Investigation of Electrical and Optical Properties of Highly Transparent TCO/Ag/TCO Multilayer.

PubMed

Kim, Sunbo; Lee, Jaehyeong; Dao, Vinh Ai; Ahn, Shihyun; Hussain, Shahzada Qamar; Park, Jinjoo; Jung, Junhee; Lee, Chan; Song, Bong-Shik; Choi, Byoungdeog; Lee, Youn-Jung; Iftiquar, S M; Yi, Junsin

2015-03-01

Transparent conductive oxides (TCOs) have been widely used as transparent electrodes for opto-electronic devices, such as solar cells, flat-panel displays, and light-emitting diodes, because of their unique characteristics of high optical transmittance and low electrical resistivity. Among various TCO materials, zinc oxide based films have recently received much attention because they have advantages over commonly used indium and tin-based oxide films. Most TCO films, however, exhibit valleys of transmittance in the wavelength range of 550-700 nm, lowering the average transmittance in the visible region and decreasing short-circuit current (Isc) of solar cells. A TCO/Ag/TCO multi-layer structure has emerged as an attractive alternative because it provides optical characteristics without the valley of transmittance compared with a 100-nm-thick single-layer TCO. In this article, we report the electrical, optical and surface properties of TCO/Ag/TCO. These multi-layers were deposited at room temperature with various Ag film thicknesses from 5 to 15 nm while the thickness of TCO thin film was fixed at 40 nm. The TCO/Ag/TCO multi-layer with a 10-nm-thick Ag film showed optimum transmittance in the visible (400-800 nm) wavelength region. These multi-layer structures have advantages over TCO layers of the same thickness.

Studies of x-ray localization and thickness dependence in atomic-scale elemental mapping by STEM energy-dispersive x-ray spectroscopy using single-frame scanning method

DOE PAGES

Lu, Ping; Moya, Jaime M.; Yuan, Renliang; ...

2018-03-01

The delocalization of x-ray signals limits the spatial resolution in atomic-scale elemental mapping by scanning transmission electron microscopy (STEM) using energy-dispersive x-ray spectroscopy (EDS). In this study, using a SrTiO 3 [001] single crystal, we show that the x-ray localization to atomic columns is strongly dependent on crystal thickness, and a thin crystal is critical for improving the spatial resolution in atomic-scale EDS mapping. A single-frame scanning technique is used in this study instead of the multiple-frame technique to avoid peak broadening due to tracking error. The strong thickness dependence is realized by measuring the full width at half maximamore » (FWHM) as well as the peak-to-valley (P/V) ratio of the EDS profiles for Ti K and Sr K+L, obtained at several crystal thicknesses. A FWHM of about 0.16 nm and a P/V ratio of greater than 7.0 are obtained for Ti K for a crystal thickness of less than 20 nm. In conclusion, with increasing crystal thickness, the FWHM and P/V ratio increases and decreases, respectively, indicating the advantage of using a thin crystal for high-resolution EDS mapping.« less

Studies of x-ray localization and thickness dependence in atomic-scale elemental mapping by STEM energy-dispersive x-ray spectroscopy using single-frame scanning method

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

Lu, Ping; Moya, Jaime M.; Yuan, Renliang

The delocalization of x-ray signals limits the spatial resolution in atomic-scale elemental mapping by scanning transmission electron microscopy (STEM) using energy-dispersive x-ray spectroscopy (EDS). In this study, using a SrTiO 3 [001] single crystal, we show that the x-ray localization to atomic columns is strongly dependent on crystal thickness, and a thin crystal is critical for improving the spatial resolution in atomic-scale EDS mapping. A single-frame scanning technique is used in this study instead of the multiple-frame technique to avoid peak broadening due to tracking error. The strong thickness dependence is realized by measuring the full width at half maximamore » (FWHM) as well as the peak-to-valley (P/V) ratio of the EDS profiles for Ti K and Sr K+L, obtained at several crystal thicknesses. A FWHM of about 0.16 nm and a P/V ratio of greater than 7.0 are obtained for Ti K for a crystal thickness of less than 20 nm. In conclusion, with increasing crystal thickness, the FWHM and P/V ratio increases and decreases, respectively, indicating the advantage of using a thin crystal for high-resolution EDS mapping.« less

Studies of x-ray localization and thickness dependence in atomic-scale elemental mapping by STEM energy-dispersive x-ray spectroscopy using single-frame scanning method.

PubMed

Lu, Ping; Moya, Jaime M; Yuan, Renliang; Zuo, Jian Min

2018-03-01

The delocalization of x-ray signals limits the spatial resolution in atomic-scale elemental mapping by scanning transmission electron microscopy (STEM) using energy-dispersive x-ray spectroscopy (EDS). In this study, using a SrTiO 3 [001] single crystal, we show that the x-ray localization to atomic columns is strongly dependent on crystal thickness, and a thin crystal is critical for improving the spatial resolution in atomic-scale EDS mapping. A single-frame scanning technique is used in this study instead of the multiple-frame technique to avoid peak broadening due to tracking error. The strong thickness dependence is realized by measuring the full width at half maxima (FWHM) as well as the peak-to-valley (P/V) ratio of the EDS profiles for Ti K and Sr K + L, obtained at several crystal thicknesses. A FWHM of about 0.16 nm and a P/V ratio of greater than 7.0 are obtained for Ti K for a crystal thickness of less than 20 nm. With increasing crystal thickness, the FWHM and P/V ratio increases and decreases, respectively, indicating the advantage of using a thin crystal for high-resolution EDS mapping. Published by Elsevier B.V.

Broadband operation of rolled-up hyperlenses

NASA Astrophysics Data System (ADS)

Schwaiger, Stephan; Rottler, Andreas; Bröll, Markus; Ehlermann, Jens; Stemmann, Andrea; Stickler, Daniel; Heyn, Christian; Heitmann, Detlef; Mendach, Stefan

2012-06-01

This work is related to an earlier publication [Schwaiger , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.102.163903 102, 163903 (2009)], where we demonstrated by means of fiber-based transmission measurements that rolled-up Ag-(In)GaAs multilayers represent three-dimensional metamaterials with a plasma edge which is tunable over the visible and near-infrared regime by changing the thickness ratio of Ag and (In)GaAs, and predicted by means of finite-difference time-domain simulations that hyperlensing occurs at this frequency-tunable plasma edge. In the present work we develop a method to measure reflection curves on these structures and find that they correspond to the same tunable plasma edge. We find that retrieving the effective parameters from transmission and reflection data fails, because our realized metamaterials exceed the single-layer thicknesses of 5nm, which we analyze to be the layer thickness limit for the applicability of effective parameter retrieval. We show that our realized structures nevertheless have the functionality of an effective metamaterial by supplying a detailed finite-difference time-domain study which compares light propagation through our realized structure (17-nm-thick Ag layers and 34-nm-thick GaAs layers) and light propagation through an idealized structure of the same total thickness but with very thin layers [2-nm-thick Ag layers and 4-nm-thick (In)GaAs layers]. In particular, our simulations predict broadband hyperlensing covering a large part of the visible spectrum for both the idealized and our realized structures.

On the origins of hardness of Cu–TiN nanolayered composites

DOE PAGES

Pathak, S.; Li, N.; Maeder, X.; ...

2015-07-18

We investigated the mechanical response of physical vapor deposited Cu–TiN nanolayered composites of varying layer thicknesses from 5 nm to 200 nm. Both the Cu and TiN layers were found to consist of single phase nanometer sized grains. The grain sizes in the Cu and TiN layers, measured using transmission electron microscopy and X-ray diffraction, were found to be comparable to or smaller than their respective layer thicknesses. Indentation hardness testing revealed that the hardness of such nanolayered composites exhibits a weak dependence on the layer thickness but is more correlated to their grain size.

Analysis of Soft Error Rates in 65- and 28-nm FD-SOI Processes Depending on BOX Region Thickness and Body Bias by Monte-Carlo Based Simulations

NASA Astrophysics Data System (ADS)

Zhang, Kuiyuan; Umehara, Shigehiro; Yamaguchi, Junki; Furuta, Jun; Kobayashi, Kazutoshi

2016-08-01

This paper analyzes how body bias and BOX region thickness affect soft error rates in 65-nm SOTB (Silicon on Thin BOX) and 28-nm UTBB (Ultra Thin Body and BOX) FD-SOI processes. Soft errors are induced by alpha-particle and neutron irradiation and the results are then analyzed by Monte Carlo based simulation using PHITS-TCAD. The alpha-particle-induced single event upset (SEU) cross-section and neutron-induced soft error rate (SER) obtained by simulation are consistent with measurement results. We clarify that SERs decreased in response to an increase in the BOX thickness for SOTB while SERs in UTBB are independent of BOX thickness. We also discover SOTB develops a higher tolerance to soft errors when reverse body bias is applied while UTBB become more susceptible.

Magnetic properties of ultrathin tetragonal Heusler D022-Mn3Ge perpendicular-magnetized films

NASA Astrophysics Data System (ADS)

Sugihara, A.; Suzuki, K. Z.; Miyazaki, T.; Mizukami, S.

2015-05-01

We investigated the crystal structure and magnetic properties of Manganese-germanium (Mn3Ge) films having the tetragonal D022 structure, with varied thicknesses (5-130 nm) prepared on chromium (Cr)-buffered single crystal MgO(001) substrates. A crystal lattice elongation in the in-plane direction, induced by the lattice mismatch between the D022-Mn3Ge and the Cr buffer layer, increased with decreasing thickness of the D022-Mn3Ge layer. The films exhibited clear magnetic hysteresis loops with a squareness ratio close to unity, and a step-like magnetization reversal even at a 5-nm thickness under an external field perpendicular to the film's plane. The uniaxial magnetic anisotropy constant of the films showed a reduction to less than 10 Merg/cm3 in the small thickness range (≤20 nm), likely due to the crystal lattice elongation in the in-plane direction.

Microstructural and mechanical properties of Al2O3/ZrO2 nanomultilayer thin films prepared by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Balakrishnan, G.; Sastikumar, D.; Kuppusami, P.; Babu, R. Venkatesh; Song, Jung Il

2018-02-01

Single layer aluminium oxide (Al2O3), zirconium oxide (ZrO2) and Al2O3/ZrO2 nano multilayer films were deposited on Si (100) substrates at room temperature by pulsed laser deposition. The development of Al2O3/ZrO2 nanolayered structure is an important method used to stabilize the high temperature phase (tetragonal and cubic) of ZrO2 at room temperature. In the Al2O3/ZrO2 multilayer structure, the Al2O3 layer was kept constant at 5 nm, while the ZrO2 layer thickness varied from 5 to 20 nm (5/5, 5/10, 5/15 and 5/20 nm) with a total of 40 bilayers. The X-ray diffraction studies of single layer Al2O3 indicated the γ-Al2O3 of cubic structure, while the single layer ZrO2 indicated both monoclinic and tetragonal phases. The 5/5 and 5/10 nm multilayer films showed the nanocrystalline nature of ZrO2 with tetragonal phase. The high resolution transmission electron microscopy studies indicated the formation of well-defined Al2O3 and ZrO2 layers and that they are of uniform thickness. The atomic force microscopy studies revealed the uniform and dense distribution of nanocrystallites. The nanoindentation studies indicated the hardness of 20.8 ± 1.10 and 10 ± 0.60 GPa, for single layer Al2O3 and ZrO2, respectively, and the hardness of multilayer films varied with bilayer thickness.

940  mW 1564  nm multi-longitudinal-mode and 440  mW 1537  nm single-longitudinal-mode continuous-wave Er:Yb:Lu2Si2O7 microchip lasers.

PubMed

Huang, Jianhua; Chen, Yujin; Lin, Yanfu; Gong, Xinghong; Luo, Zundu; Huang, Yidong

2018-04-15

An Er:Yb:Lu 2 Si 2 O 7 microchip laser was constructed by placing a 1.2 mm thick, Y-cut Er:Yb:Lu 2 Si 2 O 7 microchip between two 1.2 mm thick sapphire crystals, in which input and output mirrors were directly deposited onto one face of each crystal. End-pumped by a continuous-wave 975.4 nm diode laser, a 1564 nm multi-longitudinal-mode laser with a maximum output power of 940 mW and slope efficiency of 20% was realized at an absorbed pump power of 5.5 W when the transmission of output mirror was 2.2%. When the transmission of the output mirror was increased to 6%, a 1537 nm single-longitudinal-mode laser with a maximum output power of 440 mW and slope efficiency of 12% was realized at an absorbed pump power of 4.3 W. The results indicate that the Er:Yb:Lu 2 Si 2 O 7 crystal is a promising microchip gain medium to realize a single-longitudinal-mode laser.

L10 FePtCu bit patterned media

NASA Astrophysics Data System (ADS)

Brombacher, C.; Grobis, M.; Lee, J.; Fidler, J.; Eriksson, T.; Werner, T.; Hellwig, O.; Albrecht, M.

2012-01-01

Chemically ordered 5 nm-thick L10 FePtCu films with strong perpendicular magnetic anisotropy were post-patterned by nanoimprint lithography into a dot array over a 3 mm-wide circumferential band on a 3 inch Si wafer. The dots with a diameter of 30 nm and a center-to-center pitch of 60 nm appear as single domain and reveal an enhanced switching field as compared to the continuous film. We demonstrate successful recording on a single track using shingled writing with a conventional hard disk drive write/read head.

In situ conductance measurements of copper phthalocyanine thin film growth on sapphire [0001].

PubMed

Murdey, Richard; Sato, Naoki

2011-06-21

The current flowing through a thin film of copper phthalocyanine vacuum deposited on a single crystal sapphire [0001] surface was measured during film growth from 0 to 93 nm. The results, expressed as conductance vs. nominal film thickness, indicate three distinct film growth regions. Conductive material forms below about 5 nm and again above 35 nm, but in the intermediate thicknesses the film conductance was observed to decrease with increasing film thickness. With the aid of ac-AFM topology images taken ex situ, the conductance results are explained based on the Stranski-Krastanov (2D + 3D) film growth mechanism, in which the formation of a thin wetting layer is followed by the growth of discrete islands that eventually coalesce into an interpenetrating, conductive network. © 2011 American Institute of Physics

Insulator-protected mechanically controlled break junctions for measuring single-molecule conductance in aqueous environments

NASA Astrophysics Data System (ADS)

Muthusubramanian, N.; Galan, E.; Maity, C.; Eelkema, R.; Grozema, F. C.; van der Zant, H. S. J.

2016-07-01

We present a method to fabricate insulated gold mechanically controlled break junctions (MCBJ) by coating the metal with a thin layer of aluminum oxide using plasma enhanced atomic layer deposition. The Al2O3 thickness deposited on the MCBJ devices was varied from 2 to 15 nm to test the suppression of leakage currents in deionized water and phosphate buffered saline. Junctions coated with a 15 nm thick oxide layer yielded atomically sharp electrodes and negligible conductance counts in the range of 1 to 10-4 G0 (1 G0 = 77 μS), where single-molecule conductances are commonly observed. The insulated devices were used to measure the conductance of an amphiphilic oligophenylene ethynylene derivative in deionized water.

Preparation of high-quality ultrathin transmission electron microscopy specimens of a nanocrystalline metallic powder.

PubMed

Riedl, Thomas; Gemming, Thomas; Mickel, Christine; Eymann, Konrad; Kirchner, Alexander; Kieback, Bernd

2012-06-01

This article explores the achievable transmission electron microscopy specimen thickness and quality by using three different preparation methods in the case of a high-strength nanocrystalline Cu-Nb powder alloy. Low specimen thickness is essential for spatially resolved analyses of the grains in nanocrystalline materials. We have found that single-sided as well as double-sided low-angle Ar ion milling of the Cu-Nb powders embedded into epoxy resin produced wedge-shaped particles of very low thickness (<10 nm) near the edge. By means of a modified focused ion beam lift-out technique generating holes in the lamella interior large micrometer-sized electron-transparent regions were obtained. However, this lamella displayed a higher thickness at the rim of ≥30 nm. Limiting factors for the observed thicknesses are discussed including ion damage depths, backscattering, and surface roughness, which depend on ion type, energy, current density, and specimen motion. Finally, sections cut by ultramicrotomy at low stroke rate and low set thickness offered vast, several tens of square micrometers uniformly thin regions of ∼10-nm minimum thickness. As major drawbacks, we have detected a thin coating on the sections consisting of epoxy deployed as the embedding material and considerable nanoscale thickness variations. Copyright © 2011 Wiley Periodicals, Inc.

Ultra-thin distributed Bragg reflectors via stacked single-crystal silicon nanomembranes

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

Cho, Minkyu; Seo, Jung-Hun; Lee, Jaeseong

2015-05-04

In this paper, we report ultra-thin distributed Bragg reflectors (DBRs) via stacked single-crystal silicon (Si) nanomembranes (NMs). Mesh hole-free single-crystal Si NMs were released from a Si-on-insulator substrate and transferred to quartz and Si substrates. Thermal oxidation was applied to the transferred Si NM to form high-quality SiO{sub 2} and thus a Si/SiO{sub 2} pair with uniform and precisely controlled thicknesses. The Si/SiO{sub 2} layers, as smooth as epitaxial grown layers, minimize scattering loss at the interface and in between the layers. As a result, a reflection of 99.8% at the wavelength range from 1350 nm to 1650 nm can be measuredmore » from a 2.5-pair DBR on a quartz substrate and 3-pair DBR on a Si substrate with thickness of 0.87 μm and 1.14 μm, respectively. The high reflection, ultra-thin DBRs developed here, which can be applied to almost any devices and materials, holds potential for application in high performance optoelectronic devices and photonics applications.« less

Magnetic glass-film based on single-nanosize 𝜺 -Fe2O3 nanoparticles

NASA Astrophysics Data System (ADS)

Yoshikiyo, Marie; Namai, Asuka; Nakagawa, Kosuke; Ohkoshi, Shin-ichi

2017-05-01

We report a magnetic thin film of single-nanosize ɛ-Fe2O3 in SiO2 matrix. The glass-film was prepared by sintering a silica coated iron oxide hydroxide on a quartz substrate in air. The glass-film consists of ɛ-Fe2O3 of 8.8 nm size, and its thickness was 570 nm (0.57 μm) with a roughness of 10 nm (0.01 μm). UV-vis spectrum showed that the glass-film has small absorbance of 0.043 at 500 nm. The magneto-optical effect was investigated, and Faraday ellipticity showed a magnetic hysteresis loop with a coercive field of 3.0 ± 0.2 kOe. Furthermore, single-nanosize ɛ-Fe2O3 without silica was prepared as a reference sample, and ferroelectricity was observed. Therefore, the present thin glass-film consists of single-nanosize ferroelectric-ferromagnetic nanoparticles.

Continuously tunable solution-processed organic semiconductor DFB lasers pumped by laser diode.

PubMed

Klinkhammer, Sönke; Liu, Xin; Huska, Klaus; Shen, Yuxin; Vanderheiden, Sylvia; Valouch, Sebastian; Vannahme, Christoph; Bräse, Stefan; Mappes, Timo; Lemmer, Uli

2012-03-12

The fabrication and characterization of continuously tunable, solution-processed distributed feedback (DFB) lasers in the visible regime is reported. Continuous thin film thickness gradients were achieved by means of horizontal dipping of several conjugated polymer and blended small molecule solutions on cm-scale surface gratings of different periods. We report optically pumped continuously tunable laser emission of 13 nm in the blue, 16 nm in the green and 19 nm in the red spectral region on a single chip respectively. Tuning behavior can be described with the Bragg-equation and the measured thickness profile. The laser threshold is low enough that inexpensive laser diodes can be used as pump sources.

Size distribution and mixing state of black carbon particles during a heavy air pollution episode in Shanghai

NASA Astrophysics Data System (ADS)

Gong, Xianda; Zhang, Ci; Chen, Hong; Nizkorodov, Sergey A.; Chen, Jianmin; Yang, Xin

2016-04-01

A Single Particle Aerosol Mass Spectrometer (SPAMS), a Single Particle Soot Photometer (SP2) and various meteorological instruments were employed to investigate the chemical and physical properties of black carbon (BC) aerosols during a regional air pollution episode in urban Shanghai over a 5-day period in December 2013. The refractory black carbon (rBC) mass concentrations measured by SP2 averaged 3.2 µg m-3, with the peak value of 12.1 µg m-3 at 04:26 LT on 7 December. The number of BC-containing particles captured by SPAMS in the size range 200-1200 nm agreed very well with that detected by SP2 (R2 = 0.87). A cluster analysis of the single particle mass spectra allowed for the separation of BC-containing particles into five major classes: (1) Pure BC; (2) BC attributed to biomass burning (BBBC); (3) K-rich BC-containing (KBC); (4) BC internally mixed with OC and ammonium sulfate (BCOC-SOx); (5) BC internally mixed with OC and ammonium nitrate (BCOC-NOx). The size distribution of internally mixed BC particles was bimodal. Detected by SP2, the condensation mode peaked around ˜ 230 nm and droplet mode peaked around ˜ 380 nm, with a clear valley in the size distribution around ˜ 320 nm. The condensation mode mainly consisted of traffic emissions, with particles featuring a small rBC core (˜ 60-80 nm) and a relatively thin absolute coating thickness (ACT, ˜ 50-130 nm). The droplet mode included highly aged traffic emission particles and biomass burning particles. The biomass burning particles had a larger rBC core (˜ 80-130 nm) and a thick ACT (˜ 110-300 nm). The highly aged traffic emissions had a smaller core (˜ 60-80 nm) and a very thick ACT (˜ 130-300 nm), which is larger than reported in any previous literature. A fast growth rate (˜ 20 nm h-1) of rBC with small core sizes was observed during the experiment. High concentrations pollutants like NO2 likely accelerated the aging process and resulted in a continuous size growth of rBC-containing particles from traffic emission.

Synthesis and magnetic properties of the thin film exchange spring system of MnBi/FeCo

NASA Astrophysics Data System (ADS)

Sabet, S.; Hildebrandt, E.; Alff, L.

2017-10-01

Manganese bismuth thin films with a nominal thickness of ∼40 nm were grown at room temperature onto quartz glass substrate in a DC magnetron sputtering unit. In contrast to the usual multilayer approach, the MnBi films were deposited using a single sputtering target with a stoichiometry of Mn55Bi45 (at. %). A subsequent in-situ annealing step was performed in vacuum in order to form the ferromagnetic LTP of MnBi. X-ray diffraction confirmed the formation of a textured LTP MnBi hard phase after annealing at 330 °C. This film shows a maximum saturation magnetization of 530 emu/cm3, high out-of-plane coercivity of 15 kOe induced by unreacted bismuth. The exchange coupling effect was investigated by deposition of a second layer of FeCo with 1 nm and 2 nm thickness onto the LTP MnBi films. The MnBi/FeCo double layer showed as expected higher saturation magnetization with increasing thickness of the FeCo layer while the coercive field remained constant. The fabrication of the MnBi/FeCo double layer for an exchange spring magnet was facilitated by deposition from a single stoichiometric target.

Silicon induced stability and mobility of indium zinc oxide based bilayer thin film transistors

NASA Astrophysics Data System (ADS)

Chauhan, Ram Narayan; Tiwari, Nidhi; Liu, Po-Tsun; Shieh, Han-Ping D.; Kumar, Jitendra

2016-11-01

Indium zinc oxide (IZO), silicon containing IZO, and IZO/IZO:Si bilayer thin films have been prepared by dual radio frequency magnetron sputtering on glass and SiO2/Si substrates for studying their chemical compositions and electrical characteristics in order to ascertain reliability for thin film transistor (TFT) applications. An attempt is therefore made here to fabricate single IZO and IZO/IZO:Si bilayer TFTs to study the effect of film thickness, silicon incorporation, and bilayer active channel on device performance and negative bias illumination stress (NBIS) stability. TFTs with increasing single active IZO layer thickness exhibit decrease in carrier mobility but steady improvement in NBIS; the best values being μFE ˜ 27.0, 22.0 cm2/Vs and ΔVth ˜ -13.00, -6.75 V for a channel thickness of 7 and 27 nm, respectively. While silicon incorporation is shown to reduce the mobility somewhat, it raises the stability markedly (ΔVth ˜ -1.20 V). Further, IZO (7 nm)/IZO:Si (27 nm) bilayer based TFTs display useful characteristics (field effect mobility, μFE = 15.3 cm2/Vs and NBIS value, ΔVth =-0.75 V) for their application in transparent electronics.

Thickness effect of ultra-thin Ta2O5 resistance switching layer in 28 nm-diameter memory cell

NASA Astrophysics Data System (ADS)

Park, Tae Hyung; Song, Seul Ji; Kim, Hae Jin; Kim, Soo Gil; Chung, Suock; Kim, Beom Yong; Lee, Kee Jeung; Kim, Kyung Min; Choi, Byung Joon; Hwang, Cheol Seong

2015-11-01

Resistance switching (RS) devices with ultra-thin Ta2O5 switching layer (0.5-2.0 nm) with a cell diameter of 28 nm were fabricated. The performance of the devices was tested by voltage-driven current—voltage (I-V) sweep and closed-loop pulse switching (CLPS) tests. A Ta layer was placed beneath the Ta2O5 switching layer to act as an oxygen vacancy reservoir. The device with the smallest Ta2O5 thickness (0.5 nm) showed normal switching properties with gradual change in resistance in I-V sweep or CLPS and high reliability. By contrast, other devices with higher Ta2O5 thickness (1.0-2.0 nm) showed abrupt switching with several abnormal behaviours, degraded resistance distribution, especially in high resistance state, and much lower reliability performance. A single conical or hour-glass shaped double conical conducting filament shape was conceived to explain these behavioural differences that depended on the Ta2O5 switching layer thickness. Loss of oxygen via lateral diffusion to the encapsulating Si3N4/SiO2 layer was suggested as the main degradation mechanism for reliability, and a method to improve reliability was also proposed.

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%.

Measurement of the third order non-linearity of gold-graphene hybrid nanocomposite for near-infrared wavelengths

NASA Astrophysics Data System (ADS)

Syed, Salmaan R.; Lim, Guh-Hwan; Lim, Byungkwon; Chon, James W. M.

2016-04-01

We present measurements of nonlinear refraction (NLR) and nonlinear absorption (NLA) of single crystalline gold nanosheets (single crystalline-GNSs) and sputter coated polycrystalline thin gold metal film hybridized with multilayer grapheme (MLG) using Z-Scan technique for near-infrared wavelengths (NIR) ranging from 700 nm to 900 nm. Single crystalline GNSs of 20 nm thickness were prepared through chemical synthesis. MLG was found to have few monolayers of graphene, usually between 1-7 layers with an average of 4 monolayer thickness. The composite of GNSs and MLG was prepared by drop casting GNSs on MLG. Z-Scan experimental was carried out using Ti:sapphire femtosecond pulsed laser (700 nm - 900 nm wavelength, 115-130 fs pulse width and 0.82 MHz-82 MHz repetition rate). Intensity dependence on open aperture Z-scan was studied in detail for all materials. The NLA of polycrystalline thin gold metal film was found to be fractionally higher than that of single crystalline-GNSs. This is thought to be due to field enhancement around of gold islands formed on polycrystalline thin gold metal film during sputtering process. At higher repetition rates NLA phenomenon is diminished due to the temperature accumulation effect. As the repetition rate decreases the nonlinear effect is enhanced. On the other hand MLG exhibited saturable absorption (NSA) . Z-Scan results for single crystalline and poly crystalline gold-MLG nanocomposite exhibit NSA characteristics. The measured NSA coefficient `α' was found to be approximately ≍1.7×10-5-4.5×10-5 cmW-1 which is lower than that of MLG, clearly demonstrating the effect of hybridization.

Controlled deterministic implantation by nanostencil lithography at the limit of ion-aperture straggling

NASA Astrophysics Data System (ADS)

Alves, A. D. C.; Newnham, J.; van Donkelaar, J. A.; Rubanov, S.; McCallum, J. C.; Jamieson, D. N.

2013-04-01

Solid state electronic devices fabricated in silicon employ many ion implantation steps in their fabrication. In nanoscale devices deterministic implants of dopant atoms with high spatial precision will be needed to overcome problems with statistical variations in device characteristics and to open new functionalities based on controlled quantum states of single atoms. However, to deterministically place a dopant atom with the required precision is a significant technological challenge. Here we address this challenge with a strategy based on stepped nanostencil lithography for the construction of arrays of single implanted atoms. We address the limit on spatial precision imposed by ion straggling in the nanostencil—fabricated with the readily available focused ion beam milling technique followed by Pt deposition. Two nanostencils have been fabricated; a 60 nm wide aperture in a 3 μm thick Si cantilever and a 30 nm wide aperture in a 200 nm thick Si3N4 membrane. The 30 nm wide aperture demonstrates the fabricating process for sub-50 nm apertures while the 60 nm aperture was characterized with 500 keV He+ ion forward scattering to measure the effect of ion straggling in the collimator and deduce a model for its internal structure using the GEANT4 ion transport code. This model is then applied to simulate collimation of a 14 keV P+ ion beam in a 200 nm thick Si3N4 membrane nanostencil suitable for the implantation of donors in silicon. We simulate collimating apertures with widths in the range of 10-50 nm because we expect the onset of J-coupling in a device with 30 nm donor spacing. We find that straggling in the nanostencil produces mis-located implanted ions with a probability between 0.001 and 0.08 depending on the internal collimator profile and the alignment with the beam direction. This result is favourable for the rapid prototyping of a proof-of-principle device containing multiple deterministically implanted dopants.

Single-crystal diamond nanomechanical resonators with quality factors exceeding one million

NASA Astrophysics Data System (ADS)

Tao, Y.; Boss, J. M.; Moores, B. A.; Degen, C. L.

2014-04-01

Diamond has gained a reputation as a uniquely versatile material, yet one that is intricate to grow and process. Resonating nanostructures made of single-crystal diamond are expected to possess excellent mechanical properties, including high-quality factors and low dissipation. Here we demonstrate batch fabrication and mechanical measurements of single-crystal diamond cantilevers with thickness down to 85 nm, thickness uniformity better than 20 nm and lateral dimensions up to 240 μm. Quality factors exceeding one million are found at room temperature, surpassing those of state-of-the-art single-crystal silicon cantilevers of similar dimensions by roughly an order of magnitude. The corresponding thermal force noise for the best cantilevers is ~5·10-19 N Hz-1/2 at millikelvin temperatures. Single-crystal diamond could thus directly improve existing force and mass sensors by a simple substitution of resonator material. Presented methods are easily adapted for fabrication of nanoelectromechanical systems, optomechanical resonators or nanophotonic devices that may lead to new applications in classical and quantum science.

RBS, XRR and optical reflectivity measurements of Ti-TiO{sub 2} thin films deposited by magnetron sputtering

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

Drogowska, K.; Institute of Materials Science, Technische Universitaet Darmstadt, Petersenstrasse 23, 64287 Darmstadt; Tarnawski, Z., E-mail: tarnawsk@agh.edu.pl

2012-02-15

Highlights: Black-Right-Pointing-Pointer The single-, bi- and tri-layered films of Ti-TiO{sub 2} deposited onto Si(1 1 1) substrates. Black-Right-Pointing-Pointer Three methods RBS, XRR, optical reflectometer were used. Black-Right-Pointing-Pointer The real thickness of each layer was smaller than 50 nm. Black-Right-Pointing-Pointer Ti and TiO{sub 2} film-densities were slightly lower than the corresponding bulk values. -- Abstract: Single-, bi- and tri-layered films of Ti-TiO{sub 2} system were deposited by d.c. pulsed magnetron sputtering from metallic Ti target in an inert Ar or reactive Ar + O{sub 2} atmosphere. The nominal thickness of each layer was 50 nm. The chemical composition and its depthmore » profile were determined by Rutherford backscattering spectroscopy (RBS). Crystallographic structure was analysed by means of X-ray diffraction (XRD) at glancing incidence. X-ray reflectometry (XRR) was used as a complementary method for the film thickness and density evaluation. Modelling of the optical reflectivity spectra of Ti-TiO{sub 2} thin films deposited onto Si(1 1 1) substrates provided an independent estimate of the layer thickness. The combined analysis of RBS, XRR and reflectivity spectra indicated the real thickness of each layer less than 50 nm with TiO{sub 2} film density slightly lower than the corresponding bulk value. Scanning Electron Microscopy (SEM) cross-sectional images revealed the columnar growth of TiO{sub 2} layers. Thickness estimated directly from SEM studies was found to be in a good agreement with the results of RBS, XRR and reflectivity spectra.« less

Dosimetric effects of polyethylene glycol surface coatings on gold nanoparticle radiosensitization

NASA Astrophysics Data System (ADS)

Koger, B.; Kirkby, C.

2017-11-01

One of the main appeals of using gold nanoparticles (GNPs) as radiosensitizers is that their surface coatings can be altered to manipulate their pharmacokinetic properties. However, Monte Carlo studies of GNP dosimetry tend to neglect these coatings, potentially changing the dosimetric results. This study quantifies the dosimetric effects of including a polyethylene glycol (PEG) surface coating on GNPs over both nanoscopic and microscopic ranges. Two dosimetric scales were explored using PENELOPE Monte Carlo simulations. In microscopic simulations, 500-1000 GNPs, with and without coatings, were placed in cavities of side lengths 0.8-4 µm, and the reduction of dose deposited to surrounding medium within these volumes due to the coating was quantified. Including PEG surface coatings of up to 20 nm thickness resulted in reductions of up to 7.5%, 4.0%, and 2.0% for GNP diameters of 10, 20, and 50 nm, respectively. Nanoscopic simulations observed the dose falloff in the first 500 nm surrounding a single GNP both with and without surface coatings of various thicknesses. Over the first 500 nm surrounding a single GNP, the presence of a PEG surface coating reduced dose by 5-26%, 8-28%, 8-30%, and 8-34% for 2, 10, 20, and 50 nm diameter GNPs, respectively, for various energies and coating thicknesses. Reductions in dose enhancement due to the inclusion of a GNP surface coating are non-negligible and should be taken into consideration when investigating GNP dose enhancement. Further studies should be carried out to investigate the biological effects of these coatings.

Antiferromagnetic layer thickness dependence of noncollinear uniaxial and unidirectional anisotropies in NiFe/FeMn/CoFe trilayers

NASA Astrophysics Data System (ADS)

Choi, Hyeok-Cheol; You, Chun-Yeol; Kim, Ki-Yeon; Lee, Jeong-Soo; Shim, Je-Ho; Kim, Dong-Hyun

2010-06-01

We have investigated the dependence of magnetic anisotropies of the exchange-biased NiFe/FeMn/CoFe trilayers on the antiferromagnetic (AF) layer thickness (tAF) by measuring in-plane angular-dependent ferromagnetic resonance fields. The resonance fields of NiFe and CoFe sublayers are shifted to lower and higher values compared to those of single unbiased ferromagnetic (F) layers, respectively, due to the interfacial exchange coupling when tAF≥2nm . In-plane angular dependence of resonance field reveals that uniaxial and unidirectional anisotropies coexist in the film plane, however, they are not collinear with each other. It is found that these peculiar noncollinear anisotropies significantly depend on tAF . The angle of misalignment displays a maximum around tAF=5nm and converges to zero when tAF is thicker than 10 nm. Contributions from thickness-dependent AF anisotropy and spin frustrations at both F/AF interfaces due to the structural imperfections should be accounted in order to understand the AF-layer thickness dependence of noncollinear magnetic anisotropies.

Emission Behavior of Fluorescently Labeled Silver Nanoshell: Enhanced Self-Quenching by Metal Nanostructure.

PubMed

Zhang, Jian; Fu, Yi; Lakowicz, Joseph R

2007-02-08

Labeled silica beads with an average diameter of 100 nm were synthesized by incorporating with 20-600 μM Ru(bpy)(3) (2+) complexes. Silver shells were deposited on the beads layer-by-layer with the shell thickness of 5-50 nm. The emission band became narrower and the intensity was enhanced depending on the shell thickness. Self-quenching of the probe was observed at high concentration. Poisson statistics were employed to analyze self-quenching of the fluorophores. The estimated quenching distance was extended from 6 to 16 nm with shell growth from 0 to 50 nm. Moreover, the silver shells were also labeled with Rhodamine 6G. Fluorescence enhancement and reduced lifetime were also observed for silver-silica shell containing R6G. We found that by adjustment of probe concentration and silver shell thickness, a Ru(bpy)(3) (2+)-labeled particle could be 600 times brighter than an isolated Ru(bpy)(3) (2+) molecule. We expect labeled metal core-shell structures can become useful probes for high sensitivity and/or single particle assay.

Spin-valve Josephson junctions for cryogenic memory

NASA Astrophysics Data System (ADS)

Niedzielski, Bethany M.; Bertus, T. J.; Glick, Joseph A.; Loloee, R.; Pratt, W. P.; Birge, Norman O.

2018-01-01

Josephson junctions containing two ferromagnetic layers are being considered for use in cryogenic memory. Our group recently demonstrated that the ground-state phase difference across such a junction with carefully chosen layer thicknesses could be controllably toggled between zero and π by switching the relative magnetization directions of the two layers between the antiparallel and parallel configurations. However, several technological issues must be addressed before those junctions can be used in a large-scale memory. Many of these issues can be more easily studied in single junctions, rather than in the superconducting quantum interference device (SQUID) used for phase-sensitive measurements. In this work, we report a comprehensive study of spin-valve junctions containing a Ni layer with a fixed thickness of 2.0 nm and a NiFe layer of thickness varying between 1.1 and 1.8 nm in steps of 0.1 nm. We extract the field shift of the Fraunhofer patterns and the critical currents of the junctions in the parallel and antiparallel magnetic states, as well as the switching fields of both magnetic layers. We also report a partial study of similar junctions containing a slightly thinner Ni layer of 1.6 nm and the same range of NiFe thicknesses. These results represent the first step toward mapping out a "phase diagram" for phase-controllable spin-valve Josephson junctions as a function of the two magnetic layer thicknesses.

Investigation and characterization of ZnO single crystal microtubes

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

Al-Naser, Qusay A.H.; Zhou, Jian, E-mail: jianzhou@whut.edu.cn; Liu, Guizhen

2016-04-15

Morphological, structural, and optical characterization of microwave synthesized ZnO single crystal microtubes were investigated in this work. The structure and morphology of the ZnO microtubes are characterized using X-ray diffraction (XRD), single crystal diffraction (SCD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). The results reveal that the as-synthesized ZnO microtube has a highly regular hexagonal cross section and smooth surfaces with an average length of 650–700 μm, an average outer diameter of 50 μm and wall thickness of 1–3 μm, possessing a single crystal wurtzite hexagonal structure. Optical properties of ZnOmore » single crystal microtubes were investigated by photoluminescence (PL) and ultraviolet-visible (UV-vis) absorption techniques. Room-temperature PL spectrum of the microtube reveal a strong UV emission peak at around 375.89 nm and broad and a weak visible emission with a main peak identified at 577 nm, which was assigned to the nearest band-edge emission and the deep-level emission, respectively. The band gap energy of ZnO microtube was found to be 3.27 eV. - Highlights: • ZnO microtube length of 650–700 μm, diameter of 50 μm, wall thickness of 1–3 μm • ZnO microtube possesses a single crystal wurtzite hexagonal structure. • The crystal system is hexahedral oriented along a-axis with indices of (100). • A strong and sharp UV emission at 375.89 nm (3.29 eV) • One prominent absorption band around 378.88 nm (3.27 eV)« less

Indium droplet formation in InGaN thin films with single and double heterojunctions prepared by MOCVD

PubMed Central

2014-01-01

Indium gallium nitride (InGaN) samples with single heterojunction (SH) and double heterojunction (DH) were prepared using metal-organic chemical vapor deposition. SH has a layer of InGaN thin film (thicknesses, 25, 50, 100, and 200 nm) grown on an uGaN film (thickness, 2 μm). The DH samples are distinguished by DH uGaN film (thickness, 120 nm) grown on the InGaN layer. Reciprocal space mapping measurements reveal that the DH samples are fully strained with different thicknesses, whereas the strain in the SH samples are significantly relaxed with the increasing thickness of the InGaN film. Scanning electron microscopy results show that the surface roughness of the sample increases when the sample is relaxed. High-resolution transmission electron microscopy images of the structure of indium droplets in the DH sample indicate that the thickness of the InGaN layer decreases with the density of indium droplets. The formation of these droplets is attributed to the insufficient kinetic energy of indium atom to react with the elements of group V, resulting to aggregation. The gallium atoms in the GaN thin film will not be uniformly replaced by indium atoms; the InGaN thin film has an uneven distribution of indium atoms and the quality of the epitaxial layer is degraded. PMID:25024692

Insulator-protected mechanically controlled break junctions for measuring single-molecule conductance in aqueous environments

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

Muthusubramanian, N.; Zant, H. S. J. van der; Galan, E.

We present a method to fabricate insulated gold mechanically controlled break junctions (MCBJ) by coating the metal with a thin layer of aluminum oxide using plasma enhanced atomic layer deposition. The Al{sub 2}O{sub 3} thickness deposited on the MCBJ devices was varied from 2 to 15 nm to test the suppression of leakage currents in deionized water and phosphate buffered saline. Junctions coated with a 15 nm thick oxide layer yielded atomically sharp electrodes and negligible conductance counts in the range of 1 to 10{sup −4} G{sub 0} (1 G{sub 0} = 77 μS), where single-molecule conductances are commonly observed. The insulated devices were usedmore » to measure the conductance of an amphiphilic oligophenylene ethynylene derivative in deionized water.« less

Characterization of nanometer-thick polycrystalline silicon with phonon-boundary scattering enhanced thermoelectric properties and its application in infrared sensors.

PubMed

Zhou, Huchuan; Kropelnicki, Piotr; Lee, Chengkuo

2015-01-14

Although significantly reducing the thermal conductivity of silicon nanowires has been reported, it remains a challenge to integrate silicon nanowires with structure materials and electrodes in the complementary metal-oxide-semiconductor (CMOS) process. In this paper, we investigated the thermal conductivity of nanometer-thick polycrystalline silicon (poly-Si) theoretically and experimentally. By leveraging the phonon-boundary scattering, the thermal conductivity of 52 nm thick poly-Si was measured as low as around 12 W mK(-1) which is only about 10% of the value of bulk single crystalline silicon. The ZT of n-doped and p-doped 52 nm thick poly-Si was measured as 0.067 and 0.024, respectively, while most previously reported data had values of about 0.02 and 0.01 for a poly-Si layer with a thickness of 0.5 μm and above. Thermopile infrared sensors comprising 128 pairs of thermocouples made of either n-doped or p-doped nanometer-thick poly-Si strips in a series connected by an aluminium (Al) metal interconnect layer are fabricated using microelectromechanical system (MEMS) technology. The measured vacuum specific detectivity (D*) of the n-doped and p-doped thermopile infrared (IR) sensors are 3.00 × 10(8) and 1.83 × 10(8) cm Hz(1/2) W(-1) for sensors of 52 nm thick poly-Si, and 5.75 × 10(7) and 3.95 × 10(7) cm Hz(1/2) W(-1) for sensors of 300 nm thick poly-Si, respectively. The outstanding thermoelectric properties indicate our approach is promising for diverse applications using ultrathin poly-Si technology.

Chemical Structure, Ensemble and Single-Particle Spectroscopy of Thick-Shell InP-ZnSe Quantum Dots.

PubMed

Reid, Kemar R; McBride, James R; Freymeyer, Nathaniel J; Thal, Lucas B; Rosenthal, Sandra J

2018-02-14

Thick-shell (>5 nm) InP-ZnSe colloidal quantum dots (QDs) grown by a continuous-injection shell growth process are reported. The growth of a thick crystalline shell is attributed to the high temperature of the growth process and the relatively low lattice mismatch between the InP core and ZnSe shell. In addition to a narrow ensemble photoluminescence (PL) line-width (∼40 nm), ensemble and single-particle emission dynamics measurements indicate that blinking and Auger recombination are reduced in these heterostructures. More specifically, high single-dot ON-times (>95%) were obtained for the core-shell QDs, and measured ensemble biexciton lifetimes, τ 2x ∼ 540 ps, represent a 7-fold increase compared to InP-ZnS QDs. Further, high-resolution energy dispersive X-ray (EDX) chemical maps directly show for the first time significant incorporation of indium into the shell of the InP-ZnSe QDs. Examination of the atomic structure of the thick-shell QDs by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) reveals structural defects in subpopulations of particles that may mitigate PL efficiencies (∼40% in ensemble), providing insight toward further synthetic refinement. These InP-ZnSe heterostructures represent progress toward fully cadmium-free QDs with superior photophysical properties important in biological labeling and other emission-based technologies.

Magneto-optical microcavity with Au plasmonic layer

NASA Astrophysics Data System (ADS)

Mikhailova, T. V.; Lyashko, S. D.; Tomilin, S. V.; Karavainikov, A. V.; Prokopov, A. R.; Shaposhnikov, A. N.; Berzhansky, V. N.

2017-11-01

Optical and Faraday rotation spectra of magneto-optical microcavity coated with Au plasmonic layer of gradient thickness were investigated theoretically and experimentally. It was shown that the Tamm plasmon-polaritons mode forms near the long-wavelength edge of photonic band gap. The presence of Au coating of thickness of 90.4 nm increase the Faraday rotation at Tamm plasmon-polaritons and cavity resonances in 1.3 and 7 times, respectively. By transfer matrix method it were found that the incorporation of SiO2 buffer layer with a thickness in the range from 155 to 180 nm between microcavity and Au coating leads to the strong coupling between cavity mode and Tamm plasmon-polaritons. In this case, one or two resonances arise in the vicinity of the cavity mode depending on the thickness of plasmonic layer. The Faraday rotation for coupled mode in twice less than the value of rotation for single cavity mode.

Tg and Structural Recovery of Single Ultrathin Films

NASA Astrophysics Data System (ADS)

Simon, Sindee

The behavior of materials confined at the nanoscale has been of considerable interest over the past two decades. Here, the focus is on recent results for single polystyrene ultrathin films studied with ultrafast scanning chip calorimetry. The Tg depression of a 20 nm-thick high-molecular-weight polystyrene film is found to be a function of cooling rate, decreasing with increasing cooling rate; whereas, at high enough cooling rates (e.g., 1000 K/s), Tg is the same as the bulk within the error of the measurements. Structural recovery is also performed with chip calorimetry as a function of aging time and temperature, and the evolution of the fictive temperature is followed. The advantages of the Flash DSC include sufficient sensitivity to measure enthalpy recovery for a single 20 nm-thick film, as well as extension of the measurements to aging temperatures as high as 15 K above nominal Tg and to aging times as short as 0.01 s. The aging behavior and relaxation time-temperature map for single ultrathin films are compared to those for bulk material. Comparison to behavior in other geometries will also be discussed.

The design of broad band anti-reflection coatings for solar cell applications

NASA Astrophysics Data System (ADS)

Siva Rama Krishna, Angirekula; Sabat, Samrat Lagnajeet; Ghanashyam Krishna, Mamidipudi

2017-01-01

The design of broadband anti-reflection coatings (ARCs) for solar cell applications using multiobjective differential evolutionary (MODE) algorithms is reported. The effect of thickness and refractive index contrast within the layers of the ARC on the bandwidth of reflectance is investigated in detail. In the case of the hybrid plasmonic ARC structures the effect of size, shape and filling fraction of silver (Ag) nanoparticles on the reflectance is studied. Bandwidth is defined as the spectral region of wavelengths over which the reflectance is below 2%. Single, two and three layers ARCs (consisting of MgF2, Al2O3, Si3N4, TiO2 and ZnS or combinations of these materials) were simulated for performance evaluation on an a-Si photovoltaic cell. It is observed that the three layer ARC consisting of MgF2/Si3N4/TiO2(ZnTe) of 81/42/36 nm thicknesses, respectively, exhibited a weighted reflectance of 1.9% with a bandwidth of 450 nm over the wavelength range of 300-900 nm. The ARC bandwidth could be further improved by embedding randomly distributed Ag nanoparticles of size between 100 and 120 nm on a two layer ARC consisting of Al2O3/TiO2 with thickness of 42 nm and 56 nm respectively. This plasmon-dielectric hybrid ARC design exhibited a weighted reflectance of 0.6% with a bandwidth of 560 nm over the wavelength range of 300-900 nm.

The study of genomic DNA adsorption and subsequent interactions using total internal reflection ellipsometry.

PubMed

Nabok, Alexei; Tsargorodskaya, Anna; Davis, Frank; Higson, Séamus P J

2007-10-31

The adsorption of genomic DNA and subsequent interactions between adsorbed and solvated DNA was studied using a novel sensitive optical method of total internal reflection ellipsometry (TIRE), which combines spectroscopic ellipsometry with surface plasmon resonance (SPR). Single strands of DNA of two species of fish (herring and salmon) were electrostatically adsorbed on top of polyethylenimine films deposited upon gold coated glass slides. The ellipsometric spectra were recorded and data fitting utilized to extract optical parameters (thickness and refractive index) of adsorbed DNA layers. The further adsorption of single stranded DNA from an identical source, i.e. herring ss-DNA on herring ss-DNA or salmon ss-DNA on salmon ss-DNA, on the surface was observed to give rise to substantial film thickness increases at the surface of about 20-21 nm. Conversely adsorption of DNA from alternate species, i.e. salmon ss-DNA on herring ss-DNA or herring ss-DNA on salmon ss-DNA, yielded much smaller changes in thickness of 3-5 nm. AFM studies of the surface roughness of adsorbed layers were in line with the TIRE data.

Uniform, dense arrays of vertically aligned, large-diameter single-walled carbon nanotubes.

PubMed

Han, Zhao Jun; Ostrikov, Kostya

2012-04-04

Precisely controlled reactive chemical vapor synthesis of highly uniform, dense arrays of vertically aligned single-walled carbon nanotubes (SWCNTs) using tailored trilayered Fe/Al(2)O(3)/SiO(2) catalyst is demonstrated. More than 90% population of thick nanotubes (>3 nm in diameter) can be produced by tailoring the thickness and microstructure of the secondary catalyst supporting SiO(2) layer, which is commonly overlooked. The proposed model based on the atomic force microanalysis suggests that this tailoring leads to uniform and dense arrays of relatively large Fe catalyst nanoparticles on which the thick SWCNTs nucleate, while small nanotubes and amorphous carbon are effectively etched away. Our results resolve a persistent issue of selective (while avoiding multiwalled nanotubes and other carbon nanostructures) synthesis of thick vertically aligned SWCNTs whose easily switchable thickness-dependent electronic properties enable advanced applications in nanoelectronic, energy, drug delivery, and membrane technologies.

Structural and electrical properties of single crystalline SrZrO 3 epitaxially grown on Ge (001)

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

Lim, Z. H.; Ahmadi-Majlan, K.; Grimley, E. D.

We present structural and electrical characterization of SrZrO3 that has been epitaxially grown on Ge(001) by oxide molecular beam epitaxy. Single crystalline SrZrO3 can be nucleated on Ge via deposition at low temperatures followed by annealing at 550 ºC in ultra-high vacuum. Photoemission spectroscopy measurements reveal that SrZrO3 exhibits a type-I band arrangement with respect to Ge, with conduction and valence band offsets of 1.4 eV and 3.65 eV, respectively. As a standalone film, SrZrO3 exhibits several characteristics that are ideal for applications as a gate dielectric on Ge. We find that 4 nm thick films exhibit low leakage currentmore » densities, and a dielectric constant of κ ~ 25 that corresponds to an equivalent oxide thickness of 0.70 nm.« less

Thermoelectric La-doped SrTiO3 epitaxial layers with single-crystal quality: from nano to micrometers

NASA Astrophysics Data System (ADS)

Apreutesei, Mihai; Debord, Régis; Bouras, Mohamed; Regreny, Philippe; Botella, Claude; Benamrouche, Aziz; Carretero-Genevrier, Adrian; Gazquez, Jaume; Grenet, Geneviève; Pailhès, Stéphane; Saint-Girons, Guillaume; Bachelet, Romain

2017-12-01

High-quality thermoelectric La0.2Sr0.8TiO3 (LSTO) films, with thicknesses ranging from 20 nm to 0.7 μm, have been epitaxially grown on SrTiO3(001) substrates by enhanced solid-source oxide molecular-beam epitaxy. All films are atomically flat (with rms roughness < 0.2 nm), with low mosaicity (<0.1°), and present very low electrical resistivity (<5 × 10-4 Ω cm at room temperature), one order of magnitude lower than standard commercial Nb-doped SrTiO3 single-crystalline substrate. The conservation of transport properties within this thickness range has been confirmed by thermoelectric measurements where Seebeck coefficients of approximately -60 μV/K have been recorded for all films. These LSTO films can be integrated on Si for non-volatile memory structures or opto-microelectronic devices, functioning as transparent conductors or thermoelectric elements.

Suppression of superconductivity in epitaxial MgB2 ultrathin films

NASA Astrophysics Data System (ADS)

Zhang, Chen; Wang, Yue; Wang, Da; Zhang, Yan; Liu, Zheng-Hao; Feng, Qing-Rong; Gan, Zi-Zhao

2013-07-01

MgB2 ultrathin films have potential to make sensitive superconducting devices such as superconducting single-photon detectors working at relatively high temperatures. We have grown epitaxial MgB2 films in thicknesses ranging from about 40 nm to 6 nm by using the hybrid physical-chemical vapor deposition method and performed electrical transport measurements to study the thickness dependence of the superconducting critical temperature Tc. With reducing film thickness d, although a weak depression of the Tc has been observed, which could be attributed to an increase of disorder (interband impurity scattering) in the film, the Tc retains close to the bulk value of MgB2 (39 K), being about 35 K in the film of 6 nm thick. We show that this result, beneficial to the application of MgB2 ultrathin films and in accordance with recent theoretical calculations, is in contrast to previous findings in MgB2 films prepared by other methods such as co-evaporation and molecular-beam epitaxy, where a severe Tc suppression has been observed with Tc about one third of the bulk value in films of ˜5 nm thick. We discuss this apparent discrepancy in experiments and suggest that, towards the ultrathin limit, the different degrees of Tc suppression displayed in currently obtained MgB2 films by various techniques may arise from the different levels of disorder present in the film or different extents of proximity effect at the film surface or film-substrate interface.

3D single-molecule super-resolution microscopy with a tilted light sheet.

PubMed

Gustavsson, Anna-Karin; Petrov, Petar N; Lee, Maurice Y; Shechtman, Yoav; Moerner, W E

2018-01-09

Tilted light sheet microscopy with 3D point spread functions (TILT3D) combines a novel, tilted light sheet illumination strategy with long axial range point spread functions (PSFs) for low-background, 3D super-localization of single molecules as well as 3D super-resolution imaging in thick cells. Because the axial positions of the single emitters are encoded in the shape of each single-molecule image rather than in the position or thickness of the light sheet, the light sheet need not be extremely thin. TILT3D is built upon a standard inverted microscope and has minimal custom parts. The result is simple and flexible 3D super-resolution imaging with tens of nm localization precision throughout thick mammalian cells. We validate TILT3D for 3D super-resolution imaging in mammalian cells by imaging mitochondria and the full nuclear lamina using the double-helix PSF for single-molecule detection and the recently developed tetrapod PSFs for fiducial bead tracking and live axial drift correction.

Sacrificial template method of fabricating a nanotube

DOEpatents

Yang, Peidong [Berkeley, CA; He, Rongrui [Berkeley, CA; Goldberger, Joshua [Berkeley, CA; Fan, Rong [El Cerrito, CA; Wu, Yi-Ying [Albany, CA; Li, Deyu [Albany, CA; Majumdar, Arun [Orinda, CA

2007-05-01

Methods of fabricating uniform nanotubes are described in which nanotubes were synthesized as sheaths over nanowire templates, such as using a chemical vapor deposition process. For example, single-crystalline zinc oxide (ZnO) nanowires are utilized as templates over which gallium nitride (GaN) is epitaxially grown. The ZnO templates are then removed, such as by thermal reduction and evaporation. The completed single-crystalline GaN nanotubes preferably have inner diameters ranging from 30 nm to 200 nm, and wall thicknesses between 5 and 50 nm. Transmission electron microscopy studies show that the resultant nanotubes are single-crystalline with a wurtzite structure, and are oriented along the <001> direction. The present invention exemplifies single-crystalline nanotubes of materials with a non-layered crystal structure. Similar "epitaxial-casting" approaches could be used to produce arrays and single-crystalline nanotubes of other solid materials and semiconductors. Furthermore, the fabrication of multi-sheath nanotubes are described as well as nanotubes having multiple longitudinal segments.

Effect of different thickness h-BN coatings on interface shear strength of quartz fiber reinforced Sisbnd Osbnd Csbnd N composite

NASA Astrophysics Data System (ADS)

Wang, Shubin; Zheng, Yu

2014-02-01

Hexagonal boron nitride (h-BN) coatings with different thickness were prepared on quartz fibers to improve mechanical properties of quartz fiber reinforced Sisbnd Osbnd Csbnd N composite. Scanning electron microscopy (SEM), push-out test and single edge notched beam (SENB) in three point bending test were employed to study morphology, interface shear strength and fracture toughness of the composite. The results showed that h-BN coatings changed the crack growth direction and weaken the interface shear strength efficiently. When the h-BN coating was 308.2 nm, the interface shear strength was about 5.2 MPa, which was about one-quarter of that of the sample without h-BN coatings. After the heating process for obtaining composite, the h-BN nanometer-sized grains would grow up to micron-sized hexagonal grains. Different thickness h-BN coatings had different structure. When the coatings were relatively thin, the hexagonal grains were single layer structure, and when the coatings were thicker, the hexagonal grains were multiple layer structure. This multiple layer interface phase would consume more power of cracks, thus interface shear strength of the composite decreased steadily with the increasing of h-BN coatings thickness. When the coating thickness was 238.8 nm, KIC reaches the peak value 3.8 MPa m1/2, which was more than two times of that of composites without h-BN coatings.

Comparative measurements of piezoelectric coefficient of PZT films by Berlincourt, interferometer, and vibrometer methods.

PubMed

Huang, Zhaorong; Zhang, Qi; Corkovic, Silvana; Dorey, Robert; Whatmore, Roger W

2006-12-01

Chemical solution deposition (CSD) techniques were used to prepare lead zirconate (Zr) titanate (Ti) (PZT) thin films with Zr/Ti ratios of 30/70 and 52/48. Usually CSD processing is restricted to making crack-free, single-layer films of 70-nm thick, but modifications to the sol-gel process have permitted the fabrication of dense, crack-free, single layers up to 200 to 300 nm thick, which can be built-up into layers up to 3-microm thick. Thicker PZT films (> 2-microm single layer) can be produced by using a composite sol-gel/ceramic process. Knowledge of the electroactive properties of these materials is essential for modeling and design of novel micro-electromechanical systems (MEMS) devices, but accurate measurement of these properties is by no means straightforward. A novel, double-beam, common-path laser interferometer has been developed to measure the longitudinal (d33) piezoelectric coefficient in films; the results were compared with the values obtained by Berlin-court and laser scanning vibrometer methods. It was found that, for thin-film samples, the d(33,f) values obtained from the Berlincourt method are usually larger: than those obtained from the interferometer and the vibrometer methods; the reasons for this are discussed.

The influence of interface on spin pumping effect in Ni{sub 80}Fe{sub 20} /Tb bilayer

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

Yue, Jinjin; Jiang, Sheng; Zhang, Dong

2016-05-15

Focusing on the interface effect of the Ni{sub 80}Fe{sub 20} (Py)/terbium (Tb) bilayer, the influence of interface on the magnetization dynamic damping is investigated systematically. Two series of Py (12 nm)/Tb (d nm) films with and without copper (Cu) (1 nm) interlayer are deposited on silicon (Si) substrates by DC magnetron sputtering at room temperature. From vibrating sample magnetometer (VSM) measurements, the saturation magnetization (M{sub s}) decreases with increasing Tb thickness in Py/Tb bilayer while the decrease of M{sub s} is suppressed efficiently by inserting a Cu layer with even 1 nm of thickness. From the frequency dependence of ferromagneticmore » resonance (FMR) linewidth, we can obtain the Gilbert damping coefficient (α), α is found to exhibit an extreme enhancement in comparison to the single Py layer and shows an increasing trend with increasing Tb thickness. By inserting the Cu layer, α decreases significantly. From theoretical fitting, the spin diffusion length (λ{sub SD}) and spin mixing conductance (g{sup ↑↓}) are determined. It shows that the interface structure influences the spin mixing conductance but not the spin diffusion length.« less

Free-Standing β-Ga2O3 Thin Diaphragms

NASA Astrophysics Data System (ADS)

Zheng, Xu-Qian; Lee, Jaesung; Rafique, Subrina; Han, Lu; Zorman, Christian A.; Zhao, Hongping; Feng, Philip X.-L.

2018-02-01

Free-standing, very thin, single-crystal β-gallium oxide (β-Ga2O3) diaphragms have been constructed and their dynamical mechanical properties characterized by noncontact, noninvasive optical measurements harnessing the multimode nanomechanical resonances of these suspended nanostructures. We synthesized single-crystal β-Ga2O3 using low-pressure chemical vapor deposition (LPCVD) on a 3C-SiC epilayer grown on Si substrate at temperature of 950°C for 1.5 h. The synthesized single-crystal nanoflakes had widths of ˜ 2 μm to 30 μm and thicknesses of ˜ 20 nm to 140 nm, from which we fabricated free-standing circular drumhead β-Ga2O3 diaphragms with thicknesses of ˜ 23 nm to 73 nm and diameters of ˜ 3.2 μm and ˜ 5.2 μm using a dry stamp-transfer technique. Based on measurements of multiple flexural-mode mechanical resonances using ultrasensitive laser interferometric detection and performing thermal annealing at 250°C for 1.5 h, we quantified the effects of annealing and adsorption of atmospheric gas molecules on the resonant characteristics of the diaphragms. Furthermore, we studied the effects of structural nonidealities on these free-standing β-Ga2O3 nanoscale diaphragms. We present extensive characterization of the mechanical and optical properties of free-standing β-Ga2O3 diaphragms, paving the way for realization of resonant transducers using such nanomechanical structures for use in applications including gas sensing and ultraviolet radiation detection.

Small-sized PdCu nanocapsules on 3D graphene for high-performance ethanol oxidation

NASA Astrophysics Data System (ADS)

HuThese Authors Contributed Equally To This Work., Chuangang; Zhai, Xiangquan; Zhao, Yang; Bian, Ke; Zhang, Jing; Qu, Liangti; Zhang, Huimin; Luo, Hongxia

2014-02-01

A one-pot solvothermal process has been developed for direct preparation of PdCu nanocapsules (with a size of ca. 10 nm) on three-dimensional (3D) graphene. Due to the 3D pore-rich network of graphene and the unique hollow structure of PdCu nanocapsules with a wall thickness of ca. 3 nm, the newly-prepared PdCu/3D graphene hybrids activated electrochemically have great electrocatalytic activity towards ethanol oxidation in alkaline media, much better than single-phase Pd and commercial E-TEK 20% Pt/C catalysts promising for application in direct ethanol fuel cells.A one-pot solvothermal process has been developed for direct preparation of PdCu nanocapsules (with a size of ca. 10 nm) on three-dimensional (3D) graphene. Due to the 3D pore-rich network of graphene and the unique hollow structure of PdCu nanocapsules with a wall thickness of ca. 3 nm, the newly-prepared PdCu/3D graphene hybrids activated electrochemically have great electrocatalytic activity towards ethanol oxidation in alkaline media, much better than single-phase Pd and commercial E-TEK 20% Pt/C catalysts promising for application in direct ethanol fuel cells. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr05722d

Transport properties of ultrathin BaFe1.84Co0.16As2 superconducting nanowires

NASA Astrophysics Data System (ADS)

Yuan, Pusheng; Xu, Zhongtang; Li, Chen; Quan, Baogang; Li, Junjie; Gu, Changzhi; Ma, Yanwei

2018-07-01

Superconducting nanowire single-photon detectors (SNSPDs) have an absolute advantage over other types of single-photon detectors, except for the low operating temperature. Therefore, much effort has been devoted to finding high-temperature superconducting materials that are suitable for preparing SNSPDs. Copper-based and MgB2 ultrathin superconducting nanowires have already been reported. However, the transport properties of iron-based ultrathin superconducting nanowires have not been studied. In this work, a 10 nm thick × 200 nm wide × 30 μm long high-quality superconducting nanowire was fabricated from ultrathin BaFe1.84Co0.16As2 films by a lift-off process. The precursor BaFe1.84Co0.16As2 film with a thickness of 10 nm and root-mean-square roughness of 1 nm was grown on CaF2 substrates by pulsed laser deposition. The nanowire shows a high superconducting critical temperature {T}{{c}}{{zero}} = 20 K with a narrow transition width of ΔT = 2.5 K and exhibits a high critical current density J c of 1.8 × 107 A cm-2 at 10 K. These results of ultrathin BaFe1.84Co0.16As2 nanowire will attract interest in electronic applications, including SNSPDs.

A grating coupler with a trapezoidal hole array for perfectly vertical light coupling between optical fibers and waveguides

NASA Astrophysics Data System (ADS)

Mizutani, Akio; Eto, Yohei; Kikuta, Hisao

2017-12-01

A grating coupler with a trapezoidal hole array was designed and fabricated for perfectly vertical light coupling between a single-mode optical fiber and a silicon waveguide on a silicon-on-insulator (SOI) substrate. The grating coupler with an efficiency of 53% was computationally designed at a 1.1-µm-thick buried oxide (BOX) layer. The grating coupler and silicon waveguide were fabricated on the SOI substrate with a 3.0-µm-thick BOX layer by a single full-etch process. The measured coupling efficiency was 24% for TE-polarized light at 1528 nm wavelength, which was 0.69 times of the calculated coupling efficiency for the 3.0-µm-thick BOX layer.

High-quality AlN film grown on a nanosized concave-convex surface sapphire substrate by metalorganic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Yoshikawa, Akira; Nagatomi, Takaharu; Morishita, Tomohiro; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu

2017-10-01

We developed a method for fabricating high-crystal-quality AlN films by combining a randomly distributed nanosized concavo-convex sapphire substrate (NCC-SS) and a three-step growth method optimized for NCC-SS, i.e., a 3-nm-thick nucleation layer (870 °C), a 150-nm-thick high-temperature layer (1250 °C), and a 3.2-μm-thick medium-temperature layer (1110 °C). The NCC-SS is easily fabricated using a conventional metalorganic vapor phase epitaxy reactor equipped with a showerhead plate. The resultant AlN film has a crack-free and single-step surface with a root-mean-square roughness of 0.5 nm. The full-widths at half-maxima of the X-ray rocking curve were 50/250 arcsec for the (0002)/(10-12) planes, revealing that the NCC surface is critical for achieving such a high-quality film. Hexagonal-pyramid-shaped voids at the AlN/NCC-SS interface and confinement of dislocations within the 150-nm-thick high-temperature layer were confirmed. The NCC surface feature and resultant faceted voids play an important role in the growth of high-crystal-quality AlN films, likely via localized and/or disordered growth of AlN at the initial stage, contributing to the alignment of high-crystal-quality nuclei and dislocations.

Single-step fabrication of thin-film linear variable bandpass filters based on metal-insulator-metal geometry.

PubMed

Williams, Calum; Rughoobur, Girish; Flewitt, Andrew J; Wilkinson, Timothy D

2016-11-10

A single-step fabrication method is presented for ultra-thin, linearly variable optical bandpass filters (LVBFs) based on a metal-insulator-metal arrangement using modified evaporation deposition techniques. This alternate process methodology offers reduced complexity and cost in comparison to conventional techniques for fabricating LVBFs. We are able to achieve linear variation of insulator thickness across a sample, by adjusting the geometrical parameters of a typical physical vapor deposition process. We demonstrate LVBFs with spectral selectivity from 400 to 850 nm based on Ag (25 nm) and MgF₂ (75-250 nm). Maximum spectral transmittance is measured at ∼70% with a Q-factor of ∼20.

Determination of the effective refractive index spectrum of a quantum-well semiconductor laser diode from the measured modal gain spectrum

NASA Astrophysics Data System (ADS)

Wu, Linzhang; Tian, Wei; Gao, Feng

2004-09-01

This paper presents a self-consistent method to directly determine the effective refractive-index spectrum of a semiconductor quantum-well (QW) laser diode from the measured modal gain spectrum for a given current. The dispersion spectra of the optical waveguide confinement factor and the strongly carrier-density-dependent refractive index of the QW active layer of the test laser are also accurately obtained. The experimental result from a single QW GaInP/AlGaInP laser diode, which has 6 nm thick compressively strained Ga0.4InP active layer sandwiched by two 80 nm thick Al0.33GaInP, is presented.

Kinetic Characterization of Nonmuscle Myosin IIB at the Single Molecule Level*

PubMed Central

Nagy, Attila; Takagi, Yasuharu; Billington, Neil; Sun, Sara A.; Hong, Davin K. T.; Homsher, Earl; Wang, Aibing; Sellers, James R.

2013-01-01

Nonmuscle myosin IIB (NMIIB) is a cytoplasmic myosin, which plays an important role in cell motility by maintaining cortical tension. It forms bipolar thick filaments with ∼14 myosin molecule dimers on each side of the bare zone. Our previous studies showed that the NMIIB is a moderately high duty ratio (∼20–25%) motor. The ADP release step (∼0.35 s−1) of NMIIB is only ∼3 times faster than the rate-limiting phosphate release (0.13 ± 0.01 s−1). The aim of this study was to relate the known in vitro kinetic parameters to the results of single molecule experiments and to compare the kinetic and mechanical properties of single- and double-headed myosin fragments and nonmuscle IIB thick filaments. Examination of the kinetics of NMIIB interaction with actin at the single molecule level was accomplished using total internal reflection fluorescence (TIRF) with fluorescence imaging with 1-nm accuracy (FIONA) and dual-beam optical trapping. At a physiological ATP concentration (1 mm), the rate of detachment of the single-headed and double-headed molecules was similar (∼0.4 s−1). Using optical tweezers we found that the power stroke sizes of single- and double-headed heavy meromyosin (HMM) were each ∼6 nm. No signs of processive stepping at the single molecule level were observed in the case of NMIIB-HMM in optical tweezers or TIRF/in vitro motility experiments. In contrast, robust motility of individual fluorescently labeled thick filaments of full-length NMIIB was observed on actin filaments. Our results are in good agreement with the previous steady-state and transient kinetic studies and show that the individual nonprocessive nonmuscle myosin IIB molecules form a highly processive unit when polymerized into filaments. PMID:23148220

Microcutting characteristics on the single crystal diamond tool with edge radius using molecular dynamics

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

Kim, Jeong-Du; Moon, Chan-Hong

1995-12-31

Ultraprecision metal cutting (UPMC) technology which makes possible submicrometer form accuracy and manometer roughness is developed to reach the 1nm nominal (undeformed) thickness of cut. At this thickness level, a few of atom`s layers should be considered. In this paper using the Molecuar Dynamics simulation, the phenomena of microcutting with a subnanometer chip thickness, the cutting mechanism for tool edge configuration to consider the sharp edge and round edge tool, the cut material and cutting speed are evaluated. Cutting mechanism of subnanometer depth of cut is evaluated.

Silver-free solar cell interconnection by laser spot welding of thin aluminum layers: analysis of process limits for ns- and μs-lasers

NASA Astrophysics Data System (ADS)

Schulte-Huxel, H.; Blankemeyer, S.; Kajari-Schröder, S.; Brendel, R.

2014-03-01

We investigate a laser welding process for contacting aluminum metallized crystalline silicon solar cells to a 10-μm-thick aluminum layers on a glass substrate. The reduction of the solar cell metallization thickness is analyzed with respect to laser induced damage using SiNx passivated silicon wafers. Additionally, we measure the mechanical stress of the laser welds by perpendicular tear-off as well as the electrical contact resistance. We apply two types of laser processes; one uses one to eight 20-ns-laser pulses at 355 nm with fluences between 12 and 40 J/cm2 and the other single 1.2-μs-laser pulses at 1064 nm with 33 to 73 J/cm2. Ns laser pulses can contact down to 1-μm-thick aluminum layers on silicon without inducing laser damage to the silicon and lead to sufficient strong mechanical contact. In case of μs laser pulses the limiting thickness is 2 μm.

Progress in thin-film silicon solar cells based on photonic-crystal structures

NASA Astrophysics Data System (ADS)

Ishizaki, Kenji; De Zoysa, Menaka; Tanaka, Yoshinori; Jeon, Seung-Woo; Noda, Susumu

2018-06-01

We review the recent progress in thin-film silicon solar cells with photonic crystals, where absorption enhancement is achieved by using large-area resonant effects in photonic crystals. First, a definitive guideline for enhancing light absorption in a wide wavelength range (600–1100 nm) is introduced, showing that the formation of multiple band edges utilizing higher-order modes confined in the thickness direction and the introduction of photonic superlattice structures enable significant absorption enhancement, exceeding that observed for conventional random scatterers. Subsequently, experimental evidence of this enhancement is demonstrated for a variety of thin-film Si solar cells: ∼500-nm-thick ultrathin microcrystalline silicon cells, few-µm-thick microcrystalline silicon cells, and ∼20-µm-thick thin single-crystalline silicon cells. The high short-circuit current densities and/or efficiencies observed for each cell structure confirm the effectiveness of using multiple band-edge resonant modes of photonic crystals for enhancing broadband absorption in actual solar cells.

Pulsed laser-assisted removal of powder coating from galvanised steel surface: a characterisation study

NASA Astrophysics Data System (ADS)

Kumar, Aniruddha; Prasad, Manisha; Shail, Shailini; Bhatt, R. B.; Behere, P. G.; Afzal, Md.; Kumar, Arun; Kar, Rajib; Nilaya, J. P.; Biswas, D. J.

2015-06-01

Removal of pure polyester powder coating from galvanised steel surface is studied using the fundamental, second and third harmonic radiations obtained from a Q-switched Nd-YAG laser capable of delivering pulses of duration 10 ns. Removal of the coating was found to be most effective for 1064 nm radiation followed by 532 and 355 nm radiations. Measurement of absorption of the incident radiation by the paint layer carried out with an integrating sphere has helped to gain insight into the removal mechanisms operative at these wavelengths. Single shot removal of the entire thickness of the powder coating was successfully achieved using 1064 nm radiation. Characterisation study of the laser-treated surface revealed that the coating removal was achieved leaving the underneath zinc layer as before. Usage of pulsed emission at 1064 nm of fluence 0.7 J/cm2 and repetition rate 5 Hz allowed stripping of 60-micron-thick coating at the rate of ~35 cm2 per minute.

Effects of dc bias on the kinetics and electrical properties of silicon dioxide grown in an electron cyclotron resonance plasma

NASA Astrophysics Data System (ADS)

Carl, D. A.; Hess, D. W.; Lieberman, M. A.; Nguyen, T. D.; Gronsky, R.

