R6G aqueous solution reached 10−6 mol/L. PMID:28245618

Interfacial layer thickness dependent electrical characteristics of Au/(Zn-doped PVA)/n-4H-SiC (MPS) structures at room temperature

NASA Astrophysics Data System (ADS)

Lapa, Havva Elif; Kökce, Ali; Al-Dharob, Mohammed; Orak, İkram; Özdemir, Ahmet Faruk; Altındal, Semsettin

2017-10-01

Au/(Zn-doped PVA)/n-4H-SiC metal/polymer/semiconductor (MPS) structures with different interfacial layer thickness values (50, 150, 500 nm) were fabricated and their electrical characteristics were compared. Their electrical parameters (i.e. reverse-bias saturation current (Io), ideality factor (n), zero-bias barrier height (BH) (Φbo), series and shunt resistances (Rs, Rsh)) were calculated from the forward bias current-voltage (IF-VF) data whereas other parameters (i.e. Fermi energy level (EF), BH (Vb) and donor concentration (Nd)) were calculated from the linear part of C-2-V characteristics at room temperature. Obtained results confirmed that the values of n, Φbo, Rs and Rsh increase with increasing interlayer thickness, and linear correlation between n and Φbo was observed. The high values of n for three structures can be ascribed to the presence of an interlayer, surface states (Nss) and barrier inhomogeneities. The energy density distribution profile of Nss was obtained from the IF-VF data by taking into account voltage-dependent effective BH (Ve) and n for each structure. The Ri vs V plot for these structures was obtained using both Ohm's law and Nicollian-Brews method. All these experimental results show that the interfacial layer and its thickness play an important role in main electric parameters of these structures.

Silicide surface phases on gold

NASA Technical Reports Server (NTRS)

Green, A. K.; Bauer, E.

1981-01-01

The crystalline silicide layers formed on (111) and (100) surfaces of Au films on various Si single-crystal substrates are studied by LEED and AES in conjunction with sputter-depth profiling as a function of annealing temperature. On the (111) surface, three basic silicide structures are obtained corresponding to layers of various thicknesses as obtained by different preparation conditions. The (100) surface shows only two different structures. None of the structures is compatible with the various bulk silicide structures deduced from X-ray diffraction. Using LEED as a criterion for the presence or absence of silicide on the surface, smaller layer thicknesses are obtained than reported previously on the basis of AES studies.

Spontaneous synthesis of gold nanoparticles on gum arabic-modified iron oxide nanoparticles as a magnetically recoverable nanocatalyst.

PubMed

Wu, Chien-Chen; Chen, Dong-Hwang

2012-06-19

A novel magnetically recoverable Au nanocatalyst was fabricated by spontaneous green synthesis of Au nanoparticles on the surface of gum arabic-modified Fe3O4 nanoparticles. A layer of Au nanoparticles with thickness of about 2 nm was deposited on the surface of gum arabic-modified Fe3O4 nanoparticles, because gum arabic acted as a reducing agent and a stabilizing agent simultaneously. The resultant magnetically recoverable Au nanocatalyst exhibited good catalytic activity for the reduction of 4-nitrophenol with sodium borohydride. The rate constants evaluated in terms of pseudo-first-order kinetic model increased with increase in the amount of Au nanocatalyst or decrease in the initial concentration of 4-nitrophenol. The kinetic data suggested that this catalytic reaction was diffusion-controlled, owing to the presence of gum arabic layer. In addition, this nanocatalyst exhibited good stability. Its activity had no significant decrease after five recycles. This work is useful for the development and application of magnetically recoverable Au nanocatalyst on the basis of green chemistry principles.

Spontaneous synthesis of gold nanoparticles on gum arabic-modified iron oxide nanoparticles as a magnetically recoverable nanocatalyst

PubMed Central

2012-01-01

A novel magnetically recoverable Au nanocatalyst was fabricated by spontaneous green synthesis of Au nanoparticles on the surface of gum arabic-modified Fe3O4 nanoparticles. A layer of Au nanoparticles with thickness of about 2 nm was deposited on the surface of gum arabic-modified Fe3O4 nanoparticles, because gum arabic acted as a reducing agent and a stabilizing agent simultaneously. The resultant magnetically recoverable Au nanocatalyst exhibited good catalytic activity for the reduction of 4-nitrophenol with sodium borohydride. The rate constants evaluated in terms of pseudo-first-order kinetic model increased with increase in the amount of Au nanocatalyst or decrease in the initial concentration of 4-nitrophenol. The kinetic data suggested that this catalytic reaction was diffusion-controlled, owing to the presence of gum arabic layer. In addition, this nanocatalyst exhibited good stability. Its activity had no significant decrease after five recycles. This work is useful for the development and application of magnetically recoverable Au nanocatalyst on the basis of green chemistry principles. PMID:22713480

Conductive atomic force microscopy study of the photoexcitation effect on resistive switching in ZrO2(Y) films with Au nanoparticles

NASA Astrophysics Data System (ADS)

Novikov, A. S.; Filatov, D. O.; Antonov, D. A.; Antonov, I. N.; Shenina, M. E.; Gorshkov, O. N.

2018-03-01

We report on the experimental observation of the effect of optical excitation on resistive switching in ultrathin ZrO2(Y) films with single-layered arrays of Au nanoparticles. The samples were prepared by depositing nanometer-thick Au films sandwiched between two ZrO2(Y) layers by magnetron sputtering followed by annealing. Resistive switching was studied by conductive atomic force microscopy by measuring cyclic current-voltage curves of a probe-to-sample contact. The contact area was illuminated by radiation of a semiconductor laser diode with the wavelength corresponding to the plasmon resonance in an Au nanoparticle array. The enhancement of the hysteresis in cyclic current-voltage curves due to bipolar resistive switching under illumination was observed. The effect was attributed to heating of Au nanoparticles due to plasmonic optical absorption and a plasmon resonance, which enhances internal photoemission of electrons from the Fermi level in Au nanoparticles into the conduction band of ZrO2(Y). Both factors promote resistive switching in a ZrO2(Y) matrix.

Design and numerical analysis of highly sensitive Au-MoS2-graphene based hybrid surface plasmon resonance biosensor

NASA Astrophysics Data System (ADS)

Rahman, M. Saifur; Anower, Md. Shamim; Hasan, Md. Rabiul; Hossain, Md. Biplob; Haque, Md. Ismail

2017-08-01

We demonstrate a highly sensitive Au-MoS2-Graphene based hybrid surface plasmon resonance (SPR) biosensor for the detection of DNA hybridization. The performance parameters of the proposed sensor are investigated in terms of sensitivity, detection accuracy and quality factor at operating wavelength of 633 nm. We observed in the numerical study that sensitivity can be greatly increased by adding MoS2 layer in the middle of a Graphene-on-Au layer. It is shown that by using single layer of MoS2 in between gold and graphene layer, the proposed biosensor exhibits simultaneously high sensitivity of 87.8 deg/RIU, high detection accuracy of 1.28 and quality factor of 17.56 with gold layer thickness of 50 nm. This increased performance is due to the absorption ability and optical characteristics of graphene biomolecules and high fluorescence quenching ability of MoS2. On the basis of changing in SPR angle and minimum reflectance, the proposed sensor can sense nucleotides bonding happened between double-stranded DNA (dsDNA) helix structures. Therefore, this sensor can successfully detect the hybridization of target DNAs to the probe DNAs pre-immobilized on the Au-MoS2-Graphene hybrid with capability of distinguishing single-base mismatch.

Ordered arrays of Au catalysts by FIB assisted heterogeneous dewetting.

PubMed

Benkouider, A; Ronda, A; David, T; Favre, L; Abbarchi, M; Naffouti, M; Osmond, J; Delobbe, A; Sudraud, P; Berbezier, I

2015-12-18

Synthesizing Au0.8Si0.2 nanocatalysts that are homogeneous in size and have controlled position is becoming a challenging and crucial prequisite for the fabrication of ordered semiconductor nanowires. In this study, Au0.8Si0.2 nanocatalysts are synthesized via dewetting of Au layers on Si(111) during thermal annealing in an ultra-high vacuum. In the first part of the paper, the mechanism of homogeneous dewetting is analyzed as a function of the Au-deposited thickness (h Au). We distinguish three different dewetting regimes: (I) for a low thickness ([Formula: see text]), a submonolyer coverage of Au is stabilized and there is no dewetting. (II) For an intermediate thickness ([Formula: see text]), there is both dewetting and Au0.8Si0.2 phase formation. The size and density of the Au0.8Si0.2 clusters are directly related to h Au. When cooling down to room temperature, the clusters decompose and reject the Si at the Au/Si substrate interface. (III) For a large thickness ([Formula: see text]), only dewetting takes place, without forming AuSi clusters. In this regime, the dewetting is kinetically controlled by the self-diffusion of Au (activation energy ∼0.43 eV) without evidence of an Si-alloying effect. As a practical consequence, when relying solely on the homogeneous dewetting of Au/Si(111) to form the Au0.8Si0.2 catalysts (without a supply of Si atoms from vapor), regime II should be used to obtain good size and density control. In the second part of the paper, a process for ordering the catalysts using focused ion beam-(FIB) assisted dewetting (heterogeneous dewetting) is developed. We show that no matter what the FIB milling conditions and the Au nominal thickness are, dewetting is promoted by ion beam irradiation and is accompanied by the formation of Au0.8Si0.2 droplets. The droplets preferentially form on the patterned areas, while in similar annealing conditions, they do not form on the unpatterned areas. This behavior is attributed to the larger Au-Si interdiffusion in the patterned areas, which results from the Si amorphization induced by the FIB. A systematic analysis of the position of the nanodroplets shows their preferential nucleation inside the patterns, while thicker platelets of almost pure Au are observed between the patterns. The evolutions of the size homogeneity and the occupancy rate of the patterns are quantified as a function of the FIB dose and annealing temperature. Nice arrays of perfectly ordered AuSi catalysts are obtained after optimizing the FIB and dewetting conditions.

Nanoporous Au: An experimental study on the porosity of dealloyed AuAg leafs

NASA Astrophysics Data System (ADS)

Grillo, R.; Torrisi, V.; Ruffino, F.

2016-12-01

We present a study on the fraction of porosity for dealloyed nanoporous Au leafs. Nanoporous Au is attracting great scientific interest due to its peculiar plasmonic properties and the high exposed surface (∼10 m2/g). As examples, it was used in prototypes of chemical and biological devices. However, the maximization of the devices sensitivity is subjected to the maximization of the exposed surface by the nanoporous Au, i. e. maximization of the porosity fraction. So, we report on the analyses of the porosity fraction in nanoporous Au leafs as a function of the fabrication process parameters. We dealloyed 60 μm-thick Au23Ag77 at.% leafs and we show that: a) for dealloying time till to 6 h, only a 450 nm-thick surface layer of the leafs assumes a nanoporous structure with a porosity fraction of 32%. For a dealloying time of 20 h the leafs result fragmented in small black pieces with a porosity fraction increased to 60%. b) After 600 °C-30 minutes annealing of the previous samples, the nanopores disappear due to the Au/residual Ag inter-diffusion. c) After a second dealloying process on the previously annealed samples, the surface nanoporous structure is, again, obtained with the porosity fraction increased to 50%.

Brazing open cell reticulated copper foam to stainless steel tubing with vacuum furnace brazed gold/indium alloy plating

DOEpatents

Howard, Stanley R [Windsor, SC; Korinko, Paul S [Aiken, SC

2008-05-27

A method of fabricating a heat exchanger includes brush electroplating plated layers for a brazing alloy onto a stainless steel tube in thin layers, over a nickel strike having a 1.3 .mu.m thickness. The resultant Au-18 In composition may be applied as a first layer of indium, 1.47 .mu.m thick, and a second layer of gold, 2.54 .mu.m thick. The order of plating helps control brazing erosion. Excessive amounts of brazing material are avoided by controlling the electroplating process. The reticulated copper foam rings are interference fit to the stainless steel tube, and in contact with the plated layers. The copper foam rings, the plated layers for brazing alloy, and the stainless steel tube are heated and cooled in a vacuum furnace at controlled rates, forming a bond of the copper foam rings to the stainless steel tube that improves heat transfer between the tube and the copper foam.

Free-standing and flexible graphene papers as disposable non-enzymatic electrochemical sensors.

PubMed

Zhang, Minwei; Halder, Arnab; Hou, Chengyi; Ulstrup, Jens; Chi, Qijin

2016-06-01

We have explored AuNPs (13 nm) both as a catalyst and as a core for synthesizing water-dispersible and highly stable core-shell structural gold@Prussian blue (Au@PB) nanoparticles (NPs). Systematic characterization by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) disclosed AuNPs coated uniformly by a 5 nm thick PB layer. Au@PB NPs were attached to single-layer graphene oxide (GO) to form Au@PB decorated GO sheets. The resulting hybrid material was filtered layer-by-layer into flexible and free-standing GO paper, which was further converted into conductive reduced GO (RGO)/Au@PB paper via hydrazine vapour reduction. High-resolution TEM images suggested that RGO papers are multiply sandwich-like structures functionalized with core-shell NPs. Resulting sandwich functionalized graphene papers have high conductivity, sufficient flexibility, and robust mechanical strength, which can be cut into free-standing electrodes. Such electrodes, used as non-enzymatic electrochemical sensors, were tested systematically for electrocatalytic sensing of hydrogen peroxide. The high performance was indicated by some of the key parameters, for example the linear H2O2 concentration response range (1-30 μM), the detection limit (100 nM), and the high amperometric sensitivity (5 A cm(-2) M(-1)). With the advantages of low cost and scalable production capacity, such graphene supported functional papers are of particular interest in the use as flexible disposable sensors. Copyright © 2016 Elsevier B.V. All rights reserved.

Influence of Passivation Layers for Metal Grating-Based Quantum Well Infrared Photodetectors

NASA Astrophysics Data System (ADS)

Liu, Dong; Fu, Yong-Qi; Yang, Le-Chen; Zhang, Bao-Shun; Li, Hai-Jun; Fu, Kai; Xiong, Min

2012-06-01

To improve absorption of quantum well infrared photodetectors (QWIPs), a coupling layer with metallic grating is designed and fabricated above the quantum well. The metal grating is composed of 100 nm Au film on top, and a 20-nm Ti thin layer between the Au film and the sapphire substrate is coated as an adhesion/buffer layer. To protect the photodetector from oxidation and to decrease leakage, a SiO2 film is deposited by means of plasma-enhanced chemical vapor deposition. A value of about 800 nm is an optimized thickness for the SiO2 applied in the metallic grating-based mid-infrared QWIP. In addition, a QWIP passivation layer is studied experimentally. The results demonstrate that the contribution from the layer is positive for metal grating coupling with the quantum well. The closer the permittivity of the two dielectric layers (SiO2 and the passivation layers), and the closer the two transmission peaks, the greater the QWIP enhancement will be.

Fabrication of Metallic Magnetic Calorimeter for Radionuclide Analysis

NASA Astrophysics Data System (ADS)

Yoon, W. S.; Kim, G. B.; Lee, H. J.; Lee, J. Y.; Lee, J. H.; Jang, Y. S.; Lee, S. J.; Lee, M. K.; Kim, Y. H.

2014-09-01

We present a detailed report on the fabrication process of a metallic magnetic calorimeter (MMC). The MMC is configured in a planar geometry with a meander-shaped pickup coil covered with a Au:Er temperature sensor layer. The meander coil is used to apply a magnetic field to magnetize the erbium ions and to measure the magnetization change of the spin system. The MMC is designed to have a large area (1 mm) and 3 m thickness Au:Er layer, which is suited for large metal absorbers with a few nJ/K heat capacity in radionuclide analysis applications. The completed devices are used in alpha and Q spectrometries.

Fabrication of X-ray Microcalorimeter Focal Planes Composed of Two Distinct Pixel Types.

PubMed

Wassell, E J; Adams, J S; Bandler, S R; Betancourt-Martinez, G L; Chiao, M P; Chang, M P; Chervenak, J A; Datesman, A M; Eckart, M E; Ewin, A J; Finkbeiner, F M; Ha, J Y; Kelley, R; Kilbourne, C A; Miniussi, A R; Sakai, K; Porter, F; Sadleir, J E; Smith, S J; Wakeham, N A; Yoon, W

2017-06-01

We are developing superconducting transition-edge sensor (TES) microcalorimeter focal planes for versatility in meeting specifications of X-ray imaging spectrometers including high count-rate, high energy resolution, and large field-of-view. In particular, a focal plane composed of two sub-arrays: one of fine-pitch, high count-rate devices and the other of slower, larger pixels with similar energy resolution, offers promise for the next generation of astrophysics instruments, such as the X-ray Integral Field Unit (X-IFU) instrument on the European Space Agency's Athena mission. We have based the sub-arrays of our current design on successful pixel designs that have been demonstrated separately. Pixels with an all gold X-ray absorber on 50 and 75 micron scales where the Mo/Au TES sits atop a thick metal heatsinking layer have shown high resolution and can accommodate high count-rates. The demonstrated larger pixels use a silicon nitride membrane for thermal isolation, thinner Au and an added bismuth layer in a 250 micron square absorber. To tune the parameters of each sub-array requires merging the fabrication processes of the two detector types. We present the fabrication process for dual production of different X-ray absorbers on the same substrate, thick Au on the small pixels and thinner Au with a Bi capping layer on the larger pixels to tune their heat capacities. The process requires multiple electroplating and etching steps, but the absorbers are defined in a single ion milling step. We demonstrate methods for integrating heatsinking of the two types of pixel into the same focal plane consistent with the requirements for each sub-array, including the limiting of thermal crosstalk. We also discuss fabrication process modifications for tuning the intrinsic transition temperature (T c ) of the bilayers for the different device types through variation of the bilayer thicknesses. The latest results on these "hybrid" arrays will be presented.

Fabrication of X-ray Microcalorimeter Focal Planes Composed of Two Distinct Pixel Types

PubMed Central

Wassell, E. J.; Adams, J. S.; Bandler, S. R.; Betancourt-Martinez, G. L.; Chiao, M. P.; Chang, M. P.; Chervenak, J. A.; Datesman, A. M.; Eckart, M. E.; Ewin, A. J.; Finkbeiner, F. M.; Ha, J. Y.; Kelley, R.; Kilbourne, C. A.; Miniussi, A. R.; Sakai, K.; Porter, F.; Sadleir, J. E.; Smith, S. J.; Wakeham, N. A.; Yoon, W.

2017-01-01

We are developing superconducting transition-edge sensor (TES) microcalorimeter focal planes for versatility in meeting specifications of X-ray imaging spectrometers including high count-rate, high energy resolution, and large field-of-view. In particular, a focal plane composed of two sub-arrays: one of fine-pitch, high count-rate devices and the other of slower, larger pixels with similar energy resolution, offers promise for the next generation of astrophysics instruments, such as the X-ray Integral Field Unit (X-IFU) instrument on the European Space Agency’s Athena mission. We have based the sub-arrays of our current design on successful pixel designs that have been demonstrated separately. Pixels with an all gold X-ray absorber on 50 and 75 micron scales where the Mo/Au TES sits atop a thick metal heatsinking layer have shown high resolution and can accommodate high count-rates. The demonstrated larger pixels use a silicon nitride membrane for thermal isolation, thinner Au and an added bismuth layer in a 250 micron square absorber. To tune the parameters of each sub-array requires merging the fabrication processes of the two detector types. We present the fabrication process for dual production of different X-ray absorbers on the same substrate, thick Au on the small pixels and thinner Au with a Bi capping layer on the larger pixels to tune their heat capacities. The process requires multiple electroplating and etching steps, but the absorbers are defined in a single ion milling step. We demonstrate methods for integrating heatsinking of the two types of pixel into the same focal plane consistent with the requirements for each sub-array, including the limiting of thermal crosstalk. We also discuss fabrication process modifications for tuning the intrinsic transition temperature (Tc) of the bilayers for the different device types through variation of the bilayer thicknesses. The latest results on these “hybrid” arrays will be presented. PMID:28804229

Fabrication of X-ray Microcalorimeter Focal Planes Composed of Two Distinct Pixel Types

NASA Technical Reports Server (NTRS)

Wassell, Edward J.; Adams, Joseph S.; Bandler, Simon R.; Betancour-Martinez, Gabriele L; Chiao, Meng P.; Chang, Meng Ping; Chervenak, James A.; Datesman, Aaron M.; Eckart, Megan E.; Ewin, Audrey J.;

Mechanical properties and structure evolution of single-crystalline silicon irradiated by 1 MeV Au+ and Cu+ ions

NASA Astrophysics Data System (ADS)

Liang, Wei; Zhu, Fei; Ling, Yunhan; Liu, Kezhao; Hu, Yin; Pan, Qifa; Chen, Limin; Zhang, Zhengjun

2018-05-01

Mechanical and structural evolutions of single-crystalline silicon irradiated by a series of doses 1 MeV Au+ ions and Cu+ ions are characterized by Surface laser-acoustic wave spectroscopy by (LA wave), Rutherford backscattering spectrometry and channeling (RBS/C) and transmission electron microscopy (TEM). The behavior of implanted Au+ and Cu+ ions was also simulated by using Stopping and range of ions in matter (SRIM) software package, respectively. It is demonstrated that LA wave and RBS could be applied for accurate evaluation of the TEM observed amorphous layer's thickness. The modified mechanical properties depend on the species and the dose of implantation. For 1 MeV Au+ ions, the threshold dose of completely amorphous is 5 × 1014 atoms/cm2, while the one for Cu+ ions is 5 × 1015 atoms/cm2. Upon completely amorphous, the young's modulus and layer density decreased significantly while saturated with the dose increasing sequentially.

Effect of Pd Surface Roughness on the Bonding Process and High Temperature Reliability of Au Ball Bonds

NASA Astrophysics Data System (ADS)

Huang, Y.; Kim, H. J.; McCracken, M.; Viswanathan, G.; Pon, F.; Mayer, M.; Zhou, Y. N.

2011-06-01

A 0.3- μm-thick electrolytic Pd layer was plated on 1 μm of electroless Ni on 1 mm-thick polished and roughened Cu substrates with roughness values ( R a) of 0.08 μm and 0.5 μm, respectively. The rough substrates were produced with sand-blasting. Au wire bonding on the Ni/Pd surface was optimized, and the electrical reliability was investigated under a high temperature storage test (HTST) during 800 h at 250°C by measuring the ball bond contact resistance, R c. The average value of R c of optimized ball bonds on the rough substrate was 1.96 mΩ which was about 40.0% higher than that on the smooth substrate. The initial bondability increased for the rougher surface, so that only half of the original ultrasonic level was required, but the reliability was not affected by surface roughness. For both substrate types, HTST caused bond healing, reducing the average R c by about 21% and 27%, respectively. Au diffusion into the Pd layer was observed in scanning transmission electron microscopy/ energy dispersive spectroscopy (STEM-EDS) line-scan analysis after HTST. It is considered that diffusion of Au or interdiffusion between Au and Pd can provide chemically strong bonding during HTST. This is supported by the R c decrease measured as the aging time increased. Cu migration was indicated in the STEM-EDS analysis, but its effect on reliability can be ignored. Au and Pd tend to form a complete solid solution at the interface and can provide reliable interconnection for high temperature (250°C) applications.

Assembling Bare Au Nanoparticles at Positively Charged Templates

DOE PAGES

Wang, Wenjie; Zhang, Honghu; Kuzmenko, Ivan; ...

2016-05-26

In-situ X-ray reflectivity (XRR) and grazing incidence X-ray small-angle scattering (GISAXS) reveal that unfunctionalized (bare) gold nanoparticles (AuNP) spontaneously adsorb to a cationic lipid template formed by a Langmuir monolayer of DPTAP (1,2-dihexadecanoyl-3-trimethylammonium-propane) at vapor/aqueous interfaces. Analysis of the XRR yields the electron density profile across the charged-interfaces along the surface normal showing the AuNPs assemble with vertical thickness comparable to the particle size. The GISAXS analysis indicates that the adsorbed mono-particle layer exhibits short-range in-plane correlations. By contrast, single-stranded DNA-functionalized AuNPs, while attracted to the positively charged surface (more efficiently with the addition of salt to the solution), displaymore » less in-plane regular packing compared to bare AuNPs.« less

Nanostructured diamond layers enhance the infrared spectroscopy of biomolecules.

PubMed

Kozak, Halyna; Babchenko, Oleg; Artemenko, Anna; Ukraintsev, Egor; Remes, Zdenek; Rezek, Bohuslav; Kromka, Alexander

2014-03-04

We report on the fabrication and practical use of high-quality optical elements based on Au mirrors coated with diamond layers with flat, nanocolumnar, and nanoporous morphologies. Diamond layers (100 nm thickness) are grown at low temperatures (about 300 °C) from a methane, carbon dioxide, and hydrogen gas mixture by a pulsed microwave plasma system with linear antennas. Using grazing angle reflectance (GAR) Fourier transform infrared spectroscopy with p-polarized light, we compare the IR spectra of fetal bovine serum proteins adsorbed on diamond layers with oxidized (hydrophilic) surfaces. We show that the nanoporous diamond layers provide IR spectra with a signal gain of about 600% and a significantly improved sensitivity limit. This is attributed to its enhanced internal surface area. The improved sensitivity enabled us to distinguish weak infrared absorption peaks of <10-nm-thick protein layers and thereby to analyze the intimate diamond-molecule interface.

Signal Enhancement Strategies for Refractive Index-Sensitive Nanobiosensor.

PubMed

Syahir, Amir; Kajikawa, Kotaro; Mihara, Hisakazu

2018-01-01

Direct bio-monitoring essentially involves optical means since photon has insignificant effects over biomolecules. Over the years, laser induced surface Plasmon resonance method with various modifications as well as versatile localized Plasmon excited by incoherent light have facilitated in recording many nanobiological activities. Yet, monitoring interactions of small molecules including drugs requires signal amplification and improvement on signal-to-noise ratio. This paper focused on how the refractive index based nanobio-sensoring gold platform can produce more efficient, adaptable and more practical detection techniques to observe molecular interactions at high degree of sensitivity. It discusses surface chemistry approach, optimisation of the refractive index of gold platform and manipulation of gold geometry augmenting signal quality. In a normal-incidence reflectivity, r0 can be calculated using the Fresnel equation. Particularly at λ = 470 nm the ratio of r / r0 showed significant amplitude reduction mainly stemmed from the imaginary part of the Au refractive index. Hence, the fraction of reduction, Δr = 1 - r / r0. Experimentally, in a common reference frame reflectivity of a bare gold surface, R0 is compared with the reflectivity of gold surface in the presence of biolayer, R. The reduction rate (%) of reflectivity, ΔR = 1 - R / R0 is denoted as the AR signal. The method therefore enables quantitative measurement of the surface-bound protein by converting ΔR to the thickness, d, and subsequently the protein mass. We discussed four strategies to improve the AR signal by changing the effective refractive index of the biosensing platform. They are; a) Thickness optimisation of Au thin layer, b) Au / Ag bimetallic layer, c) composing alloy or Au composite, and d) Au thinlayer with nano or micro holes. As the result we successfully 'move' the refractive index, ε of the AR platform (gold only) to ε = -0.948 + 3.455i, a higher sensitivity platform. This was done by composing Au-Ag2O composite with ratio = 1:1. The results were compared to the potential sensitivity improvement of the AR substrate using other that could be done by further tailoring the ε advanced method. We suggested four strategies in order to realize this purpose. It is apparent that sensitivity has been improved through Au/Ag bimetallic layer or Au-Ag2O composite thin layer, This study is an important step towards fabrication of sensitive surface for detection of biomolecular interactions. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Graphene based resonance structure to enhance the optical pressure between two planar surfaces.

PubMed

Hassanzadeh, Abdollah; Azami, Darya

2015-12-28

To enhance the optical pressure on a thin dielectric sample, a resonance structure using graphene layers coated over a metal film on a high index prism sputtered with MgF2 was theoretically analyzed. The number of graphene layers and the thicknesses of metal and MgF2 films were optimized to achieve the highest optical pressure on the sample. Effects of three different types of metals on the optical pressure were investigated numerically. In addition, simulations were carried out for samples with various thicknesses. Our numerical results show that the optical pressure increased by more than five orders of magnitude compared to the conventional metal-film-base resonance structure. The highest optical pressure was obtained for 10 layers of graphene deposited on 29-nm thick Au film and 650 nm thickness of MgF2 at 633nm wavelength, The proposed graphene based resonance structure can open new possibilities for optical tweezers, nanomechnical devices and surface plasmon based sensing and imaging techniques.

Theoretical study of modulated multi-layer SPR device for improved refractive index sensing

NASA Astrophysics Data System (ADS)

Mohapatra, Saswat; Moirangthem, Rakesh S.

2018-02-01

In the present work, a theoretical investigation of Surface Plasmon Resonance (SPR) properties of a multilayer film (Au-SiO2-Au) coated on a glass prism is being carried out. In this multilayer structure, each interface corresponds to multiple SPR modes. To obtain the maximum reflection dips in the SPR modes, the thickness of SiO2 layer is optimized by varying it from 100-600 nm. Our calculation also reveals that SPR mode corresponding to Au-ambient interface is very sensitive to the changes in the surrounding medium, least affecting other SPR modes. The sensing performance of the proposed nano-plasmonic sensor is theoretically calculated using bulk refractive index sensing. Such multilayer SPR sensing device has advantages over conventional SPR devices in terms of their bulk sensitivity and self-referencing, claiming itself as a potential candidate for the development of highly sensitive biological sensor.

‘Spotted Nanoflowers’: Gold-seeded Zinc Oxide Nanohybrid for Selective Bio-capture

NASA Astrophysics Data System (ADS)

Perumal, Veeradasan; Hashim, U.; Gopinath, Subash C. B.; Haarindraprasad, R.; Foo, K. L.; Balakrishnan, S. R.; Poopalan, P.

2015-07-01

Hybrid gold nanostructures seeded into nanotextured zinc oxide (ZnO) nanoflowers (NFs) were created for novel biosensing applications. The selected ‘spotted NFs’ had a 30-nm-thick gold nanoparticle (AuNP) layer, chosen from a range of AuNP thicknesses, sputtered onto the surface. The generated nanohybrids, characterized by morphological, physical and structural analyses, were uniformly AuNP-seeded onto the ZnO NFs with an average length of 2-3 μm. Selective capture of molecular probes onto the seeded AuNPs was evidence for the specific interaction with DNA from pathogenic Leptospirosis-causing strains via hybridization and mis-match analyses. The attained detection limit was 100 fM as determined via impedance spectroscopy. High levels of stability, reproducibility and regeneration of the sensor were obtained. Selective DNA immobilization and hybridization were confirmed by nitrogen and phosphorus peaks in an X-ray photoelectron spectroscopy analysis. The created nanostructure hybrids illuminate the mechanism of generating multiple-target, high-performance detection on a single NF platform, which opens a new avenue for array-based medical diagnostics.

Fabrication of Ag-Au bimetallic nanoparticles by laser-induced dewetting of bilayer films

NASA Astrophysics Data System (ADS)

Oh, Yoonseok; Lee, Jeeyoung; Lee, Myeongkyu

2018-03-01

We here show that Ag-Au bimetallic nanoparticles (NPs) can be produced by dewetting an Ag/Au bilayer film coated on glass using a nanosecond-pulsed laser beam. Elemental analysis revealed that the obtained bimetallic NPs are Ag-Au alloys, with two elements well mixed over the whole volume of the particle. The composition of the produced particles was controllable by changing the relative thickness of each layer. The localized surface plasmon resonance (LSPR) peak was red-shifted with an increasing Au content and the LSPR wavelength could be tuned from 415 to 525 nm by varying the alloy composition. A film area of several square centimeters could be transformed into Ag-Au NPs by a single laser pulse of 6 ns duration. This study provides a facile and scalable route to prepare bimetallic NPs for plasmonic and other applications.

Synthesis of graphene and graphene nanostructures by ion implantation and pulsed laser annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xiaotie; Rudawski, Nicholas G.; Appleton, Bill R.

2016-07-14

In this paper, we report a systematic study that shows how the numerous processing parameters associated with ion implantation (II) and pulsed laser annealing (PLA) can be manipulated to control the quantity and quality of graphene (G), few-layer graphene (FLG), and other carbon nanostructures selectively synthesized in crystalline SiC (c-SiC). Controlled implantations of Si{sup −} plus C{sup −} and Au{sup +} ions in c-SiC showed that both the thickness of the amorphous layer formed by ion damage and the doping effect of the implanted Au enhance the formation of G and FLG during PLA. The relative contributions of the amorphousmore » and doping effects were studied separately, and thermal simulation calculations were used to estimate surface temperatures and to help understand the phase changes occurring during PLA. In addition to the amorphous layer thickness and catalytic doping effects, other enhancement effects were found to depend on other ion species, the annealing environment, PLA fluence and number of pulses, and even laser frequency. Optimum II and PLA conditions are identified and possible mechanisms for selective synthesis of G, FLG, and carbon nanostructures are discussed.« less

Theoretical modeling of a coupled plasmon waveguide resonance sensor based on multimode optical fiber

NASA Astrophysics Data System (ADS)

Liu, Kun; Xue, Meng; Jiang, Junfeng; Wang, Tao; Chang, Pengxiang; Liu, Tiegen

2018-03-01

A coupled plasmon waveguide resonance (CPWR) sensor based on metal/dielectric-coated step index multimode optical fiber is proposed. Theoretical simulations using the four-layer Fresnel equations based on a bi-dimensional optical fiber model were implemented on four structures: Ag-ZnO, Au-ZnO, Ag-TiO2 and Au-TiO2. By controlling the thickness of dielectric layer, we managed to manipulate the CPWR resonance wavelengths. When a CPWR resonance dip is in the short wavelength region, it is insensitive to the change of surrounding refractive index (SRI) and can be used as a reference to improve the sensing accuracy of surface plasmon resonance (SPR) mode. With the increase of the thickness of the dielectric layer, the CPWR resonance dips shift to longer wavelength and the corresponding sensitivities increase. When the 1st CPWR resonance wavelength is near 1550 nm and SRI is around 1.333, the sensitivities of four structures reach 1360.61 nm/RIU, 1375.76 nm/RIU, 1048.48 nm/RIU and 1015.15 nm/RIU, respectively. The values are close to that of the conventional SPR optical fiber sensor while the spectral bandwidths of the optical fiber CPWR sensors are narrower.

Interaction of metal layers with polycrystalline Si

NASA Technical Reports Server (NTRS)

Nakamura, K.; Olowolafe, J. O.; Lau, S. S.; Nicolet, M.-A.; Mayer, J. W.; Shima, R.

1976-01-01

Solid-phase reactions of metal films deposited on 0.5-micron-thick polycrystalline layers of Si grown by chemical vapor deposition at 640 C were investigated by MeV He-4 backscattering spectrometry, glancing angle X-ray diffraction, and SEM observations. For the metals Al, Ag, and Au, which form simple eutectics, heat treatment at temperatures below the eutectic results in erosion of the poly-Si layer and growth of Si crystallites in the metal film. Crystallite formation is observed at temperatures exceeding 550 C for Ag, at those exceeding 400 C for Al, and at those exceeding 200 C for Au films. For Pd, Ni, and Cr, heat treatment results in silicide formation. The same initial silicides (Pd2Si, Ni2Si, and CrSi2), are formed at similar temperatures on single-crystal substrates.

Influences of top electrode reduction potential and operation ambient on the switching characteristics of tantalum oxide resistive switching memories

NASA Astrophysics Data System (ADS)

Ding, Tse-Ming; Chen, Yi-Ju; Jeng, Jiann-Shing; Chen, Jen-Sue

2017-12-01

Modulation of the oxygen distribution is liable for the electrical performance of oxide-based devices. When the top electrode (TE) is deposited on the active layer, an oxygen exchange layer (OEL) may be formed at the interface. Oxygen ions can be absorbed and offered in OEL to assist resistive switching (RS). In this study, the impact of different TEs (Al, Zr, Ta and Au) on the active layer TaOx is investigated. TEs are chosen based on the reduction potential (E0Al=-2.13V, E0Zr=-1.55V, E0Ta=-0.75V, E0Au=1.52V), which determines whether OEL is formed. Based on TEM micrographs, as the difference of TE reduction potential to E0Ta becomes more negative, a thicker OEL exists. We find that Zr TE device has the most stable I-V characteristic and data retention, while Al TE device suffers from the reset failure, and Au TE device fails to switch. Moreover, we fabricate two different thicknesses (20 nm and 120 nm) of Zr TE and alter the operation ambient to vacuum (10-5 Torr) to study the influence on RS. The magnitude of reset voltage becomes larger when the devices are measured in vacuum ambient. According to these findings, the RS mechanism with different TE materials, thicknesses and at the different operation ambient is established.

UV sensing using film bulk acoustic resonators based on Au/n-ZnO/piezoelectric-ZnO/Al structure.

PubMed

Bian, Xiaolei; Jin, Hao; Wang, Xiaozhi; Dong, Shurong; Chen, Guohao; Luo, J K; Deen, M Jamal; Qi, Bensheng

2015-03-16

A new type of ultraviolet (UV) light sensor based on film bulk acoustic wave resonator (FBAR) is proposed. The new sensor uses gold and a thin n-type ZnO layer deposited on the top of piezoelectric layer of FBAR to form a Schottky barrier. The Schottky barrier's capacitance can be changed with UV light, resulting in an enhanced shift in the entire FBAR's resonant frequency. The fabricated UV sensor has a 50 nm thick n-ZnO semiconductor layer with a carrier concentration of ~ 10(17) cm(-3). A large frequency downshift is observed when UV light irradiates the FBAR. With 365 nm UV light of intensity 1.7 mW/cm(2), the FBAR with n-ZnO/Au Schottky diode has 250 kHz frequency downshift, much larger than the 60 kHz frequency downshift in a conventional FBAR without the n-ZnO layer. The shift in the new FBAR's resonant frequency is due to the junction formed between Au and n-ZnO semiconductor and its properties changes with UV light. The experimental results are in agreement with the theoretical analysis using an equivalent circuit model of the new FBAR structure.

Determination of fermentable sugars in beer wort by gold nanoparticles@polydopamine: A layer-by-layer approach for Localized Surface Plasmon Resonance measurements at fixed wavelength.

PubMed

Scarano, S; Pascale, E; Palladino, P; Fratini, E; Minunni, M

2018-06-01

Polydopamine decorated in-situ with Localized Surface Plasmon Resonance (LSPR)-active gold nanoparticles (AuNPs) may extend the applicability of nanoplasmonic materials to original and innovative applications in several fields. Here we report the modification of disposable UV-Vis polystyrene cuvettes with AuNPs@PDA for refractive index LSPR-based measurements. An original layer-by-layer deposition method of PDA followed by AuNPs growth is here developed, showing linear correlation between PDA thickness and optical properties. In particular, the modulation from wavelength sensitivity toward absorbance sensitivity is obtained, allowing measurements at fixed wavelength (578 nm). As applicative example of the photonic cuvettes, the measurement of fermentable sugars in beer wort is here reported. The analytical performance of our approach has been directly compared to portable refractometer of reference, displaying excellent results in terms of the precise estimation of sugars in beer wort (expressed in degrees Brix), reproducibility and sensitivity. The approach may be extended to other materials of interest in LSPR based optical sensors, e.g. optical fibers. Copyright © 2018 Elsevier B.V. All rights reserved.

Formation, structure, and orientation of gold silicide on gold surfaces

NASA Technical Reports Server (NTRS)

Green, A. K.; Bauer, E.

1976-01-01

The formation of gold silicide on Au films evaporated onto Si(111) surfaces is studied by Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). Surface condition, film thickness, deposition temperature, annealing temperature, and heating rate during annealing are varied. Several oriented crystalline silicide layers are observed.

Effect of pH on film structure and electrical property of PMMA-Au composite particles prepared by redox transmetalation

NASA Astrophysics Data System (ADS)

Wu, Hong-Mao; Lin, Kuan-Ju; Yu, Yi-Hsiuan; Ho, Chan-Yuan; Wei, Ming-Hsiung; Lu, Fu-Hsing; Tseng, Wenjea J.

2014-01-01

Surface-selective deposition of gold (Au) on electroless plated poly(methyl methacrylate)-nickel (PMMA-Ni) beads was prepared chemically by a facile redox-transmetalation route in which the Ni atoms on the PMMA surface were reacted with Au precursors, i.e., chloroauric acid (HAuCl4), in water to form predominately core-shell PMMA-Au composite particles without the need of reducing agent. The Ni layer acted as a sacrificial template to facilitate the selective transmetalation deposition of a metallic Au film. When pH of the precursor solution was adjusted from 6 to 9, morphology of the Au film changed from a uniform particulate film consisting of assemblies of Au nanoparticles, to densely packed, continuous film with platelet Au crystals, and finally to isolated Au islands on the PMMA surface with a raspberry-like core-shell morphology. Uniformly dense Au coating with a thickness of about 200 nm was formed on the PMMA beads at pH of 7 to 8, which gave rise to an electrical resistivity as low as 3 × 10-2 Ω cm.

X Ray Mask Of Gold-Carbon Mixture Absorber On BCN Compound Substrate Fabricated By Plasma Processes

NASA Astrophysics Data System (ADS)

Aiyer, Chandrasekhar R.; Itoh, Satoshi; Yamada, Hitomi; Morita, Shinzo; Hattori, Shuzo

1988-06-01

X-ray mask fabrication based on BCN compound membrane and gold containing polymeric carbon ( Au-C ) absorber by totally dry processes is proposed. The Au-C films were depo-sited by plasma polymerization of propylene or styrene monomers and co-evaporation of gold. These films have 2 to 5 times higher etching rate than that of pure gold for 09 RIE, depending on the Au content. The stress in the films could be reduced to 1.9 E 7 N/m2 by annealing. The BCN films were deposited on silicon wafers by rf (13.56 MHz) plasma CVD with diborane, methane and nitrogen as source gases at typical deposition rate of 30 nm/min. The optical (633nm) and X ray (Pd L~) transparencies were nearly 80% for film thickness of 6 um. Patterning of Au-C was achieved by using tungsten as intermediate layer and PMMA electron beam resist. CF4 RIE was used to etch the tungsten layer which in turn acted as mask for the gold carbide 02 RIE. The process parameters and the characteristics of the Au-C and BCN films are presented.

SU-F-T-361: Dose Enhancement Due to Nanoparticle Addition in Skin Radiotherapy: A Monte Carlo Study Using Kilovoltage Photon Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, X; Chow, J

Purpose: This study investigated the dose enhancement due to addition of nanoparticles with different types and concentrations in skin radiotherapy using kilovoltage photon beams. Methods: An inhomogeneous water phantom (15×15×10 cm{sup 3}) having the skin target layer (0.5–5 mm), added with different concentrations (3–40 mg/ml) of nanoparticles (Au, Pt, I, Ag and Fe{sub 2}O{sub 3}), was irradiated by the 105 and 220 kVp photon beams produced by a Gulmay D3225 Orthovoltage unit. The circular cone of 5-cm diameter and source-to-surface distance of 20 cm were used. Doses in the skin target layer with and without adding the nanoparticles were calculatedmore » using Monte Carlo simulation (the EGSnrc code) through the macroscopic approach. Dose enhancement ratio (DER), defined as the ratio of dose at the target with nanoparticle addition to the dose without addition, was calculated for each type and concentration of nanoparticle in different target thickness. Results: For Au nanoparticle, DER dependence on target thickness for the 220 kVp photon beams was not significant. However, DER for Au nanoparticle was found decreasing with an increase of target thickness when the nanoparticle concentration was increased from 18 to 40 mg/ml using the 105 kVp photon beams. For nanoparticle concentration of 40 mg/ml, DER variation with target thickness was not significant for the 220 kVp photon beams, but DEF was found decreasing with the target thickness when lower energy of photon beam (105 kVp) was used. DEF was found increasing with an increase of nanoparticle concentration. The higher the DEF increasing rate, the higher the atomic number of the nanoparticle except I and Ag for the same target thickness. Conclusion: It is concluded that nanoparticle addition can result in dose enhancement in kilovoltage skin radiotherapy. Moreover, the DER is related to the photon beam energy, target thickness, atomic number and concentration of nanoparticles.« less

Au nanorods-incorporated plasmonic-enhanced inverted organic solar cells

NASA Astrophysics Data System (ADS)

Peng, Ling; Mei, Yang; Chen, Shu-Fen; Zhang, Yu-Pei; Hao, Jing-Yu; Deng, Ling-Ling; Huang, Wei

2015-11-01

The effect of Au nanorods (NRs) on optical-to-electric conversion efficiency is investigated in inverted polymer solar cells, in which Au NRs are sandwiched between two layers of ZnO. Accompanied by the optimization of thickness of ZnO covered on Au NRs, a high-power conversion efficiency of 3.60% and an enhanced short-circuit current density (JSC) of 10.87 mA/cm2 are achieved in the poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC60BM)-based inverted cell and the power conversion efficiency (PCE) is enhanced by 19.6% compared with the control device. The detailed analyses of the light absorption characteristics, the simulated scattering induced by Au NRs, and the electromagnetic field around Au NRs show that the absorption improvement in the photoactive layer due to the light scattering from the longitudinal axis and the near-field increase around Au NRs induced by localized surface plasmon resonance plays a key role in enhancing the performances. Project supported by the Ministry of Science and Technology, China (Grant No. 2012CB933301), the National Natural Science Foundation of China (Grant Nos. 61274065, 51173081, 61136003, BZ2010043, 51372119, and 51172110), and the Priority Academic Program Development of Jiangsu Provincial Higher Education Institutions and Synergetic Innovation Center for Organic Electronics and Information Displays, China.

Nano-scaled Pt/Ag/Ni/Au contacts on p-type GaN for low contact resistance and high reflectivity.

PubMed

Kwon, Y W; Ju, I C; Kim, S K; Choi, Y S; Kim, M H; Yoo, S H; Kang, D H; Sung, H K; Shin, K; Ko, C G

2011-07-01

We synthesized the vertical-structured LED (VLED) using nano-scaled Pt between p-type GaN and Ag-based reflector. The metallization scheme on p-type GaN for high reflectance and low was the nano-scaled Pt/Ag/Ni/Au. Nano-scaled Pt (5 A) on Ag/Ni/Au exhibited reasonably high reflectance of 86.2% at the wavelength of 460 nm due to high transmittance of light through nano-scaled Pt (5 A) onto Ag layer. Ohmic behavior of contact metal, Pt/Ag/Ni/Au, to p-type GaN was achieved using surface treatments of p-type GaN prior to the deposition of contact metals and the specific contact resistance was observed with decreasing Pt thickness of 5 A, resulting in 1.5 x 10(-4) ohms cm2. Forward voltages of Pt (5 A)/Ag/Ni contact to p-type GaN showed 4.19 V with the current injection of 350 mA. Output voltages with various thickness of Pt showed the highest value at the smallest thickness of Pt due to its high transmittance of light onto Ag, leading to high reflectance. Our results propose that nano-scaled Pt/Ag/Ni could act as a promising contact metal to p-type GaN for improving the performance of VLEDs.

Metal diffusion barriers for GaAs solar cells.

PubMed

van Leest, R H; Mulder, P; Bauhuis, G J; Cheun, H; Lee, H; Yoon, W; van der Heijden, R; Bongers, E; Vlieg, E; Schermer, J J

2017-03-15

In this study accelerated ageing testing (AAT), J-V characterization and TEM imaging in combination with phase diagram data from literature are used to assess the potential of Ti, Ni, Pd and Pt as diffusion barriers for Au/Cu-based metallization of III-V solar cells. Ni barriers show the largest potential as at an AAT temperature of 250 °C both cells with 10 and 100 nm thick Ni barriers show significantly better performance compared to Au/Cu cells, with the cells with 10 nm Ni barriers even showing virtually no degradation after 7.5 days at 250 °C (equivalent to 10 years at 100 °C at an E a of 0.70 eV). Detailed investigation shows that Ni does not act as a barrier in the classical sense, i.e. preventing diffusion of Cu and Au across the barrier. Instead Ni modifies or slows down the interactions taking place during device degradation and thus effectively acts as an 'interaction' barrier. Different interactions occur at temperatures below and above 250 °C and for thin (10 nm) and thick (100 nm) barriers. The results of this study indicate that 10-100 nm thick Ni intermediate layers in the Cu/Au based metallization of III-V solar cells may be beneficial to improve the device stability upon exposure to elevated temperatures.

Identifying the Assembly Configuration and Fluorescence Spectra of Nanoscale Zinc-Tetraphenylporphyrin Aggregates with Scanning Tunneling Microscopy

PubMed Central

Zhang, Xiao-Lei; Jiang, Jian-Wei; Liu, Yi-Ting; Lou, Shi-Tao; Gao, Chun-Lei; Jin, Qing-Yuan

2016-01-01

ZnTPP (Zinc-Tetraphenylporphyrin) is one of the most common nanostructured materials, having high stability and excellent optoelectronic properties. In this paper, the fluorescence features of self-assembled ZnTPP monomers and aggregates on Au(111) surface are investigated in detail on the nanometer scale with scanning tunneling microscopy (STM). The formation of ZnTPP dimers is found in thick layers of a layer-by-layer molecular assembly on Au substrate with its specific molecular arrangement well characterized. Tip-induced luminescence shows a red shift from tilted dimers comparing with the behavior from monomers, which can be attributed to the change of vibrational states due to the intermolecular interaction and the increasing dielectric effect. The nanoscale configuration dependence of electroluminescence is demonstrated to provide a powerful tool aiding the design of functional molecular photoelectric devices. PMID:26948654

Plasmonic nanotweezers: strong influence of adhesion layer and nanostructure orientation on trapping performance.

PubMed

Roxworthy, Brian J; Toussaint, Kimani C

2012-04-23

Using Au bowtie nanoantennas arrays (BNAs), we demonstrate that the performance and capability of plasmonic nanotweezers is strongly influenced by both the material comprising the thin adhesion layer used to fix Au to a glass substrate and the nanostructure orientation with respect to incident illumination. We find that a Ti adhesion layer provides up to 30% larger trap stiffness and efficiency compared to a Cr layer of equal thickness. Orientation causes the BNAs to operate as either (1) a 2D optical trap capable of efficient trapping and manipulation of particles as small as 300 nm in diameter, or (2) a quasi-3D trap, with the additional capacity for size-dependent particle sorting utilizing axial Rayleigh-Bénard convection currents caused by heat generation. We show that heat generation is not necessarily deleterious to plasmonic nanotweezers and achieve dexterous manipulation of nanoparticles with non-resonant illumination of BNAs. © 2012 Optical Society of America

Thin-Film Nanocapacitor and Its Characterization

ERIC Educational Resources Information Center

Hunter, David N.; Pickering, Shawn L.; Jia, Dongdong

2007-01-01

An undergraduate thin-film nanotechnology laboratory was designed. Nanocapacitors were fabricated on silicon substrates by sputter deposition. A mask was designed to form the shape of the capacitor and its electrodes. Thin metal layers of Au with a 80 nm thickness were deposited and used as two infinitely large parallel plates for a capacitor.…

Pt monolayer coating on complex network substrate with high catalytic activity for the hydrogen evolution reaction

PubMed Central

Li, Man; Ma, Qiang; Zi, Wei; Liu, Xiaojing; Zhu, Xuejie; Liu, Shengzhong (Frank)

2015-01-01

A deposition process has been developed to fabricate a complete-monolayer Pt coating on a large-surface-area three-dimensional (3D) Ni foam substrate using a buffer layer (Ag or Au) strategy. The quartz crystal microbalance, current density analysis, cyclic voltammetry integration, and X-ray photoelectron spectroscopy results show that the monolayer deposition process accomplishes full coverage on the substrate and the deposition can be controlled to a single atomic layer thickness. To our knowledge, this is the first report on a complete-monolayer Pt coating on a 3D bulk substrate with complex fine structures; all prior literature reported on submonolayer or incomplete-monolayer coating. A thin underlayer of Ag or Au is found to be necessary to cover a very reactive Ni substrate to ensure complete-monolayer Pt coverage; otherwise, only an incomplete monolayer is formed. Moreover, the Pt monolayer is found to work as well as a thick Pt film for catalytic reactions. This development may pave a way to fabricating a high-activity Pt catalyst with minimal Pt usage. PMID:26601247

Ultrafast excited-state dynamics in shape- and composition-controlled gold–silver bimetallic nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zarick, Holly F.; Boulesbaa, Abdelaziz; Talbert, Eric M.

In this paper, we have examined the ultrafast dynamics of shape- and composition-controlled bimetallic Au/Ag core/shell nanostructures with transient absorption spectroscopy (TAS) as a function of Ag layer thickness (0–15 nm) and pump excitation fluence (50–500 nJ/pulse). Our synthesis approach generated both bimetallic nanocubes and nanopyramids with distinct dipolar plasmon resonances and plasmon dephasing behavior at the resonance. Lifetimes obtained from TAS at low powers (50 nJ/pulse) demonstrated minimal dependence on the Ag layer thickness, whereas at high power (500 nJ/pulse) a rise in electron–phonon coupling lifetime (τ 1) was observed with increasing Ag shell thickness for both nanocubes andmore » nanopyramids. This is attributable to the stronger absorption of the 400 nm pump pulse with higher Ag content, which induced higher electron temperatures. The phonon–phonon scattering lifetime (τ 2) also rises with increasing Ag layer, contributed both by the increasing size of the Au/Ag nanostructures as well as by surface chemistry effects. Further, we observed that even the thinnest, 2 nm, Ag shell strongly impacts both τ 1 and τ 2 at high power despite minimal change in overall size, indicating that the nanostructure composition also strongly impacts the thermalization temperature following absorption of 400 nm light. We also observed a shape-dependent trend at high power, where τ 2 increased for the nanopyramids with increasing Ag shell thickness and nanostructure size, but bimetallic nanocubes demonstrated an unexpected decrease in τ 2 for the thickest, 15 nm, Ag shell. This was attributed to the larger number of corners and edges in the nanocubes relative to the nanopyramids.« less

Tailored plasmon-induced transparency in attenuated total reflection response in a metal-insulator-metal structure.

PubMed

Matsunaga, Kouki; Hirai, Yusuke; Neo, Yoichiro; Matsumoto, Takahiro; Tomita, Makoto

2017-12-19

We demonstrated tailored plasmon-induced transparency (PIT) in a metal (Au)-insulator (SiO 2 )-metal (Ag) (MIM) structure, where the Fano interference between the MIM waveguide mode and the surface plasmon polariton (SPP) resonance mode induced a transparency window in an otherwise opaque wavenumber (k) region. A series of structures with different thicknesses of the Ag layer were prepared and the attenuated total reflection (ATR) response was examined. The height and width of the transparency window, as well as the relevant k-domain dispersion, were controlled by adjusting the Ag layer thickness. To confirm the dependency of PIT on Ag layer thickness, we performed numerical calculations to determine the electric field amplitude inside the layers. The steep k-domain dispersion in the transparency window is capable of creating a lateral beam shift known as the Goos-Hänchen shift, for optical device and sensor applications. We also discuss the Fano interference profiles in a ω - k two-dimensional domain on the basis of Akaike information criteria.

Voltage Controlled Hot Carrier Injection Enables Ohmic Contacts Using Au Island Metal Films on Ge.

PubMed

Ganti, Srinivas; King, Peter J; Arac, Erhan; Dawson, Karl; Heikkilä, Mikko J; Quilter, John H; Murdoch, Billy; Cumpson, Peter; O'Neill, Anthony

2017-08-23

We introduce a new approach to creating low-resistance metal-semiconductor ohmic contacts, illustrated using high conductivity Au island metal films (IMFs) on Ge, with hot carrier injection initiated at low applied voltage. The same metallization process simultaneously allows ohmic contact to n-Ge and p-Ge, because hot carriers circumvent the Schottky barrier formed at metal/n-Ge interfaces. A 2.5× improvement in contact resistivity is reported over previous techniques to achieve ohmic contact to both n- and p- semiconductor. Ohmic contacts at 4.2 K confirm nonequilibrium current transport. Self-assembled Au IMFs are strongly orientated to Ge by annealing near the Au/Ge eutectic temperature. Au IMF nanostructures form, provided the Au layer is below a critical thickness. We anticipate that optimized IMF contacts may have applicability to many material systems. Optimizing this new paradigm for metal-semiconductor contacts offers the prospect of improved nanoelectronic systems and the study of voltage controlled hot holes and electrons.

High-performance metal mesh/graphene hybrid films using prime-location and metal-doped graphene.

PubMed

Min, Jung-Hong; Jeong, Woo-Lim; Kwak, Hoe-Min; Lee, Dong-Seon

2017-08-31

We introduce high-performance metal mesh/graphene hybrid transparent conductive layers (TCLs) using prime-location and metal-doped graphene in near-ultraviolet light-emitting diodes (NUV LEDs). Despite the transparency and sheet resistance values being similar for hybrid TCLs, there were huge differences in the NUV LEDs' electrical and optical properties depending on the location of the graphene layer. We achieved better physical stability and current spreading when the graphene layer was located beneath the metal mesh, in direct contact with the p-GaN layer. We further improved the contact properties by adding a very thin Au mesh between the thick Ag mesh and the graphene layer to produce a dual-layered metal mesh. The Au mesh effectively doped the graphene layer to create a p-type electrode. Using Raman spectra, work function variations, and the transfer length method (TLM), we verified the effect of doping the graphene layer after depositing a very thin metal layer on the graphene layers. From our results, we suggest that the nature of the contact is an important criterion for improving the electrical and optical performance of hybrid TCLs, and the method of doping graphene layers provides new opportunities for solving contact issues in other semiconductor devices.

The Achievement of Near-Theoretical-Minimum Contact Resistance to InP

NASA Technical Reports Server (NTRS)

Fatemi, Navid S.; Weizer, Victor G.

1993-01-01

We have investigated the electrical and metallurgical behavior of the InP/Au/Ni contact system. We show that when a layer of Au, 100 A or more in thickness, is introduced between n-InP and Ni contact metallization, specific contact resistivity R, values in the low 10(exp -8) Omega cm(exp 2) range are achieved after sintering. It is suggested that these ultralow values of R(sub c) are due to the presence, at the metal-InP interface, of a Ni3P layer combined with a stoichiometry change in the InP surface. We show, in addition, that it is possible to achieve very low R(sub c) values with this system without incurring device destroying sinter-induced metallurgical interdiffusion.

Refurbishing of carbon contaminated pre-mirror of reflectivity beam line at Indus-1

NASA Astrophysics Data System (ADS)

Yadav, P. K.; Kumar, M.; Gupta, R. K.; Sinha, M.; Patel, H. S.; Modi, M. H.

2018-04-01

In recent days optics contamination and its refurbishing is a serious issue for synchrotron radiation beam line community. Here we refurbished a carbon contaminated mirror by Ar and O2 gas mixed (1:1) radio frequency plasma. For structural analysis pre and post characterization of the mirror was done by Soft X-ray reflectivity (SXRR), Raman Spectroscopy (RS) and Atomic force microscopy (AFM). Before refurbishing mirror, a low density graphitic carbon layer of thickness 400 Å with surface roughness about 55 Å and Au surface roughness 14Å was estimated by SXRR. After one hour RF plasma exposure it is observed by SXRR and Raman spectroscopy that carbon layer is completely removed. The AFM and SXRR results show that roughness of Au surface not increase after plasma exposure.

Transport properties of ultrathin YBa2Cu3O7 -δ nanowires: A route to single-photon detection

NASA Astrophysics Data System (ADS)

Arpaia, Riccardo; Golubev, Dmitri; Baghdadi, Reza; Ciancio, Regina; Dražić, Goran; Orgiani, Pasquale; Montemurro, Domenico; Bauch, Thilo; Lombardi, Floriana

2017-08-01

We report on the growth and characterization of ultrathin YBa2Cu3O7 -δ (YBCO) films on MgO (110) substrates, which exhibit superconducting properties at thicknesses down to 3 nm. YBCO nanowires, with thicknesses down to 10 nm and widths down to 65 nm, have also been successfully fabricated. The nanowires protected by a Au capping layer show superconducting properties close to the as-grown films and critical current densities, which are limited by only vortex dynamics. The 10-nm-thick YBCO nanowires without the Au capping present hysteretic current-voltage characteristics, characterized by a voltage switch which drives the nanowires directly from the superconducting to the normal state. We associate such bistability to the presence of localized normal domains within the superconductor. The presence of the voltage switch in ultrathin YBCO nanostructures, characterized by high sheet resistance values and high critical current values, makes our nanowires very attractive devices to engineer single-photon detectors.

UV sensing using film bulk acoustic resonators based on Au/n-ZnO/piezoelectric-ZnO/Al structure

PubMed Central

Bian, Xiaolei; Jin, Hao; Wang, Xiaozhi; Dong, Shurong; Chen, Guohao; Luo, J. K.; Deen, M. Jamal; Qi, Bensheng

2015-01-01

A new type of ultraviolet (UV) light sensor based on film bulk acoustic wave resonator (FBAR) is proposed. The new sensor uses gold and a thin n-type ZnO layer deposited on the top of piezoelectric layer of FBAR to form a Schottky barrier. The Schottky barrier's capacitance can be changed with UV light, resulting in an enhanced shift in the entire FBAR's resonant frequency. The fabricated UV sensor has a 50 nm thick n-ZnO semiconductor layer with a carrier concentration of ~ 1017 cm−3. A large frequency downshift is observed when UV light irradiates the FBAR. With 365 nm UV light of intensity 1.7 mW/cm2, the FBAR with n-ZnO/Au Schottky diode has 250 kHz frequency downshift, much larger than the 60 kHz frequency downshift in a conventional FBAR without the n-ZnO layer. The shift in the new FBAR's resonant frequency is due to the junction formed between Au and n-ZnO semiconductor and its properties changes with UV light. The experimental results are in agreement with the theoretical analysis using an equivalent circuit model of the new FBAR structure. PMID:25773146

Effects of Different Materials Used for Internal Floating Electrode on the Photovoltaic Properties of Tandem Type Organic Solar Cell

NASA Astrophysics Data System (ADS)

Triyana, Kuwat; Yasuda, Takeshi; Fujita, Katsuhiko; Tsutsui, Tetsuo

2004-04-01

Three thin heterojunctions sandwiched between indium tin oxide (ITO) and the top electrode as triple-heterojunction organic solar cells have been fabricated. Each heterojunction cell consists of CuPc as a donor layer and perilene tetracrboxylic-bis-benzimidazole (PTCBI) as an acceptor layer. Ultra thin (1 nm average thickness) layers of Ag or Au have been inserted between two heterojunctions as an internal electrode. Ag and Au were chosen as materials both for internal floating and top electrodes. Influences of different deposition sequences of the organic layer in each heterojunction cell and different electrode materials were also investigated. The optimum devices were obtained when the same material was used both as an internal electrode and a top electrode. When the deposition sequence of the heterojunction is PTCBI/CuPc, the most suitable electrode is Au and the ITO is negative relative to the top electrode. Meanwhile, Ag is suitable for an electrode when the deposition sequence is CuPc/PTCBI. In this second deposition sequence, the ITO is positive relative to the top electrode. The open circuit voltage (Voc) of both optimum devices is on the order of 1.35-1.5 V. These values are approximately three times higher than that in single-heterojunction organic solar cells.

Improved contact resistance stability in a MEMS separable electrical connector

NASA Astrophysics Data System (ADS)

Larsson, M. P.

2005-12-01

A MEMS in-line separable electrical connector with improved contact resistance stability to thermal fluctuations and mating cycles is described. The design allows sliding, in-line connection between separate halves, inducing vertical deflections on a set of flexible conductors to establish stable electrical contacts. Features are present on both halves to ensure precise lateral and vertical self-alignment; preventing shorts and maintaining consistent conductor deflections. Characterisation on early prototypes revealed significant variability in contact resistance with thermal fluctuations and mating cycle history. As flexible conductors are multi-layered structures of Au supported by a thick structural layer of Ni, they undergo differential thermal expansion, introducing variability in contact resistance with temperature. Sliding contact wear during repeated mating leads to removal of portions of the Au surface coating, and electrical contact between underlying (non-noble) Ni layers. By using a harder Co-Au alloy as the contact surface layer and modifying the arrangement of constituent conductor layers to balance thermal stresses, improvements to both wear and thermal tolerance of contact resistance can be obtained. Devices implementing the above design modifications show stable contact resistance over 100 mating cycles and an increase in contact resistance of between 3.5 and 7% over a temperature rise of 60°C. The electrical performance improvements increase the attractiveness of the MEMS in-line separable connector concept for applications in portable electronics and MEMS integration.

Enhanced photoelectrocatalytic performance of α-Fe2O3 thin films by surface plasmon resonance of Au nanoparticles coupled with surface passivation by atom layer deposition of Al2O3.

PubMed

Liu, Yuting; Xu, Zhen; Yin, Min; Fan, Haowen; Cheng, Weijie; Lu, Linfeng; Song, Ye; Ma, Jing; Zhu, Xufei

2015-12-01

The short lifetime of photogenerated charge carriers of hematite (α-Fe2O3) thin films strongly hindered the PEC performances. Herein, α-Fe2O3 thin films with surface nanowire were synthesized by electrodeposition and post annealing method for photoelectrocatalytic (PEC) water splitting. The thickness of the α-Fe2O3 films can be precisely controlled by adjusting the duration of the electrodeposition. The Au nanoparticles (NPs) and Al2O3 shell by atom layer deposition were further introduced to modify the photoelectrodes. Different constructions were made with different deposition orders of Au and Al2O3 on Fe2O3 films. The Fe2O3-Au-Al2O3 construction shows the best PEC performance with 1.78 times enhancement by localized surface plasmon resonance (LSPR) of NPs in conjunction with surface passivation of Al2O3 shells. Numerical simulation was carried out to investigate the promotion mechanisms. The high PEC performance for Fe2O3-Au-Al2O3 construction electrode could be attributed to the Al2O3 intensified LSPR, effective surface passivation by Al2O3 coating, and the efficient charge transfer due to the Fe2O3-Au Schottky junctions.

The United States Army Medical Department Journal, April - June 2011. Prehospital combat casualty care; The starting point of battlefield survival

DTIC Science & Technology

2011-04-01

74-78. 30. Cotton BA, Guy JS, Morris JA Jr, Abumrad NN. The cellular, metabolic, and systemic consequences of aggressive fluid resuscitation...civilian trauma patients. Ann Surg. 2008;248:447-458. 55. Gunter OL Jr, Au BK, Isbell JM, Mowery NT, Young PP, Cotton BA. Optimizing outcomes in...AFB is composed of a thick layer of absorbent cotton wrapped in layers of gauze and attached to 2 long straps for wrapping around the wound. It

Film growth arising from the deposition of Au onto an i-Al Pd Mn quasicrystal: a medium energy ion scattering study

NASA Astrophysics Data System (ADS)

Noakes, T. C. Q.; Bailey, P.; Draxler, M.; McConville, C. F.; Ross, A. R.; Lograsso, T. A.; Leung, L.; Smerdon, J. A.; McGrath, R.

2006-06-01

The room temperature deposition of 7 ML of Au onto the fivefold symmetric surface of icosahedral Al-Pd-Mn leads to the formation of a several monolayers thick Au-Al alloy film. An AlAu film with 1:1 stoichiometry is formed, which shows no evidence of ordered structure, being either amorphous or polycrystalline. Annealing to 325 °C causes more Al to diffuse into the film, producing Al2Au but still with no indication of structure. Experiments using 0.5 ML of pre-deposited In demonstrated a surfactant effect as the In 'floated' on the surface during growth and produced a reduction in film roughness. However, contrary to previous findings the film was still either amorphous or polycrystalline, with no evidence of quasi-crystalline or aperiodic structure. Experiments were also conducted using smaller doses of Au to look for the formation of an epitaxial layer and, if formed, determine the registry with the substrate. However, no change in the Pd blocking curves for the surface could be seen, suggesting that the Au does not adsorb in well defined sites. This result is not surprising when considering that even for these low doses Al is drawn into the film, changing the composition and probably the structure of the topmost layers of the substrate, so that the potential adsorption sites on the clean surface may no longer exist.

Memory effects in annealed hybrid gold nanoparticles/block copolymer bilayers

PubMed Central

2011-01-01

We report on the use of the self-organization process of sputtered gold nanoparticles on a self-assembled block copolymer film deposited by horizontal precipitation Langmuir-Blodgett (HP-LB) method. The morphology and the phase-separation of a film of poly-n-butylacrylate-block-polyacrylic acid (PnBuA-b-PAA) were studied at the nanometric scale by using atomic force microscopy (AFM) and Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS). The templating capability of the PnBuA-b-PAA phase-separated film was studied by sputtering gold nanoparticles (NPs), forming a film of nanometric thickness. The effect of the polymer chain mobility onto the organization of gold nanoparticle layer was assessed by heating the obtained hybrid PnBuA-b-PAA/Au NPs bilayer at T >Tg. The nanoparticles' distribution onto the different copolymer domains was found strongly affected by the annealing treatment, showing a peculiar memory effect, which modifies the AFM phase response of the Au NPs layer onto the polar domains, without affecting their surfacial composition. The effect is discussed in terms of the peculiar morphological features induced by enhanced mobility of polymer chains on the Au NPs layer. PMID:21711674

Seed layer effect on different properties and UV detection capability of hydrothermally grown ZnO nanorods over SiO2/p-Si substrate

NASA Astrophysics Data System (ADS)

Sannakashappanavar, Basavaraj S.; Byrareddy, C. R.; Kumar, Pesala Sudheer; Yadav, Aniruddh Bahadur

2018-05-01

Hydrothermally grown one dimensional ZnO nanostructures are among the most widely used semiconductor materials to build high-efficiency electronic devices for various applications. Few researchers have addressed the growth mechanism and effect of ZnO seed layer on different properties of ZnO nanorods grown by hydrothermal method, instead, no one has synthesized ZnO nanorod over SiO2/p-Si substrate. The aim of this study is to study the effect of ZnO seed layer and the growth mechanism of ZnO nanorods over SiO2/p-Si substrate. To achieve the goal, we have synthesized ZnO nanorods over different thickness ZnO seed layers by using the hydrothermal method on SiO2/p-Si substrate. The effects of c-plane area ratio were identified for the growth rate of c-plane, reaction rate constant and stagnant layer thickness also calculated by using a modified rate growth equation. We have identified maximum seed layer thickness for the growth of vertical ZnO nanorod. A step dislocation in the ZnO nanorods grown on 150and 200 nm thick seed layers was observed, the magnitude of Burges vector was calculated for this disorder. The seed layer and ZnO nanorods were characterized by AFM, XPS, UV-visible, XRD (X-ray diffraction, and SEM(scanning electron microscope). To justify the application of the grown ZnO nanorods Ti/Au was deposited over ZnO nanorods grown over all seed layers for the fabrication of photoconductor type UV detector.

