Biosensors Based on Ultrathin Film Composite Membranes

DTIC Science & Technology

1994-01-25

composite membranes should have a number C •’ of potential advantages including fast response time, simplicity of construction, and applicability to a number...The support membrane for the ultrathin film composite was an Anopore ( Alltech Associates) microporous alumina filter, these membranes are 55 Pm thick...constant 02 concentration in this solution. Finally, one of the most important potential advantage of a sensor based on an ultrathin film composite

Effect of heat treatment on interface driven magnetic properties of CoFe films

NASA Astrophysics Data System (ADS)

Singh, Akhilesh Kr.; Hsu, Jen-Hwa

2017-06-01

We report systematic studies on non-magnetic Ta underlayer and cap layer driven microstructural and magnetic properties at a wide temperature range for CoFe films. All the films were grown at room temperature and post annealed at different annealing temperatures (TA = 200 °C, 250 °C, 300 °C, 350 °C, 400 °C and 450 °C). The in-plane magnetic hysteresis (M-H) loops of 10 nm thick CoFe single layer films, grown directly on thermally oxidized Si substrate, exhibit anisotropic nature for TA above 250 °C. However, the CoFe (10 nm) films grown on the 5 nm thick Ta underlayer show reduced anisotropy. Moreover, with underlayer and cap layers (2 nm) the anisotropy is disappeared. The in-plane coercivity (HC) shows a strong variation with TA, underlayer and cap layers. HC increases significantly with Ta underlayer and cap layers. The out of plane M-H loops exhibit increase in the remanence magnetization and squareness with both Ta underlayer and cap layers due to transition of in-plane magnetization component to the out of plane direction. The atomic force microscopic observations revealed that grain/particle size and shape depend strongly on TA and Ta layers. Moreover, a large reduction in the surface roughness is observed with the Ta cap layer. The magnetic domain patterns depend on the TA, and Ta layers. However, for Ta/CoFe/Ta films no clear domains were observed for all the TA. Hence, the Ta cap layers not only protect the CoFe magnetic layer against the heat treatment, but also show a smooth surface at a wide temperature range. These results could be discussed on the basis of random anisotropy model, TA, underlayer and cap layers driven microstructure and magnetization orientation of the CoFe films.

Two-dimensional tantalum disulfide: controlling structure and properties via synthesis

NASA Astrophysics Data System (ADS)

Zhao, Rui; Grisafe, Benjamin; Krishna Ghosh, Ram; Holoviak, Stephen; Wang, Baoming; Wang, Ke; Briggs, Natalie; Haque, Aman; Datta, Suman; Robinson, Joshua

2018-04-01

Tantalum disulfide (TaS2) is a transition metal dichalcogenide (TMD) that exhibits phase transition induced electronic property modulation at low temperature. However, the appropriate phase must be grown to enable the semiconductor/metal transition that is of interest for next generation electronic applications. In this work, we demonstrate direct and controllable synthesis of ultra-thin 1T-TaS2 and 2H-TaS2 on a variety of substrates (sapphire, SiO2/Si, and graphene) via powder vapor deposition. The synthesis process leads to single crystal domains ranging from 20 to 200 nm thick and 1-10 µm on a side. The TaS2 phase (1T or 2H) is controlled by synthesis temperature, which subsequently is shown to control the electronic properties. Furthermore, this work constitutes the first demonstration of a metal-insulator phase transition in directly synthesized 1T-TaS2 films and domains by electronic means.

Effect of ultra-thin liner materials on copper nucleation/wetting and copper grain growth

NASA Astrophysics Data System (ADS)

Mueller, Justin E.

One of the key challenges facing future integrated circuit copper (Cu) interconnect manufacturing is to achieve uniform coverage of PVD Cu seed layer at minimum thickness on a liner and barrier. We have therefore characterized the nucleation and wetting of PVD Cu on various liner surfaces by monitoring in-situ the film's electrical conductance during the initial stages of deposition (0 to 25 nm). Our results showed that the Cu wetting is sensitive to the Cu/liner interfacial properties, while the nucleation depends on the liner microstructure. It was found that a ruthenium (Ru) liner has a good Cu wetting characteristic and allows at the onset nearly layer by layer Cu growth. Because of good wetting, Cu growth is not significantly affected by Ru liner grain size. Tantalum (Ta), however, exhibits poor Cu wetting, which results in an initial stage of three dimensional island growth of Cu. In this case, Cu island coalescing occurs sooner, at a smaller Cu film thickness, when the nucleation site density is increased with a smaller grain size Ta liner. To optimize the seed layer's conductance and step coverage, a liner with combined properties of Ta (for adhesion and barrier formation) and Ru (for wetting and grain growth) may be desired. A hybrid magnetron target has been developed for depositing TaRu liner films at various compositions. The microstructure of the compound liners and their effects on the overgrown Cu seed layer over a wide range of TaRu composition is presented. It was found that below 80% Ru concentration, TaRu films are amorphous. An amorphous liner results in poor Cu nucleation as compared with a crystalline Ta or Ru liner. A comparison of the microstructure of thin Cu films deposited on bcc alpha-Ta and tetragonal beta-Ta surfaces has been carried out. Cu resistivity is lower by 10-15%, accompanied by larger Cu grain size, in as-deposited Cu films of various thickness' (30-120 nm) on beta-Ta as compared to those deposited on alpha-Ta. This is due to the presence of an epitaxial relationship between Cu (111) and beta-Ta (002) planes. After annealing, the difference was only seen in films thinner than 60 nm. Results were confirmed when Cu film resistance was measured in-situ during deposition on each phase of Ta liner. Serpentine interconnect line structures of various line widths and aspect ratios were fabricated using either alpha- or beta-Ta liners, and subjected to a similar heat treatment. Results showed a similar ˜10% lower resistivity in the thinnest interconnects (˜40 nm) when a beta-Ta liner was used.

The effect of growth sequence on magnetization damping in Ta/CoFeB/MgO structures

NASA Astrophysics Data System (ADS)

Liu, Bo; Huang, Dawei; Gao, Ming; Tu, Hongqing; Wang, Kejie; Ruan, Xuezhong; Du, Jun; Cai, Jian-Wang; He, Liang; Wu, Jing; Wang, Xinran; Xu, Yongbing

2018-03-01

Magnetization damping is a key parameter to control the critical current and the switching speed in magnetic random access memory, and here we report the effect of the growth sequence on the magnetic dynamics properties of perpendicularly magnetized Ta/CoFeB/MgO structures. Ultrathin CoFeB films have been grown between Ta and MgO but with different stack sequences, i.e. substrate/Ta/CoFeB/MgO/Ta and substrate/Ta/MgO/CoFeB/Ta. The magnetization dynamics induced by femtosecond laser was investigated by using all-optical pump-probe measurements. We found that the Gilbert damping constant was modulated by reversing stack structures, which offers the potential to tune the damping parameter by the growth sequence. The Gilbert damping constant was enhanced from 0.017 for substrate/Ta/CoFeB/MgO/Ta to 0.027 for substrate/Ta/MgO/CoFeB/Ta. We believe that this enhancement originates from the increase of intermixing at the CoFeB/Ta when the Ta atom layer was grown after the CoFeB layer.

Physical properties of spin-valve films grown on naturally oxidized metal nano-oxide surfaces

NASA Astrophysics Data System (ADS)

Mao, Ming; Cerjan, Charlie; Kools, Jacques

2002-05-01

The physical properties of spin-valve films NiFe 25 Å/CoFe 10 Å/Cu(tCu)/CoFe 30 Å/IrMn 70 Å/Ta 20 Å with graded Cu layer thickness (tCu=18-45 Å) grown on the surface of metal nano-oxide layers (NOLs) were studied. The NOLs were formed from ultrathin Al, Cr, Cu, Nb, Ta, CoFe, NiFe, and NiFeCr layers by natural oxidation. The growth of the spin-valve films on NOLs has led to an enhancement in giant magnetoresistance value by up to 48%. A corresponding reduction in minimum film resistance by over 10% confirms that this enhancement originates from an increase in the mean free path of spin-polarized electrons due to the resultant specular reflection at the nano-oxide surfaces. A wide spectrum of oscillatory interlayer exchange coupling dependence on tCu for these NOL-bearing films suggests that a specular nano-oxide surface does not necessarily result in a smoother multilayer structure. The observation of an enhanced exchange biasing among these spin-valve films appears in contradiction to the observed deterioration of their crystallographic quality. As an important application, TaOx, CrOx, and NbOx could be employed as an alternative to AlOx as the barrier layer for magnetic tunnel junctions.

Oxidation processes in magneto-optic and related materials

NASA Technical Reports Server (NTRS)

Lee, Paul A.; Armstrong, Neal R.; Danzinger, James L.; England, Craig D.

1992-01-01

The surface oxidation processes of thin films of magneto-optic materials, such as the rare-earth transition metal alloys have been studied, starting in ultrahigh vacuum environments, using surface analysis techniques, as a way of modeling the oxidation processes which occur at the base of a defect in an overcoated material, at the instant of exposure to ambient environments. Materials examined have included FeTbCo alloys, as well as those same materials with low percentages of added elements, such a Ta, and their reactivities to both O2 and H2O compared with materials such as thin Fe films coated with ultrathin adlayers of Ti. The surface oxidation pathways for these materials is reviewed, and XPS data presented which indicates the type of oxides formed, and a critical region of Ta concentration which provides optimum protection.

A molecular dynamics analysis of ion irradiation of ultrathin amorphous carbon films

NASA Astrophysics Data System (ADS)

Qi, J.; Komvopoulos, K.

2016-09-01

Molecular dynamics (MD) simulations provide insight into nanoscale problems where continuum description breaks down, such as the modeling of ultrathin films. Amorphous carbon (a-C) films are commonly used as protective overcoats in various contemporary technologies, including microelectromechanical systems, bio-implantable devices, optical lenses, and hard-disk drives. In all of these technologies, the protective a-C film must be continuous and very thin. For example, to achieve high storage densities (e.g., on the order of 1 Tb/in.2) in magnetic recording, the thickness of the a-C film used to protect the magnetic media and the recording head against mechanical wear and corrosion must be 2-3 nm. Inert ion irradiation is an effective post-deposition method for reducing the film thickness, while preserving the mechanical and chemical characteristics. In this study, MD simulations of Ar+ ion irradiated a-C films were performed to elucidate the effects of the ion incidence angle and ion kinetic energy on the film thickness and structure. The MD results reveal that the film etching rate exhibits a strong dependence on the ion kinetic energy and ion incidence angle, with a maximum etching rate corresponding to an ion incidence angle of ˜20°. It is also shown that Ar+ ion irradiation mainly affects the structure of the upper half of the ultrathin a-C film and that carbon atom hybridization is a strong function of the ion kinetic energy and ion incidence angle. The results of this study elucidate the effects of important ion irradiation parameters on the structure and thickness of ultrathin films and provide fundamental insight into the physics of dry etching.

Platelet adhesion on phosphorus-incorporated tetrahedral amorphous carbon films

NASA Astrophysics Data System (ADS)

Liu, Aiping; Zhu, Jiaqi; Liu, Meng; Dai, Zhifei; Han, Xiao; Han, Jiecai

2008-11-01

The haemocompatibility of phosphorus-incorporated tetrahedral amorphous carbon (ta-C:P) films, synthesized by filtered cathodic vacuum arc technique with PH 3 as the dopant source, was assessed by in vitro platelet adhesion tests. Results based on scanning electron microscopy and contact angle measurements reveal that phosphorus incorporation improves the wettability and blood compatibility of ta-C film. Our studies may provide a novel approach for the design and synthesis of doped ta-C films to repel platelet adhesion and reduce thrombosis risk.

Variable substrate temperature deposition of CoFeB film on Ta for manipulating the perpendicular coercive forces

NASA Astrophysics Data System (ADS)

Lakshmanan, Saravanan; Rao, Subha Krishna; Muthuvel, Manivel Raja; Chandrasekaran, Gopalakrishnan; Therese, Helen Annal

2017-08-01

Magnetization of Ta/CoFeB/Ta trilayer films with thick layer of CoFeB deposited under different substrate temperatures (Ts) via ultra-high vacuum DC sputtering technique has been measured with the applied magnetic field parallel and perpendicular to the plane of the film respectively to study the perpendicular coercive forces of the film. The samples were further analyzed for its structural, topological, morphological, and electrical transport properties. The core chemical states for the elements present in the CoFeB thin film were analyzed by XPS studies. Magnetization studies reveal the existence of perpendicular coercive forces in CoFeB films deposited only at certain temperatures such as RT, 450 °C, 475 °C and 500 °C. CoFeB film deposited at 475 °C exhibited a maximum coercivity of 315 Oe and a very low saturation magnetization (Ms) of 169 emu/cc in perpendicular direction. This pronounced effect in perpendicular coercive forces observed for CoFeB475 could be attributed to the effect of temperature in enhancing the crystallization of the film at the Ta/CoFeB interfaces. However at temperatures higher than 475 °C the destruction of the Ta/CoFeB interface due to intermixing of Ta and CoFeB results in the disappearance of magnetic anisotropy.

Skin dose for head and neck cancer patients treated with intensity-modulated radiation therapy(IMRT)

NASA Astrophysics Data System (ADS)

Fu, Hsiao-Ju; Li, Chi-Wei; Tsai, Wei-Ta; Chang, Chih-Chia; Tsang, Yuk-Wah

2017-11-01

The reliability of thermoluminescent dosimeters (ultrathin TLD) and ISP Gafchromic EBT2 film to measure the surface dose in phantom and the skin dose in head-and-neck patients treated with intensity-modulated radiation therapy technique(IMRT) is the research focus. Seven-field treatment plans with prescribed dose of 180 cGy were performed on Eclipse treatment planning system which utilized pencil beam calculation algorithm(PBC). In calibration tests, the variance coefficient of the ultrathin TLDs were within 3%. The points on the calibration curve of the Gafchromic film was within 1% variation. Five measurements were taken on phantom using ultrathin TLD and EBT2 film respectively. The measured mean surface doses between ultrathin TLD or EBT2 film were within 5% deviation. Skin doses of 6 patients were measured for initial 5 fractions and the mean dose per-fraction was calculated. If the extrapolated doses for 30 fractions were below 4000 cGy, the skin reaction grading observed according to Radiation Therapy Oncology Group (RTOG) was either grade 1 or grade 2. If surface dose exceeded 5000 cGy in 32 fractions, then grade 3 skin reactions were observed.

"Un-annealed and Annealed Pd Ultra-Thin Film on SiC Characterized by Scanning Probe Microscopy and X-ray Photoelectron Spectroscopy"

NASA Technical Reports Server (NTRS)

Lu, W. J.; Shi, D. T.; Elshot, K.; Bryant, E.; Lafate, K.; Chen, H.; Burger, A.; Collins, W. E.

1998-01-01

Pd/SiC has been used as a hydrogen and a hydrocarbon gas sensor operated at high temperature. UHV (Ultra High Vacuum)-Scanning Tunneling Microscopy (STM), Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) techniques were applied to study the relationship between the morphology and chemical compositions for Pd ultra-thin films on SiC (less than 30 angstroms) at different annealing temperatures. Pd ultra-thin film on 6H-SiC was prepared by the RF sputtering method. The morphology from UHV-STM and AFM shows that the Pd thin film was well deposited on SiC substrate, and the Pd was partially aggregated to round shaped participates at an annealing temperature of 300 C. At 400 C, the amount of surface participates decreases, and some strap shape participates appear. From XPS, Pd2Si was formed on the surface after annealing at 300 C, and all Pd reacted with SiC to form Pd2Si after annealing at 400 C. The intensity of the XPS Pd peak decreases enormously at 400 C. The Pd film diffused into SiC, and the Schottky barrier height has almost no changes. The work shows the Pd sicilides/SiC have the same electronic properties with Pd/SiC, and explains why the Pd/SiC sensor still responds to hydrogen at high operating temperatures.

Ultrathin Carbon Film Protected Silver Nanostructures for Surface-Enhanced Raman Scattering.

PubMed

Peng, Yinshan; Zheng, Xianliang; Tian, Hongwei; Cui, Xiaoqiang; Chen, Hong; Zheng, Weitao

2016-06-23

In this article, ultrathin carbon film protected silver substrate (Ag/C) was prepared via a plasma-enhanced chemical vapor deposition (PECVD) method. The morphological evolution of silver nanostructures underneath, as well as the surface-enhanced Raman scattering (SERS) activity of Ag/C hybrid can be tuned by controlling the deposition time. The stability and reproducibility of the as-prepared hybrid were also studied. © The Author(s) 2016.

Defect-free erbium silicide formation using an ultrathin Ni interlayer.

PubMed

Choi, Juyun; Choi, Seongheum; Kang, Yu-Seon; Na, Sekwon; Lee, Hoo-Jeong; Cho, Mann-Ho; Kim, Hyoungsub

2014-08-27

An ultrathin Ni interlayer (∼1 nm) was introduced between a TaN-capped Er film and a Si substrate to prevent the formation of surface defects during thermal Er silicidation. A nickel silicide interfacial layer formed at low temperatures and incurred uniform nucleation and the growth of a subsequently formed erbium silicide film, effectively inhibiting the generation of recessed-type surface defects and improving the surface roughness. As a side effect, the complete transformation of Er to erbium silicide was somewhat delayed, and the electrical contact property at low annealing temperatures was dominated by the nickel silicide phase with a high Schottky barrier height. After high-temperature annealing, the early-formed interfacial layer interacted with the growing erbium silicide, presumably forming an erbium silicide-rich Er-Si-Ni mixture. As a result, the electrical contact property reverted to that of the low-resistive erbium silicide/Si contact case, which warrants a promising source/drain contact application for future high-performance metal-oxide-semiconductor field-effect transistors.

Metal Immiscibility Route to Synthesis of Ultrathin Carbides, Borides, and Nitrides.

PubMed

Wang, Zixing; Kochat, Vidya; Pandey, Prafull; Kashyap, Sanjay; Chattopadhyay, Soham; Samanta, Atanu; Sarkar, Suman; Manimunda, Praveena; Zhang, Xiang; Asif, Syed; Singh, Abhisek K; Chattopadhyay, Kamanio; Tiwary, Chandra Sekhar; Ajayan, Pulickel M

2017-08-01

Ultrathin ceramic coatings are of high interest as protective coatings from aviation to biomedical applications. Here, a generic approach of making scalable ultrathin transition metal-carbide/boride/nitride using immiscibility of two metals is demonstrated. Ultrathin tantalum carbide, nitride, and boride are grown using chemical vapor deposition by heating a tantalum-copper bilayer with corresponding precursor (C 2 H 2 , B powder, and NH 3 ). The ultrathin crystals are found on the copper surface (opposite of the metal-metal junction). A detailed microscopy analysis followed by density functional theory based calculation demonstrates the migration mechanism, where Ta atoms prefer to stay in clusters in the Cu matrix. These ultrathin materials have good interface attachment with Cu, improving the scratch resistance and oxidation resistance of Cu. This metal-metal immiscibility system can be extended to other metals to synthesize metal carbide, boride, and nitride coatings. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Interfacial structure and electrical properties of ultrathin HfO2 dielectric films on Si substrates by surface sol-gel method

NASA Astrophysics Data System (ADS)

Gong, You-Pin; Li, Ai-Dong; Qian, Xu; Zhao, Chao; Wu, Di

2009-01-01

Ultrathin HfO2 films with about ~3 nm thickness were deposited on n-type (1 0 0) silicon substrates using hafnium chloride (HfCl4) source by the surface sol-gel method and post-deposition annealing (PDA). The interfacial structure and electrical properties of ultrathin HfO2 films were investigated. The HfO2 films show amorphous structures and smooth surface morphologies with a very thin interfacial oxide layer of ~0.5 nm and small surface roughness (~0.45 nm). The 500 °C PDA treatment forms stronger Hf-O bonds, leading to passivated traps, and the interfacial layer is mainly Hf silicate (HfxSiyOz). Equivalent oxide thickness of around 0.84 nm of HfO2/Si has been obtained with a leakage current density of 0.7 A cm-2 at Vfb + 1 V after 500 °C PDA. It was found that the current conduction mechanism of HfO2/Si varied from Schottky-Richardson emission to Fowler-Nordheim tunnelling at an applied higher positive voltage due to the activated partial traps remaining in the ultrathin HfO2 films.

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

Iyer, Ajai, E-mail: ajai.iyer@aalto.fi; Etula, Jarkko; Liu, Xuwen

Single walled carbon nanotube networks (SWCNTNs) were coated by tetrahedral amorphous carbon (ta-C) to improve the mechanical wear properties of the composite film. The ta-C deposition was performed by using pulsed filtered cathodic vacuum arc method resulting in the generation of C+ ions in the energy range of 40–60 eV which coalesce to form a ta-C film. The primary disadvantage of this process is a significant increase in the electrical resistance of the SWCNTN post coating. The increase in the SWCNTN resistance is attributed primarily to the intrinsic stress of the ta-C coating which affects the inter-bundle junction resistance between themore » SWCNTN bundles. E-beam evaporated carbon was deposited on the SWCNTNs prior to the ta-C deposition in order to protect the SWCNTN from the intrinsic stress of the ta-C film. The causes of changes in electrical resistance and the effect of evaporated carbon thickness on the changes in electrical resistance and mechanical wear properties have been studied.« less

Interface perpendicular magnetic anisotropy in ultrathin Ta/NiFe/Pt layered structures

NASA Astrophysics Data System (ADS)

Hirayama, Shigeyuki; Kasai, Shinya; Mitani, Seiji

2018-01-01

Interface perpendicular magnetic anisotropy (PMA) in ultrathin Ta/NiFe/Pt layered structures was investigated through magnetization measurements. Ta/NiFe/Pt films with NiFe layer thickness (t) values of 2 nm or more showed typical in-plane magnetization curves, which was presumably due to the dominant contribution of the shape magnetic anisotropy. The thickness dependence of the saturation magnetization of the entire NiFe layer (M s) was well analyzed using the so-called dead-layer model, showing that the magnetically active part of the NiFe layer has saturation magnetization (M\\text{s}\\text{act}) independent of t and comparable to the bulk value. In the perpendicular direction, the saturation field H k was found to clearly decrease with decreasing t, while the effective field of shape magnetic anisotropy due to the active NiFe saturation magnetization M\\text{s}\\text{act} should be independent of t. These observations show that there exists interface PMA in the layered structures. The interface PMA energy density was determined to be ∼0.17 erg/cm2 using the dead-layer model. Motivated by the correlation observed between M s and H k, we also attempted to interpret the experimental results using an alternative approach beyond the dead-layer model; however, it gives only implications on the incomplete validity of the dead-layer model and no better understanding.

Phase Composition of Samarium Niobate and Tantalate Thin Films Prepared by Sol-Gel Method

NASA Astrophysics Data System (ADS)

Bruncková, H.; Medvecký, Ľ.; Múdra, E.; Kovalčiková, A.; Ďurišin, J.; Šebek, M.; Girman, V.

2017-12-01

Samarium niobate SmNbO4 (SNO) and tantalate SmTaO4 (STO) thin films ( 100 nm) were prepared by sol-gel/spin-coating process on alumina substrates with PZT interlayer and annealing at 1000°C. The precursors of films were synthesized using Nb or Ta tartrate complexes. The improvement of the crystallinity of monoclinic M'-SmTaO4 phase via heating was observed through the coexistence of small amounts of tetragonal T-SmTa7O19 phase in STO precursor at 1000°C. The XRD results of SNO and STO films confirmed monoclinic M-SmNbO4 and M'-SmTaO4 phases, respectively, with traces of orthorhombic O-SmNbO4 (in SNO). In STO film, the single monoclinic M'-SmTaO4 phase was revealed. The surface morphology and topography of thin films were investigated by SEM and AFM analysis. STO film was smoother with roughness 3.2 nm in comparison with SNO (6.3 nm). In the microstructure of SNO film, small spherical ( 50 nm) and larger cuboidal particles ( 100 nm) of the SmNbO4 phase were observed. In STO, compact clusters composed of fine spherical SmTaO4 particles ( 20-50 nm) were found. Effect of samarium can contribute to the formation different polymorphs of these films for the application to environmental electrolytic thin film devices.

Tribological Behaviour of Ti:Ta-DLC Films Under Different Tribo-Test Conditions

NASA Astrophysics Data System (ADS)

Efeoglu, İhsan; Keleş, Ayşenur; Totik, Yaşar; Çiçek, Hikmet; Emine Süküroglu, Ebru

2018-01-01

Diamond-like carbon (DLC) films are suitable applicants for cutting tools due to their high hardness, low friction coefficient and wear rate. Doping metals in DLC films have been improved its tribological properties. In this study, titanium and tantalum doped hydrogenated DLC films were deposited by closed-field unbalanced magnetron sputtering system onto M2 high speed steels in Ar/N2/C2H2 atmosphere. The friction and wear properties of Ti:Ta-DLC film were investigated under different tribo-test conditions including in atmospheric pressure, distilled water, commercial oil and Ar atmosphere. The coated specimens were characterized by SEM and X-ray diffraction techniques. The bonding state of C-C (sp3) and C=C (sp2) were obtained with XPS. The tribological properties of Ti:Ta-DLC were investigated with pin-on-disc wear test. Hardness measurements performed by micro-indentation. Our results suggest that Ti:Ta-doped DLC film shows very dense columnar microstructure, high hardness (38.2 GPa) with low CoF (µ≈0.02) and high wear resistance (0.5E-6 mm3/Nm).

FABRICATION AND OPTOELECTRONIC PROPERTIES OF MgxZn1-xO ULTRATHIN FILMS BY LANGMUIR-BLODGETT TECHNOLOGY

NASA Astrophysics Data System (ADS)

Tang, Dongyan; Feng, Qian; Jiang, Enying; He, Baozhu

2012-08-01

By transferring MgxZn1-xO sol and stearic acid onto a hydrophilic silicon wafer or glass plate, the Langmuir-Blodgett (LB) multilayers of MgxZn1-xO (x:0, 0.2, 0.4) were deposited. After calcinations at 350°C for 0.5 h and at 500°C for 3 h, MgxZn1-xO ultrathin films were fabricated. The optimized parameters for monolayer formation and multilayer deposition were determined by the surface pressure-surface (Π-A) area and the transfer coefficient, respectively. The expended areas of stearic acid with MgxZn1-xO sols under Π-A isotherms inferred the interaction of stearic acid with MgxZn1-xO sols during the formation of monolayer at air-water interface. X-ray diffraction (XRD) was used to determine the crystal structures of MgxZn1-xO nanoparticles and ultrathin films. The surface morphologies of MgxZn1-xO ultrathin films were observed by scanning probe microscopy (AFM). And the optoelectronic properties of MgxZn1-xO were detected and discussed based on photoluminescence (PL) spectra.

Diffusion barrier properties of single- and multilayered quasi-amorphous tantalum nitride thin films against copper penetration

NASA Astrophysics Data System (ADS)

Chen, G. S.; Chen, S. T.

2000-06-01

Tantalum-related thin films containing different amounts of nitrogen are sputter deposited at different argon-to-nitrogen flow rate ratios on (100) silicon substrates. Using x-ray diffractometry, transmission electron microscopy, composition and resistivity analyses, and bending-beam stress measurement technique, this work examines the impact of varying the nitrogen flow rate, particularly on the crystal structure, composition, resistivity, and residual intrinsic stress of the deposited Ta2N thin films. With an adequate amount of controlled, reactive nitrogen in the sputtering gas, thin films of the tantalum nitride of nominal formula Ta2N are predominantly amorphous and can exist over a range of nitrogen concentrations slightly deviated from stoichiometry. The single-layered quasi-amorphous Ta2N (a-Ta2N) thin films yield intrinsic compressive stresses in the range 3-5 GPa. In addition, the use of the 40-nm-thick a-Ta2N thin films with different nitrogen atomic concentrations (33% and 36%) and layering designs as diffusion barriers between silicon and copper are also evaluated. When subjected to high-temperature annealing, the single-layered a-Ta2N barrier layers degrade primarily by an amorphous-to-crystalline transition of the barrier layers. Crystallization of the single-layered stoichiometric a-Ta2N (Ta67N33) diffusion barriers occurs at temperatures as low as 450 °C. Doing so allows copper to preferentially penetrate through the grain boundaries or thermal-induced microcracks of the crystallized barriers and react with silicon, sequentially forming {111}-facetted pyramidal Cu3Si precipitates and TaSi2 Overdoping nitrogen into the amorphous matrix can dramatically increase the crystallization temperature to 600 °C. This temperature increase slows down the inward diffusion of copper and delays the formation of both silicides. The nitrogen overdoped Ta2N (Ta64N36) diffusion barriers can thus be significantly enhanced so as to yield a failure temperature 100 °C greater than that of the Ta67N33 diffusion barriers. Moreover, multilayered films, formed by alternately stacking the Ta67N33 and Ta64N36 layers with an optimized bilayer thickness (λ) of 10 nm, can dramatically reduce the intrinsic compressive stress to only 0.7 GPa and undergo high-temperature annealing without crystallization. Therefore, the Ta67N33/Ta64N36 multilayered films exhibit a much better barrier performance than the highly crystallization-resistant Ta64N36 single-layered films.

Room Temperature Ferroelectricity in Ultrathin SnTe Films

NASA Astrophysics Data System (ADS)

Chang, Kai; Liu, Junwei; Lin, Haicheng; Zhao, Kun; Zhong, Yong; Ji, Shuai-Hua; He, Ke; Wang, Lili; Ma, Xucun; Fu, Liang; Chen, Xi; Xue, Qi-Kun

2015-03-01

The ultrathin SnTe films with several unit cell thickness grown on graphitized SiC(0001) surface have been studied by the scanning tunneling microscopy and spectroscopy (STM/S). The domain structures, local lattice distortion and the electronic band bending at film edges induced by the in-plane spontaneous polarization along < 110 > have been revealed at atomic scale. The experiments at variant temperature show that the Curie temperature Tc of the one unit cell thick (two atomic layers) SnTe film is as high as 280K, much higher than that of the bulk counterpart (~100K) and the 2-4 unit cell thick films even indicate robust ferroelectricity at room temperature. This Tc enhancement is attributed to the stress-free interface, larger electronic band gap and greatly reduced Sn vacancy concentration in the ultrathin films. The lateral domain size varies from several tens to several hundreds of nanometers, and the spontaneous polarization direction could be modified by STM tip. Those properties of ultrathin SnTe films show the potential application on ferroelectric devices. The work was financially supported by Ministry of Science and Technology of China, National Science Foundation and Ministry of Education of China.

Ultrathin pyrolytic carbon films on a magnetic substrate

NASA Astrophysics Data System (ADS)

Umair, Ahmad; Raza, Tehseen Z.; Raza, Hassan

2016-07-01

We report the growth of ultrathin pyrolytic carbon (PyC) films on nickel substrate by using chemical vapor deposition at 1000 °C under methane ambience. We find that the ultra-fast cooling is crucial for PyC film uniformity by controlling the segregation of carbon on nickel. We characterize the in-plane crystal size of the PyC film by using Raman spectroscopy. The Raman peaks at ˜1354 and ˜1584 cm-1 wavenumbers are used to extract the D and G bands. The corresponding peak intensities are then used in an excitation energy dependent equation to calculate the in-plane crystal size. Using Raman area mapping, the mean value of in-plane crystal size over an area of 100 μm × 100 μm is about 22.9 nm with a standard deviation of about 2.4 nm.

320-nm Flexible Solution-Processed 2,7-dioctyl[1] benzothieno[3,2-b]benzothiophene Transistors.

PubMed

Ren, Hang; Tang, Qingxin; Tong, Yanhong; Liu, Yichun

2017-08-09

Flexible organic thin-film transistors (OTFTs) have received extensive attention due to their outstanding advantages such as light weight, low cost, flexibility, large-area fabrication, and compatibility with solution-processed techniques. However, compared with a rigid substrate, it still remains a challenge to obtain good device performance by directly depositing solution-processed organic semiconductors onto an ultrathin plastic substrate. In this work, ultrathin flexible OTFTs are successfully fabricated based on spin-coated 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) films. The resulting device thickness is only ~320 nm, so the device has the ability to adhere well to a three-dimension curved surface. The ultrathin C8-BTBT OTFTs exhibit a mobility as high as 4.36 cm² V -1 s -1 and an on/off current ratio of over 10⁶. These results indicate the substantial promise of our ultrathin flexible C8-BTBT OTFTs for next-generation flexible and conformal electronic devices.

320-nm Flexible Solution-Processed 2,7-dioctyl[1] benzothieno[3,2-b]benzothiophene Transistors

PubMed Central

Ren, Hang; Tang, Qingxin; Tong, Yanhong; Liu, Yichun

2017-01-01

Flexible organic thin-film transistors (OTFTs) have received extensive attention due to their outstanding advantages such as light weight, low cost, flexibility, large-area fabrication, and compatibility with solution-processed techniques. However, compared with a rigid substrate, it still remains a challenge to obtain good device performance by directly depositing solution-processed organic semiconductors onto an ultrathin plastic substrate. In this work, ultrathin flexible OTFTs are successfully fabricated based on spin-coated 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) films. The resulting device thickness is only ~320 nm, so the device has the ability to adhere well to a three-dimension curved surface. The ultrathin C8-BTBT OTFTs exhibit a mobility as high as 4.36 cm2 V−1 s−1 and an on/off current ratio of over 106. These results indicate the substantial promise of our ultrathin flexible C8-BTBT OTFTs for next-generation flexible and conformal electronic devices. PMID:28792438

Plasma-enhanced pulsed-laser deposition of single-crystalline M o2C ultrathin superconducting films

NASA Astrophysics Data System (ADS)

Zhang, Fan; Zhang, Zhi; Wang, Huichao; Chan, Cheuk Ho; Chan, Ngai Yui; Chen, Xin Xin; Dai, Ji-Yan

2017-08-01

Transition-metal carbides (TMCs) possess many intriguing properties and inspiring application potentials, and recently the study of a two-dimensional form of TMCs has attracted great attention. Herein, we report successful fabrication of continuous M o2C ultrathin single-crystalline films at 700 ∘C with an approach of plasma-enhanced pulsed-laser deposition. By sophisticated structural analyses, the M o2C films are characterized as single crystal with a rarely reported face-centered cubic structure. In further electrical transport measurements, superconductivity observed in the M o2C films demonstrates a typical two-dimensional feature, which is consistent with Berezinskii-Kosterlitz-Thouless transitions. Besides, large upper critical magnetic fields are discovered in this system. Our work offers an approach to grow large-area and high-quality TMCs at relatively low temperatures. This study may stimulate more related investigations on the synthesis, characterizations, and applications of two-dimensional TMCs.

Fabrication of Ultra-thin Color Films with Highly Absorbing Media Using Oblique Angle Deposition.

PubMed

Yoo, Young Jin; Lee, Gil Ju; Jang, Kyung-In; Song, Young Min

2017-08-29

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.  We present an advanced method for fabricating ultra-thin color films with improved characteristics. The proposed process addresses several fabrication issues, including large area processing. Specifically, the protocol describes a process for fabricating ultra-thin color films using an electron beam evaporator for oblique angle deposition of germanium (Ge) and gold (Au) on silicon (Si) substrates.  Film porosity produced by the oblique angle deposition induces color changes in the ultra-thin film. The degree of color change depends on factors such as deposition angle and film thickness. Fabricated samples of the ultra-thin color films showed improved color tunability and color purity. In addition, the measured reflectance of the fabricated samples was converted into chromatic values and analyzed in terms of color. Our ultra-thin film fabricating method is expected to be used for various ultra-thin film applications such as flexible color electrodes, thin film solar cells, and optical filters. Also, the process developed here for analyzing the color of the fabricated samples is broadly useful for studying various color structures.

Coupling of microphase separation and dewetting in weakly segregated diblock co-polymer ultrathin films.

PubMed

Yan, Derong; Huang, Haiying; He, Tianbai; Zhang, Fajun

2011-10-04

We have studied the coupling behavior of microphase separation and autophobic dewetting in weakly segregated poly(ε-caprolactone)-block-poly(L-lactide) (PCL-b-PLLA) diblock co-polymer ultrathin films on carbon-coated mica substrates. At temperatures higher than the melting point of the PLLA block, the co-polymer forms a lamellar structure in bulk with a long period of L ∼ 20 nm, as determined using small-angle X-ray scattering. The relaxation procedure of ultrathin films with an initial film thickness of h = 10 nm during annealing has been followed by atomic force microscopy (AFM). In the experimental temperature range (100-140 °C), the co-polymer dewets to an ultrathin film of itself at about 5 nm because of the strong attraction of both blocks with the substrate. Moreover, the dewetting velocity increases with decreasing annealing temperatures. This novel dewetting kinetics can be explained by a competition effect of the composition fluctuation driven by the microphase separation with the dominated dewetting process during the early stage of the annealing process. While dewetting dominates the relaxation procedure and leads to the rupture of the ultrathin films, the composition fluctuation induced by the microphase separation attempts to stabilize them because of the matching of h to the long period (h ∼ 1/2L). The temperature dependence of these two processes leads to this novel relaxation kinetics of co-polymer thin films. © 2011 American Chemical Society

Interfacial Control of Dzyaloshinskii-Moriya Interaction in Heavy Metal/Ferromagnetic Metal Thin Film Heterostructures

NASA Astrophysics Data System (ADS)

Ma, Xin; Yu, Guoqiang; Li, Xiang; Wang, Tao; Wu, Di; Olsson, Kevin; Chu, Zhaodong; An, Kyongmo; Xiao, John; Wang, Kang; Li, Xiaoqin

The interfacial Dzyaloshinskii-Moriya Interaction (DMI) in ultrathin magnetic thin film heterostructures provides a new approach for controlling spin textures on mesoscopic length scales. Here we investigate the dependence of the interfacial DMI constant D on a Pt wedge insertion layer in Ta/CoFeB/Pt(wedge)/MgO thin films by observing the asymmetric spin wave dispersion using Brillouin light scattering. Continuous tuning of D by more than a factor of three is realized by inserting less than one monolayer of Pt. The observations provide new insights for designing magnetic thin film heterostructures with tailored D for controlling skyrmions and magnetic domain wall chirality and dynamics. The work at UT-Austin and UCLA are supported by SHINES, an Energy Frontier Research Center funded by the U.S. DoE, Office of Science, Basic Energy Science (BES) under award # DE-SC0012670.

Magneto-ionic effect in CoFeB thin films with in-plane and perpendicular-to-plane magnetic anisotropy

NASA Astrophysics Data System (ADS)

Baldrati, L.; Tan, A. J.; Mann, M.; Bertacco, R.; Beach, G. S. D.

2017-01-01

The magneto-ionic effect is a promising method to control the magnetic properties electrically. Charged mobile oxygen ions can easily be driven by an electric field to modify the magnetic anisotropy of a ferromagnetic layer in contact with an ionic conductor in a solid-state device. In this paper, we report on the room temperature magneto-ionic modulation of the magnetic anisotropy of ultrathin CoFeB films in contact with a GdOx layer, as probed by polar micro-Magneto Optical Kerr Effect during the application of a voltage across patterned capacitors. Both Pt/CoFeB/GdOx films with perpendicular magnetic anisotropy and Ta/CoFeB/GdOx films with uniaxial in-plane magnetic anisotropy in the as-grown state exhibit a sizable dependence of the magnetic anisotropy on the voltage (amplitude, polarity, and time) applied across the oxide. In Pt/CoFeB/GdOx multilayers, it is possible to reorient the magnetic anisotropy from perpendicular-to-plane to in-plane, with a variation of the magnetic anisotropy energy greater than 0.2 mJ m-2. As for Ta/CoFeB/GdOx multilayers, magneto-ionic effects still lead to a sizable variation of the in-plane magnetic anisotropy, but the anisotropy axis remains in-plane.

Scaling of structure and electrical properties in ultrathin epitaxial ferroelectric heterostructures

NASA Astrophysics Data System (ADS)

Nagarajan, V.; Junquera, J.; He, J. Q.; Jia, C. L.; Waser, R.; Lee, K.; Kim, Y. K.; Baik, S.; Zhao, T.; Ramesh, R.; Ghosez, Ph.; Rabe, K. M.

2006-09-01

Scaling of the structural order parameter, polarization, and electrical properties was investigated in model ultrathin epitaxial SrRuO3/PbZr0.2Ti0.8O3/SrRuO3/SrTiO3 heterostructures. High-resolution transmission electron microscopy images revealed the interfaces to be sharp and fully coherent. Synchrotron x-ray studies show that a high tetragonality (c /a˜1.058) is maintained down to 50Å thick films, suggesting indirectly that ferroelectricity is fully preserved at such small thicknesses. However, measurement of the switchable polarization (ΔP) using a pulsed probe setup and the out-of-plane piezoelectric response (d33) revealed a systematic drop from ˜140μC/cm2 and 60pm/V for a 150Å thick film to 11μC/cm2 and 7pm/V for a 50Å thick film. This apparent contradiction between the structural measurements and the measured switchable polarization is explained by an increasing presence of a strong depolarization field, which creates a pinned 180° polydomain state for the thinnest films. Existence of a polydomain state is demonstrated by piezoresponse force microscopy images of the ultrathin films. These results suggest that the limit for a ferroelectric memory device may be much larger than the fundamental limit for ferroelectricity.