1991-09-01

Thin (3-300-nm) oxides were grown on single-crystal silicon substrates at temperatures from 523 to 673 K in a low-pressure electron cyclotron resonance (ECR) oxygen plasma. Oxides were grown under floating, anodic or cathodic bias conditions, although only the oxides grown under floating or anodic bias conditions are acceptable for use as gate dielectrics in metal-oxide-semiconductor technology. Oxide thickness uniformity as measured by ellipsometry decreased with increasing oxidation time for all bias conditions. Oxidation kinetics under anodic conditions can be explained by negatively charged atomic oxygen, O-, transport limited growth. Constant current anodizations yielded three regions of growth: (1) a concentration gradient dominated regime for oxides thinner than 10 nm, (2) a field dominated regime with ohmic charged oxidant transport for oxide thickness in the range of 10 nm to approximately 100 nm, and (3) a space-charge limited regime for films thicker than approximately 100 nm. The relationship between oxide thickness (xox), overall potential drop (Vox) and ion current (ji) in the space-charge limited transport region was of the form: ji ∝ V2ox/x3ox. Transmission electron microscopy analysis of 5-60-nm-thick anodized films indicated that the silicon-silicon dioxide interface was indistinguishable from that of thermal oxides grown at 1123 K. High-frequency capacitance-voltage (C-V) and ramped bias current-voltage (I-V) studies performed on 5.4-30-nm gate thickness capacitors indicated that the as-grown ECR films had high levels of fixed oxide charge (≳1011 cm-2) and interface traps (≳1012 cm-2 eV-1). The fixed charge level could be reduced to ≊4×1010 cm-2 by a 20 min polysilicon gate activation anneal at 1123 K in nitrogen; the interface trap density at mid-band gap decreased to ≊(1-2)×1011 cm-2 eV-1 after this process. The mean breakdown strength for anodic oxides grown under optimum conditions was 10.87±0.83 MV cm-1. Electrical properties of the 5.4-8-nm gates compared well with thicker films and control dry thermal oxides of similar thicknesses.

Physical Characterization of Orthorhombic AgInS2 Nanocrystalline Thin Films

NASA Astrophysics Data System (ADS)

El Zawawi, I. K.; Mahdy, Manal A.

2017-11-01

Nanocrystalline thin films of AgInS2 were synthesized using an inert gas condensation technique. The grazing incident in-plane x-ray diffraction technique was used to detect the crystal structure of the deposited and annealed thin films. The results confirmed that the as-deposited film shows an amorphous behavior and that the annealed film has a single phase crystallized in an orthorhombic structure. The orthorhombic structure and particle size were detected using high-resolution transmission electron microscopy. The particle size ( P_{{s}}) estimated from micrograph images of the nanocrystalline films were increased from 6 nm to 12 nm as the film thickness increased from 11 nm to 110 nm. Accordingly, increasing the film thickness up to 110 nm reflects varying the optical band gap from 2.75 eV to 2.1 eV. The photocurrent measurements were studied where the fast rise and decay of the photocurrent are governed by the recombination mechanism. The electrical conductivity behavior was demonstrated by two transition mechanisms: extrinsic transition for a low-temperature range (300-400 K) and intrinsic transition for the high-temperature region above 400 K.

The new oxide paradigm for solid state ultraviolet photodetectors

NASA Astrophysics Data System (ADS)

Rogers, D. J.; Bove, P.; Arrateig, X.; Sandana, V. E.; Teherani, F. H.; Razeghi, M.; McClintock, R.; Frisch, E.; Harel, S.

2018-03-01

The bandgap of wurzite ZnO layers grown on 2 inch diameter c-Al2O3 substrates by pulsed laser deposition was engineered from 3.7 to 4.8 eV by alloying with Mg. Above this Mg content the layers transformed from single phase hcp to mixed hcp/fcc phase before becoming single phase fcc above a bandgap of about 5.5 eV. Metal-Semiconductor-Metal (MSM) photodetectors based on gold Inter-Digitated-Transducer structures were fabricated from the single phase hcp layers by single step negative photolithography and then packaged in TO5 cans. The devices gave over 6 orders of magnitude of separation between dark and light signal with solar rejection ratios (I270 : I350) of over 3 × 105 and dark signals of 300 pA (at a bias of -5V). Spectral responsivities were engineered to fit the "Deutscher Verein des Gas- und Wasserfaches" industry standard form and gave over two decade higher responsivities (14 A/W, peaked at 270 nm) than commercial SiC based devices. Homogeneous Ga2O3 layers were also grown on 2 inch diameter c-Al2O3 substrates by PLD. Optical transmission spectra were coherent with a bandgap that increased from 4.9 to 5.4 eV when film thickness was decreased from 825 to 145 nm. X-ray diffraction revealed that the films were of the β-Ga2O3 (monoclinic) polytype with strong (-201) orientation. β-Ga2O3 MSM photodetectors gave over 4 orders of magnitude of separation between dark and light signal (at -5V bias) with dark currents of 250 pA and spectral responsivities of up to 40 A/W (at -0.75V bias). It was found that the spectral responsivity peak position could be decreased from 250 to 230 nm by reducing film thickness from 825 to 145 nm. This shift in peak responsivity wavelength with film thickness (a) was coherent with the apparent bandgap shift that was observed in transmission spectroscopy for the same layers and (b) conveniently provides a coverage of the spectral region in which MgZnO layers show fcc/hcp phase mixing.

Metastable bcc phase formation in 3d ferromagnetic transition metal thin films sputter-deposited on GaAs(100) substrates

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

Minakawa, Shigeyuki, E-mail: s-minakawa@futamoto.elect.chuo-u.ac.jp; Ohtake, Mitsuru; Futamoto, Masaaki

2015-05-07

Co{sub 100−x}Fe{sub x} and Ni{sub 100−y}Fe{sub y} (at. %, x = 0–30, y = 0–60) films of 10 nm thickness are prepared on GaAs(100) substrates at room temperature by using a radio-frequency magnetron sputtering system. The detailed growth behavior is investigated by in-situ reflection high-energy electron diffraction. (100)-oriented Co and Ni single-crystals with metastable bcc structure are formed in the early stage of film growth, where the metastable structure is stabilized through hetero-epitaxial growth. With increasing the thickness up to 2 nm, the Co and the Ni films start to transform into more stable hcp and fcc structures through atomic displacements parallel to bcc(110) slide planes,more » respectively. The stability of bcc phase is improved by adding a small volume of Fe atoms into a Co film. The critical thickness of bcc phase formation is thicker than 10 nm for Co{sub 100−x}Fe{sub x} films with x ≥ 10. On the contrary, the stability of bcc phase for Ni-Fe system is less than that for Co-Fe system. The critical thicknesses for Ni{sub 100−y}Fe{sub y} films with y = 20, 40, and 60 are 1, 3, and 5 nm, respectively. The Co{sub 100−x}Fe{sub x} single-crystal films with metastable bcc structure formed on GaAs(100) substrates show in-plane uniaxial magnetic anisotropies with the easy direction along GaAs[011], similar to the case of Fe film epitaxially grown on GaAs(100) substrate. A Co{sub 100−x}Fe{sub x} film with higher Fe content shows a higher saturation magnetization and a lower coercivity.« less

Shear-band thickness and shear-band cavities in a Zr-based metallic glass

DOE PAGES

Liu, C.; Roddatis, V.; Kenesei, P.; ...

2017-08-14

Strain localization into shear bands in metallic glasses is typically described as a mechanism that occurs at the nano-scale, leaving behind a shear defect with a thickness of 10–20 nm. Here we sample the structure of a single system-spanning shear band that has carried all plastic flow with high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and high-energy x-ray tomography (XRT). It is found that the shear-band thickness and the density change relative to the matrix sensitively depend on position along the shear band. A wide distribution of shear-band thickness (10 nm–210 nm) and density change (–1% to –12%)more » is revealed. There is no obvious correlation between shear-band thickness and density change, but larger thicknesses correspond typically to higher density changes. More than 100 micron-size shear-band cavities were identified on the shear-band plane, and their three-dimensional arrangement suggests a strongly fluctuating local curvature of the shear plane. As a result, these findings urge for a more complex view of a shear band than a simple nano-scale planar defect.« less

Shear-band thickness and shear-band cavities in a Zr-based metallic glass

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

Liu, C.; Roddatis, V.; Kenesei, P.

Strain localization into shear bands in metallic glasses is typically described as a mechanism that occurs at the nano-scale, leaving behind a shear defect with a thickness of 10–20 nm. Here we sample the structure of a single system-spanning shear band that has carried all plastic flow with high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and high-energy x-ray tomography (XRT). It is found that the shear-band thickness and the density change relative to the matrix sensitively depend on position along the shear band. A wide distribution of shear-band thickness (10 nm–210 nm) and density change (–1% to –12%)more » is revealed. There is no obvious correlation between shear-band thickness and density change, but larger thicknesses correspond typically to higher density changes. More than 100 micron-size shear-band cavities were identified on the shear-band plane, and their three-dimensional arrangement suggests a strongly fluctuating local curvature of the shear plane. As a result, these findings urge for a more complex view of a shear band than a simple nano-scale planar defect.« less

Growth rate dependence of boron incorporation into BxGa1-xAs layers

NASA Astrophysics Data System (ADS)

Detz, H.; MacFarland, D.; Zederbauer, T.; Lancaster, S.; Andrews, A. M.; Schrenk, W.; Strasser, G.

2017-11-01

This work provides a comprehensive study of the incorporation behavior of B in growing GaAs under molecular beam epitaxy conditions. Structural characterization of superlattices revealed a strong dependence of the BAs growth rate on the GaAs growth rate used. In general, higher GaAs growth rates lead to a higher apparent BAs growth rate, although lower B cell temperatures showed saturation behavior. Each B cell temperature requires a minimum GaAs growth rate for producing smooth films. The B incorporation into single thick layers was found to be reduced to 75-80% compared to superlattice structures. The p-type carrier densities in 1000 nm thick layers were found to be indirectly proportional to the B content. Furthermore, 500 nm thick BxGa1-xAs layers showed significantly lower carrier concentrations, indicating B segregation on the surface during growth of thicker layers.

Soft X-ray imaging of thick carbon-based materials using the normal incidence multilayer optics.

PubMed

Artyukov, I A; Feschenko, R M; Vinogradov, A V; Bugayev, Ye A; Devizenko, O Y; Kondratenko, V V; Kasyanov, Yu S; Hatano, T; Yamamoto, M; Saveliev, S V

2010-10-01

The high transparency of carbon-containing materials in the spectral region of "carbon window" (lambda approximately 4.5-5nm) introduces new opportunities for various soft X-ray microscopy applications. The development of efficient multilayer coated X-ray optics operating at the wavelengths of about 4.5nm has stimulated a series of our imaging experiments to study thick biological and synthetic objects. Our experimental set-up consisted of a laser plasma X-ray source generated with the 2nd harmonics of Nd-glass laser, scandium-based thin-film filters, Co/C multilayer mirror and X-ray film UF-4. All soft X-ray images were produced with a single nanosecond exposure and demonstrated appropriate absorption contrast and detector-limited spatial resolution. A special attention was paid to the 3D imaging of thick low-density foam materials to be used in design of laser fusion targets.

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

Aldosary, Mohammed; Li, Junxue; Tang, Chi

30-80 nm thick yttrium iron garnet (YIG) films are grown by pulsed laser deposition on a 5 nm thick sputtered Pt atop gadolinium gallium garnet substrate (GGG) (110). Upon post-growth rapid thermal annealing, single crystal YIG(110) emerges as if it were epitaxially grown on GGG(110) despite the presence of the intermediate Pt film. The YIG surface shows atomic steps with the root-mean-square roughness of 0.12 nm on flat terraces. Both Pt/YIG and GGG/Pt interfaces are atomically sharp. The resulting YIG(110) films show clear in-plane uniaxial magnetic anisotropy with a well-defined easy axis along 〈001〉 and a peak-to-peak ferromagnetic resonance linewidth of 7.5 Oe atmore » 9.32 GHz, similar to YIG epitaxially grown on GGG. Both spin Hall magnetoresistance and longitudinal spin Seebeck effects in the inverted bilayers indicate excellent Pt/YIG interface quality.« less

Improved dielectric properties of CaCu3Ti4O12 films with a CaTiO3 interlayer on Pt/TiO2/SiO2/Si substrates prepared by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Lee, Sung-Yun; Kim, Hui Eun; Jo, William; Kim, Young-Hwan; Yoo, Sang-Im

2015-11-01

We report the greatly improved dielectric properties of CaCu3Ti4O12 (CCTO) films with a 60 nm-thick CaTiO3 (CTO) interlayer on Pt/TiO2/SiO2/Si substrates. Both CCTO films and CTO interlayers were prepared by pulsed laser deposition (PLD). With increasing the thickness of CCTO from 200 nm to 1.3 μm, the dielectric constants ( ɛ r ) at 10 kHz in both CCTO single-layered and CCTO/CTO double-layered films increased from ˜260 to ˜6000 and from ˜630 to ˜3700, respectively. Compared with CCTO single-layered films, CCTO/CTO double-layered films irrespective of CCTO film thickness exhibited a remarkable decrease in their dielectric losses ( tanδ) (<0.1 at the frequency region of 1 - 100 kHz) and highly reduced leakage current density at room temperature. The reduced leakage currents in CCTO/CTO double-layered films are attributable to relatively higher trap ionization energies in the Poole-Frenkel conduction model. [Figure not available: see fulltext.

Tuning dipolar magnetic interactions by controlling individual silica coating of iron oxide nanoparticles

NASA Astrophysics Data System (ADS)

Rivas Rojas, P. C.; Tancredi, P.; Moscoso Londoño, O.; Knobel, M.; Socolovsky, L. M.

2018-04-01

Single and fixed size core, core-shell nanoparticles of iron oxides coated with a silica layer of tunable thickness were prepared by chemical routes, aiming to generate a frame of study of magnetic nanoparticles with controlled dipolar interactions. The batch of iron oxides nanoparticles of 4.5 nm radii, were employed as cores for all the coated samples. The latter was obtained via thermal decomposition of organic precursors, resulting on nanoparticles covered with an organic layer that was subsequently used to promote the ligand exchange in the inverse microemulsion process, employed to coat each nanoparticle with silica. The amount of precursor and times of reaction was varied to obtain different silica shell thicknesses, ranging from 0.5 nm to 19 nm. The formation of the desired structures was corroborated by TEM and SAXS measurements, the core single-phase spinel structure was confirmed by XRD, and superparamagnetic features with gradual change related to dipolar interaction effects were obtained by the study of the applied field and temperature dependence of the magnetization. To illustrate that dipolar interactions are consistently controlled, the main magnetic properties are presented and analyzed as a function of center to center minimum distance between the magnetic cores.

Nanometer-Thick Yttrium Iron Garnet Film Development and Spintronics-Related Study

NASA Astrophysics Data System (ADS)

Chang, Houchen

In the last decade, there has been a considerable interest in using yttrium iron garnet (Y3Fe5O12, YIG) materials for magnetic insulator-based spintronics studies. This interest derives from the fact that YIG materials have very low intrinsic damping. The development of YIG-based spintronics demands YIG films that have a thickness in the nanometer (nm) range and at the same time exhibit low damping similar to single-crystal YIG bulk materials. This dissertation reports comprehensive experimental studies on nm-thick YIG films by magnetron sputtering techniques. Optimization of sputtering control parameters and post-deposition annealing processes are discussed in detail. The feasibility of low-damping YIG nm-thick film growth via sputtering is demonstrated. A 22.3-nm-thick YIG film, for example, shows a Gilbert damping constant of less than 1.0 x 10-4. The demonstration is of great technological significance because sputtering is a thin film growth technique most widely used in industry. The spin Seebeck effect (SSE) refers to the generation of spin voltage in a ferromagnet (FM) due to a temperature gradient. The spin voltage can produce a pure spin current into a normal metal (NM) that is in contact with the FM. Various theoretical models have been proposed to interpret the SSE, although a complete understanding of the effect has not been realized yet. In this dissertation the study of the role of damping on the SSE in YIG thin films is conducted for the first time. With the thin film development method mentioned in the last paragraph, a series of YIG thin films showing very similar structural and static magnetic properties but rather different Gilbert damping values were prepared. A Pt capping layer was grown on each YIG film to probe the strength of the SSE. The experimental data show that the YIG films with a smaller intrinsic Gilbert damping shows a stronger SSE. The majority of the previous studies on YIG spintronics utilized YIG films that were grown on single-crystal Gd3Ga5O 12 (GGG) substrates first and then capped with either a thin NM layer or a thin topological insulator (TI) layer. The use of the GGG substrates is crucial in terms of realizing high-quality YIG films, because GGG not only has a crystalline structure almost perfectly matching that of YIG but is also extremely stable at high temperature in oxygen that is the condition needed for YIG crystallization. The feasibility of growing high-quality YIG thin films on Pt thin films is explored in this dissertation. This work is of great significance because it enables the fabrication of sandwich-like NM/YIG/NM or NM/YIG/TI structures. Such tri-layered structures will facilitate various interesting fundamental studies as well as device developments. The demonstration of a magnon-mediated electric current drag phenomenon is presented as an example for such tri-layered structures.

Structural analysis of viral replicative intermediates isolated from adenovirus type 2-infected HeLa cell nuclei.

PubMed Central

Kedinger, C; Brison, O; Perrin, F; Wilhelm, J

1978-01-01

Deoxyribonucleoprotein complexes released 17 h postinfection from adenovirus type 1 (Ad2)-infected HeLa cell nuclei were shown by electron microscopy to contain filaments much thicker (about 200 A [20 nm]) than double-stranded DNA (about 20 A [2 nm]). The complexes were partially purified through a linear sucrose gradient, concentrated, and further purified in a metrizamide gradient. The major protein present in the complexes was identified as the 72,000-dalton (72K), adenovirus-coded single-stranded DNA-binding protein (72K DBP). Three types of complexes have been visualized by electron microscopy. Some linear complexes were uniformly thick, and their length corresponded roughly to that of the adenovirus genome. Other linear genome-length complexes appeared to consist of a thick filament connected to a thinner filament with the diameter of double-stranded DNA. Forked complexes consisting of one thick filament connected to a genome-length, thinner double-stranded DNA filament were also visualized. Both thick and thin filaments were sensitive to DNase and not to RNase, but only the thick filaments were digested by the single-strand-specific Neurospora crassa nuclease, indicating that they correspond to a complex of 72K DBP and Ad2 single-stranded DNA. Experiments with anti-72K DBP immunoglobulins indicated that these nucleoprotein complexes, containing the 72K DBP, correspond to replicative intermediates. Both strands of the Ad2 genome were found associated to the 72K DBP. Altogether, our results establish the in vivo association of the 72K DBP with adenovirus single-stranded DNA, as previously suggested from in vitro studies, and support a strand displacement mechanism for Ad2 DNA replication, in which both strands can be displaced. In addition, our results indicate that, late in infection, histones are not bound to adenovirus DNA in the form of a nucleosomal chromatine-like structure. Images PMID:207893

Structural analysis of viral replicative intermediates isolated from adenovirus type 2-infected HeLa cell nuclei.

PubMed

Kedinger, C; Brison, O; Perrin, F; Wilhelm, J

1978-05-01

Deoxyribonucleoprotein complexes released 17 h postinfection from adenovirus type 1 (Ad2)-infected HeLa cell nuclei were shown by electron microscopy to contain filaments much thicker (about 200 A [20 nm]) than double-stranded DNA (about 20 A [2 nm]). The complexes were partially purified through a linear sucrose gradient, concentrated, and further purified in a metrizamide gradient. The major protein present in the complexes was identified as the 72,000-dalton (72K), adenovirus-coded single-stranded DNA-binding protein (72K DBP). Three types of complexes have been visualized by electron microscopy. Some linear complexes were uniformly thick, and their length corresponded roughly to that of the adenovirus genome. Other linear genome-length complexes appeared to consist of a thick filament connected to a thinner filament with the diameter of double-stranded DNA. Forked complexes consisting of one thick filament connected to a genome-length, thinner double-stranded DNA filament were also visualized. Both thick and thin filaments were sensitive to DNase and not to RNase, but only the thick filaments were digested by the single-strand-specific Neurospora crassa nuclease, indicating that they correspond to a complex of 72K DBP and Ad2 single-stranded DNA. Experiments with anti-72K DBP immunoglobulins indicated that these nucleoprotein complexes, containing the 72K DBP, correspond to replicative intermediates. Both strands of the Ad2 genome were found associated to the 72K DBP. Altogether, our results establish the in vivo association of the 72K DBP with adenovirus single-stranded DNA, as previously suggested from in vitro studies, and support a strand displacement mechanism for Ad2 DNA replication, in which both strands can be displaced. In addition, our results indicate that, late in infection, histones are not bound to adenovirus DNA in the form of a nucleosomal chromatine-like structure.

Chalcogenide thin films deposited by rfMS technique using a single quaternary target

NASA Astrophysics Data System (ADS)

Prepelita, P.; Stavarache, I.; Negrila, C.; Garoi, F.; Craciun, V.

2017-12-01

Thin films of chalcogenide, Cu(In,Ga)Se2 have been obtained using a single quaternary target by radio frequency magnetron sputtering method, with thickness in the range 750 nm to 1200 nm. X-ray photoelectron spectroscopy investigations showed, that the composition of Cu(In,Ga)Se2 thin films was very similar to that of the used target CuIn0.75Ga0.25Se2. Identification of the chemical composition of Cu(In,Ga)Se2 thin films by XPS performed in high vacuum, emphasized that the samples exhibit surface features suitable to be integrated into the structure of solar cells. Atomic Force Microscopy and Scanning Electron Microscopy investigations showed that surface morphology was influenced by the increase in thickness of the Cu(In,Ga)Se2 layer. From X-Ray Diffraction investigations it was found that all films were polycrystalline, having a tetragonal lattice with a preferential orientation along the (112) direction. The optical reflectance as a function of wavelength was measured for the studied samples. The increase in thickness of the Cu(In,Ga)Se2 absorber determined a decrease of its optical bandgap value from 1.53 eV to 1.44 eV. The results presented in this paper showed an excellent alternative of obtaining Cu(In,Ga)Se2 compound thin films from a single target.

Specific features of single-pulse femtosecond laser micron and submicron ablation of a thin silver film coated with a micron-thick photoresist layer

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

Zayarnyi, D A; Ionin, A A; Kudryashov, S I

Specific features of ablation of a thin silver film with a 1-μm-thick layer of a highly transparent photoresist and the same film without a photoresist layer under single tightly focused femtosecond laser pulses in the visible range (515 nm) are experimentally investigated. Interference effects of internal modification of the photoresist layer, its spallation ablation from the film surface and formation of through hollow submicron channels in the resist without its spallation but with ablation of the silver film lying under the resist are found and discussed. (extreme light fields and their applications)

Airborne Polarimetric, Two-Color Laser Altimeter Measurements of Lake Ice Cover: A Pathfinder for NASA's ICESat-2 Spaceflight Mission

NASA Technical Reports Server (NTRS)

Harding, David; Dabney, Philip; Valett, Susan; Yu, Anthony; Vasilyev, Aleksey; Kelly, April

2011-01-01

The ICESat-2 mission will continue NASA's spaceflight laser altimeter measurements of ice sheets, sea ice and vegetation using a new measurement approach: micropulse, single photon ranging at 532 nm. Differential penetration of green laser energy into snow, ice and water could introduce errors in sea ice freeboard determination used for estimation of ice thickness. Laser pulse scattering from these surface types, and resulting range biasing due to pulse broadening, is assessed using SIMPL airborne data acquired over icecovered Lake Erie. SIMPL acquires polarimetric lidar measurements at 1064 and 532 nm using the micropulse, single photon ranging measurement approach.

Laser-induced periodic surface structures of thin, complex multi-component films

NASA Astrophysics Data System (ADS)

Reif, Juergen; Varlamova, Olga; Ratzke, Markus; Uhlig, Sebastian

2016-04-01

Femtosecond laser-induced regular nanostructures are generated on a complex multilayer target, namely a piece of a commercial, used hard disk memory. It is shown that after single-shot 800-nm irradiation at 0.26 J/cm2 only the polymer cover layer and—in the center—a portion of the magnetic multilayer are ablated. A regular array of linearly aligned spherical 450-nm features at the uncovered interface between cover and magnetic layers appears not to be produced by the irradiation. Only after about 10 pulses on one spot, classical ripples perpendicular to the laser polarization with a period of ≈700 nm are observed, with a modulation between 40 nm above and 40 nm below the pristine surface and an ablation depth only slightly larger than the thickness of the multilayer magnetic film. Further increase of the pulse number does not result in deeper ablation. However, 770-nm ripples become parallel to the polarization and are swelling to more than 120 nm above zero, much more than the full multilayer film thickness. In the spot periphery, much shallower 300-nm ripples are perpendicular to the strong modulation and the laser polarization. Irradiation with 0.49-J/cm2 pulses from an ultrafast white-light continuum results—in the spot periphery—in the formation of 200-nm ripples, only swelling above zero after removal of the polymer cover, without digging into the magnetic film.

Structure and corrosion behavior of sputter deposited cerium oxide based coatings with various thickness on Al 2024-T3 alloy substrates

NASA Astrophysics Data System (ADS)

Liu, Yuanyuan; Huang, Jiamu; Claypool, James B.; Castano, Carlos E.; O'Keefe, Matthew J.

2015-11-01

Cerium oxide based coatings from ∼100 to ∼1400 nm in thickness were deposited onto Al 2024-T3 alloy substrates by magnetron sputtering of a 99.99% pure CeO2 target. The crystallite size of CeO2 coatings increased from 15 nm to 46 nm as the coating thickness increased from ∼100 nm to ∼1400 nm. The inhomogeneous lattice strain increased from 0.36% to 0.91% for the ∼100 nm to ∼900 nm thick coatings and slightly decreased to 0.89% for the ∼1400 nm thick coating. The highest adhesion strength to Al alloy substrates was for the ∼210 nm thick coating, due to a continuous film coverage and low internal stress. Electrochemical measurements indicated that sputter deposited crystalline CeO2 coatings acted as physical barriers that provide good cathodic inhibition for Al alloys in saline solution. The ∼900 nm thick CeO2 coated sample had the best corrosion performance that increased the corrosion resistance by two orders magnitude and lowered the cathodic current density 30 times compared to bare Al 2024-T3 substrates. The reduced defects and exposed surface, along with suppressed charge mobility, likely accounts for the improved corrosion performance as coating thickness increased from ∼100 nm to ∼900 nm. The corrosion performance decreased for ∼1400 nm thick coatings due in part to an increase in coating defects and porosity along with a decrease in adhesion strength.

Zebrafish Cardiac Muscle Thick Filaments: Isolation Technique and Three-Dimensional Structure

PubMed Central

González-Solá, Maryví; AL-Khayat, Hind A.; Behra, Martine; Kensler, Robert W.

2014-01-01

To understand how mutations in thick filament proteins such as cardiac myosin binding protein-C or titin, cause familial hypertrophic cardiomyopathies, it is important to determine the structure of the cardiac thick filament. Techniques for the genetic manipulation of the zebrafish are well established and it has become a major model for the study of the cardiovascular system. Our goal is to develop zebrafish as an alternative system to the mammalian heart model for the study of the structure of the cardiac thick filaments and the proteins that form it. We have successfully isolated thick filaments from zebrafish cardiac muscle, using a procedure similar to those for mammalian heart, and analyzed their structure by negative-staining and electron microscopy. The isolated filaments appear well ordered with the characteristic 42.9 nm quasi-helical repeat of the myosin heads expected from x-ray diffraction. We have performed single particle image analysis on the collected electron microscopy images for the C-zone region of these filaments and obtained a three-dimensional reconstruction at 3.5 nm resolution. This reconstruction reveals structure similar to the mammalian thick filament, and demonstrates that zebrafish may provide a useful model for the study of the changes in the cardiac thick filament associated with disease processes. PMID:24739166

Single-Walled Carbon Nanotube Film Supported Nanofiltration Membrane with a Nearly 10 nm Thick Polyamide Selective Layer for High-Flux and High-Rejection Desalination.

PubMed

Zhu, Yuzhang; Xie, Wei; Gao, Shoujian; Zhang, Feng; Zhang, Wenbin; Liu, Zhaoyang; Jin, Jian

2016-09-01

Fabricating nanofiltration (NF) membranes with high permeating flux and simultaneous high rejection rate for desalination is rather significant and highly desired. A new avenue is reported in this work to design NF membrane by using polydopamine wrapped single-walled carbon nanotube (PD/SWCNTs) ultrathin film as support layer instead of the use of traditional polymer-based underlying layers. Thanks to the high porosity, smooth surface, and more importantly optimal hydrophilic surface of PD/SWCNTs film, a defect-free polyamide selective layer for NF membrane with thickness of as thin as 12 nm is achieved. The obtained NF membrane exhibits an extremely high performance with a permeating flux of 32 L m -2 h -1 bar -1 and a rejection rate of 95.9% to divalent ions. This value is two to five times higher than the traditional NF membranes with similar rejection rate. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Leakage current and capacitance characteristics of Si/SiO2/Si single-barrier varactor

NASA Astrophysics Data System (ADS)

Mamor, M.; Fu, Y.; Nur, O.; Willander, M.; Bengtsson, S.

We investigate, both experimentally and theoretically, current and capacitance (I-V/C-V) characteristics and the device performance of Si/SiO2/Si single-barrier varactor diodes (SBVs). Two diodes were fabricated with different SiO2 layer thicknesses using the state-of-the-art wafer bonding technique. The devices have very low leakage currents (about 5×10-2 and 1.8×10-2 mA/mm2) and intrinsic capacitance levels of typically 1.5 and 50 nF/mm2 for diodes with 5-nm and 20-nm oxide layers, respectively. With the present device physical parameters (25-mm2 device area, 760-μm modulation layer thickness and 1015-cm-3 doping level), the estimated cut-off frequency is about 5×107 Hz. With the physical parameters of the present existing III-V triplers, the cut-off frequency of our Si-based SBV can be as high as 0.5 THz.

An Ultrathin Single Crystalline Relaxor Ferroelectric Integrated on a High Mobility Semiconductor.

PubMed

Moghadam, Reza M; Xiao, Zhiyong; Ahmadi-Majlan, Kamyar; Grimley, Everett D; Bowden, Mark; Ong, Phuong-Vu; Chambers, Scott A; Lebeau, James M; Hong, Xia; Sushko, Peter V; Ngai, Joseph H

2017-10-11

The epitaxial growth of multifunctional oxides on semiconductors has opened a pathway to introduce new functionalities to semiconductor device technologies. In particular, the integration of gate materials that enable nonvolatile or hysteretic functionality in field-effect transistors could lead to device technologies that consume less power or allow for novel modalities in computing. Here we present electrical characterization of ultrathin single crystalline SrZr x Ti 1-x O 3 (x = 0.7) films epitaxially grown on a high mobility semiconductor, Ge. Epitaxial films of SrZr x Ti 1-x O 3 exhibit relaxor behavior, characterized by a hysteretic polarization that can modulate the surface potential of Ge. We find that gate layers as thin as 5 nm corresponding to an equivalent-oxide thickness of just 1.0 nm exhibit a ∼2 V hysteretic window in the capacitance-voltage characteristics. The development of hysteretic metal-oxide-semiconductor capacitors with nanoscale gate thicknesses opens new vistas for nanoelectronic devices.

Thermoelectric La-doped SrTiO3 epitaxial layers with single-crystal quality: from nano to micrometers

PubMed Central

Apreutesei, Mihai; Debord, Régis; Bouras, Mohamed; Regreny, Philippe; Botella, Claude; Benamrouche, Aziz; Carretero-Genevrier, Adrian; Gazquez, Jaume; Grenet, Geneviève; Pailhès, Stéphane; Saint-Girons, Guillaume; Bachelet, Romain

2017-01-01

Abstract High-quality thermoelectric La0.2Sr0.8TiO3 (LSTO) films, with thicknesses ranging from 20 nm to 0.7 μm, have been epitaxially grown on SrTiO3(001) substrates by enhanced solid-source oxide molecular-beam epitaxy. All films are atomically flat (with rms roughness < 0.2 nm), with low mosaicity (<0.1°), and present very low electrical resistivity (<5 × 10−4 Ω cm at room temperature), one order of magnitude lower than standard commercial Nb-doped SrTiO3 single-crystalline substrate. The conservation of transport properties within this thickness range has been confirmed by thermoelectric measurements where Seebeck coefficients of approximately –60 μV/K have been recorded for all films. These LSTO films can be integrated on Si for non-volatile memory structures or opto-microelectronic devices, functioning as transparent conductors or thermoelectric elements. PMID:28740558

Thermoelectric La-doped SrTiO3 epitaxial layers with single-crystal quality: from nano to micrometers.

PubMed

Apreutesei, Mihai; Debord, Régis; Bouras, Mohamed; Regreny, Philippe; Botella, Claude; Benamrouche, Aziz; Carretero-Genevrier, Adrian; Gazquez, Jaume; Grenet, Geneviève; Pailhès, Stéphane; Saint-Girons, Guillaume; Bachelet, Romain

2017-01-01

High-quality thermoelectric La 0.2 Sr 0.8 TiO 3 (LSTO) films, with thicknesses ranging from 20 nm to 0.7 μm, have been epitaxially grown on SrTiO 3 (001) substrates by enhanced solid-source oxide molecular-beam epitaxy. All films are atomically flat (with rms roughness < 0.2 nm), with low mosaicity (<0.1°), and present very low electrical resistivity (<5 × 10 -4 Ω cm at room temperature), one order of magnitude lower than standard commercial Nb-doped SrTiO 3 single-crystalline substrate. The conservation of transport properties within this thickness range has been confirmed by thermoelectric measurements where Seebeck coefficients of approximately -60 μV/K have been recorded for all films. These LSTO films can be integrated on Si for non-volatile memory structures or opto-microelectronic devices, functioning as transparent conductors or thermoelectric elements.

Solid-state nanopore localization by controlled breakdown of selectively thinned membranes

NASA Astrophysics Data System (ADS)

Carlsen, Autumn T.; Briggs, Kyle; Hall, Adam R.; Tabard-Cossa, Vincent

2017-02-01

We demonstrate precise positioning of nanopores fabricated by controlled breakdown (CBD) on solid-state membranes by spatially varying the electric field strength with localized membrane thinning. We show 100 × 100 nm2 precision in standard SiN x membranes (30-100 nm thick) after selective thinning by as little as 25% with a helium ion beam. Control over nanopore position is achieved through the strong dependence of the electric field-driven CBD mechanism on membrane thickness. Confinement of pore formation to the thinned region of the membrane is confirmed by TEM imaging and by analysis of DNA translocations. These results enhance the functionality of CBD as a fabrication approach and enable the production of advanced nanopore devices for single-molecule sensing applications.

Defect properties of InGaAsN layers grown as sub-monolayer digital alloys by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Baranov, Artem I.; Gudovskikh, Alexander S.; Kudryashov, Dmitry A.; Lazarenko, Alexandra A.; Morozov, Ivan A.; Mozharov, Alexey M.; Nikitina, Ekaterina V.; Pirogov, Evgeny V.; Sobolev, Maxim S.; Zelentsov, Kirill S.; Egorov, Anton Yu.; Darga, Arouna; Le Gall, Sylvain; Kleider, Jean-Paul

2018-04-01

The defect properties of InGaAsN dilute nitrides grown as sub-monolayer digital alloys (SDAs) by molecular beam epitaxy for photovoltaic application were studied by space charge capacitance spectroscopy. Alloys of i-InGaAsN (Eg = 1.03 eV) were lattice-matched grown on GaAs wafers as a superlattice of InAs/GaAsN with one monolayer of InAs (<0.5 nm) between wide GaAsN (7-12 nm) layers as active layers in single-junction solar cells. Low p-type background doping was demonstrated at room temperature in samples with InGaAsN layers 900 nm and 1200 nm thick (less 1 × 1015 cm-3). According to admittance spectroscopy and deep-level transient spectroscopy measurements, the SDA approach leads to defect-free growth up to a thickness of 900 nm. An increase in thickness to 1200 nm leads to the formation of non-radiative recombination centers with an activation energy of 0.5 eV (NT = 8.4 × 1014 cm-3) and a shallow defect level at 0.20 eV. The last one leads to the appearance of additional doping, but its concentration is low (NT = 5 × 1014 cm-3) so it does not affect the photoelectric properties. However, further increase in thickness to 1600 nm, leads to significant growth of its concentration to (3-5) × 1015 cm-3, while the concentration of deep levels becomes 1.3 × 1015 cm-3. Therefore, additional free charge carriers appearing due to ionization of the shallow level change the band diagram from p-i-n to p-n junction at room temperature. It leads to a drop of the external quantum efficiency due to the effect of pulling electric field decrease in the p-n junction and an increased number of non-radiative recombination centers that negatively impact lifetimes in InGaAsN.

1.5 W high efficiency and tunable single-longitudinal-mode Ho:YLF ring laser based on Faraday effect.

PubMed

Wu, Jing; Ju, Youlun; Dai, Tongyu; Yao, Baoquan; Wang, Yuezhu

2017-10-30

We demonstrated an efficient and tunable single-longitudinal-mode Ho:YLF ring laser based on Faraday effect for application to measure atmospheric carbon dioxide (CO 2 ). Single-longitudinal-mode power at 2051.65 nm achieved 528 mW with the slope efficiency of 39.5% and the M 2 factor of 1.07, and the tunable range of about 178 GHz was obtained by inserting a Fabry-Perot (F-P) etalon with the thickness of 0.5 mm. In addition, the maximum single-longitudinal-mode power reached 1.5 W with the injected power of 528 mW at 2051.65 nm by master oscillator power amplifier (MOPA) technique. High efficiency and tunable single-longitudinal-mode based on Faraday effect around 2 μm has not been reported yet to the best of our knowledge.

SHG in DASMS single-crystal film producing ultraviolet

NASA Astrophysics Data System (ADS)

Ahyi, Ayayi; Khatavkar, Sanchit; Thakur, Mrinal

2002-03-01

Single-crystal film of the molecular salt, DASMS (noncentrosymmetric phase), has been grown using the modified shear method.^1 The DASMS film is orange in color, showing strong birefringence. The absorption spectrum of DASMS has a maximum at 590 nm, with the onset at about 600 nm and continuing to UV but with a dip around 400 nm. Such a spectrum allows efficient SHG at short wavelengths (400 nm). A Ti:Sapphire laser producing 200 fs pulses at 82 MHz with an average power of 50mW was used for the SHG experiment. The fundamental wavelength was 760nm giving SHG at 380 nm corresponding to the dip in the absorption spectrum. The beam was focused on the film using a 4" focal length lens. From the power measurements, an efficiency of 0.1% in SHG has been observed in a 1μm thick film indicating that the magnitude of d-coefficient is larger than 2000 pm/V. 1. M. Thakur and S. Meyler, Macromolecules, 18 2341 (1985); M. Thakur, Y. Shani, G.C. Chi and K. O'Brien, Synth. Met., 28 D595 (1989).

Flexure-based nanomagnetic actuators

NASA Astrophysics Data System (ADS)

Vasquez, Daniel James

Nanometer-scale actuators powered through applied-magnetic fields have been designed, fabricated, and tested. These actuators consist of one or more ferromagnetic elements attached to a mechanical flexure. Two types of flexures were studied including a cantilever beam that is fixed on one end, and free on the other. The free end of the cantilever is attached to a, ferromagnetic element allowing a bending torque to be applied by a magnetic field. The second type of actuator design uses a set of torsion beams that are each anchored on one end, and attached to the magnetic element on the other end. The torsion beams are designed such that the application of a magnetic field will result in a twist along the long axis of the beam with little to no bending. The smallest fabricated and tested device is a cantilever-based ferromagnetic actuator that consists of a single 1.5-mum-long, 338-nm-wide, and 50-nm-thick nickel element, and a 2.2-mum-long, 110-nm-wide, and 30-nm-thick gold cantilever beam. A deflection of over 17° was measured for this actuator, while a similar one with a 10.1-mum long cantilever beam experienced measured deflections up to 57°. Torsion-based ferromagnetic actuators have been fabricated and tested with 110-nm-wide, and 50-rim-thick magnetic elements. Such magnetic elements contain only a single saturated magnetic domain. The ultimate scalability of ferromagnetic actuation is limited by the ability of thermal noise to affect the temporal stability of a nanometer-scale magnet. Theory to describe thermal noise and ultimate scalability of the ferromagnetic actuators has been developed. The size of the ferromagnetic actuators studied in this manuscript are smaller than most plant and animal cells. This enables the possibility of such actuators to manipulate a, living cell on an intracellular level. Other potential applications of such small actuators include MHz, to GHz frequency resonators, and tunable optical filters.

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

Raghuwanshi, Vikram Singh; Garusinghe, Uthpala Manavi; Ilavsky, Jan

Controlling nanoparticles (NPs) aggregation in cellulose/NPs composites allows to optimise NPs driven properties and their applications. Polyelectrolytes are used to control NPs aggregation and their retention within the fibrous matrix. Here in this study, we aim at evaluating how a polyelectrolyte (Cationic Polyacrylamide; CPAM, molecular weight: 13 MDa, charge: 50%, Radius of gyration: 30–36 nm) adsorbs and re-conforms onto the surface of silica(SiO 2) NPs differing in diameter (8, 22 and 74 nm) and to investigate the respective NPs aggregation in cellulose matrices. SEM shows the local area distribution of NPs in composites. Ultra-SAXS (USAXS) allows to evaluate the averagemore » NPs size distribution and the inter-particle interactions at length scale ranging from 1 to 1000 nm. USAXS data analysis reveals that CPAM covers multiple NPs of the smaller diameter (8 nm), presumably with a single chain to form large size NPs aggregates. As the NPs diameter is increased to 22 nm, CPAM re-conforms over NP surface forming a large shell of thickness 5.5 nm. For the composites with NPs of diameter 74 nm, the CPAM chain re-conforms further onto NP surface and the surrounding shell thickness decreases to 2.2 nm. Lastly, structure factor analysis reveals higher structural ordering for NPs as increases their diameter, which is caused by different conformations adopted by CPAM onto NPs surface.« less

Effect of nanoparticles size and polyelectrolyte on nanoparticles aggregation in a cellulose fibrous matrix

DOE PAGES

Raghuwanshi, Vikram Singh; Garusinghe, Uthpala Manavi; Ilavsky, Jan; ...

2017-09-18

Controlling nanoparticles (NPs) aggregation in cellulose/NPs composites allows to optimise NPs driven properties and their applications. Polyelectrolytes are used to control NPs aggregation and their retention within the fibrous matrix. Here in this study, we aim at evaluating how a polyelectrolyte (Cationic Polyacrylamide; CPAM, molecular weight: 13 MDa, charge: 50%, Radius of gyration: 30–36 nm) adsorbs and re-conforms onto the surface of silica(SiO 2) NPs differing in diameter (8, 22 and 74 nm) and to investigate the respective NPs aggregation in cellulose matrices. SEM shows the local area distribution of NPs in composites. Ultra-SAXS (USAXS) allows to evaluate the averagemore » NPs size distribution and the inter-particle interactions at length scale ranging from 1 to 1000 nm. USAXS data analysis reveals that CPAM covers multiple NPs of the smaller diameter (8 nm), presumably with a single chain to form large size NPs aggregates. As the NPs diameter is increased to 22 nm, CPAM re-conforms over NP surface forming a large shell of thickness 5.5 nm. For the composites with NPs of diameter 74 nm, the CPAM chain re-conforms further onto NP surface and the surrounding shell thickness decreases to 2.2 nm. Lastly, structure factor analysis reveals higher structural ordering for NPs as increases their diameter, which is caused by different conformations adopted by CPAM onto NPs surface.« less

Grain size engineering for ferroelectric Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films by an insertion of Al{sub 2}O{sub 3} interlayer

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

Kim, Han Joon; Park, Min Hyuk; Kim, Yu Jin

2014-11-10

The degradation of ferroelectric (FE) properties of atomic layer deposited Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films with increasing thickness was mitigated by inserting 1 nm-thick Al{sub 2}O{sub 3} interlayer at middle position of the thickness of the FE film. The large P{sub r} of 10 μC/cm{sup 2}, which is 11 times larger than that of single layer Hf{sub 0.5}Zr{sub 0.5}O{sub 2} film with equivalent thickness, was achieved from the films as thick as 40 nm. The Al{sub 2}O{sub 3} interlayer could interrupt the continual growth of Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films, and the resulting decrease of grain size prevented the formation of non-ferroelectricmore » monoclinic phase. The Al{sub 2}O{sub 3} interlayer also largely decreased the leakage current of the Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films.« less

Mechanism and Characteristics of Humidity Sensing with Polyvinyl Alcohol-Coated Fiber Surface Plasmon Resonance Sensor.

PubMed

Shao, Yu; Wang, Ying; Cao, Shaoqing; Huang, Yijian; Zhang, Longfei; Zhang, Feng; Liao, Changrui; Wang, Yiping

2018-06-25

A surface plasmon resonance (SPR) sensor based on a side-polished single mode fiber coated with polyvinyl alcohol (PVA) is demonstrated for relative humidity (RH) sensing. The SPR sensor exhibits a resonant dip in the transmission spectrum in ambient air after PVA film coating, and the resonant wavelength shifts to longer wavelengths as the thickness of the PVA film increases. When RH changes, the resonant dip of the sensor with different film-thicknesses exhibits interesting characteristics for optical spectrum evolution. For sensors with initial wavelengths between 550 nm and 750 nm, the resonant dip shifts to longer wavelengths with increasing RH. The averaged sensitivity increases firstly and then drops, and shows a maximal sensitivity of 1.01 nm/RH%. Once the initial wavelength of the SPR sensor exceeds 850 nm, an inflection point of the resonant wavelength shift can be observed with RH increasing, and the resonant dip shifts to shorter wavelengths for RH values exceeding this point, and sensitivity as high as −4.97 nm/RH% can be obtained in the experiment. The sensor is expected to have potential applications in highly sensitive and cost effective humidity sensing.

Thickness and Elasticity of Gram-Negative Murein Sacculi Measured by Atomic Force Microscopy

PubMed Central

Yao, X.; Jericho, M.; Pink, D.; Beveridge, T.

1999-01-01

Atomic force microscopy was used to measure the thickness of air-dried, collapsed murein sacculi from Escherichia coli K-12 and Pseudomonas aeruginosa PAO1. Air-dried sacculi from E. coli had a thickness of 3.0 nm, whereas those from P. aeruginosa were 1.5 nm thick. When rehydrated, the sacculi of both bacteria swelled to double their anhydrous thickness. Computer simulation of a section of a model single-layer peptidoglycan network in an aqueous solution with a Debye shielding length of 0.3 nm gave a mass distribution full width at half height of 2.4 nm, in essential agreement with these results. When E. coli sacculi were suspended over a narrow groove that had been etched into a silicon surface and the tip of the atomic force microscope used to depress and stretch the peptidoglycan, an elastic modulus of 2.5 × 107 N/m2 was determined for hydrated sacculi; they were perfectly elastic, springing back to their original position when the tip was removed. Dried sacculi were more rigid with a modulus of 3 × 108 to 4 × 108 N/m2 and at times could be broken by the atomic force microscope tip. Sacculi aligned over the groove with their long axis at right angles to the channel axis were more deformable than those with their long axis parallel to the groove axis, as would be expected if the peptidoglycan strands in the sacculus were oriented at right angles to the long cell axis of this gram-negative rod. Polar caps were not found to be more rigid structures but collapsed to the same thickness as the cylindrical portions of the sacculi. The elasticity of intact E. coli sacculi is such that, if the peptidoglycan strands are aligned in unison, the interstrand spacing should increase by 12% with every 1 atm increase in (turgor) pressure. Assuming an unstressed hydrated interstrand spacing of 1.3 nm (R. E. Burge, A. G. Fowler, and D. A. Reaveley, J. Mol. Biol. 117:927–953, 1977) and an internal turgor pressure of 3 to 5 atm (or 304 to 507 kPa) (A. L. Koch, Adv. Microbial Physiol. 24:301–366, 1983), the natural interstrand spacing in cells would be 1.6 to 2.0 nm. Clearly, if large macromolecules of a diameter greater than these spacings are secreted through this layer, the local ordering of the peptidoglycan must somehow be disrupted. PMID:10559150

Direct, concurrent measurements of the forces and currents affecting DNA in a nanopore with comparable topography.

PubMed

Nelson, Edward M; Li, Hui; Timp, Gregory

2014-06-24

We report direct, concurrent measurements of the forces and currents associated with the translocation of a single-stranded DNA molecule tethered to the tip of an atomic force microscope (AFM) cantilever through synthetic pores with topagraphies comparable to the DNA. These measurements were performed to gauge the signal available for sequencing and the electric force required to impel a single molecule through synthetic nanopores ranging from 1.0 to 3.5 nm in diameter in silicon nitride membranes 6-10 nm thick. The measurements revealed that a molecule can slide relatively frictionlessly through a pore, but regular fluctuations are observed intermittently in the force (and the current) every 0.35-0.72 nm, which are attributed to individual nucleotides translating through the nanopore in a turnstile-like motion.

M-plane core-shell InGaN/GaN multiple-quantum-wells on GaN wires for electroluminescent devices.

PubMed

Koester, Robert; Hwang, Jun-Seok; Salomon, Damien; Chen, Xiaojun; Bougerol, Catherine; Barnes, Jean-Paul; Dang, Daniel Le Si; Rigutti, Lorenzo; de Luna Bugallo, Andres; Jacopin, Gwénolé; Tchernycheva, Maria; Durand, Christophe; Eymery, Joël

2011-11-09

Nonpolar InGaN/GaN multiple quantum wells (MQWs) grown on the {11-00} sidewalls of c-axis GaN wires have been grown by organometallic vapor phase epitaxy on c-sapphire substrates. The structural properties of single wires are studied in detail by scanning transmission electron microscopy and in a more original way by secondary ion mass spectroscopy to quantify defects, thickness (1-8 nm) and In-composition in the wells (∼16%). The core-shell MQW light emission characteristics (390-420 nm at 5 K) were investigated by cathodo- and photoluminescence demonstrating the absence of the quantum Stark effect as expected due to the nonpolar orientation. Finally, these radial nonpolar quantum wells were used in room-temperature single-wire electroluminescent devices emitting at 392 nm by exploiting sidewall emission.

Nanopore arrays in a silicon membrane for parallel single-molecule detection: fabrication

NASA Astrophysics Data System (ADS)

Schmidt, Torsten; Zhang, Miao; Sychugov, Ilya; Roxhed, Niclas; Linnros, Jan

2015-08-01

Solid state nanopores enable translocation and detection of single bio-molecules such as DNA in buffer solutions. Here, sub-10 nm nanopore arrays in silicon membranes were fabricated by using electron-beam lithography to define etch pits and by using a subsequent electrochemical etching step. This approach effectively decouples positioning of the pores and the control of their size, where the pore size essentially results from the anodizing current and time in the etching cell. Nanopores with diameters as small as 7 nm, fully penetrating 300 nm thick membranes, were obtained. The presented fabrication scheme to form large arrays of nanopores is attractive for parallel bio-molecule sensing and DNA sequencing using optical techniques. In particular the signal-to-noise ratio is improved compared to other alternatives such as nitride membranes suffering from a high-luminescence background.

Nanopore arrays in a silicon membrane for parallel single-molecule detection: fabrication.

PubMed

Schmidt, Torsten; Zhang, Miao; Sychugov, Ilya; Roxhed, Niclas; Linnros, Jan

2015-08-07

Solid state nanopores enable translocation and detection of single bio-molecules such as DNA in buffer solutions. Here, sub-10 nm nanopore arrays in silicon membranes were fabricated by using electron-beam lithography to define etch pits and by using a subsequent electrochemical etching step. This approach effectively decouples positioning of the pores and the control of their size, where the pore size essentially results from the anodizing current and time in the etching cell. Nanopores with diameters as small as 7 nm, fully penetrating 300 nm thick membranes, were obtained. The presented fabrication scheme to form large arrays of nanopores is attractive for parallel bio-molecule sensing and DNA sequencing using optical techniques. In particular the signal-to-noise ratio is improved compared to other alternatives such as nitride membranes suffering from a high-luminescence background.

High density nonmagnetic cobalt in thin films

NASA Astrophysics Data System (ADS)

Banu, Nasrin; Singh, Surendra; Basu, Saibal; Roy, Anupam; Movva, Hema C. P.; Lauter, V.; Satpati, B.; Dev, B. N.

2018-05-01

Recently high density (HD) nonmagnetic cobalt has been discovered in a nanoscale cobalt thin film, grown on Si(111) single crystal. This form of cobalt is not only nonmagnetic but also superconducting. These promising results have encouraged further investigations of the growth of the nonmagnetic (NM) phase of cobalt. In the original investigation, the cobalt film had a natural cobalt oxide at the top. We have investigated whether the growth of HD NM cobalt layers in the thin film depends on (i) a capping layer on the cobalt film, (ii) the thickness of the cobalt film and (iii) the nature of the substrate on which the cobalt film is grown. The results of such investigations indicate that for cobalt films capped with a thin gold layer, and for various film thicknesses, HD NM cobalt layers are formed. However, instead of a Si substrate, when the cobalt films are grown on oxide substrates, such as silicon oxide or cobalt oxide, HD NM cobalt layers are not formed. The difference is attributed to the nature—crystalline or amorphous—of the substrate.

Static magnetism and thermal switching in randomly oriented L10 FePt thin films

NASA Astrophysics Data System (ADS)

Lisfi, A.; Pokharel, S.; Alqarni, A.; Akioya, O.; Morgan, W.; Wuttig, M.

2018-05-01

Static magnetism and thermally activated magnetic relaxation were investigated in granular FePt films (20 nm-200 nm thick) with random magnetic anisotropy through hysteresis loop, torque curve and magnetization time dependence measurements. While the magnetism of thicker film (200 nm thick) is dominated by a single switching of the ordered L10 phase, thinner film (20 nm) displays a double switching, which is indicative of the presence of the disordered cubic phase. The pronounced behavior of double switching in thinner film suggests that the film grain boundary is composed of soft cubic magnetic phase. The magnetic relaxation study reveals that magnetic viscosity S of the films is strongly dependent on the external applied field and exhibits a maximum value (12 kAm) around the switching field and a vanishing behavior at low (1 kOe) and large (12 kOe) fields. The activation volume of the thermal switching was found to be much smaller than the physical volume of the granular structure due to the incoherent rotation mode of the magnetization reversal mechanism, which is established to be domain wall nucleation.

Growth of highly strained CeO 2 ultrathin films

DOE PAGES

Shi, Yezhou; Lee, Sang Chul; Monti, Matteo; ...

2016-11-07

Large biaxial strain is a promising route to tune the functionalities of oxide thin films. However, large strain is often not fully realized due to the formation of misfit dislocations at the film/substrate interface. In this work, we examine the growth of strained ceria (CeO 2) thin films on (001)-oriented single crystal yttria-stabilized zirconia (YSZ) via pulsed-laser deposition. By varying the film thickness systematically between 1 and 430 nm, we demonstrate that ultrathin ceria films are coherently strained to the YSZ substrate for thicknesses up to 2.7 nm, despite the large lattice mismatch (~5%). The coherency is confirmed by bothmore » X-ray diffraction and high-resolution transmission electron microscopy. This thickness is several times greater than the predicted equilibrium critical thickness. Partial strain relaxation is achieved by forming semirelaxed surface islands rather than by directly nucleating dislocations. In situ reflective high-energy electron diffraction during growth confirms the transition from 2-D (layer-by-layer) to 3-D (island) at a film thickness of ~1 nm, which is further supported by atomic force microscopy. We propose that dislocations likely nucleate near the surface islands and glide to the film/substrate interface, as evidenced by the presence of 60° dislocations. Finally, an improved understanding of growing oxide thin films with a large misfit lays the foundation to systematically explore the impact of strain and dislocations on properties such as ionic transport and redox chemistry.« less

Glass transition in thin supported polystyrene films probed by temperature-modulated ellipsometry in vacuum.

PubMed

Efremov, Mikhail Yu; Kiyanova, Anna V; Last, Julie; Soofi, Shauheen S; Thode, Christopher; Nealey, Paul F

2012-08-01

Glass transition in thin (1-200 nm thick) spin-cast polystyrene films on silicon surfaces is probed by ellipsometry in a controlled vacuum environment. A temperature-modulated modification of the method is used alongside a traditional linear temperature scan. A clear glass transition is detected in films with thicknesses as low as 1-2 nm. The glass transition temperature (T(g)) shows no substantial dependence on thickness for coatings greater than 20 nm. Thinner films demonstrate moderate T(g) depression achieving 18 K for thicknesses 4-7 nm. Less than 4 nm thick samples are excluded from the T(g) comparison due to significant thickness nonuniformity (surface roughness). The transition in 10-20 nm thick films demonstrates excessive broadening. For some samples, the broadened transition is clearly resolved into two separate transitions. The thickness dependence of the glass transition can be well described by a simple 2-layer model. It is also shown that T(g) depression in 5 nm thick films is not sensitive to a wide range of experimental factors including molecular weight characteristics of the polymer, specifications of solvent used for spin casting, substrate composition, and pretreatment of the substrate surface.

Dark-field microscopy studies of single metal nanoparticles: understanding the factors that influence the linewidth of the localized surface plasmon resonance

PubMed Central

Hu, Min; Novo, Carolina; Funston, Alison; Wang, Haining; Staleva, Hristina; Zou, Shengli; Mulvaney, Paul; Xia, Younan; Hartland, Gregory V.

2008-01-01

This article provides a review of our recent Rayleigh scattering measurements on single metal nanoparticles. Two different systems will be discussed in detail: gold nanorods with lengths between 30 and 80 nm, and widths between 8 and 30 nm; and hollow gold–silver nanocubes (termed nanoboxes or nanocages depending on their exact morphology) with edge lengths between 100 and 160 nm, and wall thicknesses of the order of 10 nm. The goal of this work is to understand how the linewidth of the localized surface plasmon resonance depends on the size, shape, and environment of the nanoparticles. Specifically, the relative contributions from bulk dephasing, electron–surface scattering, and radiation damping (energy loss via coupling to the radiation field) have been determined by examining particles with different dimensions. This separation is possible because the magnitude of the radiation damping effect is proportional to the particle volume, whereas, the electron–surface scattering contribution is inversely proportional to the dimensions. For the nanorods, radiation damping is the dominant effect for thick rods (widths greater than 20 nm), while electron–surface scattering is dominant for thin rods (widths less than 10 nm). Rods with widths in between these limits have narrow resonances—approaching the value determined by the bulk contribution. For nanoboxes and nanocages, both radiation damping and electron–surface scattering are significant at all sizes. This is because these materials have thin walls, but large edge lengths and, therefore, relatively large volumes. The effect of the environment on the localized surface plasmon resonance has also been studied for nanoboxes. Increasing the dielectric constant of the surroundings causes a red-shift and an increase in the linewidth of the plasmon band. The increase in linewidth is attributed to enhanced radiation damping. PMID:18846243

Dark-field microscopy studies of single metal nanoparticles: understanding the factors that influence the linewidth of the localized surface plasmon resonance.

PubMed

Hu, Min; Novo, Carolina; Funston, Alison; Wang, Haining; Staleva, Hristina; Zou, Shengli; Mulvaney, Paul; Xia, Younan; Hartland, Gregory V

2008-01-01

This article provides a review of our recent Rayleigh scattering measurements on single metal nanoparticles. Two different systems will be discussed in detail: gold nanorods with lengths between 30 and 80 nm, and widths between 8 and 30 nm; and hollow gold-silver nanocubes (termed nanoboxes or nanocages depending on their exact morphology) with edge lengths between 100 and 160 nm, and wall thicknesses of the order of 10 nm. The goal of this work is to understand how the linewidth of the localized surface plasmon resonance depends on the size, shape, and environment of the nanoparticles. Specifically, the relative contributions from bulk dephasing, electron-surface scattering, and radiation damping (energy loss via coupling to the radiation field) have been determined by examining particles with different dimensions. This separation is possible because the magnitude of the radiation damping effect is proportional to the particle volume, whereas, the electron-surface scattering contribution is inversely proportional to the dimensions. For the nanorods, radiation damping is the dominant effect for thick rods (widths greater than 20 nm), while electron-surface scattering is dominant for thin rods (widths less than 10 nm). Rods with widths in between these limits have narrow resonances-approaching the value determined by the bulk contribution. For nanoboxes and nanocages, both radiation damping and electron-surface scattering are significant at all sizes. This is because these materials have thin walls, but large edge lengths and, therefore, relatively large volumes. The effect of the environment on the localized surface plasmon resonance has also been studied for nanoboxes. Increasing the dielectric constant of the surroundings causes a red-shift and an increase in the linewidth of the plasmon band. The increase in linewidth is attributed to enhanced radiation damping.

Experimental Investigation on Cutting Characteristics in Nanometric Plunge-Cutting of BK7 and Fused Silica Glasses

PubMed Central

An, Qinglong; Ming, Weiwei; Chen, Ming

2015-01-01

Ductile cutting are most widely used in fabricating high-quality optical glass components to achieve crack-free surfaces. For ultra-precision machining of brittle glass materials, critical undeformed chip thickness (CUCT) commonly plays a pivotal role in determining the transition point from ductile cutting to brittle cutting. In this research, cutting characteristics in nanometric cutting of BK7 and fused silica glasses, including machined surface morphology, surface roughness, cutting force and specific cutting energy, were investigated with nanometric plunge-cutting experiments. The same cutting speed of 300 mm/min was used in the experiments with single-crystal diamond tool. CUCT was determined according to the mentioned cutting characteristics. The results revealed that 320 nm was found as the CUCT in BK7 cutting and 50 nm was determined as the size effect of undeformed chip thickness. A high-quality machined surface could be obtained with the undeformed chip thickness between 50 and 320 nm at ductile cutting stage. Moreover, no CUCT was identified in fused silica cutting with the current cutting conditions, and brittle-fracture mechanism was confirmed as the predominant chip-separation mode throughout the nanometric cutting operation. PMID:28788010

Experimental Investigation on Cutting Characteristics in Nanometric Plunge-Cutting of BK7 and Fused Silica Glasses.

PubMed

An, Qinglong; Ming, Weiwei; Chen, Ming

2015-03-27

Ductile cutting are most widely used in fabricating high-quality optical glass components to achieve crack-free surfaces. For ultra-precision machining of brittle glass materials, critical undeformed chip thickness (CUCT) commonly plays a pivotal role in determining the transition point from ductile cutting to brittle cutting. In this research, cutting characteristics in nanometric cutting of BK7 and fused silica glasses, including machined surface morphology, surface roughness, cutting force and specific cutting energy, were investigated with nanometric plunge-cutting experiments. The same cutting speed of 300 mm/min was used in the experiments with single-crystal diamond tool. CUCT was determined according to the mentioned cutting characteristics. The results revealed that 320 nm was found as the CUCT in BK7 cutting and 50 nm was determined as the size effect of undeformed chip thickness. A high-quality machined surface could be obtained with the undeformed chip thickness between 50 and 320 nm at ductile cutting stage. Moreover, no CUCT was identified in fused silica cutting with the current cutting conditions, and brittle-fracture mechanism was confirmed as the predominant chip-separation mode throughout the nanometric cutting operation.

Amorphous SiC as a structural layer in microbridge-based RF MEMS switches for use in software-defined radio

NASA Astrophysics Data System (ADS)

Parro, Rocco J.; Scardelletti, Maximilian C.; Varaljay, Nicholas C.; Zimmerman, Sloan; Zorman, Christian A.

2008-10-01

This paper reports an effort to develop amorphous silicon carbide (a-SiC) films for use in shunt capacitor RF MEMS microbridge-based switches. The films were deposited using methane and silane as the precursor gases. Switches were fabricated using 500 nm and 300 nm-thick a-SiC films to form the microbridges. Switches made from metallized 500 nm-thick SiC films exhibited favorable mechanical performance but poor RF performance. In contrast, switches made from metallized 300 nm-thick SiC films exhibited excellent RF performance but poor mechanical performance. Load-deflection testing of unmetallized and metallized bulk micromachined SiC membranes indicates that the metal layers have a small effect on the Young's modulus of the 500 nm and 300 nm-thick SiC MEMS. As for residual stress, the metal layers have a modest effect on the 500 nm-thick structures, but a significant affect on the residual stress in the 300 nm-thick structures.

Flexible single-layer ionic organic-inorganic frameworks towards precise nano-size separation

NASA Astrophysics Data System (ADS)

Yue, Liang; Wang, Shan; Zhou, Ding; Zhang, Hao; Li, Bao; Wu, Lixin

2016-02-01

Consecutive two-dimensional frameworks comprised of molecular or cluster building blocks in large area represent ideal candidates for membranes sieving molecules and nano-objects, but challenges still remain in methodology and practical preparation. Here we exploit a new strategy to build soft single-layer ionic organic-inorganic frameworks via electrostatic interaction without preferential binding direction in water. Upon consideration of steric effect and additional interaction, polyanionic clusters as connection nodes and cationic pseudorotaxanes acting as bridging monomers connect with each other to form a single-layer ionic self-assembled framework with 1.4 nm layer thickness. Such soft supramolecular polymer frameworks possess uniform and adjustable ortho-tetragonal nanoporous structure in pore size of 3.4-4.1 nm and exhibit greatly convenient solution processability. The stable membranes maintaining uniform porous structure demonstrate precisely size-selective separation of semiconductor quantum dots within 0.1 nm of accuracy and may hold promise for practical applications in selective transport, molecular separation and dialysis systems.

Toward Single Atom Chains with Exfoliated Tellurium.

PubMed

Churchill, Hugh O H; Salamo, Gregory J; Yu, Shui-Qing; Hironaka, Takayuki; Hu, Xian; Stacy, Jeb; Shih, Ishiang

2017-08-10

We demonstrate that the atom chain structure of Te allows it to be exfoliated as ultra-thin flakes and nanowires. Atomic force microscopy of exfoliated Te shows that thicknesses of 1-2 nm and widths below 100 nm can be exfoliated with this method. The Raman modes of exfoliated Te match those of bulk Te, with a slight shift (4 cm -1 ) due to a hardening of the A 1 and E modes. Polarized Raman spectroscopy is used to determine the crystal orientation of exfoliated Te flakes. These experiments establish exfoliation as a route to achieve nanoscale trigonal Te while also demonstrating the potential for fabrication of single atom chains of Te.

100μJ-level single frequency linearly-polarized nanosecond pulsed laser at 775 nm (Conference Presentation)

NASA Astrophysics Data System (ADS)

Shi, Wei; Fang, Qiang; Fan, Jingli; Cui, Xuelong; Zhang, Zhuo; Li, Jinhui; Zhou, Guoqing

2017-02-01

We report a single frequency, linearly polarized, near diffraction-limited, pulsed laser source at 775 nm by frequency doubling a single frequency nanosecond pulsed all fiber based master oscillator-power amplifier, seeded by a fiber coupled semiconductor DFB laser diode at 1550 nm. The laser diode was driven by a pulsed laser driver to generate 5 ns laser pulses at 260 Hz repetition rate with 50 pJ pulse energy. The pulse energy was boosted to 200 μJ using two stages of core-pumped fiber amplifiers and two stages of cladding-pumped fiber amplifiers. The multi-stage synchronous pulse pumping technique was adopted in the four stages of fiber amplifiers to mitigate the ASE. The frequency doubling is implemented in a single pass configuration using a periodically poled lithium niobate (PPLN) crystal. The crystal is 3 mm long, 1.4 mm wide, 1 mm thick, with a 19.36 μm domain period chosen for quasi-phase matching at 33°C. It was AR coated at both 1550 nm and 775 nm. The maximum pulse energy of 97 μJ was achieved when 189 μJ fundamental laser was launched. The corresponding conversion efficiency is about 51.3%. The pulse duration was measured to be 4.8 ns. So the peak power of the generated 775 nm laser pulses reached 20 kW. To the best of our knowledge, this is the first demonstration of a 100 μJ-level, tens of kilowatts-peak-power-level single frequency linearly polarized 775 nm laser based on the frequency doubling of the fiber lasers.

Nanocrystalline-to-amorphous transition in nanolaminates grown by low temperature atomic layer deposition and related mechanical properties

NASA Astrophysics Data System (ADS)

Raghavan, R.; Bechelany, M.; Parlinska, M.; Frey, D.; Mook, W. M.; Beyer, A.; Michler, J.; Utke, I.

2012-05-01

We report on a comprehensive structural and nanoindentation study of nanolaminates of Al2O3 and ZnO synthesized by atomic layer deposition (ALD). By reducing the bilayer thickness from 50 nm to below 1 nm, the nanocrystal size could be controlled in the nanolaminate structure. The softer and more compliant response of the multilayers as compared to the single layers of Al2O3 and ZnO is attributed to the structural change from nanocrystalline to amorphous at smaller bilayer thicknesses. It is also shown that ALD is a unique technique for studying the inverse Hall-Petch softening mechanism (E. Voce and D. Tabor, J. Inst. Metals 79(12), 465 (1951)) related to grain size effects in nanomaterials.

Microstructure evolution of the Ir-inserted Ni silicides with additional annealing

NASA Astrophysics Data System (ADS)

Yoon, Kijeong; Song, Ohsung

2009-02-01

Thermally-evaporated 10 nm-Ni/1 nm-Ir/(poly)Si structures were fabricated in order to investigate the thermal stability of Ir-inserted nickel silicide after additional annealing. The silicide samples underwent rapid thermal annealing at 300 ° C to 1200 ° C for 40 s, followed by 30 min annealing at the given RTA temperatures. Silicides suitable for the salicide process were formed on the top of the single crystal and polycrystalline silicon substrates, mimicking actives and gates. The sheet resistance was measured using a four-point probe. High resolution x-ray diffraction and Auger depth profiling were used for phase and chemical composition analysis, respectively. Transmission electron microscope and scanning probe microscope were used to determine the cross-section structure and surface roughness. The silicide, which formed on single crystal silicon substrate with surface agglomeration after additional annealing, could defer the transformation of Ni(Ir)Si to Ni(Ir)Si2 and was stable at temperatures up to 1200 °C. Moreover, the silicide thickness doubled. There were no outstanding changes in the silicide thickness on polycrystalline silicon. However, after additional annealing, the silicon-silicide mixing became serious and showed high resistance at temperatures >700 °C. Auger depth profiling confirmed the increased thickness of the silicide layers after additional annealing without a change in composition. For a single crystal silicon substrate, the sheet resistance increased slightly due to the significant increases in surface roughness caused by surface agglomeration after additional annealing. Otherwise, there were almost no changes in surface roughness on the polycrystalline silicon substrate. The Ir-inserted nickel monosilicide was able to maintain a low resistance in a wide temperature range and is considered suitable for the nano-thick silicide process.

Gas diffusion ultrabarriers on polymer substrates using Al2O3 atomic layer deposition and SiN plasma-enhanced chemical vapor deposition

NASA Astrophysics Data System (ADS)

Carcia, P. F.; McLean, R. S.; Groner, M. D.; Dameron, A. A.; George, S. M.

2009-07-01

Thin films grown by Al2O3 atomic layer deposition (ALD) and SiN plasma-enhanced chemical vapor deposition (PECVD) have been tested as gas diffusion barriers either individually or as bilayers on polymer substrates. Single films of Al2O3 ALD with thicknesses of ≥10 nm had a water vapor transmission rate (WVTR) of ≤5×10-5 g/m2 day at 38 °C/85% relative humidity (RH), as measured by the Ca test. This WVTR value was limited by H2O permeability through the epoxy seal, as determined by the Ca test for the glass lid control. In comparison, SiN PECVD films with a thickness of 100 nm had a WVTR of ˜7×10-3 g/m2 day at 38 °C/85% RH. Significant improvements resulted when the SiN PECVD film was coated with an Al2O3 ALD film. An Al2O3 ALD film with a thickness of only 5 nm on a SiN PECVD film with a thickness of 100 nm reduced the WVTR from ˜7×10-3 to ≤5×10-5 g/m2 day at 38 °C/85% RH. The reduction in the permeability for Al2O3 ALD on the SiN PECVD films was attributed to either Al2O3 ALD sealing defects in the SiN PECVD film or improved nucleation of Al2O3 ALD on SiN.

Quantum oscillations in strong magnetic fields, berry phase, and superconductivity in three-dimensional topological Bi{sub 2–x}Cu{sub x}Se{sub 3} insulators

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

Vedeneev, S. I., E-mail: vedeneev@sci.lebedev.ru; Knyazev, D. A.; Prudkoglyad, V. A.

2015-07-15

Two-dimensional (2D) Shubnikov–de Haas oscillations and 2D Hall oscillations are observed in 3D copper-doped Bi{sub 2}Se{sub 3} single crystals in magnetic fields up to 19.5 T at temperatures down to 0.3 K. Three samples with a high bulk carrier concentration (n ≈ 10{sup 19}–10{sup 20} cm{sup –3}) are studied. The rotation of the samples in a magnetic field shows that these oscillations are related to numerous parallel 2D conducting channels 1–5 nm thick. Their basic kinetic parameters are found. Quantized Hall resistance R{sub xy} is detected in 1-nm-thick 2D conducting channels at high fields. The distance Δ(1/R{sub xy}) between themore » steps in the field dependence of 1/R{sub xy} is found to be constant for different Landau levels, 1.3e{sup 2}/h per 1-nm-thick layer. The constructed fan diagrams of 2D Landau levels for various angles of sample inclination with respect to the magnetic field direction allowed us to conclude that the Berry phase in the 2D conducting channels is γ ≈ π and independent of the magnetic field direction. When studying the angular dependence of upper resistive critical magnetic field H{sub c2} in one of the superconducting samples, we showed that it can be considered as a bulk superconductor consisting of superconducting layers with an effective thickness of about 50 nm.« less

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.

X-ray diffraction and Raman investigations of thickness dependent stress effects on Pb(ZrxTi1-x)O3 thin films

NASA Astrophysics Data System (ADS)

Lappalainen, Jyrki; Lantto, Vilho; Frantti, Johannes; Hiltunen, Jussi

2006-06-01

Microstructure, film orientation, and optical transmission spectra of polycrystalline Nd-modified Pb(ZrxTi1-x)O3 films were studied as a function of film thickness. Pulsed laser deposition was used for the fabrication of films with thickness from 80to465nm on single-crystal MgO(100) substrates. Raman spectroscopy, x-ray diffraction, and spectrophotometry measurements were utilized in the film characterization. With the decreasing film thickness, films first oriented with c axis perpendicular to film surface, and then, after some critical thickness, changed to a-axis orientation. At the same time, compressive stress increased up to 1.3GPa and a clear blueshift of the optical absorption edge was found in transmission spectra.

Real time measurements of surface growth evolution in magnetron sputtered single crystal Mo/V superlattices using in situ reflection high energy electron diffraction analysis

NASA Astrophysics Data System (ADS)

Svedberg, E. B.; Birch, J.; Edvardsson, C. N. L.; Sundgren, J.-E.