Graphene-bimetal plasmonic platform for ultra-sensitive biosensing

NASA Astrophysics Data System (ADS)

Tong, Jinguang; Jiang, Li; Chen, Huifang; Wang, Yiqin; Yong, Ken-Tye; Forsberg, Erik; He, Sailing

2018-03-01

A graphene-bimetal plasmonic platform for surface plasmon resonance biosensing with ultra-high sensitivity was proposed and optimized. In this hybrid configuration, graphene nanosheets was employed to effectively absorb the excitation light and serve as biomolecular recognition elements for increased adsorption of analytes. Coating of an additional Au film prevents oxidation of the Ag substrate during manufacturing process and enhances the sensitivity at the same time. Thus, a bimetal Au-Ag substrate enables improved sensing performance and promotes stability of this plasmonic sensor. In this work we optimized the number of graphene layers as well as the thickness of the Au film and the Ag substrate based on the phase-interrogation sensitivity. We found an optimized configuration consisting of 6 layers of graphene coated on a bimetal surface consisting of a 5 nm Au film and a 30 nm Ag film. The calculation results showed the configuration could achieve a phase sensitivity as high as 1 . 71 × 106 deg/RIU, which was more than 2 orders of magnitude higher than that of bimetal structure and graphene-silver structure. Due to this enhanced sensing performance, the graphene-bimetal plasmonic platform proposed in this paper is potential for ultra-sensitive plasmonic sensing.

Spin-dependent heat transport and thermal boundary resistance

NASA Astrophysics Data System (ADS)

Jeong, Taehee

In this thesis, thermal conductivity change depending on the magnetic configurations has been studied. In order to make different magnetic configurations, we developed a spin valve structure, which has high MR ratio and low saturation field. The high MR ratio was achieved using Co/Cu multilayer and 21A or 34A thick Cu layer. The low saturation field was obtained by implementing different coercivities of the successive ferromagnetic layers. For this purpose, Co/Cu/Cu tri-layered structure was used with the thicknesses of the Co layers; 15 A and 30 A. For the thermal conductivity measurement, a three-omega method was employed with a thermally isolated microscale rod. We fabricated the microscale rod using optical lithography and MEMS process. Then the rod was wire-bonded to a chip-carver for further electrical measurement. For the thermal conductivity measurement, we built the three-omega measurement system using two lock-in amplifiers and two differential amplifiers. A custom-made electromagnet was added to the system to investigate the impact of magnetic field. We observed titanic thermal conductivity change depending on the magnetic configurations of the Co/Cu/Co multilayer. The thermal conductivity change was closely correlated with that of the electric conductivity in terms of the spin orientation, but the thermal conductivity was much more sensitive than that of the electric conductivity. The relative thermal conductivity change was 50% meanwhile that of electric resistivity change was 8.0%. The difference between the two ratios suggests that the scattering mechanism for charge and heat transport in the Co/Cu/Co multilayer is different. The Lorentz number in Weidemann-Franz law is also spin-dependent. Thermal boundary resistance between metal and dielectrics was also studied in this thesis. The thermal boundary resistance becomes critical for heat transport in a nanoscale because the thermal boundary resistance can potentially determine overall heat transport in thin film structures. A transient theraroreflectance (TTR) technique can be used for measuring the thermal conductivity of thin films in cross-sectional direction. In this study, a pump-probe scheme was employed for the TTR technique. We built an optical pump-probe system by using a nanosecond pulse laser for pumping and a continuous-wave laser for probing. A short-time heating event occured at the surface of a sample by shining a laser pulse on the surface. Then the time-resolved thermoreflectance signals were detected using a photodetector and an oscilloscope. The increased temperature decreases slowly and its thermal decay depends on the thermal properties of a sample. Since the reflectivity is linearly proportional to the temperature, the time-resolved thermoreflectance signals have the information of the thermal properties of a sample. In order to extract the thermal properties of a sample, a thermal analysis was performed by fitting the experimental data with thermal models. We developed 2-layered and 3-layered thermal models using the analogies between thermal conduction and electric conduction and a transmission-line concept. We used two sets of sample structures: Au/SiNx/Si substrate and Au/CoFe/SiNx/Si substrate with various thickness of SiN x layer. Using the pump-probe system, we measured the time-resolved thermoreflectance signals for each sample. Then, the thermal conductivity and thermal boundary resistance were obtained by fitting the experimental data with the thermal models. The thermal conductivity of SiNx films was measured to be 2.0 W/mK for both structures. In the case of the thermal boundary resistance, it was 0.81x10-5 m 2K/W at the Au/SiNx interface and 0.54x10 -5 m2K/W at the CoFe/SiNx interface, respectively. The difference of the thermal boundary resistance between Au/SiNx and CoFe/SiNx might be came from the different phonon dispersion of Au and CoFe. The thermal conductivity did not depend on the thickness of SiNx films in the thickness range of 50-200nm. However, the thermal boundary resistance at metal/SiNx interfaces will impact overall thermal conduction when the thickness of SiNx thin films is in a nanometer order. For example, apparent thermal conductivity of SiN x film becomes half of the intrinsic thermal conductivity when the thickness decreases to 16nm. Therefore, it is advised that the thermal boundary resistance between metal and dielectrics should be counted in nano-scale electronic devices. (Abstract shortened by UMI.)

Plasmon enhanced fluorescence studies from aligned gold nanorod arrays modified with SiO{sub 2} spacer layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Damm, Signe; Fedele, Stefano; Rice, James H., E-mail: james.rice@ucd.ie

Here, we demonstrate that quasi self-standing Au nanorod arrays prepared with plasma polymerisation deposited SiO{sub 2} dielectric spacers support surface enhanced fluorescence (SEF) while maintaining high signal reproducibility. We show that it is possible to find a balance between enhanced radiative and non-radiative decay rates at which the fluorescent intensity is maximized. The SEF signal optimised with a 30 nm spacer layer thickness showed a 3.5-fold enhancement with a signal variance of <15% thereby keeping the integrity of the nanorod array. We also demonstrate the decreased importance of obtaining resonance conditions when localized surface plasmon resonance is positioned within the spectralmore » region of Au interband transitions. Procedures for further increasing the SEF enhancement factor are also discussed.« less

Growth kinetics and microstructural evolution during hot isostatic pressing of U-10 wt.% Mo monolithic fuel plate in AA6061 cladding with Zr diffusion barrier

DOE Office of Scientific and Technical Information (OSTI.GOV)

Y. Park; J. Yoo; K. Huang

2014-04-01

Phase constituents and microstructure changes in RERTR fuel plate assemblies as functions of temperature and duration of hot-isostatic pressing (HIP) during fabrication were examined. The HIP process was carried out as functions of temperature (520, 540, 560 and 580 °C for 90 min) and time (45–345 min at 560 °C) to bond 6061 Al-alloy to the Zr diffusion barrier that had been co-rolled with U-10 wt.% Mo (U10Mo) fuel monolith prior to the HIP process. Scanning and transmission electron microscopies were employed to examine the phase constituents, microstructure and layer thickness of interaction products from interdiffusion. At the interface betweenmore » the U10Mo and Zr, following the co-rolling, the UZr2 phase was observed to develop adjacent to Zr, and the a-U phase was found between the UZr2 and U10Mo, while the Mo2Zr was found as precipitates mostly within the a-U phase. The phase constituents and thickness of the interaction layer at the U10Mo-Zr interface remained unchanged regardless of HIP processing variation. Observable growth due to HIP was only observed for the (Al,Si)3Zr phase found at the Zr/AA6061 interface, however, with a large activation energy of 457 ± 28 kJ/mole. Thus, HIP can be carried to improve the adhesion quality of fuel plate without concern for the excessive growth of the interaction layer, particularly at the U10Mo-Zr interface with the a-U, Mo2Zr, and UZr2 phases.« less

High Resolution Quantitative Microbeam Analysis of Ir-coated Geological Specimens Using Conventionally Coated Standards

NASA Astrophysics Data System (ADS)

Armstrong, J. T.; Crispin, K. L.

2012-12-01

Traditionally, quantitative electron microbeam analyses of insulating specimens are performed after coating the materials with thin conducting layers of carbon. For x-ray lines greater than 1 keV in energy and beam voltages in excess of 10 keV, the results are insensitive to the exact thickness of the carbon coat. High resolution imaging, low voltage analysis, and analysis of specimens containing low levels of carbon require the use of substitute conductive coats. Typical substitutes for carbon coats (e.g., Au, Au-Pd, Cr, Al) require either using similarly coated standards or substantial corrections to be applied. Even when using modern multi-layer correction algorithms or Monte Carlo calculations, significant errors can result (e.g., Armstrong 2009, Armstrong and Crispin, 2012). We propose the use of ultra-thin layers of Ir as a substitute for C in the analysis of insulating geological specimens. Ir has been found to be an excellent coating material for high resolution imaging (e.g., Echlin, 2009). Sputtered layers as thin as 0.5 nm are found to be conductive, and layers of just a few nm provide good protection against beam damage with sub-nm grain size (Sebring et al., 1999). We have analyzed a series of geological materials with Ir coats between 1 - 8 nm and found similar levels of effects on emitted x-ray intensities as produced with typical carbon coat thicknesses (10-25 nm). E.g., for Ir thicknesses less than 5 nm, the reduction of intensity for x-ray lines between 1 and 7 keV are between 1-3% for a beam energy of 15 keV. The reduction in intensity for higher-energy lines such as Fe-K is actually less than produced by typical C-coats. We will present the results of these experiments and propose simple algorithmic equations which fit these data.

Au coated PS nanopillars as a highly ordered and reproducible SERS substrate

NASA Astrophysics Data System (ADS)

Kim, Yong-Tae; Schilling, Joerg; Schweizer, Stefan L.; Sauer, Guido; Wehrspohn, Ralf B.

2017-07-01

Noble metal nanostructures with nanometer gap size provide strong surface-enhanced Raman scattering (SERS) which can be used to detect trace amounts of chemical and biological molecules. Although several approaches were reported to obtain active SERS substrates, it still remains a challenge to fabricate SERS substrates with high sensitivity and reproducibility using low-cost techniques. In this article, we report on the fabrication of Au sputtered PS nanopillars based on a template synthetic method as highly ordered and reproducible SERS substrates. The SERS substrates are fabricated by anodic aluminum oxide (AAO) template-assisted infiltration of polystyrene (PS) resulting in hemispherical structures, and a following Au sputtering process. The optimum gap size between adjacent PS nanopillars and thickness of the Au layers for high SERS sensitivity are investigated. Using the Au sputtered PS nanopillars as an active SERS substrate, the Raman signal of 4-methylbenzenethiol (4-MBT) with a concentration down to 10-9 M is identified with good signal reproducibility, showing great potential as promising tool for SERS-based detection.

A dewetting route to grow heterostructured nanoparticles based on thin film heterojunctions.

PubMed

Li, Junjie; Yin, Deqiang; Li, Qiang; Chen, Chunlin; Huang, Sumei; Wang, Zhongchang

2015-12-21

Heterostructured nanoparticles have received considerable attention for their various applications due to their unique and tunable functionalities with respect to their individual bulk constituents. However, the current wet chemical synthesis of multicomponent heterostructured nanoparticles is rather complicated. Here, we report a simple and quick method to fabricate Co-Au dumbbell arrays by dewetting Co/Au heterojunctions on a Si substrate and demonstrate that the Co-Au dumbbells vary in size from 2 to 28 nm. We further show by chemical mapping that Co bells are covered by a pseudomorphic Au wetting layer of ∼4 Å, preventing the bells from oxidation. By controlling the thickness of metal heterojunctions and the annealing time, the morphology of the Co-Au nanoparticle is found to be transformed from the dumbbell to the core shell. This facile route is demonstrated to be useful for fabricating other metal-metal and metal-oxide heterostructures and hence holds technological promise for functional applications.

Structure and magnetism of epitaxially strained Pd(001) films on Fe(001): Experiment and theory

NASA Astrophysics Data System (ADS)

Fullerton, Eric E.; Stoeffler, D.; Ounadjela, K.; Heinrich, B.; Celinski, Z.; Bland, J. A. C.

1995-03-01

We present an experimental and theoretical description of the structure and magnetism of epitaxially strained Pd(001) films on Fe(001) and in Fe/Pd/Fe(001) trilayers. The structure is determined by combining reflection high-energy electron diffraction and x-ray diffraction. For Fe/Au(001) bilayers and Fe/Pd/Au(001) trilayers grown by molecular-beam epitaxy on Ag(001), the Fe and Au layers are well represented by their bulk structure, whereas, thin Pd layers have a face-centered tetragonal structure with an in-plane expansion of 4.2% and an out-of-plane contraction of 7.2% (c/a=0.89). Theoretical ab initio studies of the interfacial structure indicate that the structural ground state of the epitaxially strained Pd layer is well described by a fct structure which maintains the bulk Pd atomic volume with small deviations at the interface. For Fe/Pd/Fe trilayers, the interlayer coupling oscillates with a period of 4 monolayers (ML) on a ferromagnetic background that crosses to weak antiferromagnetic coupling for thicknesses >12 ML of Pd. Strong ferromagnetic coupling observed below 5 ML of Pd indicates that 2 ML of Pd at each interface are ferromagnetically ordered. Theoretical studies of Fe3Pdn superlattices (where n is the number of Pd atomic layers) determine the polarization of the Pd layer and the interlayer magnetic coupling to depend strongly on the c/a ratio of the Pd layers. Modeling of a Pd layer with a constant-volume fct structure and one monolayer interfacial roughness find that the first 2 ML of the Pd is polarized in close agreement with the experimental results. Polarized neutron reflectivity results on an Fe(5.6 ML)/Pd(7 ML)/Au(20 ML) sample determine the average moment per Fe atom of 2.66+/-0.05μB. Calculations for the same structure show that this value is consistent with the induced Pd polarization.

Electrically Tunable and Negative Schottky Barriers in Multi-layered Graphene/MoS2 Heterostructured Transistors.

PubMed

Qiu, Dongri; Kim, Eun Kyu

2015-09-03

We fabricated multi-layered graphene/MoS2 heterostructured devices by positioning mechanically exfoliated bulk graphite and single-crystalline 2H-MoS2 onto Au metal pads on a SiO2/Si substrate via a contamination-free dry transfer technique. We also studied the electrical transport properties of Au/MoS2 junction devices for systematic comparison. A previous work has demonstrated the existence of a positive Schottky barrier height (SBH) in the metal/MoS2 system. However, analysis of the SBH indicates that the contacts of the multi-layered graphene/MoS2 have tunable negative barriers in the range of 300 to -46 meV as a function of gate voltage. It is hypothesized that this tunable SBH is responsible for the modulation of the work function of the thick graphene in these devices. Despite the large number of graphene layers, it is possible to form ohmic contacts, which will provide new opportunities for the engineering of highly efficient contacts in flexible electronics and photonics.

Electrically Tunable and Negative Schottky Barriers in Multi-layered Graphene/MoS2 Heterostructured Transistors

NASA Astrophysics Data System (ADS)

Qiu, Dongri; Kim, Eun Kyu

2015-09-01

We fabricated multi-layered graphene/MoS2 heterostructured devices by positioning mechanically exfoliated bulk graphite and single-crystalline 2H-MoS2 onto Au metal pads on a SiO2/Si substrate via a contamination-free dry transfer technique. We also studied the electrical transport properties of Au/MoS2 junction devices for systematic comparison. A previous work has demonstrated the existence of a positive Schottky barrier height (SBH) in the metal/MoS2 system. However, analysis of the SBH indicates that the contacts of the multi-layered graphene/MoS2 have tunable negative barriers in the range of 300 to -46 meV as a function of gate voltage. It is hypothesized that this tunable SBH is responsible for the modulation of the work function of the thick graphene in these devices. Despite the large number of graphene layers, it is possible to form ohmic contacts, which will provide new opportunities for the engineering of highly efficient contacts in flexible electronics and photonics.

Controlling the exciton emission of gold coated GaAs-AlGaAs core-shell nanowires with an organic spacer layer

NASA Astrophysics Data System (ADS)

Kaveh, M.; Gao, Q.; Jagadish, C.; Ge, J.; Duscher, G.; Wagner, H. P.

2016-12-01

Excitons are the most prominent optical excitations and controlling their emission is an important step towards new optical devices. We have investigated the exciton emission from uncoated and gold/aluminum quinoline (Alq3) coated GaAs-AlGaAs-GaAs core-shell nanowires (NWs) using temperature-, intensity- and polarization dependent photoluminescence (PL). Plasmonic GaAs-AlGaAs-GaAs NWs with a ˜10 nm thick Au coating but without an Alq3 spacer layer reveal a significant reduction of the PL intensity of the exciton emission compared with the uncoated NW sample. Plasmonic NW samples with the same nominal Au coverage and an additional Alq3 interlayer of 3 or 6 nm thickness show a clearly stronger PL intensity which increases with rising Alq3 spacer thickness. Time-resolved (TR) PL measurements reveal an increase of the exciton decay rate by a factor of up to two with decreasing Alq3 spacer thickness suggesting the presence of Förster energy transfer from NW excitons to plasmon oscillations in the gold film. The weak change of the decay time, however, indicates that Förster energy-transfer is only partially responsible for the PL quenching in the gold coated NWs. The main reason for the reduction of the PL emission is attributed to a gold induced band-bending in the GaAs NW core which causes exciton dissociation. With increasing Alq3 spacer thickness the band-bending decreases leading to a reduction of the exciton dissociation and PL quenching. Our interpretation is supported by electron energy loss spectroscopy measurements which show a signal reduction and blue shift of defect (possibly EL2) transitions when gold particles are deposited on NWs compared with bare or Alq3 coated NWs.

Controlling the exciton emission of gold coated GaAs-AlGaAs core-shell nanowires with an organic spacer layer.

PubMed

Kaveh, M; Gao, Q; Jagadish, C; Ge, J; Duscher, G; Wagner, H P

2016-12-02

Excitons are the most prominent optical excitations and controlling their emission is an important step towards new optical devices. We have investigated the exciton emission from uncoated and gold/aluminum quinoline (Alq 3 ) coated GaAs-AlGaAs-GaAs core-shell nanowires (NWs) using temperature-, intensity- and polarization dependent photoluminescence (PL). Plasmonic GaAs-AlGaAs-GaAs NWs with a ∼10 nm thick Au coating but without an Alq 3 spacer layer reveal a significant reduction of the PL intensity of the exciton emission compared with the uncoated NW sample. Plasmonic NW samples with the same nominal Au coverage and an additional Alq 3 interlayer of 3 or 6 nm thickness show a clearly stronger PL intensity which increases with rising Alq 3 spacer thickness. Time-resolved (TR) PL measurements reveal an increase of the exciton decay rate by a factor of up to two with decreasing Alq 3 spacer thickness suggesting the presence of Förster energy transfer from NW excitons to plasmon oscillations in the gold film. The weak change of the decay time, however, indicates that Förster energy-transfer is only partially responsible for the PL quenching in the gold coated NWs. The main reason for the reduction of the PL emission is attributed to a gold induced band-bending in the GaAs NW core which causes exciton dissociation. With increasing Alq 3 spacer thickness the band-bending decreases leading to a reduction of the exciton dissociation and PL quenching. Our interpretation is supported by electron energy loss spectroscopy measurements which show a signal reduction and blue shift of defect (possibly EL2) transitions when gold particles are deposited on NWs compared with bare or Alq 3 coated NWs.

Application of neural networks to prediction of advanced composite structures mechanical response and behavior

NASA Technical Reports Server (NTRS)

Cios, K. J.; Vary, A.; Berke, L.; Kautz, H. E.

1992-01-01

Two types of neural networks were used to evaluate acousto-ultrasonic (AU) data for material characterization and mechanical reponse prediction. The neural networks included a simple feedforward network (backpropagation) and a radial basis functions network. Comparisons of results in terms of accuracy and training time are given. Acousto-ultrasonic (AU) measurements were performed on a series of tensile specimens composed of eight laminated layers of continuous, SiC fiber reinforced Ti-15-3 matrix. The frequency spectrum was dominated by frequencies of longitudinal wave resonance through the thickness of the specimen at the sending transducer. The magnitude of the frequency spectrum of the AU signal was used for calculating a stress-wave factor based on integrating the spectral distribution function and used for comparison with neural networks results.

Thermoelectric properties of Zn4Sb3/CeFe(4-x)CoxSb12 nano-layered superlattices modified by MeV Si ion beam

NASA Astrophysics Data System (ADS)

Budak, S.; Guner, S.; Minamisawa, R. A.; Muntele, C. I.; Ila, D.

2014-08-01

We prepared multilayers of superlattice thin film system with 50 periodic alternating nano-layers of semiconducting half-Heusler β-Zn4Sb3 and skutterudite CeFe2Co2Sb12 compound thin films using ion beam assisted deposition (IBAD) with Au layers deposited on both sides as metal contacts. The deposited multilayer thin films have alternating layers about 5 nm thick. The total thickness of the multilayer system is 275 nm. The superlattices were then bombarded by 5 MeV Si ion at six different fluences to form nano-cluster structures. The film thicknesses and composition were monitored by Rutherford backscattering spectrometry (RBS) before and after MeV ion bombardment. We have measured the thermoelectric efficiency, Figure of Merit ZT, of the fabricated device by measuring the cross plane thermal conductivity by the 3rd harmonic (3ω) method, the cross plane Seebeck coefficient, and the electrical conductivity using the van der Pauw method before and after the MeV ion bombardments. We reached the remarkable thermoelectric Figure of Merit results at optimal fluences.

Position-dependent performance of copper phthalocyanine based field-effect transistors by gold nanoparticles modification.

PubMed

Luo, Xiao; Li, Yao; Lv, Wenli; Zhao, Feiyu; Sun, Lei; Peng, Yingquan; Wen, Zhanwei; Zhong, Junkang; Zhang, Jianping

2015-01-21

A facile fabrication and characteristics of copper phthalocyanine (CuPc)-based organic field-effect transistor (OFET) using the gold nanoparticles (Au NPs) modification is reported, thereby achieving highly improved performance. The effect of Au NPs located at three different positions, that is, at the SiO2/CuPc interface (device B), embedding in the middle of CuPc layer (device C), and on the top of CuPc layer (device D), is investigated, and the results show that device D has the best performance. Compared with the device without Au NPs (reference device A), device D displays an improvement of field-effect mobility (μ(sat)) from 1.65 × 10(-3) to 5.51 × 10(-3) cm(2) V(-1) s(-1), and threshold voltage decreases from -23.24 to -16.12 V. Therefore, a strategy for the performance improvement of the CuPc-based OFET with large field-effect mobility and saturation drain current is developed, on the basis of the concept of nanoscale Au modification. The model of an additional electron transport channel formation by FET operation at the Au NPs/CuPc interface is therefore proposed to explain the observed performance improvement. Optimum CuPc thickness is confirmed to be about 50 nm in the present study. The device-to-device uniformity and time stability are discussed for future application.

New possibilities for tuning ultrathin cobalt film magnetic properties by a noble metal overlayer.

PubMed

Kisielewski, M; Maziewski, A; Tekielak, M; Wawro, A; Baczewski, L T

2002-08-19

Complementary multiscale magneto-optical studies based on the polar Kerr effect are carried out on an ultrathin cobalt wedge covered with a silver wedge and subsequently with the Au thick layer. A few monolayers of Ag are found to have a substantial effect on magnetic anisotropy, the coercivity field, and Kerr rotation. The silver overlayer thickness-driven magnetic reorientation from easy axis to easy plane generates a new type of 90 degrees magnetic wall for cobalt thicknesses between 1.3 and 1.8 nm. The tuning of the wall width in a wide range is possible. Tailoring of the overlayer structure can be used for ultrathin film magnetic patterning.

ELSA flood stack for MIS 2-3 from dry maar lakestructure Auel (Eifel/Germany)

NASA Astrophysics Data System (ADS)

Brunck, Heiko; Sirocko, Frank

2015-04-01

Lacustrine sediments are very sensitive to natural and anthropogenically enviromental changes. Thus, lake sediments are excellent climate archives and can be used for reconstructions of past precipitation and flood events. However, until now, there is no continous flood record for the entire last 60 000 years for Central Europe. The present study reconstructs paleo floods from event layers in the sediment, of dry maar lakestructure Auel (Eifel). This silted up basin has an inflow by a local stream. Accordingly the sedimentation rate is directly linked to runoff activity. The bioturbation was low so that event layers become visible, but varves are not preserved. The maar site is near to the town of Gerolstein in the Eifel; the core AU2 was drilled in the ELSA (Eifel Laminated Sediment archive) project and is 123m long. AU2 has the highest sedimentation rate of all ELSA cores, due to abundant fluvial input. The Eifel area is well suited to approximate Central European weather, because modern water level gauge data from Eifel rivers correlate with respective data from the Rhine (Wernli and Pfahl, 2009). Due to the high inflow into the maar, Auel has the highest number of botanical macro remains of all ELSA cores. These specific conditions explain why only in AU2 all 21 Greenland interstadials can be observed in the abundance of wood remains and the organic carbon concentration. In a final stratigraphic step the time series of Corg was tuned to the Greenland ice core chronology to link the central European landscape evolution directly to the Greenland climate curve (Svensson et al., 2008). Combined sedimentological, paleobotanical and geochemical data received from AU2 builds the foundation of the 14C based chronology. The synchronisation of the record with other cores is controlled by tephra time markers and pollen. Both are used to align the main cores of the ELSA project and construct an integrated age model for the last 220 000 years [b2k] (Förster and Sirocko, 2014). To study the past flood events in detail, 10 cm long thin sections were analyzed to distinguish flood layers from distal turbidites. Turbidites have a continuous grain size gradation; the grains size profile of flood events is in contrast characterized by several grain size maxima over the entire layer thickness. A flood event over several days shows numerous peaks of intense discharge, which lead to a discontinuous grain size gradient. The thickness of each flood layer was measured for the classification of the event intensity. As a consequence, 88 flood layers over 7.5 mm thickness were detected. Our time-series represents the first highly-resolved chronology for flood events from 60 000 years until present times and indicates variable periodicities of flood activity linked to predominant climatic development. The fore main sections of all flood layers are: 44 000 - 45 500, 30 000 - 37 000, 20 000 - 22 500 and 11 000 - 17 000 years [b2k].

Enhanced characteristics of blue InGaN /GaN light-emitting diodes by using selective activation to modulate the lateral current spreading length

NASA Astrophysics Data System (ADS)

Lin, Ray-Ming; Lu, Yuan-Chieh; Chou, Yi-Lun; Chen, Guo-Hsing; Lin, Yung-Hsiang; Wu, Meng-Chyi

2008-06-01

We have studied the characteristics of blue InGaN /GaN multiquantum-well light-emitting diodes (LEDs) after reducing the length of the lateral current path through the transparent layer through formation of a peripheral high-resistance current-blocking region in the Mg-doped GaN layer. To study the mechanism of selective activation in the Mg-doped GaN layer, we deposited titanium (Ti), gold (Au), Ti /Au, silver, and copper individually onto the Mg-doped GaN layer and investigated their effects on the hole concentration in the p-GaN layer. The Mg-doped GaN layer capped with Ti effectively depressed the hole concentration in the p-GaN layer by over one order of magnitude relative to that of the as-grown layer. This may suggest that high resistive regions are formed by diffusion of Ti and depth of high resistive region from the p-GaN surface depends on the capped Ti film thickness. Selective activation of the Mg-doped GaN layer could be used to modulate the length of the lateral current path. Furthermore, the external quantum efficiency of the LEDs was improved significantly after reducing the lateral current spreading length. In our best result, the external quantum efficiency was 52.3% higher (at 100mA) than that of the as-grown blue LEDs.

Manipulation of surface plasmon resonance of a graphene-based Au aperture antenna in visible and near-infrared regions

NASA Astrophysics Data System (ADS)

Wan, Yuan; An, Yashuai; Tao, Zhi; Deng, Luogen

2018-03-01

Behaviors of surface plasmon resonance (SPR) of a graphene-based Au aperture antenna are investigated in visible and near-infrared (vis-NIR) regions. Compared with the SPR wavelength of a traditional Au aperture antenna, the SPR wavelength of the graphene-based Au aperture antenna shows a remarkable blue shift due to the redistribution of the electric field in the proposed structure. The electric field of the graphene-based Au aperture antenna is highly localized on the surface of the graphene in the aperture and redistributed to be a standing wave. Moreover, the SPR of a graphene-based Au aperture antenna is sensitive to the thickness and the refractive index of the dielectric layer, the graphene Fermi energy, the refractive index of the environment and the polarization direction of the incident light. Finally, we find the wavelength, intensity and phase of the reflected light of the graphene-based Au aperture antenna array can be actively modulated by varying the graphene Fermi energy. The proposed structure provides a promising platform for realizing a tunable optical filter, a highly sensitive refractive index sensor, and other actively tunable optical and optoelectronic devices.

Self-Assembly of Nanoclusters into Mono-, Few-, and Multilayered Sheets via Dipole-Induced Asymmetric van der Waals Attraction.

PubMed

Wu, Zhennan; Liu, Jiale; Li, Yanchun; Cheng, Ziyi; Li, Tingting; Zhang, Hao; Lu, Zhongyuan; Yang, Bai

2015-06-23

Two-dimensional (2D) nanomaterials possessing regular layered structures and versatile chemical composition are highly expected in many applications. Despite the importance of van der Waals (vdW) attraction in constructing and maintaining layered structures, the origin of 2D anisotropy is not fully understood, yet. Here, we report the 2D self-assembly of ligand-capped Au15 nanoclusters into mono-, few-, and multilayered sheets in colloidal solution. Both the experimental results and computer simulation reveal that the 2D self-assembly is initiated by 1D dipolar attraction common in nanometer-sized objects. The dense 1D attachment of Au15 leads to a redistribution of the surface ligands, thus generating asymmetric vdW attraction. The deliberate control of the coordination of dipolar and vdW attraction further allows to manipulate the thickness and morphologies of 2D self-assembly architectures.

Distance-dependent plasmon-enhanced fluorescence of upconversion nanoparticles using polyelectrolyte multilayers as tunable spacers.

PubMed

Feng, Ai Ling; You, Min Li; Tian, Limei; Singamaneni, Srikanth; Liu, Ming; Duan, Zhenfeng; Lu, Tian Jian; Xu, Feng; Lin, Min

2015-01-14

Lanthanide-doped upconversion nanoparticles (UCNPs) have attracted widespread interests in bioapplications due to their unique optical properties by converting near infrared excitation to visible emission. However, relatively low quantum yield prompts a need for developing methods for fluorescence enhancement. Plasmon nanostructures are known to efficiently enhance fluorescence of the surrounding fluorophores by acting as nanoantennae to focus electric field into nano-volume. Here, we reported a novel plasmon-enhanced fluorescence system in which the distance between UCNPs and nanoantennae (gold nanorods, AuNRs) was precisely tuned by using layer-by-layer assembled polyelectrolyte multilayers as spacers. By modulating the aspect ratio of AuNRs, localized surface plasmon resonance (LSPR) wavelength at 980 nm was obtained, matching the native excitation of UCNPs resulting in maximum enhancement of 22.6-fold with 8 nm spacer thickness. These findings provide a unique platform for exploring hybrid nanostructures composed of UCNPs and plasmonic nanostructures in bioimaging applications.

Combination of surface- and interference-enhanced Raman scattering by CuS nanocrystals on nanopatterned Au structures

PubMed Central

Yeryukov, Nikolay A; Sveshnikova, Larisa L; Duda, Tatyana A; Rodyakina, Ekaterina E; Gridchin, Victor A; Sheremet, Evgeniya S; Zahn, Dietrich R T

2015-01-01

Summary We present the results of a Raman study of optical phonons in CuS nanocrystals (NCs) with a low areal density fabricated through the Langmuir–Blodgett technology on nanopatterned Au nanocluster arrays using a combination of surface- and interference-enhanced Raman scattering (SERS and IERS, respectively). Micro-Raman spectra of one monolayer of CuS NCs deposited on a bare Si substrate reveal only features corresponding to crystalline Si. However, a new relatively strong peak occurs in the Raman spectrum of CuS NCs on Au nanocluster arrays at 474 cm−1. This feature is related to the optical phonon mode in CuS NCs and manifests the SERS effect. For CuS NCs deposited on a SiO2 layer this phonon mode is also observed due to the IERS effect. Its intensity changes periodically with increasing SiO2 layer thickness for different laser excitation lines and is enhanced by a factor of about 30. CuS NCs formed on Au nanocluster arrays fabricated on IERS substrates combine the advantages of SERS and IERS and demonstrate stronger SERS enhancement allowing for the observation of Raman signals from CuS NCs with an ultra-low areal density. PMID:25977845

Structural and electrical properties of AlN layers grown on silicon by reactive RF magnetron sputtering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bazlov, N., E-mail: n.bazlov@spbu.ru; Pilipenko, N., E-mail: nelly.pilipenko@gmail.com; Vyvenko, O.

2016-06-17

AlN films of different thicknesses were deposited on n-Si (100) substrates by reactive radio frequency (rf) magnetron sputtering. Dependences of structure and electrical properties on thickness of deposited films were researched. The structures of the films were analyzed with scanning electron microscopy (SEM) and with transmitting electron microscopy (TEM). Electrical properties of the films were investigated on Au-AlN-(n-Si) structures by means of current-voltage (I-V), capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) techniques. Electron microscopy investigations had shown that structure and chemical composition of the films were thickness stratified. Near silicon surface layer was amorphous aluminum oxide one contained trapsmore » of positive charges with concentration of about 4 × 10{sup 18} cm{sup −3}. Upper layers were nanocrystalline ones consisted of both wurzite AlN and cubic AlON nanocrystals. They contained traps both positive and negative charges which were situated within 30 nm distance from silicon surface. Surface densities of these traps were about 10{sup 12} cm{sup −2}. Electron traps with activation energies of (0.2 ÷ 0.4) eV and densities of about 10{sup 10} cm{sup −2} were revealed on interface between aluminum oxide layer and silicon substrate. Their densities varied weakly with the film thickness.« less

Coupling effects in 3D plasmonic structures templated by Morpho butterfly wings.

PubMed

He, Jiaqing; Shen, Qingchen; Yang, Shuai; He, Gufeng; Tao, Peng; Song, Chengyi; Wu, Jianbo; Deng, Tao; Shang, Wen

2018-01-03

This paper presents the study of the coupling effects of three dimensional (3D) plasmonic nanostructures templated by Morpho butterfly wings. Different from the random deposition of metallic nanoparticles (NPs) or conformal coating of metallic layers on butterfly wings reported previously, the 3D plasmonic nanostructures studied in this work consist of gold (Au) nanostrips quasi-periodically arranged in 3D, which allows us to investigate the plasmonic coupling effects. Through refractive index (RI) matching, the plasmonic coupling can be differentiated from the optical contribution of butterfly wings. By tuning the deposition thickness of Au from 30 to 90 nm, the plasmonic coupling effects between the 3D Au nanostrips are gradually enhanced. In particular, the near-field coupling results in two resonant modes and enhances the surface-enhanced Raman scattering (SERS) signals.

Dimensional effects on the tunneling conductivity of gold-implanted nanocomposite films

NASA Astrophysics Data System (ADS)

Grimaldi, C.; Cattani, M.; Salvadori, M. C.

2015-03-01

We study the dependence of the electrical conductivity on the gold concentration of Au-implanted polymethylmethacrylate (PMMA) and alumina nanocomposite thin films. For Au contents larger than a critical concentration, the conductivity of Au-PMMA and Au-alumina is well described by percolation in two dimensions, indicating that the critical correlation length for percolation is larger than the thickness of the films. Below the critical loading, the conductivity is dominated by tunneling processes between isolated Au particles dispersed in PMMA or alumina continuous matrices. Using an effective medium analysis of the tunneling conductivity, we show that Au-PMMA behaves as a tunneling system in two dimensions, as the film thickness is comparable to the mean Au particle size. On the contrary, the conductivity of Au-alumina films is best described by tunneling in three dimensions, although the film thickness is only a few times larger than the particle size. We interpret the enhancement of the effective dimensionality of Au-alumina films in the tunneling regime as due to the larger film thickness as compared to the mean interparticle distances.

Effect of the Silver Content of SnAgCu Solder on the Interfacial Reaction and on the Reliability of Angle Joints Fabricated by Laser-Jet Soldering

NASA Astrophysics Data System (ADS)

Ji, Hongjun; Ma, Yuyou; Li, Mingyu; Wang, Chunqing

2015-02-01

The silver content of lead-free solders affects their microstructure, the interfacial reaction, and the performance of the joints in reliability tests. In this study, Sn3.0Ag0.5Cu (wt.%, SAC305) and Sn1.0Ag0.5Cu (wt.%, SAC105) solder balls of diameter 55 μm were reflowed on gold surface pads by laser-jet soldering. It was found that four types of layered intermetallic compound (IMC) were formed at the interfaces; these were Au5Sn/AuSn, AuSn, AuSn2, and AuSn4 from the pad side to the solder matrix. The Au5Sn/AuSn eutectic region, thickness 400 nm, formed because of the high cooling rate induced by the laser-jet soldering. During high-temperature storage tests, the silver became segregated at the interfaces between the Au-Sn IMC and the solder matrix, resulting in inhibition of IMC growth in SAC305 joints, the shear strengths of which were higher than those of SAC105 joints. In mechanical drop tests, however, percentage failure of the SAC305 joints was twice that of the SAC105 joints.

Crack injection in silver gold alloys

NASA Astrophysics Data System (ADS)

Chen, Xiying

Stress corrosion cracking (SCC) is a materials degradation phenomena resulting from a combination of stress and a corrosive environment. Among the alphabet soup of proposed mechanism of SCC the most important are film-rupture, film-induced cleavage and hydrogen embrittlement. This work examines various aspects of film-induced cleavage in gold alloys for which the operation of hydrogen embrittlement processes can be strictly ruled out on thermodynamic grounds. This is so because in such alloys SCC occurs under electrochemical conditions within which water is stable to hydrogen gas evolution. The alloy system examined in this work is AgAu since the corrosion processes in this system occur by a dealloying mechanism that results in the formation of nanoporous gold. The physics behind the dealloying process as well as the resulting formation of nanoporous gold is today well understood. Two important aspects of the film-induced cleavage mechanism are examined in this work: dynamic fracture in monolithic nanoporous gold and crack injection. In crack injection there is a finite thickness dealloyed layer formed on a AgAu alloy sample and the question of whether or not a crack that nucleates within this layer can travel for some finite distance into the un-corroded parent phase alloy is addressed. Dynamic fracture tests were performed on single edge-notched monolithic nanoporous gold samples as well as "infinite strip" sample configurations for which the stress intensity remains constant over a significant portion of the crack length. High-speed photography was used to measure the crack velocity. In the dynamic fracture experiments cracks were observed to travel at speeds as large as 270 m/s corresponding to about 68% of the Raleigh wave velocity. Crack injection experiments were performed on single crystal Ag77Au23, polycrystalline Ag72Au28 and pure gold, all of which had thin nanoporous gold layers on the surface of samples. Through-thickness fracture was seen in both the single crystal and polycrystalline samples and there was an indication of ~ 1 mum injected cracks into pure gold. These results have important implications for the operation of the film-induced cleavage mechanism and represent a first step in the development of a fundamental model of SCC.

Comparison of gold leaf thickness in Namban folding screens using X-ray fluorescence

NASA Astrophysics Data System (ADS)

Pessanha, Sofia; Madeira, Teresa I.; Manso, Marta; Guerra, Mauro; Le Gac, Agnès; Carvalho, Maria Luisa

2014-09-01

In this work, the thickness of the gold leaf applied in six Japanese folding screens is compared using a nondestructive approach. Four screens belonging to the Momoyama period (~1573-1603) and two screens belonging to the early Edo period (~1603-1868) were analyzed in situ using energy dispersive X-ray fluorescence, and the thickness of the applied gold leaf was evaluated using a methodology based on the attenuation of the different characteristic lines of gold in the gold leaf layer. Considering that the leaf may well not be made of pure gold, we established that, for the purpose of comparing the intensity ratios of the Au lines, layers made with gold leaf of high grade can be considered identical. The gold leaf applied in one of the screens from the Edo period was found to be thinner than the gold leaf applied in the other ones. This is consistent with the development of the beating technology to obtain ever more thin gold leafs.

Robust and Recyclable Substrate Template with an Ultrathin Nanoporous Counter Electrode for Organic-Hole-Conductor-Free Monolithic Perovskite Solar Cells.

PubMed

Li, Ming-Hsien; Yang, Yu-Syuan; Wang, Kuo-Chin; Chiang, Yu-Hsien; Shen, Po-Shen; Lai, Wei-Chih; Guo, Tzung-Fang; Chen, Peter

2017-12-06

A robust and recyclable monolithic substrate applying all-inorganic metal-oxide selective contact with a nanoporous (np) Au:NiO x counter electrode is successfully demonstrated for efficient perovskite solar cells, of which the perovskite active layer is deposited in the final step for device fabrication. Through annealing of the Ni/Au bilayer, the nanoporous NiO/Au electrode is formed in virtue of interconnected Au network embedded in oxidized Ni. By optimizing the annealing parameters and tuning the mesoscopic layer thickness (mp-TiO 2 and mp-Al 2 O 3 ), a decent power conversion efficiency (PCE) of 10.25% is delivered. With mp-TiO 2 /mp-Al 2 O 3 /np-Au:NiO x as a template, the original perovskite solar cell with 8.52% PCE can be rejuvenated by rinsing off the perovskite material with dimethylformamide and refilling with newly deposited perovskite. A renewed device using the recycled substrate once and twice, respectively, achieved a PCE of 8.17 and 7.72% that are comparable to original performance. This demonstrates that the novel device architecture is possible to recycle the expensive transparent conducting glass substrates together with all the electrode constituents. Deposition of stable multicomponent perovskite materials in the template also achieves an efficiency of 8.54%, which shows its versatility for various perovskite materials. The application of such a novel NiO/Au nanoporous electrode has promising potential for commercializing cost-effective, large scale, and robust perovskite solar cells.

Thickness Dependent Nanostructural, Morphological, Optical and Impedometric Analyses of Zinc Oxide-Gold Hybrids: Nanoparticle to Thin Film

PubMed Central

Perumal, Veeradasan; Hashim, Uda; Gopinath, Subash C. B.; Haarindraprasad, R.; Liu, Wei-Wen; Poopalan, P.; Balakrishnan, S. R.; Thivina, V.; Ruslinda, A. R.

2015-01-01

The creation of an appropriate thin film is important for the development of novel sensing surfaces, which will ultimately enhance the properties and output of high-performance sensors. In this study, we have fabricated and characterized zinc oxide (ZnO) thin films on silicon substrates, which were hybridized with gold nanoparticles (AuNPs) to obtain ZnO-Aux (x = 10, 20, 30, 40 and 50 nm) hybrid structures with different thicknesses. Nanoscale imaging by field emission scanning electron microscopy revealed increasing film uniformity and coverage with the Au deposition thickness. Transmission electron microscopy analysis indicated that the AuNPs exhibit an increasing average diameter (5–10 nm). The face center cubic Au were found to co-exist with wurtzite ZnO nanostructure. Atomic force microscopy observations revealed that as the Au content increased, the overall crystallite size increased, which was supported by X-ray diffraction measurements. The structural characterizations indicated that the Au on the ZnO crystal lattice exists without any impurities in a preferred orientation (002). When the ZnO thickness increased from 10 to 40 nm, transmittance and an optical bandgap value decreased. Interestingly, with 50 nm thickness, the band gap value was increased, which might be due to the Burstein-Moss effect. Photoluminescence studies revealed that the overall structural defect (green emission) improved significantly as the Au deposition increased. The impedance measurements shows a decreasing value of impedance arc with increasing Au thicknesses (0 to 40 nm). In contrast, the 50 nm AuNP impedance arc shows an increased value compared to lower sputtering thicknesses, which indicated the presence of larger sized AuNPs that form a continuous film, and its ohmic characteristics changed to rectifying characteristics. This improved hybrid thin film (ZnO/Au) is suitable for a wide range of sensing applications. PMID:26694656

Thickness Dependent Nanostructural, Morphological, Optical and Impedometric Analyses of Zinc Oxide-Gold Hybrids: Nanoparticle to Thin Film.

PubMed

Perumal, Veeradasan; Hashim, Uda; Gopinath, Subash C B; Haarindraprasad, R; Liu, Wei-Wen; Poopalan, P; Balakrishnan, S R; Thivina, V; Ruslinda, A R

2015-01-01

The creation of an appropriate thin film is important for the development of novel sensing surfaces, which will ultimately enhance the properties and output of high-performance sensors. In this study, we have fabricated and characterized zinc oxide (ZnO) thin films on silicon substrates, which were hybridized with gold nanoparticles (AuNPs) to obtain ZnO-Aux (x = 10, 20, 30, 40 and 50 nm) hybrid structures with different thicknesses. Nanoscale imaging by field emission scanning electron microscopy revealed increasing film uniformity and coverage with the Au deposition thickness. Transmission electron microscopy analysis indicated that the AuNPs exhibit an increasing average diameter (5-10 nm). The face center cubic Au were found to co-exist with wurtzite ZnO nanostructure. Atomic force microscopy observations revealed that as the Au content increased, the overall crystallite size increased, which was supported by X-ray diffraction measurements. The structural characterizations indicated that the Au on the ZnO crystal lattice exists without any impurities in a preferred orientation (002). When the ZnO thickness increased from 10 to 40 nm, transmittance and an optical bandgap value decreased. Interestingly, with 50 nm thickness, the band gap value was increased, which might be due to the Burstein-Moss effect. Photoluminescence studies revealed that the overall structural defect (green emission) improved significantly as the Au deposition increased. The impedance measurements shows a decreasing value of impedance arc with increasing Au thicknesses (0 to 40 nm). In contrast, the 50 nm AuNP impedance arc shows an increased value compared to lower sputtering thicknesses, which indicated the presence of larger sized AuNPs that form a continuous film, and its ohmic characteristics changed to rectifying characteristics. This improved hybrid thin film (ZnO/Au) is suitable for a wide range of sensing applications.

Degradation of Au-Ti contacts of SiGe HBTs during electromagnetic field stress

NASA Astrophysics Data System (ADS)

Alaeddine, A.; Genevois, C.; Kadi, M.; Cuvilly, F.; Daoud, K.

2011-02-01

This paper addresses electromagnetic field stress effects on SiGe heterojunction bipolar transistors (HBTs)' reliability issues, focusing on the relationship between the stress-induced current and device structure degradations. The origin of leakage currents and electrical parameter shifts in failed transistors has been studied by complementary failure analysis techniques. Characterization of the structure before and after ageing was performed by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). For the stressed samples, interface deformations of the titanium (Ti) thin film around all gold (Au) contacts have been clearly detected. These degradations include localized interface reaction between Au and Ti layers as well as their lateral atomic migration causing a significant reduction of Ti thickness. EDS analysis of the disordered region which is near the Si3N4 interface has shown significant signals from Au. These observations could be attributed to the coupling between high current densities induced by stress and thermal effects due to local heating effects.

Materials science in pre-plated leadframes for electronic packages

NASA Astrophysics Data System (ADS)

Liu, Lilin

Au/Pd/Ni pre-plated leadframes (PPF) are high performance frames for accommodating high-end electronic packages. Cost and reliability are major concerns in their wide application. The present work, from a materials science point view, deepens the understanding of PPFs, optimizes the conventional PPFs, develops a novel PPF architecture and models the residual stress relaxation in heteroepitaxial thin films. The wire pull test, the solderability test, and High-Resolution Transmission Electron Microscopy (HRTEM) were employed to characterize the PPFs in order to understand the relationship between performance and microstructure. We optimized the electroplating profiles and determined the minimum thickness of the Pd layer with the PPF performance satisfying the industry standards. Further increasing the Pd layer thickness beyond the critical thickness will not enhance the performance more, but increase the product cost. With the optimized electroplating profile, the electroplated Au layer is epitaxially deposited on the Pd layer, and so does the Pd layer on the Ni layer. Misfit dislocations and nanotwins are present at the interface between the Pd and Ni layers, which are generated to release the about 10.4% misfit strain between the Pd and Ni lattices. This work demonstrates that the electro-deposition technique can electroplate epitaxy-like Pd films on the highly (200) textured Ni films, which are grown on the Cu substrates. A novel technique for impeding Cu out-diffusion in Cu alloy based pre-plated leadframes was developed by electroplating a 3-4 nm thick Sn layer on a Cu alloy base prior to electroplating a Ni layer. A 10-14 nm thick epitaxy-like and dense (Cu,Ni)3Sn intermetallic compound (IMC) layer is automatically formed en route of diffuse reaction, which leads to a drastic reduction in Cu out-diffusion and hence improves significantly the protection of the leadframes against oxidation and corrosion attack. The oxidation behaviours were quantified by Electron Diffraction X-ray (EX) incorporated in Scanning Electron Microscopy (SEM) in the present work, which is a good complementary to the traditional weight gain test by a balance. A diffusion/oxidation model was developed to estimate the effective diffusion coefficient of Cu in the formed IMC nanolayers. The estimated Cu diffusion coefficient in the IMC interlayer is about 1.6x10 -22m2/s at 250°C, which is around 7~11 orders lower than the interdiffusion coefficients for eta- Cu6Sn5 and epsilon- Cu3Sn phases at corresponding temperatures. Based on the dislocation theory of twinning, analytical solutions by using the hybrid superposition and Fourier transformation approach were derived for the calculation of various energies involved in the misfit twinning process. For a given epilayer thickness and lattice mismatch strain, the twin formation energy should reach its minimum to determine the twin width and a zero minimum formation energy determines the critical thickness for misfit twinning. The effect of elastic mismatch between the epilayer and the substrate on the critical thickness was studied comprehensively, revealing that an elastically soft epilayer has a large critical thickness. Moreover, a misfit-twin-and-perfect-dislocation predominance chart is constructed to predict the predominant regions of misfit twinning and perfect dislocation in the mismatch strain and the specific twin boundary energy domain. Multiple misfit twins in epilayer/substrate systems were studied by summing up the stress and displacement fields of individual twins. In principle, the energy minimization approach can be applied to multiple misfit twins, although only periodic arrays of parallel and alternating twins were investigated here in detail. The equilibrium twin width and equilibrium twin spacing of a periodic array of twins represent the misfit twin morphology. The theoretical results indicate that the difference in elastic constants between an epilayer and its substrate has great effects on the morphology of equilibrium twins. The theoretical predictions agree with experimental observations.

Highly anisotropic black phosphorous-graphene hybrid architecture for ultrassensitive plasmonic biosensing: Theoretical insight

NASA Astrophysics Data System (ADS)

Yuan, Yufeng; Yu, Xiantong; Ouyang, Qingling; Shao, Yonghong; Song, Jun; Qu, Junle; Yong, Ken-Tye

2018-04-01

This study proposed a novel highly anisotropic surface plasmon resonance (SPR) biosensor employing emerging 2D black phosphorus (BP) and graphene atomic layers. Light absorption and energy loss were well balanced by optimizing gold film thickness and number of BP layers to generate the strongest SPR excitation. The proposed SPR biosensor was designed by the phase-modulation approach and is more sensitive to biomolecule bindings, providing 3 orders of magnitude higher sensitivity than the red-shift in SPR angle. Our results show the optimized configuration was 48 nm Au film coated with 4-layer BP crystal to produce the sharpest phase variation (up to 89.8975°), and lowest minimum reflectivity (1.9119  ×  10-7). Detection sensitivity up to 7.4914  ×  104 degree/refractive index unit is almost 4.5 times enhanced compared to monolayer graphene-based SPR sensors with 48 nm Au film. The anisotropic BP layers act as a polarizer, so the proposed SPR biosensor would exhibit optically tunable detection sensitivity, making it a promising candidate for exploring highly anisotropic platforms in biosensing.

Optically pumped lasing in a rolled-up dot-in-a-well (DWELL) microtube via the support of Au pad

NASA Astrophysics Data System (ADS)

Chai, Zhaoer; Wang, Qi; Cao, Jiawei; Mao, Guoming; Liu, Hao; Ren, Xiaomin; Maleev, Nikolai A.; Vasil'ev, Alexey P.; Zhukov, Alexey E.; Ustinov, Victor M.

2018-02-01

We report the observation of optically pumped continuous wave lasing in a self-rolled-up InGaAs/GaAs quantum dot microtube at room temperature. Single layer of InAs quantum dots ( 2.6 ML coverage) in a GaAs well sandwiched by two AlGaAs barriers are incorporated into the tube wall as the gain media. As-fabricated microtube is supported by a 300-nm-thick Au pad, aiming to separate the tube from GaAs substrate and thus to decrease the substrate loss, which finally enables lasing with ultralow threshold power ( 4 µW) from an microtube ring resonator.

A Molecular- and Nano-Electronics Test (MONET) platform fabricated using extreme ultraviolet lithography.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dentinger, Paul M.; Cardinale, Gregory F.; Hunter, Luke L.

2003-12-01

We describe the fabrication and characterization of an electrode array test structure, designed for electrical probing of molecules and nanocrystals. We use Extreme Ultraviolet Lithography (EUVL) to define the electrical test platform features. As fabricated, the platform includes nominal electrode gaps of 0 nm, 40 nm, 60 nm, and 80 nm. Additional variation in electrode gap is achieved by controlling the exposure conditions, such as dose and focus. To enable EUVL based nanofabrication, we develop a novel bi-level photoresist process. The bi-level photoresist consists of a combination of a commercially available polydimethylglutarimide (PMGI) bottom layer and an experimental EUVL photoresistmore » top (imaging) layer. We measure the sensitivity of PMGI to EUV exposure dose as a function of photoresist pre-bake temperature, and using this data, optimize a metal lift-off process. Reliable fabrication of 700 Angstrom thick Au structures with sub-1000 Angstrom critical dimensions is achieved, even without the use of a Au adhesion layer, such as Ti. Several test platforms are used to characterize electrical properties of organic molecules deposited as self assembled monolayers.« less

Electrically pumped 1.3 microm room-temperature InAs/GaAs quantum dot lasers on Si substrates by metal-mediated wafer bonding and layer transfer.

PubMed

Tanabe, Katsuaki; Guimard, Denis; Bordel, Damien; Iwamoto, Satoshi; Arakawa, Yasuhiko

2010-05-10

An electrically pumped InAs/GaAs quantum dot laser on a Si substrate has been demonstrated. The double-hetero laser structure was grown on a GaAs substrate by metal-organic chemical vapor deposition and layer-transferred onto a Si substrate by GaAs/Si wafer bonding mediated by a 380-nm-thick Au-Ge-Ni alloy layer. This broad-area Fabry-Perot laser exhibits InAs quantum dot ground state lasing at 1.31 microm at room temperature with a threshold current density of 600 A/cm(2). (c) 2010 Optical Society of America.

Porous silicon technology for integrated microsystems

NASA Astrophysics Data System (ADS)

Wallner, Jin Zheng

With the development of micro systems, there is an increasing demand for integrable porous materials. In addition to those conventional applications, such as filtration, wicking, and insulating, many new micro devices, including micro reactors, sensors, actuators, and optical components, can benefit from porous materials. Conventional porous materials, such as ceramics and polymers, however, cannot meet the challenges posed by micro systems, due to their incompatibility with standard micro-fabrication processes. In an effort to produce porous materials that can be used in micro systems, porous silicon (PS) generated by anodization of single crystalline silicon has been investigated. In this work, the PS formation process has been extensively studied and characterized as a function of substrate type, crystal orientation, doping concentration, current density and surfactant concentration and type. Anodization conditions have been optimized for producing very thick porous silicon layers with uniform pore size, and for obtaining ideal pore morphologies. Three different types of porous silicon materials: meso porous silicon, macro porous silicon with straight pores, and macro porous silicon with tortuous pores, have been successfully produced. Regular pore arrays with controllable pore size in the range of 2mum to 6mum have been demonstrated as well. Localized PS formation has been achieved by using oxide/nitride/polysilicon stack as masking materials, which can withstand anodization in hydrofluoric acid up to twenty hours. A special etching cell with electrolytic liquid backside contact along with two process flows has been developed to enable the fabrication of thick macro porous silicon membranes with though wafer pores. For device assembly, Si-Au and In-Au bonding technologies have been developed. Very low bonding temperature (˜200°C) and thick/soft bonding layers (˜6mum) have been achieved by In-Au bonding technology, which is able to compensate the potentially rough surface on the porous silicon sample without introducing significant thermal stress. (Abstract shortened by UMI.)

Simultaneous reflectometry and interferometry for measuring thin-film thickness and curvature

NASA Astrophysics Data System (ADS)

Arends, A. A.; Germain, T. M.; Owens, J. F.; Putnam, S. A.

2018-05-01

A coupled reflectometer-interferometer apparatus is described for thin-film thickness and curvature characterization in the three-phase contact line region of evaporating fluids. Validation reflectometry studies are provided for Au, Ge, and Si substrates and thin-film coatings of SiO2 and hydrogel/Ti/SiO2. For interferometry, liquid/air and solid/air interferences are studied, where the solid/air samples consisted of glass/air/glass wedges, cylindrical lenses, and molded polydimethylsiloxane lenses. The liquid/air studies are based on steady-state evaporation experiments of water and isooctane on Si and SiO2/Ti/SiO2 wafers. The liquid thin-films facilitate characterization of both (i) the nano-scale thickness of the absorbed fluid layer and (ii) the macro-scale liquid meniscus thickness, curvature, and curvature gradient profiles. For our validation studies with commercial lenses, the apparatus is shown to measure thickness profiles within 4.1%-10.8% error.

An analysis of the pull strength behaviors of fine-pitch, flip chip solder interconnections using a Au-Pt-Pd thick film conductor on Low-Temperature, Co-fired Ceramic (LTCC) substrates.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uribe, Fernando R.; Kilgo, Alice C.; Grazier, John Mark

2008-09-01

The assembly of the BDYE detector requires the attachment of sixteen silicon (Si) processor dice (eight on the top side; eight on the bottom side) onto a low-temperature, co-fired ceramic (LTCC) substrate using 63Sn-37Pb (wt.%, Sn-Pb) in a double-reflow soldering process (nitrogen). There are 132 solder joints per die. The bond pads were gold-platinum-palladium (71Au-26Pt-3Pd, wt.%) thick film layers fired onto the LTCC in a post-process sequence. The pull strength and failure modes provided the quality metrics for the Sn-Pb solder joints. Pull strengths were measured in both the as-fabricated condition and after exposure to thermal cycling (-55/125 C; 15more » min hold times; 20 cycles). Extremely low pull strengths--referred to as the low pull strength phenomenon--were observed intermittently throughout the product build, resulting in added program costs, schedule delays, and a long-term reliability concern for the detector. There was no statistically significant correlation between the low pull strength phenomenon and (1) the LTCC 'sub-floor' lot; (2) grit blasting the LTCC surfaces prior to the post-process steps; (3) the post-process parameters; (4) the conductor pad height (thickness); (5) the dice soldering assembly sequence; or (5) the dice pull test sequence. Formation of an intermetallic compound (IMC)/LTCC interface caused by thick film consumption during either the soldering process or by solid-state IMC formation was not directly responsible for the low-strength phenomenon. Metallographic cross sections of solder joints from dice that exhibited the low pull strength behavior, revealed the presence of a reaction layer resulting from an interaction between Sn from the molten Sn-Pb and the glassy phase at the TKN/LTCC interface. The thick film porosity did not contribute, explicitly, to the occurrence of reaction layer. Rather, the process of printing the very thin conductor pads was too sensitive to minor thixotropic changes to ink, which resulted in inconsistent proportions of metal and glassy phase particles present during the subsequent firing process. The consequences were subtle, intermittent changes to the thick film microstructure that gave rise to the reaction layer and, thus, the low pull strength phenomenon. A mitigation strategy would be the use of physical vapor deposition (PVD) techniques to create thin film bond pads; this is multi-chip module, deposited (MCM-D) technology.« less

In-depth evolution of chemical states and sub-10-nm-resolution crystal orientation mapping of nanograins in Ti(5 nm)/Au(20 nm)/Cr(3 nm) tri-layer thin films

NASA Astrophysics Data System (ADS)

Zhu, Xiaoli; Todeschini, Matteo; Bastos da Silva Fanta, Alice; Liu, Lintao; Jensen, Flemming; Hübner, Jörg; Jansen, Henri; Han, Anpan; Shi, Peixiong; Ming, Anjie; Xie, Changqing

2018-09-01

The applications of Au thin films and their adhesion layers often suffer from a lack of sufficient information about the chemical states of adhesion layers and about the high-lateral-resolution crystallographic morphology of Au nanograins. Here, we demonstrate the in-depth evolution of the chemical states of adhesive layers at the interfaces and the crystal orientation mapping of gold nanograins with a lateral resolution of less than 10 nm in a Ti/Au/Cr tri-layer thin film system. Using transmission electron microscopy, the variation in the interdiffusion at Cr/Au and Ti/Au interfaces was confirmed. From X-ray photoelectron spectroscopy (XPS) depth profiling, the chemical states of Cr, Au and Ti were characterized layer by layer, suggesting the insufficient oxidation of the adhesive layers. At the interfaces the Au 4f peaks shift to higher binding energies and this behavior can be described by a proposed model based on electron reorganization and substrate-induced final-state neutralization in small Au clusters supported by the partially oxidized Ti layer. Utilizing transmission Kikuchi diffraction (TKD) in a scanning electron microscope, the crystal orientation of Au nanograins between two adhesion layers was non-destructively characterized with sub-10 nm spatial resolution. The results provide nanoscale insights into the Ti/Au/Cr thin film system and contribute to our understanding of its behavior in nano-optic and nano-electronic devices.

Surface plasmon resonance phenomenon of the insulating state polyaniline

DOE Office of Scientific and Technical Information (OSTI.GOV)

Umiati, Ngurah Ayu Ketut, E-mail: ngurahayuketutumiati@gmail.com; Jurusan Fisika FMIPA Universitas Diponegoro, Jalan Prof. Soedarto, SH Tembalang Semarang 50275; Triyana, Kuwat

2015-04-16

Surface Plasmon Resonance (SPR) phenomenon of the insulating polyaniline (PANI) is has been observed. Surface Plasmon (SP) is the traveled electromagnetic wave that passes through the interface of dielectric metal and excited by attenuated total reflection (ATR) method in Kretschmannn configuration (Au-PANI prism). The resonance condition is observed through the angle of SPR in such condition that SP wave is coupled by the evanescent constant of laser beam. In this research, the laser beam was generated by He–Ne and its wavelength (λ) was 632,8 nm. SPR curve is obtained through observation of incidence angles of the laser beam in prism.more » SPR phenomenon at the boundary between Au – PANI layer has showed by reflection dip when the laser beam passes through the prism. In this early study, the observation was carried out through simulation Winspall 3.02 software and preliminary compared with some experimental data reported in other referred literatures. The results shows that the optimum layer of Au and polyaniline are 50 and 1,5 nm thick respectively. Our own near future experimental work would be further performed and reported elsewhere.« less

Plasmonic Three-Dimensional Transparent Conductor Based on Al-Doped Zinc Oxide-Coated Nanostructured Glass Using Atomic Layer Deposition

DOE PAGES

Malek, Gary A.; Aytug, Tolga; Liu, Qingfeng; ...

2015-04-02

Transparent nanostructured glass coatings, fabricated on glass substrates, with a unique three-dimensional (3D) architecture were utilized as the foundation for the design of plasmonic 3D transparent conductors. Transformation of the non-conducting 3D structure to a conducting 3D network was accomplished through atomic layer deposition of aluminum-doped zinc oxide (AZO). After AZO growth, gold nanoparticles (AuNPs) were deposited by electronbeam evaporation to enhance light trapping and decrease the overall sheet resistance. Field emission scanning electron microscopy and atomic force microcopy images revealed the highly porous, nanostructured morphology of the AZO coated glass surface along with the in-plane dimensions of the depositedmore » AuNPs. Sheet resistance measurements conducted on the coated samples verified that the electrical properties of the 3D network are comparable to that of the untextured two-dimensional AZO coated glass substrates. In addition, transmittance measurements of the glass samples coated with various AZO thicknesses showed preservation of the highly transparent nature of each sample, while the AuNPs demonstrated enhanced light scattering as well as light-trapping capability.« less

Plasmonic Three-Dimensional Transparent Conductor Based on Al-Doped Zinc Oxide-Coated Nanostructured Glass Using Atomic Layer Deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malek, Gary A.; Aytug, Tolga; Liu, Qingfeng

Transparent nanostructured glass coatings, fabricated on glass substrates, with a unique three-dimensional (3D) architecture were utilized as the foundation for the design of plasmonic 3D transparent conductors. Transformation of the non-conducting 3D structure to a conducting 3D network was accomplished through atomic layer deposition of aluminum-doped zinc oxide (AZO). After AZO growth, gold nanoparticles (AuNPs) were deposited by electronbeam evaporation to enhance light trapping and decrease the overall sheet resistance. Field emission scanning electron microscopy and atomic force microcopy images revealed the highly porous, nanostructured morphology of the AZO coated glass surface along with the in-plane dimensions of the depositedmore » AuNPs. Sheet resistance measurements conducted on the coated samples verified that the electrical properties of the 3D network are comparable to that of the untextured two-dimensional AZO coated glass substrates. In addition, transmittance measurements of the glass samples coated with various AZO thicknesses showed preservation of the highly transparent nature of each sample, while the AuNPs demonstrated enhanced light scattering as well as light-trapping capability.« less

A study of growth and thermal dewetting behavior of ultra-thin gold films using transmission electron microscopy

NASA Astrophysics Data System (ADS)

Sudheer, Mondal, Puspen; Rai, V. N.; Srivastava, A. K.

2017-07-01

The growth and solid-state dewetting behavior of Au thin films (0.7 to 8.4 nm) deposited on the formvar film (substrate) by sputtering technique have been studied using transmission electron microscopy. The size and number density of the Au nanoparticles (NPs) change with an increase in the film thickness (0.7 to 2.8 nm). Nearly spherical Au NPs are obtained for <3 nm thickness films whereas percolated nanostructures are observed for ≥3 nm thickness films as a consequence of the interfacial interaction of Au and formvar film. The covered area fraction (CAF) increases from ˜13 to 75 % with the change in film thickness from 0.7 to 8.4 nm. In-situ annealing of ≤3 nm film produces comparatively bigger size and better sphericity Au NPs along with their narrow distributions, whereas just percolated film produces broad distribution in size having spherical as well as elongated Au NPs. The films with thickness ≤3 nm show excellent thermal stability. The films having thickness >6 nm show capability to be used as an irreversible temperature sensor with a sensitivity of ˜0.1 CAF/°C. It is observed that annealing affects the crystallinity of the Au grains in the films. The electron diffraction measurement also shows annealing induced morphological evolution in the percolated Au thin films (≥3 nm) during solid-state dewetting and recrystallization of the grains.

Growth of well-aligned ZnO nanorods using auge catalyst by vapor phase transportation.

PubMed

Ha, S Y; Jung, M N; Park, S H; Ko, H J; Ko, H; Oh, D C; Yao, T; Chang, J H

2006-11-01

Well-aligned ZnO nanorods have been achieved using new alloy (AuGe) catalyst. Zn powder was used as a source material and it was transported in a horizontal tube furnace onto an AuGe deposited Si substrates. The structural and optical properties of ZnO nanorods were characterized by scanning electron microscopy, high resolution X-ray diffraction, and photoluminescence. ZnO nanorods grown at 650 degrees C on 53 nm thick AuGe layer show uniform shape with the length of 8 +/- 0.5 microm and the diameter of 150 +/- 5 nm. Also, the tilting angle of ZnO nanorods (+/- 5.5 degrees) is confirmed by HRXRD. High structural quality of the nanorods is conformed by the photoluminescence measurement. All samples show strong UV emission without considerable deep level emission. However, weak deep level emission appears at high (700 degrees C) temperature due to the increase of oxygen desertion.

Design and comparative study of vertical LEDs with graphene, ITO and Ni/Au as contact/current spreading layer

NASA Astrophysics Data System (ADS)

Singh, Sumitra; Mahala, Pramila; Pal, Suchandan

2018-01-01

This work evaluates the effect of graphene, indium tin oxide (ITO) and Ni/Au as contact/current spreading layer/current spreading layer for GaN vertical light emitting diodes (V-LEDs). In this simulation study, the effect of these contact/current spreading layers on different performance parameters of GaN V-LEDs has been studied. By using these three different types of contact/current spreading layers, we have comparatively studied the effect on light extraction efficiency (LEE), optical output power, wall plug efficiency and radiant intensity of V-LEDs. As per the simulation results, it shows that using graphene contact/current spreading layers, it is possible to achieve better performance than using ITO and Ni/Au contact/current spreading layers. For graphene/(Ni/Au) contact/current spreading layers, the LEE is improved by 36.77% whereas for ITO/(Ni/Au) contact/current spreading layers it is improved by 13.74%. Also, by using graphene/(Ni/Au) contact/current spreading layers, the optical output power of LEDs improved by 11.11% whereas for ITO/(Ni/Au) contact/current spreading layers shown 4.16% improvement. The radiant intensity is enhanced by 37.65% for graphene/(Ni/Au) contact/current spreading layers and 13.5% for ITO/(Ni/Au) contact/current spreading layers. In this report, we have given a detailed analysis of the obtained simulation results. The simulation was carried out in SimuLED tool.

Extensive Penetration of Evaporated Electrode Metals into Fullerene Films: Intercalated Metal Nanostructures and Influence on Device Architecture.

PubMed

Zhang, Guangye; Hawks, Steven A; Ngo, Chilan; Schelhas, Laura T; Scholes, D Tyler; Kang, Hyeyeon; Aguirre, Jordan C; Tolbert, Sarah H; Schwartz, Benjamin J

2015-11-18

Although it is known that evaporated metals can penetrate into films of various organic molecules that are a few nanometers thick, there has been little work aimed at exploring the interaction of the common electrode metals used in devices with fullerene derivatives, such as organic photovoltaics (OPVs) or perovskite solar cells that use fullerenes as electron transport layers. In this paper, we show that when commonly used electrode metals (e.g., Au, Ag, Al, Ca, etc.) are evaporated onto films of fullerene derivatives (such as [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)), the metal penetrates many tens of nanometers into the fullerene layer. This penetration decreases the effective electrical thickness of fullerene-based sandwich structure devices, as measured by the device's geometric capacitance, and thus significantly alters the device physics. For the case of Au/PCBM, the metal penetrates a remarkable 70 nm into the fullerene, and we see penetration of similar magnitude in a wide variety of fullerene derivative/evaporated metal combinations. Moreover, using transmission electron microscopy to observed cross-sections of the films, we show that when gold is evaporated onto poly(3-hexylthiophene) (P3HT)/PCBM sequentially processed OPV quasi-bilayers, Au nanoparticles with diameters of ∼3-20 nm are formed and are dispersed entirely throughout the fullerene-rich overlayer. The plasmonic absorption and scattering from these nanoparticles are readily evident in the optical transmission spectrum, demonstrating that the interpenetrated metal significantly alters the optical properties of fullerene-rich active layers. This opens a number of possibilities in terms of contact engineering and light management so that metal penetration in devices that use fullerene derivatives could be used to advantage, making it critical that researchers are aware of the electronic and optical consequences of exposing fullerene-derivative films to evaporated electrode metals.