Impact of laser power density on tribological properties of Pulsed Laser Deposited DLC films

NASA Astrophysics Data System (ADS)

Gayathri, S.; Kumar, N.; Krishnan, R.; AmirthaPandian, S.; Ravindran, T. R.; Dash, S.; Tyagi, A. K.; Sridharan, M.

2013-12-01

Fabrication of wear resistant and low friction carbon films on the engineered substrates is considered as a challenging task for expanding the applications of diamond-like carbon (DLC) films. In this paper, pulsed laser deposition (PLD) technique is used to deposit DLC films on two different types of technologically important class of substrates such as silicon and AISI 304 stainless steel. Laser power density is one of the important parameter used to tailor the fraction of sp2 bonded amorphous carbon (a-C) and tetrahedral amorphous carbon (ta-C) made by sp3 domain in the DLC film. The I(D)/I(G) ratio decreases with the increasing laser power density which is associated with decrease in fraction of a-C/ta-C ratio. The fraction of these chemical components is quantitatively analyzed by EELS which is well supported to the data obtained from the Raman spectroscopy. Tribological properties of the DLC are associated with chemical structure of the film. However, the super low value of friction coefficient 0.003 is obtained when the film is predominantly constituted by a-C and sp2 fraction which is embedded within the clusters of ta-C. Such a particular film with super low friction coefficient is measured while it was deposited on steel at low laser power density of 2 GW/cm2. The super low friction mechanism is explained by low sliding resistance of a-C/sp2 and ta-C clusters. Combination of excellent physical and mechanical properties of wear resistance and super low friction coefficient of DLC films is desirable for engineering applications. Moreover, the high friction coefficient of DLC films deposited at 9GW/cm2 is related to widening of the intergrain distance caused by transformation from sp2 to sp3 hybridized structure.

Optimization of ion-atomic beam source for deposition of GaN ultrathin films.

PubMed

Mach, Jindřich; Šamořil, Tomáš; Kolíbal, Miroslav; Zlámal, Jakub; Voborny, Stanislav; Bartošík, Miroslav; Šikola, Tomáš

2014-08-01

We describe the optimization and application of an ion-atomic beam source for ion-beam-assisted deposition of ultrathin films in ultrahigh vacuum. The device combines an effusion cell and electron-impact ion beam source to produce ultra-low energy (20-200 eV) ion beams and thermal atomic beams simultaneously. The source was equipped with a focusing system of electrostatic electrodes increasing the maximum nitrogen ion current density in the beam of a diameter of ≈15 mm by one order of magnitude (j ≈ 1000 nA/cm(2)). Hence, a successful growth of GaN ultrathin films on Si(111) 7 × 7 substrate surfaces at reasonable times and temperatures significantly lower (RT, 300 °C) than in conventional metalorganic chemical vapor deposition technologies (≈1000 °C) was achieved. The chemical composition of these films was characterized in situ by X-ray Photoelectron Spectroscopy and morphology ex situ using Scanning Electron Microscopy. It has been shown that the morphology of GaN layers strongly depends on the relative Ga-N bond concentration in the layers.

Controlled Growth of Ultrathin Film of Organic Semiconductors by Balancing the Competitive Processes in Dip-Coating for Organic Transistors.

PubMed

Wu, Kunjie; Li, Hongwei; Li, Liqiang; Zhang, Suna; Chen, Xiaosong; Xu, Zeyang; Zhang, Xi; Hu, Wenping; Chi, Lifeng; Gao, Xike; Meng, Yancheng

2016-06-28

Ultrathin film with thickness below 15 nm of organic semiconductors provides excellent platform for some fundamental research and practical applications in the field of organic electronics. However, it is quite challenging to develop a general principle for the growth of uniform and continuous ultrathin film over large area. Dip-coating is a useful technique to prepare diverse structures of organic semiconductors, but the assembly of organic semiconductors in dip-coating is quite complicated, and there are no reports about the core rules for the growth of ultrathin film via dip-coating until now. In this work, we develop a general strategy for the growth of ultrathin film of organic semiconductor via dip-coating, which provides a relatively facile model to analyze the growth behavior. The balance between the three direct factors (nucleation rate, assembly rate, and recession rate) is the key to determine the growth of ultrathin film. Under the direction of this rule, ultrathin films of four organic semiconductors are obtained. The field-effect transistors constructed on the ultrathin film show good field-effect property. This work provides a general principle and systematic guideline to prepare ultrathin film of organic semiconductors via dip-coating, which would be highly meaningful for organic electronics as well as for the assembly of other materials via solution processes.

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.

Electrochemical behavior of gold nanoparticles modified nitrogen incorporated tetrahedral amorphous carbon and its application in glucose sensing.

PubMed

Liu, Aiping; Wu, Huaping; Qiu, Xu; Tang, Weihua

2011-12-01

Gold nanoparticles (NPs) with 10-50 nm in diameter were synthesized on nitrogen incorporated tetrahedral amorphous carbon (ta-C:N) thin film electrode by electrodeposition. The deposition and nucleation processes of Au on ta-C:N surface were investigated by cyclic voltammetry and chronoamperometry. The morphology of Au NPs was characterized by scanned electron microscopy. The electrochemical properties of Au NPs modified ta-C:N (ta-C:N/Au) electrode and its ability to sense glucose were investigated by voltammetric and amperometric measurements. The potentiostatic current-time transients showed a progressive nucleation process and diffusion growth of Au on the surface of ta-C:N film according to the Scharifker-Hills model. The Au NPs acted as microelectrodes improved the electron transfer and electrocatalytic oxidation of glucose on ta-C:N electrode. The ta-C:N/Au electrode exhibited fast current response, a linear detection range of glucose from 0.5 to 25 mM and a detection limit of 120 microM, which hinted its potential application as a glucose biosensor.

Polarized neutron reflectivity study of perpendicular magnetic anisotropy in MgO/CoFeB/W thin films

NASA Astrophysics Data System (ADS)

Ambaye, Haile; Zhan, Xiao; Li, Shufa; Lauter, Valeria; Zhu, Tao

In this work we study the origin of PMA in MgO/CoFeB/W trilayer systems using polarized neutron reflectivity. Recently, the spin Hall effect in the heavy metals, such as Pt and Ta, has been of significant interest for highly efficient magnetization switching of the ultrathin ferromagnets sandwiched by such a heavy metal and an oxide, which can be used for spintronic based memory and logic devices. Most work has focused on heavy-metal/ferromagnet/oxide trilayer (HM/FM/MO) structures with perpendicular magnetic anisotropy (PMA), where the oxide layer plays the role of breaking inversion symmetry .No PMA was found in W/CoFeB/MgO films. An insertion of Hf layer in between the W and CoFeB layers, however, has been found to create a strong PMA. Roughness and formation of interface alloys by interdiffusion influences the extent of PMA. We intend to identify these influences using the depth sensitive technique of PNR. In our previous study, we have successfully performed polarized neutron reflectometry (PNR) measurements on the Ta/CoFeB/MgO/CoFeB/Ta thin film with MgO thickness of 1 nm. The PNR measurements were carried out using the BL-4A Magnetic Reflectometer at SNS. This work has been supported by National Basic Research Program of China (2012CB933102). Research at SNS was supported by the Office of BES, DOE.

Growth of <111>-oriented Cu layer on thin TaWN films

NASA Astrophysics Data System (ADS)

Takeyama, Mayumi B.; Sato, Masaru

2017-07-01

In this study, we examine the growth of a <111>-oriented Cu layer on a thin TaWN ternary alloy barrier for good electromigration reliability. The strongly preferentially oriented Cu(111) layer is observed on a thin TaWN barrier even in the as-deposited Cu (100 nm)/TaWN (5 nm)/Si system. Also, this system tolerates annealing at 700 °C for 1 h without silicide reaction. It is revealed that the TaWN film is one of the excellent barriers with thermal stability and low resistivity. Simultaneously, the TaWN film is a candidate for a superior underlying material to achieve the Cu(111) preferential orientation.

HIGH-k GATE DIELECTRIC: AMORPHOUS Ta/La2O3 FILMS GROWN ON Si AT LOW PRESSURE

NASA Astrophysics Data System (ADS)

Bahari, Ali; Khorshidi, Zahra

2014-09-01

In the present study, Ta/La2O3 films (La2O3 doped with Ta2O5) as a gate dielectric were prepared using a sol-gel method at low pressure. Ta/La2O3 film has some hopeful properties as a gate dielectric of logic device. The structure and morphology of Ta/La2O3 films were studied using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Electrical properties of films were performed using capacitance-voltage (C-V) and current density-voltage (J-V) measurements. The optical bandgap of samples was studied by UV-visible optical absorbance measurement. The optical bandgap, Eopt, is determined from the absorbance spectra. The obtained results show that Ta/La2O3 film as a good gate dielectric has amorphous structure, good thermal stability, high dielectric constant (≈ 25), low leakage current and wide bandgap (≈ 4.7 eV).

An easily accessible carbon material derived from carbonization of polyacrylonitrile ultrathin films: ambipolar transport properties and application in a CMOS-like inverter.

PubMed

Jiao, Fei; Zhang, Fengjiao; Zang, Yaping; Zou, Ye; Di, Chong'an; Xu, Wei; Zhu, Daoben

2014-03-04

Ultrathin carbon films were prepared by carbonization of a solution processed polyacrylonitrile (PAN) film in a moderate temperature range (500-700 °C). The films displayed balanced hole (0.50 cm(2) V(-1) s(-1)) and electron mobilities (0.20 cm(2) V(-1) s(-1)) under ambient conditions. Spectral characterization revealed that the electrical transport is due to the formation of sp(2) hybridized carbon during the carbonization process. A CMOS-like inverter demonstrated the potential application of this material in the area of carbon electronics, considering its processability and low-cost.

The microwave properties of Ag(Ta0.8Nb0.2)O3 thick film interdigital capacitors on alumina substrates

NASA Astrophysics Data System (ADS)

Lee, Ku-Tak; Koh, Jung-Hyuk

2012-01-01

In this paper, we will introduce the microwave properties of Ag(Ta0.8Nb0.2)O3 thick film planar type interdigital capacitors fabricated on alumina substrates. The tailored paraelectric state of Ag(Ta,Nb)O3 allows the material to be regarded as a part of the family of microwave materials. As thick films formed in our experiment, Ag(Ta,Nb)O3 exhibited extremely low dielectric loss with relatively high dielectric permittivity. This low dielectric loss is a very important issue for microwave applications. Therefore, we investigated the microwave properties of Ag(Ta0.8Nb0.2)O3 thick film planar type interdigital capacitors. Ag(Ta0.8Nb0.2)O3 thick films were prepared by a screen-printing method on alumina substrates and were sintered at 1140 °C for 2 hrs. The XRD analysis results showed that the Ag(Ta0.8Nb0.2)O3 thick film has the perovskite structure. The frequency dependent dielectric permittivity showed that these Ag(Ta0.8Nb0.2)O3 thick film planar type interdigital capacitors have very weak frequency dispersions with low loss tangents in the microwave range.

BEOL compatible high tunnel magneto resistance perpendicular magnetic tunnel junctions using a sacrificial Mg layer as CoFeB free layer cap

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

Swerts, J., E-mail: Johan.Swerts@imec.be; Mertens, S.; Lin, T.

Perpendicularly magnetized MgO-based tunnel junctions are envisaged for future generation spin-torque transfer magnetoresistive random access memory devices. Achieving a high tunnel magneto resistance and preserving it together with the perpendicular magnetic anisotropy during BEOL CMOS processing are key challenges to overcome. The industry standard technique to deposit the CoFeB/MgO/CoFeB tunnel junctions is physical vapor deposition. In this letter, we report on the use of an ultrathin Mg layer as free layer cap to protect the CoFeB free layer from sputtering induced damage during the Ta electrode deposition. When Ta is deposited directly on CoFeB, a fraction of the surface ofmore » the CoFeB is sputtered even when Ta is deposited with very low deposition rates. When depositing a thin Mg layer prior to Ta deposition, the sputtering of CoFeB is prevented. The ultra-thin Mg layer is sputtered completely after Ta deposition. Therefore, the Mg acts as a sacrificial layer that protects the CoFeB from sputter-induced damage during the Ta deposition. The Ta-capped CoFeB free layer using the sacrificial Mg interlayer has significantly better electrical and magnetic properties than the equivalent stack without protective layer. We demonstrate a tunnel magneto resistance increase up to 30% in bottom pinned magnetic tunnel junctions and tunnel magneto resistance values of 160% at resistance area product of 5 Ω.μm{sup 2}. Moreover, the free layer maintains perpendicular magnetic anisotropy after 400 °C annealing.« less

Reconstructing the energy band electronic structure of pulsed laser deposited CZTS thin films intended for solar cell absorber applications

NASA Astrophysics Data System (ADS)

Pandiyan, Rajesh; Oulad Elhmaidi, Zakaria; Sekkat, Zouheir; Abd-lefdil, Mohammed; El Khakani, My Ali

2017-02-01

We report here on the use of pulsed KrF-laser deposition (PLD) technique for the growth of high-quality Cu2ZnSnS4 (CZTS) thin films onto Si, and glass substrates without resorting to any post sulfurization process. The PLD-CZTS films were deposited at room temperature (RT) and then subjected to post annealing at different temperatures ranging from 200 to 500 °C in Argon atmosphere. The X-ray diffraction and Raman spectroscopy confirmed that the PLD films crystallize in the characteristic kesterite CZTS structure regardless of their annealing temperature (Ta), but their crystallinity is much improved for Ta ≥ 400 °C. The PLD-CZTS films were found to exhibit a relatively dense morphology with a surface roughness (RMS) that increases with Ta (from ∼14 nm at RT to 70 nm at Ta = 500 °C with a value around 40 nm for Ta = 300-400 °C). The optical bandgap of the PLD-CZTS films, was derived from UV-vis transmission spectra analysis, and found to decrease from 1.73 eV for non-annealed films to ∼1.58 eV for those annealed at Ta = 300 °C. These band gap values are very close to the optimum value needed for an ideal solar cell absorber. In order to achieve a complete reconstruction of the one-dimensional energy band structure of these PLD-CZTS absorbers, we have combined both XPS and UPS spectroscopies to determine their chemical bondings, the position of their valence band maximum (relative to Fermi level), and their work function values. This enabled us to sketch out, as accurately as possible, the band alignment of the heterojunction interface formed between CZTS and both CdS and ZnS buffer layer materials.

Materials Study of NbN and Ta x N Thin Films for SNS Josephson Junctions

DOE PAGES

Missert, Nancy; Brunke, Lyle; Henry, Michael D.; ...

2017-02-15

We investigated properties of NbN and Ta xN thin films grown at ambient temperatures on SiO 2/Si substrates by reactive-pulsed laser deposition and reactive magnetron sputtering (MS) as a function of N 2 gas flow. Both techniques produced films with smooth surfaces, where the surface roughness did not depend on the N 2 gas flow during growth. High crystalline quality, (111) oriented NbN films with T c up to 11 K were produced by both techniques for N contents near 50%. The low temperature transport properties of the Ta xN films depended upon both the N 2 partial pressure usedmore » during growth and the film thickness. Furthermore, the root mean square surface roughness of Ta xN films grown by MS increased as the film thickness decreased down to 10 nm.« less

Investigations of Topological Surface States in Sb (111) Ultrathin Films by STM/STS Experiments and DFT Calculations

NASA Astrophysics Data System (ADS)

Luo, Ziyu; Yao, Guanggeng; Xu, Wentao; Feng, Yuanping; Wang, Xue-Sen

2014-03-01

Bulk Sb was regarded as a semimetal with a nontrivial topological order. It is worth exploring whether the Sb ultrathin film has the potential to be an elementary topological insulator. In the presence of quantum confinement effect, we investigated the evolution of topological surface states in Sb (111) ultrathin films with different thickness by the scanning tunneling microscopy/ spectroscopy (STM/STS) experiments and density functional theory (DFT) calculations. By comparing the quasiparticle interference (QPI) patterns obtained from Fourier-transform scanning tunneling spectroscopy (FT-STS) and from DFT calculations, we successfully derive the spin properties of topological surface states on Sb (111) ultrathin films. In addition, based on the DFT calculations, the 8BL Sb (111) ultrathin film was proved to possess up to 30% spinseparated topological surface states within the bandgap. Therefore, the highquality 8BL Sb (111) ultrathin film could be regarded as an elementary topological insulator.

Coordination-Enabled One-Step Assembly of Ultrathin, Hybrid Microcapsules with Weak pH-Response.

PubMed

Yang, Chen; Wu, Hong; Yang, Xiao; Shi, Jiafu; Wang, Xiaoli; Zhang, Shaohua; Jiang, Zhongyi

2015-05-06

In this study, an ultrathin, hybrid microcapsule is prepared though coordination-enabled one-step assembly of tannic acid (TA) and titanium(IV) bis(ammonium lactate) dihydroxide (Ti-BALDH) upon a hard-templating method. Briefly, the PSS-doped CaCO3 microspheres with a diameter of 5-8 μm were synthesized and utilized as the sacrificial templates. Then, TA-Ti(IV) coatings were formed on the surface of the PSS-doped CaCO3 templates through soaking in TA and Ti-BALDH aqueous solutions under mild conditions. After removing the template by EDTA treatment, the TA-Ti(IV) microcapsules with a capsule wall thickness of 15 ± 3 nm were obtained. The strong coordination bond between polyphenol and Ti(IV) conferred the TA-Ti(IV) microcapsules high structural stability in the range of pH values 3.0-11.0. Accordingly, the enzyme-immobilized TA-Ti(IV) microcapsules exhibited superior pH and thermal stabilities. This study discloses the formation of TA-Ti(IV) microcapsules that are suitable for use as supports in catalysis due to their extensive pH and thermal stabilities.

Influence of inserted Mo layer on the thermal stability of perpendicularly magnetized Ta/Mo/Co{sub 20}Fe{sub 60}B{sub 20}/MgO/Ta films

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

Li, Minghua, E-mail: mhli@ustb.edu.cn; Department of Electrical Engineering, University of California, Los Angeles, California 90095; Lu, Jinhui

2016-04-15

We studied the thermal stability of perpendicular magnetic anisotropy (PMA) in Ta/Mo/CoFeB/MgO/Ta films with and without inserted Mo layers. In the absence of a Mo layer, the films show PMA at annealing temperatures below 300 °C. On the other hand, the insertion of a Mo layer preserves PMA at annealing temperatures of up to 500 °C; however, a higher annealing temperature leads to the collapse of PMA. X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) were used to study the microstructure of the films to understand the deterioration of PMA. The XPS results show that the segregation ofmore » Ta is partly suppressed by inserting a Mo layer. Once inserted, Mo does not remain at the interface of Ta and CoFeB but migrates to the surface of the films. The HRTEM results show that the crystallization of the MgO (001) texture is improved owing to the higher annealing temperature of the Mo inserted sample. A smooth and clear CoFeB/MgO interface is evident. The inserted Mo layer not only helps to obtain sharper and smoother interfaces but also contributes to the crystallization after the higher annealing temperature of films.« less

Ultrathin Ferroelectric Films: Growth, Characterization, Physics and Applications.

PubMed

Wang, Ying; Chen, Weijin; Wang, Biao; Zheng, Yue

2014-09-11

Ultrathin ferroelectric films are of increasing interests these years, owing to the need of device miniaturization and their wide spectrum of appealing properties. Recent advanced deposition methods and characterization techniques have largely broadened the scope of experimental researches of ultrathin ferroelectric films, pushing intensive property study and promising device applications. This review aims to cover state-of-the-art experimental works of ultrathin ferroelectric films, with a comprehensive survey of growth methods, characterization techniques, important phenomena and properties, as well as device applications. The strongest emphasis is on those aspects intimately related to the unique phenomena and physics of ultrathin ferroelectric films. Prospects and challenges of this field also have been highlighted.

Ultrathin Ferroelectric Films: Growth, Characterization, Physics and Applications

PubMed Central

Wang, Ying; Chen, Weijin; Wang, Biao; Zheng, Yue

2014-01-01

Ultrathin ferroelectric films are of increasing interests these years, owing to the need of device miniaturization and their wide spectrum of appealing properties. Recent advanced deposition methods and characterization techniques have largely broadened the scope of experimental researches of ultrathin ferroelectric films, pushing intensive property study and promising device applications. This review aims to cover state-of-the-art experimental works of ultrathin ferroelectric films, with a comprehensive survey of growth methods, characterization techniques, important phenomena and properties, as well as device applications. The strongest emphasis is on those aspects intimately related to the unique phenomena and physics of ultrathin ferroelectric films. Prospects and challenges of this field also have been highlighted. PMID:28788196

Characteristics of the Energetic Igniters Through Integrating B/Ti Nano-Multilayers on TaN Film Bridge

NASA Astrophysics Data System (ADS)

Yan, YiChao; Shi, Wei; Jiang, HongChuan; Cai, XianYao; Deng, XinWu; Xiong, Jie; Zhang, WanLi

2015-05-01

The energetic igniters through integrating B/Ti nano-multilayers on tantalum nitride (TaN) ignition bridge are designed and fabricated. The X-ray diffraction (XRD) and temperature coefficient of resistance (TCR) results show that nitrogen content has a great influence on the crystalline structure and TCR. TaN films under nitrogen ratio of 0.99 % exhibit a near-zero TCR value of approximately 10 ppm/°C. The scanning electron microscopy demonstrates that the layered structure of the B/Ti multilayer films is clearly visible with sharp and smooth interfaces. The electrical explosion characteristics employing a capacitor discharge firing set at the optimized charging voltage of 45 V reveal an excellent explosion performance by (B/Ti) n /TaN integration film bridge with small ignition delay time, high explosion temperature, much more bright flash of light, and much large quantities of the ejected product particles than TaN film bridge.

Thin Films

NASA Astrophysics Data System (ADS)

Khorshidi, Zahra; Bahari, Ali; Gholipur, Reza

2014-11-01

Effect of annealing temperature on the characteristics of sol-gel-driven Ta ax La(1- a) x O y thin film spin-coated on Si substrate as a high- k gate dielectric was studied. Ta ax La(1- a) x O y thin films with different amounts of a were prepared (as-prepared samples). X-ray diffraction measurements of the as-prepared samples indicated that Ta0.3 x La0.7 x Oy film had an amorphous structure. Therefore, Ta0.3 x La0.7 x O y film was chosen to continue the present studies. The morphology of Ta0.3 x La0.7 x O y films was studied using scanning electron microscopy and atomic force microscopy techniques. The obtained results showed that the size of grain boundaries on Ta0.3 x La0.7 x O y film surfaces was increased with increasing annealing temperature. Electrical and optical characterizations of the as-prepared and annealed films were investigated as a function of annealing temperature using capacitance-voltage ( C- V) and current density-voltage ( J- V) measurements and the Tauc method. The obtained results demonstrated that Ta0.3 x La0.7 x O y films had high dielectric constant (≈27), wide band gap (≈4.5 eV), and low leakage current density (≈10-6 A/cm2 at 1 V).

Plasmonic detection of possible defects in multilayer nanohole array consisting of essential materials in simplified STT-RAM cell

NASA Astrophysics Data System (ADS)

Sadri-Moshkenani, Parinaz; Khan, Mohammad Wahiduzzaman; Zhao, Qiancheng; Krivorotov, Ilya; Nilsson, Mikael; Bagherzadeh, Nader; Boyraz, Ozdal

2017-08-01

Plasmonic nanostructures are highly used for sensing purposes since they support plasmonic modes which make them highly sensitive to the refractive index change of their surrounding medium. Therefore, they can also be used to detect changes in optical properties of ultrathin layer films in a multilayer plasmonic structure. Here, we investigate the changes in optical properties of ultrathin films of macro structures consisting of STT-RAM layers. Among the highest sensitive plasmonic structures, nanohole array has attracted many research interest because of its ease of fabrication, small footprint, and simplified optical alignment. Hence it is more suitable for defect detection in STT-RAM geometries. Moreover, the periodic nanohole pattern in the nanohole array structure makes it possible to couple the light to the surface plasmon polariton (SPP) mode supported by the structure. To assess the radiation damages and defects in STT-RAM cells we have designed a multilayer nanohole array based on the layers used in STT-RAM structure, consisting 4nm- Ta/1.5nm-CoFeB/2nm-MgO/1.5nm-CoFeB/4nm-Ta layers, all on a 300nm silver layer on top of a PEC boundary. The nanoholes go through all the layers and become closed by the PEC boundary on one side. The dimensions of the designed nanoholes are 313nm depth, 350nm diameter, and 700nm period. Here, we consider the normal incidence of light and investigate zeroth-order reflection coefficient to observe the resonance. Our simulation results show that a 10% change in refractive index of the 2nm-thick MgO layer leads to about 122GHz shift in SPP resonance in reflection pattern.

Preparation of TiO2/boron-doped diamond/Ta multilayer films and use as electrode materials for supercapacitors

NASA Astrophysics Data System (ADS)

Shi, Chao; Li, Hongji; Li, Cuiping; Li, Mingji; Qu, Changqing; Yang, Baohe

2015-12-01

We report nanostructured TiO2/boron-doped diamond (BDD)/Ta multilayer films and their electrochemical performances as supercapacitor electrodes. The BDD films were grown on Ta substrates using electron-assisted hot filament chemical vapor deposition. Ti metal layers were deposited on the BDD surfaces by radio frequency magnetron sputtering, and nanostructured TiO2/BDD/Ta thin films were prepared by electrochemical etching and thermal annealing. The successful formation of TiO2 and Ta layered nanostructures was demonstrated using scanning electron and transmission electron microscopies. The electrochemical responses of these electrodes were evaluated by examining their use as electrical double-layer capacitors, using cyclic voltammetry, and galvanostatic charge/discharge and impedance measurements. When the TiO2/BDD/Ta film was used as the working electrode with 0.1 M Na2SO4 as the electrolyte, the capacitor had a specific capacitance of 5.23 mF cm-2 at a scan rate of 5 mV s-1 for a B/C ratio of 0.1% w/w. Furthermore, the TiO2/BDD/Ta film had improved electrochemical stability, with a retention of 89.3% after 500 cycles. This electrochemical behavior is attributed to the quality of the BDD, the surface roughness and electrocatalytic activities of the TiO2 layer and Ta nanoporous structures, and the synergies between them. These results show that TiO2/BDD/Ta films are promising as capacitor electrodes for special applications.

Dependence of Interfacial Dzyaloshinskii-Moriya Interaction on Layer Thicknesses in Ta /Co -Fe -B /TaOx Heterostructures from Brillouin Light Scattering

NASA Astrophysics Data System (ADS)

Chaurasiya, Avinash Kumar; Choudhury, Samiran; Sinha, Jaivardhan; Barman, Anjan

2018-01-01

The interfacial Dzyaloshinskii-Moriya interaction (IDMI) has recently drawn extensive research interest due to its fundamental role in stabilizing chiral spin textures in ultrathin ferromagnets, which are suitable candidates for future magnetic-memory devices. Here, we explore the ferromagnetic and heavy-metal layer-thickness dependence of IDMI in technologically important Ta /Co20Fe60B20/TaOx heterostructures by measuring nonreciprocity in spin-wave frequency using the Brillouin light-scattering technique. The observed value of the IDMI constant agrees with that obtained from a separate measurement of in-plane angular dependence of frequency nonreciprocity, which is also in good agreement with the theory predicted by Cortes-Ortuno and Landeros. Linear scaling behavior of IDMI with the inverse of Co-Fe-B thicknesses suggests that IDMI originates primarily from the interface in these heterostructures, whereas we observe a weak dependence of Ta thickness on the strength of IDMI. Importantly, the observed value of the IDMI constant is reasonably large by a factor of 3 compared to annealed Ta /Co -Fe -B /MgO heterostructures. We propose that the observation of large IDMI is likely due to the absence of boron diffusion towards the Ta /Co -Fe -B interface as the heterostructures are as deposited. Our detailed investigation opens up a route to designing thin-film heterostructures with the tailored IDMI constant for controlling Skyrmion-based magnetic-memory devices.

Injection doping of ultrathin microcrystalline silicon films prepared by CC-CVD

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

Koynov, S.; Grebner, S.; Schwarz, R.

1997-07-01

Recently, the authors have proposed a cyclic method, referred to as Closed Chamber CVD (CC-CVD), for the preparation of {micro}c-Si films of high crystalline fraction at increased deposition rates. In this work, they first report new process conditions of CC-CVD, which result in growth of highly crystalline films with a sharp interface on a foreign substrate. Then these conditions are further used together with a pulsed injection of B{sub 2}H{sub 6} in an appropriate moment of each cycle, so that the disturbance of the crystallization process is prevented. A series of ultrathin {micro}c-Si films, doped by this technique, is characterizedmore » by conductivity measurements, SEM, Raman Scattering, optical transmission and UV reflection. A strong reduction of the transient interface layer is achieved and conductivity as high as 2 S/cm with an activation energy of 27 meV is reached.« less

Critical current enhancement driven by suppression of superconducting fluctuation in ion-gated ultrathin FeSe

NASA Astrophysics Data System (ADS)

Harada, T.; Shiogai, J.; Miyakawa, T.; Nojima, T.; Tsukazaki, A.

2018-05-01

The framework of phase transition, such as superconducting transition, occasionally depends on the dimensionality of materials. Superconductivity is often weakened in the experimental conditions of two-dimensional thin films due to the fragile superconducting state against defects and interfacial effects. In contrast to this general trend, superconductivity in the thin limit of FeSe exhibits an opposite trend, such as an increase in critical temperature (T c) and the superconducting gap exceeding the bulk values; however, the dominant mechanism is still under debate. Here, we measured thickness-dependent electrical transport properties of the ion-gated FeSe thin films to evaluate the superconducting critical current (I c) in the ultrathin FeSe. Upon systematically decreasing the FeSe thickness by the electrochemical etching technique in the Hall bar-shaped electric double-layer transistors, we observed a dramatic enhancement of I c reaching about 10 mA and corresponding to about 107 A cm‑2 in the thinnest condition. By analyzing the transition behavior, we clarify that the suppressed superconducting fluctuation is one of the origins of the large I c in the ion-gated ultrathin FeSe films. These results indicate the existence of a robust superconducting state possibly with dense Cooper pairs at the thin limit of FeSe.

Ultrathin and Atomically Flat Transition-Metal Oxide: Promising Building Blocks for Metal-Insulator Electronics.

PubMed

Cui, Qingsong; Sakhdari, Maryam; Chamlagain, Bhim; Chuang, Hsun-Jen; Liu, Yi; Cheng, Mark Ming-Cheng; Zhou, Zhixian; Chen, Pai-Yen

2016-12-21

We present a new and viable template-assisted thermal synthesis method for preparing amorphous ultrathin transition-metal oxides (TMOs) such as TiO 2 and Ta 2 O 5 , which are converted from crystalline two-dimensional (2D) transition-metal dichalcogenides (TMDs) down to a few atomic layers. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning transmission electron microscopy (STEM) were used to characterize the chemical composition and bonding, surface morphology, and atomic structure of these ultrathin amorphous materials to validate the effectiveness of our synthesis approach. Furthermore, we have fabricated metal-insulator-metal (MIM) diodes using the TiO 2 and Ta 2 O 5 as ultrathin insulating layers with low potential barrier heights. Our MIM diodes show a clear transition from direct tunneling to Fowler-Nordheim tunneling, which was not observed in previously reported MIM diodes with TiO 2 or Ta 2 O 5 as the insulating layer. We attribute the improved performance of our MIM diodes to the excellent flatness and low pinhole/defect densities in our TMO insulting layers converted from 2D TMDs, which enable the low-threshold and controllable electron tunneling transport. We envision that it is possible to use the ultrathin TMOs converted from 2D TMDs as the insulating layer of a wide variety of metal-insulator and field-effect electronic devices for various applications ranging from microwave mixing, parametric conversion, infrared photodetection, emissive energy harvesting, to ultrafast electronic switching.

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.

Influence of C or In buffer layer on photoluminescence behaviour of ultrathin ZnO film

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

Saravanan, K., E-mail: saravanan@igcar.gov.in; Jayalakshmi, G.; Krishnan, R.

We study the effect of the indium or carbon buffer layer on the photoluminescence (PL) property of ZnO ultrathin films deposited on a Si(100) substrate. The surface morphology of the films obtained using scanning tunnelling microscopy shows spherical shaped ZnO nanoparticles of size ∼8 nm in ZnO/C/Si and ∼22 nm in ZnO/Si samples, while the ZnO/In/Si sample shows elliptical shaped ZnO particles. Further, the ZnO/C/Si sample shows densely packed ZnO nanoparticles in comparison with other samples. Strong band edge emission has been observed in the presence of In or C buffer layer, whereas the ZnO/Si sample exhibits poor PL emission. The influencemore » of C and In buffer layers on the PL behaviour of ZnO films is studied in detail using temperature dependent PL measurements in the range of 4 K–300 K. The ZnO/C/Si sample exhibits a multi-fold enhancement in the PL emission intensity with well-resolved free and bound exciton emission lines. Our experimental results imply that the ZnO films deposited on the C buffer layer showed higher particle density and better exciton emission desired for optoelectronic applications.« less

Influence of interface layer on optical properties of sub-20 nm-thick TiO2 films

NASA Astrophysics Data System (ADS)

Shi, Yue-Jie; Zhang, Rong-Jun; Li, Da-Hai; Zhan, Yi-Qiang; Lu, Hong-Liang; Jiang, An-Quan; Chen, Xin; Liu, Juan; Zheng, Yu-Xiang; Wang, Song-You; Chen, Liang-Yao

2018-02-01

The sub-20 nm ultrathin titanium dioxide (TiO2) films with tunable thickness were deposited on Si substrates by atomic layer deposition (ALD). The structural and optical properties were acquired by transmission electron microscopy, atomic force microscopy and spectroscopic ellipsometry. Afterwards, a constructive and effective method of analyzing interfaces by applying two different optical models consisting of air/TiO2/Ti x Si y O2/Si and air/effective TiO2 layer/Si, respectively, was proposed to investigate the influence of interface layer (IL) on the analysis of optical constants and the determination of band gap of TiO2 ultrathin films. It was found that two factors including optical constants and changing components of the nonstoichiometric IL could contribute to the extent of the influence. Furthermore, the investigated TiO2 ultrathin films of 600 ALD cycles were selected and then annealed at the temperature range of 400-900 °C by rapid thermal annealing. Thicker IL and phase transition cause the variation of optical properties of TiO2 films after annealing and a shorter electron relaxation time reveals the strengthened electron-electron and electron-phonon interactions in the TiO2 ultrathin films at high temperature. The as-obtained results in this paper will play a role in other studies of high dielectric constants materials grown on Si substrates and in the applications of next generation metal-oxide-semiconductor devices.

Characteristics of the Energetic Igniters Through Integrating B/Ti Nano-Multilayers on TaN Film Bridge.

PubMed

Yan, YiChao; Shi, Wei; Jiang, HongChuan; Cai, XianYao; Deng, XinWu; Xiong, Jie; Zhang, WanLi

2015-12-01

The energetic igniters through integrating B/Ti nano-multilayers on tantalum nitride (TaN) ignition bridge are designed and fabricated. The X-ray diffraction (XRD) and temperature coefficient of resistance (TCR) results show that nitrogen content has a great influence on the crystalline structure and TCR. TaN films under nitrogen ratio of 0.99 % exhibit a near-zero TCR value of approximately 10 ppm/°C. The scanning electron microscopy demonstrates that the layered structure of the B/Ti multilayer films is clearly visible with sharp and smooth interfaces. The electrical explosion characteristics employing a capacitor discharge firing set at the optimized charging voltage of 45 V reveal an excellent explosion performance by (B/Ti) n /TaN integration film bridge with small ignition delay time, high explosion temperature, much more bright flash of light, and much large quantities of the ejected product particles than TaN film bridge.

Intense photoluminescence from amorphous tantalum oxide films

NASA Astrophysics Data System (ADS)

Zhu, Minmin; Zhang, Zhengjun; Miao, Wei

2006-07-01

Tantalum oxide films were deposited on silicon substrates at a temperature of ˜450°C by heating a pure tantalum foil in a rough vacuum. The films were amorphous in structure and consisted of fully oxidized Ta2O5 and (TaOx, x <2.5) suboxides. This feature resulted in strong visible light emission from the films further oxidized in the air at temperatures of 200-300°C. The mechanism for this photoluminescence behavior of the amorphous tantalum oxide films was also investigated and discussed. This study suggests that wide-band-gap materials could act as effective visible light emitters and provides a simple route to synthesize such materials.

2D Superparamagnetic Tantalum Carbide Composite MXenes for Efficient Breast-Cancer Theranostics

PubMed Central

Liu, Zhuang; Lin, Han; Zhao, Menglong; Dai, Chen; Zhang, Shengjian; Peng, Weijun; Chen, Yu

2018-01-01

Background: The emergence of two-dimensional MXenes has spurred their versatile applications in broad fields, but the exploring of novel MXene-based family members and their potential applications in theranostic nanomedicine (concurrent diagnostic imaging and therapy) have been rarely explored. In this work, we report the construction of a novel superparamagnetic MXene-based theranostic nanoplatform for efficient breast-cancer theranostics, which was based on intriguing tantalum carbide (Ta4C3) MXene and its further rational surface-superparamagnetic iron-oxide functionalization (Ta4C3-IONP-SPs composite MXenes) for efficient breast-cancer theranostic. Methods: The fabrication of ultrathin Ta4C3 nanosheets was based on an exfoliation strategy and superparamagnetic iron oxide nanoparticles were in-situ grown onto the surface of Ta4C3 MXene according to the redox reaction of MXene. Ta4C3-IONP MXenes were modified with soybean phospholipid (SP) to guarantee high stability in physiological conditions. The photothermal therapy, contrast-enhanced CT, T2-weighted magnetic resonance imaging and the high biocompatibility of these composite nanosheets have also been evaluated in vitro at cellular level and in vivo on mice breast tumor allograft tumor model. Results: The Ta component of Ta4C3-IONP-SPs exhibits high performance for contrast-enhanced CT imaging because of its high atomic number and high X-ray attenuation coefficient, and the integrated superparamagnetic IONPs act as excellent contrast agents for T2-weighted magnetic resonance imaging. Especially, these Ta4C3-IONP-SPs composite nanosheets with high photothermal-conversion efficiency (η: 32.5%) has achieved complete tumor eradication without reoccurrence, verifying their highly efficient breast-tumor photo-ablation performance. Conclusion: This work not only significantly broadens the biomedical applications of MXene-based nanoplatforms (Ta4C3 MXene) by exploring their novel family members and further functionalization strategies (magnetic functionalization in this work), but also provides a novel and efficient theranostic nanoplatform for efficient breast-cancer theranostics. PMID:29556347

Employing Synergetic Effect of Doping and Thin Film Coating to Boost the Performance of Lithium-Ion Battery Cathode Particles

PubMed Central

Patel, Rajankumar L.; Jiang, Ying-Bing; Choudhury, Amitava; Liang, Xinhua

2016-01-01

Atomic layer deposition (ALD) has evolved as an important technique to coat conformal protective thin films on cathode and anode particles of lithium ion batteries to enhance their electrochemical performance. Coating a conformal, conductive and optimal ultrathin film on cathode particles has significantly increased the capacity retention and cycle life as demonstrated in our previous work. In this work, we have unearthed the synergetic effect of electrochemically active iron oxide films coating and partial doping of iron on LiMn1.5Ni0.5O4 (LMNO) particles. The ionic Fe penetrates into the lattice structure of LMNO during the ALD process. After the structural defects were saturated, the iron started participating in formation of ultrathin oxide films on LMNO particle surface. Owing to the conductive nature of iron oxide films, with an optimal film thickness of ~0.6 nm, the initial capacity improved by ~25% at room temperature and by ~26% at an elevated temperature of 55 °C at a 1C cycling rate. The synergy of doping of LMNO with iron combined with the conductive and protective nature of the optimal iron oxide film led to a high capacity retention (~93% at room temperature and ~91% at 55 °C) even after 1,000 cycles at a 1C cycling rate. PMID:27142704

Coexistence of Topological Edge State and Superconductivity in Bismuth Ultrathin Film.

PubMed

Sun, Hao-Hua; Wang, Mei-Xiao; Zhu, Fengfeng; Wang, Guan-Yong; Ma, Hai-Yang; Xu, Zhu-An; Liao, Qing; Lu, Yunhao; Gao, Chun-Lei; Li, Yao-Yi; Liu, Canhua; Qian, Dong; Guan, Dandan; Jia, Jin-Feng

2017-05-10

Ultrathin freestanding bismuth film is theoretically predicted to be one kind of two-dimensional topological insulators. Experimentally, the topological nature of bismuth strongly depends on the situations of the Bi films. Film thickness and interaction with the substrate often change the topological properties of Bi films. Using angle-resolved photoemission spectroscopy, scanning tunneling microscopy or spectroscopy and first-principle calculation, the properties of Bi(111) ultrathin film grown on the NbSe 2 superconducting substrate have been studied. We find the band structures of the ultrathin film is quasi-freestanding, and one-dimensional edge state exists on Bi(111) film as thin as three bilayers. Superconductivity is also detected on different layers of the film and the pairing potential exhibits an exponential decay with the layer thicknesses. Thus, the topological edge state can coexist with superconductivity, which makes the system a promising platform for exploring Majorana Fermions.