1999-07-01

The use of video recording of reflection high energy electron diffraction (RHEED) patterns for assessing the dynamic evolution of the surface morphology and crystallinity during growth was evaluated. As an example, Mo/V(001) superlattices with varying layer thickness (with periods Λ of 2.5 to 8.9 nm and a constant Mo:V ratio of 1:1) were examined. During the deposition, changes from two- to three-dimensional growth were observed in situ. From prior transmission electron microscopy (TEM) and X-ray diffraction (XRD) studies, it is known that this transition is associated with a critical thickness and concurrent roughening of the V layer. Video recording and subsequent image and data processing allowed the surface morphology to be continuously followed during growth. Post-growth analyses of the recorded data provided the evolution of surface lattice parameters and short range [1-2 monolayer (ML)] surface roughnesses with a time resolution of 200-400 ms (0.02-0.04 nm thickness resolution). During growth of Mo, a smoothening effect could be observed while the growth of V evidently increased the surface roughness from 1 to 2 ML. Furthermore, the onset of coherency strain relaxation of the topmost growing layers was observed to occur at 2.0-2.5 nm layer thicknesses for both materials, which is in qualitative agreement with theoretical predictions.

A simplified method for generating periodic nanostructures by interference lithography without the use of an anti-reflection coating

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

Kapon, Omree; Muallem, Merav; Palatnik, Alex

Interference lithography has proven to be a useful technique for generating periodic sub-diffraction limited nanostructures. Interference lithography can be implemented by exposing a photoresist polymer to laser light using a two-beam arrangement or more simply a one beam configuration based on a Lloyd's Mirror Interferometer. For typical photoresist layers, an anti-reflection coating must be deposited on the substrate to prevent adverse reflections from cancelling the holographic pattern of the interfering beams. For silicon substrates, such coatings are typically multilayered and complex in composition. By thinning the photoresist layer to a thickness well below the quarter wavelength of the exposing beam,more » we demonstrate that interference gratings can be generated without an anti-reflection coating on the substrate. We used ammonium dichromate doped polyvinyl alcohol as the positive photoresist because it provides excellent pinhole free layers down to thicknesses of 40 nm, and can be cross-linked by a low-cost single mode 457 nm laser, and can be etched in water. Gratings with a period of 320 nm and depth of 4 nm were realized, as well as a variety of morphologies depending on the photoresist thickness. This simplified interference lithography technique promises to be useful for generating periodic nanostructures with high fidelity and minimal substrate treatments.« less

Zebrafish cardiac muscle thick filaments: isolation technique and three-dimensional structure.

PubMed

González-Solá, Maryví; Al-Khayat, Hind A; Behra, Martine; Kensler, Robert W

2014-04-15

To understand how mutations in thick filament proteins such as cardiac myosin binding protein-C or titin, cause familial hypertrophic cardiomyopathies, it is important to determine the structure of the cardiac thick filament. Techniques for the genetic manipulation of the zebrafish are well established and it has become a major model for the study of the cardiovascular system. Our goal is to develop zebrafish as an alternative system to the mammalian heart model for the study of the structure of the cardiac thick filaments and the proteins that form it. We have successfully isolated thick filaments from zebrafish cardiac muscle, using a procedure similar to those for mammalian heart, and analyzed their structure by negative-staining and electron microscopy. The isolated filaments appear well ordered with the characteristic 42.9 nm quasi-helical repeat of the myosin heads expected from x-ray diffraction. We have performed single particle image analysis on the collected electron microscopy images for the C-zone region of these filaments and obtained a three-dimensional reconstruction at 3.5 nm resolution. This reconstruction reveals structure similar to the mammalian thick filament, and demonstrates that zebrafish may provide a useful model for the study of the changes in the cardiac thick filament associated with disease processes. Copyright © 2014 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Fluorocarbon-based single-layer resist for 157-nm lithography

NASA Astrophysics Data System (ADS)

Song, Ki-Yong; Yoon, Kwang-Sub; Choi, Sang-Jun; Woo, Sang-Gyun; Han, Woo-Sung; Lee, Jae-Jun; Lee, Sang-Kyun; Noh, Chang-Ho; Honda, Kenji

2002-07-01

We have designed and synthesized a number of unique polymer systems composed of acrylate and styrene even though it had moderate transparency. Our first model of 157nm photoresist was based on a (alpha) trifluoromethylacrylate and styrene bearing a pendent hexafluoroisopropanol with pentafluoroisopropyl t-butyl carbonate (PFITBC) as the transparent enhancer and acid labile compound. PFITBC was obtained from perfluorinated enolate with di-t-butyl carbonate with high yield. All of the absorbance of our system ranged over 3.0~3.4micrometers -1 for base resin, which corresponded to a resist thickness of 110~125 nm at the optical density of 0.4. We have formulated several resists based on these polymers and these formulations have shown high resolution and contrast at 248 nm. We were able to obtain 240nm 1:1 image when exposed at 248 nm by a Nikon stepper with 0.45NA. To overcome the weak etch resistance with thin thickness film, we investigated the vapor phase silylation treatment (SILYAL) in which the treated pattern was more persistent against the O2 plasma and turned to smoother surface. DMSMDA with Bi(DMA)MS of 30-40 wt% showed not only good control resist flow but also the improvement of line-edge roughness. Our results suggested that a facile approach to fluorine incorporated resin with SILYAL process can accelerate the 157nm lithography.

Profilometry of thin films on rough substrates by Raman spectroscopy

PubMed Central

Ledinský, Martin; Paviet-Salomon, Bertrand; Vetushka, Aliaksei; Geissbühler, Jonas; Tomasi, Andrea; Despeisse, Matthieu; De Wolf , Stefaan; Ballif , Christophe; Fejfar, Antonín

2016-01-01

Thin, light-absorbing films attenuate the Raman signal of underlying substrates. In this article, we exploit this phenomenon to develop a contactless thickness profiling method for thin films deposited on rough substrates. We demonstrate this technique by probing profiles of thin amorphous silicon stripes deposited on rough crystalline silicon surfaces, which is a structure exploited in high-efficiency silicon heterojunction solar cells. Our spatially-resolved Raman measurements enable the thickness mapping of amorphous silicon over the whole active area of test solar cells with very high precision; the thickness detection limit is well below 1 nm and the spatial resolution is down to 500 nm, limited only by the optical resolution. We also discuss the wider applicability of this technique for the characterization of thin layers prepared on Raman/photoluminescence-active substrates, as well as its use for single-layer counting in multilayer 2D materials such as graphene, MoS2 and WS2. PMID:27922033

Exploring the Nature of Cellulose Microfibrils

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

Su, Ying; Burger, Christian; Ma, Hongyang

2015-03-20

Ultrathin cellulose microfibril fractions were extracted from spruce wood powder using combined delignification, TEMPO-catalyzed oxidation, and sonication processes. Small-angle X-ray scattering of these microfibril fractions in a “dilute” aqueous suspension (concentration 0.077 wt %) revealed that their shape was in the form of nanostrip with 4 nm width and only about 0.5 nm thicknesses. We found that these dimensions were further confirmed by TEM and AFM measurements. The 0.5 nm thickness implied that the nanostrip could contain only a single layer of cellulose chains. At a higher concentration (0.15 wt %), SAXS analysis indicated that these nanostrips aggregated into amore » layered structure. The X-ray diffraction of samples collected at different preparation stages suggested that microfibrils were delaminated along the (110) planes from the Iβ cellulose crystals. Moreover, the degree of oxidation and solid-state 13C NMR characterizations indicated that, in addition to the surface molecules, some inner molecules of microfibrils were also oxidized, facilitating the delamination into cellulose nanostrips.« less

Exploring the nature of cellulose microfibrils.

PubMed

Su, Ying; Burger, Christian; Ma, Hongyang; Chu, Benjamin; Hsiao, Benjamin S

2015-04-13

Ultrathin cellulose microfibril fractions were extracted from spruce wood powder using combined delignification, TEMPO-catalyzed oxidation, and sonication processes. Small-angle X-ray scattering of these microfibril fractions in a "dilute" aqueous suspension (concentration 0.077 wt %) revealed that their shape was in the form of nanostrip with 4 nm width and only about 0.5 nm thicknesses. These dimensions were further confirmed by TEM and AFM measurements. The 0.5 nm thickness implied that the nanostrip could contain only a single layer of cellulose chains. At a higher concentration (0.15 wt %), SAXS analysis indicated that these nanostrips aggregated into a layered structure. The X-ray diffraction of samples collected at different preparation stages suggested that microfibrils were delaminated along the (11̅0) planes from the Iβ cellulose crystals. The degree of oxidation and solid-state (13)C NMR characterizations indicated that, in addition to the surface molecules, some inner molecules of microfibrils were also oxidized, facilitating the delamination into cellulose nanostrips.

Axially adjustable magnetic properties in arrays of multilayered Ni/Cu nanowires with variable segment sizes

NASA Astrophysics Data System (ADS)

Shirazi Tehrani, A.; Almasi Kashi, M.; Ramazani, A.; Montazer, A. H.

2016-07-01

Arrays of multilayered Ni/Cu nanowires (NWs) with variable segment sizes were fabricated into anodic aluminum oxide templates using a pulsed electrodeposition method in a single bath for designated potential pulse times. Increasing the pulse time between 0.125 and 2 s in the electrodeposition of Ni enabled the formation of segments with thicknesses ranging from 25 to 280 nm and 10-110 nm in 42 and 65 nm diameter NWs, respectively, leading to disk-shaped, rod-shaped and/or near wire-shaped geometries. Using hysteresis loop measurements at room temperature, the axial and perpendicular magnetic properties were investigated. Regardless of the segment geometry, the axial coercivity and squareness significantly increased with increasing Ni segment thickness, in agreement with a decrease in calculated demagnetizing factors along the NW length. On the contrary, the perpendicular magnetic properties were found to be independent of the pulse times, indicating a competition between the intrawire interactions and the shape demagnetizing field.

Demonstration of high-energy 2 omega (526.5 nm) operation on the National Ignition Facility Laser System.

PubMed

Heestand, G M; Haynam, C A; Wegner, P J; Bowers, M W; Dixit, S N; Erbert, G V; Henesian, M A; Hermann, M R; Jancaitis, K S; Knittel, K; Kohut, T; Lindl, J D; Manes, K R; Marshall, C D; Mehta, N C; Menapace, J; Moses, E; Murray, J R; Nostrand, M C; Orth, C D; Patterson, R; Sacks, R A; Saunders, R; Shaw, M J; Spaeth, M; Sutton, S B; Williams, W H; Widmayer, C C; White, R K; Whitman, P K; Yang, S T; Van Wonterghem, B M

2008-07-01

A single beamline of the National Ignition Facility (NIF) has been operated at a wavelength of 526.5 nm (2 omega) by frequency converting the fundamental 1053 nm (1 omega) wavelength with an 18.2 mm thick type-I potassium dihydrogen phosphate (KDP) second-harmonic generator (SHG) crystal. Second-harmonic energies of up to 17.9 kJ were measured at the final optics focal plane with a conversion efficiency of 82%. For a similarly configured 192-beam NIF, this scales to a total 2 omega energy of 3.4 MJ full NIF equivalent (FNE).

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

Subsurface optical stimulation of rat prostate cavernous nerves using a continuous wave, single mode, 1490 nm diode laser

NASA Astrophysics Data System (ADS)

Tozburun, Serhat; Stahl, Charlotte S. D.; Hutchens, Thomas C.; Lagoda, Gwen A.; Burnett, Arthur L.; Fried, Nathaniel M.

2013-03-01

Successful identification of the cavernous nerves (CN's) during radical prostatectomy requires detection of the CN's through a thin layer of overlying fascia. This study explores the 1490 nm infrared (IR) diode laser wavelength for rapid and deep subsurface CN stimulation in a rat model, in vivo. A 150-mW, 1490-nm diode laser providing an optical penetration depth of 520 μm was used to stimulate the CN's in 8 rats through a single mode fiber optic probe with 1-mm-diameter spot and 15 s irradiation time. Successful ONS was judged by an intracavernous pressure response (ICP) in the rat penis. Subsurface ONS at 1490 nm was also compared with previous studies using 1455 and 1550 nm IR diode laser wavelengths. ONS was observed through fascia layers up to 380 μm thick using an incident laser power of 50 mW. ICP response times as short as 4.6 +/- 0.2 s were recorded using higher laser powers bust still below the nerve damage threshold. The 1490-nm diode laser represents a compact, low cost, high power, and high quality infrared light source for use in ONS. This wavelength provides deeper optical penetration than 1455 nm and more rapid and efficient nerve stimulation than 1550 nm.

Structural and optical properties of ZnO thin films prepared by RF sputtering at different thicknesses

NASA Astrophysics Data System (ADS)

Hammad, Ahmed H.; Abdel-wahab, M. Sh.; Vattamkandathil, Sajith; Ansari, Akhalakur Rahman

2018-07-01

Hexagonal nanocrystallites of ZnO in the form of thin films were prepared by radio frequency sputtering technique. X-ray diffraction analysis reveals two prominent diffraction planes (002) and (103) at diffraction angles around 34.3 and 62.8°, respectively. The crystallite size increases through (103) plane from 56.1 to 64.8 Å as film thickness changed from 31 nm up to 280 nm while crystallites growth through (002) increased from 124 to 136 Å as film thickness varies from 31 to 107 nm and dropped to 115.8 Å at thickness 280 nm. The particle shape changes from spherical to longitudinal form. The particle size is 25 nm for films of thickness below 107 nm and increases at higher thicknesses (134 and 280 nm) from 30 to 40 nm, respectively. Optical band gap is deduced to be direct with values varied from 3.22 to 3.28 eV and the refractive index are evaluated based on the optical band values according to Moss, Ravindra-Srivastava, and Dimitrov-Sakka models. All refractive index models gave values around 2.3.

Carbon Nanotube Microarrays Grown on Nanoflake Substrates

NASA Technical Reports Server (NTRS)

Schmidt, Howard K.; Hauge, Robert H.; Pint, Cary; Pheasant, Sean

2013-01-01

This innovation consists of a new composition of matter where single-walled carbon nanotubes (SWNTs) are grown in aligned arrays from nanostructured flakes that are coated in Fe catalyst. This method of growth of aligned SWNTs, which can yield well over 400 percent SWNT mass per unit substrate mass, exceeds current yields for entangled SWNT growth. In addition, processing can be performed with minimal wet etching treatments, leaving aligned SWNTs with superior properties over those that exist in entangled mats. The alignment of the nanotubes is similar to that achieved in vertically aligned nanotubes, which are called "carpets. " Because these flakes are grown in a state where they are airborne in a reactor, these flakes, after growing SWNTs, are termed "flying carpets. " These flakes are created in a roll-to-roll evaporator system, where three subsequent evaporations are performed on a 100-ft (approx. =30-m) roll of Mylar. The first layer is composed of a water-soluble "release layer, " which can be a material such as NaCl. After depositing NaCl, the second layer involves 40 nm of supporting layer material . either Al2O3 or MgO. The thickness of the layer can be tuned to synthesize flakes that are larger or smaller than those obtained with a 40-nm deposition. Finally, the third layer consists of a thin Fe catalyst layer with a thickness of 0.5 nm. The thickness of this layer ultimately determines the diameter of SWNT growth, and a layer that is too thick will result in the growth of multiwalled carbon nanotubes instead of single-wall nanotubes. However, between a thickness of 0.5 nm to 1 nm, single-walled carbon nanotubes are known to be the primary constituent. After this three-layer deposition process, the Mylar is rolled through a bath of water, which allows catalyst-coated flakes to detach from the Mylar. The flakes are then collected and dried. The method described here for making such flakes is analogous to that which is used to make birefringent ink that is coated on U.S. currency. After deposition, the growth is carried out in a hot-filament chemical vapor deposition apparatus. A tungsten hot filament placed in the flow of H2 at a temperature greater than 1,600 C creates atomic hydrogen, which serves to reduce the Fe catalyst into a metallic state. The catalyst can now precipitate SWNTs in the presence of growth gases. The gases used for the experiments reported are C2H2, H2O, and H2, at rates of 2, 2, and 400 standard cubic centimeters per minute (sccm), respectively. In order to retain the flakes, a cage is constructed by spot welding stainless steel or copper mesh to form an enclosed area, in which the flakes are placed prior to growth. This allows growth gases and atomic hydrogen to reach the flakes, but does not allow the flakes, which rapidly nucleate SWNTs, to escape from the cage.

Morphology and stability in a half-metallic ferromagnetic CrO 2 compound of nanoparticles synthesized via a polymer precursor

NASA Astrophysics Data System (ADS)

Biswas, S.; Ram, S.

2004-11-01

Nanoparticles of stable CrO2 of a half-metallic ferromagnet are synthesized with a novel chemical method involving a Cr4+-polymer composite precursor. A single phase CrO2 of D4h 14 : P42 / mnm tetragonal crystal structure (lattice parameters a = 0.4250 and c = 0.3190 nm) lies after firing the precursor at 350 °C for 1 h in air. Microstructure reveals single domain CrO2 particles of thin platelets (aspect ratio ∼1) of average 50 nm diameter and 35 nm thickness. In air, unless heating at temperatures above 500 °C, no due CrO2 → Cr2O3 phase transformation encounters. The results are presented in terms of X-ray diffraction and thermal or thermogravimetric analysis of precursor and derived CrO2 powder.

Characteristics of blue organic light emitting diodes with different thick emitting layers

NASA Astrophysics Data System (ADS)

Li, Chong; Tsuboi, Taiju; Huang, Wei

2014-08-01

We fabricated blue organic light emitting diodes (called blue OLEDs) with emitting layer (EML) of diphenylanthracene derivative 9,10-di(2-naphthyl)anthracene (ADN) doped with blue-emitting DSA-ph (1-4-di-[4-(N,N-di-phenyl)amino]styryl-benzene) to investigate how the thickness of EML and hole injection layer (HIL) influences the electroluminescence characteristics. The driving voltage was observed to increase with increasing EML thickness from 15 nm to 70 nm. The maximum external quantum efficiency of 6.2% and the maximum current efficiency of 14 cd/A were obtained from the OLED with 35 nm thick EML and 75 nm thick HIL. High luminance of 120,000 cd/m2 was obtained at 7.5 V from OLED with 15 nm thick EML.

Single-longitudinal-mode Er:GGG microchip laser operating at 2.7  μm.

PubMed

You, Zhenyu; Wang, Yan; Xu, Jinlong; Zhu, Zhaojie; Li, Jianfu; Wang, Hongyan; Tu, Chaoyang

2015-08-15

We reported on a diode-end-pumped single-longitudinal-mode microchip laser using a 600-μm-thick Er:GGG crystal at ∼2.7  μm, generating a maximum output power of 50.8 mW and the maximum pulsed energy of 0.306 mJ, with repetition rates of pumping light of 300, 200, and 100 Hz, respectively. The maximum slope efficiency of the laser was 20.1%. The laser was operated in a single-longitudinal mode centered at about 2704 nm with a FWHM of 0.42 nm. The laser had a fundamental beam profile and the beam quality parameter M(2) was measured as 1.46. These results indicate that the Er:GGG microchip laser is a potential compact mid-infrared laser source.

Development of Ceramics with Highly Organized Microstructures

DTIC Science & Technology

2007-03-01

time for reviev AFRL- SR -AR-TR-08_00 6 8 gathering and maintaining the data needed, and completing and reviewing the collection of information. Send...formation the single crystal substrate was cleaned prior to sputter coating a 100 nm thick nickel seed layer on the polished surface. A positive photoresist...growth of the single crystal was accomplished without an interfacial layer and with no applied load. The main difference was Ba /Ti ratio of the starting

All-optical measurement of interlayer exchange coupling in Fe/Pt/FePt thin films

NASA Astrophysics Data System (ADS)

Berk, C.; Ganss, F.; Jaris, M.; Albrecht, M.; Schmidt, H.

2018-01-01

Time Resolved Magneto Optic Kerr Effect spectroscopy was used to all-optically study the dynamics in exchange coupled Fe(10 nm)/Pt(x = 0-5 nm)/FePt (10 nm) thin films. As the Pt spacer decreases, the effective magnetization of the layers is seen to evolve towards the strong coupling limit where the two films can be described by a single effective magnetization. The coupling begins at x = 1.5 nm and reaches a maximum exchange coupling constant of 2.89 erg/cm2 at x = 0 nm. The films are ferromagnetically coupled at all Pt thicknesses in the exchange coupled regime (x ≤ 1.5 nm). A procedure for extracting the interlayer exchange constant by measuring the magnetic precession frequencies at multiple applied fields and angles is outlined. The dynamics are well reproduced using micromagnetic simulations.

Intrinsic superconducting transport properties of ultra-thin Fe1+ y Te0.6Se0.4 microbridges

NASA Astrophysics Data System (ADS)

Sun, HanCong; Lv, YangYang; Lu, DaChuan; Yang, ZhiBao; Zhou, XianJing; Hao, LuYao; Xing, XiangZhuo; Zou, Wei; Li, Jun; Shi, ZhiXiang; Xu, WeiWei; Wang, HuaBing; Wu, PeiHeng

2017-11-01

We investigated the superconducting properties of Fe1+ y Te0.6Se0.4 single-crystalline microbridges with a width of 4 μm and thicknesses ranging from 20.8 to 136.2 nm. The temperature-dependent in-plane resistance of the bridges exhibited a type of metal-insulator transition in the normal state. The critical current density ( J c) of the microbridge with a thickness of 136.2 nm was 82.3 kA/cm2 at 3K and reached 105 kA/cm2 after extrapolation to T = 0 K. The current versus voltage characteristics of the microbridges showed a Josephson-like behavior with an obvious hysteresis. These results demonstrate the potential application of ultra-thin Fe-based microbridges in superconducting electronic devices such as bolometric detectors.

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

He Liang; Xiu Faxian; Huang Guan

In this paper, we report the epitaxial growth of Bi{sub 2}Se{sub 3} thin films on Si (111) substrate, using molecular beam epitaxy (MBE). We show that the as-grown samples have good crystalline quality, and their surfaces exhibit terracelike quintuple layers. Angel-resolved photoemission experiments demonstrate single-Dirac-conelike surface states. These results combined with the temperature- and thickness-dependent magneto-transport measurements, suggest the presence of a shallow impurity band. Below a critical temperature of {approx}100K, the surface states of a 7 nm thick film contribute up to 50% of the total conduction.

Electron microscopy of whole cells in liquid with nanometer resolution

PubMed Central

de Jonge, N.; Peckys, D. B.; Kremers, G. J.; Piston, D. W.

2009-01-01

Single gold-tagged epidermal growth factor (EGF) molecules bound to cellular EGF receptors of fixed fibroblast cells were imaged in liquid with a scanning transmission electron microscope (STEM). The cells were placed in buffer solution in a microfluidic device with electron transparent windows inside the vacuum of the electron microscope. A spatial resolution of 4 nm and a pixel dwell time of 20 μs were obtained. The liquid layer was sufficiently thick to contain the cells with a thickness of 7 ± 1 μm. The experimental findings are consistent with a theoretical calculation. Liquid STEM is a unique approach for imaging single molecules in whole cells with significantly improved resolution and imaging speed over existing methods. PMID:19164524

Ultra-hard AlMgB14 coatings fabricated by RF magnetron sputtering from a stoichiometric target

NASA Astrophysics Data System (ADS)

Grishin, A. M.; Khartsev, S. I.; Böhlmark, J.; Ahlgren, M.

2015-01-01

For the first time hard aluminum magnesium boride films were fabricated by RF magnetron sputtering from a single stoichiometric ceramic AlMgB14 target. Optimized processing conditions (substrate temperature, target sputtering power and target-to-substrate distance) enable fabrication of stoichiometric in-depth compositionally homogeneous films with the peak values of nanohardness 88 GPa and Young's modulus 517 GPa at the penetration depth of 26 nm and, respectively, 35 and 275 GPa at 200 nm depth in 2 μm thick film.

Large-scale synthesis and photoluminescence of single-crystalline β-Ga 2O 3 nanobelts

NASA Astrophysics Data System (ADS)

Geng, Baoyou; Zhang, Lide; Meng, Guowen; Xie, Ting; Peng, Xinsheng; Lin, Yu

2003-12-01

Gallium oxide ( β-Ga 2O 3) nanobelts were synthesized on a large scale by a simple thermal evaporation method from a mixture of gallium (Ga) and silicon oxide (SiO 2) nanopowder at 850°C in argon atmosphere, which is 200-300°C less than that of thermal evaporation methods reported formerly. The nanobelts had a uniform single-crystal monoclinic structure with width ranging from 50 to 300 nm, thickness about 10-20 nm and lengths up to several tens or hundreds of micrometers. The growth of β-Ga 2O 3 nanobelts is controlled by vapor-solid crystal growth mechanism. Photoluminescence measurement shows that the nanobelts have one broad, strong blue emission and a UV emission.

High performance novel gadolinium doped ceria/yttria stabilized zirconia/nickel layered and hybrid thin film anodes for application in solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Garcia-Garcia, F. J.; Beltrán, A. M.; Yubero, F.; González-Elipe, A. R.; Lambert, R. M.

2017-09-01

Magnetron sputtering under oblique angle deposition was used to produce Ni-containing ultra thin film anodes comprising alternating layers of gadolinium doped ceria (GDC) and yttria stabilized zirconia (YSZ) of either 200 nm or 1000 nm thickness. The evolution of film structure from initial deposition, through calcination and final reduction was examined by XRD, SEM, TEM and TOF-SIMS. After subsequent fuel cell usage, the porous columnar architecture of the two-component layered thin film anodes was maintained and their resistance to delamination from the underlying YSZ electrolyte was superior to that of corresponding single component Ni-YSZ and Ni-GDC thin films. Moreover, the fuel cell performance of the 200 nm layered anodes compared favorably with conventional commercially available thick anodes. The observed dependence of fuel cell performance on individual layer thicknesses prompted study of equivalent but more easily fabricated hybrid anodes consisting of simultaneously deposited Ni-GDC and Ni-YSZ, which procedure resulted in exceptionally intimate mixing and interaction of the components. The hybrids exhibited very unusual and favorable Isbnd V characteristics, along with exceptionally high power densities at high currents. Their discovery is the principal contribution of the present work.

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

Zheng, Pengyuan; Ozsdolay, Brian D.; Gall, Daniel, E-mail: galld@rpi.edu

Smooth single crystal W(001) layers were grown on MgO(001) substrates by magnetron sputtering at 900 °C. X-ray diffraction ω–2θ scans, ω-rocking curves, pole figures, and reciprocal space maps indicate a 45°-rotated epitaxial relationship: (001){sub W}‖(001){sub MgO} and [010]{sub W}‖[110]{sub MgO}, and a relaxed lattice constant of 3.167 ± 0.001 nm. A residual in-plane biaxial compressive strain is primarily attributed to differential thermal contraction after growth and decreases from −0.012 ± 0.001 to −0.001 ± 0.001 with increasing layer thickness d = 4.8–390 nm, suggesting relaxation during cooling by misfit dislocation growth through threading dislocation glide. The in-plane x-ray coherence length increases from 3.4 to 33.6 nm for d = 4.8–390 nm, while the out-of-plane x-raymore » coherence length is identical to the layer thickness for d ≤ 20 nm, but is smaller than d for d ≥ 49.7 nm, indicating local strain variations along the film growth direction. X-ray reflectivity analyses indicate that the root-mean-square surface roughness increases from 0.50 ± 0.05 to 0.95 ± 0.05 nm for d = 4.8–19.9 nm, suggesting a roughness exponent of 0.38, but remains relatively constant for d > 20 nm with a roughness of 1.00 ± 0.05 nm at d = 47.9 nm.« less

Electron Scattering at Surfaces of Epitaxial Metal Layers

NASA Astrophysics Data System (ADS)

Chawla, Jasmeet Singh

In the field of electron transport in metal films and wires, the 'size effect' refers to the increase in the resistivity of the films and wires as their critical dimensions (thickness of film, width and height of wires) approach or become less than the electron mean free path lambda, which is, for example, 39 nm for bulk copper at room temperature. This size-effect is currently of great concern to the semiconductor industry because the continued downscaling of feature sizes has already lead to Cu interconnect wires in this size effect regime, with a reported 2.5 times higher resistivity for 40 nm wide Cu wires than for bulk Cu. Silver is a possible alternate material for interconnect wires and titanium nitride is proposed as a gate metal in novel field-effect-transistors. Therefore, it is important to develop an understanding of how the growth, the surface morphology, and the microstructure of ultrathin (few nanometers) Cu, Ag and TiN layers affect their electrical properties. This dissertation aims to advance the scientific knowledge of electron scattering at surfaces (external surfaces and grain boundaries), that are, the primary reasons for the size-effect in metal conductors. The effect of surface and grain boundary scattering on the resistivity of Cu thin films and nanowires is separately quantified using (i) in situ transport measurements on single-crystal, atomically smooth Cu(001) layers, (ii) textured polycrystalline Cu(111) layers and patterned wires with independently varying grain size, thickness and line width, and (iii) in situ grown interfaces including Cu-Ta, Cu-MgO, Cu-vacuum and Cu-oxygen. In addition, the electron surface scattering is also measured in situ for single-crystal Ag(001), (111) twinned epitaxial Ag(001), and single-crystal TiN(001) layers. Cu(001), Ag(001), and TiN(001) layers with a minimum continuous thickness of 4, 3.5 and 1.8 nm, respectively, are grown by ultra-high vacuum magnetron sputter deposition on MgO(001) substrates with and without thin epitaxial TiN(001) wetting layers and are studied for structure, crystalline quality, surface morphology, density and composition by a combination of x-ray diffraction theta-2theta scans, o-rocking curves, pole figures, reciprocal space mapping, Rutherford backscattering, x-ray reflectometry and transmission electron microscopy. The TiN(001) surface suppresses Cu and Ag dewetting, yielding lower defect density, no twinning, and smaller surface roughness than if grown on MgO(001). Textured polycrystalline Cu(111) layers 25-50-nm-thick are deposited on a stack of 7.5-nm-Ta on SiO2/Si(001), and subsequent in situ annealing at 350°C followed by sputter etching in Ar plasma yields Cu layers with independently variable thickness and grain size. Cu nanowires, 75 to 350 nm wide, are fabricated from Cu layers with different average grain size using a subtractive patterning process. In situ electron transport measurements at room temperature in vacuum and at 77 K in liquid nitrogen for single-crystal Cu and Ag layers is consistent with the Fuchs-Sondheimer (FS) model and indicates specular scattering at the metal-vacuum boundary with an average specularity parameter p = 0.8 and 0.6, respectively. In contrast, layers measured ex situ show diffuse surface scattering due to sub-monolayer oxidation. Also, addition of Ta atoms on Cu(001) surface perturbs the smooth interface potential and results in completely diffuse scattering at the Cu-Ta interface, and in turn, a higher resistivity of single-crystal Cu layers. In situ exposure of Cu(001) layers to O2 between 10 -3 and 105 Pa-s results in a sequential increase, decrease and increase of the electrical resistance which is attributed to specular surface scattering for clean Cu(001) and for surfaces with a complete adsorbed monolayer, but diffuse scattering at partial coverage and after chemical oxidation. Electron transport measurements for polycrystalline Cu layers and wires show a 10-15% and 7-9% decrease in resistivity, respectively, when increasing the average lateral grain size by a factor of 1.8. The maximum resistivity decrease that can be achieved by increasing the grain size of polycrystalline Cu layers with an average grain size approximately ˜2.5x the layer thickness is 20-26%.

Tailoring Curie temperature and magnetic anisotropy in ultrathin Pt/Co/Pt films

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

Parakkat, Vineeth Mohanan; Ganesh, K. R.; Anil Kumar, P. S., E-mail: anil@physics.iisc.ernet.in

The dependence of perpendicular magnetization and Curie temperature (T{sub c}) of Pt/Co/Pt thin films on the thicknesses of Pt seed (Pt{sub s}) and presence of Ta buffer layer has been investigated in this work. Pt and Co thicknesses were varied between 2 to 8 nm and 0.35 to 1.31 nm (across the spin reorientation transition thickness) respectively and the T{sub c} was measured using SQUID magnetometer. We have observed a systematic dependence of T{sub c} on the thickness of Pt{sub s}. For 8 nm thickness of Pt{sub s} the Co layer of 0.35 nm showed ferromagnetism with perpendicular anisotropy atmore » room temperature. As the thickness of the Pt{sub s} was decreased to 2 nm, the T{sub c} went down below 250 K. XRD data indicated polycrystalline growth of Pt{sub s} on SiO{sub 2}. On the contrary Ta buffer layer promoted the growth of Pt(111). As a consequence Ta(5 nm)/Pt(3 nm)/Co(0.35 nm)/Pt(2 nm) had much higher T{sub c} (above 300 K) with perpendicular anisotropy when compared to the same stack without the Ta layer. Thus we could tune the ferromagnetic T{sub c} and anisotropy by varying the Pt{sub s} thickness and also by introducing Ta buffer layer. We attribute these observations to the micro-structural evolution of Pt{sub s} layer which hosts the Co layer.« less

Plasma assisted molecular beam epitaxy growth and effect of varying buffer thickness on the formation of ultra-thin In{sub 0.17}Al{sub 0.83}N/GaN heterostructure on Si(111)

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

Chowdhury, Subhra, E-mail: subhra1109@gmail.com; Biswas, Dhrubes; Department of E and E C E, Indian Institute of Technology Kharagpur, Kharagpur 721302

2015-02-23

This work reports on the detailed plasma-assisted molecular beam epitaxy (PAMBE) growth of ultra-thin In{sub 0.17}Al{sub 0.83}N/GaN heterostructures on Si(111) substrate with three different buffer thickness (600 nm, 400 nm, and 200 nm). Growth through critical optimization of growth conditions is followed by the investigation of impact of varying buffer thickness on the formation of ultra-thin 1.5 nm, In{sub 0.17}Al{sub 0.83}N–1.25 nm, GaN–1.5 nm, In{sub 0.17}Al{sub 0.83}N heterostructure, in terms of threading dislocation (TD) density. Analysis reveals a drastic reduction of TD density from the order 10{sup 10 }cm{sup −2} to 10{sup 8 }cm{sup −2} with increasing buffer thickness resulting smooth ultra-thin active region for thick buffer structure.more » Increasing strain with decreasing buffer thickness is studied through reciprocal space mapping analysis. Surface morphology through atomic force microscopy analysis also supports our study by observing an increase of pits and root mean square value (0.89 nm, 1.2 nm, and 1.45 nm) with decreasing buffer thickness which are resulted due to the internal strain and TDs.« less

Anti-reflection coating design for metallic terahertz meta-materials

DOE PAGES

Pancaldi, Matteo; Freeman, Ryan; Hudl, Matthias; ...

2018-01-26

We demonstrate a silicon-based, single-layer anti-reflection coating that suppresses the reflectivity of metals at near-infrared frequencies, enabling optical probing of nano-scale structures embedded in highly reflective surroundings. Our design does not affect the interaction of terahertz radiation with metallic structures that can be used to achieve terahertz near-field enhancement. We have verified the functionality of the design by calculating and measuring the reflectivity of both infrared and terahertz radiation from a silicon/gold double layer as a function of the silicon thickness. We have also fabricated the unit cell of a terahertz meta-material, a dipole antenna comprising two 20-nm thick extendedmore » gold plates separated by a 2 μm gap, where the terahertz field is locally enhanced. We used the time-domain finite element method to demonstrate that such near-field enhancement is preserved in the presence of the anti-reflection coating. Finally, we performed magneto-optical Kerr effect measurements on a single 3-nm thick, 1-μm wide magnetic wire placed in the gap of such a dipole antenna. The wire only occupies 2% of the area probed by the laser beam, but its magneto-optical response can be clearly detected. Our design paves the way for ultrafast time-resolved studies, using table-top femtosecond near-infrared lasers, of dynamics in nano-structures driven by strong terahertz radiation.« less

Anti-reflection coating design for metallic terahertz meta-materials

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

Pancaldi, Matteo; Freeman, Ryan; Hudl, Matthias

We demonstrate a silicon-based, single-layer anti-reflection coating that suppresses the reflectivity of metals at near-infrared frequencies, enabling optical probing of nano-scale structures embedded in highly reflective surroundings. Our design does not affect the interaction of terahertz radiation with metallic structures that can be used to achieve terahertz near-field enhancement. We have verified the functionality of the design by calculating and measuring the reflectivity of both infrared and terahertz radiation from a silicon/gold double layer as a function of the silicon thickness. We have also fabricated the unit cell of a terahertz meta-material, a dipole antenna comprising two 20-nm thick extendedmore » gold plates separated by a 2 μm gap, where the terahertz field is locally enhanced. We used the time-domain finite element method to demonstrate that such near-field enhancement is preserved in the presence of the anti-reflection coating. Finally, we performed magneto-optical Kerr effect measurements on a single 3-nm thick, 1-μm wide magnetic wire placed in the gap of such a dipole antenna. The wire only occupies 2% of the area probed by the laser beam, but its magneto-optical response can be clearly detected. Our design paves the way for ultrafast time-resolved studies, using table-top femtosecond near-infrared lasers, of dynamics in nano-structures driven by strong terahertz radiation.« less

Anti-reflection coating design for metallic terahertz meta-materials.

PubMed

Pancaldi, Matteo; Freeman, Ryan; Hudl, Matthias; Hoffmann, Matthias C; Urazhdin, Sergei; Vavassori, Paolo; Bonetti, Stefano

2018-02-05

We demonstrate a silicon-based, single-layer anti-reflection coating that suppresses the reflectivity of metals at near-infrared frequencies, enabling optical probing of nano-scale structures embedded in highly reflective surroundings. Our design does not affect the interaction of terahertz radiation with metallic structures that can be used to achieve terahertz near-field enhancement. We have verified the functionality of the design by calculating and measuring the reflectivity of both infrared and terahertz radiation from a silicon/gold double layer as a function of the silicon thickness. We have also fabricated the unit cell of a terahertz meta-material, a dipole antenna comprising two 20-nm thick extended gold plates separated by a 2 μm gap, where the terahertz field is locally enhanced. We used the time-domain finite element method to demonstrate that such near-field enhancement is preserved in the presence of the anti-reflection coating. Finally, we performed magneto-optical Kerr effect measurements on a single 3-nm thick, 1-μm wide magnetic wire placed in the gap of such a dipole antenna. The wire only occupies 2% of the area probed by the laser beam, but its magneto-optical response can be clearly detected. Our design paves the way for ultrafast time-resolved studies, using table-top femtosecond near-infrared lasers, of dynamics in nano-structures driven by strong terahertz radiation.

Camphor-Enabled Transfer and Mechanical Testing of Centimeter-Scale Ultrathin Films.

PubMed

Wang, Bin; Luo, Da; Li, Zhancheng; Kwon, Youngwoo; Wang, Meihui; Goo, Min; Jin, Sunghwan; Huang, Ming; Shen, Yongtao; Shi, Haofei; Ding, Feng; Ruoff, Rodney S

2018-05-21

Camphor is used to transfer centimeter-scale ultrathin films onto custom-designed substrates for mechanical (tensile) testing. Compared to traditional transfer methods using dissolving/peeling to remove the support-layers, camphor is sublimed away in air at low temperature, thereby avoiding additional stress on the as-transferred films. Large-area ultrathin films can be transferred onto hollow substrates without damage by this method. Tensile measurements are made on centimeter-scale 300 nm-thick graphene oxide film specimens, much thinner than the ≈2 μm minimum thickness of macroscale graphene-oxide films previously reported. Tensile tests were also done on two different types of large-area samples of adlayer free CVD-grown single-layer graphene supported by a ≈100 nm thick polycarbonate film; graphene stiffens this sample significantly, thus the intrinsic mechanical response of the graphene can be extracted. This is the first tensile measurement of centimeter-scale monolayer graphene films. The Young's modulus of polycrystalline graphene ranges from 637 to 793 GPa, while for near single-crystal graphene, it ranges from 728 to 908 GPa (folds parallel to the tensile loading direction) and from 683 to 775 GPa (folds orthogonal to the tensile loading direction), demonstrating the mechanical performance of large-area graphene in a size scale relevant to many applications. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Near infrared spectroscopy for body fat sensing in neonates: quantitative analysis by GAMOS simulations.

PubMed

Mustafa, Fatin Hamimi; Jones, Peter W; McEwan, Alistair L

2017-01-11

Under-nutrition in neonates is closely linked to low body fat percentage. Undernourished neonates are exposed to immediate mortality as well as unwanted health impacts in their later life including obesity and hypertension. One potential low cost approach for obtaining direct measurements of body fat is near-infrared (NIR) interactance. The aims of this study were to model the effect of varying volume fractions of melanin and water in skin over NIR spectra, and to define sensitivity of NIR reflection on changes of thickness of subcutaneous fat. GAMOS simulations were used to develop two single fat layer models and four complete skin models over a range of skin colour (only for four skin models) and hydration within a spectrum of 800-1100 nm. The thickness of the subcutaneous fat was set from 1 to 15 mm in 1 mm intervals in each model. Varying volume fractions of water in skin resulted minimal changes of NIR intensity at ranges of wavelengths from 890 to 940 nm and from 1010 to 1100 nm. Variation of the melanin volume in skin meanwhile was found to strongly influence the NIR intensity and sensitivity. The NIR sensitivities and NIR intensity over thickness of fat decreased from the Caucasian skin to African skin throughout the range of wavelengths. For the relationship between the NIR reflection and the thickness of subcutaneous fat, logarithmic relationship was obtained. The minimal changes of NIR intensity values at wavelengths within the ranges from 890 to 940 nm and from 1010 to 1100 nm to variation of volume fractions of water suggests that wavelengths within those two ranges are considered for use in measurement of body fat to solve the variation of hydration in neonates. The stronger influence of skin colour on NIR shows that the melanin effect needs to be corrected by an independent measurement or by a modeling approach. The logarithmic response obtained with higher sensitivity at the lower range of thickness of fat suggests that implementation of NIRS may be suited for detecting under-nutrition and monitoring nutritional interventions for malnutrition in neonates in resource-constrained communities.

Fabrication and characterization of homogeneous surface-enhanced Raman scattering substrates by single pulse UV-laser treatment of gold and silver films.

PubMed

Christou, Konstantin; Knorr, Inga; Ihlemann, Jürgen; Wackerbarth, Hainer; Beushausen, Volker

2010-12-07

The fabrication of SERS-active substrates, which offer high enhancement factors as well as spatially homogeneous distribution of the enhancement, plays an important role in the expansion of surface-enhanced Raman scattering (SERS) spectroscopy to a powerful, quantitative, and noninvasive measurement technique for analytical applications. In this paper, a novel method for the fabrication of SERS-active substrates by laser treatment of 20, 40, and 60 nm thick gold and of 40 nm thick silver films supported on quartz glass is presented. Single 308 nm UV-laser pulses were applied to melt the thin gold and silver films. During the cooling process of the noble metal, particles were formed. The particle size and density were imaged by atomic force microscopy. By varying the fluence, the size of the particles can be controlled. The enhancement factors of the nanostructures were determined by recording self-assembled monolayers of benzenethiol. The intensity of the SERS signal from benzenethiol is correlated to the mean particle size and thus to the fluence. Enhancement factors up to 10(6) with a high reproducibility were reached. Finally we have analyzed the temperature dependence of the SERS effect by recording the intensity of benzenethiol vibrations from 300 to 120 K. The temperature dependence of the SERS effect is discussed with regard to the metal properties.

Thickness-dependent carrier mobility of ambipolar MoTe2: Interplay between interface trap and Coulomb scattering

NASA Astrophysics Data System (ADS)

Ji, Hyunjin; Lee, Gwanmu; Joo, Min-Kyu; Yun, Yoojoo; Yi, Hojoon; Park, Ji-Hoon; Suh, Dongseok; Lim, Seong Chu

2017-05-01

The correlation between the channel thickness and the carrier mobility is investigated by conducting static and low frequency (LF) noise characterization for ambipolar carriers in multilayer MoTe2 transistors. For channel thicknesses in the range of 5-15 nm, both the low-field carrier mobility and the Coulomb-scattering-limited carrier mobility (μC) are maximal at a thickness of ˜10 nm. For LF noise, the interplay of interface trap density (NST), which was minimal at ˜10 nm, and the interfacial Coulomb scattering parameter (αSC), which decreased up to 10 nm and saturated above 10 nm, explained the mobility (μC) peaked near 10 nm by the carrier fluctuation and charge distribution.

Magnetic anisotropy and magnetization reversal in Co/Cu multilayers nanowires

NASA Astrophysics Data System (ADS)

Ahmad, Naeem; Chen, J. Y.; Shi, D. W.; Iqbal, Javed; Han, Xiufeng

2012-04-01

The Co/Cu multilayer nanowires fabricated in an array using anodized aluminum oxide (AAO) template by electrodeposition method, have been investigated. It has been observed that the magnetization reversal mode and magnetic anisotropy depend upon the Co and Cu layer thicknesses. Magnetization reversal occurs by curling mode at around Co = 400 nm and Cu = 10 nm, while for Co = 30 nm and Cu = 60 nm, magnetization reversal occurs by nucleation mode. A change of magnetic anisotropy from out of plane to in plane is observed when thickness of Cu layer tCu = 60 nm and that of Co tCo = 30 nm. Magnetic anisotropy is lost when thickness of the Co layer tCo = 400 nm and that of Cu tCu= 10 nm. Magnetic properties have been explained by the competition among shape anisotropy, magnetostatic interactions and magnetocrystalline anisotropy. Magnetic properties can be tuned accordingly depending upon the thickness of the Co and Cu nanodisks.

Changes in Macular Retinal Layers and Peripapillary Nerve Fiber Layer Thickness after 577-nm Pattern Scanning Laser in Patients with Diabetic Retinopathy

PubMed Central

Shin, Ji Soo

2017-01-01

Purpose The aim of this study was to evaluate the changes in thickness of each macular retinal layer, the peripapillary retinal nerve fiber layer (RNFL), and central macular thickness (CMT) after 577-nm pattern scanning laser (PASCAL) photocoagulation in patients with diabetic retinopathy. Methods This retrospective study included 33 eyes with diabetic retinopathy that underwent 577-nm PASCAL photocoagulation. Each retinal layer thickness, peripapillary RNFL thickness, and CMT were measured by spectral-domain optical coherence tomography before 577-nm PASCAL photocoagulation, as well as at 1, 6, and 12 months after 577-nm PASCAL photocoagulation. Computerized intraretinal segmentation of optical coherence tomography was performed to identify the thickness of each retinal layer. Results The average thickness of the RNFL, ganglion cell layer, inner plexiform layer, inner nuclear layer, inner retinal layer, and CMT at each follow-up increased significantly from baseline (p < 0.001), whereas that of the retinal pigment epithelium at each follow-up decreased significantly from baseline (p < 0.001). The average thickness of the peripapillary RNFL increased significantly at one month (p < 0.001). This thickness subsequently recovered to 7.48 µm, and there were no significant changes at six or 12 months compared to baseline (p > 0.05). Conclusions Each macular retinal layer and CMT had a tendency to increase for one year after 577-nm PASCAL photocoagulation, whereas the average thickness of retinal pigment epithelium decreased at one-year follow-up compared to the baseline. Although an increase in peripapillary RNFL thickness was observed one month after 577-nm PASCAL photocoagulation, there were no significant changes at the one-year follow-up compared to the baseline. PMID:29022292

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.

Changes in Macular Retinal Layers and Peripapillary Nerve Fiber Layer Thickness after 577-nm Pattern Scanning Laser in Patients with Diabetic Retinopathy.

PubMed

Shin, Ji Soo; Lee, Young Hoon

2017-12-01

The aim of this study was to evaluate the changes in thickness of each macular retinal layer, the peripapillary retinal nerve fiber layer (RNFL), and central macular thickness (CMT) after 577-nm pattern scanning laser (PASCAL) photocoagulation in patients with diabetic retinopathy. This retrospective study included 33 eyes with diabetic retinopathy that underwent 577-nm PASCAL photocoagulation. Each retinal layer thickness, peripapillary RNFL thickness, and CMT were measured by spectral-domain optical coherence tomography before 577-nm PASCAL photocoagulation, as well as at 1, 6, and 12 months after 577-nm PASCAL photocoagulation. Computerized intraretinal segmentation of optical coherence tomography was performed to identify the thickness of each retinal layer. The average thickness of the RNFL, ganglion cell layer, inner plexiform layer, inner nuclear layer, inner retinal layer, and CMT at each follow-up increased significantly from baseline (p < 0.001), whereas that of the retinal pigment epithelium at each follow-up decreased significantly from baseline (p < 0.001). The average thickness of the peripapillary RNFL increased significantly at one month (p < 0.001). This thickness subsequently recovered to 7.48 μm, and there were no significant changes at six or 12 months compared to baseline (p > 0.05). Each macular retinal layer and CMT had a tendency to increase for one year after 577-nm PASCAL photocoagulation, whereas the average thickness of retinal pigment epithelium decreased at one-year follow-up compared to the baseline. Although an increase in peripapillary RNFL thickness was observed one month after 577-nm PASCAL photocoagulation, there were no significant changes at the one-year follow-up compared to the baseline. © 2017 The Korean Ophthalmological Society

Enhancement of electron injection in inverted bottom-emitting organic light-emitting diodes using Al/LiF compound thin film

NASA Astrophysics Data System (ADS)

Nie, Qu-yang; Zhang, Fang-hui

2018-05-01

The inverted bottom-emitting organic light-emitting devices (IBOLEDs) were prepared, with the structure of ITO/Al ( x nm)/LiF (1 nm)/Bphen (40 nm)/CBP: GIr1 (14%):R-4b (2%) (10 nm)/BCP (3 nm)/CBP:GIr1 (14%):R-4b (2%) (20 nm)/TCTA (10 nm)/NPB (40 nm)/MoO3 (40 nm)/Al (100 nm), where the thickness of electron injection layer Al ( x) are 0 nm, 2 nm, 3 nm, 4 nm and 5 nm, respectively. In this paper, the electron injection condition and luminance properties of inverted devices were investigated by changing the thickness of Al layer in Al/LiF compound thin film. It turns out that the introduction of Al layer can improve electron injection of the devices dramatically. Furthermore, the device exerts lower driving voltage and higher current efficiency when the thickness of electron injection Al layer is 3 nm. For example, the current efficiency of the device with 3-nm-thick Al layer reaches 19.75 cd·A-1 when driving voltage is 7 V, which is 1.24, 1.17 and 17.03 times larger than those of the devices with 2 nm, 4 nm and 5 nm Al layer, respectively. The device property reaches up to the level of corresponding conventional device. In addition, all inverted devices with electron injection Al layer show superior stability of color coordinate due to the adoption of co-evaporation emitting layer and BCP spacer-layer, and the color coordinate of the inverted device with 3-nm-thick Al layer only changes from (0.580 6, 0.405 6) to (0.532 8, 0.436 3) when driving voltage increases from 6 V to 10 V.

Gradient polymer-disposed liquid crystal single layer of large nematic droplets for modulation of laser light.

PubMed

Hadjichristov, Georgi B; Marinov, Yordan G; Petrov, Alexander G

2011-06-01

The light modulating ability of gradient polymer-disposed liquid crystal (PDLC) single layer of large droplets formed by nematic E7 in UV-cured polymer NOA65 is studied. Operating at relatively low voltages, such PDLC film with a of thickness 10-25 μm and droplet size up to 50 μm exhibits a good contrast ratio and is capable of producing a large phase shift for the propagating coherent light. For a linearly polarized He-Ne laser (λ=633 nm), an electrically commanded phase shift as large as π/2 can be obtained by the large-droplet region of the film. The electrically produced phase shift and its spatial profile controlled by the thickness of the gradient PDLC single layers of large nematic droplets can be useful for tunable spatial light modulators and other devices for active control of laser light.

Programming scheme based optimization of hybrid 4T-2R OxRAM NVSRAM

NASA Astrophysics Data System (ADS)

Majumdar, Swatilekha; Kingra, Sandeep Kaur; Suri, Manan

2017-09-01

In this paper, we present a novel single-cycle programming scheme for 4T-2R NVSRAM, exploiting pulse engineered input signals. OxRAM devices based on 3 nm thick bi-layer active switching oxide and 90 nm CMOS technology node were used for all simulations. The cell design is implemented for real-time non-volatility rather than last-bit, or power-down non-volatility. Detailed analysis of the proposed single-cycle, parallel RRAM device programming scheme is presented in comparison to the two-cycle sequential RRAM programming used for similar 4T-2R NVSRAM bit-cells. The proposed single-cycle programming scheme coupled with the 4T-2R architecture leads to several benefits such as- possibility of unconventional transistor sizing, 50% lower latency, 20% improvement in SNM and ∼20× reduced energy requirements, when compared against two-cycle programming approach.

Substrate Oxide Layer Thickness Optimization for a Dual-Width Plasmonic Grating for Surface-Enhanced Raman Spectroscopy (SERS) Biosensor Applications

PubMed Central

Bauman, Stephen J.; Brawley, Zachary T.; Darweesh, Ahmad A.; Herzog, Joseph B.

2017-01-01

This work investigates a new design for a plasmonic SERS biosensor via computational electromagnetic models. It utilizes a dual-width plasmonic grating design, which has two different metallic widths per grating period. These types of plasmonic gratings have shown larger optical enhancement than standard single-width gratings. The new structures have additional increased enhancement when the spacing between the metal decreases to sub-10 nm dimensions. This work integrates an oxide layer to improve the enhancement even further by carefully studying the effects of the substrate oxide thickness on the enhancement and reports ideal substrate parameters. The combined effects of varying the substrate and the grating geometry are studied to fully optimize the device’s enhancement for SERS biosensing and other plasmonic applications. The work reports the ideal widths and substrate thickness for both a standard and a dual-width plasmonic grating SERS biosensor. The ideal geometry, comprising a dual-width grating structure atop an optimal SiO2 layer thickness, improves the enhancement by 800%, as compared to non-optimized structures with a single-width grating and a non-optimal oxide thickness. PMID:28665308

Magnetization dynamics of Ni80Fe20 nanowires with continuous width modulation

NASA Astrophysics Data System (ADS)

Xiong, L. L.; Kostylev, M.; Adeyeye, A. O.

2017-06-01

A systematic investigation of the magnetization reversal and the dynamic behaviors of uncoupled Ni80Fe20 nanowires (NWs) with artificial continuous width modulation is presented. In contrast with the single resonance mode observed in the homogeneous NWs from the broadband ferromagnetic resonance spectroscopy, the NWs with continuous width modulation display three to five distinct resonance modes with increasing wire thickness in the range from 5 to 70 nm due to the nonuniform demagnetizing field. The highest frequency mode and the frequency difference between the two distinct highest modes are shown to be markedly sensitive to the NW thickness. Interestingly, we found that these modes can be described in terms of the quantization of the standing spin waves due to confined varied width. In addition, the easy axis coercive field for the width modulated NWs is much higher than homogeneous NWs of the same thickness when less than 70 nm. Our experimental results are in good qualitative agreement with the micromagnetic simulations. The results may find potential applications in the design and optimization of tunable magnonic filters.

Thermal annealing effect on structural and thermoelectric properties of hexagonal Bi2Te3 nanoplate thin films by drop-casting technique

NASA Astrophysics Data System (ADS)

Hosokawa, Yuichi; Wada, Kodai; Tanaka, Masaki; Tomita, Koji; Takashiri, Masayuki

2018-02-01

High-purity hexagonal bismuth telluride (Bi2Te3) nanoplates were prepared by a solvothermal synthesis method, followed by the fabrication of nanoplate thin films by the drop-casting technique. The Bi2Te3 nanoplates exhibited a single-crystalline phase with a rhombohedral crystal structure. The nanoplates had a flat surface with edge sizes ranging from 500 to 2000 nm (average size of 1000 nm) and a thickness of less than 50 nm. The resulting Bi2Te3 nanoplate thin films were composed of well-aligned hexagonal nanoplates along the surface direction with an approximate film thickness of 40 µm. To tightly connect the nanoplates together within the thin films, thermal annealing was performed at different temperatures. We found that the thermoelectric properties, especially the Seebeck coefficient, were very sensitive to the annealing temperature. Finally, the optimum annealing temperature was determined to be 250 °C and the Seebeck coefficient and power factor were -300 µV/K and 3.5 µW/(cm·K2), respectively.

Direct synthesis of ultrathin SOI structure by extremely low-energy oxygen implantation

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

Hoshino, Yasushi, E-mail: yhoshino@kanagawa-u.ac.jp; Yachida, Gosuke; Inoue, Kodai

2016-06-15

We performed extremely low-energy {sup 16}O{sup +} implantation at 10 keV (R{sub p} ∼ 25 nm) followed by annealing aiming at directly synthesizing an ultrathin Si layer separated by a buried SiO{sub 2} layer in Si(001) substrates, and then investigated feasible condition of recrystallization and stabilization of the superficial Si and the buried oxide layer by significantly low temperature annealing. The elemental compositions were analyzed by Rutherford backscattering (RBS) and secondary ion mass spectroscopy (SIMS). The crystallinity of the superficial Si layer was quantitatively confirmed by ananlyzing RBS-channeling spectra. Cross-sectional morphologies and atomic configurations were observed by transmission electron microscopemore » (TEM). As a result, we succeeded in directly synthesizing an ultrathin single-crystalline silicon layer with ≤20 nm thick separated by a thin buried stoichiometric SiO{sub 2} layer with ≤20 nm thick formed by extremely low-energy {sup 16}O{sup +} implantation followed by surprisingly low temperature annealing at 1050{sup ∘} C.« less

Magnetic domain wall shift registers for data storage applications

NASA Astrophysics Data System (ADS)

Read, Dan; O'Brien, L.; Zeng, H. T.; Lewis, E. R.; Petit, D.; Sampaio, J.; Thevenard, L.; Cowburn, R. P.

2009-03-01

Data storage devices based on magnetic domain walls (DWs) propagating through permalloy (Py) nanowires have been proposed [Allwood et al. Science 309, 1688 (2005), S. S. Parkin, US Patent 6,834,005 (2004)] and have attracted a great deal of attention. We experimentally demonstrate such a device using shift registers constructed from magnetic NOT gates used in combination with a globally applied rotating magnetic field. We have demonstrated data writing, propagation, and readout in individually addressable Py nanowires 90 nm wide and 10 nm thick. Electrical data writing is achieved using the Oersted field due to current pulses in gold stripes (4 μm wide, 150 nm thick), patterned on top of and perpendicular to the nanowires. The conduit-like properties of the nanowires allow the propagation of data sequences over distances greater than 100 μm. Using spatially resolved magneto-optical Kerr effect (MOKE) measurements we can directly detect the propagation of single DWs in individual nanostructures without requiring data averaging. Electrical readout was demonstrated by detecting the presence of DWs at deliberately introduced pinning sites in the wire.

Influences of film thickness on the structural, electrical and optical properties of CuAlO2 thin films

NASA Astrophysics Data System (ADS)

Dong, Guobo; Zhang, Ming; Wang, Mei; Li, Yingzi; Gao, Fangyuan; Yan, Hui; Diao, Xungang

2014-07-01

CuAlO2 films with different thickness were prepared by the radio frequency magnetron sputtering technique. The structural, electrical and optical properties of CuAlO2 were studied by X-ray diffraction, atomic force microscope, UV-Vis double-beam spectrophotometer and Hall measurements. The results indicate that the single phase hexagonal CuAlO2 is formed and the average grain size of CuAlO2 films increases with increasing film thickness. The results also exhibit that the lowering of bandgap and the increase of electrical conductivity of CuAlO2 films with the increase of their thickness, which are attributed to the improvement of the grain size and the anisotropic electrical property. According to the electrical and optical properties, the biggest figure of merit is achieved for the CuAlO2 film with the appropriate thickness of 165 nm.

Single mode wavelength control of modulated AlGaAs lasers with external and internal etalon feedback

NASA Technical Reports Server (NTRS)

Maynard, William L.

1989-01-01

Single mode lasing without mode hops has been obtained for VSIS and CSP laser diodes with an external etalon attached to the laser's front facet for up to an 8 C range CW and a 4 C range pulsed, with .07 nm/C tuning. Tests of thin tapered-thickness (TTT) laser diodes show CW and pulsed single mode lasing over 10 C and 2 C ranges, respectively, with .08 nm/C tuning. An analysis of the TTT structure reveals the equivalent of an internal etalon. The time-resolved pulsed behavior for both types of lasers show single mode lasing within the proper temperature ranges with minor modes present only early in the optical pulse, if at all. The external etalon produces noticeable interference fringes in the farfield pattern, while those of the TTT lasers are smooth. Ongoing CW lifetest results indicate stability to within one longitudinal mode after a few hundred hours of operation, along with at least several thousand hours lifetime.

The low coherence Fabry-Pérot interferometer with diamond and ZnO layers

NASA Astrophysics Data System (ADS)

Majchrowicz, D.; Den, W.; Hirsch, M.

2016-09-01

The authors present a fiber-optic Fabry-Pérot interferometer built with the application of diamond and zinc oxide (ZnO) thin layers. Thin ZnO films were deposited on the tip of a standard telecommunication single-mode optical fiber (SMF- 28) while the diamond layer was grown on the plate of silicon substrate. Investigated ZnO layers were fabricated by atomic layer deposition (ALD) and the diamond films were deposited using Microwave Plasma Enhanced Chemical Vapor Deposition (μPE CVD) system. Different thickness of layers was examined. The measurements were performed for the fiber-optic Fabry-Pérot interferometer working in the reflective mode. Spectra were registered for various thicknesses of ZnO layer and various length of the air cavity. As a light source, two superluminescent diodes (SLD) with central wavelength of 1300 nm and 1550 nm were used in measurement set-up.

Structural-dependent thermal conductivity of aluminium nitride produced by reactive direct current magnetron sputtering

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

Belkerk, B. E.; Soussou, A.; Carette, M.

This Letter reports the thermal conductivity of aluminium nitride (AlN) thin-films deposited by reactive DC magnetron sputtering on single-crystal silicon substrates (100) with varying plasma and magnetic conditions achieving different crystalline qualities. The thermal conductivity of the films was measured at room temperature with the transient hot-strip technique for film thicknesses ranging from 100 nm to 4000 nm. The thermal conductivity was found to increase with the thickness depending on the synthesis conditions and film microstructure. The conductivity in the bulk region of the films, so-called intrinsic conductivity, and the boundary resistance were in the range [120-210] W m{sup -1}more » K{sup -1} and [2-30 Multiplication-Sign 10{sup -9}] K m{sup 2} W{sup -1}, respectively, in good agreement with microstructures analysed by x-ray diffraction, high-resolution-scanning-electron-microscopy, and transmission-electron-microscopy.« less

A comparative study of the influence of nickel oxide layer on the FTO surface of organic light emitting diode

NASA Astrophysics Data System (ADS)

Saikia, Dhrubajyoti; Sarma, Ranjit

2018-03-01

The influence of thin layer of nickel oxide (NiO) over the fluorine-doped tin oxide (FTO) surface on the performance of Organic light-emitting diode (OLED) is reported. With an optimal thickness of NiO (10 nm), the luminance efficiency is found to be increased as compared to the single FTO OLED. The performance of OLED is studied by depositing NiO films at different thicknesses on the FTO surface and analyzed their J-V and L-V characteristics. Further analysis is carried out by measuring sheet resistance and optical transmittance. The surface morphology is studied with the help of FE-SEM images. Our results indicate that NiO (10 nm) buffer layer is an excellent choice to increase the efficiency of FTO based OLED devices within the charge tunneling region. The maximum value of current efficiency is found to be 7.32 Cd/A.

Fabrication and room temperature operation of semiconductor nano-ring lasers using a general applicable membrane transfer method

NASA Astrophysics Data System (ADS)

Fan, Fan; Yu, Yueyang; Amiri, Seyed Ebrahim Hashemi; Quandt, David; Bimberg, Dieter; Ning, C. Z.

2017-04-01

Semiconductor nanolasers are potentially important for many applications. Their design and fabrication are still in the early stage of research and face many challenges. In this paper, we demonstrate a generally applicable membrane transfer method to release and transfer a strain-balanced InGaAs quantum-well nanomembrane of 260 nm in thickness onto various substrates with a high yield. As an initial device demonstration, nano-ring lasers of 1.5 μm in outer diameter and 500 nm in radial thickness are fabricated on MgF2 substrates. Room temperature single mode operation is achieved under optical pumping with a cavity volume of only 0.43λ03 (λ0 in vacuum). Our nano-membrane based approach represents an advantageous alternative to other design and fabrication approaches and could lead to integration of nanolasers on silicon substrates or with metallic cavity.

NbN superconducting nanowire single-photon detector fabricated on MgF2 substrate

NASA Astrophysics Data System (ADS)

Wu, J. J.; You, L. X.; Zhang, L.; Zhang, W. J.; Li, H.; Liu, X. Y.; Zhou, H.; Wang, Z.; Xie, X. M.; Xu, Y. X.; Fang, W.; Tong, L. M.

2016-06-01

The performance of superconducting nanowire single-photon detectors (SNSPDs) relies on substrate materials. Magnesium fluoride (MgF2) exhibits outstanding optical properties, such as large optical transmission range and low refractive index (n = 1.38), making it an attractive substrate. We present the fabrication and the performance of SNSPDs made of a 4.5 nm thick NbN thin film deposited on MgF2 substrate for the wavelength of 1550 nm. The front-side illuminated SNSPDs without an optical cavity showed a maximal detection efficiency of 12.8% at a system dark count rate (DCR) of 100 Hz, while the backside illuminated SNSPDs with a SiO2/Au optical cavity atop displayed a maximal detection efficiency of 33% at a DCR of 100 Hz.

Tilted light sheet microscopy with 3D point spread functions for single-molecule super-resolution imaging in mammalian cells

NASA Astrophysics Data System (ADS)

Gustavsson, Anna-Karin; Petrov, Petar N.; Lee, Maurice Y.; Shechtman, Yoav; Moerner, W. E.

2018-02-01

To obtain a complete picture of subcellular nanostructures, cells must be imaged with high resolution in all three dimensions (3D). Here, we present tilted light sheet microscopy with 3D point spread functions (TILT3D), an imaging platform that combines a novel, tilted light sheet illumination strategy with engineered long axial range point spread functions (PSFs) for low-background, 3D super localization of single molecules as well as 3D super-resolution imaging in thick cells. TILT3D is built upon a standard inverted microscope and has minimal custom parts. The axial positions of the single molecules are encoded in the shape of the PSF rather than in the position or thickness of the light sheet, and the light sheet can therefore be formed using simple optics. The result is flexible and user-friendly 3D super-resolution imaging with tens of nm localization precision throughout thick mammalian cells. We validated TILT3D for 3D superresolution imaging in mammalian cells by imaging mitochondria and the full nuclear lamina using the double-helix PSF for single-molecule detection and the recently developed Tetrapod PSF for fiducial bead tracking and live axial drift correction. We envision TILT3D to become an important tool not only for 3D super-resolution imaging, but also for live whole-cell single-particle and single-molecule tracking.

Recombination zone in white organic light emitting diodes with blue and orange emitting layers

NASA Astrophysics Data System (ADS)

Tsuboi, Taiju; Kishimoto, Tadashi; Wako, Kazuhiro; Matsuda, Kuniharu; Iguchi, Hirofumi

2012-10-01

White fluorescent OLED devices with a 10 nm thick blue-emitting layer and a 31 nm thick orange-emitting layer have been fabricated, where the blue-emitting layer is stacked on a hole transport layer. An interlayer was inserted between the two emitting layers. The thickness of the interlayer was changed among 0.3, 0.4, and 1.0 nm. White emission with CIE coordinates close to (0.33, 0.33) was observed from all the OLEDs. OLED with 0.3 nm thick interlayer gives the highest maximum luminous efficiency (11 cd/A), power efficiency (9 lm/W), and external quantum efficiency (5.02%). The external quantum efficiency becomes low with increasing the interlayer thickness from 0 nm to 1.0 nm. When the location of the blue- and orange-emitting layers is reversed, white emission was not obtained because of too weak blue emission. It is suggested that the electron-hole recombination zone decreases nearly exponentially with a distance from the hole transport layer.

Surface chemistry and wear behavior of single-crystal silicon carbide sliding against iron at temperatures to 1500 C in vacuum

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1982-01-01

X-ray photoelectron and Auger electron spectroscopy analyses and morphological studies of wear and metal transfer were conducted with a single-crystal silicon carbide 0001 surface in contact with iron at various temperatures to 1500 C in a vacuum of 10 to the minus 8th power pascal. The results indicate that below 800 C, carbide-carbon and silicon are primarily seen on the silicon carbide surface. Above 800 C the graphite increases rapidly with increase in temperature. The outermost surficial layer, which consists mostly of graphite and little silicon at temperatures above 1200 C is about 2 nm thick. A thicker layer, which consists of a mixture of graphite, carbide, and silicon is approximately 100 nm thick. The closer the surface sliding temperature is to 800 C, the more the metal transfer produced. Above 800 C, there was a transfer of rough, discontinuous, and thin iron debris instead of smooth, continuous and thin iron film which was observed to transfer below 800 C. Two kinds of fracture pits were observed on the silicon carbide surface: (1) a pit with a spherical asperity; and (2) multiangular shaped pits.

Magnetic vortices in nanocaps induced by curvature

NASA Astrophysics Data System (ADS)

Abdelgawad, Ahmed M.; Nambiar, Nikhil; Bapna, Mukund; Chen, Hao; Majetich, Sara A.

2018-05-01

Magnetic nanoparticles with room temperature remanent magnetic vortices stabilized by their curvature are very intriguing due to their potential use in biomedicine. In the present study, we investigate room temperature magnetic chirality in 100 nm diameter permalloy spherical caps with 10 nm and 30 nm thicknesses. Micromagnetic OOMMF simulations predict the equilibrium spin structure for these caps to form a vortex state. We fabricate the permalloy caps by sputtering permalloy on both close-packed and sparse arrays of polystyrene nanoparticles. Magnetic force microscopy scans show a clear signature of a vortex state in close-packed caps of both 10 nm and 30 nm thicknesses. Alternating gradient magnetometry measurements of the caps are consistent with a remnant vortex state in 30 nm thick caps and a transition to an onion state followed by a vortex state in 10 nm thick caps. Out-of-plane measurements supported by micromagnetic simulations shows that an out-of-plane field can stabilize a vortex state down to a diameter of 15 nm.

Real-time growth study of plasma assisted atomic layer epitaxy of InN films by synchrotron x-ray methods

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

Nepal, Neeraj; Anderson, Virginia R.; Johnson, Scooter D.

The temporal evolution of high quality indium nitride (InN) growth by plasma-assisted atomic layer epitaxy (ALEp) on a-plane sapphire at 200 and 248 °C was probed by synchrotron x-ray methods. The growth was carried out in a thin film growth facility installed at beamline X21 of the National Synchrotron Light Source at Brookhaven National Laboratory and at beamline G3 of the Cornell High Energy Synchrotron Source, Cornell University. Measurements of grazing incidence small angle x-ray scattering (GISAXS) during the initial cycles of growth revealed a broadening and scattering near the diffuse specular rod and the development of scattering intensities duemore » to half unit cell thick nucleation islands in the Yoneda wing with correlation length scale of 7.1 and 8.2 nm, at growth temperatures (Tg) of 200 and 248 °C, respectively. At about 1.1 nm (two unit cells) of growth thickness nucleation islands coarsen, grow, and the intensity of correlated scattering peak increased at the correlation length scale of 8.0 and 8.7 nm for Tg = 200 and 248 °C, respectively. The correlated peaks at both growth temperatures can be fitted with a single peak Lorentzian function, which support single mode growth. Post-growth in situ x-ray reflectivity measurements indicate a growth rate of ~0.36 Å/cycle consistent with the growth rate previously reported for self-limited InN growth in a commercial ALEp reactor. Consistent with the in situ GISAXS study, ex situ atomic force microscopy power spectral density measurements also indicate single mode growth. Electrical characterization of the resulting film revealed an electron mobility of 50 cm2/V s for a 5.6 nm thick InN film on a-plane sapphire, which is higher than the previously reported mobility of much thicker InN films grown at higher temperature by molecular beam epitaxy directly on sapphire. These early results indicated that in situ synchrotron x-ray study of the epitaxial growth kinetics of InN films is a very powerful method to understand nucleation and growth mechanisms of ALEp to enable improvement in material quality and broaden its application.« less

Single virus particle mass detection using microresonators with nanoscale thickness

NASA Astrophysics Data System (ADS)

Gupta, A.; Akin, D.; Bashir, R.

2004-03-01

In this letter, we present the microfabrication and application of arrays of silicon cantilever beams as microresonator sensors with nanoscale thickness to detect the mass of individual virus particles. The dimensions of the fabricated cantilever beams were in the range of 4-5 μm in length, 1-2 μm in width and 20-30 nm in thickness. The virus particles we used in the study were vaccinia virus, which is a member of the Poxviridae family and forms the basis of the smallpox vaccine. The frequency spectra of the cantilever beams, due to thermal and ambient noise, were measured using a laser Doppler vibrometer under ambient conditions. The change in resonant frequency as a function of the virus particle mass binding on the cantilever beam surface forms the basis of the detection scheme. We have demonstrated the detection of a single vaccinia virus particle with an average mass of 9.5 fg. These devices can be very useful as components of biosensors for the detection of airborne virus particles.

A tunable single-polarization photonic crystal fiber filter based on surface plasmon resonance

NASA Astrophysics Data System (ADS)

Zhang, Shuhuan; Li, Jianshe; Li, Shuguang; Liu, Qiang; Liu, Yingchao; Zhang, Zhen; Wang, Yujun

2018-06-01

A tunable single polarizing filter is proposed by selectively coating gold film on the air holes of photonic crystal fiber (PCF). The polarization properties of the PCF filter are evaluated by the finite-element method. Simulation results show that the loss of y-polarized core mode at 1250 and 1550 nm is 136.23 and 839.73 dB/cm, respectively. Furthermore, we innovatively combine stable modulation with flexible modulation. To be specific, the resonance wavelengths are slowly controlled in a small wavelength range by altering the diameter of the air-hole-coated gold film, while the resonance wavelengths are flexibly controlled in a wide wavelength range by altering the thickness of the gold film or the diameter of the small air holes. When the length of the PCF is 500 µm, the bandwidth of extinction ratio greater than - 20 dB is only 60 nm at the communication window of 1550 nm. It is beneficial to fabricate a narrow-band polarization filter.

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.

Thickness-dependent metal-to-insulator transition in epitaxial VO2 films

NASA Astrophysics Data System (ADS)

Zhi, Bowen; Gao, Guanyin; Tan, Xuelian; Chen, Pingfan; Wang, Lingfei; Jin, Shaowei; Wu, Wenbin

2014-12-01

The metal-to-insulator transition (MIT) of VO2 films with a thickness of 3-100 nm on TiO2(001) substrates has been investigated. When varying the film thickness from 10 to 100 nm, the MIT temperature was first kept at 290 K in the range of 10-14 nm, and then increased with thickness increasing due to the strain relaxation. The origin of the suppressed transition in VO2 films thinner than 6 nm was also investigated. When prolonging the in situ annealing time, the sharpness, amplitude and width of the transition for 4 nm thick films were all increased, suggesting improved crystallinity rather than Ti diffusion from the substrates. In addition, the MIT was suppressed when the VO2 films were covered by a TiO2 layer, indicating that the interface effect via the confinement of the dimerization of the V atoms should be the main reason.