GaN membrane MSM ultraviolet photodetectors

NASA Astrophysics Data System (ADS)

Muller, A.; Konstantinidis, G.; Kostopoulos, A.; Dragoman, M.; Neculoiu, D.; Androulidaki, M.; Kayambaki, M.; Vasilache, D.; Buiculescu, C.; Petrini, I.

2006-12-01

GaN exhibits unique physical properties, which make this material very attractive for wide range of applications and among them ultraviolet detection. For the first time a MSM type UV photodetector structure was manufactured on a 2.2 μm. thick GaN membrane obtained using micromachining techniques. The low unintentionally doped GaN layer structure was grown by MOCVD on high resistivity (ρ>10kΩcm) <111> oriented silicon wafers, 500μm thick. The epitaxially grown layers include a thin AlN layer in order to reduce the stress in the GaN layer and avoid cracking. Conventional contact lithography, e-gun Ni/Au (10nm /200nm) evaporation and lift-off techniques were used to define the interdigitated Schottky metalization on the top of the wafer. Ten digits with a width of 1μm and a length of 100μm were defined for each electrode. The distance between the digits was also 1μm. After the backside lapping of the wafer to a thickness of approximately 150μm, a 400nm thick Al layer was patterned and deposited on the backside, to be used as mask for the selective reactive ion etching of silicon. The backside mask, for the membrane formation, was patterned using double side alignment techniques and silicon was etched down to the 2.2μm thin GaN layer using SF 6 plasma. A very low dark current (30ρA at 3V) was obtained. Optical responsivity measurements were performed at 1.5V. A maximum responsivity of 18mA/W was obtained at a wavelength of 370nm. This value is very good and can be further improved using transparent contacts for the interdigitated structure.

Nanostructuring of thin Au films deposited on ordered Ti templates for applications in SERS

NASA Astrophysics Data System (ADS)

Grochowska, Katarzyna; Siuzdak, Katarzyna; Macewicz, Łukasz; Skiba, Franciszek; Szkoda, Mariusz; Karczewski, Jakub; Burczyk, Łukasz; Śliwiński, Gerard

2017-10-01

In this work the results on thermal nanostructuring of the Au films on Ti templates as well as morphology and optical properties of the obtained structures are reported. The bimetal nanostructures are fabricated in a multi-step process. First, the titania nanotubes are produced on the surface of Ti foil by anodization in an ethylene glycol-water solution containing fluoride ions. This is followed by chemical etching in oxalic acid and results in a highly ordered dimpled surface. Subsequently, thin gold films (5-20 nm) are deposited onto prepared Ti substrates by magnetron sputtering. The as-prepared layers are then dewetted by the UV nanosecond laser pulses or alternatively in the furnace (temperature < 500 °C). The SEM inspection reveals formation of honeycomb nanostructures (cavity diameter: ∼100 nm) covered with Au nanoparticles (NPs). It is observed that both the laser annealing and continuous thermal treatment in furnace can lead to the creation of NPs inside every Ti dimple and result in uniform coating of the whole area of structured templates. The size and localization of NPs obtained via both dewetting processes as well as their shape can be tuned by the annealing time and the laser processing parameters and also by initial thickness of Au layer and presence of the dimples themselves in the substrate. Results confirm that the prepared material can be used as substrate for SERS (Surface Enhanced Raman Spectroscopy).

Solid state dewetting of thin plasmonic films under focused cw-laser irradiation

DOE PAGES

Abbott, William M.; Corbett, Simon; Cunningham, Graeme; ...

2017-12-21

Elevated temperatures and large thermal gradients are a significant source of component failure in microelectronics, and is the limiting factor in heat-assisted magnetic recording (HAMR). Here, we have investigated the effect of solid-state dewetting in Au thin films, as a function of local temperature, film thickness, and substrate adhesion. In this work, a localised temperature rise is induced in thin (≤ 50 nm) polycrystalline Au films on SiO 2 substrates via focused continuous-wave laser irradiation at 488 nm. The magnitude and distribution of the total temperature rise is measured using CCD-based thermoreflectance. This also allows a sensitive measurement of themore » temperature at which dewetting occurs, showing that for thin (≤ 50 nm) Au films without adhesion layers, rapid dewetting can occur at temperatures as low as 50° C. The time decay of the reflected light from the illuminating laser is used to monitor locally the dynamics of solid state dewetting. TEM diffraction analysis shows significant changes in the microstructure and crystallographic texture of the films as far as 10 µm away from the illuminated area. The use of a thin metallic adhesion layer (such as Ti or Cr) is shown to significantly improve the adhesion of the Au to the substrate and reduce the tendency towards dewetting, but does not entirely protect it from changes to the crystallographic texture.« less

Solid state dewetting of thin plasmonic films under focused cw-laser irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abbott, William M.; Corbett, Simon; Cunningham, Graeme

Elevated temperatures and large thermal gradients are a significant source of component failure in microelectronics, and is the limiting factor in heat-assisted magnetic recording (HAMR). Here, we have investigated the effect of solid-state dewetting in Au thin films, as a function of local temperature, film thickness, and substrate adhesion. In this work, a localised temperature rise is induced in thin (≤ 50 nm) polycrystalline Au films on SiO 2 substrates via focused continuous-wave laser irradiation at 488 nm. The magnitude and distribution of the total temperature rise is measured using CCD-based thermoreflectance. This also allows a sensitive measurement of themore » temperature at which dewetting occurs, showing that for thin (≤ 50 nm) Au films without adhesion layers, rapid dewetting can occur at temperatures as low as 50° C. The time decay of the reflected light from the illuminating laser is used to monitor locally the dynamics of solid state dewetting. TEM diffraction analysis shows significant changes in the microstructure and crystallographic texture of the films as far as 10 µm away from the illuminated area. The use of a thin metallic adhesion layer (such as Ti or Cr) is shown to significantly improve the adhesion of the Au to the substrate and reduce the tendency towards dewetting, but does not entirely protect it from changes to the crystallographic texture.« less

Thermal annealing and SHI irradiation induced modifications in sandwiched structured Carbon-gold-Carbon (a-C/Au/a-C) nanocomposite thin film

NASA Astrophysics Data System (ADS)

Singh, S. K.; Singhal, R.

2017-09-01

In the present work, we study the annealing and swift heavy ion (SHI) beam induced modifications in the optical and structural properties of sandwiched structured Carbon-gold-Carbon (a-C/Au/a-C) nanocomposite (NCs) thin films. The NCs thin films were synthesized by electron-beam evaporation technique at room temperature with ∼30 nm thickness for both carbon layer and ∼6 nm for gold layer. Gold-carbon NCs thin films were annealed in the presence of argon at a temperature of 500 °C, 600 °C and 750 °C. The NCs thin films were also irradiated with 90 MeV Ni ions beam with different ion fluences in the range from 3 × 1012, 6 × 1012 and 1 × 1013 ions/cm2. Surface plasmon resonance (SPR) of Au nanoparticles are not observed in the pristine film but, after annealing at temperature of 600 °C and 750 °C, it was clearly seen at ∼534 nm as confirmed by UV-visible absorption spectroscopy. 90 MeV Ni irradiated thin film at the fluence of 1 × 1013 ions/cm2 also show strong absorption band at ∼534 nm. The growth and size of Au nanoparticle for pristine and 90 MeV Ni ion irradiated thin film with fluence of 1 × 1013 ions/cm2, were estimated by Transmission electron microscopy (TEM) images with the bi-model distribution. The size of the gold nanoparticle (NPs) was found to be ∼4.5 nm for the pristine film and ∼5.4 nm for the irradiated film at a fluence of 1 × 1013 ions/cm2. The thickness and metal atomic fraction in carbon matrix were estimated by Rutherford backscattering spectroscopy (RBS). The effect of annealing as well as heavy ion irradiation on D and G band of carbon matrix were studied by Raman spectroscopy.

Comparison of Ti/Pd/Ag, Pd/Ti/Pd/Ag and Pd/Ge/Ti/Pd/Ag contacts to n-type GaAs for electronic devices handling high current densities

NASA Astrophysics Data System (ADS)

Huo, Pengyun; Galiana, Beatriz; Rey-Stolle, Ignacio

2017-04-01

In the quest for metal contacts for electronic devices handling high current densities, we report the results of Pd/Ti/Pd/Ag and Pd/Ge/Ti/Pd/Ag contacts to n-GaAs and compare them to Ti/Pd/Ag and AuGe/Ni/Au. These metal systems have been designed with the goal of producing an electrical contact with (a) low metal-semiconductor specific contact resistance, (b) very high sheet conductance, (c) good bondability, (d) long-term durability and (e) cost-effectiveness. The structure of the contacts consists of an interfacial layer (either Pd or Pd/Ge) intended to produce a low metal-semiconductor specific contact resistance; a diffusion barrier (Ti/Pd) and a thick top layer of Ag to provide the desired high sheet conductance, limited cost and good bondability. The results show that both systems can achieve very low metal resistivity (ρ M ˜ 2 × 10-6 Ω cm), reaching values close to that of pure bulk silver. This fact is attributed to the Ti/Pd bilayer acting as an efficient diffusion barrier, and thus the metal sheet resistance can be controlled by the thickness of the deposited silver layer. Moreover, the use of Pd as interfacial layer produces contacts with moderate specific contact resistance (ρ C ˜ 10-4 Ω cm2) whilst the use of Pd/Ge decreases the specific contact resistance to ρ C ˜ 1.5 × 10-7 Ω cm2, as a result of the formation of a Pd4(GaAs, Ge2) compound at the GaAs interface.

Synthesis of Self-Assembled Multifunctional Nanocomposite Catalysts with Highly Stabilized Reactivity and Magnetic Recyclability

NASA Astrophysics Data System (ADS)

Yu, Xu; Cheng, Gong; Zheng, Si-Yang

2016-05-01

In this paper, a multifunctional Fe3O4@SiO2@PEI-Au/Ag@PDA nanocomposite catalyst with highly stabilized reactivity and magnetic recyclability was synthesized by a self-assembled method. The magnetic Fe3O4 nanoparticles were coated with a thin layer of the SiO2 to obtain a negatively charged surface. Then positively charged poly(ethyleneimine) polymer (PEI) was self-assembled onto the Fe3O4@SiO2 by electrostatic interaction. Next, negatively charged glutathione capped gold nanoparticles (GSH-AuNPs) were electrostatically self-assembled onto the Fe3O4@SiO2@PEI. After that, silver was grown on the surface of the nanocomposite due to the reduction of the dopamine in the alkaline solution. An about 5 nm thick layer of polydopamine (PDA) was observed to form the Fe3O4@SiO2@PEI-Au/Ag@PDA nanocomposite. The Fe3O4@SiO2@PEI-Au/Ag@PDA nanocomposite was carefully characterized by the SEM, TEM, FT-IR, XRD and so on. The Fe3O4@SiO2@PEI-Au/Ag@PDA nanocomposite shows a high saturation magnetization (Ms) of 48.9 emu/g, which allows it to be attracted rapidly to a magnet. The Fe3O4@SiO2@PEI-Au/Ag@PDA nanocomposite was used to catalyze the reduction of p-nitrophenol (4-NP) to p-aminophenol (4-AP) as a model system. The reaction kinetic constant k was measured to be about 0.56 min-1 (R2 = 0.974). Furthermore, the as-prepared catalyst can be easily recovered and reused for 8 times, which didn’t show much decrease of the catalytic capability.

La2/3Sr1/3MnO3-La0.1Bi0.9MnO3 heterostructures for spin filtering

NASA Astrophysics Data System (ADS)

Gajek, M.; Bibes, M.; Varela, M.; Fontcuberta, J.; Herranz, G.; Fusil, S.; Bouzehouane, K.; Barthélémy, A.; Fert, A.

2006-04-01

We have grown heterostructures associating half-metallic La2/3Sr1/3MnO3 (LSMO) bottom electrodes and ferromagnetic La0.1Bi0.9MnO3 (LBMO) tunnel barriers. The layers in the heterostructures have good structural properties and top LBMO films (4 nm thick) have a very low roughness when deposited onto LSMO/SrTiO3(1.6 nm) templates. The LBMO films show an insulating behavior and a ferromagnetic character that are both preserved down to very low thicknesses. They are thus suitable for being used as tunnel barriers. Spin-dependent transport measurements performed on tunnel junctions defined from LSMO/SrTiO3/LBMO/Au samples show a magnetoresistance of up to ~90% at low temperature and bias. This evidences a spin-filtering effect by the LBMO layer, with a spin-filtering efficiency of ~35%.

Exploration of new methods for growing Ag films on Au(111) studied by ARPES

NASA Astrophysics Data System (ADS)

Luh, Dah-An; Cheng, Cheng-Maw; Tsai, Chi-Ting; Tsuei, Ku-Ding

2007-03-01

Ag/Au(111) thin films have attracted lots of interests as a model system in the past decades. Ag and Au are lattice-matched, and thin Ag films of very high quality are expected to grow on Au(111). However, the intermixing between Ag and Au at elevated temperatures has been a major concern during the growth of Ag films on the Au(111) surface. In many previous studies, Ag was deposited on the Au(111) surface at near room temperature to avoid the intermixing problem. Investigating the results from these studies, the Ag films on Au(111) grown by this recipe still show clear thickness variation. This thickness variation may result from Ag-Au intermixing or film roughening during the process of room temperature deposition. We are revisiting this classical model system with new growth methods. Our goal is to find growth methods that will stop the intermixing between Ag and Au and reduce the variation in the thickness of Ag films. Preliminary results from our study will be presented in this poster.

Effects of P3HT concentration on the electrical properties of the Au/PEDOT:PSS/P3HT/n-GaN hybrid junction structure

NASA Astrophysics Data System (ADS)

Noh, Ji-yeon; Lee, Ha Young; Lim, Kyung-won; Ahn, Hyung Soo; Yi, Sam Nyung; Jeon, Hunsoo; Shin, Min Jeong; Yu, Young Moon; Ha, Dong Han

2017-09-01

An inorganic-organic hybrid junction has been fabricated by spin coating the p-type poly(3- hexylthiophene-2,5-diyl)(P3HT) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT: PSS) on an n-type GaN layer. The GaN layer was formed on Al2O3 by metal organic chemical vapor deposition(MOCVD) method. To investigate the effects of P3HT concentration on the electrical properties, we changed P3HT solution concentration and speed of spin coater. The currentvoltage (I-V ) characteristic of Au/PEDOT:PSS/P3HT/n-GaN shows rectifying behavior. The I-V characteristic was examined in the frame work of the thermionic emission model. The most proper rectifying behavior was obtained for 0.6 wt% and thickness below 65 nm of P3HT used diode. We expect that such hybrid structures, suitably developed, might be enable the fabrication of highquality electronic and optoelectronic devices.

Distance-Dependent Plasmon-Enhanced Fluorescence of Upconversion Nanoparticles using Polyelectrolyte Multilayers as Tunable Spacers

PubMed Central

Feng, Ai Ling; You, Min Li; Tian, Limei; Singamaneni, Srikanth; Liu, Ming; Duan, Zhenfeng; Lu, Tian Jian; Xu, Feng; Lin, Min

2015-01-01

Lanthanide-doped upconversion nanoparticles (UCNPs) have attracted widespread interests in bioapplications due to their unique optical properties by converting near infrared excitation to visible emission. However, relatively low quantum yield prompts a need for developing methods for fluorescence enhancement. Plasmon nanostructures are known to efficiently enhance fluorescence of the surrounding fluorophores by acting as nanoantennae to focus electric field into nano-volume. Here, we reported a novel plasmon-enhanced fluorescence system in which the distance between UCNPs and nanoantennae (gold nanorods, AuNRs) was precisely tuned by using layer-by-layer assembled polyelectrolyte multilayers as spacers. By modulating the aspect ratio of AuNRs, localized surface plasmon resonance (LSPR) wavelength at 980 nm was obtained, matching the native excitation of UCNPs resulting in maximum enhancement of 22.6-fold with 8 nm spacer thickness. These findings provide a unique platform for exploring hybrid nanostructures composed of UCNPs and plasmonic nanostructures in bioimaging applications. PMID:25586238

Single-mode surface plasmon distributed feedback lasers.

PubMed

Karami Keshmarzi, Elham; Tait, R Niall; Berini, Pierre

2018-03-29

Single-mode surface plasmon distributed feedback (DFB) lasers are realized in the near infrared using a two-dimensional non-uniform long-range surface plasmon polariton structure. The surface plasmon mode is excited onto a 20 nm-thick, 1 μm-wide metal stripe (Ag or Au) on a silica substrate, where the stripe is stepped in width periodically, forming a 1st order Bragg grating. Optical gain is provided by optically pumping a 450 nm-thick IR-140 doped PMMA layer as the top cladding, which covers the entire length of the Bragg grating, thus creating a DFB laser. Single-mode lasing peaks of very narrow linewidth were observed for Ag and Au DFBs near 882 nm at room temperature. The narrow linewidths are explained by the low spontaneous emission rate into the surface plasmon lasing mode as well as the high quality factor of the DFB structure. The lasing emission is exclusively TM polarized. Kinks in light-light curves accompanied by spectrum narrowing were observed, from which threshold pump power densities can be clearly identified (0.78 MW cm-2 and 1.04 MW cm-2 for Ag and Au DFB lasers, respectively). The Schawlow-Townes linewidth for our Ag and Au DFB lasers is estimated and very narrow linewidths are predicted for the lasers. The lasers are suitable as inexpensive, recyclable and highly coherent sources of surface plasmons, or for integration with other surface plasmon elements of similar structure.

Nanoscale strengthening mechanisms in metallic thin film systems

NASA Astrophysics Data System (ADS)

Schoeppner, Rachel Lynn

Nano-scale strengthening mechanisms for thin films were investigated for systems governed by two different strengthening techniques: nano-laminate strengthening and oxide dispersion strengthening. Films were tested under elevated temperature conditions to investigate changes in deformation mechanisms at different operating temperatures, and the structural stability. Both systems exhibit remarkable stability after annealing and thus long-term reliability. Nano-scale metallic multilayers with smaller layer thicknesses show a greater relative resistance to decreasing strength at higher temperature testing conditions than those with larger layer thicknesses. This is seen in both Cu/Ni/Nb multilayers as well as a similar tri-component bi-layer system (Cu-Ni/Nb), which removed the coherent interface from the film. Both nanoindentation and micro-pillar compression tests investigated the strain-hardening ability of these two systems to determine what role the coherent interface plays in this mechanism. Tri-layer films showed a higher strain-hardening ability as the layer thickness decreased and a higher strain-hardening exponent than the bi-layer system: verifying the presence of a coherent interface increases the strain-hardening ability of these multilayer systems. Both systems exhibited hardening of the room temperature strength after annealing, suggesting a change in microstructure has occurred, unlike that seen in other multilayer systems. Oxide dispersion strengthened Au films showed a marked increase in hardness and wear resistance with the addition of ZnO particles. The threshold for stress-induced grain-refinement as opposed to grain growth is seen at concentrations of at least 0.5 vol%. These systems exhibited stable microstructures during thermal cycling in films containing at least 1.0%ZnO. Nanoindentation experiments show the drop in hardness following annealing is almost completely attributed to the resulting grain growth. Four-point probe resistivity measurements on annealed films showed a significant drop in resistivity for the higher concentration ZnO films, which is proposed to be the result of a change in the particle-matrix interface structure. A model connecting the hardness and resistivity as a function of ZnO concentration has been developed based on the assumption that the impact of nm-scale ZnO precipitates on the mechanical and electrical behavior of Au films is likely dominated by a transition from semi-coherent to incoherent interfaces.

Tuning the thickness of electrochemically grafted layers in large area molecular junctions

NASA Astrophysics Data System (ADS)

Fluteau, T.; Bessis, C.; Barraud, C.; Della Rocca, M. L.; Martin, P.; Lacroix, J.-C.; Lafarge, P.

2014-09-01

We have investigated the thickness, the surface roughness, and the transport properties of oligo(1-(2-bisthienyl)benzene) (BTB) thin films grafted on evaporated Au electrodes, thanks to a diazonium-based electro-reduction process. The thickness of the organic film is tuned by varying the number of electrochemical cycles during the growth process. Atomic force microscopy measurements reveal the evolution of the thickness in the range of 2-27 nm. Its variation displays a linear dependence with the number of cycles followed by a saturation attributed to the insulating behavior of the organic films. Both ultrathin (2 nm) and thin (12 and 27 nm) large area BTB-based junctions have then been fabricated using standard CMOS processes and finally electrically characterized. The electronic responses are fully consistent with a tunneling barrier in case of ultrathin BTB film whereas a pronounced rectifying behavior is reported for thicker molecular films.

Microfluidic Platform for High-throughput Screening of Leach Chemistry.

PubMed

Yang, Die; Priest, Craig

2018-06-20

We demonstrate an optofluidic screening platform for studying thiosulfate leaching of Au in a transparent microchannel. The approach permits in situ (optical) monitoring of Au thickness, reduced reagent use, rapid optimization of reagent chem-istry, screening of temperature, and determination of the activation energy. The results demonstrate the critical importance of the (1) preparation and storage of the leach solution, (2) deposition and annealing of the Au film, and (3) lixiviant chem-istry. The density of sputter deposited Au films decreased with depth resulting in accelerating leach rates during experiments. Atomic leach rates were determined and were constant throughout each experiment. Annealing above 270 °C was found to prevent leaching, which can be attributed to diffusion of the chromium adhesion layer into the Au film. The optofluidic analysis revealed leach rates that are sensitive to the stoichiometric ratio of thiosulphate, ammonia and copper in the leach solution, and optimized for 10 mM CuSO 4 , 1 M Na 2 S 2 O 3 and 1 M NH 4 OH. The temperature dependence of the leach rate gave an apparent activation energy of ~ 40 kJ.mol -1 , based on Arrhenius' relationship.

The effects of high-energy uranium ion irradiation on Au/n-GaN Schottky diodes

NASA Astrophysics Data System (ADS)

Gou, J.; Zhang, C. H.; Zhang, L. Q.; Song, Y.; Wang, L. X.; Li, J. J.; Meng, Y. C.; Li, H. X.; Yang, Y. T.; Lu, Z. W.

2014-11-01

The I-V and C-V characteristics of Au/n-GaN Schottky diodes irradiated with 290-MeV 238U32+ ions are presented. The U ions can penetrate the n-type GaN epi-layer with a thickness about 3 μm grown on the c-plane of a sapphire substrate using the MOCVD technique, leaving a purely electronic energy deposition. The Au/n-GaN Schottky diodes were irradiated to successively increasing fluences from 1 × 109 to 5 × 1011 ions cm-2. The measured I-V curves show that the height of the Schottky barrier decreases after irradiation and that the Schottky barrier almost disappears when the ion fluence reaches 5 × 1010 ions cm-2. Meanwhile, the irradiation increases the series resistance. The C-V curves show that the capacitance drops sharply when the ion fluence reaches 5 × 1010 ions cm-2. The dielectric constant also decreases following the irradiation. The changes of the electrical properties are ascribed to the neutralization of the donor-like surface state and the acceptor-like surface state due to the migration of Au atoms at the interface of Au/n-GaN under energetic U ions irradiations.

Thermal sensors utilizing thin layer technology applied to the analysis of aeronautical thermal exchanges

NASA Astrophysics Data System (ADS)

Godefroy, J. C.; Gageant, C.; Francois, D.

Thin film surface thermometers and thermal gradient fluxmeters developed by ONERA to monitor thermal exchanges in aircraft engines to predict the remaining service life of the components are described. The sensors, less than 80 microns thick, with flexible Kapton dielectric layers and metal substrates, are integrated into the shape of the surface being monitored. Features of Cu-n, Ni-, Au-, and Cr-based films, including mounting and circuitry methods that permit calibration and accurate signal analysis, are summarized. Results are discussed from sample applications of the devices on a symmetric NACA 65(1)-012 airfoil and on a turbine blade.

Rough gold films as broadband absorbers for plasmonic enhancement of TiO2 photocurrent over 400–800 nm

PubMed Central

Tan, Furui; Li, Tenghao; Wang, Ning; Lai, Sin Ki; Tsoi, Chi Chung; Yu, Weixing; Zhang, Xuming

2016-01-01

Recent years have witnessed an increasing interest in highly-efficient absorbers of visible light for the conversion of solar energy into electrochemical energy. This study presents a TiO2-Au bilayer that consists of a rough Au film under a TiO2 film, which aims to enhance the photocurrent of TiO2 over the whole visible region and may be the first attempt to use rough Au films to sensitize TiO2. Experiments show that the bilayer structure gives the optimal optical and photoelectrochemical performance when the TiO2 layer is 30 nm thick and the Au film is 100 nm, measuring the absorption 80–90% over 400–800 nm and the photocurrent intensity of 15 μA·cm−2, much better than those of the TiO2-AuNP hybrid (i.e., Au nanoparticle covered by the TiO2 film) and the bare TiO2 film. The superior properties of the TiO2-Au bilayer can be attributed to the rough Au film as the plasmonic visible-light sensitizer and the photoactive TiO2 film as the electron accepter. As the Au film is fully covered by the TiO2 film, the TiO2-Au bilayer avoids the photocorrosion and leakage of Au materials and is expected to be stable for long-term operation, making it an excellent photoelectrode for the conversion of solar energy into electrochemical energy in the applications of water splitting, photocatalysis and photosynthesis. PMID:27608836

Wafer-Scale Hierarchical Nanopillar Arrays Based on Au Masks and Reactive Ion Etching for Effective 3D SERS Substrate.

PubMed

Men, Dandan; Wu, Yingyi; Wang, Chu; Xiang, Junhuai; Yang, Ganlan; Wan, Changjun; Zhang, Honghua

2018-02-04

Two-dimensional (2D) periodic micro/nanostructured arrays as SERS substrates have attracted intense attention due to their excellent uniformity and good stability. In this work, periodic hierarchical SiO₂ nanopillar arrays decorated with Ag nanoparticles (NPs) with clean surface were prepared on a wafer-scale using monolayer Au NP arrays as masks, followed by reactive ion etching (RIE), depositing Ag layer and annealing. For the prepared SiO₂ nanopillar arrays decorated with Ag NPs, the size of Ag NPs was tuned from ca. 24 to 126 nanometers by controlling the deposition thickness of Ag film. Importantly, the SiO₂ nanopillar arrays decorated with Ag NPs could be used as highly sensitive SERS substrate for the detection of 4-aminothiophenol (4-ATP) and rhodamine 6G (R6G) due to the high loading of Ag NPs and a very uniform morphology. With a deposition thickness of Ag layer of 30 nm, the SiO₂ nanopillar arrays decorated with Ag NPs exhibited the best sensitive SERS activity. The excellent SERS performance of this substrate is mainly attributed to high-density "hotspots" derived from nanogaps between Ag NPs. Furthermore, this strategy might be extended to synthesize other nanostructured arrays with a large area, which are difficult to be prepared only via conventional wet-chemical or physical methods.

Etude de L'interface Or/silicium Par Analyse de Surface et Microscopie Electronique

NASA Astrophysics Data System (ADS)

Lamontagne, Boris

In order to start with the cleanest c-Si surface achievable, two cleaning procedures have been used and compared: aqueous chemical cleaning with HF, and sputter cleaning followed by high temperature annealing; the former is found to be the most efficient of the two. We have observed the formation of Si-C bonds induced by energetic particles associated to sputtering and sputter deposition. One of the main objectives of this work was to compare the Au/Si interfaces obtained by e-beam evaporation and by sputter deposition; Ag/Si, Cu/Si and Al/Si interfaces have also been examined. X-ray photoelectron diffraction has allowed us to judge the quality of the substrate crystallinity under the metallic overlayer, a method which readily showed the amorphisation of the c-Si substrate induced by sputter deposition. Moreover, XPD has indicated the Au overlayer to be amorphous, while the Ag and Cu appear to grow heteroepitaxially on c-Si(100). A new XPS parameter has been developed to characterize the metal/Si interface state, in particular, broadening of the interface induced by the sputter deposition. For the case of evaporated layers, it indicates that Au/Si and Cu/Si interfaces are diffuse, while Ag/Si and Al/Si interfaces are abrupt. Atomic force microscopy has revealed that sputter deposition reduces the tendency to form metal islands, characteristic of some overlayer/substrate systems such as Ag/Si. Our experiments have illustrated the role of two "new" parameters which lead to better knowledge and control of the sputter deposition process, namely the ion masses and the sample position relative to that of the target position. In the scientific literature, the value of the critical thickness, d_{rm c} , for reaction between Au and Si is still a controversial issue, probably on account of calibration problems. By using newly observed XPS discontinuities, corresponding to the completion of the first and second Au monolayers, we have been able to resolve this problem, and thereby precisely evaluate the critical thickness, d_ {rm c} = 2 ML. We obtained various new information about the Au/Si interface using complementary methods (XPD, XPS, TEM, AFM, etc.) information from which we developed a new model of the Au/Si interface; this so called "cluster model" correlates the observed overlayer structural transition with the beginning of the reaction between Au and Si. It suggests that reconstruction of the overlayer at 2 ML thickness activates the reaction between Si and Au (Si-Si bonds disruption, followed by Si outdiffusion). This model seems to be the only one capable of explaining the difference in reactivity between Au/Si and Ag/Si interfaces. (Abstract shortened by UMI.).

Structural properties and diffusion processes of the Cu 3Au (0 0 1) surface

NASA Astrophysics Data System (ADS)

Wang, Fang; Zhang, Jian-Min; Zhang, Yan; Ji, Vincent

2010-09-01

The surface relaxation and surface energy of both the mixed AuCu and pure Cu terminated Cu 3Au (0 0 1) surfaces are simulated and calculated by using the modified analytical embedded-atom method. We find that the mixed AuCu termination is energetically preferred over the pure Cu termination thereby the mono-vacancy diffusion is also investigated in the topmost few layers of the mixed AuCu terminated Cu 3Au (0 0 1) surface. In the mixed AuCu terminated surface the relaxed Au atoms are raised above Cu atoms for 0.13 Å in the topmost layer. All the surface atoms displace outwards, this effect occurs in the first three layers and changes the first two inter-layer spacing. For mono-vacancy migration in the first layer, the migration energies of Au and Cu mono-vacancy via two-type in-plane displace: the nearest neighbor jump (NNJ) and the second nearest neighbor jump (2NNJ), are calculated and the results show that the NNJ requires a much lower energy than 2NNJ. For the evolution of the energy requirements for successive nearest neighbor jumps (SNNJ) along three different paths: circularity, zigzag and beeline, we find that the circularity path is preferred over the other two paths due to its minimum energy barriers and final energies. In the second layer, the NN jumps in intra- and inter-layer of the Cu mono-vacancy are investigated. The calculated energy barriers and final energies show that the vacancy prefer jump up to a proximate Cu site. This replacement between the Cu vacancy in the second layer and Cu atom in the first layer is remunerative for the Au atoms enrichment in the topmost layer.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jagannathan, Kaushik; Benson, David M.; Robinson, David B.

Nanofilms of Pd were grown using an electrochemical form of atomic layer deposition (E-ALD) on 100 nm evaporated Au films on glass. Multiple cycles of surface-limited redox replacement (SLRR) were used to grow deposits. Each SLRR involved the underpotential deposition (UPD) of a Cu atomic layer, followed by open circuit replacement via redox exchange with tetrachloropalladate, forming a Pd atomic layer: one E-ALD deposition cycle. That cycle was repeated in order to grow deposits of a desired thickness. 5 cycles of Pd deposition were performed on the Au on glass substrates, resulting in the formation of 2.5 monolayers of Pd.more » Those Pd films were then modified with varying coverages of Pt, also formed using SLRR. The amount of Pt was controlled by changing the potential for Cu UPD, and by increasing the number of Pt deposition cycles. Hydrogen absorption was studied using coulometry and cyclic voltammetry in 0.1 M H 2SO 4 as a function of Pt coverage. The presence of even a small fraction of a Pt monolayer dramatically increased the rate of hydrogen desorption. However, this did not reduce the films’ hydrogen storage capacity. The increase in desorption rate in the presence of Pt was over an order of magnitude.« less

Graphene/MoS2 heterostructures as templates for growing two-dimensional metals: Predictions from ab initio calculations

NASA Astrophysics Data System (ADS)

Šljivančanin, Željko; Belić, Milivoj

2017-09-01

Preparation of single-atom-thick layers of ordinary metals has been a challenging task since their closely packed atoms lack layered structure with highly anisotropic bonding. Using computational modeling based on density functional theory we showed that graphene/MoS2 heterostructures can be used as suitable templates to grow stable two-dimensional (2D) clusters, as well as extended monoatomic layers of metals with nonlayered structure in the bulk. Considering gold and lithium as two metals with markedly different properties, we found that Li intercalants strengthen coupling between graphene (G) and MoS2, mainly due to electrostatic attraction of 2D materials with positively charged Li atoms. However, intercalation with large Au atoms gives rise to a significant increase in the distance between G and MoS2 and thus, weakens their interaction. In addition to strong preference for 2D growth, we demonstrated that Au intercalants weakly interact with both G and MoS2, and hence G /MoS2 vertical heterostructures could be a promising framework to prepare gold 2D structures with electronic properties closely resembling those of the hypothetical free-standing hexagonal gold monolayer.

Directed-assembled multi-band moiré plasmonic metasurfaces

NASA Astrophysics Data System (ADS)

Nagavalli Yogeesh, Maruthi; Wu, Zilong; Li, Wei; Akinwande, Deji; Zheng, Yuebing

With the large number of component sets and high rotational symmetry, plasmonic metamaterials with moiré patterns can support multiple plasmonic modes for multi-functional applications. Herein, we introduce moiré plasmonic metasurfaces using both gold and graphene, by a recently developed directed-assembled method known as moiré nanosphere lithography (MNSL). The graphene moiré metasurfaces show multiple and tunable resonance modes in the mid-infrared wavelength regime. The number and wavelength of the resonance modes can be tuned by controlling the moiré patterns, which can be easily achieved by changing the relative in-plane rotation angle during MNSL. Furthermore, we have designed a metal-insulator-metal (MIM) patch structure with a thin Au moiré metasurface layer and an optically thick Au layer separated by a dielectric spacer layer. Benefiting from the combination of moiré patterns and field enhancement from the MIM configuration, the moiré metasurface patch exhibits strong broadband absorption in the NIR ( 1.3 μm) and MIR ( 5 μm) range. The dual-band optical responses make moiré metasurface patch a multi-functional platform for surface-enhanced infrared spectroscopy, optical capture and patterning of bacteria, and photothermal denaturation of proteins.

Formation of Au nano-patterns on various substrates using simplified nano-transfer printing method

NASA Astrophysics Data System (ADS)

Kim, Jong-Woo; Yang, Ki-Yeon; Hong, Sung-Hoon; Lee, Heon

2008-06-01

For future device applications, fabrication of the metal nano-patterns on various substrates, such as Si wafer, non-planar glass lens and flexible plastic films become important. Among various nano-patterning technologies, nano-transfer print method is one of the simplest techniques to fabricate metal nano-patterns. In nano-transfer printing process, thin Au layer is deposited on flexible PDMS mold, containing surface protrusion patterns, and the Au layer is transferred from PDMS mold to various substrates due to the difference of bonding strength of Au layer to PDMS mold and to the substrate. For effective transfer of Au layer, self-assembled monolayer, which has strong bonding to Au, is deposited on the substrate as a glue layer. In this study, complicated SAM layer coating process was replaced to simple UV/ozone treatment, which can activates the surface and form the -OH radicals. Using simple UV/ozone treatments on both Au and substrate, Au nano-pattern can be successfully transferred to as large as 6 in. diameter Si wafer, without SAM coating process. High fidelity transfer of Au nano-patterns to non-planar glass lens and flexible PET film was also demonstrated.

Multi-layered nanocomposite dielectrics for high density organic memory devices

NASA Astrophysics Data System (ADS)

Kang, Moonyeong; Chung, Kyungwha; Baeg, Kang-Jun; Kim, Dong Ha; Kim, Choongik

2015-01-01

We fabricated organic memory devices with metal-pentacene-insulator-silicon structure which contain double dielectric layers comprising 3D pattern of Au nanoparticles (Au NPs) and block copolymer (PS-b-P2VP). The role of Au NPs is to charge/discharge carriers upon applied voltage, while block copolymer helps to form highly ordered Au NP patterns in the dielectric layer. Double-layered nanocomposite dielectrics enhanced the charge trap density (i.e., trapped charge per unit area) by Au NPs, resulting in increase of the memory window (ΔVth).

The Influence of Beam Broadening on the Spatial Resolution of Annular Dark Field Scanning Transmission Electron Microscopy.

PubMed

de Jonge, Niels; Verch, Andreas; Demers, Hendrix

2018-02-01

The spatial resolution of aberration-corrected annular dark field scanning transmission electron microscopy was studied as function of the vertical position z within a sample. The samples consisted of gold nanoparticles (AuNPs) positioned in different horizontal layers within aluminum matrices of 0.6 and 1.0 µm thickness. The highest resolution was achieved in the top layer, whereas the resolution was reduced by beam broadening for AuNPs deeper in the sample. To examine the influence of the beam broadening, the intensity profiles of line scans over nanoparticles at a certain vertical location were analyzed. The experimental data were compared with Monte Carlo simulations that accurately matched the data. The spatial resolution was also calculated using three different theoretical models of the beam blurring as function of the vertical position within the sample. One model considered beam blurring to occur as a single scattering event but was found to be inaccurate for larger depths of the AuNPs in the sample. Two models were adapted and evaluated that include estimates for multiple scattering, and these described the data with sufficient accuracy to be able to predict the resolution. The beam broadening depended on z 1.5 in all three models.

Morphology and current-voltage characteristics of nanostructured pentacene thin films probed by atomic force microscopy.

PubMed

Zorba, S; Le, Q T; Watkins, N J; Yan, L; Gao, Y

2001-09-01

Atomic force microscopy was used to study the growth modes (on SiO2, MoS2, and Au substrates) and the current-voltage (I-V) characteristics of organic semiconductor pentacene. Pentacene films grow on SiO2 substrate in a layer-by-layer manner with full coverage at an average thickness of 20 A and have the highest degree of molecular ordering with large dendritic grains among the pentacene films deposited on the three different substrates. Films grown on MoS2 substrate reveal two different growth modes, snowflake-like growth and granular growth, both of which seem to compete with each other. On the other hand, films deposited on Au substrate show granular structure for thinner coverages (no crystal structure) and dendritic growth for higher coverages (crystal structure). I-V measurements were performed with a platinum tip on a pentacene film deposited on a Au substrate. The I-V curves on pentacene film reveal symmetric tunneling type character. The field dependence of the current indicates that the main transport mechanism at high field intensities is hopping (Poole-Frenkel effect). From these measurements, we have estimated a field lowering coefficient of 9.77 x 10(-6) V-1/2 m1/2 and an ideality factor of 18 for pentacene.

Hydroxynaphthoquinone ultrathin films obtained by diazonium electroreduction: toward design of biosensitive electroactive interfaces.

PubMed

March, Gregory; Reisberg, Steeve; Piro, Benoit; Pham, Minh-Chau; Fave, Claire; Noel, Vincent

2010-05-01

Electroactive 2-(phenylsulfanyl)-8-hydroxy-1,4-naphthoquinone has been electrodeposited via the reduction of the corresponding diazonium salt on Au electrodes. Surface characterizations by X-ray photoelectron spectroscopy (XPS) and infrared reflection-absorption spectroscopy (IRRAS) reveal that the mechanism of film deposition follows an aryl radical formation and its immobilization on the electrode surface. Electrochemical study shows that the surface coverage can be finely tuned (thickness between one and four layers) by adjusting the potential and the deposition time. By managing the potential applied when reducing diazonium in potentiostatic mode, the formed layer could mediate or not charge transfer. This is the first time that the films obtained by diazonium process are demonstrated to act as mediators in the growth process. Hence, with potentials higher than the formal potential of quinone group, very thin and homogeneous layers are obtained, whereas thicker films are formed when more cathodic potentials than that of quinone are applied. The possibility to manage the charge-transfer kinetics, the thickness, and the homogeneity of electroactive deposits is interesting in the scope of designing electrochemical transducers.

Effect of dispersion correction on the Au(1 1 1)-H2O interface: A first-principles study

NASA Astrophysics Data System (ADS)

Nadler, Roger; Sanz, Javier Fdez.

2012-09-01

A theoretical study of the H2O-Au(1 1 1) interface based on first principles density functional theory (DFT) calculations with and without inclusion of dispersion correction is reported. Three different computational approaches are considered. First, the standard generalized gradient approximation (GGA) functional PBE is employed. Second, an additional energy term is further included that adds a semi-empirically derived dispersion correction (PBE-D2), and, finally, a recently proposed functional that includes van der Waals (vdW) interactions directly in its functional form (optB86b-vdW) was used to represent the state-of-the art of DFT functionals. The monomeric water adsorption was first considered in order to explore the dependency of geometry on the details of the model slab used to represent it (size, thickness, coverage). When the dispersion corrections are included the Au-H2O interaction is stronger, as manifested by the smaller dAu-O and stronger adsorption energies. Additionally, the interfacial region between Au(1 1 1) slab surfaces and a liquid water layer was investigated with Born-Oppenheimer molecular dynamics (BOMD) using the same functionals. Two or three interfacial orientations can be determined, depending on the theoretical methodology applied. Closest to the surface, H2O is adsorbed O-down, whereas further away it is oriented with one OH bond pointing to the surface and the molecular plane parallel to the normal direction. For the optB86b-vdW functional a third orientation is found where one H atom points into the bulk water layer and the second OH bond is oriented parallel to the metal surface. As for the water density in the first adsorption layer we find a very small increase of roughly 8%. From the analysis of vibrational spectra a weakening of the H-bond network is observed upon the inclusion of the Au(1 1 1) slab, however, no disruption of H-bonds is observed. While the PBE and PBE-D2 spectra are very similar, the optB86b-vdW spectrum shows that the H-bonds are even more weakened.

Broadband absorption enhancement in amorphous Si solar cells using metal gratings and surface texturing

NASA Astrophysics Data System (ADS)

Magdi, Sara; Swillam, Mohamed A.

2017-02-01

The efficiencies of thin film amorphous silicon (a-Si) solar cells are restricted by the small thickness required for efficient carrier collection. This thickness limitations result in poor light absorption. In this work, broadband absorption enhancement is theoretically achieved in a-Si solar cells by using nanostructured back electrode along with surface texturing. The back electrode is formed of Au nanogratings and the surface texturing consists of Si nanocones. The results were then compared to random texturing surfaces. Three dimensional finite difference time domain (FDTD) simulations are used to design and optimize the structure. The Au nanogratings achieved absorption enhancement in the long wavelengths due to sunlight coupling to surface plasmon polaritons (SPP) modes. High absorption enhancement was achieved at short wavelengths due to the decreased reflection and enhanced scattering inside the a-Si absorbing layer. Optimizations have been performed to obtain the optimal geometrical parameters for both the nanogratings and the periodic texturing. In addition, an enhancement factor (i.e. absorbed power in nanostructured device/absorbed power in reference device) was calculated to evaluate the enhancement obtained due to the incorporation of each nanostructure.

Effect of copper phthalocyanine thickness on surface morphology, optical and electrical properties of Au/CuPc/n-Si heterojunction

NASA Astrophysics Data System (ADS)

Reddy, P. R. Sekhar; Janardhanam, V.; Jyothi, I.; Harsha, Cirandur Sri; Reddy, V. Rajagopal; Lee, Sung-Nam; Won, Jonghan; Choi, Chel-Jong

2018-02-01

Effects of the thickness of copper phthalocyanine (CuPc) film (2, 5, 10, 15, 20, 30 and 40 nm) on the surface morphology, optical and electrical properties of Au/CuPc/n-Si heterojunction have been investigated. The optical band gap of CuPc film was increased with increase in the thickness of the CuPc film. The electrical properties of the Au/n-Si Schottky junction and Au/CuPc/n-Si heterojunctions were characterized by current-voltage ( I-V) and capacitance-voltage ( C-V) measurements. The barrier height, ideality factor and series resistance were estimated based on the I-V, Cheung's and Norde's methods. The barrier heights increased with increasing CuPc interlayer thickness up to 15 nm and remained constant for thickness above 20 nm, associated with the incapability of the generated carriers to reach the interface. The discrepancy in the barrier heights obtained from I-V and C-V measurements indicates the presence of barrier inhomogeneity at the interface as evidenced by higher ideality factor values. It can be concluded that the electrical properties of Au/n-Si Schottky junction can be significantly altered with the variation of CuPc thickness as interlayer.

An investigation of Au/Ti multilayer thin-films: surface morphology, structure and interfacial/surface migration of constituents under applied thermal stress

NASA Astrophysics Data System (ADS)

Senevirathne, Indrajith; Kemble, Eric; Lavoie, John

2014-03-01

Multilayer thin films are ubiquitous in industry. Au/Ti/substrate is unique due to possible biological applications in proof of concept devices. Material used for substrates include borosilicate glass, and quartz. Typical Ti depositions on substrates give rise to Stanski-Krastonov (SK) like growth while Frank-van der Merwe (FM) like growth is preferred. Ti films with thickness of ~ 100nm were deposited onto varying substrates using a thermal evaporator. The additional Au layer is then deposited via magnetron sputter deposition at 100mtorr at low deposition rates (~ 1ML/min) onto the Ti thin film. These systems were annealed at varying temperatures and at different durations. Systems were investigated via AFM (Atomic Force Microscopy) probes to examine the surface morphology, and structure. Further, the ambient contamination and elemental distribution/diffusion at annealing was investigated via Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX). PASSHE FPDC Annual Grant (LOU # 2010-LHU-03)

Electrodeposition of Au/Ag bimetallic dendrites assisted by Faradaic AC-electroosmosis flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ji, Jianlong; Li, Pengwei; Sang, Shengbo, E-mail: sbsang@tyut.edu.cn

2014-03-15

Au/Ag bimetallic dendrites were synthesized successfully from the corresponding aqueous solution via the AC electrodeposition method. Both of the morphologies and compositions could be tuned by the electrolyte concentration and AC frequency. The prepared bimetallic dendrites were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM) and UV–vis spectroscopy. The underlying dendrite growth mechanism was then proposed in the context of the Directed Electrochemical Nanowires Assembly (DENA) models. Owing to the unscreened voltage dropping in the electrolyte bulk, electromigration dominates the species flux process, and cations tend to accumulate in areas with strong electricmore » field intensity, such as electrode edges. Moreover, Faradaic AC-electro-osmosis (ACEO) flow could increase the effective diffusion layer thickness in these areas during the electrochemical reaction, and leads to dendrite growth. Further Micro-Raman observations illustrated that the Au/Ag bimetallic dendrites exhibited pronounced surface-enhanced Raman scattering (SERS) activity, using 4-mercaptopyridine (4-MP) as model molecules.« less

Characterization of Cu buffer layers for growth of L10-FeNi thin films

NASA Astrophysics Data System (ADS)

Mizuguchi, M.; Sekiya, S.; Takanashi, K.

2010-05-01

A Cu(001) layer was fabricated on a Au(001) layer to investigate the use of Cu as a buffer layer for growing L10-FeNi thin films. The epitaxial growth of a Cu buffer layer was observed using reflection high-energy electron diffraction. The flatness of the layer improved drastically with an increase in the substrate temperature although the layer was an alloy (AuCu3). An FeNi thin film was epitaxially grown on the AuCu3 buffer layer by alternate monatomic layer deposition and the formation of an L10-FeNi ordered alloy was expected. The AuCu3 buffer layer is thus a promising candidate material for the growth of L10-FeNi thin films.

Characterization and modeling of microstructural evolution of near-eutectic tin-silver-copper solder joints

NASA Astrophysics Data System (ADS)

Zbrzezny, Adam R.

Near-eutectic Sn-Ag-Cu (SAC) solders are currently considered as major lead-free replacement candidates for Sn-Pb eutectic alloys in microelectronics applications. In this thesis, the microstructural thermal stability including recrystallization, grain growth behavior, Pb and Au contamination effects and interaction of the SAC solder with Cu and Ni substrates were investigated. The true eutectic composition of the Sn-Ag-Cu alloy was verified to be Sn3.5Ag0.9Cu wt.%, and the eutectic melting temperature was determined to be 217.4 +/- 0.8°C. The system was classified as belonging to faceting (Cu6Sn5)-faceting (Ag3Sn)-nonfaceting (Sn matrix) ternary eutectic. The most significant consequence of Pb contamination was the formation of a quaternary eutectic phase (Sn-Ag-Cu-Pb) with a melting point at 176°C. Similarly, the presence of gold in the SAC alloy led to a development of a new quaternary phase (Sn-Ag-Cu-Au) melting at 204°C. Prolonged aging of SAC-4 wt.% Au on nickel resulted in the deposition of a new, previously unreported, intermetallic (IMC) layer, ((Au1-xCUx)6Sn 5, 15 wt.% of Au) on top of the existing (Cu1-yNi y)6Sn5 layer. The interfacial products that formed during soldering to copper were Cu6Sn5 and Cu3Sn. Soldering to nickel resulted in the formation of one layer, (Cu1-yNiy) 6Sn5, which was different from the expected Ni3Sn 4 layer. A small copper content in the SAC solder (0.7 wt.%) was sufficient to promote this thermodynamic shift. Intermetallic growth on Cu during solid state aging was established to be bulk diffusion controlled. The IMC layers in the SAC system grew at a slower rate than in the Sn-Pb system. It was found that the reliability of SAC solder joints on copper was considerably better than on nickel due to copper enrichment during reflow and subsequent Cu6Sn5 intermetallic precipitation. Enhanced copper and silver diffusion followed by tin recrystallization and grain growth, cavity nucleation and subsequent micro-crack linkage formed the framework of a proposed microstructural model of solder degradation mechanisms under cyclic creep conditions. A multilayer diffusion model of the SAC/Cu couple was proposed and employed for predicting intermetallic layer growth kinetics. In general, the calculated IMC thicknesses for short and intermediate aging times were in reasonable agreement with the experimental data.

Nanoparticle Over Mirror plasmonic structures prepared with use of Au colloid produced by laser ablation in water

NASA Astrophysics Data System (ADS)

Sawczak, Mirosław; Zyskowski, Marcin; Karczewski, Jakub; Atanasov, Petar A.; Nedyalkov, Nikolay N.; Nikov, Rumen G.; Stankova, Nadya A.; Śliwiński, Gerard

2016-01-01

Recently, an intensive research is carried out on plasmonic structures due to their potential application in many areas such as sensing, light harvesting and energy conversion and storage. In particular, a growing interest is observed in the Nanoparticle Over Mirror (NOM) structures for which the lithography and surface chemical functionalization represent the most popular production routes1. However, the application of those techniques is limited by the low efficacy, process complexity and chemical contamination of nanoparticles (NP). In this work, we report the contamination-free and low cost fabrication method of NOMs based on wet coating and ultrasonic-assisted nanocolloid drying process. The glass plates covered with magnetron sputtered 100 nm thick Au film and subsequently with Al2O3 layers (6 - 36 nm) by means of pulsed laser deposition are used as substrates. Au NPs are produced in the form of colloidal suspension by means of laser ablation in water using the 1064 nm, 6 ns Nd:YAG laser. The NOM synthesis is finalized by imposing of the Au NP suspension onto the as prepared Au-Al2O3/glass substrates and dried. To avoid NP agglomeration, the wet coated substrates are sonicated using 20W, 20 kHz ultrasound generator. SEM inspection of the obtained NOM structures confirms the positive sonication effect, i.e. the presence of agglomerate-free, homogenous layers. These consist of NPs (36 nm average diameter) which are characterized by the resonance absorption band at 528 nm. For NOM structures the UV-vis spectra reveal increased infrared activity and peak shift in agreement with theoretical modeling2. The NOM structure characterization is completed by analysis of the SEM and profilometry measurement results.

Evidence for Defect-Mediated Tunneling in Hexagonal Boron Nitride-Based Junctions.

PubMed

Chandni, U; Watanabe, K; Taniguchi, T; Eisenstein, J P

2015-11-11

We investigate electron tunneling through atomically thin layers of hexagonal boron nitride (hBN). Metal (Cr/Au) and semimetal (graphite) counter-electrodes are employed. While the direct tunneling resistance increases nearly exponentially with barrier thickness as expected, the thicker junctions also exhibit clear signatures of Coulomb blockade, including strong suppression of the tunnel current around zero bias and step-like features in the current at larger biases. The voltage separation of these steps suggests that single-electron charging of nanometer-scale defects in the hBN barrier layer are responsible for these signatures. We find that annealing the metal-hBN-metal junctions removes these defects and the Coulomb blockade signatures in the tunneling current.

Chemical variations in the Triple Group of the Skaergaard intrusion: insights for the mineralization and crystallization process

NASA Astrophysics Data System (ADS)

Nielsen, T. F.; Bernstein, S.

2009-12-01

The 54 Ma. old Skaergaard intrusion ( East Greenland) is a type example for fractionation of basaltic melt along the Fenner Trend. The Triple Group is the upper most 100 m of the Middle Zone and consists of FeTi-oxide rich layered gabbro with three distinct leugabbro layers 2-5 m thick ( L-layers; L1-L3, 2-5m thick) and a less marked layer (L0) c.20 m below L1. These are the most marked of many such layers. Apart from the pronounced layering the lower part of the Triple Group also hosts a world class Au-PGE mineralization. The mineralization is perfectly concordant with the L-layers, and the Triple Group invites investigation of the relationship between host and mineralization. The mineralization includes 5 main levels defined by palladium concentration. The chemical variation across the mineralization is covered by ca. 250 bulk major and trace element compositions, each representing 25cm of stratigraphy giving a continuum of ca. 60m. Proportions of normative plagioclase (plag) and pyroxene (px, including cpx and opx) are complementary, except in mineralized gabbro which is rich in FeTi-oxides. Cumulus ilmenite (ilm) is strongly enriched in layers (7m apart). They occur in both plag- and px-rich gabbro, whereas magnetite (mt) shows no simple correlation with ilm and is mainly a poikilitic intercumulus phase. The L-layers are composed of an upper part rich in plag and px and poor in FeTi-oxides, and a lower part rich in plag and FeTi-oxides and poor in px. The marked breaks in the mineralogy in the L-layers separate one layered succession from the next. The layered successions consist of a lower oxide-poor px-plag adcumulate, followed by complex mesocratic orthocumulate with poikilitic interstitial FeTi-oxide, and an upper part of increasingly simple plag-rich adcumulate with decreasing content of interstitial mt. The Au-PGE mineralized levels are found in the complex FeTi-rich gabbros at and in the base of the leucogabbro layers. The stratigraphic variation in density and densities of melt and liquidus phases suggest plag to have neutral buoyancy (floating), whereas all other phases would sink. The repeated successions are suggested to be the result of repeated “self-stratification” in the mush zone at the crystallization front, characterized by separation of px and plag leaving a transitional zone enriched in Fe-rich melt. In this melt, crystallization of mt led to S-saturation and formation of immiscible sulfide globules (30µm) in which PGE-minerals crystallize. During solidification, residual or immiscible Si-rich melt and volatiles rose from the transitional zone and took Au, Ag, Pt, Te, As, Pb, Sb, Sn, a.o. along to the main magma above and at late stage to granophyric veins. The Fe-enriched gabbros in the transitional zone are commonly accepted as average gabbros, but are in the Triple Group mixes of cumulus phases and evolved Fe-rich melt and should be used with care in the modeling of lines of liquid descent.

Influences of ultra-thin Ti seed layers on the dewetting phenomenon of Au films deposited on Si oxide substrates

NASA Astrophysics Data System (ADS)

Kamiko, Masao; Kim, So-Mang; Jeong, Young-Seok; Ha, Jae-Ho; Koo, Sang-Mo; Ha, Jae-Geun

2018-05-01

The influences of a Ti seed layer (1 nm) on the dewetting phenomenon of Au films (5 nm) grown onto amorphous SiO2 substrates have been studied and compared. Atomic force microscopy results indicated that the introduction of Ti between the substrate and Au promoted the dewetting phenomenon. X-ray diffraction measurements suggested that the initial deposition of Ti promoted crystallinity of Au. A series of Auger electron spectroscopy and X-ray photoelectron spectroscopy results revealed that Ti transformed to a Ti oxide layer by reduction of the amorphous SiO2 substrate surface, and that the Ti seed layer remained on the substrate, without going through the dewetting process during annealing. We concluded that the enhancement of Au dewetting and the improvement in crystallinity of Au by the insertion of Ti could be attributed to the fact that Au location was changed from the surface of the amorphous SiO2 substrate to that of the Ti oxide layer.

Metal/silicon Interfaces and Their Oxidation Behavior - Photoemission Spectroscopy Analysis.

NASA Astrophysics Data System (ADS)

Yeh, Jyh-Jye

Synchrotron radiation photoemission spectroscopy was used to study Ni/Si and Au/Si interface properties on the atomic scale at room temperature, after high temperature annealing and after oxygen exposures. Room temperature studies of metal/Si interfaces provide background for an understanding of the interface structure after elevated temperature annealing. Oxidation studies of Si surfaces covered with metal overlayers yield insight about the effect of metal atoms in the Si oxidation mechanisms and are useful in the identification of subtle differences in bonding relations between atoms at the metal/Si interfaces. Core level and valence band spectra with variable surface sensitivities were used to study the interactions between metal, Si, and oxygen for metal coverages and oxide thickness in the monolayer region. Interface morphology at the initial stage of metal/Si interface formation and after oxidation was modeled on the basis of the evolutions of metal and Si signals at different probing depths in the photoemission experiment. Both Ni/Si and Au/Si interfaces formed at room temperature have a diffusive region at the interface. This is composed of a layer of metal-Si alloy, formed by Si outdiffusion into the metal overlayer, above a layer of interstitial metal atoms in the Si substrate. Different atomic structures of these two regions at Ni/Si interface can account for the two different growth orientations of epitaxial Ni disilicides on the Si(111) surface after thermal annealing. Annealing the Au/Si interface at high temperature depletes all the Au atoms except for one monolayer of Au on the Si(111) surface. These phenomena are attributed to differences in the metal-Si chemical bonding relations associated with specific atomic structures. After oxygen exposures, both the Ni disilicide surface and Au covered Si surfaces (with different coverages and surface orderings) show silicon in higher oxidation states, in comparison to oxidized silicon on a clean surface. Preferential Si dioxide growth on the Au/Si surface is related to the strong distortion of the Si lattice when Au-Si bonds are formed. In comparison, a monolayer of Ni on a Si surface, with its weaker Ni-Si bond, does not enhance oxide formation.

Convergent Geometry Foam Buffered Direct Drive Experiments*

NASA Astrophysics Data System (ADS)

Watt, R. G.; Wilson, D. C.; Hollis, R. V.; Gobby, P. L.; Chrien, R. E.; Mason, R. J.; Kopp, R. A.; Willi, O.; Iwase, A.; Barringer, L. H.; Gaillard, R.; Kalantar, D. H.; Lerche, R. A.; MacGowan, B.; Nelson, M.; Phillips, T.; Knauer, J. P.; McKenty, P. W.

1996-11-01

A serious concern for directly driven ICF implosions is the asymmetry imparted to the capsule by laser drive non-uniformities, particularly the ``early time imprint'' remaining despite the use of random phase plates and smoothing with spectral dispersion. The use of a foam buffer has been proposed as a means to reduce this imprint. Two types of convergent geometry tests of the technique to correct static nonuniformities have been studied to date; cylindrical implosions at the Trident and Vulcan lasers, and spherical implosions at the NOVA laser, all using 527 nm laser drive. Cylindrical implosions used end on x-ray backlighter imaging of inner surface disruption due an intentional hole in the drive footprint, using 50 mg/cc acyrlate foam with a thin Au preheat layer. Spherical implosions used 50 mg/cc polystyrene foam plus Au to study yield and imploded core symmetry of capsules with and without a foam buffer, in comparison to ``clean 1D'' calculations. For thick enough layers, all cases showed improvement. Details of the experiments and theoretical unpinnings will be shown. *Work performed under US DOE Contract No. W-7405-Eng-36.

Growth of periodic nano-layers of nano-crystals of Au, Ag, Cu by ion beam

NASA Technical Reports Server (NTRS)

Smith, Cydale C.; Zheng, B.; Muntele, C. I.; Muntele, I. C.; Ila, D.

2005-01-01

Multilayered thin films of SiO2/AU+ SiO2/, SiO2/Ag+ SiO2/, and SiO2/Cu+ SiO2/, were grown by deposition. We have previously shown that MeV ion Bombardment of multi-nano-layers of SiO2/AU+ SiO2/ produces Au nanocrystals in the AU+ SiO2 layers. An increased number of nano-layers followed by MeV ion bombardment produces a wide optical absorption band, of which its FWHM depends on the number of nano-layers of SiO2/AU+ SiO2/. We have successfully repeated this process for nano-layers of SiO2/Ag+ SiO2/, and SiO2/Cu+ SiO2/. In this work we used 5 MeV Si as the post deposition bombardment ion and monitored the location as well as the optical absorption's FWHM for each layered structure using Optical Absorption Photospectrometry. The concentration and location of the metal nano-crystals were measured by Rutherford Backscattering Spectrometry. We will report on the results obtained for nano-layered structures produced by post deposition bombardment of SiO2/AU+ SiO2/, SiO2/Ag+ SiO2/, and SiO2/Cu+ SiO2/ layered systems as well as the results obtained from a system containing a periodic combination of SiO2/AU+ SiO2/, SiO2/Ag+ SiO2/, and SiO2/Cu+ SiO2/.

Hydrogen Sorption Kinetics on Bare and Platinum-Modified Palladium Nanofilms, Grown by Electrochemical Atomic Layer Deposition (E-ALD)

DOE PAGES

Jagannathan, Kaushik; Benson, David M.; Robinson, David B.; ...

2016-01-01

Nanofilms of Pd were grown using an electrochemical form of atomic layer deposition (E-ALD) on 100 nm evaporated Au films on glass. Multiple cycles of surface-limited redox replacement (SLRR) were used to grow deposits. Each SLRR involved the underpotential deposition (UPD) of a Cu atomic layer, followed by open circuit replacement via redox exchange with tetrachloropalladate, forming a Pd atomic layer: one E-ALD deposition cycle. That cycle was repeated in order to grow deposits of a desired thickness. 5 cycles of Pd deposition were performed on the Au on glass substrates, resulting in the formation of 2.5 monolayers of Pd.more » Those Pd films were then modified with varying coverages of Pt, also formed using SLRR. The amount of Pt was controlled by changing the potential for Cu UPD, and by increasing the number of Pt deposition cycles. Hydrogen absorption was studied using coulometry and cyclic voltammetry in 0.1 M H 2SO 4 as a function of Pt coverage. The presence of even a small fraction of a Pt monolayer dramatically increased the rate of hydrogen desorption. However, this did not reduce the films’ hydrogen storage capacity. The increase in desorption rate in the presence of Pt was over an order of magnitude.« less

Nanoporous Au structures by dealloying Au/Ag thermal- or laser-dewetted bilayers on surfaces

NASA Astrophysics Data System (ADS)

Ruffino, F.; Torrisi, V.; Grillo, R.; Cacciato, G.; Zimbone, M.; Piccitto, G.; Grimaldi, M. G.

2017-03-01

Nanoporous Au attracts great technological interest and it is a promising candidate for optical and electrochemical sensors. In addition to nanoporous Au leafs and films, recently, interest was focused on nanoporous Au micro- and nano-structures on surfaces. In this work we report on the study of the characteristics of nanoporous Au structures produced on surfaces. We developed the following procedures to fabricate the nanoporous Au structures: we deposited thin Au/Ag bilayers on SiO2 or FTO (fluorine-doped tin oxide) substrates with thickness xAu and xAg of the Au and Ag layers; we induced the alloying and dewetting processes of the bilayers by furnace annealing processes of the bilayers deposited on SiO2 and by laser irradiations of the bilayers deposited on FTO; the alloying and dewetting processes result in the formation of AuxAgy alloy sub-micron particles being x and y tunable by xAu and xAg. These particles are dealloyed in HNO3 solution to remove the Ag atoms. We obtain, so, nanoporous sub-micron Au particles on the substrates. Analyzing the characteristics of these particles we find that: a) the size and shape of the particles depend on the nature of the dewetting process (solid-state dewetting on SiO2, molten-state dewetting on FTO); b) the porosity fraction of the particles depends on how the alloying process is reached: about 32% of porosity for the particles fabricated by the furnace annealing at 900 °C, about 45% of porosity for the particles fabricated by the laser irradiation at 0.5 J/cm2, in both cases independently on the Ag concentration in the alloy; c) After the dealloying process the mean volume of the Au particles shrinks of about 39%; d) After an annealing at 400 °C the nanoporous Au particles reprise their initial volume while the porosity fraction is reduced. Arguments to justify these behaviors are presented.

Hierarchical paramecium-like hollow and solid Au/Pt bimetallic nanostructures constructed using goethite as template

NASA Astrophysics Data System (ADS)

Liu, Wei; Repo, Eveliina; Heikkilä, Mikko; Leskelä, Markku; Sillanpää, Mika

2010-10-01

Novel hollow and solid paramecium-like hierarchical Au/Pt bimetallic nanostructures were constructed using goethite as template via a seed-mediated growth method. Transmission electron microscopy (TEM), ξ-potential measurement, UV-vis spectroscopy, energy dispersive x-ray spectroscopy (EDS), ICP-AES measurement, x-ray powder diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) were utilized to systematically characterize the bimetallic nanostructures. It is found that the core structure of the paramecium-like bimetallic nanomaterial is closely related to reducing agent. When ascorbic acid is used as reducing agent, goethite serves as in situ sacrificed template and hollow paramecium-like bimetallic structure is obtained. When NH2OH·HCl is used, solid nanostructure with preserved goethite core is produced. Heating the reaction solution is necessary to obtain the paramecium-like morphology with rough interconnected Pt cilia shell. The thickness of Pt cilia layer can be controlled by adjusting the molar ratio of H2PtCl6 to Au nanoseeds. The overgrowth of the rough Pt cilia is proposed to be via an autocatalytic and three-dimensional heterogeneous nucleation process first through flower-like morphology. Both the hollow and solid hierarchical paramecium-like Au/Pt bimetallic nanostructures show good catalytic activities.

Hierarchical paramecium-like hollow and solid Au/Pt bimetallic nanostructures constructed using goethite as template.

PubMed

Liu, Wei; Repo, Eveliina; Heikkilä, Mikko; Leskelä, Markku; Sillanpää, Mika

2010-10-01

Novel hollow and solid paramecium-like hierarchical Au/Pt bimetallic nanostructures were constructed using goethite as template via a seed-mediated growth method. Transmission electron microscopy (TEM), xi-potential measurement, UV-vis spectroscopy, energy dispersive x-ray spectroscopy (EDS), ICP-AES measurement, x-ray powder diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) were utilized to systematically characterize the bimetallic nanostructures. It is found that the core structure of the paramecium-like bimetallic nanomaterial is closely related to reducing agent. When ascorbic acid is used as reducing agent, goethite serves as in situ sacrificed template and hollow paramecium-like bimetallic structure is obtained. When NH(2)OH.HCl is used, solid nanostructure with preserved goethite core is produced. Heating the reaction solution is necessary to obtain the paramecium-like morphology with rough interconnected Pt cilia shell. The thickness of Pt cilia layer can be controlled by adjusting the molar ratio of H(2)PtCl(6) to Au nanoseeds. The overgrowth of the rough Pt cilia is proposed to be via an autocatalytic and three-dimensional heterogeneous nucleation process first through flower-like morphology. Both the hollow and solid hierarchical paramecium-like Au/Pt bimetallic nanostructures show good catalytic activities.

Coaxially gated in-wire thin-film transistors made by template assembly.

PubMed

Kovtyukhova, Nina I; Kelley, Brian K; Mallouk, Thomas E

2004-10-13

Nanowire field effect transistors were prepared by a wet chemical template replication method using anodic aluminum oxide membranes. The membrane pores were first lined with a thin SiO2 layer by the surface sol-gel method. Au, CdS (or CdSe), and Au wire segments were then sequentially electrodeposited within the pores, and the resulting nanowires were released by dissolution of the membrane. Electrofluidic alignment of these nanowires between source and drain leads and evaporation of gold over the central CdS (CdSe) stripe affords a "wrap-around gate" structure. At VDS = -2 V, the Au/CdS/Au devices had an ON/OFF current ratio of 103, a threshold voltage of 2.4 V, and a subthreshold slope of 2.2 V/decade. A 3-fold decrease in the subthreshold slope relative to that of planar nanocrystalline CdSe devices can be attributed to coaxial gating. The control of dimensions afforded by template synthesis should make it possible to reduce the gate dielectric thickness, channel length, and diameter of the semiconductor segment to sublithographic dimensions while retaining the simplicity of the wet chemical synthetic method.

Snapshots of crystal growth: Nanoclusters of organic conductors on Au(111) surfaces

NASA Astrophysics Data System (ADS)

Schott, J. H.; Ward, M. D.

1994-06-01

Mono- and multilayer crystalline nanoclusters of tetra-hiafulvalene-tetracyanoquinodimethane ((TTF) (TCNO)), a low-dimensional organic conductor in the bulk form, can be formed readily on Au(111) surfaces by vapor phase sublimation under ambient conditions. Scanning tunneling microscopy of monolayer (TTF)(TCNQ) films reveals a two-dimensional density of states (DOS) that is consistent with the arrangement of TTF and TCNO molecules in the ac face of bulk (TTF)(TCNO), in which the molecular planes are nearly parallel to the Au(111) substrate. In contrast, clusters with thicknesses corresponding to two or three molecular layers exhibit a transformation to a highly anisotropic DOS that can be attributed to interlayer molecular overlap in segregated TTF and TCNQ molecular chains along the c-axis, which can be described as 'molecular wires'. The orientation of the crystalline (TTF)(TCNO) clusters is preserved throughout the crystal growth sequence, leading to meso- and macroscopic (TTF)(TCNO) needles that are oriented perpendicular to the Au(111) substrate. These studies provide visualization of crystal growth from the initial stages of nucleation to macroscopic crystals, and a revealing example of the changes in electronic structure that occur during the evolution of molecular (TTF)(TCNQ) nuclei into a bulk crystalline phase.

Coated semiconductor devices for neutron detection

DOEpatents

Klann, Raymond T.; McGregor, Douglas S.