Electrical properties of spin coated ultrathin titanium oxide films on GaAs

NASA Astrophysics Data System (ADS)

Dutta, Shankar; Pal, Ramjay; Chatterjee, Ratnamala

2015-04-01

In recent years, ultrathin (<50 nm) metal oxide films have been being extensively studied as high-k dielectrics for future metal oxide semiconductor (MOS) technology. This paper discusses deposition of ultrathin TiO2 films (˜10 nm) on GaAs substrates (one sulfur-passivated, another unpassivated) by spin coating technique. The sulfur passivation is done to reduce the surface states of GaAs substrate. After annealing at 400 °C in a nitrogen environment, the TiO2 films are found to be polycrystalline in nature with rutile phase. The TiO2 films exhibit consistent grain size of 10-20 nm with thickness around 10-12 nm. Dielectric constants of the films are found to be 65.4 and 47.1 corresponding to S-passivated and unpassivated substrates, respectively. Corresponding threshold voltages of the MOS structures are measured to be -0.1 V to -0.3 V for the S-passivated and unpassivated samples, respectively. The S-passivated TiO2 film showed improved (lower) leakage current density (5.3 × 10-4 A cm-2 at 3 V) compared to the unpassivated film (1.8 × 10-3 A/cm2 at 3 V). Dielectric breakdown-field of the TiO2 films on S-passivated and unpassivated GaAs samples are found to be 8.4 MV cm-1 and 7.2 MV cm-1 respectively.

Improved metal-insulator-transition characteristics of ultrathin VO2 epitaxial films by optimized surface preparation of rutile TiO2 substrates

NASA Astrophysics Data System (ADS)

Martens, Koen; Aetukuri, Nagaphani; Jeong, Jaewoo; Samant, Mahesh G.; Parkin, Stuart S. P.

2014-02-01

Key to the growth of epitaxial, atomically thin films is the preparation of the substrates on which they are deposited. Here, we report the growth of atomically smooth, ultrathin films of VO2 (001), only ˜2 nm thick, which exhibit pronounced metal-insulator transitions, with a change in resistivity of ˜500 times, at a temperature that is close to that of films five times thicker. These films were prepared by pulsed laser deposition on single crystalline TiO2(001) substrates that were treated by dipping in acetone, HCl and HF in successive order, followed by an anneal at 700-750 °C in flowing oxygen. This pretreatment removes surface contaminants, TiO2 defects, and provides a terraced, atomically smooth surface.

Ultrathin NiGe films prepared via catalytic solid-vapor reaction of Ni with GeH(4).

PubMed

Peter, Antony P; Opsomer, Karl; Adelmann, Christoph; Schaekers, Marc; Meersschaut, Johan; Richard, Olivier; Vaesen, Inge; Moussa, Alain; Franquet, Alexis; Zsolt, Tokei; Van Elshocht, Sven

2013-10-09

A low-temperature (225-300 °C) solid-vapor reaction process is reported for the synthesis of ultrathin NiGe films (∼6-23 nm) on 300 mm Si wafers covered with thermal oxide. The films were prepared via catalytic chemical vapor reaction of germane (GeH4) gas with physical vapor deposited (PVD) Ni films of different thickness (2-10 nm). The process optimization by investigating GeH4 partial pressure, reaction temperature, and time shows that low resistive, stoichiometric, and phase pure NiGe films can be formed within a broad window. NiGe films crystallized in an orthorhombic structure and were found to exhibit a smooth morphology with homogeneous composition as evidenced by glancing angle X-ray diffraction (GIXRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and Rutherford back-scattering (RBS) analysis. Transmission electron microscopy (TEM) analysis shows that the NiGe layers exhibit a good adhesion without voids and a sharp interface on the thermal oxide. The NiGe films were found to be morphologically and structurally stable up to 500 °C and exhibit a resistivity value of 29 μΩ cm for 10 nm NiGe films.

Native oxide transport and removal during the atomic layer deposition of Ta{sub 2}O{sub 5} on InAs(100) surfaces

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

Henegar, Alex J.; Gougousi, Theodosia, E-mail: gougousi@umbc.edu

Atomic layer deposition (ALD) was used to deposit Ta{sub 2}O{sub 5} on etched and native oxide-covered InAs(100) using pentakis dimethyl amino tantalum and H{sub 2}O at 200–300 °C. The transport and removal of the native oxides during the ALD process was investigated using x-ray photoelectron spectroscopy (XPS). Depositions above 200 °C on etched surfaces protected the interface from reoxidation. On native oxide-covered surfaces, depositions resulted in enhanced native oxide removal at higher temperatures. The arsenic oxides were completely removed above 250 °C after 3 nm of film growth, but some of the As{sub 2}O{sub 3} remained in the film at lower temperatures. Angle-resolved andmore » sputter depth profiling XPS confirmed indium and arsenic oxide migration into the Ta{sub 2}O{sub 5} film at deposition temperatures as low as 200 °C. Continuous removal of both arsenic and indium oxides was confirmed even after the deposition of several monolayers of a coalesced Ta{sub 2}O{sub 5} film, and it was demonstrated that native oxide transport is a prevalent component of the interface “clean-up” mechanism.« less

Theoretical Methods of Domain Structures in Ultrathin Ferroelectric Films: A Review

PubMed Central

Liu, Jianyi; Chen, Weijin; Wang, Biao; Zheng, Yue

2014-01-01

This review covers methods and recent developments of the theoretical study of domain structures in ultrathin ferroelectric films. The review begins with an introduction to some basic concepts and theories (e.g., polarization and its modern theory, ferroelectric phase transition, domain formation, and finite size effects, etc.) that are relevant to the study of domain structures in ultrathin ferroelectric films. Basic techniques and recent progress of a variety of important approaches for domain structure simulation, including first-principles calculation, molecular dynamics, Monte Carlo simulation, effective Hamiltonian approach and phase field modeling, as well as multiscale simulation are then elaborated. For each approach, its important features and relative merits over other approaches for modeling domain structures in ultrathin ferroelectric films are discussed. Finally, we review recent theoretical studies on some important issues of domain structures in ultrathin ferroelectric films, with an emphasis on the effects of interfacial electrostatics, boundary conditions and external loads. PMID:28788198

Sintered tantalum carbide coatings on graphite substrates: Highly reliable protective coatings for bulk and epitaxial growth

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

Nakamura, Daisuke; Suzumura, Akitoshi; Shigetoh, Keisuke

2015-02-23

Highly reliable low-cost protective coatings have been sought after for use in crucibles and susceptors for bulk and epitaxial film growth processes involving wide bandgap materials. Here, we propose a production technique for ultra-thick (50–200 μmt) tantalum carbide (TaC) protective coatings on graphite substrates, which consists of TaC slurry application and subsequent sintering processes, i.e., a wet ceramic process. Structural analysis of the sintered TaC layers indicated that they have a dense granular structure containing coarse grain with sizes of 10–50 μm. Furthermore, no cracks or pinholes penetrated through the layers, i.e., the TaC layers are highly reliable protective coatings. The analysismore » also indicated that no plastic deformation occurred during the production process, and the non-textured crystalline orientation of the TaC layers is the origin of their high reliability and durability. The TaC-coated graphite crucibles were tested in an aluminum nitride (AlN) sublimation growth process, which involves extremely corrosive conditions, and demonstrated their practical reliability and durability in the AlN growth process as a TaC-coated graphite. The application of the TaC-coated graphite materials to crucibles and susceptors for use in bulk AlN single crystal growth, bulk silicon carbide (SiC) single crystal growth, chemical vapor deposition of epitaxial SiC films, and metal-organic vapor phase epitaxy of group-III nitrides will lead to further improvements in crystal quality and reduced processing costs.« less

Highly stable, protein resistant thin films on SiC-modified silicon substrates.

PubMed

Qin, Guoting; Zhang, Rui; Makarenko, Boris; Kumar, Amit; Rabalais, Wayne; López Romero, J Manuel; Rico, Rodrigo; Cai, Chengzhi

2010-05-21

Thin films terminated with oligo(ethylene glycol) (OEG) could be photochemically grafted onto ultrathin silicon carbide layers that were generated on silicon substrates via carbonization with acetylene at 820 degrees C. The OEG coating reduced the non-specific adsorption of fibrinogen on the substrates by 99.5% and remained resistant after storage in PBS for 4 weeks at 37 degrees C.

Conductive tracks of 30-MeV C60 clusters in doped and undoped tetrahedral amorphous carbon

NASA Astrophysics Data System (ADS)

Krauser, J.; Gehrke, H.-G.; Hofsäss, H.; Trautmann, C.; Weidinger, A.

2013-07-01

In insulating tetrahedral amorphous carbon (ta-C), the irradiation with 30-MeV C60 cluster ions leads to the formation of well conducting tracks. While electrical currents through individual tracks produced with monoatomic projectiles (e.g. Au or U) often exhibit rather large track to track fluctuations, C60 clusters are shown to generate highly conducting tracks with very narrow current distributions. Additionally, all recorded current-voltage curves show linear characteristics. These findings are attributed to the large specific energy loss dE/dx of the 30-MeV C60 clusters. We also investigated C60 tracks in ta-C films which were slightly doped with B, N or Fe during film growth. Doping apparently increases the ion track conductivity. However, at the same time the insulating characteristics of the pristine ta-C film can be reduced. The present C60 results are compared with data from earlier experiments with monoatomic heavy ion beams. The investigations were performed by means of atomic force microscopy including temperature dependent conductivity measurements of single ion tracks.

Pulsed laser deposited metal oxide thin films mediated controlled adsorption of proteins

NASA Astrophysics Data System (ADS)

Kim, Se Jin

Several metal oxide thin films were grown on Si substrate by pulsed laser deposition for controlling adsorption of proteins. No intentional heating of substrate and introduction of oxygen gas during growth were employed. Additionally, fibrinogen, bovine serum albumin (BSA), and lysozyme were used as model protein in this study. The film properties such as cyratllinity, surface roughness, surface electrical charge and chemistry were investigated by many techniques in order to obtain the relationship with protein adsorption. Firstly, as grown Ta2O5 and ZnO thin film were used to study the effects of surface charge on the behaviors of BSA and lysozyme adsorption. The protein thickness results by ellipsometry showed that negatively charged Ta2O5 had a stronger affinity to positively charged lysozyme, while positively charged ZnO had a stronger affinity to negatively charged BSA. The results confirmed electrostatic interaction due to surface charge is one of main factors for determining adsorption of proteins. Furthermore, annealing studies were performed by heat treatment of as grown Ta2O5 and ZnO at 800°C in air ambience. Annealed Ta2O5 thin film had almost wetting property (from 10.02° to less than 1˜2°) and the change of cystallinity (from amorphous to cyrsalline) while annealed ZnO thin film had a reduced contact angle (from 75.65° to 39.41°) and remained to crystalline structure. The fibrinogen thickness on annealed Ta2O5 film was increased compared with as grown sample, while heat treated ZnO film showed much reduction of fibrinogen adsorption. Binary Ta-Zn oxide thin films (TZ) were grown by preparing PLD target composed of 50 wt% Ta2O5 and 50 wt% ZnO. This binary film had IEP pH 7.1 indicating nearly neutral charge in pH 7.4 PBS solution, and hydrophilic property. Ellipsometrical results showed that TZ film had the lowest fibrinogen, BSA and lysozyme thickness after 120 min adsorption compared with Ta2O5 and ZnO. Other samples, bilayer oxide films in which Ta2O5 and ZnO coexist were also employed to study adsorption behaviors. Especially, Ta2O 5-based bilayer films revealed zero adsorption of lysozyme.

In situ study of the electronic structure of atomic layer deposited oxide ultrathin films upon oxygen adsorption using ambient pressure XPS

DOE PAGES

Mao, Bao-Hua; Crumlin, Ethan; Tyo, Eric C.; ...

2016-07-21

In this work, ambient pressure X-ray photoelectron spectroscopy (APXPS) was used to investigate the effect of oxygen adsorption on the band bending and electron affinity of Al 2O 3, ZnO and TiO 2 ultrathin films (~1 nm in thickness) deposited on a Si substrate by atomic layer deposition (ALD). Upon exposure to oxygen at room temperature (RT), upward band bending was observed on all three samples, and a decrease in electron affinity was observed on Al 2O 3 and ZnO ultrathin films at RT. At 80°C, the magnitude of the upward band bending decreased, and the change in the electronmore » affinity vanished. These results indicate the existence of two surface oxygen species: a negatively charged species that is strongly adsorbed and responsible for the observed upward band bending, and a weakly adsorbed species that is polarized, lowering the electron affinity. Based on the extent of upward band bending on the three samples, the surface coverage of the strongly adsorbed species exhibits the following order: Al 2O 3 > ZnO > TiO 2. This finding is in stark contrast to the trend expected on the surface of these bulk oxides, and highlights the unique surface activity of ultrathin oxide films with important implications, for example, in oxidation reactions taking place on these films or in catalyst systems where such oxides are used as a support material.« less

SEMICONDUCTOR TECHNOLOGY: TaN wet etch for application in dual-metal-gate integration technology

NASA Astrophysics Data System (ADS)

Yongliang, Li; Qiuxia, Xu

2009-12-01

Wet-etch etchants and the TaN film method for dual-metal-gate integration are investigated. Both HF/HN O3/H2O and NH4OH/H2O2 solutions can etch TaN effectively, but poor selectivity to the gate dielectric for the HF/HNO3/H2O solution due to HF being included in HF/HNO3/H2O, and the fact that TaN is difficult to etch in the NH4OH/H2O2 solution at the first stage due to the thin TaOxNy layer on the TaN surface, mean that they are difficult to individually apply to dual-metal-gate integration. A two-step wet etching strategy using the HF/HNO3/H2O solution first and the NH4OH/H2O2 solution later can fully remove thin TaN film with a photo-resist mask and has high selectivity to the HfSiON dielectric film underneath. High-k dielectric film surfaces are smooth after wet etching of the TaN metal gate and MOSCAPs show well-behaved C-V and Jg-Vg characteristics, which all prove that the wet etching of TaN has little impact on electrical performance and can be applied to dual-metal-gate integration technology for removing the first TaN metal gate in the PMOS region.

Reactive magnetron cosputtering of hard and conductive ternary nitride thin films: Ti-Zr-N and Ti-Ta-N

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

Abadias, G.; Koutsokeras, L. E.; Dub, S. N.

2010-07-15

Ternary transition metal nitride thin films, with thickness up to 300 nm, were deposited by dc reactive magnetron cosputtering in Ar-N{sub 2} plasma discharges at 300 deg. C on Si substrates. Two systems were comparatively studied, Ti-Zr-N and Ti-Ta-N, as representative of isostructural and nonisostructural prototypes, with the aim of characterizing their structural, mechanical, and electrical properties. While phase-separated TiN-ZrN and TiN-TaN are the bulk equilibrium states, Ti{sub 1-x}Zr{sub x}N and Ti{sub 1-y}Ta{sub y}N solid solutions with the Na-Cl (B1-type) structure could be stabilized in a large compositional range (up to x=1 and y=0.75, respectively). Substituting Ti atoms by eithermore » Zr or Ta atoms led to significant changes in film texture, microstructure, grain size, and surface morphology, as evidenced by x-ray diffraction, x-ray reflectivity, and scanning electron and atomic force microscopies. The ternary Ti{sub 1-y}Ta{sub y}N films exhibited superior mechanical properties to Ti{sub 1-x}Zr{sub x}N films as well as binary compounds, with hardness as high as 42 GPa for y=0.69. All films were metallic, the lowest electrical resistivity {rho}{approx}65 {mu}{Omega} cm being obtained for pure ZrN, while for Ti{sub 1-y}Ta{sub y}N films a minimum was observed at y{approx}0.3. The evolution of the different film properties is discussed based on microstructrural investigations.« less

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.

Structure Formation of Ultrathin PEO Films at Solid Interfaces—Complex Pattern Formation by Dewetting and Crystallization

PubMed Central

Braun, Hans-Georg; Meyer, Evelyn

2013-01-01

The direct contact of ultrathin polymer films with a solid substrate may result in thin film rupture caused by dewetting. With crystallisable polymers such as polyethyleneoxide (PEO), molecular self-assembly into partial ordered lamella structures is studied as an additional source of pattern formation. Morphological features in ultrathin PEO films (thickness < 10 nm) result from an interplay between dewetting patterns and diffusion limited growth pattern of ordered lamella growing within the dewetting areas. Besides structure formation of hydrophilic PEO molecules, n-alkylterminated (hydrophobic) PEO oligomers are investigated with respect to self-organization in ultrathin films. Morphological features characteristic for pure PEO are not changed by the presence of the n-alkylgroups. PMID:23385233

Tribological properties of self-lubricating Ta-Cu films

NASA Astrophysics Data System (ADS)

Qin, Wen; Fu, Licai; Zhu, Jiajun; Yang, Wulin; Li, Deyi; Zhou, Lingping

2018-03-01

In this paper, Ta and TaCu films were deposited by using magnetron sputtering, and the tribological properties of the films against Si3N4 balls were investigated under the loads of 2 N and 5 N. The average grain sizes of both films are below 25 nm. Ta and TaCu films have approximate hardness. While the wear rate of TaCu film is much smaller than that of Ta film. Post-wear testing XRD, Raman and XPS revealed the formation of tantalum oxide on the worn surface of both Ta and TaCu films. Tantalum oxidation is effectively lubricating to reduce friction coefficient. So the friction coefficient of both Ta and TaCu film is about 0.45 under different applied loads. Meanwhile, the addition of Cu could increase the toughness of the film, and avoid the generation of wear debris, resulting in a significant increase in wear resistance.

Controllable fabrication of ultrathin free-standing graphene films

PubMed Central

Chen, Jianyi; Guo, Yunlong; Huang, Liping; Xue, Yunzhou; Geng, Dechao; Liu, Hongtao; Wu, Bin; Yu, Gui; Hu, Wenping; Liu, Yunqi; Zhu, Daoben

2014-01-01

Graphene free-standing film-like or paper-like materials have attracted great attention due to their intriguing electronic, optical and mechanical properties and potential application in chemical filters, molecular storage and supercapacitors. Although significant progress has been made in fabricating graphene films or paper, there is still no effective method targeting ultrathin free-standing graphene films (UFGFs). Here, we present a modified filtration assembly method to prepare these ultrathin films. With this approach, we have fabricated a series of ultrathin free-standing graphene oxide films and UFGFs, up to 40 mm in diameter, with controllable thickness from micrometre to nanoscale (approx. 40 nm) dimensions. This method can be easily scaled up and the films display excellent optical, electrical and electrochemical properties. The ability to produce UFGFs from graphene oxide with a scalable, low-cost approach should take us a step closer to real-world applications of graphene. PMID:24615152

The evolution of in-plane magnetic anisotropy in CoFeB/GaAs(001) films annealed at different temperatures

NASA Astrophysics Data System (ADS)

Tu, Hongqing; Wang, Ji; Wei, Lujun; Yuan, Yuan; Zhang, W.; You, Biao; Du, Jun

2018-05-01

A considerable in-plane uniaxial magnetic anisotropy (UMA) field (Hu ˜ 300 Oe) could be achieved when the amorphous CoFeB film was deposited on the GaAs(001) wafer by magnetron-sputtering after proper etch-annealed procedure. In order to get deep insights into the mechanism of the UMA, the film was annealed at different temperatures and the evolution of the in-plane magnetic anisotropy was investigated carefully. With increasing the annealing temperature (TA), the UMA could be maintained well when TA reached 250°C, but became very weak at 300°C. However, when TA was elevated to 400°C, another UMA (Hu ˜ 130 Oe) was built accompanied with a fourfold magnetic anisotropy with its strength of about 50 Oe. In terms of the magnetic anisotropy evolution along with TA, the anelastic strain, which is thought to be resulted from the interfacial interaction between CoFeB and GaAs, may play a dominant role in producing the enhanced UMA based on the `bond-orientational' anisotropy (BOA) model.

Nano-structured variable capacitor based on P(VDF-TrFE) copolymer and carbon nanotubes

NASA Astrophysics Data System (ADS)

Lakbita, I.; El-Hami, K.

2018-02-01

A newly organic capacitor was conceived with a variable capacitance using the inverse piezoelectric effect. The device consists of two parallel plates of carbon nanotubes (CNTs), known for their large surface area, high sensitivity and high electric conductivity, separated by a thin film of a dielectric layer of Polyinylidene fluoride and trifluoroehtylene (P(VDF-TrFE)) promising material for piezoelectric and ferroelectric properties. The obtained architecture is the CNT/PVDF-TrFE/CNT capacitor device. In this study, an ultra-thin film of P(VDF-TrFE) (54/46) with thickness of 20 nm was elaborated on highly oriented pyrolytic graphite (HOPG) by spin-coating. The morphology of the ultra-thin film and the mechanical behavior of CNT/P(VDF-TrFE)/CNT system were studied using the atomic force microscopy (AFM) combined with a lock-in amplifier in contact mode. All changes in applied voltage induce a change in thin film thickness according to the inverse piezoelectric effect that affect, consequently the capacitance. The results showed that the ratio of capacitance change ΔC to initial capacitance C0 is ΔC/C0=5%. This value is sufficient to use P(VDF-TrFE) as variable organic capacitor.

Ultrathin Polymer Films, Patterned Arrays, and Microwells

NASA Astrophysics Data System (ADS)

Yan, Mingdi

2002-05-01

The ability to control and tailor the surface and interface properties of materials is important in microelectronics, cell growth control, and lab-on-a-chip devices. Modification of material surfaces with ultrathin polymer films is attractive due to the availability of a variety of polymers either commercially or by synthesis. We have developed two approaches to the attachment of ultrathin polymer films on solid substrates. In the first method, a silane-functionalized perfluorophenyl azide (PFPA-silane) was synthesized and used to covalently immobilize polymer thin films on silicon wafers. Silanization of the wafer surface with the PFPA-silane introduced a monolayer of azido groups which in turn covalently attached the polymer film by way of photochemically initiated insertion reactions. The thickness of the film could be adjusted by the type and the molecular weight of the polymer. The method is versatile due to the general C-H and/or N-H insertion reactions of crosslinker; and therefore, no specific reactive functional groups on the polymers are required. Using this method, a new type of microwell array was fabricated from covalently immobilized polymer thin films on flat substrates. The arrays were characterized with AFM, XPS, and TOF-SIMS. The second method describes the attachment of polymer thin films on solid substrates via UV irradiation. The procedure consisted of spin-coating a polymer film and irradiating the film with UV light. Following solvent extraction, a thin film remained. The thickness of the film, from a few to over a hundred nanometers, was controlled by varying solution concentration and the molecular weight of the polymer.

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.

Transparent ALD-grown Ta2O5 protective layer for highly stable ZnO photoelectrode in solar water splitting.

PubMed

Li, Chengcheng; Wang, Tuo; Luo, Zhibin; Zhang, Dong; Gong, Jinlong

2015-04-30

This communication describes a highly stable ZnO/Ta2O5 photoanode with Ta2O5 deposited by atomic layer deposition. The ultrathin Ta2O5 protective layer prevents corrosion of ZnO and reduces surface carrier recombination, leading to a nearly two-fold increase of photo-conversion efficiency. The transparency of Ta2O5 to sunlight is identified as the main reason for the excellent stability of the photoelectrode for 5 hours.

Physical and structural characterisation of starch/polyester blends with tartaric acid.

PubMed

Olivato, J B; Müller, C M O; Carvalho, G M; Yamashita, F; Grossmann, M V E

2014-06-01

Starch/PBAT blends were produced by reactive extrusion with tartaric acid (TA) as an additive. The effects of TA, glycerol and starch+PBAT on the mechanical, optical and structural properties of the films were evaluated, with formulations based in a constrained mixture design. Tartaric acid acts as a compatibiliser and promotes the acid hydrolysis of starch chains. These two functions explain the observed film resistance and opacity. TA reduced the weight loss in water. Scanning electron microscopy (SEM) images showed that TA reduces the interfacial tension between the polymeric phases, resulting in more homogeneous films. Nuclear magnetic resonance ((13)C CPMAS) and Fourier transform infrared spectroscopy (FT-IR) suggest that tartaric acid is able to react with the hydroxyl groups of the starch by esterification/transesterification reactions, confirming its role as a compatibiliser. The addition of TA results in materials with better properties that are suitable for use in food packaging. Published by Elsevier B.V.

Fabrication of Large-area Free-standing Ultrathin Polymer Films

PubMed Central

Stadermann, Michael; Baxamusa, Salmaan H.; Aracne-Ruddle, Chantel; Chea, Maverick; Li, Shuaili; Youngblood, Kelly; Suratwala, Tayyab

2015-01-01

This procedure describes a method for the fabrication of large-area and ultrathin free-standing polymer films. Typically, ultrathin films are prepared using either sacrificial layers, which may damage the film or affect its mechanical properties, or they are made on freshly cleaved mica, a substrate that is difficult to scale. Further, the size of ultrathin film is typically limited to a few square millimeters. In this method, we modify a surface with a polyelectrolyte that alters the strength of adhesion between polymer and deposition substrate. The polyelectrolyte can be shown to remain on the wafer using spectroscopy, and a treated wafer can be used to produce multiple films, indicating that at best minimal amounts of the polyelectrolyte are added to the film. The process has thus far been shown to be limited in scalability only by the size of the coating equipment, and is expected to be readily scalable to industrial processes. In this study, the protocol for making the solutions, preparing the deposition surface, and producing the films is described. PMID:26066738

Single crystalline silicene consist of various superstructures using a flexible ultrathin Ag(111) template on Si(111)

NASA Astrophysics Data System (ADS)

Hsu, Hung-Chang; Lu, Yi-Hung; Su, Tai-Lung; Lin, Wen-Chin; Fu, Tsu-Yi

2018-07-01

Using scanning tunneling microscopy, we studied the formation of silicene on an ultrathin Ag(111) film with a thickness of 6–12 monolayers, which was prepared on a Si(111) substrate. A low-energy electron diffraction pattern with an oval spot indicated that the ultrathin Ag(111) film is more disordered than the single-crystal Ag(111). After Si epitaxy growth, we still measured the classical 4 × 4, √13 × √13, and 2√3 × 2√3 silicene superstructures, which are the same as the silicene superstructure on single-crystal Ag(111). Growing silicene on a single-crystal Ag(111) bulk usually results in the formation of a defect boundary due to the inconsistent orientation of various superstructures. By comparing the angles and boundary conditions between various silicene superstructures on the ultrathin film and single-crystal Ag(111), we discovered that a consistent orientation of various superstructures without obvious boundary defects formed on the ultrathin Ag(111) film. The results indicated single crystalline silicene formation, which was attributed to the domain rotation and lateral shift of the disordered ultrathin Ag(111) film.

Effect of structure on the tribology of ultrathin graphene and graphene oxide films.

PubMed

Chen, Hang; Filleter, Tobin

2015-03-27

The friction and wear properties of graphene and graphene oxide (GO) with varying C/O ratio were investigated using friction force microscopy. When applied as solid lubricants between a sliding contact of a silicon (Si) tip and a SiO2/Si substrate, graphene and ultrathin GO films (as thin as 1-2 atomic layers) were found to reduce friction by ∼6 times and ∼2 times respectively as compared to the unlubricated contact. The differences in measured friction were attributed to different interfacial shear strengths. Ultrathin films of GO with a low C/O ratio of ∼2 were found to wear easily under small normal load. The onset of wear, and the location of wear initiation, is attributed to differences in the local shear strength of the sliding interface as a result of the non-homogeneous surface structure of GO. While the exhibited low friction of GO as compared to SiO2 makes it an economically viable coating for micro/nano-electro-mechanical systems with the potential to extend the lifetime of devices, its higher propensity for wear may limit its usefulness. To address this limitation, the wear resistance of GO samples with a higher C/O ratio (∼4) was also studied. The higher C/O ratio GO was found to exhibit much improved wear resistance which approached that of the graphene samples. This demonstrates the potential of tailoring the structure of GO to achieve graphene-like tribological properties.

Mechanism of the reset process in bipolar-resistance-switching Ta/TaOx/Pt capacitors based on observation of the capacitance and resistance

NASA Astrophysics Data System (ADS)

Na, Sang-Chul; Kim, Jae-Jun; Chul Chun, Min; Hee Jin, Da; Ahn, Seung-Eon; Soo Kang, Bo

2014-03-01

The capacitance (C) and the resistance (R) were measured at various states as the reset process progressed in bipolar-resistance-switching Ta/TaOx/Pt thin film capacitors. The reset process was found to undergo three sequential stages where C and R showed different behavior: increasing C and constant R before an abrupt reset transition, the rapid increase of both C and R upon transition, and saturated C thereafter. These behaviors can be explained in terms of the annihilation of the oxygen vacancies followed by rupture of the conducting channels.

New Cu(GeNx) film in barrierless metallization for LED heat dissipation

NASA Astrophysics Data System (ADS)

Lin, Chon-Hsin

2015-05-01

In this study, we explore new Cu(Ge) and Cu(GeNx) films for LED heat dissipation. The films are Cu-alloy seed layers, fabricated by co-sputtering Cu and Ge in an Ar or N2 atmosphere on either Ta/Al2O3 or polyimide substrates. The Cu alloy films are then annealed at 600 and 730 °C, respectively, for 1 h without notable Cu oxide formation at the Cu-Ta/Al2O3 interface. No Cu oxide is formed at the Cu-polyimide interface either after annealing the films at 310 °C for 1 h. The film formed atop an Al2O3 substrate contains a trace amount of GeNx and is thermally stable up to 730 °C, and the film formed atop a polyimide substrate is thermally stable up to 310 °C, both exhibiting a low resistivity and a high thermal conductivity. Such a thermal feature makes the Cu(GeNx) film a good candidate material in barrierless metallization for many industrial applications, such as LED heat sinks.

Patterning of magnetic thin films and multilayers using nanostructured tantalum gettering templates.

PubMed

Qiu, Wenlan; Chang, Long; Lee, Dahye; Dannangoda, Chamath; Martirosyan, Karen; Litvinov, Dmitri

2015-03-25

This work demonstrates that a nonmagnetic thin film of cobalt oxide (CoO) sandwiched between Ta seed and capping layers can be effectively reduced to a magnetic cobalt thin film by annealing at 200 °C, whereas CoO does not exhibit ferromagnetic properties at room temperature and is stable at up to ∼400 °C. The CoO reduction is attributed to the thermodynamically driven gettering of oxygen by tantalum, similar to the exothermic reduction-oxidation reaction observed in thermite systems. Similarly, annealing at 200 °C of a nonmagnetic [CoO/Pd]N multilayer thin film sandwiched between Ta seed and Ta capping layers results in the conversion into a magnetic [Co/Pd]N multilayer, a material with perpendicular magnetic anisotropy that is of interest for magnetic data storage applications. A nanopatterning approach is introduced where [CoO/Pd]N multilayers is locally reduced into [Co/Pd]N multilayers to achieve perpendicular magnetic anisotropy nanostructured array. This technique can potentially be adapted to nanoscale patterning of other systems for which thermodynamically favorable combination of oxide and gettering layers can be identified.

Dependence of electrical and optical properties of amorphous SiC:H thin films grown by rf plasma enhanced chemical vapor deposition on annealing temperature

NASA Astrophysics Data System (ADS)

Park, M. G.; Choi, W. S.; Hong, B.; Kim, Y. T.; Yoon, D. H.

2002-05-01

In this article, we investigated the dependence of optical and electrical properties of hydrogenated amorphous silicon carbide (a-SiC:H) films on annealing temperature (Ta) and radio frequency (rf) power. The substrate temperature (Ts) was 250 °C, the rf power was varied from 30 to 400 W, and the range of Ta was from 400 to 600 °C. The a-SiC:H films were deposited by using the plasma enhanced chemical vapor deposition system on Corning 7059 glasses and p-type Si (100) wafers with a SiH4+CH4 gas mixture. The experimental results have shown that the optical bandgap energy (Eg) of the a-SiC:H thin films changed little on the annealing temperature while Eg increased with the rf power. The Raman spectrum of the thin films annealed at high temperatures showed that graphitization of carbon clusters and microcrystalline silicon occurs. The current-voltage characteristics have shown good electrical properties in relation to the annealed films.

TOPICAL REVIEW: Ultra-thin film encapsulation processes for micro-electro-mechanical devices and systems

NASA Astrophysics Data System (ADS)

Stoldt, Conrad R.; Bright, Victor M.

2006-05-01

A range of physical properties can be achieved in micro-electro-mechanical systems (MEMS) through their encapsulation with solid-state, ultra-thin coatings. This paper reviews the application of single source chemical vapour deposition and atomic layer deposition (ALD) in the growth of submicron films on polycrystalline silicon microstructures for the improvement of microscale reliability and performance. In particular, microstructure encapsulation with silicon carbide, tungsten, alumina and alumina-zinc oxide alloy ultra-thin films is highlighted, and the mechanical, electrical, tribological and chemical impact of these overlayers is detailed. The potential use of solid-state, ultra-thin coatings in commercial microsystems is explored using radio frequency MEMS as a case study for the ALD alloy alumina-zinc oxide thin film.

Determining thickness and refractive index from free-standing ultra-thin polymer films with spectroscopic ellipsometry

DOE PAGES

Hilfiker, James N.; Stadermann, Michael; Sun, Jianing; ...

2016-08-27

It is a well-known challenge to determine refractive index (n) from ultra-thin films where the thickness is less than about 10 nm. In this paper, we discovered an interesting exception to this issue while characterizing spectroscopic ellipsometry (SE) data from isotropic, free-standing polymer films. Ellipsometry analysis shows that both thickness and refractive index can be independently determined for free-standing films as thin as 5 nm. Simulations further confirm an orthogonal separation between thickness and index effects on the experimental SE data. Effects of angle of incidence and wavelength on the data and sensitivity are discussed. Finally, while others have demonstratedmore » methods to determine refractive index from ultra-thin films, our analysis provides the first results to demonstrate high-sensitivity to the refractive index from ultra-thin layers.« less

Effective passivation of silicon surfaces by ultrathin atomic-layer deposited niobium oxide

NASA Astrophysics Data System (ADS)

Macco, B.; Bivour, M.; Deijkers, J. H.; Basuvalingam, S. B.; Black, L. E.; Melskens, J.; van de Loo, B. W. H.; Berghuis, W. J. H.; Hermle, M.; Kessels, W. M. M. Erwin

2018-06-01

This letter reports on effective surface passivation of n-type crystalline silicon by ultrathin niobium oxide (Nb2O5) films prepared by atomic layer deposition (ALD) and subjected to a forming gas anneal at 300 °C. A champion recombination parameter J0 of 20 fA/cm2 and a surface recombination velocity Seff of 4.8 cm/s have been achieved for ultrathin films of 1 nm. The surface pretreatment was found to have a strong impact on the passivation. Good passivation can be achieved on both HF-treated c-Si surfaces and c-Si surfaces with a wet-chemically grown interfacial silicon oxide layer. On HF-treated surfaces, a minimum film thickness of 3 nm is required to achieve a high level of surface passivation, whereas the use of a wet chemically-grown interfacial oxide enables excellent passivation even for Nb2O5 films of only 1 nm. This discrepancy in passivation between both surface types is attributed to differences in the formation and stoichiometry of interfacial silicon oxide, resulting in different levels of chemical passivation. On both surface types, the high level of passivation of ALD Nb2O5 is aided by field-effect passivation originating from a high fixed negative charge density of 1-2 × 1012 cm-3. Furthermore, it is demonstrated that the passivation level provided by 1 nm of Nb2O5 can be further enhanced through light-soaking. Finally, initial explorations show that a low contact resistivity can be obtained using Nb2O5-based contacts. Together, these properties make ALD Nb2O5 a highly interesting building block for high-efficiency c-Si solar cells.

Nucleation of fcc Ta when heating thin films

DOE PAGES

Janish, Matthew T.; Mook, William M.; Carter, C. Barry

2014-10-25

Thin tantalum films have been studied during in-situ heating in a transmission electron microscope. Diffraction patterns from the as-deposited films were typical of amorphous materials. Crystalline grains were observed to form when the specimen was annealed in-situ at 450°C. Particular attention was addressed to the formation and growth of grains with the face-centered cubic (fcc) crystal structure. As a result, these observations are discussed in relation to prior work on the formation of fcc Ta by deformation and during thin film deposition.

Influence of Thickness on the Electrical Transport Properties of Exfoliated Bi2Te3 Ultrathin Films

NASA Astrophysics Data System (ADS)

Mo, D. L.; Wang, W. B.; Cai, Q.

2016-08-01

In this work, the mechanical exfoliation method has been utilized to fabricate Bi2Te3 ultrathin films. The thickness of the ultrathin films is revealed to be several tens of nanometers. Weak antilocalization effects and Shubnikov de Haas oscillations have been observed in the magneto-transport measurements on individual films with different thickness, and the two-dimensional surface conduction plays a dominant role. The Fermi level is found to be 81 meV above the Dirac point, and the carrier mobility can reach ~6030 cm2/(Vs) for the 10-nm film. When the film thickness decreases from 30 to 10 nm, the Fermi level will move 8 meV far from the bulk valence band. The coefficient α in the Hikami-Larkin-Nagaoka equation is shown to be ~0.5, manifesting that only the bottom surface of the Bi2Te3 ultrathin films takes part in transport conductions. These will pave the way for understanding thoroughly the surface transport properties of topological insulators.

Detection of Short-Waved Spin Waves in Individual Microscopic Spin-Wave Waveguides Using the Inverse Spin Hall Effect.

PubMed

Brächer, T; Fabre, M; Meyer, T; Fischer, T; Auffret, S; Boulle, O; Ebels, U; Pirro, P; Gaudin, G

2017-12-13

The miniaturization of complementary metal-oxide-semiconductor (CMOS) devices becomes increasingly difficult due to fundamental limitations and the increase of leakage currents. Large research efforts are devoted to find alternative concepts that allow for a larger data-density and lower power consumption than conventional semiconductor approaches. Spin waves have been identified as a potential technology that can complement and outperform CMOS in complex logic applications, profiting from the fact that these waves enable wave computing on the nanoscale. The practical application of spin waves, however, requires the demonstration of scalable, CMOS compatible spin-wave detection schemes in material systems compatible with standard spintronics as well as semiconductor circuitry. Here, we report on the wave-vector independent detection of short-waved spin waves with wavelengths down to 150 nm by the inverse spin Hall effect in spin-wave waveguides made from ultrathin Ta/Co 8 Fe 72 B 20 /MgO. These findings open up the path for miniaturized scalable interconnects between spin waves and CMOS and the use of ultrathin films made from standard spintronic materials in magnonics.

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

Giant Ferroelectric Polarization in Ultrathin Ferroelectrics via Boundary-Condition Engineering.

PubMed

Xie, Lin; Li, Linze; Heikes, Colin A; Zhang, Yi; Hong, Zijian; Gao, Peng; Nelson, Christopher T; Xue, Fei; Kioupakis, Emmanouil; Chen, Longqing; Schlom, Darrel G; Wang, Peng; Pan, Xiaoqing

2017-08-01

Tailoring and enhancing the functional properties of materials at reduced dimension is critical for continuous advancement of modern electronic devices. Here, the discovery of local surface induced giant spontaneous polarization in ultrathin BiFeO 3 ferroelectric films is reported. Using aberration-corrected scanning transmission electron microscopy, it is found that the spontaneous polarization in a 2 nm-thick ultrathin BiFeO 3 film is abnormally increased up to ≈90-100 µC cm -2 in the out-of-plane direction and a peculiar rumpled nanodomain structure with very large variation in c/a ratios, which is analogous to morphotropic phase boundaries (MPBs), is formed. By a combination of density functional theory and phase-field calculations, it is shown that it is the unique single atomic Bi 2 O 3 - x layer at the surface that leads to the enhanced polarization and appearance of the MPB-like nanodomain structure. This finding clearly demonstrates a novel route to the enhanced functional properties in the material system with reduced dimension via engineering the surface boundary conditions. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hydrogen gas sensors using a thin Ta2O5 dielectric film

NASA Astrophysics Data System (ADS)

Kim, Seongjeen

2014-12-01

A capacitive-type hydrogen gas sensor with a MIS (metal-insulator-semiconductor) structure was investigated for high-temperature applications. In this work, a tantalum oxide (Ta2O5) layer of tens of nanometers in thickness formed by oxidizing tantalum film in rapid thermal processing (RTP) was exploited with the purpose of sensitivity improvement. Silicon carbide (SiC), which is good even at high temperatures over 500 °C, was used as the substrate. We fabricated sensors composed of Pd/Ta2O5/SiC, and the dependences of the capacitance response properties and the I-V characteristics on the hydrogen concentration were analyzed from the temperature range of room temperature to 500 °C. As a result, our hydrogen sensor showed promising performance with respect to the sensitivity and the adaptability at high temperature.

Electrical and thermal properties of Cu-Ta films prepared by magnetron sputtering

NASA Astrophysics Data System (ADS)

Qin, Wen; Fu, Licai; Zhu, Jiajun; Yang, Wulin; Sang, Jianquan; Li, Deyi; Zhou, Lingping

2018-06-01

The microstructure, electrical resistivity and thermal conductivity of the sputtering deposited Cu-Ta films were investigated as a function of Ta content. The results showed that the amorphous phase formed between 20 at.% and 60 at.% Ta, and out of this range α-Cu(Ta) and β-Ta(Cu) solid solutions formed. Because the lattice distortion and β-Ta structure could significantly increase the probability of electron scattering, the electrical resistivity of the Cu-Ta films shows a 'N' type change with the increase of Ta content, and the inflection point appears at 50 at.% Ta and 60 at.% Ta respectively. As the thermal conductance is also dominated by electrons in metals films, an opposite variation tendency is found in the thermal conductivity of the Cu-Ta films. According to our knowledge, this is the first time to measure the thermal conductivity of Cu-Ta thin films.