Structural, magnetic and magnetocaloric properties of sputtered Gd films

NASA Astrophysics Data System (ADS)

Kumar, N. Pavan; Shaleni, V.; Satyanarayana, L.; Manorama, S. V.; Raja, M. Manivel

2018-05-01

Gd films with different thicknesses varying from 100 nm to 750 nm have been deposited on single crystal Si (100) substrate by ultra high vacuum magnetron sputtering system. X-ray diffraction analysis reveals the crystalline nature and hcp crystal structure of the films. Microstructure investigations have been carried to study the surface morphology of the films. Thermo magnetic studies confirm the magnetic transition of the films and are ˜275 K, close to bulk. Magnetocaloric effect (MCE) has been studied from magnetic isotherms measured around magnetic transition and the maximum isothermal entropy change of 2.0 J/kg-K is achieved for a magnetic field change of 2 T for the 750 nm film. The sputtered Gd films are useful for micro cooling device applications.

Electroluminescence dependence on the organic thickness in ZnO nano rods/Alq3 heterostructure devices.

PubMed

Kan, Pengzhi; Wang, Yongsheng; Zhao, Suling; Xu, Zheng; Wang, Dawei

2011-04-01

ZnO nanorods are synthesised by a hydrothermal method on ITO glass. Their crystallization and morphology are detected by XRD and SEM, respectively. The results show that the ZnO nanorod array has grown primarily along a direction aligned perpendicular to the ITO substrate. The average height and diameter of the nanorods is about 130 nm and 30 nm, respectively. Then ZnO nano rods/Alq3 heterostructure LEDs are prepared by thermal evaporation of Alq3 molecules. The thicknesses of the Alq3 layers are 130 nm, 150 nm, 170 nm and 190 nm, respectively. The electroluminescence of the devices is detected under different DC bias voltages. The exciton emission of Alq3 is detected in all devices. When the thickness of Alq3 is 130 nm, the UV electroluminescence of ZnO is around 382 nm, and defect emissions around 670 nm and 740 nm are detected. Defect emissions of ZnO nanorods are prominent. When the thickness of Alq3 increases to over 170 nm, it is difficult to observe defect emissions from the ZnO nano rods. In such devices, the exciton emission of Alq3 is more prominent than other emissions under different bias voltage.

The dynamics of complex formation between amylose brushes on gold and fatty acids by QCM-D.

PubMed

Cao, Zheng; Tsoufis, Theodoros; Svaldo-Lanero, Tiziana; Duwez, Anne-Sophie; Rudolf, Petra; Loos, Katja

2013-10-14

Amylose brushes were synthesized by enzymatic polymerization with glucose-1-phosphate as monomer and rabbit muscle phosphorylase b as catalyst on gold-covered surfaces of a quartz crystal microbalance. Fourier transform infrared (FT-IR) spectra confirmed the presence of the characteristic absorption peaks of amylose between 3100 cm(-1) and 3500 cm(-1). The thickness of the amylose brushes-measured by Spectroscopic Ellipsometry--can be tailored from 4 to 20 nm, depending on the reaction time. The contour length of the stretched amylose chains on gold surfaces has been evaluated by single molecule force spectroscopy, and a total chain length of about 20 nm for 16.2 nm thick amylose brushes was estimated. X-ray photoelectron spectroscopy (XPS) was employed to characterize the amylose brushes before and after the adsorption of fatty acids. The dynamics of inclusion complex formation between amylose brushes and two fatty acids (octanoic acid and myristic acid) with different chain length was investigated as a function of time using a quartz crystal microbalance with dissipation monitoring (QCM-D) immersed in the liquid phase. QCM-D signals including the frequency and dissipation shifts elucidated the effects of the fatty acid concentration, the solvent types, the chain length of the fatty acids and the thickness of the amylose brushes on the dynamics of fatty acid molecule adsorption on the amylose brush-modified sensor surfaces.

Fractional versus ablative erbium:yttrium-aluminum-garnet laser resurfacing for facial rejuvenation: an objective evaluation.

PubMed

El-Domyati, Moetaz; Abd-El-Raheem, Talal; Abdel-Wahab, Hossam; Medhat, Walid; Hosam, Wael; El-Fakahany, Hasan; Al Anwer, Mustafa

2013-01-01

Laser is one of the main tools for skin resurfacing. Erbium:yttrium-aluminum-garnet (Er:YAG) was the second ablative laser, after carbon dioxide, emitting wavelength of 2940 nm. Fractional laser resurfacing has been developed to overcome the drawbacks of ablative lasers. We aimed to objectively evaluate the histopathological and immunohistochemical effects of Er:YAG 2940-nm laser for facial rejuvenation (multiple sessions of fractional vs single session of ablative Er:YAG laser). Facial resurfacing with single-session ablative Er:YAG laser was performed on 6 volunteers. Another 6 were resurfaced using fractional Er:YAG laser (4 sessions). Histopathological (hematoxylin-eosin, orcein, Masson trichrome, and picrosirius red stains) and immunohistochemical assessment for skin biopsy specimens were done before laser resurfacing and after 1 and 6 months. Histometry for epidermal thickness and quantitative assessment for neocollagen formation; collagen I, III, and VII; elastin; and tropoelastin were done for all skin biopsy specimens. Both lasers resulted in increased epidermal thickness. Dermal collagen showed increased neocollagen formation with increased concentration of collagen types I, III, and VII. Dermal elastic tissue studies revealed decreased elastin whereas tropoelastin concentration increased after laser resurfacing. Neither laser showed significant difference between their effects clinically and on dermal collagen. Changes in epidermal thickness, elastin, and tropoelastin were significantly more marked after ablative laser. The small number of patients is a limitation, yet the results show significant improvement. Multiple sessions of fractional laser have comparable effects to a single session of ablative Er:YAG laser on dermal collagen but ablative laser has more effect on elastic tissue and epidermis. Copyright © 2012 American Academy of Dermatology, Inc. Published by Mosby, Inc. All rights reserved.

Optimized sensitivity of Silicon-on-Insulator (SOI) strip waveguide resonator sensor

PubMed Central

TalebiFard, Sahba; Schmidt, Shon; Shi, Wei; Wu, WenXuan; Jaeger, Nicolas A. F.; Kwok, Ezra; Ratner, Daniel M.; Chrostowski, Lukas

2017-01-01

Evanescent field sensors have shown promise for biological sensing applications. In particular, Silicon-on-Insulator (SOI)-nano-photonic based resonator sensors have many advantages for lab-on-chip diagnostics, including high sensitivity for molecular detection and compatibility with CMOS foundries for high volume manufacturing. We have investigated the optimum design parameters within the fabrication constraints of Multi-Project Wafer (MPW) foundries that result in the highest sensitivity for a resonator sensor. We have demonstrated the optimum waveguide thickness needed to achieve the maximum bulk sensitivity with SOI-based resonator sensors to be 165 nm using the quasi-TM guided mode. The closest thickness offered by MPW foundry services is 150 nm. Therefore, resonators with 150 nm thick silicon waveguides were fabricated resulting in sensitivities as high as 270 nm/RIU, whereas a similar resonator sensor with a 220 nm thick waveguide demonstrated sensitivities of approximately 200 nm/RIU. PMID:28270963

First principles calculation for Gilbert damping constants in ferromagnetic/non-magnetic junctions

NASA Astrophysics Data System (ADS)

Hiramatsu, R.; Miura, D.; Sakuma, A.

2018-05-01

We evaluated an intrinsic α in ferromagnetic (FM)/non-magnetic (NM) junctions from first principles (FM = Co, Fe, and Ni and NM = Cu, Pd, and Pt) to investigate the effects of the inserted NM layer. α is calculated by liner muffin-tin orbital methods based on the torque-correlation model. We confirmed that Gilbert damping is enhanced and saturated as NM thickness increases, and that the enhancement is greater in NM materials having a stronger spin-orbital interaction. By contrast, the calculated FM thickness dependences of α show that Gilbert damping tends to decrease and be saturated as the FM thickness increases. Under the torque-correlation model, the dependences of α on FM and NM thickness can be explained by considering the electronic structure of the total system, including junction interfaces, which exhibit similar behaviors derived by spin pumping theory.

Configuration of twins in glass-embedded silver nanoparticles of various origin

NASA Astrophysics Data System (ADS)

Hofmeister, H.; Dubiel, M.; Tan, G. L.; Schicke, K.-D.

2005-09-01

Structural characterization using high resolution electron microscopy and diffractogram analysis of silver nanoparticles embedded in glass by various routes of fabrication was aimed at revealing the characteristic features of twin faults occuring in such particles. Nearly spherical silver nanoparticles well below 10 nm size embedded in commercial soda-lime silicate float glass have been fabricated either by silver/sodium ion exchange or by Ag+ ion implantation. Twinned nanoparticles, besides single crystalline species, have frequently been observed for both fabrication routes, mainly at sizes above 5 nm, but also at smaller sizes, even around 1 nm. The variety of particle forms comprises single crystalline particles of nearly cuboctahedron shape, particles containing single twin faults, and multiply twinned particles containing parallel twin lamellae, or cyclic twinned segments arranged around axes of fivefold symmetry. Parallel twinning is distinctly favoured by ion implantation whereas cyclic twinning preferably occurs upon ion exchange processing. Regardless of single or repeated twinning, parallel or cyclic twin arrangement, one may classify simple twin faults of regular atomic configuration and compound twin faults whose irregular configuration consists of additional planar defects like associated stacking faults or secondary twin faults. Besides, a particular superstructure composed of parallel twin lamellae of only three atomic layers thickness is observed.

Study on the occurrence of spontaneously established perpendicular exchange bias in Co{sub 49}Pt{sub 51}/IrMn bilayers

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

Tsai, C. Y.; Lin, K. F.; Hsu, Jen-Hwa, E-mail: jhhsu@phys.ntu.edu.tw

2014-05-07

In this study, perpendicular exchange bias (PEB) effect in the as-grown Co{sub 49}Pt{sub 51}/IrMn bilayers was demonstrated at room temperature using single-layered Co{sub 49}Pt{sub 51} alloy thin film as ferromagnetic (FM) layer. Several unusual features were observed in this system, viz.,: (i) the PEB was spontaneously established without any external magnetic field treatments, (ii) single-shifted loops were obtained rather than double-shifted ones, and (iii) the spontaneous PEB effect was accompanied by a reduction in perpendicular coercivity, H{sub c⊥} from 1024 to 632 Oe. The results of x–ray diffraction revealed the formation of IrMn (111) texture. Training effect studies indicate that themore » PEB effect is stable in this system with less than 5% variation in PEB value within 15 repetitive scans. Significant reduction in the PEB effect was found for the CoPt/IrMn films either grown or subjected to post-annealing under external magnetic field (H{sub ind}). The thickness dependence of PEB effect with respect to the FM and antiferromagnetic layers were also investigated and a largest PEB value of 533 Oe was obtained for the sample grown with 3-nm thick CoPt and 10-nm thick IrMn layers. The results of present study thus establish an opportunity to realize PEB effect in the absence of external field during fabrication.« less

Benzothiazolium Single Crystals: A New Class of Nonlinear Optical Crystals with Efficient THz Wave Generation.

PubMed

Lee, Seung-Heon; Lu, Jian; Lee, Seung-Jun; Han, Jae-Hyun; Jeong, Chan-Uk; Lee, Seung-Chul; Li, Xian; Jazbinšek, Mojca; Yoon, Woojin; Yun, Hoseop; Kang, Bong Joo; Rotermund, Fabian; Nelson, Keith A; Kwon, O-Pil

2017-08-01

Highly efficient nonlinear optical organic crystals are very attractive for various photonic applications including terahertz (THz) wave generation. Up to now, only two classes of ionic crystals based on either pyridinium or quinolinium with extremely large macroscopic optical nonlinearity have been developed. This study reports on a new class of organic nonlinear optical crystals introducing electron-accepting benzothiazolium, which exhibit higher electron-withdrawing strength than pyridinium and quinolinium in benchmark crystals. The benzothiazolium crystals consisting of new acentric core HMB (2-(4-hydroxy-3-methoxystyryl)-3-methylbenzo[d]thiazol-3-ium) exhibit extremely large macroscopic optical nonlinearity with optimal molecular ordering for maximizing the diagonal second-order nonlinearity. HMB-based single crystals prepared by simple cleaving method satisfy all required crystal characteristics for intense THz wave generation such as large crystal size with parallel surfaces, moderate thickness and high optical quality with large optical transparency range (580-1620 nm). Optical rectification of 35 fs pulses at the technologically very important wavelength of 800 nm in 0.26 mm thick HMB crystal leads to one order of magnitude higher THz wave generation efficiency with remarkably broader bandwidth compared to standard inorganic 0.5 mm thick ZnTe crystal. Therefore, newly developed HMB crystals introducing benzothiazolium with extremely large macroscopic optical nonlinearity are very promising materials for intense broadband THz wave generation and other nonlinear optical applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thickness dependence of exchange anisotropy for (0 0 1) oriented Mn 89Pt 11/NiFe and Mn 80Ir 20/NiFe bilayers

NASA Astrophysics Data System (ADS)

Kume, T.; Yamato, T.; Kato, T.; Tsunashima, S.; Iwata, S.

2007-03-01

Antiferromagnetic layer thickness dependences of exchange anisotropy for (0 0 1) oriented Mn 89Pt 11 ( tAF nm)/Ni 80Fe 20 (5 nm) and Mn 80Ir 20 ( tAF nm)/Ni 80Fe 20 (5 nm) were investigated. For Mn 89Pt 11/NiFe, the exchange bias field appeared at tAF⩾5 nm. This critical thickness was found to be thicker than that of Mn 80Ir 20/NiFe ( tAF=3 nm). The thickness dependence of exchange bias field agreed well with that of 1-fold Fourier amplitude estimated from in-plane torque curves. The large coercivity of about 100 Oe was found for Mn 89Pt 11/NiFe at tAF=30 nm compared to that of Mn 80Ir 20/NiFe. The large coercivity in Mn 89Pt 11/NiFe bilayers seems to result from the large 4-fold anisotropy in their torque curve.

Single cell isolation process with laser induced forward transfer.

PubMed

Deng, Yu; Renaud, Philippe; Guo, Zhongning; Huang, Zhigang; Chen, Ying

2017-01-01

A viable single cell is crucial for studies of single cell biology. In this paper, laser-induced forward transfer (LIFT) was used to isolate individual cell with a closed chamber designed to avoid contamination and maintain humidity. Hela cells were used to study the impact of laser pulse energy, laser spot size, sacrificed layer thickness and working distance. The size distribution, number and proliferation ratio of separated cells were statistically evaluated. Glycerol was used to increase the viscosity of the medium and alginate were introduced to soften the landing process. The role of laser pulse energy, the spot size and the thickness of titanium in energy absorption in LIFT process was theoretically analyzed with Lambert-Beer and a thermal conductive model. After comprehensive analysis, mechanical damage was found to be the dominant factor affecting the size and proliferation ratio of the isolated cells. An orthogonal experiment was conducted, and the optimal conditions were determined as: laser pulse energy, 9 μJ; spot size, 60 μm; thickness of titanium, 12 nm; working distance, 700 μm;, glycerol, 2% and alginate depth, greater than 1 μm. With these conditions, along with continuous incubation, a single cell could be transferred by the LIFT with one shot, with limited effect on cell size and viability. LIFT conducted in a closed chamber under optimized condition is a promising method for reliably isolating single cells.

Fine tuning of nanopipettes using atomic layer deposition for single molecule sensing.

PubMed

Sze, Jasmine Y Y; Kumar, Shailabh; Ivanov, Aleksandar P; Oh, Sang-Hyun; Edel, Joshua B

2015-07-21

Nanopipettes are an attractive single-molecule tool for identification and characterisation of nucleic acids and proteins in solutions. They enable label-free analysis and reveal individual molecular properties, which are generally masked by ensemble averaging. Having control over the pore dimensions is vital to ensure that the dimensions of the molecules being probed match those of the pore for optimization of the signal to noise. Although nanopipettes are simple and easy to fabricate, challenges exist, especially when compared to more conventional solid-state analogues. For example, a sub-20 nm pore diameter can be difficult to fabricate and the batch-to-batch reproducibility is often poor. To improve on this limitation, atomic layer deposition (ALD) is used to deposit ultrathin layers of alumina (Al2O3) on the surface of the quartz nanopipettes enabling sub-nm tuning of the pore dimensions. Here, Al2O3 with a thickness of 8, 14 and 17 nm was deposited onto pipettes with a starting pore diameter of 75 ± 5 nm whilst a second batch had 5 and 8 nm Al2O3 deposited with a starting pore diameter of 25 ± 3 nm respectively. This highly conformal process coats both the inner and outer surfaces of pipettes and resulted in the fabrication of pore diameters as low as 7.5 nm. We show that Al2O3 modified pores do not interfere with the sensing ability of the nanopipettes and can be used for high signal-to-noise DNA detection. ALD provides a quick and efficient (batch processing) for fine-tuning nanopipettes for a broad range of applications including the detection of small biomolecules like RNA, aptamers and DNA-protein interactions at the single molecule level.

Studies of Second Order Optical Nonlinearities of 4-Aminobenzophenone (ABP) Single Crystal Films

NASA Astrophysics Data System (ADS)

Bhowmik, Achintya; Thakur, Mrinal

1998-03-01

Specific organic materials exhibit very high second order optical susceptibilities. Growth of single crystal films of these materials and characterization of nonlinear optical properties are necessary for implementation of device applications. We have grown large-area films ( 1 cm^2 area, 4 μm thick) of ABP by a modification of the shear method. Single crystal nature of the films was confirmed by polarized optical microscopy. X-ray diffraction analysis showed a [100] surface orientation. The absorption spectra revealed transparency from 390 nm to 1940 nm. Significant elements of the second order optical susceptibility tensor were measured by detailed SHG experiments using a Nd:YAG laser (1064 nm, 100 ps, 82 MHz). Second-harmonic power was measured using lock-in detection with carefully selected polarization conditions while the film was rotated about the propagation direction. Using LiNbØas the reference, d-coefficients of ABP were found to be d_23=7.2 pm/V and d_22=0.7 pm/V. Type-I and type-II phase-matching directions were identified on the film by analyzing the optical indicatrix surfaces at fundamental and second-harmonic frequencies.

Large exchange bias induced by polycrystalline Mn3Ga antiferromagnetic films with controlled layer thickness

NASA Astrophysics Data System (ADS)

Wu, Haokaifeng; Sudoh, Iori; Xu, Ruihan; Si, Wenshuo; Vaz, C. A. F.; Kim, Jun-young; Vallejo-Fernandez, Gonzalo; Hirohata, Atsufumi

2018-05-01

Polycrystalline Mn3Ga layers with thickness in the range from 6–20 nm were deposited at room temperature by a high target utilisation sputtering. To investigate the onset of exchange-bias, a ferromagnetic Co0.6Fe0.4 layer (3.3–9 nm thick) capped with 5 nm Ta, were subsequently deposited. X-ray diffraction measurements confirm the presence of Mn3Ga (0 0 0 2) and (0 0 0 4) peaks characteristic of the D019 antiferromagnetic structure. The 6 nm thick Mn3Ga film shows the largest exchange bias of 430 Oe at 120 K with a blocking temperature of 225 K. The blocking temperature is found to decrease with increasing Mn3Ga thickness. These results in combination with x-ray reflectivity measurements confirm that the quality of the Mn3Ga/Co0.6Fe0.4 interface controls the exchange bias, with the sharp interface with the 6-nm-thick Mn3Ga inducing the largest exchange bias. The magneto-crystalline anisotropy for 6 nm thick Mn3Ga thin film sample is calculated to be . Such a binary antiferromagnetic Heusler alloy is compatible with the current memory fabrication process and hence has a great potential for antiferromagnetic spintronics.

Effect of Ru thickness on spin pumping in Ru/Py bilayer

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

Behera, Nilamani; Singh, M. Sanjoy; Chaudhary, Sujeet

2015-05-07

We report the effect of Ru thickness (t{sub Ru}) on ferromagnetic resonance (FMR) line-width of Ru(t{sub Ru})/Py(23 nm) bilayer samples grown on Si(100)/SiO{sub 2} substrates at room temperature by magnetron sputtering. The FMR line-width is found to vary linearly with frequency for all thicknesses of Ru, indicating intrinsic origin of damping. For Ru thicknesses below 15 nm, Gilbert-damping parameter, α is almost constant. We ascribe this behavior to spin back flow that is operative for Ru thicknesses lower than the spin diffusion length in Ru, λ{sub sd}. For thicknesses >15 nm (>λ{sub sd}), the damping constant increases with Ru thickness, indicating spin pumpingmore » from Py into Ru.« less

Nearly Blinking-Free, High-Purity Single-Photon Emission by Colloidal InP/ZnSe Quantum Dots.

PubMed

Chandrasekaran, Vigneshwaran; Tessier, Mickaël D; Dupont, Dorian; Geiregat, Pieter; Hens, Zeger; Brainis, Edouard

2017-10-11

Colloidal core/shell InP/ZnSe quantum dots (QDs), recently produced using an improved synthesis method, have a great potential in life-science applications as well as in integrated quantum photonics and quantum information processing as single-photon emitters. Single-particle spectroscopy of 10 nm QDs with 3.2 nm cores reveals strong photon antibunching attributed to fast (70 ps) Auger recombination of multiple excitons. The QDs exhibit very good photostability under strong optical excitation. We demonstrate that the antibunching is preserved when the QDs are excited above the saturation intensity of the fundamental-exciton transition. This result paves the way toward their usage as high-purity on-demand single-photon emitters at room temperature. Unconventionally, despite the strong Auger blockade mechanism, InP/ZnSe QDs also display very little luminescence intermittency ("blinking"), with a simple on/off blinking pattern. The analysis of single-particle luminescence statistics places these InP/ZnSe QDs in the class of nearly blinking-free QDs, with emission stability comparable to state-of-the-art thick-shell and alloyed-interface CdSe/CdS, but with improved single-photon purity.

Subsurface optical stimulation of the rat prostate nerves using continuous-wave near-infrared laser radiation

NASA Astrophysics Data System (ADS)

Tozburun, Serhat; Lagoda, Gwen A.; Burnett, Arthur L.; Fried, Nathaniel M.

2012-02-01

Successful identification and preservation of the cavernous nerves (CN), which are responsible for sexual function, during prostate cancer surgery, will require subsurface detection of the CN beneath a thin fascia layer. This study explores optical nerve stimulation (ONS) in the rat with a fascia layer placed over the CN. Two near-IR diode lasers (1455 nm and 1550 nm lasers) were used to stimulate the CN in CW mode with a 1-mm-diameter spot in 8 rats. The 1455 nm wavelength provides an optical penetration depth (OPD) of ~350 μm, while 1550 nm provides an OPD of ~1000 μm (~3 times deeper than 1455 nm and 1870 nm wavelengths previously tested). Fascia layers with thicknesses of 85 - 600 μm were placed over the CN. Successful ONS was confirmed by an intracavernous pressure (ICP) response in the rat penis at 1455 nm through fascia 110 μm thick and at 1550 nm through fascia 450 μm thick. Higher incident laser power was necessary and weaker and slower ICP responses were observed as fascia thickness was increased. Subsurface ONS of the rat CN at a depth of 450 μm using a 1550 nm laser is feasible.

Optical properties of hybrid quantum-well–dots nanostructures grown by MOCVD

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

Mintairov, S. A., E-mail: mintairov@scell.ioffe.ru; Kalyuzhnyy, N. A.; Nadtochiy, A. M.

The deposition of In{sub x}Ga{sub 1–x}As with an indium content of 0.3–0.5 and an average thickness of 3–27 single layers on a GaAs wafer by metalorganic chemical vapor deposition (MOCVD) at low temperatures results in the appearance of thickness and composition modulations in the layers being formed. Such structures can be considered to be intermediate nanostructures between ideal quantum wells and quantum dots. Depending on the average thickness and composition of the layers, the wavelength of the photoluminescence peak for the hybrid InGaAs quantum well–dots nanostructures varies from 950 to 1100 nm. The optimal average In{sub x}Ga{sub 1–x}As thicknesses andmore » compositions at which the emission wavelength is the longest with a high quantum efficiency retained are determined.« less

Ion transport in sub-5-nm graphene nanopores.

PubMed

Suk, Myung E; Aluru, N R

2014-02-28

Graphene nanopore is a promising device for single molecule sensing, including DNA bases, as its single atom thickness provides high spatial resolution. To attain high sensitivity, the size of the molecule should be comparable to the pore diameter. However, when the pore diameter approaches the size of the molecule, ion properties and dynamics may deviate from the bulk values and continuum analysis may not be accurate. In this paper, we investigate the static and dynamic properties of ions with and without an external voltage drop in sub-5-nm graphene nanopores using molecular dynamics simulations. Ion concentration in graphene nanopores sharply drops from the bulk concentration when the pore radius is smaller than 0.9 nm. Ion mobility in the pore is also smaller than bulk ion mobility due to the layered liquid structure in the pore-axial direction. Our results show that a continuum analysis can be appropriate when the pore radius is larger than 0.9 nm if pore conductivity is properly defined. Since many applications of graphene nanopores, such as DNA and protein sensing, involve ion transport, the results presented here will be useful not only in understanding the behavior of ion transport but also in designing bio-molecular sensors.

Optical fiber plasmonic lens for near-field focusing fabricated through focused ion beam

NASA Astrophysics Data System (ADS)

Sloyan, Karen; Melkonyan, Henrik; Moreira, Paulo; Dahlem, Marcus S.

2017-02-01

We report on numerical simulations and fabrication of an optical fiber plasmonic lens for near-field focusing applications. The plasmonic lens consists of an Archimedean spiral structure etched through a 100 nm-thick Au layer on the tip of a single-mode SM600 optical fiber operating at a wavelength of 632:8 nm. Three-dimensional finite-difference time-domain computations show that the relative electric field intensity of the focused spot increases 2:1 times when the number of turns increases from 2 to 12. Furthermore, a reduction of the intensity is observed when the initial inner radius is increased. The optimized plasmonic lens focuses light into a spot with a full-width at half-maximum of 182 nm, beyond the diffraction limit. The lens was fabricated by focused ion beam milling, with a 200nm slit width.

Dark-field transmission electron microscopy of cortical bone reveals details of extrafibrillar crystals.

PubMed

Schwarcz, Henry P; McNally, Elizabeth A; Botton, Gianluigi A

2014-12-01

In a previous study we showed that most of the mineral in bone is present in the form of "mineral structures", 5-6nm-thick, elongated plates which surround and are oriented parallel to collagen fibrils. Using dark-field transmission electron microscopy, we viewed mineral structures in ion-milled sections of cortical human bone cut parallel to the collagen fibrils. Within the mineral structures we observe single crystals of apatite averaging 5.8±2.7nm in width and 28±19nm in length, their long axes oriented parallel to the fibril axis. Some appear to be composite, co-aligned crystals as thin as 2nm. From their similarity to TEM images of crystals liberated from deproteinated bone we infer that we are viewing sections through platy crystals of apatite that are assembled together to form the mineral structures. Copyright © 2014 Elsevier Inc. All rights reserved.

Structural and magnetic properties of self-assembled cobalt on porous silicon; experimental and micromagnetic investigations

NASA Astrophysics Data System (ADS)

Saidani, M.; Belkacem, W.; Bessais, L.; Mliki, N.

2017-08-01

In this paper, we report on self-assembled Co nanoparticles deposited in and on porous silicon (PS) matrix by using UHV evaporation. Four samples were prepared by varying the Co deposited thickness (t = 3, 5, 7 and 10 nm). All samples have been investigated by means of Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Physical Properties Measurement System (PPMS). The increase of t has induced an increase of the nanoparticle diameter from 3 nm to about 150 nm. Referring to the magnetic characterizations, this increase has been followed by a single to multi-domain transition. Therefore, this has been evidenced by a switching from superparamagnetism to purely ferromagnetism accompanied by a change in the magnetic reversal dynamics. Thus, by performing micromagnetic calculation, we have shown that a transition from the uniform rotation to vortex state occurs at a critical diameter of about 55 nm.

Tilted Light Sheet Microscopy with 3D Point Spread Functions for Single-Molecule Super-Resolution Imaging in Mammalian Cells.

PubMed

Gustavsson, Anna-Karin; Petrov, Petar N; Lee, Maurice Y; Shechtman, Yoav; Moerner, W E

2018-02-01

To obtain a complete picture of subcellular nanostructures, cells must be imaged with high resolution in all three dimensions (3D). Here, we present tilted light sheet microscopy with 3D point spread functions (TILT3D), an imaging platform that combines a novel, tilted light sheet illumination strategy with engineered long axial range point spread functions (PSFs) for low-background, 3D super localization of single molecules as well as 3D super-resolution imaging in thick cells. TILT3D is built upon a standard inverted microscope and has minimal custom parts. The axial positions of the single molecules are encoded in the shape of the PSF rather than in the position or thickness of the light sheet, and the light sheet can therefore be formed using simple optics. The result is flexible and user-friendly 3D super-resolution imaging with tens of nm localization precision throughout thick mammalian cells. We validated TILT3D for 3D super-resolution imaging in mammalian cells by imaging mitochondria and the full nuclear lamina using the double-helix PSF for single-molecule detection and the recently developed Tetrapod PSF for fiducial bead tracking and live axial drift correction. We envision TILT3D to become an important tool not only for 3D super-resolution imaging, but also for live whole-cell single-particle and single-molecule tracking.

Anodic Oxidation in Aluminum Electrode by Using Hydrated Amorphous Aluminum Oxide Film as Solid Electrolyte under High Electric Field.

PubMed

Yao, Manwen; Chen, Jianwen; Su, Zhen; Peng, Yong; Zou, Pei; Yao, Xi

2016-05-04

Dense and nonporous amorphous aluminum oxide (AmAO) film was deposited onto platinized silicon substrate by sol-gel and spin coating technology. The evaporated aluminum film was deposited onto the AmAO film as top electrode. The hydrated AmAO film was utilized as a solid electrolyte for anodic oxidation of the aluminum electrode (Al) film under high electric field. The hydrated AmAO film was a high efficiency electrolyte, where a 45 nm thick Al film was anodized completely on a 210 nm thick hydrated AmAO film. The current-voltage (I-V) characteristics and breakdown phenomena of a dry and hydrated 210 nm thick AmAO film with a 150 nm thick Al electrode pad were studied in this work. Breakdown voltage of the dry and hydrated 210 nm thick AmAO film were 85 ± 3 V (405 ± 14 MV m(-1)) and 160 ± 5 V (762 ± 24 MV m(-1)), respectively. The breakdown voltage of the hydrated AmAO film increased about twice, owing to the self-healing behavior (anodic oxidation reaction). As an intuitive phenomenon of the self-healing behavior, priority anodic oxidation phenomena was observed in a 210 nm thick hydrated AmAO film with a 65 nm thick Al electrode pad. The results suggested that self-healing behavior (anodic oxidation reaction) was occurring nearby the defect regions of the films during I-V test. It was an effective electrical self-healing method, which would be able to extend to many other simple and complex oxide dielectrics and various composite structures.

Three Temperature Regimes in Superconducting Photon Detectors: Quantum, Thermal and Multiple Phase-Slips as Generators of Dark Counts

PubMed Central

Murphy, Andrew; Semenov, Alexander; Korneev, Alexander; Korneeva, Yulia; Gol’tsman, Gregory; Bezryadin, Alexey

2015-01-01

We perform measurements of the switching current distributions of three w ≈ 120 nm wide, 4 nm thick NbN superconducting strips which are used for single-photon detectors. These strips are much wider than the diameter of the vortex cores, so they are classified as quasi-two-dimensional (quasi-2D). We discover evidence of macroscopic quantum tunneling by observing the saturation of the standard deviation of the switching distributions at temperatures around 2 K. We analyze our results using the Kurkijärvi-Garg model and find that the escape temperature also saturates at low temperatures, confirming that at sufficiently low temperatures, macroscopic quantum tunneling is possible in quasi-2D strips and can contribute to dark counts observed in single photon detectors. At the highest temperatures the system enters a multiple phase-slip regime. In this range single phase-slips are unable to produce dark counts and the fluctuations in the switching current are reduced. PMID:25988591

Three temperature regimes in superconducting photon detectors: quantum, thermal and multiple phase-slips as generators of dark counts.

PubMed

Murphy, Andrew; Semenov, Alexander; Korneev, Alexander; Korneeva, Yulia; Gol'tsman, Gregory; Bezryadin, Alexey

2015-05-19

We perform measurements of the switching current distributions of three w ≈ 120 nm wide, 4 nm thick NbN superconducting strips which are used for single-photon detectors. These strips are much wider than the diameter of the vortex cores, so they are classified as quasi-two-dimensional (quasi-2D). We discover evidence of macroscopic quantum tunneling by observing the saturation of the standard deviation of the switching distributions at temperatures around 2 K. We analyze our results using the Kurkijärvi-Garg model and find that the escape temperature also saturates at low temperatures, confirming that at sufficiently low temperatures, macroscopic quantum tunneling is possible in quasi-2D strips and can contribute to dark counts observed in single photon detectors. At the highest temperatures the system enters a multiple phase-slip regime. In this range single phase-slips are unable to produce dark counts and the fluctuations in the switching current are reduced.

Small-sized PdCu nanocapsules on 3D graphene for high-performance ethanol oxidation.

PubMed

Hu, Chuangang; Zhai, Xiangquan; Zhao, Yang; Bian, Ke; Zhang, Jing; Qu, Liangti; Zhang, Huimin; Luo, Hongxia

2014-03-07

A one-pot solvothermal process has been developed for direct preparation of PdCu nanocapsules (with a size of ca. 10 nm) on three-dimensional (3D) graphene. Due to the 3D pore-rich network of graphene and the unique hollow structure of PdCu nanocapsules with a wall thickness of ca. 3 nm, the newly-prepared PdCu/3D graphene hybrids activated electrochemically have great electrocatalytic activity towards ethanol oxidation in alkaline media, much better than single-phase Pd and commercial E-TEK 20% Pt/C catalysts promising for application in direct ethanol fuel cells.

Slow DNA Transport through Nanopores in Hafnium Oxide Membranes

PubMed Central

Bell, David C.; Cohen-Karni, Tzahi; Rosenstein, Jacob K.; Wanunu, Meni

2016-01-01

We present a study of double- and single-stranded DNA transport through nanopores fabricated in ultrathin (2–7 nm thick) free-standing hafnium oxide (HfO2) membranes. The high chemical stability of ultrathin HfO2 enables long-lived experiments with <2 nm diameter pores that last several hours, in which we observe >50 000 DNA translocations with no detectable pore expansion. Mean DNA velocities are slower than velocities through comparable silicon nitride pores, providing evidence that HfO2 nanopores have favorable physicochemical interactions with nucleic acids that can be leveraged to slow down DNA in a nanopore. PMID:24083444

Junctionless tri-gate InGaAs MOSFETs

NASA Astrophysics Data System (ADS)

Zota, Cezar B.; Borg, Mattias; Wernersson, Lars-Erik; Lind, Erik

2017-12-01

We demonstrate and characterize junctionless tri-gate InGaAs MOSFETs, fabricated using a simplified process with gate lengths down to L g = 25 nm at a nanowire dimension of 7 × 16 nm2. These devices use a single 7-nm-thick In0.80Ga0.20As (N D = 1 × 1019 cm-3) layer as both channel and contacts. The devices show SSsat = 76 mV/dec, peak g m = 1.6 mS/µm and I ON = 160 µA/µm (at I OFF = 100 nA/µm and V DD = 0.5 V), the latter which is the highest reported value for a junctionless FET. We also show that device performance is mainly limited by high parasitic access resistance due to the narrow and thin contact layer.

Battery-powered thin film deposition process for coating telescope mirrors in space

NASA Astrophysics Data System (ADS)

Sheikh, David A.

2016-07-01

Aluminum films manufactured in the vacuum of space may increase the broadband reflectance response of a space telescope operating in the EUV (50-nm to 115-nm) by eliminating absorbing metal-fluorides and metal-oxides, which significantly reduce aluminum's reflectance below 115-nm. Recent developments in battery technology allow small lithium batteries to rapidly discharge large amounts of energy. It is therefore conceivable to power an array of resistive evaporation filaments in a space environment, using a reasonable mass of batteries and other hardware. This paper presents modeling results for coating thickness as a function of position, for aluminum films made with a hexagonal array of battery powered evaporation sources. The model is based on measured data from a single battery-powered evaporation source.

Scanning transmission electron microscopy through-focal tilt-series on biological specimens.

PubMed

Trepout, Sylvain; Messaoudi, Cédric; Perrot, Sylvie; Bastin, Philippe; Marco, Sergio

2015-10-01

Since scanning transmission electron microscopy can produce high signal-to-noise ratio bright-field images of thick (≥500 nm) specimens, this tool is emerging as the method of choice to study thick biological samples via tomographic approaches. However, in a convergent-beam configuration, the depth of field is limited because only a thin portion of the specimen (from a few nanometres to tens of nanometres depending on the convergence angle) can be imaged in focus. A method known as through-focal imaging enables recovery of the full depth of information by combining images acquired at different levels of focus. In this work, we compare tomographic reconstruction with the through-focal tilt-series approach (a multifocal series of images per tilt angle) with reconstruction with the classic tilt-series acquisition scheme (one single-focus image per tilt angle). We visualised the base of the flagellum in the protist Trypanosoma brucei via an acquisition and image-processing method tailored to obtain quantitative and qualitative descriptors of reconstruction volumes. Reconstructions using through-focal imaging contained more contrast and more details for thick (≥500 nm) biological samples. Copyright © 2015 Elsevier Ltd. All rights reserved.

Thickness Dependence of Magnetic Blocking in Granular Metallic Thin Films

NASA Astrophysics Data System (ADS)

Wang, J.-Q.; Zhao, Z.-D.; Whittenburg, S. L.

2002-03-01

Inter-particle interaction among single domain nano-size magnetic particles embedded in nonmagnetic matrix was studied. Attention was paid to concentrated Cu-Co granular thin films with a fixed magnetic volume fraction. By analyzing theoretical models and comparing with experimental results, we studied a dimensional constraint on the magnetic properties and found that as the film thickness reduces toward thin limit the inter-particle interaction plays important roles in modifying magnetic behavior. Experimental evidence showed that the peak temperature of the susceptibility for Cu80Co20 granular thin films strongly depends on the film thickness in the range of 0 120 nm (1). It was also observed that the spontaneous magnetization of the Co phase varies with the thickness though particle size remains constant. We calculated the dipolar interaction energy among magnetic particles including far-neighbor interaction for films with different thickness values. The calculation revealed that the interaction energy varies across the film from edge to edge and the average interaction energy is strongly dependent on film thickness. Good quantitative agreement of the calculated energy curve with the experimental blocking curve was achieved after taking the magnetization variation into account. In the calculation it is assumed the existence of 100 nm sized domain structures in granular film as demonstrate (2) by previous studies. *supported by DoD/DARPA grant No. MDA972-97-1-003. (1) L. M. Malkinski, J.-Q. Wang, et al, Appl. Phys. Lett. 75, 844 (1999). (2) A. Gavrin, et al, Appl. Phys. Lett. 66, 1683 (1995); Y. J. Chen, et al, Appl. Phys. Lett. 72, 2472 (1998).

Dependencies of microstructure and stress on the thickness of GdBa2Cu3O7 − δ thin films fabricated by RF sputtering

PubMed Central

2013-01-01

GdBa2Cu3O7 − δ (GdBCO) films with different thicknesses from 200 to 2,100 nm are deposited on CeO2/yttria-stabilized zirconia (YSZ)/CeO2-buffered Ni-W substrates by radio-frequency magnetron sputtering. Both the X-ray diffraction and scanning electron microscopy analyses reveal that the a-axis grains appear at the upper layers of the films when the thickness reaches to 1,030 nm. The X-ray photoelectron spectroscopy measurement implies that the oxygen content is insufficient in upper layers beyond 1,030 nm for a thicker film. The Williamson-Hall method is used to observe the variation of film stress with increasing thickness of our films. It is found that the highest residual stresses exist in the thinnest film, while the lowest residual stresses exist in the 1,030-nm-thick film. With further increasing film thickness, the film residual stresses increase again. However, the critical current (Ic) of the GdBCO film first shows a nearly linear increase and then shows a more slowly enhancing to a final stagnation as film thickness increases from 200 to 1,030 nm and then to 2,100 nm. It is concluded that the roughness and stress are not the main reasons which cause the slow or no increase in Ic. Also, the thickness dependency of GdBa2Cu3O7 − δ films on the Ic is attributed to three main factors: a-axis grains, gaps between a-axis grains, and oxygen deficiency for the upper layers of a thick film. PMID:23816137

Controlling contamination in Mo/Si multilayer mirrors by Si surface capping modifications

NASA Astrophysics Data System (ADS)

Malinowski, Michael E.; Steinhaus, Chip; Clift, W. Miles; Klebanoff, Leonard E.; Mrowka, Stanley; Soufli, Regina

2002-07-01

The performance of Mo/Si multilayer mirrors (MLMs) used to reflect UV (EUV) radiation in an EUV + hydrocarbon (NC) vapor environment can be improved by optimizing the silicon capping layer thickness on the MLM in order to minimize the initial buildup of carbon on MLMs. Carbon buildup is undesirable since it can absorb EUV radiation and reduce MLM reflectivity. A set of Mo/Si MLMs deposited on Si wafers was fabricated such that each MLM had a different Si capping layer thickness ranging form 2 nm to 7 nm. Samples from each MLM wafer were exposed to a combination of EUV light + (HC) vapors at the Advanced Light Source (ALS) synchrotron in order to determine if the Si capping layer thickness affected the carbon buildup on the MLMs. It was found that the capping layer thickness had a major influence on this 'carbonizing' tendency, with the 3 nm layer thickness providing the best initial resistance to carbonizing and accompanying EUV reflectivity loss in the MLM. The Si capping layer thickness deposited on a typical EUV optic is 4.3 nm. Measurements of the absolute reflectivities performed on the Calibration and Standards beamline at the ALS indicated the EUV reflectivity of the 3 nm-capped MLM was actually slightly higher than that of the normal, 4 nm Si-capped sample. These results show that he use of a 3 nm capping layer represents an improvement over the 4 nm layer since the 3 nm has both a higher absolute reflectivity and better initial resistance to carbon buildup. The results also support the general concept of minimizing the electric field intensity at the MLM surface to minimize photoelectron production and, correspondingly, carbon buildup in a EUV + HC vapor environment.

On-shot characterization of single plasma mirror temporal contrast improvement

NASA Astrophysics Data System (ADS)

Obst, L.; Metzkes-Ng, J.; Bock, S.; Cochran, G. E.; Cowan, T. E.; Oksenhendler, T.; Poole, P. L.; Prencipe, I.; Rehwald, M.; Rödel, C.; Schlenvoigt, H.-P.; Schramm, U.; Schumacher, D. W.; Ziegler, T.; Zeil, K.

2018-05-01

We report on the setup and commissioning of a compact recollimating single plasma mirror (PM) for temporal contrast enhancement at the Draco 150 TW laser during laser-proton acceleration experiments. The temporal contrast with and without PM is characterized single-shot by means of self-referenced spectral interferometry with extended time excursion at unprecedented dynamic and temporal range. This allows for the first single-shot measurement of the PM trigger point, which is interesting for the quantitative investigation of the complex pre-plasma formation process at the surface of the target used for proton acceleration. As a demonstration of high contrast laser plasma interaction we present proton acceleration results with ultra-thin liquid crystal targets of ∼ 1 μm down to 10 nm thickness. Focus scans of different target thicknesses show that highest proton energies are reached for the thinnest targets at best focus. This indicates that the contrast enhancement is effective such that the acceleration process is not limited by target pre-expansion induced by laser light preceding the main laser pulse.

Transparent Nanotubular TiO₂ Photoanodes Grown Directly on FTO Substrates.

PubMed

Paušová, Šárka; Kment, Štěpán; Zlámal, Martin; Baudys, Michal; Hubička, Zdeněk; Krýsa, Josef

2017-05-10

This work describes the preparation of transparent TiO₂ nanotube (TNT) arrays on fluorine-doped tin oxide (FTO) substrates. An optimized electrolyte composition (0.2 mol dm -3 NH₄F and 4 mol dm -3 H₂O in ethylene glycol) was used for the anodization of Ti films with different thicknesses (from 100 to 1300 nm) sputtered on the FTO glass substrates. For Ti thicknesses 600 nm and higher, anodization resulted in the formation of TNT arrays with an outer nanotube diameter around 180 nm and a wall thickness around 45 nm, while for anodized Ti thicknesses of 100 nm, the produced nanotubes were not well defined. The transmittance in the visible region (λ = 500 nm) varied from 90% for the thinnest TNT array to 65% for the thickest TNT array. For the fabrication of transparent TNT arrays by anodization, the optimal Ti thickness on FTO was around 1000 nm. Such fabricated TNT arrays with a length of 2500 nm exhibit stable photocurrent densities in aqueous electrolytes (~300 µA cm -2 at potential 0.5 V vs. Ag/AgCl). The stability of the photocurrent response and a sufficient transparency (≥65%) enables the use of transparent TNT arrays in photoelectrochemical applications when the illumination from the support/semiconductor interface is a necessary condition and the transmitted light can be used for another purpose (photocathode or photochemical reaction in the electrolyte).

Electrical resistivity of CuAlMo thin films grown at room temperature by dc magnetron sputtering

NASA Astrophysics Data System (ADS)

Birkett, Martin; Penlington, Roger

2016-07-01

We report on the thickness dependence of electrical resistivity of CuAlMo films grown by dc magnetron sputtering on glass substrates at room temperature. The electrical resistance of the films was monitored in situ during their growth in the thickness range 10-1000 nm. By theoretically modelling the evolution of resistivity during growth we were able to gain an insight into the dominant electrical conduction mechanisms with increasing film thickness. For thicknesses in the range 10-25 nm the electrical resistivity is found to be a function of the film surface roughness and is well described by Namba’s model. For thicknesses of 25-40 nm the experimental data was most accurately fitted using the Mayadas and Shatkes model which accounts for grain boundary scattering of the conduction electrons. Beyond 40 nm, the thickness of the film was found to be the controlling factor and the Fuchs-Sonheimer (FS) model was used to fit the experimental data, with diffuse scattering of the conduction electrons at the two film surfaces. By combining the Fuchs and Namba (FN) models a suitable correlation between theoretical and experimental resistivity can be achieved across the full CuAlMo film thickness range of 10-1000 nm. The irreversibility of resistance for films of thickness >200 nm, which demonstrated bulk conductivity, was measured to be less than 0.03% following subjection to temperature cycles of -55 and +125 °C and the temperature co-efficient of resistance was less than ±15 ppm °C-1.

Photonic bandpass filter characteristics of multimode SOI waveguides integrated with submicron gratings.

PubMed

Sah, Parimal; Das, Bijoy Krishna

2018-03-20

It has been shown that a fundamental mode adiabatically launched into a multimode SOI waveguide with submicron grating offers well-defined flat-top bandpass filter characteristics in transmission. The transmitted spectral bandwidth is controlled by adjusting both waveguide and grating design parameters. The bandwidth is further narrowed down by cascading two gratings with detuned parameters. A semi-analytical model is used to analyze the filter characteristics (1500  nm≤λ≤1650  nm) of the device operating in transverse-electric polarization. The proposed devices were fabricated with an optimized set of design parameters in a SOI substrate with a device layer thickness of 250 nm. The pass bandwidth of waveguide devices integrated with single-stage gratings are measured to be ∼24  nm, whereas the device with two cascaded gratings with slightly detuned periods (ΔΛ=2  nm) exhibits a pass bandwidth down to ∼10  nm.

Co thickness dependence of structural and magnetic properties in spin quantum cross devices utilizing stray magnetic fields

NASA Astrophysics Data System (ADS)

Kaiju, H.; Kasa, H.; Komine, T.; Mori, S.; Misawa, T.; Abe, T.; Nishii, J.

2015-05-01

We investigate the Co thickness dependence of the structural and magnetic properties of Co thin-film electrodes sandwiched between borate glasses in spin quantum cross (SQC) devices that utilize stray magnetic fields. We also calculate the Co thickness dependence of the stray field between the two edges of Co thin-film electrodes in SQC devices using micromagnetic simulation. The surface roughness of Co thin films with a thickness of less than 20 nm on borate glasses is shown to be as small as 0.18 nm, at the same scanning scale as the Co film thickness, and the squareness of the hysteresis loop is shown to be as large as 0.96-1.0. As a result of the establishment of polishing techniques for Co thin-film electrodes sandwiched between borate glasses, we successfully demonstrate the formation of smooth Co edges and the generation of stray magnetic fields from Co edges. Theoretical calculation reveals that a strong stray field beyond 6 kOe is generated when the Co thickness is greater than 10 nm at a junction gap distance of 5 nm. From these experimental and calculation results, it can be concluded that SQC devices with a Co thickness of 10-20 nm can be expected to function as spin-filter devices.

Thickness measurement of a thin hetero-oxide film with an interfacial oxide layer by X-ray photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Kim, Kyung Joong; Lee, Seung Mi; Jang, Jong Shik; Moret, Mona

2012-02-01

The general equation Tove = L cos θ ln(Rexp/R0 + 1) for the thickness measurement of thin oxide films by X-ray photoelectron spectroscopy (XPS) was applied to a HfO2/SiO2/Si(1 0 0) as a thin hetero-oxide film system with an interfacial oxide layer. The contribution of the thick interfacial SiO2 layer to the thickness of the HfO2 overlayer was counterbalanced by multiplying the ratio between the intensity of Si4+ from a thick SiO2 film and that of Si0 from a Si(1 0 0) substrate to the intensity of Si4+ from the HfO2/SiO2/Si(1 0 0) film. With this approximation, the thickness levels of the HfO2 overlayers showed a small standard deviation of 0.03 nm in a series of HfO2 (2 nm)/SiO2 (2-6 nm)/Si(1 0 0) films. Mutual calibration with XPS and transmission electron microscopy (TEM) was used to verify the thickness of HfO2 overlayers in a series of HfO2 (1-4 nm)/SiO2 (3 nm)/Si(1 0 0) films. From the linear relation between the thickness values derived from XPS and TEM, the effective attenuation length of the photoelectrons and the thickness of the HfO2 overlayer could be determined.

Latitudinal Variations In Vertical Cloud Structure Of Jupiter As Determined By Ground- based Observation With Multispectral Imaging

NASA Astrophysics Data System (ADS)

Sato, T.; Kasaba, Y.; Takahashi, Y.; Murata, I.; Uno, T.; Tokimasa, N.; Sakamoto, M.

2008-12-01

We conducted ground-based observation of Jupiter with the liquid crystal tunable filter (LCTF) and EM-CCD camera in two methane absorption bands (700-757nm, 872-950nm at 3 nm step: total of 47 wavelengths) to derive detailed Jupiter's vertical cloud structure. The 2-meter reflector telescope at Nishi-Harima astronomical observatory in Japan was used for our observation on 26-30 May, 2008. After a series of image processing (composition of high quality images in each wavelength and geometry calibration), we converted observed intensity to absolute reflectivity at each pixel using standard star. As a result, we acquired Jupiter's data cubes with high-spatial resolution (about 1") and narrow band imaging (typically 7nm) in each methane absorption band by superimposing 30 Jupiter's images obtained in short exposure time (50 ms per one image). These data sets enable us to probe different altitudes of Jupiter from 100 mbar down to 1bar level with higher vertical resolution than using convectional interference filters. To interpret observed center-limb profiles, we developed radiative transfer code based on layer adding doubling algorithm to treat multiple scattering of solar light theoretically and extracted information on aerosol altitudes and optical properties using two-cloud model. First, we fit 5 different profiles simultaneously in continuum data (745-757 nm) to retrieve information on optical thickness of haze and single scattering albedo of cloud. Second, we fit 15 different profiles around 727nm methane absorption band and 13 different profiles around 890 nm methane absorption band to retrieve information on the aerosol altitude location and optical thickness of cloud. In this presentation, we present the results of these modeling simulations and discuss the latitudinal variations of Jupiter's vertical cloud structure.

Dimensional scaling of perovskite ferroelectric thin films

NASA Astrophysics Data System (ADS)

Keech, Ryan R.

Dimensional size reduction has been the cornerstone of the exponential improvement in silicon based logic devices for decades. However, fundamental limits in the device physics were reached ˜2003, halting further reductions in clock speed without significant penalties in power consumption. This has motivated the research into next generation transistors and switching devices to reinstate the scaling laws for clock speed. This dissertation aims to support the scaling of devices that are based on ferroelectricity and piezoelectricity and to provide a roadmap for the corresponding materials performance. First, a scalable growth process to obtain highly {001}-oriented lead magnesium niobate - lead titanate (PMN-PT) thin films was developed, motivated by the high piezoelectric responses observed in bulk single crystals. It was found that deposition of a 2-3 nm thick PbO buffer layer on {111} Pt thin film bottom electrodes, prior to chemical solution deposition of PMN-PT reduces the driving force for Pb diffusion from the PMN-PT to the bottom electrode, and facilitates nucleation of {001}-oriented perovskite grains. Energy dispersive spectroscopy demonstrated that up to 10% of the Pb from a PMN-PT precursor solution may diffuse into the bottom electrode. PMN-PT grains with a mixed {101}/{111} orientation in a matrix of Pb-deficient pyrochlore phase were then promoted near the interface. When this is prevented, phase pure films with {001} orientation with Lotgering factors of 0.98-1.0, can be achieved. The resulting films of only 300 nm in thickness exhibit longitudinal effective d33,f coefficients of ˜90 pm/V and strain values of ˜1% prior to breakdown. 300 nm thick epitaxial and polycrystalline lead magnesium niobate - lead titanate (70PMN-30PT) blanket thin films were studied for the relative contributions to property thickness dependence from interfacial and grain boundary low permittivity layers. Epitaxial PMN-PT films were grown on SrRuO 3 /(001)SrTiO3, while polycrystalline films with {001}-Lotgering factors >0.96 were grown on Pt/TiO2/SiO2/Si substrates via chemical solution deposition. It was found that both film types exhibited similar, thickness-independent high-field epsilonr of ˜300 with highly crystalline electrode/dielectric interfaces. The dielectric data suggest that irreversible domain wall motion is the major contributor to the overall dielectric response and its thickness dependence. In epitaxial films the irreversible Rayleigh coefficients reduced 85% upon decreasing thickness from 350 to 100 nm. Tmax was the only measured small signal quantity which was more thickness dependent in polycrystalline than epitaxial films. This was attributed to the relaxor nature present in the films, potentially stabilized by defect concentrations, and/or chemical inhomogeneity. The effective interfacial layers are found to contribute to the measured thickness dependence in d33,f measured by X-ray diffraction. Finally, high field piezoelectric characterization revealed a field-induced rhombohedral to tetragonal phase transition in epitaxial films. While the mechanisms causing thickness dependence are mostly understood, the functional properties of blanket PMN-PT films remain about an order of magnitude lower than what is achieved in constraint-free bulk single crystals. These property reductions are attributed to substrate clamping, and the process of declamping via lateral subdivision was studied in 300-350 nm thick, {001} oriented 70PMN-30PT films on Si substrates. In the clamped state, the films exhibit relative permittivity near 1500 and loss tangents of approximately 0.01. The films showed slim hysteresis loops with remanent polarizations of about 8 muC/cm2 and breakdown fields over 1500 kV/cm. Using optical and electron beam lithography combined with reactive ion etching, the PMN-PT films were systematically patterned down to lateral feature sizes of 200 nm in spatial scale with nearly vertical sidewalls. Upon lateral scaling, which produced partially declamped films, there was an increase in both small and large signal dielectric properties, including a doubling of the relative permittivity in structures with width-to-thickness aspect ratios of 0.7. In addition, declamping resulted in a counterclockwise rotation of the hysteresis loops, increasing the remanent polarization to 13.5 muC/cm2. Rayleigh analysis, Preisach modeling, and the relative permittivity as a function of temperature also indicated changes in the domain wall motion and intrinsic response of the laterally scaled PMN-PT. The longitudinal piezoelectric coefficient, d33,f, was interrogated as a function of position across the patterned structures by finite element modeling, piezoresponse force microscopy, and nanoprobe synchrotron X-ray diffraction. It was found that d33,f increased from the clamped value of 40-50 pm/V to ˜160 pm/V at the free sidewall under 200 kV/cm excitation. The sidewalls partially declamped the piezoelectric response 500-600 nm into the patterned structure, raising the piezoelectric response at the center of features with lateral dimensions less than 1 mum (3:1 width to thickness aspect ratio). The normalized data from all three characterization techniques are in excellent agreement, with quantitative differences providing insight to the field dependence of the piezoelectric coefficient and its declamping behavior.

Thickness-dependent blue shift in the excitonic peak of conformally grown ZnO:Al on ion-beam fabricated self-organized Si ripples

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

Basu, T.; Kumar, M.; Som, T., E-mail: tsom@iopb.res.in

2015-09-14

Al-doped ZnO (AZO) thin films of thicknesses 5,10, 15, 20, and 30 nm were deposited on 500 eV argon ion-beam fabricated nanoscale self-organized rippled-Si substrates at room temperature and are compared with similar films deposited on pristine-Si substrates (without ripples). It is observed that morphology of self-organized AZO films is driven by the underlying substrate morphology. For instance, for pristine-Si substrates, a granular morphology evolves for all AZO films. On the other hand, for rippled-Si substrates, morphologies having chain-like arrangement (anisotropic in nature) are observed up to a thickness of 20 nm, while a granular morphology evolves (isotropic in nature) for 30 nm-thick film.more » Photoluminescence studies reveal that excitonic peaks corresponding to 5–15 nm-thick AZO films, grown on rippled-Si templates, show a blue shift of 8 nm and 3 nm, respectively, whereas the peak shift is negligible for 20-nm thick film (with respect to their pristine counter parts). The observed blue shifts are substantiated by diffuse reflectance study and attributed to quantum confinement effect, associated with the size of the AZO grains and their spatial arrangements driven by the anisotropic morphology of underlying rippled-Si templates. The present findings will be useful for making tunable AZO-based light-emitting devices.« less

Morphological evolution of carbon nanofibers encapsulating SnCo alloys and its effect on growth of the solid electrolyte interphase layer.

PubMed

Shin, Jungwoo; Ryu, Won-Hee; Park, Kyu-Sung; Kim, Il-Doo

2013-08-27

Two distinctive one-dimensional (1-D) carbon nanofibers (CNFs) encapsulating irregularly and homogeneously segregated SnCo nanoparticles were synthesized via electrospinning of polyvinylpyrrolidone (PVP) and polyacrylonitrile (PAN) polymers containing Sn-Co acetate precursors and subsequent calcination in reducing atmosphere. CNFs synthesized with PVP, which undergoes structural degradation of the polymer during carbonization processes, exhibited irregular segregation of heterogeneous alloy particles composed of SnCo, Co3Sn2, and SnO with a size distribution of 30-100 nm. Large and exposed multiphase SnCo particles in PVP-driven amorphous CNFs (SnCo/PVP-CNFs) kept decomposing liquid electrolyte and were partly detached from CNFs during cycling, leading to a capacity fading at the earlier cycles. The closer study of solid electrolyte interphase (SEI) layers formed on the CNFs reveals that the gradual growth of fiber radius due to continuous increment of SEI layer thickness led to capacity fading. In contrast, SnCo particles in PAN-driven CNFs (SnCo/PAN-CNFs) showed dramatically reduced crystallite sizes (<10 nm) of single phase SnCo nanoparticles which were entirely embedded in dense, semicrystalline, and highly conducting 1-D carbon matrix. The growth of SEI layer was limited and saturated during cycling. As a result, SnCo/PAN-CNFs showed much improved cyclability (97.9% capacity retention) and lower SEI layer thickness (86 nm) after 100 cycles compared to SnCo/PVP-CNFs (capacity retention, 71.9%; SEI layer thickness, 593 nm). This work verifies that the thermal behavior of carbon precursor is highly responsible for the growth mechanism of SEI layer accompanied with particles detachment and cyclability of alloy particle embedded CNFs.

Exchange coupling and microwave absorption in core/shell-structured hard/soft ferrite-based CoFe2O4/NiFe2O4 nanocapsules

NASA Astrophysics Data System (ADS)

Feng, Chao; Liu, Xianguo; Or, Siu Wing; Ho, S. L.

2017-05-01

Core/shell-structured, hard/soft spinel-ferrite-based CoFe2O4/NiFe2O4 (CFO/NFO) nanocapsules with an average diameter of 17 nm are synthesized by a facile two-step hydrothermal process using CFO cores of ˜15 nm diameter as the hard magnetic phase and NFO shells of ˜1 nm thickness as the soft magnetic phase. The single-phase-like hysteresis loop with a high remnant-to-saturation magnetization ratio of 0.7, together with a small grain size of ˜16 nm, confirms the existence of exchange-coupling interaction between the CFO cores and the NFO shells. The effect of hard/soft exchange coupling on the microwave absorption properties is studied. Comparing to CFO and NFO nanoparticles, the finite-size NFO shells and the core/shell structure enable a significant reduction in electric resistivity and an enhancement in dipole and interfacial polarizations in the CFO/NFO nanocapsules, resulting in an obvious increase in dielectric permittivity and loss in the whole S-Ku bands of microwaves of 2-18 GHz, respectively. The exchange-coupling interaction empowers a more favorable response of magnetic moment to microwaves, leading to enhanced exchange resonances in magnetic permeability and loss above 10 GHz. As a result, strong absorption, as characterized by a large reflection loss (RL) of -20.1 dB at 9.7 GHz for an absorber thickness of 4.5 mm as well as a broad effective absorption bandwidth (for RL<-10 dB) of 8.4 GHz (7.8-16.2 GHz) at an absorber thickness range of 3.0-4.5 mm, is obtained.

Improved performance of organic light-emitting diode with vanadium pentoxide layer on the FTO surface

NASA Astrophysics Data System (ADS)

Saikia, D.; Sarma, R.

2017-06-01

Vanadium pentoxide layer deposited on the fluorine-doped tin oxide (FTO) anode by vacuum deposition has been investigated in organic light-emitting diode (OLED). With 12 nm optimal thickness of V2O5, the luminance efficiency is increased by 1.66 times compared to the single FTO-based OLED. The improvement of current efficiency implies that there is a better charge injection and better controlling of hole current. To investigate the performance of OLED by the buffer layer, V2O5 films of different thicknesses were deposited on the FTO anode and their J- V and L- V characteristics were studied. Further analysis was carried out by measuring sheet resistance, optical transmittance and surface morphology with the FE-SEM images. This result indicates that the V2O5 (12 nm) buffer layer is a good choice for increasing the efficiency of FTO-based OLED devices within the tunnelling region. Here the maximum value of current efficiency is found to be 2.83 cd / A.

Magnetization pinning in conducting films demonstrated using broadband ferromagnetic resonance

NASA Astrophysics Data System (ADS)

Kostylev, M.; Stashkevich, A. A.; Adeyeye, A. O.; Shakespeare, C.; Kostylev, N.; Ross, N.; Kennewell, K.; Magaraggia, R.; Roussigné, Y.; Stamps, R. L.

2010-11-01

The broadband microstrip ferromagnetic resonance (FMR), cavity FMR, and Brillouin light scattering spectroscopy techniques have been applied for detection and characterization of a magnetic inhomogeneity in a film sample. In the case of a 100 nm thick permalloy film, an additional magnetically depleted top sublayer has been detected due to pinning effect it produces on the magnetization in the bulk of the film. The pinning results in appearance of an exchange standing spin wave mode in the broadband FMR absorption spectrum, whose amplitudes are different depending on whether the film or the film substrate faces the microstrip transducer. Comparison of the experimental amplitudes for this mode with results of our theory for both film placements revealed that the depleted layer is located at the film surface facing away from the film substrate. Subsequent broadband FMR characterization of a large number of other presumably single-layer films with thicknesses in the range 30-100 nm showed the same result.

A Eu/Tb mixed lanthanide coordination polymer with rare 2D thick layers: Synthesis, characterization and ratiometric temperature sensing

NASA Astrophysics Data System (ADS)

Zhu, Yuanyuan; Xia, Tifeng; Zhang, Qi; Cui, Yuanjing; Yang, Yu; Qian, Guodong

2018-03-01

A series of lanthanide coordination polymers LnBTPTA (Ln = Eu, Tb, EuxTb1-x), was synthesized using a tricarbocylic ligand 4,4‧,4‧‧-(benzene-1,3,5-triyltris(1H-pyrazole-3,1-diyl))tribenzoic acid (H3BTPTA). X-ray single crystal analyses reveal that the asymmetric unit cell contains seven crystallographically independent metal ions and seven crystallographically independent ligands which is quite unusual. The 3D framework is comprised of 2D thick layers stacked through van der Waals force, π-π interactions and hydrogen bonding interactions. Eu0.0316Tb0.9684BTPTA presents a dual-emission of Tb3+ at 543 nm and Eu3+ at 617 nm, and the intensity ratio shows an excellent linear relationship with the temperature changing in 25-225 K. The relative sensitivity 0.45-5.12% K-1 is much higher than those have been reported in the same detection range.

The optimal thickness of a transmission-mode GaN photocathode

NASA Astrophysics Data System (ADS)

Wang, Xiao-Hui; Shi, Feng; Guo, Hui; Hu, Cang-Lu; Cheng, Hong-Chang; Chang, Ben-Kang; Ren, Ling; Du, Yu-Jie; Zhang, Jun-Ju

2012-08-01

A 150-nm-thick GaN photocathode with a Mg doping concentration of 1.6 × 1017 cm-3 is activated by Cs/O in an ultrahigh vacuum chamber, and a quantum efficiency (QE) curve of the negative electron affinity transmission-mode (t-mode) of the GaN photocathode is obtained. The maximum QE reaches 13.0% at 290 nm. According to the t-mode QE equation solved from the diffusion equation, the QE curve is fitted. From the fitting results, the electron escape probability is 0.32, the back-interface recombination velocity is 5 × 104 cm·s-1, and the electron diffusion length is 116 nm. Based on these parameters, the influence of GaN thickness on t-mode QE is simulated. The simulation shows that the optimal thickness of GaN is 90 nm, which is better than the 150-nm GaN.

Sub-nanometer pore formation in single-molecule-thick polyurea molecular-sieving membrane: a computational study.

PubMed

Park, Seongjin; Lansac, Yves; Jang, Yun Hee

2018-06-07

A polymeric network of 1-(4-tritylphenyl)urea (TPU) built via layer-by-layer cross-linking polymerization has been proposed to be an excellent mesh equipped with single-molecule-thick pores (i.e., cyclic poly-TPU rings), which can sieve glucose (∼0.7 nm) out of its mixture with urea for hemodialysis applications. Monte Carlo search for the lowest-energy conformation of various sizes of poly-TPU rings unravels the origin of narrow pore size distribution, which is around the sizes of dimer and trimer rings (0.3-0.8 nm). Flexible rings larger than the dimer and trimer rings, in particular tetramer rings, prefer a twisted conformation in the shape of the infinity symbol (∞, which looks like two dimer rings joined together) locked by a hydrogen bond between diphenylurea linker groups facing each other. Translocation energy profiles across these TPU rings reveal their urea-versus-glucose sieving mechanism: glucose is either too large (to enter dimers and twisted tetramers) or too perfectly fit (to exit trimers), leaving only a dimer-sized free space in the ring, whereas smaller-sized urea and water pass through these effective dimer-sized rings (bare dimers, twisted tetramers, and glucose-filled trimers) without encountering a substantial energy barrier or trap.

Nanomagnetic behavior of fullerene thin films in Earth magnetic field in dark and under polarization light influences.

PubMed

Koruga, Djuro; Nikolić, Aleksandra; Mihajlović, Spomenko; Matija, Lidija

2005-10-01

In this paper magnetic fields intensity of C60 thin films of 60 nm and 100 nm thickness under the influence of polarization lights are presented. Two proton magnetometers were used for measurements. Significant change of magnetic field intensity in range from 2.5 nT to 12.3 nT is identified as a difference of dark and polarization lights of 60 nm and 100 nm thin films thickness, respectively. Specific power density of polarization light was 40 mW/cm2. Based on 200 measurement data average value of difference between magnetic intensity of C60 thin films, with 60 nm and 100 nm thickness, after influence of polarization light, were 3.9 nT and 9.9 nT respectively.

Polypeptide multilayer films on colloidal particles: an in situ electro-optical study.

PubMed

Radeva, Tsetska; Kamburova, Kamelia

2007-04-15

The buildup of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) multilayers on beta-FeOOH colloidal particles was investigated by means of electro-optics and electrophoresis. The films were built at different (acidic) pH in the absence of salt. We found that the thickness of the film grows linearly when the fully charged PLL (at pH 5.5) is combined with almost fully charged PGA (at pH 6.5), with a thickness of about 2 nm per single layer. When the fully charged PLL is combined with weakly charged PGA (at pH 4.5), the film thickness increases exponentially with the number of deposited layers. The thickness of the exponentially growing film increases to 300 nm after deposition of 16 layers. The exponential film growth is attributed to the ability of the PLL to diffuse "in" and "out" of the film bulk at each deposition step. The variation in the electrical polarizability of the film-coated particles was also monitored as a function of the number of adsorbed layers. The result reveals that the PLL chains, which can diffuse into the film bulk, have no measurable contribution to the electro-optical effect of the films terminated with PLL. It is only due to the polarization of counterions of the PLL adsorbed on the film surface.

Spin wave filtering and guiding in Permalloy/iron nanowires

NASA Astrophysics Data System (ADS)

Silvani, R.; Kostylev, M.; Adeyeye, A. O.; Gubbiotti, G.

2018-03-01

We have investigated the spin wave filtering and guiding properties of periodic array of single (Permalloy and Fe) and bi-layer (Py/Fe) nanowires (NWs) by means of Brillouin light scattering measurements and micromagnetic simulations. For all the nanowire arrays, the thickness of the layers is 10 nm while all NWs have the same width of 340 nm and edge-to-edge separation of 100 nm. Spin wave dispersion has been measured in the Damon-Eshbach configuration for wave vector either parallel or perpendicular to the nanowire length. This study reveals the filtering property of the spin waves when the wave vector is perpendicular to the NW length, with frequency ranges where the spin wave propagation is permitted separated by frequency band gaps, and the guiding property of NW when the wave vector is oriented parallel to the NW, with spin wave modes propagating in parallel channels in the central and edge regions of the NW. The measured dispersions were well reproduced by micromagnetic simulations, which also deliver the spatial profiles for the modes at zero wave vector. To reproduce the dispersion of the modes localized close to the NW edges, uniaxial anisotropy has been introduced. In the case of Permalloy/iron NWs, the obtained results have been compared with those for a 20 nm thick effective NW having average magnetic properties of the two materials.

Enhanced Electro-Static Discharge Endurance of GaN-Based Light-Emitting Diodes with Specially Designed Electron Blocking Layer

NASA Astrophysics Data System (ADS)

Wang, Chunxia; Zhang, Xiong; Guo, Hao; Chen, Hongjun; Wang, Shuchang; Yang, Hongquan; Cui, Yiping

2013-10-01

GaN-based light-emitting diodes (LEDs) with specially designed electron blocking layers (EBLs) between the multiple quantum wells (MQWs) and the top p-GaN layer have been developed. The EBLs consist of Mg-doped p-AlGaN/GaN superlattice (SL) with the layer thickness of p-AlGaN varied from 1 to 10 nm and the layer thickness of p-GaN fixed at 1 nm in this study. It was found that under a 2000 V reverse bias voltage condition, the electro-static discharge (ESD) yield increased from 61.98 to 99.51% as the thickness of p-AlGaN in the EBLs was increased from 1 to 10 nm. Since the ESD yield was 97.80%, and maximum value for LEDs' light output power (LOP) and minimum value for the forward voltage (Vf) were achieved when the thickness of p-AlGaN in the EBLs was 9 nm with a 20 mA injection current, it was concluded that the p-AlGaN/GaN SL EBLs with the combination of 9-nm-thick p-AlGaN and 1-nm-thick p-GaN would be beneficial to the fabrication of the GaN-based LEDs with high brightness, high ESD endurance, and low Vf.

Reaching state-of-the art requirements for MIM capacitors with a single-layer anodic Al2O3 dielectric and imprinted electrodes

NASA Astrophysics Data System (ADS)

Hourdakis, Emmanouel; Nassiopoulou, Androula G.

2017-07-01

Metal-Insulator-Metal (MIM) capacitors with a high capacitance density and low non-linearity coefficient using a single-layer dielectric of barrier-type anodic alumina (Al2O3) and an imprinted bottom Al electrode are presented. Imprinting of the bottom electrode aimed at increasing the capacitor effective surface area by creating a three-dimensional MIM capacitor architecture. The bottom Al electrode was only partly nanopatterned so as to ensure low series resistance of the MIM capacitor. With a 3 nm thick anodic Al2O3 dielectric, the capacitor with the imprinted electrode showed a 280% increase in capacitance density compared to the flat electrode capacitor, reaching a value of 20.5 fF/μm2. On the other hand, with a 30 nm thick anodic Al2O3 layer, the capacitance density was 7.9 fF/μm2 and the non-linearity coefficient was as low as 196 ppm/V2. These values are very close to reaching all requirements of the last International Technology Roadmap for Semiconductors for MIM capacitors [ITRS, http://www.itrs2.net/2013-itrs.html for ITRS Roadmap (2013)], and they are achieved by a single-layer dielectric instead of the complicated dielectric stacks of the literature. The obtained results constitute a real progress compared to previously reported results by our group for MIM capacitors using imprinted electrodes.

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

Papernov, Semyon; Kozlov, Alexei A.; Oliver, James B.

Here, the role of thin-film interfaces in the near-ultraviolet (near-UV) absorption and pulsed laser-induced damage was studied for ion-beam-sputtered and electron-beam-evaporated coatings comprised from HfO 2 and SiO 2 thin-film pairs. To separate contributions from the bulk of the film and from interfacial areas, absorption and damage threshold measurements were performed for a one-wave (355-nm wavelength) thick, HfO 2 single-layer film and for a film containing seven narrow HfO 2 layers separated by SiO 2 layers. The seven-layer film was designed to have a total optical thickness of HfO 2 layers, equal to one wave at 355 nm and anmore » E-field peak and average intensity similar to a single-layer HfO 2 film. Absorption in both types of films was measured using laser calorimetry and photothermal heterodyne imaging. The results showed a small contribution to total absorption from thin-film interfaces as compared to HfO 2 film material. The relevance of obtained absorption data to coating near-UV, nanosecond-pulse laser damage was verified by measuring the damage threshold and characterizing damage morphology. The results of this study revealed a higher damage resistance in the seven-layer coating as compared to the single-layer HfO 2 film in both sputtered and evaporated coatings. The results are explained through the similarity of interfacial film structure with structure formed during the codeposition of HfO 2 and SiO 2 materials.« less

Formation of ultrathin Ni germanides: solid-phase reaction, morphology and texture

NASA Astrophysics Data System (ADS)

van Stiphout, K.; Geenen, F. A.; De Schutter, B.; Santos, N. M.; Miranda, S. M. C.; Joly, V.; Detavernier, C.; Pereira, L. M. C.; Temst, K.; Vantomme, A.