2002-01-01

A device for detecting neutrons includes a semi-insulated bulk semiconductor substrate having opposed polished surfaces. A blocking Schottky contact comprised of a series of metals such as Ti, Pt, Au, Ge, Pd, and Ni is formed on a first polished surface of the semiconductor substrate, while a low resistivity ("ohmic") contact comprised of metals such as Au, Ge, and Ni is formed on a second, opposed polished surface of the substrate. In one embodiment, n-type low resistivity pinout contacts comprised of an Au/Ge based eutectic alloy or multi-layered Pd/Ge/Ti/Au are also formed on the opposed polished surfaces and in contact with the Schottky and ohmic contacts. Disposed on the Schottky contact is a neutron reactive film, or coating, for detecting neutrons. The coating is comprised of a hydrogen rich polymer, such as a polyolefin or paraffin; lithium or lithium fluoride; or a heavy metal fissionable material. By varying the coating thickness and electrical settings, neutrons at specific energies can be detected. The coated neutron detector is capable of performing real-time neutron radiography in high gamma fields, digital fast neutron radiography, fissile material identification, and basic neutron detection particularly in high radiation fields.

Efficient CH3NH3PbI3 perovskite/fullerene planar heterojunction hybrid solar cells with oxidized Ni/Au/Cu transparent electrode

NASA Astrophysics Data System (ADS)

Lai, Wei-Chih; Lin, Kun-Wei; Guo, Tzung-Fang; Chen, Peter; Liao, Yuan-Yu

2018-02-01

We demonstrated the performance of inverted CH3NH3PbI3 perovskite-based solar cells (SCs) with a thermally oxidized nickel/gold/copper (Ni/Au/Cu) trilayer transparent electrode. Oxidized Ni/Au/Cu is a high transparent layer and has less resistance than the oxidized Ni/Au layer. Like the oxidized Ni/Au layer, oxidized Ni and Cu in oxidized Ni/Au/Cu could perform as a hole transport layer of the perovskite-based SCs. It leads to improved perovskite SC performance on an open circuit voltage of 1.01 V, a short circuit current density of 14.36 mA/cm2, a fill factor of 76.7%, and a power conversion efficiency (η%) of 11.1%. The η% of perovskite SCs with oxidized Ni (10 nm)/Au (6 nm)/Cu (1 nm) improved by approximately 10% compared with that of perovskite SCs with oxidized Ni/Au.

Functionalization and Characterization of Gold Nanoparticles

NASA Astrophysics Data System (ADS)

Techane, Sirnegeda D.

2011-12-01

Surface characterization of gold nanoparticles (AuNPs) is necessary to obtain a thorough understanding of the AuNP properties and ultimately realize their full potential in applications. The work described in this dissertation strives to the structure and composition of AuNPs using highly surface sensitive techniques such as X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) in addition to the more widely used characterization techniques such as transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR) and UV-VIS spectroscopy. Self-assembled monolayers (SAMs) of alkanethiols were used to modify AuNPs surfaces to create positively and negatively charged surfaces. Functionalization with carboxylic acid terminated alkanethiol SAMs (COON-SAMs) was first optimized to produce clean and stable negatively charged AuNPs. Using 14nm and 40nm diameter AuNPs in combination with C11 and C16 chain length COOH-SAMs, it was found that addition of NH4OH during functionalization coupled with dialysis purification produced AuNPs that did not aggregate and did not have unbound thiols. Effects of AuNP size and COOH-SAM chain lengths were studied using 14, 25 and 40nm average diameter AuNPs functionalized with C6, C8, C11 and C16 COOH-SAMs. Flat Au surfaces were also functionalized with the COOH-SAMs for comparison. It was shown that the 14nm AuNPs with C16 COOH-SAMs were the most stable and had crystalline-like, well-ordered SAM structures. The SAMs on the 40nm AuNPs had similar surface chemistry as the SAMs on the flat Au surfaces. The effective photoelectron take-off angle of the C16 COOH-SAM decreased when the size of the AuNP increased. It was also shown that when using Kratos AxisUltra DLD XPS instrument in the hybrid mode, it was important to consider effects of both the hybrid mode and the AuNPs curvature when calculating overlayer thickness of the SAMs on AuNPs. Using the Kratos in the electrostatic mode, the overlayer thickness of C16 COON-SAM was 21A on a flat Au surface, which was comparable with previously reported values. However, the apparent thickness of the same SAM on the 14nm AuNPs was 31A, indicating the curvature of the AuNPs had an effect on the XPS measurements. To produce the positively charged AuNP surfaces, amine terminated alkanethiols (NH2 -thiols) with a C2 chain length were used in one-step AuNP synthesis and functionalization process followed by a ligand-exchange reaction with C11 chain length NH2-thiols. It was found that 14 days were needed for the ligand-exchange to be complete. After the ligand-exchange, it was found that the AuNPs with C11 NH2-SAMs were stable and could be purified, unlike AuNPs with C2 NH2-SAMs which aggregated upon purification. The C11 NH2-SAMs had both unbound and oxidized sulfur, which could be removed/converted after hydrochloric acid treatment. SESSA (simulation of electron spectra for surface analysis) allowed better interpretation of the XPS data of SAMs on AuNPs and flat Au. Comparing SESSA and experimental XPS data, it was found that C16 COON-SAM on a flat Au surface was 20A thick with a 1.5A hydrocarbon contamination overlayer and 1.05 relative surface roughness. After geometric weighing of angle-resolved XPS and SESSA data, it was found that C16 COOH-SAMs on 14nm AuNPs were 17A thick with a 1.5A hydrocarbon contamination. The decreased SAM thickness on the AuNPs is likely due to an increased tilt angle of the alkane chains or increased disorder in the SAM.

MoS2: a two-dimensional hole-transporting material for high-efficiency, low-cost perovskite solar cells

NASA Astrophysics Data System (ADS)

Kohnehpoushi, Saman; Nazari, Pariya; Abdollahi Nejand, Bahram; Eskandari, Mehdi

2018-05-01

In this work MoS2 thin film was studied as a potential two-dimensional (2D) hole-transporting material for fabrication of low-cost, durable and efficient perovskite solar cells. The thickness of MoS2 was studied as a potential factor in reaching high power conversion efficiency in perovskite solar cells. The thickness of the perovskite layer and the different metal back contacts gave distinct photovoltaic properties to the designed cells. The results show that a single sheet of MoS2 could considerably improve the power conversion efficacy of the device from 10.41% for a hole transport material (HTM)-free device to 20.43% for a device prepared with a 0.67 nm thick MoS2 layer as a HTM. On the back, Ag and Al collected the carriers more efficiently than Au due to the value of their metal contact work function with the TiO2 conduction band. The present work proposes a new architecture for the fabrication of low-cost, durable and efficient perovskite solar cells made from a low-cost and robust inorganic HTM and electron transport material.

MoS2: a two-dimensional hole-transporting material for high-efficiency, low-cost perovskite solar cells.

PubMed

Kohnehpoushi, Saman; Nazari, Pariya; Nejand, Bahram Abdollahi; Eskandari, Mehdi

2018-05-18

In this work MoS 2 thin film was studied as a potential two-dimensional (2D) hole-transporting material for fabrication of low-cost, durable and efficient perovskite solar cells. The thickness of MoS 2 was studied as a potential factor in reaching high power conversion efficiency in perovskite solar cells. The thickness of the perovskite layer and the different metal back contacts gave distinct photovoltaic properties to the designed cells. The results show that a single sheet of MoS 2 could considerably improve the power conversion efficacy of the device from 10.41% for a hole transport material (HTM)-free device to 20.43% for a device prepared with a 0.67 nm thick MoS 2 layer as a HTM. On the back, Ag and Al collected the carriers more efficiently than Au due to the value of their metal contact work function with the TiO 2 conduction band. The present work proposes a new architecture for the fabrication of low-cost, durable and efficient perovskite solar cells made from a low-cost and robust inorganic HTM and electron transport material.

Near-ultraviolet light-emitting diodes with transparent conducting layer of gold-doped multi-layer graphene

NASA Astrophysics Data System (ADS)

Cho, Chu-Young; Choe, Minhyeok; Lee, Sang-Jun; Hong, Sang-Hyun; Lee, Takhee; Lim, Wantae; Kim, Sung-Tae; Park, Seong-Ju

2013-03-01

We report on gold (Au)-doped multi-layer graphene (MLG), which can be used as a transparent conducting layer in near-ultraviolet light-emitting diodes (NUV-LEDs). The optical output power of NUV-LEDs with thermally annealed Au-doped MLG was increased by 34% compared with that of NUV-LEDs with a bare MLG. This result is attributed to the reduced sheet resistance and the enhanced current injection efficiency of NUV-LEDs by the thermally annealed Au-doped MLG film, which shows high transmittance in NUV and UV regions and good adhesion of Au-doped MLG on p-GaN layer of NUV-LEDs.

Layer-by-Layer Self-Assembling Gold Nanorods and Glucose Oxidase onto Carbon Nanotubes Functionalized Sol-Gel Matrix for an Amperometric Glucose Biosensor.

PubMed

Wu, Baoyan; Hou, Shihua; Miao, Zhiying; Zhang, Cong; Ji, Yanhong

2015-09-18

A novel amperometric glucose biosensor was fabricated by layer-by-layer self-assembly of gold nanorods (AuNRs) and glucose oxidase (GOD) onto single-walled carbon nanotubes (SWCNTs)-functionalized three-dimensional sol-gel matrix. A thiolated aqueous silica sol containing SWCNTs was first assembled on the surface of a cleaned Au electrode, and then the alternate self-assembly of AuNRs and GOD were repeated to assemble multilayer films of AuNRs-GOD onto SWCNTs-functionalized silica gel for optimizing the biosensor. Among the resulting glucose biosensors, the four layers of AuNRs-GOD-modified electrode showed the best performance. The sol-SWCNTs-(AuNRs- GOD)₄/Au biosensor exhibited a good linear range of 0.01-8 mM glucose, high sensitivity of 1.08 μA/mM, and fast amperometric response within 4 s. The good performance of the proposed glucose biosensor could be mainly attributed to the advantages of the three-dimensional sol-gel matrix and stereo self-assembly films, and the natural features of one-dimensional nanostructure SWCNTs and AuNRs. This study may provide a new facile way to fabricate the enzyme-based biosensor with high performance.

Vertical Diaphragm Electrostatic Actuator for a High Density Ink Jet Printer Head

NASA Astrophysics Data System (ADS)

Norimatsu, Takayuki; Tanaka, Shuji; Esashi, Masayoshi

This paper describes the design, fabrication process and preliminary evaluation of an electrostatic ink jet printer head with vertical diaphragms in deep trenches. By adopting the novel structure where an ink cavity is surrounded by the vertical diaphragm, the footprint of each unit (40 μm × 500 μm) becomes approximately one fifth as small as that of a conventional one. Such small footprint is advantageous in cost, resolution and printing speed. To make the vertical diaphragms, a 0.5 μm thick sacrificial thermally-oxidized layer and a 4.5 μm thick poly-silicon layer are sequentially formed in deep-reactive-ion-etched trenches, and then the sacrificial layer is etched away by fluoric acid. The nozzles are fabricated on a Pyrex glass substrate by femtosecond laser ablation, and the nozzle outside is covered with a water repellant Au/Pt/Ti layer. Impedance measurement found that the electrostatic gaps were in contact or closely approaching. This could be because the diaphragms buckled by compressive stress induced in low pressure chemical vapor deposition (LPCVD). Ink ejection was tried using commercially-available blue ink, but failed. The nozzles were covered with the ink, because the water repellant finish of the nozzle outside was not good.

Graphene enhanced surface plasmon resonance sensing based on Goos-Hänchen shift

NASA Astrophysics Data System (ADS)

Chen, Huifang; Tong, Jinguang; Wang, Yiqin; Jiang, Li

2018-03-01

A graphene/Ag structure is engineered as an enhanced platform for surface plasmon resonance sensing due to the high impermeability nature of graphene and the superior surface plasmon resonance performance of Ag. This structure is ultrasensitive to even tiny refractive index change of analytes based on Goos-Hänchen shift measurement compared to the traditional SPR sensor with bare Au film. The graphene/Ag configuration is consisted of five components, including BK7 glass slide, titanium thin film, silver thin film, two-dimensional graphene layers and biomolecular analyte layer. We have optimized the parameters of each layer and theoretically analyzed Goos-Hänchen shift of the plasmonic structure under surface plasmon resonance effect. The optimized graphene/Ag structure is monolayer graphene coated on Ag thin film with the thickness of 42 nm.

Quantitative resonant soft x-ray reflectivity of ultrathin anisotropic organic layers: Simulation and experiment of PTCDA on Au.

PubMed

Capelli, R; Mahne, N; Koshmak, K; Giglia, A; Doyle, B P; Mukherjee, S; Nannarone, S; Pasquali, L

2016-07-14

Resonant soft X-ray reflectivity at the carbon K edge, with linearly polarized light, was used to derive quantitative information of film morphology, molecular arrangement, and electronic orbital anisotropies of an ultrathin 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) film on Au(111). The experimental spectra were simulated by computing the propagation of the electromagnetic field in a trilayer system (vacuum/PTCDA/Au), where the organic film was treated as an anisotropic medium. Optical constants were derived from the calculated (through density functional theory) absorption cross sections of the single molecule along the three principal molecular axes. These were used to construct the dielectric tensor of the film, assuming the molecules to be lying flat with respect to the substrate and with a herringbone arrangement parallel to the substrate plane. Resonant soft X-ray reflectivity proved to be extremely sensitive to film thickness, down to the single molecular layer. The best agreement between simulation and experiment was found for a film of 1.6 nm, with flat laying configuration of the molecules. The high sensitivity to experimental geometries in terms of beam incidence and light polarization was also clarified through simulations. The optical anisotropies of the organic film were experimentally determined and through the comparison with calculations, it was possible to relate them to the orbital symmetry of the empty electronic states.

Quantitative resonant soft x-ray reflectivity of ultrathin anisotropic organic layers: Simulation and experiment of PTCDA on Au

DOE Office of Scientific and Technical Information (OSTI.GOV)

Capelli, R.; Koshmak, K.; Giglia, A.

Resonant soft X-ray reflectivity at the carbon K edge, with linearly polarized light, was used to derive quantitative information of film morphology, molecular arrangement, and electronic orbital anisotropies of an ultrathin 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) film on Au(111). The experimental spectra were simulated by computing the propagation of the electromagnetic field in a trilayer system (vacuum/PTCDA/Au), where the organic film was treated as an anisotropic medium. Optical constants were derived from the calculated (through density functional theory) absorption cross sections of the single molecule along the three principal molecular axes. These were used to construct the dielectric tensor of themore » film, assuming the molecules to be lying flat with respect to the substrate and with a herringbone arrangement parallel to the substrate plane. Resonant soft X-ray reflectivity proved to be extremely sensitive to film thickness, down to the single molecular layer. The best agreement between simulation and experiment was found for a film of 1.6 nm, with flat laying configuration of the molecules. The high sensitivity to experimental geometries in terms of beam incidence and light polarization was also clarified through simulations. The optical anisotropies of the organic film were experimentally determined and through the comparison with calculations, it was possible to relate them to the orbital symmetry of the empty electronic states.« less

Comprehensive analysis of heat transfer of gold-blood nanofluid (Sisko-model) with thermal radiation

NASA Astrophysics Data System (ADS)

Eid, Mohamed R.; Alsaedi, Ahmed; Muhammad, Taseer; Hayat, Tasawar

Characteristics of heat transfer of gold nanoparticles (Au-NPs) in flow past a power-law stretching surface are discussed. Sisko bio-nanofluid flow (with blood as a base fluid) in existence of non-linear thermal radiation is studied. The resulting equations system is abbreviated to model the suggested problem in non-linear PDEs. Along with initial and boundary-conditions, the equations are made non-dimensional and then resolved numerically utilizing 4th-5th order Runge-Kutta-Fehlberg (RKF45) technique with shooting integration procedure. Various flow quantities behaviors are examined for parametric consideration such as the Au-NPs volume fraction, the exponentially stretching and thermal radiation parameters. It is observed that radiation drives to shortage the thermal boundary-layer thickness and therefore resulted in better heat transfer at surface.

Synthesis of CO2/N2-triggered reversible stability-controllable poly(2-(diethylamino)ethyl methacrylate)-grafted-AuNPs by surface-initiated atom transfer radical polymerization.

PubMed

Kitayama, Yukiya; Takeuchi, Toshifumi

2014-10-28

CO2/N2-triggered stability-controllable gold nanoparticles (AuNPs) grafted with poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) layers (PDEAEMA-g-AuNPs) were synthesized by the surface-initiated atom transfer radical polymerization of DEAEMA with AuNPs bearing the bis[2-(2-bromoisobutyryloxy)undecyl] layer (grafting from method). Extension of the PDEAEMA chain length increased the stability of the PDEAEMA-g-AuNPs in CO2-bubbled water because of the electrosteric repulsion of the protonated PDEAEMA layer. The chain-length-dependent stability of PDEAEMA-g-AuNPs was confirmed by DLS and UV-vis spectra by using the localized surface plasmon resonance property of the AuNPs, where the extinction wavelength was shifted toward shorter wavelength with increasing PDEAEMA chain length. The reversible stability change with the gas stimuli of CO2/N2 was also successfully demonstrated. Finally, the transfer across the immiscible interface between water and organic solvent was successfully demonstrated by N2-triggered insolubilization of PDEAEMA layer on AuNPs in the aqueous phase, leading to the successful collection of AuNPs using organic solvent from the aqueous phase. Our "grafting from" method of reversible stability-controllable AuNPs can be applied to develop advanced materials such as reusable optical AuNP-based nanosensors because the molecular recognition layer can be constructed by two-step polymerization.

Formation of precise 2D Au particle arrays via thermally induced dewetting on pre-patterned substrates

PubMed Central

Ji, Ran

2011-01-01

Summary The fabrication of precise 2D Au nanoparticle arrays over a large area is presented. The technique was based on pre-patterning of the substrate before the deposition of a thin Au film, and the creation of periodic particle arrays by subsequent dewetting induced by annealing. Two types of pre-patterned substrates were used: The first comprised an array of pyramidal pits and the second an array of circular holes. For the dewetting of Au films on the pyramidal pit substrate, the structural curvature-driven diffusion cooperates with capillarity-driven diffusion, resulting in the formation of precise 2D particle arrays for films within a structure dependent thickness-window. For the dewetting of Au films on the circular hole substrate, the periodic discontinuities in the films, induced by the deposition, can limit the diffusion paths and lead to the formation of one particle per individual separated region (holes or mesas between holes), and thus, result in the evolution of precise 2D particle arrays. The influence of the pre-patterned structures and the film thickness is analyzed and discussed. For both types of pre-patterned substrate, the Au film thickness had to be adjusted in a certain thickness-window in order to achieve the precise 2D particle arrays. PMID:21977445

Preparation and photovoltaic properties of perovskite solar cell based on ZnO nanorod arrays

NASA Astrophysics Data System (ADS)

Xu, Yang; Liu, Tian; Li, Zhaosong; Feng, Bingjie; Li, Siqian; Duan, Jinxia; Ye, Cong; Zhang, Jun; Wang, Hao

2016-12-01

A careful control of ZnO nanorod arrays with various densities and thickness were achieved by hydrothermal method. An obvious increase in the ZnO nanorod density is observed as the concentrations of zinc acetate dropped as expected through the surface SEM images. On the other hand, samples with and without TiO2 compact layer were also studied and results had been analyzed to seek for an optimized substrate structure for light absorbing layer and increase the efficiency. What's more, a deep research for the drying temperature for perovskite layer was also conducted. As a result, SEM images discribe a promising surface appearance of perovskite layer which is finely attached onto the nanorod structure. Final power conversion efficiency (PCE) of FTO/ZnO seed layer/ZnO nanorods/perovskite/spiro-OMe-TAD/Au electrode photovoltaic device reached ∼9.15% together with open-circuit voltage of 957 mV, short-circuit current density of 17.8 mA/cm2 and fill factor of 0.537.

Optimization of figure of merit in magnetoplasmonic waveguides with Fe/Au multilayer for optical isolator based on nonreciprocal coupling on Si waveguides

NASA Astrophysics Data System (ADS)

Shimizu, Hiromasa; Shimodaira, Takahiro

2018-04-01

We report on magnetoplasmonic Si waveguides with a ferromagnetic Fe/conductive metal Au multilayer for realizing a sizable magnetooptic effect with a low propagation loss for integrated optical isolators. By combining the ferromagnetic metal Fe with a highly conductive Au layer, the largest nonreciprocal differences in effective index were estimated for propagation lengths of 1-20 µm. Mode analysis with and without a Au layer clarified that the insertion of a Au layer on an Fe layer improves the optical confinement in the Fe layer with reduced propagation loss and is effective in enlarging the magnetooptic effect for the same propagation length. On the basis of the optimized Fe/Au multilayer structure, we designed waveguide optical isolators based on nonreciprocal coupling by the finite difference time domain (FDTD) method. We estimated an optical isolation of 10.8 dB with a forward insertion loss of 13.4 dB in a 34-µm-long nonreciprocal directional coupler.

Efficient charge injection in p-type polymer field-effect transistors with low-cost molybdenum electrodes through V2O5 interlayer.

PubMed

Baeg, Kang-Jun; Bae, Gwang-Tae; Noh, Yong-Young

2013-06-26

Here we report high-performance polymer OFETs with a low-cost Mo source/drain electrode by efficient charge injection through the formation of a thermally deposited V2O5 thin film interlayer. A thermally deposited V2O5 interlayer is formed between a regioregular poly(3-hexylthiophene) (rr-P3HT) or a p-type polymer semiconductor containing dodecyl-substituted thienylenevinylene (TV) and dodecylthiophene (PC12TV12T) and the Mo source/drain electrode. The P3HT or PC12TV12T OFETs with the bare Mo electrode exhibited lower charge carrier mobility than those with Au owing to a large barrier height for hole injection (0.5-1.0 eV). By forming the V2O5 layer, the P3HT or PC12TV12T OFETs with V2O5 on the Mo electrode exhibited charge carrier mobility comparable to that of a pristine Au electrode. Best P3HT or PC12TV12T OFETs with 5 nm thick V2O5 on Mo electrode show the charge carrier mobility of 0.12 and 0.38 cm(2)/(V s), respectively. Ultraviolet photoelectron spectroscopy results exhibited the work-function of the Mo electrode progressively changed from 4.3 to 4.9 eV with an increase in V2O5 thickness from 0 to 5 nm, respectively. Interestingly, the V2O5-deposited Mo exhibits comparable Rc to Au, which mainly results from the decreased barrier height for hole carrier injection from the low-cost metal electrode to the frontier molecular orbital of the p-type polymer semiconductor after the incorporation of the transition metal oxide hole injection layer, such as V2O5. This enables the development of large-area, low-cost electronics with the Mo electrodes and V2O5 interlayer.

Plasmonic behaviour of sputtered Au nanoisland arrays

NASA Astrophysics Data System (ADS)

Tvarožek, V.; Szabó, O.; Novotný, I.; Kováčová, S.; Škriniarová, J.; Šutta, P.

2017-02-01

The specificity of the formation of Au sputtered nanoisland arrays (NIA) on a glass substrate or on a ZnO thin film doped by Ga is demonstrated. Statistical analysis of morphology images (SEM, AFM) exhibited the Log-normal distribution of the size (area) of nanoislands-their modus AM varied from 8 to 328 nm2 depending on the sputtering power density, which determined the nominal thicknesses in the range of 2-8 nm. Preferential polycrystalline texture (111) of Au NIA increased with the power density and after annealing. Transverse localised surface plasmonic resonance (LSPR; evaluated by transmission UV-vis spectroscopy) showed the red shift of the extinction peaks (Δl ≤ 100 nm) with an increase of the nominal thickness, and the blue shift (Δλ ≤ -65 nm) after annealing of Au NIA. The plasmonic behaviour of Au NIA was described by modification of a size-scaling universal model using the nominal thin film thickness as a technological scaling parameter. Sputtering of a Ti intermediate adhesive ultrathin film between the glass substrate and gold improves the adhesion of Au nanoislands as well as supporting the formation of more defined Au NIA structures of smaller dimensions.

Small Pitch Transition-Edge Sensors with Broadband High Spectral Resolution for Solar Physics

NASA Technical Reports Server (NTRS)

Smith, S. J.; Adams, J. S.; Eckart, M. E.; Smith, Adams; Bailey, C. N.; Bandler, S. R.; Chevenak, J. A.; Finkbeiner, F. M.; Kelley, R. L.; Kilbourne, C. A.;

Frictional and morphological properties of Au-MoS2 films sputtered from a compact target

NASA Technical Reports Server (NTRS)

Spalvins, T.

1984-01-01

AuMoS2 films 0.02 to 1.2 microns thick were sputtered from target compacted from 5 wt % Au + 95 wt % MoS2, to investigate the frictional and morphological film growth characteristics. The gold dispersion effects in MoS2 films are of interest to increase the densitification and strengthening of the film structure. Three microstructural growth stages were identified on the nano-micro-macrostructural level. During sliding both sputtered Au-MoS2 and MoS2 films have a tendency to break within the columner region. The remaining or effective film, about 0.2 microns thick, performs the lubrication. The Au-MoS2 films displayed a lower friction coefficient with a high degree of frictional stability and less wear debris generation as compared to pure MoS2 films. The more favorable frictional characteristics of the Au-MoS2 films are attributed to the effective film thickness and the high density packed columner zone which has a reduced effect on the fragmentation of the tapered crystallites during fracture.

Au-coated 3-D nanoporous titania layer prepared using polystyrene-b-poly(2-vinylpyridine) block copolymer nanoparticles.

PubMed

Shin, Won-Jeong; Basarir, Fevzihan; Yoon, Tae-Ho; Lee, Jae-Suk

2009-04-09

New nanoporous structures of Au-coated titania layers were prepared by using amphiphilic block copolymer nanoparticles as a template. A 3-D template composed of self-assembled quaternized polystyrene-b-poly(2-vinylpyridine) (Q-PS-b-P2VP) block copolymer nanoparticles below 100 nm was prepared. The core-shell-type nanoparticles were well ordered three-dimensionally using the vertical immersion method on the substrate. The polar solvents were added to the polymer solution to prevent particle merging at 40 degrees C when considering the interaction between polymer nanoparticles and solvents. Furthermore, Au-coated PS-b-P2VP nanoparticles were prepared using thiol-capped Au nanoparticles (3 nm). The 3-D arrays with Au-coated PS-b-P2VP nanoparticles as a template contributed to the preparation of the nanoporous Au-coated titania layer. Therefore, the nanoporous Au-coated titania layer was fabricated by removing PS-b-P2VP block copolymer nanoparticles by oxygen plasma etching.

Pt skin on AuCu intermetallic substrate: a strategy to maximize Pt utilization for fuel cells.

PubMed

Wang, Gongwei; Huang, Bing; Xiao, Li; Ren, Zhandong; Chen, Hao; Wang, Deli; Abruña, Héctor D; Lu, Juntao; Zhuang, Lin

2014-07-09

The dependence on Pt catalysts has been a major issue of proton-exchange membrane (PEM) fuel cells. Strategies to maximize the Pt utilization in catalysts include two main approaches: to put Pt atoms only at the catalyst surface and to further enhance the surface-specific catalytic activity (SA) of Pt. Thus far there has been no practical design that combines these two features into one single catalyst. Here we report a combined computational and experimental study on the design and implementation of Pt-skin catalysts with significantly improved SA toward the oxygen reduction reaction (ORR). Through screening, using density functional theory (DFT) calculations, a Pt-skin structure on AuCu(111) substrate, consisting of 1.5 monolayers of Pt, is found to have an appropriately weakened oxygen affinity, in comparison to that on Pt(111), which would be ideal for ORR catalysis. Such a structure is then realized by substituting the Cu atoms in three surface layers of AuCu intermetallic nanoparticles (AuCu iNPs) with Pt. The resulting Pt-skinned catalyst (denoted as Pt(S)AuCu iNPs) has been characterized in depth using synchrotron XRD, XPS, HRTEM, and HAADF-STEM/EDX, such that the Pt-skin structure is unambiguously identified. The thickness of the Pt skin was determined to be less than two atomic layers. Finally the catalytic activity of Pt(S)AuCu iNPs toward the ORR was measured via rotating disk electrode (RDE) voltammetry through which it was established that the SA was more than 2 times that of a commercial Pt/C catalyst. Taking into account the ultralow Pt loading in Pt(S)AuCu iNPs, the mass-specific catalytic activity (MA) was determined to be 0.56 A/mg(Pt)@0.9 V, a value that is well beyond the DOE 2017 target for ORR catalysts (0.44 A/mg(Pt)@0.9 V). These findings provide a strategic design and a realizable approach to high-performance and Pt-efficient catalysts for fuel cells.

Au/Ti resistors used for Nb/Pb-alloy Josephson junctions. II. Thermal stability

NASA Astrophysics Data System (ADS)

Murakami, Masanori; Kim, K. K.

1984-10-01

In the preceding paper bilayered Au/Ti resistors were found to have excellent electrical stability during storage at room temperature after preannealing at an elevated temperature, which is essential to design logic and memory circuits of Nb/Pb-alloy Josephson junction devices. The resistors could contact directly with the Pb-alloy control lines in which Pb and In atoms which are known to intermix easily with Au atoms are contained. Since Pb and In atoms in the control lines are separated from Au atoms of the resistors by thin Ti layers, thermal stability at the contacts is a major concern for use of the Au/Ti resistor material in the Josephson devices. In the present study, surface morphology change and diffusion mechanism at the resistor/control-line contacts were studied using x-ray diffraction and scanning electron microscopy for square-shaped Au/Ti resistors covered by Pb-In layers. The samples were isothermally annealed at temperatures ranging from 353 to 423 K. The diffusion did not occur immediately after annealing at these temperatures. After the incubation period, the interdiffusion was observed to initiate at the edges of the resistors facing to the center of the cathode. Significant amounts of the In atoms in the Pb-In layers were observed to diffuse into the Au layers of the resistors, forming AuIn2 compounds under the Ti layers. By measuring growth rates of the AuIn2 layers, the diffusion coefficients and the activation energy for the layer growth were determined. Also, by analyzing changes in the In concentration in the Pb-In layers during annealing, interdiffusion coefficients of In atoms in the Pb-In layers were determined using a computer simulation technique. The activation energy was about 1.1 eV. Since these diffusion coefficients were found to be very close to those determined previously in bulk materials, the diffusion kinetics is believed to be controlled by the lattice diffusion. Based on the present results, several methods to reduce the interdiffusion between Pb-alloy and Au/Ti resistors were proposed.

The intermetallic formation and growth kinetics at the interface of near eutectic tin-silver-copper solder alloys and gold/nickel metallization

NASA Astrophysics Data System (ADS)

Gao, Mao

The formation of a one micron thick layer of an intermetallic compound between a solder alloy and a metallic substrate generally constitutes a good solder joint in an electronic device. However, if the compound grows too thick, and/or if multiple intermetallic compounds form, poor solder joint reliability may result. Thus significant interest has been focused on intermetallic compound phase selection and growth kinetics at such solder/metal interfaces. The present study focuses on one such specific problem, the formation and growth of intermetallic compounds at near eutectic Sn-Ag-Cu solder alloy/Ni interfaces. Sn-3.0Ag-0.5Cu solder was reflowed on Au/Ni substrates, resulting in the initial formation and growth of (CuNi)6Sn 5 at Sn-3.0Ag-0.5Cu /Ni interfaces. (NiCu)3Sn4 formed between the (CuNi)6Sn5 and the Ni substrate when the concentration of Cu in the liquid SnAgCu solder decreased to a critical value which depended upon temperature: 0.37, 0.31 and 0.3(wt.%) at reflow temperatures of 260°C, 245°C and 230°C respectively. The growth rate of (CuNi)6Sn5 was found to be consistent with extrapolations of a diffusion limited growth model formulated for lower temperature, solid state diffusion couples. The long range diffusion of Cu did not limit growth rates. The spalling of (CuNiAu)6Sn5 from (NiCu)3 Sn4 surfaces during reflow was also examined. When the Cu concentration in the solder decreased to approximately 0.28wt.%, the (Cu,Ni,Au) 6Sn5 was observed to spall. Compressive stress in (CuNiAu) 6Sn5 and weak adhesion between (CuNiAu)6Sn 5 and (NiCu)3Sn4 was found to cause this effect.

Sample-morphology effects on x-ray photoelectron peak intensities. III. Simulated spectra of model core–shell nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Powell, Cedric J., E-mail: cedric.powell@nist.gov; Chudzicki, Maksymilian; Werner, Wolfgang S. M.

2015-09-15

The National Institute of Standards and Technology database for the simulation of electron spectra for surface analysis has been used to simulate Cu 2p photoelectron spectra for four types of spherical copper–gold nanoparticles (NPs). These simulations were made to extend the work of Tougaard [J. Vac. Sci. Technol. A 14, 1415 (1996)] and of Powell et al. [J. Vac. Sci. Technol. A 31, 021402 (2013)] who performed similar simulations for four types of planar copper–gold films. The Cu 2p spectra for the NPs were compared and contrasted with analogous results for the planar films and the effects of elastic scatteringmore » were investigated. The new simulations were made for a monolayer of three types of Cu/Au core–shell NPs on a Si substrate: (1) an Au shell of variable thickness on a Cu core with diameters of 0.5, 1.0, 2.0, 5.0, and 10.0 nm; (2) a Cu shell of variable thickness on an Au core with diameters of 0.5, 1.0, 2.0, 5.0, and 10.0 nm; and (3) an Au shell of variable thickness on a 1 nm Cu shell on an Au core with diameters of 0.5, 1.0, 2.0, 5.0, and 10.0 nm. For these three morphologies, the outer-shell thickness was varied until the Cu 2p{sub 3/2} peak intensity was the same (within 2%) as that found in our previous work with planar Cu/Au morphologies. The authors also performed similar simulations for a monolayer of spherical NPs consisting of a CuAu{sub x} alloy (also on a Si substrate) with diameters of 0.5, 1.0, 2.0, 5.0, and 10.0 nm. In the latter simulations, the relative Au concentration (x) was varied to give the same Cu 2p{sub 3/2} peak intensity (within 2%) as that found previously. For each morphology, the authors performed simulations with elastic scattering switched on and off. The authors found that elastic-scattering effects were generally strong for the Cu-core/Au-shell and weak for the Au-core/Cu-shell NPs; intermediate elastic-scattering effects were found for the Au-core/Cu-shell/Au-shell NPs. The shell thicknesses required to give the selected Cu 2p{sub 3/2} peak intensity for the three types of core–shell NPs were less than the corresponding film thicknesses of planar samples since Cu 2p photoelectrons can be detected from the sides and, for the smaller NPs, bottoms of the NPs. Elastic-scattering effects were also observed on the Au atomic fractions found for the CuAu{sub x} NP alloys with different diameters.« less

Magnetic field directional discontinuities. 2: Characteristics between 0.46 and 1.0 AU. [interplanetary magnetic fields

NASA Technical Reports Server (NTRS)

Lepping, R. P.; Benhannon, K. W.

1980-01-01

The characteristics of directional discontinuities (DD's) in the interplanetary magnetic field are studied using data from the Mariner 10 primary mission between 1.0 and 0.46 AU. Statistical and visual survey methods for DD identification resulted in a total of 644 events. Two methods were used to estimate the ratio of the number of tangential discontinuities (TD's) to the number of rotational discontinuities (RD's). Both methods show that the ratio of TD's to RD's varied with time and decreased with decreasing radial distance. A decrease in average discontinuity thickness of approx. 40 percent was found between 1.0 and 0.72 AU and approx. 54 percent between 1.0 and 0.46 AU, independent of type (TD or RD). This decrease in thickness for decreasing r is in qualitative agreement with Pioneer 10 observations between 1 and 5 AU. When the individual DD thickness are normalized with respect to the estimated local proton gyroradius (RA sub L), the average thickness at the three locations is nearly constant, 43 + or - 6 R sub L. This also holds true for both RD's and TD's separately. Statistical distributions of other properties, such as normal components and discontinuity plane angles, are presented.

Layer-by-Layer Self-Assembling Gold Nanorods and Glucose Oxidase onto Carbon Nanotubes Functionalized Sol-Gel Matrix for an Amperometric Glucose Biosensor

PubMed Central

Wu, Baoyan; Hou, Shihua; Miao, Zhiying; Zhang, Cong; Ji, Yanhong

2015-01-01

A novel amperometric glucose biosensor was fabricated by layer-by-layer self-assembly of gold nanorods (AuNRs) and glucose oxidase (GOD) onto single-walled carbon nanotubes (SWCNTs)-functionalized three-dimensional sol-gel matrix. A thiolated aqueous silica sol containing SWCNTs was first assembled on the surface of a cleaned Au electrode, and then the alternate self-assembly of AuNRs and GOD were repeated to assemble multilayer films of AuNRs-GOD onto SWCNTs-functionalized silica gel for optimizing the biosensor. Among the resulting glucose biosensors, the four layers of AuNRs-GOD-modified electrode showed the best performance. The sol-SWCNTs-(AuNRs-GOD)4/Au biosensor exhibited a good linear range of 0.01–8 mM glucose, high sensitivity of 1.08 μA/mM, and fast amperometric response within 4 s. The good performance of the proposed glucose biosensor could be mainly attributed to the advantages of the three-dimensional sol-gel matrix and stereo self-assembly films, and the natural features of one-dimensional nanostructure SWCNTs and AuNRs. This study may provide a new facile way to fabricate the enzyme-based biosensor with high performance. PMID:28347080

3D metamaterial absorber for attomole molecular detection (Conference Presentation)

NASA Astrophysics Data System (ADS)

Tanaka, Takuo; Ishikawa, Atsushi

2016-09-01

3D Metamaterial absorber was used for a background-suppressed surface-enhanced molecular detection technique. By utilizing the resonant coupling of plasmonic modes of a metamaterial absorber and infrared (IR) vibrational modes of a self-assembled monolayer (SAM), attomole level molecular sensitivity was experimentally demonstrated. IR absorption spectroscopy of molecular vibrations is of importance in chemical, material, medical science and so on, since it provides essential information of the molecular structure, composition, and orientation. In the vibrational spectroscopic techniques, in addition to the weak signals from the molecules, strong background degrades the signal-to-noise ratio, and suppression of the background is crucial for the further improvement of the sensitivity. Here, we demonstrate low-background resonant Surface enhanced IR absorption (SEIRA) by using the metamaterial IR absorber that offers significant background suppression as well as plasmonic enhancement. The fabricated metamaterial consisted of 1D array of Au micro-ribbons on a thick Au film separated by a transparent gap layer made of MgF2. The surface structures were designed to exhibit an anomalous IR absorption at 3000 cm-1, which spectrally overlapped with C-H stretching vibrational modes. 16-Mercaptohexadecanoic acid (16-MHDA) was used as a test molecule, which formed a 2-nm thick SAM with their thiol head-group chemisorbed on the Au surface. In the FTIR measurements, the symmetric and asymmetric C-H stretching modes were clearly observed as reflection peaks within a broad plasmonic absorption of the metamaterial.

Au-nanoparticles grafted on plasma treated PE

NASA Astrophysics Data System (ADS)

Švorčík, V.; Chaloupka, A.; Řezanka, P.; Slepička, P.; Kolská, Z.; Kasálková, N.; Hubáček, T.; Siegel, J.

2010-03-01

Polyethylene (PE) surface was treated with Ar plasma. Activated surface was grafted from methanol solution of 1,2-ethanedithiol. Then the sample was immersed into freshly prepared colloid solution of Au-nanoparticles. Finally Au layer was sputtered on the samples. Properties of the modified PE were studied using various methods: AFM, EPR, RBS and nanoindentation. It was shown that the plasma treatment results in degradation of polymer chain (AFM) and creation of free radicals by EPR. After grafting with dithiol, the concentration of free radicals declines. The presence of Au and S in the surface layer after the coating with Au-nanoparticles was proved by RBS. Plasma treatment changes PE surface morphology and increases surface roughness, too. Another significant change in surface morphology and roughness was observed after deposition of Au-nanoparticles. Nanoindentation measurements show that the grafting with Au-nanoparticles increases adhesion of subsequently sputtered Au layer.

The critical particle size for enhancing thermal conductivity in metal nanoparticle-polymer composites

NASA Astrophysics Data System (ADS)

Lu, Zexi; Wang, Yan; Ruan, Xiulin

2018-02-01

Polymers used as thermal interface materials are often filled with high-thermal conductivity particles to enhance the thermal performance. Here, we have combined molecular dynamics and the two-temperature model in 1D to investigate the impact of the metal filler size on the overall thermal conductivity. A critical particle size has been identified above which thermal conductivity enhancement can be achieved, caused by the interplay between high particle thermal conductivity and the added electron-phonon and phonon-phonon thermal boundary resistance brought by the particle fillers. Calculations on the SAM/Au/SAM (self-assembly-monolayer) system show a critical thickness Lc of around 10.8 nm. Based on the results, we define an effective thermal conductivity and propose a new thermal circuit analysis approach for the sandwiched metal layer that can intuitively explain simulation and experimental data. The results show that when the metal layer thickness decreases to be much smaller than the electron-phonon cooling length (or as the "thin limit"), the effective thermal conductivity is just the phonon portion, and electrons do not participate in thermal transport. As the thickness increases to the "thick limit," the effective thermal conductivity recovers the metal bulk value. Several factors that could affect Lc are discussed, and it is discovered that the thermal conductivity, thermal boundary resistance, and the electron-phonon coupling factor are all important in controlling Lc.

Large area space qualified thermoelectrically (TE) cooled HgCdTe MW photovoltaic detectors for the Halogen Occultation Experiment (HALOE)

NASA Technical Reports Server (NTRS)

Norton, P. W.; Zimmermann, P. H.; Briggs, R. J.; Hartle, N. M.

1986-01-01

Large-area, HgCdTe MW photovoltaic detectors have been developed for the NASA-HALOE instrument scheduled for operation on the Upper Atmospheric Research Satellite. The photodiodes will be TE-cooled and were designed to operate in the 5.1-5.4 micron band at 185 K to measure nitric oxide concentrations in the atmosphere. The active area required 15 micron thick devices and a full backside common contact. Reflections from the backside contact doubled the effective thickness of the detectors. Optical interference from reflections was eliminated with a dual layer front surface A/R coating. Bakeout reliability was optimized by having Au metallization for both n and p interconnects. Detailed performance data and a model for the optical stack are presented.

Magnetic field directional discontinuities - Characteristics between 0.46 and 1.0 AU

NASA Technical Reports Server (NTRS)

Lepping, R. P.; Behannon, K. W.

1986-01-01

Based on Mariner 10 data, a statistical survey and an application of the Sonnerup-Cahill variance procedure to a visual identification with 1.2-s averages for time intervals corresponding to the equally spaced heliocentric distances of 1.0, 0.72 and 0.46 AU, are employed to study the characteristics of directional discontinuities (DDs) in the interplanetary magnetic field. Analysis using two methods demonstrated that the ratio of tangential discontinuities (TDs) to rotational discontinuities (RDs) decreased with decreasing radial distance. Decreases in average discontinuity thickness of 41 percent between 1.0 and 0.72 AU, and 56 percent between 1.0 and 0.46 AU, were found for both TDs and RDs, in agreement with Pioneer 10 data between 1 and 5 AU. Normalization of the individual DD thicknesses with respect to the estimated local proton gyroradius (R sub L) gave a nearly constant average thickness at the three locations, 36 + or - 5 R sub L, for both RDs and TDs.

Properties of ordered titanium templates covered with Au thin films for SERS applications

NASA Astrophysics Data System (ADS)

Grochowska, Katarzyna; Siuzdak, Katarzyna; Sokołowski, Michał; Karczewski, Jakub; Szkoda, Mariusz; Śliwiński, Gerard

2016-12-01

Currently, roughened metal nanostructures are widely studied as highly sensitive Raman scattering substrates that show application potential in biochemistry, food safety or medical diagnostic. In this work the structural properties and the enhancement effect due to surface enhanced Raman scattering (SERS) of highly ordered nano-patterned titanium templates covered with thin (5-20 nm) gold films are reported. The templates are formed by preparation of a dense structure of TiO2 nanotubes on a flat Ti surface (2 × 2 cm2) and their subsequent etching down to the substrate. SEM images reveal the formation of honeycomb nanostructures with the cavity diameter of 80 nm. Due to the strongly inhomogeneous distribution of the electromagnetic field in the vicinity of the Au film discontinuities the measured average enhancement factor (107-108) is markedly higher than observed for bare Ti templates. The enhancement factor and Raman signal intensity can be optimized by adjusting the process conditions and thickness of the deposited Au layer. Results confirm that the obtained structures can be used in surface enhanced sensing.

XAS and XMCD studies of magnetic properties modifications of Pt/Co/Au and Pt/Co/Pt trilayers induced by Ga⁺ ions irradiation.

PubMed

Mazalski, Piotr; Sveklo, Iosif; Kurant, Zbigniew; Ollefs, Katharina; Rogalev, Andrei; Wilhelm, Fabrice; Fassbender, Juergen; Baczewski, Lech Tomasz; Wawro, Andrzej; Maziewski, Andrzej

2015-05-01

Magnetic and magneto-optical properties of Pt/Co/Au and Pt/Co/Pt trilayers subjected to 30 keV Ga(+) ion irradiation are compared. In two-dimensional maps of these properties as a function of cobalt thickness and ion fluence, two branches with perpendicular magnetic anisotropy (PMA) for Pt/Co/Pt trilayers are well distinguished. The replacement of the Pt capping layer with Au results in the two branches still being visible but the in-plane anisotropy for the low-fluence branch is suppressed whereas the high-fluence branch displays PMA. The X-ray absorption spectra and X-ray magnetic circular dichroism (XMCD) spectra are discussed and compared with non-irradiated reference samples. The changes of their shapes and peak amplitude, particularly for the high-fluence branch, are related to the modifications of the local environment of Co(Pt) atoms and the etching effects induced by ion irradiation. Additionally, in irradiated trilayers the XMCD measurements at the Pt L2,3-edge reveal an increase of the magnetic moment induced in Pt atoms.

A gas sensor comprising two back-to-back connected Au/TiO2 Schottky diodes

NASA Astrophysics Data System (ADS)

Dehghani, Niloofar; Yousefiazari, Ehsan

2018-04-01

A miniature, but sturdy, gas sensor capable of operation at temperatures as high as 600 °C is presented. The device comprises two back-to-back connected gold/rutile Schottky diodes, which are fabricated on the opposite bases of a self-standing 100 μm-thick pellet of polycrystalline rutile. The rutile layer is formed by the direct oxidation of titanium metal in air at 900 °C, and the Au/rutile diodes are formed by the diffusion bonding of the gold wire segments to the pellet bases. The current versus voltage diagrams and gas sensing properties of the Au/rutile/Au structured device are recorded at different voltage sweeping frequencies and operating temperatures. The interesting features of these diagrams are explained based on an equivalent circuit of the device, which considers Schottky-type contacts at both bases and memristive conduction for the rutile in between. The device current is controlled by the leakage current of the reverse biased diode, which depends on the concentration of the oxygen vacancy at the Au/rutile interface and, hence, on the composition of the surrounding atmosphere. The device current increases 15 times in response to the presence of 1000 ppm of ethanol vapor in air. Consisting only of bulk gold and bulk rutile, the device is resilient to harsh environments and elevated temperatures; a suitable gas sensor for in-exhaust installation.

A study of the Au/Ni ohmic contact on p-GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qiao, D.; Yu, L. S.; Lau, S. S.

2000-10-01

The formation mechanism of the ohmic Au/Ni/p-GaN contact has been investigated. We found that it is essential to (i) deposit a structure of Au and Ni in the proper deposition sequence, and (ii) anneal the bilayer structure in an oxygen containing ambient. Our findings indicated that oxygen assists the layer-reversal reactions of the metallized layers to form a structure of NiO/Au/p-GaN. The presence of oxygen during annealing appears to increase the conductivity of the p-GaN. It is further suggested that Ni removes or reduces the surface contamination of the GaN sample before or during layer reversal. In the final contactmore » structure, an Au layer, which has a large work function, is in contact with the p-GaN substrate. The presence of Au in the entire contacting layer improves the conductivity of the contact. An ohmic formation mechanism based on our experimental results is proposed and discussed in this work. (c) 2000 American Institute of Physics.« less

Electrical characterization of FIB processed metal layers for reliable conductive-AFM on ZnO microstructures

NASA Astrophysics Data System (ADS)

Pea, M.; Maiolo, L.; Giovine, E.; Rinaldi, A.; Araneo, R.; Notargiacomo, A.

2016-05-01

We report on the conductive-atomic force microscopy (C-AFM) study of metallic layers in order to find the most suitable configuration for electrical characterization of individual ZnO micro-pillars fabricated by focused ion beam (FIB). The electrical resistance between the probe tip and both as deposited and FIB processed metal layers (namely, Cr, Ti, Au and Al) has been investigated. Both chromium and titanium evidenced a non homogenous and non ohmic behaviour, non negligible scanning probe induced anodic oxidation associated to electrical measurements, and after FIB milling they exhibited significantly higher tip-sample resistance. Aluminium had generally a more apparent non conductive behaviour. Conversely, gold films showed very good tip-sample conduction properties being less sensitive to FIB processing than the other investigated metals. We found that a reliable C-AFM electrical characterization of ZnO microstructures obtained by FIB machining is feasible by using a combination of metal films as top contact layer. An Au/Ti bilayer on top of ZnO was capable to sustain the FIB fabrication process and to form a suitable ohmic contact to the semiconductor, allowing for reliable C-AFM measurement. To validate the consistency of this approach, we measured the resistance of ZnO micropillars finding a linear dependence on the pillar height, as expected for an ohmic conductor, and evaluated the resistivity of the material. This procedure has the potential to be downscaled to nanometer size structures by a proper choice of metal films type and thickness.

Thickness engineering of atomic layer deposited Al2O3 films to suppress interfacial reaction and diffusion of Ni/Au gate metal in AlGaN/GaN HEMTs up to 600 °C in air

NASA Astrophysics Data System (ADS)

Suria, Ateeq J.; Yalamarthy, Ananth Saran; Heuser, Thomas A.; Bruefach, Alexandra; Chapin, Caitlin A.; So, Hongyun; Senesky, Debbie G.

2017-06-01

In this paper, we describe the use of 50 nm atomic layer deposited (ALD) Al2O3 to suppress the interfacial reaction and inter-diffusion between the gate metal and semiconductor interface, to extend the operation limit up to 600 °C in air. Suppression of diffusion is verified through Auger electron spectroscopy (AES) depth profiling and X-ray diffraction (XRD) and is further supported with electrical characterization. An ALD Al2O3 thin film (10 nm and 50 nm), which functions as a dielectric layer, was inserted between the gate metal (Ni/Au) and heterostructure-based semiconductor material (AlGaN/GaN) to form a metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT). This extended the 50 nm ALD Al2O3 MIS-HEMT (50-MIS) current-voltage (Ids-Vds) and gate leakage (Ig,leakage) characteristics up to 600 °C. Both, the 10 nm ALD Al2O3 MIS-HEMT (10-MIS) and HEMT, failed above 350 °C, as evidenced by a sudden increase of approximately 50 times and 5.3 × 106 times in Ig,leakage, respectively. AES on the HEMT revealed the formation of a Ni-Au alloy and Ni present in the active region. Additionally, XRD showed existence of metal gallides in the HEMT. The 50-MIS enables the operation of AlGaN/GaN based electronics in oxidizing high-temperature environments, by suppressing interfacial reaction and inter-diffusion of the gate metal with the semiconductor.

Organic nonvolatile resistive memory devices based on thermally deposited Au nanoparticle

NASA Astrophysics Data System (ADS)

Jin, Zhiwen; Liu, Guo; Wang, Jizheng

2013-05-01

Uniform Au nanoparticles (NPs) are formed by thermally depositing nominal 2-nm thick Au film on a 10-nm thick polyimide film formed on a Al electrode, and then covered by a thin polymer semiconductor film, which acts as an energy barrier for electrons to be injected from the other Al electrode (on top of polymer film) into the Au NPs, which are energetically electron traps in such a resistive random access memory (RRAM) device. The Au NPs based RRAM device exhibits estimated retention time of 104 s, cycle times of more than 100, and ON-OFF ratio of 102 to 103. The carrier transport properties are also analyzed by fitting the measured I-V curves with several conduction models.

The effect of underlayers on the reversal of perpendicularly magnetized multilayer thin films for magnetic micro- and nanoparticles

NASA Astrophysics Data System (ADS)

Vemulkar, T.; Mansell, R.; Petit, D. C. M. C.; Cowburn, R. P.; Lesniak, M. S.

2017-01-01

Perpendicularly magnetized microparticles offer the ability to locally apply high torques on soft matter under an applied magnetic field. These particles are engineered to have a zero remanence magnetic configuration via synthetic antiferromagnetic coupling using a Ru coupling interlayer. The flexibility offered by the top down thin film fabrication process in a CoFeB/Pt perpendicular thin film is demonstrated by using the Pt interlayer thicknesses in a Pt/Ru/Pt antiferromagnetic coupling multilayer to tune the applied magnetic field value of the easy axis spin-flip transition to saturation and hence the field value at which the magnetic particles are magnetically activated via a distinct transition to saturation. The importance of a Ta buffer layer on the magnetic behavior of the stack is shown. While Au capping layers are desirable for biotechnology applications, we demonstrate that they can drastically change the nucleation and propagation of domains in the film, thereby altering the reversal behavior of the thin film. The effect of Au underlayers on a multilayer thin film composed of repeated motifs of a synthetic antiferromagnetic building block is also investigated.

The fractional laser-induced coagulation zone characterized over time by laser scanning confocal microscopy-A proof of concept study.

PubMed

Banzhaf, Christina A; Lin, Lynlee L; Dang, Nhung; Freeman, Michael; Haedersdal, Merete; Prow, Tarl W

2018-01-01

Ablative fractional laser (AFXL) is an acknowledged technique to increase uptake of topical agents in skin. Micro thermal ablation zones (MAZs) consist of ablated vertical channels surrounded by a coagulation zone (CZ). Laser scanning confocal microscopy (LSCM) images individual MAZs at 733 nm (reflectance confocal microscopy (RCM)). Further, LSCM can image sodium fluorescein (NaF) fluorescence with 488 nm excitation (fluorescence confocal microcopy (FCM)), a small hydrophilic test molecule (370 MW, log P -1.52), which may simulate uptake, bio-distribution and kinetics of small hydrophilic drugs. To explore LSCM for combined investigations of CZ thickness and uptake, bio-distribution and kinetics of NaF in AFXL-exposed skin. Excised human abdominal skin samples were exposed to AFXL (15 mJ/microbeam, 2% density) and NaF gel (1000 μg/ml, 10 μl/cm2) in six repetitions, including untreated control samples. CZ thickness and spatiotemporal fluorescence intensities (FI) were quantified up to four hours after NaF application by RCM and FCM. Test sites were scanned to a depth of 200 μm, quantifying thickness of skin compartments (stratum corneum, epidermis, upper dermis), individual CZ thicknesses and FI in CZ and surrounding skin. RCM images established skin morphology to a depth of 200 μm. The CZ thickness measurements were feasible to a depth of 50 μm, and remained unchanged over time at 50 μm (P > 0.5). FI were detected to a depth of 160 μm and remained constant in CZ up to four hours after NaF application (15 minutes: 79 AU (73-92 AU), 60 minutes: 72 AU (58-82 AU), four hours: 78 AU (71-90 AU), P > 0.1). In surrounding skin, FI increased significantly over time, but remained lower than FI in CZ (15 minutes: 21 AU (17-22 AU), 60 minutes: 21 AU (19-26 AU), four hours: 42 (31- 48 AU), P = 0.03). AFXL-processed skin generated higher FI compared to non-laser processed skin in epidermis and upper dermis at 60 minutes and four hours (P = 0.03). By LSCM, assessment of the AFXL-induced CZ thickness was feasible to a depth of 50 μm, and assessment of FI from a small hydrophilic test molecule, NaF in CZ and surrounding skin feasible to a depth of 160 μm. Lasers Surg. Med. 50:70-77, 2018. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Wrinkled substrate and Indium Tin Oxide-free transparent electrode making organic solar cells thinner in active layer

NASA Astrophysics Data System (ADS)

Liu, Kong; Lu, Shudi; Yue, Shizhong; Ren, Kuankuan; Azam, Muhammad; Tan, Furui; Wang, Zhijie; Qu, Shengchun; Wang, Zhanguo

2016-11-01

To enable organic solar cells with a competent charge transport efficiency, reducing the thickness of active layer without sacrificing light absorption efficiency turns out to be of high feasibility. Herein, organic solar cells on wrinkled metal surface are designed. The purposely wrinkled Al/Au film with a smooth surface provides a unique scaffold for constructing thin organic photovoltaic devices by avoiding pinholes and defects around sharp edges in conventional nanostructures. The corresponding surface light trapping effect enables the thin active layer (PTB7-Th:PC71BM) with a high absorption efficiency. With the innovative MoO3/Ag/ZnS film as the top transparent electrode, the resulting Indium Tin Oxide-free wrinkled devices show a power conversion efficiency as 7.57% (50 nm active layer), higher than the planner counterparts. Thus, this paper provides a new methodology to improve the performance of organic solar cells by balancing the mutual restraint factors to a high level.

Radiation transmission data for radionuclides and materials relevant to brachytherapy facility shielding.

PubMed

Papagiannis, P; Baltas, D; Granero, D; Pérez-Calatayud, J; Gimeno, J; Ballester, F; Venselaar, J L M

2008-11-01

To address the limited availability of radiation shielding data for brachytherapy as well as some disparity in existing data, Monte Carlo simulation was used to generate radiation transmission data for 60Co, 137CS, 198Au, 192Ir 169Yb, 170Tm, 131Cs, 125I, and 103pd photons through concrete, stainless steel, lead, as well as lead glass and baryte concrete. Results accounting for the oblique incidence of radiation to the barrier, spectral variation with barrier thickness, and broad beam conditions in a realistic geometry are compared to corresponding data in the literature in terms of the half value layer (HVL) and tenth value layer (TVL) indices. It is also shown that radiation shielding calculations using HVL or TVL values could overestimate or underestimate the barrier thickness required to achieve a certain reduction in radiation transmission. This questions the use of HVL or TVL indices instead of the actual transmission data. Therefore, a three-parameter model is fitted to results of this work to facilitate accurate and simple radiation shielding calculations.

Internal stress-assisted epitaxial lift-off process for flexible thin film (In)GaAs solar cells on metal foil

NASA Astrophysics Data System (ADS)

Kim, Youngjo; Kim, Kangho; Jung, Sang Hyun; Kim, Chang Zoo; Shin, Hyun-Beom; Choi, JeHyuk; Kang, Ho Kwan

2017-12-01

Flexible thin film (In)GaAs solar cells are grown by metalorganic chemical vapor deposition on GaAs substrates and transferred to 30 μm thick Au foil by internal stress-assisted epitaxial lift-off processes. The internal stress is induced by replacing the solar cell epi-layers from GaAs to In0.015Ga0.985As, which has a slightly larger lattice constant. The compressive strained layer thickness was varied from 0 to 4.5 μm to investigate the influence of the internal stress on the epitaxial lift-off time. The etching time in the epitaxial lift-off process was reduced from 36 to 4 h by employing a GaAs/In0.015Ga0.985As heterojunction structure that has a compressive film stress of -59.0 MPa. We found that the partially strained epi-structure contributed to the much faster lateral etching rate with spontaneous bending. Although an efficiency degradation problem occurred in the strained solar cell, it was solved by optimizing the epitaxial growth conditions.

Stability of surface and subsurface hydrogen on and in Au/Ni near-surface alloys

DOE PAGES

Celik, Fuat E.; Mavrikakis, Manos

2015-01-12

Periodic, self-consistent DFT-GGA (PW91) calculations were used to study the interaction of hydrogen atoms with the (111) surfaces of substitutional near-surface alloys (NSAs) of Au and Ni with different surface layer compositions and different arrangements of Au atoms in the surface layer. The effect of hydrogen adsorption on the surface and in the first and second subsurface layers of the NSAs was studied. Increasing the Au content in the surface layer weakens hydrogen binding on the surface, but strengthens subsurface binding, suggesting that the distribution of surface and subsurface hydrogen will be different than that on pure Ni(111). While themore » metal composition of the surface layer has an effect on the binding energy of hydrogen on NSA surfaces, the local composition of the binding site has a stronger effect. For example, fcc hollow sites consisting of three Ni atoms bind H nearly as strongly as on Ni(111), and fcc sites consisting of three Au atoms bind H nearly as weakly as on Au(111). Sites with one or two Au atoms show intermediate binding energies. The preference of hydrogen for three-fold Ni hollow sites alters the relative stabilities of different surface metal atom arrangements, and may provide a driving force for adsorbate-induced surface rearrangement.« less

Stability of Surface and Subsurface Hydrogen on and in Au/Ni Near-Surface Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Celik, Fuat E.; Mavrikakis, Manos

2015-10-01

Periodic, self-consistent DFT-GGA (PW91) calculations were used to study the interaction of hydrogen atoms with the (111) surfaces of substitutional near-surface alloys (NSAs) of Au and Ni with different surface layer compositions and different arrangements of Au atoms in the surface layer. The effect of hydrogen adsorption on the surface and in the first and second subsurface layers of the NSAs was studied. Increasing the Au content in the surface layer weakens hydrogen binding on the surface, but strengthens subsurface binding, suggesting that the distribution of surface and subsurface hydrogen will be different than that on pure Ni(111). While themore » metal composition of the surface layer has an effect on the binding energy of hydrogen on NSA surfaces, the local composition of the binding site has a stronger effect. For example, fcc hollow sites consisting of three Ni atoms bind H nearly as strongly as on Ni(111), and fcc sites consisting of three Au atoms bind H nearly as weakly as on Au(111). Sites with one or two Au atoms show intermediate binding energies. The preference of hydrogen for three-fold Ni hollow sites alters the relative stabilities of different surface metal atom arrangements, and may provide a driving force for adsorbate-induced surface rearrangement.« less

Stability of surface and subsurface hydrogen on and in Au/Ni near-surface alloys

NASA Astrophysics Data System (ADS)

Celik, Fuat E.; Mavrikakis, Manos

2015-10-01

Periodic, self-consistent DFT-GGA (PW91) calculations were used to study the interaction of hydrogen atoms with the (111) surfaces of substitutional near-surface alloys (NSAs) of Au and Ni with different surface layer compositions and different arrangements of Au atoms in the surface layer. The effect of hydrogen adsorption on the surface and in the first and second subsurface layers of the NSAs was studied. Increasing the Au content in the surface layer weakens hydrogen binding on the surface, but strengthens subsurface binding, suggesting that the distribution of surface and subsurface hydrogen will be different than that on pure Ni(111). While the metal composition of the surface layer has an effect on the binding energy of hydrogen on NSA surfaces, the local composition of the binding site has a stronger effect. For example, fcc hollow sites consisting of three Ni atoms bind H nearly as strongly as on Ni(111), and fcc sites consisting of three Au atoms bind H nearly as weakly as on Au(111). Sites with one or two Au atoms show intermediate binding energies. The preference of hydrogen for three-fold Ni hollow sites alters the relative stabilities of different surface metal atom arrangements, and may provide a driving force for adsorbate-induced surface rearrangement.

Gold Nanoclusters@Ru(bpy)₃²⁺-Layered Double Hydroxide Ultrathin Film as a Cathodic Electrochemiluminescence Resonance Energy Transfer Probe.

PubMed

Yu, Yingchang; Lu, Chao; Zhang, Meining

2015-08-04

Herein, it is the first report that a cathodic electrochemiluminescence (ECL) resonance energy transfer (ERET) system is fabricated by layer-by-layer (LBL) electrostatic assembly of CoAl layered double hydroxide (LDH) nanosheets with a mixture of blue BSA-gold nanoclusters (AuNCs) and Ru(bpy)3(2+) (denoted as AuNCs@Ru) on an Au electrode. The possible ECL mechanism indicates that the appearance of CoAl-LDH nanosheets generates a long-range stacking order of the AuNCs@Ru on an Au electrode, facilitating the occurrence of the ERET between BSA-AuNC donors and Ru(bpy)3(2+) acceptors on the as-prepared AuNCs@Ru-LDH ultrathin films (UTFs). Furthermore, it is observed that the cathodic ECL intensity can be quenched efficiently in the presence of 6-mercaptopurine (6-MP) in a linear range of 2.5-100 nM with a detection limit of 1.0 nM. On the basis of these interesting phenomena, a facile cathodic ECL sensor has successfully distinguished 6-MP from other thiol-containing compounds (e.g., cysteine and glutathione) in human serum and urine samples. The proposed sensing scheme opens a way for employing the layered UTFs as a platform for the cathodic ECL of Ru(bpy)3(2+).

Epitaxial growth of a mono-crystalline metastable AuIn layer at the Au/InP(001) interface

NASA Astrophysics Data System (ADS)

Renda, M.; Morita, K.

1990-01-01

Thermal annealing of a gold layer deposited on the InP(001)-p(2×4) surface has been studied in-situ by means of LEED, AES and RBS techniques and by post analysis of RBS-channeling and glancing incidence X-ray diffraction. A clean LEED pattern of p(2×2) spots was observed for the specimen annealed for 10 min at 300°C. The composition ratio of Au/In in the epitaxial compound layer was found to be 49/51 by RBS and several at% of P was also detected by post sputter-AES analysis. It was also found that the epitaxial layer shows a clear channeling dip for an incident ion beam which is aligned along the <001> axis of InP substrate. The glancing incidence X-ray diffraction analysis indicates diffraction peaks from the pseudo-orthorombic phase of AuIn. From these experimental results, it is concluded that the epitaxial Au-compound layer is a mono-crystalline metastable phase of AuIn, of which every three atomic rows of Au or In in the [110] direction would be situated on every four atomic rows in the [010] direction of the In(001) face of the InP crystal.

Optical and structural properties of protein/gold hybrid bio-nanofilms prepared by layer-by-layer method.

PubMed

Pál, Edit; Hornok, Viktória; Sebok, Dániel; Majzik, Andrea; Dékány, Imre

2010-08-01

Lysozyme/gold thin layers were prepared by layer-by-layer (LbL) self-assembly method. The build-up of the films was followed by UV-vis-absorbance spectra, quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) techniques. The structural property of films was examined by X-ray diffraction (XRD) measurements, while their morphology was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). It was found that gold nanoparticles (NPs) had cubic crystalline structure, the primary particles form aggregates in the thin layer due to the presence of lysozyme molecules. The UV-vis measurements prove change in particle size while the colour of the film changes from wine-red to blue. The layer thickness of films was determined using the above methods and the loose, porous structure of the films explains the difference in the results. The vapour adsorption property of hybrid layers was also studied by QCM using different saturated vapours and ammonia gas. The lysozyme/Au films were most sensitive for ammonia gas among the tested gases/vapours due to the strongest interaction between the functional groups of the protein. Copyright 2010 Elsevier B.V. All rights reserved.

Formation of alternating interfacial layers in Au-12Ge/Ni joints

PubMed Central

Lin, Shih-kang; Tsai, Ming-yueh; Tsai, Ping-chun; Hsu, Bo-hsun

2014-01-01

Au-Ge alloys are promising materials for high-power and high-frequency packaging, and Ni is frequently used as diffusion barriers. This study investigates interfacial reactions in Au-12Ge/Ni joints at 300°C and 400°C. For the reactions at 300°C, typical interfacial morphology was observed and the diffusion path was (Au) + (Ge)/NiGe/Ni5Ge3/Ni. However, an interesting phenomenon – the formation of (Au,Ni,Ge)/NiGe alternating layers – was observed for the reactions at 400°C. The diffusion path across the interface was liquid/(Au,Ni,Ge)/NiGe/···/(Au,Ni,Ge)/NiGe/Ni2Ge/Ni. The periodic thermodynamic instability at the NiGe/Ni2Ge interface caused the subsequent nucleation of new (Au,Ni,Ge)/NiGe pairs. The thermodynamic foundation and mechanism of formation of the alternating layers are elaborated in this paper. PMID:24690992

Cross section of α-induced reactions on iridium isotopes obtained from thick target yield measurement for the astrophysical γ process

NASA Astrophysics Data System (ADS)

Szücs, T.; Kiss, G. G.; Gyürky, Gy.; Halász, Z.; Fülöp, Zs.; Rauscher, T.

2018-01-01

The stellar reaction rates of radiative α-capture reactions on heavy isotopes are of crucial importance for the γ process network calculations. These rates are usually derived from statistical model calculations, which need to be validated, but the experimental database is very scarce. This paper presents the results of α-induced reaction cross section measurements on iridium isotopes carried out at first close to the astrophysically relevant energy region. Thick target yields of 191Ir(α,γ)195Au, 191Ir(α,n)194Au, 193Ir(α,n)196mAu, 193Ir(α,n)196Au reactions have been measured with the activation technique between Eα = 13.4 MeV and 17 MeV. For the first time the thick target yield was determined with X-ray counting. This led to a previously unprecedented sensitivity. From the measured thick target yields, reaction cross sections are derived and compared with statistical model calculations. The recently suggested energy-dependent modification of the α + nucleus optical potential gives a good description of the experimental data.

Development of a flat-field spectrometer with a wideband Ni/C multilayer grating in the 1–3.5 keV range

DOE Office of Scientific and Technical Information (OSTI.GOV)

Imazono, Takashi

2016-07-27

To develop a flat-field spectrometer with coverage of the 1–3.5 keV range, a wideband Ni/C multilayer grating was invented. The multilayer consists of two kinds of layer structures. One is a conventional periodic multilayer of thickness D{sub 1} = 5.6 nm, Ni thickness ratio to the multilayer period γ{sub 1} = 0.5 and the number of layers N{sub 1} = 79. Both the first and last layers are Ni. The other is a C/Ni bilayer of D{sub 2} = 8.4 nm, γ{sub 2} = 0.53 and N{sub 2} = 2. The first layer is C and then Ni. The aperiodicmore » multilayer from the topmost C/Ni bilayer was coated on a laminar-type grating having an effective grating constant of 1/2400 mm, groove depth of 2.8 nm, and duty ratio (land width/groove period) of 0.5. In a preliminary experiment, the diffraction efficiency was in excess of 0.8% in the energy range of 2.1-3.3 keV and the maximum of 5.4% at 3.1 keV at a constant angle of incidence of 88.54°, which is considerably higher than that of an Au-coated grating before deposition of the multilayer.« less

In0.53Ga0.47As/InP conventional and inverted thermophotovoltaic cells with back surface reflector

NASA Astrophysics Data System (ADS)

Karlina, L. B.; Kulagina, M. M.; Timoshina, N. Kh.; Vlasov, A. S.; Andreev, V. M.