Chemical sporulation and germination: cytoprotective nanocoating of individual mammalian cells with a degradable tannic acid-FeIII complex

NASA Astrophysics Data System (ADS)

Lee, Juno; Cho, Hyeoncheol; Choi, Jinsu; Kim, Doyeon; Hong, Daewha; Park, Ji Hun; Yang, Sung Ho; Choi, Insung S.

2015-11-01

Individual mammalian cells were coated with cytoprotective and degradable films by cytocompatible processes maintaining the cell viability. Three types of mammalian cells (HeLa, NIH 3T3, and Jurkat cells) were coated with a metal-organic complex of tannic acid (TA) and ferric ion, and the TA-FeIII nanocoat effectively protected the coated mammalian cells against UV-C irradiation and a toxic compound. More importantly, the cell proliferation was controlled by programmed formation and degradation of the TA-FeIII nanocoat, mimicking the sporulation and germination processes found in nature.Individual mammalian cells were coated with cytoprotective and degradable films by cytocompatible processes maintaining the cell viability. Three types of mammalian cells (HeLa, NIH 3T3, and Jurkat cells) were coated with a metal-organic complex of tannic acid (TA) and ferric ion, and the TA-FeIII nanocoat effectively protected the coated mammalian cells against UV-C irradiation and a toxic compound. More importantly, the cell proliferation was controlled by programmed formation and degradation of the TA-FeIII nanocoat, mimicking the sporulation and germination processes found in nature. Electronic supplementary information (ESI) available: Experimental details, LSCM images, and SEM and TEM images. See DOI: 10.1039/c5nr05573c

Modeling of UV laser-induced patterning of ultrathin Co films on bulk SiO2: verification of short- and long-range ordering mechanisms

NASA Astrophysics Data System (ADS)

Trice, Justin; Favazza, Christopher; Kalyanaraman, Ramki; Sureshkumar, R.

2006-03-01

Irradiating ultrathin Co films (1 to 10 nm) by a short-pulsed UV laser leads to pattern formation with both short- and long-range order (SRO, LRO). Single beam irradiation produces SRO, while two-beam interference irradiation produces a quasi-2D arrangement of nanoparticles with LRO and SRO. The pattern formation primarily occurs in the molten phase. An estimate of the thermal behavior of the film/substrate composite following a laser pulse is presented. The thermal behavior includes the lifetime of the liquid phase and the thermal gradient during interference heating. Based on this evidence, the SRO is attributed to spinodal dewetting of the film while surface tension gradients induced by the laser interference pattern appear to influence LRO [1]. [1] C.Favazza, J.Trice, H.Krishna, R.Sureshkumar, and R.Kalyanaraman, unpublished.

Influences of annealing temperature on sprayed CuFeO2 thin films

NASA Astrophysics Data System (ADS)

Abdelwahab, H. M.; Ratep, A.; Abo Elsoud, A. M.; Boshta, M.; Osman, M. B. S.

2018-06-01

Delafossite CuFeO2 thin films were successfully prepared onto quartz substrates using simple spray pyrolysis technique. Post annealing under nitrogen atmosphere for 2 h was necessary to form delafossite CuFeO2 phase. The effect of alteration in annealing temperature (TA) 800, 850 and 900 °C was study on structural, morphology and optical properties. The XRD results for thin film annealed at TA = 850 °C show single phase CuFeO2 with rhombohedral crystal system and R 3 bar m space group with preferred orientation along (0 1 2). The prepared copper iron oxide thin films have an optical transmission ranged ∼40% in the visible region. The optical direct optical band gap of the prepared thin films was ranged ∼2.9 eV.

Structural and electrical characterization of annealed Si1-xCx/SiC thin film prepared by magnetron sputtering

NASA Astrophysics Data System (ADS)

Huang, Shi-Hua; Liu, Jian

2014-05-01

Si-rich Si1—xCx /SiC multilayer thin films are prepared using magnetron sputtering, subsequently followed by thermal annealing in the range of 800-1200 °C. The influences of annealing temperature (Ta) on the formation of Si and/or SiC nanocrystals (NCs) and on the electrical characteristics of the multilayer film are investigated by using a variety of analytical techniques, including X-ray diffraction (XRD), Raman spectroscopy and Fourier transform infrared spectrometry (FT-IR), current—voltage (I—V) technique, and capacitance-voltage (C—V) technique. XRD and Raman analyses indicate that Si NCs begin to form in samples for Ta >= 800 °C. At annealing temperatures of 1000 °C or higher, the formation of Si NCs is accompanied by the formation of SiC NCs. With the increase in the annealing temperature, the shift of FT-IR Si—C bond absorption spectra toward a higher wave number along with the change of band shape can be explained by a Si—C transitional phase between the loss of substitutional carbon and the formation of SiC precipitates and a precursor for the growth of SiC crystalline. The C—V and I—V results indicate that the interface quality of Si1—xCx/SiC multilayer film is improved significantly and the leakage current is reduced rapidly for Ta >= 1000 °C, which can be ascribed to the formation of Si and SiC NCs.

Fabrication and characterization of NiO based metal-insulator-metal diode using Langmuir-Blodgett method for high frequency rectification

NASA Astrophysics Data System (ADS)

Azad, Ibrahim; Ram, Manoj K.; Goswami, D. Yogi; Stefanakos, Elias

2018-04-01

Thin film metal-insulator-metal (MIM) diodes have attracted significant attention for use in infrared energy harvesting and detection applications. As demonstrated over the past decades, MIM or metal-insulator-insulator-metal (MIIM) diodes can operate at the THz frequencies range by quantum tunneling of electrons. The aim of this work is to synthesize required ultra-thin insulating layers and fabricate MIM diodes using the Langmuir-Blodgett (LB) technique. The nickel stearate (NiSt) LB precursor film was deposited on glass, silicon (Si), ITO glass and gold coated silicon substrates. The photodesorption (UV exposure) and the thermodesorption (annealing at 100 °C and 350 °C) methods were used to remove organic components from the NiSt LB film and to achieve a uniform homogenous nickel oxide (NiO) film. These ultrathin NiO films were characterized by EDS, AFM, FTIR and cyclic voltammetry methods, respectively. The MIM diode was fabricated by depositing nickel (Ni) on the NiO film, all on a gold (Au) plated silicon (Si) substrate. The current (I)-voltage (V) characteristics of the fabricated diode were studied to understand the conduction mechanism assumed to be tunneling of electron through the ultra-thin insulating layer. The sensitivity of the diode was measured to be as high as 35 V-1. The diode resistance was ˜100 ohms (at a bias voltage of 0.60 V), and the rectification ratio was about 22 (for a signal voltage of ±200 mV). At the bias point, the diode response demonstrated significant non-linearity and high asymmetry, which are very desirable characteristics for applications in infrared detection and harvesting.

Growth, stability and decomposition of Mg2Si ultra-thin films on Si (100)

NASA Astrophysics Data System (ADS)

Sarpi, B.; Zirmi, R.; Putero, M.; Bouslama, M.; Hemeryck, A.; Vizzini, S.

2018-01-01

Using Auger Electron Spectroscopy (AES), Scanning Tunneling Microscopy/Spectroscopy (STM/STS) and Low Energy Electron Diffraction (LEED), we report an in-situ study of amorphous magnesium silicide (Mg2Si) ultra-thin films grown by thermally enhanced solid-phase reaction of few Mg monolayers deposited at room temperature (RT) on a Si(100) surface. Silicidation of magnesium films can be achieved in the nanometric thickness range with high chemical purity and a high thermal stability after annealing at 150 °C, before reaching a regime of magnesium desorption for temperatures higher than 350 °C. The thermally enhanced reaction of one Mg monolayer (ML) results in the appearance of Mg2Si nanometric crystallites leaving the silicon surface partially uncovered. For thicker Mg deposition nevertheless, continuous 2D silicide films are formed with a volcano shape surface topography characteristic up to 4 Mg MLs. Due to high reactivity between magnesium and oxygen species, the thermal oxidation process in which a thin Mg2Si film is fully decomposed (0.75 eV band gap) into a magnesium oxide layer (6-8 eV band gap) is also reported.

Fabrication of vanadium dioxide polycrystalline films with higher temperature coefficient of resistance

NASA Astrophysics Data System (ADS)

Li, Jinhua; Yuan, Ningyi; Jiang, Meiping; Kun, Li

2011-08-01

Vanadium Dioxide Polycrystalline Films with High Temperature Coefficient of Resistance(TCR) were fabricated by modified Ion Beam Enhanced Deposition(IBED) method. The TCR of the Un-doping VO2 was about -4%/K at room temperature after appropriate thermal annealing. The XRD results clearly showed that IBED polycrystalline VO2 films had a single [002] orientation of VO2(M). The TCR of 5at.%W and 7at.% Ta doped Vanadium Dioxide Polycrystalline Films were high up to -18%/K and -12%/K at room temperature, respectively. Using 7at.% Ta and 2at.% Ti co-doping, the TCR of the co-doped vanadium oxide film was -7%/K and without hysteresis during temperature increasing and decresing from 0-80°C. It should indicate that the W-doped vanadium dioxide films colud be used for high sensing IR detect and the Ta/Ti co-doped film without hysteresis is suitable for infrarid imaging application.

Ultrathin g-C3N4 films supported on Attapulgite nanofibers with enhanced photocatalytic performance

NASA Astrophysics Data System (ADS)

Xu, Yongshuai; Zhang, Lili; Yin, Minghui; Xie, Dengyu; Chen, Jiaqi; Yin, Jingzhou; Fu, Yongsheng; Zhao, Pusu; Zhong, Hui; Zhao, Yijiang; Wang, Xin

2018-05-01

A novel visible-light-responsive photocatalyst is fabricated by introducing g-C3N4 ultrathin films onto the surface of attapulgite (ATP) via a simple in-situ depositing technique, in which ATP was pre-grafted using (3-Glycidyloxypropyl) trimethoxysilane (KH560) as the surfactant. A combination of XRD, FT-IR, BET, XPS, UV-vis, TEM and SEM techniques are utilized to characterize the composition, morphology and optical properties of the products. The results show that with the help of KH560, g-C3N4 presented as ultrathin layer is uniformly loaded onto the surface of ATP by forming a new chemical bond (Sisbnd Osbnd C). Comparing with g-C3N4 and ATP, ATP/g-C3N4 exhibits remarkably enhanced visible-light photocatalytic activity in degradation of methyl orange (MO) because of its high surface area, appropriate band gap and the synergistic effect between g-C3N4 and ATP. To achieve the best photocatalyst, the ratio of g-C3N4 was adjusted by controlling the mass portion between ATP-KH560 and melamine (r = m (ATP-KH560)/m (melamine)). The highest decomposition rate of methyl orange (MO) was 96.06% when r = 0.5 and this degradation efficiency remained unchanged after 4 cycles, which is 10 times as that of pure g-C3N4 particles. Possible photocatalytic mechanism is presented.

Ion-beam mixed ultra-thin cobalt suicide (CoSi2) films by cobalt sputtering and rapid thermal annealing

NASA Astrophysics Data System (ADS)

Kal, S.; Kasko, I.; Ryssel, H.

1995-10-01

The influence of ion-beam mixing on ultra-thin cobalt silicide (CoSi2) formation was investigated by characterizing the ion-beam mixed and unmixed CoSi2 films. A Ge+ ion-implantation through the Co film prior to silicidation causes an interface mixing of the cobalt film with the silicon substrate and results in improved silicide-to-silicon interface roughness. Rapid thermal annealing was used to form Ge+ ion mixed and unmixed thin CoSi2 layer from 10 nm sputter deposited Co film. The silicide films were characterized by secondary neutral mass spectroscopy, x-ray diffraction, tunneling electron microscopy (TEM), Rutherford backscattering, and sheet resistance measurements. The experi-mental results indicate that the final rapid thermal annealing temperature should not exceed 800°C for thin (<50 nm) CoSi2 preparation. A comparison of the plan-view and cross-section TEM micrographs of the ion-beam mixed and unmixed CoSi2 films reveals that Ge+ ion mixing (45 keV, 1 × 1015 cm-2) produces homogeneous silicide with smooth silicide-to-silicon interface.

Vanadium dioxide film protected with an atomic-layer-deposited Al{sub 2}O{sub 3} thin film

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

Wang, Xiao; Cao, Yunzhen, E-mail: yzhcao@mail.sic.ac.cn; Yang, Chao

2016-01-15

A VO{sub 2} film exposed to ambient air is prone to oxidation, which will degrade its thermochromic properties. In this work, the authors deposited an ultrathin Al{sub 2}O{sub 3} film with atomic layer deposition (ALD) to protect the underlying VO{sub 2} film from degradation, and then studied the morphology and crystalline structure of the films. To assess the protectiveness of the Al{sub 2}O{sub 3} capping layer, the authors performed a heating test and a damp heating test. An ultrathin 5-nm-thick ALD Al{sub 2}O{sub 3} film was sufficient to protect the underlying VO{sub 2} film heated at 350 °C. However, in amore » humid environment at prolonged durations, a thicker ALD Al{sub 2}O{sub 3} film (15 nm) was required to protect the VO{sub 2}. The authors also deposited and studied a TiO{sub 2}/Al{sub 2}O{sub 3} bilayer, which significantly improved the protectiveness of the Al{sub 2}O{sub 3} film in a humid environment.« less

0D/2D Z-Scheme Heterojunctions of Bismuth Tantalate Quantum Dots/Ultrathin g-C3N4 Nanosheets for Highly Efficient Visible Light Photocatalytic Degradation of Antibiotics.

PubMed

Wang, Kai; Zhang, Gaoke; Li, Jun; Li, Yuan; Wu, Xiaoyong

2017-12-20

Constructing 0D/2D Z-scheme photocatalysts is a great promising path to improve photocatalytic activity by  efficiently enhancing charge separation. Herein, we fabricated a visible-light-responsive Bi 3 TaO 7 quantum dots (QDs)/g-C 3 N 4 nanosheets (NSs) 0D/2D Z-scheme composite via a facile ultrasound method, and Bi 3 TaO 7 QDs could be interspersed on the surface of g-C 3 N 4 NSs uniformly. Furthermore, the strong interaction between Bi 3 TaO 7 QDs and g-C 3 N 4 NSs disturbed the CN heterocycles by forming C═O bonds between C atoms of the N-(C) 3 group and O atoms of the Ta-O bond. The optimum composite with 20 wt % g-C 3 N 4 NSs showed the superior photocatalytic activity for degradation of ciprofloxacin (CIP) over the composites prepared by mechanical mixing and solid-state methods, the photocatalytic efficiency of which were 4 and 12.2 times higher than those of bare Bi 3 TaO 7 and g-C 3 N 4 . Photoluminescence (PL), time-resolved transient PL decay spectra, and photocurrent together verify that the photogenerated hole-electron pairs in this 0D/2D Z-scheme composite have been effectively separated. The enhanced photocatalytic activity of as-synthesized photocatalysts could be attributed to the synergistic effect of efficient Z-scheme charge separation, highly dispersed 0D Bi 3 TaO 7 nanocrystals, coordinating sites of 2D g-C 3 N 4 NSs and the strong coupling between them. This study might pave the way toward designing novel visible-light-induced 0D/2D photocatalyst systems for highly efficient degradation of antibiotics.

Exploitation of a Self-limiting Process for Reproducible Formation of Ultrathin Ni(1-x)Pt(x) Silicide Films

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

Z Zhang; B Yang; Y Zhu

This letter reports on a process scheme to obtain highly reproducible Ni{sub 1-x}Pt{sub x} silicide films of 3-6 nm thickness formed on a Si(100) substrate. Such ultrathin silicide films are readily attained by sputter deposition of metal films, metal stripping in wet chemicals, and final silicidation by rapid thermal processing. This process sequence warrants an invariant amount of metal intermixed with Si in the substrate surface region independent of the initial metal thickness, thereby leading to a self-limiting formation of ultrathin silicide films. The crystallographic structure, thickness, uniformity, and morphological stability of the final silicide films depend sensitively on themore » initial Pt fraction.« less

Atomic layer deposition and post-growth thermal annealing of ultrathin MoO3 layers on silicon substrates: Formation of surface nanostructures

NASA Astrophysics Data System (ADS)

Liu, Hongfei; Yang, Ren Bin; Yang, Weifeng; Jin, Yunjiang; Lee, Coryl J. J.

2018-05-01

Ultrathin MoO3 layers have been grown on Si substrates at 120 °C by atomic layer deposition (ALD) using molybdenum hexacarbonyl [Mo(CO)6] and ozone (O3) as the Mo- and O-source precursors, respectively. The ultrathin films were further annealed in air at Tann = 550-750 °C for 15 min. Scanning-electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy have been employed to evaluate the morphological and elemental properties as well as their evolutions upon annealing of the thin films. They revealed an interfacial SiOx layer in between the MoO3 layer and the Si substrate; this SiOx layer converted into SiO2 during the annealing; and the equivalent thickness of the MoO3 (SiO2) layer decreased (increased) with the increase in Tann. Particles with diameters smaller than 50 nm emerged at Tann = 550 °C and their sizes (density) were reduced (increased) by increasing Tann to 650 °C. A further increase of Tann to 750 °C resulted in telephone-cord-like MoO3 structures, initiated from isolated particles on the surface. These observations have been discussed and interpreted based on temperature-dependent atomic interdiffusions, surface evaporations, and/or melting of MoO3, which shed new light on ALD MoO3 towards its electronic applications.

Effect of deposition temperature on morphological, magnetic and elastic properties of ultrathin Co49Pt51 films

NASA Astrophysics Data System (ADS)

Si Abdallah, F.; Chérif, S. M.; Bouamama, Kh.; Roussigné, Y.; Hsu, J.-H.

2018-03-01

Morphological, magnetic and elastic properties of 5 nm-thick Co49Pt51 films, sputtered on glass substrates, with 20 nm-thick Ta (seed) and Pt (buffer) layers were studied as function of the deposition temperature Td ranging between room temperature and 350° C. Atomic and magnetic force microscopy, vibrating sample magnetometer and Brillouin light scattering techniques were used to investigate the root mean square (RMS) roughness, the magnetic domain configuration, the coercive field (Hc), the perpendicular magnetic anisotropy (PMA), and the dynamic magnetic and elastic properties of the films with Td. The results show that surface uniformity was enhanced since the RMS roughness decreases with Td while magnetic domains typical of films with high PMA are observed. Hc and PMA are found to sensibly increase with Td. The dynamic magnetization behavior is characterized by magnetic modes related with the co-existence of hard and soft magnetic areas within the samples. The elastic properties of the stack were first analyzed by means of a model describing the main variation of the elastic wave frequencies within the frame of weighted average thickness, density, Young's modulus and Poisson coefficient of all the layers constituting the stacks. However, while Hc and PMA keep increasing with Td, a more precise experimental analysis of the mechanical behavior shows that the group velocity starts increasing and finally decreases with Td, suggesting that knowledge of the influence of Td on the mechanical properties of each individual layer composing the stack is required to obtain a more accurate analysis.

Appearance and disappearance of ferromagnetism in ultrathin LaMnO3 on SrTiO3 substrate: A viewpoint from first principles

NASA Astrophysics Data System (ADS)

An, Ming; Weng, Yakui; Zhang, Huimin; Zhang, Jun-Jie; Zhang, Yang; Dong, Shuai

2017-12-01

The intrinsic magnetic state (ferromagnetic or antiferromagnetic) of ultrathin LaMnO3 films on the most commonly used SrTiO3 substrate is a long-existing question under debate. Either strain effect or nonstoichiometry was argued to be responsible for the experimental ferromagnetism. In a recent experiment [X. R. Wang, C. J. Li, W. M. Lü, T. R. Paudel, D. P. Leusink, M. Hoek, N. Poccia, A. Vailionis, T. Venkatesan, J. M. D. Coey, E. Y. Tsymbal, Ariando, and H. Hilgenkamp, Science 349, 716 (2015), 10.1126/science.aaa5198], one more mechanism, namely, the self-doping due to polar discontinuity, was argued to be the driving force of ferromagnetism beyond the critical thickness. Here systematic first-principles calculations have been performed to check these mechanisms in ultrathin LaMnO3 films as well as superlattices. Starting from the very precise descriptions of both LaMnO3 and SrTiO3, it is found that the compressive strain is the dominant force for the appearance of ferromagnetism, while the open surface with oxygen vacancies leads to the suppression of ferromagnetism. Within LaMnO3 layers, the charge reconstructions involve many competitive factors and certainly go beyond the intuitive polar catastrophe model established for LaAlO3/SrTiO3 heterostructures. Our paper not only explains the long-term puzzle regarding the magnetism of ultrathin LaMnO3 films but also sheds light on how to overcome the notorious magnetic dead layer in ultrathin manganites.

A repeated halving approach to fabricate ultrathin single-walled carbon nanotube films for transparent supercapacitors.

PubMed

Niu, Zhiqiang; Zhou, Weiya; Chen, Jun; Feng, Guoxing; Li, Hong; Hu, Yongsheng; Ma, Wenjun; Dong, Haibo; Li, Jinzhu; Xie, Sishen

2013-02-25

Ultrathin SWCNT transparent and conductive films on flexible and transparent substrates are prepared via repeatedly halving the directly grown SWCNT films and flexible and transparent supercapacitors with excellent performance were fabricated. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nucleation of C60 on ultrathin SiO2

NASA Astrophysics Data System (ADS)

Conrad, Brad; Groce, Michelle; Cullen, William; Pimpinelli, Alberto; Williams, Ellen; Einstein, Ted

2012-02-01

We utilize scanning tunneling microscopy to characterize the nucleation, growth, and morphology of C60 on ultrathin SiO2 grown at room temperature. C60 thin films are deposited in situ by physical vapor deposition with thicknesses varying from <0.05 to ˜1 ML. Island size and capture zone distributions are examined for a varied flux rate and substrate deposition temperature. The C60 critical nucleus size is observed to change between monomers and dimers non-monotonically from 300 K to 500 K. Results will be discussed in terms of recent capture zone studies and analysis methods. Relation to device fabrication will be discussed. doi:10.1016/j.susc.2011.08.020

Comparison of molecular orientation and phase transition behaviors in the two kinds of ordered ultrathin films of reversed duckweed polymer ES-3 studied by infrared grazing reflection-absorption spectroscopy

NASA Astrophysics Data System (ADS)

Wang, Qiang; Xu, Weiqing; Zhao, Bing

2003-03-01

A multilayer LB film and a casting film of reversed duckweed polymer ES-3 on Au-evaporated glass slides were investigated by Fourier Transform infrared grazing reflection-absorption spectroscopy. It is found that the two kinds of ordered ultrathin films have different orientation of alkyl chains, nearly perpendicular to the substrate surface for the LB film while rather tilted for the casting film. The studies on their thermal transition behaviors indicate that both of the films have three phase transition processes, respectively, occurring near 65, 105 and 140 °C for the former while near 80, 105 and 140 °C for the latter, but show different transition behavior in the each corresponding transition process. It is referred that at room temperature there are island-like domain structures formed in the LB film, but no ones in the casting film; however, the latter can form the domain structures between the first two transition points due to the desorption of solvents. The formation of domain structure seems to play two important roles, one of which is to make alkyl chains more perpendicular to the substrate surface, and the other to make alkyl chains more packed closely. Thermal cyclic experiments reveal that neither of the films could return to its original state after thermal cyclic treatment up to the temperature, which is above the third transition point, although its alkyl chain becomes highly ordered again.

Enhanced magnetic moment in ultrathin Fe-doped CoFe2O4 films

NASA Astrophysics Data System (ADS)

Moyer, J. A.; Vaz, C. A. F.; Kumah, D. P.; Arena, D. A.; Henrich, V. E.

2012-11-01

The effect of film thickness on the magnetic properties of ultrathin Fe-doped cobalt ferrite (Co1-xFe2+xO4) grown on MgO (001) substrates is investigated by superconducting quantum interference device magnetometry and x-ray magnetic linear dichroism, while the distribution of the Co2+ cations between the octahedral and tetrahedral lattice sites is studied with x-ray absorption spectroscopy. For films thinner than 10 nm, there is a large enhancement of the magnetic moment; conversely, the remanent magnetization and coercive fields both decrease, while the magnetic spin axes of all the cations become less aligned with the [001] crystal direction. In particular, at 300 K the coercive fields of the thinnest films vanish. The spectroscopy data show that no changes occur in the cation distribution as a function of film thickness, ruling this out as the origin of the enhanced magnetic moment. However, the magnetic measurements all support the possibility that these ultrathin Fe-doped CoFe2O4 films are transitioning into a superparamagnetic state, as has been seen in ultrathin Fe3O4. A weakening of the magnetic interactions at the antiphase boundaries, leading to magnetically independent domains within the film, could explain the enhanced magnetic moment in ultrathin Fe-doped CoFe2O4 and the onset of superparamagnetism at room temperature.

Physicochemically functional ultrathin films by interfacial polymerization

DOEpatents

Lonsdale, Harold K.; Babcock, Walter C.; Friensen, Dwayne T.; Smith, Kelly L.; Johnson, Bruce M.; Wamser, Carl C.

1990-01-01

Interfacially-polymerized ultrathin films containing physicochemically functional groups are disclosed, both with and without supports. Various applications are disclsoed, including membrane electrodes, selective membranes and sorbents, biocompatible materials, targeted drug delivery, and narrow band optical absorbers.

Application of cluster-plus-glue-atom model to barrierless Cu–Ni–Ti and Cu–Ni–Ta films

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

Li, Xiaona, E-mail: lixiaona@dlut.edu.cn; Ding, Jianxin; Wang, Miao

To improve the thermal stability of copper and avoid its diffusion into surrounding dielectrics or interfacial reactions with them, the authors applied the cluster-plus-glue-atom model to investigate barrierless Cu–Ni–M (M = Ti or Ta) seed layers. The dissolution of the third element (Ti or Ta) in the Cu lattice with the aid of Ni significantly improved the thermal stability of the Cu seed layer. The appropriate M/Ni (M = Ti or Ta) ratio was selected to obtain a low resistivity: the resistivity was as low as 2.5 μΩ cm for the (Ti{sub 1.5/13.5}Ni{sub 12/13.5}){sub 0.3}Cu{sub 99.7} film and 2.8 μΩ cm for the (Ta{sub 1.1/13.1}Ni{sub 12/13.1}){submore » 0.4}Cu{sub 99.6} film after annealing at 500 °C for 1 h. After annealing at 500 °C for 40 h, the two films remained stable without forming a Cu{sub 3}Si compound. The authors confirmed that the range of applications of the cluster-plus-glue-atom model could be extended. Therefore, a third element M with negative enthalpies of mixing with both Cu and Ni could be selected, under the premise that the mixing enthalpy of M–Ni is more negative than that of M–Cu.« less

Molecular Imaging of Ultrathin Pentacene Films: Evidence for Homoepitaxy

NASA Astrophysics Data System (ADS)

Wu, Yanfei; Haugstad, Greg; Frisbie, C. Daniel

2013-03-01

Ultrathin polycrystalline films of organic semiconductors have received intensive investigations due to the critical role they play in governing the performance of organic thin film transistors. In this work, a variety of scanning probe microscopy (SPM) techniques have been employed to investigate ultrathin polycrystalline films (1-3 nm) of the benchmark organic semiconductor pentacene. By using spatially resolved Friction Force Microscopy (FFM), Kelvin Probe Force Microscopy (KFM) and Electrostatic Force Microscopy (EFM), an interesting multi-domain structure is revealed within the second layer of the films, characterized as two distinct friction and surface potential domains correlating with each other. The existence of multiple homoepitaxial modes within the films is thus proposed and examined. By employing lattice-revolved imaging using contact mode SPM, direct molecular evidence for the unusual homoepitaxy is obtained.

High-temperature wear and oxidation behaviors of TiNi/Ti2Ni matrix composite coatings with TaC addition prepared on Ti6Al4V by laser cladding

NASA Astrophysics Data System (ADS)

Lv, Y. H.; Li, J.; Tao, Y. F.; Hu, L. F.

2017-04-01

TiNi/Ti2Ni matrix composite coatings were produced on Ti6Al4V surfaces by laser cladding the mixed powders of Ni-based alloy and different contents of TaC (0, 5, 10, 15, 20, 30 and 40 wt.%). Microstructures of the coatings were investigated. High-temperature wear tests of the substrate and the coatings were carried out at 600 °C in air for 30 min. High-temperature oxidation tests of the substrate and the coatings were performed at 1000 °C in air for 50 h. Wear and oxidation mechanisms were revealed in detail. The results showed that TiNi/Ti2Ni as the matrix and TiC/TiB2/TiB as the reinforcements are the main phases of the coatings. The friction coefficients of the substrate and the coatings with different contents of TaC were 0.431 (the substrate), 0.554 (0 wt.%), 0.486 (5 wt.%), 0.457 (10 wt.%), 0.458 (15 wt.%), 0.507 (20 wt.%), 0.462 (30 wt.%) and 0.488 (40 wt.%). The wear rates of the coatings were decreased by almost 83%-98% than that of the substrate and presented a decreasing tendency with increasing TaC content. The wear mechanism of the substrate was a combination of serious oxidation, micro-cutting and brittle debonding. For the coatings, oxidation and slight scratching were predominant during wear, accompanied by slight brittle debonding in partial zones. With the increase in content of TaC, the oxidation film better shielded the coatings from destruction due to the effective friction-reducing role of Ta2O5. The oxidation rates of the substrate and the coatings with different contents of TaC at 1000 °C were 12.170 (the substrate), 5.886 (0 wt.%), 4.937 (5 wt.%), 4.517 (10 wt.%), 4.394 (15 wt.%), 3.951 (20 wt.%), 4.239 (30 wt.%) and 3.530 (40 wt.%) mg2 cm-4 h-1, respectively. The oxidation film formed outside the coating without adding TaC was composed of TiO2, NiO, Cr2O3, Al2O3 and SiO2. When TaC was added, Ta2O5 and TaC were also detected, which effectively improved the oxidation resistance of the coatings. The addition of TaC contributed to the improvement in high-temperature wear and oxidation resistance.

Method for laser welding ultra-thin metal foils

DOEpatents

Pernicka, J.C.; Benson, D.K.; Tracy, C.E.

1996-03-26

A method for simultaneously cutting and welding ultra-thin foils having a thickness of less than 0.002 inches wherein two ultra-thin films are stacked and clamped together. A pulsed laser such as of the Neodymium: YAG type is provided and the beam of the laser is directed onto the stacked films to cut a channel through the films. The laser is moved relative to the stacked foils to cut the stacked foils at successive locations and to form a plurality of connected weld beads to form a continuous weld. 5 figs.

Method for laser welding ultra-thin metal foils

DOEpatents

Pernicka, John C.; Benson, David K.; Tracy, C. Edwin

1996-01-01

A method for simultaneously cutting and welding ultra-thin foils having a thickness of less than 0.002 inches wherein two ultra-thin films are stacked and clamped together. A pulsed laser such as of the Neodymium: YAG type is provided and the beam of the laser is directed onto the stacked films to cut a channel through the films. The laser is moved relative to the stacked foils to cut the stacked foils at successive locations and to form a plurality of connected weld beads to form a continuous weld.

Tunable anomalous hall effect induced by interfacial catalyst in perpendicular multilayers

NASA Astrophysics Data System (ADS)

Zhang, J. Y.; Peng, W. L.; Sun, Q. Y.; Liu, Y. W.; Dong, B. W.; Zheng, X. Q.; Yu, G. H.; Wang, C.; Zhao, Y. C.; Wang, S. G.

2018-04-01

The interfacial structures, playing a critical role on the transport properties and the perpendicular magnetic anisotropy in thin films and multilayers, can be modified by inserting an ultrathin functional layer at the various interfaces. The anomalous Hall effect (AHE) in the multilayers with core structure of Ta/CoFeB/X/MgO/Ta (X: Hf or Pt) is tuned by interfacial catalytic engineering. The saturation anomalous Hall resistance (RAH) is increased by 16.5% with 0.1 nm Hf insertion compared with the reference sample without insertion. However, the RAH value is decreased by 9.0% with 0.1 nm Pt insertion. The interfacial states were characterized by the X-ray photoelectron spectroscopy (XPS). The XPS results indicate that a strong bonding between Hf and O for Hf insertion, but no bonding between Pt and O for Pt insertion. The bonding between metal and oxygen leads to various oxygen migration behavior at the interfaces. Therefore, the opposite behavior about the RAH originates from the different oxygen behavior due to various interfacial insertion. This work provides a new approach to manipulate spin transport property for the potential applications.

Impact of Ultrathin C60 on Perovskite Photovoltaic Devices.

PubMed

Liu, Dianyi; Wang, Qiong; Traverse, Christopher J; Yang, Chenchen; Young, Margaret; Kuttipillai, Padmanaban S; Lunt, Sophia Y; Hamann, Thomas W; Lunt, Richard R

2018-01-23

Halide perovskite solar cells have seen dramatic progress in performance over the past several years. Certified efficiencies of inverted structure (p-i-n) devices have now exceeded 20%. In these p-i-n devices, fullerene compounds are the most popular electron-transfer materials. However, the full function of fullerenes in perovskite solar cells is still under investigation, and the mechanism of photocurrent hysteresis suppression by fullerene remains unclear. In previous reports, thick fullerene layers (>20 nm) were necessary to fully cover the perovskite film surface to make good contact with perovskite film and avoid large leakage currents. In addition, the solution-processed fullerene layer has been broadly thought to infiltrate into the perovskite film to passivate traps on grain boundary surfaces, causing suppressed photocurrent hysteresis. In this work, we demonstrate an efficient perovskite photovoltaic device with only 1 nm C 60 deposited by vapor deposition as the electron-selective material. Utilizing a combination of fluorescence microscopy and impedance spectroscopy, we show that the ultrathin C 60 predominately acts to extract electrons from the perovskite film while concomitantly suppressing the photocurrent hysteresis by reducing space charge accumulation at the interface. This work ultimately helps to clarify the dominant role of fullerenes in perovskite solar cells while simplifying perovskite solar cell design to reduce manufacturing costs.

Physicochemically functional ultrathin films by interfacial polymerization

DOEpatents

Lonsdale, H.K.; Babcock, W.C.; Friensen, D.T.; Smith, K.L.; Johnson, B.M.; Wamser, C.C.

1990-08-14

Interfacially-polymerized ultrathin films containing physicochemically functional groups are disclosed, both with and without supports. Various applications are disclosed, including membrane electrodes, selective membranes and sorbents, biocompatible materials, targeted drug delivery, and narrow band optical absorbers. 3 figs.

Electrochemical Corrosion Behavior of Ta2N Nanoceramic Coating in Simulated Body Fluid

PubMed Central

Cheng, Jian; Xu, Jiang; Liu, Lin Lin; Jiang, Shuyun

2016-01-01

In order to improve the corrosion and wear resistance of biomedical Ti-6Al-4V implants, a Ta2N nanoceramic coating was synthesized on a Ti-6Al-4V substrate by the double glow discharge plasma process. The Ta2N coating, composed of fine nanocrystals, with an average grain size of 12.8 nm, improved the surface hardness of Ti-6Al-4V and showed good contact damage tolerance and good adhesion strength to the substrate. The corrosion resistance of the Ta2N coating in Ringer’s physiological solution at 37 °C was evaluated by different electrochemical techniques: potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), potentiostatic polarization and capacitance measurements (Mott-Schottky approach). The evolution of the surface composition of the passive films at different applied potentials was determined by X-ray photoelectron spectroscopy (XPS). The results indicated that the Ta2N coating showed higher corrosion resistance than both commercially pure Ta and uncoated Ti-6Al-4V in this solution, because of the formed oxide film on the Ta2N coating having a smaller carrier density (Nd) and diffusivity (Do) of point defects. The composition of the surface passive film formed on the Ta2N coating changed with the applied potential. At low applied potentials, the oxidation of the Ta2N coating led to the formation of tantalum oxynitride (TaOxNy) but, subsequently, the tantalum oxynitride (TaOxNy) could be chemically converted to Ta2O5 at higher applied potentials. PMID:28773893

Fabrication of micromachined ceramic thin-film-type pressure sensors for overpressure tolerance and its characteristics

NASA Astrophysics Data System (ADS)

Chung, Gwiy-Sang; Kim, Jae-Min

2004-04-01

This paper describes the fabrication process and characteristics of ceramic thin-film pressure sensors based on Ta-N strain gauges for harsh environment applications. The Ta-N thin-film strain gauges are sputter-deposited on a thermally oxidized micromachined Si diaphragm with buried cavities for overpressure tolerance. The proposed device takes advantage of the good mechanical properties of single-crystalline Si as a diaphragm fabricated by SDB and electrochemical etch-stop technology, and in order to extend the temperature range, it has relatively higher resistance, stability and gauge factor of Ta-N thin-films more than other gauges. The fabricated pressure sensor presents a low temperature coefficient of resistance, high-sensitivity, low nonlinearity and excellent temperature stability. The sensitivity is 1.21-1.097 mV/V×kgf/cm2 in temperature ranges of 25-200°C and a maximum non-linearity is 0.43 %FS.

Formation and investigation of ultrathin layers of Co2FeSi ferromagnetic alloy synthesized on silicon covered with a CaF2 barrier layer

NASA Astrophysics Data System (ADS)

Grebenyuk, G. S.; Gomoyunova, M. V.; Pronin, I. I.; Vyalikh, D. V.; Molodtsov, S. L.

2016-03-01

Ultrathin (∼2 nm) films of Co2FeSi ferromagnetic alloy were formed on silicon by solid-phase epitaxy and studied in situ. Experiments were carried out in an ultrahigh vacuum (UHV) using substrates of Si(1 1 1) single crystals covered with a 5 nm thick CaF2 barrier layer. The elemental and phase composition as well as the magnetic properties of the synthesized films were analyzed by photoelectron spectroscopy using synchrotron radiation and by magnetic linear dichroism in photoemission of Fe 3p and Co 3p electrons. The study shows that the synthesis of the Co2FeSi ferromagnetic alloy occurs in the temperature range of 200-400 °C. At higher temperatures, the films become island-like and lose their ferromagnetic properties, as the CaF2 barrier layer is unable to prevent a mass transfer between the film and the Si substrate, which violates the stoichiometry of the alloy.

Preferred orientation in Cr- and Co-based thin films and its effects on the read/write performance of the media

NASA Astrophysics Data System (ADS)

Tsai, Hsiao-chu; Lal, Brij B.; Eltoukhy, Atef

1992-04-01

This work investigates the formation of preferred crystallographic orientation (PO) in Cr underlayer as well as CoCrTa and CoCrPtTa thin films and its effects on the recording performance of longitudinal media. The results show that the thin-film media with comparable coercivity but different crystalline PO as measured by x-ray diffraction exhibit significant difference in high-frequency signal amplitude, pulse width, and signal-to-noise ratio. To illustrate the effect of PO on parametric performance, CoCrTa/Cr and CoCrPtTa/Cr media were sputtered on different substrates and/or using special sputtering processes to achieve comparable coercivity but different PO in the films. A PO of Cr(200), which normally occurs on the NiP/Al substrates under adequate sputtering conditions, is found to be the key to obtaining a PO of Co(11.0) in Co-alloy media. The consequence of preferred in-plane c-axis orientation is a higher coercivity and better parametric performance of the medium. The formation of PO in the Cr underlayer is found to be related to the substrate material and the oxygen content in the sputtered films. The nonmetallic canasite substrates tend to promote PO of more stable Cr(110) rather than Cr(200). Consequently, this leads to a PO of out-of-plane c axis on the following Co films. The PO of magnetic layer appears to be an important factor in determining the parametric performance of the media.

Ultra thin metallic coatings to control near field radiative heat transfer

NASA Astrophysics Data System (ADS)

Esquivel-Sirvent, R.

2016-09-01

We present a theoretical calculation of the changes in the near field radiative heat transfer between two surfaces due to the presence of ultra thin metallic coatings on semiconductors. Depending on the substrates, the radiative heat transfer is modulated by the thickness of the ultra thin film. In particular we consider gold thin films with thicknesses varying from 4 to 20 nm. The ultra-thin film has an insulator-conductor transition close to a critical thickness of dc = 6.4 nm and there is an increase in the near field spectral heat transfer just before the percolation transition. Depending on the substrates (Si or SiC) and the thickness of the metallic coatings we show how the near field heat transfer can be increased or decreased as a function of the metallic coating thickness. The calculations are based on available experimental data for the optical properties of ultrathin coatings.