2017-11-01

The solid-phase reaction of ultrathin (⩽10 nm) Ni films with different Ge substrates (single-crystalline (1 0 0), polycrystalline, and amorphous) was studied. As thickness goes down, thin film texture becomes a dominant factor in both the film’s phase formation and morphological evolution. As a consequence, certain metastable microstructures are epitaxially stabilized on crystalline substrates, such as the ɛ-Ni5Ge3 phase or a strained NiGe crystal structure on the single-crystalline substrates. Similarly, the destabilizing effect of axiotaxial texture on the film’s morphology becomes more pronounced as film thicknesses become smaller. These effects are contrasted by the evolution of germanide films on amorphous substrates, on which neither epitaxy nor axiotaxy can form, i.e. none of the (de)stabilizing effects of texture are observed. The crystallization of such amorphous substrates however, drives the film breakup.

Satellite measurements of large-scale air pollution - Methods

NASA Technical Reports Server (NTRS)

Kaufman, Yoram J.; Ferrare, Richard A.; Fraser, Robert S.

1990-01-01

A technique for deriving large-scale pollution parameters from NIR and visible satellite remote-sensing images obtained over land or water is described and demonstrated on AVHRR images. The method is based on comparison of the upward radiances on clear and hazy days and permits simultaneous determination of aerosol optical thickness with error Delta tau(a) = 0.08-0.15, particle size with error + or - 100-200 nm, and single-scattering albedo with error + or - 0.03 (for albedos near 1), all assuming accurate and stable satellite calibration and stable surface reflectance between the clear and hazy days. In the analysis of AVHRR images of smoke from a forest fire, good agreement was obtained between satellite and ground-based (sun-photometer) measurements of aerosol optical thickness, but the satellite particle sizes were systematically greater than those measured from the ground. The AVHRR single-scattering albedo agreed well with a Landsat albedo for the same smoke.

Simulations of single-particle imaging of hydrated proteins with x-ray free-electron lasers

NASA Astrophysics Data System (ADS)

Fortmann-Grote, C.; Bielecki, J.; Jurek, Z.; Santra, R.; Ziaja-Motyka, B.; Mancuso, A. P.

2017-08-01

We employ start-to-end simulations to model coherent diffractive imaging of single biomolecules using x-ray free electron lasers. This technique is expected to yield new structural information about biologically relevant macromolecules thanks to the ability to study the isolated sample in its natural environment as opposed to crystallized or cryogenic samples. The effect of the solvent on the diffraction pattern and interpretability of the data is an open question. We present first results of calculations where the solvent is taken into account explicitly. They were performed with a molecular dynamics scheme for a sample consisting of a protein and a hydration layer of varying thickness. Through R-factor analysis of the simulated diffraction patterns from hydrated samples, we show that the scattering background from realistic hydration layers of up to 3 Å thickness presents no obstacle for the resolution of molecular structures at the sub-nm level.

Optical and Thermo-optical Properties of Polyimide-Single-Walled Carbon Nanotube Films: Experimental Results and Empirical Equations

NASA Technical Reports Server (NTRS)

Smith, Joseph G., Jr.; Connell, John W.; Watson, Kent A.; Danehy, Paul M.

2005-01-01

The incorporation of single-walled carbon nanotubes (SWNTs) into the bulk of space environmentally durable polymers at loading levels greater than or equal to 0.05 wt % has afforded thin films with surface and volume resistivities sufficient for electrostatic charge mitigation. However, the optical transparency at 500 nm decreased and the thermo-optical properties (solar absorptivity and thermal emissivity) increased with increaed SWNT loading. These properties were also dependent on film thickness. The absorbance characteristics of the films as a function of SWNT loading and film thickness were measured and determined to follow the classical Beer-Lambert law. Based on these results, an empirical relationship was derived and molar absorptivities determined for both the SWNTs and polymer matrix to provide a predictive approximation of these properties. The molar absorptivity determined for SWNTs dispersed in the polymer was comparable to reported solution determined values for HiPco SWNTs.

Tunable in-line fiber optic comb filter using a side-polished single-mode fiber coupler with LiNbO 3 overlay and intermediate coupling layer

NASA Astrophysics Data System (ADS)

Sohn, Kyung-Rak; Song, Jae-Won

2002-03-01

Using a side-polished single-mode fiber covered with a polished LiNbO 3 overlay and an intermediate coupling layer, tunable fiber-optic comb filters are demonstrated. The device behaviors based on the modal properties of the fiber and the planar LiNbO 3 waveguide are analyzed by two dimensional beam propagation methods (2-D BPM) and discussed the role of an intermediate coupling layer in terms of coupling efficiency. We also show that the thermo-optic effects of this layer can be utilized to tune the comb filter. When the polished x-cut LiNbO 3 with 200 μm thickness is used as a multimode overlay waveguide, the comb output spectra with free spectral range of 4 nm are measured in 1550 nm wavelength range. The tuning rate as a function of the refractive index of an intermediate coupling layer, Δλ/ Δnb, is about -0.129 nm/-0.001. The experimental results are in good agreement with the calculated results.

DNA Physical Mapping via the Controlled Translocation of Single Molecules through a 5-10nm Silicon Nitride Nanopore

NASA Astrophysics Data System (ADS)

Stein, Derek; Reisner, Walter; Jiang, Zhijun; Hagerty, Nick; Wood, Charles; Chan, Jason

2009-03-01

The ability to map the binding position of sequence-specific markers, including transcription-factors, protein-nucleic acids (PNAs) or deactivated restriction enzymes, along a single DNA molecule in a nanofluidic device would be of key importance for the life-sciences. Such markers could give an indication of the active genes at particular stage in a cell's transcriptional cycle, pinpoint the location of mutations or even provide a DNA barcode that could aid in genomics applications. We have developed a setup consisting of a 5-10 nm nanopore in a 20nm thick silicon nitride film coupled to an optical tweezer setup. The translocation of DNA across the nanopore can be detected via blockades in the electrical current through the pore. By anchoring one end of the translocating DNA to an optically trapped microsphere, we hope to stretch out the molecule in the nanopore and control the translocation speed, enabling us to slowly scan across the genome and detect changes in the baseline current due to the presence of bound markers.

Broadband sum-frequency generation using d₃₃ in periodically poled LiNbO₃ thin film in the telecommunications band.

PubMed

Li, Guangzhen; Chen, Yuping; Jiang, Haowei; Chen, Xianfeng

2017-03-01

We demonstrate the first, to the best of our knowledge, type-0 broadband sum-frequency generation (SFG) based on single-crystal periodically poled LiNbO₃ (PPLN) thin film. The broad bandwidth property was largely tuned from mid-infrared region to the telecommunications band by engineering the thickness of PPLN from bulk crystal to nanoscale. It provides SFG a solution with both broadband and high efficiency by using the highest nonlinear coefficient d₃₃ instead of d₃₁ in type-I broadband SFG or second-harmonic generation. The measured 3 dB upconversion bandwidth is about 15.5 nm for a 4 cm long single crystal at 1530 nm wavelength. It can find applications in chip-scale spectroscopy, quantum information processing, LiNbO₃-thin-film-based microresonator and optical nonreciprocity devices, etc.

Measurement of Spectral Broadening in PTS-Polydiacetylene

NASA Astrophysics Data System (ADS)

Bhowmik, Achintya; Thakur, Mrinal

1998-03-01

PTS-polydiacetylene has significant potential for future applications in ultrafast all-optical switches and logic gates.(R. Quintero-Torres and M. Thakur, Appl. Phys. Lett., 66, 1310 (1995).) In this work, we have made detailed measurements of the instantaneous spectral line broadening in a 500 μm thick PTS single-crystal as a function of intensity and wavelength. A mode-locked Ti-Sapphire laser with 2 ps pulse-width at 82 MHz repetition rate, and a Nd:YAG laser with 60 ps pulse-width at 10 Hz repetition rate were used for measurements at 720-840 nm and 1064 nm wavelength respectively. The spectral bandwidth of the beam was recorded before and after passing through the PTS single-crystal by a high-resolution spectrometer. The nonlinear refractive index (n_2) of PTS as a function of wavelength has been determined from the spectral broadening data.

Electrical, optical and structural properties of transparent conducting Al doped ZnO (AZO) deposited by sol-gel spin coating

NASA Astrophysics Data System (ADS)

Tonny, Kaniz Naila; Rafique, Rosaleena; Sharmin, Afrina; Bashar, Muhammad Shahriar; Mahmood, Zahid Hasan

2018-06-01

Al doped ZnO (AZO) films are fabricated by using sol-gel spin coating method and changes in electrical, optical and structural properties due to variation in film thickness is studied. AZO films provide c-axis orientation along the (002) plane and peak sharpness increased with film thickness is evident from XRD analysis. Conductivity (σ) of AZO films has increased from 2.34 (Siemens/cm) to 20156.27 (Siemens/cm) whereas sheet resistance (Rsh) decreases from 606300 (ohms/sq.) to 2.08 (ohm/sq.) with increase of film thickness from 296 nm to 1030 nm. Optical transmittance (T%) of AZO films is decreased from around 82% to 62% in the visible region. And grain size (D) of AZO thin films has been found to increase from 19.59 nm to 25.25 nm with increase of film thickness. Figure of Merit is also calculated for prepared sample of AZO. Among these four sample of AZO thin films, L-15 sample (having thickness in 895 nm) has provided highest figure of merit which is 5.49*10^-4 (Ω-1).

Photoconductivity of Macroporous and Nonporous Silicon with Ultrathin Oxide Layers

NASA Astrophysics Data System (ADS)

Konin, K. P.; Goltvyansky, Yu. V.; Karachevtseva, L. A.; Karas, M. I.; Morozovs'ka, D. V.

2018-06-01

The photoconductivity of macroporous silicon with ultrathin oxide layers of 2.7-30 nm in thickness at short-wave optical excitation was studied. The following feature was revealed: a nonmonotonic change in the photoconductivity as a function of the oxide thickness. At a minimum thickness, the photoconductivity is negative; in the interval 6.8-15 nm, it is very much suppressed; at 15-30 nm, it is positive. Suppression of photoconductivity over a wide thickness range indicates an abnormally high concentration of traps and capture centers for charge carriers of both signs. Such a change in the photoconductivity corresponds to the known results on the continuous morphological rearrangement of the oxide in the thickness range from 6-7 nm to 12-15 nm from the coesite-like (4-membered SiO4 tetrahedra rings) to the tridymite-like (6-membered SiO4 tetrahedra rings). The suppression of photoconductivity in the intermediate range probably demonstrates the collective, antisynergetic action of these coexisting oxide forms on the nonequilibrium charge carriers. These coexisting oxide forms manifest themselves as an unusual collective defect.

Thermochromic VO2 thin films: solution-based processing, improved optical properties, and lowered phase transformation temperature.

PubMed

Zhang, Zongtao; Gao, Yanfeng; Chen, Zhang; Du, Jing; Cao, Chuanxiang; Kang, Litao; Luo, Hongjie

2010-07-06

This paper describes a solution-phase synthesis of high-quality vanadium dioxide thermochromic thin films. The films obtained showed excellent visible transparency and a large change in transmittance at near-infrared (NIR) wavelengths before and after the metal-insulator phase transition (MIPT). For a 59 nm thick single-layer VO(2) thin film, the integral values of visible transmittance (T(int)) for metallic (M) and semiconductive (S) states were 54.1% and 49.1%, respectively, while the NIR switching efficiencies (DeltaT) were as high as 50% at 2000 nm. Thinner films can provide much higher transmittance of visible light, but they suffer from an attenuation of the switching efficiency in the near-infrared region. By varying the film thickness, ultrahigh T(int) values of 75.2% and 75.7% for the M and S states, respectively, were obtained, while the DeltaT at 2000 nm remained high. These results represent the best data for VO(2) to date. Thicker films in an optimized range can give enhanced NIR switching efficiencies and excellent NIR blocking abilities; in a particularly impressive experiment, one film provided near-zero NIR transmittance in the switched state. The thickness-dependent performance suggests that VO(2) will be of great use in the objective-specific applications. The reflectance and emissivity at the wavelength range of 2.5-25 microm before and after the MIPT were dependent on the film thickness; large contrasts were observed for relatively thick films. This work also showed that the MIPT temperature can be reduced simply by selecting the annealing temperature that induces local nonstoichiometry; a MIPT temperature as low as 42.7 degrees C was obtained by annealing the film at 440 degrees C. These properties (the high visible transmittance, the large change in infrared transmittance, and the near room-temperature MIPT) suggest that the current method is a landmark in the development of this interesting material toward applications in energy-saving smart windows.

Efficient blue and white polymer light emitting diodes based on a well charge balanced, core modified polyfluorene derivative.

PubMed

Das, Dipjyoti; Gopikrishna, Peddaboodi; Singh, Ashish; Dey, Anamika; Iyer, Parameswar Krishnan

2016-03-14

Fabrication of efficient blue and white polymer light-emitting diodes (PLEDs) using a well charge balanced, core modified polyfluorene derivative, poly[2,7-(9,9'-dioctylfluorene)-co-N-phenyl-1,8-naphthalimide (99:01)] (PFONPN01), is presented. The excellent film forming properties as observed from the morphological study and the enhanced electron transport properties due to the inclusion of the NPN unit in the PFO main chain resulted in improved device properties. Bright blue light was observed from single layer PLEDs with PFONPN01 as an emissive layer (EML) as well as from double layer PLEDs using tris-(8-hydroxyquinoline) aluminum (Alq3) as an electron transporting layer (ETL) and LiF/Al as a cathode. The effect of ETL thickness on the device performance was studied by varying the Alq3 thickness (5 nm, 10 nm and 20 nm) and the device with an ETL thickness of 20 nm was found to exhibit the maximum brightness value of 11 662 cd m(-2) with a maximum luminous efficiency of 4.87 cd A(-1). Further, by using this highly electroluminescent blue PFONPN01 as a host and a narrow band gap, yellow emitting small molecule, dithiophene benzothiadiazole (DBT), as a guest at three different concentrations (0.2%, 0.4% and 0.6%), WPLEDs with the ITO/PEDOT:PSS/emissive layer/Alq3(20 nm)/LiF/Al configuration were fabricated and maximum brightness values of 8025 cd m(-2), 9565 cd m(-2) and 10 180 cd m(-2) were achieved respectively. 0.4% DBT in PFONPN01 was found to give white light with Commission International de l'Echairage (CIE) coordinates of (0.31, 0.38), a maximum luminous efficiency of 6.54 cd A(-1) and a color-rendering index (CRI) value of 70.

Prospects for using existing resists for evaluating 157-nm imaging systems

NASA Astrophysics Data System (ADS)

Fedynyshyn, Theodore H.; Kunz, Roderick R.; Doran, Scott P.; Goodman, Russell B.; Lind, Michele L.; Curtin, Jane E.

2000-06-01

Lithography at 157 nm represents the next evolutionary step in the Great Optical Continuum and is currently under investigation as a possible successor to 193-nm lithography. If successful, the photoresists used for this technology must be initially capable of 100-nm resolution and be extendable to less than 70 nm. Unfortunately, as with the transition to shorter wavelengths in the past, the photoresist materials developed for longer wavelengths appear to be too absorbent for practical use as a traditional high resolution single layer resist imageable with 157 nm radiation. Until new photoresist materials are developed that are sufficiently transparent to be used as single layer resists, the existing need for a resist to be used to evaluate 157 nm imaging systems, such as the prototype steppers now under development, will have to be met by employing existing resists. We have surveyed the commercial resist market with the dual purpose of identifying the general categories of commercial resists that have potential for use as tool evaluation resist and to baseline these resists for comparison against future 157 nm resist candidates. Little difference was observed in the 157- nm absorbance between different classes of resists with most resists having an absorbance between 6 and 8 per micron. Due to the high absorbance at 157 nm of polyhydroxystyrene, polyacrylate, and polycyclic copolymer based resists, the coated resist thickness will need to be under 100 nm. All four commercial resists evaluated for imaging at 157 nm showed that they are capable of acting as a tool testing resist to identify issues attributed focus, illumination, and vibration. Finally, an improved tool testing resist can be developed within the existing resist material base, that is capable of 100 nm imaging with a binary mask and 70 nm imaging with a phase shift mask. Minor formulation modification can greatly improve resist performance including improved resolution and reduced line edge roughness.

Origins of enhanced thermoelectric power factor in topologically insulating Bi{sub 0.64}Sb{sub 1.36}Te{sub 3} thin films

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

Liu, Wei; State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070; Chi, Hang

2016-01-25

In this research, we report the enhanced thermoelectric power factor in topologically insulating thin films of Bi{sub 0.64}Sb{sub 1.36}Te{sub 3} with a thickness of 6–200 nm. Measurements of scanning tunneling spectroscopy and electronic transport show that the Fermi level lies close to the valence band edge, and that the topological surface state (TSS) is electron dominated. We find that the Seebeck coefficient of the 6 nm and 15 nm thick films is dominated by the valence band, while the TSS chiefly contributes to the electrical conductivity. In contrast, the electronic transport of the reference 200 nm thick film behaves similar to bulk thermoelectric materialsmore » with low carrier concentration, implying the effect of the TSS on the electronic transport is merely prominent in the thin region. The conductivity of the 6 nm and 15 nm thick film is obviously higher than that in the 200 nm thick film owing to the highly mobile TSS conduction channel. As a consequence of the enhanced electrical conductivity and the suppressed bipolar effect in transport properties for the 6 nm thick film, an impressive power factor of about 2.0 mW m{sup −1} K{sup −2} is achieved at room temperature for this film. Further investigations of the electronic transport properties of TSS and interactions between TSS and the bulk band might result in a further improved thermoelectric power factor in topologically insulating Bi{sub 0.64}Sb{sub 1.36}Te{sub 3} thin films.« less

Diode-end-pumped continuously tunable single frequency Tm, Ho:LLF laser at 2.06 μm.

PubMed

Zhang, Xinlu; Zhang, Su; Xiao, Nana; Cui, Jinhui; Zhao, Jiaqun; Li, Li

2014-03-10

We report on a laser diode-end-pumped continuously tunable single frequency Tm, Ho:LLF laser near room temperature. For transmission of 5%, the maximum single frequency output power of 221 mW at 2064.4 nm was obtained by using two uncoated etalons. The single frequency Tm, Ho:LLF laser operated on the fundamental transverse mode with an M2 factor of 1.13, and the output frequency could be tuned continuously near 1.5 GHz by angle tuning only of the 1 mm thick etalon. Furthermore, the influence of output coupler transmission on the laser performance was also investigated. The single frequency laser can be used as a seed laser for coherent Doppler lidar and differential absorption lidar systems.

Two-layer anti-reflection strategies for implant applications

NASA Astrophysics Data System (ADS)

Guerrero, Douglas J.; Smith, Tamara; Kato, Masakazu; Kimura, Shigeo; Enomoto, Tomoyuki

2006-03-01

A two-layer bottom anti-reflective coating (BARC) concept in which a layer that develops slowly is coated on top of a bottom layer that develops more rapidly was demonstrated. Development rate control was achieved by selection of crosslinker amount and BARC curing conditions. A single-layer BARC was compared with the two-layer BARC concept. The single-layer BARC does not clear out of 200-nm deep vias. When the slower developing single-layer BARC was coated on top of the faster developing layer, the vias were cleared. Lithographic evaluation of the two-layer BARC concept shows the same resolution advantages as the single-layer system. Planarization properties of a two-layer BARC system are better than for a single-layer system, when comparing the same total nominal thicknesses.

Direct observation of resonance scattering patterns in single silicon nanoparticles

NASA Astrophysics Data System (ADS)

Valuckas, Vytautas; Paniagua-Domínguez, Ramón; Fu, Yuan Hsing; Luk'yanchuk, Boris; Kuznetsov, Arseniy I.

2017-02-01

We present the first direct observation of the scattering patterns of electric and magnetic dipole resonances excited in a single silicon nanosphere. Almost perfectly spherical silicon nanoparticles were fabricated and deposited on a 30 nm-thick silicon nitride membrane in an attempt to minimize particle—substrate interaction. Measurements were carried out at visible wavelengths by means of the Fourier microscopy in a dark-field illumination setup. The obtained back-focal plane images clearly reveal the characteristic scattering patterns associated with each resonance and are found to be in a good agreement with the simulated results.

Resveratrol increases nitric oxide production in the rat thick ascending limb via Ca2+/calmodulin.

PubMed

Gonzalez-Vicente, Agustin; Cabral, Pablo D; Garvin, Jeffrey L

2014-01-01

The thick ascending limb of the loop of Henle reabsorbs 30% of the NaCl filtered through the glomerulus. Nitric oxide (NO) produced by NO synthase 3 (NOS3) inhibits NaCl absorption by this segment. Resveratrol, a polyphenol, has beneficial cardiovascular and renal effects, many of which are mediated by NO. Resveratrol increases intracellular Ca2+ (Cai) and AMP kinase (AMPK) and NAD-dependent deacetylase sirtuin1 (SIRT1) activities, all of which could activate NO production. We hypothesized that resveratrol stimulates NO production by thick ascending limbs via a Ca2+/calmodulin-dependent mechanism. To test this, the effect of resveratrol on NO bioavailability was measured in thick ascending limb suspensions. Cai was measured in single perfused thick ascending limbs. SIRT1 activity and expression were measured in thick ascending limb lysates. Resveratrol (100 µM) increased NO bioavailability in thick ascending limb suspensions by 1.3±0.2 AFU/mg/min (p<0.03). The NOS inhibitor L-NAME blunted resveratrol-stimulated NO bioavailability by 96±11% (p<0.03). The superoxide scavenger tempol had no effect. Resveratrol elevated Cai from 48±7 to 135±24 nM (p<0.01) in single tubules. In Ca2+-free media, the resveratrol-induced increase in NO was blunted by 60±20% (p<0.05) and the rise in Cai reduced by 80%. Calmodulin inhibition prevented the resveratrol-induced increase in NO (p<0.002). AMPK inhibition had no effect. Resveratrol did not increase SIRT1 activity. We conclude that resveratrol increases NO production in thick ascending limbs via a Ca2+/calmodulin dependent mechanism, and SIRT1 and AMPK do not participate. Resveratrol-stimulated NO production in thick ascending limbs may account for part of its beneficial effects.

Dopant mapping in thin FIB prepared silicon samples by Off-Axis Electron Holography.

PubMed

Pantzer, Adi; Vakahy, Atsmon; Eliyahou, Zohar; Levi, George; Horvitz, Dror; Kohn, Amit

2014-03-01

Modern semiconductor devices function due to accurate dopant distribution. Off-Axis Electron Holography (OAEH) in the transmission electron microscope (TEM) can map quantitatively the electrostatic potential in semiconductors with high spatial resolution. For the microelectronics industry, ongoing reduction of device dimensions, 3D device geometry, and failure analysis of specific devices require preparation of thin TEM samples, under 70 nm thick, by focused ion beam (FIB). Such thicknesses, which are considerably thinner than the values reported to date in the literature, are challenging due to FIB induced damage and surface depletion effects. Here, we report on preparation of TEM samples of silicon PN junctions in the FIB completed by low-energy (5 keV) ion milling, which reduced amorphization of the silicon to 10nm thick. Additional perpendicular FIB sectioning enabled a direct measurement of the TEM sample thickness in order to determine accurately the crystalline thickness of the sample. Consequently, we find that the low-energy milling also resulted in a negligible thickness of electrically inactive regions, approximately 4nm thick. The influence of TEM sample thickness, FIB induced damage and doping concentrations on the accuracy of the OAEH measurements were examined by comparison to secondary ion mass spectrometry measurements as well as to 1D and 3D simulations of the electrostatic potentials. We conclude that for TEM samples down to 100 nm thick, OAEH measurements of Si-based PN junctions, for the doping levels examined here, resulted in quantitative mapping of potential variations, within ~0.1 V. For thinner TEM samples, down to 20 nm thick, mapping of potential variations is qualitative, due to a reduced accuracy of ~0.3 V. This article is dedicated to the memory of Zohar Eliyahou. Copyright © 2014 Elsevier B.V. All rights reserved.

High quality single shot diffraction patterns using ultrashort megaelectron volt electron beams from a radio frequency photoinjector.

PubMed

Musumeci, P; Moody, J T; Scoby, C M; Gutierrez, M S; Bender, H A; Wilcox, N S

2010-01-01

Single shot diffraction patterns using a 250-fs-long electron beam have been obtained at the UCLA Pegasus laboratory. High quality images with spatial resolution sufficient to distinguish closely spaced peaks in the Debye-Scherrer ring pattern have been recorded by scattering the 1.6 pC 3.5 MeV electron beam generated in the rf photoinjector off a 100-nm-thick Au foil. Dark current and high emittance particles are removed from the beam before sending it onto the diffraction target using a 1 mm diameter collimating hole. These results open the door to the study of irreversible phase transformations by single shot MeV electron diffraction.

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.

Laser-induced fluorescence detection strategies for sodium atoms and compounds in high-pressure combustors

NASA Technical Reports Server (NTRS)

Weiland, Karen J. R.; Wise, Michael L.; Smith, Gregory P.

1993-01-01

A variety of laser-induced fluorescence schemes were examined experimentally in atmospheric pressure flames to determine their use for sodium atom and salt detection in high-pressure, optically thick environments. Collisional energy transfer plays a large role in fluorescence detection. Optimum sensitivity, at the parts in 10 exp 9 level for a single laser pulse, was obtained with the excitation of the 4p-3s transition at 330 nm and the detection of the 3d-3p fluorescence at 818 nm. Fluorescence loss processes, such as ionization and amplified spontaneous emission, were examined. A new laser-induced atomization/laser-induced fluorescence detection technique was demonstrated for NaOH and NaCl. A 248-nm excimer laser photodissociates the salt molecules present in the seeded flames prior to atom detection by laser-induced fluorescence.

Mutual Photoluminescence Quenching and Photovoltaic Effect in Large-Area Single-Layer MoS2-Polymer Heterojunctions.

PubMed

Shastry, Tejas A; Balla, Itamar; Bergeron, Hadallia; Amsterdam, Samuel H; Marks, Tobin J; Hersam, Mark C

2016-11-22

Two-dimensional transition metal dichalcogenides (TMDCs) have recently attracted attention due to their superlative optical and electronic properties. In particular, their extraordinary optical absorption and semiconducting band gap have enabled demonstrations of photovoltaic response from heterostructures composed of TMDCs and other organic or inorganic materials. However, these early studies were limited to devices at the micrometer scale and/or failed to exploit the unique optical absorption properties of single-layer TMDCs. Here we present an experimental realization of a large-area type-II photovoltaic heterojunction using single-layer molybdenum disulfide (MoS 2 ) as the primary absorber, by coupling it to the organic π-donor polymer PTB7. This TMDC-polymer heterojunction exhibits photoluminescence intensity that is tunable as a function of the thickness of the polymer layer, ultimately enabling complete quenching of the TMDC photoluminescence. The strong optical absorption in the TMDC-polymer heterojunction produces an internal quantum efficiency exceeding 40% for an overall cell thickness of less than 20 nm, resulting in exceptional current density per absorbing thickness in comparison to other organic and inorganic solar cells. Furthermore, this work provides insight into the recombination processes in type-II TMDC-polymer heterojunctions and thus provides quantitative guidance to ongoing efforts to realize efficient TMDC-based solar cells.

An achromatic four-mirror compensator for spectral ellipsometers

NASA Astrophysics Data System (ADS)

Kovalev, V. I.; Rukovishnikov, A. I.; Kovalev, S. V.; Kovalev, V. V.; Rossukanyi, N. M.

2017-07-01

Measurement and calculation results are presented that confirm that design four-mirror compensators can be designed for the spectral range of 200-2000 nm that is widely used in modern spectral ellipsometers. Measurements and calculations according to standard ellipsometric programs have been carried out on a broadband LED spectral ellipsometer with switching of orthogonal polarization states. Mirrors with the structure of glass substrate/Al2O3 layer (20-30 nm thick)/Al layer (150 nm thick)/upper Al2O3 layer (with specified thickness d) have been prepared by vacuum-evaporation method. It is shown that the phase-shift spectra of a four-mirror compensator, two mirrors of which have a native oxide 5.5 nm thick and the two others of which have an oxide layer 36 nm thick, measured on the ellipsometer, are flattened in comparison with similar spectra of a compensator, all four mirrors of which have a native oxide, especially in the short-wavelength spectral region. The results of calculating the phase-shift spectra of the four-mirror compensator with six variable parameters (angles of incidence of radiation on the mirrors and thicknesses of oxide layers on four mirrors) are presented. High-quality achromatization in a wide spectral range can be achieved for certain sets of parameters.

Enhancement in sensitivity of graphene-based zinc oxide assisted bimetallic surface plasmon resonance (SPR) biosensor

NASA Astrophysics Data System (ADS)

Kumar, Rajeev; Kushwaha, Angad S.; Srivastava, Monika; Mishra, H.; Srivastava, S. K.

2018-03-01

In the present communication, a highly sensitive surface plasmon resonance (SPR) biosensor with Kretschmann configuration having alternate layers, prism/zinc oxide/silver/gold/graphene/biomolecules (ss-DNA) is presented. The optimization of the proposed configuration has been accomplished by keeping the constant thickness of zinc oxide (32 nm), silver (32 nm), graphene (0.34 nm) layer and biomolecules (100 nm) for different values of gold layer thickness (1, 3 and 5 nm). The sensitivity of the proposed SPR biosensor has been demonstrated for a number of design parameters such as gold layer thickness, number of graphene layer, refractive index of biomolecules and the thickness of biomolecules layer. SPR biosensor with optimized geometry has greater sensitivity (66 deg/RIU) than the conventional (52 deg/RIU) as well as other graphene-based (53.2 deg/RIU) SPR biosensor. The effect of zinc oxide layer thickness on the sensitivity of SPR biosensor has also been analysed. From the analysis, it is found that the sensitivity increases significantly by increasing the thickness of zinc oxide layer. It means zinc oxide intermediate layer plays an important role to improve the sensitivity of the biosensor. The sensitivity of SPR biosensor also increases by increasing the number of graphene layer (upto nine layer).

The effect of the MgO buffer layer thickness on magnetic anisotropy in MgO/Fe/Cr/MgO buffer/MgO(001)

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

Kozioł-Rachwał, Anna, E-mail: a.koziolrachwal@aist.go.jp; AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. Mickiewicza 30, 30-059 Kraków; Nozaki, Takayuki

2016-08-28

The relationship between the magnetic properties and MgO buffer layer thickness d was studied in epitaxial MgO/Fe(t)/Cr/MgO(d) layers grown on MgO(001) substrate in which the Fe thickness t ranged from 0.4 nm to 1.1 nm. For 0.4 nm ≤ t ≤ 0.7 nm, a non-monotonic coercivity dependence on the MgO buffer thickness was shown by perpendicular magneto-optic Kerr effect magnetometry. For thicker Fe films, an increase in the buffer layer thickness resulted in a spin reorientation transition from perpendicular to the in-plane magnetization direction. Possible origins of these unusual behaviors were discussed in terms of the suppression of carbon contamination at the Fe surface and changes inmore » the magnetoelastic anisotropy in the system. These results illustrate a method to control magnetic anisotropy in MgO/Fe/Cr/MgO(d) via an appropriate choice of MgO buffer layer thickness d.« less

Improvement of light extraction for a target wavelength in InGaN/GaN LEDs with an indium tin oxide dual layer by oblique angle deposition

NASA Astrophysics Data System (ADS)

Seo, Dong-Ju; Lee, Dong-Seon

2016-08-01

GaN-based blue LEDs were fabricated and studied with porous, dense, and dual-layer indium tin oxide (ITO) structures as transparent top electrodes to enhance light extraction. The electroluminescence intensity of the LED with a thickness-optimized and refractive-index-tuned ITO dual layer at I = 20 mA was higher by 19.7% than that of the conventional LED with a 200 nm planar ITO. This study confirmed that an ITO dual layer can be made with a single material by optimizing the thickness and tuning the refractive index, which improves the power output without any electrical property degradation.

Nano-size defects in arsenic-implanted HgCdTe films: a HRTEM study

NASA Astrophysics Data System (ADS)

Bonchyk, O. Yu.; Savytskyy, H. V.; Swiatek, Z.; Morgiel, Y.; Izhnin, I. I.; Voitsekhovskii, A. V.; Korotaev, A. G.; Mynbaev, K. D.; Fitsych, O. I.; Varavin, V. S.; Dvoretsky, S. A.; Marin, D. V.; Yakushev, M. V.

2018-02-01

Radiation damage and its transformation under annealing were studied with bright-field and high-resolution transmission electron microscopy for arsenic-implanted HgCdTe films with graded-gap surface layers. In addition to typical highly defective layers in as-implanted material, a 50 nm-thick sub-surface layer with very low defect density was observed. The main defects in other layers after implantation were dislocation loops, yet after arsenic activation annealing, the dominating defects were single dislocations. Transport (from depth to surface), transformation and annihilation of radiation-induced defects were observed as a result of annealing, with the depth with the maximum defect density decreasing from 110 to 40 nm.

Combined flame and electrodeposition synthesis of energetic coaxial tungsten-oxide/aluminum nanowire arrays.

PubMed

Dong, Zhizhong; Al-Sharab, Jafar F; Kear, Bernard H; Tse, Stephen D

2013-09-11

A nanostructured thermite composite comprising an array of tungsten-oxide (WO2.9) nanowires (diameters of 20-50 nm and lengths of >10 μm) coated with single-crystal aluminum (thickness of ~16 nm) has been fabricated. The method involves combined flame synthesis of tungsten-oxide nanowires and ionic-liquid electrodeposition of aluminum. The geometry not only presents an avenue to tailor heat-release characteristics due to anisotropic arrangement of fuel and oxidizer but also eliminates or minimizes the presence of an interfacial Al2O3 passivation layer. Upon ignition, the energetic nanocomposite exhibits strong exothermicity, thereby being useful for fundamental study of aluminothermic reactions as well as enhancing combustion characteristics.

Very thin, high Ge content Si 0.3Ge 0.7 relaxed buffer grown by MBE on SOI(0 0 1) substrate

NASA Astrophysics Data System (ADS)

Myronov, M.; Shiraki, Y.

2007-04-01

Growth procedure and excellent properties of very thin 240 nm thick, 95% relaxed, high Ge content Si 0.3Ge 0.7 buffer grown on SOI(0 0 1) substrate are demonstrated. All epilayers of the newly developed Si 0.3Ge 0.7/SOI(0 0 1) variable-temperature virtual substrate were grown in a single process by solid-source molecular beam epitaxy. Surface analysis of grown samples revealed smooth, cross-hatch free surface with low root mean square surface roughness of 0.9 nm and low threading dislocations density of 5×10 4 cm -2.

[Experimental Methods and Result Analysis of a Variety of Spectral Reflectance Properties of the Thin Oil Film].

PubMed

Ye, Zhou; Liu, Li; Wei, Chuan-xin; Gu, Qun; An, Ping-ao; Zhao, Yue-jiao; Yin, Da-yi

2015-06-01

In order to analysis the oil spill situation based on the obtained data in airborne aerial work, it's needed to get the spectral reflectance characteristics of the oil film of different oils and thickness as support and to select the appropriate operating band. An experiment is set up to measure the reflectance spectroscopy from ultraviolet to near-infrared for the film of five target samples, which means petrol, diesel, lubricating oil, kerosene and fossil, using spectral measurement device. The result is compared with the reflectance spectra of water in the same experimental environment, which shows that the spectral reflection characteristics of the oil film are related to the thickness and the type of the oil film. In case of the same thickness, the spectral reflectance curve of different types of film is far different, and for the same type of film, the spectral reflectance curve changes accordingly with the change of film thickness, therefore in terms of the single film, different film thickness can be distinguished by reflectance curves. It also shows that in terms of the same film thickness, the reflectance of diesel, kerosene, lubricants reaches peak around 380 nm wavelength, obviously different from the reflectance of water, and that the reflectance of crude oil is far less than that of water in more than 340 nm wavelength, and the obtained reflection spectrum can be used to distinguish between different types of oil film to some extent. The experiment covers main types of spilled oil, with data comprehensively covering commonly used detect spectral bands, and quantitative description of the spectral reflectance properties of film. It provides comprehensive theoretical and data support for the selection of airborne oil spill detection working band and the detection and analysis of water-surface oil spill.

Post-patterning of an electronic homojunction in atomically thin monoclinic MoTe2

NASA Astrophysics Data System (ADS)

Kim, Sera; Kim, Jung Ho; Kim, Dohyun; Hwang, Geunwoo; Baik, Jaeyoon; Yang, Heejun; Cho, Suyeon

2017-06-01

Monoclinic group 6 transition metal dichalcogenides (TMDs) have been extensively studied for their intriguing 2D physics (e.g. spin Hall insulator) as well as for ohmic homojunction contacts in 2D device applications. A critical prerequisite for those applications is thickness control of the monoclinic 2D materials, which allows subtle engineering of the topological states or electronic bandgaps. Local thickness control enables the realization of clean homojunctions between different electronic states, and novel device operation in a single material. However, conventional fabrication processes, including chemical methods, typically produce non-homogeneous and relatively thick monoclinic TMDs, due to their distorted octahedral structures. Here, we report on a post-patterning technique using laser-irradiation to fabricate homojunctions between two different thickness areas in monoclinic MoTe2. A thickness-dependent electronic change from a metallic to semiconducting state, resulting in an electronic homojunction, was realized by the optical patterning of pristine MoTe2 flakes, and a pre-patterned device channel of monoclinic MoTe2 with a thickness-resolution of 5 nm. Our work provides insight on an optical post-process method for controlling thickness, as a promising approach for fabricating impurity-free 2D TMDs homojunction devices.

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.

Ultrahigh sensitivity and layer-dependent sensing performance of phosphorene-based gas sensors

DOE PAGES

Cui, Shumao; Pu, Haihui; Wells, Spencer A.; ...

2015-10-21

Two-dimensional (2D) layered materials have attracted significant attention for device applications because of their unique structures and outstanding properties. Here, a field-effect transistor (FET) sensor device is fabricated based on 2D phosphorene nanosheets (PNSs). The PNS sensor exhibits an ultrahigh sensitivity to NO 2 in dry air and the sensitivity is dependent on its thickness. A maximum response is observed for 4.8-nm-thick PNS, with a sensitivity up to 190% at 20 parts per billion (p.p.b.) at room temperature. First-principles calculations combined with the statistical thermodynamics modelling predict that the adsorption density is ~10 15 cm -2 for the 4.8-nm-thick PNSmore » when exposed to 20 p.p.b. NO 2 at 300 K. As a result, our sensitivity modelling further suggests that the dependence of sensitivity on the PNS thickness is dictated by the band gap for thinner sheets (<10 nm) and by the effective thickness on gas adsorption for thicker sheets (>10 nm).« less

Ultrahigh sensitivity and layer-dependent sensing performance of phosphorene-based gas sensors

NASA Astrophysics Data System (ADS)

Cui, Shumao; Pu, Haihui; Wells, Spencer A.; Wen, Zhenhai; Mao, Shun; Chang, Jingbo; Hersam, Mark C.; Chen, Junhong

2015-10-01

Two-dimensional (2D) layered materials have attracted significant attention for device applications because of their unique structures and outstanding properties. Here, a field-effect transistor (FET) sensor device is fabricated based on 2D phosphorene nanosheets (PNSs). The PNS sensor exhibits an ultrahigh sensitivity to NO2 in dry air and the sensitivity is dependent on its thickness. A maximum response is observed for 4.8-nm-thick PNS, with a sensitivity up to 190% at 20 parts per billion (p.p.b.) at room temperature. First-principles calculations combined with the statistical thermodynamics modelling predict that the adsorption density is ~1015 cm-2 for the 4.8-nm-thick PNS when exposed to 20 p.p.b. NO2 at 300 K. Our sensitivity modelling further suggests that the dependence of sensitivity on the PNS thickness is dictated by the band gap for thinner sheets (<10 nm) and by the effective thickness on gas adsorption for thicker sheets (>10 nm).

Ultrahigh sensitivity and layer-dependent sensing performance of phosphorene-based gas sensors

PubMed Central

Cui, Shumao; Pu, Haihui; Wells, Spencer A.; Wen, Zhenhai; Mao, Shun; Chang, Jingbo; Hersam, Mark C.; Chen, Junhong

2015-01-01

Two-dimensional (2D) layered materials have attracted significant attention for device applications because of their unique structures and outstanding properties. Here, a field-effect transistor (FET) sensor device is fabricated based on 2D phosphorene nanosheets (PNSs). The PNS sensor exhibits an ultrahigh sensitivity to NO2 in dry air and the sensitivity is dependent on its thickness. A maximum response is observed for 4.8-nm-thick PNS, with a sensitivity up to 190% at 20 parts per billion (p.p.b.) at room temperature. First-principles calculations combined with the statistical thermodynamics modelling predict that the adsorption density is ∼1015 cm−2 for the 4.8-nm-thick PNS when exposed to 20 p.p.b. NO2 at 300 K. Our sensitivity modelling further suggests that the dependence of sensitivity on the PNS thickness is dictated by the band gap for thinner sheets (<10 nm) and by the effective thickness on gas adsorption for thicker sheets (>10 nm). PMID:26486604

Wide band antireflective coatings Al2O3 / HfO2 / MgF2 for UV region

NASA Astrophysics Data System (ADS)

Winkowski, P.; Marszałek, Konstanty W.

2013-07-01

Deposition technology of the three layers antireflective coatings consists of hafnium compound are presented in this paper. Oxide films were deposited by means of e-gun evaporation in vacuum of 5x10-5 mbar in presence of oxygen and fluoride films by thermal evaporation. Substrate temperature was 250°C. Coatings were deposited onto optical lenses made from quartz glass (Corning HPFS). Thickness and deposition rate were controlled by thickness measuring system Inficon XTC/2. Simulations leading to optimization of thickness and experimental results of optical measurements carried during and after deposition process were presented. Physical thickness measurements were made during deposition process and were equal to 43 nm/74 nm/51 nm for Al2O3 / HfO2 / MgF2 respectively. Optimization was carried out for ultraviolet region from 230nm to the beginning of visible region 400 nm. In this region the average reflectance of the antireflective coating was less than 0.5% in the whole range of application.

Colloidal CuInSe2 nanocrystals thin films of low surface roughness

NASA Astrophysics Data System (ADS)

de Kergommeaux, Antoine; Fiore, Angela; Faure-Vincent, Jérôme; Pron, Adam; Reiss, Peter

2013-03-01

Thin-film processing of colloidal semiconductor nanocrystals (NCs) is a prerequisite for their use in (opto-)electronic devices. The commonly used spin-coating is highly materials consuming as the overwhelming amount of deposited matter is ejected from the substrate during the spinning process. Also, the well-known dip-coating and drop-casting procedures present disadvantages in terms of the surface roughness and control of the film thickness. We show that the doctor blade technique is an efficient method for preparing nanocrystal films of controlled thickness and low surface roughness. In particular, by optimizing the deposition conditions, smooth and pinhole-free films of 11 nm CuInSe2 NCs have been obtained exhibiting a surface roughness of 13 nm root mean square (rms) for a 350 nm thick film, and less than 4 nm rms for a 75 nm thick film. Invited talk at the 6th International Workshop on Advanced Materials Science and Nanotechnology, 30 October-2 November 2012, Ha Long, Vietnam.

Computer simulation of single-phase nanocrystalline permanent magnets

NASA Astrophysics Data System (ADS)

Griffiths, M. K.; Bishop, J. E. L.; Tucker, J. W.; Davies, H. A.

1998-03-01

Demagnetizing curves have been calculated numerically for three-dimensional micromagnetic model assemblies of randomly oriented, magnetically hard, exchange coupled, uniaxial nanocrystals as typified by rapidly quenched Nd 2Fe 14B. The curves were obtained as a sequence of static equilibrium states in an incrementally changing applied field. The magnetization distribution in each state was obtained by minimizing the sum of the exchange, anisotropy and Zeeman energies of the assembly, using a modified LaBonte method, with computational elements as small as 1.11 nm (roughly {1}/{4} the domain wall thickness in Nd 2Fe 14B). For computational economy, internal dipolar interactions were ignored in the energy minimization. For a material with the magnetic constants of stoichiometric Nd 2Fe 14B, tests showed that these interactions contribute less than 3% to the energy. On increasing the model grain size from 4.4 to 36 nm, the reduced remanence fell from 76 to 54% and the reduced intrinsic coercivity μ0iHCMS/ KU increased from 0.16 to 0.46 (just under half the Stoner-Wohlfarth value); both sets of results are in reasonable agreement with experimental values. The energy product, evaluated for Nd 2Fe 14B, ranged from ˜224 kJ/m 3 for 10 nm grains to ˜128 kJ/m 3 for 36 nm grains. For grain sizes ⩾20 nm, spatial magnetization variation was confined to domain walls centred on the grain boundaries. For grain sizes decreasing below about twice the domain wall thickness, spatial magnetization variation extended to the interior of the grains and exhibited increasingly long-range correlations.

Characterization of electrochemically deposited films from aqueous and ionic liquid cobalt precursors toward hydrogen evolution reactions

NASA Astrophysics Data System (ADS)

Dushatinski, Thomas; Huff, Clay; Abdel-Fattah, Tarek M.

2016-11-01

Electrodepositions of cobalt films were achieved using an aqueous or an ethylene glycol based non-aqueous solution containing choline chloride (vitamin B4) with cobalt chloride hexahydrate precursor toward hydrogen evolution reactions from sodium borohydride (NaBH4) as solid hydrogen feedstock (SHF). The resulting cobalt films had reflectivity at 550 nm of 2.2% for aqueously deposited films (ACoF) and 1.3% for non-aqueously deposited films (NCoF). Surface morphology studied by scanning electron microscopy showed a positive correlation between particle size and thickness. The film thicknesses were tunable between >100 μm and <300 μm for each film. The roughness (Ra) value measurements by Dektak surface profiling showed that the NCoF (Ra = 165 nm) was smoother than the ACoF (Ra = 418 nm). The NCoFs and ACoFs contained only α phase (FCC) crystallites. The NCoFs were crystalline while the ACoFs were largely amorphous from X-ray diffraction analysis. The NCoF had an average Vickers hardness value of 84 MPa as compared to 176 MPa for ACoF. The aqueous precursor has a single absorption maximum at 510 nm and the non-aqueous precursor had three absorption maxima at 630, 670, and 695 nm. The hydrogen evolution reactions over a 1 cm2 catalytic surface with aqueous NaBH4 solutions generated rate constants (K) = equal to 4.9 × 10-3 min-1, 4.6 × 10-3 min-1, and 3.3 × 10-3 min-1 for ACoF, NCoF, and copper substrate respectively.

Wavelength tunability of laser based on Yb-doped YGAG ceramics

NASA Astrophysics Data System (ADS)

Šulc, Jan; Jelínková, Helena; Jambunathan, Venkatesan; Miura, Taisuke; Endo, Akira; Lucianetti, Antonio; Mocek, TomáÅ.¡

2015-02-01

The wavelength tunability of diode pumped laser based on Yb-doped mixed garnet Y3Ga2Al3O12 (Yb:YGAG) ceramics was investigated. The tested Yb:YGAG sample (10% Yb/Y) was in the form of 2mm thick plane-parallel face-polished plate (without AR coatings). A fiber (core diameter 100 μm, NA= 0.22) coupled laser diode (LIMO, LIMO35-F100-DL980-FG-E) with emission at wavelength 969 nm, was used for longitudinal Yb:YGAG pumping. The laser diode was operating in the pulsed regime (2 ms pulse length, 10 Hz repetition rate). The duty-cycle 2% ensured a low thermal load even under the maximum diode pumping power amplitude 20W (ceramics sample was only air-cooled). The 145mm long semi-hemispherical laser resonator consisted of a flat pumping mirror (HR @ 1.01 - 1.09 μm, HT @ 0.97 μm) and curved (r = 150mm) output coupler with a reflectivity of ˜ 97% @ 1.01 - 1.09 μm. Wavelength tuning of the ytterbium laser was accomplished by using a birefringent filter (single 1.5mm thick quartz plate) placed inside the optical resonator at the Brewster angle between the output coupler and the laser active medium. The laser was continuously tunable over ˜ 58nm (from 1022nm to 1080 nm) and the tuning band was mostly limited by the free spectral range of used birefringent filter. The maximum output power amplitude 3W was obtained at wavelength 1046nm for absorbed pump power amplitude 10.6W. The laser slope efficiency was 34%.

Domain wall structure and interactions in 50 nm wide Cobalt nanowires

NASA Astrophysics Data System (ADS)

Tu, Kun-Hua; Ojha, Shuchi; Ross, Caroline A.

2018-05-01

Arrays of cobalt nanowires with widths of 50 nm, thickness of 5 and 20 nm and periodicity of 70 nm were fabricated by pattern transfer from a self-assembled block copolymer film. Transverse domain walls (DWs) were imaged by magnetic force microscopy, indicating repulsive interactions between DWs of the same sign in the 20 nm thick wires. Micromagnetic simulations were used to identify the interactions in the six distinct cases of a pair of transverse DWs in adjacent wires, considering all the possible combinations of head-to-head and tail-to-tail DWs and the orientation of the core magnetization. The boundary between repulsive and attractive DW interactions is mapped out for wires as a function of thickness, width and interwire spacing.

Effect of Thickness on the Structural, Microstructural, Electrical and Magnetic Properties of ni Films Elaborated by Pulsed Electrodeposition on si Substrate

NASA Astrophysics Data System (ADS)

Kacel, T.; Guittoum, A.; Hemmous, M.; Dirican, E.; Öksüzoglu, R. M.; Azizi, A.; Laggoun, A.; Zergoug, M.

We have studied the effect of thickness on the structural, microstructural, electrical and magnetic properties of Ni films electrodeposited onto n-Si (100) substrates. A series of Ni films have been prepared for different potentials ranging from -1.6V to -2.6V. Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), four point probe technique, atomic force microscopy (AFM) and vibrating sample magnetometry (VSM) have been used to investigate the physical properties of elaborated Ni thin films. From the analysis of RBS spectra, we have extracted the films thickness t (t ranges from 83nm to 422nm). We found that the Ni thickness, t (nm), linearly increases with the applied potential. The Ni thin films are polycrystalline and grow with the 〈111〉 texture. The lattice parameter a (Å) monotonously decreases with increasing thickness. However, a positive strain was noted indicating that all the samples are subjected to a tensile stress. The mean grain sizes D (nm) and the strain ɛhkl decrease with increasing thickness. The electrical resistivity ρ (μΩ.cm) increases with t for t less than 328nm. The diffusion at the grain boundaries may be the important factor in the electrical resistivity. From AFM images, we have shown that the Ni surface roughness decreases with increasing thickness. The coercive field HC, the squareness factor S, the saturation field HS and the effective anisotropy constant K1eff are investigated as a function of Ni thickness and grain sizes. The correlation between the magnetic and the structural properties is discussed.

Synthesis of Ag-Cu-Pd alloy thin films by DC-magnetron sputtering: Case study on microstructures and optical properties

NASA Astrophysics Data System (ADS)

Rezaee, Sahar; Ghobadi, Nader

2018-06-01

The present study aims to investigate optical properties of Ag-Cu-Pd alloy thin films synthesized by DC-magnetron sputtering method. The thin films are deposited on the glass and silicon substrates using Argon gas and Ag-Cu-Pd target. XRD analysis confirms the successful growth of Ag, Cu, and Pd NPs with FCC crystalline structure. Moreover, UV-visible absorption spectroscopy is applied to determine optical properties of the prepared samples which are affected by changes in surface morphology. The existence of single surface plasmon resonance (SPR) peak near 350 nm proves the formation of silver nanoparticles with a slight red shift through increasing deposition time. Ineffective thickness method (ITM) and Derivation of ineffective thickness method (DITM) are applied to extract optical band gap and transition type via absorption spectrum. SEM and AFM analyses show the distribution of near-spherical nanoparticles covering the surface of thin films. Furthermore, thickness variation affects the grain size. In addition, TEM image reveals the uniform size distribution of nanoparticles with an average particle size of about 15 nm. The findings show that increasing grain size and crystallite order along with the decrease of structural defect and disorders decrease optical band gap from 3.86 eV to 2.58 eV.

Structural and Magnetic Properties of LaCoO3/SrTiO3 Multilayers.

PubMed

Zhang, Hongrui; Zhang, Jing; Yang, Huaiwen; Lan, Qianqian; Hong, Deshun; Wang, Shufang; Shen, Xi; Khan, Tahira; Yu, Richeng; Sun, Jirong; Shen, Baogen

2016-07-20

Structural and magnetic properties of the LaCoO3/SrTiO3 (LCO/STO) multilayers (MLs) with a fixed STO layer of 4 nm but varied LCO layer thicknesses have been systematically studied. The MLs grown on Sr0.7La0.3Al0.65Ta0.35O3 (LSAT) and SrTiO3 (STO) exhibit the in-plane lattice constant of the substrates, but those on LaAlO3 (LAO) show the in-plane lattice constant between those of the first two kinds of MLs. Compared with the LCO single layer (SL), the magnetic order of the MLs is significantly enhanced, as demonstrated by a very slow decrease, which is fast for the SL, of the Curie temperature and the saturation magnetization as the LCO layer thickness decreases. For example, clear ferromagnetic order is observed in the ML with the LCO layer of ∼1.5 nm, whereas it vanishes below ∼6 nm for the LCO SL. This result is consistent with the observation that the dark stripes, which are believed to be closely related to the magnetic order, remain clear in the MLs while they are vague in the corresponding LCO SL. The present work suggests a novel route to tune the magnetism of perovskite oxide films.

Observation of dark pulses in 10 nm thick YBCO nanostrips presenting hysteretic current voltage characteristics

NASA Astrophysics Data System (ADS)

Ejrnaes, M.; Parlato, L.; Arpaia, R.; Bauch, T.; Lombardi, F.; Cristiano, R.; Tafuri, F.; Pepe, G. P.

2017-12-01

We have fabricated several 10 nm thick and 65 nm wide YBa2Cu3O7-δ (YBCO) nanostrips. The nanostrips with the highest critical current densities are characterized by hysteretic current voltage characteristics (IVCs) with a direct bistable switch from the zero-voltage to the finite voltage state. The presence of hysteretic IVCs allowed the observation of dark pulses due to fluctuations phenomena. The key role of the bistable behavior is its ability to transform a small disturbance (e.g. an intrinsic fluctuation) into a measurable transient signal, i.e. a dark pulse. On the contrary, in devices characterized by lower critical current density values, the IVCs are non-hysteretic and dark pulses have not been observed. To investigate the physical origin of the dark pulses, we have measured the bias current dependence of the dark pulse rate: the observed exponential increase with the bias current is compatible with mechanisms based on thermal activation of magnetic vortices in the nanostrip. We believe that the successful amplification of small fluctuation events into measurable signals in nanostrips of ultrathin YBCO is a milestone for further investigation of YBCO nanostrips for superconducting nanostrip single photon detectors and other quantum detectors for operation at higher temperatures.

Mechanical spectroscopy of nanocrystalline aluminum films: effects of frequency and grain size on internal friction.

PubMed

Sosale, Guruprasad; Almecija, Dorothée; Das, Kaushik; Vengallatore, Srikar

2012-04-20

Energy dissipation by internal friction is a property of fundamental interest for probing the effects of scale on mechanical behavior in nanocrystalline metallic films and for guiding the use of these materials in the design of high-Q micro/nanomechanical resonators. This paper describes an experimental study to measure the effects of frequency, annealing and grain size on internal friction at room temperature in sputter-deposited nanocrystalline aluminum films with thicknesses ranging from 60 to 120 nm. Internal friction was measured using a single-crystal silicon microcantilever platform that calibrates dissipation against the fundamental limits of thermoelastic damping. Internal friction was a weak function of frequency, reducing only by a factor of two over three decades of frequency (70 Hz to 44 kHz). Annealing led to significant grain growth and the average grain size of 100 nm thick films increased from 90 to 390 nm after annealing for 1 h at 450 (∘)C. This increase in grain size was accompanied by a decrease in internal friction from 0.05 to 0.02. Taken together, these results suggest that grain-boundary sliding, characterized by a spectrum of relaxation times, contributes to internal friction in these films. © 2012 IOP Publishing Ltd

Polysilicon Gate Enhancement of the Random Dopant Induced Threshold Voltage Fluctuations in Sub-100 nm MOSFET's with Ultrathin Gate Oxide

NASA Technical Reports Server (NTRS)

Asenov, Asen; Saini, Subhash

2000-01-01

In this paper, we investigate various aspects of the polysilicon gate influence on the random dopant induced threshold voltage fluctuations in sub-100 nm MOSFET's with ultrathin gate oxides. The study is done by using an efficient statistical three-dimensional (3-D) "atomistic" simulation technique described else-where. MOSFET's with uniform channel doping and with low doped epitaxial channels have been investigated. The simulations reveal that even in devices with a single crystal gate the gate depletion and the random dopants in it are responsible for a substantial fraction of the threshold voltage fluctuations when the gate oxide is scaled-in the range of 1-2 nm. Simulation experiments have been used in order to separate the enhancement in the threshold voltage fluctuations due to an effective increase in the oxide thickness associated with the gate depletion from the direct influence of the random dopants in the gate depletion layer. The results of the experiments show that the both factors contribute to the enhancement of the threshold voltage fluctuations, but the effective increase in the oxide-thickness has a dominant effect in the investigated range of devices. Simulations illustrating the effect or the polysilicon grain boundaries on the threshold voltage variation are also presented.

Control of optical properties of metal-dielectric planar plasmonic nanostructures by adjusting their architecture in the case of TiAlN/Ag system

NASA Astrophysics Data System (ADS)

Wainstein, D. L.; Vakhrushev, V. O.; Kovalev, A. I.

2017-05-01

The multilayer Ag/(Ti34Al66)N metal-insulator-metal (MIM) heterostructures with different thicknesses of individual layers varied from several to several hundred nanometers were fabricated by DC-magnetron sputtering on the surfaces of Si single crystal wafers. The coatings structure was determined by STEM. The phase composition and crystallography of individual layers were studied by X-ray diffraction. The reflection indexes were measured in the photons energies range from 1 to 5 eV, or from 1240 to 248 nm. The spectroscopy of plasmon losses and plasmon microscopy allowed us to measure the plasmons losses characteristic energies and their surface distribution. The energies of plasmons peaks and their locations are strongly depending on Ag layers thickness in the MIM nanocomposite. The surface plasmon with energy about 4 eV was observed in the middle of 20 nm Ag layer. The plasmons were localized at the metal/dielectric interface for Ag layers 5 nm and less. The reflectance spectral profiles edges positions at long and short waves are correlated with plasmons energies and features of their spatial distribution. The MIMs based on the TiAlN/Ag can find applications as optical filters, photovoltaic energy conversion devices, etc.

Study of first electronic transition and hydrogen bonding state of ultra-thin water layer of nanometer thickness on an α-alumina surface by far-ultraviolet spectroscopy

NASA Astrophysics Data System (ADS)

Goto, Takeyoshi; Kinugasa, Tomoya

2018-05-01

The first electronic transition (A˜ ← X˜) and the hydrogen bonding state of an ultra-thin water layer of nanometer thickness between two α-alumina surfaces (0.5-20 nm) were studied using far-ultraviolet (FUV) spectroscopy in the wavelength range 140-180 nm. The ultra-thin water layer of nanometer thickness was prepared by squeezing a water droplet ( 1 μL) between a highly polished α-alumina prism and an α-alumina plate using a high pressure clamp ( 4.7 MPa), and the FUV spectra of the water layer at different thicknesses were measured using the attenuated total reflection method. As the water layer became thinner, the A˜ ← X˜ bands were gradually shifted to higher or lower energy relative to that of bulk water; at thicknesses smaller than 4 nm, these shifts were substantial (0.1-0.2 eV) in either case. The FUV spectra of the water layer with thickness < 4 nm indicate the formation of structured ice-like hydrogen bond (H-bond) layers for the higher energy shifts or the formation of slightly weaker H-bond layers as compared to those in the bulk liquid state for lower energy shifts. In either case, the H-bond structure of bulk liquid water is nearly lost at thicknesses below 4 nm, because of steric hydration forces between the α-alumina surfaces.

Sensitive Capacitive-type Hydrogen Sensor Based on Ni Thin Film in Different Hydrogen Concentrations.

PubMed

Pour, Ghobad Behzadi; Aval, Leila Fekri; Eslami, Shahnaz

2018-04-01

Hydrogen sensors are micro/nano-structure that are used to locate hydrogen leaks. They are considered to have fast response/recovery time and long lifetime as compared to conventional gas sensors. In this paper, fabrication of sensitive capacitive-type hydrogen gas sensor based on Ni thin film has been investigated. The C-V curves of the sensor in different hydrogen concentrations have been reported. Dry oxidation was done in thermal chemical vapor deposition furnace (TCVD). For oxidation time of 5 min, the oxide thickness was 15 nm and for oxidation time 10 min, it was 20 nm. The Ni thin film as a catalytic metal was deposited on the oxide film using electron gun deposition. Two MOS sensors were compared with different oxide film thickness and different hydrogen concentrations. The highest response of the two MOS sensors with 15 nm and 20 nm oxide film thickness in 4% hydrogen concentration was 87.5% and 65.4% respectively. The fast response times for MOS sensors with 15 nm and 20 nm oxide film thickness in 4% hydrogen concentration was 8 s and 21 s, respectively. By increasing the hydrogen concentration from 1% to 4%, the response time for MOS sensor (20nm oxide thickness), was decreased from 28s to 21s. The recovery time was inversely increased from 237s to 360s. The experimental results showed that the MOS sensor based on Ni thin film had a quick response and a high sensitivity.

Thickness dependencies of structural and magnetic properties of cubic and tetragonal Heusler alloy bilayer films

NASA Astrophysics Data System (ADS)

Ranjbar, R.; Suzuki, K. Z.; Sugihara, A.; Ando, Y.; Miyazaki, T.; Mizukami, S.

2017-07-01

The thickness dependencies of the structural and magnetic properties for bilayers of cubic Co-based Heusler alloys (CCHAs: Co2FeAl (CFA), Co2FeSi (CFS), Co2MnAl (CMA), and Co2MnSi (CMS)) and D022-MnGa were investigated. Epitaxy of the B2 structure of CCHAs on a MnGa film was achieved; the smallest thickness with the B2 structure was found for 3-nm-thick CMS and CFS. The interfacial exchange coupling (Jex) was antiferromagnetic (AFM) for all of the CCHAs/MnGa bilayers except for unannealed CFA/MnGa samples. A critical thickness (tcrit) at which perpendicular magnetization appears of approximately 4-10 nm for the CMA/MnGa and CMS/MnGa bilayers was observed, whereas this thickness was 1-3 nm for the CFA/MnGa and CFS/MnGa films. The critical thickness for different CCHAs materials is discussed in terms of saturation magnetization (Ms) and the Jex .

Approximately 800-nm-Thick Pinhole-Free Perovskite Films via Facile Solvent Retarding Process for Efficient Planar Solar Cells.

PubMed

Yuan, Zhongcheng; Yang, Yingguo; Wu, Zhongwei; Bai, Sai; Xu, Weidong; Song, Tao; Gao, Xingyu; Gao, Feng; Sun, Baoquan

2016-12-21

Device performance of organometal halide perovskite solar cells significantly depends on the quality and thickness of perovskite absorber films. However, conventional deposition methods often generate pinholes within ∼300 nm-thick perovskite films, which are detrimental to the large area device manufacture. Here we demonstrated a simple solvent retarding process to deposit uniform pinhole free perovskite films with thicknesses up to ∼800 nm. Solvent evaporation during the retarding process facilitated the components separation in the mixed halide perovskite precursors, and hence the final films exhibited pinhole free morphology and large grain sizes. In addition, the increased precursor concentration after solvent-retarding process led to thick perovskite films. Based on the uniform and thick perovskite films prepared by this convenient process, a champion device efficiency up to 16.8% was achieved. We believe that this simple deposition procedure for high quality perovskite films around micrometer thickness has a great potential in the application of large area perovskite solar cells and other optoelectronic devices.

Properties of thin silver films with different thickness

NASA Astrophysics Data System (ADS)

Zhao, Pei; Su, Weitao; Wang, Reng; Xu, Xiaofeng; Zhang, Fengshan

2009-01-01

In order to investigate optical properties of silver films with different film thickness, multilayer composed of thin silver film sandwiched between ZnS films are sputtered on the float glass. The crystal structures, optical and electrical properties of films are characterized by various techniques, such as X-ray diffraction (XRD), spectrum analysis, etc. The optical constants of thin silver film are calculated by fitting the transmittance ( T) and reflectance ( R) spectrum of the multilayer. Electrical and optical properties of silver films thinner than 6.2 nm exhibit sharp change. However, variation becomes slow as film thickness is larger than 6.2 nm. The experimental results indicate that 6.2 nm is the optimum thickness for properties of silver.

Brillouin Light Scattering study of Fe/Pd multilayers

NASA Astrophysics Data System (ADS)

From, Milton; Cheng, Li; Altounian, Zaven

2002-03-01

We have performed a series of Brillouin light scattering (BLS) measurements on sputtered multilayers in order to test a recent calculation[1] that predicts that the majority of spin-wave modes present in a magnetic multilayer will not be seen by BLS due to destructive interference between light scattered by different layers in the structure. We have measured the BLS spectra of a series of Si(100) + Pdx + [Fe/Pdx] x 25 sputtered multilayers. The thickness of the Fe layers was 1.5 nm and the Pd thicknesses examined were x = 0.5nm, 1.0nm, 1.5nm, 2.5nm, and 4.0nm. The BLS instrument used was a 4-pass Fabry-Perot interferometer operated in the back-scattering geometry with 514.5 nm laser light. We obtain good 2-parameter fits of the model calculation to the data for all values of Pd thickness and for applied magnetic fields in the range 0 < H < 0.7 T. [1]J.F. Cochran, Phys Rev B, vol. 64, 134406 (2001)

Evaluation of electrical properties of Cr/CrN nano-multilayers for electronic applications.

PubMed

Marulanda, D M; Olaya, J J; Patiño, E J

2011-06-01

The electrical properties of Cr/CrN nano-multilayers produced by Unbalanced Magnetron Sputtering have been studied as a function of bilayer period and total thickness. Two groups of multilayers were produced: in the first group the bilayer period varied between 20 nm, 100 nm and 200 nm with total thickness of 1 microm, and in the second group the bilayer period varied between 25 nm, 50 nm and 100 nm and a total thickness of 100 nm. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were used in order to investigate the microstructure characteristics of the multilayers, and the Four Point Probe (FPP) method was used to evaluate in-plane and transverse electrical resistivity. XRD results show (111) and (200) orientations for all the CrN coatings and the presence of a multilayer structure was confirmed through SEM studies. Transverse electrical resistivity results show that this property is strongly dependent on the bilayer period.

MgF2 prism/rhodium/graphene: efficient refractive index sensing structure in optical domain

NASA Astrophysics Data System (ADS)

Mishra, Akhilesh Kumar; Mishra, Satyendra Kumar

2017-04-01

A theoretical study of a noble surface plasmon resonance (SPR) based sensing probe has been carried out. The sensing probe consists of a magnesium fluoride (MgF2) prism with its base coated with rarely used noble metal rhodium (Rh) and a bio-compatible layer of graphene. The refractive indices (RIs) of the sensing medium vary from 1.33 to 1.36 refractive index unit (RIU). The thickness of Rh and the number of graphene layers have been optimized for maximum sensitivity in a constraint set by the detection accuracy (DA). For the operating wavelength of 632 nm, the optimized sensing probe Rh (12 nm)/graphene (single layer) demonstrates sensitivity of ~259 degree/RIU with corresponding DA of ~0.32 degree-1 while for 532 nm of excitation, the optimized sensing probe Rh (12 nm)/graphene (three layer) exhibits sensitivity of ~240 degree/RIU and DA of ~0.27 degree-1.

MgF2 prism/rhodium/graphene: efficient refractive index sensing structure in optical domain.

PubMed

Mishra, Akhilesh Kumar; Mishra, Satyendra Kumar

2017-04-12

A theoretical study of a noble surface plasmon resonance (SPR) based sensing probe has been carried out. The sensing probe consists of a magnesium fluoride (MgF 2 ) prism with its base coated with rarely used noble metal rhodium (Rh) and a bio-compatible layer of graphene. The refractive indices (RIs) of the sensing medium vary from 1.33 to 1.36 refractive index unit (RIU). The thickness of Rh and the number of graphene layers have been optimized for maximum sensitivity in a constraint set by the detection accuracy (DA). For the operating wavelength of 632 nm, the optimized sensing probe Rh (12 nm)/graphene (single layer) demonstrates sensitivity of ~259 degree/RIU with corresponding DA of ~0.32 degree -1 while for 532 nm of excitation, the optimized sensing probe Rh (12 nm)/graphene (three layer) exhibits sensitivity of ~240 degree/RIU and DA of ~0.27 degree -1 .

Single-step colloidal quantum dot films for infrared solar harvesting

NASA Astrophysics Data System (ADS)

Kiani, Amirreza; Sutherland, Brandon R.; Kim, Younghoon; Ouellette, Olivier; Levina, Larissa; Walters, Grant; Dinh, Cao-Thang; Liu, Mengxia; Voznyy, Oleksandr; Lan, Xinzheng; Labelle, Andre J.; Ip, Alexander H.; Proppe, Andrew; Ahmed, Ghada H.; Mohammed, Omar F.; Hoogland, Sjoerd; Sargent, Edward H.

2016-10-01

Semiconductors with bandgaps in the near- to mid-infrared can harvest solar light that is otherwise wasted by conventional single-junction solar cell architectures. In particular, colloidal quantum dots (CQDs) are promising materials since they are cost-effective, processed from solution, and have a bandgap that can be tuned into the infrared (IR) via the quantum size effect. These characteristics enable them to harvest the infrared portion of the solar spectrum to which silicon is transparent. To date, IR CQD solar cells have been made using a wasteful and complex sequential layer-by-layer process. Here, we demonstrate ˜1 eV bandgap solar-harvesting CQD films deposited in a single step. By engineering a fast-drying solvent mixture for metal iodide-capped CQDs, we deposited active layers greater than 200 nm in thickness having a mean roughness less than 1 nm. We integrated these films into infrared solar cells that are stable in air and exhibit power conversion efficiencies of 3.5% under illumination by the full solar spectrum, and 0.4% through a simulated silicon solar cell filter.

Single-fabrication-step Ge nanosphere/SiO2/SiGe heterostructures: a key enabler for realizing Ge MOS devices

NASA Astrophysics Data System (ADS)

Liao, P. H.; Peng, K. P.; Lin, H. C.; George, T.; Li, P. W.

2018-05-01

We report channel and strain engineering of self-organized, gate-stacking heterostructures comprising Ge-nanosphere gate/SiO2/SiGe-channels. An exquisitely-controlled dynamic balance between the concentrations of oxygen, Si, and Ge interstitials was effectively exploited to simultaneously create these heterostructures in a single oxidation step. Process-controlled tunability of the channel length (5–95 nm diameters for the Ge-nanospheres), gate oxide thickness (2.5–4.8 nm), as well as crystal orientation, chemical composition and strain engineering of the SiGe-channel was achieved. Single-crystalline (100) Si1‑x Ge x shells with Ge content as high as x = 0.85 and with a compressive strain of 3%, as well as (110) Si1‑x Ge x shells with Ge content of x = 0.35 and corresponding compressive strain of 1.5% were achieved. For each crystal orientation, our high Ge-content, highly-stressed SiGe shells feature a high degree of crystallinity and thus, provide a core ‘building block’ required for the fabrication of Ge-based MOS devices.

Single-fabrication-step Ge nanosphere/SiO2/SiGe heterostructures: a key enabler for realizing Ge MOS devices.

PubMed

Liao, P H; Peng, K P; Lin, H C; George, T; Li, P W

2018-05-18

We report channel and strain engineering of self-organized, gate-stacking heterostructures comprising Ge-nanosphere gate/SiO 2 /SiGe-channels. An exquisitely-controlled dynamic balance between the concentrations of oxygen, Si, and Ge interstitials was effectively exploited to simultaneously create these heterostructures in a single oxidation step. Process-controlled tunability of the channel length (5-95 nm diameters for the Ge-nanospheres), gate oxide thickness (2.5-4.8 nm), as well as crystal orientation, chemical composition and strain engineering of the SiGe-channel was achieved. Single-crystalline (100) Si 1-x Ge x shells with Ge content as high as x = 0.85 and with a compressive strain of 3%, as well as (110) Si 1-x Ge x shells with Ge content of x = 0.35 and corresponding compressive strain of 1.5% were achieved. For each crystal orientation, our high Ge-content, highly-stressed SiGe shells feature a high degree of crystallinity and thus, provide a core 'building block' required for the fabrication of Ge-based MOS devices.

Direct synthesis and characterization of optically transparent conformal zinc oxide nanocrystalline thin films by rapid thermal plasma CVD

NASA Astrophysics Data System (ADS)

Pedersen, Joachim D.; Esposito, Heather J.; Teh, Kwok Siong

2011-10-01

We report a rapid, self-catalyzed, solid precursor-based thermal plasma chemical vapor deposition process for depositing a conformal, nonporous, and optically transparent nanocrystalline ZnO thin film at 130 Torr (0.17 atm). Pure solid zinc is inductively heated and melted, followed by ionization by thermal induction argon/oxygen plasma to produce conformal, nonporous nanocrystalline ZnO films at a growth rate of up to 50 nm/min on amorphous and crystalline substrates including Si (100), fused quartz, glass, muscovite, c- and a-plane sapphire (Al2O3), gold, titanium, and polyimide. X-ray diffraction indicates the grains of as-deposited ZnO to be highly textured, with the fastest growth occurring along the c-axis. The individual grains are observed to be faceted by (103) planes which are the slowest growth planes. ZnO nanocrystalline films of nominal thicknesses of 200 nm are deposited at substrate temperatures of 330°C and 160°C on metal/ceramic substrates and polymer substrates, respectively. In addition, 20-nm- and 200-nm-thick films are also deposited on quartz substrates for optical characterization. At optical spectra above 375 nm, the measured optical transmittance of a 200-nm-thick ZnO film is greater than 80%, while that of a 20-nm-thick film is close to 100%. For a 200-nm-thick ZnO film with an average grain size of 100 nm, a four-point probe measurement shows electrical conductivity of up to 910 S/m. Annealing of 200-nm-thick ZnO films in 300 sccm pure argon at temperatures ranging from 750°C to 950°C (at homologous temperatures between 0.46 and 0.54) alters the textures and morphologies of the thin film. Based on scanning electron microscope images, higher annealing temperatures appear to restructure the ZnO nanocrystalline films to form nanorods of ZnO due to a combination of grain boundary diffusion and bulk diffusion. PACS: films and coatings, 81.15.-z; nanocrystalline materials, 81.07.Bc; II-VI semiconductors, 81.05.Dz.