2007-02-01

Characteristics of conventional and inverted InGaAs/InP thermophotovoltaic (TPV) cells with a back surface reflector (BSR) fabricated on electrically active n-type InP substrates are presented. Thermophotovoltaic cells based on lattice matched InP-In0.53Ga0.47As heterostructures were fabricated with the use of LPE and Zn,P diffusion technologies. In the p-n TPV cells (conventional type, spectral range 600÷1800 nm) with a frontal p-InGaAs layer, BSR was made on a n-InP substrate. In the n-p structure (inverted type, spectral range1000-1800 nm) with a frontal bulk n-InP-window-substrate, BSR was formed on a p-InGaAs layer. Antireflection coating (ARC) on the frontal cell surface consists of ZnS/MgF2 layers. Results of investigation of sub-bangap photons reflection from InP substrates with a backside MgF2/Au mirror in the range of 1800÷2000nm are described. The reflection of BSR for InP samples with the doping level in the range of 1×1017÷6×1018cm-3 evidenced a weak dependence on their thickness and doping level. A reflection of 86÷90% has been measured for substrates 100μm thick and 80% for ones 400μm thick with ARC. Study of sub-bandgap photon reflection of p-InGaAs (Zn,P) layers with surface concentration of 1÷3×1019cm-3 has been also carried out. A reflection of 68÷77% for 2÷4μm layers with "hybrid" (ohmic contact plus mirror) back-surface reflector consisted of deposited Cr/Au layers was measured. It was found, that p-n and n-p thermophotovoltaic 1×1cm2 cells with identical grid design reveal similar parameters for up to 1A/cm2 current density (VOC=465mV and FF=64%) and the 76÷80% reflection of the sub-bandgap photons for wavelengths longer than 1.86μm. The developed inverted InGaAs TPV cells have been tested under illumination of silicon carbide high temperature emitter. The photocurrent density Jsc=7A/cm2, open circuit voltage Voc=0.476V and fill factor FF=0.691 have been measured in the inverted (without BSR) InGaAs cell under SiC emitter heated to the temperature of about 1550°C. Both types of devices can successfully be used as TPV cells for conversion of radiation in the range of 1500-1900K, with 14-15% efficiency.

Electrical properties of pseudo-single-crystalline Ge films grown by Au-induced layer exchange crystallization at 250 °C

NASA Astrophysics Data System (ADS)

Higashi, H.; Kudo, K.; Yamamoto, K.; Yamada, S.; Kanashima, T.; Tsunoda, I.; Nakashima, H.; Hamaya, K.

2018-06-01

We study the electrical properties of pseudo-single-crystalline Ge (PSC-Ge) films grown by a Au-induced layer exchange crystallization method at 250 °C. By inserting the SiNx layer between PSC-Ge and SiO2, we initiatively suppress the influence of the Ge/SiO2 interfacial defective layers, which have been reported in our previous works, on the electrical properties of the PSC-Ge layers. As a result, we can detect the influence of the ionized Au+ donors on the temperature-dependent hole concentration and Hall mobility. To further examine their electrical properties in detail, we also fabricate p-thin-film transistors (TFTs) with the PSC-Ge layer. Although the off-state leakage currents are suppressed by inserting the SiNx layer, the value of on/off ratio remains poor (<102). Even after the post-annealing at 400 °C for the TFTs, the on/off ratio is still poor (˜102) because of the gate-induced drain leakage current although a nominal field effect mobility is enhanced up to ˜25 cm2/V s. Considering these features, we conclude that the Au contaminations into the PSC-Ge layer can affect the electrical properties and device performances despite a low-growth temperature of 250 °C. To achieve further high-performance p-TFTs, we have to suppress the Au contaminations into PSC-Ge during the Au-induced crystallization growth.

Optoelectric biosensor using indium-tin-oxide electrodes.

PubMed

Choi, Chang Kyoung; Kihm, Kenneth D; English, Anthony E

2007-06-01

The use of an optically thin indium-tin-oxide (ITO) electrode is presented for an optoelectric biosensor simultaneously recording optical images and microimpedance to examine time-dependent cellular growth. The transmittance of a 100 nm thick ITO electrode layer is approximately the same as the transmittance of a clean glass substrate, whereas the industry-standard Au(47.5 nm)/Ti(2.5 nm) electrode layer drops the transmittance to less than 10% of that of the glass substrate. The simultaneous optoelectric measurements permit determining the correlation of the cell-covered area increase with the microimpedance increase, and the example results obtained for live porcine pulmonary artery endothelial cells delineate the quantitative and comprehensive nature of cellular attachment and spreading to the substrate, which has not been clearly perceived before.

Facile fabrication of ultrathin Pt overlayers onto nanoporous metal membranes via repeated Cu UPD and in situ redox replacement reaction.

PubMed

Liu, Pengpeng; Ge, Xingbo; Wang, Rongyue; Ma, Houyi; Ding, Yi

2009-01-06

Ultrathin Pt films from one to several atomic layers are successfully decorated onto nanoporous gold (NPG) membranes by utilizing under potential deposition (UPD) of Cu onto Au or Pt surfaces, followed by in situ redox replacement reaction (RRR) of UPD Cu by Pt. The thickness of Pt layers can be controlled precisely by repeating the Cu-UPD-RRR cycles. TEM observations coupled with electrochemical testing suggest that the morphology of Pt overlayers changes from an ultrathin epitaxial film in the case of one or two atomic layers to well-dispersed nanoislands in the case of four and more atomic layers. Electron diffraction (ED) patterns confirm that the as-prepared NPG-Pt membranes maintain a single-crystalline structure, even though the thickness of Pt films reaches six atomic layers, indicating the decorated Pt films hold the same crystallographic relationship to the NPG substrate during the entire fabrication process. Due to the regular modulation of Pt utilization, the electrocatalytic activity of NPG-Pt exhibits interesting surface structure dependence in methanol, ethanol, and CO electrooxidation reactions. These novel bimetallic nanocatalysts show excellent electrocatalytic activity and much enhanced poison tolerance as compared to the commercial Pt/C catalysts. The success in the fabrication of NPG-Pt-type materials provides a new path to prepare electrocatalysts with ultralow Pt loading and high Pt utilization, which is of great significance in energy-related applications, such as direct alcohol fuel cells (DAFCs).

Shear stress increases nitric oxide production in thick ascending limbs

PubMed Central

Cabral, Pablo D.; Hong, Nancy J.

2010-01-01

We showed that luminal flow stimulates nitric oxide (NO) production in thick ascending limbs. Ion delivery, stretch, pressure, and shear stress all increase when flow is enhanced. We hypothesized that shear stress stimulates NO in thick ascending limbs, whereas stretch, pressure, and ion delivery do not. We measured NO in isolated, perfused rat thick ascending limbs using the NO-sensitive dye DAF FM-DA. NO production rose from 21 ± 7 to 58 ± 12 AU/min (P < 0.02; n = 7) when we increased luminal flow from 0 to 20 nl/min, but dropped to 16 ± 8 AU/min (P < 0.02; n = 7) 10 min after flow was stopped. Flow did not increase NO in tubules from mice lacking NO synthase 3 (NOS 3). Flow stimulated NO production by the same extent in tubules perfused with ion-free solution and physiological saline (20 ± 7 vs. 24 ± 6 AU/min; n = 7). Increasing stretch while reducing shear stress and pressure lowered NO generation from 42 ± 9 to 17 ± 6 AU/min (P < 0.03; n = 6). In the absence of shear stress, increasing pressure and stretch had no effect on NO production (2 ± 8 vs. 8 ± 8 AU/min; n = 6). Similar results were obtained in the presence of tempol (100 μmol/l), a O2− scavenger. Primary cultures of thick ascending limb cells subjected to shear stresses of 0.02 and 0.55 dyne/cm2 produced NO at rates of 55 ± 10 and 315 ± 93 AU/s, respectively (P < 0.002; n = 7). Pretreatment with the NOS inhibitor l-NAME (5 mmol/l) blocked the shear stress-induced increase in NO production. We concluded that shear stress rather than pressure, stretch, or ion delivery mediates flow-induced stimulation of NO by NOS 3 in thick ascending limbs. PMID:20719980

On the Effect of Native SiO2 on Si over the SPR-mediated Photocatalytic Activities of Au and Ag Nanoparticles.

PubMed

Wang, Jiale; de Freitas, Isabel C; Alves, Tiago V; Ando, Romulo A; Fang, Zebo; Camargo, Pedro H C

2017-05-29

In hybrid materials containing plasmonic nanoparticles such as Au and Ag, charge-transfer processes from and to Au or Ag can affect both activities and selectivity in plasmonic catalysis. Inspired by the widespread utilization of commercial Si wafers in surface-enhanced Raman spectroscopy (SERS) studies, we investigated herein the effect of the native SiO 2 layer on Si wafers over the surface plasmon resonance (SPR)-mediated activities of the Au and Ag nanoparticles (NPs). We prepared SERS-active plasmonic comprised of Au and Ag NPs deposited onto a Si wafer. Here, two kinds of Si wafers were employed: Si with a native oxide surface layer (Si/SiO 2 ) and Si without a native oxide surface layer (Si). This led to Si/SiO 2 /Au, Si/SiO 2 /Ag, Si/Au, and Si/Ag NPs. The SPR-mediated oxidation of p-aminothiophenol (PATP) to p,p'-dimercaptoazobenzene (DMAB) was employed as a model transformation. By comparing the performances and band structures for the Si/Au and Si/Ag relative to Si/SiO 2 /Au and Si/SiO 2 /Ag NPs, it was found that the presence of a SiO 2 layer was crucial to enable higher SPR-mediated PATP to DMAB conversions. The SiO 2 layer acts to prevent the charge transfer of SPR-excited hot electrons from Au or Ag nanoparticles to the Si substrate. This enabled SPR-excited hot electrons to be transferred to adsorbed O 2 molecules, which then participate in the selective oxidation of PATP to DMAB. In the absence of a SiO 2 layer, SPR-excited hot electrons are preferentially transferred to Si instead of adsorbed O 2 molecules, leading to much lower PATP oxidation. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Self-assembly of bimetallic AuxPd1-x alloy nanoparticles via dewetting of bilayers through the systematic control of temperature, thickness, composition and stacking sequence

NASA Astrophysics Data System (ADS)

Kunwar, Sundar; Pandey, Puran; Sui, Mao; Bastola, Sushil; Lee, Jihoon

2018-03-01

Bimetallic alloy nanoparticles (NPs) are attractive materials for various applications with their morphology and elemental composition dependent optical, electronic, magnetic and catalytic properties. This work demonstrates the evolution of AuxPd1-x alloy nanostructures by the solid-state dewetting of sequentially deposited bilayers of Au and Pd on sapphire (0001). Various shape, size and configuration of AuxPd1‑x alloy NPs are fabricated by the systematic control of annealing temperature, deposition thickness, composition as well as stacking sequence. The evolution of alloy nanostructures is attributed to the surface diffusion, interface diffusion between bilayers, surface and interface energy minimization, Volmer-Weber growth model and equilibrium configuration. Depending upon the temperature, the surface morphologies evolve with the formation of pits, grains and voids and gradually develop into isolated semi-spherical alloy NPs by the expansion of voids and agglomeration of Au and Pd adatoms. On the other hand, small isolated to enlarged elongated and over-grown layer-like alloy nanostructures are fabricated due to the coalescence, partial diffusion and inter-diffusion with the increased bilayer thickness. In addition, the composition and stacking sequence of bilayers remarkably affect the final geometry of AuxPd1‑x nanostructures due to the variation in the dewetting process. The optical analysis based on the UV–vis-NIR reflectance spectra reveals the surface morphology dependent plasmonic resonance, scattering, reflection and absorption properties of AuxPd1‑x alloy nanostructures.

Characterization of spatial manipulation on ZnO nanocomposites consisting of Au nanoparticles, a graphene layer, and ZnO nanorods

NASA Astrophysics Data System (ADS)

Huang, Shen-Che; Lu, Chien-Cheng; Su, Wei-Ming; Weng, Chen-Yuan; Chen, Yi-Cian; Wang, Shing-Chung; Lu, Tien-Chang; Chen, Ching-Pang; Chen, Hsiang

2018-01-01

Three types of ZnO-based nanocomposites were fabricated consisting of 80-nm Au nanoparticles (NPs), a graphene layer, and ZnO nanorods (NRs). To investigate interactions between the ZnO NRs and Au nanoparticle, multiple material analysis techniques including field-emission scanning electron microscopy (FESEM), surface contact angle measurements, secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopic characterizations were performed. Results indicate that incorporating a graphene layer could block the interaction between the ZnO NRs and the Au NPs. Furthermore, the Raman signal of the Au NPs could be enhanced by inserting a graphene layer on top of the ZnO NRs. Investigation of these graphene-incorporated nanocomposites would be helpful to future studies of the physical properties and Raman analysis of the ZnO-based nanostructure design.

Fabrication of hierarchical hybrid structures using bio-enabled layer-by-layer self-assembly.

PubMed

Hnilova, Marketa; Karaca, Banu Taktak; Park, James; Jia, Carol; Wilson, Brandon R; Sarikaya, Mehmet; Tamerler, Candan

2012-05-01

Development of versatile and flexible assembly systems for fabrication of functional hybrid nanomaterials with well-defined hierarchical and spatial organization is of a significant importance in practical nanobiotechnology applications. Here we demonstrate a bio-enabled self-assembly technique for fabrication of multi-layered protein and nanometallic assemblies utilizing a modular gold-binding (AuBP1) fusion tag. To accomplish the bottom-up assembly we first genetically fused the AuBP1 peptide sequence to the C'-terminus of maltose-binding protein (MBP) using two different linkers to produce MBP-AuBP1 hetero-functional constructs. Using various spectroscopic techniques, surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR), we verified the exceptional binding and self-assembly characteristics of AuBP1 peptide. The AuBP1 peptide tag can direct the organization of recombinant MBP protein on various gold surfaces through an efficient control of the organic-inorganic interface at the molecular level. Furthermore using a combination of soft-lithography, self-assembly techniques and advanced AuBP1 peptide tag technology, we produced spatially and hierarchically controlled protein multi-layered assemblies on gold nanoparticle arrays with high molecular packing density and pattering efficiency in simple, reproducible steps. This model system offers layer-by-layer assembly capability based on specific AuBP1 peptide tag and constitutes novel biological routes for biofabrication of various protein arrays, plasmon-active nanometallic assemblies and devices with controlled organization, packing density and architecture. Copyright © 2011 Wiley Periodicals, Inc.

Ultrathin efficient perovskite solar cells employing a periodic structure of a composite hole conductor for elevated plasmonic light harvesting and hole collection

NASA Astrophysics Data System (ADS)

Long, Mingzhu; Chen, Zefeng; Zhang, Tiankai; Xiao, Yubin; Zeng, Xiaoliang; Chen, Jian; Yan, Keyou; Xu, Jianbin

2016-03-01

We developed a molecule/polymer composite hole transporting material (HTM) with a periodic microstructure for morphology replication of a corrugated Au electrode, which in combination plays a dual role in the optical and electronic enhancement of high performance perovskite solar cells (PSCs). The electro-optics revealed that perovskite couldn't readily extinct the red light even though the thickness increased to 370 nm, but we found that the quasi periodic microstructure composite (PMC) HTM in combination with the conformal Au electrode could promote the absorption through the enhanced cavity effects, leading to comparable absorption even using much thinner perovskite (240 nm). We identified that the cavity was the combination of Fabry-Pérot interferometer and surface plasmonic resonance, with light harvesting enhancement through surface plasmon polariton or waveguide modes that propagate in the plane of the perovskite layer. On the other hand, the PMC HTM increased hole conductivity by one order of magnitude with respect to standard spiro-OMeTAD HTM due to molecular packing and self-assembly, embodying traceable hole mobility and density elevation up to 3 times, and thus the hysteresis was greatly avoided. Owing to dual optical and electronic enhancement, the PMC PSC afforded high efficiency PSC using as thin as 240 nm perovskite layer, delivering a Voc of 1.05 V, Jsc of 22.9 mA cm-2, FF of 0.736, and efficiency amounting to 17.7% PCE, the highest efficiency with ultrathin perovskite layer.We developed a molecule/polymer composite hole transporting material (HTM) with a periodic microstructure for morphology replication of a corrugated Au electrode, which in combination plays a dual role in the optical and electronic enhancement of high performance perovskite solar cells (PSCs). The electro-optics revealed that perovskite couldn't readily extinct the red light even though the thickness increased to 370 nm, but we found that the quasi periodic microstructure composite (PMC) HTM in combination with the conformal Au electrode could promote the absorption through the enhanced cavity effects, leading to comparable absorption even using much thinner perovskite (240 nm). We identified that the cavity was the combination of Fabry-Pérot interferometer and surface plasmonic resonance, with light harvesting enhancement through surface plasmon polariton or waveguide modes that propagate in the plane of the perovskite layer. On the other hand, the PMC HTM increased hole conductivity by one order of magnitude with respect to standard spiro-OMeTAD HTM due to molecular packing and self-assembly, embodying traceable hole mobility and density elevation up to 3 times, and thus the hysteresis was greatly avoided. Owing to dual optical and electronic enhancement, the PMC PSC afforded high efficiency PSC using as thin as 240 nm perovskite layer, delivering a Voc of 1.05 V, Jsc of 22.9 mA cm-2, FF of 0.736, and efficiency amounting to 17.7% PCE, the highest efficiency with ultrathin perovskite layer. Electronic supplementary information (ESI) available: XRD patterns corresponding to the perovskite; AFM images of 3D PMC HTM perovskite solar cells; performance statistics for 3D PMC HTM; ultraviolet photoelectron spectra (UPS) of HTMs on FTO. See DOI: 10.1039/c5nr05042a

Preparation and electrical properties of Cr 2O 3 gate insulator embedded with Fe dot

NASA Astrophysics Data System (ADS)

Yokota, Takeshi; Kuribayashi, Takaaki; Murata, Shotaro; Gomi, Manabu

2008-09-01

We investigated the electrical properties of a metal (Au)/insulator (magneto-electric materials: Cr 2O 3)/magnetic materials (Fe)/tunnel layer (Cr 2O 3)/semiconductor (Si) capacitor. This capacitor shows the typical capacitance-voltage ( C- V) properties of an Si-MIS capacitor with hysteresis depending on the Fe dispersibility which is determined by the deposition condition. The C- V curve of the only sample having a 0.5 nm Fe layer was seen to have a hysteresis window with a clockwise trace, indicating that electrons have been injected into the ultra-thin Fe layer. The samples having Fe layers of other thicknesses show a counterclockwise trace, which indicates that the film has mobile ionic charges due to the dispersed Fe. These results indicated that the charge-injection site, which works as a memory, in the Cr 2O 3 can be prepared by Fe insertion, which is deposited using well-controlled conditions. The results also revealed the possibility of an MIS capacitor containing both ferromagnetic materials and an ME insulating layer in a single system.

Tunable optical properties of plasmonic Au/Al2O3 nanocomposite thin films analyzed by spectroscopic ellipsometry accounting surface characteristics.

PubMed

Jaiswal, Jyoti; Mourya, Satyendra; Malik, Gaurav; Chandra, Ramesh

2018-05-01

In the present work, we have fabricated plasmonic gold/alumina nanocomposite (Au/Al 2 O 3 NC) thin films on a glass substrate at room temperature by RF magnetron co-sputtering. The influence of the film thickness (∼10-40  nm) on the optical and other physical properties of the samples was investigated and correlated with the structural and compositional properties. The X-ray diffractometer measurement revealed the formation of Au nanoparticles with average crystallite size (5-9.2 nm) embedded in an amorphous Al 2 O 3 matrix. The energy-dispersive X ray and X-ray photoelectron spectroscopy results confirmed the formation of Au/Al 2 O 3 NC quantitatively and qualitatively and it was observed that atomic% of Au increased by increasing thickness. The optical constants of the plasmonic Au/Al 2 O 3 NC thin films were examined by variable angle spectroscopic ellipsometry in the wide spectral range of 246-1688 nm, accounting the surface characteristics in the optical stack model, and the obtained results are expected to be unique. Additionally, a thickness-dependent blueshift (631-590 nm) of surface plasmon resonance peak was observed in the absorption spectra. These findings of the plasmonic Au/Al 2 O 3 NC films may allow the design and fabrication of small, compact, and efficient devices for optoelectronic and photonic applications.

Chemically grafted polymeric filters for chemical sensors: Hyperbranched poly(acrylic acid) films incorporating {Beta}-cyclodextrin receptors and amine-functionalized filter layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dermody, D.L.; Peez, R.F.; Bergbreiter, D.E.

1999-02-02

The authors report a new molecular-filter approach for enhancing the selectivity of chemical sensors. Specifically, they describe electrochemical sensors prepared from Au electrodes coated with {beta}-cyclodextrin-functionalized, hyperbranched poly(acrylic acid)(PAA) films capped with a chemically grafted, ultrathin polyamine layer. The hyperbranched PAA film is a highly functionalized framework for covalently binding the {beta}-cyclodextrin molecular receptors. The thin, grafted polyamine overlayer acts as a pH-sensitive molecular filter that selectively passes suitably charged analytes. Poly(amidoamine) dendrimers or poly-D-lysine is used as 10--15-nm-thick filter layers. The results show that at low pH, when the polyamines are fully protonated, positively charged redox probe molecules, suchmore » as benzyl viologen (BV), do not permeate the filter layer. However, at high pH, when the filter layer is uncharged, BV penetrates the filter layer and is reduced at the electrode. The opposite pH dependence is observed for negatively charged redox molecules such as anthraquinone-2-sulfonate (AQS). Both BV and AQS specifically interact with the {beta}-cyclodextrin receptors underlying the polyamine filter layers.« less

Metamaterial absorber for molecular detection and identification (Conference Presentation)

NASA Astrophysics Data System (ADS)

Tanaka, Takuo

2017-03-01

Metamaterial absorber was used for a background-suppressed surface-enhanced molecular detection technique. By utilizing the resonant coupling between plasmonic modes of a metamaterial absorber and infrared (IR) vibrational modes of a self-assembled monolayer (SAM), attomole level molecular sensitivity was experimentally demonstrated. IR absorption spectroscopy of molecular vibrations is of importance in chemical, material, medical science and so on, since it provides essential information of the molecular structure, composition, and orientation. In the vibrational spectroscopic techniques, in addition to the weak signals from the molecules, strong background degrades the signal-to-noise ratio, and suppression of the background is crucial for the further improvement of the sensitivity. Here, we demonstrate low-background resonant Surface enhanced IR absorption (SEIRA) by using the metamaterial IR absorber that offers significant background suppression as well as plasmonic enhancement. By using mask-less laser lithography technique, metamaterial absorber which consisted of 1D array of Au micro-ribbons on a thick Au film separated by a transparent gap layer made of MgF2 was fabricated. This metamaterial structure was designed to exhibit an anomalous IR absorption at 3000 cm-1, which spectrally overlapped with C-H stretching vibrational modes. 16-Mercaptohexadecanoic acid (16-MHDA) was used as a test molecule, which formed a 2-nm thick SAM with their thiol head-group chemisorbed on the Au surface. In the FTIR measurements, the symmetric and asymmetric C-H stretching modes were clearly observed as reflection peaks within a broad plasmonic absorption of the metamaterial, and 1.8 attomole molecular sensitivity was experimentally demonstrated.

Effect of doping on the forward current-transport mechanisms in a metal-insulator-semiconductor contact to INP:ZN grown by metal organic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Cova, P.; Singh, A.; Medina, A.; Masut, R. A.

1998-04-01

A detailed study of the effect of doping density on current transport was undertaken in Au metal-insulator-semiconductor (MIS) contacts fabricated on Zn-doped InP layers grown by metal organic vapor phase epitaxy. A recently developed method was used for the simultaneous analysis of the current-voltage ( I- V) and capacitance-voltage ( C- V) characteristics in an epitaxial MIS diode which brings out the contributions of different current-transport mechanisms to the total current. I- V and high-frequency C- V measurements were performed on two MIS diodes at different temperatures in the range 220-395 K. The barrier height at zero bias of Au/InP:Zn MIS diodes, φ0 (1.06 V±10%), was independent both of the Zn-doping density and of the surface preparation. The interface state density distribution Nss as well as the thickness of the oxide layer (2.2±15% nm) unintentionally grown before Au deposition were independent of the Zn-doping concentration in the range 10 16< NA<10 17 cm -3; not so the effective potential barrier χ of the insulator layer and the density of the mid-gap traps. χ was much lower for the highly-doped sample. Our results indicate that at high temperatures, independent of the Zn-doping concentration, the interfacial layer-thermionic (ITE) and interfacial layer-diffusion (ID) mechanisms compete with each other to control the current transport. At intermediate temperatures, however, ITE and ID will no longer be the only dominant mechanisms in the MIS diode fabricated on the highly-doped sample. In this case, the assumption of a generation-recombination current permits a better fit to the experimental data. Analysis of the data suggests that the generation-recombination current, observed only in the highly-doped sample, is associated with an increase in the Zn-doping density. From the forward I- V data for this diode we obtained the energy level (0.60 eV from the conduction band) for the most effective recombination centers.

Molecular dynamics simulation of shock wave and spallation phenomena in metal foils irradiated by femtosecond laser pulse

NASA Astrophysics Data System (ADS)

Zhakhovsky, Vasily; Demaske, Brian; Inogamov, Nail; Oleynik, Ivan

2010-03-01

Femtosecond laser irradiation of metals is an effective technique to create a high-pressure frontal layer of 100-200 nm thickness. The associated ablation and spallation phenomena can be studied in the laser pump-probe experiments. We present results of a large-scale MD simulation of ablation and spallation dynamics developing in 1,2,3μm thick Al and Au foils irradiated by a femtosecond laser pulse. Atomic-scale mechanisms of laser energy deposition, transition from pressure wave to shock, reflection of the shock from the rear-side of the foil, and the nucleation of cracks in the reflected tensile wave, having a very high strain rate, were all studied. To achieve a realistic description of the complex phenomena induced by strong compression and rarefaction waves, we developed new embedded atom potentials for Al and Au based on cold pressure curves. MD simulations revealed the complex interplay between spallation and ablation processes: dynamics of spallation depends on the pressure profile formed in the ablated zone at the early stage of laser energy absorption. It is shown that the essential information such as material properties at high strain rate and spall strength can be extracted from the simulated rear-side surface velocity as a function of time.

Emission and Dynamics of Charge Carriers in Uncoated and Organic/Metal Coated Semiconductor Nanowires

NASA Astrophysics Data System (ADS)

Kaveh Baghbadorani, Masoud

In this dissertation, the dynamics of excitons in hybrid metal/organic/nanowire structures possessing nanometer thick deposited molecular and metal films on top of InP and GaAs nanowire (NW) surfaces were investigated. Optical characterizations were carried out as a function of the semiconductor NW material, design, NW size and the type and thickness of the organic material and metal used. Hybrid organic and plasmonic semiconductor nanowire heterostructures were fabricated using organic molecular beam deposition technique. I investigated the photon emission of excitons in 150 nm diameter polytype wurtzite/zincblende InP NWs and the influence of a few ten nanometer thick organic and metal films on the emission using intensity- and temperature-dependent time-integrated and time resolved (TR) photoluminescence (PL). The plasmonic NWs were coated with an Aluminum quinoline (Alq3) interlayer and magnesium-silver (Mg0.9:Ag0.1) top layer. In addition, the nonlinear optical technique of heterodyne four-wave mixing was used (in collaboration with Prof. Wolfgang Langbein, University of Cardiff) to study incoherent and coherent carrier relaxation processes on bare nanowires on a 100 femtosecond time-scale. Alq3 covered NWs reveal a stronger emission and a longer decay time of exciton transitions indicating surface state passivation at the Alq3/NW interface. Alq3/Mg:Ag NWs reveal a strong quenching of the exciton emission which is predominantly attributed to Forster energy-transfer from excitons to plasmon oscillations in the metal cluster film. Changing the Mg:Ag to gold and the organic Alq3 spacer layer to PTCDA leads to a similar behavior, but the PL quenching is strongly increased. The observed behavior is attributed to a more continuous gold deposition leading to an increased Forster energy transfer and to a metal induced band-bending. I also investigated ensembles of bare and gold/Alq3 coated GaAs-AlGaAs-GaAs core shell NWs of 130 nm diameter. Plasmonic NWs with Au coating reveal a significant reduction of the PL intensity compared with the uncoated NWs. Organic-plasmonic NWs with an additional Alq3 interlayer show a noticeably stronger PL intensity which increases with rising Alq3 spacer thickness. Metal induced band bending is mainly attributed to be responsible for the PL quenching. TR PL measurements support our interpretation by showing an increase in the exciton decay times as we increase the spacer thickness. Au coated NWs also reveal a strong polarization dependent absorption which is mainly due to the significant dielectric mismatch between the nanowires and the adjacent vacuum environment. Finally, the amplified spontaneous emission (ASE) and possible plasmonic NW lasing from hybrid plasmonic core-shell GaAs NW heterostructures was investigated. The plasmonic heterostructures are composed of either bare NWs on an Au coated glass substrate or Au coated NWs on a bare glass substrate. Intensity-dependent PL on plasmonic NW samples reveals a super linear increase of the PL intensities which is attributed to an ASE at a threshold energy fluence of 1 GW/cm 2. Measurements above the threshold power reveal few weakly resolved broad bands around the maximum emission of the PL band which suggest plasmonic film induced lasing. This interpretation is supported by the fact that lasing from such 100 nm narrow uncoated GaAs NWs is not possible.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katoch, Neha, E-mail: nehakatoch2@gmail.com; Kapoor, Pooja; Sharma, Munish

We report stability and electronic properties of benzene molecule adsorbed on the Au atomic layer within the framework of density function theory (DFT). Horizontal configuration of benzene on the top site of Au monolayer prefers energetically over other studied configurations. On the adsorption of benzene, the ballistic conductance of Au monolayer is found to decrease from 4G{sub 0} to 2G{sub 0} suggesting its applications for the fabrications of organic sensor devices based on the Au atomic layers.

Investigation of the thickness non-uniformity of the very thin silicon-strip detectors

NASA Astrophysics Data System (ADS)

Liu, Qiang; Ye, Yanlin; Li, Zhihuan; Lin, Chengjian; Jia, Huiming; Ge, Yucheng; Li, Qite; Lou, Jianling; Yang, Xiaofei; Yang, Biao; Feng, Jun; Zang, Hongliang; Chen, Zhiqiang; Liu, Yang; Liu, Wei; Chen, Sidong; Yu, Hanzhou; Li, Jingjing; Zhang, Yun; Yang, Feng; Yang, Lei; Ma, Nanru; Sun, Lijie; Wang, Dongxi

2018-07-01

The properties of some very thin (∼ 20 μm) large-area Single-sided Silicon-Strip Detectors (SSSDs) were investigated by using the 12C-particles elastically scattered from a Au target. In the detection system, each thin SSSD was installed in front of a thick (300 μm or 500 μm) Double-sided Silicon-Strip Detector (DSSD) to form a ΔE - E particle-telescope. The energy calibration of these detectors was realized by varying the beam energy and also by the irradiation from a three-component α-particle source. The thickness distribution each SSSD is precisely determined from the energy loss in the thin layer, which was independently measured by the corresponding DSSD. It is found that, for the SSSD with the nominal thicknesses of ∼ 20 μm, the real thickness may vary by several μm over the active area. The reason for this large non-uniformity still needs to be investigated. For the present application, this non-uniformity could be corrected according to the known pixel-thickness. This correction allows to restore a good particle identification (PID) performance for the entire large-area detector, the importance of which is demonstrated by an example of measuring the cluster-decays of the highly-excited resonant states in 16O.

Improvement on controllable fabrication of streptavidin-modified three-layer core-shell Fe3O4@SiO2@Au magnetic nanocomposites with low fluorescence background.

PubMed

Jiang, Hongrong; Zeng, Xin; Xi, Zhijiang; Liu, Ming; Li, Chuanyan; Li, Zhiyang; Jin, Lian; Wang, Zhifei; Deng, Yan; He, Nongyue

2013-04-01

In present study, we put forward an approach to prepare three-layer core-shell Fe3O4@SiO2@Au magnetic nanocomposites via the combination of self-assembling, seed-mediated growing and multi-step chemical reduction. The Fe3O4@SiO2@Au magnetic nanocomposites were analyzed and characterized by transmission electron microscope (TEM), scanning electronic microscope (SEM), energy dispersive spectrometer analysis (EDS), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM), and ultraviolet and visible spectrophotometer (UV-Vis). TEM and SEM characterizations showed that the FeO4@SiO2@Au nanocomposites were obtained successfully with three-layer structures, especially a layer of thin, smooth and continuous gold shell. The average diameter of Fe3O4@SiO2@Au nanocomposites was about 600 nm and an excellent dispersity was observed for the as-prepared nanoparticles. EDS characterizations demonstrated that the nanocomposites contained three elements of the precursors, Fe, Si, and Au. Furthermore, FT-IR showed that the silica and gold shell were coated successfully. UV-Vis and VSM characterizations showed that the Fe3O4@SiO2@Au nanocomposites exhibited good optical and magnetic property, and the saturation magnetization was 25.76 emu/g. In conclusion, the Fe3O4@SiO2@Au magnetic nanocomposites with three-layer core-shell structures were prepared. Furthermore, Fe3O4@SiO2@Au magnetic nanocomposites were modified with streptavidin (SA) successfully, and it was validated that they performed low fluorescence background, suggesting that they should have good applications especially in bioassay based on fluorescence detection through bonding the biotinylated fluorescent probes.

High-Performance Ultrathin Active Chiral Metamaterials.

PubMed

Wu, Zilong; Chen, Xiaodong; Wang, Mingsong; Dong, Jianwen; Zheng, Yuebing

2018-05-22

Ultrathin active chiral metamaterials with dynamically tunable and responsive optical chirality enable new optical sensors, modulators, and switches. Herein, we develop ultrathin active chiral metamaterials of highly tunable chiroptical responses by inducing tunable near-field coupling in the metamaterials and exploit the metamaterials as ultrasensitive sensors to detect trace amounts of solvent impurities. To demonstrate the active chiral metamaterials mediated by tunable near-field coupling, we design moiré chiral metamaterials (MCMs) as model metamaterials, which consist of two layers of identical Au nanohole arrays stacked upon one another in moiré patterns with a dielectric spacer layer between the Au layers. Our simulations, analytical fittings, and experiments reveal that spacer-dependent near-field coupling exists in the MCMs, which significantly enhances the spectral shift and line shape change of the circular dichroism (CD) spectra of the MCMs. Furthermore, we use a silk fibroin thin film as the spacer layer in the MCM. With the solvent-controllable swelling of the silk fibroin thin films, we demonstrate actively tunable near-field coupling and chiroptical responses of the silk-MCMs. Impressively, we have achieved the spectral shift over a wavelength range that is more than one full width at half-maximum and the sign inversion of the CD spectra in a single ultrathin (1/5 of wavelength in thickness) MCM. Finally, we apply the silk-MCMs as ultrasensitive sensors to detect trace amounts of solvent impurities down to 200 ppm, corresponding to an ultrahigh sensitivity of >10 5 nm/refractive index unit (RIU) and a figure of merit of 10 5 /RIU.

Boundary layer friction of solvate ionic liquids as a function of potential.

PubMed

Li, Hua; Rutland, Mark W; Watanabe, Masayoshi; Atkin, Rob

2017-07-01

Atomic force microscopy (AFM) has been used to investigate the potential dependent boundary layer friction at solvate ionic liquid (SIL)-highly ordered pyrolytic graphite (HOPG) and SIL-Au(111) interfaces. Friction trace and retrace loops of lithium tetraglyme bis(trifluoromethylsulfonyl)amide (Li(G4) TFSI) at HOPG present clearer stick-slip events at negative potentials than at positive potentials, indicating that a Li + cation layer adsorbed to the HOPG lattice at negative potentials which enhances stick-slip events. The boundary layer friction data for Li(G4) TFSI shows that at HOPG, friction forces at all potentials are low. The TFSI - anion rich boundary layer at positive potentials is more lubricating than the Li + cation rich boundary layer at negative potentials. These results suggest that boundary layers at all potentials are smooth and energy is predominantly dissipated via stick-slip events. In contrast, friction at Au(111) for Li(G4) TFSI is significantly higher at positive potentials than at negative potentials, which is comparable to that at HOPG at the same potential. The similarity of boundary layer friction at negatively charged HOPG and Au(111) surfaces indicates that the boundary layer compositions are similar and rich in Li + cations for both surfaces at negative potentials. However, at Au(111), the TFSI - rich boundary layer is less lubricating than the Li + rich boundary layer, which implies that anion reorientations rather than stick-slip events are the predominant energy dissipation pathways. This is confirmed by the boundary friction of Li(G4) NO 3 at Au(111), which shows similar friction to Li(G4) TFSI at negative potentials due to the same cation rich boundary layer composition, but even higher friction at positive potentials, due to higher energy dissipation in the NO 3 - rich boundary layer.

Plasmonic extinction in gold nanoparticle-polymer films as film thickness and nanoparticle separation decrease below resonant wavelength

NASA Astrophysics Data System (ADS)

Dunklin, Jeremy R.; Bodinger, Carter; Forcherio, Gregory T.; Keith Roper, D.

2017-01-01

Plasmonic nanoparticles embedded in polymer films enhance optoelectronic properties of photovoltaics, sensors, and interconnects. This work examined optical extinction of polymer films containing randomly dispersed gold nanoparticles (AuNP) with negligible Rayleigh scattering cross-sections at particle separations and film thicknesses less than (sub-) to greater than (super-) the localized surface plasmon resonant (LSPR) wavelength, λLSPR. Optical extinction followed opposite trends in sub- and superwavelength films on a per nanoparticle basis. In ˜70-nm-thick polyvinylpyrrolidone films containing 16 nm AuNP, measured resonant extinction per particle decreased as particle separation decreased from ˜130 to 76 nm, consistent with trends from Maxwell Garnett effective medium theory and coupled dipole approximation. In ˜1-mm-thick polydimethylsiloxane films containing 16-nm AuNP, resonant extinction per particle plateaued at particle separations ≥λLSPR, then increased as particle separation radius decreased from ˜514 to 408 nm. Contributions from isolated particles, interparticle interactions and heterogeneities in sub- and super-λLSPR films containing AuNP at sub-λLSPR separations were examined. Characterizing optoplasmonics of thin polymer films embedded with plasmonic NP supports rational development of optoelectronic, biomedical, and catalytic activity using these nanocomposites.

Electrodeposition of catalytic and magnetic gold nanoparticles on dendrimer-carbon nanotube layer-by-layer films.

PubMed

Siqueira, José R; Gabriel, Rayla C; Zucolotto, Valtencir; Silva, Anielle C A; Dantas, Noelio O; Gasparotto, Luiz H S

2012-11-07

Magnetic and catalytic gold nanoparticles were electrodeposited through potential pulse on dendrimer-carbon nanotube layer-by-layer (LbL) films. A plasmon absorption band at about 550 nm revealed the presence of nanoscale gold in the film. The location of the Au nanoparticles in the film was clearly observed by selecting the magnetic force microscopy mode. To our knowledge, this is the first report on the electrochemical synthesis of magnetic Au nanoparticles. In addition to the magnetic properties, the Au nanoparticles also exhibited high catalytic activity towards ethanol and glycerol oxidation in alkaline medium.

Improved light extraction efficiency in GaN-based light emitting diode by nano-scale roughening of p-GaN surface.

PubMed

Park, Sang Jae; Sadasivam, Karthikeyan Giri; Chung, Tae Hoon; Hong, Gi Cheol; Kim, Jin Bong; Kim, Sang Mook; Park, Si-Hyun; Jeon, Seong-Ran; Lee, June Key

2008-10-01

Improvement in light extraction efficiency of Ultra Violet-Light Emitting Diode (UV-LED) is achieved by nano-scale roughening of p-type Gallium Nitride (p-GaN) surface. The process of surface roughening is carried out by using self assembled gold (Au) nano-clusters with support of nano-size silicon-oxide (SiO2) pillars on p-GaN surface as a dry etching mask and by p-GaN regrowth in the regions not covered by the mask after dry etching. Au nano-clusters are formed by rapid thermal annealing (RTA) process carried out at 600 degrees C for 1 min using 15 nm thick Au layer on top of SiO2. The p-GaN roughness is controlled by p-GaN regrowth time. Four different time values of 15 sec, 30 sec, 60 sec and 120 sec are considered for p-GaN regrowth. Among the four different p-GaN regrowth time values 30 sec regrown p-GaN sample has the optimum roughness to increase the electroluminescence (EL) intensity to a value approximately 60% higher than the EL intensity of a conventional LED.

A Dry-Etch Process for Low Temperature Superconducting Transition Edge Sensors for Far Infrared Bolometer Arrays

NASA Technical Reports Server (NTRS)

Allen, Christine A.; Chervenak, James A.; Hsieh, Wen-Ting; McClanahan, Richard A.; Miller, Timothy M.; Mitchell, Robert; Moseley, S. Harvey; Staguhn, Johannes; Stevenson, Thomas R.

2003-01-01

The next generation of ultra-low power bolometer arrays, with applications in far infrared imaging, spectroscopy and polarimetry, utilizes a superconducting bilayer as the sensing element to enable SQUID multiplexed readout. Superconducting transition edge sensors (TES s) are being produced with dual metal systems of superconductinghormal bilayers. The transition temperature (Tc) is tuned by altering the relative thickness of the superconductor with respect to the normal layer. We are currently investigating MoAu and MoCu bilayers. We have developed a dry-etching process for MoAu TES s with integrated molybdenum leads, and are working on adapting the process to MoCu. Dry etching has the advantage over wet etching in the MoAu system in that one can achieve a high degree of selectivity, greater than 10, using argon ME, or argon ion milling, for patterning gold on molybdenum. Molybdenum leads are subsequently patterned using fluorine plasma.. The dry-etch technique results in a smooth, featureless TES with sharp sidewalls, no undercutting of the Mo beneath the normal metal, and Mo leads with high critical current. The effects of individual processing parameters on the characteristics of the transition will be reported.

Ti:Pt:Au:Ni thin-film CVD diamond sensor ability for charged particle detection.

PubMed

Kasiwattanawut, Haruetai; Tchouaso, Modeste Tchakoua; Prelas, Mark A

2018-05-22

This work demonstrates the development of diamond sensors with reliable contacts using a new metallization formula, which can operate under high-pressure gas environment. The metallization was created using thin film layers of titanium, platinum, gold and nickel deposited on a single crystal electronic grade CVD diamond chip. The contacts were 2 mm in diameter with thickness of 50/5/20/150 nm of Ti:Pt:Au:Ni. The optimum operating voltage of the sensor was determined from the current-voltage measurements. The sensor was calibrated with 239 Pu and 241 Am alpha radiation sources at 300 V. The energy resolution of the Ti:Pt:Au:Ni diamond sensor was determined to be 7.6% at 5.2 MeV of 239 Pu and 2.2% at 5.48 MeV of 241 Am. The high-pressure gas loading environment under which this sensor was used is discussed. Specifically, experimental observations are described using hydrogen loading of nickel as a means of initiating low energy nuclear reactions. No neutrons, electrons, ions or other ionizing radiations were observed in these experiments. Copyright © 2018 Elsevier Ltd. All rights reserved.

Quantitative Phase Composition of TiO 2-Coated Nanoporous-Au Monoliths by X-ray Absorption Spectroscopy and Correlations to Catalytic

DOE PAGES

Bagge-Hansen, Michael; Wichmann, Andre; Wittstock, Arne; ...

2014-02-03

Porous titania/metal composite materials have many potential applications in the fields of green catalysis, energy harvesting, and storage in which both the overall morphology of the nanoporous host material and the crystallographic phase of the titania (TiO 2) guest determine the material’s performance. New insights into the structure–function relationships of these materials were obtained by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy that, for example, provides quantitative crystallographic phase composition from ultrathin, nanostructured titania films, including sensitivity to amorphous components. We demonstrate that crystallographic phase, morphology, and catalytic activity of TiO 2-functionalized nanoporous gold (np-Au) can be controlled by amore » simple annealing procedure (T < 1300 K). The material was prepared by atomic layer deposition of ~2 nm thick TiO 2 on millimeter-sized samples of np-Au (40–50 nm mean ligament size) and catalytically investigated with respect to aerobic CO oxidation. Moreover, the annealing-induced changes in catalytic activity are correlated with concurrent morphology and phase changes as provided by cross-sectional scanning electron microscopy, transmission electron microscopy, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy.« less

Synthesis, structure, and bonding in K12Au21Sn4. A polar intermetallic compound with dense Au20 and open AuSn4 layers.

PubMed

Li, Bin; Kim, Sung-Jin; Miller, Gordon J; Corbett, John D

2009-12-07

The new phase K(12)Au(21)Sn(4) has been synthesized by direct reaction of the elements at elevated temperatures. Single crystal X-ray diffraction established its orthorhombic structure, space group Pmmn (No. 59), a = 12.162(2); b = 18.058(4); c = 8.657(2) A, V = 1901.3(7) A(3), and Z = 2. The structure consists of infinite puckered sheets of vertex-sharing gold tetrahedra (Au(20)) that are tied together by thin layers of alternating four-bonded-Sn and -Au atoms (AuSn(4)). Remarkably, the dense but electron-poorer blocks of Au tetrahedra coexist with more open and saturated Au-Sn layers, which are fragments of a zinc blende type structure that maximize tetrahedral heteroatomic bonding outside of the network of gold tetrahedra. LMTO band structure calculations reveal metallic properties and a pseudogap at 256 valence electrons per formula unit, only three electrons fewer than in the title compound and at a point at which strong Au-Sn bonding is optimized. Additionally, the tight coordination of the Au framework atoms by K plays an important bonding role: each Au tetrahedra has 10 K neighbors and each K atom has 8-12 Au contacts. The appreciably different role of the p element Sn in this structure from that in the triel members in K(3)Au(5)In and Rb(2)Au(3)Tl appears to arise from its higher electron count which leads to better p-bonding (valence electron concentrations = 1.32 versus 1.22).

Au/NiFe/M(Au, MoS2, graphene) trilayer magnetoplasmonics DNA-hybridized sensors with high record of sensitivity

NASA Astrophysics Data System (ADS)

Faridi, Ehsan; Moradi, Maryam; Ansari, Narges; Ghasemi, Amir Hossein Baradaran; Afshar, Amir; Mohseni, Seyed Majid

2017-12-01

The demonstration of biosensors based on the surface plasmon effect holds promise for future high-sensitive electrodeless biodetection. The combination of magnetic effects with surface plasmon waves brings additional freedom to improve sensitivity and signal selectivity. Stacking biosensors with two-dimensional (2-D) materials, e.g., graphene (Gr) and MoS2, can influence plasmon waves and facilitate surface physiochemical properties as additional versatility aspects. We demonstrate magnetoplasmonic biosensors through the detuning of surface plasmon oscillation modes affected by magnetic effect via the presence of the NiFe (Py) layer and different light absorbers of Gr, MoS2, and Au ultrathin layers in three stacks of Au/Py/M(MoS2, Gr, Au) trilayers. We found minimum reflection, resonance angle shift, and transverse magneto-optical Kerr effect (TMOKE) responses of all sensors in the presence of the ss-DNA monolayer. Very few changes of ˜5×10-7 in the ss-DNA's refractive index result in valuable TMOKE response. We found that the presence of three-layer Gr and two-layer MoS2 on top of the Au/Py bilayer can dramatically increase the sensitivity by nine and four times, respectively, than the conventional Au/Co/Au trilayer. Our results show the highest reported DNA sensitivity based on the coupling of light with 2-D materials in magnetoplasmonic devices.

Reflective coating for near-infrared immersion gratings

NASA Astrophysics Data System (ADS)

Kuzmenko, Paul J.; Ikeda, Yuji; Kobayashi, Naoto; Mirkarimi, Paul B.; Alameda, Jennifer B.

2012-09-01

Achieving high reflectivity from an immersed grating facet can be challenging in the near infrared. The reflectivity of metallic coatings in common use, such as Al and Cr/Au, decrease with decreasing wavelength in the near IR. A layer of copper on ZnSe or ZnS should have a high, immersed reflectivity based on tabulated values of refractive index, but in fact performs poorly. We attribute this to a chemical reaction between the copper and the selenium or sulfur. A non-reactive intermediate layer can prevent this problem. Since reflectivity at an interface increases with increasing difference in refractive index, it is beneficial to choose an intermediate layer of low index. A further improvement is gained by adjusting the layer thickness so that reflections from the two interfaces of the intermediate layer add constructively. We sputtered 130 nm of SiO2 onto ZnSe and ZnS substrates followed by 200 nm of Cu. The copper was then coated with 5 nm of SiC as a protective capping layer. Immersed reflectivity measured shortly after coating exceeded 95% between 1500 and 1100 nm and exceeded 90% down to 850 nm. A repeat measurement after long term exposure to high humidity conditions showed no changes.

Infrared reflective coatings for building and automobile glass windows for heat protection

NASA Astrophysics Data System (ADS)

Butt, M. A.; Fomchenkov, S. A.; Kazanskiy, N. L.; Ullah, A.; Ali, R. Z.; Habib, M.

2017-04-01

Sunlight can be used a source of light in buildings and automobiles, however infrared wavelengths in sunlight result in heating. In this work, Infrared Reflective Coatings are designed using thin films to transmit visible wavelengths 400 700 nm while reflecting infrared wavelengths above 700 nm. Three different design approaches have been used, namely single layer of metal, sandwich structure and multilayer design. Four metals (Ag, Au, Al and Cu) and two dielectrics (TiO2 and SiO2) are used in this study. Designs with Ag show maximum reflection of Infrared wavelengths in all designs. Sandwich structures of TiO2-Ag-TiO2 on substrate with 22 nm of thickness for each layer show the maximum transmission of 87% in the visible region and maximum reflection of Infrared wavelengths.

The Morphology of Silver Layers on SU8 polymers prepared by Electroless Deposition

NASA Astrophysics Data System (ADS)

Dutta, Aniruddha; Yuan, Biao; Heinrich, Helge; Grabill, Chris; Williams, Henry; Kuebler, Stephen; Bhattacharya, Aniket

2010-03-01

Silver was deposited onto the functionalized surface of polymeric SU-8 where gold nanoparticles (Au-NPs) act as nucleation sites using electroless metallization chemistry. Here we report on the evolution of the nanoscale morphology of deposited Ag studied by Transmission Electron Microscopy (TEM). In TEM of sample cross sections correlations between the original gold and the silver nanoparticles were obtained while plan-view TEM results showed the distribution of nanoparticles on the surface. Scanning TEM with a high-angle annular dark field detector was used to obtain atomic number contrast. The morphology of the deposited Ag was controlled through the presence and absence of gum Arabic. The thickness and height fluctuations of the Ag layer were determined as a function of time and a statistical analysis of the growth process was conducted for the initial deposition periods.

The structure of epitaxial V2O3 films and their surfaces: A medium energy ion scattering study

NASA Astrophysics Data System (ADS)

Window, A. J.; Hentz, A.; Sheppard, D. C.; Parkinson, G. S.; Woodruff, D. P.; Unterberger, W.; Noakes, T. C. Q.; Bailey, P.; Ganduglia-Pirovano, M. V.; Sauer, J.

2012-11-01

Medium energy ion scattering, using 100 keV H+ incident ions, has been used to investigate the growth of epitaxial films, up to thicknesses of ~ 200 Å, of V2O3 on both Pd(111) and Au(111). Scattered-ion energy spectra provide a measure of the average film thickness and the variations in this thickness, and show that, with suitable annealing, the crystalline quality is good. Plots of the scattering yield as a function of scattering angle, so-called blocking curves, have been measured for two different incidence directions and have been used to determine the surface structure. Specifically, scattering simulations for a range of different model structures show poor agreement with experiment for half-metal (….V'O3V) and vanadyl (….V'O3V=O) terminations, with and without surface interlayer relaxations. However, good agreement with experiment is found for the modified oxygen-termination structure, first proposed by Kresse et al., in which a subsurface V half-metal layer is moved up into the outermost V buckled metal layer to produce a VO2 overlayer on the underlying V2O3, with an associated layer structure of ….O3VV''V 'O3. This result is consistent with the predictions of thermodynamic equilibrium at the surface under the surface preparation conditions, but is at variance with the conclusions of earlier studies of this system that have favoured the vanadyl termination. The results of these previous studies are re-evaluated in the light of the new result.

Pickup protons and pressure-balanced structures: Voyager 2 observations in merged interaction regions near 35 AU

NASA Astrophysics Data System (ADS)

Burlaga, L. F.; Ness, N. F.; Belcher, J. W.; Szabo, A.; Isenberg, P. A.; Lee, M. A.

1994-11-01

Five pressure-balanced structures, each with a scale of the order of a few hundredths of an astonomical unit (AU), were identified in two merged interaction regions (MIRs) near 35 AU in the Voyager 2 plasma and magnetic field data. They include a tangential discontinuity, simple and complex magnetic holes, slow correlated variations among the plasma and magnetic field parameters, and complex uncorrelated variations among the parameters. The changes in the magnetic pressure in these events are balanced by changes in the pressure of interstellar pickup protons. Thus the pickup protons probably play a major role in the dynamics of the MIRs. The solar wind proton and electron pressures are relatively unimportant in the MIRs at 35 AU and beyond. The region near 35 AU is transition region: the Sun is the source of the magnetic field, but the interstellar medium in source of pickups protons. Relative to the solar wind proton guyroadius, the thicknesses of the discontinuities and simple magnetic holes observed near 35 AU are at least an order of magnitude greater than those observed at 1 AU. However, the thicknesses of the tangential discontinuity and simple magnetic holes observed near 35 AU (in units of the pickup proton Larmor radius) are comparable to those observed at 1 AU (in units of the solar wind proton gyroradius). Thus the gyroradius of interstellar pickup protons controls the thickness of current sheets near 35 AU. We determine the interstellar pickup proton pressure in the PBSs. Using a model for the pickup proton temperature, we estimate that the average interstellar pickup proton pressure, temperature, and density in the MIRs at 35 AU are (0.53 +/- 0.14) x 10-12 erg/cu cm, (5.8 +/- 0.4) x 106 K and (7 +/- 2) x 10-4/cu cm.

Synthesis of Ti3AuC2, Ti3Au2C2 and Ti3IrC2 by noble metal substitution reaction in Ti3SiC2 for high-temperature-stable Ohmic contacts to SiC

NASA Astrophysics Data System (ADS)

Fashandi, Hossein; Dahlqvist, Martin; Lu, Jun; Palisaitis, Justinas; Simak, Sergei I.; Abrikosov, Igor A.; Rosen, Johanna; Hultman, Lars; Andersson, Mike; Lloyd Spetz, Anita; Eklund, Per

2017-08-01

The large class of layered ceramics encompasses both van der Waals (vdW) and non-vdW solids. While intercalation of noble metals in vdW solids is known, formation of compounds by incorporation of noble-metal layers in non-vdW layered solids is largely unexplored. Here, we show formation of Ti3AuC2 and Ti3Au2C2 phases with up to 31% lattice swelling by a substitutional solid-state reaction of Au into Ti3SiC2 single-crystal thin films with simultaneous out-diffusion of Si. Ti3IrC2 is subsequently produced by a substitution reaction of Ir for Au in Ti3Au2C2. These phases form Ohmic electrical contacts to SiC and remain stable after 1,000 h of ageing at 600 °C in air. The present results, by combined analytical electron microscopy and ab initio calculations, open avenues for processing of noble-metal-containing layered ceramics that have not been synthesized from elemental sources, along with tunable properties such as stable electrical contacts for high-temperature power electronics or gas sensors.

Ultrastable BSA-capped gold nanoclusters with a polymer-like shielding layer against reactive oxygen species in living cells

NASA Astrophysics Data System (ADS)

Zhou, Wenjuan; Cao, Yuqing; Sui, Dandan; Guan, Weijiang; Lu, Chao; Xie, Jianping

2016-05-01

The prevalence of reactive oxygen species (ROS) production and the enzyme-containing intracellular environment could lead to the fluorescence quenching of bovine serum albumin (BSA)-capped gold nanoclusters (AuNCs). Here we report an efficient strategy to address this issue, where a polymer-like shielding layer is designed to wrap around the Au core to significantly improve the stability of AuNCs against ROS and protease degradation. The key of our design is to covalently incorporate a thiolated AuNC into the BSA-AuNC via carbodiimide-activated coupling, leading to the formation of a AuNC pair inside the cross-linked BSA molecule. The as-designed paired AuNCs in BSA (or BSA-p-AuNCs for short) show improved performances in living cells.The prevalence of reactive oxygen species (ROS) production and the enzyme-containing intracellular environment could lead to the fluorescence quenching of bovine serum albumin (BSA)-capped gold nanoclusters (AuNCs). Here we report an efficient strategy to address this issue, where a polymer-like shielding layer is designed to wrap around the Au core to significantly improve the stability of AuNCs against ROS and protease degradation. The key of our design is to covalently incorporate a thiolated AuNC into the BSA-AuNC via carbodiimide-activated coupling, leading to the formation of a AuNC pair inside the cross-linked BSA molecule. The as-designed paired AuNCs in BSA (or BSA-p-AuNCs for short) show improved performances in living cells. Electronic supplementary information (ESI) available: Detailed experimental materials, apparatus, experimental procedures and characterization data. See DOI: 10.1039/c6nr02178f

Homoepitaxial electrodeposition on reconstructed and unreconstructed Au(100): An in-situ STM study

NASA Astrophysics Data System (ADS)

Al-Shakran, Mohammad; Kibler, Ludwig A.; Jacob, Timo

2015-01-01

A study of homoepitaxial electrodeposition on reconstructed and unreconstructed Au(100) surfaces is presented. The growth behavior has been investigated by in-situ scanning tunneling microscopy for Au(100) in contact with 0.1 M H2SO4 + 5 μM K[AuCl4]. It is shown that the initial surface structure is decisive for the emerging Au structures, giving rise to clearly different surface morphologies for electro-crystallization of Au on the unreconstructed and on the reconstructed Au(100) surface. A layer-by-layer growth is observed at more positive potentials for unreconstructed Au(100). The electrodeposition proceeds initially by the formation of Au islands followed by island coalescence due to the high mobility of surface atoms. Monatomic recessed stripes are formed as a result of the coalescence of deposited Au islands. At more negative potentials, the growth of Au proceeds strongly anisotropic on the reconstructed surface by the formation of reconstructed elongated islands.

Gallium hydride vapor phase epitaxy of GaN nanowires

PubMed Central

2011-01-01

Straight GaN nanowires (NWs) with diameters of 50 nm, lengths up to 10 μm and a hexagonal wurtzite crystal structure have been grown at 900°C on 0.5 nm Au/Si(001) via the reaction of Ga with NH3 and N2:H2, where the H2 content was varied between 10 and 100%. The growth of high-quality GaN NWs depends critically on the thickness of Au and Ga vapor pressure while no deposition occurs on plain Si(001). Increasing the H2 content leads to an increase in the growth rate, a reduction in the areal density of the GaN NWs and a suppression of the underlying amorphous (α)-like GaN layer which occurs without H2. The increase in growth rate with H2 content is a direct consequence of the reaction of Ga with H2 which leads to the formation of Ga hydride that reacts efficiently with NH3 at the top of the GaN NWs. Moreover, the reduction in the areal density of the GaN NWs and suppression of the α-like GaN layer is attributed to the reaction of H2 with Ga in the immediate vicinity of the Au NPs. Finally, the incorporation of H2 leads to a significant improvement in the near band edge photoluminescence through a suppression of the non-radiative recombination via surface states which become passivated not only via H2, but also via a reduction of O2-related defects. PMID:21711801

Gallium hydride vapor phase epitaxy of GaN nanowires.

PubMed

Zervos, Matthew; Othonos, Andreas

2011-03-28

Straight GaN nanowires (NWs) with diameters of 50 nm, lengths up to 10 μm and a hexagonal wurtzite crystal structure have been grown at 900°C on 0.5 nm Au/Si(001) via the reaction of Ga with NH3 and N2:H2, where the H2 content was varied between 10 and 100%. The growth of high-quality GaN NWs depends critically on the thickness of Au and Ga vapor pressure while no deposition occurs on plain Si(001). Increasing the H2 content leads to an increase in the growth rate, a reduction in the areal density of the GaN NWs and a suppression of the underlying amorphous (α)-like GaN layer which occurs without H2. The increase in growth rate with H2 content is a direct consequence of the reaction of Ga with H2 which leads to the formation of Ga hydride that reacts efficiently with NH3 at the top of the GaN NWs. Moreover, the reduction in the areal density of the GaN NWs and suppression of the α-like GaN layer is attributed to the reaction of H2 with Ga in the immediate vicinity of the Au NPs. Finally, the incorporation of H2 leads to a significant improvement in the near band edge photoluminescence through a suppression of the non-radiative recombination via surface states which become passivated not only via H2, but also via a reduction of O2-related defects.

Wide-range tuning of the surface plasmon resonance of silver/gold core shell and alloyed nanoparticles

NASA Astrophysics Data System (ADS)

Hubenthal, Frank; Ziegler, Torsten; Hendrich, Christian; Träger, Frank

2004-03-01

For many applications like surface enhanced Raman scattering in which the optical field enhancement associated with surface plasmon excitation is exploited, tunability of this collective resonance over a wide range is required. For this purpose we have prepared Ag/Au core shell and Ag/Au alloyed nanoparticles with different shell thicknesses and different percentages of the two metals. The nanoparticles were made by subsequent deposition of Ag and Au atoms on dielectric substrates followed by diffusion and nucleation or heat treatment. Depending on the Au shell thickness the plasmon frequency can be tuned, e.g. from 2.8 eV (442 nm) to 2.1 eV (590 nm). Annealing of the core-shell nanoparticles causes a shift of the resonance frequency to 2.6 eV. Theoretical modelling allows us to attribute this observation to the production of alloyed nanoparticles. Possible application of the Ag/Au nanoparticles will be discussed.

Encapsulation of Au Nanoparticles on a Silicon Wafer During Thermal Oxidation

PubMed Central

2013-01-01

We report the behavior of Au nanoparticles anchored onto a Si(111) substrate and the evolution of the combined structure with annealing and oxidation. Au nanoparticles, formed by annealing a Au film, appear to “float” upon a growing layer of SiO2 during oxidation at high temperature, yet they also tend to become partially encapsulated by the growing silica layers. It is proposed that this occurs largely because of the differential growth rates of the silica layer on the silicon substrate between the particles and below the particles due to limited access of oxygen to the latter. This in turn is due to a combination of blockage of oxygen adsorption by the Au and limited oxygen diffusion under the gold. We think that such behavior is likely to be seen for other metal–semiconductor systems. PMID:24163715

Tailoring dispersion and aggregation of Au nanoparticles in the BHJ layer of polymer solar cells: plasmon effects versus electrical effects.

PubMed

Kim, Wanjung; Cha, Bong Geun; Kim, Jung Kyu; Kang, Woonggi; Kim, Eunchul; Ahn, Tae Kyu; Wang, Dong Hwan; Du, Qing Guo; Cho, Jeong Ho; Kim, Jaeyun; Park, Jong Hyeok

2014-12-01

Plasmonic effects that arise from embedding metallic nanoparticles (NPs) in polymer solar cells (PSCs) have been extensively studied. Many researchers have utilized metallic NPs in PSCs by either incorporating them into the PSC interlayers (e.g., the hole extraction and electron extraction layers) or blending them into the bulk heterojunction (BHJ) active layer. In such studies, the dispersity of the metallic NPs in each layer may vary due to both the different nature of the ligands and the amount of ligands on the metallic NPs. This in turn can produce different PSC performance parameters. Here, we systematically control the amount of attached organic ligands on Au NPs to control their dispersion behavior in the BHJ active layer of PSCs. By controlling the number of capping organic ligands on the Au NPs, the dispersity of the NPs in the BHJ layer is also controlled and the positive effects (particularly the plasmonic and electrical effects) of the Au NPs in the PSCs are investigated. From the obtained results, we find that the electrical contribution of the Au NPs is a more dominant factor for enhancing cell efficiency when compared to the plasmonic effect. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cell adhesion and proliferation on poly(tetrafluoroethylene) with plasma-metal and plasma-metal-carbon interfaces

NASA Astrophysics Data System (ADS)

Reznickova, Alena; Kvitek, Ondrej; Kolarova, Katerina; Smejkalova, Zuzana; Svorcik, Vaclav

2017-06-01

The aim of this article is to investigate the effect of the interface between plasma activated, gold and carbon coated poly(tetrafluoroethylene) (PTFE) on in vitro adhesion and spreading of mouse fibroblasts (L929). Surface properties of pristine and modified PTFE were studied by several experimental techniques. The thickness of a deposited gold film is an increasing function of the sputtering time, conversely thickness of carbon layer decreases with increasing distance between carbon source and the substrate. Because all the used surface modification techniques take place in inert Ar plasma, oxidized degradation products are formed on the PTFE surface, which affects wettability of the polymer surface. Cytocompatibility tests indicate that on samples with Au/C interface, the cells accumulate on the part of sample with evaporated carbon. Number of L929 cells proliferated on the studied samples is comparable to tissue culture polystyrene standard.

Characterization of high-{kappa} LaLuO{sub 3} thin film grown on AlGaN/GaN heterostructure by molecular beam deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang Shu; Huang Sen; Chen Hongwei

2011-10-31

We report the study of high-dielectric-constant (high-{kappa}) dielectric LaLuO{sub 3} (LLO) thin film that is grown on AlGaN/GaN heterostructure by molecular beam deposition (MBD). The physical properties of LLO on AlGaN/GaN heterostrucure have been investigated with atomic force microscopy, x-ray photoelectron spectroscopy, and TEM. It is revealed that the MBD-grown 16 nm-thick LLO film is polycrystalline with a thin ({approx}2 nm) amorphous transition layer at the LLO/GaN interface. The bandgap of LLO is derived as 5.3 {+-} 0.04 eV from O1s energy loss spectrum. Capacitance-voltage (C-V) characteristics of a Ni-Au/LLO/III-nitride metal-insulator-semiconductor diode exhibit small frequency dispersion (<2%) and reveal amore » high effective dielectric constant of {approx}28 for the LLO film. The LLO layer is shown to be effective in suppressing the reverse and forward leakage current in the MIS diode. In particular, the MIS diode forward current is reduced by 7 orders of magnitude at a forward bias of 1 V compared to a conventional Ni-Au/III-nitride Schottky diode.« less

Au Nanoparticle Sub-Monolayers Sandwiched between Sol-Gel Oxide Thin Films

PubMed Central

Della Gaspera, Enrico; Menin, Enrico; Sada, Cinzia

2018-01-01

Sub-monolayers of monodisperse Au colloids with different surface coverage have been embedded in between two different metal oxide thin films, combining sol-gel depositions and proper substrates functionalization processes. The synthetized films were TiO2, ZnO, and NiO. X-ray diffraction shows the crystallinity of all the oxides and verifies the nominal surface coverage of Au colloids. The surface plasmon resonance (SPR) of the metal nanoparticles is affected by both bottom and top oxides: in fact, the SPR peak of Au that is sandwiched between two different oxides is centered between the SPR frequencies of Au sub-monolayers covered with only one oxide, suggesting that Au colloids effectively lay in between the two oxide layers. The desired organization of Au nanoparticles and the morphological structure of the prepared multi-layered structures has been confirmed by Rutherford backscattering spectrometry (RBS), Secondary Ion Mass Spectrometry (SIMS), and Scanning Electron Microscopy (SEM) analyses that show a high quality sandwich structure. The multi-layered structures have been also tested as optical gas sensors. PMID:29538338

Nanoshells as a high-pressure gauge

NASA Astrophysics Data System (ADS)

Tempere, Jacques; van den Broeck, Nick; Putteneers, Katrijn; Silvera, Isaac

2012-02-01

Nanoshells, consisting of multiple spherical layers, have an extensive list of applications, usually performing the function of a probe. We add a new application to this list in the form of a high-pressure gauge in a Diamond Anvil Cell (DAC). In a DAC, where high pressures are reached by pressing two diamonds together, existing gauges fail at higher pressures because of calibration difficulties and obscuring effects in the diamonds. The nanoshell gauge does not face this issue since its optical spectrum can be engineered by altering the thickness of its layers. Furthermore their properties are measured by broad band optical transmission spectroscopy leading to a very large signal-to-noise ratio even in the multi-megabar pressure regime where ruby measurements become challenging. Theoretical calculations based on the Maxwell equations in a spherical geometry combined with the Vinet equation of state show that a three-layer geometry (SiO2-Au-SiO2) indeed has a measurable pressure-dependent optical response desirable for gauges.

Studies of current-perpendicular-to-plane magnetoresistance (CPP-MR) and current-induced magnetization switching (CIMS)

NASA Astrophysics Data System (ADS)

Kurt, Huseyin

2005-08-01

We present two CPP-MR studies of spin-valves based upon ferromagnetic/nonmagnetic/ferromagnetic (F/N/F) trilayers. We measure the spin-diffusion lengths of N = Pd, Pt, and Au at 4.2K, and both the specific resistances (sample area A times resistance R) and spin-memory-loss of N/Cu interfaces. Pd, Pt and Au are of special device interest because they give perpendicular anisotropy when sandwiching very thin Co layers. Comparing our spin-memory-loss data at Pd/Cu and Pt/Cu interfaces with older data for Nb/Cu and W/Cu gives insight into the importance of spin-orbit coupling in producing such loss. We reproduce and extend prior studies by Eid of 'magnetic activity' at the interface of Co and N-metals (or combinations of N-metals), when the other side of the N-metal contacts a superconductor (S). Our data suggest that magnetic activity may require strong spin-flipping at the N/S interface. We present five studies of a new phenomenon, CIMS, in F1/N/F2 trilayers, with F1 a thick 'polarizing' layer and F2 a thin 'switching' layer. In all prior studies of CIMS, positive current caused the magnetization of F2 to switch from parallel (P) to anti-parallel (AP) to that of F1- 'normal' switching. By judicious addition of impurities to F-metals, we are able to controllably produce both 'normal' and 'inverse' switching- where positive current switches the magnetization of F2 from AP to P to that of F1. In the samples studied, whether the switching is normal or inverse is set by the 'net polarization' produced by F1 and is independent of the properties of F2. As scattering in the bulk of F1 and F2 is essential to producing our results, these results cannot be described by ballistic models, which allow scattering only at interfaces. Most CIMS experiments use Cu as the N-layer due to its low resistivity and long spin-diffusion length. We show that Ag and Au have low enough resistivities and long enough spin-diffusion lengths to be useful alternatives to Cu for some devices. While most technical applications of CIMS require low switching currents, some, like read-heads, require high switching currents. We show that use of a synthetic antiferromagnet can increase the switching current. Manschot et al. recently predicted that the positive critical current for switching from P to AP could be reduced by up to a factor of five by using asymmetric current leads. In magnetically uncoupled samples, we find that highly asymmetric current leads do not significantly reduce the switching current. A CIMS equation given by Katine et al. predicts that lowering the demagnetization field should reduce the switching current. To test this prediction, we compare switching currents for Co/Au/Co(t)/Au nanopillars with t = 1 to 4 nm (where the easy axis should be normal to the layer planes at least for t = 1 and 2 nm) with those for Co/Cu/Co(t)/Au nanopillars (where the easy axis should be in the layer planes). We do not find significant differences in switching currents for the two systems.