Influences of the residual argon gas and thermal annealing on Ta2O5 and SiO2 thin film filters

NASA Astrophysics Data System (ADS)

Liu, Wen-Jen; Chen, Chih-Min; Lai, Yin-Chieh

2005-04-01

Ion beam assisted deposition (IBAD) technique had widely used for improving stacking density and atomic mobility of thin films in many applications, especially adopted in optical film industries. Tantalum pentaoxide (Ta2O5) and silicon oxides (SiO2) optical thin films were deposited on the quartz glass substrate by using argon ion beam assisted deposition, and the influences of the residual argon gas and thermal annealing processes on the optical property, stress, compositional and microstructure evolution of the thin films were investigated in this study. Ta2O5 thin films were analyzed by XPS indicated that the ratio value of oxygen to tantalum was insufficient, at the same time, the residual argon gas in the thin films might result in film and device instabilities. Adopting oxygen-thermal annealing treatment at the temperature of 425°C, the thin films not only decreased the residual argon gas and the surface roughness, but also provided the sufficient stoichiometric ratio. Simultaneously, microstructure examination indicated few nano-crystallized structures and voids existed in Ta2O5 thin films, and possessed reasonable refractive index and lower extinction coefficient. By the way, we also suggested the IBAD system using the film compositional gas ion beam to replace the argon ion beam for assisting deposited optical films. The designed (HL)6H6LH(LH)6 multi-layers indicated higher insertion loss than the designed (HL)68H(LH)6 multi-layers. Therefore, using the high refractive index as spacer material represented lower insertion loss.

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.

Magnetic x-ray linear dichroism of ultrathin Fe-Ni alloy films

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

Schumann, F.O.; Willis, R.F.; Goodman, K.W.

1997-04-01

The authors have studied the magnetic structure of ultrathin Fe-Ni alloy films as a function of Fe concentration by measuring the linear dichroism of the 3p-core levels in angle-resolved photoemission spectroscopy. The alloy films, grown by molecular-beam epitaxy on Cu(001) surfaces, were fcc and approximately four monolayers thick. The intensity of the Fe dichroism varied with Fe concentration, with larger dichroisms at lower Fe concentrations. The implication of these results to an ultrathin film analogue of the bulk Invar effect in Fe-Ni alloys will be discussed. These measurements were performed at the Spectromicroscopy Facility (Beamline 7.0.1) of the Advanced Lightmore » Source.« less

Structural and electrical characterization of epitaxial Ge thin films on Si(001) formed by sputtering

NASA Astrophysics Data System (ADS)

Otsuka, Shintaro; Mori, Takahiro; Morita, Yukinori; Uchida, Noriyuki; Liu, Yongxun; O'uchi, Shin-ichi; Fuketa, Hiroshi; Migita, Shinji; Masahara, Meishoku; Matsukawa, Takashi

2017-04-01

We structurally and electrically characterize sub-10-nm-thick heteroepitaxial Ge films on Si(001), formed by heated sputtering and subsequent rapid thermal annealing (RTA). After RTA treatment at 720 °C, we find the heteroepitaxial Ge films to have smooth surfaces with a roughness root mean square value of 0.54 nm. Raman measurement reveals that the 720 °C RTA improves the crystallinity of Ge films while maintaining abrupt Ge/Si interfaces. Cross-sectional transmission electron microscopy confirms that the 720 °C RTA step effectively reduces stacking faults and dislocations in the Ge films. The Richardson plot of the TaN/Ge/n-Si diode indicates a Schottky barrier height (SBH) of 0.33 V, which is close to the height of 0.37 V measured from the capacitance-voltage measurement. These values are reasonable compared with the reported SBH of the TaN/bulk Ge Schottky barrier diode, indicating that the method involving heated sputtering and subsequent RTA provides adequate thin Ge films for Ge/Si heterostructures.

X-ray analyses of thermally grown and reactively sputtered tantalum oxide films on NiTi alloy

NASA Astrophysics Data System (ADS)

McNamara, Karrina; Tofail, Syed A. M.; Conroy, Derek; Butler, James; Gandhi, Abbasi A.; Redington, Wynette

2012-08-01

Sputter deposition of tantalum (Ta) on the surface of NiTi alloy is expected to improve the alloy's corrosion resistance and biocompatibility. Tantalum is a well-known biomaterial which is not affected by body fluids and is not irritating to human tissue. Here we compare the oxidation chemistry crystal structure evolution of tantalum oxide films grown on NiTi by reactive O2 sputtering and by thermal oxidation of sputter deposited Ta films. The effect of sputtering parameters and post-sputtering treatments on the morphology, oxidation state and crystal structure of the tantalum oxide layer have been investigated by field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The study has found that it may be better to avoid oxidation at and above 600 °C. The study establishes that reactive sputtering in presence of low oxygen mixture yields thicker film with better control of the film quality except that the surface oxidation state of Ta is slightly lower.

Dynamic response of ultrathin highly dense ZIF-8 nanofilms.

PubMed

Cookney, Joanna; Ogieglo, Wojciech; Hrabanek, Pavel; Vankelecom, Ivo; Fila, Vlastimil; Benes, Nieck E

2014-10-11

Ultrathin ZIF-8 nanofilms are prepared by facile step-by-step dip coating. A critical withdrawal speed allows for films with a very uniform minimum thickness. The high refractive index of the films denotes the absence of mesopores. The dynamic response of the films to CO2 exposure resembles behaviour observed for non-equilibrium organic polymers.

Large-Area Atomic Layers of the Charge-Density-Wave Conductor TiSe2.

PubMed

Wang, Hong; Chen, Yu; Duchamp, Martial; Zeng, Qingsheng; Wang, Xuewen; Tsang, Siu Hon; Li, Hongling; Jing, Lin; Yu, Ting; Teo, Edwin Hang Tong; Liu, Zheng

2018-02-01

Layered transition metal (Ti, Ta, Nb, etc.) dichalcogenides are important prototypes for the study of the collective charge density wave (CDW). Reducing the system dimensionality is expected to lead to novel properties, as exemplified by the discovery of enhanced CDW order in ultrathin TiSe 2 . However, the syntheses of monolayer and large-area 2D CDW conductors can currently only be achieved by molecular beam epitaxy under ultrahigh vacuum. This study reports the growth of monolayer crystals and up to 5 × 10 5 µm 2 large films of the typical 2D CDW conductor-TiSe 2 -by ambient-pressure chemical vapor deposition. Atomic resolution scanning transmission electron microscopy indicates the as-grown samples are highly crystalline 1T-phase TiSe 2 . Variable-temperature Raman spectroscopy shows a CDW phase transition temperature of 212.5 K in few layer TiSe 2 , indicative of high crystal quality. This work not only allows the exploration of many-body state of TiSe 2 in 2D limit but also offers the possibility of utilizing large-area TiSe 2 in ultrathin electronic devices. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Skyrmion morphology in ultrathin magnetic films

NASA Astrophysics Data System (ADS)

Gross, I.; Akhtar, W.; Hrabec, A.; Sampaio, J.; Martínez, L. J.; Chouaieb, S.; Shields, B. J.; Maletinsky, P.; Thiaville, A.; Rohart, S.; Jacques, V.

2018-02-01

Nitrogen-vacancy magnetic microscopy is employed in the quenching mode as a noninvasive, high-resolution tool to investigate the morphology of isolated skyrmions in ultrathin magnetic films. The skyrmion size and shape are found to be strongly affected by local pinning effects and magnetic field history. Micromagnetic simulations including a static disorder, based on the physical model of grain-to-grain thickness variations, reproduce all experimental observations and reveal the key role of disorder and magnetic history in the stabilization of skyrmions in ultrathin magnetic films. This work opens the way to an in-depth understanding of skyrmion dynamics in real, disordered media.

Flexible Mixed-Potential-Type (MPT) NO₂ Sensor Based on An Ultra-Thin Ceramic Film.

PubMed

You, Rui; Jing, Gaoshan; Yu, Hongyan; Cui, Tianhong

2017-07-29

A novel flexible mixed-potential-type (MPT) sensor was designed and fabricated for NO₂ detection from 0 to 500 ppm at 200 °C. An ultra-thin Y₂O₃-doped ZrO₂ (YSZ) ceramic film 20 µm thick was sandwiched between a heating electrode and reference/sensing electrodes. The heating electrode was fabricated by a conventional lift-off process, while the porous reference and the sensing electrodes were fabricated by a two-step patterning method using shadow masks. The sensor's sensitivity is achieved as 58.4 mV/decade at the working temperature of 200 °C, as well as a detection limit of 26.7 ppm and small response time of less than 10 s at 200 ppm. Additionally, the flexible MPT sensor demonstrates superior mechanical stability after bending over 50 times due to the mechanical stability of the YSZ ceramic film. This simply structured, but highly reliable flexible MPT NO₂ sensor may lead to wide application in the automobile industry for vehicle emission systems to reduce NO₂ emissions and improve fuel efficiency.

Flexible Mixed-Potential-Type (MPT) NO2 Sensor Based on An Ultra-Thin Ceramic Film

PubMed Central

You, Rui; Jing, Gaoshan; Yu, Hongyan; Cui, Tianhong

2017-01-01

A novel flexible mixed-potential-type (MPT) sensor was designed and fabricated for NO2 detection from 0 to 500 ppm at 200 °C. An ultra-thin Y2O3-doped ZrO2 (YSZ) ceramic film 20 µm thick was sandwiched between a heating electrode and reference/sensing electrodes. The heating electrode was fabricated by a conventional lift-off process, while the porous reference and the sensing electrodes were fabricated by a two-step patterning method using shadow masks. The sensor’s sensitivity is achieved as 58.4 mV/decade at the working temperature of 200 °C, as well as a detection limit of 26.7 ppm and small response time of less than 10 s at 200 ppm. Additionally, the flexible MPT sensor demonstrates superior mechanical stability after bending over 50 times due to the mechanical stability of the YSZ ceramic film. This simply structured, but highly reliable flexible MPT NO2 sensor may lead to wide application in the automobile industry for vehicle emission systems to reduce NO2 emissions and improve fuel efficiency. PMID:28758933

Extraordinary optical transmission in nanopatterned ultrathin metal films without holes

DOE PAGES

Peer, Akshit; Biswas, Rana

2016-02-01

In this study, we experimentally and theoretically demonstrate that a continuous gold film on a periodically textured substrate exhibits extraordinary optical transmission, even though no holes were etched in the film. Our film synthesis started by nanoimprinting a periodic array of nanocups with a period of ~750 nm on a polystyrene film over a glass substrate. A thin non-conformal gold film was sputter-deposited on the polystyrene by angle-directed deposition. The gold film was continuous with spatial thickness variation, the film being thinnest at the bottom of the nanocup. Measurements revealed an extraordinary transmission peak at a wavelength just smaller thanmore » the period, with an enhancement of ~2.5 compared to the classically expected value. Scattering matrix simulations model well the transmission and reflectance measurements when an ultrathin gold layer (~5 nm), smaller than the skin depth is retained at the bottom of the nanocups. Electric field intensities are enhanced by >100 within the nanocup, and ~40 in the ultrathin gold layer causing transmission through it. We show a wavelength red-shift of ~30 nm in the extraordinary transmission peak when the nanocups are coated with a thin film of a few nanometers, which can be utilized for biosensing. The continuous corrugated metal films are far simpler structures to observe extraordinary transmission, circumventing the difficult process of etching the metal film. Such continuous metal films with ultrathin regions are simple platforms for non-linear optics, plasmonics, and biological and chemical sensing.« less

Trace Impurity Analysis in Ta Films Using Glow Discharge Mass Spectrometry: Concentration Change of Impurities by Applying Negative Substrate Bias Voltage

NASA Astrophysics Data System (ADS)

Lim, Jae-Won; Mimura, Kouji; Isshiki, Minoru

2004-12-01

Glow discharge mass spectrometry (GDMS) was used to analyze a Ta target and Ta films for trace impurities. The Ta films were deposited on Si (100) substrate at substrate bias voltages of 0 V and -125 V using a non-mass separated ion beam deposition system. Although both Ta films were contaminated by impurities during the deposition, the Ta film deposited at a substrate bias voltage of -125 V showed lower impurity content than the Ta film deposited without the substrate bias voltage, which means that applying a negative bias voltage to the substrate decreased the total concentration of impurities. Furthermore, the concentration change of individual impurities in the Ta film is related to their ionization ratio in the argon discharge plasma. Considering the effect of the ionization potential of an individual impurity on the ionization ratio, purification by applying a negative bias voltage to the substrate results from Penning ionization and an ionization mechanism proposed in this study, as well as from the difference between the kinetic energies of Ta neutral atoms and Ta+ ions accelerated toward the substrate with/without a negative substrate bias voltage.

Ta-Pt Alloys as Gate Materials for Metal-Oxide-Semiconductor Field Effect Transistor Application

NASA Astrophysics Data System (ADS)

Huang, Chih-Feng; Tsui, Bing-Yue

2009-03-01

In this work we explore the thermal stability of sputter-deposited Ta-rich Ta-Pt alloys. The effects of group III and V impurities on their work function are also investigated. The Ta content ranges from 65 to 82 at. %. The main phase is σ Ta-Pt. The binding energies of core-level electrons of Ta and Pt are changed due to the intermixing of Ta and Pt, which is evidence that the work function of alloys is changed in metallic alloy systems. Binding energies are thermally stable up to 800 °C. Moreover, the incorporation of Pt in Ta film induces poor crystallization and a compound phase of Ta-Pt alloys. Transmission electron microscopy analysis confirmed the absence of a clear grain boundary in Ta-Pt alloys. The Ta and Pt depth profile shows uniformity in depth after 800 °C annealing for 30 min. The diffusion and distribution of impurities in the alloys were studied by secondary ion mass spectroscopy. Arsenic cannot diffuse in the alloys following annealing at 800 °C for 30 s. In contrast, boron can easily diffuse at 800 °C. The incorporation of impurities with a dosage of 5 ×1015 cm-2 in 60 nm Ta-Pt alloy by implantation did not significantly change the flat-band voltage following annealing at 800 °C.

High-Pressure CO2 Sorption in Polymers of Intrinsic Microporosity under Ultrathin Film Confinement.

PubMed

Ogieglo, Wojciech; Ghanem, Bader; Ma, Xiaohua; Wessling, Matthias; Pinnau, Ingo

2018-04-04

Ultrathin microporous polymer films are pertinent to the development and further spread of nanotechnology with very promising potential applications in molecular separations, sensors, catalysis, or batteries. Here, we report high-pressure CO 2 sorption in ultrathin films of several chemically different polymers of intrinsic microporosity (PIMs), including the prototypical PIM-1. Films with thicknesses down to 7 nm were studied using interference-enhanced in situ spectroscopic ellipsometry. It was found that all PIMs swell much more than non-microporous polystyrene and other high-performance glassy polymers reported previously. Furthermore, chemical modifications of the parent PIM-1 strongly affected the swelling magnitude. By investigating the behavior of relative refractive index, n rel , it was possible to study the interplay between micropores filling and matrix expansion. Remarkably, all studied PIMs showed a maximum in n rel at swelling of 2-2.5% indicating a threshold point above which the dissolution in the dense matrix started to dominate over sorption in the micropores. At pressures above 25 bar, all PIMs significantly plasticized in compressed CO 2 and for the ones with the highest affinity to the penetrant, a liquidlike mixing typical for rubbery polymers was observed. Reduction of film thickness below 100 nm revealed pronounced nanoconfinement effects and resulted in a large swelling enhancement and a quick loss of the ultrarigid character. On the basis of the partial molar volumes of the dissolved CO 2 , the effective reduction of the T g was estimated to be ∼200 °C going from 128 to 7 nm films.

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.

Low-temperature atomic layer epitaxy of AlN ultrathin films by layer-by-layer, in-situ atomic layer annealing.

PubMed

Shih, Huan-Yu; Lee, Wei-Hao; Kao, Wei-Chung; Chuang, Yung-Chuan; Lin, Ray-Ming; Lin, Hsin-Chih; Shiojiri, Makoto; Chen, Miin-Jang

2017-01-03

Low-temperature epitaxial growth of AlN ultrathin films was realized by atomic layer deposition (ALD) together with the layer-by-layer, in-situ atomic layer annealing (ALA), instead of a high growth temperature which is needed in conventional epitaxial growth techniques. By applying the ALA with the Ar plasma treatment in each ALD cycle, the AlN thin film was converted dramatically from the amorphous phase to a single-crystalline epitaxial layer, at a low deposition temperature of 300 °C. The energy transferred from plasma not only provides the crystallization energy but also enhances the migration of adatoms and the removal of ligands, which significantly improve the crystallinity of the epitaxial layer. The X-ray diffraction reveals that the full width at half-maximum of the AlN (0002) rocking curve is only 144 arcsec in the AlN ultrathin epilayer with a thickness of only a few tens of nm. The high-resolution transmission electron microscopy also indicates the high-quality single-crystal hexagonal phase of the AlN epitaxial layer on the sapphire substrate. The result opens a window for further extension of the ALD applications from amorphous thin films to the high-quality low-temperature atomic layer epitaxy, which can be exploited in a variety of fields and applications in the near future.

Low-temperature atomic layer epitaxy of AlN ultrathin films by layer-by-layer, in-situ atomic layer annealing

PubMed Central

Shih, Huan-Yu; Lee, Wei-Hao; Kao, Wei-Chung; Chuang, Yung-Chuan; Lin, Ray-Ming; Lin, Hsin-Chih; Shiojiri, Makoto; Chen, Miin-Jang

2017-01-01

Low-temperature epitaxial growth of AlN ultrathin films was realized by atomic layer deposition (ALD) together with the layer-by-layer, in-situ atomic layer annealing (ALA), instead of a high growth temperature which is needed in conventional epitaxial growth techniques. By applying the ALA with the Ar plasma treatment in each ALD cycle, the AlN thin film was converted dramatically from the amorphous phase to a single-crystalline epitaxial layer, at a low deposition temperature of 300 °C. The energy transferred from plasma not only provides the crystallization energy but also enhances the migration of adatoms and the removal of ligands, which significantly improve the crystallinity of the epitaxial layer. The X-ray diffraction reveals that the full width at half-maximum of the AlN (0002) rocking curve is only 144 arcsec in the AlN ultrathin epilayer with a thickness of only a few tens of nm. The high-resolution transmission electron microscopy also indicates the high-quality single-crystal hexagonal phase of the AlN epitaxial layer on the sapphire substrate. The result opens a window for further extension of the ALD applications from amorphous thin films to the high-quality low-temperature atomic layer epitaxy, which can be exploited in a variety of fields and applications in the near future. PMID:28045075

Preparation and characterization of the nanoporous ultrathin multilayer films based on molybdenum polyoxometalate (Mo 38) n

NASA Astrophysics Data System (ADS)

Wang, L.; Jiang, M.; Wang, E. B.; Duan, L. Y.; Hao, N.; Lan, Y.; Xu, L.; Li, Z.

2003-11-01

Ultrathin multilayer films of the wheel-shaped molybdenum polyoxometalate cluster (Mo 38) n and poly(allylamine hydrochloride)(PAH) have been prepared by the layer-by-layer (LbL) self-assembly method. The ((Mo 38) n/PAH) m multilayer films have been characterized by X-ray photoelectron spectra (XPS) and atomic force microscopy (AFM). UV-VIS measurements reveal regular film growth with each (Mo 38) n adsorption. The electrochemistry behavior of the film at room temperature was investigated.

Achieving high carrier mobility exceeding 70 cm2/Vs in amorphous zinc tin oxide thin-film transistors

NASA Astrophysics Data System (ADS)

Kim, Sang Tae; Shin, Yeonwoo; Yun, Pil Sang; Bae, Jong Uk; Chung, In Jae; Jeong, Jae Kyeong

2017-09-01

This paper proposes a new defect engineering concept for low-cost In- and Ga-free zinc tin oxide (ZTO) thin-film transistors (TFTs). This concept is comprised of capping ZTO films with tantalum (Ta) and a subsequent modest thermal annealing treatment at 200 °C. The Ta-capped ZTO TFTs exhibited a remarkably high carrier mobility of 70.8 cm2/Vs, low subthreshold gate swing of 0.18 V/decade, threshold voltage of -1.3 V, and excellent ION/OFF ratio of 2 × 108. The improvement (> two-fold) in the carrier mobility compared to the uncapped ZTO TFT can be attributed to the effective reduction of the number of adverse tailing trap states, such as hydroxyl groups or oxygen interstitial defects, which stems from the scavenging effect of the Ta capping layer on the ZTO channel layer. Furthermore, the Ta-capped ZTO TFTs showed excellent positive and negative gate bias stress stabilities. [Figure not available: see fulltext.

Effect of annealing temperature on microstructural evolution and electrical properties of sol-gel processed ZrO2/Si films

NASA Astrophysics Data System (ADS)

Hwang, Soo Min; Lee, Seung Muk; Park, Kyung; Lee, Myung Soo; Joo, Jinho; Lim, Jun Hyung; Kim, Hyoungsub; Yoon, Jae Jin; Kim, Young Dong

2011-01-01

High-permittivity (k) ZrO2/Si(100) films were fabricated by a sol-gel technique and the microstructural evolution with the annealing temperature (Ta) was correlated with the variation of their electrical performance. With increasing Ta, the ZrO2 films crystallized into a tetragonal (t) phase which was maintained until 700 °C at nanoscale thicknesses. Although the formation of the t-ZrO2 phase obviously enhanced the k value of the ZrO2 dielectric layer, the maximum capacitance in accumulation was decreased by the growth of a low-k interfacial layer (IL) between ZrO2 and Si with increasing Ta. On the other hand, the gate leakage current was remarkably depressed with increasing Ta probably due to the combined effects of the increased IL thickness, optical band gap of ZrO2, and density of ZrO2 and decreased remnant organic components.

Temperature-dependent nucleation and capture-zone scaling of C 60 on silicon oxide

NASA Astrophysics Data System (ADS)

Groce, M. A.; Conrad, B. R.; Cullen, W. G.; Pimpinelli, A.; Williams, E. D.; Einstein, T. L.

2012-01-01

Submonolayer films of C 60 have been deposited on ultrathin SiO 2 films for the purpose of characterizing the initial stages of nucleation and growth as a function of temperature. Capture zones extracted from the initial film morphology were analyzed using both the gamma and generalized Wigner distributions. The calculated critical nucleus size i of the C 60 islands was observed to change over the temperature range 298 K to 483 K. All fitted values of i were found to be between 0 and 1, representing stable monomers and stable dimers, respectively. With increasing temperature of film preparation, we observed i first increasing through this range and then decreasing. We discuss possible explanations of this reentrant-like behavior.

Dissolvable Films of Silk Fibroin for Ultrathin Conformal Bio-Integrated Electronics

DTIC Science & Technology

2010-06-01

the systems described in the following, ultrathin, spin- cast films of polyimide (PI) served as a support for arrays of electrodes designed for...micropatterning of optically transparent, mechanically robust, biocompatible silk fibroin films. Adv. Mater. 20, 3070–3072 (2008). 20. Murphy, A. R., John, P. S...analysis of induced colour change on periodically nanopatterned silk films. Opt. Express 17, 21271–21279 (2009). 25. Parker, S. T. et al. Biocompatible

TaC-coated graphite prepared via a wet ceramic process: Application to CVD susceptors for epitaxial growth of wide-bandgap semiconductors

NASA Astrophysics Data System (ADS)

Nakamura, Daisuke; Kimura, Taishi; Narita, Tetsuo; Suzumura, Akitoshi; Kimoto, Tsunenobu; Nakashima, Kenji

2017-11-01

A novel sintered tantalum carbide coating (SinTaC) prepared via a wet ceramic process is proposed as an approach to reducing the production cost and improving the crystal quality of bulk-grown crystals and epitaxially grown films of wide-bandgap semiconductors. Here, we verify the applicability of the SinTaC components as susceptors for chemical vapor deposition (CVD)-SiC and metal-organic chemical vapor deposition (MOCVD)-GaN epitaxial growth in terms of impurity incorporation from the SinTaC layers and also clarify the surface-roughness controllability of SinTaC layers and its advantage in CVD applications. The residual impurity elements in the SinTaC layers were confirmed to not severely incorporate into the CVD-SiC and MOCVD-GaN epilayers grown using the SinTaC susceptors. The quality of the epilayers was also confirmed to be equivalent to that of epilayers grown using conventional susceptors. Furthermore, the surface roughness of the SinTaC components was controllable over a wide range of average roughness (0.4 ≤ Ra ≤ 5 μm) and maximum height roughness (3 ≤ Rz ≤ 36 μm) through simple additional surface treatment procedures, and the surface-roughened SinTaC susceptor fabricated using these procedures was predicted to effectively reduce thermal stress on epi-wafers. These results confirm that SinTaC susceptors are applicable to epitaxial growth processes and are advantageous over conventional susceptor materials for reducing the epi-cost and improving the quality of epi-wafers.

Influence of Ta doping in resistive switching behavior of TiO2

NASA Astrophysics Data System (ADS)

Barman, Arabinda; Saini, Chetan P.; Deshmukh, Sujit; Dhar, Sankar; Kanjilal, Aloke

An approach has been made to understand the resistive switching behavior in Ta-doped TiO2 films on Pt substrates. Prior to thin film deposition, Ta-doped TiO2 powder has been synthesized chemically using Ta and Ti precursor solutions. However, the Ta doping has seriously been affected by increasing Ta concentration above 1 at% due to the segregation of Ta2O5 phase. The Ta-doped TiO2 targets have been prepared for pulsed laser deposition of the films on Pt substrates using an excitation wavelength of 248 nm. The structural and chemical properties of the Ta-doped TiO2 films have been investigated in details with the help of XRD, SIMS, XAS and XPS. The stoichiometry of the Ta-doped TiO2 films with increasing depth has been verified initially by SIMS. The electrical study of the corresponding device structures further suggests that the optimized resistive switching effect can be accomplished up to a threshold Ta-doping of 1 at%. Nevertheless, a highly conducting behavior has been shown when the TiO2 films are doped with 2 at% Ta. These results will be discussed in details in the light of defect induced resistive switching phenomenon.

Temporally and Spatially Resolved Plasma Spectroscopy in Pulsed Laser Deposition of Ultra-Thin Boron Nitride Films (Postprint)

DTIC Science & Technology

2015-04-24

AFRL-RX-WP-JA-2016-0196 TEMPORALLY AND SPATIALLY RESOLVED PLASMA SPECTROSCOPY IN PULSED LASER DEPOSITION OF ULTRA-THIN BORON NITRIDE...AND SPATIALLY RESOLVED PLASMA SPECTROSCOPY IN PULSED LASER DEPOSITION OF ULTRA-THIN BORON NITRIDE FILMS (POSTPRINT) 5a. CONTRACT NUMBER FA8650...distributions within a PVD plasma plume ablated from a boron nitride (BN) target by a KrF laser at different pressures of nitrogen gas were investigated

Subatomic deformation driven by vertical piezoelectricity from CdS ultrathin films.

PubMed

Wang, Xuewen; He, Xuexia; Zhu, Hongfei; Sun, Linfeng; Fu, Wei; Wang, Xingli; Hoong, Lai Chee; Wang, Hong; Zeng, Qingsheng; Zhao, Wu; Wei, Jun; Jin, Zhong; Shen, Zexiang; Liu, Jie; Zhang, Ting; Liu, Zheng

2016-07-01

Driven by the development of high-performance piezoelectric materials, actuators become an important tool for positioning objects with high accuracy down to nanometer scale, and have been used for a wide variety of equipment, such as atomic force microscopy and scanning tunneling microscopy. However, positioning at the subatomic scale is still a great challenge. Ultrathin piezoelectric materials may pave the way to positioning an object with extreme precision. Using ultrathin CdS thin films, we demonstrate vertical piezoelectricity in atomic scale (three to five space lattices). With an in situ scanning Kelvin force microscopy and single and dual ac resonance tracking piezoelectric force microscopy, the vertical piezoelectric coefficient (d 33) up to 33 pm·V(-1) was determined for the CdS ultrathin films. These findings shed light on the design of next-generation sensors and microelectromechanical devices.

Effects of a Ta interlayer on the phase transition of TiSi2 on Si(111)

NASA Astrophysics Data System (ADS)

Jeon, Hyeongtag; Jung, Bokhee; Kim, Young Do; Yang, Woochul; Nemanich, R. J.

2000-09-01

This study examines the effects of a thin Ta interlayer on the formation of TiSi2 on Si(111) substrate. The Ta interlayer was introduced by depositing Ta and Ti films sequentially on an atomically clean Si(111) substrate in an ultrahigh vacuum (UHV) system. Samples of 100 Å Ti with 5 and 10 Å Ta interlayers were compared to similar structures without an interlayer. After deposition, the substrates were annealed for 10 min, in situ, at temperatures between 500 and 750 °C in 50 °C increments. The TiSi2 formation with and without the Ta interlayer was analyzed with an X-ray diffractometer, Auger electron spectroscopy (AES), Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and a four-point probe. The AES analysis data showed a 1:2 ratio of Ti:Si in the Ti-silicide layer and indicated that the Ta layer remained at the interface between TiSi2 and the Si(111) substrate. The C 49-C 54 TiSi2 phase transition temperature was lowered by ˜200 °C. The C 49-C 54 TiSi2 phase transition temperature was 550 °C for the samples with a Ta interlayer and was 750 °C for the samples with no Ta interlayer. The sheet resistance of the Ta interlayered Ti silicide showed lower values of resistivity at low temperatures which indicated the change in phase transition temperature. The C 54 TiSi2 displayed different crystal orientation when the Ta interlayer was employed. The SEM and TEM micrographs showed that the TiSi2 with a Ta interlayer significantly suppressed the tendency to islanding and surface agglomeration.

Preparation, characterization and application of EVA film containing Eu3+ complex with 1-tridecanecarboxylic acid ligand

NASA Astrophysics Data System (ADS)

Dong, Jin; Lin, Baoping

2017-11-01

In this study, on the basis of complex Eu(DBM)3Phen which was widely applied in polymer matrices, quaternary complex Eu(DBM)2Phen(TA) was synthesized by the introduction of 1-tridecanecarboxylic acid (TA). XRD analyses show that Eu(DBM)2Phen(TA) inclines to amorphization compared with Eu(DBM)3Phen which is crystal. Ethylene-vinyl acetate (EVA) film doped with Eu(DBM)2Phen(TA) was prepared by casting method. SEM and AFM analyses show that the compatibility of Eu(DBM)2Phen(TA) with EVA is better than that of Eu(DBM)3Phen with EVA. Under the same addition amount of Eu3+ complexes, visible light transmittance of Eu(DBM)2Phen(TA)/EVA film is obviously greater than that of Eu(DBM)3Phen/EVA film, and the fluorescence intensity of Eu(DBM)2Phen(TA)/EVA film is only slightly lower than that of Eu(DBM)3Phen/EVA film. With the optimum addition amount of Eu3+ complexes, the energy conversion efficiency of the polycrystalline silicon solar cell coated with Eu(DBM)2Phen(TA)/EVA film is improved to 12.14%, and in comparison, that of the solar cell coated with Eu(DBM)3Phen/EVA film is only 11.98%. Hence Eu(DBM)2Phen(TA)/EVA film has a potential prospect as luminescent down-shifting material.

Precisely Controlled Ultrathin Conjugated Polymer Films for Large Area Transparent Transistors and Highly Sensitive Chemical Sensors.

PubMed

Khim, Dongyoon; Ryu, Gi-Seong; Park, Won-Tae; Kim, Hyunchul; Lee, Myungwon; Noh, Yong-Young

2016-04-13

A uniform ultrathin polymer film is deposited over a large area with molecularlevel precision by the simple wire-wound bar-coating method. The bar-coated ultrathin films not only exhibit high transparency of up to 90% in the visible wavelength range but also high charge carrier mobility with a high degree of percolation through the uniformly covered polymer nanofibrils. They are capable of realizing highly sensitive multigas sensors and represent the first successful report of ethylene detection using a sensor based on organic field-effect transistors. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Size Dependent Mechanical Behavior of Free-Standing Glassy Polymer Thin Films

DTIC Science & Technology

2014-08-31

thickness is less than 20 ( ) 1 ( / ) bulk film E EE h hδ = + 14 nm using the liquid dewetting method. Additionally, earlier studies by McKenna’s group and...coated substrates: Rupture, dewetting , and drop formation. J. Colloid Interface Sci. 178(2), 383 (1996). 8. C.B. Roth and J.R. Dutcher: Glass transition...Phys. J. E. 20(2), 143 (2006). 31. J. Wang and G.B. McKenna: Viscoelastic and Glass Transition Properties of Ultrathin Polystyrene Films by Dewetting

Anomalously deep polarization in SrTiO3 (001) interfaced with an epitaxial ultrathin manganite film

DOE PAGES

Wang, Zhen; Tao, Jing; Yu, Liping; ...

2016-10-17

Using atomically-resolved imaging and spectroscopy, we reveal a remarkably deep polarization in non-ferroelectric SrTiO 3 near its interface with an ultrathin nonmetallic film of La 2/3Sr 1/3MnO 3. Electron holography shows an electric field near the interface in SrTiO 3, yielding a surprising spontaneous polarization density of ~ 21 μC/cm 2. Combining the experimental results with first principles calculations, we propose that the observed deep polarization is induced by the electric field originating from oxygen vacancies that extend beyond a dozen unit-cells from the interface, thus providing important evidence of the role of defects in the emergent interface properties ofmore » transition metal oxides.« less

Thin-Film Ceramic Thermocouples Fabricated and Tested

NASA Technical Reports Server (NTRS)

Wrbanek, John D.; Fralick, Gustave C.; Farmer, Serene C.; Sayir, Ali; Gregory, Otto J.; Blaha, Charles A.

2004-01-01

The Sensors and Electronics Technology Branch of the NASA Glenn Research Center is developing thin-film-based sensors for surface measurement in propulsion system research. Thin-film sensors do not require special machining of the components on which they are mounted, and they are considerably thinner than wire- or foil-based sensors. One type of sensor being advanced is the thin-film thermocouple, specifically for applications in high-temperature combustion environments. Ceramics are being demonstrated as having the potential to meet the demands of thin-film thermocouples in advanced aerospace environments. The maximum-use temperature of noble metal thin-film thermocouples, 1500 C (2700 F), may not be adequate for components used in the increasingly harsh conditions of advanced aircraft and next-generation launch vehicles. Ceramic-based thermocouples are known for their high stability and robustness at temperatures exceeding 1500 C, but are typically in the form of bulky rods or probes. As part of ASTP, Glenn's Sensors and Electronics Technology Branch is leading an in-house effort to apply ceramics as thin-film thermocouples for extremely high-temperature applications as part of ASTP. Since the purity of the ceramics is crucial for the stability of the thermocouples, Glenn's Ceramics Branch and Case Western Reserve University are developing high-purity ceramic sputtering targets for fabricating high-temperature sensors. Glenn's Microsystems Fabrication Laboratory, supported by the Akima Corporation, is using these targets to fabricate thermocouple samples for testing. The first of the materials used were chromium silicide (CrSi) and tantalum carbide (TaC). These refractory materials are expected to survive temperatures in excess of 1500 C. Preliminary results indicate that the thermoelectric voltage output of a thin-film CrSi versus TaC thermocouple is 15 times that of the standard type R (platinum-rhodium versus platinum) thermocouple, producing 20 mV with a 200 C temperature gradient. The photograph on the left shows the CrSi-TaC thermocouple in a test fixture at Glenn, and the resulting output signal is shown on the right. The temperature differential across the sample, from the center of the sample inside the oven to the sample mount outside the oven, is measured using a type R thermocouple on the sample.

Real-Time Deposition Monitor for Ultrathin Conductive Films

NASA Technical Reports Server (NTRS)

Hines, Jacqueline

2011-01-01

A device has been developed that can be used for the real-time monitoring of ultrathin (2 or more) conductive films. The device responds in less than two microseconds, and can be used to monitor film depositions up to about 60 thick. Actual thickness monitoring capability will vary based on properties of the film being deposited. This is a single-use device, which, due to the very low device cost, can be disposable. Conventional quartz/crystal microbalance devices have proven inadequate to monitor the thickness of Pd films during deposition of ultrathin films for hydrogen sensor devices. When the deposited film is less than 100 , the QCM measurements are inadequate to allow monitoring of the ultrathin films being developed. Thus, an improved, high-sensitivity, real-time deposition monitor was needed to continue Pd film deposition development. The new deposition monitor utilizes a surface acoustic wave (SAW) device in a differential delay-line configuration to produce both a reference response and a response for the portion of the device on which the film is being deposited. Both responses are monitored simultaneously during deposition. The reference response remains unchanged, while the attenuation of the sensing path (where the film is being deposited) varies as the film thickness increases. This device utilizes the fact that on high-coupling piezoelectric substrates, the attenuation of an SAW undergoes a transition from low to very high, and back to low as the conductivity of a film on the device surface goes from nonconductive to highly conductive. Thus, the sensing path response starts with a low insertion loss, and as a conductive film is deposited, the film conductivity increases, causing the device insertion loss to increase dramatically (by up to 80 dB or more), and then with continued film thickness increases (and the corresponding conductivity increases), the device insertion loss goes back down to the low level at which it started. This provides a continuous, real-time monitoring of film deposition. For use with different films, the device would need to be calibrated to provide an understanding of how film thickness is related to film conductivity, as the device is responding primarily to conductivity effects (and not to mass loading effects) in this ultrathin film regime.

Feasibility demonstration for electroplating ultra-thin polyimide film. [fabricating film for space erectable structures

NASA Technical Reports Server (NTRS)

Schneier, R.; Braswell, T. V.; Vaughn, R. W.

1978-01-01

The effect of electrodeposition variables on film thickness was investigated using a dilute polyimide solution as a bath into which aluminum (as foil or as a vapor deposited coating) was immersed. The electrodeposited film was dried for 2 hours at 93 C (primarily to remove solvent) and cured for 18 hours at 186 C. Infrared studies indicate that imide formation (curing) occurs at 149 C under vacuum. From a conceptual viewpoint, satisfactory film metallized on one side can be obtained by this method. The cured ultra thin polyimide film exhibits properties equivalent to those of commercial film, and the surface appearance of the strippable polyimide film compares favorably with that of a sample of commercial film of thicker gauge. The feasibility of manufacturing approximately one million sq m of ultra thin film capable of being joined to fabricate an 800 m by 9 800 m square from starting material 0.5 to 1 m wide for space erectable structures was demonstrated.

Superconductor-Metal-Insulator transition in two dimensional Ta thin Films

NASA Astrophysics Data System (ADS)

Park, Sun-Gyu; Kim, Eunseong

2013-03-01

Superconductor-insulator transition has been induced by tuning film thickness or magnetic field. Recent electrical transport measurements of MoGe, Bi, Ta thin films revealed an interesting intermediate metallic phase which intervened superconducting and insulating phases at certain range of magnetic field. Especially, Ta thin films show the characteristic IV behavior at each phase and the disorder tuned intermediate metallic phase [Y. Li, C. L. Vicente, and J. Yoon, Physical Review B 81, 020505 (2010)]. This unexpected metallic phase can be interpreted as a consequence of vortex motion or contribution of fermionic quasiparticles. In this presentation, we report the scaling behavior during the transitions in Ta thin film as well as the transport measurements in various phases. Critical exponents v and z are obtained in samples with wide ranges of disorder. These results reveal new universality class appears when disorder exceeds a critical value. Dynamical exponent z of Superconducting sample is found to be 1, which is consistent with theoretical prediction of unity. z in a metallic sample is suddenly increased to be approximately 2.5. This critical exponent is much larger than the value found in other system and theoretical prediction. We gratefully acknowledge the financial support by the National Research Foundation of Korea through the Creative Research Initiatives.

Ultrathin Lutetium Oxide Film as an Epitaxial Hole-Blocking Layer for Crystalline Bismuth Vanadate Water Splitting Photoanodes

DOE PAGES

Zhang, Wenrui; Yan, Danhua; Tong, Xiao; ...

2018-01-08

Here a novel ultrathin lutetium oxide (Lu 2O 3) interlayer is integrated with crystalline bismuth vanadate (BiVO4) thin film photoanodes to facilitate carrier transport through atomic-scale interface control. The epitaxial Lu 2O 32O 3

Modeling the mechanical properties of ultra-thin polymer films [Structural modeling of films of atomic scale thickness

DOE PAGES

Espinosa-Loza, Francisco; Stadermann, Michael; Aracne-Ruddle, Chantel; ...

2017-11-16

A modeling method to extract the mechanical properties of ultra-thin films (10–100 nm thick) from experimental data generated by indentation of freestanding circular films using a spherical indenter is presented. The relationship between the mechanical properties of the film and experimental parameters including load, and deflection are discussed in the context of a constitutive material model, test variables, and analytical approaches. As a result, elastic and plastic regimes are identified by comparison of finite element simulation and experimental data.

Modeling the mechanical properties of ultra-thin polymer films [Structural modeling of films of atomic scale thickness

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

Espinosa-Loza, Francisco; Stadermann, Michael; Aracne-Ruddle, Chantel

A modeling method to extract the mechanical properties of ultra-thin films (10–100 nm thick) from experimental data generated by indentation of freestanding circular films using a spherical indenter is presented. The relationship between the mechanical properties of the film and experimental parameters including load, and deflection are discussed in the context of a constitutive material model, test variables, and analytical approaches. As a result, elastic and plastic regimes are identified by comparison of finite element simulation and experimental data.

Nanoscale interfacial heat transport of ultrathin epitaxial hetero films: Few monolayer Pb(111) on Si(111)

NASA Astrophysics Data System (ADS)

Witte, T.; Frigge, T.; Hafke, B.; Krenzer, B.; Horn-von Hoegen, M.

2017-06-01

We studied the phononic heat transport from ultrathin epitaxial Pb(111) films across the heterointerface into a Si(111) substrate by means of ultrafast electron diffraction. The thickness of the Pb films was varied from 15 to 4 monolayers. It was found that the thermal boundary conductance σTBC of the heterointerface is independent of the film thickness. We have no evidence for finite size effects: the continuum description of heat transport is still valid, even for the thinnest films of only 4 monolayer thickness.