[Preliminary analysis about influence of porcelain thickness on interfacial crack of PFM].

PubMed

Zhu, Ziyuan; Zhang, Baowei; Zhang, Xiuyin; Xu, Kan; Fang, Ruhua; Wang, Dongmei

2002-01-01

This study was about the influence of porcelain thickness on crack at interface. The effect of porcelain thickness on the flaw at the interface between porcelain and metal was studied in three groups with porcelain thickness of 0.5 mm, 1.5 mm and 2.5 mm (metal thickness of 0.5 mm) by means of moire interferometre and interfacial fracture mechanics. The parameter Jc was compared among the three groups and the growing of the flaw was observed. Jc and the extreme strength of group with porcelain thickness of 0.5 mm (2.813 N/m and 9.979 N) were lower than those of the groups with porcelain thickness of 1.5 mm and 2.5 mm (5.395 N/m, 19.134 N and 5.429 N/m, 19.256 N). Flaws extend along the interface in the groups with porcelain thickness of 1.5 mm and 0.5 mm. (1) Fracture resistance of the interface in the groups with porcelain thickness of 1.5 mm and 2.5 mm is similar and it decreases in the group with 0.5 mm thick porcelain. (2) When porcelain is 1.5 mm or 0.5 mm thick, flaws will extend along the interface. When porcelain is 2.5 mm thick, flaws will extend into the porcelain layer.

High mobility, dual layer, c-axis aligned crystalline/amorphous IGZO thin film transistor

NASA Astrophysics Data System (ADS)

Chung, Chen-Yang; Zhu, Bin; Greene, Raymond G.; Thompson, Michael O.; Ast, Dieter G.

2015-11-01

We demonstrate a dual layer IGZO thin film transistor (TFT) consisting of a 310 °C deposited c-axis aligned crystal (CAAC) 20 nm thick channel layer capped by a second, 30 nm thick, 260 °C deposited amorphous IGZO layer. The TFT exhibits a saturation field-effect mobility of ˜20 cm2/V s, exceeding the mobility of 50 nm thick single layer reference TFTs fabricated with either material. The deposition temperature of the second layer influences the mobility of the underlying transport layer. When the cap layer is deposited at room temperature (RT), the mobility in the 310 °C deposited CAAC layer is initially low (6.7 cm2/V s), but rises continuously with time over 58 days to 20.5 cm2/V s, i.e., to the same value as when the second layer is deposited at 260 °C. This observation indicates that the two layers equilibrate at RT with a time constant on the order of 5 × 106 s. An analysis based on diffusive transport indicates that the room temperature diffusivity must be of the order of 1 × 10-18 cm2 s-1 with an activation enthalpy EA < 0.2 eV for the mobility limiting species. The findings are consistent with a hypothesis that the amorphous layer deposited on top of the CAAC has a higher solubility for impurities and/or structural defects than the underlying nanocrystalline transport layer, and that the equilibration of the mobility limiting species is rate limited by hydrogen diffusion, whose known diffusivity fits these estimates.

Imaging of single cells and tissue using MeV ions

NASA Astrophysics Data System (ADS)

Watt, F.; Bettiol, A. A.; van Kan, J. A.; Ynsa, M. D.; Minqin, Ren; Rajendran, R.; Huifang, Cui; Fwu-Shen, Sheu; Jenner, A. M.

2009-06-01

With the attainment of sub-100 nm high energy (MeV) ion beams, comes the opportunity to image cells and tissue at nano-dimensions. The advantage of MeV ion imaging is that the ions will penetrate whole cells, or relatively thick tissue sections, without any significant loss of resolution. In this paper, we demonstrate that whole cells (cultured N2A neuroblastoma cells ATCC) and tissue sections (rabbit pancreas tissue) can be imaged at sub-100 nm resolutions using scanning transmission ion microscopy (STIM), and that sub-cellular structural details can be identified. In addition to STIM imaging we have also demonstrated for the first time, that sub-cellular proton induced fluorescence imaging (on cultured N2A neuroblastoma cells ATCC) can also be carried out at resolutions of 200 nm, compared with 300-400 nm resolutions achieved by conventional optical fluorescence imaging. The combination of both techniques offers a potentially powerful tool in the quest for elucidating cell function, particularly when it should be possible in the near future to image down to sub-50 nm.

Phonon Conduction in Silicon Nanobeam Labyrinths

DOE PAGES

Park, Woosung; Romano, Giuseppe; Ahn, Ethan C.; ...

2017-07-24

Here we study single-crystalline silicon nanobeams having 470 nm width and 80 nm thickness cross section, where we produce tortuous thermal paths (i.e. labyrinths) by introducing slits to control the impact of the unobstructed “line-of-sight” (LOS) between the heat source and heat sink. The labyrinths range from straight nanobeams with a complete LOS along the entire length to nanobeams in which the LOS ranges from partially to entirely blocked by introducing slits, s = 95, 195, 245, 295 and 395 nm. The measured thermal conductivity of the samples decreases monotonically from ~47 W m -1K -1 for straight beam tomore » ~31 W m -1 K -1 for slit width of 395 nm. A model prediction through a combination of the Boltzmann transport equation and ab initio calculations shows an excellent agreement with the experimental data to within ~8%. The model prediction for the most tortuous path (s = 395 nm) is reduced by ~14% compared to a straight beam of equivalent cross section. This study suggests that LOS is an important metric for characterizing and interpreting phonon propagation in nanostructures.« less

The anisotropic effective damping of thickness-dependent epitaxial Co2FeAl films studied by spin rectification

NASA Astrophysics Data System (ADS)

Chen, Zhendong; Kong, Wenwen; Mi, Kui; Chen, Guilin; Zhang, Peng; Fan, Xiaolong; Gao, Cunxu; Xue, Desheng

2018-03-01

Epitaxial Co2FeAl films with the thickness varying from 26.4 nm to 4.6 nm were grown on MgO(001) substrates by molecular beam epitaxy. Spin rectification was adopted to study the dynamic magnetic properties of the Co2FeAl films, considering the reported advantages of this technique with high thickness-independent sensitivity on samples. At a fixed microwave frequency, the in-plane angular dependent resonance fields and their linewidths exhibit a superposition of a uniaxial and a fourfold anisotropy for all samples. The results reveal an anisotropic damping behavior of the films. Along in-plane different azimuths of the films, frequency-dependent resonance-field linewidths were investigated. The anisotropic effective damping of the films with the thickness varying from 26.4 nm to 4.6 nm was then analyzed, which is contributed from the two-magnon scattering.

Electronic transport in bismuth selenide in the topological insulator regime

NASA Astrophysics Data System (ADS)

Kim, Dohun

The 3D topological insulators (TIs) have an insulating bulk but spin-momentum coupled metallic surface states stemming from band inversion due to strong spin-orbit interaction, whose existence is guaranteed by the topology of the band structure of the insulator. While the STI surface state has been studied spectroscopically by e.g. photoemission and scanned probes, transport experiments have failed to demonstrate clear signature of the STI due to high level of bulk conduction. In this thesis, I present experimental results on the transport properties of TI material Bi2Se3 in the absence of bulk conduction (TI regime), achieved by applying novel p-type doping methods. Field effect transistors consisting of thin (thickness: 5-17 nm) Bi2Se3 are fabricated by mechanical exfoliation of single crystals, and a combination of conventional dielectric (300 nm thick SiO2) and electrochemical or chemical gating methods are used to move the Fermi energy through the surface Dirac point inside bulk band gap, revealing the ambipolar gapless nature of transport in the Bi2Se3 surface states. The minimum conductivity of the topological surface state is understood within the self-consistent theory of Dirac electrons in the presence of charged impurities. The intrinsic finite-temperature resistivity of the topological surface state due to electron-acoustic phonon scattering is measured to be 60 times larger than that of graphene largely due to the smaller Fermi and sound velocities in Bi2Se 3, which will have implications for topological electronic devices operating at room temperature. Along with semi-classical Boltzmann transport, I also discuss 2D weak anti-localization (WAL) behavior of the topological surface states. By investigating gate-tuned WAL behavior in thin (5-17 nm) TI films, I show that WAL in the TI regime is extraordinarily sensitive to the hybridization induced quantum mechanical tunneling between top and bottom topological surfaces, and interplay of phase coherence time and inter-surface tunneling time results in a crossover from two decoupled (top and bottom) symplectic 2D metal surfaces to a coherently coupled single channel. Furthermore, a complete suppression of WAL is observed in the 5 nm thick Bi2Se 3 film which was found to occur when the hybridization gap becomes comparable to the disorder strength.

Application of scanning angle Raman spectroscopy for determining the location of buried polymer interfaces with tens of nanometer precision

DOE PAGES

Damin, Craig A.; Nguyen, Vy H. T.; Niyibizi, Auguste S.; ...

2015-02-11

In this study, near-infrared scanning angle (SA) Raman spectroscopy was utilized to determine the interface location in bilayer films (a stack of two polymer layers) of polystyrene (PS) and polycarbonate (PC). Finite-difference-time-domain (FDTD) calculations of the sum square electric field (SSEF) for films with total bilayer thicknesses of 1200–3600 nm were used to construct models for simultaneously measuring the film thickness and the location of the buried interface between the PS and PC layers. Samples with total thicknesses of 1320, 1890, 2300, and 2750 nm and varying PS/PC interface locations were analyzed using SA Raman spectroscopy. Comparing SA Raman spectroscopymore » and optical profilometry measurements, the average percent difference in the total bilayer thickness was 2.0% for films less than ~2300 nm thick. The average percent difference in the thickness of the PS layer, which reflects the interface location, was 2.5% when the PS layer was less than ~1800 nm. SA Raman spectroscopy has been shown to be a viable, non-destructive method capable of determining the total bilayer thickness and buried interface location for bilayer samples consisting of thin polymer films with comparable indices of refraction.« less

Influence of electron transport layer thickness on optical properties of organic light-emitting diodes

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

Liu, Guohong; Liu, Yong; Li, Baojun

2015-06-07

We investigate experimentally and theoretically the influence of electron transport layer (ETL) thickness on properties of typical N,N′-diphenyl-N,N′-bis(1-naphthyl)-[1,1′-biphthyl]-4,4′-diamine (NPB)/tris-(8-hydroxyquinoline) aluminum (Alq{sub 3}) heterojunction based organic light-emitting diodes (OLEDs), where the thickness of ETL is varied to adjust the distance between the emitting zone and the metal electrode. The devices showed a maximum current efficiency of 3.8 cd/A when the ETL thickness is around 50 nm corresponding to an emitter-cathode distance of 80 nm, and a second maximum current efficiency of 2.6 cd/A when the ETL thickness is around 210 nm corresponding to an emitter-cathode distance of 240 nm. We adopt a rigorous electromagnetic approach that takesmore » parameters, such as dipole orientation, polarization, light emitting angle, exciton recombination zone, and diffusion length into account to model the optical properties of devices as a function of varying ETL thickness. Our simulation results are accurately consistent with the experimental results with a widely varying thickness of ETL, indicating that the theoretical model may be helpful to design high efficiency OLEDs.« less

Thickness-dependent spontaneous dewetting morphology of ultrathin Ag films.

PubMed

Krishna, H; Sachan, R; Strader, J; Favazza, C; Khenner, M; Kalyanaraman, R

2010-04-16

We show here that the morphological pathway of spontaneous dewetting of ultrathin Ag films on SiO2 under nanosecond laser melting is dependent on film thickness. For films with thickness h of 2 nm < or = h < or = 9.5 nm, the morphology during the intermediate stages of dewetting consisted of bicontinuous structures. For films with 11.5 nm < or = h < or = 20 nm, the intermediate stages consisted of regularly sized holes. Measurement of the characteristic length scales for different stages of dewetting as a function of film thickness showed a systematic increase, which is consistent with the spinodal dewetting instability over the entire thickness range investigated. This change in morphology with thickness is consistent with observations made previously for polymer films (Sharma and Khanna 1998 Phys. Rev. Lett. 81 3463-6; Seemann et al 2001 J. Phys.: Condens. Matter 13 4925-38). Based on the behavior of free energy curvature that incorporates intermolecular forces, we have estimated the morphological transition thickness for the intermolecular forces for Ag on SiO2. The theory predictions agree well with observations for Ag. These results show that it is possible to form a variety of complex Ag nanomorphologies in a consistent manner, which could be useful in optical applications of Ag surfaces, such as in surface enhanced Raman sensing.

Efficient methylammonium lead iodide perovskite solar cells with active layers from 300 to 900 nm

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

Momblona, C.; Malinkiewicz, O.; Soriano, A.

2014-08-01

Efficient methylammonium lead iodide perovskite-based solar cells have been prepared in which the perovskite layer is sandwiched in between two organic charge transporting layers that block holes and electrons, respectively. This configuration leads to stable and reproducible devices that do not suffer from strong hysteresis effects and when optimized lead to efficiencies close to 15%. The perovskite layer is formed by using a dual-source thermal evaporation method, whereas the organic layers are processed from solution. The dual-source thermal evaporation method leads to smooth films and allows for high precision thickness variations. Devices were prepared with perovskite layer thicknesses ranging frommore » 160 to 900 nm. The short-circuit current observed for these devices increased with increasing perovskite layer thickness. The main parameter that decreases with increasing perovskite layer thickness is the fill factor and as a result optimum device performance is obtained for perovskite layer thickness around 300 nm. However, here we demonstrate that with a slightly oxidized electron blocking layer the fill factor for the solar cells with a perovskite layer thickness of 900 nm increases to the same values as for the devices with thin perovskite layers. As a result the power conversion efficiencies for the cells with 300 and 900 nm are very similar, 12.7% and 12%, respectively.« less

Metal/Dielectric Multilayers for High Resolution Imaging

DTIC Science & Technology

2012-08-07

of a silicon waveguide coated by thin metal film. The proposed PWG structure consists of narrow silicon waveguide clad by gold film without top...where the waveguide thickness is 220nm and the lower oxide cladding is 2μm. The device consists of main waveguide (of waveguide width WSOI=450nm...evaporation, where 3nm thick titanium was used as adhesion layer before 40nm gold deposition took place. Finally, the samples were spun coated with

Integration of Organic Electrochemical and Field-Effect Transistors for Ultraflexible, High Temporal Resolution Electrophysiology Arrays.

PubMed

Lee, Wonryung; Kim, Dongmin; Rivnay, Jonathan; Matsuhisa, Naoji; Lonjaret, Thomas; Yokota, Tomoyuki; Yawo, Hiromu; Sekino, Masaki; Malliaras, George G; Someya, Takao

2016-11-01

Integration of organic electrochemical transistors and organic field-effect transistors is successfully realized on a 600 nm thick parylene film toward an electrophysiology array. A single cell of an integrated device and a 2 × 2 electrophysiology array succeed in detecting electromyogram with local stimulation of the motor nerve bundle of a transgenic rat by a laser pulse. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Controlling the optical parameters of self-assembled silver films with wetting layers and annealing

NASA Astrophysics Data System (ADS)

Ciesielski, Arkadiusz; Skowronski, Lukasz; Trzcinski, Marek; Szoplik, Tomasz

2017-11-01

We investigated the influence of presence of Ni and Ge wetting layers as well as annealing on the permittivity of Ag films with thicknesses of 20, 35 and 65 nm. Most of the research on thin silver films deals with very small (<20 nm) or relatively large (≥50 nm) thicknesses. We studied the transition region (around 30 nm) from charge percolation pathways to fully continuous films and compared the values of optical parameters among silver layers with at least one fixed attribute (thickness, wetting and capping material, post-process annealing). Our study, based on atomic force microscopy, ellipsometric and X-ray photoelectron spectroscopy measurements, shows that utilizing a wetting layer is comparable to increasing the thickness of the silver film. Both operations decrease the roughness-to-thickness ratio, thus decreasing the scattering losses and both narrow the Lorentz-shaped interband transition peak. However, while increasing silver thickness increases absorption on the free carriers, the use of wetting layers influences the self-assembled internal structure of silver films in such a way, that the free carrier absorption decreases. Wetting layers also introduce additional contributions from effects like segregation or diffusion, which evolve in time and due to annealing.

Hf layer thickness dependence of resistive switching characteristics of Ti/Hf/HfO2/Au resistive random access memory device

NASA Astrophysics Data System (ADS)

Nakajima, Ryo; Azuma, Atsushi; Yoshida, Hayato; Shimizu, Tomohiro; Ito, Takeshi; Shingubara, Shoso

2018-06-01

Resistive random access memory (ReRAM) devices with a HfO2 dielectric layer have been studied extensively owing to the good reproducibility of their SET/RESET switching properties. Furthermore, it was reported that a thin Hf layer next to a HfO2 layer stabilized switching properties because of the oxygen scavenging effect. In this work, we studied the Hf thickness dependence of the resistance switching characteristics of a Ti/Hf/HfO2/Au ReRAM device. It is found that the optimum Hf thickness is approximately 10 nm to obtain good reproducibility of SET/RESET voltages with a small RESET current. However, when the Hf thickness was very small (∼2 nm), the device failed after the first RESET process owing to the very large RESET current. In the case of a very thick Hf layer (∼20 nm), RESET did not occur owing to the formation of a leaky dielectric layer. We observed the occurrence of multiple resistance states in the RESET process of the device with a Hf thickness of 10 nm by increasing the RESET voltage stepwise.

Naturally formed ultrathin V2O5 heteroepitaxial layer on VO2/sapphire(001) film

NASA Astrophysics Data System (ADS)

Littlejohn, Aaron J.; Yang, Yunbo; Lu, Zonghuan; Shin, Eunsung; Pan, KuanChang; Subramanyam, Guru; Vasilyev, Vladimir; Leedy, Kevin; Quach, Tony; Lu, Toh-Ming; Wang, Gwo-Ching

2017-10-01

Vanadium dioxide (VO2) and vanadium pentoxide (V2O5) thin films change their properties in response to external stimuli such as photons, temperature, electric field and magnetic field and have applications in electronics, optical devices, and sensors. Due to the multiple valence states of V and non-stoichiometry in thin films, it is challenging to grow epitaxial, single-phase V-oxide on a substrate, or a heterostructure of two epitaxial V-oxides. We report the formation of a heterostructure consisting of a few nm thick ultrathin V2O5 epitaxial layer on pulsed laser deposited tens of nm thick epitaxial VO2 thin films grown on single crystal Al2O3(001) substrates without post annealing of the VO2 film. The simultaneous observation of the ultrathin epitaxial V2O5 layer and VO2 epitaxial film is only possible by our unique reflection high energy electron diffraction pole figure analysis. The out-of-plane and in-plane epitaxial relationships are V2O5[100]||VO2[010]||Al2O3[001] and V2O5[03 2 bar ]||VO2[100]||Al2O3[1 1 bar 0], respectively. The existence of the V2O5 layer on the surface of the VO2 film is also supported by X-ray photoelectron spectroscopy and Raman spectroscopy.

Stimulation of Single Isolated Adult Ventricular Myocytes within a Low Volume Using a Planar Microelectrode Array

PubMed Central

Klauke, Norbert; Smith, Godfrey L.; Cooper, Jon

2003-01-01

Microchannels (40-μm wide, 10-μm high, 10-mm long, 70-μm pitch) were patterned in the silicone elastomer, polydimethylsiloxane on a microscope coverslip base. Integrated within each microchamber were individually addressable stimulation electrodes (40-μm wide, 20-μm long, 100-nm thick) and a common central pseudo-reference electrode (60-μm wide, 500-μm long, 100-nm thick). Isolated rabbit ventricular myocytes were introduced into the chamber by micropipetting and subsequently capped with a layer of mineral oil, thus creating limited volumes of saline around individual myocytes that could be varied from 5 nL to 100 pL. Excitation contraction coupling was studied by monitoring myocyte shortening and intracellular Ca2+ transients (using Fluo-3 fluorescence) . The amplitude of stimulated myocyte shortening and Ca2+ transients remained constant for 90 min in the larger volume (5 nL) configuration, although the shortening (but not the Ca2+ transient) amplitude gradually decreased to 20% of control within 60 min in the low volume (100 pL) arrangement. These studies indicate a lower limit for the extracellular volume required to stimulate isolated adult cardiac myocytes. Whereas this arrangement could be used to create a screening assay for drugs, individual microchannels (100 pL) can also be used to study the effects of limited extracellular volume on the contractility of single cardiac myocytes. PMID:12944291

Multi-band filter design with less total film thickness for short-wave infrared

NASA Astrophysics Data System (ADS)

Yan, Yung-Jhe; Chien, I.-Pen; Chen, Po-Han; Chen, Sheng-Hui; Tsai, Yi-Chun; Ou-Yang, Mang

2017-08-01

A multi-band pass filter array was proposed and designed for short wave infrared applications. The central wavelength of the multi-band pass filters are located about 905 nm, 950 nm, 1055 nm and 1550 nm. In the simulation of an optical interference band pass filter, high spectrum performance (high transmittance ratio between the pass band and stop band) relies on (1) the index gap between the selected high/low-index film materials, with a larger gap correlated to higher performance, and (2) sufficient repeated periods of high/low-index thin-film layers. When determining high and low refractive index materials, spectrum performance was improved by increasing repeated periods. Consequently, the total film thickness increases rapidly. In some cases, a thick total film thickness is difficult to process in practice, especially when incorporating photolithography liftoff. Actually the maximal thickness of the photoresist being able to liftoff will bound the total film thickness of the band pass filter. For the application of the short wave infrared with the wavelength range from 900nm to 1700nm, silicone was chosen as a high refractive index material. Different from other dielectric materials used in the visible range, silicone has a higher absorptance in the visible range opposite to higher transmission in the short wave infrared. In other words, designing band pass filters based on silicone as a high refractive index material film could not obtain a better spectrum performance than conventional high index materials like TiO2 or Ta2O5, but also its material cost would reduce about half compared to the total film thickness with the conventional material TiO2. Through the simulation and several experimental trials, the total film thickness below 4 um was practicable and reasonable. The fabrication of the filters was employed a dual electric gun deposition system with ion assisted deposition after the lithography process. Repeating four times of lithography and deposition process and black matrix coating, the optical device processes were completed.

SnO2 epitaxial films with varying thickness on c-sapphire: Structure evolution and optical band gap modulation

NASA Astrophysics Data System (ADS)

Zhang, Mi; Xu, Maji; Li, Mingkai; Zhang, Qingfeng; Lu, Yinmei; Chen, Jingwen; Li, Ming; Dai, Jiangnan; Chen, Changqing; He, Yunbin

2017-11-01

A series of a-plane SnO2 films with thickness between 2.5 nm and 1436 nm were grown epitaxially on c-sapphire by pulsed laser deposition (PLD), to allow a detailed probe into the structure evolution and optical band gap modulation of SnO2 with growing thickness. All films exhibit excellent out-of-plane ordering (lowest (200) rocking-curve half width ∼0.01°) with an orientation of SnO2(100) || Al2O3(0001), while three equivalent domains that are rotated by 120° with one another coexist in-plane with SnO2[010] || Al2O3 [11-20]. Initially the SnO2(100) film assumes a two-dimensional (2D) layer-by-layer growth mode with atomically smooth surface (minimum root-mean-square roughness of 0.183 nm), and endures compressive strain along both c and a axes as well as mild tensile strain along the b-axis. With increasing thickness, transition from the 2D to 3D island growth mode takes place, leading to formation of various defects to allow relief of the stress and thus relaxation of the film towards bulk SnO2. More interestingly, with increasing thickness from nm to μm, the SnO2 films present a non-monotonic V-shaped variation in the optical band gap energy. While the band gap of SnO2 films thinner than 6.1 nm increases rapidly with decreasing film thickness due to the quantum size effect, the band gap of thicker SnO2 films broadens almost linearly with increasing film thickness up to 374 nm, as a result of the strain effect. The present work sheds light on future design of SnO2 films with desired band gap for particular applications by thickness control and strain engineering.

Role of HfO 2/SiO 2 thin-film interfaces in near-ultraviolet absorption and pulsed laser damage

DOE PAGES

Papernov, Semyon; Kozlov, Alexei A.; Oliver, James B.; ...

2016-07-15

Here, the role of thin-film interfaces in the near-ultraviolet (near-UV) absorption and pulsed laser-induced damage was studied for ion-beam-sputtered and electron-beam-evaporated coatings comprised from HfO 2 and SiO 2 thin-film pairs. To separate contributions from the bulk of the film and from interfacial areas, absorption and damage threshold measurements were performed for a one-wave (355-nm wavelength) thick, HfO 2 single-layer film and for a film containing seven narrow HfO 2 layers separated by SiO 2 layers. The seven-layer film was designed to have a total optical thickness of HfO 2 layers, equal to one wave at 355 nm and anmore » E-field peak and average intensity similar to a single-layer HfO 2 film. Absorption in both types of films was measured using laser calorimetry and photothermal heterodyne imaging. The results showed a small contribution to total absorption from thin-film interfaces as compared to HfO 2 film material. The relevance of obtained absorption data to coating near-UV, nanosecond-pulse laser damage was verified by measuring the damage threshold and characterizing damage morphology. The results of this study revealed a higher damage resistance in the seven-layer coating as compared to the single-layer HfO 2 film in both sputtered and evaporated coatings. The results are explained through the similarity of interfacial film structure with structure formed during the codeposition of HfO 2 and SiO 2 materials.« less

Thickness-modulated tungsten-carbon superconducting nanostructures grown by focused ion beam induced deposition for vortex pinning up to high magnetic fields.

PubMed

Serrano, Ismael García; Sesé, Javier; Guillamón, Isabel; Suderow, Hermann; Vieira, Sebastián; Ibarra, Manuel Ricardo; De Teresa, José María

2016-01-01

We report efficient vortex pinning in thickness-modulated tungsten-carbon-based (W-C) nanostructures grown by focused ion beam induced deposition (FIBID). By using FIBID, W-C superconducting films have been created with thickness modulation properties exhibiting periodicity from 60 to 140 nm, leading to a strong pinning potential for the vortex lattice. This produces local minima in the resistivity up to high magnetic fields (2.2 T) in a broad temperature range due to commensurability effects between the pinning potential and the vortex lattice. The results show that the combination of single-step FIBID fabrication of superconducting nanostructures with built-in artificial pinning landscapes and the small intrinsic random pinning potential of this material produces strong periodic pinning potentials, maximizing the opportunities for the investigation of fundamental aspects in vortex science under changing external stimuli (e.g., temperature, magnetic field, electrical current).

Large-scale freestanding nanometer-thick graphite pellicles for mass production of nanodevices beyond 10 nm.

PubMed

Kim, Seul-Gi; Shin, Dong-Wook; Kim, Taesung; Kim, Sooyoung; Lee, Jung Hun; Lee, Chang Gu; Yang, Cheol-Woong; Lee, Sungjoo; Cho, Sang Jin; Jeon, Hwan Chul; Kim, Mun Ja; Kim, Byung-Gook; Yoo, Ji-Beom

2015-09-21

Extreme ultraviolet lithography (EUVL) has received much attention in the semiconductor industry as a promising candidate to extend dimensional scaling beyond 10 nm. We present a new pellicle material, nanometer-thick graphite film (NGF), which shows an extreme ultraviolet (EUV) transmission of 92% at a thickness of 18 nm. The maximum temperature induced by laser irradiation (λ = 800 nm) of 9.9 W cm(-2) was 267 °C, due to the high thermal conductivity of the NGF. The freestanding NGF was found to be chemically stable during annealing at 500 °C in a hydrogen environment. A 50 × 50 mm large area freestanding NGF was fabricated using the wet and dry transfer (WaDT) method. The NGF can be used as an EUVL pellicle for the mass production of nanodevices beyond 10 nm.

Pulsed laser deposition of epitaxial yttrium iron garnet films with low Gilbert damping and bulk-like magnetization

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

Onbasli, M. C., E-mail: onbasli@mit.edu; Kim, D. H.; Ross, C. A.

2014-10-01

Yttrium iron garnet (YIG, Y {sub 3}Fe{sub 5}O{sub 12}) films have been epitaxially grown on Gadolinium Gallium Garnet (GGG, Gd{sub 3}Ga{sub 5}O{sub 12}) substrates with (100) orientation using pulsed laser deposition. The films were single-phase, epitaxial with the GGG substrate, and the root-mean-square surface roughness varied between 0.14 nm and 0.2 nm. Films with thicknesses ranging from 17 to 200 nm exhibited low coercivity (<2 Oe), near-bulk room temperature saturation moments (∼135 emu cm{sup −3}), in-plane easy axis, and damping parameters as low as 2.2 × 10{sup −4}. These high quality YIG thin films are useful in the investigation ofmore » the origins of novel magnetic phenomena and magnetization dynamics.« less

Laser scattering induced holograms in lithium niobate. [observation of diffraction cones

NASA Technical Reports Server (NTRS)

Magnusson, R.; Gaylord, T. K.

1974-01-01

A 3.0-mm thick poled single crystal of lithium niobate doped with 0.1 mole% iron was exposed to a single beam and then to two intersecting beams of an argon ion laser operating at 515-nm wavelength. Laser scattering induced holograms were thus written and analyzed. The presence of diffraction cones was observed and is shown to result from the internally recorded interference pattern resulting from the interference of the original incident laser beam with light scattered from material inhomogeneities. This phenomenon is analyzed using Ewald sphere construction techniques which reveal the geometrical relationships existing for the diffraction cones.

Preparation of ultra-thin and high-quality WO{sub 3} compact layers and comparision of WO{sub 3} and TiO{sub 2} compact layer thickness in planar perovskite solar cells

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

Zhang, Jincheng; Shi, Chengwu, E-mail: shicw506@foxmail.com; Chen, Junjun

2016-06-15

In this paper, the ultra-thin and high-quality WO{sub 3} compact layers were successfully prepared by spin-coating-pyrolysis method using the tungsten isopropoxide solution in isopropanol. The influence of WO{sub 3} and TiO{sub 2} compact layer thickness on the photovoltaic performance of planar perovskite solar cells was systematically compared, and the interface charge transfer and recombination in planar perovskite solar cells with TiO{sub 2} compact layer was analyzed by electrochemical impedance spectroscopy. The results revealed that the optimum thickness of WO{sub 3} and TiO{sub 2} compact layer was 15 nm and 60 nm. The planar perovskite solar cell with 15 nm WO{submore » 3} compact layer gave a 9.69% average and 10.14% maximum photoelectric conversion efficiency, whereas the planar perovskite solar cell with 60 nm TiO{sub 2} compact layer achieved a 11.79% average and 12.64% maximum photoelectric conversion efficiency. - Graphical abstract: The planar perovskite solar cell with 15 nm WO{sub 3} compact layer gave a 9.69% average and 10.14% maximum photoelectric conversion efficiency, whereas the planar perovskite solar cell with 60 nm TiO{sub 2} compact layer achieved a 11.79% average and 12.64% maximum photoelectric conversion efficiency. Display Omitted - Highlights: • Preparation of ultra-thin and high-quality WO{sub 3} compact layers. • Perovskite solar cell with 15 nm-thick WO{sub 3} compact layer achieved PCE of 10.14%. • Perovskite solar cell with 60 nm-thick TiO{sub 2} compact layer achieved PCE of 12.64%.« less

Enhancing Performance of Large-Area Organic Solar Cells with Thick Film via Ternary Strategy.

PubMed

Zhang, Jianqi; Zhao, Yifan; Fang, Jin; Yuan, Liu; Xia, Benzheng; Wang, Guodong; Wang, Zaiyu; Zhang, Yajie; Ma, Wei; Yan, Wei; Su, Wenming; Wei, Zhixiang

2017-06-01

Large-scale fabrication of organic solar cells requires an active layer with high thickness tolerability and the use of environment-friendly solvents. Thick films with high-performance can be achieved via a ternary strategy studied herein. The ternary system consists of one polymer donor, one small molecule donor, and one fullerene acceptor. The small molecule enhances the crystallinity and face-on orientation of the active layer, leading to improved thickness tolerability compared with that of a polymer-fullerene binary system. An active layer with 270 nm thickness exhibits an average power conversion efficiency (PCE) of 10.78%, while the PCE is less than 8% with such thick film for binary system. Furthermore, large-area devices are successfully fabricated using polyethylene terephthalate (PET)/Silver gride or indium tin oxide (ITO)-based transparent flexible substrates. The product shows a high PCE of 8.28% with an area of 1.25 cm 2 for a single cell and 5.18% for a 20 cm 2 module. This study demonstrates that ternary organic solar cells exhibit great potential for large-scale fabrication and future applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Aggregation state and magnetic properties of magnetite nanoparticles controlled by an optimized silica coating

NASA Astrophysics Data System (ADS)

Pérez, Nicolás; Moya, C.; Tartaj, P.; Labarta, A.; Batlle, X.

2017-01-01

The control of magnetic interactions is becoming essential to expand/improve the applicability of magnetic nanoparticles (NPs). Here, we show that an optimized microemulsion method can be used to obtain homogenous silica coatings on even single magnetic nuclei of highly crystalline Fe3-xO4 NPs (7 and 16 nm) derived from a high-temperature method. We show that the thickness of this coating is controlled almost at will allowing much higher average separation among particles as compared to the oleic acid coating present on pristine NPs. Magnetic susceptibility studies show that the thickness of the silica coating allows the control of magnetic interactions. Specifically, as this effect is better displayed for the smallest particles, we show that dipole-dipole interparticle interactions can be tuned progressively for the 7 nm NPs, from almost non-interacting to strongly interacting particles at room temperature. The quantitative analysis of the magnetic properties unambiguously suggests that dipolar interactions significantly broaden the effective distribution of energy barriers by spreading the distribution of activation magnetic volumes.

Electrical and switching properties of the Se 90Te 10-xAg x (0⩽ x⩽6) films

NASA Astrophysics Data System (ADS)

Afifi, M. A.; Hegab, N. A.; Bekheet, A. E.; Sharaf, E. R.

2009-08-01

Amorphous Se 90Te 10-xAg x (0⩽ x⩽6) films are obtained by thermal evaporation technique under vacuum from the synthesized bulk materials on pyrographite and glass substrates. X-ray analysis shows the amorphous nature of the obtained films. The dc electrical conductivity was studied for different thicknesses (165-711 nm) as a function of temperature in the range (298-323 K) below the corresponding T g for the studied films. The obtained results show that the conduction activation energy has a single value through the investigated range of temperature which can be explained in accordance with Mott and Davis model. The I- V characteristic curves for the film compositions are found to be typical for a memory switch. The mean value of the threshold voltage Vbar increases linearly with increasing film thickness (165-711 nm), while it decreases exponentially with increasing temperature in the investigated range for the studied compositions. The results are explained in accordance with the electrothermal model for the switching process. The effect of Ag on the studied parameters is also investigated.

Studies on high-moment soft magnetic FeCo/Co thin films

NASA Astrophysics Data System (ADS)

Fu, Yu; Yang, Zheng; Matsumoto, Mitsunori; Liu, Xiao-Xi; Morisako, Akimitsu

2006-06-01

The dependences of soft magnetic properties and microstructures of the sputtered FeCo (=Fe65Co35) films on Co underlayer thickness tCo, FeCo thickness tFeCo, substrate temperature Ts and target-substrate spacing dT-S are studied. FeCo single layer generally shows a high coercivity with no obvious magnetic anisotropy. Excellent soft magnetic properties with saturation magnetization μ0Ms of 2.35 T and hard axis coercivity Hch of 0.25 kA/m in FeCo films can be achieved by introducing a Co underlayer. It is shown that sandwiching a Co underlayer causes a change in orientation and reduction in grain size from 70 nm to about 10 nm in the FeCo layer. The magnetic softness can be explained by the Hoffmann's ripple theory due to the effect of grain size. The magnetic anisotropy can be controlled by changing dT-S and a maximum of 14.3 kA/m for anisotropic field Hk is obtained with dT-S=18.0 cm.

Size effect in the spin glass magnetization of thin AuFe films as studied by polarized neutron reflectometry.

PubMed

Saoudi, M; Fritzsche, H; Nieuwenhuys, G J; Hesselberth, M B S

2008-02-08

We used polarized neutron reflectometry to determine the temperature dependence of the magnetization of thin AuFe films with 3% Fe concentration. We performed the measurements in a large magnetic field of 6 T in a temperature range from 295 to 2 K. For the films in the thickness range from 500 to 20 nm we observed a Brillouin-type behavior from 295 K down to 50 K and a constant magnetization of about 0.9 micro(B) per Fe atom below 30 K. However, for the 10 nm thick film we observed a Brillouin-type behavior down to 20 K and a constant magnetization of about 1.3 micro(B) per Fe atom below 20 K. These experiments are the first to show a finite-size effect in the magnetization of single spin-glass films in large magnetic fields. Furthermore, the ability to measure the deviation from the paramagnetic behavior enables us to prove the existence of the spin-glass state where other methods relying on a cusp-type behavior fail.

Formation process of graphite film on Ni substrate with improved thickness uniformity through precipitation control

NASA Astrophysics Data System (ADS)

Kim, Seul-Gi; Hu, Qicheng; Nam, Ki-Bong; Kim, Mun Ja; Yoo, Ji-Beom

2018-04-01

Large-scale graphitic thin film with high thickness uniformity needs to be developed for industrial applications. Graphitic films with thicknesses ranging from 3 to 20 nm have rarely been reported, and achieving the thickness uniformity in that range is a challenging task. In this study, a process for growing 20 nm-thick graphite films on Ni with improved thickness uniformity is demonstrated and compared with the conventional growth process. In the film grown by the process, the surface roughness and coverage were improved and no wrinkles were observed. Observations of the film structure reveal the reasons for the improvements and growth mechanisms.

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.

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.

Fabrication of plasmonic nanopore by using electron beam irradiation for optical bio-sensor

NASA Astrophysics Data System (ADS)

Choi, Seong Soo; Park, Myoung Jin; Han, Chul Hee; Oh, Seh Joong; Park, Nam Kyou; Park, Doo Jae; Choi, Soo Bong; Kim, Yong-Sang

2017-05-01

The Au nano-hole surrounded by the periodic nano-patterns would provide the enhanced optical intensity. Hence, the nano-hole surrounded with periodic groove patterns can be utilized as single molecule nanobio optical sensor device. In this report, the nano-hole on the electron beam induced membrane surrounded by periodic groove patterns were fabricated by focused ion beam technique (FIB), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). Initially, the Au films with three different thickness of 40 nm, 60 nm, and 200 nm were deposited on the SiN film by using an electron beam sputter-deposition technique, followed by removal of the supporting SiN film. The nanopore was formed on the electron beam induced membrane under the FESEM electron beam irradiation. Nanopore formation inside the Au aperture was controlled down to a few nanometer, by electron beam irradiations. The optical intensities from the biomolecules on the surfaces including Au coated pyramid with periodic groove patterns were investigated via surface enhanced Raman spectroscopy (SERS). The fabricated nanopore surrounded by periodic patterns can be utilized as a next generation single molecule bio optical sensor.

Layer-by-layer modification of thin-film metal-semiconductor multilayers with ultrashort laser pulses

NASA Astrophysics Data System (ADS)

Romashevskiy, S. A.; Tsygankov, P. A.; Ashitkov, S. I.; Agranat, M. B.

2018-05-01

The surface modifications in a multilayer thin-film structure (50-nm alternating layers of Si and Al) induced by a single Gaussian-shaped femtosecond laser pulse (350 fs, 1028 nm) in the air are investigated by means of atomic-force microscopy (AFM), scanning electron microscopy (SEM), and optical microscopy (OM). Depending on the laser fluence, various modifications of nanometer-scale metal and semiconductor layers, including localized formation of silicon/aluminum nanofoams and layer-by-layer removal, are found. While the nanofoams with cell sizes in the range of tens to hundreds of nanometers are produced only in the two top layers, layer-by-layer removal is observed for the four top layers under single pulse irradiation. The 50-nm films of the multilayer structure are found to be separated at their interfaces, resulting in a selective removal of several top layers (up to 4) in the form of step-like (concentric) craters. The observed phenomenon is associated with a thermo-mechanical ablation mechanism that results in splitting off at film-film interface, where the adhesion force is less than the bulk strength of the used materials, revealing linear dependence of threshold fluences on the film thickness.

Surface modifications of crystal-ion-sliced LiNbO3 thin films by low energy ion irradiations

NASA Astrophysics Data System (ADS)

Bai, Xiaoyuan; Shuai, Yao; Gong, Chaoguan; Wu, Chuangui; Luo, Wenbo; Böttger, Roman; Zhou, Shengqiang; Zhang, Wanli

2018-03-01

Single crystalline 128°Y-cut LiNbO3 thin films with a thickness of 670 nm are fabricated onto Si substrates by means of crystal ion slicing (CIS) technique, adhesive wafer bonding using BCB as the medium layer to alleviate the large thermal coefficient mismatch between LiNbO3 and Si, and the X-ray diffraction pattern indicates the exfoliated thin films have good crystalline quality. The LiNbO3 thin films are modified by low energy Ar+ irradiation, and the surface roughness of the films is decreased from 8.7 nm to 3.4 nm. The sputtering of the Ar+ irradiation is studied by scanning electron microscope, atomic force microscope and X-ray photoelectron spectroscopy, and the results show that an amorphous layer exists at the surface of the exfoliated film, which can be quickly removed by Ar+ irradiation. A two-stage etching mechanism by Ar+ irradiation is demonstrated, which not only establishes a new non-contact surface polishing method for the CIS-fabricated single crystalline thin films, but also is potentially useful to remove the residue damage layer produced during the CIS process.

Electron holography study of magnetization behavior in the writer pole of a perpendicular magnetic recording head by a 1 MV transmission electron microscope.

PubMed

Hirata, Kei; Ishida, Yoichi; Akashi, Tetsuya; Shindo, Daisuke; Tonomura, Akira

2012-01-01

The magnetic domain structure of the writer poles of perpendicular magnetic recording heads was studied using electron holography. Although the domain structure of a 100-nm-thick writer pole could be observed with a 300 kV transmission electron microscope, that of the 250-nm-thick writer pole could not be analyzed due to the limited transmission capability of the instrument. On the other hand, the detailed domain structure of the 250-nm-thick writer pole was successfully analyzed by a 1 MV electron microscope using its high transmission capability. The thickness and material dependency of the domain structure of a writer pole were discussed.

Large-area few-layer hexagonal boron nitride prepared by quadrupole field aided exfoliation

NASA Astrophysics Data System (ADS)

Lun Lu, Han; Zhi Rong, Min; Qiu Zhang, Ming

2018-03-01

A quadrupole electric field-mediated exfoliation method is proposed to convert micron-sized hexagonal boron nitride (h-BN) powder into few-layer hexagonal boron nitride nanosheets (h-BNNS). Under optimum conditions (400 Hz, 40 V, 32 μg ml-1, sodium deoxycholate, TAE medium), the h-BN powders (thickness >200 nm, horizontal scale ˜10 μm) are successfully exfoliated into 0.5-4 nm (1-10 layers) thick h-BNNS with the same horizontal scale. Dynamic laser scattering and atomic force microscope data show that the yield is 47.6% (for the portion with the thickness of 0.5-6 nm), and all of the vertical sizes are reduced to smaller than 18 nm (45 layers).

Nanoscale size effects on the mechanical properties of platinum thin films and cross-sectional grain morphology

NASA Astrophysics Data System (ADS)

Abbas, K.; Alaie, S.; Ghasemi Baboly, M.; Elahi, M. M. M.; Anjum, D. H.; Chaieb, S.; Leseman, Z. C.

2016-01-01

The mechanical behavior of polycrystalline Pt thin films is reported for thicknesses of 75 nm, 100 nm, 250 nm, and 400 nm. These thicknesses correspond to transitions between nanocrystalline grain morphology types as found in TEM studies. Thinner samples display a brittle behavior, but as thickness increases the grain morphology evolves, leading to a ductile behavior. During evolution of the morphology, dramatic differences in elastic moduli (105-160 GPa) and strengths (560-1700 MPa) are recorded and explained by the variable morphology. This work suggests that in addition to the in-plane grain size of thin films, the transitions in cross-sectional morphologies of the Pt films significantly affect their mechanical behavior.

Photo-ionization and modification of nanoparticles on transparent substrates by ultrashort laser pulses

NASA Astrophysics Data System (ADS)

Gruzdev, Vitaly; Komolov, Vladimir; Li, Hao; Yu, Qingsong; Przhibel'skii, Sergey; Smirnov, Dmitry

2011-02-01

The objective of this combined experimental and theoretical research is to study the dynamics and mechanisms of nanoparticle interaction with ultrashort laser pulses and related modifications of substrate surface. For the experimental effort, metal (gold), dielectric (SiO2) and dielectric with metal coating (about 30 nm thick) spherical nanoparticles deposited on glass substrate are utilized. Size of the particles varies from 20 to 200 nm. Density of the particles varies from low (mean inter-particle distance 100 nm) to high (mean inter-particle distance less than 1 nm). The nanoparticle assemblies and the corresponding empty substrate surfaces are irradiated with single 130-fs laser pulses at wavelength 775 nm and different levels of laser fluence. Large diameter of laser spot (0.5-2 mm) provides gradient variations of laser intensity over the spot and allows observing different laser-nanoparticle interactions. The interactions vary from total removal of the nanoparticles in the center of laser spot to gentle modification of their size and shape and totally non-destructive interaction. The removed particles frequently form specific sub-micrometer-size pits on the substrate surface at their locations. The experimental effort is supported by simulations of the nanoparticle interactions with high-intensity ultrashort laser pulse. The simulation employs specific modification of the molecular dynamics approach applied to model the processes of non-thermal particle ablation following laser-induced electron emission. This technique delivers various characteristics of the ablation plume from a single nanoparticle including energy and speed distribution of emitted ions, variations of particle size and overall dynamics of its ablation. The considered geometry includes single isolated particle as well a single particle on a flat substrate that corresponds to the experimental conditions. The simulations confirm existence of the different regimes of laser-nanoparticle interactions depending on laser intensity and wavelength. In particular, implantation of ions departing from the nanoparticles towards the substrate is predicted.

Micromachined single-level nonplanar polycrystalline SiGe thermal microemitters for infrared dynamic scene projection

NASA Astrophysics Data System (ADS)

Malyutenko, V. K.; Malyutenko, O. Yu.; Leonov, V.; Van Hoof, C.

2009-05-01

The technology for self-supported membraneless polycrystalline SiGe thermal microemitters, their design, and performance are presented. The 128-element arrays with a fill factor of 88% and a 2.5-μm-thick resonant cavity have been grown by low-pressure chemical vapor deposition and fabricated using surface micromachining technology. The 200-nm-thick 60×60 μm2 emitting pixels enforced with a U-shape profile pattern demonstrate a thermal time constant of 2-7 ms and an apparent temperature of 700 K in the 3-5 and 8-12 μm atmospheric transparency windows. The application of the devices to the infrared dynamic scene simulation and their benefit over conventional planar membrane-supported emitters are discussed.

Generic Superconducting Inhomogeneity in Single Crystal Fe(Te1-xSex) Probed by Nanostructure-transport

NASA Astrophysics Data System (ADS)

Yue, Chunlei; Hu, Jin; Liu, Xue; Mao, Zhiqiang; Wei, Jiang

2015-03-01

We have investigated the nano-scale electronic properties of the iron-based unconventional superconductor Fe(Te1-xSex) with optimal Se content x = 0.5. Using the microexfoliation method and ion milling thinning, we successfully produced Fe(Te1-xSex) devices with thickness varying from 90nm down to 12nm. Our transport measurements revealed a suppression of superconductivity coinciding with the loss of normal state metallicity. Through the simulation of the formation of superconducting region in nano-scale thin flakes, we show that our observation is in line with the nano-scale inhomogeneity proposed for this material; therefore it provides a more direct evidence for the nano-scale inhomogeneous superconductivity in Fe(Te1-xSex) .

Mode-locked fiber laser using SU8 resist incorporating carbon nanotubes

NASA Astrophysics Data System (ADS)

Hernandez-Romano, Ivan; Mandridis, Dimitrios; May-Arrioja, Daniel A.; Sanchez-Mondragon, Jose J.; Delfyett, Peter J.

2011-06-01

We report the fabrication of a saturable absorber made of a novel polymer SU8 doped with Single Wall Carbon Nanotubes (SWCNTs). A passive mode-locked ring cavity fiber laser was built with a 100 μm thick SU8/SWCNT film inserted between two FC/APC connectors. Self-starting passively mode-locked lasing operation was observed at 1572.04 nm, with a FWHM of 3.26 nm. The autocorrelation trace was 1.536 ps corresponding to a pulse-width of 871 fs. The time-bandwidth product was 0.344, which is close enough to transform-limited sech squared pulses. The repetition rate was 21.27 MHz, and a maximum average output power of 1 mW was also measured.

Tailoring of the Perpendicular Magnetization Component in Ferromagnetic Films on a Vicinal Substrate

NASA Astrophysics Data System (ADS)

Stupakiewicz, A.; Maziewski, A.; Matlak, K.; Spiridis, N.; Ślęzak, M.; Ślęzak, T.; Zajac, M.; Korecki, J.

2008-11-01

We have engineered the magnetic properties of 1 8 nm Co films epitaxially grown on an Au-buffered bifacial W(110)/W(540) single crystal. The surface of Au/W(110) was atomically flat, whereas the Au/W(540) followed the morphology of the vicinal W surface, showing a regular array of monoatomic steps. For Co grown on Au/W(540), the existence of the out-of-plane magnetization component extended strongly to a thickness d of about 8 nm, which was accompanied by an anomalous increase of the out-of-plane switching field with increasing d. In addition, the process of up-down magnetization switching could be realized with both a perpendicular and in-plane external magnetic field.

Integration of an Axcelis Optima HD Single Wafer High Current Implanter for p- and n-S/D Implants in an Existing Batch Implanter Production Line

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

Schmeide, Matthias; Kontratenko, Serguei; Krimbacher, Bernhard

2008-11-03

This paper is focused on the integration and qualification of an Axcelis Optima HD single wafer high current spot beam implanter in an existing 200 mm production line with different types of Axcelis batch implanters for high current applications. Both the design of the beamline and the beam shape are comparable between single wafer and batch high current spot beam implanters. In contrast to the single wafer high current ribbon beam implanter, energy contamination is not a concern for the considered spot beam tool because the drift mode can be used down to energies in the 2 keV region. Themore » most important difference between single wafer and batch high current implanters is the significantly higher dose rate and, therefore, the higher damage rate for the single wafer tool due to the different scanning architecture. The results of the integration of high dose implantations, mainly for p- and n-S/D formation, for DRAM 110 nm without pre-amorphization implantation (PAI), CMOS Logic from around 250 nm down to 90 nm without and with PAI, are presented and discussed. Dopant concentration profile analysis using SIMS was performed for different technologies and implantation conditions. The impurity activation was measured using sheet resistance and in some cases spreading resistance technique was applied. The amorphous layer thickness was measured using TEM. Finally, device data are presented in combination with dose, energy and beam current variations. The results have shown that the integration of implantation processes into crystalline structure without PAI is more complex and time consuming than implantations into amorphous layer where the damage difference due to the different dose rates is negligible.« less

Organic field effect transistors - Study of performance parameters for different dielectric layer thickness

NASA Astrophysics Data System (ADS)

Assis, Anu; Shahul Hameed T., A.; Predeep, P.

2017-06-01

Mobility and current handling capabilities of Organic Field Effect Transistor (OFET) are vitally important parameters in the electrical performance where the material parameters and thickness of different layers play significant role. In this paper, we report the simulation of an OFET using multi physics tool, where the active layer is pentacene and Poly Methyl Methacrylate (PMMA) forms the dielectric. Electrical characterizations of the OFET on varying the thickness of the dielectric layer from 600nm to 400nm are simulated and drain current, transconductance and mobility are analyzed. In the study it is found that even though capacitance increases with reduction in dielectric layer thickness, the transconductance effect is reflected many more times in the mobility which in turn could be attributed to the variations in transverse electric field. The layer thickness below 300nm may result in gate leakage current points to the requirement of optimizing the thickness of different layers for better performance.

Estimation of carrier leakage in InGaN light emitting diodes from photocurrent measurements

NASA Astrophysics Data System (ADS)

Hafiz, Shopan; Zhang, Fan; Monavarian, Morteza; Okur, Serdal; Avrutin, Vitaliy; Morkoç, Hadis; Özgür, Ümit

2014-02-01

Carrier transport in double heterostructure (DH) InGaN light emitting diodes (LEDs) was investigated using photocurrent measurements performed under CW HeCd laser (325 nm wavelength) excitation. The effect of electron injector thicknesses was investigated by monitoring the excitation density and applied bias dependent escape of photogenerated carriers from the active region and through energy band structure and carrier transport simulations using Silvaco Atlas. For quad (4x) 3-nm DH LED structures incorporating staircase electron injectors (SEIs), photocurrent increased with SEI thickness due to reduced effective barrier opposing carrier escape from the active region as confirmed by simulations. The carrier leakage percentile at -3V bias and 280 Wcm-2 optical excitation density increased from 24 % to 55 % when In 0.04Ga0.96N + In0.08Ga0.92N SEI thickness was increased from 4 nm + 4 nm to 30 nm + 30 nm. The increased leakage with thicker SEI correlates with increased carrier overflow under forward bias.

Conversion of just-continuous metallic films to large particulate substrates for metal-enhanced fluorescence

PubMed Central

Aslan, Kadir; Malyn, Stuart N.; Zhang, Yongxia; Geddes, Chris D.

2008-01-01

We report the effects of thermally annealing, non-, just-, and thick continuous silver films for their potential applications in metal-enhanced fluorescence, a near-field concept which can alter the free-space absorption and emissive properties of close-proximity fluorophores (excited states). We have chosen to anneal a noncontinuous particulate film 5 nm thick and two thicker continuous films, 15 and 25 nm thick, respectively. Our results show that the annealing of the 25 nm film has little effect on close-proximity fluorescence when coated with a monolayer of fluorophore-labeled protein. However, the 15 nm continuous film cracks upon annealing, producing large nanoparticles which are ideal for enhancing the fluorescence of close-proximity fluorophores that are indeed difficult to prepare by other wet-chemical deposition processes. The annealing of 5 nm noncontinuous particulate films (a control sample) has little influence on metal-enhanced fluorescence, as expected. PMID:19479004

Conversion of just-continuous metallic films to large particulate substrates for metal-enhanced fluorescence.

PubMed

Aslan, Kadir; Malyn, Stuart N; Zhang, Yongxia; Geddes, Chris D

2008-04-15

We report the effects of thermally annealing, non-, just-, and thick continuous silver films for their potential applications in metal-enhanced fluorescence, a near-field concept which can alter the free-space absorption and emissive properties of close-proximity fluorophores (excited states). We have chosen to anneal a noncontinuous particulate film 5 nm thick and two thicker continuous films, 15 and 25 nm thick, respectively. Our results show that the annealing of the 25 nm film has little effect on close-proximity fluorescence when coated with a monolayer of fluorophore-labeled protein. However, the 15 nm continuous film cracks upon annealing, producing large nanoparticles which are ideal for enhancing the fluorescence of close-proximity fluorophores that are indeed difficult to prepare by other wet-chemical deposition processes. The annealing of 5 nm noncontinuous particulate films (a control sample) has little influence on metal-enhanced fluorescence, as expected.

Temperature effects on nanostructure and mechanical properties of single-nanoparticle thick membranes.

DOE PAGES

Salerno, Kenneth Michael; Grest, Gary S.

2015-04-30

In this study, the properties of mechanically stable single-nanoparticle (NP)-thick membranes have largely been studied at room temperature. How these membranes soften as nanoparticle ligands disorder with increasing temperature is unknown. Molecular dynamics simulations are used to probe the temperature dependence of the mechanical and nanostructural properties of nanoparticle membranes made of 6 nm diameter Au nanoparticles coated with dodecanethiol ligands and terminated with either methyl (CH 3) or carboxyl (COOH) terminal groups. For methyl-terminated ligands, interactions along the alkane chain provide mechanical stiffness, with a Young's modulus of 1.7 GPa at 300 K. For carboxyl-terminated chains, end-group interactions aremore » significant, producing stiffer membranes at all temperatures, with a Young's modulus of 3.8 GPa at 300 K. For both end-group types, membrane stiffness is reduced to zero at about 400 K. Ligand structure and mechanical properties of membranes at 300 K that have been annealed at 400 K are comparable to samples that do not undergo thermal annealing.« less

Satellite measurements of large-scale air pollution - Measurements of forest fire smoke

NASA Technical Reports Server (NTRS)

Ferrare, Richard A.; Kaufman, Yoram J.; Fraser, Robert S.

1990-01-01

The transport, optical properties, total mass, and removal of smoke produced by forest fires in western Canada during late July and early August 1982 are studied using NOAA 7 AVHRR data. Color composite imagery is produced to track the movement of the smoke over Canada and the U.S. as the smoke traveled thousands of km from the source region. Smoke optical thickness, particle size, and single scattering albedo are computed using radiances measured by AVHRR bands 1 and 2. Results show that smoke optical thickness ranged from less that 0.1 to greater than 3.7 and the geometric mean mass radii ranged from 300 to 900 nm. The smoke single scattering albedo ranged from 0.9 to nearly 1.0. The total smoke mass over the eastern U.S. ranged from 0.1 to 0.5 Tg, which is close to the 0.5 Tg estimated from the forest fuel content. The smoke lifetime is estimated to be between 15 and 20 days.

Nanometre-thick single-crystalline nanosheets grown at the water-air interface

NASA Astrophysics Data System (ADS)

Wang, Fei; Seo, Jung-Hun; Luo, Guangfu; Starr, Matthew B.; Li, Zhaodong; Geng, Dalong; Yin, Xin; Wang, Shaoyang; Fraser, Douglas G.; Morgan, Dane; Ma, Zhenqiang; Wang, Xudong

2016-01-01

To date, the preparation of free-standing 2D nanomaterials has been largely limited to the exfoliation of van der Waals solids. The lack of a robust mechanism for the bottom-up synthesis of 2D nanomaterials from non-layered materials has become an obstacle to further explore the physical properties and advanced applications of 2D nanomaterials. Here we demonstrate that surfactant monolayers can serve as soft templates guiding the nucleation and growth of 2D nanomaterials in large area beyond the limitation of van der Waals solids. One- to 2-nm-thick, single-crystalline free-standing ZnO nanosheets with sizes up to tens of micrometres are synthesized at the water-air interface. In this process, the packing density of surfactant monolayers adapts to the sub-phase metal ions and guides the epitaxial growth of nanosheets. It is thus named adaptive ionic layer epitaxy (AILE). The electronic properties of ZnO nanosheets and AILE of other materials are also investigated.

An oscillator based on a single Au nanocluster

NASA Astrophysics Data System (ADS)

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

2017-01-01

Metal nanoclusters embedded into the ultrathin dielectric films attracted much attention in recent years due to their unusual electronic, optical, etc., properties differing from those of the bulk metals essentially and, hence, to the prospects of their applications in novel nanoelectronic, single electronic, non-volatile memory, etc., devices. Here, we report on the experimental observation of the electrical oscillations in an oscillating loop connected to a contact of a conductive probe of an Atomic Force Microscope to a tunnel-transparent ( ˜6.5 nm thick) yttria stabilized zirconia film with embedded Au nanoclusters on the Si substrate. The oscillations were attributed to the negative differential resistance of the probe-to-sample contact originating from the resonant electron tunnelling between the probe and the Si substrate via the quantum confined electron energy levels in small ( ≈2.5 nm in diameter) Au nanoclusters. This observation demonstrates the prospects of building an oscillator nanoelectronic device based on an individual nanometer-sized metal nanocluster.

Sensitive SERS detection at the single-particle level based on nanometer-separated mushroom-shaped plasmonic dimers

NASA Astrophysics Data System (ADS)

Xiang, Quan; Li, Zhiqin; Zheng, Mengjie; Liu, Qing; Chen, Yiqin; Yang, Lan; Jiang, Tian; Duan, Huigao

2018-03-01

Elevated metallic nanostructures with nanogaps (<10 nm) possess advantages for surface enhanced Raman scattering (SERS) via the synergic effects of nanogaps and efficient decoupling from the substrate through an elevated three-dimensional (3D) design. In this work, we demonstrate a pattern-transfer-free process to reliably define elevated nanometer-separated mushroom-shaped dimers directly from 3D resist patterns based on the gap-narrowing effect during the metallic film deposition. By controlling the initial size of nanogaps in resist structures and the following deposited film thickness, metallic nanogaps could be tuned at the sub-10 nm scale with single-digit nanometer precision. Both experimental and simulated results revealed that gold dimer on mushroom-shaped pillars have the capability to achieve higher SERS enhancement factor comparing to those plasmonic dimers on cylindrical pillars or on a common SiO2/Si substrate, implying that the nanometer-gapped elevated dimer is an ideal platform to achieve the highest possible field enhancement for various plasmonic applications.

Ultrastructure of the spermatozoon of Dipylidium caninum (Cestoda, Cyclophyllidea, Dilepididae), an intestinal parasite of Canis familiaris.

PubMed

Miquel, J; Marchand, B

1997-01-01

We report for the first time the ultrastructure of the spermatozoon of a Dilepididae cestode. The mature spermatozoa of Dipylidium caninum is filiform and tapered at both ends and lacks mitochondria. The anterior extremity exhibits an apical cone of electron-dense material measuring about 600 nm in length and a single helicoidal crested-like body that is 150 nm thick. This single crested-like body is spiralized at an angle of about 40 degrees to the spermatozoon axis. The axoneme, showing the 9 + "l" pattern of the Platyhelminthes, lacks a periaxonemal sheath. The cortical microtubules constitute a continuous, submembranous, electron-dense material, and they are also twisted at an angle of about 40 degrees to the spermatozoon axis. Moreover, the nucleus is coiled in a helix around the axoneme, which is centrally located throughout its length. We demonstrate for the first time the presence of peripheral microtubules twisted to the spermatozoon axis up to the posterior extremity of the gamete.

Highly-flexible, ultra-thin, and transparent single-layer graphene/silver composite electrodes for organic light emitting diodes

NASA Astrophysics Data System (ADS)

Li, Kun; Wang, Hu; Li, Huiying; Li, Ye; Jin, Guangyong; Gao, Lanlan; Marco, Mazzeo; Duan, Yu

2017-08-01

Transparent conductive electrode (TCE) platforms are required in many optoelectronic devices, including organic light emitting diodes (OLEDs). To date, indium tin oxide based electrodes are widely used in TCEs but they still have few limitations in term of achieving flexible OLEDs and display techniques. In this paper, highly-flexible and ultra-thin TCEs were fabricated for use in OLEDs by combining single-layer graphene (SLG) with thin silver layers of only several nanometers in thickness. The as-prepared SLG + Ag (8 nm) composite electrodes showed low sheet resistances of 8.5 Ω/□, high stability over 500 bending cycles, and 74% transmittance at 550 nm wavelength. Furthermore, SLG + Ag composite electrodes employed as anodes in OLEDs delivered turn-on voltages of 2.4 V, with luminance exceeding 1300 cd m-2 at only 5 V, and maximum luminance reaching up 40 000 cd m-2 at 9 V. Also, the devices could work normally under less than the 1 cm bending radius.

SiO2/ZnO Composite Hollow Sub-Micron Fibers: Fabrication from Facile Single Capillary Electrospinning and Their Photoluminescence Properties.

PubMed

Song, Guanying; Li, Zhenjiang; Li, Kaihua; Zhang, Lina; Meng, Alan

2017-02-24

In this work, SiO2/ZnO composite hollow sub-micron fibers were fabricated by a facile single capillary electrospinning technique followed by calcination, using tetraethyl orthosilicate (TEOS), polyvinylpyrrolidone (PVP) and ZnO nanoparticles as raw materials. The characterization results of the scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) spectra indicated that the asprepared composite hollow fibers consisted of amorphous SiO2 and hexagonal wurtzite ZnO. The products revealed uniform tubular structure with outer diameters of 400-500 nm and wall thickness of 50-60 nm. The gases generated and the directional escaped mechanism was proposed to illustrate the formation of SiO2/ZnO composite hollow sub-micron fibers. Furthermore, a broad blue emission band was observed in the photoluminescence (PL) of SiO2/ZnO composite hollow sub-micron fibers, exhibiting great potential applications as blue light-emitting candidate materials.

A molecular dynamics study on thin film liquid boiling characteristics under rapid linear boundary heating: Effect of liquid film thickness

NASA Astrophysics Data System (ADS)

Rabbi, Kazi Fazle; Tamim, Saiful Islam; Faisal, A. H. M.; Mukut, K. M.; Hasan, Mohammad Nasim

2017-06-01

This study is a molecular dynamics investigation of phase change phenomena i.e. boiling of thin liquid films subjected to rapid linear heating at the boundary. The purpose of this study is to understand the phase change heat transfer phenomena at nano scale level. In the simulation, a thin film of liquid argon over a platinum surface has been considered. The simulation domain herein is a three-phase system consisting of liquid and vapor argon atoms placed over a platinum wall. Initially the whole system is brought to an equilibrium state at 90 K and then the temperature of the bottom wall is increased to a higher temperature (250K) within a finite time interval. Four different liquid argon film thicknesses have been considered (3 nm, 4 nm, 5 nm and 6 nm) in this study. The boundary heating rate (40×109 K/s) is kept constant in all these cases. Variation in system temperature, pressure, net evaporation number, spatial number density of the argon region with time for different film thickness have been demonstrated and analyzed. The present study indicates that the pattern of phase transition may be significantly different (i.e. evaporation or explosive boiling) depending on the liquid film thickness. Among the four cases considered in the present study, explosive boiling has been observed only for the liquid films of 5nm and 6nm thickness, while for the other cases, evaporation take place.

Recoil hysteresis of Sm -Co/Fe exchange-spring bilayers

NASA Astrophysics Data System (ADS)

Kang, K.; Lewis, L. H.; Jiang, J. S.; Bader, S. D.

2005-12-01

The exchange-spring behavior found in Sm-Co (20nm)/Fe epitaxial bilayer films was investigated by analyzing major hysteresis and recoil curves as a function of anneal conditions. The hard layer consists of nanocrystalline intermetallic Sm-Co hexagonal phases (majority phase Sm2Co7 with SmCo3 and SmCo5). Recoil curves, obtained from the successive removal to remanence and reapplication of an increasingly negative field from the major demagnetization curve, reveal the reversible and irreversible components of the magnetization. The Sm-Co thickness was fixed at 20nm while the Fe thicknesses of 10 and 20nm were studied, with ex situ annealing carried out in evacuated, sealed silica tubes at different temperatures. The peak in the recoil curve area is associated with the coercivity of the hard phase. The development of the soft component magnetization is revealed by the departure of the recoil area from zero with application of a reverse field. These two features together confirm that annealing stabilizes the 10nm Fe bilayer sample against local magnetic reversal while it weakens the 20nm bilayer sample. Furthermore, in both its as-deposited and annealed states the Sm -Co/Fe bilayer of 10nm Fe thickness always displays a higher exchange field and smaller recoil loop areas than the bilayer of 20nm Fe thickness, consistent with a stronger exchange response and more reversible magnetization in the former.

Tm:GGAG crystal for 2μm tunable diode-pumped laser

NASA Astrophysics Data System (ADS)

Šulc, Jan; Boháček, Pavel; Němec, Michal; Fibrich, Martin; Jelínková, Helena; Trunda, Bohumil; Havlák, Lubomír.; Jurek, Karel; Nikl, Martin

2016-04-01

The spectroscopy properties and wavelength tunability of diode pumped laser based on Tm-doped mixed gadolinium-gallium-aluminium garnet Gd3(GaxAl1-x)5O12 (Tm:GGAG) single crystal were investigated for the first time. The crystal was grown by Czochralski method in a slightly oxidative atmosphere using an iridium crucible. The tested Tm:GGAG sample was cut from the grown crystal boule perpendicularly to growth direction (c-axis). The composition of sample was determined using electron microprobe X-ray elemental analysis. For spectroscopy and laser experiments 3.5mm thick plane-parallel face-polished plate (without AR coatings) with composition Gd2.76Tm0.0736Ga2.67Al2.50O12 (2.67 at.% Tm/Gd) was used. A fiber (core diameter 400 μm, NA= 0.22) coupled laser diode (emission wavelength 786 nm) was used for longitudinal Tm:GGAG pumping. The laser diode was operating in the pulsed regime (10 ms pulse length, 10 Hz repetition rate, maximum power amplitude 18 W). The 145mm long semi-hemispherical laser resonator consisted of a flat pumping mirror (HR @ 1.8- 2.10 μm, HT @ 0.78 μm) and curved (r = 150mm) output coupler with a reflectivity of » 97% @ 1.8- 2.10 µm. The maximum laser output power amplitude 1.14W was obtained at wavelength 2003nm for absorbed pump power amplitude 4.12W. The laser slope efficiency was 37% in respect to absorbed pumping power. Wavelength tuning was accomplished by using 2mm thick MgF2 birefringent filter placed inside the laser resonator at the Brewster angle. The laser was continuously tunable over 180nm in a spectral region from 1856nm to 2036 nm.

Estimation of soft X-ray and EUV transition radiation power emitted from the MIRRORCLE-type tabletop synchrotron.

PubMed

Toyosugi, N; Yamada, H; Minkov, D; Morita, M; Yamaguchi, T; Imai, S

2007-03-01

The tabletop synchrotron light sources MIRRORCLE-6X and MIRRORCLE-20SX, operating at electron energies E(el) = 6 MeV and E(el) = 20 MeV, respectively, can emit powerful transition radiation (TR) in the extreme ultraviolet (EUV) and the soft X-ray regions. To clarify the applicability of these soft X-ray and EUV sources, the total TR power has been determined. A TR experiment was performed using a 385 nm-thick Al foil target in MIRRORCLE-6X. The angular distribution of the emitted power was measured using a detector assembly based on an NE102 scintillator, an optical bundle and a photomultiplier. The maximal measured total TR power for MIRRORCLE-6X is P(max) approximately equal 2.95 mW at full power operation. Introduction of an analytical expression for the lifetime of the electron beam allows calculation of the emitted TR power by a tabletop synchrotron light source. Using the above measurement result, and the theoretically determined ratio between the TR power for MIRRORCLE-6X and MIRRORCLE-20SX, the total TR power for MIRRORCLE-20SX can be obtained. The one-foil TR target thickness is optimized for the 20 MeV electron energy. P(max) approximately equal 810 mW for MIRRORCLE-20SX is obtained with a single foil of 240 nm-thick Be target. The emitted bremsstrahlung is negligible with respect to the emitted TR for optimized TR targets. From a theoretically known TR spectrum it is concluded that MIRRORCLE-20SX can emit 150 mW of photons with E > 500 eV, which makes it applicable as a source for performing X-ray lithography. The average wavelength, \\overline\\lambda = 13.6 nm, of the TR emission of MIRRORCLE-20SX, with a 200 nm Al target, could provide of the order of 1 W EUV.

Enhanced electrical properties of oxide semiconductor thin-film transistors with high conductivity thin layer insertion for the channel region

NASA Astrophysics Data System (ADS)

Nguyen, Cam Phu Thi; Raja, Jayapal; Kim, Sunbo; Jang, Kyungsoo; Le, Anh Huy Tuan; Lee, Youn-Jung; Yi, Junsin

2017-02-01

This study examined the performance and the stability of indium tin zinc oxide (ITZO) thin film transistors (TFTs) by inserting an ultra-thin indium tin oxide (ITO) layer at the active/insulator interface. The electrical properties of the double channel device (ITO thickness of 5 nm) were improved in comparison with the single channel ITZO or ITO devices. The TFT characteristics of the device with an ITO thickness of less than 5 nm were degraded due to the formation of an island-like morphology and the carriers scattering at the active/insulator interface. The 5 nm-thick ITO inserted ITZO TFTs (optimal condition) exhibited a superior field effect mobility (∼95 cm2/V·s) compared with the ITZO-only TFTs (∼34 cm2/V·s). The best characteristics of the TFT devices with double channel layer are due to the lowest surface roughness (0.14 nm) and contact angle (50.1°) that result in the highest hydrophicility, and the most effective adhesion at the surface. Furthermore, the threshold voltage shifts for the ITO/ITZO double layer device decreased to 0.80 and -2.39 V compared with 6.10 and -6.79 V (for the ITZO only device) under positive and negative bias stress, respectively. The falling rates of EA were 0.38 eV/V and 0.54 eV/V for the ITZO and ITO/ITZO bi-layer devices, respectively. The faster falling rate of the double channel devices suggests that the trap density, including interface trap and semiconductor bulk trap, can be decreased by the ion insertion of a very thin ITO film into the ITZO/SiO2 reference device. These results demonstrate that the double active layer TFT can potentially be applied to the flat panel display.

Optical Properties and Radiation-Enhanced Evaporation of Nanofluid Fuels Containing Carbon-Based Nanostructures

DTIC Science & Technology

2012-05-29

of the large aspect ratio, the SWCNTs tend to entangle with one another and form network structures. Single and isolated SWCNTs are fewer. The...separated and show much fewer network structures because of entanglement . Also, the length of the MWCNTs is about 100 nm, significantly shorter than that...processed by a self-developed MATLAB code to derive the droplet evaporation rate. A type K thermocouple with a thickness of 76 μm was used to suspend the

Optical properties of the Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings

NASA Astrophysics Data System (ADS)

Marszałek, Konstanty; Winkowski, Paweł; Jaglarz, Janusz

2014-01-01

Investigations of bilayer and trilayer Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings are presented in this paper. The oxide films were deposited on a heated quartz glass by e-gun evaporation in a vacuum of 5 × 10-3 [Pa] in the presence of oxygen. Depositions were performed at three different temperatures of the substrates: 100 °C, 200 °C and 300 °C. The coatings were deposited onto optical quartz glass (Corning HPFS). The thickness and deposition rate were controlled with Inficon XTC/2 thickness measuring system. Deposition rate was equal to 0.6 nm/s for Al2O3, 0.6 nm - 0.8 nm/s for HfO2 and 0.6 nm/s for SiO2. Simulations leading to optimization of the thin film thickness and the experimental results of optical measurements, which were carried out during and after the deposition process, have been presented. The optical thickness values, obtained from the measurements performed during the deposition process were as follows: 78 nm/78 nm for Al2O3/SiO2 and 78 nm/156 nm/78 nm for Al2O3/HfO2/SiO2. The results were then checked by ellipsometric technique. Reflectance of the films depended on the substrate temperature during the deposition process. Starting from 240 nm to the beginning of visible region, the average reflectance of the trilayer system was below 1 % and for the bilayer, minima of the reflectance were equal to 1.6 %, 1.15 % and 0.8 % for deposition temperatures of 100 °C, 200 °C and 300 °C, respectively.