Horizontal to vertical spectral ratio measurements in Port-au-Prince (Haiti) area damaged by the 2010 Haiti earthquake

NASA Astrophysics Data System (ADS)

Navarro, M.; Enomoto, T.; Benito, B.; Belizaire, D.; Navarro, D.; García-Jerez, A.; Dorfeuille, J.

2013-05-01

In order to evaluate ground shaking characteristics due to surface soil layers in the urban area of Port-au-Prince, short-period ambient noise observation has been performed approximately in a 500x500m grid. The HVSR method was applied to this set of 36 ambient noise measurement points to determine a distribution map of soil predominant periods. This map reveals a general increasing trend in the period values, from the Miocene conglomerates in the northern and southern parts of the town to the central and western zones formed of Pleistocene and Holocene alluvial deposits respectively, where the shallow geological materials that cover the basement increase in thickness. Shorter predominant periods (less than 0.3 s) were found in mountainous and neighbouring zones, where the thickness of sediments is smaller whereas longer periods (greater than 0.5 s) appear in Holocene alluvial fans, where the thickness of sediments is larger. The shallow shear-wave velocity structure have been estimated by means of inversion of Rayleigh wave dispersion data obtained from vertical-component array records of ambient noise. The measurements were carried out at one open space located in Holocene alluvial deposits, using 3 regular pentagonal arrays with 5, 10 and 20m respectively. Reliable dispersion curves were retrieved for frequencies between 4.0 and 14 Hz, with phase velocity values ranging from 420m/s down to 270 m/s. Finally, the average shear-wave velocity of the upper 30 m (VS30) was inverted for characterization of this geological unit.

A facile approach for reducing the working voltage of Au/TiO2/Au nanostructured memristors by enhancing the local electric field

NASA Astrophysics Data System (ADS)

Arab Bafrani, Hamidreza; Ebrahimi, Mahdi; Bagheri Shouraki, Saeed; Moshfegh, Alireza Z.

2018-01-01

Memristor devices have attracted tremendous interest due to different applications ranging from nonvolatile data storage to neuromorphic computing units. Exploring the role of surface roughness of the bottom electrode (BE)/active layer interface provides useful guidelines for the optimization of the memristor switching performance. This study focuses on the effect of surface roughness of the BE electrode on the switching characteristics of Au/TiO2/Au three-layer memristor devices. An optimized wet-etching treatment condition was found to modify the surface roughness of the Au BE where the measurement results indicate that the roughness of the Au BE is affected by both duration time and solution concentrations of the wet-etching process. Then we fabricated arrays of TiO2-based nanostructured memristors sandwiched between two sets of cross-bar Au electrode lines (junction area 900 μm2). The results revealed a reduction in the working voltages in current-voltage characteristic of the device performance when increasing the surface roughness at the Au(BE)/TiO2 active layer interface. The set voltage of the device (Vset) significantly decreased from 2.26-1.93 V when we increased the interface roughness from 4.2-13.1 nm. The present work provides information for better understanding the switching mechanism of titanium-dioxide-based devices, and it can be inferred that enhancing the roughness of the Au BE/TiO2 active layer interface leads to a localized non-uniform electric field distribution that plays a vital role in reducing the energy consumption of the device.

X-ray standing wave analysis of nanostructures using partially coherent radiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tiwari, M. K., E-mail: mktiwari@rrcat.gov.in; Das, Gangadhar; Bedzyk, M. J.

2015-09-07

The effect of longitudinal (or temporal) coherence on total reflection assisted x-ray standing wave (TR-XSW) analysis of nanoscale materials is quantitatively demonstrated by showing how the XSW fringe visibility can be strongly damped by decreasing the spectral resolution of the incident x-ray beam. The correction for nonzero wavelength dispersion (δλ ≠ 0) of the incident x-ray wave field is accounted for in the model computations of TR-XSW assisted angle dependent fluorescence yields of the nanostructure coatings on x-ray mirror surfaces. Given examples include 90 nm diameter Au nanospheres deposited on a Si(100) surface and a 3 nm thick Zn layer trapped on top amore » 100 nm Langmuir-Blodgett film coating on a Au mirror surface. Present method opens up important applications, such as enabling XSW studies of large dimensioned nanostructures using conventional laboratory based partially coherent x-ray sources.« less

A Roman bronze statuette with gilded silver mask from Sardinia: an EDXRF study

NASA Astrophysics Data System (ADS)

Cesareo, Roberto; Brunetti, Antonio; D'Oriano, Rubens; Canu, Alba; Demontis, Gonaria Mattia; Celauro, Angela

2013-12-01

A Roman bronze statuette from the 2nd Century BC was recovered from a nuragic sanctuary close to Florinas, in the north of Sardinia. The facial portion of the statuette is covered by a silver mask, partially gilded and attached to the bronze by tin-lead welding. The silver mask was carefully analyzed by portable energy-dispersive X-ray fluorescence (EDXRF), a non-destructive and non-invasive method. The aim of the analysis was to reconstruct the layered structure of the silver gilt mask, and to determine homogeneity and thickness of the gold, silver and lead-tin sheets. This is possible by using the internal ratio of the X-ray lines, i.e. starting from the surface, Au (L α/L β), Ag (K α/K β), Au-L α/Ag-K α and Pb (L α/L β).The results were compared with those obtained with simulated X-ray spectra, obtained both experimentally and by using the Monte Carlo simulation technique.

Oxidation Protection Systems for Carbon-Carbon Composites Formed by Chemical Vapor Deposition and Plasma Assisted Chemical Vapor Deposition Techniques

DTIC Science & Technology

1992-04-22

Illinois University at Carbondale, 1991, in printing. I 42. E. Tatarzycki, ABS Report-4538216:#3, 10, 1990. 43. C. Ju, et. al., Proc. of 6th Materials...transducer, ie. a more positive scaleI I 34 thickness of fairly continuous conversion layer carbon 10 , •O.0000 resina 0 0 Fiber O0c00.a 0 Bundlea • 06...at 13000C, 0.1 atm. 1 93 IZ- ... an rI pia irgaho tea-ccv~ ab .. au .re ;--24- Oo. C:caI micrograpt~h ofcin th e csr ossivc sczrbc2 ccirzza Fck

Insights into semiconductor nanowire conductivity using electrodeposition

NASA Astrophysics Data System (ADS)

Liu, C.; Salehzadeh, O.; Poole, P. J.; Watkins, S. P.; Kavanagh, K. L.

2012-10-01

Copper (Cu) and iron (Fe) electrical contacts to gallium arsenide (GaAs) and indium arsenide (InAs) nanowires (NWs) have been fabricated via electrodeposition. For undoped or low carbon-doped (1017/cm-3), p-type GaAs NWs, Cu or Fe nucleate and grow only on the gold catalyst at the NW tip, avoiding the sidewalls. Metal growth is limited by the Au contact resistance due to thick sidewall depletion layers. For InAs NWs and heavier-doped, core-shell (undoped core-C-doped shell) GaAs NWs, metal nucleation and growth occurs on the sidewalls as well as on the gold catalyst limited now by the ion electrolyte diffusivity.

Formation of a 1,8-octanedithiol self-assembled monolayer on Au(111) prepared in a lyotropic liquid-crystalline medium.

PubMed

García Raya, Daniel; Madueño, Rafael; Blázquez, Manuel; Pineda, Teresa

2010-07-20

A characterization of the 1,8-octanedithiol (ODT) self-assembled monolayer (SAM) formed from a Triton X-100 lyotropic medium has been conducted by electrochemical techniques. It is found that an ODT layer of standing-up molecules is obtained at short modification time without removing oxygen from the medium. The electrochemical study shows that the ODT layer formed after 15 min of modification time has similar electron-transfer blocking properties to the layers formed from organic solvents at much longer modification times. On the basis of XPS data, it is demonstrated that the inability to bind gold nanoparticles (AuNPs) is due to the presence of extra ODT molecules either interdigited or on top of the layer. Treatment consisting of an acid washing step following the formation of the ODT-Au(111) SAM produces a layer that is able to attach AuNPs as demonstrated by electrochemical techniques and atomic force microscopy (AFM) images.

Clustering of gold particles in Au implanted CrN thin films: The effect on the SPR peak position

NASA Astrophysics Data System (ADS)

Novaković, M.; Popović, M.; Schmidt, E.; Mitrić, M.; Bibić, N.; Rakočević, Z.; Ronning, C.

2017-12-01

We report on the formation of gold particles in 280 nm thin polycrystalline CrN layers caused by Au+ ion implantation. The CrN layers were deposited at 150 °C by d.c. reactive sputtering on Si(100) wafers and then implanted at room temperature with 150 keV Au+ ions to fluences of 2 × 1016 cm-2 to 4.1 × 1016 cm-2. The implanted layers were analysed by the means of Rutherford backscattering spectrometry, X-ray diffraction, atomic force microscopy and spectroscopic ellipsometry measurements. The results revealed that the Au atoms are situated in the near-surface region of the implanted CrN layers. At the fluence of 2 × 1016 cm-2 the formation of Au particles of ∼200 nm in diameter has been observed. With increasing Au ion fluence the particles coalesce into clusters with dimensions of ∼1.7 μm. The synthesized particles show a strong absorption peak associated with the excitation of surface plasmon resonances (SPR). The position of the SPR peak shifted in the range of 426.8-690.5 nm when the Au+ ion fluence was varied from 2 × 1016 cm-2 to 4.1 × 1016 cm-2. A correlation of the shift in the peak wavelength caused by the change in the particles size and clustering has been revealed, suggesting that the interaction between Au particles dominate the surface plasmon resonance effect.

Au/NiFe/M(Au, MoS2, graphene) trilayer magnetoplasmonics DNA-hybridized sensors with high record of sensitivity.

PubMed

Faridi, Ehsan; Moradi, Maryam; Ansari, Narges; Baradaran Ghasemi, Amir Hossein; Afshar, Amir; Mohseni Armaki, Seyed Majid

2017-12-01

The demonstration of biosensors based on the surface plasmon effect holds promise for future high-sensitive electrodeless biodetection. The combination of magnetic effects with surface plasmon waves brings additional freedom to improve sensitivity and signal selectivity. Stacking biosensors with two-dimensional (2-D) materials, e.g., graphene (Gr) and MoS2, can influence plasmon waves and facilitate surface physiochemical properties as additional versatility aspects. We demonstrate magnetoplasmonic biosensors through the detuning of surface plasmon oscillation modes affected by magnetic effect via the presence of the NiFe (Py) layer and different light absorbers of Gr, MoS2, and Au ultrathin layers in three stacks of Au/Py/M(MoS2, Gr, Au) trilayers. We found minimum reflection, resonance angle shift, and transverse magneto-optical Kerr effect (TMOKE) responses of all sensors in the presence of the ss-DNA monolayer. Very few changes of ∼5×10-7 in the ss-DNA's refractive index result in valuable TMOKE response. We found that the presence of three-layer Gr and two-layer MoS2 on top of the Au/Py bilayer can dramatically increase the sensitivity by nine and four times, respectively, than the conventional Au/Co/Au trilayer. Our results show the highest reported DNA sensitivity based on the coupling of light with 2-D materials in magnetoplasmonic devices. (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE).

Gold diffusion in mercury cadmium telluride grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Selamet, Yusuf; Singh, Rasdip; Zhao, Jun; Zhou, Yong D.; Sivananthan, Sivalingam; Dhar, Nibir K.

2003-12-01

The growth and characterization of Au-doped HgCdTe layers on (211)B CdTe/Si substrates grown by molecular beam epitaxy reported. The electrical properties of these layers studied for diffusion are presented. For ex-situ experiments, thin Au layers were deposited by evaporation and annealed at various temperatures and times to investigate the p-type doping properties and diffusion of Au in HgCdTe. The atomic distribution of the diffused Au was determined by secondary ion mass spectroscopy. We found clear evidence for p-type doping of HgCdTe:Au by in-situ and ex-situ methods. For in-situ doped layers, we found that, the Au cell temperature needs to be around 900°C to get p-type behavior. The diffusion coefficient of Au in HgCdTe was calculated by fitting SIMS profiles after annealing. Both complementary error functions and gaussian fittings were used, and were in full agreement. Diffusion coefficient as low as 8x10-14cm2/s observed for a sample annealed at 250°C and slow component of a diffusion coefficient as low as 2x10-15 cm2/s observed for a sample annealed at 300°C. Our preliminary results indicate no appreciable diffusion of Au in HgCdTe under the conditions used in these studies. Further work is in progress to confirm these results and to quantify our SIMS profiles.

Probing properties of the interfacial perimeter sites in TiO x /Au/SiO 2 with 2-propanol decomposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Yi Y.; Kung, Harold H.

The decomposition of 2-propanol was studied over SiO2, SiO2 with an overlayer of TiO2 (Ti/SiO2), Au/SiO2, and Au/SiO2 with an overlayer of TiO2 (Ti/[Au/SiO2]) at 170–190 °C. There was no reaction on SiO2. Propene was the only product on Ti/SiO2, and its rate of formation increased proportionally with the Ti content. Acetone was the major product (selectivity 65–99%) on all Au-containing catalysts. Its rate of formation also increased with Ti loading. In addition, small amounts of propene were also formed on Ti/[Au/SiO2] the rate of which increased with Ti loading. Characterization of the catalysts with N2 adsorption, STEM, DR-UV-vis spectroscopy,more » XPS, XANES and EXAFS suggested that the Ti formed an amorphous TiO2 overlayer on the catalyst. At high Ti loadings (4–5 wt.%), there were patches of thick porous TiO2 layer, and some microdomains of crystalline TiO2 could be detected. Au was present as 1–3 nm nanoparticles on all catalysts, before and after used in reaction. Only Lewis acid sites were detected based on results from pyridine adsorption, and their quantities increased with Ti loading. Based on the comparison of reaction rates, the dependence of the kinetics on 2-propanol partial pressure, the apparent activation energies, and the effect of co-feeding O2 among different catalysts, it was concluded that propene was formed on the TiO2 overlayer, acetone was formed primarily at the Au-TiO2 interfacial perimeter sites, and α-C-H bond breaking preceding acetone formation was more facile on Au at the interfacial site than other surface Au atoms. Implication of these results to the selective acetone formation in the oxidation of propane in the presence of a O2/H2 mixture was discussed.« less

Interfacial and thermal energy driven growth and evolution of Langmuir-Schaefer monolayers of Au-nanoparticles.

PubMed

Mukhopadhyay, Mala; Hazra, S

2018-01-03

Structures of Langmuir-Schaefer (LS) monolayers of thiol-coated Au-nanoparticles (DT-AuNPs) deposited on H-terminated and OTS self-assembled Si substrates (of different hydrophobic strength and stability) and their evolution with time under ambient conditions, which plays an important role for their practical use as 2D-nanostructures over large areas, were investigated using the X-ray reflectivity technique. The strong effect of substrate surface energy (γ) on the initial structures and the competitive role of room temperature thermal energy (kT) and the change in interfacial energy (Δγ) at ambient conditions on the evolution and final structures of the DT-AuNP LS monolayers are evident. The strong-hydrophobic OTS-Si substrate, during transfer, seems to induce strong attraction towards hydrophobic DT-AuNPs on hydrophilic (repulsive) water to form vertically compact partially covered (with voids) monolayer structures (of perfect monolayer thickness) at low pressure and nearly covered buckled monolayer structures (of enhanced monolayer thickness) at high pressure. After transfer, the small kT-energy (in absence of repulsive water) probably fluctuates the DT-AuNPs to form vertically expanded monolayer structures, through systematic exponential growth with time. The effect is prominent for the film deposited at low pressure, where the initial film-coverage and film-thickness are low. On the other hand, the weak-hydrophobic H-Si substrate, during transfer, appears to induce optimum attraction towards DT-AuNPs to better mimic the Langmuir monolayer structures on it. After transfer, the change in the substrate surface nature, from weak-hydrophobic to weak-hydrophilic with time (i.e. Δγ-energy, apart from the kT-energy), enhances the size of the voids and weakens the monolayer/bilayer structure to form a similar expanded monolayer structure, the thickness of which is probably optimized by the available thermal energy.

Au-Interaction of Slp1 Polymers and Monolayer from Lysinibacillus sphaericus JG-B53 - QCM-D, ICP-MS and AFM as Tools for Biomolecule-metal Studies

PubMed Central

Suhr, Matthias; Raff, Johannes; Pollmann, Katrin

2016-01-01

In this publication the gold sorption behavior of surface layer (S-layer) proteins (Slp1) of Lysinibacillus sphaericus JG-B53 is described. These biomolecules arrange in paracrystalline two-dimensional arrays on surfaces, bind metals, and are thus interesting for several biotechnical applications, such as biosorptive materials for the removal or recovery of different elements from the environment and industrial processes. The deposition of Au(0) nanoparticles on S-layers, either by S-layer directed synthesis 1 or adsorption of nanoparticles, opens new possibilities for diverse sensory applications. Although numerous studies have described the biosorptive properties of S-layers 2-5, a deeper understanding of protein-protein and protein-metal interaction still remains challenging. In the following study, inductively coupled mass spectrometry (ICP-MS) was used for the detection of metal sorption by suspended S-layers. This was correlated to measurements of quartz crystal microbalance with dissipation monitoring (QCM-D), which allows the online detection of proteinaceous monolayer formation and metal deposition, and thus, a more detailed understanding on metal binding. The ICP-MS results indicated that the binding of Au(III) to the suspended S-layer polymers is pH dependent. The maximum binding of Au(III) was obtained at pH 4.0. The QCM-D investigations enabled the detection of Au(III) sorption as well as the deposition of Au(0)-NPs in real-time during the in situ experiments. Further, this method allowed studying the influence of metal binding on the protein lattice stability of Slp1. Structural properties and protein layer stability could be visualized directly after QCM-D experiment using atomic force microscopy (AFM). In conclusion, the combination of these different methods provides a deeper understanding of metal binding by bacterial S-layer proteins in suspension or as monolayers on either bacterial cells or recrystallized surfaces. PMID:26863150

Excitation mechanism of surface plasmon polaritons in a double-layer wire grid structure

NASA Astrophysics Data System (ADS)

Motogaito, Atsushi; Nakajima, Tomoyasu; Miyake, Hideto; Hiramatsu, Kazumasa

2017-12-01

We characterize the optical properties of a double-layer wire grid structure and investigate in detail the excitation mechanism of surface plasmon polaritons (SPPs). Angular spectra for the transmittance of the transverse magnetic polarized light that are obtained through the experiment reveal two peaks. In addition, simulated mapping of the transmittance and the magnetic field distribution indicate that SPPs are excited in two areas of the wire grid structures: at the interface between the Au layer and the resist layer or the glass substrate and at the interface between the Au layer and air. The experimental data are consistent with the transmittance mapping result and the distribution of the magnetic field. Accordingly, we constructed a model of SPPs propagation. We consider that SPPs excited at the interface between the Au layer and the resist layer or the glass substrate strongly contribute to the extraordinary transmission observed in the wire grid structures.

Enhancement of emission of InGaN/GaN multiple-quantum-well nanorods by coupling to Au-nanoparticle plasmons

NASA Astrophysics Data System (ADS)

Xing, Jieying; Chen, Yinsong; Liu, Yuebo; Liang, Jiezhi; Chen, Jie; Ren, Yuan; Han, Xiaobiao; Zhong, Changming; Yang, Hang; Huang, Dejia; Hou, Yaqian; Wu, Zhisheng; Liu, Yang; Zhang, Baijun

2018-05-01

We demonstrate the enhancement of emission of InGaN/GaN multiple-quantum-well nanorods by nearly a factor of 2 by coupling them to localized surface plasmons of Au nano-particles (NPs). The Au NPs are fabricated in situ on the nanorods using a Ni/SiO2/Au/SiNx compound functional layer. This layer serves as a combination dry-etch mask for fabricating the nanorods and the Au NPs, as well as providing isolation necessary to prevent fluorescence quenching. Time-resolved photoluminescence measurements confirm that emission enhancement originates from the coupling.

Ohmic contacts to p-GaN Using Au/Ni-Mg-O Metallization

NASA Astrophysics Data System (ADS)

Liday, Jozef; Vogrinčič, Peter; Hotový, Ivan; Bonanni, Alberta; Sitter, Helmut; Lalinský, Tibor; Vanko, Gabriel; Řeháček, Vlastimil; Breza, Juraj; Ecke, Gernot

2010-11-01

Electrical characteristics and elemental depth profiles of ohmic contacts to p-GaN using Au/Ni-Mg-Ox metallization have been investigated. The objective was to examine the possibilities of increasing the charge carrier concentration in the surface region of GaN by adding Mg, thus of a p-type dopant into the Au/NiOx metallization structure. For this purpose, a Ni-Mg-Ox layer with a low concentration of Mg was deposited on p-GaN by dc reactive magnetron sputtering. The top Au layer was deposited in a similar way. The fabricated contact structures were annealed in N2. When the Ni-Mg layer in the Au/Ni-Mg-Ox/p-GaN structure was deposited in an atmosphere with a low concentration of oxygen (0.2 at%), the structure exhibited a low resistance ohmic nature. The contact resistance was lower than in the case of a Au/Ni-Ox/p-GaN structure without the Mg dopant in the metallic layer. An increase in the concentration of oxygen in the working atmosphere resulted in higher values of the contact resistance of the Au/Ni-Mg-Ox/p-GaN structure. In our opinion the ohmic nature of the contact structure is related to the existence of a metal/p-NiO/p-GaN scheme. The measured values of the contact resistance in the Au/Ni-Mg-Ox/p-GaN structure in comparison with the Au/Ni-Ox/p-GaN structure are caused by an increased charge carrier concentration in the surface region of p-GaN, which is a consequence of Mg diffusion from the Ni-Mg-Ox layer.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thangadurai, P.; Lumelsky, Yulia; Silverstein, Michael S.

Transmission electron microscopy (TEM) cross-section specimens of PMMA in contact with gold and Si were prepared by focused ion beam (FIB) and compared with plan-view PMMA specimens prepared by a dip-coating technique. The specimens were characterized by TEM and electron energy loss spectroscopy (EELS). In the cross-section specimens, the thin films of PMMA were located in a Si-PMMA-Au multilayer. Different thicknesses of PMMA films were spin-coated on the Si substrates. The thickness of the TEM specimens prepared by FIB was estimated using EELS to be 0.65 of the plasmon mean-free-path. Along the PMMA-Au interface, Au particle diffusion into the PMMAmore » was observed, and the size of the Au particles was in the range of 2-4 nm. Dip-coating of PMMA directly on Cu TEM grids resulted in thin specimens with a granular morphology, with a thickness of 0.58 of the plasmon mean-free-path. The dip-coated specimens were free from ion milling induced artifacts, and thus serve as control specimens for comparison with the cross-sectioned specimens prepared by FIB.« less

Vertical Deformation of Late Quaternary Features Across Port-au-Prince Bay, Haiti

NASA Astrophysics Data System (ADS)

Cormier, M.; McHugh, C. M.; Gulick, S. P.; Braudy, N.; Davis, M. B.; Diebold, J. B.; Dieudonne, N.; Douilly, R.; Hornbach, M. J.; Johnson, H. E.; Mishkin, K.; Seeber, L.; Sorlien, C. C.; Steckler, M. S.; Symithe, S. J.; Templeton, J.

2010-12-01

As part of a project that investigated the underwater impacts of the January 12, 2010 earthquake in Haiti, we surveyed offshore structures that may have been activated during that earthquake or that might become activated in future earthquakes. Part of that survey focused on the shallow shelf area that extends north of the segment of the Enriquillo-Plantain Garden fault that just ruptured. This area is occupied by an elongated depression, 25 km long, 10 km wide, and 140 m deep. The NW-SE axis of that shallow basin is sub-parallel to that of the NW-SE anticlines that bounds Port-au-Prince Bay. The shallow basin is also rimmed by a carbonate platform that is 5-10 km-wide and ~30m deep. New multibeam bathymetric and sidescan sonar data collected across that platform highlight a series of circular dissolution structures 1-2 km across and ~80 m deep. We interpret that morphology to indicate antecedent karst topography that developed during previous glacial maxima. According to that scenario, the shallow basin off Port-au-Prince would have been isolated from the Caribbean Sea by the continuous platform, and would probably have been occupied by a lagoon. Indeed, a few high-resolution chirp profiles image what may be a paleoshoreline at about 80m depth, buried beneath a 5-8 m thick, acoustically transparent, presumably Holocene layer. Preliminary analysis indicates that the basin floor and the base of the presumably Holocene layer are perfectly horizontal in the center of the basin, but tilted down to the south at its northern edge. The presumed paleoshoreline is also shallower to the north of the basin. We propose that this tilt is driven by contraction across the NW-SE fold-and-thrust belt that runs across Hispaniola. This hypothesis remains to be tested with a more thorough geophysical and coring survey in Port-au-Prince Bay.

Binary Oxide p-n Heterojunction Piezoelectric Nanogenerators with an Electrochemically Deposited High p-Type Cu2O Layer.

PubMed

Baek, Seung Ki; Kwak, Sung Soo; Kim, Joo Sung; Kim, Sang Woo; Cho, Hyung Koun

2016-08-31

The high performance of ZnO-based piezoelectric nanogenerators (NGs) has been limited due to the potential screening from intrinsic electron carriers in ZnO. We have demonstrated a novel approach to greatly improve piezoelectric power generation by electrodepositing a high-quality p-type Cu2O layer between the piezoelectric semiconducting film and the metal electrode. The p-n heterojunction using only oxides suppresses the screening effect by forming an intrinsic depletion region, and thus sufficiently enhances the piezoelectric potential, compared to the pristine ZnO piezoelectric NG. Interestingly, a Sb-doped Cu2O layer has high mobility and low surface trap states. Thus, this doped layer is an attractive p-type material to significantly improve piezoelectric performance. Our results revealed that p-n junction NGs consisting of Au/ZnO/Cu2O/indium tin oxide with a Cu2O:Sb (cuprous oxide with a small amount of antimony) layer of sufficient thickness (3 μm) exhibit an extraordinarily high piezoelectric potential of 0.9 V and a maximum output current density of 3.1 μA/cm(2).

Atomic and electronic structures of Si(1 1 1)-(√3 x √3)R30°-Au and (6 × 6)-Au surfaces.

PubMed

Patterson, C H

2015-12-02

Si(1 1 1)-Au surfaces with around one monolayer of Au exhibit many ordered structures and structures containing disordered domain walls. Hybrid density functional theory (DFT) calculations presented here reveal the origin of these complex structures and tendency to form domain walls. The conjugate honeycomb chain trimer (CHCT) structure of the [Formula: see text]-Au phase contains Si atoms with non-bonding surface states which can bind Au atoms in pairs in interstices of the CHCT structure and make this surface metallic. Si adatoms adsorbed on the [Formula: see text]-Au surface induce a gapped surface through interaction with the non-bonding states. Adsorption of extra Au atoms in interstitial sites of the [Formula: see text]-Au surface is stabilized by interaction with the non-bonding orbitals and leads to higher coverage ordered structures including the [Formula: see text]-Au phase. Extra Au atoms bound in interstitial sites of the [Formula: see text]-Au surface result in top layer Si atoms with an SiAu4 butterfly wing configuration. The structure of a [Formula: see text]-Au phase, whose in-plane top atomic layer positions were previously determined by an electron holography technique (Grozea et al 1998 Surf. Sci. 418 32), is calculated using total energy minimization. The Patterson function for this structure is calculated and is in good agreement with data from an in-plane x-ray diffraction study (Dornisch et al 1991 Phys. Rev. B 44 11221). Filled and empty state scanning tunneling microscopy (STM) images are calculated for domain walls and the [Formula: see text]-Au structure. The [Formula: see text]-Au phase is 2D chiral and this is evident in computed and actual STM images. [Formula: see text]-Au and domain wall structures contain the SiAu4 motif with a butterfly wing shape. Chemical bonding within the Si-Au top layers of the [Formula: see text]-Au and [Formula: see text]-Au surfaces is analyzed and an explanation for the SiAu4 motif structure is given.

Effect of core-shell structure on optical properties of Au-Cu2O nanoparticles

NASA Astrophysics Data System (ADS)

Sai, Cong Doanh; Ngac, An Bang

2018-03-01

Solid Au-Cu2O core-shell nanoparticles were synthesized using gold nanoparticles of 16.6 nm in size as the core. The core-shell structure of the synthesized particles was confirmed and characterized by TEM and HRTEM images. Due to their similar crystal structure, the (111) planes of Cu2O are nucleated and grown epitaxially on the {111} facets of Au nanoparticles with the lattice mismatch of about 4.3% resulting in a polycrystallized Cu2O shell covering the Au nanocore. Due to the quantum confinement effect, the band gap energy Eg of the synthesized Cu2O shells is blue-shifted from 2.35 to 2.70 eV as the shell thickness decreases from of 24.6±3.6 to 9.0±1.7 nm. The localized SPR (Surface Plasmon Resonance) peak of the Au nanocore undergoes a large red shift of the order of a hundred of nm due to both the high refractive index and the increase of the thickness of Cu2O shell. Theoretical models within the Drude framework significantly underestimate the experimental data and predict a wrong rate of change of the SPR peak position with respect to the shell thickness.

Study of the characteristics current-voltage and capacitance-voltage in nitride GaAs Schottky diode

NASA Astrophysics Data System (ADS)

Rabehi, Abdelaziz; Amrani, Mohamed; Benamara, Zineb; Akkal, Boudali; Hatem-Kacha, Arslane; Robert-Goumet, Christine; Monier, Guillaume; Gruzza, Bernard

2015-10-01

This article reports the study of Au/GaN/GaAs Schottky diodes, where the thin GaN film is prepared by nitridation of GaAs substrates with thicknesses of 0.7 and 0.8 nm. The resulting GaN sample with thickness 0.8 nm is then treated with an annealing operation (heating to 620 °C) to improve the current transport. The current-voltage (I-V) and capacitance-voltage (C-V) of the Au/GaN/GaAs structures were investigated at room temperature. In fact, the I-V characteristics show that the annealed sample has low series resistance (Rs) and ideality factor (n) (63 Ω, 2.27 respectively) when compared to the values obtained in the untreated sample (1.83 kΩ, 3.31 respectively). The formation of the GaN layer on the gallium arsenide surface is investigated through calculation of the interface state density NSS with and without the presence of series resistance Rs. The value of the interface state density NSS(E) close to the mid-gap was estimated to be in the order of 4.7×1012 cm-2 eV-1 and 1.02× 1013 cm-2 eV-1 with and without the annealing operation, respectively. However, nitridation with the annealing operation at 620 °C improves the electrical properties of the resultant Schottky diode.

Coating and functionalization of high density ion track structures by atomic layer deposition

NASA Astrophysics Data System (ADS)

Mättö, Laura; Szilágyi, Imre M.; Laitinen, Mikko; Ritala, Mikko; Leskelä, Markku; Sajavaara, Timo

2016-10-01

In this study flexible TiO2 coated porous Kapton membranes are presented having electron multiplication properties. 800 nm crossing pores were fabricated into 50 μm thick Kapton membranes using ion track technology and chemical etching. Consecutively, 50 nm TiO2 films were deposited into the pores of the Kapton membranes by atomic layer deposition using Ti(iOPr)4 and water as precursors at 250 °C. The TiO2 films and coated membranes were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray reflectometry (XRR). Au metal electrode fabrication onto both sides of the coated foils was achieved by electron beam evaporation. The electron multipliers were obtained by joining two coated membranes separated by a conductive spacer. The results show that electron multiplication can be achieved using ALD-coated flexible ion track polymer foils.

Ultraselective Toluene-Gas Sensor: Nanosized Gold Loaded on Zinc Oxide Nanoparticles.

PubMed

Suematsu, Koichi; Watanabe, Kosuke; Tou, Akihiro; Sun, Yongjiao; Shimanoe, Kengo

2018-02-06

Selectivity is an important parameter of resistive-type gas sensors that use metal oxides. In this study, a highly selective toluene sensor is prepared using highly dispersed gold-nanoparticle-loaded zinc oxide nanoparticles (Au-ZnO NPs). Au-ZnO NPs are synthesized by coprecipitation and calcination at 400 °C with Au loadings of 0.15, 0.5, and 1.5 mol %. The Au NPs on ZnO are about 2-4 nm in size, and exist in a metallic state. Porous gas-sensing layers are fabricated by screen printing. The responses of the sensor to 200 ppm hydrogen, 200 ppm carbon monoxide, 100 ppm ethanol, 100 ppm acetaldehyde, 100 ppm acetone, and 100 ppm toluene are evaluated at 377 °C in a dry atmosphere. The sensor response of 0.15 mol % Au-ZnO NPs to toluene is about 92, whereas its sensor responses to other combustible gases are less than 7. Such selective toluene detection is probably caused by the utilization efficiency of the gas-sensing layer. Gas diffusivity into the sensing layer of Au-ZnO NPs is lowered by the catalytic oxidation of combustible gases during their diffusion through the layer. The present approach is an effective way to improve the selectivity of resistive-type gas sensors.

Patterning of supported gold monolayers via chemical lift-off lithography

PubMed Central

Slaughter, Liane S; Cheung, Kevin M; Kaappa, Sami; Cao, Huan H; Yang, Qing; Young, Thomas D; Serino, Andrew C; Malola, Sami; Olson, Jana M; Link, Stephan

2017-01-01

The supported monolayer of Au that accompanies alkanethiolate molecules removed by polymer stamps during chemical lift-off lithography is a scarcely studied hybrid material. We show that these Au–alkanethiolate layers on poly(dimethylsiloxane) (PDMS) are transparent, functional, hybrid interfaces that can be patterned over nanometer, micrometer, and millimeter length scales. Unlike other ultrathin Au films and nanoparticles, lifted-off Au–alkanethiolate thin films lack a measurable optical signature. We therefore devised fabrication, characterization, and simulation strategies by which to interrogate the nanoscale structure, chemical functionality, stoichiometry, and spectral signature of the supported Au–thiolate layers. The patterning of these layers laterally encodes their functionality, as demonstrated by a fluorescence-based approach that relies on dye-labeled complementary DNA hybridization. Supported thin Au films can be patterned via features on PDMS stamps (controlled contact), using patterned Au substrates prior to lift-off (e.g., selective wet etching), or by patterning alkanethiols on Au substrates to be reactive in selected regions but not others (controlled reactivity). In all cases, the regions containing Au–alkanethiolate layers have a sub-nanometer apparent height, which was found to be consistent with molecular dynamics simulations that predicted the removal of no more than 1.5 Au atoms per thiol, thus presenting a monolayer-like structure. PMID:29259879

Influence of the Metal-MoS2 interface on MoS2 Transistor Performance

NASA Astrophysics Data System (ADS)

Yuan, Hui; Cheng, Guangjun; Hight Walker, Angela; You, Lin; Kopanski, Joseph J.; Li, Qiliang; Richter, Curt A.

2015-03-01

We compare the electrical characteristics of MoS2 field-effect transistors (FETS) with Ag source/drain contacts with transistors with Ti contacts, and we demonstrate that the metal-MoS2 interface is crucial to the final device performance. The topography of 5nm Au/5nm Ag (contact layer) and 5nm Au/5nm Ti metal films deposited onto mono- and few-layer MoS2 was characterized by using scanning electron microscopy and atomic force microscopy. The surface morphology of the Au/Ti films on MoS2 shows a rough, dewetting pattern while Au/Ag forms smooth, dense films. These smoother and denser Au/Ag contacts lead to improved carrier transport efficiency. FETs with Ag contacts show more than 60 times higher on-state current and a steeper subthreshold slope. Raman spectroscopy of MoS2 covered with Au/Ag or Au/Ti films revealed that the contact layer is Ag or Ti, respectively. In addition, there is a dramatic difference in the heat transfer between the MoS2 and the two metals: while laser heating is observed in Au/Ti covered MoS2, no heating effects are seen in Au/Ag covered MoS2. It is reasonable to conclude that the smoother and denser Ag contact leads to higher carrier transport efficiency and contributes to the improved thermal properties.

Single-layer ZnS supported on Au(111): A combined XPS, LEED, STM and DFT study

DOE PAGES

Deng, Xingyi; Sorescu, Dan C.; Lee, Junseok

2016-12-31

Single-layer of ZnS, consisting of one atomic layer of ZnS(111) plane, has been grown on Au(111) and characterized using X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). While the LEED measurement indicates a coincidence structure of ZnS-(3×3)/Au(111)-(4×4), high resolution STM images reveal hexagonal unit cells of 6.7×6.7 Å 2 and 11.6×11.6 Å 2, corresponding to √3 and 3 times the unit cell of the ideal zincblende ZnS-(1×1), respectively, depending on the tunneling conditions. Calculations based on density functional theory (DFT) indicate a significantly reconstructed non-planar structure of ZnS single-layer on Au(111) with 2/3 ofmore » the S anions being located nearly in the plane of the Zn cations and the rest 1/3 of the S anions protruding above the Zn plane. In conclusion, the calculated STM image shows similar characteristics to those of the experimental STM image. Additionally, the DFT calculations reveal the different bonding nature of the S anions in ZnS single-layer supported on Au(111).« less

UV-LIGA technique for ECF micropumps using back UV exposure and self-alignment

NASA Astrophysics Data System (ADS)

Han, D.; Xia, Y.; Yokota, S.; Kim, J. W.

2017-12-01

This paper proposes and develops a novel UV-LIGA technique using back UV exposure and self-alignment to realize high aspect ratio micromachining (HARM) in high power density electro-conjugate fluid (ECF) micropumps. ECF is a functional fluid designed to be able to generate strong and active jet flow (ECF jetting) between anode and cathode in ECF when high DC voltage is applied. We have developed high power density ECF micropumps consisting of triangular prism and slit electrode pairs (TPSEs) fabricated by HARM. The traditional UV-LIGA technique for HARM is mainly divided into two approaches: (a) single thick layer and (b) multiple thin layers. Both methods have limitations—deformed molds in the former and misalignment between layers in the latter. Using the finite element method software COMSOL Multiphysics, we demonstrate that the deformed micro-molds critically impair the performance of ECF micropumps. In addition, we experimentally prove that the misalignment would easily trigger electric discharge in the ECF micropumps. To overcome these limitations, we conceive a new concept utilizing the seed electrode layer for electroforming as the UV shield and pattern photoresist (KMPR) by back UV exposure. The seed electrode layer should be composed of a non-transparent conductor (Au/Ti) for patterning and a transparent conductor (ITO) for wiring. Instead of ITO, we propose the concept of transparency-like electrodes comprised of thin metal line patterns. To verify this concept, KMPR layers with thicknesses of 70, 220, and 500 µm are experimentally investigated. In the case of 500 µm KMPR thickness, the concept of transparency-like electrode was partially proved. As a result, TPSEs with a height of 440 µm were successfully fabricated. Characteristic experiments demonstrated that ECF micropumps (367 mW cm-3) fabricated by back UV achieved almost the same output power density as ECF micropumps (391 mW cm-3) fabricated by front UV. This paper proves that the proposed UV-LIGA technique, using back UV exposure and self-alignment, can effectively fabricate TPSEs for ECF micropumps with high output power density.

A new bimetallic plasmonic photocatalyst consisting of gold(core)-copper(shell) nanoparticle and titanium(IV) oxide support

NASA Astrophysics Data System (ADS)

Sato, Yuichi; Naya, Shin-ichi; Tada, Hiroaki

2015-10-01

Ultrathin Cu layers (˜2 atomic layers) have been selectively formed on the Au surfaces of Au nanoparticle-loaded rutile TiO2 (Au@Cu/TiO2) by a deposition precipitation-photodeposition technique. Cyclic voltammetry and photochronopotentiometry measurements indicate that the reaction proceeds via the underpotential deposition. The ultrathin Cu shell drastically increases the activity of Au/TiO2 for the selective oxidation of amines to the corresponding aldehydes under visible-light irradiation (λ > 430 nm). Photochronoamperometry measurements strongly suggest that the striking Cu shell effect stems from the enhancement of the charge separation in the localized surface plasmon resonance-excited Au/TiO2.

Interfacial kinetics in nanosized Au/Ge films: An in situ TEM study

NASA Astrophysics Data System (ADS)

Kryshtal, Aleksandr P.; Minenkov, Alexey A.; Ferreira, Paulo J.

2017-07-01

We investigate the morphology and crystalline structure of Au/Ge films in a wide range of temperatures by in situ TEM heating. Au/Ge films with Au mass thickness of 0.2-0.3 nm and Ge thickness of 5 nm were produced in vacuum by the sequential deposition of components on a carbon substrate at room temperature. It has been shown that particles with an average size of 4 nm, formed by Au film de-wetting, melt on the germanium substrate at temperatures 110-160 °C, which are below the eutectic temperature for the bulk. The effect of crystallization-induced capillary motion of liquid eutectic particles over Ge surface has been found in this work. Formation of metastable fcc phase of Ge has been observed at the liquid-germanium interface and behind the moving particle. Formation of a liquid phase with its subsequent crystallization at the metal-semiconductor interface seems to play a key role in the metal-induced crystallization effect.

A preliminary investigation of acousto-ultrasonic NDE of metal matrix composite test specimens

NASA Technical Reports Server (NTRS)

Kautz, Harold E.; Lerch, Brad A.

1991-01-01

Acousto-ultrasonic (AU) measurements were performed on a series of tensile specimens composed of 8 laminated layers of continuous, SiC fiber reinforced Ti-15-3 matrix. The following subject areas are covered: AU signal analysis; tensile behavior; AU and interrupted tensile tests; AU and thermally cycled specimens; AU and stiffness; and AU and specimen geometry.

Safe and simple detection of sparse hydrogen by Pd-Au alloy/air based 1D photonic crystal sensor

NASA Astrophysics Data System (ADS)

Mitra, S.; Biswas, T.; Chattopadhyay, R.; Ghosh, J.; Bysakh, S.; Bhadra, S. K.

2016-11-01

A simple integrated hydrogen sensor using Pd-Au alloy/air based one dimensional photonic crystal with an air defect layer is theoretically modeled. Structural parameters of the photonic crystal are delicately scaled to generate photonic band gap frequencies in a visible spectral regime. An optimized defect thickness permits a localized defect mode operating at a frequency within the photonic band gap region. Hydrogen absorption causes modification in the band gap characteristics due to variation of refractive index and lattice parameters of the alloy. As a result, the transmission peak appeared due to the resonant defect state gets shifted. This peak shifting is utilized to detect sparse amount of hydrogen present in the surrounding environment. A theoretical framework is built to calculate the refractive index profile of hydrogen loaded alloy using density functional theory and Bruggeman's effective medium approximation. The calculated refractive index variation of Pd3Au alloy film due to hydrogen loading is verified experimentally by measuring the reflectance characteristics. Lattice expansion properties of the alloy are studied through X-ray diffraction analyses. The proposed structure shows about 3 nm red shift of the transmission peak for a rise of 1% atomic hydrogen concentration in the alloy.

Calix[4]arene-Functionalised Silver Nanoparticles as Hosts for Pyridinium-Loaded Gold Nanoparticles as Guests.

PubMed

Vita, Francesco; Boccia, Alice; Marrani, Andrea G; Zanoni, Robertino; Rossi, Francesca; Arduini, Arturo; Secchi, Andrea

2015-10-19

A series of lipophilic gold nanoparticles (AuNPs) circa 5 nm in diameter and having a mixed organic layer consisting of 1-dodecanethiol and 1-(11-mercaptoundecyl) pyridinium bromide was synthesised by reacting tetraoctylammonium bromide stabilised AuNPs in toluene with different mixtures of the two thiolate ligands. A bidentate ω-alkylthiolate calix[4]arene derivative was instead used as a functional protecting layer on AgNPs of approximately 3 nm. The functionalised nanoparticles were characterised by transmission electron microscopy (TEM), and by UV/Vis and X-ray photoelectron spectroscopy (XPS). Recognition of the pyridinium moieties loaded on the AuNPs by the calix[4]arene units immobilised on the AgNPs was demonstrated in solution of weakly polar solvents by UV/Vis titrations and DLS measurements. The extent of Au-AgNPs aggregation, shown through the low-energy shift of their surface plasmon bands (SPB), was strongly dependent on the loading of the pyridinium moieties present in the organic layer of the AuNPs. Extensive aggregation between dodecanethiol-capped AuNPs and the Ag calix[4]arene-functionalised NPs was also promoted by the action of a simple N-octyl pyridinium difunctional supramolecular linker. This linker can interdigitate through its long fatty tail in the organic layer of the dodecanethiol-capped AuNPs, and simultaneously interact through its pyridinium moiety with the calix[4]arene units at the surface of the modified AgNPs. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effects of interfaces on the thermal conductivity in Si/Si0.75Ge0.25 multilayer with varying Au layers

NASA Astrophysics Data System (ADS)

Hu, Yangsen; Wu, Zhenghua; Ye, Fengjie; Hu, Zhiyu

2018-02-01

The manoeuvre of thermal transport property across multilayer films with inserted metal layers through controlling the metal-nonmetal interfaces is of fundamental interest. In this work, amorphous Si/Si0.75Ge0.25 multilayer films inserted with varying Au layers were fabricated by magnetron sputtering. The structure and sharp interface of multilayers films were characterized by low angle x-ray diffraction (LAXRD), grazing incidence small angle x-ray scattering (GISAXS) and scanning electron microscopy (SEM). A differential 3ω method was applied to measure the effective thermal conductivity. The measurements show that thermal conductivity has changed as varying Au layers. Thermal conductivity increased from 0.94 to 1.31 Wm-1K-1 while Si0.75Ge0.25 layer was replaced by different Au layers, which was attributed to the strong electron-phonon coupling and interface thermal resistance in a metal-nonmetal multilayered system. Theoretical calculation combined with experimental results indicate that the thermal conductivity of the multilayer film could be facilely controlled by introducing different number of nanoconstructed metal-nonmetal interfaces, which provide a more insightful understanding of the thermal transport manipulation mechanism of the thin film system with inserting metal layers.

Versatile plasmonic-effects at the interface of inverted perovskite solar cells.

PubMed

Shalan, Ahmed Esmail; Oshikiri, Tomoya; Sawayanagi, Hiroki; Nakamura, Keisuke; Ueno, Kosei; Sun, Quan; Wu, Hui-Ping; Diau, Eric Wei-Guang; Misawa, Hiroaki

2017-01-19

Plasmonics is a highly promising approach to enhancing the light-harvesting properties of hybrid organic/inorganic perovskite solar cells. In the present work, our cells have a p-i-n inverted planar structure. An ultrathin NiO film with two different thicknesses of 5 and 10 nm prepared by a pulsed laser deposition process on an ITO substrate with a faceted and furrowed surface enabled the formation of a continuous and compact layer of well-crystallized CH 3 NH 3 PbI 3 via an anti-solvent chlorobenzene process. The coverage mechanism of the NiO film on the ITO was clearly demonstrated through the J-V and external quantum efficiency (EQE) curves. Moreover, the results demonstrated that the gold nanoislands (Au NIs) increased the power conversion efficiency to 5.1%, almost double that of the samples without Au NIs. This result is due to the excitation of surface plasmons, which is characterized by strong scattering and enhancement of the electric field in the vicinity of the Au NIs loaded at the interface between the NiO and perovskite films. Additionally, we observed an enhancement of the EQE at wavelengths shorter than the plasmon resonance peak. In the current state, we speculate that the plasmoelectric potential effect is considered to be a good explanation of the photocurrent enhancement at the off-resonance region. Our work provides good guidance for the design and fabrication of solar-energy-related devices employing NiO electrodes and plasmonic Au NIs.

The Effect of the Electron Tunneling on the Photoelectric Hot Electrons Generation in Metallic-Semiconductor Nanostructures

NASA Astrophysics Data System (ADS)

Elsharif, Asma M.

2018-01-01

Semiconductor photonic crystals (MSPhC) were used to convert solar energy into hot electrons. An experimental model was designed by using metallic semiconductor photonic crystals (MSPhC). The designed MSPhC is based on TiO2/Au schottky contact. The model has similar nanocavity structure for broad gold absorption, but the materials on top of the cavity were changed to a metal and a semiconductor in order to collect the hot electrons. Detailed design steps and characterization have shown a broadband sub-bandgap photoresponse at a wavelength of 590 nm. This is due to the surface plasmon absorption by the wafer-scale Au/TiO2 metallic-semiconductor photonic crystal. Analytical calculation of the hot electron transport from the Au thin layer to the TiO2 conduction band is discussed. This theoretical study is based on the quantum tunneling effect. The photo generation of the hot electrons was undertaken at different wavelengths in Au absorber followed by tunneling through a schottky barrier into a TiO2 collector. The presence of a tunnel current from the absorber to the collector under illumination, offers a method to extract carriers from a hot-electron distribution at few bias voltages is presented in this study. The effects of doping different concentrations of the semiconductor on the evolution of the current characteristics were also investigated and discussed. The electrical characteristics were found to be sensitive to any change in the thickness of the barrier.

Improved conductivity of indium-tin-oxide film through the introduction of intermediate layer

NASA Astrophysics Data System (ADS)

Ng, S. W.; Yam, F. K.; Beh, K. P.; Tneh, S. S.; Hassan, Z.

2016-09-01

A thin intermediate layer (Ag, AuSn, In, Ni, Sn, SiO2) was individually deposited on glass substrates prior to the deposition of indium-tin-oxide (ITO) thin film by radio-frequency (RF) magnetron sputtering employing ITO target (composition ratio of In2O3:SnO2 = 9:1). The structural, optical and electrical properties were investigated to compare the ITO thin film with and without an intermediate layer. The preferential orientation of all ITO films was along (222) plane. Although all thin films were polycrystalline, the presence of intermediate layer promoted the overall crystallinity. The sheet resistance and resistivity of the ITO film were reduced from ∼68 Ω/□ to ∼29-45 Ω/□, and 16.2 × 10-4 Ω cm up to 7.58 × 10-4 Ω cm, respectively, by inserting a thin metal layer underneath the ITO film, and it is dependent on the degree of crystallization. The optical transmittance in the visible region varies from 40 to 88% for different samples. Based on the evaluation from Tauc plot, the optical band gap falls in the range of 4.02-4.12 eV. Physical film thickness was compared with that evaluated by optical measurement in the visible range and the physical thickness was found to be smaller. Similarly, the carrier concentration/scattering time from Hall effect measurement were also compared with that from optical measurement in the infrared region. Haacke's figure of merit (FOM) was employed to assess the quality of the ITO films, and the highest FOM is credited to ITO/In up to ∼8 × 10-3 Ω-1 in the visible light region.

Electrical and morphological characterization of transfer-printed Au/Ti/TiO{sub x}/p{sup +}-Si nano- and microstructures with plasma-grown titanium oxide layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weiler, Benedikt, E-mail: benedikt.weiler@nano.ei.tum.de; Nagel, Robin; Albes, Tim

2016-04-14

Highly-ordered, sub-70 nm-MOS-junctions of Au/Ti/TiO{sub x}/p{sup +}-Si were efficiently and reliably fabricated by nanotransfer-printing (nTP) over large areas and their functionality was investigated with respect to their application as MOS-devices. First, we used a temperature-enhanced nTP process and integrated the plasma-oxidation of a nm-thin titanium film being e-beam evaporated directly on the stamp before the printing step without affecting the p{sup +}-Si substrate. Second, morphological investigations (scanning electron microscopy) of the nanostructures confirm the reliable transfer of Au/Ti/TiO{sub x}-pillars of 50 nm, 75 nm, and 100 nm size of superior quality on p{sup +}-Si by our transfer protocol. Third, the fabricated nanodevices are alsomore » characterized electrically by conductive AFM. Fourth, the results are compared to probe station measurements on identically processed, i.e., transfer-printed μm-MOS-structures including a systematic investigation of the oxide formation. The jV-characteristics of these MOS-junctions demonstrate the electrical functionality as plasma-grown tunneling oxides and the effectivity of the transfer-printing process for their large-scale fabrication. Next, our findings are supported by fits to the jV-curves of the plasma-grown titanium oxide by kinetic-Monte-Carlo simulations. These fits allowed us to determine the dominant conduction mechanisms, the material parameters of the oxides and, in particular, a calibration of the thickness depending on applied plasma time and power. Finally, also a relative dielectric permittivity of 12 was found for such plasma-grown TiO{sub x}-layers.« less

GaAs buffer layer technique for vertical nanowire growth on Si substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Xiaoqing, E-mail: steelxu@stanford.edu; Parizi, Kokab B.; Huo, Yijie

2014-02-24

Gold catalyzed vapor-liquid-solid method is widely applied to III–V nanowire (NW) growth on Si substrate. However, the easy oxidation of Si, possible Si contamination in the NWs, high defect density in the NWs, and high sensitivity of the NW morphology to growth conditions largely limit its controllability. In this work, we developed a buffer layer technique by introducing a GaAs thin film with predefined polarity as a template. It is found that samples grown on these buffer layers all have high vertical NW yields in general, due to the single-orientation of the buffer layers. Low temperature buffer with smoother surfacemore » leads to highest yield of vertical NWs, while high temperature (HT) buffer with better crystallinity results in perfect NW quality. The defect-free property we observed here is very promising for optoelectronic device applications based on GaAs NW. Moreover, the buffer layers can eliminate Si contamination by preventing Si-Au alloy formation and by increasing the thickness of the Si diffusion barrier, thus providing more flexibility to vertical NW growth. The buffer layer technique we demonstrated here could be easily extended to other III-V on Si system for electronic and photonic applications.« less

Green synthesis and characterization of size tunable silica-capped gold core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Wangoo, Nishima; Shekhawat, Gajendra; Wu, Jin-Song; Bhasin, Aman K. K.; Suri, C. R.; Bhasin, K. K.; Dravid, Vinayak

2012-08-01

Silica-coated gold nanoparticles (Au@SiO2) with controlled silica-shell thickness were prepared by a modified Stober's method using 10-nm gold nanoparticles (AuNPs) as seeds. The AuNPs were silica-coated with a sol-gel reaction using tetraethylorthosilicate (TEOS) as a silica source and ammonia as a catalyst. An increase in TEOS concentration resulted in an increase in shell thickness. The NPs were characterized by transmission electron microscopy, selected area electron diffraction, energy-dispersive X-ray spectroscopy, scanning near-field ultrasound holography and scanning transmission electron microscopy. The method required no surface modification and the synthesized core shell nanoparticles can be used for various types of biological applications.

Au Foil Activation Measurement and Simulation of the Concrete Neutron Shielding Ability for the Proposed New SANRAD Facility

NASA Astrophysics Data System (ADS)

Radebe, M. J.; Korochinsky, S.; Strydom, W. J.; De Beer, F. C.

The purpose of this study was to measure the effective neutron shielding characteristics of the new shielding material designed and manufactured to be used for the construction of the new SANRAD facility at Necsa, South Africa, through Au foil activation as well as MCNP simulations. The shielding capability of the high density shielding material was investigated in the worst case region (the neutron beam axis) of the experimental chamber for two operational modes. The everyday operational mode includes the 15 cm thick poly crystalline Bismuth filter at room temperature (assumed) to filter gamma-rays and some neutron spectrum energies. The second mode, dynamic imaging, will be conducted without the Bi-filter. The objective was achieved through a foil activation measurement at the current SANRAD facility and MCNP calculations. Several Au foilswere imbedded at different thicknesses(two at each position) of shielding material up to 80 cm thick to track the attenuation of the neutron beam over distance within the shielding material. The neutron flux and subsequently the associated dose rates were calculated from the activation levels of the Au foils. The concrete shielding material was found to provide adequate shielding for all energies of neutrons emerging from beam port no-2 of the SAFARI-1 research reactorwithin a thickness of 40 cm of concrete.

Magnon Valve Effect between Two Magnetic Insulators.

PubMed

Wu, H; Huang, L; Fang, C; Yang, B S; Wan, C H; Yu, G Q; Feng, J F; Wei, H X; Han, X F

2018-03-02

The key physics of the spin valve involves spin-polarized conduction electrons propagating between two magnetic layers such that the device conductance is controlled by the relative magnetization orientation of two magnetic layers. Here, we report the effect of a magnon valve which is made of two ferromagnetic insulators (YIG) separated by a nonmagnetic spacer layer (Au). When a thermal gradient is applied perpendicular to the layers, the inverse spin Hall voltage output detected by a Pt bar placed on top of the magnon valve depends on the relative orientation of the magnetization of two YIG layers, indicating the magnon current induced by the spin Seebeck effect at one layer affects the magnon current in the other layer separated by Au. We interpret the magnon valve effect by the angular momentum conversion and propagation between magnons in two YIG layers and conduction electrons in the Au layer. The temperature dependence of the magnon valve ratio shows approximately a power law, supporting the above magnon-electron spin conversion mechanism. This work opens a new class of valve structures beyond the conventional spin valves.

Magnon Valve Effect between Two Magnetic Insulators

NASA Astrophysics Data System (ADS)

Wu, H.; Huang, L.; Fang, C.; Yang, B. S.; Wan, C. H.; Yu, G. Q.; Feng, J. F.; Wei, H. X.; Han, X. F.

2018-03-01

The key physics of the spin valve involves spin-polarized conduction electrons propagating between two magnetic layers such that the device conductance is controlled by the relative magnetization orientation of two magnetic layers. Here, we report the effect of a magnon valve which is made of two ferromagnetic insulators (YIG) separated by a nonmagnetic spacer layer (Au). When a thermal gradient is applied perpendicular to the layers, the inverse spin Hall voltage output detected by a Pt bar placed on top of the magnon valve depends on the relative orientation of the magnetization of two YIG layers, indicating the magnon current induced by the spin Seebeck effect at one layer affects the magnon current in the other layer separated by Au. We interpret the magnon valve effect by the angular momentum conversion and propagation between magnons in two YIG layers and conduction electrons in the Au layer. The temperature dependence of the magnon valve ratio shows approximately a power law, supporting the above magnon-electron spin conversion mechanism. This work opens a new class of valve structures beyond the conventional spin valves.

Fabrication of wear-resistant silicon microprobe tips for high-speed surface roughness scanning devices

NASA Astrophysics Data System (ADS)

Wasisto, Hutomo Suryo; Yu, Feng; Doering, Lutz; Völlmeke, Stefan; Brand, Uwe; Bakin, Andrey; Waag, Andreas; Peiner, Erwin

2015-05-01

Silicon microprobe tips are fabricated and integrated with piezoresistive cantilever sensors for high-speed surface roughness scanning systems. The fabrication steps of the high-aspect-ratio silicon microprobe tips were started with photolithography and wet etching of potassium hydroxide (KOH) resulting in crystal-dependent micropyramids. Subsequently, thin conformal wear-resistant layer coating of aluminum oxide (Al2O3) was demonstrated on the backside of the piezoresistive cantilever free end using atomic layer deposition (ALD) method in a binary reaction sequence with a low thermal process and precursors of trimethyl aluminum and water. The deposited Al2O3 layer had a thickness of 14 nm. The captured atomic force microscopy (AFM) image exhibits a root mean square deviation of 0.65 nm confirming the deposited Al2O3 surface quality. Furthermore, vacuum-evaporated 30-nm/200-nm-thick Au/Cr layers were patterned by lift-off and served as an etch mask for Al2O3 wet etching and in ICP cryogenic dry etching. By using SF6/O2 plasma during inductively coupled plasma (ICP) cryogenic dry etching, micropillar tips were obtained. From the preliminary friction and wear data, the developed silicon cantilever sensor has been successfully used in 100 fast measurements of 5- mm-long standard artifact surface with a speed of 15 mm/s and forces of 60-100 μN. Moreover, the results yielded by the fabricated silicon cantilever sensor are in very good agreement with those of calibrated profilometer. These tactile sensors are targeted for use in high-aspect-ratio microform metrology.

Silver flip chip interconnect technology and solid state bonding

NASA Astrophysics Data System (ADS)

Sha, Chu-Hsuan

In this dissertation, fluxless transient liquid phase (TLP) bonding and solid state bonding between thermal expansion mismatch materials have been developed using Ag-In binary systems, pure Au, Ag, and Cu-Ag composite. In contrast to the conventional soldering process, fluxless bonding technique eliminates any corrosion and contamination problems caused by flux. Without flux, it is possible to fabricate high quality joints in large bonding areas where the flux is difficult to clean entirely. High quality joints are crucial to bonding thermal expansion mismatch materials since shear stress develops in the bonded pair. Stress concentration at voids in joints could increases breakage probability. In addition, intermetallic compound (IMC) formation between solder and underbump metallurgy (UBM) is essential for interconnect joint formation in conventional soldering process. However, the interface between IMC and solder is shown to be the weak interface that tends to break first during thermal cycling and drop tests. In our solid state bonding technique, there is no IMC involved in the bonding between Au to Au, Ag and Cu, and Ag and Au. All the reliability issues related to IMC or IMC growth is not our concern. To sum up, ductile bonding media, such as Ag or Au, and proper metallic layered structure are utilized in this research to produce high quality joints. The research starts with developing a low temperature fluxless bonding process using electroplated Ag/In/Ag multilayer structures between Si chip and 304 stainless steel (304SS) substrate. Because the outer thin Ag layer effectively protects inner In layer from oxidation, In layer dissolves Ag layer and joints to Ag layer on the to-be-bonded Si chip when temperature reaches the reflow temperature of 166ºC. Joints consist of mainly Ag-rich Ag-In solid solution and Ag2In. Using this fluxless bonding technique, two 304SS substrates can be bonded together as well. From the high magnification SEM images taken at cross-section, there is no void or gap observed. The new bonding technique presented should be valuable in packaging high power electronic devices for high temperature operations. It should also be useful to bond two 304SS parts together at low bonding temperature of 190ºC. Solid state bonding technique is then introduced to bond semiconductor chips, such as Si, to common substrates, such as Cu or alumina, using pure Ag and Au at a temperature matching the typical reflow temperature used in packaging industries, 260°C. In bonding, we realize the possibilities of solid state bonding of Au to Au, Au to Ag, and Ag to Cu. The idea comes from that Cu, Ag, and Au are located in the same column on periodic table, meaning that they have similar electronic configuration. They therefore have a better chance to share electrons. Also, the crystal lattice of Cu, Ag, and Au is the same, face-centered cubic. In the project, the detailed bonding mechanism is beyond the scope and here we determine the bonding by the experimental result. Ag is chosen as the joint material because of its superior physical properties. It has the highest electrical and thermal conductivities among all metals. It has low yield strength and is relatively ductile. Au is considered as well because its excellent ductility and fatigue resistance. Thus, the Ag or Au joints can deform to accommodate the shear strain caused by CTE mismatch between Si and Cu. Ag and Au have melting temperatures higher than 950°C, so the pure Ag or Au joints are expected to sustain in high operating temperature. The resulting joints do not contain any intermetallic compound. Thus, all reliability issues associated with intermetallic growth in commonly used solder joints do not exist anymore. We finally move to the applications of solid state Ag bonding in flip chip interconnects design. At present, nearly all large-scale integrated circuit (IC) chips are packaged with flip-chip technology. This means that the chip is flipped over and the active (front) side is connected to the package using a large number of tiny solder joints, which provide mechanical support, electrical connection, and heat conduction. For chip-to-package level interconnects, a challenge is the severe mismatch in coefficient of thermal expansion (CTE) between chips and package substrates. The interconnect material thus needs to be compliant to deal with the CTE mismatch. At present, nearly all flip-chip interconnects in electronic industries are made of lead-free Sn-based solders. Soft solders are chosen due to high ductility, low yield strength, relatively low melting temperature, and reasonably good electrical and thermal conductivities. In the never ending scaling down trend, more and more transistors are placed on the same Si chip size. This results in larger pin-out numbers and smaller solder joints. According to International Technology Roadmap for Semiconductors (ITRS), by 2018, the pitch in flip-chip interconnects will become smaller than 70mum for high performance applications. Two problems occur. The first is increase in shear strain. The aspect ratio of flip-chip joints is constrained to 0.7 because it goes through molten phase in the reflow process. Therefore, smaller joints become shorter as well, resulting in larger shear strain arising from CTE mismatch between Si chips and package substrates. The second is increase in stress in the joints. Since intermetallic (IMC) thickness in the joint does not scale down with joint size, ratio of IMC thickness to joint height increases. This further enlarges the shear stress because the IMC does not deform as the soft solder does to accommodate CTE mismatch. In this research, the smallest dimension we achieve for Ag flip chip interconnect joint is 15mum in diameter. The ten advantages of Ag flip chip interconnect technology can be identified as (a) High electrical conductivity, 7.7 times of that of Pb-free solders, (b) High thermal conductivity, 5.2 times of that of Pb-free solders, (c) Completely fluxless, (d) No IMCs; all reliability issues associated with IMC and IMC growth do not exist, (e) Ag is very ductile and can manage CTE mismatch between chips and packages, (f) Ag joints can sustain at very high operation temperature because Ag has high melting temperature of 961°C, (g) No molten phase involved; the bump can better keep its shape and geometry, (h) No molten phase involved; bridging of adjacent bumps is less likely to occur, i. Aspect ratio of bumps can be made greater than 1, (j) The size of the bumps is only limited by the lithographic process. Cu-Ag composite flip chip interconnect joints is developed based on three reasons. The first is lower material cost. The second is to strengthen the columns because the yield strength of Cu is 6 times of that of Ag. The third is to avoid possible Ag migration between Ag electrodes under voltage at temperatures above 250°C. This Cu-Ag composite design presents a solution in the path to the scale down roadmap.

Coordination-based gold nanoparticle layers.

PubMed

Wanunu, Meni; Popovitz-Biro, Ronit; Cohen, Hagai; Vaskevich, Alexander; Rubinstein, Israel

2005-06-29

Gold nanoparticle (NP) mono- and multilayers were constructed on gold surfaces using coordination chemistry. Hydrophilic Au NPs (6.4 nm average core diameter), capped with a monolayer of 6-mercaptohexanol, were modified by partial substitution of bishydroxamic acid disulfide ligand molecules into their capping layer. A monolayer of the ligand-modified Au NPs was assembled via coordination with Zr4+ ions onto a semitransparent Au substrate (15 nm Au, evaporated on silanized glass and annealed) precoated with a self-assembled monolayer of the bishydroxamate disulfide ligand. Layer-by-layer construction of NP multilayers was achieved by alternate binding of Zr4+ ions and ligand-modified NPs onto the first NP layer. Characterization by atomic force microscopy (AFM), ellipsometry, wettability, transmission UV-vis spectroscopy, and cross-sectional transmission electron microscopy showed regular growth of NP layers, with a similar NP density in successive layers and gradually increased roughness. The use of coordination chemistry enables convenient step-by-step assembly of different ligand-possessing components to obtain elaborate structures. This is demonstrated by introducing nanometer-scale vertical spacing between a NP layer and the gold surface, using a coordination-based organic multilayer. Electrical characterization of the NP films was carried out using conductive AFM, emphasizing the barrier properties of the organic spacer multilayer. The results exhibit the potential of coordination self-assembly in achieving highly controlled composite nanostructures comprising molecules, NPs, and other ligand-derivatized components.

On the nature of L1{sub 0} ordering in equiatomic AuNi and AuCu thin films grown on Au(001)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dynna, M.; Marty, A.; Gilles, B.

1997-01-01

The L1{sub 0} ordering of thin epitaxial films having a (001) surface normal subject to elastic constraints imposed by a similarly oriented substrate has been investigated both experimentally and theoretically. Thin AuNi films grown by MBE at room temperature on Au(001) by means of the alternating deposition of Au and Ni are found to possess a L1{sub 0} structure free of periodic antiphase boundaries when growth is controlled in such a way as to ensure that the quantity of Au or Ni deposited is almost exactly equal to one monolayer. If such control is not exercised during growth, a structuremore » having periodic antiphase boundaries is formed. This behavior stands in contrast to that of AuCu during room temperature MBE growth on Au(001), where a strongly ordered L2{sub 0} structure free of antiphase boundaries is formed even on the codeposition of Au and Cu. The effect of elastic constraints on the state of order in an alloy film which undergoes an L2{sub 0} order-disorder transition is examined as a function of temperature, lattice mismatch, and film thickness within the context of a model which allows for the introduction of dislocations in order to relieve misfit strain. Calculations are performed in detail for the case of AuCu, where particular attention is paid to the coupling between film thickness, the number of misfit dislocations present at equilibrium, and the state of order.« less

Atomic and electronic structures of Si(1 1 1)-\\left(\\sqrt{\\mathbf{3}}\\times\\sqrt{\\mathbf{3}}\\right)\\text{R}\\mathbf{3}{{\\mathbf{0}}^{\\circ}} -Au and (6 × 6)-Au surfaces

NASA Astrophysics Data System (ADS)

Patterson, C. H.

2015-12-01

Si(1 1 1)-Au surfaces with around one monolayer of Au exhibit many ordered structures and structures containing disordered domain walls. Hybrid density functional theory (DFT) calculations presented here reveal the origin of these complex structures and tendency to form domain walls. The conjugate honeycomb chain trimer (CHCT) structure of the \\sqrt{3} -Au phase contains Si atoms with non-bonding surface states which can bind Au atoms in pairs in interstices of the CHCT structure and make this surface metallic. Si adatoms adsorbed on the \\sqrt{3} -Au surface induce a gapped surface through interaction with the non-bonding states. Adsorption of extra Au atoms in interstitial sites of the \\sqrt{3} -Au surface is stabilized by interaction with the non-bonding orbitals and leads to higher coverage ordered structures including the ≤ft(6× 6\\right) -Au phase. Extra Au atoms bound in interstitial sites of the \\sqrt{3} -Au surface result in top layer Si atoms with an SiAu4 butterfly wing configuration. The structure of a ≤ft(6× 6\\right) -Au phase, whose in-plane top atomic layer positions were previously determined by an electron holography technique (Grozea et al 1998 Surf. Sci. 418 32), is calculated using total energy minimization. The Patterson function for this structure is calculated and is in good agreement with data from an in-plane x-ray diffraction study (Dornisch et al 1991 Phys. Rev. B 44 11221). Filled and empty state scanning tunneling microscopy (STM) images are calculated for domain walls and the ≤ft(6× 6\\right) -Au structure. The ≤ft(6× 6\\right) -Au phase is 2D chiral and this is evident in computed and actual STM images. ≤ft(6× 6\\right) -Au and domain wall structures contain the SiAu4 motif with a butterfly wing shape. Chemical bonding within the Si-Au top layers of the \\sqrt{3} -Au and ≤ft(6× 6\\right) -Au surfaces is analyzed and an explanation for the SiAu4 motif structure is given.