Preparation of c-axis perpendicularly oriented ultra-thin L10-FePt films on MgO and VN underlayers

NASA Astrophysics Data System (ADS)

Futamoto, Masaaki; Shimizu, Tomoki; Ohtake, Mitsuru

2018-05-01

Ultra-thin L10-FePt films of 2 nm average thickness are prepared on (001) oriented MgO and VN underlayers epitaxially grown on base substrate of SrTiO3(001) single crystal. Detailed cross-sectional structures are observed by high-resolution transmission electron microscopy. Continuous L10-FePt(001) thin films with very flat surface are prepared on VN(001) underlayer whereas the films prepared on MgO(001) underlayer consist of isolated L10-FePt(001) crystal islands. Presence of misfit dislocation and lattice bending in L10-FePt material is reducing the effective lattice mismatch with respect to the underlayer to be less than 0.5 %. Formation of very flat and continuous FePt layer on VN underlayer is due to the large surface energy of VN material where de-wetting of FePt material at high temperature annealing process is suppressed under a force balance between the surface and interface energies of FePt and VN materials. An employment of underlayer or substrate material with the lattice constant and the surface energy larger than those of L10-FePt is important for the preparation of very thin FePt epitaxial thin continuous film with the c-axis controlled to be perpendicular to the substrate surface.

Temperature Controlled Electrostatic Disorder and Polymorphism in Ultrathin Films of α-Sexithiophene

NASA Astrophysics Data System (ADS)

Hoffman, Benjamin; Jafari, Sara; McAfee, Terry; Apperson, Aubrey; O'Connor, Brendan; Dougherty, Daniel

Competing phases in well-ordered alpha-sexithiophene (α-6T) are shown to contribute to electrostatic disorder observed by differences in surface potential between mono- and bi-layer crystallites. Ultrathin films are of key importance to devices in which charge transport occurs in the first several monolayers nearest to a dielectric interface (e.g. thin film transistors) and complex structures in this regime impact the general electrostatic landscape. This study is comprised of 1.5 ML sample crystals grown via organic molecular beam deposition onto a temperature controlled hexamethyldisilazane (HMDS) passivated SiO2 substrate to produce well-ordered layer-by-layer type growth. Sample topography and surface potential were characterized simultaneously using Kelvin Probe Force Microscopy to then isolate contact potential differences by first and second layer α-6T regions. Films grown on 70° C, 120° C substrates are observed to have a bilayer with lower, higher potential than the monolayer, respectively. Resulting interlayer potential differences are a clear source of electrostatic disorder and are explained as subtle shifts in tilt-angles between layers relative to the substrate. These empirical results continue our understanding of how co-existing orientations contribute to the complex electrostatics influencing charge transport. NSF CAREER award DMR-1056861.

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

Hilfiker, James N.; Stadermann, Michael; Sun, Jianing

It is a well-known challenge to determine refractive index (n) from ultra-thin films where the thickness is less than about 10 nm. In this paper, we discovered an interesting exception to this issue while characterizing spectroscopic ellipsometry (SE) data from isotropic, free-standing polymer films. Ellipsometry analysis shows that both thickness and refractive index can be independently determined for free-standing films as thin as 5 nm. Simulations further confirm an orthogonal separation between thickness and index effects on the experimental SE data. Effects of angle of incidence and wavelength on the data and sensitivity are discussed. Finally, while others have demonstratedmore » methods to determine refractive index from ultra-thin films, our analysis provides the first results to demonstrate high-sensitivity to the refractive index from ultra-thin layers.« less

Using granular C0-AI2O3 spacer for optimization of functional parameters of the FeMn/Fe20Ni80 magnetoresistive films

NASA Astrophysics Data System (ADS)

Gorkovenko, A. N.; Lepalovskij, V. N.; Adanakova, O. A.; Vas'kovskiy, V. O.

2016-03-01

In this paper we studied the possibility of tailoring the functional properties of the multilayer magnetoresistive medium with unidirectional anisotropy and the anisotropic magnetoresistance effect (AMR). Objects of the research were composite Co-Al2O3 films and Ta/Fe20Ni80/Fe50Mn50/Fe20Ni80/Co-Al2O3/Fe20Ni80/Ta multilayers structures obtained by magnetron sputtering and selectively subjected vacuum annealing. Structure, magnetic and magnetoresistive properties of the films in the temperature range 77÷440 K were investigated.

Subatomic deformation driven by vertical piezoelectricity from CdS ultrathin films

PubMed Central

Wang, Xuewen; He, Xuexia; Zhu, Hongfei; Sun, Linfeng; Fu, Wei; Wang, Xingli; Hoong, Lai Chee; Wang, Hong; Zeng, Qingsheng; Zhao, Wu; Wei, Jun; Jin, Zhong; Shen, Zexiang; Liu, Jie; Zhang, Ting; Liu, Zheng

2016-01-01

Driven by the development of high-performance piezoelectric materials, actuators become an important tool for positioning objects with high accuracy down to nanometer scale, and have been used for a wide variety of equipment, such as atomic force microscopy and scanning tunneling microscopy. However, positioning at the subatomic scale is still a great challenge. Ultrathin piezoelectric materials may pave the way to positioning an object with extreme precision. Using ultrathin CdS thin films, we demonstrate vertical piezoelectricity in atomic scale (three to five space lattices). With an in situ scanning Kelvin force microscopy and single and dual ac resonance tracking piezoelectric force microscopy, the vertical piezoelectric coefficient (d33) up to 33 pm·V−1 was determined for the CdS ultrathin films. These findings shed light on the design of next-generation sensors and microelectromechanical devices. PMID:27419234

Electrical and optical properties of sub-10 nm nickel silicide films for silicon solar cells

NASA Astrophysics Data System (ADS)

Brahmi, Hatem; Ravipati, Srikanth; Yarali, Milad; Shervin, Shahab; Wang, Weijie; Ryou, Jae-Hyun; Mavrokefalos, Anastassios

2017-01-01

Highly conductive and transparent films of ultra-thin p-type nickel silicide films have been prepared by RF magnetron sputtering of nickel on silicon substrates followed by rapid thermal annealing in an inert environment in the temperature range 400-600 °C. The films are uniform throughout the wafer with thicknesses in the range of 3-6 nm. The electrical and optical properties are presented for nickel silicide films with varying thickness. The Drude-Lorentz model and Fresnel equations were used to calculate the dielectric properties, sheet resistance, absorption and transmission of the films. These ultrathin nickel silicide films have excellent optoelectronic properties for p-type contacts with optical transparencies up to 80% and sheet resistance as low as ~0.15 µΩ cm. Furthermore, it was shown that the use of a simple anti-reflection (AR) coating can recover most of the reflected light approaching the values of a standard Si solar cell with the same AR coating. Overall, the combination of ultra-low thickness, high transmittance, low sheet resistance and ability to recover the reflected light by utilizing standard AR coating makes them ideal for utilization in silicon based photovoltaic technologies as a p-type transparent conductor.

Development of an ultra-thin film comprised of a graphene membrane and carbon nanotube vein support.

PubMed

Lin, Xiaoyang; Liu, Peng; Wei, Yang; Li, Qunqing; Wang, Jiaping; Wu, Yang; Feng, Chen; Zhang, Lina; Fan, Shoushan; Jiang, Kaili

2013-01-01

Graphene, exhibiting superior mechanical, thermal, optical and electronic properties, has attracted great interest. Considering it being one-atom-thick, and the reduced mechanical strength at grain boundaries, the fabrication of large-area suspended chemical vapour deposition graphene remains a challenge. Here we report the fabrication of an ultra-thin free-standing carbon nanotube/graphene hybrid film, inspired by the vein-membrane structure found in nature. Such a square-centimetre-sized hybrid film can realize the overlaying of large-area single-layer chemical vapour deposition graphene on to a porous vein-like carbon nanotube network. The vein-membrane-like hybrid film, with graphene suspended on the carbon nanotube meshes, possesses excellent mechanical performance, optical transparency and good electrical conductivity. The ultra-thin hybrid film features an electron transparency close to 90%, which makes it an ideal gate electrode in vacuum electronics and a high-performance sample support in transmission electron microscopy.

Robust Polymer Films: Nanoscale Stiffening as a Route to Strong Materials

DTIC Science & Technology

2011-10-20

Rheological Methods," Drexel University, Philadelphia, PA, March 4, 2011. S.Xu, "Geometry and molecular architecture effects in nanobubble inflation...2007. G.B. McKenna, "The viscoelastic properties of ultrathin polymer films as measured with a novel nanobubble inflation technique.” March Meeting of...mechanical response of ultrathin polymer films using the Texas Tech nanobubble inflation technique as the means to determine the viscoelastic

Engineering epitaxial γ-Al2O3 gate dielectric films on 4H-SiC

NASA Astrophysics Data System (ADS)

Tanner, Carey M.; Toney, Michael F.; Lu, Jun; Blom, Hans-Olof; Sawkar-Mathur, Monica; Tafesse, Melat A.; Chang, Jane P.

2007-11-01

The formation of epitaxial γ-Al2O3 thin films on 4H-SiC was found to be strongly dependent on the film thickness. An abrupt interface was observed in films up to 200 Å thick with an epitaxial relationship of γ-Al2O3(111)‖4H-SiC(0001) and γ-Al2O3(44¯0)‖4H-SiC(112¯0). The in-plane alignment between the film and the substrate is nearly complete for γ-Al2O3 films up to 115 Å thick, but quickly diminishes in thicker films. The films are found to be slightly strained laterally in tension; the strain increases with thickness and then decreases in films thicker than 200 Å, indicating strain relaxation which is accompanied by increased misorientation. By controlling the structure of ultrathin Al2O3 films, metal-oxide-semiconductor capacitors with Al2O3 gate dielectrics on 4H-SiC were found to have a very low leakage current density, suggesting suitability of Al2O3 for SiC device integration.

Structural and mechanical properties of lanthanide doped La1/3Nb0.8Ta0.2O3 thin films prepared by sol-gel method

NASA Astrophysics Data System (ADS)

Brunckova, Helena; Medvecky, Lubomir; Kovalcikova, Alexandra; Fides, Martin; Mudra, Erika; Durisin, Juraj; Skvarla, Jiri; Kanuchova, Maria

2017-04-01

Transparent Eu and Nd doped lanthanum niobate tantalate La1/3Nb0.8Ta0.2O3 (LNT) thin films (˜150 nm) were prepared by sol-gel/spin-coating process on Pt/SiO2/Si substrates and annealing at 1100 °C. The x-ray diffraction analysis of films confirmed formation of the perovskite La1/3NbO3 and La1/3TaO3 phases with traces of pyrochlore LaNbO4. Eu and Nd doped LNT films were smoother with roughness 17.1 and 25.4 nm in comparison with LNT (43.3 nm). In all films was observed heterogeneous microstructure with the perovskite spherical and pyrochlore needle-like particles. The mechanical properties of films were characterized for the first time by conventional and continuous stiffness (CSM) nanoindentation. The Eu and Nd doped LNT film modulus (E) and hardness (H) were higher than LNT (˜99.8 and 4.4 GPa) determined by conventional nanoindentation. It was measured the significant effect of substrate on properties of Eu or Nd films (H ˜ 5.9 or 4.9 GPa and E ˜ 107.3 or 104.1 GPa) by CSM nanoindentation.

Substrate-dependent structural and CO sensing properties of LaCoO3 epitaxial films

NASA Astrophysics Data System (ADS)

Liu, Haifeng; Sun, Hongjuan; Xie, Ruishi; Zhang, Xingquan; Zheng, Kui; Peng, Tongjiang; Wu, Xiaoyu; Zhang, Yanping

2018-06-01

LaCoO3 thin films were grown on different (0 0 1) oriented LaAlO3, SrTiO3 and (LaAlO3)0.3(Sr2AlTaO6)0.7 by the polymer assisted deposition method, respectively. All the LaCoO3 thin films are in epitaxial growth on these substrates, with tetragonal distortion of CoO6 octahedrons. Due to different in-plane lattice mismatch, the LaCoO3 film on LaAlO3 has the largest tetragonal distortion of CoO6 octahedrons while the film grown on (LaAlO3)0.3(Sr2AlTaO6)0.7 has the smallest tetragonal distortion. The relative contents of the surface absorbed oxygen species are found to increase for the LaCoO3 epitaxial films grown on (0 0 1) oriented (LaAlO3)0.3(Sr2AlTaO6)0.7, SrTiO3 and LaAlO3 substrates, sequentially. The film sensors exhibit good CO sensing properties at 150 °C, and the LaCoO3 film on LaAlO3 shows the highest response but the film on (LaAlO3)0.3(Sr2AlTaO6)0.7 shows the lowest. It reveals that the larger degree of Jahn-Teller-like tetragonal distortion of CoO6 octahedrons may greatly improve the surface absorbing and catalytic abilities, corresponding to more excellent CO sensing performance. The present study suggests that the formation of epitaxial films is an efficient methodology for controlling the octahedral distortion and thereby improving the gas sensing performance of perovskite transition metal oxides.

Coexistence of colossal stress and texture gradients in sputter deposited nanocrystalline ultra-thin metal films

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

Kuru, Yener; Welzel, Udo; Mittemeijer, Eric J.

2014-12-01

This paper demonstrates experimentally that ultra-thin, nanocrystalline films can exhibit coexisting colossal stress and texture depth gradients. Their quantitative determination is possible by X-ray diffraction experiments. Whereas a uniform texture by itself is known to generally cause curvature in so-called sin{sup 2}ψ plots, it is shown that the combined action of texture and stress gradients provides a separate source of curvature in sin{sup 2}ψ plots (i.e., even in cases where a uniform texture does not induce such curvature). On this basis, the texture and stress depth profiles of a nanocrystalline, ultra-thin (50 nm) tungsten film could be determined.

The influence of the surface parameter changes onto the phonon states in ultrathin crystalline films

NASA Astrophysics Data System (ADS)

Šetrajčić, Jovan P.; Ilić, Dušan I.; Jaćimovski, Stevo K.

2018-04-01

In this paper, we have analytically investigated how the changes in boundary surface parameters influence the phonon dispersion law in ultrathin films of the simple cubic crystalline structure. Spectra of possible phonon states are analyzed using the method of two-time dependent Green's functions and for the diverse combination of boundary surface parameters, this problem was presented numerically and graphically. It turns out that for certain values and combinations of parameters, displacement of dispersion branches outside of bulk zone occurs, leading to the creation of localized phonon states. This fact is of great importance for the heat removal, electrical conductivity and superconducting properties of ultrathin films.

Ultrathin planar hematite film for solar photoelectrochemical water splitting

DOE PAGES

Liu, Dong; Bierman, David M.; Lenert, Andrej; ...

2015-10-08

Hematite holds promise for photoelectrochemical (PEC) water splitting due to its stability, low-cost, abundance and appropriate bandgap. However, it suffers from a mismatch between the hole diffusion length and light penetration length. We have theoretically designed and characterized an ultrathin planar hematite/silver nanohole array/silver substrate photoanode. Due to the supported destructive interference and surface plasmon resonance, photons are efficiently absorbed in an ultrathin hematite film. In conclusion, compared with ultrathin hematite photoanodes with nanophotonic structures, this photoanode has comparable photon absorption but with intrinsically lower recombination losses due to its planar structure and promises to exceed the state-of-the-art photocurrent ofmore » hematite photoanodes.« less

Carrier Compensation Induced by Thermal Annealing in Al-Doped ZnO Films

PubMed Central

Koida, Takashi; Kaneko, Tetsuya; Shibata, Hajime

2017-01-01

This study investigated carrier compensation induced by thermal annealing in sputtered ZnO:Al (Al2O3: 0.25, 0.5, 1.0, and 2.0 wt %) films. The films were post-annealed in a N2 atmosphere at low (1 × 10−23 atm) and high (1 × 10−4 atm) oxygen partial pressures (PO2). In ZnO:Al films with low Al contents (i.e., 0.25 wt %), the carrier density (n) began to decrease at annealing temperatures (Ta) of 600 °C at low PO2. At higher PO2 and/or Al contents, n values began to decrease significantly at lower Ta (ca. 400 °C). In addition, Zn became desorbed from the films during heating in a high vacuum (i.e., <1 × 10−7 Pa). These results suggest the following: (i) Zn interstitials and Zn vacancies are created in the ZnO lattice during post-annealing treatments, thereby leading to carrier compensation by acceptor-type Zn vacancies; (ii) The compensation behavior is significantly enhanced for ZnO:Al films with high Al contents. PMID:28772501

Thickness-dependent enhancement of damping in C o2FeAl /β -Ta thin films

NASA Astrophysics Data System (ADS)

Akansel, Serkan; Kumar, Ankit; Behera, Nilamani; Husain, Sajid; Brucas, Rimantas; Chaudhary, Sujeet; Svedlindh, Peter

2018-04-01

In the present work C o2FeAl (CFA) thin films were deposited by ion beam sputtering on Si (100) substrates at the optimized deposition temperature of 300 °C. A series of CFA films with different thicknesses (tCFA), 8, 10, 12, 14, 16, 18, and 20 nm, were prepared and all samples were capped with a 5-nm-thick β-Ta layer. The thickness-dependent static and dynamic properties of the films were studied by SQUID magnetometry, in-plane as well as out-of-plane broadband vector network analyzer-ferromagnetic resonance (FMR) measurements, and angle-dependent cavity FMR measurements. The saturation magnetization and the coercive field were found to be weakly thickness dependent and lie in the range 900-950 kA/m and 0.53-0.87 kA/m, respectively. The effective damping parameter (αeff) extracted from in-plane and out-of-plane FMR results reveals a 1/tCFA dependence, the values for the in-plane αeff being larger due to two-magnon scattering (TMS). The origin of the αeff thickness dependence is spin pumping into the nonmagnetic β-Ta layer and in the case of the in-plane αeff, also a thickness-dependent TMS contribution. From the out-of-plane FMR results, it was possible to disentangle the different contributions to αeff and to the extract values for the intrinsic Gilbert damping (αG) and the effective spin-mixing conductance (geff↑↓) of the CFA/ β-Ta interface, yielding αG=(1.1 ±0.2 ) ×10-3 and geff↑↓=(2.90 ±0.10 ) ×1019m-2 .

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

PubMed

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

2009-01-06

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

Dynamic XPS measurements of ultrathin polyelectrolyte films containing antibacterial Ag–Cu nanoparticles

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

Taner-Camcı, Merve; Suzer, Sefik, E-mail: suzer@fen.bilkent.edu.tr

Ultrathin films consisting of polyelectrolyte layers prepared by layer-by-layer deposition technique and containing also Ag and Cu nanoparticles exhibit superior antibacterial activity toward Escherichia coli. These films have been investigated with XPS measurements under square wave excitation at two different frequencies, in order to further our understanding about the chemical/physical nature of the nanoparticles. Dubbed as dynamical XPS, such measurements bring out similarities and differences among the surface structures by correlating the binding energy shifts of the corresponding XPS peaks. Accordingly, it is observed that the Cu2p, Ag3d of the metal nanoparticles, and S2p of cysteine, the stabilizer and themore » capping agent, exhibit similar shifts. On the other hand, the C1s, N1s, and S2p peaks of the polyelectrolyte layers shift differently. This finding leads us the claim that the Ag and Cu atoms are in a nanoalloy structure, capped with cystein, as opposed to phase separated entities.« less

Vertical Alignment of Single-Walled Carbon Nanotubes on Nanostructure Fabricated by Atomic Force Microscope

DTIC Science & Technology

2007-05-01

SWNTs by blending them with liquid crystal,7 assem- bling SWNT films by Langmuir - Blodgett methods,8 and chemical assembly of SWNTs on a large substrate...Ulman, A. An Introduction to Ultrathin Organic Films from Langmuir - Blodgett to Self-Assembly. Academic: New York, (1991). [10] Moon, J.H., Shin, J.W...Fang, J. Langmuir , 16, 2651, (2000). [8] FT-IR data (Bruker IFS48, KBr Pellet): 1720 cm-1 (νC=O, SWNT-COOH) and 1770 cm-1 (νC=O, SWNT- COCl). [9

Nanodiamonds on tetrahedral amorphous carbon significantly enhance dopamine detection and cell viability.

PubMed

Peltola, Emilia; Wester, Niklas; Holt, Katherine B; Johansson, Leena-Sisko; Koskinen, Jari; Myllymäki, Vesa; Laurila, Tomi

2017-02-15

We hypothesize that by using integrated carbon nanostructures on tetrahedral amorphous carbon (ta-C), it is possible to take the performance and characteristics of these bioelectrodes to a completely new level. The integrated carbon electrodes were realized by combining nanodiamonds (NDs) with ta-C thin films coated on Ti-coated Si-substrates. NDs were functionalized with mixture of carboxyl and amine groups ND andante or amine ND amine , carboxyl ND vox or hydroxyl groups ND H and drop-casted or spray-coated onto substrate. By utilizing these novel structures we show that (i) the detection limit for dopamine can be improved by two orders of magnitude [from 10µM to 50nM] in comparison to ta-C thin film electrodes and (ii) the coating method significantly affects electrochemical properties of NDs and (iii) the ND coatings selectively promote cell viability. ND andante and ND H showed most promising electrochemical properties. The viability of human mesenchymal stem cells and osteoblastic SaOS-2 cells was increased on all ND surfaces, whereas the viability of mouse neural stem cells and rat neuroblastic cells was improved on ND andante and ND H and reduced on ND amine and ND vox. The viability of C6 cells remained unchanged, indicating that these surfaces will not cause excess gliosis. In summary, we demonstrated here that by using functionalized NDs on ta-C thin films we can significantly improve sensitivity towards dopamine as well as selectively promote cell viability. Thus, these novel carbon nanostructures provide an interesting concept for development of various in vivo targeted sensor solutions. Copyright © 2016 Elsevier B.V. All rights reserved.

Ultrathin Polyaniline-based Buffer Layer for Highly Efficient Polymer Solar Cells with Wide Applicability

PubMed Central

Zhao, Wenchao; Ye, Long; Zhang, Shaoqing; Fan, Bin; Sun, Mingliang; Hou, Jianhui

2014-01-01

Interfacial buffer layers often attribute the improved device performance in organic optoelectronic device. Herein, a water-soluble hydrochloric acid doped polyanilines (HAPAN) were utilized as p-type electrode buffer layer in highly efficient polymer solar cells (PSC) based on PBDTTT-EFT and several representative polymers. The PBDTTT-EFT-based conventional PSC featuring ultrathin HAPAN (1.3 nm) delivered high PCE approximately 9%, which is one of the highest values among conventional PSC devices. Moreover, ultrathin HAPAN also exhibited wide applicability in a variety of efficient photovoltaic polymers including PBDTTT-C-T, PTB7, PBDTBDD, PBTTDPP-T, PDPP3T and P3HT. The excellent performances were originated from the high transparency, small film roughness and suitable work function. PMID:25300365

Responsive Plasma Polymerized Ultrathin Nanocomposite Films

DTIC Science & Technology

2012-01-01

29 74 32 75 Ab so rb an ce (a .u .) Wavenumber, cm-1 pNIPAAM A B C D E Fig . 2. FTIR spectra of A) NIPAAM monomer B) Spun- cast P-NIPAAM film and...self- actuating response to specific stimuli are desirable in a wide range of applications including thermalandchemical sensing, tunableoptics...targeteddrug delivery, switchable surfaces and micro actuators [1e6]. Designing materials which are capable of generating a response from the stim- ulus

Transport in ultrathin gold films decorated with magnetic Gd atoms

NASA Astrophysics Data System (ADS)

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

2008-03-01

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

Superstable Ultrathin Water Film Confined in a Hydrophilized Carbon Nanotube.

PubMed

Tomo, Yoko; Askounis, Alexandros; Ikuta, Tatsuya; Takata, Yasuyuki; Sefiane, Khellil; Takahashi, Koji

2018-03-14

Fluids confined in a nanoscale space behave differently than in the bulk due to strong interactions between fluid molecules and solid atoms. Here, we observed water confined inside "open" hydrophilized carbon nanotubes (CNT), with diameter of tens of nanometers, using transmission electron microscopy (TEM). A 1-7 nm water film adhering to most of the inner wall surface was observed and remained stable in the high vacuum (order of 10 -5 Pa) of the TEM. The superstability of this film was attributed to a combination of curvature, nanoroughness, and confinement resulting in a lower vapor pressure for water and hence inhibiting its vaporization. Occasional, suspended ultrathin water film with thickness of 3-20 nm were found and remained stable inside the CNT. This film thickness is 1 order of magnitude smaller than the critical film thickness (about 40 nm) reported by the Derjaguin-Landau-Verwey-Overbeek theory and previous experimental investigations. The stability of the suspended ultrathin water film is attributed to the additional molecular interactions due to the extended water meniscus, which balances the rest of the disjoining pressures.

Structural and electrical properties of atomic layer deposited Al-doped ZrO2 films and of the interface with TaN electrode

NASA Astrophysics Data System (ADS)

Spiga, S.; Rao, R.; Lamagna, L.; Wiemer, C.; Congedo, G.; Lamperti, A.; Molle, A.; Fanciulli, M.; Palma, F.; Irrera, F.

2012-07-01

Al-doped ZrO2 (Al-ZrO2) films deposited by atomic layer deposition onto silicon substrates and the interface with the TaN metal gate are investigated. In particular, structural properties of as-grown and annealed films in the 6-26 nm thickness range, as well as leakage and capacitive behavior of metal-oxide-semiconductor stacks are characterized. As-deposited Al-ZrO2 films in the mentioned thickness range are amorphous and crystallize in the ZrO2 cubic phase after thermal treatment at 900 °C. Correspondingly, the dielectric constant (k) value increases from 20 ± 1 to 27 ± 2. The Al-ZrO2 layers exhibit uniform composition through the film thickness and are thermally stable on Si, whereas chemical reactions take place at the TaN/Al-ZrO2 interface. A transient capacitance technique is adopted for monitoring charge trapping and flat band instability at short and long time scales. The role of traps nearby the TaN/Al-ZrO2 interface is discussed and compared with other metal/high-k oxide films. Further, analytical modeling of the flat band voltage shift with a power-law dependence on time allows extracting features of bulk traps close to the silicon/oxide interface, which exhibit energy levels in the 1.4-1.9 eV range above the valence band of the Al-ZrO2.

Effect of dopants on the soft magnetic properties and high frequency characteristics of FeCoBM (M = Ti, Nb, Hf, and Ta) thin films.

PubMed

Hsieh, C C; Lin, T H; Chang, H W; Chang, C W; Chang, W C; Yang, C C

2011-03-01

Effect of dopants on the soft magnetic properties and high frequency characteristics of FeCoBM thin films (M = Ti, Nb, Hf, and Ta) have been studied. For (Fe0.55Co0.45)(100-x)B(x) (x = 5-15) thin films, with the increase of B content, the resistivity was increased because B could decrease the crystallinity of the films. The (Fe0.55Co0.45)90B10 thin film showed the optimum properties, where 4piM(s) = 16.1 kG, H(ce) = 64.2 Oe, H(ch) = 13.5 Oe, H(k) = 310 Oe and p = 338 microomega-cm. To reduce the coercivity of the film, the elements M, including Ti, Nb, Hf, and Ta, were selected to substitute for B in the FeCoB films. It was found that (Fe0.55Co0.45)90B6Ti2Nb2 thin film after annealing at a temperature of 200 degrees C for 30 min showed the optimal properties, where 4piM(s) = 15.8 kG, H(ce) = 4.8 Oe, H(ch) = 3.6 Oe, H(k) = 224 Oe and p = 290 microomega-cm. The theoretically calculated ferromagnetic resonance frequency of the developed films can be higher than 5 GHz.

Biocompatibility and mechanical properties of diamond-like coatings on cobalt-chromium-molybdenum steel and titanium-aluminum-vanadium biomedical alloys.

PubMed

Hinüber, C; Kleemann, C; Friederichs, R J; Haubold, L; Scheibe, H J; Schuelke, T; Boehlert, C; Baumann, M J

2010-11-01

Diamond-like carbon (DLC) films are favored for wear components because of diamond-like hardness, low friction, low wear, and high corrosion resistance (Schultz et al., Mat-wiss u Werkstofftech 2004;35:924-928; Lappalainen et al., J Biomed Mater Res B Appl Biomater 2003;66B:410-413; Tiainen, Diam Relat Mater 2001;10:153-160). Several studies have demonstrated their inertness, nontoxicity, and the biocompatibility, which has led to interest among manufacturers of surgical implants (Allen et al., J Biomed Mater Res B Appl Biomater 2001;58:319-328; Uzumaki et al., Diam Relat Mater 2006;15:982-988; Hauert, Diam Relat Mater 2003;12:583-589; Grill, Diam Relat Mater 2003;12:166-170). In this study, hydrogen-free amorphous, tetrahedrally bonded DLC films (ta-C) were deposited at low temperatures by physical vapor deposition on medical grade Co28Cr6Mo steel and the titanium alloy Ti6Al4V (Scheibe et al., Surf Coat Tech 1996;85:209-214). The mechanical performance of the ta-C was characterized by measuring its surface roughness, contact angle, adhesion, and wear behavior, whereas the biocompatibility was assessed by osteoblast (OB) attachment and cell viability via Live/Dead assay. There was no statistical difference found in the wettability as measured by contact angle measurements for the ta-C coated and the uncoated samples of either Co28Cr6Mo or Ti6Al4V. Rockwell C indentation and dynamic scratch testing on 2-10 μm thick ta-C films on Co28Cr6Mo substrates showed excellent adhesion with HF1 grade and up to 48 N for the critical load L(C2) during scratch testing. The ta-C coating reduced the wear from 3.5 × 10(-5) mm(3)/Nm for an uncoated control sample (uncoated Co28Cr6Mo against uncoated stainless steel) to 1.1 × 10(-7) mm(3)/Nm (coated Co28Cr6Mo against uncoated stainless steel) in reciprocating pin-on-disk testing. The lowest wear factor of 3.9 × 10(-10) mm(3)/Nm was measured using a ta-C coated steel ball running against a ta-C coated and polished Co28Cr6Mo disk. Student's t-test found that the ta-C coating had no statistically significant (p < 0.05) effect on OB attachment, when compared with the uncoated control samples. There was no significant difference (p < 0.05) in the Live/Dead assay results in cell death between the ta-C coated Co28Cr6Mo and Ti6Al4V samples and the uncoated controls. Therefore, these ta-C coatings show improved wear and corrosion (Dorner-Reisel et al., Diam Relat Mater 2003;11:823-827; Affato et al., J Biomed Mater Res B Appl Biomater 2000;53:221-226; Dorner-Reisel et al., Surf Coat Tech 2004;177-178:830-837; Kim et al., Diam Relat Mater 2004;14:35-41) performance and excellent in vitro cyto-compatibility, when compared with currently used uncoated Co28Cr6Mo and Ti6Al4V implant materials.

Effect of oxygen deficiency on electronic properties and local structure of amorphous tantalum oxide thin films

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

Denny, Yus Rama; Firmansyah, Teguh; Oh, Suhk Kun

2016-10-15

Highlights: • The effect of oxygen flow rate on electronic properties and local structure of tantalum oxide thin films was studied. • The oxygen deficiency induced the nonstoichiometric state a-TaOx. • A small peak at 1.97 eV above the valence band side appeared on nonstoichiometric Ta{sub 2}O{sub 5} thin films. • The oxygen flow rate can change the local electronic structure of tantalum oxide thin films. - Abstract: The dependence of electronic properties and local structure of tantalum oxide thin film on oxygen deficiency have been investigated by means of X-ray photoelectron spectroscopy (XPS), Reflection Electron Energy Loss Spectroscopy (REELS),more » and X-ray absorption spectroscopy (XAS). The XPS results showed that the oxygen flow rate change results in the appearance of features in the Ta 4f at the binding energies of 23.2 eV, 24.4 eV, 25.8, and 27.3 eV whose peaks are attributed to Ta{sup 1+}, Ta{sup 2+}, Ta{sup 3+}/Ta{sup 4+}, and Ta{sup 5+}, respectively. The presence of nonstoichiometric state from tantalum oxide (TaOx) thin films could be generated by the oxygen vacancies. In addition, XAS spectra manifested both the increase of coordination number of the first Ta-O shell and a considerable reduction of the Ta-O bond distance with the decrease of oxygen deficiency.« less

Improvement in temperature dependence and dielectric tunability properties of PbZr0.52Ti0.48O3 thin films using Ba(Mg1/3Ta2/3)O3 buffer layer

NASA Astrophysics Data System (ADS)

Wu, Zhi; Zhou, Jing; Chen, Wen; Shen, Jie; Yang, Huimin; Zhang, Shisai; Liu, Yueli

2016-12-01

In this paper, Pb(Zr0.52Ti0.48)O3 (PZT) thin films were prepared via sol-gel method. The effects of Ba(Mg1/3Ta2/3)O3 (BMT) buffer layer on the temperature dependence and dielectric tunability properties of PZT thin films were studied. As the thickness of BMT buffer layer increases, the tan δ and tunability of PZT thin films decrease while tunability still maintains above 10%. This result shows that BMT buffer layer can improve the dielectric tunability properties of PZT thin films. Furthermore, the temperature coefficient of the dielectric constant decreases from 2333.4 to 906.9 ppm/°C with the thickness of BMT buffer layer increasing in the range from 25 to 205 °C, indicating that BMT buffer layer can improve the temperature stability of PZT thin films. Therefore, BMT buffer layer plays a critical role in improving temperature dependence and dielectric tunability properties of PbZr0.52Ti0.48O3 thin films.

Formation and characterization of Ta2O5/TaOx films formed by O ion implantation

NASA Astrophysics Data System (ADS)

Ruffell, S.; Kurunczi, P.; England, J.; Erokhin, Y.; Hautala, J.; Elliman, R. G.

2013-07-01

Ta2O5/TaOx (oxide/suboxide) heterostructures are fabricated by high fluence O ion-implantation into deposited Ta films. The resultant films are characterized by depth profiling X-ray photoelectron spectroscopy (XPS), cross-sectional transmission electron microscopy (XTEM), four-point probe, and current-voltage and capacitance-voltage measurements. The measurements show that Ta2O5/TaOx oxide/suboxide heterostructures can be fabricated with the relative thicknesses of the layers controlled by implantation energy and fluence. Electrical measurements show that this approach has promise for high volume manufacturing of resistive switching memory devices based on oxide/suboxide heterostructures.

Discovery of Overcoating Metal Oxides on Photoelectrode for Water Splitting by Automated Screening.

PubMed

Saito, Rie; Miseki, Yugo; Nini, Wang; Sayama, Kazuhiro

2015-10-12

We applied an automated semiconductor synthesis and screen system to discover overcoating film materials and optimize coating conditions on the BiVO4/WO3 composite photoelectrode to enhance stability and photocurrent. Thirteen metallic elements for overcoating oxides were examined with various coating amounts. The stability of the BiVO4/WO3 photoelectrode in a highly concentrated carbonate electrolyte aqueous solution was significantly improved by overcoating with Ta2O5 film, which was amorphous and porous when calcined at 550 °C. The photocurrent for the water oxidation reaction was only minimally inhibited by the presence of the Ta2O5 film on the BiVO4/WO3 photoelectrode.

Aerosol-assisted chemical vapor deposition of ultra-thin CuOx films as hole transport material for planar perovskite solar cells

NASA Astrophysics Data System (ADS)

Zhang, Zhixin; Chen, Shuqun; Li, Pingping; Li, Hongyi; Wu, Junshu; Hu, Peng; Wang, Jinshu

This paper reports on the fabrication of CuOx films to be used as hole transporting layer (HTL) in CH3NH3PbI3 perovskite solar cells (PSCs). Ultra-thin CuOx coatings were grown onto FTO substrates for the first time via aerosol-assisted chemical vapor deposition (AACVD) of copper acetylacetonate in methanol. After incorporating into the PSCs prepared at ambient air, a highest power conversion efficiency (PCE) of 8.26% with HTL and of 3.34% without HTL were achieved. Our work represents an important step in the development of low-cost CVD technique for fabricating ultra-thin metal oxide functional layers in thin film photovoltaics.

Spin fluctuation induced linear magnetoresistance in ultrathin superconducting FeSe films

DOE PAGES

Wang, Qingyan; Zhang, Wenhao; Chen, Weiwei; ...

2017-07-21

The discovery of high-temperature superconductivity in FeSe/STO has trigged great research interest to reveal a range of exotic physical phenomena in this novel material. Here we present a temperature dependent magnetotransport measurement for ultrathin FeSe/STO films with different thickness and protection layers. Remarkably, a surprising linear magnetoresistance (LMR) is observed around the superconducting transition temperatures but absent otherwise. The experimental LMR can be reproduced by magnetotransport calculations based on a model of magnetic field dependent disorder induced by spin fluctuation. Thus, the observed LMR in coexistence with superconductivity provides the first magnetotransport signature for spin fluctuation around the superconducting transitionmore » region in ultrathin FeSe/STO films.« less

Supramolecular architectures of iron phthalocyanine Langmuir-Blodgett films: The role played by the solution solvents

NASA Astrophysics Data System (ADS)

Rubira, Rafael Jesus Gonçalves; Aoki, Pedro Henrique Benites; Constantino, Carlos José Leopoldo; Alessio, Priscila

2017-09-01

The developing of organic-based devices has been widely explored using ultrathin films as the transducer element, whose supramolecular architecture plays a central role in the device performance. Here, Langmuir and Langmuir-Blodgett (LB) ultrathin films were fabricated from iron phthalocyanine (FePc) solutions in chloroform (CHCl3), dichloromethane (CH2Cl2), dimethylformamide (DMF), and tetrahydrofuran (THF) to determine the influence of different solvents on the supramolecular architecture of the ultrathin films. The UV-vis absorption spectroscopy shows a strong dependence of the FePc aggregation on these solvents. As a consequence, the surface pressure vs. mean molecular area (π-A) isotherms and Brewster angle microscopy (BAM) reveal a more homogeneous (surface morphology) Langmuir film at the air/water interface for FePc in DMF. The same morphological pattern observed for the Langmuir films is preserved upon LB deposition onto solid substrates. The Raman and FTIR analyses indicate the DMF-FePc interaction relies on coordination bonds between N atom (from DMF) and Fe atom (from FePc). Besides, the FePc molecular organization was also found to be affected by the DMF-FePc chemical interaction. It is interesting to note that, if the DMF-FePc leads to less aggregated FePc either in solution or ultrathin films (Langmuir and LB), with time (one week) the opposite trend is found. Taking into account the N-Fe interaction, the performance of the FePc ultrathin films with distinct supramolecular architectures composing sensing units was explored as proof-of-principle in the detection of trace amounts of atrazine herbicide in water using impedance spectroscopy. Further statistical and computational analysis reveal not only the role played by FePc supramolecular architecture but also the sensitivity of the system to detect atrazine solutions down to 10-10 mol/L, which is sufficient to monitor the quality of drinking water even according to the most stringent international regulations.

Optical and electrical properties of sol-gel spin coated titanium dioxide thin films

NASA Astrophysics Data System (ADS)

Sahoo, Anusuya; Jayakrishnan, A. R.; Kamakshi, K.; Silva, J. P. B.; Sekhar, K. C.; Gomes, M. J. M.

2017-08-01

In this work; TiO2 thin films were deposited on glass and stainless steel substrates by sol-gel spin coating method. The films deposited on glass were annealed at different temperatures (Ta) in the range of 200 to 500 0C and that are deposited on steel substrate were annealed at 800 0C. The optical properties of TiO2 thin films were studied by using UV-VIS spectroscopy and photoluminescence (PL) spectroscopy. The transmittance on the average was found to ≥ 80 % and is found to sensitive to Ta. The PL spectra exhibited the strong emission band associated with band- to- band transition around 390 nm and the two weak bands at 480 and 510 nm associated to the oxygen defects and surface defects respectively. The current-voltage (I-V) characteristics of the Al/TiO2/steel capacitors were studied and analysed with application of various current mechanisms. Analysis reveals that the conduction in Al/TiO2/steel capacitors is governed by Poole-Frenkel mechanism.

Effects of thickness and annealing condition on magnetic properties and thermal stabilities of Ta/Nd/NdFeB/Nd/Ta sandwiched films

NASA Astrophysics Data System (ADS)

Liu, Wen-Feng; Zhang, Min-Gang; Zhang, Ke-Wei; Zhang, Hai-Jie; Xu, Xiao-Hong; Chai, Yue-Sheng

2016-11-01

Ta/Nd/NdFeB/Nd/Ta sandwiched films are deposited by magnetron sputtering on Si (100) substrates, and subsequently annealed in vacuum at different temperatures for different time. It is found that both the thickness of NdFeB and Nd layer and the annealing condition can affect the magnetic properties of Ta/Nd/NdFeB/Nd/Ta films. Interestingly, the thickness and annealing temperature show the relevant behaviors that can affect the magnetic properties of the film. The high coercivity of 24.1 kOe (1 Oe = 79.5775 A/m) and remanence ratio (remanent magnetization/saturation magnetization) of 0.94 can be obtained in a Ta/Nd(250 nm)/NdFeB(600 nm)/Nd(250 nm)/Ta film annealed for 3 min at 1023 K. In addition, the thermal stability of the film is also linked to the thickness of NdFeB and Nd layer and the annealing temperature as well. The excellent thermal stability can be achieved in a Ta/Nd(250 nm)/NdFeB(600 nm)/Nd(250 nm)/Ta film annealed at 1023 K. Program supported by the National Natural Science Foundation of China (Grant No. 51305290), the Higher Education Technical Innovation Project of Shanxi Province, China (Grant No. 2013133), the Fund Program for the Scientific Activities of Selected Returned Overseas Professionals of Shanxi Province, China (Grant No. 2015003), and the Program for the Key Team of Scientific and Technological Innovation of Shanxi Province, China (Grant No. 2013131009).