Strong Effect of Azodye Layer Thickness on RM-Stabilized Photoalignment

DTIC Science & Technology

2017-05-21

to thicker layers (~40 nm). Author Keywords photoalignment; azodye; reactive mesogen 1. Introduction Photoalignment of liquid crystals by azodye...Polymerizable azodyes[3] as well as passivation of the azodye film by spin-coating with a layer of reactive mesogen[4] are currently proposed solutions...thick alignment film rather than a ~40 nm thick alignment film ; cells with thin alignment layers are stable to exposure to polarized light for at

CNT-based saturable absorbers with scalable modulation depth for Thulium-doped fiber lasers operating at 1.9 μm

PubMed Central

Sobon, Grzegorz; Duzynska, Anna; Świniarski, Michał; Judek, Jarosław; Sotor, Jarosław; Zdrojek, Mariusz

2017-01-01

In this work, we demonstrate a comprehensive study on the nonlinear parameters of carbon nanotube (CNT) saturable absorbers (SA) as a function of the nanotube film thickness. We have fabricated a set of four saturable absorbers with different CNT thickness, ranging from 50 to 200 nm. The CNTs were fabricated via a vacuum filtration technique and deposited on fiber connector end facets. Each SA was characterized in terms of nonlinear transmittance (i.e. optical modulation depth) and tested in a Thulium-doped fiber laser. We show, that increasing the thickness of the CNT layer significantly increases the modulation depth (up to 17.3% with 200 nm thick layer), which strongly influences the central wavelength of the laser, but moderately affects the pulse duration. It means, that choosing the SA with defined CNT thickness might be an efficient method for wavelength-tuning of the laser, without degrading the pulse duration. In our setup, the best performance in terms of bandwidth and pulse duration (8.5 nm and 501 fs, respectively) were obtained with 100 nm thick CNT layer. This is also, to our knowledge, the first demonstration of a fully polarization-maintaining mode-locked Tm-doped laser based on CNT saturable absorber. PMID:28368014

Formation and decay of charge carriers in aggregate nanofibers consisting of poly(3-hexylthiophene)-coated gold nanoparticles.

PubMed

Lee, Dongki; Lee, Jaewon; Song, Ki-Hee; Rhee, Hanju; Jang, Du-Jeon

2016-01-21

Thin nanofibers (NFs) of J-dominant aggregates with a thickness of 15 nm and thick NFs of H-dominant aggregates with a thickness of 25 nm were fabricated by the self-assembly of poly(3-hexylthiophene)-coated gold nanoparticles. The formation and decay dynamics of the charge carriers, which are dependent on the aggregate types of NFs, was investigated by time-resolved emission and transient-absorption spectroscopy. With increasing excitation energy, the fraction of the fast emission decay component decreased, suggesting that the fast formation of polaron pairs (PP), localized (LP), and delocalized polarons (DP) results from higher singlet exciton states produced by the singlet fusion. The faster decay dynamics of DP and LP in the thick NFs than in thin NFs is due to the increased delocalization of DP and LP. As the interchain aggregation is weaker than intrachain aggregation, PP decays faster in thin NFs than in thick NFs. In both thin and thick NFs, although triplet (T1) excitons were barely observed with excitation at 532 nm on a nanosecond time scale, they were observed with excitation at 355 nm, showing that T1 excitons within NFs are generated mainly through the singlet fission from a higher singlet exciton state rather than through intersystem crossing.

Patterned Growth of Carbon Nanotubes or Nanofibers

NASA Technical Reports Server (NTRS)

Delzeit, Lance D.

2004-01-01

A method and apparatus for the growth of carbon nanotubes or nanofibers in a desired pattern has been invented. The essence of the method is to grow the nanotubes or nanofibers by chemical vapor deposition (CVD) onto a patterned catalyst supported by a substrate. The figure schematically depicts salient aspects of the method and apparatus in a typical application. A substrate is placed in a chamber that contains both ion-beam sputtering and CVD equipment. The substrate can be made of any of a variety of materials that include several forms of silicon or carbon, and selected polymers, metals, ceramics, and even some natural minerals and similar materials. Optionally, the substrate is first coated with a noncatalytic metal layer (which could be a single layer or could comprise multiple different sublayers) by ion-beam sputtering. The choice of metal(s) and thickness(es) of the first layer (if any) and its sublayers (if any) depends on the chemical and electrical properties required for subsequent deposition of the catalyst and the subsequent CVD of the carbon nanotubes. A typical first-sublayer metal is Pt, Pd, Cr, Mo, Ti, W, or an alloy of two or more of these elements. A typical metal for the second sublayer or for an undivided first layer is Al at a thickness .1 nm or Ir at a thickness .5 nm. Proper choice of the metal for a second sublayer of a first layer makes it possible to use a catalyst that is chemically incompatible with the substrate. In the next step, a mask having holes in the desired pattern is placed over the coated substrate. The catalyst is then deposited on the coated substrate by ion-beam sputtering through the mask. Optionally, the catalyst could be deposited by a technique other than sputtering and/or patterned by use of photolithography, electron- beam lithography, or another suitable technique. The catalytic metal can be Fe, Co, Ni, or an alloy of two or more of these elements, deposited to a typical thickness in the range from 0.1 to 20 nm.

Interface layer to tailor the texture and surface morphology of Al-doped ZnO polycrystalline films on glass substrates

NASA Astrophysics Data System (ADS)

Nomoto, Junichi; Inaba, Katsuhiko; Kobayashi, Shintaro; Makino, Hisao; Yamamoto, Tetsuya

2017-06-01

A 10-nm-thick radio frequency magnetron-sputtered aluminum-doped zinc oxide (AZO) showing a texture with a preferential (0001) orientation on amorphous glass substrates was used as an interface layer for tailoring the orientation of 490-nm-thick polycrystalline AZO films subsequently deposited by direct current (DC) magnetron sputtering at a substrate temperature of 200 °C. Wide-angle X-ray diffraction pole figure analysis showed that the resulting 500-nm-thick AZO films showed a texture with a highly preferential c-axis orientation. This showed that DC-magnetron-sputtered AZO films grew along with the orientation matching that of the interface layer, whereas 500-nm-thick AZO films deposited on bare glass substrates by DC magnetron sputtering exhibited a mixed orientation of the c-plane and other planes. The surface morphology was also improved while retaining the lateral grain size by applying the interface layer as revealed by atomic force microscopy.

Thickness dependent optical and electrical properties of CdSe thin films

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

Purohit, A., E-mail: anuradha.purohit34@gmail.com; Chander, S.; Nehra, S. P.

2016-05-06

The effect of thickness on the optical and electrical properties of CdSe thin films is investigated in this paper. The films of thickness 445 nm, 631 nm and 810 nm were deposited on glass and ITO coated glass substrates using thermal evaporation technique. The deposited thin films were thermally annealed in air atmosphere at temperature 100°C and were subjected to UV-Vis spectrophotometer and source meter for optical and electrical analysis respectively. The absorption coefficient is observed to increase with photon energy and found maximum in higher photon energy region. The extinction coefficient and refractive index are also calculated. The electrical analysis shows thatmore » the electrical resistivity is observed to be decreased with thickness.« less

Structural and magnetic properties of ultra-thin Fe films on metal-organic chemical vapour deposited GaN(0001)

NASA Astrophysics Data System (ADS)

Kim, Jun-Young; Ionescu, Adrian; Mansell, Rhodri; Farrer, Ian; Oehler, Fabrice; Kinane, Christy J.; Cooper, Joshaniel F. K.; Steinke, Nina-Juliane; Langridge, Sean; Stankiewicz, Romuald; Humphreys, Colin J.; Cowburn, Russell P.; Holmes, Stuart N.; Barnes, Crispin H. W.

2017-01-01

Structural and magnetic properties of 1-10 nm thick Fe films deposited on GaN(0001) were investigated. In-situ reflecting high energy electron diffraction images indicated a α-Fe(110)/GaN(0001) growth of the 3D Volmer-Weber type. The α-Fe(110) X-ray diffraction peak showed a 1° full-width at half-maximum, indicating ≈20 nm grain sizes. A significant reduction in Fe atomic moment from its bulk value was observed for films thinner than 4 nm. Both GaN/Fe interface roughness and Fe film coercivity increased with Fe thickness, indicating a possible deterioration of Fe crystalline quality. Magnetic anisotropy was mainly uniaxial for all films while hexagonal anisotropies appeared for thicknesses higher than 3.7 nm.

Polycrystalline Ba0.6Sr0.4TiO3 thin films on r-plane sapphire: Effect of film thickness on strain and dielectric properties

NASA Astrophysics Data System (ADS)

Fardin, E. A.; Holland, A. S.; Ghorbani, K.; Akdogan, E. K.; Simon, W. K.; Safari, A.; Wang, J. Y.

2006-10-01

Polycrystalline Ba0.6Sr0.4TiO3 (BST) films grown on r-plane sapphire exhibit strong variation of in-plane strain over the thickness range of 25-400nm. At a critical thickness of ˜200nm, the films are strain relieved; in thinner films, the strain is tensile, while compressive strain was observed in the 400nm film. Microwave properties of the films were measured from 1to20GHz by the interdigital capacitor method. A capacitance tunability of 64% was observed in the 200nm film, while thinner films showed improved Q factor. These results demonstrate the possibility of incorporating frequency agile BST-based devices into the silicon on sapphire process.

Large Area Few Layers Hexagonal Boron Nitride Prepared by Quadrupole Field Aided Exfoliation.

PubMed

Hanlun, Lu; Rong, Min Zhi; Zhang, Ming Qiu

2018-01-16

A quadrupole electric field mediated exfoliation method is proposed to convert micron sized hexagonal boron nitride (hBN) powders into few layers hexagonal boron nitride nano-sheets (h-BNNS). Under the optimum conditions (400 Hz, 40 V, 32μg/mL, sodium deoxycholate, TAE medium), the hBN powders (thickness > 200 nm, horizontal scale ~ 10 μm) are successfully exfoliated into 0.5-4 nm (1-10 layers) thick h-BNNS with the same horizontal scale. Dynamic laser scattering (DLS) and atomic force microscope (AFM) statistics show that the yield is 47.6 % (for the portion with the thickness of 0.5-6 nm), and all of the vertical sizes are reduced to smaller than 18 nm (45 layers). © 2018 IOP Publishing Ltd.

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

Pratap, Surender; Sarkar, Niladri, E-mail: niladri@pilani.bits-pilani.ac.in

Self-Consistent Quantum Method using Schrodinger-Poisson equations have been used for determining the Channel electron density of Nano-Scale MOSFETs for 6nm and 9nm thick channels. The 6nm thick MOSFET show the peak of the electron density at the middle where as the 9nm thick MOSFET shows the accumulation of the electrons at the oxide/semiconductor interface. The electron density in the channel is obtained from the diagonal elements of the density matrix; [ρ]=[1/(1+exp(β(H − μ)))] A Tridiagonal Hamiltonian Matrix [H] is constructed for the oxide/channel/oxide 1D structure for the dual gate MOSFET. This structure is discretized and Finite-Difference method is used formore » constructing the matrix equation. The comparison of these results which are obtained by Quantum methods are done with Semi-Classical methods.« less

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.

Asymmetric quantum-well structures for AlGaN/GaN/AlGaN resonant tunneling diodes

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

Yang, Lin'an, E-mail: layang@xidian.edu.cn; Li, Yue; Wang, Ying

Asymmetric quantum-well (QW) structures including the asymmetric potential-barrier and the asymmetric potential-well are proposed for AlGaN/GaN/AlGaN resonant tunneling diodes (RTDs). Theoretical investigation gives that an appropriate decrease in Al composition and thickness for emitter barrier as well as an appropriate increase of both for collector barrier can evidently improve the negative-differential-resistance characteristic of RTD. Numerical simulation shows that RTD with a 1.5-nm-thick GaN well sandwiched by a 1.3-nm-thick Al{sub 0.15}Ga{sub 0.85}N emitter barrier and a 1.7-nm-thick Al{sub 0.25}Ga{sub 0.75}N collector barrier can yield the I-V characteristic having the peak current (Ip) and the peak-to-valley current ratio (PVCR) of 0.39 A andmore » 3.6, respectively, about double that of RTD with a 1.5-nm-thick Al{sub 0.2}Ga{sub 0.8}N for both barriers. It is also found that an introduction of InGaN sub-QW into the diode can change the tunneling mode and achieve higher transmission coefficient of electron. The simulation demonstrates that RTD with a 2.8-nm-thick In{sub 0.03}Ga{sub 0.97}N sub-well in front of a 2.0-nm-thick GaN main-well can exhibit the I-V characteristic having Ip and PVCR of 0.07 A and 11.6, about 7 times and double the value of RTD without sub-QW, respectively. The purpose of improving the structure of GaN-based QW is to solve apparent contradiction between the device structure and the device manufacturability of new generation RTDs for sub-millimeter and terahertz applications.« less

Resveratrol Increases Nitric Oxide Production in the Rat Thick Ascending Limb via Ca2+/Calmodulin

PubMed Central

Gonzalez-Vicente, Agustin; Cabral, Pablo D.; Garvin, Jeffrey L.

2014-01-01

The thick ascending limb of the loop of Henle reabsorbs 30% of the NaCl filtered through the glomerulus. Nitric oxide (NO) produced by NO synthase 3 (NOS3) inhibits NaCl absorption by this segment. Resveratrol, a polyphenol, has beneficial cardiovascular and renal effects, many of which are mediated by NO. Resveratrol increases intracellular Ca2+ (Cai) and AMP kinase (AMPK) and NAD-dependent deacetylase sirtuin1 (SIRT1) activities, all of which could activate NO production. We hypothesized that resveratrol stimulates NO production by thick ascending limbs via a Ca2+/calmodulin-dependent mechanism. To test this, the effect of resveratrol on NO bioavailability was measured in thick ascending limb suspensions. Cai was measured in single perfused thick ascending limbs. SIRT1 activity and expression were measured in thick ascending limb lysates. Resveratrol (100 µM) increased NO bioavailability in thick ascending limb suspensions by 1.3±0.2 AFU/mg/min (p<0.03). The NOS inhibitor L-NAME blunted resveratrol-stimulated NO bioavailability by 96±11% (p<0.03). The superoxide scavenger tempol had no effect. Resveratrol elevated Cai from 48±7 to 135±24 nM (p<0.01) in single tubules. In Ca2+-free media, the resveratrol-induced increase in NO was blunted by 60±20% (p<0.05) and the rise in Cai reduced by 80%. Calmodulin inhibition prevented the resveratrol-induced increase in NO (p<0.002). AMPK inhibition had no effect. Resveratrol did not increase SIRT1 activity. We conclude that resveratrol increases NO production in thick ascending limbs via a Ca2+/calmodulin dependent mechanism, and SIRT1 and AMPK do not participate. Resveratrol-stimulated NO production in thick ascending limbs may account for part of its beneficial effects. PMID:25314136

Nucleation-controlled low-temperature solid-phase crystallization for Sn-doped polycrystalline-Ge film on insulator with high carrier mobility (˜550 cm2/V s)

NASA Astrophysics Data System (ADS)

Xu, Chang; Gao, Hongmiao; Sugino, Takayuki; Miyao, Masanobu; Sadoh, Taizoh

2018-06-01

High-speed thin-film transistors (TFTs) are required to develop the next generation of electronics, such as three-dimensional large-scale integrated circuits and advanced system-in-displays. For this purpose, high-carrier-mobility semiconductor films on insulator structures should be fabricated with low-temperature processing conditions (≤500 °C). To achieve this, we investigate solid-phase crystallization of amorphous-GeSn (a-GeSn) films (Sn concentration: 2% and thickness: 50-200 nm) on insulating substrates, where thin a-Si under-layers (thickness: 0-20 nm) are introduced between a-GeSn films and insulating substrates. The GeSn films are polycrystallized by annealing (450 °C, 20 h) for all samples irrespective of a-GeSn and a-Si thickness conditions, while the Si films remain amorphous. Analysis of crystal structures of GeSn films (thickness: 50 nm) reveals that grain sizes decrease from ˜10 μm to 2-3 μm by the introduction of a-Si under-layers (thickness: 3-20 nm). This phenomenon is attributed to the change in dominant nucleation sites from the interface to the bulk, which significantly decreases grain-boundary scattering of carriers through a decrease in the barrier heights at grain boundaries. Bulk-nucleation further becomes dominant by increasing the GeSn film thickness. As a result, a high carrier mobility of ˜550 cm2/V s is realized for GeSn films (thickness: 100 nm) grown with a-Si under-layers. This mobility is the largest among ever reported data for Ge and GeSn grown on an insulator. This technique will facilitate realization of high-speed TFTs for use in the next generation of electronics.

Study of ion beam sputtered Fe/Si interfaces as a function of Si layer thickness

NASA Astrophysics Data System (ADS)

Kumar, Anil; Brajpuriya, Ranjeet; Singh, Priti

2018-01-01

The exchange interaction in metal/semiconductor interfaces is far from being completely understood. Therefore, in this paper, we have investigated the nature of silicon on the Fe interface in the ion beam deposited Fe/Si/Fe trilayers keeping the thickness of the Fe layers fixed at 3 nm and varying the thickness of the silicon sandwich layer from 1.5 nm to 4 nm. Grazing incidence x-ray diffraction and atomic force microscopy techniques were used, respectively, to study the structural and morphological changes in the deposited films as a function of layer thickness. The structural studies show silicide formation at the interfaces during deposition and better crystalline structure of Fe layers at a lower spacer layer thickness. The magnetization behavior was investigated using magneto-optical Kerr effect, which clearly shows that coupling between the ferromagnetic layers is highly influenced by the semiconductor spacer layer thickness. A strong antiferromagnetic coupling was observed for a value of tSi = 2.5 nm but above this value an unexpected behavior of hysteresis loop (step like) with two coercivity values is recorded. For spacer layer thickness greater than 2.5 nm, an elemental amorphous Si layer starts to appear in the spacer layer in addition to the silicide layer at the interfaces. It is observed that in the trilayer structure, Fe layers consist of various stacks, viz., Si doped Fe layers, ferromagnetic silicide layer, and nonmagnetic silicide layer at the interfaces. The two phase hysteresis loop is explained on the basis of magnetization reversal of two ferromagnetic layers, independent of each other, with different coercivities. X-ray photo electron spectroscopy technique was also used to study interfaces characteristics as a function of tSi.

Polymer-modified opal nanopores.

PubMed

Schepelina, Olga; Zharov, Ilya

2006-12-05

The surface of nanopores in opal films, assembled from 205 nm silica spheres, was modified with poly(acrylamide) brushes using surface-initiated atom transfer radical polymerization. The colloidal crystal lattice remained unperturbed by the polymerization. The polymer brush thickness was controlled by polymerization time and was monitored by measuring the flux of redox species across the opal film using cyclic voltammetry. The nanopore size and polymer brush thickness were calculated on the basis of the limiting current change. Polymer brush thickness increased over the course of 26 h of polymerization in a logarithmic manner from 1.3 to 8.5 nm, leading to nanopores as small as 7.5 nm.

Effect of film thickness on morphological evolution in dewetting and crystallization of polystyrene/poly(ε-caprolactone) blend films.

PubMed

Ma, Meng; He, Zhoukun; Yang, Jinghui; Chen, Feng; Wang, Ke; Zhang, Qin; Deng, Hua; Fu, Qiang

2011-11-01

In this Article, the morphological evolution in the blend thin film of polystyrene (PS)/poly(ε-caprolactone) (PCL) was investigated via mainly AFM. It was found that an enriched two-layer structure with PS at the upper layer and PCL at the bottom layer was formed during spinning coating. By changing the solution concentration, different kinds of crystal morphologies, such as finger-like, dendritic, and spherulitic-like, could be obtained at the bottom PCL layer. These different initial states led to the morphological evolution processes to be quite different from each other, so the phase separation, dewetting, and crystalline morphology of PS/PCL blend films as a function of time were studied. It was interesting to find that the morphological evolution of PS at the upper layer was largely dependent on the film thickness. For the ultrathin (15 nm) blend film, a liquid-solid/liquid-liquid dewetting-wetting process was observed, forming ribbons that rupture into discrete circular PS islands on voronoi finger-like PCL crystal. For the thick (30 nm) blend film, the liquid-liquid dewetting of the upper PS layer from the underlying adsorbed PCL layer was found, forming interconnected rim structures that rupture into discrete circular PS islands embedded in the single lamellar PCL dendritic crystal due to Rayleigh instability. For the thicker (60 nm) blend film, a two-step liquid-liquid dewetting process with regular holes decorated with dendritic PCL crystal at early annealing stage and small holes decorated with spherulite-like PCL crystal among the early dewetting holes at later annealing stage was observed. The mechanism of this unusual morphological evolution process was discussed on the basis of the entropy effect and annealing-induced phase separation.

Microstructure, Chemistry, and Origin of Grain Rims on ilmenite from the Lunar Soil Finest Fraction

NASA Technical Reports Server (NTRS)

Christoffersen, Roy; Keller, Lindsay P.; McKay, David S.

1996-01-01

Analytical transmission electron microscope (TEM) observations reveal that ilmenite grains sampled from the sub-10 micron size fraction of Apollo 11 (10084) and Apollo 16 (61221, 67701) soils have rims 10-300 nm thick that are chemically and microstructurally distinct from the host ilmenite. The rims have a thin outer sublayer 10-50 nm thick that contains the ilmenite-incompatible elements Si, Al, Ca and S. This overlies a relatively thicker (50-250 nm) inner sublayer of nanocrystalline Ti-oxide precipitates in a matrix of single-crystal ilmenite that is structurally continuous with the underlying host grain. Microstructural information, as well as data from x-ray spectrometry (EDS) and electron energy loss spectrometry (EELS) analysis of the inner sublayer, suggest that both the inner and outer sublayer assemblages are reduced and that the inner layer is depleted in Fe relative to the underlying ilmenite. The chemistry of the outer sublayer suggests that it is a surface deposit of sputtered or impact-vaporized components from the bulk lunar soil. The inner sublayer is part of the original host grain that has been physically and chemically processed, but not amorphized, by solar ion irradiation and possibly some subsolidus heating. The fact that the deposited outer sublayer is consistently much thinner than the radiation-altered inner sublayer indicates that only a minor fraction of the total rim volume is a product of vapor or sputter deposition. This finding is in contrast to recent descriptions of thick deposited layers on one-third of regolith silicate grains and indicates that ilmenite and silicate rims as a group are different in the fraction of deposited material that they contain.

Atomic layer deposited high-k nanolaminate capacitors

NASA Astrophysics Data System (ADS)

Smith, S. W.; McAuliffe, K. G.; Conley, J. F., Jr.

2010-10-01

Al 2O 3-Ta 2O 5 nanolaminate films were prepared via atomic layer deposition (ALD) on silicon with a single overall composition and thickness, but with a varying number of Al 2O 3/Ta 2O 5 bilayers. The composition of the films was roughly 57% Al 2O 3 and 43% Ta 2O 5 and the total film thickness was held at ˜58 nm, while the number of bilayers was varied from 3 to 192 by changing the target bilayer thickness from ˜19.2 nm to ˜0.3 nm. Varying the number of bilayers was found to impact electrical properties. Although, almost all laminate films exhibited leakage, breakdown, hysteresis, and overall dielectric constant intermediate between pure Al 2O 3 and Ta 2O 5 films, laminates with few bilayers exhibited leakage current density lower than Al 2O 3 over the range of ˜3.5-4.5 MV/cm. Select samples annealed at temperatures from 400 to 900 °C were compared with as-deposited laminates. Annealing the laminate films at low temperatures improved leakage and breakdown while higher temperature anneals degraded both leakage and breakdown but improved the effective dielectric constant. A figure of merit was used to evaluate the overall ability of the various films to store charge. It was found that the few bilayer laminates were ranked higher than the many bilayer laminates as well as above both the pure Ta 2O 5 and pure Al 2O 3 films. These results indicate that even for a fixed overall composition, the electrical properties of a nanolaminate can be adjusted by varying the number of bilayers.

Strain relaxation in nm-thick Cu and Cu-alloy films bonded to a rigid substrate

NASA Astrophysics Data System (ADS)

Herrmann, Ashley Ann Elizabeth

In the wide scope of modern technology, nm-thick metallic films are increasingly used as lubrication layers, optical coatings, plating seeds, diffusion barriers, adhesion layers, metal contacts, reaction catalyzers, etc. A prominent example is the use of nm-thick Cu films as electroplating seed layers in the manufacturing of integrated circuits (ICs). These high density circuits are linked by on-chip copper interconnects, which are manufactured by filling Cu into narrow trenches by electroplating. The Cu fill by electroplating requires a thin Cu seed deposited onto high-aspect-ratio trenches. In modern ICs, these trenches are approaching 10 nm or less in width, and the seed layers less than 1 nm in thickness. Since nm-thick Cu seed layers are prone to agglomeration or delamination, achieving uniform, stable and highly-conductive ultra-thin seeds has become a major manufacturing challenge. A fundamental understanding of the strain behavior and thermal stability of nm-thick metal films adhered to a rigid substrate is thus critically needed. In this study, we focus on understanding the deformation modes of nm-thick Cu and Cu-alloy films bonded to a rigid Si substrate and under compressive stress. The strengthening of Cu films through alloying is also studied. In-situ transport measurements are used to monitor the deformation of such films as they are heated from room temperature to 400 °C. Ex-situ AFM is then used to help characterize the mode of strain relaxation. The relaxation modes are known to be sensitive to the wetting and adhesive properties of the film-substrate interface. We use four different liners (Ta, Ru, Mo and Co), interposed between the film and substrate to provide a wide range of interfacial properties to study their effect on the film's thermal stability. Our measurements indicate that when the film/liner interfacial energy is low, grain growth is the dominant relaxation mechanism. As the interface energy increases, grain growth is suppressed, and the strain is relaxed through hillock/island formation instead. The kinetics-limiting parameters for these relaxation modes are identified and used to simulate their kinetics, and a deformation map is then constructed to delineate the conditions under which each mode would prevail. Such a deformation map would prove useful when one seeks to optimize the thermal stability or other mechanical properties in any ultra-thin film system.

Preparation and characterization of B4C coatings for advanced research light sources.

PubMed

Störmer, Michael; Siewert, Frank; Sinn, Harald

2016-01-01

X-ray optical elements are required for beam transport at the current and upcoming free-electron lasers and synchrotron sources. An X-ray mirror is a combination of a substrate and a coating. The demand for large mirrors with single layers consisting of light or heavy elements has increased during the last few decades; surface finishing technology is currently able to process mirror lengths up to 1 m with microroughness at the sub-nanometre level. Additionally, thin-film fabrication is able to deposit a suitable single-layer material, such as boron carbide (B4C), some tens of nanometres thick. After deposition, the mirror should provide excellent X-ray optical properties with respect to coating thickness errors, microroughness values and slope errors; thereby enabling the mirror to transport the X-ray beam with high reflectivity, high beam flux and an undistorted wavefront to an experimental station. At the European XFEL, the technical specifications of the future mirrors are extraordinarily challenging. The acceptable shape error of the mirrors is below 2 nm along the whole length of 1 m. At the Helmholtz-Zentrum Geesthacht (HZG), amorphous layers of boron carbide with thicknesses in the range 30-60 nm were fabricated using the HZG sputtering facility, which is able to cover areas up to 1500 mm long by 120 mm wide in one step using rectangular B4C sputtering targets. The available deposition area is suitable for the specified X-ray mirror dimensions of upcoming advanced research light sources such as the European XFEL. The coatings produced were investigated by means of X-ray reflectometry and interference microscopy. The experimental results for the B4C layers are discussed according to thickness uniformity, density, microroughness and thermal stability. The variation of layer thickness in the tangential and sagittal directions was investigated in order to estimate the achieved level of uniformity over the whole deposition area, which is considerably larger than the optical area of a mirror. A waisted mask was positioned during deposition between the sputtering source and substrate to improve the thickness uniformity; particularly to prevent the formation a convex film shape in the sagittal direction. Additionally the inclination of the substrate was varied to change the layer uniformity in order to optimize the position of the mirror quality deposited area during deposition. The level of mirror microroughness was investigated for different substrates before and after deposition of a single layer of B4C. The thermal stability of the B4C layers on the various substrate materials was investigated.

Preparation and characterization of B4C coatings for advanced research light sources

PubMed Central

Störmer, Michael; Siewert, Frank; Sinn, Harald

2016-01-01

X-ray optical elements are required for beam transport at the current and upcoming free-electron lasers and synchrotron sources. An X-ray mirror is a combination of a substrate and a coating. The demand for large mirrors with single layers consisting of light or heavy elements has increased during the last few decades; surface finishing technology is currently able to process mirror lengths up to 1 m with microroughness at the sub-nanometre level. Additionally, thin-film fabrication is able to deposit a suitable single-layer material, such as boron carbide (B4C), some tens of nanometres thick. After deposition, the mirror should provide excellent X-ray optical properties with respect to coating thickness errors, microroughness values and slope errors; thereby enabling the mirror to transport the X-ray beam with high reflectivity, high beam flux and an undistorted wavefront to an experimental station. At the European XFEL, the technical specifications of the future mirrors are extraordinarily challenging. The acceptable shape error of the mirrors is below 2 nm along the whole length of 1 m. At the Helmholtz-Zentrum Geesthacht (HZG), amorphous layers of boron carbide with thicknesses in the range 30–60 nm were fabricated using the HZG sputtering facility, which is able to cover areas up to 1500 mm long by 120 mm wide in one step using rectangular B4C sputtering targets. The available deposition area is suitable for the specified X-ray mirror dimensions of upcoming advanced research light sources such as the European XFEL. The coatings produced were investigated by means of X-ray reflectometry and interference microscopy. The experimental results for the B4C layers are discussed according to thickness uniformity, density, microroughness and thermal stability. The variation of layer thickness in the tangential and sagittal directions was investigated in order to estimate the achieved level of uniformity over the whole deposition area, which is considerably larger than the optical area of a mirror. A waisted mask was positioned during deposition between the sputtering source and substrate to improve the thickness uniformity; particularly to prevent the formation a convex film shape in the sagittal direction. Additionally the inclination of the substrate was varied to change the layer uniformity in order to optimize the position of the mirror quality deposited area during deposition. The level of mirror microroughness was investigated for different substrates before and after deposition of a single layer of B4C. The thermal stability of the B4C layers on the various substrate materials was investigated. PMID:26698045

Broadband absorption and enhanced photothermal conversion property of octopod-like Ag@Ag2S core@shell structures with gradually varying shell thickness.

PubMed

Jiang, Qian; Zeng, Wenxia; Zhang, Canying; Meng, Zhaoguo; Wu, Jiawei; Zhu, Qunzhi; Wu, Daxiong; Zhu, Haitao

2017-12-19

Photothermal conversion materials have promising applications in many fields and therefore they have attracted tremendous attention. However, the multi-functionalization of a single nanostructure to meet the requirements of multiple photothermal applications is still a challenge. The difficulty is that most nanostructures have specific absoprtion band and are not flexible to different demands. In the current work, we reported the synthesis and multi-band photothermal conversion of Ag@Ag 2 S core@shell structures with gradually varying shell thickness. We synthesized the core@shell structures through the sulfidation of Ag nanocubes by taking the advantage of their spatially different reactivity. The resulting core@shell structures show an octopod-like mopgorlogy with a Ag 2 S bulge sitting at each corner of the Ag nanocubes. The thickness of the Ag 2 S shell gradually increases from the central surface towards the corners of the structure. The synthesized core@shell structures show a broad band absorption spectrum from 300 to 1100 nm. Enhanced photothermal conversion effect is observed under the illuminations of 635, 808, and 1064 nm lasers. The results indicate that the octopod-like Ag@Ag 2 S core@shell structures have characteristics of multi-band photothermal conversion. The current work might provide a guidance for the design and synthesis of multifunctional photothermal conversion materials.

Nanoselective area growth of GaN by metalorganic vapor phase epitaxy on 4H-SiC using epitaxial graphene as a mask

NASA Astrophysics Data System (ADS)

Puybaret, Renaud; Patriarche, Gilles; Jordan, Matthew B.; Sundaram, Suresh; El Gmili, Youssef; Salvestrini, Jean-Paul; Voss, Paul L.; de Heer, Walt A.; Berger, Claire; Ougazzaden, Abdallah

2016-03-01

We report the growth of high-quality triangular GaN nanomesas, 30-nm thick, on the C-face of 4H-SiC using nanoselective area growth (NSAG) with patterned epitaxial graphene grown on SiC as an embedded mask. NSAG alleviates the problems of defects in heteroepitaxy, and the high mobility graphene film could readily provide the back low-dissipative electrode in GaN-based optoelectronic devices. A 5-8 graphene-layer film is first grown on the C-face of 4H-SiC by confinement-controlled sublimation of silicon carbide. Graphene is then patterned and arrays of 75-nm-wide openings are etched in graphene revealing the SiC substrate. A 30-nm-thick GaN is subsequently grown by metal organic vapor phase epitaxy. GaN nanomesas grow epitaxially with perfect selectivity on SiC, in the openings patterned through graphene. The up-or-down orientation of the mesas on SiC, their triangular faceting, and cross-sectional scanning transmission electron microscopy show that they are biphasic. The core is a zinc blende monocrystal surrounded with single-crystal wurtzite. The GaN crystalline nanomesas have no threading dislocations or V-pits. This NSAG process potentially leads to integration of high-quality III-nitrides on the wafer scalable epitaxial graphene/silicon carbide platform.

Sensing Characteristics of Flame-Spray-Made Pt/ZnO Thick Films as H2 Gas Sensor

PubMed Central

Tamaekong, Nittaya; Liewhiran, Chaikarn; Wisitsoraat, Anurat; Phanichphant, Sukon

2009-01-01

Hydrogen sensing of thick films of nanoparticles of pristine, 0.2, 1.0 and 2.0 atomic percentage of Pt concentration doped ZnO were investigated. ZnO nanoparticles doped with 0.2–2.0 at.% Pt were successfully produced in a single step by flame spray pyrolysis (FSP) technique using zinc naphthenate and platinum(II) acetylacetonate as precursors dissolved in xylene. The particle properties were analyzed by XRD, BET, SEM and TEM. Under the 5/5 (precursor/oxygen) flame condition, ZnO nanoparticles and nanorods were observed. The crystallite sizes of ZnO spheroidal and hexagonal particles were found to be ranging from 5 to 20 nm while ZnO nanorods were seen to be 5–20 nm wide and 20–40 nm long. ZnO nanoparticles paste composed of ethyl cellulose and terpineol as binder and solvent respectively was coated on Al2O3 substrate interdigitated with gold electrodes to form thin films by spin coating technique. The thin film morphology was analyzed by SEM technique. The gas sensing properties toward hydrogen (H2) was found that the 0.2 at.% Pt/ZnO sensing film showed an optimum H2 sensitivity of ∼164 at hydrogen concentration in air of 1 volume% at 300 °C and a low hydrogen detection limit of 50 ppm at 300 °C operating temperature. PMID:22399971

Two-Functional Direct Current Sputtered Silver-Containing Titanium Dioxide Thin Films

NASA Astrophysics Data System (ADS)

Musil, J.; Louda, M.; Cerstvy, R.; Baroch, P.; Ditta, I. B.; Steele, A.; Foster, H. A.

2009-04-01

The article reports on structure, mechanical, optical, photocatalytic and biocidal properties of Ti-Ag-O films. The Ti-Ag-O films were reactively sputter-deposited from a composed Ti/Ag target at different partial pressures of oxygen p_{O2} on unheated glass substrate held on floating potential U fl. It was found that addition of 2 at.% of Ag into TiO2 film has no negative influence on UV-induced hydrophilicity of TiO2 film. Thick ( 1,500 nm) TiO2/Ag films containing (200) anatase phase exhibit the best hydrophilicity with water droplet contact angle (WDCA) lower than 10° after UV irradiation for 20 min. Thick ( 1,500 nm) TiO2/Ag films exhibited a better UV-induced hydrophilicity compared to that of thinner ( 700 nm) TiO2/Ag films. Further it was found that hydrophilic TiO2/Ag films exhibit a strong biocidal effect under both the visible light and the UV irradiation with 100% killing efficiency of Escherichia coli ATCC 10536 after UV irradiation for 20 min. Reported results show that single layer of TiO2 with Ag distributed in its whole volume exhibits, after UV irradiation, simultaneously two functions: (1) excellent hydrophilicity with WDCA < 10° and (2) strong power to kill E. coli even under visible light due to direct toxicity of Ag.

Nanoselective area growth of GaN by metalorganic vapor phase epitaxy on 4H-SiC using epitaxial graphene as a mask

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

Puybaret, Renaud; Jordan, Matthew B.; Voss, Paul L.

We report the growth of high-quality triangular GaN nanomesas, 30-nm thick, on the C-face of 4H-SiC using nanoselective area growth (NSAG) with patterned epitaxial graphene grown on SiC as an embedded mask. NSAG alleviates the problems of defects in heteroepitaxy, and the high mobility graphene film could readily provide the back low-dissipative electrode in GaN-based optoelectronic devices. A 5–8 graphene-layer film is first grown on the C-face of 4H-SiC by confinement-controlled sublimation of silicon carbide. Graphene is then patterned and arrays of 75-nm-wide openings are etched in graphene revealing the SiC substrate. A 30-nm-thick GaN is subsequently grown by metalmore » organic vapor phase epitaxy. GaN nanomesas grow epitaxially with perfect selectivity on SiC, in the openings patterned through graphene. The up-or-down orientation of the mesas on SiC, their triangular faceting, and cross-sectional scanning transmission electron microscopy show that they are biphasic. The core is a zinc blende monocrystal surrounded with single-crystal wurtzite. The GaN crystalline nanomesas have no threading dislocations or V-pits. This NSAG process potentially leads to integration of high-quality III-nitrides on the wafer scalable epitaxial graphene/silicon carbide platform.« less

Formation of nickel germanides from Ni layers with thickness below 10 nm

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

Jablonka, Lukas; Kubart, Tomas; Primetzhofer, Daniel

2017-03-01

The authors have studied the reaction between a Ge (100) substrate and thin layers of Ni ranging from 2 to 10 nm in thickness. The formation of metal-rich Ni5Ge3Ni5Ge3 was found to precede that of the monogermanide NiGe by means of real-time in situ x-ray diffraction during ramp-annealing and ex situ x-ray pole figure analyses for phase identification. The observed sequential growth of Ni5Ge3Ni5Ge3 and NiGe with such thin Ni layers is different from the previously reported simultaneous growth with thicker Ni layers. The phase transformation from Ni5Ge3Ni5Ge3 to NiGe was found to be nucleation-controlled for Ni thicknesses <5 nm<5more » nm, which is well supported by thermodynamic considerations. Specifically, the temperature for the NiGe formation increased with decreasing Ni (rather Ni5Ge3Ni5Ge3) thickness below 5 nm. In combination with sheet resistance measurement and microscopic surface inspection of samples annealed with a standard rapid thermal processing, the temperature range for achieving morphologically stable NiGe layers was identified for this standard annealing process. As expected, it was found to be strongly dependent on the initial Ni thickness« less

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.

Demonstration of enhanced continuous-wave operation of blue laser diodes on a semipolar 202¯1¯ GaN substrate using indium-tin-oxide/thin-p-GaN cladding layers.

PubMed

Mehari, Shlomo; Cohen, Daniel A; Becerra, Daniel L; Nakamura, Shuji; DenBaars, Steven P

2018-01-22

The benefits of utilizing transparent conductive oxide on top of a thin p-GaN layer for continuous-wave (CW) operation of blue laser diodes (LDs) were investigated. A very low operating voltage of 5.35 V at 10 kA/cm 2 was obtained for LDs with 250 nm thick p-GaN compared to 7.3 V for LDs with conventional 650 nm thick p-GaN. An improved thermal performance was also observed for the thin p-GaN samples resulting in a 40% increase in peak light output power and a 32% decrease in surface temperature. Finally, a tradeoff was demonstrated between low operating voltage and increased optical modal loss in the indium tin oxide (ITO) with thinner p-GaN. LDs lasing at 445 nm with 150 nm thick p-GaN had an excess modal loss while LDs with an optimal 250 nm thick p-GaN resulted in optical output power of 1.1 W per facet without facet coatings and a wall-plug efficiency of 15%.

High breakdown single-crystal GaN p-n diodes by molecular beam epitaxy

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

Qi, Meng; Zhao, Yuning; Yan, Xiaodong

2015-12-07

Molecular beam epitaxy grown GaN p-n vertical diodes are demonstrated on single-crystal GaN substrates. A low leakage current <3 nA/cm{sup 2} is obtained with reverse bias voltage up to −20 V. With a 400 nm thick n-drift region, an on-resistance of 0.23 mΩ cm{sup 2} is achieved, with a breakdown voltage corresponding to a peak electric field of ∼3.1 MV/cm in GaN. Single-crystal GaN substrates with very low dislocation densities enable the low leakage current and the high breakdown field in the diodes, showing significant potential for MBE growth to attain near-intrinsic performance when the density of dislocations is low.

Admittance Investigation of MIS Structures with HgTe-Based Single Quantum Wells.

PubMed

Izhnin, Ihor I; Nesmelov, Sergey N; Dzyadukh, Stanislav M; Voitsekhovskii, Alexander V; Gorn, Dmitry I; Dvoretsky, Sergey A; Mikhailov, Nikolaj N

2016-12-01

This work presents results of the investigation of admittance of metal-insulator-semiconductor structure based on Hg1 - x Cd x Te grown by molecular beam epitaxy. The structure contains a single quantum well Hg0.35Cd0.65Te/HgTe/Hg0.35Cd0.65Te with thickness of 5.6 nm in the sub-surface layer of the semiconductor. Both the conductance-voltage and capacitance-voltage characteristics show strong oscillations when the metal-insulator-semiconductor (MIS) structure with a single quantum well based on HgTe is biased into the strong inversion mode. Also, oscillations on the voltage dependencies of differential resistance of the space charge region were observed. These oscillations were related to the recharging of quantum levels in HgTe.

High efficiency white organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Zhang, Gang; Dong, Weili; Gao, Hongyan; Tian, Xiaocui; Zhao, Lina; Jiang, Wenlong; Zhang, Xiyan

2015-06-01

The light emitting diodes with the structure of ITO/ m-MTDATA(20 nm)/NPB(10 nm)/CBP BCzVBi ( x, nm, 10%)/CBP(3 nm)/CBP: Ir(ppy)3: DCJTB(10 nm, 8 and 1%)/Bphen(30 nm)/Cs2CO3: Ag2O (2 nm, 20%)/Al (100 nm) employing phosphorescence sensitization and fluorescence doping, were manufactured. The performance of the devices was studied by adjusting the thickness of fluorescence dopant layer ( x = 15, 20, 25, and 30). The best performance was achieved when its thickness was 25 nm. The device has the maximum luminance of 20260 cd/m2 at applied voltage of 14 V and the maximum current efficiency of 11.70 cd/A at 7 V. The device displays a continuous change of color from yellow to white. The CIE coordinates change from (0.49, 0.48) to (0.32, 0.39) when the driving voltage is varied from 5 to 15 V.

Magnetization reversal in ferromagnetic wires patterned with antiferromagnetic gratings

NASA Astrophysics Data System (ADS)

Sani, S. R.; Liu, F.; Ross, C. A.

2017-04-01

The magnetic reversal behavior is examined for exchange-biased ferromagnetic/antiferromagnetic nanostructures consisting of an array of 10 nm thick Ni80Fe20 stripes with width 200 nm and periodicity 400 nm, underneath an orthogonal array of 10 nm thick IrMn stripes with width ranging from 200 nm to 500 nm and periodicity from 400 nm to 1 μm. The Ni80Fe20 stripes show a hysteresis loop with one step when the IrMn width and spacing are small. However, upon increasing the IrMn width and spacing, the hysteresis loops showed two steps as the pinned and unpinned sections of the Ni80Fe20 stripes switch at different fields. Micromagnetic modeling reveals the influence of geometry on the reversal behavior.

Tailoring single-cycle electromagnetic pulses in the 2-9 THz frequency range using DAST/SiO₂ multilayer structures pumped at Ti:sapphire wavelength.

PubMed

Stepanov, Andrei G; Rogov, Andrii; Bonacina, Luigi; Wolf, Jean-Pierre; Hauri, Christoph P

2014-09-08

We present a numerical parametric study of single-cycle electromagnetic pulse generation in a DAST/SiO₂multilayer structure via collinear optical rectification of 800 nm femtosecond laser pulses. It is shown that modifications of the thicknesses of the DAST and SiO₂layers allow tuning of the average frequency of the generated THz pulses in the frequency range from 3 to 6 THz. The laser-to-THz energy conversion efficiency in the proposed structures is compared with that in a bulk DAST crystal and a quasi-phase-matching periodically poled DAST crystal and shows significant enhancement.

Thickness dependent charge transfer states and dark carriers density in vacuum deposited small molecule organic photocell

NASA Astrophysics Data System (ADS)

Shekhar, Himanshu; Tzabari, Lior; Solomeshch, Olga; Tessler, Nir

2016-10-01

We have investigated the influence of the active layer thickness on the balance of the internal mechanisms affecting the efficiency of copper phthalocyanine - fullerene (C60) based vacuum deposited bulk heterojunction organic photocell. We fabricated a range of devices for which we varied the thickness of the active layer from 40 to 120 nm and assessed their performance using optical and electrical characterization techniques. As reported previously for phthalocyanine:C60, the performance of the device is highly dependent on the active layer thickness and of all the thicknesses we tried, the 40 nm thin active layer device showed the best solar cell characteristic parameters. Using the transfer matrix based optical model, which includes interference effects, we calculated the optical power absorbed in the active layers for the entire absorption band, and we found that this cannot explain the trend with thickness. Measurement of the cell quantum efficiency as a function of light intensity showed that the relative weight of the device internal processes changes when going from 40 nm to 120 nm thick active layer. Electrical modeling of the device, which takes different internal processes into account, allowed to quantify the changes in the processes affecting the generation - recombination balance. Sub gap external quantum efficiency and morphological analysis of the surface of the films agree with the model's result. We found that as the thickness grows the density of charge transfer states and of dark carriers goes up and the uniformity in the vertical direction is reduced.

Indium oxide based fiber optic SPR sensor

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

Shukla, Sarika; Sharma, Navneet K., E-mail: navneetk.sharma@jiit.ac.in

2016-05-06

Surface plasmon resonance based fiber optic sensor using indium oxide layer is presented and theoretically studied. It has been found that with increase in thickness of indium oxide layer beyond 170 nm, the sensitivity of SPR sensor decreases. 170 nm thick indium oxide layer based SPR sensor holds maximum sensitivity.

The role of film interfaces in near-ultraviolet absorption and pulsed-laser damage in ion-beam-sputtered coatings based on HfO 2/SiO 2 thin-film pairs

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

Ristau, Detlev; Papernov, S.; Kozlov, A. A.

2015-11-23

The role of thin-film interfaces in the near-ultraviolet absorption and pulsed-laser–induced damage was studied for ion-beam–sputtered and electron-beam–evaporated coatings comprised from HfO 2 and SiO 2 thin-film pairs. To separate contributions from the bulk of the film and from interfacial areas, absorption and damage-threshold measurements were performed for a one-wave (355-nm wavelength) thick, HfO 2 single-layer film and for a film containing seven narrow HfO 2 layers separated by SiO 2 layers. The seven-layer film was designed to have a total optical thickness of HfO 2 layers, equal to one wave at 355 nm and an E-field peak and averagemore » intensity similar to a single-layer HfO 2 film. Absorption in both types of films was measured using laser calorimetry and photothermal heterodyne imaging. The results showed a small contribution to total absorption from thin-film interfaces, as compared to HfO 2 film material. The relevance of obtained absorption data to coating near-ultraviolet, nanosecond-pulse laser damage was verified by measuring the damage threshold and characterizing damage morphology. The results of this study revealed a higher damage resistance in the seven-layer coating as compared to the single-layer HfO 2 film in both sputtered and evaporated coatings. Here, the results are explained through the similarity of interfacial film structure with structure formed during the co-deposition of HfO 2 and SiO 2 materials.« less

Model for thickness dependence of mobility and concentration in highly conductive ZnO

NASA Astrophysics Data System (ADS)

Look, D. C.; Leedy, K. D.; Kiefer, A.; Claflin, B.; Itagaki, N.; Matsushima, K.; Suhariadi, I.

2013-03-01

The dependences of the 294-K and 10-K mobility μ and volume carrier concentration n on thickness (d = 25 - 147 nm) were examined in Al-doped ZnO (AZO) layers grown in Ar ambient at 200 °C on quartz-glass substrates. Two AZO layers were grown at each thickness, one with and one without a 20-nm-thick ZnON buffer layer grown at 300 °C in Ar/N2 ambient. Plots of the 10-K sheet concentration ns vs d for buffered (B) and unbuffered (UB) samples give straight lines of similar slope, n = 8.36 x 1020 and 8.32 x 1020 cm-3, but different x-axis intercepts, δd = -4 and +13 nm, respectively. Thus, the electrical thicknesses are d - δd = d + 4 and d - 13 nm, respectively. Plots of ns vs d at 294 K produced substantially the same results. Plots of μ vs d can be well fitted with the equation μ(d) = μ(infinity symbol)/[1 + d*/(d-δd)], where d* is the thickness for which μ(infinity symbol) is reduced by a factor 2. For the B and UB samples, d* = 7 and 23 nm, respectively, showing the efficacy of the ZnON buffer. Finally, from n and μ(infinity symbol) we can use degenerate electron scattering theory to calculate bulk donor and acceptor concentrations of 1.23 x 1021 cm-3 and 1.95 x 1020 cm-3, respectively, and Drude theory to predict a plasmonic resonance at1.34 μm. The latter is confirmed by reflectance measurements.

Temperature dependence of copper diffusion in different thickness amorphous tungsten/tungsten nitride layer

NASA Astrophysics Data System (ADS)

Asgary, Somayeh; Hantehzadeh, Mohammad Reza; Ghoranneviss, Mahmood

2017-11-01

The amorphous W/WN films with various thickness (10, 30 and 40 nm) and excellent thermal stability were successfully prepared on SiO2/Si substrate with evaporation and reactive evaporation method. The W/WN bilayer has technological importance because of its low resistivity, high melting point, and good diffusion barrier properties between Cu and Si. The thermal stability was evaluated by X-ray diffractometer (XRD) and Scanning Electron Microscope (SEM). In annealing process, the amorphous W/WN barrier crystallized and this phenomenon is supposed to be the start of Cu atoms diffusion through W/WN barrier into Si. With occurrence of the high-resistive Cu3Si phase, the W/WN loses its function as a diffusion barrier. The primary mode of Cu diffusion is the diffusion through grain boundaries that form during heat treatments. The amorphous structure with optimum thickness is the key factor to achieve a superior diffusion barrier characteristic. The results show that the failure temperature increased by increasing the W/WN film thickness from 10 to 30 nm but it did not change by increasing the W/WN film thickness from 30 to 40 nm. It is found that the 10 and 40 nm W/WN films are good diffusion barriers at least up to 800°C while the 30 nm W/WN film shows superior properties as a diffusion barrier, but loses its function as a diffusion barrier at about 900°C (that is 100°C higher than for 10 and 40 nm W/WN films).

Novel spot size converter for coupling standard single mode fibers to SOI waveguides

NASA Astrophysics Data System (ADS)

Sisto, Marco Michele; Fisette, Bruno; Paultre, Jacques-Edmond; Paquet, Alex; Desroches, Yan

2016-03-01

We have designed and numerically simulated a novel spot size converter for coupling standard single mode fibers with 10.4μm mode field diameter to 500nm × 220nm SOI waveguides. Simulations based on the eigenmode expansion method show a coupling loss of 0.4dB at 1550nm for the TE mode at perfect alignment. The alignment tolerance on the plane normal to the fiber axis is evaluated at +/-2.2μm for <=1dB excess loss, which is comparable to the alignment tolerance between two butt-coupled standard single mode fibers. The converter is based on a cross-like arrangement of SiOxNy waveguides immersed in a 12μm-thick SiO2 cladding region deposited on top of the SOI chip. The waveguides are designed to collectively support a single degenerate mode for TE and TM polarizations. This guided mode features a large overlap to the LP01 mode of standard telecom fibers. Along the spot size converter length (450μm), the mode is first gradually confined in a single SiOxNy waveguide by tapering its width. Then, the mode is adiabatically coupled to a SOI waveguide underneath the structure through a SOI inverted taper. The shapes of SiOxNy and SOI tapers are optimized to minimize coupling loss and structure length, and to ensure adiabatic mode evolution along the structure, thus improving the design robustness to fabrication process errors. A tolerance analysis based on conservative microfabrication capabilities suggests that coupling loss penalty from fabrication errors can be maintained below 0.3dB. The proposed spot size converter is fully compliant to industry standard microfabrication processes available at INO.

Thickness-dependently enhanced photodetection performance of vertically grown SnS2 nanoflakes with large size and high production.

PubMed

Jia, Xiansheng; Tang, Chengchun; Pan, Ruhao; Long, Yun-Ze; Gu, Changzhi; Li, Junjie

2018-05-10

Photodetection based on Two-dimensional (2D) SnS2 has attracted a growing interest due to its superiority in response rate and responsivity, but high-quality growth and high performance photodetecting of 2D SnS2still face great challenges. Here, high-quality SnS2 nanoflakes with large-size and high-production are vertically grown on Si substrate by a modified CVD method, having an average size of 30 m with different thicknesses. Then a single SnS2 nanoflake-based phototransistor was fabricated to obtain a high current on/off ratio of 107 and excellent performances in photodetection, including fast response rates, low dark current, high responsivity and detectivity. Specifically, the SnS2 nanoflakes show the thickness-dependent photodetection capability and the highest responsivity of 354.4 A W-1 is obtained at the average thickness of 100.5 nm. A sensitized process using HfO2 nanolayer can further enhance the responsivity up to 1922 A W-1. Our work provides an efficient path to select SnS2 crystal samples with the optimal thickness as promising candidates for high-performance optoelectronic applications.

Growth and characterization of MnAu2 films

NASA Astrophysics Data System (ADS)

Cheng, S. F.; Bussmann, K. M.

2017-01-01

MnAu2 films ranging from 60 to 200 nm thickness are deposited by co-sputtering from elemental targets. X-ray diffraction confirmed these films to be nearly single phase with tetragonal lattice parameters of a=0.336 nm and c=0.872 nm that compare well to the bulk values of a=0.336 nm and c=0.876 nm. The density of the films is analyzed using x-ray reflectivity to be 14.95 g/cm3 and within experimental error of previously determined value of 15.00 g/cm3. The films grown on c-plane sapphire, (100)MgO and (100)MgF2 are randomly oriented polycrystalline, while the films grown on a-plane sapphire, (111)MgO and (111)Si/(0001)AlN showed that the (110) plane is parallel to the film plane and there are three sets of domains in equal amount differing by 60° in-plane rotation. Magnetic order is found to become paramagnetic near 360 K which is in close proximity to the bulk value. There are deviations in the slope of hysteresis loops observed at 10 K around 10 kOe that indicate complex magnetic switching.

Compliant deformable mirror approach for wavefront improvement

NASA Astrophysics Data System (ADS)

Clark, James H.; Penado, F. Ernesto

2016-04-01

We describe a compliant static deformable mirror approach to reduce the wavefront concavity at the Navy Precision Optical Interferometer (NPOI). A single actuator pressing on the back surface of just one of the relay mirrors deforms the front surface in a correcting convex shape. Our design uses the mechanical advantage gained from a force actuator sandwiched between a rear flexure plate and the back surface of the mirror. We superimpose wavefront contour measurements with our finite element deformed mirror model. An example analysis showed improvement from 210-nm concave-concave wavefront to 51-nm concave-concave wavefront. With our present model, a 100-nm actuator increment displaces the mirror surface by 1.1 nm. We describe the need for wavefront improvement that arises from the NPOI reconfigurable array, offer a practical design approach, and analyze the support structure and compliant deformable mirror using the finite element method. We conclude that a 20.3-cm-diameter, 1.9-cm-thick Zerodur® mirror shows that it is possible to deform the reflective surface and cancel out three-fourths of the wavefront deformation without overstressing the material.

The effect of a nonmagnetic cap layer on the spin-polarized tunneling and magnetoresistance in double-barrier planar junctions

NASA Astrophysics Data System (ADS)

Xie, Zheng-Wei; Li, Bo-Zang; Li, Yu-Xian

2003-10-01

Within the framework of the free-electron model, the tunneling magnetoresistance (TMR) and tunneling conductance (TC) in double magnetic tunnel junctions (DMTJ) with nonmagnetic cap layer, i.e. the NM/FM/I/NM/(FM)/I/FM/NM junction is investigated. FM, NM and I represent the ferromagnetic metal, nonmagnetic metal and insulator, respectively, NM(FM) indicates that the middle layer can be NM or FM. Our results show that, due to the spin-dependent interfacial potential barriers, the influences of the thickness of the FM layer on TC and TMR in DMTJ are large, and when the thicknesses of these two FM layers are suitable a large TMR can be obtained. (

Unexpected behavior of ultra-thin films of blends of polystyrene/poly(vinyl methyl ether) studied by specific heat spectroscopy

NASA Astrophysics Data System (ADS)

Madkour, Sherif; Szymoniak, Paulina; Schick, Christoph; Schönhals, Andreas

2017-05-01

Specific heat spectroscopy (SHS) employing AC nanochip calorimetry was used to investigate the glassy dynamics of ultra-thin films (thicknesses: 10 nm-340 nm) of a polymer blend, which is miscible in the bulk. In detail, a Poly(vinyl methyl ether) (PVME)/Polystyrene (PS) blend with the composition of 25/75 wt. % was studied. The film thickness was controlled by ellipsometry while the film topography was checked by atomic force microscopy. The results are discussed in the framework of the balance between an adsorbed and a free surface layer on the glassy dynamics. By a self-assembling process, a layer with a reduced mobility is irreversibly adsorbed at the polymer/substrate interface. This layer is discussed employing two different scenarios. In the first approach, it is assumed that a PS-rich layer is adsorbed at the substrate. Whereas in the second approach, a PVME-rich layer is suggested to be formed at the SiO2 substrate. Further, due to the lower surface tension of PVME, with respect to air, a nanometer thick PVME-rich surface layer, with higher molecular mobility, is formed at the polymer/air interface. By measuring the glassy dynamics of the thin films of PVME/PS in dependence on the film thickness, it was shown that down to 30 nm thicknesses, the dynamic Tg of the whole film was strongly influenced by the adsorbed layer yielding a systematic increase in the dynamic Tg with decreasing the film thickness. However, at a thickness of ca. 30 nm, the influence of the mobile surface layer becomes more pronounced. This results in a systematic decrease in Tg with the further decrease of the film thickness, below 30 nm. These results were discussed with respect to thin films of PVME/PS blend with a composition of 50/50 wt. % as well as literature results.

Dependence of the optical constants and the performance in the SPREE gas measurement on the thickness of doped tin oxide over coatings

NASA Astrophysics Data System (ADS)

Fischer, D.; Hertwig, A.; Beck, U.; Negendank, D.; Lohse, V.; Kormunda, M.; Esser, N.

2017-11-01

In this study, thickness related changes of the optical properties of doped tin oxide were studied. Two different sets of samples were prepared. The first set was doped with iron or nickel on silicon substrate with thicknesses of 29-56 nm, the second was iron doped on gold/glass substrate with 1.6-6.3 nm. The optical constants were determined by using spectral ellipsometry (SE) followed by modelling of the dielectric function with an oscillator model using Gaussian peaks. The analysis of the optical constants shows a dependence of the refraction and the absorption on the thickness of the doped tin oxide coating. In addition to the tin oxide absorption in the UV, one additional absorption peak was found in the near-IR/red which is related to plasmonic effects due to the doping. This peak shifts from the near-IR to the red part of the visible spectrum and becomes stronger by reducing the thickness, probably due to the formation of metal nanoparticles in this layer. These results were found for two different sets of samples by using the same optical model. Afterwards the second sample set was tested in the Surface Plasmon Resonance Enhanced Ellipsometric (SPREE) gas measurement with CO gas. It was found that the thickness has significant influence on the sensitivity and thus the adsorption of the CO gas. By increasing the thickness from 1.6 nm to 5.1 nm, the sensing ability is enhanced due to a higher coverage of the surface with the over coating. This is explained by the high affinity of CO molecules to the incorporated Fe-nanoparticles in the tin oxide coating. By increasing the thickness further to 6.3 nm, the sensing ability drops because the layer disturbs the SPR sensing effect too much.

Vertical resistivity in nanocrystalline ZnO and amorphous InGaZnO

NASA Astrophysics Data System (ADS)

McCandless, Jonathan P.; Leedy, Kevin D.; Schuette, Michael L.

2018-02-01

The goal is to gain additional insight into physical mechanisms and the role of microstructure on the formation of ohmic contacts and the reduction of contact resistance. We have measured a decreasing film resistivity in the vertical direction with increasing thickness of pulsed-laser deposited ZnO and IGZO. As the ZnO thickness increases from 122 nm to 441 nm, a reduction in resistivity from 3.29 Ω-cm to 0.364 Ω-cm occurred. The IGZO resistivity changes from 72.4 Ω-cm to 0.642 Ω-cm as the film is increased from 108nm to 219 nm. In the ZnO, the size of nanocolumnar grains increase with thickness resulting in fewer grain boundaries, and in the amorphous IGZO, the thicker region exhibits tunnel-like artifacts which may contribute to the reduced resistivity.

Sensing of Streptococcus mutans by microscopic imaging ellipsometry

NASA Astrophysics Data System (ADS)

Khaleel, Mai Ibrahim; Chen, Yu-Da; Chien, Ching-Hang; Chang, Yia-Chung

2017-05-01

Microscopic imaging ellipsometry is an optical technique that uses an objective and sensing procedure to measure the ellipsometric parameters Ψ and Δ in the form of microscopic maps. This technique is well known for being noninvasive and label-free. Therefore, it can be used to detect and characterize biological species without any impact. Microscopic imaging ellipsometry was used to measure the optical response of dried Streptococcus mutans cells on a glass substrate. The ellipsometric Ψ and Δ maps were obtained with the Optrel Multiskop system for specular reflection in the visible range (λ=450 to 750 nm). The Ψ and Δ images at 500, 600, and 700 nm were analyzed using three different theoretical models with single-bounce, two-bounce, and multibounce light paths to obtain the optical constants and height distribution. The obtained images of the optical constants show different aspects when comparing the single-bounce analysis with the two-bounce or multibounce analysis in detecting S. mutans samples. Furthermore, the height distributions estimated by two-bounce and multibounce analyses of S. mutans samples were in agreement with the thickness values measured by AFM, which implies that the two-bounce and multibounce analyses can provide information complementary to that obtained by a single-bounce light path.

Single-crystal gallium nitride nanotubes.

PubMed

Goldberger, Joshua; He, Rongrui; Zhang, Yanfeng; Lee, Sangkwon; Yan, Haoquan; Choi, Heon-Jin; Yang, Peidong

2003-04-10

Since the discovery of carbon nanotubes in 1991 (ref. 1), there have been significant research efforts to synthesize nanometre-scale tubular forms of various solids. The formation of tubular nanostructure generally requires a layered or anisotropic crystal structure. There are reports of nanotubes made from silica, alumina, silicon and metals that do not have a layered crystal structure; they are synthesized by using carbon nanotubes and porous membranes as templates, or by thin-film rolling. These nanotubes, however, are either amorphous, polycrystalline or exist only in ultrahigh vacuum. The growth of single-crystal semiconductor hollow nanotubes would be advantageous in potential nanoscale electronics, optoelectronics and biochemical-sensing applications. Here we report an 'epitaxial casting' approach for the synthesis of single-crystal GaN nanotubes with inner diameters of 30-200 nm and wall thicknesses of 5-50 nm. Hexagonal ZnO nanowires were used as templates for the epitaxial overgrowth of thin GaN layers in a chemical vapour deposition system. The ZnO nanowire templates were subsequently removed by thermal reduction and evaporation, resulting in ordered arrays of GaN nanotubes on the substrates. This templating process should be applicable to many other semiconductor systems.

Single-primer fluorescent sequencing

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

Ruth, J.L.; Morgan, C.A.; Middendorf, L.R.

Modified linker arm oligonucleotides complementary to standard M13 priming sites were synthesized, labelled with either one, two, or three fluoresceins, and purified by reverse-phase HPLC. When used as primers in standard dideoxy M13 sequencing with /sup 32/P-dNTPs, normal autoradiographic patterns were obtained. To eliminate the radioactivity, direct on-line fluorescence detection was achieved by the use of a scanning 10 mW Argon laser emitting 488 nm light. Fluorescent bands were detected directly in standard 0.2 or 0.35 mm thick polyacrylamide gels at a distance of 24 cm from the loading wells by a photomultiplier tube filtered at 520 nm. Horizontal andmore » temporal location of each band was displayed by computer as a band in real time, providing visual appearance similar to normal 4-lane autoradiograms. Using a single primer labelled with two fluoresceins, sequences of between 500 and 600 bases have been read in a single loading with better than 98% accuracy; up to 400 bases can be read reproducibly with no errors. More than 50 sequences have been determined by this method. This approach requires only 1-2 ug of cloned template, and produces continuous sequence data at about one band per minute.« less

Single resonance monolithic Fabry-Perot filters formed by volume Bragg gratings and multilayer dielectric mirrors

NASA Astrophysics Data System (ADS)

Lumeau, Julien; Koc, Cihan; Mokhun, Oleksiy; Smirnov, Vadim; Lequime, Michel; Glebov, Leonid B.

2012-02-01

High efficiency reflecting volume Bragg gratings (VBGs) recorded in PTR glass plates have shown un-preceded performances that make them very good candidates for narrowband spectral filtering with sub-nanometer spectral widths. However, decreasing the bandwidth to value below 30-50 pm is very challenging as it requires increasing the thickness of the RBG to more than 15-20 mm. To overcome this limitation, we propose a new approach which is a monolithic Fabry-Perot cavity which consists from a reflecting VBG with a multilayer dielectric mirror (MDM) deposited on its surface. A VBG with a grating vector perpendicular to its surface and a MDM produce a Fabry-Perot resonator with a single transmission band inside of the reflection spectrum of the VBG. We present a theoretical description of this new class of filters that allow achieving a single ultra-narrowband resonance associated with several hundred nanometers rejection band. Then we show the methods for designing and fabricating such filter. Finally, we present the steps that we followed in order to fabricate a first prototype for 852 nm and 1062 nm region that demonstrates a 30 pm bandwidth, 90+% transmission at resonance and a good agreement with theoretical simulation.

Effect of QW thickness and numbers on performance characteristics of deep violet InGaN MQW lasers

NASA Astrophysics Data System (ADS)

Alahyarizadeh, Gh.; Amirhoseiny, M.; Hassan, Z.

2015-03-01

The performance characteristics of deep violet indium gallium nitride (InGaN) multiquantum well (MQW) laser diodes (LDs) with an emission wavelength of around 390 nm have been investigated using the integrated system engineering technical computer aided design (ISE-TCAD) software. A comparative study on the effect of quantum well (QW) thickness and number on electrical and optical performance of deep violet In0.082Ga0.918N/GaN MQW LDs have been carried out. The simulation results showed that the highest slope efficiency and external differential quantum efficiency (DQE), as well as the lowest threshold current are obtained when the number of wells is two. The different QW thickness values of 2.2, 2.5, 2.8, 3 and 3.2 nm were compared and the best results were achieved for 2.5 nm QW thickness. The radiative recombination rate decreases with increasing QW thickness because of decreasing electron and hole carrier densities in wells. By increasing QW thickness, output power decreases and threshold current increases.

Novel behaviors of anomalous Hall effect in TbFeCo ferrimagnetic thin films

NASA Astrophysics Data System (ADS)

Ando, Ryo; Komine, Takashi; Sato, Shiori; Kaneta, Shingo; Hara, Yoshiaki

2018-05-01

We investigate the temperature dependence and the thickness dependence of anomalous Hall effect (AHE) of TbFeCo ultra-thin films under high magnetic field. The sign change on temperature dependence of AHE in 20nm-thick TbFeCo film with rare-earth (RE) rich composition was observed. The AHE sign at low temperature is negative while it gradually becomes positive as the temperature increases. Moreover, the AHE sign for 5nm-thick TbFeCo film remains positive while that for 50nm-thick TbFeCo film remains negative at temperature in the range from 5 K to 400 K. The similar thickness dependence of AHE in TM-rich samples was also observed. From the mean-field approximation, the sign change temperature in AHE is related to the compensation temperature and the existence of interfacial region, which has the TM-rich composition and the weak anisotropy. Therefore, We clarified that the novel behavior of AHE sign changes in TbFeCo thin films with different thickness can be explained by the interfacial layer with weak anisotropy and two phase model.

Effect of film thickness on soft magnetic behavior of Fe2CoSi Heusler alloy for spin transfer torque device applications

NASA Astrophysics Data System (ADS)

Asvini, V.; Saravanan, G.; Kalaiezhily, R. K.; Raja, M. Manivel; Ravichandran, K.

2018-04-01

Fe2CoSi based Heusler alloy thin films were deposited on Si (111) wafer (substrate) of varying thickness using ultra high vacuum DC magnetron sputtering. The structural behavior was observed and found to be hold the L21 structure. The deposited thin films were characterized magnetic properties using vibrating sample magnetometer; the result shows a very high saturated magnetization (Ms), lowest coercivity (Hc), high curie transition temperature (Tc) and low hysteresis loss. Thin film thickness of 75 nm Fe2CoSi sample maintained at substrate temperature 450°C shows the lowest coercivity (Hc=7 Oe). In general, Fe2CoSi Heusler alloys curie transition temperature is very high, due to strong exchange interaction between the Fe and Co atoms. The substrate temperature was kept constant at 450°C for varying thickness (e.g. 5, 20, 50, 75 and 100 nm) of thin film sample. The 75 nm thickness thin film sample shows well crystallanity and good magnetic properties, further squareness ratio in B-H loop increases with the increase in film thickness.

Few-layer nanoplates of Bi 2 Se 3 and Bi 2 Te 3 with highly tunable chemical potential.

PubMed

Kong, Desheng; Dang, Wenhui; Cha, Judy J; Li, Hui; Meister, Stefan; Peng, Hailin; Liu, Zhongfan; Cui, Yi

2010-06-09

A topological insulator (TI) represents an unconventional quantum phase of matter with insulating bulk band gap and metallic surface states. Recent theoretical calculations and photoemission spectroscopy measurements show that group V-VI materials Bi(2)Se(3), Bi(2)Te(3), and Sb(2)Te(3) are TIs with a single Dirac cone on the surface. These materials have anisotropic, layered structures, in which five atomic layers are covalently bonded to form a quintuple layer, and quintuple layers interact weakly through van der Waals interaction to form the crystal. A few quintuple layers of these materials are predicted to exhibit interesting surface properties. Different from our previous nanoribbon study, here we report the synthesis and characterizations of ultrathin Bi(2)Te(3) and Bi(2)Se(3) nanoplates with thickness down to 3 nm (3 quintuple layers), via catalyst-free vapor-solid (VS) growth mechanism. Optical images reveal thickness-dependent color and contrast for nanoplates grown on oxidized silicon (300 nm SiO(2)/Si). As a new member of TI nanomaterials, ultrathin TI nanoplates have an extremely large surface-to-volume ratio and can be electrically gated more effectively than the bulk form, potentially enhancing surface state effects in transport measurements. Low-temperature transport measurements of a single nanoplate device, with a high-k dielectric top gate, show decrease in carrier concentration by several times and large tuning of chemical potential.

Do age and extended culture affect the architecture of the zona pellucida of human oocytes and embryos?

PubMed

Kilani, Suha S; Cooke, Simon; Kan, Andrew K; Chapman, Michael G

2006-02-01

Advanced female age and extended in vitro culture have both been implicated in zona pellucida (ZP) hardening and thickening. This study aimed to determine the influence of (i) the woman's age and (ii) prolonged in vitro culture of embryos on ZP thickness and density using non-invasive polarized light (LC-PolScope) microscopy. ZP thickness and density (measured as retardance) were determined in oocytes, embryos and blastocysts in women undergoing intracytoplasmic sperm injection (ICSI) in two age groups (older, > 38 years; younger, < or = 38 years). A total of 193 oocytes from 29 patients were studied. The younger group contained 100 oocytes and the older group 93 oocytes. The ZP was significantly thicker in metaphase II oocytes in the older group compared with the younger group (mean +/- SD: 24.1 +/- 2.5 microm vs 23.1 +/- 3.3 microm; p = 0.01) but ZP density was equal (2.8 +/- 0.7 nm). By day 2 of culture, embryos from the two groups had similar ZP thickness (22.2 +/- 2.2 microm vs 21.7 +/- 1.6 microm; p = 0.28) and density (2.9 +/- 0.7 nm vs 2.8 +/- 0.8 nm; p = 0.57). For the embryos cultured to blastocyst (older: n = 20; younger: n = 18) ZP thickness was similar in the two groups (19.2 +/- 2.7 microm vs 19.1 +/- 5.0 microm; p = 0.8) but thinner than on day 2. The older group had significantly denser ZP than the younger group (4.2 +/- 0.5 nm vs 3.3 +/- 1.0 nm, p < 0.01). Blastocysts from both groups had significantly denser ZP than their corresponding day 2 embryos (older: 4.2 +/- 0.5 nm vs 2.9 +/- 0.7 nm, p < 0.001; younger: 3.3 +/- 1.0 nm vs 2.8 +/- 0.8 nm, p = 0.013). It is concluded that there is little relationship between ZP thickness and its density as measured by polarized light microscopy. While ZP thickness decreases with extended embryo culturing, the density of the ZP increases. ZP density increases in both age groups with extended culture and, interestingly, more in embryos from older compared with younger women.

Deposition of zinc sulfide thin films by chemical bath process

NASA Astrophysics Data System (ADS)

Oladeji, Isaiah O.; Chow, Lee

1996-11-01

Deposition of high quality zinc sulfide (ZnS) thin film over a large area is required if it is to be effectively used in electroluminescent devices, solar cells, and other optoelectronic devices. Of all deposition techniques, chemical bath deposition (CBD) is the least costly technique that meets the above requirements. Recently it is found that the growth of ZnS film, of thickness less than 100 nm in a single dip, by CBD is facilitated by the use of ammonia and hydrazine as complexing agents. Here we report that the thickness of the deposited ZnS film can be increased if ammonium salt is used as a buffer. We also present an analytical study to explain our results and to further understand the ZnS growth process in CBD.