Resistive switching of organic–inorganic hybrid devices of conductive polymer and permeable ultra-thin SiO2 films

NASA Astrophysics Data System (ADS)

Yamamoto, Shunsuke; Kitanaka, Takahisa; Miyashita, Tokuji; Mitsuishi, Masaya

2018-06-01

We propose a resistive switching device composed of conductive polymer (PEDOT:PSS) and SiO2 ultra-thin films. The SiO2 film was fabricated from silsesquioxane polymer nanosheets as a resistive switching layer. Devices with metal (Ag or Au)∣SiO2∣PEDOT:PSS architecture show good resistive switching performance with set–reset voltages as low as several hundred millivolts. The device properties and the working mechanism were investigated by varying the electrode material, surrounding atmosphere, and SiO2 film thickness. Results show that resistive switching is based on water and ion migration at the PEDOT:PSS∣SiO2 interface.

Resistive switching of organic-inorganic hybrid devices of conductive polymer and permeable ultra-thin SiO2 films.

PubMed

Yamamoto, Shunsuke; Kitanaka, Takahisa; Miyashita, Tokuji; Mitsuishi, Masaya

2018-06-29

We propose a resistive switching device composed of conductive polymer (PEDOT:PSS) and SiO 2 ultra-thin films. The SiO 2 film was fabricated from silsesquioxane polymer nanosheets as a resistive switching layer. Devices with metal (Ag or Au)∣SiO 2 ∣PEDOT:PSS architecture show good resistive switching performance with set-reset voltages as low as several hundred millivolts. The device properties and the working mechanism were investigated by varying the electrode material, surrounding atmosphere, and SiO 2 film thickness. Results show that resistive switching is based on water and ion migration at the PEDOT:PSS∣SiO 2 interface.

Quantum mechanism of nonlocal Gilbert damping in magnetic trilayers

NASA Astrophysics Data System (ADS)

Barati, Ehsan; Cinal, Marek

2015-06-01

A fully quantum-mechanical calculation of the Gilbert damping constant α in magnetic trilayers is done by employing the torque-correlation formula within a realistic tight-binding model. A remarkable enhancement of α in Co/NM1/NM2 trilayers is obtained due to adding the caps NM2=Pd, Pt, and it decays with the thickness of the spacers NM1=Cu, Ag, Au in agreement with experiment. Nonlocal origin of the Gilbert damping is visualized with its atomic layer contributions. It is shown that magnetization in Co is damped remotely by strong spin-orbit coupling in NM2 via quantum states with large amplitude in both Co and NM2.

Targeting mitochondria in cancer cells using gold nanoparticle-enhanced radiotherapy: A Monte Carlo study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirkby, Charles, E-mail: charles.kirkby@albertahealthservices.ca; Ghasroddashti, Esmaeel; Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4

2015-02-15

Purpose: Radiation damage to mitochondria has been shown to alter cellular processes and even lead to apoptosis. Gold nanoparticles (AuNPs) may be used to enhance these effects in scenarios where they collect on the outer membranes of mitochondria. A Monte Carlo (MC) approach is used to estimate mitochondrial dose enhancement under a variety of conditions. Methods: The PENELOPE MC code was used to generate dose distributions resulting from photons striking a 13 nm diameter AuNP with various thicknesses of water-equivalent coatings. Similar dose distributions were generated with the AuNP replaced by water so as to estimate the gain in dosemore » on a microscopic scale due to the presence of AuNPs within an irradiated volume. Models of mitochondria with AuNPs affixed to their outer membrane were then generated—considering variation in mitochondrial size and shape, number of affixed AuNPs, and AuNP coating thickness—and exposed (in a dose calculation sense) to source spectra ranging from 6 MV to 90 kVp. Subsequently dose enhancement ratios (DERs), or the dose with the AuNPs present to that for no AuNPs, for the entire mitochondrion and its components were tallied under these scenarios. Results: For a representative case of a 1000 nm diameter mitochondrion affixed with 565 AuNPs, each with a 13 nm thick coating, the mean DER over the whole organelle ranged from roughly 1.1 to 1.6 for the kilovoltage sources, but was generally less than 1.01 for the megavoltage sources. The outer membrane DERs remained less than 1.01 for the megavoltage sources, but rose to 2.3 for 90 kVp. The voxel maximum DER values were as high as 8.2 for the 90 kVp source and increased further when the particles clustered together. The DER exhibited dependence on the mitochondrion dimensions, number of AuNPs, and the AuNP coating thickness. Conclusions: Substantial dose enhancement directly to the mitochondria can be achieved under the conditions modeled. If the mitochondrion dose can be directly enhanced, as these simulations show, this work suggests the potential for both a tool to study the role of mitochondria in cellular response to radiation and a novel avenue for radiation therapy in that the mitochondria may be targeted, rather than the nuclear DNA.« less

Growth dynamics of L-cysteine SAMs on single-crystal gold surfaces: a metastable deexcitation spectroscopy study

NASA Astrophysics Data System (ADS)

Canepa, M.; Lavagnino, L.; Pasquali, L.; Moroni, R.; Bisio, F.; DeRenzi, V.; Terreni, S.; Mattera, L.

2009-07-01

We report on a metastable deexcitation spectroscopy investigation of the growth of L-cysteine layers deposited under UHV conditions on well-defined Au(110)- (1 × 2) and Au(111) surfaces. The interaction of He* with molecular orbitals gave rise to well-defined UPS-like Penning spectra which provided information on the SAM assembly dynamics and adsorption configurations. Penning spectra have been interpreted through comparison with molecular orbital DFT calculations of the free molecule and have been compared with XPS results of previous works. Regarding adsorption of first-layer molecules at room temperature (RT), two different growth regimes were observed. On Au(110), the absence of spectral features related to orbitals associated with SH groups indicated the formation of a compact SAM of thiolate molecules. On Au(111), the data demonstrated the simultaneous presence, since the early stages of growth, of strongly and weakly bound molecules, the latter showing intact SH groups. The different growth mode was tentatively assigned to the added rows of the reconstructed Au(110) surface which behave as extended defects effectively promoting the formation of the S-Au bond. The growth of the second molecular layer was instead observed to proceed similarly for both substrates. Second-layer molecules preferably adopt an adsorption configuration in which the SH group protrudes into the vacuum side.

Enhanced activity of CaFeMg layered double hydroxides-supported gold nanodendrites for the electrochemical evolution of oxygen and hydrogen in alkaline media

NASA Astrophysics Data System (ADS)

Havakeshian, Elaheh; Salavati, Hossein; Taei, Masoumeh; Hasheminasab, Fatemeh; Seddighi, Mohadeseh

2018-02-01

In this study, Au was electrodeposited on a support of CaFeMg layered double hydroxide and then, its catalytic activity was investigated for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Field emission scanning electron microscopy images showed that a uniform porous film of aggregated nano-particles of the LDH has been decorated with Au nanodendrite-like structures (AuNDs@LDH). The results obtained from polarization curves, Tafel plots and electrochemical impedance spectroscopy showed that the AuNDs@LDH exhibits lower overpotential, higher current density, faster kinetics and enhanced stability for both of the OER and HER, in comparison with the single AuNPs and LDH catalysts.

Investigation of sacrificial layer and building block for layered nanofabrication (LNF)

NASA Astrophysics Data System (ADS)

Shih, Ting-Yu

Layered Nanoscale Fabrication (LNF) is a "bottom-up" procedure that uses multiple layers to build 3-dimensional nanoscale structures. Here, in this dissertation, several candidates for sacrificial layers were explored, The thermal stability of gold nanoparticles and simple patterns are also reported. In order to obtain information on layer thickness and film quality; the samples were characterized using atomic force microscopy (AFM) and ellipsometry. Octadecyltrichlorosilane (OTS) was first investigated for use as a sacrificial layer and we studied filth growth by targeted self-replication of silane multilayers with and without the presence of thiolated gold nanoparticles on silicon oxide substrates. The particles adhered to the substrate during layer grafting. The film grew selectively on the substrate, without covering the particles. AFM was used to investigate the growth mechanism and the process of embedding the nanoparticles. OTS multilayer films up to 9 layers were grown in a linear, bilayer-by bilayer mode, free of islands and defects. We also report on studies of monolayer and multilayer formation of Methyl-11-dimethylmonochlorosilyl-undecanoate films. Flat multilayers up to 3-layers thick were grown. AFM was used to measure the height of an observable "edge" of the multilayer film and this provides and independent determination of the MOSUD layer height of 1.5 nm: However, the particles detached from the surface when we attempted to grow multilayer. One strategy of linking the particles to form 2D arrays, thermal activation in ambient air, was investigated. The morphological properties of flaked nanoparticles and structures on silicon oxide substrates before and after heating were characterized by using AFM. For widely separated 5 nm gold nanoparticles height decreased over 50% at 600 °C. Further heating to 630 °C caused most particles to completely disappear, with small amount of particle residue left on the surface. Particles positioned near to other particles first formed a neck-like structure at 570 °C and then deformed into one wide particle with tail-shape residue at 650 °C. Clusters of Au nanoparticles rearranged and became one large collide with particles residues left on the surface at 630 °C.

Preparation, characterization and dye adsorption of Au nanoparticles/ZnAl layered double oxides nanocomposites

NASA Astrophysics Data System (ADS)

Zhang, Yu Xin; Hao, Xiao Dong; Kuang, Min; Zhao, Han; Wen, Zhong Quan

2013-10-01

In this work, Au/ZnAl-layer double oxides (LDO) nanocomposties were prepared through a facile calcination process of AuCl4- intercalated ZnAl-layered double hydroxides (LDHs) nanocomposites. The morphology and crystal structure of these nanocomposites were characterized by Scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), and N2 sorption analysis. By tailoring the process parameter, such as calcination temperature, heating time and the component composition, the adsorption properties of methyl orange (MO) on the Au/ZnAl-LDO nanocomposites were investigated in this work. In a typical adsorption process, it was found that 0.985 mg of MO (0.01 g L-1, 100 mL, 1 mg of MO in total) can be removed in 60 min by utilizing only 2.5 mg of Au/ZnAl-LDO (Au content, 1%) as adsorbents. Our adsorption data obtained from the Langmuir model also gave good values of the determination coefficient, and the saturated adsorption capacity of Au/ZnAl-LDO nanocomposites for MO was found to be 627.51 mg/g under ambient condition (e.g., room temperature, 1 atm). In principle, these hybrid nanostructures with higher adsorption abilities could be very promising adsorbents for wastewater treatment.

Packaging Technology Designed, Fabricated, and Assembled for High-Temperature SiC Microsystems

NASA Technical Reports Server (NTRS)

Chen, Liang-Yu

2003-01-01

A series of ceramic substrates and thick-film metalization-based prototype microsystem packages designed for silicon carbide (SiC) high-temperature microsystems have been developed for operation in 500 C harsh environments. These prototype packages were designed, fabricated, and assembled at the NASA Glenn Research Center. Both the electrical interconnection system and the die-attach scheme for this packaging system have been tested extensively at high temperatures. Printed circuit boards used to interconnect these chip-level packages and passive components also are being fabricated and tested. NASA space and aeronautical missions need harsh-environment, especially high-temperature, operable microsystems for probing the inner solar planets and for in situ monitoring and control of next-generation aeronautical engines. Various SiC high-temperature-operable microelectromechanical system (MEMS) sensors, actuators, and electronics have been demonstrated at temperatures as high as 600 C, but most of these devices were demonstrated only in the laboratory environment partially because systematic packaging technology for supporting these devices at temperatures of 500 C and beyond was not available. Thus, the development of a systematic high-temperature packaging technology is essential for both in situ testing and the commercialization of high-temperature SiC MEMS. Researchers at Glenn developed new prototype packages for high-temperature microsystems using ceramic substrates (aluminum nitride and 96- and 90-wt% aluminum oxides) and gold (Au) thick-film metalization. Packaging components, which include a thick-film metalization-based wirebond interconnection system and a low-electrical-resistance SiC die-attachment scheme, have been tested at temperatures up to 500 C. The interconnection system composed of Au thick-film printed wire and 1-mil Au wire bond was tested in 500 C oxidizing air with and without 50-mA direct current for over 5000 hr. The Au thick-film metalization-based wirebond electrical interconnection system was also tested in an extremely dynamic thermal environment to assess thermal reliability. The I-V curve1 of a SiC high-temperature diode was measured in oxidizing air at 500 C for 1000 hr to electrically test the Au thick-film material-based die-attach assembly.

SERS study of surface plasmon resonance induced carrier movement in Au@Cu2O core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Chen, Lei; Zhang, Fan; Deng, Xin-Yu; Xue, Xiangxin; Wang, Li; Sun, Yantao; Feng, Jing-Dong; Zhang, Yongjun; Wang, Yaxin; Jung, Young Mee

2018-01-01

A plasmon induced carrier movement enhanced mechanism of surface-enhanced Raman scattering (SERS) was investigated using a charge-transfer (CT) enhancement mechanism. Here, we designed a strategy to study SERS in Au@Cu2O nanoshell nanoparticles with different shell thicknesses. Among the plasmonically coupled nanostructures, Au spheres with Cu2O shells have been of special interest due to their ultrastrong electromagnetic fields and controllable carrier transfer properties, which are useful for SERS. Au@Cu2O nanoshell nanoparticles (NPs) with shell thicknesses of 48-56 nm are synthesized that exhibit high SERS activity. This high activity originates from plasmonic-induced carrier transfer from Au@Cu2O to 4-mercaptobenzoic acid (MBA). The CT transition from the valence band (VB) of Cu2O to the second excited π-π* transition of MBA, and is of b2 electronic symmetry, which was enhanced significantly. The Herzberg-Teller selection rules were employed to predict the observed enhanced b2 symmetry modes. The system constructed in this study combines the long-range electromagnetic effect of Au NPs, localized surface plasmon resonance (LSPR) of the Au@Cu2O nanoshell, and the CT contribution to assist in understanding the SERS mechanism based on LSPR-induced carrier movement in metal/semiconductor nanocomposites.

Macular Choroidal Small-Vessel Layer, Sattler's Layer and Haller's Layer Thicknesses: The Beijing Eye Study.

PubMed

Zhao, Jing; Wang, Ya Xing; Zhang, Qi; Wei, Wen Bin; Xu, Liang; Jonas, Jost B

2018-03-13

To study macular choroidal layer thickness, 3187 study participants from the population-based Beijing Eye Study underwent spectral-domain optical coherence tomography with enhanced depth imaging for thickness measurements of the macular small-vessel layer, including the choriocapillaris, medium-sized choroidal vessel layer (Sattler's layer) and large choroidal vessel layer (Haller's layer). In multivariate analysis, greater thickness of all three choroidal layers was associated (all P < 0.05) with higher prevalence of age-related macular degeneration (AMD) (except for geographic atrophy), while it was not significantly (all P > 0.05) associated with the prevalence of open-angle glaucoma or diabetic retinopathy. There was a tendency (0.07 > P > 0.02) toward thinner choroidal layers in chronic angle-closure glaucoma. The ratio of small-vessel layer thickness to total choroidal thickness increased (P < 0.001; multivariate analysis) with older age and longer axial length, while the ratios of Sattler's layer and Haller's layer thickness to total choroidal thickness decreased. A higher ratio of small-vessel layer thickness to total choroidal thickness was significantly associated with a lower prevalence of AMD (early type, intermediate type, late geographic type). Axial elongation-associated and aging-associated choroidal thinning affected Haller's and Sattler's layers more markedly than the small-vessel layer. Non-exudative and exudative AMD, except for geographic atrophy, was associated with slightly increased choroidal thickness.

Dynamics of gold nanoparticles in synthetic and biopolymer solutions

NASA Astrophysics Data System (ADS)

Kohli, Indermeet

Soft matter systems of colloidal particles, polymers, amphiphiles and liquid crystals are ubiquitous in our everyday life. Food, plastics, soap and even human body is comprised of soft materials. Research conducted to understand the behavior of these soft matter systems at molecular level is essential for many interdisciplinary fields of study as well as important for many technological applications. We used gold nanoparticles (Au NPs) to investigate the length-scale dependent dynamics in semidilute poly(ethylene glycol) (PEG)-water, bovine serum albumin (BSA)-phosphate buffer, dextran and particulate solutions. In case of PEG-water solutions, fluctuation correlation spectroscopy was used to measure the diffusion coefficients (D) of the NPs as a function of their radius, Ro (2.5-10 nm), PEG volume fraction, φ (0-0.37) and molecular weight, Mw (5 kg/mol and 35 kg/mol). Our results indicate that the radius of gyration, Rg of the polymer chain is the crossover length scale for the NPs experiencing nanoviscosity or macroviscosity. In BSA-phosphate buffer solutions, we observed a monolayer formation at the NP surface with a thickness of 3.8 nm. The thickness of the adsorbed layer was independent of NP size. Best fit was obtained by the anticooperative binding model with the Hill coefficient of n = 0.63. Dissociation constant (KD) increased with particle size indicating stronger interaction of BSA with smaller sized NPs. We also contrasted the diffusion of gold nanoparticles (AuNPs) in crowded solutions of randomly branched polymer (dextran) and rigid, spherical particles (silica) to understand the roles played by the probe size and structure of the crowding agent in determining the probe diffusion. AuNPs of two different sizes (2.5 nm & 10 nm), dextran of molecular weight 70 kDa and silica particles of radius 10 nm were used. Our results indicated that the AuNP diffusion can be described using the bulk viscosity of the matrix and hydrodynamically dextran behaved similar to soft colloid. In all situations, we observed normal diffusion except for 2.5 nm sized AuNP particles in dextran solution at higher volume fraction. This was caused by transient trapping of particles within the random branches. The results showed the importance of macromolecular architecture in determining the transport properties in intracellular matrix and in cells with spiny dendrites.

Layered double hydroxide supported gold nanoclusters by glutathione-capped Au nanoclusters precursor method for highly efficient aerobic oxidation of alcohols.

PubMed

Li, Lun; Dou, Liguang; Zhang, Hui

2014-04-07

M3Al-layered double hydroxide (LDH, M = Mg, Ni, Co) supported Au nanoclusters (AuNCs) catalysts have been prepared for the first time by using water-soluble glutathione-capped Au nanoclusters as precursor. Detailed characterizations show that the ultrafine Au nanoclusters (ca. 1.5 ± 0.6 nm) were well dispersed on the surface of LDH with a loading of Au below ∼0.23 wt% upon synergetic interaction between AuNCs and M3Al-LDH. AuNCs/Mg3Al-LDH-0.23 exhibits much higher catalytic performance for the oxidation of 1-phenylethanol in toluene than Au/Mg3Al-LDH(DP) by the conventional deposition precipitation method and can be applied for a wide range of alcohols without basic additives. This catalyst can also be reused without loss of activity or selectivity. The AuNCs/M(= Ni, Co)3Al-LDH catalysts present even higher alcohol oxidation activity than AuNCs/Mg3Al-LDH. Particularly, AuNCs/Ni3Al-LDH-0.22 exhibits the highest activity (46 500 h(-1)) for the aerobic oxidation of 1-phenylethanol under solvent-free conditions attributed to its strongest Au-support synergy. The excellent activity and stability of AuNCs/M3Al-LDH catalysts render these materials promising candidates for green base-free selective oxidation of alcohols by molecular oxygen.

Synthesis of NiAu alloy and core-shell nanoparticles in water-in-oil microemulsions

NASA Astrophysics Data System (ADS)

Chiu, Hsin-Kai; Chiang, I.-Chen; Chen, Dong-Hwang

2009-07-01

NiAu alloy nanoparticles with various Ni/Au molar ratios were synthesized by the hydrazine reduction of nickel chloride and hydrogen tetrachloroaurate in the microemulsion system. They had a face-centered cubic structure and a mean diameter of 6-13 nm, decreasing with increasing Au content. As Au nanoparticles did, they showed a characteristic absorption peak at about 520 nm but the intensity decreased with increasing Ni content. Also, they were nearly superparamagnetic, although the magnetization decreased significantly with increasing Au content. Under an external magnetic field, they could be self-organized into the parallel lines. In addition, the core-shell nanoparticles, Ni3Au1@Au, were prepared by the Au coating on the surface of Ni3Au1 alloy nanoparticles. By increasing the hydrogen tetrachloroaurate concentration for Au coating, the thickness of Au shells could be raised and led to an enhanced and red-shifted surface plasmon absorption.

Visualization of Individual Images in Patterned Organic-Inorganic Multilayers Using GISAXS-CT.

PubMed

Ogawa, Hiroki; Nishikawa, Yukihiro; Takenaka, Mikihito; Fujiwara, Akihiko; Nakanishi, Yohei; Tsujii, Yoshinobu; Takata, Masaki; Kanaya, Toshiji

2017-05-16

Using grazing-incidence small-angle scattering (GISAXS) with computed tomography (CT), we have individually reconstructed the spatial distribution of a thin gold (Au) layer buried under a thin poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) layer. Owing to the difference between total reflection angles of Au and PS-b-P2VP, the scattering profiles for Au nanoparticles and self-assembled nanostructures of PS-b-P2VP could be independently obtained by changing the X-ray angle of incidence. Reconstruction of scattering profiles allows one to separately characterize spatial distributions in Au and PS-b-P2VP nanostructures.

Low frequency noise in the unstable contact region of Au-to-Au microcontact for microelectromechanical system switches

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qiu, Haodong; Wang, Hong, E-mail: ewanghong@ntu.edu.sg; Ke, Feixiang

The noise behavior of Au-to-Au microcontact for microelectromechanical system switches has been experimentally studied in the unstable contact region. The results suggest that the electrical conduction remains nonmetallic at the initial stage during contact formation due to the existence of alien films, and traps in the alien layer located at the contact interface could play an important role in determining the conduction noise. The conduction fluctuation induced by electron trapping-detrapping associated with the hydrocarbon layer is found to be an intrinsic noise source contributing to the low frequency noise in the unstable contact region.

Low frequency noise in the unstable contact region of Au-to-Au microcontact for microelectromechanical system switches

NASA Astrophysics Data System (ADS)

Qiu, Haodong; Wang, Hong; Ke, Feixiang

2014-06-01

The noise behavior of Au-to-Au microcontact for microelectromechanical system switches has been experimentally studied in the unstable contact region. The results suggest that the electrical conduction remains nonmetallic at the initial stage during contact formation due to the existence of alien films, and traps in the alien layer located at the contact interface could play an important role in determining the conduction noise. The conduction fluctuation induced by electron trapping-detrapping associated with the hydrocarbon layer is found to be an intrinsic noise source contributing to the low frequency noise in the unstable contact region.

Third-order optical nonlinearity studies of bilayer Au/Ag metallic films

NASA Astrophysics Data System (ADS)

Mezher, M. H.; Chong, W. Y.; Zakaria, R.

2016-05-01

This paper presents nonlinear optical studies of bilayer metallic films of gold (Au) and silver (Ag) on glass substrate prepared using electron beam evaporation. The preparation of Au and Ag nanoparticles (NPs) on the substrate involved the use of electron beam deposition, then thermal annealing at 600 °C and 270 °C, respectively, to produce a randomly distributed layer of Au and a layer of Ag NPs. Observation of field-effect scanning electron microscope images indicated the size of the NPs. Details of the optical properties related to peak absorption of surface plasmon resonance of the nanoparticle were revealed by use of UV-Vis spectroscopy. The Z-scan technique was used to measure the nonlinear absorption and nonlinear refraction of the fabricated NP layers. The third-order nonlinear refractive index coefficients for Au and Ag are (-9.34 and  -1.61)  ×  10-11 cm2 W-1 given lower n 2, in comparison with bilayer (Au and Ag) NPs at  -1.24  ×  10-10 cm2 W-1. The results show bilayer NPs have higher refractive index coefficients thus enhance the nonlinearity effects.

Time-resolved X-ray Absorption Spectroscopy for Electron Transport Study in Warm Dense Gold

NASA Astrophysics Data System (ADS)

Lee, Jong-Won; Bae, Leejin; Engelhorn, Kyle; Heimann, Philip; Ping, Yuan; Barbrel, Ben; Fernandez, Amalia; Beckwith, Martha Anne; Cho, Byoung-Ick; GIST Team; IBS Team; LBNL Collaboration; SLAC Collaboration; LLNL Collaboration

2015-11-01

The warm dense Matter represents states of which the temperature is comparable to Fermi energy and ions are strongly coupled. One of the experimental techniques to create such state in the laboratory condition is the isochoric heating of thin metal foil with femtosecond laser pulses. This concept largely relies on the ballistic transport of electrons near the Fermi-level, which were mainly studied for the metals in ambient conditions. However, they were barely investigated in warm dense conditions. We present a time-resolved x-ray absorption spectroscopy measured for the Au/Cu dual layered sample. The front Au layer was isochorically heated with a femtosecond laser pulse, and the x-ray absorption changes around L-edge of Cu, which was attached on the backside of Au, was measured with a picosecond resolution. Time delays between the heating of the `front surface' of Au layer and the alternation of x-ray spectrum of Cu attached on the `rear surface' of Au indicate the energetic electron transport mechanism through Au in the warm dense conditions. IBS (IBS-R012-D1) and the NRF (No. 2013R1A1A1007084) of Korea.

Structure and giant magnetoresistance of granular Co-Cu nanolayers prepared by cross-beam pulsed laser deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jesche, A.; Stoecker, H.; Levin, A. A.

2010-01-15

A series of Co{sub x}Cu{sub 100-x} (x=0, 40-75, 100) layers with thicknesses between 13 and 55 nm were prepared on silicon substrates using cross-beam pulsed laser deposition. Wide-angle x-ray diffraction (WAXRD), transmission electron microscopy (TEM), and electrical transport measurements revealed a structure consisting of decomposed cobalt and copper grains with grain sizes of about 10 nm. The influence of cobalt content and layer thickness on the grain size is discussed. Electron diffraction indicates the presence of an intermetallic Co-Cu phase of Cu{sub 3}Au structure type. Thermal treatment at temperatures between 525 and 750 K results in the progressive decomposition ofmore » Co and Cu, with an increase of the grain sizes up to about 100 nm. This is tunable by controlling the temperature and duration of the anneal, and is directly observable in WAXRD patterns and TEM images. A careful analysis of grain size and the coherence length of the radiation used allows for an accurate interpretation of the x-ray diffraction patterns, by taking into account coherent and noncoherent scattering. The alloy films show a giant magnetoresistance of 1%-2.3% with the maximum obtained after annealing at around 725 K.« less

Efficient semitransparent perovskite solar cells for 23.0%-efficiency perovskite/silicon four-terminal tandem cells

DOE PAGES

Chen, Bo; Bai, Yang; Yu, Zhengshan; ...

2016-07-19

Here, we have investigated semi-transparent perovskite solar cells and infrared enhanced silicon heterojunction cells for high-efficiency tandem devices. A semi-transparent metal electrode with good electrical conductivity and optical transparency has been fabricated by thermal evaporation of 7 nm of Au onto a 1-nm-thick Cu seed layer. For this electrode to reach its full potential, MAPbI3 thin films were formed by a modified one-step spin-coating method, resulting in a smooth layer that allowed the subsequent metal thin film to remain continuous. The fabricated semi-transparent perovskite solar cells demonstrated 16.5% efficiency under one-sun illumination, and were coupled with infrared-enhanced silicon heterojunction cellsmore » tuned specifically for perovskite/Si tandem devices. A double-layer antireflection coating at the front side and MgF2 reflector at rear side of the silicon heterojunction cells reduced parasitic absorption of near-infrared light, leading to 6.5% efficiency after filtering with a perovskite device and 23.0% summed efficiency for the perovskite/Si tandem device.« less

Efficient semitransparent perovskite solar cells for 23.0%-efficiency perovskite/silicon four-terminal tandem cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Bo; Bai, Yang; Yu, Zhengshan

Here, we have investigated semi-transparent perovskite solar cells and infrared enhanced silicon heterojunction cells for high-efficiency tandem devices. A semi-transparent metal electrode with good electrical conductivity and optical transparency has been fabricated by thermal evaporation of 7 nm of Au onto a 1-nm-thick Cu seed layer. For this electrode to reach its full potential, MAPbI3 thin films were formed by a modified one-step spin-coating method, resulting in a smooth layer that allowed the subsequent metal thin film to remain continuous. The fabricated semi-transparent perovskite solar cells demonstrated 16.5% efficiency under one-sun illumination, and were coupled with infrared-enhanced silicon heterojunction cellsmore » tuned specifically for perovskite/Si tandem devices. A double-layer antireflection coating at the front side and MgF2 reflector at rear side of the silicon heterojunction cells reduced parasitic absorption of near-infrared light, leading to 6.5% efficiency after filtering with a perovskite device and 23.0% summed efficiency for the perovskite/Si tandem device.« less

Layer-by-Layer-Assembled AuNPs-Decorated First-Generation Poly(amidoamine) Dendrimer with Reduced Graphene Oxide Core as Highly Sensitive Biosensing Platform with Controllable 3D Nanoarchitecture for Rapid Voltammetric Analysis of Ultratrace DNA Hybridization.

PubMed

Jayakumar, Kumarasamy; Camarada, María Belén; Dharuman, Venkataraman; Rajesh, Rajendiran; Venkatesan, Rengarajan; Ju, Huangxian; Maniraj, Mahalingam; Rai, Abhishek; Barman, Sudipta Roy; Wen, Yangping

2018-06-27

The structure and electrochemical properties of layer-by-layer-assembled gold nanoparticles (AuNPs)-decorated first-generation (G1) poly(amidoamine) dendrimer (PD) with reduced graphene oxide (rGO) core as a highly sensitive and label-free biosensing platform with a controllable three-dimensional (3D) nanoarchitecture for the rapid voltammetric analysis of DNA hybridization at ultratrace levels were characterized. Mercaptopropinoic acid (MPA) was self-assembled onto Au substrate, then GG1PD formed by the covalent functionalization between the amino terminals of G1PD and carboxyl terminals of rGO was covalently linked onto MPA, and finally AuNPs were decorated onto GG1PD by strong physicochemical interaction between AuNPs and -OH of rGO in GG1PD, which was characterized through different techniques and confirmed by computational calculation. This 3D controllable thin-film electrode was optimized and evaluated using [Fe(CN) 6 ] 3-/4- as the redox probe and employed to covalently immobilize thiol-functionalized single-stranded DNA as biorecognition element to form the DNA nanobiosensor, which achieved fast, ultrasensitive, and high-selective differential pulse voltammetric analysis of DNA hybridization in a linear range from 1 × 10 -6 to 1 × 10 -13 g m -1 with a low detection limit of 9.07 × 10 -14 g m -1 . This work will open a new pathway for the controllable 3D nanoarchitecture of the layer-by-layer-assembled metal nanoparticles-functionalized lower-generation PD with two-dimensional layered nanomaterials as cores that can be employed as ultrasensitive and label-free nanobiodevices for the fast diagnosis of specific genome diseases in the field of biomedicine.

Interface observation in Au/Ni/p-GaN studied by HREM and energy-filtering TEM.

PubMed

Lim, Sung-Hwan; Ra, Tae-Yeub; Kim, Won-Yong

2003-01-01

The contact resistance of Au/Ni/p-GaN ohmic contacts for different annealing conditions was measured. This was then correlated with microstructure, including phase distribution, observed by high-resolution electron microscopy combined with energy-filtering imaging. A contact resistance of 2.22 x 10(-4) ohms cm2 for Au/Ni contacts to p-GaN after annealing at 500 degrees C for 5 min in air ambient was obtained. NiO layers were identified at the interface and upper area of annealed Ni/Au/p-GaN for air ambient. In addition, an Au layer was found at the interface of p-GaN due to a reversal reaction during annealing. Identification of the observed phases is discussed, along with possible formation mechanisms for the ohmic contacts in the Au/Ni/p-GaN system.

A first principles study on the electronic origins of silver segregation at the Ag-Au (111) surface

NASA Astrophysics Data System (ADS)

Hoppe, Sandra; Müller, Stefan

2017-12-01

The special electronic structure of gold gives rise to many interesting phenomena, such as its color. The surface segregation of the silver-gold system has been the subject of numerous experimental and theoretical studies, yielding conflicting results ranging from strong Ag surface enrichment to Au surface segregation. Via a combined approach of density functional theory (DFT) and statistical physics, we have analyzed the segregation at the Ag-Au (111) surface with different Ag bulk concentrations. Interestingly, we observe a moderate Au surface segregation, which is due to a charge transfer from the less electronegative Ag to Au. Canonical Monte Carlo simulations suggest that the calculated concentration profile with a Au-enriched surface layer remains stable up to higher temperatures. However, the presence of adsorbed oxygen reverses the segregation behavior and leads to strong Ag enrichment of the surface layer.

Fabrication of a Flexible Amperometric Glucose Sensor Using Additive Processes

PubMed Central

Du, Xiaosong; Durgan, Christopher J.; Matthews, David J.; Motley, Joshua R.; Tan, Xuebin; Pholsena, Kovit; Árnadóttir, Líney; Castle, Jessica R.; Jacobs, Peter G.; Cargill, Robert S.; Ward, W. Kenneth; Conley, John F.; Herman, Gregory S.

2015-01-01

This study details the use of printing and other additive processes to fabricate a novel amperometric glucose sensor. The sensor was fabricated using a Au coated 12.7 μm thick polyimide substrate as a starting material, where micro-contact printing, electrochemical plating, chloridization, electrohydrodynamic jet (e-jet) printing, and spin coating were used to pattern, deposit, chloridize, print, and coat functional materials, respectively. We have found that e-jet printing was effective for the deposition and patterning of glucose oxidase inks with lateral feature sizes between ~5 to 1000 μm in width, and that the glucose oxidase was still active after printing. The thickness of the permselective layer was optimized to obtain a linear response for glucose concentrations up to 32 mM and no response to acetaminophen, a common interfering compound, was observed. The use of such thin polyimide substrates allow wrapping of the sensors around catheters with high radius of curvature ~250 μm, where additive and microfabrication methods may allow significant cost reductions. PMID:26634186

Facile deposition of gold nanoparticles on core-shell Fe3O4@polydopamine as recyclable nanocatalyst

NASA Astrophysics Data System (ADS)

Zhao, Yan; Yeh, Yaowen; Liu, Rui; You, Jinmao; Qu, Fengli

2015-07-01

A simple and green method for the controllable synthesis of core-shell Fe3O4 polydopamine nanoparticles (Fe3O4@PDA NPs) with tunable shell thickness and their application as a recyclable nanocatalyst support is presented. Magnetite Fe3O4 NPs formed in a one-pot process by the hydrothermal approach with a diameter of ˜240 nm were coated with a polydopamine shell layer with a tunable thickness of 15-45 nm. The facile deposition of Au NPs atop Fe3O4@PDA NPs was achieved by utilizing PDA as both the reducing agent and the coupling agent. The satellite nanocatalysts exhibited high catalytic performance for the reduction of p-nitrophenol. Furthermore, the recovery and reuse of the catalyst was demonstrated 8 times without detectible loss in activity. The synergistic combination of unique features of PDA and magnetic nanoparticles establishes these core-shell NPs as a versatile platform for potential applications.

Landau damping and steepening of interplanetary nonlinear hydromagnetic waves

NASA Technical Reports Server (NTRS)

Barnes, A.; Chao, J. K.

1977-01-01

According to collisionless shock theories, the thickness of a shock front should be of the order of the characteristic lengths of the plasmas (the Debye length, the proton and Larmor radii, etc.). Chao and Lepping (1974), found, however, that 30% of the observed interplanetary shocks at 1 AU have thicknesses much larger than these characteristic lengths. It is the objective of the present paper to investigate whether the competition between nonlinear steepening and Landau damping can result in a wave of finite width that does not steepen into a shock. A heuristic model of such a wave is developed and tested by the examples of two structures that are qualitatively shocklike, but thicker than expected from theory. It is found that both events are in the process of steepening and their limiting thicknesses due to Landau damping are greater than the corresponding proton Larmor radius for both structures as observed at Mariner 5 (nearer the sun than 1 AU) but are comparable to the proton Larmor radius for Explorer (near 1 AU) observations.

Colloidal domain lithography for regularly arranged artificial magnetic out-of-plane monodomains in Au/Co/Au layers.

PubMed

Kuświk, Piotr; Ehresmann, Arno; Tekielak, Maria; Szymański, Bogdan; Sveklo, Iosif; Mazalski, Piotr; Engel, Dieter; Kisielewski, Jan; Lengemann, Daniel; Urbaniak, Maciej; Schmidt, Christoph; Maziewski, Andrzej; Stobiecki, Feliks

2011-03-04

Regularly arranged magnetic out-of-plane patterns in continuous and flat films are promising for applications in data storage technology (bit patterned media) or transport of individual magnetic particles. Whereas topographic magnetic structures are fabricated by standard lithographical techniques, the fabrication of regularly arranged artificial domains in topographically flat films is difficult, since the free energy minimization determines the existence, shape, and regularity of domains. Here we show that keV He(+) ion bombardment of Au/Co/Au layer systems through a colloidal mask of hexagonally arranged spherical polystyrene beads enables magnetic patterning of regularly arranged cylindrical magnetic monodomains with out-of-plane magnetization embedded in a ferromagnetic matrix with easy-plane anisotropy. This colloidal domain lithography creates artificial domains via periodic lateral anisotropy variations induced by periodic defect density modulations. Magnetization reversal of the layer system observed by magnetic force microscopy shows individual disc switching indicating monodomain states.

Organic-inorganic Au/PVP/ZnO/Si/Al semiconductor heterojunction characteristics

NASA Astrophysics Data System (ADS)

Mokhtari, H.; Benhaliliba, M.

2017-11-01

The paper reports the fabrication and characterization of a novel Au/PVP/ZnO/Si/Al semiconductor heterojunction (HJ) diode. Both inorganic n type ZnO and organic polyvinyl pyrrolidone (PVP) layers have grown by sol-gel spin-coating route at 2000 rpm. The front and back metallic contacts are thermally evaporated in a vacuum at pressure of 10-6 Torr having a diameter of 1.5 mm and a thickness of 250 nm. The detailed analysis of the forward and reverse bias current-voltage characteristics has been provided. Consequently, many electronic parameters, such as ideality factor, rectification coefficient, carrier concentration, series resistance, are then extracted. Based upon our results a non-ideal diode behavior is revealed and ideality factor exceeds the unity (n > 4). A high rectifying (~4.6 × 10 4) device is demonstrated. According to Cheung-Cheung and Norde calculation models, the barrier height and series resitance are respectively of 0.57 eV and 30 kΩ. Ohmic and space charge limited current (SCLC) conduction mechanisms are demonstrated. Such devices will find applications as solar cell, photodiode and photoconductor.

ELECTRON THERMAL CONDUCTION AS A POSSIBLE PHYSICAL MECHANISM TO MAKE THE INNER HELIOSHEATH THINNER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Izmodenov, V. V.; Alexashov, D. B.; Ruderman, M. S., E-mail: izmod@ipmnet.ru

2014-11-01

We show that electron thermal conductivity may strongly affect the heliosheath plasma flow and the global pattern of the solar wind's interaction with the local interstellar medium. In particular, it leads to strong reduction of the inner heliosheath thickness, which makes it possible to explain (qualitatively) why Voyager 1 (V1) has crossed the heliopause at an unexpectedly small heliocentric distance of 122 AU. To estimate the effect of thermal conductivity, we consider a limiting case when thermal conduction is very effective. To do that, we assume the plasma flow in the entire heliosphere is nearly isothermal. Due to this effect,more » the heliospheric distance of the termination shock has increased by about 15 AU in the V1 direction compared with the adiabatic case with γ = 5/3. The heliospheric distance of the heliopause has decreased by about 27 AU. As a result, the thickness of the inner heliosheath in the model has decreased by about 42 AU and has become equal to 32 AU.« less

Facile synthesis of gold nanomaterials with unusual crystal structures.

PubMed

Fan, Zhanxi; Huang, Xiao; Chen, Ye; Huang, Wei; Zhang, Hua

2017-11-01

Gold (Au) nanomaterials have attracted wide research attention, owing to their high chemical stability, promising catalytic properties, excellent biocompatibility, unique electronic structure and outstanding localized surface plasmon resonance (LSPR) absorption properties; all of which are closely related to their size and shape. Recently, crystal-phase-controlled synthesis of noble metal nanomaterials has emerged as a promising strategy to tune their physicochemical properties. This protocol describes the detailed experimental procedures for the crystal-phase-controlled syntheses of Au nanomaterials with unusual crystal structures under mild conditions. Briefly, pure hexagonal close-packed (hcp) Au square sheets (AuSSs) with a thickness of ∼2.4 nm are synthesized using a graphene-oxide-assisted method in which HAuCl 4 is reduced by oleylamine in a mixture of hexane and ethanol. By using pure hexane as the solvent, well-dispersed ultrathin hcp/face-centered cubic (fcc) Au nanowires with a diameter of ∼1.6 nm on graphene oxide can be obtained. Meanwhile, hcp/fcc Au square-like plates with a side length of 200-400 nm are prepared via the secondary growth of Au on the hcp AuSSs. Remarkably, hexagonal (4H) Au nanoribbons with a thickness of 2.0-6.0 nm can be synthesized with a one-pot colloidal method in which HAuCl 4 is reduced by oleylamine in a mixed solvent of hexane and 1,2-dichloropropane. It takes 17-37 h for the synthesis of these Au nanomaterials with unusual crystal structures. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) are used to characterize the resultant Au nanomaterials, which could have many promising applications, such as biosensing, near-IR photothermal therapy, catalysis and surface-enhanced Raman scattering (SERS).

Electrical and Optical Properties of Green Polymer Light Emitting Diodes with Various Structures of Au Nanoparticles.

PubMed

Park, Byung Min; Kim, Gi Ppeum; Mun, Sae Chan; Chang, Ho Jung

2015-10-01

The green polymer light emitting diodes (PLEDs) were fabricated using the solution precursor synthesis method. To improve the device's electrical. and optical properties, gold (Au) nanoparticles (NPs) were added to the hole injection layer (HIL) with poly(3,4-ethylene- dioxythiophene):poly(styrenesulfolnate) ( PSS) organic material. The green PLED devices with a structure of glass/ITO/PEDOT:PSS+Au NPs/PVK:Ir(ppy)3/TPBi/LiF/Al were prepared by conventional spin-coating and thermal evaporation methods. Various concentrations of Au NPs were doped to the HILs to optimize the device's light emitting characteristic. The effects of Au NPs concentrations on the properties of PLEDs were investigated. The doping concentrations of Au NPs were changed ranging from 0.0 to 1.0 vol%. At the optimized Au NPs concentration of 0.5 vol%, we also studied the effects of various film layers with and without Au NPs on the properties of PLEDs. The maximum luminance and external quantum efficiency of the devices were found to be 20,430 cd/m2 and 7.49%, respectively.

[Sb{sub 4}Au{sub 4}Sb{sub 4}]{sup 2−}: A designer all-metal aromatic sandwich

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian, Wen-Juan; You, Xue-Rui; Guo, Jin-Chang

We report on the computational design of an all-metal aromatic sandwich, [Sb{sub 4}Au{sub 4}Sb{sub 4}]{sup 2−}. The triple-layered, square-prismatic sandwich complex is the global minimum of the system from Coalescence Kick and Minima Hopping structural searches. Following a standard, qualitative chemical bonding analysis via canonical molecular orbitals, the sandwich complex can be formally described as [Sb{sub 4}]{sup +}[Au{sub 4}]{sup 4−}[Sb{sub 4}]{sup +}, showing ionic bonding characters with electron transfers in between the Sb{sub 4}/Au{sub 4}/Sb{sub 4} layers. For an in-depth understanding of the system, one needs to go beyond the above picture. Significant Sb → Au donation and Sb ←more » Au back-donation occur, redistributing electrons from the Sb{sub 4}/Au{sub 4}/Sb{sub 4} layers to the interlayer Sb–Au–Sb edges, which effectively lead to four Sb–Au–Sb three-center two-electron bonds. The complex is a system with 30 valence electrons, excluding the Sb 5s and Au 5d lone-pairs. The two [Sb{sub 4}]{sup +} ligands constitute an unusual three-fold (π and σ) aromatic system with all 22 electrons being delocalized. An energy gap of ∼1.6 eV is predicted for this all-metal sandwich. The complex is a rare example for rational design of cluster compounds and invites forth-coming synthetic efforts.« less

A novel platform designed by Au core/inorganic shell structure conjugated onto MTX/LDH for chemo-photothermal therapy.

PubMed

Tian, De-Ying; Wang, Wei-Yuan; Li, Shu-Ping; Li, Xiao-Dong; Sha, Zhao-Lin

2016-05-30

A novel platform making up of methotrexate intercalated layered double hydroxide (MTX/LDH) hybrid doped with gold nanoparticles (NPs) may have great potential both in chemo-photothermal therapy and the simultaneous drug delivery. In this paper, a promising platform of Au@PDDA-MTX/LDH was developed for anti-tumor drug delivery and synergistic therapy. Firstly, Au NPs were coated using Layer-by-Layer (LbL) technology by alternate deposition of poly (diallyldimethylammonium chloride) (PDDA) and MTX molecules, and then the resulting core-shell structures (named as Au@PDDA-MTX) were directly conjugated onto the surface of MTX/LDH hybrid by electrostatic attraction to afford Au@PDDA-MTX/LDH NPs. Here MTX was used as both the agent for surface modification and the anti-tumor drug for chemotherapy. The platform of Au@PDDA-MTX/LDH NPs not only had a high drug-loading capacity, but also showed excellent colloidal stability and interesting pH-responsive release profile. In vitro drug release studies demonstrated that MTX released from Au@PDDA-MTX/LDH was relatively slow under normal physiological pH, but it was enhanced significantly at a weak acidic pH value. Furthermore, the combined treatment of cancer cells by using Au@PDDA-MTX/LDH for synergistic hyperthermia ablation and chemotherapy was demonstrated to exhibit higher therapeutic efficacy than either single treatment alone, underscoring the great potential of the platform for cancer therapy. Copyright © 2016 Elsevier B.V. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zou, Lianfeng; Li, Jonathan; Zakharov, Dmitri

Using in situ transmission electron microscopy that spatially and temporally resolves the evolution of the atomic structure in the surface and subsurface regions, we Find that the surface segregation of Au atoms in a Cu(Au) solid solution results in the nucleation and growth of a (2 × 1) missing-row reconstructed, half-unit-cell thick L1 2 Cu 3Au(110) surface alloy. Our in situ electron microscopy observations and atomistic simulations demonstrate that the (2 × 1) reconstruction of the Cu 3Au(110) surface alloy remains as a stable surface structure as a result of the favored Cu-Au diatom configuration.

Corrosion investigation of fire-gilded bronze involving high surface resolution spectroscopic imaging

NASA Astrophysics Data System (ADS)

Masi, G.; Chiavari, C.; Avila, J.; Esvan, J.; Raffo, S.; Bignozzi, M. C.; Asensio, M. C.; Robbiola, L.; Martini, C.

2016-03-01

Gilded bronzes are often affected by severe corrosion, due to defects in the Au layer and Au/Cu alloy galvanic coupling, stimulated by large cathodic area of the gilded layer. Galvanic corrosion, triggered by gilding defects, leads to products growth at the Au/bronze interface, inducing blistering or break-up of the Au layer. In this context, fire-gilded bronze replicas prepared by ancient methods (use of spreadable Au-Hg paste) was specifically characterised by compiling complementary spectroscopic and imaging information before/after accelerated ageing with synthetic rain. Fire-gilded bronze samples were chemically imaged in cross-section at nano-metric scale (<200 nm) using high energy and lateral resolution synchrotron radiation photoemission (HR-SRPES) of core levels and valence band after conventional characterisation of the samples by Glow Discharge optical Emission Spectroscopy (GD-OES) and conventional X-ray photoelectron spectroscopy (XPS). We have found a net surface enrichment in Zn and Sn after fire-gilding and presence of metallic Hg, Pb and Cu within the Au layer. Moreover, the composition distribution of the elements together with their oxidation has been determined. It was also revealed that metallic phases including Hg and Pb remain in the gilding after corrosion. Moreover, selective dissolution of Zn and Cu occurs in the crater due to galvanic coupling, which locally induces relative Sn species enrichment (decuprification). The feasibility advantages and disadvantages of chemical imaging using HR-SRPES to study artworks have been investigated on representative replicas.

Metal-phthalocyanine ordered layers on Au(110): Metal-dependent adsorption energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Massimi, Lorenzo, E-mail: lorenzo.massimi@uniroma1.it; Angelucci, Marco; Gargiani, Pierluigi

2014-06-28

Iron-phthalocyanine and cobalt-phthalocyanine chains, assembled along the Au(110)-(1×2) reconstructed channels, present a strong interaction with the Au metallic states, via the central metal ion. X-ray photoemission spectroscopy from the metal-2p core-levels and valence band high-resolution ultraviolet photoelectron spectroscopy bring to light signatures of the interaction of the metal-phthalocyanine single-layer with gold. The charge transfer from Au to the molecule causes the emerging of a metal-2p core level component at lower binding energy with respect to that measured in the molecular thin films, while the core-levels associated to the organic macrocycle (C and N 1s) are less influenced by the adsorption,more » and the macrocycles stabilize the interaction, inducing a strong interface dipole. Temperature Programmed Desorption experiments and photoemission as a function of temperature allow to estimate the adsorption energy for the thin-films, mainly due to the molecule-molecule van der Waals interaction, while the FePc and CoPc single-layers remain adsorbed on the Au surface up to at least 820 K.« less

Mechanical modeling and characteristic study for the adhesive contact of elastic layered media

NASA Astrophysics Data System (ADS)

Zhang, Yuyan; Wang, Xiaoli; Tu, Qiaoan; Sun, Jianjun; Ma, Chenbo

2017-11-01

This paper investigates the adhesive contact between a smooth rigid sphere and a smooth elastic layered medium with different layer thicknesses, layer-to-substrate elastic modulus ratios and adhesion energy ratios. A numerical model is established by combining elastic responses of the contact system and an equation of equivalent adhesive contact pressure which is derived based on the Hamaker summation method and the Lennard-Jones intermolecular potential law. Simulation results for hard layer cases demonstrate that variation trends of the pull-off force with the layer thickness and elastic modulus ratio are complex. On one hand, when the elastic modulus ratio increases, the pull-off force decreases at smaller layer thicknesses, decreases at first and then increases at middle layer thicknesses, while increases monotonously at larger layer thicknesses. On the other hand, the pull-off force decreases at first and then increases with the increase in the layer thickness. Furthermore, a critical layer thickness above which the introduction of hard layer cannot reduce adhesion and an optimum layer thickness under which the pull-off force reaches a minimum are found. Both the critical and optimum layer thicknesses become larger with an increase in the Tabor parameter, while they tend to decrease with the increase in the elastic modulus ratio. In addition, the pull-off force increases sublinearly with the adhesion energy ratio if the layer thickness and elastic modulus ratio are fixed.

Reactive Capture of Gold Nanoparticles by Strongly Physisorbed Monolayers on Graphite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wei, Xiaoliang; Tong, Wenjun; Fidler, Vlastimil

2012-12-01

Anthracene Diels Alder adducts (DAa) bearing two long side chains (H-(CH2)22O(CH2)6OCH2-) at the 1- and 5-positions form self-assembled monolayers (SAMs) at the phenyloctane - highly oriented pyrolytic graphite (HOPG) interface. The long DAa side chains promote strong physisorption of the monolayer to HOPG and maintain the monolayer morphology upon rinsing or incubation in ethanol and air-drying of the substrate. Incorporating a carboxylic acid group on the DAa core enables capture of 1 - 4 nm diameter gold nanoparticles (AuNP) provided (i) the monolayer containing DAa-carboxylic acids is treated with Cu2+ ions and (ii) the organic coating on the AuNP containsmore » carboxylic acids (11-mercaptoundecanoic acid, MUA-AuNP). AuNP capture by the monolayer proceeds with formation of Cu2+ - carboxylate coordination complexes. The captured AuNP appear as mono- and multi-layered clusters at high coverage on HOPG. The surface density of the captured AuNPs can be adjusted from AuNP multi-layers to isolated AuNPs by varying incubation times, MUA-AuNP concentration, the number density of carboxylic acids in the monolayer, the number of MUA per AuNP, and the post-incubation treatments.« less

Next Generation Proton Beam Writing: A Platform Technology for Nanowire Integration

DTIC Science & Technology

2010-06-01

Final Report AOARD 09-4020 Next Generation Proton Beam Writing: a platform technology for Nanowire Integration JA van Kan1, AA Bettiol1, T...PBW with a finely focused 2 MeV beam was used to write holes in a matrix of thick PMMA . A G-G developer was used to develop the PMMA patterns. The...solution. The deposition speed was about 1 μm of plated Au in every 5 min. When a sufficient thickness of Au had been deposited, the PMMA around the

The Next Generation Focusing Lenses for Proton Beam Writing

DTIC Science & Technology

2009-07-28

Final Report AOARD 07-4017 The Next Generation Focusing Lenses for Proton Beam Writing JA van Kan1, AA Bettiol1, T. Osipowicz2, MBH Breese3, and F...with a finely focused 2 MeV beam was used to write holes in a matrix of thick PMMA . A G-G developer was used to develop the PMMA patterns. The G-G...The deposition speed was about 1 μm of plated Au in every 5 min. When a sufficient thickness of Au had been deposited, the PMMA around the gold

Ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Weiquan; Becker, Jacob; Liu, Shi

2014-05-28

This paper reports the proposal, design, and demonstration of ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer to optimize light management and minimize non-radiative recombination. According to our recently developed semi-analytical model, this design offers one of the highest potential achievable efficiencies for GaAs solar cells possessing typical non-radiative recombination rates found among commercially available III-V arsenide and phosphide materials. The structure of the demonstrated solar cells consists of an In{sub 0.49}Ga{sub 0.51}P/GaAs/In{sub 0.49}Ga{sub 0.51}P double-heterostructure PN junction with an ultra-thin 300 nm thick GaAs absorber, combined with a 5 μm thick Al{sub 0.52}In{sub 0.48}P layer with amore » textured as-grown surface coated with Au used as a reflective back scattering layer. The final devices were fabricated using a substrate-removal and flip-chip bonding process. Solar cells with a top metal contact coverage of 9.7%, and a MgF{sub 2}/ZnS anti-reflective coating demonstrated open-circuit voltages (V{sub oc}) up to 1.00 V, short-circuit current densities (J{sub sc}) up to 24.5 mA/cm{sup 2}, and power conversion efficiencies up to 19.1%; demonstrating the feasibility of this design approach. If a commonly used 2% metal grid coverage is assumed, the anticipated J{sub sc} and conversion efficiency of these devices are expected to reach 26.6 mA/cm{sup 2} and 20.7%, respectively.« less

A Nanostructured Bifunctional platform for Sensing of Glucose Biomarker in Artificial Saliva: Synergy in hybrid Pt/Au surfaces.

PubMed

Raymundo-Pereira, Paulo A; Shimizu, Flávio M; Coelho, Dyovani; Piazzeta, Maria H O; Gobbi, Angelo L; Machado, Sergio A S; Oliveira, Osvaldo N

2016-12-15

We report on a bimetallic, bifunctional electrode where a platinum (Pt) surface was patterned with nanostructured gold (Au) fingers with different film thicknesses, which was functionalized with glucose oxidase (GOx) to yield a highly sensitive glucose biosensor. This was achieved by using selective adsorption of a self-assembled monolayer (SAM) onto Au fingers, which allowed GOx immobilization only onto the Au-SAM surface. This modified electrode was termed bifunctional because it allowed to simultaneously immobilize the biomolecule (GOx) on gold to catalyze glucose, and detect hydrogen peroxide on Pt sites. Optimized electrocatalytic activity was reached for the architecture Pt/Au-SAM/GOx with 50nm thickness of Au, where synergy between Pt and Au allowed for detection of hydrogen peroxide (H2O2) at a low applied potential (0V vs. Ag/AgCl). Detection was performed for H2O2 in the range between 4.7 and 102.7 nmol L(-1), with detection limit of 3.4×10(-9) mol L(-1) (3.4 nmol L(-1)) and an apparent Michaelis-Menten rate constant of 3.2×10(-6)molL(-1), which is considerably smaller than similar devices with monometallic electrodes. The methodology was validated by measuring glucose in artificial saliva, including in the presence of interferents. The synergy between Pt and Au was confirmed in electrochemical impedance spectroscopy measurements with an increased electron transfer, compared to bare Pt and Au electrodes. The approach for fabricating the reproducible bimetallic Pt/Au electrodes is entirely generic and may be explored for other types of biosensors and biodevices where advantage can be taken of the combination of the two metals. Copyright © 2016 Elsevier B.V. All rights reserved.

Au/ZnS core/shell nanocrystals as an efficient anode photocatalyst in direct methanol fuel cells.

PubMed

Chen, Wei-Ta; Lin, Yin-Kai; Yang, Ting-Ting; Pu, Ying-Chih; Hsu, Yung-Jung

2013-10-04

Au/ZnS core/shell nanocrystals with controllable shell thicknesses were synthesized using a cysteine-assisted hydrothermal method. Incorporating Au/ZnS nanocrystals into the traditional Pt-catalyzed half-cell reaction led to a 43.3% increase in methanol oxidation current under light illumination, demonstrating their promising potential for metal/semiconductor hybrid nanocrystals as the anode photocatalyst in direct methanol fuel cells.

Synthesis and magnetic property of T4 virus-supported gold-coated iron ternary nanocomposite

NASA Astrophysics Data System (ADS)

Xu, Ziming; Sun, Hongjing; Gao, Faming; Hou, Li; Li, Na

2012-12-01

Herein, we present a novel method based on the use of the symmetrical T4 bacteriophage capsid as a scaffold for preparing the gold-coated iron ternary core/shell nanostructure. Results showed that the thick gold shell was obtained to effectively protect Fe core from oxidation. Magnetic measurements showed that the nanocomposites were superparamagnetic at room temperature with a blocking temperature of about 35 K. At 3 K, its coercivity of 1142.86 Oe was larger than the existing experimental values. The magnetic property of Au/T4 was also tested, demonstrating the source of the magnetic sample arising from the Fe core only. The absorption spectrum of the Fe@Au/T4 complex was measured and compared with gold/virus. Different thickness gold shells were controlled in the synthesis by tuning the Au salt addition. On the basis of results and discussion, we further speculated the general growing mechanism of the template-supported Fe@Au process.

Induced Superconductivity and Engineered Josephson Tunneling Devices in Epitaxial (111)-Oriented Gold/Vanadium Heterostructures.

PubMed

Wei, Peng; Katmis, Ferhat; Chang, Cui-Zu; Moodera, Jagadeesh S

2016-04-13

We report a unique experimental approach to create topological superconductors by inducing superconductivity into epitaxial metallic thin film with strong spin-orbit coupling. Utilizing molecular beam epitaxy technique under ultrahigh vacuum conditions, we are able to achieve (111) oriented single phase of gold (Au) thin film grown on a well-oriented vanadium (V) s-wave superconductor film with clean interface. We obtained atomically smooth Au thin films with thicknesses even down to below a nanometer showing near-ideal surface quality. The as-grown V/Au bilayer heterostructure exhibits superconducting transition at around 3.9 K. Clear Josephson tunneling and Andreev reflection are observed in S-I-S tunnel junctions fabricated from the epitaxial bilayers. The barrier thickness dependent tunneling and the associated subharmonic gap structures (SGS) confirmed the induced superconductivity in Au (111), paving the way for engineering thin film heterostructures based on p-wave superconductivity and nano devices exploiting Majorana Fermions for quantum computing.

Multifunctional Virus-Nanoshell Assembly for Targeted Hyperthermia and Viral Gene Therapy for Breast Cancer

DTIC Science & Technology

2012-06-01

thin layer of Au. The unique property of Au NS is the tunability of its plasma resonance. Au NS can accumulate heat upon irradiation with NIR light...which is very useful for biomedical applications because tissues are transparent to NIR. Using NIR irradiation , the Au NS can be induced to...and 6161.5 Dalton for the product. Figure 1. (a) UV_VIS spectrum of Au nanoshell. Insect is TEM image of Au Nanoshell, scale bar: 20 nm. (b

Nanoporous gold membranes: From morphological control to fuel cell catalysis

NASA Astrophysics Data System (ADS)

Ding, Yi

Porous noble metals are particularly attractive for scientific research and industrial applications such as catalysis, sensing, and filtration. In this thesis, I will discuss the fabrication, characterization, and application of a new class of porous metals, called nanoporous metals (NPM). NPM is made during selective dissolution (also called dealloying) of reactive components (e.g., silver) from multi-component alloys (e.g., Ag/Au alloy). Commercially available white gold leaf (Ag65Au35) can, for example, be etched into nanoporous gold (NPG) membrane by simply floating the leaf on concentrated nitric acid for periods of a few minutes. NPG leaf adopts a single crystal porous structure within individual grains. The microstructure of NPG, such as the pore size, is tunable between a few nanometers to sub-micron length scale by either thermal annealing or post-treatment in nitric acid for extended period of time. A new gas-liquid-solid interface electroless plating technique is developed to uniformly cover the NPG surface with other metals, such as silver and platinum. This technique allows new opportunities of making functionalized nanostructures. We show that a combination of silver plating and dealloying can be used to make multimodal porous metals, which are expected to have application in sensing field. Electroless platinum plating onto NPG shows very usual growth mode. TEM observation indicates that the platinum layer on NPG surface takes a novel form of layer-islanding growth (Stranski-Krastanov growth). Annealing the Pt/NPG composite smoothens the Pt islands and forms a 1 nm coherent Pt layer on the NPG backbone, possibly with dislocation formation at the Pt/Au interface. Furthermore, it was found that we could dissolve the gold away in aqueous gold etchant, leaving behind the 1 nm-thick Pt shell, a structure we call nanotubular mesoporous platinum (NMP). Pt plated NPG has a series of unique structural properties, such as high active surface area, thermally stable, low Pt usage, and better tolerance to CO poisoning. We incorporated it as a membrane electrode into a working proton exchange membrane fuel cells (PEMFC). Preliminary results show that Pt/NPG has very good fuel cell performance at a very low platinum loading.

The influence of titanium adhesion layer oxygen stoichiometry on thermal boundary conductance at gold contacts

NASA Astrophysics Data System (ADS)

Olson, David H.; Freedy, Keren M.; McDonnell, Stephen J.; Hopkins, Patrick E.

2018-04-01

We experimentally demonstrate the role of oxygen stoichiometry on the thermal boundary conductance across Au/TiOx/substrate interfaces. By evaporating two different sets of Au/TiOx/substrate samples under both high vacuum and ultrahigh vacuum conditions, we vary the oxygen composition in the TiOx layer from 0 ≤ x ≤ 2.85. We measure the thermal boundary conductance across the Au/TiOx/substrate interfaces with time-domain thermoreflectance and characterize the interfacial chemistry with x-ray photoemission spectroscopy. Under high vacuum conditions, we speculate that the environment provides a sufficient flux of oxidizing species to the sample surface such that one essentially co-deposits Ti and these oxidizing species. We show that slower deposition rates correspond to a higher oxygen content in the TiOx layer, which results in a lower thermal boundary conductance across the Au/TiOx/substrate interfacial region. Under the ultrahigh vacuum evaporation conditions, pure metallic Ti is deposited on the substrate surface. In the case of quartz substrates, the metallic Ti reacts with the substrate and getters oxygen, leading to a TiOx layer. Our results suggest that Ti layers with relatively low oxygen compositions are best suited to maximize the thermal boundary conductance.

Naphthalenetetracarboxylic diimide layer-based transistors with nanometer oxide and side chain dielectrics operating below one volt.

PubMed

Jung, Byung Jun; Martinez Hardigree, Josue F; Dhar, Bal Mukund; Dawidczyk, Thomas J; Sun, Jia; See, Kevin Cua; Katz, Howard E

2011-04-26

We designed a new naphthalenetetracarboxylic diimide (NTCDI) semiconductor molecule with long fluoroalkylbenzyl side chains. The side chains, 1.2 nm long, not only aid in self-assembly and kinetically stabilize injected electrons but also act as part of the gate dielectric in field-effect transistors. On Si substrates coated only with the 2 nm thick native oxide, NTCDI semiconductor films were deposited with thicknesses from 17 to 120 nm. Top contact Au electrodes were deposited as sources and drains. The devices showed good transistor characteristics in air with 0.1-1 μA of drain current at 0.5 V of V(G) and V(DS) and W/L of 10-20, even though channel width (250 μm) is over 1000 times the distance (20 nm) between gate and drain electrodes. The extracted capacitance-times-mobility product, an expression of the sheet transconductance, can exceed 100 nS V(-1), 2 orders of magnitude higher than typical organic transistors. The vertical low-frequency capacitance with gate voltage applied in the accumulation regime reached as high as 650 nF/cm(2), matching the harmonic sum of capacitances of the native oxide and one side chain and indicating that some gate-induced carriers in such devices are distributed among all of the NTCDI core layers, although the preponderance of the carriers are still near the gate electrode. Besides demonstrating and analyzing thickness-dependent NTCDI-based transistor behavior, we also showed <1 V detection of dinitrotoluene vapor by such transistors.

Near-IR-Absorbing Gold Nanoframes with Enhanced Physiological Stability and Improved Biocompatibility for In Vivo Biomedical Applications.

PubMed

Wang, Liying; Chen, Yunching; Lin, Hsin Yao; Hou, Yung-Te; Yang, Ling-Chu; Sun, Aileen Y; Liu, Jia-Yu; Chang, Chien-Wen; Wan, Dehui

2017-02-01

This paper describes the synthesis of near-infrared (NIR)-absorbing gold nanoframes (GNFs) and a systematic study comparing their physiological stability and biocompatibility with those of hollow Au-Ag nanoshells (GNSs), which have been used widely as photothermal agents in biomedical applications because of their localized surface plasmon resonance (LSPR) in the NIR region. The GNFs were synthesized in three steps: galvanic replacement, Au deposition, and Ag dealloying, using silver nanospheres (SNP) as the starting material. The morphology and optical properties of the GNFs were dependent on the thickness of the Au coating layer and the degree of Ag dealloying. The optimal GNF exhibited a robust spherical skeleton composed of a few thick rims, but preserved the distinctive LSPR absorbance in the NIR region-even when the Ag content within the skeleton was only 10 wt %, 4-fold lower than that of the GNSs. These GNFs displayed an attractive photothermal conversion ability and great photothermal stability, and could efficiently kill 4T1 cancer cells through light-induced heating. Moreover, the GNFs preserved their morphology and optical properties after incubation in biological media (e.g., saline, serum), whereas the GNSs were unstable under the same conditions because of rapid dissolution of the considerable silver content with the shell. Furthermore, the GNFs had good biocompatibility with normal cells (e.g., NIH-3T3 and hepatocytes; cell viability for both cells: >90%), whereas the GNSs exhibited significant dose-dependent cytotoxicity (e.g., cell viability for hepatocytes at 1.14 nM: ca. 11%), accompanied by the induction of reactive oxygen species. Finally, the GNFs displayed good biocompatibility and biosafety in an in vivo mouse model; in contrast, the accumulation of GNSs caused liver injury and inflammation. Our results suggest that GNFs have great potential to serve as stable, biocompatible NIR-light absorbers for in vivo applications, including cancer detection and combination therapy.

Paper-Based Device for Rapid Visualization of NADH Based on Dissolution of Gold Nanoparticles.

PubMed

Liang, Pingping; Yu, Haixiang; Guntupalli, Bhargav; Xiao, Yi

2015-07-15

We describe a paper-based device that enables rapid and sensitive room-temperature detection of dihydronicotinamide adenine dinucleotide (NADH) via a colorimetric readout and demonstrate its value for monitoring NAD+-driven enzymatic reactions. Our system is based on NADH-mediated inhibition of gold nanoparticle (AuNPs) dissolution in a Au3+-cetyltrimethylammonium bromide (CTAB) solution. We fabricated a device consisting of a mixed cellulose ester paper featuring a wax-encircled, AuNP-coated film atop a cotton absorbent layer sandwiched between two plastic cover layers. In the absence of NADH, the Au3+-CTAB complex dissolves the AuNP layer completely, generating a white color in the test zone. In the presence of NADH, Au3+ is rapidly reduced to Au+, greatly decreasing the dissolution of AuNPs and yielding a red color that becomes stronger at increasing concentrations of NADH. This device exploits capillary force-assisted vertical diffusion, allowing us to apply a 25 μL sample to a surface-confined test zone to achieve a detection limit of 12.5 μM NADH. We used the enzyme glucose dehydrogenase as a model to demonstrate that our paper-based device can monitor NAD+-driven biochemical processes with and without selective dehydrogenase inhibitors by naked-eye observation within 4 min at room temperature in a small sample volume. We believe that our paper-based device could offer a valuable and low-cost analytical tool for monitoring NAD+-associated enzymatic reactions and screening for dehydrogenase inhibitors in a variety of testing contexts.

Tessellated gold nanostructures from Au144(SCH2CH2Ph)60 molecular precursors and their use in organic solar cell enhancement

NASA Astrophysics Data System (ADS)

Bauld, Reg; Hesari, Mahdi; Workentin, Mark S.; Fanchini, Giovanni

2014-06-01

We report for the first time the fabrication of nanocomposite hole-blocking layers consisting of poly-3,4-ethylene-dioxythiophene:poly-styrene-sulfonate (PEDOT:PSS) thin films incorporating networks of gold nanoparticles assembled from Au144(SCH2CH2Ph)60, a molecular gold precursor. These thin films can be prepared reproducibly on indium tin oxide by spinning on it Au144(SCH2CH2Ph)60 solutions in chlorobenzene, annealing the resulting thin film at 400 °C, and subsequently spinning PEDOT:PSS on top. The use of our nanocomposite hole-blocking layers for enhancing the photoconversion efficiency of bulk heterojunction organic solar cells is demonstrated. By varying the concentration of Au144(SCH2CH2Ph)60 in the starting solution and the annealing time, different gold nanostructures were obtained ranging from individual gold nanoparticles (AuNPs) to tessellated networks of gold nanostructures (Tess-AuNPs). Improvement in organic solar cell efficiencies up to 10% relative to a reference cell is demonstrated with Tess-AuNPs embedded in PEDOT:PSS.

Enhancement of plasmon-induced charge separation efficiency by coupling silver nanocubes with a thin gold film

NASA Astrophysics Data System (ADS)

Akiyoshi, Kazutaka; Saito, Koichiro; Tatsuma, Tetsu

2016-10-01

Plasmon-induced charge separation (PICS), in which an energetic electron is injected from a plasmonic nanoparticle (NP) to a semiconductor on contact, is often inhibited by a protecting agent adsorbed on the NP. We addressed this issue for an Ag nanocube-TiO2 system by coating it with a thin Au layer or by inserting the Au layer between the nanocubes (NCs) and TiO2. Both of the electrodes exhibit much higher photocurrents due to PICS than the electrodes without the Au film or the Ag NCs. These photocurrent enhancements can be explained in terms of PICS with accelerated electron transfer, in which electron injection from the Ag NCs or Ag@Au core-shell NCs to TiO2 is promoted by the Au film, or PICS enhanced by a nanoantenna effect, in which the electron injection from the Au film to TiO2 is enhanced by optical near field generated by the Ag NC.