Mechanical Properties of TiTaHfNbZr High-Entropy Alloy Coatings Deposited on NiTi Shape Memory Alloy Substrates

NASA Astrophysics Data System (ADS)

Motallebzadeh, A.; Yagci, M. B.; Bedir, E.; Aksoy, C. B.; Canadinc, D.

2018-04-01

TiTaHfNbZr high-entropy alloy (HEA) thin films with thicknesses of about 750 and 1500 nm were deposited on NiTi substrates by RF magnetron sputtering using TiTaHfNbZr equimolar targets. The thorough experimental analysis on microstructure and mechanical properties of deposited films revealed that the TiTaHfNbZr films exhibited amorphous and cauliflower-like structure, where grain size and surface roughness increased concomitant with film thickness. More importantly, the current findings demonstrate that the TiTaHfNbZr HEA films with mechanical properties of the same order as those of the NiTi substrate constitute promising biomedical coatings effective in preventing Ni release.

Mechanical Properties of TiTaHfNbZr High-Entropy Alloy Coatings Deposited on NiTi Shape Memory Alloy Substrates

NASA Astrophysics Data System (ADS)

Motallebzadeh, A.; Yagci, M. B.; Bedir, E.; Aksoy, C. B.; Canadinc, D.

2018-06-01

TiTaHfNbZr high-entropy alloy (HEA) thin films with thicknesses of about 750 and 1500 nm were deposited on NiTi substrates by RF magnetron sputtering using TiTaHfNbZr equimolar targets. The thorough experimental analysis on microstructure and mechanical properties of deposited films revealed that the TiTaHfNbZr films exhibited amorphous and cauliflower-like structure, where grain size and surface roughness increased concomitant with film thickness. More importantly, the current findings demonstrate that the TiTaHfNbZr HEA films with mechanical properties of the same order as those of the NiTi substrate constitute promising biomedical coatings effective in preventing Ni release.

Effect of processing parameters on microstructure of MoS{sub 2} ultra-thin films synthesized by chemical vapor deposition method

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

Song, Yang; You, Suping; Sun, Kewei

2015-06-15

MoS{sub 2} ultra-thin layers are synthesized using a chemical vapor deposition method based on the sulfurization of molybdenum trioxide (MoO{sub 3}). The ultra-thin layers are characterized by X-ray diffraction (XRD), photoluminescence (PL) spectroscopy and atomic force microscope (AFM). Based on our experimental results, all the processing parameters, such as the tilt angle of substrate, applied voltage, heating time and the weight of source materials have effect on the microstructures of the layers. In this paper, the effects of such processing parameters on the crystal structures and morphologies of the as-grown layers are studied. It is found that the film obtainedmore » with the tilt angle of 0.06° is more uniform. A larger applied voltage is preferred to the growth of MoS{sub 2} thin films at a certain heating time. In order to obtain the ultra-thin layers of MoS{sub 2}, the weight of 0.003 g of source materials is preferred. Under our optimal experimental conditions, the surface of the film is smooth and composed of many uniformly distributed and aggregated particles, and the ultra-thin MoS{sub 2} atomic layers (1∼10 layers) covers an area of more than 2 mm×2 mm.« less

Out-of-plane chiral domain wall spin-structures in ultrathin in-plane magnets

DOE PAGES

Chen, Gong; Kang, Sang Pyo; Ophus, Colin; ...

2017-05-19

Chiral spin textures in ultrathin films, such as skyrmions or chiral domain walls, are believed to offer large performance advantages in the development of novel spintronics technologies. While in-plane magnetized films have been studied extensively as media for current- and field-driven domain wall dynamics with applications in memory or logic devices, the stabilization of chiral spin textures in in-plane magnetized films has remained rare. Here we report a phase of spin structures in an in-plane magnetized ultrathin film system where out-of-plane spin orientations within domain walls are stable. Moreover, while domain walls in in-plane films are generally expected to bemore » non-chiral, we show that right-handed spin rotations are strongly favoured in this system, due to the presence of the interfacial Dzyaloshinskii-Moriya interaction. These results constitute a platform to explore unconventional spin dynamics and topological phenomena that may enable high-performance in-plane spin-orbitronics devices.« less

Ultralight shape-recovering plate mechanical metamaterials

NASA Astrophysics Data System (ADS)

Davami, Keivan; Zhao, Lin; Lu, Eric; Cortes, John; Lin, Chen; Lilley, Drew E.; Purohit, Prashant K.; Bargatin, Igor

2015-12-01

Unusual mechanical properties of mechanical metamaterials are determined by their carefully designed and tightly controlled geometry at the macro- or nanoscale. We introduce a class of nanoscale mechanical metamaterials created by forming continuous corrugated plates out of ultrathin films. Using a periodic three-dimensional architecture characteristic of mechanical metamaterials, we fabricate free-standing plates up to 2 cm in size out of aluminium oxide films as thin as 25 nm. The plates are formed by atomic layer deposition of ultrathin alumina films on a lithographically patterned silicon wafer, followed by complete removal of the silicon substrate. Unlike unpatterned ultrathin films, which tend to warp or even roll up because of residual stress gradients, our plate metamaterials can be engineered to be extremely flat. They weigh as little as 0.1 g cm-2 and have the ability to `pop-back' to their original shape without damage even after undergoing multiple sharp bends of more than 90°.

Nonbolometric bottleneck in electron-phonon relaxation in ultrathin WSi films

NASA Astrophysics Data System (ADS)

Sidorova, Mariia V.; Kozorezov, A. G.; Semenov, A. V.; Korneeva, Yu. P.; Mikhailov, M. Yu.; Devizenko, A. Yu.; Korneev, A. A.; Chulkova, G. M.; Goltsman, G. N.

2018-05-01

We developed the model of the internal phonon bottleneck to describe the energy exchange between the acoustically soft ultrathin metal film and acoustically rigid substrate. Discriminating phonons in the film into two groups, escaping and nonescaping, we show that electrons and nonescaping phonons may form a unified subsystem, which is cooled down only due to interactions with escaping phonons, either due to direct phonon conversion or indirect sequential interaction with an electronic system. Using an amplitude-modulated absorption of the sub-THz radiation technique, we studied electron-phonon relaxation in ultrathin disordered films of tungsten silicide. We found an experimental proof of the internal phonon bottleneck. The experiment and simulation based on the proposed model agree well, resulting in τe -ph˜14 0 -19 0 ps at TC=3.4 K , supporting the results of earlier measurements by independent techniques.

Substrate bias effects on composition and coercivity of CoCrTa/Cr thin films on canasite and glass

NASA Astrophysics Data System (ADS)

Deng, Y.; Lambeth, D. N.; Sui, X.; Lee, L.-L.; Laughlin, D. E.

1993-05-01

CoCrTa/Cr thin films were prepared by rf diode sputtering onto canasite and glass substrates at various bias voltages from two targets of different compositions (Co82.8Cr14.6Ta2.6 and Co86Cr12Ta2). While Auger depth profile analysis indicates that there is some broadening at the CoCrTa-Cr interface, x-ray fluorescence spectroscopy reveals that changes in alloy composition due to the resputtering processes are even more prominent. For both targets, as the substrate bias increases the Co content in the films declines, and the magnetization decreases. The maximum film coercivity appears to correlate to the final film composition. By investigating the results from both targets, it is concluded that the coercivity reaches a maximum when the film composition is in the neighborhood of Co84Cr13Ta3. Thus, to optimize the coercivity different bias voltages are required for each target. Excessive substrate bias, however, leads to films with low magnetization and coercivity.

Investigation of microstructural and electrical properties of composition dependent co-sputtered Hf1-x Ta x O2 thin films

NASA Astrophysics Data System (ADS)

Das, K. C.; Tripathy, N.; Ghosh, S. P.; Mohanta, S. K.; Nakamura, A.; Kar, J. P.

2017-11-01

Tantalum doped HfO2 gate dielectric thin films were deposited on silicon substrates using RF reactive co-sputtering by varying RF power of Ta target from 15 W to 90 W. The morphological, compositional and electrical properties of Hf1-x Ta x O2 films were systematically investigated. The Ta content was found to be increased up to 21% for a Ta target power of 90 W. The evolution of monoclinic phase of Hf1-x Ta x O2 was seen from XRD study upto RF power of 60 W and afterwards, the amorphous like behaviour is appeared. The featureless smooth surface with the decrease in granular morphology has been observed from FESEM micrographs of the doped films at higher RF powers of Ta. The flatband voltage is found to be shifted towards negative voltage in the capacitance-voltage plot, which was attributed to the enhancement in positive oxide charge density with rise in RF power. The interface charge density has a minimum value of 7.85  ×  1011 eV-1 cm-2 for the film deposited at Ta RF power of 75 W. The Hf1-x Ta x O2 films deposited at Ta target RF power of 90 W has shown lower leakage current. The high on/off ratio of the current during the set process in Hf1-x Ta x O2 based memristors is found suitable for bipolar resistive switching memory device applications.

Unique system of FE/PD for magneto-optical recording and magnetic switching devices

DOEpatents

Liu, Chian Q.; Bader, Samuel D.

1992-01-01

A high density magneto-optical information storage medium utilizing the properties of an ultrathin iron film on a palladium substrate. The present invention comprises a magneto-optical medium capable of thermal and magnetic stability and capable of possessing a vertical orientation of the magnetization vector for the magnetic material. Data storage relies on the temperature dependence of the coercivity of the ultrathin film. Data retrieval derives from the Kerr effect which describes the direction of rotation of a plane of polarized light traversing the ultrathin magnetic material as a function of the orientation of the magnetization vector.

Patterned FePt nanostructures using ultrathin self-organized templates

NASA Astrophysics Data System (ADS)

Deng, Chen Hua; Zhang, Min; Wang, Fang; Xu, Xiao Hong

2018-02-01

Patterned magnetic thin films are both scientifically interesting and technologically useful. Ultrathin self-organized anodic aluminum oxide (AAO) template can be used to fabricate large area nanodot and antidot arrays. The magnetic properties of these nanostructures may be tuned by the morphology of the AAO template, which in turn can be controlled by synthetic parameters. In this work, ultrathin AAO templates were used as etching masks for the fabrication of both FePt nanodot and antidot arrays with high areal density. The perpendicular magnetic anisotropy of L10 FePt thin films are preserved in the nanostructures.

Thermally generated metals for plasmonic coloring and surface-enhanced Raman sensing

NASA Astrophysics Data System (ADS)

Huang, Zhenping; Chen, Jian; Liu, Guiqiang; Wang, Yan; Liu, Yi; Tang, Li; Liu, Zhengqi

2018-03-01

Spectral coloring glass and its application on the surface-enhanced Raman scattering are demonstrated experimentally via a simple and moderate heat-treating of the top ultrathin gold film to create discrete nanoparticles, which can produce localized surface plasmon resonances and strong plasmonic near-field coupling effects. Ultrathin metal films with a wide range of thicknesses are investigated by different heat-treatment processes. The annealed metal films have been demonstrated with a series of spectral coloring responses. Moreover, the microscopy images of the metal film structures confirm the formation of distinct geometry features in these operation procedures. Densely packed nanoparticles are observed for the ultrathin metal film with the single-digit level of thickness. With increasing the film thickness over 10 nm, metallic clusters and porous morphologies can be obtained. Importantly, the metallic resonators can provide enhanced Raman scattering with the detection limit down to 10 - 7 molL - 1 of Rhodamine 6G molecules due to the excitation of plasmon resonances and strong near-field coupling effects. These features hold great potential for large-scale and low-cost production of colored glass and Raman substrate.

Interplay between quantum confinement and surface effects in thickness selective stability of thin Ag and Eu films

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

Liu, Xiaojie; Wang, Cai -Zhuang

Using first-principles calculations, we show that both face-centered cubic (fcc) Ag (1 1 0) ultrathin films and body-centered cubic (bcc) Eu(1 1 0) ultrathin films exhibit thickness selective stability. Furthermore, the origin of such thickness selection is different. While the thickness selective stability in fcc Ag(1 1 0) films is mainly due to the well-known quantum well states ascribed to the quantum confinement effects in free-electron-like metal films, the thickness selection in bcc Eu(1 1 0) films is more complex and also strongly correlated with the occupation of the surface and surface resonance states.

Interplay between quantum confinement and surface effects in thickness selective stability of thin Ag and Eu films

DOE PAGES

Liu, Xiaojie; Wang, Cai -Zhuang

2017-04-03

Using first-principles calculations, we show that both face-centered cubic (fcc) Ag (1 1 0) ultrathin films and body-centered cubic (bcc) Eu(1 1 0) ultrathin films exhibit thickness selective stability. Furthermore, the origin of such thickness selection is different. While the thickness selective stability in fcc Ag(1 1 0) films is mainly due to the well-known quantum well states ascribed to the quantum confinement effects in free-electron-like metal films, the thickness selection in bcc Eu(1 1 0) films is more complex and also strongly correlated with the occupation of the surface and surface resonance states.

Parameter Space of Atomic Layer Deposition of Ultrathin Oxides on Graphene

PubMed Central

2016-01-01

Atomic layer deposition (ALD) of ultrathin aluminum oxide (AlOx) films was systematically studied on supported chemical vapor deposition (CVD) graphene. We show that by extending the precursor residence time, using either a multiple-pulse sequence or a soaking period, ultrathin continuous AlOx films can be achieved directly on graphene using standard H2O and trimethylaluminum (TMA) precursors even at a high deposition temperature of 200 °C, without the use of surfactants or other additional graphene surface modifications. To obtain conformal nucleation, a precursor residence time of >2s is needed, which is not prohibitively long but sufficient to account for the slow adsorption kinetics of the graphene surface. In contrast, a shorter residence time results in heterogeneous nucleation that is preferential to defect/selective sites on the graphene. These findings demonstrate that careful control of the ALD parameter space is imperative in governing the nucleation behavior of AlOx on CVD graphene. We consider our results to have model system character for rational two-dimensional (2D)/non-2D material process integration, relevant also to the interfacing and device integration of the many other emerging 2D materials. PMID:27723305

Electrical transport of spin-polarized carriers in disordered ultrathin films.

PubMed

Hernandez, L M; Bhattacharya, A; Parendo, Kevin A; Goldman, A M

2003-09-19

Slow, nonexponential relaxation of electrical transport accompanied by memory effects has been induced in quench-condensed ultrathin amorphous Bi films by the application of a parallel magnetic field. This behavior, which is very similar to space-charge limited current flow, is found in extremely thin films well on the insulating side of the thickness-tuned superconductor-insulator transition. It may be the signature of a collective state that forms when the carriers are spin polarized at low temperatures and in high magnetic fields.

Resistive switching in a few nanometers thick tantalum oxide film formed by a metal oxidation

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

Ohno, Takeo, E-mail: t-ohno@wpi-aimr.tohoku.ac.jp; Japan Science and Technology Agency; Samukawa, Seiji, E-mail: samukawa@ifs.tohoku.ac.jp

2015-04-27

Resistive switching in a Cu/Ta{sub 2}O{sub 5}/Pt structure that consisted of a few nanometer-thick Ta{sub 2}O{sub 5} film was demonstrated. The Ta{sub 2}O{sub 5} film with thicknesses of 2–5 nm was formed with a combination of Ta metal film deposition and neutral oxygen particle irradiation at room temperature. The device exhibited a bipolar resistive switching with a threshold voltage of 0.2 V and multilevel switching operation.

Atomic Scale Control of Competing Electronic Phases in Ultrathin Correlated Oxides

NASA Astrophysics Data System (ADS)

Shen, Kyle

2015-03-01

Ultrathin epitaxial thin films offer a number of unique advantages for engineering the electronic properties of correlated transition metal oxides. For example, atomically thin films can be synthesized to artificially confine electrons in two dimensions. Furthermore, using a substrate with a mismatched lattice constant can impose large biaxial strains of larger than 3% (Δa / a), much larger than can achieved in bulk single crystals. Since these dimensionally confined or strained systems may necessarily be less than a few unit cells thick, investigating their properties and electronic structure can be particularly challenging. We employ a combination of reactive oxide molecular beam epitaxy (MBE) and angle-resolved photoemission spectroscopy (ARPES) to investigate how dimensional confinement and epitaxial strain can be used to manipulate electronic properties and structure in correlated transition metal oxide thin films. We describe some of our recent work manipulating and studying the electronic structure of ultrathin LaNiO3 through a thickness-driven metal-insulator transition between three and two unit cells (Nature Nanotechnology 9, 443, 2014), where coherent Fermi liquid-like quasiparticles are suppressed at the metal-insulator transition observed in transport. We also will describe some recent unpublished work using epitaxial strain to drive a Lifshitz transition in atomically thin films of the spin-triplet ruthenate superconductor Sr2RuO4, where we also can dramatically alter the quasiparticle scattering rates and drive the system towards non-Fermi liquid behavior near the critical point (B. Burganov, C. Adamo, in preparation). Funding provided by the Office of Naval Research and Air Force Office of Scientific Research.

Characterization of the Micro-Abrasive Wear in Coatings of TaC-HfC/Au for Biomedical Implants

PubMed Central

Guzmán, Pablo; Yate, Luis; Sandoval, Mercy; Caballero, Jose

2017-01-01

The object of this work was the deposition of a Ta-Hf-C thin film with a gold interlayer on stainless steel, via the physical vapor deposition (PVD) technique, in order to evaluate the properties of different systems subjected to micro-abrasive wear phenomena generated by alumina particles in Ringer's solution. The surface characterization was performed using a scanning electron microscope (SEM) and atomic force microscope (AFM). The crystallographic phases exhibited for each coating were obtained by X-ray diffraction (XRD). As a consequence of modifying the composition of Ta-Hf there was evidence of an improvement in the micro-abrasive wear resistance and, for each system, the wear constants that confirm the enhancement of the surface were calculated. Likewise, these surfaces can be bioactive, generating an alternative to improve the biological fixation of the implants, therefore, the coatings of TaC-HfC/Au contribute in the development of the new generation of orthopedic implants. PMID:28773207

Effects of Processing Variables on Tantalum Nitride by Reactive-Ion-Assisted Magnetron Sputtering Deposition

NASA Astrophysics Data System (ADS)

Wei, Chao‑Tsang; Shieh, Han‑Ping D.

2006-08-01

The binary compound tantalum nitride (TaN) and ternary compounds tantalum tungsten nitrides (Ta1-xWxNy) exhibit interesting properties such as high melting point, high hardness, and chemical inertness. Such nitrides were deposited on a tungsten carbide (WC) die and silicon wafers by ion-beam-sputter evaporation of the respective metal under nitrogen ion-assisted deposition (IAD). The effects of N2/Ar flux ratio, post annealing, ion-assisted deposition, deposition rate, and W doping in coating processing variables on hardness, load critical scratching, oxidation resistance, stress and surface roughness were investigated. The optimum N2/Ar flux ratios in view of the hardness and critical load of TaN and Ta1-xWxNy films were ranged from 0.9 to 1.0. Doping W into TaN to form Ta1-xWxNy films led significant increases in hardness, critical load, oxidation resistance, and reduced surface roughness. The optimum doping ratio was [W/(W+Ta)]=0.85. From the deposition rate and IAD experiments, the stress in the films is mainly contributed by sputtering atoms. The lower deposition rate at a high N2/Ar flux ratio resulted in a higher compressive stress. A high compressive residual stress accounts for a high hardness. The relatively high compressive stress was attributed primarily to peening by atoms, ions and electrons during film growth, the Ta1-xWxNy films showed excellent hardness and strength against a high temperature, and sticking phenomena can essentially be avoided through their use. Ta1-xWxNy films showed better performance than the TaN film in terms of mechanical properties and oxidation resistance.

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

PubMed Central

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

2017-01-01

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

Nano suboxide layer generated in Ta{sub 2}O{sub 5} by Ar{sup +} ion irradiation

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

Song, W. D., E-mail: song-wendong@dsi.a-star.edu.sg, E-mail: ying-ji-feng@dsi.a-star.edu.sg; Ying, J. F., E-mail: song-wendong@dsi.a-star.edu.sg, E-mail: ying-ji-feng@dsi.a-star.edu.sg; He, W.

2015-01-19

Ta{sub 2}O{sub 5}/TaO{sub x} heterostructure has become a leading oxide layer in memory cells and/or a bidirectional selector for resistive random access memory (RRAM). Although atomic layer deposition (ALD) was found to be uniquely suitable for depositing uniform and conformal films on complex topographies, it is hard to use ALD to grow suboxide TaO{sub x} layer. In this study, tantalum oxide films with a composition of Ta{sub 2}O{sub 5} were grown by ALD. Using Ar{sup +} ion irradiation, the suboxide was formed in the top layer of Ta{sub 2}O{sub 5} films by observing the Ta core level shift toward lowermore » binding energy with angle-resolved X-ray photoelectron spectroscopy. By controlling the energy and irradiation time of an Ar{sup +} ion beam, Ta{sub 2}O{sub 5}/TaO{sub x} heterostructure can be reliably produced on ALD films, which provides a way to fabricate the critical switching layers of RRAM.« less

(Na{sub x}k{sub 1−x}){sub 2}Ta{sub 4}O{sub 11}(x≈0.93) piezoelectric phase from the transformation of Ta{sub 2}O{sub 5} thin films of monoclinic structure

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

Le Gallic, M., E-mail: Marie.Le-Gallic@grenoble-inp.fr; Roussel, H.

2013-04-15

A phase of trigonal structure has been reported in previous articles to be piezoelectric with a very high longitudinal d{sub 33} coefficient of several thousand pm/V (J. Solid State Chem. 184 (2011) 2023, 2033). It was observed in Ta{sub 2}O{sub 5} thin films and assumed to be the result of a reversible monoclinic–trigonal phase transition. However, new investigations are reported because the cell parameters of this phase are actually very close to those of the natrotantite mineral Na{sub 2}Ta{sub 4}O{sub 11}. From analyses by X-ray energy dispersive spectroscopy (XEDS), the chemical composition of this trigonal phase corresponds to (Na{sub x}K{submore » 1−x}){sub 2}Ta{sub 4}O{sub 11} with x≈0.93. The origin of sodium, potassium, iron and oxygen atoms is found to be due to a pollution coming from alumina crucibles used for thermal treatments. Knowing both atomic structures Ta{sub 2}O{sub 5} and Na{sub 2}Ta{sub 4}O{sub 11} and their structural relationships, observed by high resolution transmission electron microscopy (HRTEM), the mechanism of the reaction of transformation is re-examined and discussed. This mechanism implies that Ta{sup 5+} vacancies likely exist in monoclinic structures of tantalum oxide and that electrical neutrality could be due to incorporated proton H{sup +} instead of O{sup 2−} vacancies or Ta{sup 5+} interstitials. - Graphical abstract: (a, b) TEM images of interfaces between Ta{sub 2}O{sub 5} monoclinic and (Na{sub 0.93}K{sub 0.07}){sub 2}Ta{sub 4}O{sub 11} trigonal phases where it appears that the ratio of periods for the transformation monoclinic-to-trigonal is 3/2 (c, d) corresponding schema of the reaction of transformation, (a, c) viewed along the zone axes [010]{sub o}∥[1{sup ¯}21{sup ¯}]{sub R} and (b, d) along the zone axes [100]{sub o}∥[101{sup ¯}]{sub R}. Highlights: ► The formation of a piezoelectric phase in Ta{sub 2}O{sub 5} thin films, reported in previous articles, is re-examined. ► Its composition is actually (Na{sub x},K{sub 1}−x){sub 2}Ta{sub 4}O{sub 11} with x=0.93, instead of Ta{sub 2}O{sub 5}. ► Ta{sup 5+} vacancies, compensated by protons within tantalumoxide, are involved in a new analysis of the transformation.« less

Fabrication of AgInSe2 heterojunction solar cell

NASA Astrophysics Data System (ADS)

Khudayer, Iman Hameed

2018-05-01

Silver, Indium Selenium thin film with a thickness (5001±30) nm, deposited by thermal evaporation methods at RT and annealing3temperature (Ta = 400, 500 and 600) K on a substrate of glass to study structural and optical properties of thin films and on p-Si wafer to fabricate the AgInSe2/p-Si heterojunction solar cell. XRD analysis shows that the AgInSe2 (AIS) deposited film at RT and annealing3temperature (Ta = 400, 500 and 600) K have polycrystalline structure. The average grain size has been estimated from AFM images. The energy gap was estimated from the optical transmittance using a spectrometer type (UV.-Visible 1800 spectra photometer). From I-V characterization, the photovoltaic parameters such as, open-circuit voltage, short-circuit current density, fill factor, ideality factor, and efficiencies, were computed. As well as the built-in potential, carrier concentration and depletion width were determined under RT and (Ta = 400, 500 and 600) K from C-V measurement.

High-mobility ultrathin semiconducting films prepared by spin coating.

PubMed

Mitzi, David B; Kosbar, Laura L; Murray, Conal E; Copel, Matthew; Afzali, Ali

2004-03-18

The ability to deposit and tailor reliable semiconducting films (with a particular recent emphasis on ultrathin systems) is indispensable for contemporary solid-state electronics. The search for thin-film semiconductors that provide simultaneously high carrier mobility and convenient solution-based deposition is also an important research direction, with the resulting expectations of new technologies (such as flexible or wearable computers, large-area high-resolution displays and electronic paper) and lower-cost device fabrication. Here we demonstrate a technique for spin coating ultrathin (approximately 50 A), crystalline and continuous metal chalcogenide films, based on the low-temperature decomposition of highly soluble hydrazinium precursors. We fabricate thin-film field-effect transistors (TFTs) based on semiconducting SnS(2-x)Se(x) films, which exhibit n-type transport, large current densities (>10(5) A cm(-2)) and mobilities greater than 10 cm2 V(-1) s(-1)--an order of magnitude higher than previously reported values for spin-coated semiconductors. The spin-coating technique is expected to be applicable to a range of metal chalcogenides, particularly those based on main group metals, as well as for the fabrication of a variety of thin-film-based devices (for example, solar cells, thermoelectrics and memory devices).

High-mobility ultrathin semiconducting films prepared by spin coating

NASA Astrophysics Data System (ADS)

Mitzi, David B.; Kosbar, Laura L.; Murray, Conal E.; Copel, Matthew; Afzali, Ali

2004-03-01

The ability to deposit and tailor reliable semiconducting films (with a particular recent emphasis on ultrathin systems) is indispensable for contemporary solid-state electronics. The search for thin-film semiconductors that provide simultaneously high carrier mobility and convenient solution-based deposition is also an important research direction, with the resulting expectations of new technologies (such as flexible or wearable computers, large-area high-resolution displays and electronic paper) and lower-cost device fabrication. Here we demonstrate a technique for spin coating ultrathin (~50Å), crystalline and continuous metal chalcogenide films, based on the low-temperature decomposition of highly soluble hydrazinium precursors. We fabricate thin-film field-effect transistors (TFTs) based on semiconducting SnS2-xSex films, which exhibit n-type transport, large current densities (>105Acm-2) and mobilities greater than 10cm2V-1s-1-an order of magnitude higher than previously reported values for spin-coated semiconductors. The spin-coating technique is expected to be applicable to a range of metal chalcogenides, particularly those based on main group metals, as well as for the fabrication of a variety of thin-film-based devices (for example, solar cells, thermoelectrics and memory devices).

Deposition and dielectric characterization of strontium and tantalum-based oxide and oxynitride perovskite thin films

NASA Astrophysics Data System (ADS)

Jacq, S.; Le Paven, C.; Le Gendre, L.; Benzerga, R.; Cheviré, F.; Tessier, F.; Sharaiha, A.

2016-04-01

We have synthesized the composition x = 0.01 of the (Sr1-xLax)2(Ta1-xTix)2O7 solid solution, mixing the ferroelectric perovskite phases Sr2Ta2O7 and La2Ti2O7. Related oxide and oxynitride materials have been produced as thin films by magnetron radio frequency sputtering. Reactive sputter deposition was conducted at 750 °C under a 75 vol.% (Ar) + 25 vol.% (N2,O2) mixture. An oxygen-free plasma leads to the deposition of an oxynitride film (Sr0.99La0.01) (Ta0.99Ti0.01)O2N, characterized by a band gap Eg = 2.30 eV and a preferential (001) epitaxial growth on (001) SrTiO3 substrate. Its dielectric constant and loss tangent are respectively Epsilon' = 60 (at 1 kHz) and tanDelta = 62.5 × 10-3. In oxygen-rich conditions (vol.%N2 ≤ 15%), (110) epitaxial (Sr0.99La0.01)2(Ta0.99Ti0.01)2O7 oxides films are deposited, associated to a larger band gap value (Eg = 4.55 eV). The oxide films permittivity varies from 45 to 25 (at 1 kHz) in correlation with the decrease in crystalline orientation; measured losses are lower than 5.10-3. For 20 ≤ vol.% N2 ≤ 24.55, the films are poorly crystallized, leading to very low permittivities (minimum Epsilon' = 3). A correlation between the dielectric losses and the presence of an oxynitride phase in the samples is highlighted.

Ultrathin Cr added Ru film as a seedless Cu diffusion barrier for advanced Cu interconnects

NASA Astrophysics Data System (ADS)

Hsu, Kuo-Chung; Perng, Dung-Ching; Yeh, Jia-Bin; Wang, Yi-Chun

2012-07-01

A 5 nm thick Cr added Ru film has been extensively investigated as a seedless Cu diffusion barrier. High-resolution transmission electron microscopy micrograph, X-ray diffraction (XRD) pattern and Fourier transform-electron diffraction pattern reveal that a Cr contained Ru (RuCr) film has a glassy microstructure and is an amorphous-like film. XRD patterns and sheet resistance data show that the RuCr film is stable up to 650 °C, which is approximately a 200 °C improvement in thermal stability as compared to that of the pure Ru film. X-ray photoelectron spectroscopy depth profiles show that the RuCr film can successfully block Cu diffusion, even after a 30-min 650 °C annealing. The leakage current of the Cu/5 nm RuCr/porous SiOCH/Si stacked structure is about two orders of magnitude lower than that of a pristine Ru sample for electric field below 1 MV/cm. The RuCr film can be a promising Cu diffusion barrier for advanced Cu metallization.

Development of hot-electron THz bolometric mixers using MgB2 thin films

NASA Astrophysics Data System (ADS)

Cunnane, Daniel; Kawamura, Jonathan; Karasik, Boris S.; Wolak, Matthaeus A.; Xi, X. X.

2014-07-01

Terahertz high-resolution spectroscopy of interstellar molecular clouds greatly relies on hot-electron superconducting bolometric (HEB) mixers. Current state-of-the-art receivers use mixer devices made from ultrathin (~ 3-5 nm) films of NbN with critical temperature ~ 9-11 K. Such mixers have been deployed on a number of groundbased, suborbital, and orbital platforms including the HIFI instrument on the Hershel Space Observatory. Despite its good sensitivity and well-established fabrication process, the NbN HEB mixer suffers from the narrow intermediate frequency (IF) bandwidth ~ 2-3 GHz and is limited to operation at liquid Helium temperature. As the heterodyne receivers are now trending towards "high THz" frequencies, the need in a larger IF bandwidth becomes more pressing since the same velocity resolution for a Doppler shifted line at 5 THz requires a 5-times greater IF bandwidth than at 1 THz. Our work is focusing on the realization of practical HEB mixers using ultrathin (10-20 nm) MgB2 films. They are prepared using a Hybrid Physical-Chemical Vapor Deposition (HPCVD) process yielding ultrathin films with critical temperature ~ 37-39 K. The expectation is that the combination of small thickness, high acoustic phonon transparency at the interface with the substrate, and very short electron-phonon relaxation time may lead to IF bandwidth ~ 10 GHz or even higher. SiC continues to be the most favorable substrate for MgB2 growth and as a result, a study has been conducted on the transparency of SiC at THz frequencies. FTIR measurements show that semi-insulating SiC substrates are at least as transparent as Si up to 2.5 THz. Currently films are passivated using a thin (10 nm) SiO2 layer which is deposited ex-situ via RF magnetron sputtering. Micron-sized spiral antenna-coupled HEB mixers have been fabricated using MgB2 films as thin as 10 nm. Fabrication was done using contact UV lithography and Ar Ion milling, with E-beam evaporated Au films deposited for the antenna. Measurements have been carried out on these devices in the DC, Microwave, and THz regimes. The devices are capable of mixing signals above 20 K indicating that operation may be possible using a cryogen-free cooling system. We will report the results of all measurements taken to indicate the local oscillator power requirements and the IF bandwidth of MgB2 HEB mixers.

Evolution of sp{sup 2} networks with substrate temperature in amorphous carbon films: Experiment and theory

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

Gago, R.; Centro de Micro-Analisis de Materiales, Universidad Autonoma de Madrid, Campus de Cantoblanco, 28049 Madrid; Vinnichenko, M.

2005-07-01

The evolution of sp{sup 2} hybrids in amorphous carbon (a-C) films deposited at different substrate temperatures was studied experimentally and theoretically. The bonding structure of a-C films prepared by filtered cathodic vacuum arc was assessed by the combination of visible Raman spectroscopy, x-ray absorption, and spectroscopic ellipsometry, while a-C structures were generated by molecular-dynamics deposition simulations with the Brenner interatomic potential to determine theoretical sp{sup 2} site distributions. The experimental results show a transition from tetrahedral a-C (ta-C) to sp{sup 2}-rich structures at {approx}500 K. The sp{sup 2} hybrids are mainly arranged in chains or pairs whereas graphitic structures aremore » only promoted for sp{sup 2} fractions above 80%. The theoretical analysis confirms the preferred pairing of isolated sp{sup 2} sites in ta-C, the coalescence of sp{sup 2} clusters for medium sp{sup 2} fractions, and the pronounced formation of rings for sp{sup 2} fractions >80%. However, the dominance of sixfold rings is not reproduced theoretically, probably related to the functional form of the interatomic potential used.« less

Mechanical Properties of Robust Ultrathin Silk Fibroin Films

DTIC Science & Technology

2007-01-01

extracted from the cocoons prior to sericin removal in order to avoid contamination of the fibroin protein. Silk fibers were prepared as previously...the glue-like sericin proteins. The extracted silk fibroin was dissolved in 9.3 M LiBr solution at 60 °C for 4 h, yielding a 20 wt % solution. The

Ultrathin MoS2 Nanosheets with Superior Extreme Pressure Property as Boundary Lubricants.

PubMed

Chen, Zhe; Liu, Xiangwen; Liu, Yuhong; Gunsel, Selda; Luo, Jianbin

2015-08-07

In this paper, a new kind of oil-soluble ultrathin MoS2 nanosheets is prepared through a one-pot process. A superior extreme pressure property, which has not been attained with other nano-additives, is discovered when the nanosheets are used as lubricant additives. The as-synthesized MoS2 nanosheet is only a few atomic layers thick and tens of nanometers wide, and it is surface-modified with oleylamine so it can be well dispersed in oil or lubricant without adscititious dispersants or surfactants. By adding 1 wt% ultrathin MoS2 nanosheets, at the temperature of 120 °C, the highest load liquid paraffin can bear is tremendously improved from less than 50 N to more than 2000 N. Based on the tribological tests and analysis of the wear scar, a lubrication mechanism is proposed. It is believed that the good dispersion and the ultrathin shape of the nanosheets ensure that they can enter the contact area of the opposite sliding surfaces and act like a protective film to prevent direct contact and seizure between them. This work enriches the investigation of ultrathin MoS2 and has potential application in the mechanical industry.

Ultrathin MoS2 Nanosheets with Superior Extreme Pressure Property as Boundary Lubricants

NASA Astrophysics Data System (ADS)

Chen, Zhe; Liu, Xiangwen; Liu, Yuhong; Gunsel, Selda; Luo, Jianbin

2015-08-01

In this paper, a new kind of oil-soluble ultrathin MoS2 nanosheets is prepared through a one-pot process. A superior extreme pressure property, which has not been attained with other nano-additives, is discovered when the nanosheets are used as lubricant additives. The as-synthesized MoS2 nanosheet is only a few atomic layers thick and tens of nanometers wide, and it is surface-modified with oleylamine so it can be well dispersed in oil or lubricant without adscititious dispersants or surfactants. By adding 1 wt% ultrathin MoS2 nanosheets, at the temperature of 120 °C, the highest load liquid paraffin can bear is tremendously improved from less than 50 N to more than 2000 N. Based on the tribological tests and analysis of the wear scar, a lubrication mechanism is proposed. It is believed that the good dispersion and the ultrathin shape of the nanosheets ensure that they can enter the contact area of the opposite sliding surfaces and act like a protective film to prevent direct contact and seizure between them. This work enriches the investigation of ultrathin MoS2 and has potential application in the mechanical industry.

Ultrathin MoS2 Nanosheets with Superior Extreme Pressure Property as Boundary Lubricants

PubMed Central

Chen, Zhe; Liu, Xiangwen; Liu, Yuhong; Gunsel, Selda; Luo, Jianbin

2015-01-01

In this paper, a new kind of oil-soluble ultrathin MoS2 nanosheets is prepared through a one-pot process. A superior extreme pressure property, which has not been attained with other nano-additives, is discovered when the nanosheets are used as lubricant additives. The as-synthesized MoS2 nanosheet is only a few atomic layers thick and tens of nanometers wide, and it is surface-modified with oleylamine so it can be well dispersed in oil or lubricant without adscititious dispersants or surfactants. By adding 1 wt% ultrathin MoS2 nanosheets, at the temperature of 120 °C, the highest load liquid paraffin can bear is tremendously improved from less than 50 N to more than 2000 N. Based on the tribological tests and analysis of the wear scar, a lubrication mechanism is proposed. It is believed that the good dispersion and the ultrathin shape of the nanosheets ensure that they can enter the contact area of the opposite sliding surfaces and act like a protective film to prevent direct contact and seizure between them. This work enriches the investigation of ultrathin MoS2 and has potential application in the mechanical industry. PMID:26249536

Chitosan-based nanocoatings for hypothermic storage of living cells.

PubMed

Bulwan, Maria; Antosiak-Iwańska, Magdalena; Godlewska, Ewa; Granicka, Ludomira; Zapotoczny, Szczepan; Nowakowska, Maria

2013-11-01

The formation of ultrathin chitosan-based nanocoating on HL-60 model cells and their protective function in hypothermic storage are presented. HL-60 cells are encapsulated in ultrathin shells by adsorbing cationic and anionic chitosan derivatives in a stepwise, layer-by-layer, procedure carried out in an aqueous medium under mild conditions. The chitosan-based films are also deposited on model lipid bilayer and the interactions are studied using ellipsometry and atomic force microscopy. The cells covered with the chitosan-based films and stored at 4 °C for 24 h express viability comparable to that of the control sample incubated at 37 °C, while the unprotected cells stored under the same conditions do not show viability. It is shown that the chitosan-based shell protects HL-60 cells against damaging effect of hypothermic storage. Such nanocoatings provide protection, mechanical stability, and support the cell membrane, while ensuring penetration of small molecules such as nutrients/gases what is essential for cell viability. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Conducting transition metal nitride thin films with tailored cell sizes: The case of {delta}-Ti{sub x}Ta{sub 1-x}N

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

Koutsokeras, L. E.; Laboratoire PHYMAT, Universite de Poitiers-CNRS, UMR 6630, SP2MI, Teleport 2, Bd Marie et Pierre Curie, 86962 Chasseneuil-Futuroscope; Abadias, G.

2008-07-07

We present results on the stability and tailoring of the cell size of conducting {delta}-Ti{sub x}Ta{sub 1-x}N obtained by film growth and ab initio calculations. Despite the limited solubility of Ta in Ti, we show that TiN and TaN are soluble due to the hybrization of the d and sp electrons of the metal and N, respectively, that stabilizes the ternary system to the rocksalt structure. The stress-free cell sizes follow the Vegard's rule; nevertheless, process-dependent stresses expand the cell size of the as-grown films. The electronic properties of {delta}-Ti{sub x}Ta{sub 1-x}N films ({rho}=180 {omega} cm) are similar to thosemore » of TiN and TaN.« less

Vanadium dioxide as a material to control light polarization in the visible and near infrared

NASA Astrophysics Data System (ADS)

Cormier, Patrick; Son, Tran Vinh; Thibodeau, Jacques; Doucet, Alexandre; Truong, Vo-Van; Haché, Alain

2017-01-01

We report on the possible use of vanadium dioxide to produce ultrathin (<100 nm) adjustable phase retarders working over a wide spectral range. The refractive index of vanadium dioxide undergoes large changes when the material undergoes a phase transition from semiconductor to metal at a temperature of 68 °C. In a thin film, the resulting optical phase shift is different for s- and p-polarizations in both reflection and transmission, and under certain conditions the polarization state changes between linear or circular or between linear polarizations oriented differently when the material phase transitions. Specific ultrathin modulators are proposed based on the results.