Properties of AlF3 and LaF3 films at 193nm

NASA Astrophysics Data System (ADS)

Xue, Chunrong; Shao, Jianda

2010-10-01

In order to develop low loss, high-performance 193nm Fluoride HR mirrors and anti-reflection coatings, LaF3 and AlF3 materials, used for a single-layer coating, were deposited by a molybdenum boat evaporation process. Various microstructures that formed under different substrate temperatures and with deposition rates were investigated. The relation between these microstructures (including cross section morphology, surface roughness and crystalline structure), the optical properties (including refractive index and optical loss) and mechanical properties (stress) were investigated. Furthermore, AlF3 used as a low-index material and LaF3 used as a high-index material were designed and deposited for multilayer coatings. Transmittance, reflectance, stress, and the laser-induced damage threshold (LIDT) were studied. It is shown that AlF3 and LaF3 thin films, deposited on the substrate at a temperature of 300 °C, obtained good quality thin films with high transmittance and little optical loss at 193 nm. For multilayer coatings, the absorption mainly comes from LaF3. Based on these studies, The thickness of 193nm films was controled by a 1/3 baffle with pre-coating technology. the LaF3/AlF3 AR coantings and HR mirrors at 193nm were designed and deposited. Under the present experimental conditions, the reflectance of LaF3/AlF3 HR mirror is up to 96%, and its transmittance is 1.5%. the LaF3/AlF3 AR coanting's residual reflectance is less than 0.14%, and single-sided transmittance is 93.85%. To get a high-performance 193nm AR coating, super-polished substrate is the best choice.

Properties of thin SiC membrane for x-ray mask

NASA Astrophysics Data System (ADS)

Shoki, Tsutomu; Nagasawa, Hiroyuki; Kosuga, Hiroyuki; Yamaguchi, Yoichi; Annaka, Noromichi; Amemiya, Isao; Nagarekawa, Osamu

1993-06-01

We have investigated the effects of film thickness, anti-reflective (AR) coating and surface roughness on the optical transparency of silicon carbide (SiC) membrane. Peak transmittances monotonously increased as the thickness decreased. The transmittance at 633 nm for 1.05 micrometers thick SiC membrane adjusted by reactive ion etching was 70%, and increased up to 80% by an AR coating. SiC membrane with extremely smooth surface of 0.12 nm (Ra) has been obtained by polishing, and had peak transmittances of 69% and 80% at 633 nm for 2.0 micrometers and 1.0 micrometers in thickness, respectively. Poly-crystalline (beta) -SiC membrane in the suitable tensile stress range of 0.3 to 2.0 X 108 Pa and with high Young's modulus of 4.5 X 1011 Pa has been prepared by a hot wall type low pressure chemical vapor deposition, and been found to need to have thickness over 0.7 micrometers to maintain sufficient mechanical strength in processing.

Effect of ZrO2 film thickness on the photoelectric properties of mixed-cation perovskite solar cells

NASA Astrophysics Data System (ADS)

Li, Yanyan; Zhao, Li; Wei, Shoubin; Xiao, Meng; Dong, Binghai; Wan, Li; Wang, Shimin

2018-05-01

In this work, perovskite solar cells (PSCs) were fabricated in the ambient air, with a scaffold layer composed of TiO2/ZrO2 double layer as the mesoscopic layer and carbon as the counter electrode. The effect of ZrO2 thin film thickness on the photovoltaic performances of PSCs was also studied in detail. Results showed that the photoelectric properties of as-prepared PSCs largely depend on the thin film thickness due to a series of factors, including surface roughness, charge transport resistance, and electron-hole recombination rate. The power conversion efficiency of PSCs increased from 8.37% to 11.33% by varying the thin film thickness from 75 nm to 305 nm, and the optimal power conversion efficiency was realized up to the 11.33% with a thin film thickness of 167 nm. This research demonstrates a promising route for the high-efficiency and low-cost photovoltaic technology.

Stability of Polymer Ultrathin Films (<7 nm) Made by a Top-Down Approach.

PubMed

Bal, Jayanta Kumar; Beuvier, Thomas; Unni, Aparna Beena; Chavez Panduro, Elvia Anabela; Vignaud, Guillaume; Delorme, Nicolas; Chebil, Mohamed Souheib; Grohens, Yves; Gibaud, Alain

2015-08-25

In polymer physics, the dewetting of spin-coated polystyrene ultrathin films on silicon remains mysterious. By adopting a simple top-down method based on good solvent rinsing, we are able to prepare flat polystyrene films with a controlled thickness ranging from 1.3 to 7.0 nm. Their stability was scrutinized after a classical annealing procedure above the glass transition temperature. Films were found to be stable on oxide-free silicon irrespective of film thickness, while they were unstable (<2.9 nm) and metastable (>2.9 nm) on 2 nm oxide-covered silicon substrates. The Lifshitz-van der Waals intermolecular theory that predicts the domains of stability as a function of the film thickness and of the substrate nature is now fully reconciled with our experimental observations. We surmise that this reconciliation is due to the good solvent rinsing procedure that removes the residual stress and/or the density variation of the polystyrene films inhibiting thermodynamically the dewetting on oxide-free silicon.

Multilayer Black Phosphorus Near-Infrared Photodetectors.

PubMed

Hou, Chaojian; Yang, Lijun; Li, Bo; Zhang, Qihan; Li, Yuefeng; Yue, Qiuyang; Wang, Yang; Yang, Zhan; Dong, Lixin

2018-05-23

Black phosphorus (BP), owing to its distinguished properties, has become one of the most competitive candidates for photodetectors. However, there has been little attention paid on photo-response performance of multilayer BP nanoflakes with large layer thickness. In fact, multilayer BP nanoflakes with large layer thickness have greater potential from the fabrication viewpoint as well as due to the physical properties than single or few layer ones. In this report, the thickness-dependence of the intrinsic property of BP photodetectors in the dark was initially investigated. Then the photo-response performance (including responsivity, photo-gain, photo-switching time, noise equivalent power, and specific detectivity) of BP photodetectors with relative thicker thickness was explored under a near-infrared laser beam ( λ IR = 830 nm). Our experimental results reveal the impact of BP's thickness on the current intensity of the channel and show degenerated p-type BP is beneficial for larger current intensity. More importantly, the photo-response of our thicker BP photodetectors exhibited a larger responsivity up to 2.42 A/W than the few-layer ones and a fast response photo-switching speed (response time is ~2.5 ms) comparable to thinner BP nanoflakes was obtained, indicating BP nanoflakes with larger layer thickness are also promising for application for ultra-fast and ultra-high near-infrared photodetectors.

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

Park, Wug-Dong; Tanioka, Kenkichi

Amorphous selenium (a-Se) high-gain avalanche rushing amorphous photoconductor (HARP) film has been used for highly sensitive imaging devices. To improve the spectral response of a-Se HARP photoconductive film at a long wavelength, the tellurium (Te) doping effect in an 8-μm-thick a-Se HARP film was investigated. The thickness of the Te-doped a-Se layer in the 8-μm-thick a-Se HARP films was varied from 60 to 120 nm. The signal current increases significantly due to the avalanche multiplication when the target voltage is increased over the threshold voltage. In the 8-μm-thick a-Se HARP film with a Te-doped layer, the spectral response at a longmore » wavelength was improved in comparison with the a-Se HARP film without a Te-doped layer. In addition, the increase of the lag in the 8-μm-thick a-Se HARP target with a Te-doped layer of 120 nm is caused by the photoconductive lag due to the electrons trapped in the Te-doped layer. Based on the current-voltage characteristics, spectral response, and lag characteristics of the 8-μm-thick a-Se HARP targets, the Te-doped layer thickness of 90 nm is suitable for the 8-μm-thick a-Se HARP film.« less

Band-to-band tunneling in Γ valley for Ge source lateral tunnel field effect transistor: Thickness scaling

NASA Astrophysics Data System (ADS)

Jain, Prateek; Rastogi, Priyank; Yadav, Chandan; Agarwal, Amit; Chauhan, Yogesh Singh

2017-07-01

The direct and indirect valleys in Germanium (Ge) are separated by a very small offset, which opens up the prospect of direct tunneling in the Γ valley of an extended Ge source tunnel field effect transistor (TFET). We explore the impact of thickness scaling of extended Ge source lateral TFET on the band to band tunneling (BTBT) current. The Ge source is extended inside the gate by 2 nm to confine the tunneling in Ge only. We observe that as the thickness is scaled, the band alignment at the Si/Ge heterojunction changes significantly, which results in an increase in Ge to Si BTBT current. Based on density functional calculations, we first obtain the band structure parameters (bandgap, effective masses, etc.) for the Ge and Si slabs of varying thickness, and these are then used to obtain the thickness dependent Kane's BTBT tunneling parameters. We find that electrostatics improves as the thickness is reduced in the ultra-thin Ge film ( ≤ 10 nm). The ON current degrades as we scale down in thickness; however, the subthreshold slope ( S S AVG ) improves remarkably with thickness scaling due to subsurface BTBT. We predict that 8 nm thin devices offer the best option for optimized ON current and S S AVG .

Tellurium doping effect in avalanche-mode amorphous selenium photoconductive film

NASA Astrophysics Data System (ADS)

Park, Wug-Dong; Tanioka, Kenkichi

2014-11-01

Amorphous selenium (a-Se) high-gain avalanche rushing amorphous photoconductor (HARP) film has been used for highly sensitive imaging devices. To improve the spectral response of a-Se HARP photoconductive film at a long wavelength, the tellurium (Te) doping effect in an 8-μm-thick a-Se HARP film was investigated. The thickness of the Te-doped a-Se layer in the 8-μm-thick a-Se HARP films was varied from 60 to 120 nm. The signal current increases significantly due to the avalanche multiplication when the target voltage is increased over the threshold voltage. In the 8-μm-thick a-Se HARP film with a Te-doped layer, the spectral response at a long wavelength was improved in comparison with the a-Se HARP film without a Te-doped layer. In addition, the increase of the lag in the 8-μm-thick a-Se HARP target with a Te-doped layer of 120 nm is caused by the photoconductive lag due to the electrons trapped in the Te-doped layer. Based on the current-voltage characteristics, spectral response, and lag characteristics of the 8-μm-thick a-Se HARP targets, the Te-doped layer thickness of 90 nm is suitable for the 8-μm-thick a-Se HARP film.

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

Gelles, D. S.; Browning, James Frederick; Snow, Clark Sheldon

Er(D,T){sub 2-x} {sup 3}He{sub x}, erbium di-tritide, films of thicknesses 500 nm, 400 nm, 300 nm, 200 nm, and 100 nm were grown and analyzed by Transmission Electron Microscopy, X-Ray Diffraction, and Ion Beam Analysis to determine variations in film microstructure as a function of film thickness and age, due to the time-dependent build-up of {sup 3}He in the film from the radioactive decay of tritium. Several interesting features were observed: One, the amount of helium released as a function of film thickness is relatively constant. This suggests that the helium is being released only from the near surface regionmore » and that the helium is not diffusing to the surface from the bulk of the film. Two, lenticular helium bubbles are observed as a result of the radioactive decay of tritium into {sup 3}He. These bubbles grow along the [111] crystallographic direction. Three, a helium bubble free zone, or 'denuded zone' is observed near the surface. The size of this region is independent of film thickness. Four, an analysis of secondary diffraction spots in the Transmission Electron Microscopy study indicate that small erbium oxide precipitates, 5-10 nm in size, exist throughout the film. Further, all of the films had large erbium oxide inclusions, in many cases these inclusions span the depth of the film.« less

Phase Transitions and Domain Structure in Mixed Tetragonal-Rhombohedral BiFeO3 thin films using Raman Spectroscopy and Nonlinear Optics

NASA Astrophysics Data System (ADS)

Vlahos, E.; Kumar, A.; Denev, S.; Melville, A.; Adamo, C.; Ihlefeld, J. F.; Sheng, G.; Zeches, R. J.; Zhang, J. X.; He, Q.; Yang, C. H.; Erni, R.; Rossell, M. D.; J, A.; Hatt; Chu, Y.-H.; Wang, C. H.; Ederer, C.; Gopalan, V.; Chen, L. Q.; Schlom, D. G.; Spaldin, N. A.; Martin, L. W.; Ramesh, R.; Tenne, Dmitri

2010-03-01

We have shown that biaxially strained BiFeO3 thin films can undergo an isosymmetric phase transition from a rhombohedral-like to a tetragonal-like phase. This talk discusses the evolution of the tetragonal and the mixed phases in BiFeO3/YAlO3 thin films with varying film thickness using optical second harmonic generation (SHG) and Raman spectroscopy. 25nm, 75nm, and 225 nm thick films were studied; thinner films are dominated by the tetragonal phase, whereas thicker films exhibit both tetragonal and rhombohedral phases. The evolution of these phases as function of film thickness and temperature was experimentally determined.

Fluoride Thin Films: from Exchange Bias to Multferroicity

NASA Astrophysics Data System (ADS)

Johnson, Trent A.

This dissertation concerns research into the growth and characterization fluoride thin films by molecular beam epitaxy. After a discussion of relevant background material and experimental procedures in the first two chapters, we study exchange bias in magnetic multilayers incorporating the uniaxial antiferromagnet FeF2, grown to varying thicknesses, sandwiched between ferromagnetic Co layers with fixed thicknesses of 5 and 20 nm. Several bilayers with only the 20 nm thick Co layer were grown for comparative study. The samples were grown on Al2O3 (112¯0) substrates at room temperature. In-situ RHEED and x-ray diffraction indicated the films were polycrystalline. The films were determined to have low surface and interlayer roughness, as determined by AFM and x-ray reflectivity. After field-cooling to below the Neel temperature of FeF2 in a magnetic field of 1 kOe, magnetic hysteresis loops were measured as a function of temperature. We found that both layers had a negative exchange bias, with the exchange bias of the thinner layer larger than that of the thicker layer. In addition, the coercivity below the blocking temperature TB of the thinner layer was significantly larger than that of the thick layer, even though the coercivity of the two layers was the same for T > TB. The exchange bias effect, manifested by a shift in these hysteresis loops, showed a strong dependence on the thickness of the antiferromagnet. Anisotropic magnetoresistance measurements provided additional insight into the magnetization reversal mechanism within the ferromagnets. The thickness dependent exchange anisotropy of trilayer and bilayer samples is explained by adapting a random field model to the antiferromagnet/ferromagnet interface. Finally, We investigate the temperature dependent growth, as well as the magnetic and ferroelectric properties of thin films of the multiferroic compounds BaMF4, where M = Fe, Co, Ni. The films were grown to thicknesses of 50 or 100 nm on single crystal Al2O3 (0001) substrates. X-ray diffraction showed that this family of films grew epitaxially in the (010) orientation, but were twinned in the plane, with three domain orientations rotated by 120 degrees relative to one another. Measurements of the remanent hysteresis via interdigitated electrodes showed that the compounds M = Co, and Ni were ferroelectric, but no switching behavior was observed in the Fe system at electric fields up to 400 kV/cm. Measurements of the field-cooled and zero-field-cooled magnetic moment confirmed low temperature antiferromagnetic behavior, and found new weak ferromagnetic phases induced by strain.

Surface and magnetic characteristics of Ni-Mn-Ga/Si (100) thin film

NASA Astrophysics Data System (ADS)

Kumar, S. Vinodh; Raja, M. Manivel; Pandi, R. Senthur; Pandyan, R. Kodi; Mahendran, M.

2016-05-01

Polycrystalline Ni-Mn-Ga thin films have been deposited on Si (100) substrate with different film thickness. The influence of film thickness on the phase structure and magnetic domain of the films has been examined by scanning electron microscope, atomic force microscopy and magnetic force microscopy. Analysis of structural parameters indicates that the film at lower thickness exhibits the coexistence of both austenite and martensite phase, whereas at higher thickness L12 cubic non magnetic phase is noticed. The grains size and the surface roughness increase along with the film thickness and attain the maximum of 45 nm and 34.96 nm, respectively. At lower film thickness, the magnetic stripe domain is found like maze pattern with dark and bright images, while at higher thickness the absence of stripe domains is observed. The magnetic results reveal that the films strongly depend on their phase structure and microstructure which influence by the film thickness.

In situ nanoindentation study of plastic Co-deformation in Al-TiN nanocomposites

DOE PAGES

Li, N.; Wang, H.; Misra, A.; ...

2014-10-16

We performed in situ indentation in a transmission electron microscope on Al-TiN multilayers with individual layer thicknesses of 50 nm, 5 nm and 2.7 nm to explore the effect of length scales on the plastic co-deformability of a metal and a ceramic. At 50 nm, plasticity was confined to the Al layers with easy initiation of cracks in the TiN layers. At 5 nm and below, cracking in TiN was suppressed and post mortem measurements indicated a reduction in layer thickness in both layers. Our results demonstrate the profound size effect in enhancing plastic co-deformability in nanoscale metal-ceramic multilayers.

Correlation between skin, bone, and cerebrospinal fluid layer thickness and optical coefficients measured by multidistance frequency-domain near-infrared spectroscopy in term and preterm infants.

PubMed

Demel, Anja; Feilke, Katharina; Wolf, Martin; Poets, Christian F; Franz, Axel R

2014-01-01

Near-infrared spectroscopy (NIRS) is increasingly used in neonatal intensive care. We investigated the impact of skin, bone, and cerebrospinal fluid (CSF) layer thickness in term and preterm infants on absorption-(μa) and/or reduced scattering coefficients (μs') measured by multidistance frequency-domain (FD)-NIRS. Transcranial ultrasound was performed to measure the layer thicknesses. Correlations were only statistically significant for μa at 692 nm with bone thickness and μs' at 834 nm with skin thickness. There is no evidence that skin, bone, or CSF thickness have an important effect on μa and μs'. Layer thicknesses of skin, bone, and CSF in the range studied do not seem to affect cerebral oxygenation measurements by multidistance FD-NIRS significantly.

Breakthrough to Non-Vacuum Deposition of Single-Crystal, Ultra-Thin, Homogeneous Nanoparticle Layers: A Better Alternative to Chemical Bath Deposition and Atomic Layer Deposition

PubMed Central

Liao, Yu-Kuang; Liu, Yung-Tsung; Hsieh, Dan-Hua; Shen, Tien-Lin; Hsieh, Ming-Yang; Tzou, An-Jye; Chen, Shih-Chen; Tsai, Yu-Lin; Lin, Wei-Sheng; Chan, Sheng-Wen; Shen, Yen-Ping; Cheng, Shun-Jen; Chen, Chyong-Hua; Wu, Kaung-Hsiung; Chen, Hao-Ming; Kuo, Shou-Yi; Charlton, Martin D. B.; Hsieh, Tung-Po; Kuo, Hao-Chung

2017-01-01

Most thin-film techniques require a multiple vacuum process, and cannot produce high-coverage continuous thin films with the thickness of a few nanometers on rough surfaces. We present a new ”paradigm shift” non-vacuum process to deposit high-quality, ultra-thin, single-crystal layers of coalesced sulfide nanoparticles (NPs) with controllable thickness down to a few nanometers, based on thermal decomposition. This provides high-coverage, homogeneous thickness, and large-area deposition over a rough surface, with little material loss or liquid chemical waste, and deposition rates of 10 nm/min. This technique can potentially replace conventional thin-film deposition methods, such as atomic layer deposition (ALD) and chemical bath deposition (CBD) as used by the Cu(In,Ga)Se2 (CIGS) thin-film solar cell industry for decades. We demonstrate 32% improvement of CIGS thin-film solar cell efficiency in comparison to reference devices prepared by conventional CBD deposition method by depositing the ZnS NPs buffer layer using the new process. The new ZnS NPs layer allows reduction of an intrinsic ZnO layer, which can lead to severe shunt leakage in case of a CBD buffer layer. This leads to a 65% relative efficiency increase. PMID:28383488

Surface texture of single-crystal silicon oxidized under a thin V{sub 2}O{sub 5} layer

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

Nikitin, S. E., E-mail: nikitin@mail.ioffe.ru; Verbitskiy, V. N.; Nashchekin, A. V.

The process of surface texturing of single-crystal silicon oxidized under a V{sub 2}O{sub 5} layer is studied. Intense silicon oxidation at the Si–V{sub 2}O{sub 5} interface begins at a temperature of 903 K which is 200 K below than upon silicon thermal oxidation in an oxygen atmosphere. A silicon dioxide layer 30–50 nm thick with SiO{sub 2} inclusions in silicon depth up to 400 nm is formed at the V{sub 2}O{sub 5}–Si interface. The diffusion coefficient of atomic oxygen through the silicon-dioxide layer at 903 K is determined (D ≥ 2 × 10{sup –15} cm{sup 2} s{sup –1}). A modelmore » of low-temperature silicon oxidation, based on atomic oxygen diffusion from V{sub 2}O{sub 5} through the SiO{sub 2} layer to silicon, and SiO{sub x} precipitate formation in silicon is proposed. After removing the V{sub 2}O{sub 5} and silicon-dioxide layers, texture is formed on the silicon surface, which intensely scatters light in the wavelength range of 300–550 nm and is important in the texturing of the front and rear surfaces of solar cells.« less

On-Chip Waveguide Coupling of a Layered Semiconductor Single-Photon Source.

PubMed

Tonndorf, Philipp; Del Pozo-Zamudio, Osvaldo; Gruhler, Nico; Kern, Johannes; Schmidt, Robert; Dmitriev, Alexander I; Bakhtinov, Anatoly P; Tartakovskii, Alexander I; Pernice, Wolfram; Michaelis de Vasconcellos, Steffen; Bratschitsch, Rudolf

2017-09-13

Fully integrated quantum technology based on photons is in the focus of current research, because of its immense potential concerning performance and scalability. Ideally, the single-photon sources, the processing units, and the photon detectors are all combined on a single chip. Impressive progress has been made for on-chip quantum circuits and on-chip single-photon detection. In contrast, nonclassical light is commonly coupled onto the photonic chip from the outside, because presently only few integrated single-photon sources exist. Here, we present waveguide-coupled single-photon emitters in the layered semiconductor gallium selenide as promising on-chip sources. GaSe crystals with a thickness below 100 nm are placed on Si 3 N 4 rib or slot waveguides, resulting in a modified mode structure efficient for light coupling. Using optical excitation from within the Si 3 N 4 waveguide, we find nonclassicality of generated photons routed on the photonic chip. Thus, our work provides an easy-to-implement and robust light source for integrated quantum technology.

Optical resonance analysis of reflected long period fiber gratings with metal film overlay

NASA Astrophysics Data System (ADS)

Zhang, Guiju; Cao, Bing; Wang, Chinua; Zhao, Minfu

2008-11-01

We present the experimental results of a novel single-ended reflecting surface plasma resonance (SPR) based long period fiber grating (LPFG) sensor. A long period fiber grating sensing device is properly designed and fabricated with a pulsed CO2 laser writing system. Different nm-thick thin metal films are deposited on the fiber cladding and the fiber end facet for the excitation of surface plasma waves (SPWs) and the reflection of the transmission spectrum of the LPFG with doubled interaction between metal-dielectric interfaces of the fiber to enhance the SPW of the all-fiber SPR-LPFG sensing system. Different thin metal films with different thicknesses are investigated. The effect of the excited SPW transmission along the fiber cladding-metal interface with silver and aluminum films is observed. It is found that different thicknesses of the metal overlay show different resonant behaviors in terms of resonance peak situation, bandwidth and energy loss. Within a certain range, thinner metal film shows narrower bandwidth and deeper peak loss.

ITO/Au/ITO sandwich structure for near-infrared plasmonics.

PubMed

Fang, Xu; Mak, Chee Leung; Dai, Jiyan; Li, Kan; Ye, Hui; Leung, Chi Wah

2014-09-24

ITO/Au/ITO trilayers with varying gold spacer layer thicknesses were deposited on glass substrates by pulsed laser deposition. Transmission electron microscopy measurements demonstrated the continuous nature of the Au layer down to 2.4 nm. XRD patterns clearly showed an enhanced crystallinity of the ITO films promoted by the insertion of the gold layer. Compared with a single layer of ITO with a carrier concentration of 7.12 × 10(20) cm(-3), the ITO/Au/ITO structure achieved an effective carrier concentration as high as 3.26 × 10(22) cm(-3). Transmittance and ellipsometry measurements showed that the optical properties of ITO/Au/ITO films were greatly influenced by the thickness of the inserted gold layer. The cross-point wavelength of the trilayer samples was reduced with increasing gold layer thickness. Importantly, the trilayer structure exhibited a reduced loss (compared with plain Au) in the near-infrared region, suggesting its potential for plasmonic applications in the near-infrared range.

Three-dimensional phonon population anisotropy in silicon nanomembranes

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

McElhinny, Kyle M.; Gopalakrishnan, Gokul; Holt, Martin V.

Nanoscale single crystals possess modified phonon dispersions due to the truncation of the crystal. The introduction of surfaces alters the population of phonons relative to the bulk and introduces anisotropy arising from the breaking of translational symmetry. Such modifications exist throughout the Brillouin zone, even in structures with dimensions of several nanometers, posing a challenge to the characterization of vibrational properties and leading to uncertainty in predicting the thermal, optical, and electronic properties of nanomaterials. Synchrotron x-ray thermal diffuse scattering studies find that freestanding Si nanomembranes with thicknesses as large as 21 nm exhibit a higher scattering intensity per unitmore » thickness than bulk silicon. In addition, the anisotropy arising from the finite thickness of these membranes produces particularly intense scattering along reciprocal-space directions normal to the membrane surface compared to corresponding in-plane directions. These results reveal the dimensions at which calculations of materials properties and device characteristics based on bulk phonon dispersions require consideration of the nanoscale size of the crystal.« less

Reaching the Ionic Current Detection Limit in Silicon-Based Nanopores

NASA Astrophysics Data System (ADS)

Puster, Matthew; Rodriguez-Manzo, Julio Alejandro; Nicolai, Adrien; Meunier, Vincent; Drndic, Marija

2015-03-01

Solid-state nanopores act as single-molecule sensors whereby passage of an individual molecule in aqueous electrolyte through a nanopore is registered as a change in ionic conductance (ΔG). Future nanopore applications such as DNA sequencing at high bandwidth require high ΔG for optimal signal-to-noise ratio. Reducing the nanopore diameter and thickness increase ΔG. Molecule size limits the diameter, thus efforts concentrate on minimizing the thickness by thinning oxide/nitride films or using 2D materials. Weighted by electrolyte conductivity the highest ΔG reported to date for DNA translocations were obtained with nanopores made in oxide/nitride films. We present a controlled electron irradiation technique to thin such films to the limit of their stability, producing nanopores tailored to molecule size in amorphous Si with thicknesses less than 2 nm. We compare ΔG values with results found in the literature for DNA translocation through these nanopores, where access resistance becomes comparable to the resistance through the nanopore itself.

Bandgap Engineering of InP QDs Through Shell Thickness and Composition

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

Dennis, Allison M.; Mangum, Benjamin D.; Piryatinski, Andrei

2012-06-21

Fields as diverse as biological imaging and telecommunications utilize the unique photophysical and electronic properties of nanocrystal quantum dots (NQDs). The development of new NQD compositions promises material properties optimized for specific applications, while addressing material toxicity. Indium phosphide (InP) offers a 'green' alternative to the traditional cadmium-based NQDs, but suffers from extreme susceptibility to oxidation. Coating InP cores with more stable shell materials significantly improves nanocrystal resistance to oxidation and photostability. We have investigated several new InP-based core-shell compositions, correlating our results with theoretical predictions of their optical and electronic properties. Specifically, we can tailor the InP core-shell QDsmore » to a type-I, quasi-type-II, or type-II bandgap structure with emission wavelengths ranging from 500-1300 nm depending on the shell material used (ZnS, ZnSe, CdS, or CdSe) and the thickness of the shell. Single molecule microscopy assessments of photobleaching and blinking are used to correlate NQD properties with shell thickness.« less

Structural, morphological and optical properties of ZnSe quantum dot thin films.

PubMed

Zedan, I T; Azab, A A; El-Menyawy, E M

2016-02-05

ZnSe powder was prepared via hydrothermal technique using zinc acetate and sodium selenite as source materials. The prepared ZnSe powder was used for preparing film with different thickness values (95, 135 and 230 nm) via thermal evaporation technique. X-ray diffraction showed that the prepared powder has cubic zinc-blende structure with a space group, F43m. The high resolution transmittance electron microscope results show that the films are composed of spherical-shaped nanoparticles with a diameter in the range of 2-8 nm. The optical properties of ZnSe films with differing thicknesses are investigated by means of spectrophotometric measurements of the photoluminescence, transmittance and reflectance. The absorption coefficient of the films is calculated and the optical band gap is estimated. The refractive index of the films is determined and its normal dispersion behavior is analyzed on the basis of a single oscillator model, in which oscillator energy, dispersion energy and dielectric constant at high frequency are evaluated. Drude model is also applied to determine the lattice dielectric constant and the ratio of the carriers' concentration to their effective mass. Copyright © 2015 Elsevier B.V. All rights reserved.

Noble metal free photocatalytic H 2 generation on black TiO 2: On the influence of crystal facets vs. crystal damage

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

Liu, Ning; Steinrück, Hans-Georg; Osvet, Andres

In this study, we investigate noble metal free photocatalytic water splitting on natural anatase single crystal facets and on wafer slices of the [001] plane before and after these surfaces have been modified by high pressure hydrogenation and hydrogen ion-implantation. Here, we find that on the natural, intact low index planes, photocatalytic H 2 evolution (in the absence of a noble metal co-catalyst) can only be achieved when the hydrogenation treatment is accompanied by the introduction of crystal damage, such as simple scratching and miscut in the crystal, or by implantation damage. X-ray reflectivity, Raman, and optical reflection measurements showmore » that plain hydrogenation leads to a ≈ 1 nm thick black titania surface layer without activity, while a colorless, density modified, and ≈7 nm thick layer with broken crystal symmetry is present on the ion implanted surface. These results demonstrate that (i) the H-treatment of an intact anatase surface needs to be combined with defect formation for catalytic activation and (ii) activation does not necessarily coincide with the presence of black color.« less

Laser-induced damage of fused silica optics at 355 nm due to backward stimulated Brillouin scattering: experimental and theoretical results.

PubMed

Lamaignère, Laurent; Gaudfrin, Kévin; Donval, Thierry; Natoli, Jeanyves; Sajer, Jean-Michel; Penninckx, Denis; Courchinoux, Roger; Diaz, Romain

2018-04-30

Forward pump pulses with nanosecond duration are able to generate an acoustic wave via electrostriction through a few centimeters of bulk silica. Part of the incident energy is then scattered back on this sound wave, creating a backward Stokes pulse. This phenomenon known as stimulated Brillouin scattering (SBS) might induce first energy-loss, variable change of the temporal waveform depending on the location in the spatial profile making accurate metrology impossible, and moreover it might also initiate front surface damage making the optics unusable. Experiments performed on thick fused silica optics at 355 nm with single longitudinal mode pulses allowed us to detect, observe and quantify these backward pulses. Experimental results are first compared to theoretical calculations in order to strengthen our confidence in metrology. On this basis a phase-modulator has been implemented on the continuous-wave seeders of the lasers leading to pulses with a wide spectrum that suppress SBS and do not exhibit temporal overshoots that also reduce Kerr effects. The developed set-ups are used to check the reduction of the backward stimulated Brillouin scattering and they allow measuring with accuracy the rear surface damage of thick fused silica optics.

Fluorinated benzothiadiazole-based conjugated polymers for high-performance polymer solar cells without any processing additives or post-treatments.

PubMed

Wang, Ning; Chen, Zheng; Wei, Wei; Jiang, Zhenhua

2013-11-13

Thanks to their many favorable advantages, polymer solar cells exhibit great potential for next-generation clean energy sources. Herein, we have successfully designed and synthesized a series of new fluorinated benzothiadiazole-based conjugated copolymers PBDT(TEH)-DT(H)BTff (P1), PBDT(TEH)-DT(EH)BTff (P2), and PBDT(HDO)-DT(H)BTff (P3). The power conversion efficiencies of 4.46, 6.20, and 8.30% were achieved for P1-, P2-, and P3-based devices within ~100 nm thickness active layers under AM 1.5G illumination without any processing additives or post-treatments, respectively. The PCE of 8.30% for P3 is the highest value for the reported traditional single-junction polymer solar cells via a simple fabrication architecture without any additives or post-treatments. In addition, it is noteworthy that P3 also allows making high efficient polymer solar cells with high PCEs of 7.27 and 6.56% under the same condition for ~200 and ~300 nm thickness active layers, respectively. Excellent photoelectric properties and good solubility make polymer P3 become an alternative material for high-performance polymer solar cells.

Noble metal free photocatalytic H 2 generation on black TiO 2: On the influence of crystal facets vs. crystal damage

DOE PAGES

Liu, Ning; Steinrück, Hans-Georg; Osvet, Andres; ...

2017-02-13

In this study, we investigate noble metal free photocatalytic water splitting on natural anatase single crystal facets and on wafer slices of the [001] plane before and after these surfaces have been modified by high pressure hydrogenation and hydrogen ion-implantation. Here, we find that on the natural, intact low index planes, photocatalytic H 2 evolution (in the absence of a noble metal co-catalyst) can only be achieved when the hydrogenation treatment is accompanied by the introduction of crystal damage, such as simple scratching and miscut in the crystal, or by implantation damage. X-ray reflectivity, Raman, and optical reflection measurements showmore » that plain hydrogenation leads to a ≈ 1 nm thick black titania surface layer without activity, while a colorless, density modified, and ≈7 nm thick layer with broken crystal symmetry is present on the ion implanted surface. These results demonstrate that (i) the H-treatment of an intact anatase surface needs to be combined with defect formation for catalytic activation and (ii) activation does not necessarily coincide with the presence of black color.« less

He+ ion irradiation response of Fe–TiO2 multilayers

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

Anderoglu, O.; Zhou, M. J.; Zhang, J.

2013-04-01

The accumulation of radiation-induced defect clusters and He bubble formation in He+ ion irradiated nanocrystalline TiO2 and Fe–TiO2 multilayer thin films were investigated using transmission electron microscopy (TEM). Prior to ion irradiation it was found that the crystallinity of TiO2 layers depends on the individual layer thickness: While all TiO2 layers are amorphous at 5 nm individual layer thickness, at 100 nm they are crystalline with a rutile polymorph. After He+ irradiation up to ~6 dpa at room temperature, amorphization of TiO2 layers was not observed in both nanocrystalline TiO2 single layers and Fe–TiO2 multilayers. The suppression of radiation-induced amorphizationmore » in TiO2 is interpreted in terms of a high density of defect sinks in these nano-composites in the form of Fe–TiO2 interphase boundaries and columnar grains within each layer with nano-scale intercolumnar porosity. In addition, a high concentration of He is believed to be trapped at these interfaces in the form of sub-nanometer-scale clusters retarding the formation of relatively larger He bubbles that can be resolved in TEM.« less

Preparation and characterization of molecularly homogeneous silica-titania film by sol-gel process with different synthetic strategies.

PubMed

Chen, Hsueh-Shih; Huang, Sheng-Hsin; Perng, Tsong-Pyng

2012-10-24

Three silica-titania thin films with various degrees of molecular homogeneity were synthesized by the sol-gel process with the same precursor formula but different reaction paths. The dried films prepared by a single spin-coating process have a thickness of 500-700 nm and displayed no cracks or pin holes. The transmittances and refractive indices of the samples are >97.8% in the range of 350-1800 nm and 1.62-1.65 at 500 nm, respectively. The in-plane and out-of-plane chemical homogeneities of the films were analyzed by X-ray photoelectron spectroscopy and Auger electron spectroscopy, respectively. For the film with the highest degree of homogeneity, the deviations of O, Si, and Ti atomic contents in both in-plane and out-of-plane directions are less than 1.5%, indicating that the film is highly molecularly homogeneous. It also possesses the highest transparency and the lowest refractive index among the three samples.

Annealing Effects on the Surface Plasmon of MgO Implanted with Gold

NASA Technical Reports Server (NTRS)

Ueda, A.; Mu, R.; Tung, Y. -S.; Henderson, D. O.; White, C. W.; Zuhr, R. A.; Zhu, Jane G.; Wang, P. W.

1997-01-01

Gold ion implantation was carried out with the energy of 1.1 MeV into (100) oriented MgO single crystal. Implanted doses are 1, 3, 6, 10 x 10(exp 16) ions/sq cm. The gold irradiation results in the formation of gold ion implanted layer with a thickness of 0.2 microns and defect formation. In order to form gold colloids from the as-implanted samples, we annealed the gold implanted MgO samples in three kinds of atmospheres: (1)Ar only, (2)H2 and Ar, and (3)O2 and Ar. The annealing over 1200 C enhanced the gold colloid formation which shows surface plasmon resonance band of gold. The surface plasmon bands of samples annealed in three kinds of atmospheres were found to be at 535 nm (Ar only), 524 nm(H2+Ar), and 560 nm (02+Ar), The band positions of surface plasmon can be reversibly changed by an additional annealing.

High efficiency fluorescent white OLEDs based on DOPPP

NASA Astrophysics Data System (ADS)

Zhang, Gang; Chen, Chen; Lang, Jihui; Zhao, Lina; Jiang, Wenlong

2017-08-01

The white organic light-emitting devices (WOLED) with the structures of ITO/m-MTDATA (10 nm)/NPB (30 nm)/Rubrene (0.2 nm)/DOPPP (x nm)/TAz (10 nm)/Alq3 (30 nm)/LiF (0.5 nm)/Al and ITO/NPB (30 nm)/DPAVBi:Rubrene (2 wt.%, 20 nm)/ DOPPP (x nm)/TAZ (10 nm)/Alq3 (30 nm)/LiF (0.5 nm)/Al (100 nm) have been fabricated by the vacuum thermal evaporation method. The results show that the chroma of the non-doped device is the best and the color coordinates are in the range of white light. The maximum luminance is 12,750 cd/m2 and the maximum current efficiency is 8.55 cd/A. The doped device A has the maximum luminance (16,570 cd/m2), when the thickness of blue layer DOPPP is 25 nm, and the doped device B achieves the highest efficiency (10.47 cd/A), when the thickness of DOPPP is 15 nm. All the performances of the doped devices are better than the non-doped one. The results demonstrate that the doped structures can realize the energy transfer and then improve the performance of the device effectively.

Effects of lattice deformation on magnetic properties of electron-doped La0.8Hf0.2MnO3 thin films

NASA Astrophysics Data System (ADS)

Wu, Z. P.; Jiang, Y. C.; Gao, J.

2013-05-01

The lattice deformation effects on electric and magnetic properties of electron-doped La0.8Hf0.2MnO3 (LHMO) thin films have been systematically investigated. LHMO films with various thicknesses (15 nm, 40 nm, and 80 nm) were grown on (001) SrTiO3 and (001) LaAlO3 substrates, which induces in-plane tensile and compressive biaxial stress, respectively. The metal-insulator phase transition temperature (TP) and magnetoresistance (MR) effect show a strong dependence on film thickness. TP increases with a decrease in thickness and is enhanced as the lattice strain rises, regardless of whether it is tensile or compressive. The maximum MR ratio is suppressed by reduction of the film thickness. These anomalous phenomena may be attributed to the competition between the strain induced modification of the Mn-O bond length and the eg orbital stability.

Probing the thermal decomposition behaviors of ultrathin HfO2 films by an in situ high temperature scanning tunneling microscope.

PubMed

Xue, Kun; Wang, Lei; An, Jin; Xu, Jianbin

2011-05-13

The thermal decomposition of ultrathin HfO(2) films (∼0.6-1.2 nm) on Si by ultrahigh vacuum annealing (25-800 °C) is investigated in situ in real time by scanning tunneling microscopy. Two distinct thickness-dependent decomposition behaviors are observed. When the HfO(2) thickness is ∼ 0.6 nm, no discernible morphological changes are found below ∼ 700 °C. Then an abrupt reaction occurs at 750 °C with crystalline hafnium silicide nanostructures formed instantaneously. However, when the thickness is about 1.2 nm, the decomposition proceeds gradually with the creation and growth of two-dimensional voids at 800 °C. The observed thickness-dependent behavior is closely related to the SiO desorption, which is believed to be the rate-limiting step of the decomposition process.

Increased magnetic damping in ultrathin films of Co2FeAl with perpendicular anisotropy

NASA Astrophysics Data System (ADS)

Takahashi, Y. K.; Miura, Y.; Choi, R.; Ohkubo, T.; Wen, Z. C.; Ishioka, K.; Mandal, R.; Medapalli, R.; Sukegawa, H.; Mitani, S.; Fullerton, E. E.; Hono, K.

2017-06-01

We estimated the magnetic damping constant α of Co2FeAl (CFA) Heusler alloy films of different thicknesses with an MgO capping layer by means of time-resolved magneto-optical Kerr effect and ferromagnetic resonance measurements. CFA films with thicknesses of 1.2 nm and below exhibited perpendicular magnetic anisotropy arising from the presence of the interface with MgO. While α increased gradually with decreasing CFA film thickness down to 1.2 nm, it was increased substantially when the thickness was reduced further to 1.0 nm. Based on the microstructure analyses and first-principles calculations, we attributed the origin of the large α in the ultrathin CFA film primarily to the Al deficiency in the CFA layer, which caused an increase in the density of states and thereby in the scatterings of their spins.

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.

Effect of thermal fatigue on the structure and properties of Ni3Al-based alloy single crystals

NASA Astrophysics Data System (ADS)

Povarova, K. B.; Drozdov, A. A.; Bazyleva, O. A.; Bulakhtina, M. A.; Alad'ev, N. A.; Antonova, A. V.; Arginbaeva, E. G.; Morozov, A. E.

2014-05-01

The effect of thermal fatigue during tests of <001> and <111> single crystals according to the schedules 100 ai 850°C, 100 ai 1050°C, 100 ai 1100°C at a peak-to-peak stress Δσtc = 700-1000 MPa (sum of the maximum tensile and compressive stresses in a thermal cycle) on the structure, the fracture, and the fatigue life of an Ni3Al-based VKNA-1V alloy is studied. It is found that, at 103 thermal cycles, the <111> single crystals have the maximum thermal fatigue resistance at the maximum cycle temperature of 850 and 1050°C, and the properties of the <001> and <111> samples are almost the same at the maximum thermal cycle temperature of 1100°C. After thermal cycling at the maximum temperature of 850°C, the γ layers in the two-phase γ' + γ region in dendrites remain a single-phase structure, as in the as-cast material, and the layer thickness is 100-150 nm. When the maximum thermal cycle temperature increases to 1050 or 1100°C, the discontinuous γ-phase layers in the γ'(Ni3Al) matrix change their morphology and become shorter and wider (their thickness is 300-700 nm). The nickel-based supersaturated solid solution in these layers decomposes with the formation of secondary γ'(Ni3Al)-phase (γ'sec) precipitates in the form of cuboids 50 and 100 nm in size at the maximum cycle temperature of 1050 and 1100°C, respectively. The alternating stresses that appear during thermal cycling cause plastic deformation. As in nickel superalloys, this deformation at the first stage proceeds via the slip of screw dislocations along octahedral {111} planes. Networks of 60° dislocation segments form at γ'/γ interfaces in this case. Fracture begins at the lines of intersection of the slip planes of the {111} octahedron with the sample surface. During fractional, a crack passes from one octahedral plane to another and forms terraces and steps (crystallographic fracture); as a result, the fracture surface bends and becomes curved. In all cases, the fracture surfaces have a mixed brittle-ductile character with a combination of crystallographic and ductile (dimple) fracture elements.

Research on subsurface deformed layer in ultra-precision cutting of single crystal copper by focused ion beam etching method

NASA Astrophysics Data System (ADS)

Chen, Y.; Huang, X. J.; Kong, J. X.

2018-03-01

In this paper, the focused ion beam was used to study the subsurface deformed layer of single crystal copper caused by the nanoscale single-point diamond fly cutting, and the possibility of using nanometer ultra-precision cutting to remove the larger deformation layer caused by traditional rough cutting process was explored. The maximum cutting thickness of single-point diamond cutting was about 146 nm, and the surface of the single-crystal copper after cutting was etched and observed by using the focused ion beam method. It was found that the morphology of the near-surface layer and the intermediate layer of the copper material were larger differences: the near-surface of the material was smaller and more compact, and the intermediate material layer of the material was more coarse sparse. The results showed that the traditional precision cutting would residual significant subsurface deformed layer and the thickness was on micron level. Even more, the subsurface deformed layer was obviously removed from about 12μm to 5μm after single-point diamond fly cutting in this paper. This paper proved that the large-scale subsurface deformed layer caused by traditional cutting process could be removed by nanometer ultra-precision cutting. It was of great significance to further establish the method that control of the deformation of weak rigid components by reducing the depth of the subsurface deformed layers.

Effects of the PPy layer thickness on Co-PPy composite films

NASA Astrophysics Data System (ADS)

Haciismailoglu, Murside

2015-11-01

Co-PPy composite films were electrodeposited on ITO substrate from two different solutions potentiostatically. Firstly, the PPy layers with the thicknesses changing from 20 to 5000 nm were produced on ITO. Then Co was electrodeposited on these PPy/ITO substrates with a charge density of 1000 mC cm-2. The electrochemical properties were investigated by the current density-time transients and the variation of the elapsed time for the Co deposition depending on the PPy layer thickness. X-ray photoelectron (XPS) spectra indicated the presence of both Co metal and its oxides on the surface. The weak reflections of the Co3O4, CoO and hcp Co were detected by the X-ray diffraction (XRD) technique. According to scanning electron microscopy (SEM) images, the thickness of the PPy layer strongly affects the Co nucleation. The composite films with the PPy layer thinner than 200 nm and thicker than 2000 nm have an isotropic magnetic behavior due to the symmetrical crystal field. The composite films with the PPy layer thicknesses between 200 and 2000 nm have an anisotropic magnetic behavior attributable to the deterioration of this symmetrical crystal field by the PPy bubbles on the surface. All films are hard magnetic material, since the coercivities are larger than 125 Oe.

Observation of positive and small electron affinity of Si-doped AlN films grown by metalorganic chemical vapor deposition on n-type 6H-SiC

NASA Astrophysics Data System (ADS)

Feng, Liang; Ping, Chen; De-Gang, Zhao; De-Sheng, Jiang; Zhi-Juan, Zhao; Zong-Shun, Liu; Jian-Jun, Zhu; Jing, Yang; Wei, Liu; Xiao-Guang, He; Xiao-Jing, Li; Xiang, Li; Shuang-Tao, Liu; Hui, Yang; Li-Qun, Zhang; Jian-Ping, Liu; Yuan-Tao, Zhang; Guo-Tong, Du

2016-05-01

We have investigated the electron affinity of Si-doped AlN films (N Si = 1.0 × 1018-1.0 × 1019 cm-3) with thicknesses of 50, 200, and 400 nm, synthesized by metalorganic chemical vapor deposition (MOCVD) under low pressure on the n-type (001)6H-SiC substrates. The positive and small electron affinity of AlN films was observed through the ultraviolet photoelectron spectroscopy (UPS) analysis, where an increase in electron affinity appears with the thickness of AlN films increasing, i.e., 0.36 eV for the 50-nm-thick one, 0.58 eV for the 200-nm-thick one, and 0.97 eV for the 400-nm-thick one. Accompanying the x-ray photoelectron spectroscopy (XPS) analysis on the surface contaminations, it suggests that the difference of electron affinity between our three samples may result from the discrepancy of surface impurity contaminations. Project supported by the National Natural Science Foundation of China (Grant Nos. 61574135, 61574134, 61474142, 61474110, 61377020, 61376089, 61223005, and 61321063), the One Hundred Person Project of the Chinese Academy of Sciences, and the Basic Research Project of Jiangsu Province, China (Grant No. BK20130362).

Structural and optical properties of CuS thin films deposited by Thermal co-evaporation

NASA Astrophysics Data System (ADS)

Sahoo, A. K.; Mohanta, P.; Bhattacharyya, A. S.

2015-02-01

Copper sulfide (CuS) thin films with thickness 100, 150 and 200 nm have been deposited on glass substrates by thermal co-evaporation of Copper and Sulphur. The effect of CuS film thickness on the structural and optical properties have investigated and discussed. Structural and optical investigations of the films were carried out by X-ray diffraction, atomic force microscopy, high-resolution transmission electron microscopy and UV spectroscopy. XRD and selected area electron diffraction conforms that polycrystalline in nature with hexagonal crystal structure. AFM studies revealed a smooth surface morphology with root mean-square roughness values increases from 24 nm to 42 nm as the film thickness increase from 100 nm to 200 nm. AFM image showed that grain size increases with thickness of film increases and good agreement with the calculated from full width half maximum of the X-ray diffraction peak using Scherrer's formula and Williamson-Hall plot. The absorbance of the thin films were absorbed decreases with wavelength through UV-visible regions but showed a increasing in the near-infrared regions. The reflectance spectra also showed lower reflectance peak (25% to 32%) in visible region and high reflectance peak (49 % to 54 %) in near-infrared region. These high absorbance films made them for photo-thermal conversion of solar energy.

Structural phase diagram for ultra-thin epitaxial Fe 3O 4 / MgO(0 01) films: thickness and oxygen pressure dependence

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

Alraddadi, S.; Hines, W.; Yilmaz, T.

2016-02-19

A systematic investigation of the thickness and oxygen pressure dependence for the structural properties of ultra-thin epitaxial magnetite (Fe 3O 4) films has been carried out; for such films, the structural properties generally differ from those for the bulk when the thickness ≤10 nm. Iron oxide ultra-thin films with thicknesses varying from 3 nm to 20 nm were grown on MgO (001) substrates using molecular beam epitaxy under different oxygen pressures ranging from 1 × 10 -7 torr to 1 × 10 -5 torr. The crystallographic and electronic structures of the films were characterized using low energy electron diffraction (LEED)more » and x-ray photoemission spectroscopy (XPS), respectively. Moreover, the quality of the epitaxial Fe 3O 4 ultra-thin films was judged by magnetic measurements of the Verwey transition, along with complementary XPS spectra. We observed that under the same growth conditions the stoichiometry of ultra-thin films under 10 nm transforms from the Fe 3O 4 phase to the FeO phase. In this work, a phase diagram based on thickness and oxygen pressure has been constructed to explain the structural phase transformation. It was found that high-quality magnetite films with thicknesses ≤20 nm formed within a narrow range of oxygen pressure. An optimal and controlled growth process is a crucial requirement for the accurate study of the magnetic and electronic properties for ultra-thin Fe 3O 4 films. Furthermore, these results are significant because they may indicate a general trend in the growth of other oxide films, which has not been previously observed or considered.« less

[Studies on the saliva adsorption and the salivary film property on the hydroxyapatite surface].

PubMed

Yao, Jiang-wu; Chen, Guo-yang; Lin, Feng; Lin, Chang-jian; Tao, Tao

2012-07-01

To evaluate the thickness and viscoelasticity of whole saliva (WS), parotid saliva (PS) and submandibular/sublingual gland saliva (SMSLS) film adsorption on the hydroxyapatite (HA) surface. Ultra-thin layer of HA nanocrystals was coated on the dissipation TiO(2) sensor of gold quartz crystal microbalance using electrophoretic deposition technique. The thickness of the HA layer was measured by the ellipsometer, and element analysis was conducted using X-ray photoelectron spectroscopy. Atomic force microscopy and scanning electron microscope were used to observe its morphology. The in-situ adsorption thickness, the shear elastic modulus and the shear viscosity of salivary layers (WS, PS and SMSLS) on HA surfaces were investigated. The statistical data were analysed by an one-way ANOVA analysis followed by a SNK-q test. The results show that the HA layer was a plate-like morphology with 1.53 ± 0.12 in Ca/P molar ratio, (19.1 ± 0.9) nm in the thickness and (6.5 ± 1.6) nm in the roughness. The thickness of salivary film was SMSLS [(21.84 ± 1.25) nm] > WS[(17.91 ± 1.35) nm] > PS [(14.30 ± 1.03 nm) (P < 0.05). The shear elastic modulus of salivary film was PS [(0.61 ± 0.01) MPa] > SMSLS [(0.31 ± 0.09) MPa] and WS [(0.25 ± 0.03) MPa] (P < 0.05). The trend of the shear viscosity was opposite to one of thickness. The characteristics of saliva adsorption on HA surface suggest that the thicker, softer and more hydrated properties for the SMSLS and WS films are likely to afford a stronger lubrication to protect oral surfaces from wear and dehydration. The viscoelasticity of the PS film is probably related to the retention covering the oral cavity.

Electron density and currents of AlN/GaN high electron mobility transistors with thin GaN/AlN buffer layer

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

Bairamis, A.; Zervos, Ch.; Georgakilas, A., E-mail: alexandr@physics.uoc.gr

2014-09-15

AlN/GaN high electron mobility transistor (HEMT) structures with thin GaN/AlN buffer layer have been analyzed theoretically and experimentally, and the effects of the AlN barrier and GaN buffer layer thicknesses on two-dimensional electron gas (2DEG) density and transport properties have been evaluated. HEMT structures consisting of [300 nm GaN/ 200 nm AlN] buffer layer on sapphire were grown by plasma-assisted molecular beam epitaxy and exhibited a remarkable agreement with the theoretical calculations, suggesting a negligible influence of the crystalline defects that increase near the heteroepitaxial interface. The 2DEG density varied from 6.8 × 10{sup 12} to 2.1 × 10{sup 13} cm{sup −2} as themore » AlN barrier thickness increased from 2.2 to 4.5 nm, while a 4.5 nm AlN barrier would result to 3.1 × 10{sup 13} cm{sup −2} on a GaN buffer layer. The 3.0 nm AlN barrier structure exhibited the highest 2DEG mobility of 900 cm{sup 2}/Vs for a density of 1.3 × 10{sup 13} cm{sup −2}. The results were also confirmed by the performance of 1 μm gate-length transistors. The scaling of AlN barrier thickness from 1.5 nm to 4.5 nm could modify the drain-source saturation current, for zero gate-source voltage, from zero (normally off condition) to 0.63 A/mm. The maximum drain-source current was 1.1 A/mm for AlN barrier thickness of 3.0 nm and 3.7 nm, and the maximum extrinsic transconductance was 320 mS/mm for 3.0 nm AlN barrier.« less

New magnetic phase and magnetic coherence in Nd/Sm(001) superlattices

NASA Astrophysics Data System (ADS)

Soriano, S.; Dufour, C.; Dumesnil, K.; Stunault, A.

2006-06-01

In order to investigate magnetic phenomena in Nd and Sm layers separately, resonant x-ray magnetic scattering experiments have been performed to study Nd/Sm(001) superlattices with different relative layers thickness. The samples were grown using molecular beam epitaxy, and optimized to yield dhcp Sm growth and thus a coherent dhcp stacking across the Nd/Sm superlattices. The magnetic phases in Sm layers are very close to the ones evidenced in dhcp thick films. In contrast, the magnetism in Nd layers shows strong differences with the bulk case. In superlattices with a large Sm thickness (>8 nm), no magnetic scattering usually associated with Nd magnetic structure was detected. In superlattices with smaller Sm thickness (<4 nm), new Nd magnetic phases have been observed. A detailed analysis of the propagation of the magnetic structures in the cubic and hexagonal sublattices of both Sm and Nd is presented. Both Sm hexagonal and cubic magnetic phases propagate coherently through 3.7 nm thick Nd layers but remain confined in Sm layers when the Nd layers are 7.1 nm thick. In contrast, the critical Sm thickness allowing a coherent propagation of Nd magnetic order is different for the hexagonal and cubic sublattices above 5 K. Finally, we show that: (i) a spin-density wave and a 4f magnetic order with perpendicular polarization are exclusive on a given crystallographic site (either hexagonal or cubic); (ii) a 4f magnetic order on a crystallographic site does not perturb the establishment of a spin-density wave with a perpendicular polarization on the other site.

Martian airfall dust on smooth, inclined surfaces as observed on the Phoenix Mars Lander telltale mirror

NASA Astrophysics Data System (ADS)

Moores, John E.; Ha, Taesung; Lemmon, Mark T.; Gunnlaugsson, Haraldur Páll

2015-10-01

The telltale mirror, a smooth inclined surface raised over 1 m above the deck of the Phoenix Mars Lander, was observed by the Surface Stereo Imager (SSI) several times per sol during the Phoenix Mars Lander mission. These observations were combined with a radiative transfer model to determine the thickness of dust on the wind telltale mirror as a function of time. 239 telltale sequences were analyzed and dustiness was determined on a diurnal and seasonal basis. The thickness of accumulated dust did not follow any particular diurnal or seasonal trend. The dust thickness on the mirror over the mission was 0.82±0.39 μm, which suggests a similar thickness to the modal scattering particle diameter. This suggests that inclining a surface beyond the angle of repose and polishing it to remove surface imperfections is an effective way to mitigate the accumulation of dust to less than a micron over a wide range of meteorological conditions and could be beneficial for surfaces which can tolerate some dust but not thick accumulations, such as solar panels. However, such a surface will not remain completely dust free through this action alone and mechanical or electrical clearing must be employed to remove adhered dust if a pristine surface is required. The single-scattering phase function of the dust on the mirror was consistent with the single-scattering phase function of martian aerosol dust at 450 nm, suggesting that this result is inconsistent with models of the atmosphere which require vertically or horizontally separated components or broad size distributions to explain the scattering behavior of these aerosols in the blue. The single-scattering behavior of the dust on the mirror is also consistent with Hapke modeling of spherical particles. The presence of a monolayer of particles would tend to support the spherical conclusion: such particles would be most strongly adhered electrostatically.

Highly Efficient White Organic Light Emitting Diodes Using New Blue Fluorescence Emitter.

PubMed

Kim, Seungho; Kim, Beomjin; Lee, Jaehyun; Yu, Young-Jun; Park, Jongwook

2015-07-01

Two different emitting compounds, 1-[1,1';3',1"]Terphenyl-5'-yl-6-(10-[1,1';3',1"]terpheny-5'-yl- anthracen-9-yl)-pyrene (TP-AP-TP) and Poly-phenylene vinylene derivative (PDY 132) were used to white OLED device. By incorporating adjacent blue and yellow emitting layers in a multi-layered structure, highly efficient white emission has been attained. The device was fabricated with a hybrid configuration structure: ITO/PEDOT (40 nm)/PDY-132 (8-50 nm)/ NPB (10 nm)/TP-AP-TP (30 nm)/Alq3 (20 nm)/LiF (1 nm)/Al (200 nm). After fixing TP-AP-TP thickness of 30 nm by evaporation, PDY-132 thickness varied with 8, 15, 35, and 50 nm by spin coating in device. The luminance efficiency of the white devices at 10 mA/cm2 were 2.93 cd/A-6.55 cd/A. One of white devices showed 6.55 cd/A and white color of (0.290, 0.331).

Direct evidence of single quantum dot emission from GaN islands formed at threading dislocations using nanoscale cathodoluminescence: A source of single photons in the ultraviolet

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

Schmidt, Gordon, E-mail: Gordon.Schmidt@ovgu.de; Berger, Christoph; Veit, Peter

2015-06-22

Intense emission from GaN islands embedded in AlN resulting from GaN/AlN quantum well growth is directly resolved by performing cathodoluminescence spectroscopy in a scanning transmission electron microscope. Line widths down to 440 μeV are measured in a wavelength region between 220 and 310 nm confirming quantum dot like electronic properties in the islands. These quantum dot states can be structurally correlated to islands of slightly enlarged thicknesses of the GaN/AlN quantum well layer preferentially formed in vicinity to dislocations. The quantum dot states exhibit single photon emission in Hanbury Brown-Twiss experiments with a clear antibunching in the second order correlation function atmore » zero time delay.« less

Stripe domains and magnetoresistance in thermally deposited nickel films

NASA Astrophysics Data System (ADS)

Sparks, P. D.; Stern, N. P.; Snowden, D. S.; Kappus, B. A.; Checkelsky, J. G.; Harberger, S. S.; Fusello, A. M.; Eckert, J. C.

2004-05-01

We report a study of the domain structure and magnetoresistance of thermally deposited nickel films. For films thicker than 17nm, we observe striped domains with period varying with film thickness as a power law with exponent 0.21+/-0.02 up to 120nm thickness. There is a negative magnetoresistance for fields out of the plane.

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.

Molecular beam epitaxy of large-area SnSe2 with monolayer thickness fluctuation

NASA Astrophysics Data System (ADS)

Park, Young Woon; Jerng, Sahng-Kyoon; Jeon, Jae Ho; Roy, Sanjib Baran; Akbar, Kamran; Kim, Jeong; Sim, Yumin; Seong, Maeng-Je; Kim, Jung Hwa; Lee, Zonghoon; Kim, Minju; Yi, Yeonjin; Kim, Jinwoo; Noh, Do Young; Chun, Seung-Hyun

2017-03-01

The interest in layered materials is largely based on the expectation that they will be beneficial for a variety of applications, from low-power-consuming, wearable electronics to energy harvesting. However, the properties of layered materials are highly dependent on thickness, and the difficulty of controlling thickness over a large area has been a bottleneck for commercial applications. Here, we report layer-by-layer growth of SnSe2, a layered semiconducting material, via van der Waals epitaxy. The films were fabricated on insulating mica substrates with substrate temperatures in the range of 210 °C-370 °C. The surface consists of a mixture of N and (N ± 1) layers, showing that the thickness of the film can be defined with monolayer accuracy (±0.6 nm). High-resolution transmission electron microscopy reveals a polycrystalline film with a grain size of ˜100 nm and clear Moiré patterns from overlapped grains with similar thickness. We also report field effect mobility values of 3.7 cm2 V-1 s-1 and 6.7 cm2 V-1 s-1 for 11 and 22 nm thick SnSe2, respectively. SnSe2 films with customizable thickness can provide valuable platforms for industry and academic researchers to fully exploit the potential of layered materials.

Growth mechanism, surface and optical properties of ZnO nanostructures deposited on various Au-seeded thickness obtained by mist-atomization

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

Afaah, A. N., E-mail: afaahabdullah@yahoo.com; Aadila, A., E-mail: aadilaazizali@gmail.com; Asib, N. A. M., E-mail: amierahasib@yahoo.com

2016-07-06

In this paper, growth mechanisms of ZnO nanostructures on non-seeded glass, 6 nm and 12 nm Au seed layer obtained by mist-atomization was proposed. ZnO films were successfully deposited on glass substrate with different thickness of Au seed layer i.e. 6 nm and 12 nm. The surface and optical properties of the prepared samples were investigated using Field emission scanning electron microscopy (FESEM) and photoluminescence (PL). FESEM micrograph show that ZnO nanostructure deposited on 6 nm Au seed layer has uniform formation and well distributed. From PL spectroscopy, the UV emission shows that ZnO deposited on 6 nm Au seedmore » layer has the more intense UV intensity which proved that high crystal quality of nanostructured ZnO deposited on 6 nm Au seed layer.« less

Mechanical characteriztion of single-stranded DNA and single-walled carbon nanotube hybrid structures

NASA Astrophysics Data System (ADS)

Rokadia, Husein Juzer

Hybrid nanostructures of single-stranded DNA (ssDNA) and single-walled carbon nanotubes are being proposed as the basis for the next generation of biosensors. For such biosensors, mechanical properties such as the Young's modulus of the hybrid structures play a critical role, which to the best of the author's knowledge is still unknown. Thus, the determination of the Young's modulus of the ssDNA/swCNT hybrid structures was the primary objective of this study. Hybrid structures of 30mer polyT ssDNA and HiPCORTM swCNTs were conjugated using a well known non-covalent interaction protocol. Atomic force microscopy (AFM) was used to scan and generate topographic images and perform nanoindentation tests on the hybrid structures. Molecular dynamics (MD) simulations using a commercial MD program, Materials StudioRTM were performed to study the nature of non-covalent interactions between the ssDNA and the swCNT on the pico-second timescale. AFM topography scans of the bare control HiPCORTM swCNTs indicated an average diameter of about 1.0 nm and length of 800 nm. Similarly, the control 30mer polyT ssDNA was found to resemble a half-hemispherical domed structure with an average height of 2.1 nm. Nanoindentation tests yielded the transverse Young's modulus of the control swCNTs to be 78.0 GPa. The control ssDNA were found to have a Young's modulus of 3.3 GPa and 4.0 MPa in dry and wet environments, respectively. Topographic scans of the ssDNA/swCNT hybrid structures showed the slender swCNTs fully or partially coated along their lengths by ssDNA. The height of the hybrid structures ranged from 2.5 nm to 7.5 nm. Nanoindentation tests on the ssDNA coated portions of the hybrid structures indicated that, their Young's modulus exponentially decreased with increasing coating thickness. Thinly coated sections were found to have a Young's modulus of 100.0 GPa and 7.0 MPa in dry and wet conditions respectively. The thick walled hybrid sections were found to have an average Young's modulus of 4.5 GPa and 1.0 GPa in the dry and wet environments, respectively. MD results indicated that the wrapping of the ssDNA had a significant impact on the hybrid structures. The longitudinal Young's modulus of a hybrid structure was found to be approximately 50.0 GPa, compared to a bare nanotube whose Young's modulus was approximately 800 GPa. Overall, the experimental and numerical results displayed consistent trends. The experimental results reported the swCNTs to have the highest transverse Young's modulus followed by the hybrids and the ssDNA. Similarly, the numerical simulations predicted the highest longitudinal Young's modulus for the swCNTs, followed by the hybrids and the DNA.

Electrical, structural and optical properties of tellurium thin films on silicon substrate

NASA Astrophysics Data System (ADS)

Arora, Swati; Vijay, Y. K.

2018-05-01

Tellurium (Te) thin films of various thicknesses (200nm, 275nm, 350nm & 500nm) were prepared on Silicon (Si) using thermal evaporation at vacuum of 10-5 torr. It is observed that the resistivity decreases exponentially with the Increases Temperature. A direct band gap between 0.368 eV to 0.395 eV is obtained at different temperatures with Four Probe Method which shows that when we increase the thickness of material the band gap will exponentially decreases. Samples were analysed through X-ray diffraction and atomic force microscopy to attain complete and reliable micro structural in order.

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

Lee, Taehoon; Jung, Yong Chan; Seong, Sejong

The metal gate electrodes of Ni, W, and Pt have been investigated for their scavenging effect: a reduction of the GeO{sub x} interfacial layer (IL) between HfO{sub 2} dielectric and Ge substrate in metal/HfO{sub 2}/GeO{sub x}/Ge capacitors. All the capacitors were fabricated using the same process except for the material used in the metal electrodes. Capacitance-voltage measurements, scanning transmission electron microscopy, and electron energy loss spectroscopy were conducted to confirm the scavenging of GeO{sub x} IL. Interestingly, these metals are observed to remotely scavenge the interfacial layer, reducing its thickness in the order of Ni, W, and then Pt. Themore » capacitance equivalent thickness of these capacitors with Ni, W, and Pt electrodes are evaluated to be 2.7 nm, 3.0 nm, and 3.5 nm, and each final remnant physical thickness of GeO{sub x} IL layer is 1.1 nm 1.4 nm, and 1.9 nm, respectively. It is suggested that the scavenging effect induced by the metal electrodes is related to the concentration of oxygen vacancies generated by oxidation reaction at the metal/HfO{sub 2} interface.« less

Analysis and optimization of RC delay in vertical nanoplate FET

NASA Astrophysics Data System (ADS)

Woo, Changbeom; Ko, Kyul; Kim, Jongsu; Kim, Minsoo; Kang, Myounggon; Shin, Hyungcheol

2017-10-01

In this paper, we have analyzed short channel effects (SCEs) and RC delay with Vertical nanoplate FET (VNFET) using 3-D Technology computer-aided design (TCAD) simulation. The device is based on International Technology Road-map for Semiconductor (ITRS) 2013 recommendations, and it has initially gate length (LG) of 12.2 nm, channel thickness (Tch) of 4 nm, and spacer length (LSD) of 6 nm. To obtain improved performance by reducing RC delay, each dimension is adjusted (LG = 12.2 nm, Tch = 6 nm, LSD = 11.9 nm). It has each characteristic in this dimension (Ion/Ioff = 1.64 × 105, Subthreshold swing (S.S.) = 73 mV/dec, Drain-induced barrier lowering (DIBL) = 60 mV/V, and RC delay = 0.214 ps). Furthermore, with long shallow trench isolation (STI) length and thick insulator thickness (Ti), we can reduce RC delay from 0.214 ps to 0.163 ps. It is about a 23.8% reduction. Without decreasing drain current, there is a reduction of RC delay as reducing outer fringing capacitance (Cof). Finally, when source/drain spacer length is set to be different, we have verified RC delay to be optimum.

Effects of pressure and deposition time on the characteristics of In2Se3 films grown by magnetron sputtering

NASA Astrophysics Data System (ADS)

Yan, Yong; Li, Shasha; Ou, Yufeng; Ji, Yaxin; Yu, Zhou; Liu, Lian; Yan, Chuanpeng; Zhang, Yong; Zhao, Yong

2014-11-01

Crystalline In2Se3 films were fabricated by magnetron sputtering from a sintered In2Se3-compound target and the effects of the deposition parameters, including the working pressure and deposition time, on the phase composition, structure, morphology, and optical properties were clarified. Single-phase κ-In2Se3 was prepared at 4.0 Pa, but γ-In2Se3 was recognized when the working pressure was lower than 4.0 Pa. The optical transmittance of the films decreased to 45% and the optical band gap varied from 2.9 to 2.0 eV with increasing film thickness from 80 to 967 nm. Metal-semiconductor-metal (MSM) photodetectors based on γ-In2Se3 thin films with various thicknesses were also fabricated. The result of photosensitivity research on such MSM photodetectors suggests that it may be impossible to fabricate wide-absorption-range MSM devices by just using a single material ( γ-In2Se3) because of spatial potential fluctuations in the layers. [Figure not available: see fulltext.

Effect of Channel Thickness, Annealing Temperature and Channel Length on Nanoscale Ga2O3-In2O3-ZnO Thin Film Transistor Performance.

PubMed

Kumaresan, Yogeenth; Pak, Yusin; Lim, Namsoo; Lee, Ryeri; Song, Hui; Kim, Tae Heon; Choi, Boran; Jung, Gun Young

2016-06-01

We demonstrated the effect of active layer (channel) thickness and annealing temperature on the electrical performances of Ga2O3-In2O3-ZnO (GIZO) thin film transistor (TFT) having nanoscale channel width (W/L: 500 nm/100 μm). We found that the electron carrier concentration of the channel was decreased significantly with increasing the annealing temperature (100 degrees C to 300 degrees C). Accordingly, the threshold voltage (V(T)) was shifted towards positive voltage (-12.2 V to 10.8 V). In case of channel thickness, the V(T) was shifted towards negative voltage with increasing the channel thickness. The device with channel thickness of 90 nm annealed at 200 degrees C revealed the best device performances in terms of mobility (10.86 cm2/Vs) and V(T) (0.8 V). The effect of channel length was also studied, in which the channel width, thickness and annealing temperature were kept constant such as 500 nm, 90 nm and 200 degrees C, respectively. The channel length influenced the on-current level significantly with small variation of V(T), resulting in lower value of on/off current ratio with increasing the channel length. The device with channel length of 0.5 μm showed enhanced on/off current ratio of 10(6) with minimum V(T) of 0.26 V.

GaN microring waveguide resonators bonded to silicon substrate by a two-step polymer process.

PubMed

Hashida, Ryohei; Sasaki, Takashi; Hane, Kazuhiro

2018-03-20

Using a polymer bonding technique, GaN microring waveguide resonators were fabricated on a Si substrate for future hybrid integration of GaN and Si photonic devices. The designed GaN microring consisted of a rib waveguide having a core of 510 nm in thickness, 1000 nm in width, and a clad of 240 nm in thickness. A GaN crystalline layer of 1000 nm in thickness was grown on a Si(111) substrate by metal organic chemical vapor deposition using a buffer layer of 300 nm in thickness for the compensation of lattice constant mismatch between GaN and Si crystals. The GaN/Si wafer was bonded to a Si(100) wafer by a two-step polymer process to prevent it from trapping air bubbles. The bonded GaN layer was thinned from the backside by a fast atom beam etching to remove the buffer layer and to generate the rib waveguides. The transmission characteristics of the GaN microring waveguide resonators were measured. The losses of the straight waveguides were measured to be 4.0±1.7  dB/mm around a wavelength of 1.55 μm. The microring radii ranged from 30 to 60 μm, where the measured free-spectral ranges varied from 2.58 to 5.30 nm. The quality factors of the microring waveguide resonators were from 1710 to 2820.

Simple electrodepositing of CoFe/Cu multilayers: Effect of ferromagnetic layer thicknesses

NASA Astrophysics Data System (ADS)

Tekgül, Atakan; Alper, Mürsel; Kockar, Hakan

2017-01-01

The CoFe/Cu magnetic multilayers were produced by changing CoFe ferromagnetic layers from 3 nm to 10 nm using electrodeposition. By now, the thinnest Cu (0.5 nm) layer thicknesses were used to see whether the GMR effect in the multilayers can be obtained or not since the pinning of non-magnetic layer between the ferromagnetic layers is required. For the proper depositions, the cyclic voltammograms was used, and the current-time transients were obtained. The Cu and CoFe layers were deposited at a cathode potential of -0.3 and -1.5 V with respect to saturated calomel electrode, respectively. From the XRD patterns, the multilayers were shown to be fcc crystal structures. For the magnetization measurements, saturation magnetization increases from 160 to 600 kA/m from 3 to 8 nm ferromagnetic layer thicknesses. And, the coercivity values increase until the 8 nm of the CoFe layer thickness. It is seen that the thin Cu layer (fixed at 0.5 nm) and pinholes support the random magnetization orientation and thus all multilayers exhibited the giant magnetoresistance (GMR) effect, and the highest GMR value was observed about 5.5%. And, the variation of GMR field sensitivity was calculated. The results show that the GMR and GMR sensitivity are compatible among the multilayers. The CoFe/Cu magnetic multilayers having GMR properties are used in GMR sensors and hard disk drive of the nano-technological devices.

Synthesis of subnanometer-diameter vertically aligned single-walled carbon nanotubes with copper-anchored cobalt catalysts.

PubMed

Cui, Kehang; Kumamoto, Akihito; Xiang, Rong; An, Hua; Wang, Benjamin; Inoue, Taiki; Chiashi, Shohei; Ikuhara, Yuichi; Maruyama, Shigeo

2016-01-21

We synthesize vertically aligned single-walled carbon nanotubes (VA-SWNTs) with subnanometer diameters on quartz (and SiO2/Si) substrates by alcohol CVD using Cu-anchored Co catalysts. The uniform VA-SWNTs with a nanotube diameter of 1 nm are synthesized at a CVD temperature of 800 °C and have a thickness of several tens of μm. The diameter of SWNTs was reduced to 0.75 nm at 650 °C with the G/D ratio maintained above 24. Scanning transmission electron microscopy energy-dispersive X-ray spectroscopy (EDS-STEM) and high angle annular dark field (HAADF-STEM) imaging of the Co/Cu bimetallic catalyst system showed that Co catalysts were captured and anchored by adjacent Cu nanoparticles, and thus were prevented from coalescing into a larger size, which contributed to the small diameter of SWNTs. The correlation between the catalyst size and the SWNT diameter was experimentally clarified. The subnanometer-diameter and high-quality SWNTs are expected to pave the way to replace silicon for next-generation optoelectronic and photovoltaic devices.