Atomically Visualizing Elemental Segregation-Induced Surface Alloying and Restructuring

DOE PAGES

Zou, Lianfeng; Li, Jonathan; Zakharov, Dmitri; ...

2017-12-01

Using in situ transmission electron microscopy that spatially and temporally resolves the evolution of the atomic structure in the surface and subsurface regions, we Find that the surface segregation of Au atoms in a Cu(Au) solid solution results in the nucleation and growth of a (2 × 1) missing-row reconstructed, half-unit-cell thick L1 2 Cu 3Au(110) surface alloy. Our in situ electron microscopy observations and atomistic simulations demonstrate that the (2 × 1) reconstruction of the Cu 3Au(110) surface alloy remains as a stable surface structure as a result of the favored Cu-Au diatom configuration.

The Influence of Interstitial Ga and Interfacial Au (sub 2)P (sub 3) on the Electrical and Metallurgical Behavior of Au-Contacted III-V Semiconductors

NASA Technical Reports Server (NTRS)

Weizer, Victor G.; Fatemi, Navid S.

1991-01-01

The introduction of a very small amount of Ga into Au contact metallization on InP is shown to have a significant effect on both the metallurgical and electrical behavior of that contact system. Ga atoms in the interstices of the Au lattice are shown to be effective in preventing the solid state reactions that normally take place between Au and InP during contact sintering. In addition to suppressing the metallurgical interaction, the presence of small amounts of Ga is shown to cause an order of magnitude reduction in the specific contact resistivity. Evidence is presented that the reactions of GaP and GaAs with Au contacts are also drastically affected by the presence of Ga. The sintering behavior of the Au-GaP and the Au-GaAs systems (as contrasted with that of the Au-InP system) is explained as due to the presence of interstitial Ga in the contact metallization. Finally the large, two-to-three order of magnitude drop in the contact resistance that occurs in the Au-InP system upon sintering at 400 degrees Centigrade is shown to be a result of the formation of an Au (sub 2) P (sub 3) layer at the metal-semiconductor interface. Contact resistivities in the 10 (sup -6) ohm square centimeter range are obtained for as-deposited Au on InP when a thin (20 Angstrom) layer of Au (sub 2) P (sub 3) is introduced between the InP and the Au contacts.

Layered double hydroxide supported gold nanoclusters by glutathione-capped Au nanoclusters precursor method for highly efficient aerobic oxidation of alcohols

NASA Astrophysics Data System (ADS)

Li, Lun; Dou, Liguang; Zhang, Hui

2014-03-01

M3Al-layered double hydroxide (LDH, M = Mg, Ni, Co) supported Au nanoclusters (AuNCs) catalysts have been prepared for the first time by using water-soluble glutathione-capped Au nanoclusters as precursor. Detailed characterizations show that the ultrafine Au nanoclusters (ca. 1.5 +/- 0.6 nm) were well dispersed on the surface of LDH with a loading of Au below ~0.23 wt% upon synergetic interaction between AuNCs and M3Al-LDH. AuNCs/Mg3Al-LDH-0.23 exhibits much higher catalytic performance for the oxidation of 1-phenylethanol in toluene than Au/Mg3Al-LDH(DP) by the conventional deposition precipitation method and can be applied for a wide range of alcohols without basic additives. This catalyst can also be reused without loss of activity or selectivity. The AuNCs/M(= Ni, Co)3Al-LDH catalysts present even higher alcohol oxidation activity than AuNCs/Mg3Al-LDH. Particularly, AuNCs/Ni3Al-LDH-0.22 exhibits the highest activity (46 500 h-1) for the aerobic oxidation of 1-phenylethanol under solvent-free conditions attributed to its strongest Au-support synergy. The excellent activity and stability of AuNCs/M3Al-LDH catalysts render these materials promising candidates for green base-free selective oxidation of alcohols by molecular oxygen.M3Al-layered double hydroxide (LDH, M = Mg, Ni, Co) supported Au nanoclusters (AuNCs) catalysts have been prepared for the first time by using water-soluble glutathione-capped Au nanoclusters as precursor. Detailed characterizations show that the ultrafine Au nanoclusters (ca. 1.5 +/- 0.6 nm) were well dispersed on the surface of LDH with a loading of Au below ~0.23 wt% upon synergetic interaction between AuNCs and M3Al-LDH. AuNCs/Mg3Al-LDH-0.23 exhibits much higher catalytic performance for the oxidation of 1-phenylethanol in toluene than Au/Mg3Al-LDH(DP) by the conventional deposition precipitation method and can be applied for a wide range of alcohols without basic additives. This catalyst can also be reused without loss of activity or selectivity. The AuNCs/M(= Ni, Co)3Al-LDH catalysts present even higher alcohol oxidation activity than AuNCs/Mg3Al-LDH. Particularly, AuNCs/Ni3Al-LDH-0.22 exhibits the highest activity (46 500 h-1) for the aerobic oxidation of 1-phenylethanol under solvent-free conditions attributed to its strongest Au-support synergy. The excellent activity and stability of AuNCs/M3Al-LDH catalysts render these materials promising candidates for green base-free selective oxidation of alcohols by molecular oxygen. Electronic supplementary information (ESI) available: Details in experimental and further characterization. See DOI: 10.1039/c3nr05604j

Interface doping of conjugated organic films by means of diffusion of atomic components from the surfaces of semiconductors and of metal oxides.

PubMed

Komolov, A S; Akhremtchik, S N; Lazneva, E F

2011-08-15

The paper reports the results on the interface formation of 5-10 nm thick conjugated layers of Cu-phthalocyanine (CuPc) with a number of solid surfaces: polycrystalline Au, (SiO(2))n-Si, ZnO(0 0 0 1), Si(1 0 0), Ge(1 1 1), CdS(0 0 0 1) and GaAs(1 0 0). The results were obtained using Auger electron spectroscopy (AES) and low-energy target current electron spectroscopy (TCS). The organic overlayers were thermally deposited in situ in UHV onto substrate surfaces. The island-like organic deposits were excluded from the analysis so that only uniform organic deposits were considered. In the cases of polycrystalline Au, Si(1 0 0) and Ge(1 1 1) substrates the AES peaks of the substrate material attenuated down to the zero noise level upon the increase of the CuPc film thickness of 8-10 nm. The peaks corresponding to oxygen atoms in the case of SiO(2) substrate, and to atoms from the ZnO, GaAs and CdS substrates were clearly registered in the AES spectra of the 8-10 nm thick CuPc deposits. The relative concentration of the substrate atomic components diffused into the film was different from their relative concentration at the pure substrate surface. The concentration of the substrate dopant atoms in the CuPc film was estimated as one atom per one CuPc molecule. Using the target current electron spectroscopy, it was shown that the substrate atoms admixed in the CuPc film account for the appearance of a new peak in the density of unoccupied electronic states. Formation of intermediate TCS spectra until the CuPc deposit reaches 2-3 nm was observed in the cases of GaAs(1 0 0), ZnO(0 0 0 1), Ge(1 1 1) surfaces. The intermediate spectra show a less pronounced peak structure different from the one typical for the CuPc films. It was suggested that the intermediate layer was formed by the CuPc molecules fully or partially decomposed due to the interaction with the relatively reactive semiconductor surfaces. Copyright © 2010 Elsevier B.V. All rights reserved.

Electrochemical Sensor Coating Based on Electrophoretic Deposition of Au-Doped Self-Assembled Nanoparticles.

PubMed

Zhang, Rongli; Zhu, Ye; Huang, Jing; Xu, Sheng; Luo, Jing; Liu, Xiaoya

2018-02-14

The electrophoretic deposition (EPD) of self-assembled nanoparticles (NPs) on the surface of an electrode is a new strategy for preparing sensor coating. By simply changing the deposition conditions, the electrochemical response for an analyte of deposited NPs-based coating can be controlled. This advantage can decrease the difference between different batches of sensor coating and ensure the reproducibility of each sensor. This work investigated the effects of deposition conditions (including deposition voltage, pH value of suspension, and deposition time) on the structure and the electrochemical response for l-tryptophan of sensor coating formed from Au-doped poly(sodium γ-glutamate) with pendant dopamine units nanohybrids (Au/γ-PGA-DA NBs) via the EPD method. The structure and thickness of the deposited sensor coating were measured by atomic force microscopy, which demonstrated that the structure and thickness of coating can be affected by the deposition voltage, the pH value of the suspension, and the deposition time. The responsive current for l-tryptophan of the deposited sensor coating were measured by differential pulse voltammetry, which showed that the responsive current value was affected by the structure and thickness of the deposited coating. These arguments suggested that a rich design-space for tuning the electrochemical response for analyte and a source of variability in the structure of sensor coating can be provided by the deposition conditions. When Au/γ-PGA-DA NBs were deposited on the electrode surface and formed a continuous coating with particle morphology and thinner thickness, the deposited sensor coating exhibited optimal electrochemical response for l-tryptophan.

Impacts of age and sex on retinal layer thicknesses measured by spectral domain optical coherence tomography with Spectralis.

PubMed

Nieves-Moreno, María; Martínez-de-la-Casa, José M; Morales-Fernández, Laura; Sánchez-Jean, Rubén; Sáenz-Francés, Federico; García-Feijoó, Julián

2018-01-01

To examine differences in individual retinal layer thicknesses measured by spectral domain optical coherence tomography (SD-OCT) (Spectralis®) produced with age and according to sex. Cross-sectional, observational study. The study was conducted in 297 eyes of 297 healthy subjects aged 18 to 87 years. In one randomly selected eye of each participant the volume and mean thicknesses of the different macular layers were measured by SD-OCT using the instrument's macular segmentation software. Volume and mean thickness of macular retinal nerve fiber layer (mRNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), retinal pigmentary epithelium (RPE) and photoreceptor layer (PR). Retinal thickness was reduced by 0.24 μm for every one year of age. Age adjusted linear regression analysis revealed mean GCL, IPL, ONL and PR thickness reductions and a mean OPL thickness increase with age. Women had significantly lower mean GCL, IPL, INL, ONL and PR thicknesses and volumes and a significantly greater mRNFL volume than men. The thickness of most retinal layers varies both with age and according to sex. Longitudinal studies are needed to determine the rate of layer thinning produced with age.

Non-destructive prediction of enteric coating layer thickness and drug dissolution rate by near-infrared spectroscopy and X-ray computed tomography.

PubMed

Ariyasu, Aoi; Hattori, Yusuke; Otsuka, Makoto

2017-06-15

The coating layer thickness of enteric-coated tablets is a key factor that determines the drug dissolution rate from the tablet. Near-infrared spectroscopy (NIRS) enables non-destructive and quick measurement of the coating layer thickness, and thus allows the investigation of the relation between enteric coating layer thickness and drug dissolution rate. Two marketed products of aspirin enteric-coated tablets were used in this study, and the correlation between the predicted coating layer thickness and the obtained drug dissolution rate was investigated. Our results showed correlation for one product; the drug dissolution rate decreased with the increase in enteric coating layer thickness, whereas, there was no correlation for the other product. Additional examination of the distribution of coating layer thickness by X-ray computed tomography (CT) showed homogenous distribution of coating layer thickness for the former product, whereas the latter product exhibited heterogeneous distribution within the tablet, as well as inconsistent trend in the thickness distribution between the tablets. It was suggested that this heterogeneity and inconsistent trend in layer thickness distribution contributed to the absence of correlation between the layer thickness of the face and side regions of the tablets, which resulted in the loss of correlation between the coating layer thickness and drug dissolution rate. Therefore, the predictability of drug dissolution rate from enteric-coated tablets depended on the homogeneity of the coating layer thickness. In addition, the importance of micro analysis, X-ray CT in this study, was suggested even if the macro analysis, NIRS in this study, are finally applied for the measurement. Copyright © 2017 Elsevier B.V. All rights reserved.

The synthesis of four-layer gold-silver-polymer-silver core-shell nanomushroom with inbuilt Raman molecule for surface-enhanced Raman scattering

NASA Astrophysics Data System (ADS)

Jiang, Tao; Wang, Xiaolong; Zhou, Jun

2017-12-01

A facial two-step reduction method was proposed to synthesize four-layer gold-silver-polymer-silver (Au@Ag@PSPAA@Ag) core-shell nanomushrooms (NMs) with inbuilt Raman molecule. The surface-enhanced Raman scattering (SERS) intensity of 4MBA adhered on the surface of Au core gradually increased with the modification of middle Ag shell and then Ag mushroom cap due to the formation of two kinds of ultra-small interior nanogap. Compared with the initial Au nanoparticles, the SERS enhancement ratio of the Au@Ag@PSPAA@Ag NMs approached to nearly 40. The novel core-shell NMs also exhibited homogeneous SERS signals for only one sample and reproducible signals for 10 different samples, certified by the low relative standard deviation values of less than 10% and 15% for the character peaks of 4-mercaptobenzoic acid, respectively. Such a novel four-layer core-shell nanostructure with reliable SERS performance has great potential application in quantitative SERS-based immunoassay.

Investigation on the adsorption characteristics of sodium benzoate and taurine on gold nanoparticle film by ATR-FTIR spectroscopy

NASA Astrophysics Data System (ADS)

Kumar, Naveen; Thomas, S.; Tokas, R. B.; Kshirsagar, R. J.

2014-01-01

Fourier transform infrared (FTIR) spectroscopic studies of sodium benzoate and taurine adsorbed on gold nanoparticle (AuNp) film on silanised glass slides have been studied by attenuated total reflection technique (ATR). The surface morphology of the AuNp films has been measured by Atomic Force Microscopy. The ATR spectra of sodium benzoate and taurine deposited on AuNp film are compared with ATR spectra of their powdered bulk samples. A new red-shifted band appeared along with the symmetric and asymmetric stretches of carboxylate group of sodium benzoate leading to a broadening of the above peaks. Similar behavior is also seen in the case of symmetric and asymmetric stretches of sulphonate group of taurine. The results indicate presence of both chemisorbed and physisorbed layers of both sodium benzoate and taurine on the AuNp film with bottom layer chemically bound to AuNp through carboxylate and sulphonate groups respectively.

[INVITED] Design of turn around point long period fiber grating sensor with Au-nanoparticle self monolayer

NASA Astrophysics Data System (ADS)

Bandyopadhyay, Sankhyabrata; Basumallick, Nandini; Bysakh, Sandip; Dey, Tanoy Kumar; Biswas, Palas; Bandyopadhyay, Somnath

2018-06-01

In this paper studies on the design and fabrication of a long period fiber grating (LPFG) with a self mono layer of gold nanoparticle (AuNP) has been presented. Refractive index (RI) sensitivity of a dispersed cladding mode (DCM) near turn around point (TAP) of its phase matching curve (PMC) has been investigated with and also without AuNP coated LPFG. The typical role played by the intermediate layer of AuNP on the effective index and thus on the sensitivity of the cladding mode to the surrounding RI has also been explored by carrying out coupled mode analysis of the requisite multilayer waveguide. Deposition of AuNP enhanced the sensitivity by more than a factor of 2. Measured sensitivity was found to be ∼3928 nm/refractive index unit (RIU) in the range of 1.3333-1.3428.

Microwave properties of peeled HEMT devices sapphire substrates

NASA Technical Reports Server (NTRS)

Young, Paul G.; Alterovitz, Samuel A.; Mena, Rafael A.; Smith, Edwyn D.

1992-01-01

The focus of this research is to demonstrate the first full radio frequency characterization of high electron mobility transistor (HEMT) device parameters. The results of this research are used in the design of circuits with peeled HEMT devices, e.g. 10 GHz amplifiers. Devices were fabricated using two HEMT structures grown by molecular beam epitaxy methods. A 500 A AlAs release layer for 'peel off' was included under the active layers of the structure. The structures are a homogeneously doped Al(0.3)GA(0.7)As/GaAs and a delta doped square well Al(.23)Ga(.77)As/GaAs HEMT structure. Devices were fabricated using a mesa isolation process. Contacts were done by sequentially evaporating Au/Ge/Au/Ni/Au followed by rapid thermal anneal at 400 C for 15 seconds. Gates were wet etch recessed and 1 to 1.4 micron Ti/Au gate metal was deposited. Devices were peeled off the GaAs substrate using Apiezon wax to support the active layer and a HF:DI (1:10) solution to remove the AlAs separation layer. Devices were then attached to sapphire substrates using van der Waals bonding.

Performance Analysis of GaN Capping Layer Thickness on GaN/AlGaN/GaN High Electron Mobility Transistors.

PubMed

Sharma, N; Periasamy, C; Chaturvedi, N

2018-07-01

In this paper, we present an investigation of the impact of GaN capping layer and AlGaN layer thickness on the two-dimensional (2D)-electron mobility and the carrier concentration which was formed close to the AlGaN/GaN buffer layer for Al0.25Ga0.75N/GaN and GaN/Al0.25Ga0.75N/GaN heterostructures deposited on sapphire substrates. The results of our analysis clearly indicate that expanding the GaN capping layer thickness from 1 nm to 100 nm prompts an increment in the electron concentration at hetero interface. As consequence of which drain current was additionally increments with GaN cap layer thicknesses, and eventually saturates at approximately 1.85 A/mm for capping layer thickness greater than 40 nm. Interestingly, for the same structure, the 2D-electron mobility, decrease monotonically with GaN capping layer thickness, and saturate at approximately 830 cm2/Vs for capping layer thickness greater than 50 nm. A device with a GaN cap layer didn't exhibit gate leakage current. Furthermore, it was observed that the carrier concentration was first decrease 1.03 × 1019/cm3 to 6.65 × 1018/cm3 with AlGaN Layer thickness from 5 to 10 nm and after that it increases with the AlGaN layer thickness from 10 to 30 nm. The same trend was followed for electric field distributions. Electron mobility decreases monotonically with AlGaN layer thickness. Highest electron mobility 1354 cm2/Vs were recorded for the AlGaN layer thickness of 5 nm. Results obtained are in good agreement with published experimental data.

Seeded Growth Synthesis of Gold Nanotriangles: Size Control, SAXS Analysis, and SERS Performance.

PubMed

Kuttner, Christian; Mayer, Martin; Dulle, Martin; Moscoso, Ana; López-Romero, Juan Manuel; Förster, Stephan; Fery, Andreas; Pérez-Juste, Jorge; Contreras-Cáceres, Rafael

2018-04-04

We studied the controlled growth of triangular prismatic Au nanoparticles with different beveled sides for surface-enhanced Raman spectroscopy (SERS) applications. First, in a seedless synthesis using 3-butenoic acid (3BA) and benzyldimethylammonium chloride (BDAC), gold nanotriangles (AuNTs) were synthesized in a mixture with gold nanooctahedra (AuNOCs) and separated by depletion-induced flocculation. Here, the influence of temperature, pH, and reducing agent on the reaction kinetics was initially investigated by UV-vis and correlated to the size and yield of AuNT seeds. In a second step, the AuNT size was increased by seed-mediated overgrowth with Au. We show for the first time that preformed 3BA-synthesized AuNT seeds can be overgrown up to a final edge length of 175 nm and a thickness of 80 nm while maintaining their triangular shape and tip sharpness. The NT morphology, including edge length, thickness, and tip rounding, was precisely characterized in dispersion by small-angle X-ray scattering and in dry state by transmission electron microscopy and field-emission scanning electron microscopy. For sensor purposes, we studied the size-dependent SERS performance of AuNTs yielding analytical enhancement factors between 0.9 × 10 4 and 5.6 × 10 4 and nanomolar limit of detection (10 -8 -10 -9 M) for 4-mercaptobenzoic acid and BDAC. These results confirm that the 3BA approach allows the fabrication of AuNTs in a whole range of sizes maintaining the NT morphology. This enables tailoring of localized surface plasmon resonances between 590 and 740 nm, even in the near-infrared window of a biological tissue, for use as colloidal SERS sensing agents or for optoelectronic applications.

Effect of Ni-P Plating Temperature on Growth of Interfacial Intermetallic Compound in Electroless Nickel Immersion Gold/Sn-Ag-Cu Solder Joints

NASA Astrophysics Data System (ADS)

Seo, Wonil; Kim, Kyoung-Ho; Kim, Young-Ho; Yoo, Sehoon

2018-01-01

The growth of interfacial intermetallic compound and the brittle fracture behavior of Sn-3.0Ag-0.5-Cu solder (SAC305) joints on electroless nickel immersion gold (ENIG) surface finish have been investigated using Ni-P plating solution at temperatures from 75°C to 85°C and fixed pH of 4.5. SAC305 solder balls with diameter of 450 μm were mounted on the prepared ENIG-finished Cu pads and reflowed with peak temperature of 250°C. The interfacial intermetallic compound (IMC) thickness after reflow decreased with increasing Ni-P plating temperature. After 800 h of thermal aging, the IMC thickness of the sample prepared at 85°C was higher than for that prepared at 75°C. Scanning electron microscopy of the Ni-P surface after removal of the Au layer revealed a nodular structure on the Ni-P surface. The nodule size of the Ni-P decreased with increasing Ni-P plating temperature. The Cu content near the IMC layer increased to 0.6 wt.%, higher than the original Cu content of 0.5 wt.%, indicating that Cu diffused from the Cu pad to the solder ball through the Ni-P layer at a rate depending on the nodule size. The sample prepared at 75°C with thicker interfacial IMC showed greater high-speed shear strength than the sample prepared at 85°C. Brittle fracture increased with decreasing Ni-P plating temperature.

Effect of atomic-arrangement matching on La{sub 2}O{sub 3}/Ge heterostructures for epitaxial high-k-gate-stacks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kanashima, T., E-mail: kanashima@ee.es.osaka-u.ac.jp; Zenitaka, M.; Kajihara, Y.

2015-12-14

We demonstrate a high-quality La{sub 2}O{sub 3} layer on germanium (Ge) as an epitaxial high-k-gate-insulator, where there is an atomic-arrangement matching condition between La{sub 2}O{sub 3}(001) and Ge(111). Structural analyses reveal that (001)-oriented La{sub 2}O{sub 3} layers were grown epitaxially only when we used Ge(111) despite low growth temperatures less than 300 °C. The permittivity (k) of the La{sub 2}O{sub 3} layer is roughly estimated to be ∼19 from capacitance-voltage (C-V) analyses in Au/La{sub 2}O{sub 3}/Ge structures after post-metallization-annealing treatments, although the C-V curve indicates the presence of carrier traps near the interface. By using X-ray photoelectron spectroscopy analyses, we findmore » that only Ge–O–La bonds are formed at the interface, and the thickness of the equivalent interfacial Ge oxide layer is much smaller than that of GeO{sub 2} monolayer. We discuss a model of the interfacial structure between La{sub 2}O{sub 3} and Ge(111) and comment on the C-V characteristics.« less

InAs/Ga(In)Sb type-II superlattices short/middle dual color infrared detectors

NASA Astrophysics Data System (ADS)

Shi, Yanli; Hu, Rui; Deng, Gongrong; He, Wenjing; Feng, Jiangmin; Fang, Mingguo; Li, Xue; Deng, Jun

2015-06-01

Short wavelength and middle wavelength dual color infrared detector were designed and prepared with InAs/Ga(In)Sb type-II superlattices materials. The Crosslight software was used to calculate the relation between wavelength and material parameter such as thickness of InAs, GaSb, then energy strucutre of 100 periods 8ML/8ML InAs/GaSb and the absorption wavelength was calculated. After fixing InAs/GaSb thickness parameter, devices with nBn and pin structure were designed and prepared to compare performance of these two structures. Comparison results showed both structure devices were available for high temperature operation which black detectivity under 200K were 7.9×108cmHz1/2/W for nBn and 1.9×109cmHz1/2/W for pin respectively. Considering the simultaneous readout requirement for further FPAs application the NIP/PIN InAs/GaSb dual-color structure was grown by MBE method. Both two mesas and one mesa devices structure were designed and prepared to appreciate the short/middle dual color devices. Cl2-based ICP etching combined with phosphoric acid based chemicals were utilized to form mesas, silicon dioxide was deposited via PECVD as passivation layer. Ti/Au was used as metallization. Once the devices were finished, the electro-optical performance was measured. Measurement results showed that optical spectrum response with peak wavelength of 2.7μm and 4.3μm under 77K temperature was gained, the test results agree well with calculated results. Peak detectivity was measured as 2.08×1011cmHz1/2/W and 6.2×1010cmHz1/2/W for short and middle wavelength infrared detector respectively. Study results disclosed that InAs/Ga(In)Sb type-II SLs is available for both short and middle wavelength infrared detecting with good performance by simply altering the thickness of InAs layer and GaSb layer.

Applying gold nanoparticles as tumor-vascular disrupting agents during brachytherapy: estimation of endothelial dose enhancement

NASA Astrophysics Data System (ADS)

Ngwa, Wilfred; Makrigiorgos, G. Mike; Berbeco, Ross I.

2010-11-01

Tumor vascular disrupting agents (VDAs) represent a promising approach to the treatment of cancer, in view of the tumor vasculature's pivotal role in tumor survival, growth and metastasis. VDAs targeting the tumor's dysmorphic endothelial cells can cause selective and rapid occlusion of the tumor vasculature, leading to tumor cell death from ischemia and extensive hemorrhagic necrosis. In this study, the potential for applying gold nanoparticles (AuNPs) as VDAs, during brachytherapy, is examined. Analytic calculations based on the electron energy loss formula of Cole were carried out to estimate the endothelial dose enhancement caused by radiation-induced photo/Auger electrons originating from AuNPs targeting the tumor endothelium. The endothelial dose enhancement factor (EDEF), representing the ratio of the dose to the endothelium with and without gold nanoparticles was calculated for different AuNP local concentrations, and endothelial cell thicknesses. Four brachytherapy sources were investigated, I-125, Pd-103, Yb-169, as well as 50 kVp x-rays. The results reveal that, even at relatively low intra-vascular AuNP concentrations, ablative dose enhancement to tumor endothelial cells due to photo/Auger electrons from the AuNPs can be achieved. Pd-103 registered the highest EDEF values of 7.4-271.5 for local AuNP concentrations ranging from 7 to 350 mg g-1, respectively. Over the same concentration range, I-125, 50 kVp and Yb-169 yielded values of 6.4-219.9, 6.3-214.5 and 4.0-99.7, respectively. Calculations of the EDEF as a function of endothelial cell thickness showed that lower energy sources like Pd-103 reach the maximum EDEF at smaller thicknesses. The results also reveal that the highest contribution to the EDEF comes from Auger electrons, apparently due to their shorter range. Overall, the data suggest that ablative dose enhancement to tumor endothelial cells can be achieved by applying tumor vasculature-targeted AuNPs as adjuvants to brachytherapy, with lower energy sources. Such ablative magnitude dose enhancement in a relatively small endothelial volume may rapidly disrupt or cause severe biological damage to tumor endothelial cells, without increased toxicity to healthy tissues not containing AuNPs. The findings provide significant impetus for considering the application of AuNPs as VDAs during brachytherapy.

Defect-rich Ni-Ti layered double hydroxide as a highly efficient support for Au nanoparticles in base-free and solvent-free selective oxidation of benzyl alcohol.

PubMed

Liu, Mengran; Fan, Guoli; Yu, Jiaying; Yang, Lan; Li, Feng

2018-04-17

Tuning the surface properties of supported metal catalysts is of vital importance for governing their catalytic performances in nanocatalysis. Here, we report highly dispersed nanometric gold nanoparticles (NPs) supported on Ni-Ti layered double hydroxides (NiTi-LDHs), which were employed in solvent-free and base-free selective oxidation of benzyl alcohol. A series of characterization techniques demonstrated that defect-rich NiTi-LDHs could efficiently stabilize Au NPs and decrease surface electron density of Au NPs. The as-formed Au/NiTi-LDH catalyst with a Ni/Ti molar ratio of 3 : 1 and an Au loading of 0.71 wt% yielded the highest turnover frequency value of ∼4981 h-1 at 120 °C among tested Au/NiTi-LDH catalysts with different Ni/Ti molar ratios, along with a high benzaldehyde selectivity of 98%. High catalytic efficiency of the catalyst was mainly correlated with surface cooperation between unique defects (i.e. defective Ti3+ species and oxygen vacancies) and abundant hydroxyl groups on the brucite-like layers of the NiTi-LDH support, which could lead to the preferential adsorption and activation of an alcohol hydroxyl moiety in benzyl alcohol and oxygen molecule, as well as the formation of more electron-deficient Ni3+ and Au0 species on the catalyst surface. Furthermore, the present Au/NiTi-LDH catalyst tolerated the oxidation of a wide variety of substrate structures into the corresponding aldehydes, acids or ketones. Our primary results illustrate that defect-rich NiTi-LDHs are promising supports which can efficiently modify surface structure and electronic properties of supported metal catalysts and consequently improve their catalytic performances.

Polarization of gold in nanopores leads to ion current rectification

DOE PAGES

Yang, Crystal; Hinkle, Preston; Menestrina, Justin; ...

2016-10-03

Biomimetic nanopores with rectifying properties are relevant components of ionic switches, ionic circuits, and biological sensors. Rectification indicates that currents for voltages of one polarity are higher than currents for voltages of the opposite polarity. Ion current rectification requires the presence of surface charges on the pore walls, achieved either by the attachment of charged groups or in multielectrode systems by applying voltage to integrated gate electrodes. Here we present a simpler concept for introducing surface charges via polarization of a thin layer of Au present at one entrance of a silicon nitride nanopore. In an electric field applied bymore » two electrodes placed in bulk solution on both sides of the membrane, the Au layer polarizes such that excess positive charge locally concentrates at one end and negative charge concentrates at the other end. Consequently, a junction is formed between zones with enhanced anion and cation concentrations in the solution adjacent to the Au layer. This bipolar double layer together with enhanced cation concentration in a negatively charged silicon nitride nanopore leads to voltage-controlled surface-charge patterns and ion current rectification. The experimental findings are supported by numerical modeling that confirm modulation of ionic concentrations by the Au layer and ion current rectification even in low-aspect ratio nanopores. Lastly, our findings enable a new strategy for creating ionic circuits with diodes and transistors.« less

Finite-size effects and magnetic exchange coupling in thin CoO layers

NASA Astrophysics Data System (ADS)

Ambrose, Thomas Francis

Finite size effects in CoO have been observed in CoO/SiOsb2 multilayers. The Neel temperatures of the CoO layers, as determined by dc susceptibility measurements, follow a finite-size scaling relation with a shift exponent lambda = 1.55 ± 0.05. This determined exponent is close to the theoretical value for finite size scaling in an Ising system. The value of the zero temperature correlation length has also been determined to be 18A, while antiferromagnetic ordering persists down to a CoO layer thickness of 10A. The properties of exchange biasing have been extensively studied in NiFe/CoO bilayers. The effects of the cooling field (Hsb{FC}), up to 50 kOe, on the resultant exchange field (Hsb{E}) and coercivity (Hsb{C}) have been examined. The value of Hsb{E} increases rapidly at low cooling fields (Hsb{FC} < 1kOe) and levels off for Hsb{FC} larger than 4 kOe. The value of Hsb{C} also depends upon Hsb{FC}, but less sensitively. The bilayer thickness also influences exchange biasing. We find that Hsb{E} varies inversely proprotional to both tsb{FM} and tsb{AF} where tsb{FM} and tsb{AF} are the ferromagnetic and antiferromagnetic layer thickness respectively. Because of the 1/tsb{AF}, the simple picture of interfacial coupling between ferromagnet and antiferromagnet spins appears to be inadequate. The assertion of long range coupling between ferromagnetic and antiferromagnetic layers has been verified by the observation of antiferromagnetic exchange coupling across spacer layers in NiFe/NM/CoO trilayers, where NM is a non-magnetic material. Exchange biasing has been observed in trilayers with metallic spacer layers up to 50A thick using Ag, Cu and Au, while no exchange field was observed for insulating spacer layers of any thickness using Alsb2Osb3, SiOsb2 and MgO. The temperature dependence of Hsb{E} and Hsb{C} and the effect of the deposition order have been studied in a series of bilayer (NiFe/CoO and CoO/NiFe) and trilayer (NiFe/CoO/NiFe) films. A profound difference in Hsb{E} was observed in samples with NiFe deposited on top of CoO compared to samples with CoO deposited on top of NiFe. When CoO is on top of NiFe Hsb{E} varies linearly with temperature, while for samples with NiFe on top of CoO Hsb{E} has a plateau followed by a rapid decrease. These distinct temperature dependences have been reproduced in NiFe/CoO/NiFe trilayers which contain both geometries. Structural analysis using Transmission Electron Microscopy indicate no apparent differences in the top and bottom interfaces. The angular dependence of the exchange coupling in a NiFe/CoO bilayer has been measured. Both Hsb{E} and Hsb{C} with unidirectional and uniaxial characteristics, respectively, are integral parts of the exchange coupling. The values of Hsb{E} can be expressed by a series of odd angle cosine terms, while the values of Hsb{C} can be expressed by a series of even angle cosine terms. Finally, exchange biasing has been used to "spin engineer" ferromagnetic layers in NiFe/CoO/NiFe trilayers. Four different spin structures have been observed. A phase diagram, for the four spin structures and the conditions with which each spin structure is obtained, has been determined. (Abstract shortened by UMI.)

Sensitivity Enhancement of Transition Metal Dichalcogenides/Silicon Nanostructure-based Surface Plasmon Resonance Biosensor

PubMed Central

Ouyang, Qingling; Zeng, Shuwen; Jiang, Li; Hong, Liying; Xu, Gaixia; Dinh, Xuan-Quyen; Qian, Jun; He, Sailing; Qu, Junle; Coquet, Philippe; Yong, Ken-Tye

2016-01-01

In this work, we designed a sensitivity-enhanced surface plasmon resonance biosensor structure based on silicon nanosheet and two-dimensional transition metal dichalcogenides. This configuration contains six components: SF10 triangular prism, gold thin film, silicon nanosheet, two-dimensional MoS2/MoSe2/WS2/WSe2 (defined as MX2) layers, biomolecular analyte layer and sensing medium. The minimum reflectivity, sensitivity as well as the Full Width at Half Maximum of SPR curve are systematically examined by using Fresnel equations and the transfer matrix method in the visible and near infrared wavelength range (600 nm to 1024 nm). The variation of the minimum reflectivity and the change in resonance angle as the function of the number of MX2 layers are presented respectively. The results show that silicon nanosheet and MX2 layers can be served as effective light absorption medium. Under resonance conditions, the electrons in these additional dielectric layers can be transferred to the surface of gold thin film. All silicon-MX2 enhanced sensing models show much better performance than that of the conventional sensing scheme where pure Au thin film is used, the highest sensitivity can be achieved by employing 600 nm excitation light wavelength with 35 nm gold thin film and 7 nm thickness silicon nanosheet coated with monolayer WS2. PMID:27305974

Coaxial metal-oxide-semiconductor (MOS) Au/Ga2O3/GaN nanowires.

PubMed

Hsieh, Chin-Hua; Chang, Mu-Tung; Chien, Yu-Jen; Chou, Li-Jen; Chen, Lih-Juann; Chen, Chii-Dong

2008-10-01

Coaxial metal-oxide-semiconductor (MOS) Au-Ga2O3-GaN heterostructure nanowires were successfully fabricated by an in situ two-step process. The Au-Ga2O3 core-shell nanowires were first synthesized by the reaction of Ga powder, a mediated Au thin layer, and a SiO2 substrate at 800 degrees C. Subsequently, these core-shell nanowires were nitridized in ambient ammonia to form a GaN coating layer at 600 degrees C. The GaN shell is a single crystal, an atomic flat interface between the oxide and semiconductor that ensures that the high quality of the MOS device is achieved. These novel 1D nitride-based MOS nanowires may have promise as building blocks to the future nitride-based vertical nanodevices.

Alterations in Retinal Layer Thickness and Reflectance at Different Stages of Diabetic Retinopathy by En Face Optical Coherence Tomography

PubMed Central

Wanek, Justin; Blair, Norman P.; Chau, Felix Y.; Lim, Jennifer I.; Leiderman, Yannek I.; Shahidi, Mahnaz

2016-01-01

Purpose This article reports a method for en face optical coherence tomography (OCT) imaging and quantitative assessment of alterations in both thickness and reflectance of individual retinal layers at different stages of diabetic retinopathy (DR). Methods High-density OCT raster volume scans were acquired in 29 diabetic subjects divided into no DR (NDR) or non-proliferative DR (NPDR) groups and 22 control subjects (CNTL). A customized image segmentation method identified eight retinal layer interfaces and generated en face thickness maps and reflectance images for nerve fiber layer (NFL), ganglion cell and inner plexiform layers (GCLIPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), photoreceptor outer segment layer (OSL), and retinal pigment epithelium (RPE). Mean thickness and intensity values were calculated in nine macular subfields for each retinal layer. Results En face thickness maps and reflectance images of retinal layers in CNTL subjects corresponded to normal retinal anatomy. Total retinal thickness correlated negatively with age in nasal subfields (R ≤−0.31; P ≤ 0.03, N = 51). In NDR subjects, NFL and OPL thickness were decreased (P = 0.05), and ONL thickness was increased (P = 0.04) compared to CNTL. In NPDR subjects, GCLIPL thickness was increased in perifoveal subfields (P < 0.05) and INL intensity was higher in all macular subfields (P = 0.04) compared to CNTL. Conclusions Depth and spatially resolved retinal thickness and reflectance measurements are potential biomarkers for assessment and monitoring of DR. PMID:27409491

Effect of layer thickness on the elution of bulk-fill composite components.

PubMed

Rothmund, Lena; Reichl, Franz-Xaver; Hickel, Reinhard; Styllou, Panorea; Styllou, Marianthi; Kehe, Kai; Yang, Yang; Högg, Christof

2017-01-01

An increment layering technique in a thickness of 2mm or less has been the standard to sufficiently convert (co)monomers. Bulk fill resin composites were developed to accelerate the restoration process by enabling up to 4mm thick increments to be cured in a single step. The aim of the present study is to investigate the effect of layer thickness on the elution of components from bulk fill composites. The composites ELS Bulk fill, SDR Bulk fill and Venus Bulkfill were polymerized according to the instruction of the manufacturers. For each composite three groups with four samples each (n=4) were prepared: (1) samples with a layer thickness of 2mm; (2) samples with a layer thickness of 4mm and (3) samples with a layer thickness of 6mm. The samples were eluted in methanol and water for 24h and 7 d. The eluates were analyzed by gas chromatography/mass spectrometry (GC/MS). A total of 11 different elutable substances have been identified from the investigated composites. Following methacrylates showed an increase of elution at a higher layer thickness: TEGDMA (SDR Bulk fill, Venus Bulk fill), EGDMA (Venus Bulk fill). There was no significant difference in the elution of HEMA regarding the layer thickness. The highest concentration of TEGDMA was 146μg/mL for SDR Bulk fill at a layer thickness of 6mm after 7 d in water. The highest HEMA concentration measured at 108μg/mL was detected in the methanol eluate of Venus Bulk fill after 7 d with a layer thickness of 6mm. A layer thickness of 4mm or more can lead to an increased elution of some bulk fill components, compared to the elution at a layer thickness of 2mm. Copyright © 2016 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Investigating the Modification of Spontaneous Emission using Layer-by-Layer Self-Assembly

NASA Astrophysics Data System (ADS)

Ashry, Islam Ahmed Ibrahim Youssef

The process of spontaneous emission can be dramatically modified by optical micro- and nanostructures. We studied the modification of fluorescence dynamics using a polymer spacer layer fabricated through layer-by-layer (LbL) self-assembly. The advantages of this method are numerous: The self-assembled spacers can possess exceptional smooth surface morphology; The thickness of the spacer can be controlled with nanometer accuracy; And depending on fabrication conditions, the spacer layer is stimuli responsive and its thickness can be dynamically tuned. This thesis contains three interlinked components. First, we vary LbL spacer layer thickness and explore the change in fluorescence lifetime induced by the modified photonic density of states (PDOS), i.e., Purcell effects. Our experimental results agree well with theoretical predictions based on a classical dipole model, which also yields consistent values for the fluorophores' intrinsic fluorescence lifetime and quantum yield near a dielectric as well as a plasmonic interface. Based on this observation, we further demonstrate that self-assembled fluorophores can be used to probe the modified PDOS near optical micro- and nano-structures. These results naturally lead to the second component of our research. In particularly, based on the PDOS-induced changes in fluorescent lifetime, we develop a non-contact method that can measure morphological changes with nanoscale resolution. Our method relies on quantitatively linking fluorophore position with PDOS, and is validated through direct comparison with ellipsometry and atomic force microscopy (AFM) measurements. To demonstrate the potential application of this method, we investigated the swelling/deswelling of LbL films induced by pH changes. Our results indicate significant difference between a LbL film composed of a single polymer monolayer and a LbL film with 3 monolayers. Such stimuli-responsive polymers can be used to construct active and tunable plasmonic nano-devices. As a proof-of-principle demonstration, we experimentally confirm that it is possible to utilize the swelling/deswelling behavior of stimuli-responsive films to dynamically control the separation between Au nanoparticles and Texas Red (TR) dyes. This result is based on the strong correlation of TR fluorescence lifetime and nanoparticles-TR separation. Finally, we investigate the impact of different lithography processes on the fluorescence properties of self-assembled fluorophores. We consider three methods: direct fluorophore patterning through ultraviolet (UV) ablation, focused ion beam (FIB) milling of self-assembled fluorophores, and self-assembly of fluorescent materials over plasmonic nano-patterns.

Implosion dynamics measurements at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Hicks, D. G.; Meezan, N. B.; Dewald, E. L.; Mackinnon, A. J.; Olson, R. E.; Callahan, D. A.; Döppner, T.; Benedetti, L. R.; Bradley, D. K.; Celliers, P. M.; Clark, D. S.; Di Nicola, P.; Dixit, S. N.; Dzenitis, E. G.; Eggert, J. E.; Farley, D. R.; Frenje, J. A.; Glenn, S. M.; Glenzer, S. H.; Hamza, A. V.; Heeter, R. F.; Holder, J. P.; Izumi, N.; Kalantar, D. H.; Khan, S. F.; Kline, J. L.; Kroll, J. J.; Kyrala, G. A.; Ma, T.; MacPhee, A. G.; McNaney, J. M.; Moody, J. D.; Moran, M. J.; Nathan, B. R.; Nikroo, A.; Opachich, Y. P.; Petrasso, R. D.; Prasad, R. R.; Ralph, J. E.; Robey, H. F.; Rinderknecht, H. G.; Rygg, J. R.; Salmonson, J. D.; Schneider, M. B.; Simanovskaia, N.; Spears, B. K.; Tommasini, R.; Widmann, K.; Zylstra, A. B.; Collins, G. W.; Landen, O. L.; Kilkenny, J. D.; Hsing, W. W.; MacGowan, B. J.; Atherton, L. J.; Edwards, M. J.

2012-12-01

Measurements have been made of the in-flight dynamics of imploding capsules indirectly driven by laser energies of 1-1.7 MJ at the National Ignition Facility [Miller et al., Nucl. Fusion 44, 228 (2004)]. These experiments were part of the National Ignition Campaign [Landen et al., Phys. Plasmas 18, 051002 (2011)] to iteratively optimize the inputs required to achieve thermonuclear ignition in the laboratory. Using gated or streaked hard x-ray radiography, a suite of ablator performance parameters, including the time-resolved radius, velocity, mass, and thickness, have been determined throughout the acceleration history of surrogate gas-filled implosions. These measurements have been used to establish a dynamically consistent model of the ablative drive history and shell compressibility throughout the implosion trajectory. First results showed that the peak velocity of the original 1.3-MJ Ge-doped polymer (CH) point design using Au hohlraums reached only 75% of the required ignition velocity. Several capsule, hohlraum, and laser pulse changes were then implemented to improve this and other aspects of implosion performance and a dedicated effort was undertaken to test the sensitivity of the ablative drive to the rise time and length of the main laser pulse. Changing to Si rather than Ge-doped inner ablator layers and increasing the pulse length together raised peak velocity to 93% ± 5% of the ignition goal using a 1.5 MJ, 420 TW pulse. Further lengthening the pulse so that the laser remained on until the capsule reached 30% (rather than 60%-70%) of its initial radius, reduced the shell thickness and improved the final fuel ρR on companion shots with a cryogenic hydrogen fuel layer. Improved drive efficiency was observed using U rather than Au hohlraums, which was expected, and by slowing the rise time of laser pulse, which was not. The effect of changing the Si-dopant concentration and distribution, as well as the effect of using a larger initial shell thickness were also examined, both of which indicated that instabilities seeded at the ablation front are a significant source of hydrodynamic mix into the central hot spot. Additionally, a direct test of the surrogacy of cryogenic fuel layered versus gas-filled targets was performed. Together all these measurements have established the fundamental ablative-rocket relationship describing the dependence of implosion velocity on fractional ablator mass remaining. This curve shows a lower-than-expected ablator mass at a given velocity, making the capsule more susceptible to feedthrough of instabilities from the ablation front into the fuel and hot spot. This combination of low velocity and low ablator mass indicates that reaching ignition on the NIF will require >20 μm (˜10%) thicker targets and laser powers at or beyond facility limits.

Implosion dynamics measurements at the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hicks, D. G.; Meezan, N. B.; Dewald, E. L.

2012-12-15

Measurements have been made of the in-flight dynamics of imploding capsules indirectly driven by laser energies of 1-1.7 MJ at the National Ignition Facility [Miller et al., Nucl. Fusion 44, 228 (2004)]. These experiments were part of the National Ignition Campaign [Landen et al., Phys. Plasmas 18, 051002 (2011)] to iteratively optimize the inputs required to achieve thermonuclear ignition in the laboratory. Using gated or streaked hard x-ray radiography, a suite of ablator performance parameters, including the time-resolved radius, velocity, mass, and thickness, have been determined throughout the acceleration history of surrogate gas-filled implosions. These measurements have been used tomore » establish a dynamically consistent model of the ablative drive history and shell compressibility throughout the implosion trajectory. First results showed that the peak velocity of the original 1.3-MJ Ge-doped polymer (CH) point design using Au hohlraums reached only 75% of the required ignition velocity. Several capsule, hohlraum, and laser pulse changes were then implemented to improve this and other aspects of implosion performance and a dedicated effort was undertaken to test the sensitivity of the ablative drive to the rise time and length of the main laser pulse. Changing to Si rather than Ge-doped inner ablator layers and increasing the pulse length together raised peak velocity to 93% {+-} 5% of the ignition goal using a 1.5 MJ, 420 TW pulse. Further lengthening the pulse so that the laser remained on until the capsule reached 30% (rather than 60%-70%) of its initial radius, reduced the shell thickness and improved the final fuel {rho}R on companion shots with a cryogenic hydrogen fuel layer. Improved drive efficiency was observed using U rather than Au hohlraums, which was expected, and by slowing the rise time of laser pulse, which was not. The effect of changing the Si-dopant concentration and distribution, as well as the effect of using a larger initial shell thickness were also examined, both of which indicated that instabilities seeded at the ablation front are a significant source of hydrodynamic mix into the central hot spot. Additionally, a direct test of the surrogacy of cryogenic fuel layered versus gas-filled targets was performed. Together all these measurements have established the fundamental ablative-rocket relationship describing the dependence of implosion velocity on fractional ablator mass remaining. This curve shows a lower-than-expected ablator mass at a given velocity, making the capsule more susceptible to feedthrough of instabilities from the ablation front into the fuel and hot spot. This combination of low velocity and low ablator mass indicates that reaching ignition on the NIF will require >20 {mu}m ({approx}10%) thicker targets and laser powers at or beyond facility limits.« less

Synergistic interaction between gold nanoparticles and nickel phthalocyanine in layer-by-layer (LbL) films: evidence of constitutional dynamic chemistry (CDC).

PubMed

Alencar, Wagner S; Crespilho, Frank N; Martins, Marccus V A; Zucolotto, Valtencir; Oliveira, Osvaldo N; Silva, Welter C

2009-07-07

The concept of constitutional dynamic chemistry (CDC) based on the control of non-covalent interactions in supramolecular structures is promising for having a large impact on nanoscience and nanotechnology if adequate nanoscale manipulation methods are used. In this study, we demonstrate that the layer-by-layer (LbL) technique may be used to produce electroactive electrodes with ITO coated by tetrasulfonated nickel phthalocyanine (NiTsPc) alternated with poly(allylamine hydrochloride) (PAH) incorporating gold nanoparticles (AuNP), in which synergy has been achieved in the interaction between the nanoparticles and NiTsPc. The catalytic activity toward hydrogen peroxide (H(2)O(2)) in multilayer films was investigated using cyclic voltammetry, where oxidation of H(2)O(2) led to increased currents in the PAH-AuNP/NiTsPc films for the electrochemical processes associated with the phthalocyanine ring and nickel at 0.52 and 0.81 V vs. SCE, respectively, while for PAH/NiTsPc films (without AuNP) only the first redox process was affected. In control experiments we found out that the catalytic activity was not solely due to the presence of AuNP, but rather to the nanoparticles inducing NiTsPc supramolecular structures that favored access to their redox sites, thus yielding strong charge transfer. The combined effects of NiTsPc and AuNP, which could only be observed in nanostructured LbL films, point to another avenue to pursue within the CDC paradigm.

Deep thermal infrared imaging of HR 8799 bcde: new atmospheric constraints and limits on a fifth planet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Currie, Thayne; Cloutier, Ryan; Jayawardhana, Ray

2014-11-10

We present new L' (3.8 μm) and Brα (4.05 μm) data and reprocessed archival L' data for the young, planet-hosting star HR 8799 obtained with Keck/NIRC2, VLT/NaCo, and Subaru/IRCS. We detect all four HR 8799 planets in each data set at a moderate to high signal-to-noise ratio (S/N ≳ 6-15). We fail to identify a fifth planet, 'HR 8799 f', at r < 15 AU at a 5σ confidence level: one suggestive, marginally significant residual at 0.''2 is most likely a point-spread function artifact. Assuming companion ages of 30 Myr and the Baraffe planet cooling models, we rule out anmore » HR 8799 f with a mass of 5 M{sub J} (7 M{sub J} ), 7 M{sub J} (10 M{sub J} ), or 12 M{sub J} (13 M{sub J} ) at r {sub proj} ∼ 12 AU, 9 AU, and 5 AU, respectively. All four HR 8799 planets have red early T dwarf-like L' – [4.05] colors, suggesting that their spectral energy distributions peak in between the L' and M' broadband filters. We find no statistically significant difference in HR 8799 cde's color. Atmosphere models assuming thick, patchy clouds appear to better match HR 8799 bcde's photometry than models assuming a uniform cloud layer. While non-equilibrium carbon chemistry is required to explain HR 8799 b and c's photometry/spectra, evidence for it from HR 8799 d and e's photometry is weaker. Future, deep-IR spectroscopy/spectrophotometry with the Gemini Planet Imager, SCExAO/CHARIS, and other facilities may clarify whether the planets are chemically similar or heterogeneous.« less

Characterization of Gold-Sputtered Zinc Oxide Nanorods-a Potential Hybrid Material.

PubMed

Perumal, Veeradasan; Hashim, Uda; Gopinath, Subash C B; Rajintra Prasad, Haarindraprasad; Wei-Wen, Liu; Balakrishnan, S R; Vijayakumar, Thivina; Rahim, Ruslinda Abdul

2016-12-01

Generation of hybrid nanostructures has been attested as a promising approach to develop high-performance sensing substrates. Herein, hybrid zinc oxide (ZnO) nanorod dopants with different gold (Au) thicknesses were grown on silicon wafer and studied for their impact on physical, optical and electrical characteristics. Structural patterns displayed that ZnO crystal lattice is in preferred c-axis orientation and proved the higher purities. Observations under field emission scanning electron microscopy revealed the coverage of ZnO nanorods by Au-spots having diameters in the average ranges of 5-10 nm, as determined under transmission electron microscopy. Impedance spectroscopic analysis of Au-sputtered ZnO nanorods was carried out in the frequency range of 1 to 100 MHz with applied AC amplitude of 1 V RMS. The obtained results showed significant changes in the electrical properties (conductance and dielectric constant) with nanostructures. A clear demonstration with 30-nm thickness of Au-sputtering was apparent to be ideal for downstream applications, due to the lowest variation in resistance value of grain boundary, which has dynamic and superior characteristics.

Vapochromic Behaviour of M[Au(CN)2]2-Based Coordination Polymers (M = Co, Ni)

PubMed Central

Lefebvre, Julie; Korčok, Jasmine L.; Katz, Michael J.; Leznoff, Daniel B.

2012-01-01

A series of M[Au(CN)2]2(analyte)x coordination polymers (M = Co, Ni; analyte = dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF), pyridine; x = 2 or 4) was prepared and characterized. Addition of analyte vapours to solid M(μ-OH2)[Au(CN)2]2 yielded visible vapochromic responses for M = Co but not M = Ni; the IR νCN spectral region changed in every case. A single crystal structure of Zn[Au(CN)2]2(DMSO)2 revealed a corrugated 2-D layer structure with cis-DMSO units. Reacting a Ni(II) salt and K[Au(CN)2] in DMSO yielded the isostructural Ni[Au(CN)2]2(DMSO)2 product. Co[Au(CN)2]2(DMSO)2 and M[Au(CN)2]2(DMF)2 (M = Co, Ni) complexes have flat 2-D square-grid layer structures with trans-bound DMSO or DMF units; they are formed via vapour absorption by solid M(μ-OH2)[Au(CN)2]2 and from DMSO or DMF solution synthesis. Co[Au(CN)2]2(pyridine)4 is generated via vapour absorption by Co(μ-OH2)[Au(CN)2]2; the analogous Ni complex is synthesized by immersion of Ni(μ-OH2)[Au(CN)2]2 in 4% aqueous pyridine. Similar immersion of Co(μ-OH2)[Au(CN)2]2 yielded Co[Au(CN)2]2(pyridine)2, which has a flat 2-D square-grid structure with trans-pyridine units. Absorption of pyridine vapour by solid Ni(μ-OH2)[Au(CN)2]2 was incomplete, generating a mixture of pyridine-bound complexes. Analyte-free Co[Au(CN)2]2 was prepared by dehydration of Co(μ-OH2)[Au(CN)2]2 at 145 °C; it has a 3-D diamondoid-type structure and absorbs DMSO, DMF and pyridine to give the same materials as by vapour absorption from the hydrate. PMID:22737031

Surface acoustic waves in one-dimensional piezoelectric-metallic phononic crystal: Effect of a cap layer.

PubMed

Alami, M; El Boudouti, E H; Djafari-Rouhani, B; El Hassouani, Y; Talbi, A

2018-06-18

We study the propagation of transverse acoustic waves associated with the surface of a semi-infinite superlattice (SL) composed of piezoelectric-metallic layers and capped with a piezoelectric layer. We present closed-form expressions for localized surface waves, the so-called Bleustein-Gulyaev (BG) waves depending on whether the cap layer is open-circuited or short-circuited. These expressions are obtained by means of the Green's function method which enables to deduce also the densities of states. These theoretical results are illustrated by a few numerical applications to SLs made of piezoelectric layers of hexagonal symmetry belonging to the 6 mm class such as PZT4 and ZnO in contact with metallic layers such as Fe, Al, Au, Cu and boron-doped-diamond. We demonstrate a rule about the existence of surface modes when considering two complementary semi-infinite SLs obtained by the cleavage of an infinite SL along a plane parallel to the piezoelectric layers. Indeed, when the surface layers are open-circuited, one obtains one surface mode per gap, this mode is associated with one of the two complementary SLs. However, when the surface layers are short-circuited, this rule is not fulfilled and one can obtain zero, one or two modes inside each gap of the two complementary SLs depending on the position of the plane where the cleavage is produced. We show that in addition to the BG surface waves localized at the surface of the cap layer, there may exist true guided waves and pseudo-guided waves (i.e. leaky waves) induced by the cap layer either inside the gaps or inside the bands of the SL respectively. Also, we highlight the possibility of existence of interface modes between the SL and a cap layer as well as an interaction between these modes and the BG surface mode when both modes fall in the same band gaps of the SL. The strength of the interaction depends on the width of the cap layer. Finally, we show that the electromechanical coupling coefficient (ECC) is very sensitive to the cap layer thickness, in particular we calculate and discuss the behavior of the ECC as a function of the adlayer thickness for the low velocity surface modes of the SL which exhibit the highest ECC values. The effect of the nature of the metallic layers inside the SL on the ECC is also investigated. The different surface modes discussed in this work should have applications in sensing applications. Copyright © 2018. Published by Elsevier B.V.

Hafnia-based resistive switching devices for non-volatile memory applications and effects of gamma irradiation on device performance

NASA Astrophysics Data System (ADS)

Arun, N.; Kumar, K. Vinod; Pathak, A. P.; Avasthi, D. K.; Nageswara Rao, S. V. S.

2018-04-01

Non-volatile memory (NVM) devices were fabricated as a Metal- Insulator-Metal (MIM) structures by sandwiching Hafnium dioxide (HfO2) thin film in between two metal electrodes. The top and bottom metal electrodes were deposited by using the thermal evaporation, and the oxide layer was deposited by using the RF magnetron sputtering technique. The Resistive Random Access Memory (RRAM) device structures such as Ag/HfO2/Au/Si were fabricated and I-V characteristics for the pristine and gamma-irradiated devices with a dose 24 kGy were measured. Further we have studied the thermal annealing effects, in the range of 100°-400°C in a tubular furnace for the HfO2/Au/Si samples. The X-ray diffraction (XRD), Rutherford Backscattering Spectrometry (RBS), field emission-scanning electron microscopy (FESEM) analysis measurements were performed to determine the thickness, crystallinity and stoichiometry of these films. The electrical characteristics such as resistive switching, endurance, retention time and switching speed were measured by a semiconductor device analyser. The effects of gamma irradiation on the switching properties of these RRAM devices have been studied.

Wavelength tunable single nanowire lasers based on surface plasmon polariton enhanced Burstein-Moss effect.

PubMed

Liu, Xinfeng; Zhang, Qing; Yip, Jing Ngei; Xiong, Qihua; Sum, Tze Chien

2013-01-01

Wavelength tunable semiconductor nanowire (NW) lasers are promising for multifunctional applications ranging from optical communication to spectroscopy analysis. Here, we present a demonstration of utilizing the surface plasmon polariton (SPP) enhanced Burstein-Moss (BM) effect to tune the lasing wavelength of a single semiconductor NW. The photonic lasing mode of the CdS NW (with length ~10 μm and diameter ~220 nm) significantly blue shifts from 504 to 483 nm at room temperature when the NW is in close proximity to the Au film. Systematic steady state power dependent photoluminescence (PL) and time-resolved PL studies validate that the BM effect in the hybrid CdS NW devices is greatly enhanced as a consequence of the strong coupling between the SPP and CdS excitons. With decreasing dielectric layer thickness h from 100 to 5 nm, the enhancement of the BM effect becomes stronger, leading to a larger blue shift of the lasing wavelength. Measurements of enhanced exciton emission intensities and recombination rates in the presence of Au film further support the strong interaction between SPP and excitons, which is consistent with the simulation results.

Comparative study of I- V methods to extract Au/FePc/p-Si Schottky barrier diode parameters

NASA Astrophysics Data System (ADS)

Oruç, Çiğdem; Altındal, Ahmet

2018-01-01

So far, various methods have been proposed to extract the Schottky diode parameters from measured current-voltage characteristics. In this work, Schottky barrier diode with structure of Au/2(3),9(10),16(17),23(24)-tetra(4-(4-methoxyphenyl)-8-methylcoumarin-7 oxy) phthalocyaninatoiron(II) (FePc)/p-Si was fabricated and current-voltage measurements were carried out on it. In addition, current-voltage measurements were also performed on Au/p-Si structure, without FePc, to clarify the influence of the presence of an interface layer on the device performance. The measured current-voltage characteristics indicate that the interface properties of a Schottky barrier diode can be controlled by the presence of an organic interface layer. It is found that the room temperature barrier height of Au/FePc/p-Si structure is larger than that of the Au/p-Si structure. The obtained forward bias current-voltage characteristics of the Au/FePc/p-Si device was analysed by five different analytical methods. It is found that the extracted values of SBD parameters strongly depends on the method used.

An ordered array of hierarchical spheres for surface-enhanced Raman scattering detection of traces of pesticide

NASA Astrophysics Data System (ADS)

Hu, Xiaoye; Zheng, Peng; Meng, Guowen; Huang, Qing; Zhu, Chuhong; Han, Fangming; Huang, Zhulin; Li, Zhongbo; Wang, Zhaoming; Wu, Nianqiang

2016-09-01

An ordered array of hierarchically-structured core-nanosphere@space-layer@shell-nanoparticles has been fabricated for surface-enhanced Raman scattering (SERS) detection. To fabricate this hierarchically-structured chip, a long-range ordered array of Au/Ag-nanospheres is first patterned in the nano-bowls on the planar surface of ordered nanoporous anodic titanium oxide template. A ultra-thin alumina middle space-layer is then conformally coated on the Au/Ag-nanospheres, and Ag-nanoparticles are finally deposited on the surface of the alumina space-layer to form an ordered array of Au/Ag-nanosphere@Al2O3-layer@Ag-nanoparticles. Finite-difference time-domain simulation shows that SERS hot spots are created between the neighboring Ag-nanoparticles. The ordered array of hierarchical nanostructures is used as the SERS-substrate for a trial detection of methyl parathion (a pesticide) in water and a limit of detection of 1 nM is reached, indicating its promising potential in rapid monitoring of organic pollutants in aquatic environment.

Effect of NiFeCr seed and capping layers on exchange bias and planar Hall voltage response of NiFe/Au/IrMn trilayer structures

NASA Astrophysics Data System (ADS)

Talantsev, Artem; Elzwawy, Amir; Kim, CheolGi

2018-05-01

Thin films and cross junctions, based on NiFe/Au/IrMn structures, were grown on Ta and NiFeCr seed layers by magnetron sputtering. The effects of substitution of Ta with NiFeCr in seed and capping layers on an exchange bias field are studied. A threefold improvement of the exchange bias value in the structures, grown with NiFeCr seed and capping layers, is demonstrated. The reasons for this effect are discussed. Formation of clusters in the NiFeCr capping layer is proved by atomic force microscopy technique. Ta replacement on NiFeCr in the capping layer results in the enhancement of magnetoresistive response and a reduction of noise.

Evaluation of metal/indium-tin-oxide for transparent low-resistance contacts to p-type GaN.

PubMed

Hou, Wenting; Stark, Christoph; You, Shi; Zhao, Liang; Detchprohm, Theeradetch; Wetzel, Christian

2012-08-10

In search of a better transparent contact to p-GaN, we analyze various metal/indium-tin-oxide (ITO) (Ag/ITO, AgCu/ITO, Ni/ITO, and NiZn/ITO) contact schemes and compare to Ni/Au, NiZn/Ag, and ITO. The metal layer boosts conductivity while the ITO thickness can be adjusted to constructive transmission interference on GaN that exceeds extraction from bare GaN. We find a best compromise for an Ag/ITO (3 nm/67 nm) ohmic contact with a relative transmittance of 97% of the bare GaN near 530 nm and a specific contact resistance of 0.03 Ω·cm2. The contact proves suitable for green light-emitting diodes in epi-up geometry.

A Study on the Plasmonic Properties of Silver Core Gold Shell Nanoparticles: Optical Assessment of the Particle Structure

NASA Astrophysics Data System (ADS)

Mott, Derrick; Lee, JaeDong; Thi Bich Thuy, Nguyen; Aoki, Yoshiya; Singh, Prerna; Maenosono, Shinya

2011-06-01

This paper reports a qualitative comparison between the optical properties of a set of silver core, gold shell nanoparticles with varying composition and structure to those calculated using the Mie solution. To achieve this, silver nanoparticles were synthesized in aqueous phase from a silver hydroxide precursor with sodium acrylate as dual reducing-capping agent. The particles were then coated with a layer of gold with controllable thickness through a reduction-deposition process. The resulting nanoparticles reveal well defined optical properties that make them suitable for comparison to ideal calculated results using the Mie solution. The discussion focuses on the correlation between the synthesized core shell nanoparticles with varying Au shell thickness and the Mie solution results in terms of the optical properties. The results give insight in how to design and synthesize silver core, gold shell nanoparticles with controllable optical properties (e.g., SPR band in terms of intensity and position), and has implications in creating nanoparticle materials to be used as biological probes and sensing elements.

Studying Dynamic Processes of Nano-sized Objects in Liquid using Scanning Transmission Electron Microscopy.

PubMed

Hermannsdörfer, Justus; de Jonge, Niels

2017-02-05

Samples fully embedded in liquid can be studied at a nanoscale spatial resolution with Scanning Transmission Electron Microscopy (STEM) using a microfluidic chamber assembled in the specimen holder for Transmission Electron Microscopy (TEM) and STEM. The microfluidic system consists of two silicon microchips supporting thin Silicon Nitride (SiN) membrane windows. This article describes the basic steps of sample loading and data acquisition. Most important of all is to ensure that the liquid compartment is correctly assembled, thus providing a thin liquid layer and a vacuum seal. This protocol also includes a number of tests necessary to perform during sample loading in order to ensure correct assembly. Once the sample is loaded in the electron microscope, the liquid thickness needs to be measured. Incorrect assembly may result in a too-thick liquid, while a too-thin liquid may indicate the absence of liquid, such as when a bubble is formed. Finally, the protocol explains how images are taken and how dynamic processes can be studied. A sample containing AuNPs is imaged both in pure water and in saline.

Studying Dynamic Processes of Nano-sized Objects in Liquid using Scanning Transmission Electron Microscopy

PubMed Central

Hermannsdörfer, Justus; de Jonge, Niels

2017-01-01

Samples fully embedded in liquid can be studied at a nanoscale spatial resolution with Scanning Transmission Electron Microscopy (STEM) using a microfluidic chamber assembled in the specimen holder for Transmission Electron Microscopy (TEM) and STEM. The microfluidic system consists of two silicon microchips supporting thin Silicon Nitride (SiN) membrane windows. This article describes the basic steps of sample loading and data acquisition. Most important of all is to ensure that the liquid compartment is correctly assembled, thus providing a thin liquid layer and a vacuum seal. This protocol also includes a number of tests necessary to perform during sample loading in order to ensure correct assembly. Once the sample is loaded in the electron microscope, the liquid thickness needs to be measured. Incorrect assembly may result in a too-thick liquid, while a too-thin liquid may indicate the absence of liquid, such as when a bubble is formed. Finally, the protocol explains how images are taken and how dynamic processes can be studied. A sample containing AuNPs is imaged both in pure water and in saline. PMID:28190028

DOE Office of Scientific and Technical Information (OSTI.GOV)

Junay, A.; Guézo, S., E-mail: sophie.guezo@univ-rennes1.fr; Turban, P.

We study structural and electronic inhomogeneities in Metal—Organic Molecular monoLayer (OML)—semiconductor interfaces at the sub-nanometer scale by means of in situ Ballistic Electron Emission Microscopy (BEEM). BEEM imaging of Au/1-hexadecanethiols/GaAs(001) heterostructures reveals the evolution of pinholes density as a function of the thickness of the metallic top-contact. Using BEEM in spectroscopic mode in non-short-circuited areas, local electronic fingerprints (barrier height values and corresponding spectral weights) reveal a low-energy tunneling regime through the insulating organic monolayer. At higher energies, BEEM evidences new conduction channels, associated with hot-electron injection in the empty molecular orbitals of the OML. Corresponding band diagrams at buriedmore » interfaces can be thus locally described. The energy position of GaAs conduction band minimum in the heterostructure is observed to evolve as a function of the thickness of the deposited metal, and coherently with size-dependent electrostatic effects under the molecular patches. Such BEEM analysis provides a quantitative diagnosis on metallic top-contact formation on organic molecular monolayer and appears as a relevant characterization for its optimization.« less

Bi-Directional Ion Emission from Massive Gold Cluster Impacts on Nanometric Carbon Foils.

PubMed

Debord, J Daniel; Della-Negra, Serge; Fernandez-Lima, Francisco A; Verkhoturov, Stanislav V; Schweikert, Emile A

2012-04-12

Carbon cluster emission from thin carbon foils (5-40 nm) impacted by individual Au(n) (+q) cluster projectiles (95-125 qkeV, n/q = 3-200) reveals features regarding the energy deposition, projectile range, and projectile fate in matter as a function of the projectile characteristics. For the first time, the secondary ion emission from thin foils has been monitored simultaneously in both forward and backward emission directions. The projectile range and depth of emission were examined as a function of projectile size, energy, and target thickness. A key finding is that the massive cluster impact develops very differently from that of a small polyatomic projectile. The range of the 125 qkeV Au(100q) (+q) (q ≈ 4) projectile is estimated to be 20 nm (well beyond the range of an equal velocity Au(+)) and projectile disintegration occurs at the exit of even a 5 nm thick foil.

Ion-beam-induced nanodots formation from Au/Si thin films on quartz surface

NASA Astrophysics Data System (ADS)

Datta, D. P.; Siva, V.; Singh, A.; Joshi, S. R.; Kanjilal, D.; Sahoo, P. K.

2016-07-01

We report the synthesis of Si nanodots on quartz surface using ion irradiation. When a bi-layer of ultrathin Au and Si on quartz surface is irradiated by 500 keV Xe-ion beam, the bi-layer spontaneously transforms into nanodots at a fluence of 5 × 1014 ions cm-2. The spatial density and diameter of the nanodots are reduced with increase in applied ion fluence. The nanostructures exhibit photoluminescence in the visible range at room temperature where the intensity and wavelength depends upon ion fluence. The observed evolution seems to be correlated to ion beam mixing induced silicide formation at Au-Si interface.

First-principles study of Ti intercalation between graphene and Au surface

NASA Astrophysics Data System (ADS)

Kaneko, T.; Imamura, H.

2011-06-01

We investigate the effects of Ti intercalation between graphene and Au surface on binding energy and charge doping by using the first-principles calculations. We show that the largest binding energy is realized by the intercalation of single mono-layer of Ti. We also show that electronic structure is very sensitive to the arrangement of metal atoms at the interface. If the composition of the interface layer is Ti0.33Au0.67 and the Ti is located at the top site, the Fermi level lies closely at the Dirac point, i.e., the Dirac cone of the ideal free-standing graphene is recovered.

Experimental optimization during SERS application

NASA Astrophysics Data System (ADS)

Laha, Ranjit; Das, Gour Mohan; Ranjan, Pranay; Dantham, Venkata Ramanaiah

2018-05-01

The well known surface enhanced Raman scattering (SERS) needs a lot of experimental optimization for its proper implementation. In this report, we demonstrate the efficient SERS using gold nanoparticles (AuNPs) on quartz plate. The AuNPs were prepared by depositing direct current sputtered Au thin film followed by suitable annealing. The parameters varied for getting best SERS effect were 1) Numerical Aperture of Raman objective lens and 2) Sputtering duration of Au film. It was found that AuNPs formed from the Au layer deposited for 40s and Raman objective lens of magnification 50X are the best combination for obtaining efficient SERS effect.