Nanoscale Investigation of New Fe-Based Superconductors

DTIC Science & Technology

2012-10-15

temperature over 55K in one unit cell FeSe film on SrTiO3 substrate [4]. In addition, a clear diamagnetic signal around 40K was observed in as-grown FeSe nano ...scale. Comparing with other two kinds of nano -scale samples, ultrathin film and Report Documentation Page Form ApprovedOMB No. 0704-0188 Public...unclassified c. THIS PAGE unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 nano -particles, crystalline nanowire (NW) in

Growth of an Ultrathin Zirconia Film on Pt3Zr Examined by High-Resolution X-ray Photoelectron Spectroscopy, Temperature-Programmed Desorption, Scanning Tunneling Microscopy, and Density Functional Theory.

PubMed

Li, Hao; Choi, Joong-Il Jake; Mayr-Schmölzer, Wernfried; Weilach, Christian; Rameshan, Christoph; Mittendorfer, Florian; Redinger, Josef; Schmid, Michael; Rupprechter, Günther

2015-02-05

Ultrathin (∼3 Å) zirconium oxide films were grown on a single-crystalline Pt 3 Zr(0001) substrate by oxidation in 1 × 10 -7 mbar of O 2 at 673 K, followed by annealing at temperatures up to 1023 K. The ZrO 2 films are intended to serve as model supports for reforming catalysts and fuel cell anodes. The atomic and electronic structure and composition of the ZrO 2 films were determined by synchrotron-based high-resolution X-ray photoelectron spectroscopy (HR-XPS) (including depth profiling), low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. Oxidation mainly leads to ultrathin trilayer (O-Zr-O) films on the alloy; only a small area fraction (10-15%) is covered by ZrO 2 clusters (thickness ∼0.5-10 nm). The amount of clusters decreases with increasing annealing temperature. Temperature-programmed desorption (TPD) of CO was utilized to confirm complete coverage of the Pt 3 Zr substrate by ZrO 2 , that is, formation of a closed oxide overlayer. Experiments and DFT calculations show that the core level shifts of Zr in the trilayer ZrO 2 films are between those of metallic Zr and thick (bulklike) ZrO 2 . Therefore, the assignment of such XPS core level shifts to substoichiometric ZrO x is not necessarily correct, because these XPS signals may equally well arise from ultrathin ZrO 2 films or metal/ZrO 2 interfaces. Furthermore, our results indicate that the common approach of calculating core level shifts by DFT including final-state effects should be taken with care for thicker insulating films, clusters, and bulk insulators.

Enhanced electrical stability of nitrate ligand-based hexaaqua complexes solution-processed ultrathin a-IGZO transistors

NASA Astrophysics Data System (ADS)

Choi, C.; Baek, Y.; Lee, B. M.; Kim, K. H.; Rim, Y. S.

2017-12-01

We report solution-processed, amorphous indium-gallium-zinc-oxide-based (a-IGZO-based) thin-film transistors (TFTs). Our proposed solution-processed a-IGZO films, using a simple spin-coating method, were formed through nitrate ligand-based metal complexes, and they were annealed at low temperature (250 °C) to achieve high-quality oxide films and devices. We investigated solution-processed a-IGZO TFTs with various thicknesses, ranging from 4 to 16 nm. The 4 nm-thick TFT films had smooth morphology and high-density, and they exhibited excellent performance, i.e. a high saturation mobility of 7.73  ±  0.44 cm2 V-1 s-1, a sub-threshold swing of 0.27 V dec-1, an on/off ratio of ~108, and a low threshold voltage of 3.10  ±  0.30 V. However, the performance of the TFTs degraded as the film thickness was increased. We further performed positive and negative bias stress tests to examine their electrical stability, and it was noted that the operating behavior of the devices was highly stable. Despite a small number of free charges, the high performance of the ultrathin a-IGZO TFTs was attributed to the small effect of the thickness of the channel, low bulk resistance, the quality of the a-IGZO/SiO2 interface, and high film density.

Selective etching of TiN over TaN and vice versa in chlorine-containing plasmas

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

Shin, Hyungjoo; Zhu Weiye; Liu Lei

2013-05-15

Selectivity of etching between physical vapor-deposited TiN and TaN was studied in chlorine-containing plasmas, under isotropic etching conditions. Etching rates for blanket films were measured in-situ using optical emission of the N{sub 2} (C{sup 3}{Pi}{sub u}{yields}B{sup 3}{Pi}{sub g}) bandhead at 337 nm to determine the etching time, and transmission electron microscopy to determine the starting film thickness. The etching selectivity in Cl{sub 2}/He or HCl/He plasmas was poor (<2:1). There was a window of very high selectivity of etching TiN over TaN by adding small amounts (<1%) of O{sub 2} in the Cl{sub 2}/He plasma. Reverse selectivity (10:1 of TaNmore » etching over TiN) was observed when adding small amounts of O{sub 2} to the HCl/He plasma. Results are explained on the basis of the volatility of plausible reaction products.« less

Enhancement of as-sputtered silver-tantalum oxide thin film coating on biomaterial stainless steel by surface thermal treatment

NASA Astrophysics Data System (ADS)

Alias, Rodianah; Mahmoodian, Reza; Shukor, Mohd Hamdi Abd; Yew, Been Seok; Muhamad, Martini

2018-04-01

Stainless steel 316L (SS316L) is extensively used as surgical/clinical tools due to its low carbon content and excellent mechanical characteristic. The fabrication of metal ceramic based on this metallic biomaterial favor its biofunctionality properties. However, instability phase of amorphous thin film lead to degradation, corrosion and oxidation. Thus, thin film coating requires elevated adhesion strength and higher surface hardness to meet clinical tools criteria. In this study, the SS316L was deposited with micron thickness of Ag-TaO thin film by using magnetron sputtering. The microstructure, elemental analysis and phase identification of Ag-TaO thin film were characterized by using FESEM, EDX and XRD, respectively; whereas the micro scratch test and micro hardness test were performed by using Micro Scratch Testing System and Vickers Micro Hardness Tester, respectively. It was found that the coating thin film's adhesion and hardness strength were improved from 672 to 2749 mN and 142 to 158 Hv respectively. It was found that the as-deposited surface were treated at 500 °C of temperatures with 2 °C/min ramping rate enhance 4.1 times of the adhesion strength value. Furthermore, FESEM characterization revealed coarsening structure of the thin film coating which can provide high durability service.

Bottom Extreme-Ultraviolet-Sensitive Coating for Evaluation of the Absorption Coefficient of Ultrathin Film

NASA Astrophysics Data System (ADS)

Hijikata, Hayato; Kozawa, Takahiro; Tagawa, Seiichi; Takei, Satoshi

2009-06-01

A bottom extreme-ultraviolet-sensitive coating (BESC) for evaluation of the absorption coefficients of ultrathin films such as extreme ultraviolet (EUV) resists was developed. This coating consists of a polymer, crosslinker, acid generator, and acid-responsive chromic dye and is formed by a conventional spin-coating method. By heating the film after spin-coating, a crosslinking reaction is induced and the coating becomes insoluble. A typical resist solution can be spin-coated on a substrate covered with the coating film. The evaluation of the linear absorption coefficients of polymer films was demonstrated by measuring the EUV absorption of BESC substrates on which various polymers were spin-coated.

Enhancement of absorption and color contrast in ultra-thin highly absorbing optical coatings

NASA Astrophysics Data System (ADS)

Kats, Mikhail A.; Byrnes, Steven J.; Blanchard, Romain; Kolle, Mathias; Genevet, Patrice; Aizenberg, Joanna; Capasso, Federico

2013-09-01

Recently a new class of optical interference coatings was introduced which comprises ultra-thin, highly absorbing dielectric layers on metal substrates. We show that these lossy coatings can be augmented by an additional transparent subwavelength layer. We fabricated a sample comprising a gold substrate, an ultra-thin film of germanium with a thickness gradient, and several alumina films. The experimental reflectivity spectra showed that the additional alumina layer increases the color range that can be obtained, in agreement with calculations. More generally, this transparent layer can be used to enhance optical absorption, protect against erosion, or as a transparent electrode for optoelectronic devices.

Electric field effect on exchange interaction in ultrathin Co films with ionic liquids

NASA Astrophysics Data System (ADS)

Ishibashi, Mio; Yamada, Kihiro T.; Shiota, Yoichi; Ando, Fuyuki; Koyama, Tomohiro; Kakizakai, Haruka; Mizuno, Hayato; Miwa, Kazumoto; Ono, Shimpei; Moriyama, Takahiro; Chiba, Daichi; Ono, Teruo

2018-06-01

Electric-field modulations of magnetic properties have been extensively studied not only for practical applications but also for fundamental interest. In this study, we investigated the electric field effect on the exchange interaction in ultrathin Co films with ionic liquids. The exchange coupling J was characterized from the direct magnetization measurement as a function of temperature using Pt/ultrathin Co/MgO structures. The trend of the electric field effect on J is in good agreement with that of the theoretical prediction, and a large change in J by applying a gate voltage was observed by forming an electric double layer using ionic liquids.

Endurance and Cycle-to-cycle Uniformity Improvement in Tri-Layered CeO2/Ti/CeO2 Resistive Switching Devices by Changing Top Electrode Material

PubMed Central

Rana, Anwar Manzoor; Akbar, Tahira; Ismail, Muhammad; Ahmad, Ejaz; Hussain, Fayyaz; Talib, Ijaz; Imran, Muhammad; Mehmood, Khalid; Iqbal, Khalid; Nadeem, M. Younus

2017-01-01

Resistance switching characteristics of CeO2/Ti/CeO2 tri-layered films sandwiched between Pt bottom electrode and two different top electrodes (Ti and TaN) with different work functions have been investigated. RRAM memory cells composed of TaN/CeO2/Ti/CeO2/Pt reveal better resistive switching performance instead of Ti/CeO2/Ti/CeO2/Pt memory stacks. As compared to the Ti/CeO2 interface, much better ability of TaN/CeO2 interface to store and exchange plays a key role in the RS performance improvement, including lower forming/SET voltages, large memory window (~102) and no significant data degradation during endurance test of >104 switching cycles. The formation of TaON thinner interfacial layer between TaN TE and CeO2 film is found to be accountable for improved resistance switching behavior. Partial charge density of states is analyzed using density functional theory. It is found that the conductive filaments formed in CeO2 based devices is assisted by interstitial Ti dopant. Better stability and reproducibility in cycle-to-cycle (C2C) resistance distribution and Vset/Vreset uniformity were achieved due to the modulation of current conduction mechanism from Ohmic in low field region to Schottky emission in high field region. PMID:28079056

Theoretical requirements for broadband perfect absorption of acoustic waves by ultra-thin elastic meta-films

PubMed Central

Duan, Yuetao; Luo, Jie; Wang, Guanghao; Hang, Zhi Hong; Hou, Bo; Li, Jensen; Sheng, Ping; Lai, Yun

2015-01-01

We derive and numerically demonstrate that perfect absorption of elastic waves can be achieved in two types of ultra-thin elastic meta-films: one requires a large value of almost pure imaginary effective mass density and a free space boundary, while the other requires a small value of almost pure imaginary effective modulus and a hard wall boundary. When the pure imaginary density or modulus exhibits certain frequency dispersions, the perfect absorption effect becomes broadband, even in the low frequency regime. Through a model analysis, we find that such almost pure imaginary effective mass density with required dispersion for perfect absorption can be achieved by elastic metamaterials with large damping. Our work provides a feasible approach to realize broadband perfect absorption of elastic waves in ultra-thin films. PMID:26184117

Determination of magnetic anisotropy constants in Fe ultrathin film on vicinal Si(111) by anisotropic magnetoresistance

PubMed Central

Ye, Jun; He, Wei; Wu, Qiong; Liu, Hao-Liang; Zhang, Xiang-Qun; Chen, Zi-Yu; Cheng, Zhao-Hua

2013-01-01

The epitaxial growth of ultrathin Fe film on Si(111) surface provides an excellent opportunity to investigate the contribution of magnetic anisotropy to magnetic behavior. Here, we present the anisotropic magnetoresistance (AMR) effect of Fe single crystal film on vicinal Si(111) substrate with atomically flat ultrathin p(2 × 2) iron silicide as buffer layer. Owing to the tiny misorientation from Fe(111) plane, the symmetry of magnetocrystalline anisotropy energy changes from the six-fold to a superposition of six-fold, four-fold and a weakly uniaxial contribution. Furthermore, the magnitudes of various magnetic anisotropy constants were derived from torque curves on the basis of AMR results. Our work suggests that AMR measurements can be employed to figure out precisely the contributions of various magnetic anisotropy constants. PMID:23828508

Study of anisotropy, magnetization reversal and damping in ultrathin Co films on MgO (0 0 1) substrate

NASA Astrophysics Data System (ADS)

Mallik, Srijani; Bedanta, Subhankar

2018-01-01

Ultrathin Co films of 3 nm thickness have been prepared on MgO (0 0 1) substrate in presence or absence of substrate pre-annealing. Uniaxial anisotropy is induced in the samples due to the deposition under oblique angle of incidence. Along with the oblique deposition induced anisotropy, another uniaxial anisotropy contribution has been observed due to pre-annealing. However, no cubic anisotropy has been observed here as compared to the thicker films. Angle dependent ferromagnetic resonance (FMR) measurement confirms the presence of two anisotropies in the pre-annealed sample with ∼18° misalignment with each other. The two anisotropy constants were calculated from both superconducting quantum interference device (SQUID) magnetometry and FMR spectroscopy. The magnetization reversal is governed by nucleation dominated aftereffect followed by domain wall motion for the pre-annealed sample. Branched domains are observed for the sample prepared without pre-annealing which indicates grain disorientation of Co. However, in the thicker (25 nm) Co films ripple domains were observed in contrary to ultrathin (3 nm) films.

Ultrathin nanofibrous films prepared from cadmium hydroxide nanostrands and anionic surfactants.

PubMed

Peng, Xinsheng; Karan, Santanu; Ichinose, Izumi

2009-08-04

We developed a simple fabrication method of ultrathin nanofibrous films from the dispersion of cadmium hydroxide nanostrands and anionic surfactants. The nanostrands were prepared in a dilute aqueous solution of cadmium chloride by using 2-aminoethanol. They were highly positively charged and gave bundlelike fibers upon mixing an aqueous solution of anionic surfactant. The nanostrand/surfactant composite fibers were filtered on an inorganic membrane filter. The resultant nanofibrous film was very uniform in the area of a few centimeters square when the thickness was not less than 60 nm. The films obtained with sodium tetradecyl sulfate (STS) had a composition close to the electroneutral complex, [Cd37(OH)68(H2O)n] x 6(STS), as confirmed by energy dispersive X-ray analysis. They were water-repellent with a contact angle of 117 degrees, and the value slightly decreased with the alkyl chain length of anionic surfactants. Ultrathin nanofibrous films were stable enough to be used for ultrafiltration at pressure difference of 90 kPa. We could effectively separate Au nanoparticles of 40 nm at an extremely high filtration rate of 14000 L/(h m2 bar).

Polarity compensation in ultra-thin films of complex oxides: The case of a perovskite nickelate

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

Middey, S.; Rivero, P.; Meyers, D.

2014-10-29

In this study, we address the fundamental issue of growth of perovskite ultra-thin films under the condition of a strong polar mismatch at the heterointerface exemplified by the growth of a correlated metal LaNiO 3 on the band insulator SrTiO 3 along the pseudo cubic [111] direction. While in general the metallic LaNiO 3 film can effectively screen this polarity mismatch, we establish that in the ultra-thin limit, films are insulating in nature and require additional chemical and structural reconstruction to compensate for such mismatch. A combination of in-situ reflection high-energy electron diffraction recorded during the growth, X-ray diffraction, andmore » synchrotron based resonant X-ray spectroscopy reveal the formation of a chemical phase La 2Ni 2O 5 (Ni 2+) for a few unit-cell thick films. First-principles layer-resolved calculations of the potential energy across the nominal LaNiO 3/SrTiO 3 interface confirm that the oxygen vacancies can efficiently reduce the electric field at the interface.« less

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.

Three-configurational surface magneto-optical Kerr effect measurement system for an ultrahigh vacuum in situ study of ultrathin magnetic films

NASA Astrophysics Data System (ADS)

Lee, J.-W.; Jeong, J.-R.; Kim, D.-H.; Ahn, J. S.; Kim, J.; Shin, S.-C.

2000-10-01

We have constructed a three-configurational surface magneto-optical Kerr effect system, which provides the simultaneous measurements of the "polar," "longitudinal," and "transverse" Kerr hysteresis loops at the position where deposition is carried out in an ultrahigh vacuum growth chamber. The present system enables in situ three-dimensional vectorial studies of ultrathin film magnetism with a submonolayer sensitivity. We present three-configurational hysteresis loops measured during the growth of Co films on Pd(111), glass, and Pd/glass substrates.

Ferroelectric ultrathin perovskite films

DOEpatents

Rappe, Andrew M; Kolpak, Alexie Michelle

2013-12-10

Disclosed herein are perovskite ferroelectric thin-film. Also disclosed are methods of controlling the properties of ferroelectric thin films. These films can be used in a variety materials and devices, such as catalysts and storage media, respectively.

Influence of annealing temperature on structural and magnetic properties of pulsed laser-deposited YIG films on SiO2 substrate

NASA Astrophysics Data System (ADS)

Nag, Jadupati; Ray, Nirat

2018-05-01

Yttrium Iron Garnet (Y3Fe5O12) was synthesized by solid state/ceramic process. Thin films of YIG were deposited on SiO2 substrate at room temperature(RT) and at substrate temperature (Ts) 700 °C using pulsed laser deposition (PLD) technique. RT deposited thin films are amorphous in nature and non-magnetic. After annealing at temperature 800 ° RT deposited thin films showed X-ray peaks as well as the magnetic order. Magnetic ordering is enhanced by annealing temperature(Ta ≥ 750 °C) and resulted good quality of films with high magnetization value.

Copper drift in high-dielectric-constant tantalum oxide thin films under bias temperature stress

NASA Astrophysics Data System (ADS)

Jain, Pushkar; Juneja, Jasbir S.; Mallikarjunan, A.; Rymaszewski, E. J.; Lu, T.-M.

2006-04-01

The use of high-dielectric-constant (high-κ) materials for embedded capacitors is becoming increasingly important. Tantalum oxide (Ta2O5) is a prominent candidate as a high-κ material for embedded capacitor use. Metal drift in Ta2O5 (κ˜25) was investigated by bias temperature stress and triangular voltage sweep testing techniques on metal/Ta2O5/SiO2/Si structures. At a temperature of 300°C and 0.75MV/cm bias conditions, Al, Ta, and Ti do not diffuse in Ta2O5, but Cu clearly showed a drift. The Cu drift is attributed to the lack of a stable Cu oxide which can limit Cu ion generation and penetration.

Studies of local structural distortions in strained ultrathin BaTiO3 films using scanning transmission electron microscopy.

PubMed

Park, Daesung; Herpers, Anja; Menke, Tobias; Heidelmann, Markus; Houben, Lothar; Dittmann, Regina; Mayer, Joachim

2014-06-01

Ultrathin ferroelectric heterostructures (SrTiO3/BaTiO3/BaRuO3/SrRuO3) were studied by scanning transmission electron microscopy (STEM) in terms of structural distortions and atomic displacements. The TiO2-termination at the top interface of the BaTiO3 layer was changed into a BaO-termination by adding an additional BaRuO3 layer. High-angle annular dark-field (HAADF) imaging by aberration-corrected STEM revealed that an artificially introduced BaO-termination can be achieved by this interface engineering. By using fast sequential imaging and frame-by-frame drift correction, the effect of the specimen drift was significantly reduced and the signal-to-noise ratio of the HAADF images was improved. Thus, a quantitative analysis of the HAADF images was feasible, and an in-plane and out-of-plane lattice spacing of the BaTiO3 layer of 3.90 and 4.22 Å were determined. A 25 pm shift of the Ti columns from the center of the unit cell of BaTiO3 along the c-axis was observed. By spatially resolved electron energy-loss spectroscopy studies, a reduction of the crystal field splitting (CFS, ΔL3=1.93 eV) and an asymmetric broadening of the eg peak were observed in the BaTiO3 film. These results verify the presence of a ferroelectric polarization in the ultrathin BaTiO3 film.

On the role of ultra-thin oxide cathode synthesis on the functionality of micro-solid oxide fuel cells: Structure, stress engineering and in situ observation of fuel cell membranes during operation

NASA Astrophysics Data System (ADS)

Lai, Bo-Kuai; Kerman, Kian; Ramanathan, Shriram

Microstructure and stresses in dense La 0.6Sr 0.4Co 0.8Fe 0.2O 3 (LSCF) ultra-thin films have been investigated to increase the physical thickness of crack-free cathodes and active area of thermo-mechanically robust micro-solid oxide fuel cell (μSOFC) membranes. Processing protocols employ low deposition rates to create a highly granular nanocrystalline microstructure in LSCF thin films and high substrate temperatures to produce linear temperature-dependent stress evolution that is dominated by compressive stresses in μSOFC membranes. Insight and trade-off on the synthesis are revealed by probing microstructure evolution and electrical conductivity in LSCF thin films, in addition to in situ monitoring of membrane deformation while measuring μSOFC performance at varying temperatures. From these studies, we were able to successfully fabricate failure-resistant square μSOFC (LSCF/YSZ/Pt) membranes with width of 250 μm and crack-free cathodes with thickness of ∼70 nm. Peak power density of ∼120 mW cm -2 and open circuit voltage of ∼0.6 V at 560 °C were achieved on a μSOFC array chip containing ten such membranes. Mechanisms affecting fuel cell performance are discussed. Our results provide fundamental insight to pathways of microstructure and stress engineering of ultra-thin, dense oxide cathodes and μSOFC membranes.

Understanding Metal-Insulator transitions in ultra-thin films of LaNiO3

NASA Astrophysics Data System (ADS)

Ravichandran, Jayakanth; King, Philip D. C.; Schlom, Darrell G.; Shen, Kyle M.; Kim, Philip

2014-03-01

LaNiO3 (LNO) is a bulk paramagnetic metal and a member of the family of RENiO3 Nickelates (RE = Rare Earth Metals), which is on the verge of the metal-insulator transition. Ultra-thin films of LNO has been studied extensively in the past and due to its sensitivity to disorder, the true nature of the metal-insulator transition in these films have been hard to decipher. We grow high quality ultra-thin films of LNO using reactive molecular beam epitaxy (MBE) and use a combination of ionic liquid gating and magneto-transport measurements to understand the nature and tunability of metal-insulator transition as a function of thickness for LNO. The underlying mechanisms for the transition are discussed in the framework of standard transport models. These results are discussed in the light of other Mott insulators such as Sr2IrO4, where we have performed similar measurements around the insulating state.

Chemical surface deposition of ultra-thin semiconductors

DOEpatents

McCandless, Brian E.; Shafarman, William N.

2003-03-25

A chemical surface deposition process for forming an ultra-thin semiconducting film of Group IIB-VIA compounds onto a substrate. This process eliminates particulates formed by homogeneous reactions in bath, dramatically increases the utilization of Group IIB species, and results in the formation of a dense, adherent film for thin film solar cells. The process involves applying a pre-mixed liquid coating composition containing Group IIB and Group VIA ionic species onto a preheated substrate. Heat from the substrate causes a heterogeneous reaction between the Group IIB and VIA ionic species of the liquid coating composition, thus forming a solid reaction product film on the substrate surface.

Novel self-organization mechanism in ultrathin liquid films: theory and experiment.

PubMed

Trice, Justin; Favazza, Christopher; Thomas, Dennis; Garcia, Hernando; Kalyanaraman, Ramki; Sureshkumar, Radhakrishna

2008-07-04

When an ultrathin metal film of thickness h (<20 nm) is melted by a nanosecond pulsed laser, the film temperature is a nonmonotonic function of h and achieves its maximum at a certain thickness h*. This is a consequence of the h and time dependence of energy absorption and heat flow. Linear stability analysis and nonlinear dynamical simulations that incorporate such intrinsic interfacial thermal gradients predict a characteristic pattern length scale Lambda that decreases for h>h*, in contrast to the classical spinodal dewetting behavior where Lambda increases monotonically as h2. These predictions agree well with experimental observations for Co and Fe films on SiO2.

Solution-processed ultrathin chemically derived graphene films as soft top contacts for solid-state molecular electronic junctions.

PubMed

Li, Tao; Hauptmann, Jonas Rahlf; Wei, Zhongming; Petersen, Søren; Bovet, Nicolas; Vosch, Tom; Nygård, Jesper; Hu, Wenping; Liu, Yunqi; Bjørnholm, Thomas; Nørgaard, Kasper; Laursen, Bo W

2012-03-08

A novel method using solution-processed ultrathin chemically derived graphene films as soft top contacts for the non-destructive fabrication of molecular junctions is demonstrated. We believe this protocol will greatly enrich the solid-state test beds for molecular electronics due to its low-cost, easy-processing and flexible nature. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis and characterization of novel electronic materials with volatile species

NASA Astrophysics Data System (ADS)

Zhizhong, Tang

In this thesis, two novel electronic materials, including semiconductor ZnGeAs2 and dielectric Ba(Zn1/3Ta 2/3)O3 were studied. The growth, characterization and application of ZnGeAs2 in photovoltaics were explored. The structure, optic and electric properties of expitaxial Ba(Zn1/3Ta2/3)O 3 films were also reported. ZnGeAs2 films were grown by pulsed laser deposition from the home-made target. The composition study showed that the Ge element incorporation rate remained constant, while the Zn and As incorporation rates decrease monotonically at elevated growth temperatures. Prototype of photovoltaic cell made with heterojunction p-ZnGeAs2/n-CdS/n+-SnO2 diode showed 0.14 Volt open circuit voltage under ˜100 mW/cm2 lab lamp illumination (1 sun) and 0.45 Volt Voc under 100 mW/cm 2 green LED illumination. Thermal decomposition studied of bulk ZnGeAs2 showed that the Zn and As dissociation rate from ZnGeAs2 approaches one monolayer per second at around 425 °C with activation energy of 1.08 eV. Thermodynamic and kinetic analysis showed that synthesis of ZnGeAs2 thin film is a metastable process involving a competition between the forward reaction which depends on the arrival of reactants at the growth surface, and the reverse kinetically-limited decomposition reaction. Ba(Zn1/3Ta2/3)O3 (100) dielectric thin films grown on MgO (100) substrates by pulsed laser deposition. The thin film structure, optic and electric properties were systematically characterized. Advanced electronic structure calculations were used to guide the interpretation of the experimental data. The Ba(Zn1/3Ta2/3)O3 films have an indirect optical band gap of ˜3.0 eV and a refractive index of 1.91 in the visible spectral range, with dielectric constant of 25 and dissipation factor of 0.0025 at 100 kHz. The Ba(Zn1/3Ta 2/3)O3 films exhibit a small thermally-activated Ohmic leakage current at high fields (<250 KV/cm) and high temperatures (<200 °C) with an activation energy of 0.85 eV. Ba(Zn1/3Ta2/3)O3 dielectric ceramics powder was used to synthesize Metallo-Dielectric Electromagnetic Band Gap structures by ceramic injection molding. Capacitive series and shunt defects were introduced in Metallo-Dielectric Electromagnetic Band Gap structures to generate sub-wavelength resonances. The frequency responses of both defect-free and defect-laden EBG structures were characterized at microwave frequencies and were found to agree with the results of electromagnetic simulations using the commercial HFSS modeling package.

Archetypal structure of ultrathin alumina films: Grazing-incidence x-ray diffraction on Ni(111)

NASA Astrophysics Data System (ADS)

Prévot, G.; Le Moal, S.; Bernard, R.; Croset, B.; Lazzari, R.; Schmaus, D.

2012-05-01

We have studied by grazing-incidence x-ray diffraction the atomic structure of an ultrathin alumina film grown on Ni(111). We show that, since there is neither registry between the film and the substrate nor induced Ni relaxations, this system appears to be a prototypical freestanding oxide layer. We have been able to unambiguously determine the three-dimensional structure of the film, which consists of a substrate/Al16/O24/Al24/O28 stacking within a (18.23 × 10.53 Å) R0° unit cell. From the different Al coordinations (3/4/5) in the layer and from the precise determination of the Al-O interatomic distances, we conclude that the film structure presents some similarities with the η phase of bulk alumina, which also has a high surface/bulk ratio. The precise comparison between these two structures allows us to explain that the perfect 3 ratio between the two sides of the mesh of the film is governed by the stacking of the two central planes, combining oxygen close-packed atoms below Al atoms in tetrahedral or pyramidal positions. Moreover, Al atoms at the interface plane of the ultrathin film adopt a quasitrihedral configuration, which confirms that, in the alumina η phase, Al atoms with such a coordination are located near the surface of the nanocrystals. The atomic structure is also very close to the one first proposed by Kresse [G. Kresse, M. Schmid, E. Napetschnig, M. Shishkin, L. Köhler, and P. Varga, ScienceSCIEAS0036-807510.1126/science.1107783 308, 1440 (2005)] for alumina films on NiAl(110). This strongly suggests that this atomic model, within small variations, can be extended to ultrathin alumina film on numerous other metal substrates and may be quasi-intrinsic to a freestanding layer rather than governed by the interactions between the film and the substrate.

Impact of oxygen stoichiometry on electroforming and multiple switching modes in TiN/TaOx/Pt based ReRAM

NASA Astrophysics Data System (ADS)

Sharath, S. U.; Joseph, M. J.; Vogel, S.; Hildebrandt, E.; Komissinskiy, P.; Kurian, J.; Schroeder, T.; Alff, L.

2016-10-01

We have investigated the material and electrical properties of tantalum oxide thin films (TaOx) with engineered oxygen contents grown by RF-plasma assisted molecular beam epitaxy. The optical bandgap and the density of the TaOx films change consistently with oxygen contents in the range of 3.63 to 4.66 eV and 12.4 to 9.0 g/cm3, respectively. When exposed to atmosphere, an oxidized Ta2O5-y surface layer forms with a maximal thickness of 1.2 nm depending on the initial oxygen deficiency of the film. X-ray photoelectron spectroscopy studies show that multiple sub-stoichiometric compositions occur in oxygen deficient TaOx thin films, where all valence states of Ta including metallic Ta are possible. Devices of the form Pt/Ta2O5-y/TaOx/TiN exhibit highly tunable forming voltages of 10.5 V to 1.5 V with decreasing oxygen contents in TaOx. While a stable bipolar resistive switching (BRS) occurs in all devices irrespective of oxygen content, unipolar switching was found to coexist with BRS only at higher oxygen contents, which transforms to a threshold switching behaviour in the devices grown under highest oxidation.

Simultaneous determination of the residual stress, elastic modulus, density and thickness of ultrathin film utilizing vibrating doubly clamped micro-/nanobeams

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

Stachiv, Ivo, E-mail: stachiv@fzu.cz; Institute of Physics, Czech Academy of Sciences, Prague; Kuo, Chih-Yun

2016-04-15

Measurement of ultrathin film thickness and its basic properties can be highly challenging and time consuming due to necessity of using several very sophisticated devices. Here, we report an easy accessible resonant based method capable to simultaneously determinate the residual stress, elastic modulus, density and thickness of ultrathin film coated on doubly clamped micro-/nanobeam. We show that a general dependency of the resonant frequencies on the axial load is also valid for in-plane vibrations, and the one depends only on the considered vibrational mode. As a result, we found that the film elastic modulus, density and thickness can be evaluatedmore » from two measured in-plane and out-plane fundamental resonant frequencies of micro-/nanobeam with and without film under different prestress forces. Whereas, the residual stress can be determined from two out-plane (in-plane) measured consecutive resonant frequencies of beam with film under different prestress forces without necessity of knowing film and substrate properties and dimensions. Moreover, we also reveal that the common uncertainties in force (and thickness) determination have a negligible (and minor) impact on the determined film properties. The application potential of the present method is illustrated on the beam made of silicon and SiO{sub 2} with deposited 20 nm thick AlN and 40 nm thick Au thin films, respectively.« less

Process for obtaining multiple sheet resistances for thin film hybrid microcircuit resistors

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

Norwood, D P

1989-01-31

A standard thin film circuit containing Ta/sub 2/N (100 ohms/square) resistors is fabricated by depositing on a dielectric substrate successive layers of Ta/sub 2/N, Ti and Pd, with a gold layer to provide conductors. The addition of a few simple photoprocessing steps to the standard TFN (thin film network) manufacturing process enables the formation of Ta/sub 2/N + Ti (10 ohms/square) and Ta/sub 2/N + Ti + Pd (1 ohm/square) resistors in the same otherwise standard thin film circuit structure. All three types of resistors are temperature-stable and laser-trimmable for precise definition of resistance values.

The Electrochemical Behavior of Mo-Ta Alloy in Phosphoric Acid Solution for TFT-LCD Application.

PubMed

Lee, Sang-Hyuk; Kim, Byoung O; Seo, Jong Hyun

2015-10-01

Molybdenum-tantalum alloy thin film is a suitable material for the higher corrosion resistance and low resistivity for gate and data metal lines. In this study, Mo-Ta alloy thin films were prepared by using a DC magnetron co-sputtering system on a glass substrate. An abrupt increase in the etching rates of low Mo-Ta alloys was observed. From the observed impedance analysis, the defect densities in the MoTa oxide films increased from 5.4 x 10(21) (cm(-3)) to 8.02 x 10(21) (cm(-3)) up to the 6 at% of tantalum level; and above the 6 at% of tantalum level, the defect densities decreased. This electrochemical behavior is explained by the mechanical instability of the MoTa oxide film.

Dynamics of ultrathin metal films on amorphous substrates under fast thermal processing

NASA Astrophysics Data System (ADS)

Favazza, Christopher; Kalyanaraman, Ramki; Sureshkumar, Radhakrishna

2007-11-01

A mathematical model is developed to analyze the growth/decay rate of surface perturbations of an ultrathin metal film on an amorphous substrate (SiO2). The formulation combines the approach of Mullins [W. W. Mullins, J. Appl. Phys. 30, 77 (1959)] for bulk surfaces, in which curvature-driven mass transport and surface deformation can occur by surface/volume diffusion and evaporation-condensation processes, with that of Spencer etal . [B. J. Spencer, P. W. Voorhees, and S. H. Davis, Phys. Rev. Lett. 67, 26 (1991)] to describe solid-state transport in thin films under epitaxial strain. Modifications of the Mullins model to account for thin-film boundary conditions result in qualitatively different dispersion relationships especially in the limit as kho≪1, where k is the wavenumber of the perturbation and ho is the unperturbed film height. The model is applied to study the relative rate of solid-state mass transport as compared to that of liquid phase dewetting in a thin film subjected to a fast thermal pulse. Specifically, we have recently shown that multiple cycles of nanosecond (ns) pulsed laser melting and resolidification of ultrathin metal films on amorphous substrates can lead to the formation of various types of spatially ordered nanostructures [J. Trice, D. Thomas, C. Favazza, R. Sureshkumar, and R. Kalyanaraman, Phys. Rev. B 75, 235439 (2007)]. The pattern formation has been attributed to the dewetting of the thin film by a hydrodynamic instability. In such experiments the film is in the solid state during a substantial fraction of each thermal cycle. However, results of a linear stability analysis based on the aforementioned model suggest that solid-state mass transport has a negligible effect on morphological changes of the surface. Further, a qualitative analysis of the effect of thermoelastic stress, induced by the rapid temperature changes in the film-substrate bilayer, suggests that stress relaxation does not appreciably contribute to surface deformation. Hence, surface deformation caused by liquid phase instabilities is rapidly quenched-in during the cooling phase. This deformed state is further evolved by subsequent laser pulses. These results have implications to developing accurate computer simulations of thin-film dewetting by energetic beams aimed at the manufacturing of optically active nanoscale materials for applications including information processing, optical devices, and solar energy harvesting.

Magnetic properties influenced by interfaces in ultrathin Co/Ge(1 0 0) and Co/Ge(1 1 1) films

NASA Astrophysics Data System (ADS)

Tsay, J. S.; Yao, Y. D.; Cheng, W. C.; Tseng, T. K.; Wang, K. C.; Yang, C. S.

2003-10-01

Magnetic properties influenced by interfaces in ultrathin Co/Ge(1 0 0) and Co/Ge(1 1 1) films with thickness below 28 monolayers (ML) have been studied using the surface magneto-optic Kerr effect (SMOKE) technique. In both systems, the nonferromagnetic layer, as an interface between Co and Ge, plays an important role during annealing. In general, ultrathin Co films with fixed total thickness but fabricated at different temperatures on the same substrate, their Kerr hysteresis loops disappear roughly at the same temperature. This suggests that the thickness of the interfacial layer could inversely prevent the diffusion between Co and Ge substrate. From the annealing studies for both systems with total film thickness of 28 monolayers, we have found that Kerr signal disappears at 375 K for Co/Ge(1 1 1) and 425 K for Co/Ge(1 0 0) films. This suggests that Co/Ge(1 1 1) films possess a lower thermal stability than that of the Co/Ge(1 0 0) films. Our experimental data could be explained by different interfacial condition between Ge(1 0 0) and Ge(1 1 1), the different onset of interdiffusion, and the surface structure condition of Ge(1 0 0) and Ge(1 1 1).

Low emissivity Ag/Ta/glass multilayer thin films deposited by sputtering

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

Park, Sun Ho; Lee, Kee Sun; Green Home Energy Technology Center, Cheonan City

Ta is deposited on a glass substrate as an interlayer for the two-dimensional growth of Ag thin films because Ta has good thermal stability and can induce a negative surface-energy change in Ag/glass. From the transmission electron microscopy results, we concluded that the Ag crystals in the bottom layer (seemingly on Ag/Ta) were flattened; this was rarely observed in the three-dimensional growth mode. Comparing Ag/Ta/glass with Ag/glass, we found that the Ta interlayer was effective in reducing both the resistance and the emissivity, accompanied by the relatively high transmittance in the visible region. In particular, Ag(9 nm)/Ta(1 nm)/glass film showedmore » 0.08 of the emissivity, including {approx}61% of the transmittance in the visible region (wavelength: 550 nm).« less

Ultrathin free-standing graphene oxide film based flexible touchless sensor

NASA Astrophysics Data System (ADS)

Liu, Lin; Wang, Yingyi; Li, Guanghui; Qin, Sujie; Zhang, Ting

2018-01-01

Ultrathin free-standing graphene oxide (GO) films were fabricated by vacuum filtration method assisted with Ni(OH)2 nanosheets as the sacrifice layer. The surface of the obtained GO film is very clean as the Ni(OH)2 nanosheets can be thoroughly etched by HCl. The thickness of the GO films can be well-controlled by changing the volume of GO dispersion, and the thinnest GO film reached ~12 nm. As a novel and transparent dielectric material, the GO film has been applied as the dielectric layer for the flexible touchless capacitive sensor which can effectively distinguish the approaching of an insulator or a conductor. Project supported by the National Natural Science Foundation of China (No. 61574163) and the Foundation Research Project of Jiangsu Province (Nos. BK20160392, BK20170008).

Effect of Sb on physical properties and microstructures of laser nano/amorphous-composite film

NASA Astrophysics Data System (ADS)

Li, Jia-Ning; Gong, Shui-Li; Sun, Mei; Shan, Fei-Hu; Wang, Xi-Chang; Jiang, Shuai

2013-11-01

A nano/amorphous-composite film was fabricated by laser cladding (LC) of the Co-Ti-B4C-Sb mixed powders on a TA15 alloy. Such film mainly consisted of Ti-Al, Co-Ti, Co-Sb intermetallics, TiC, TiB2, TiB, and the amorphous phases. Experimental results indicated that the crystal systems of TiB2 (hexagonal)/TiC (cubic) and Sb (rhombohedral) played important role on the formation of such film. Due to the mismatch of these crystals systems and mutual immiscibility of the metallic components, Sb was not incorporated in TiB2/TiC, but formed separate nuclei during the film growth. Thus, the growth of TiB2/TiC was stopped by the Sb nucleus in such LC molten pool, so as to form the nanoscale particles.

The Role of Partial Surface Charge Compensation in the Properties of Ferroelectric and Antiferroelectric Thin Films

NASA Astrophysics Data System (ADS)

Swedberg, Elena

Ferroelectric and antiferroelectric ultrathin films have attracted a lot of attention recently due to their remarkable properties and their potential to allow for device miniaturization in numerous applications. However, when the ferroelectric films are scaled down, it brings about an unavoidable depolarizing field. A partial surface charge compensation allows to control the residual depolarizing field and manipulate the properties of ultrathin ferroelectric films. In this dissertation we take advantage of atomistic first-principles-based simulations to expand our understanding of the role of the partial surface charge compensation in the properties of ferroelectric and antiferroelectric ultrathin films. The application of our computational methodology to study the effect of the partial surface charge compensation in ferroelectric ultrathin films led to the prediction that, depending on the quality of the surface charge compensation, ferroelectric thin films respond to an electric field in a qualitatively different manner. They can be tuned to behave like a linear dielectric, a ferroelectric or even an antiferroelectric. This effect was shown to exist in films with different mechanical boundary conditions and different crystal symmetries. There are a number of potential applications where such properties of ferroelectric thin films can be used. One of these potential applications is energy storage. We will show that, in the antiferroelectric regime, ferroelectric thin films exhibit drastic enhancement of energy storage density which is a desirable property. One of the most promising applications of ferroelectric ultrathin films that emerged only recently is the harvesting of the giant electrocaloric effect. Interestingly, despite numerous studies of the electrocaloric effect in ferroelectric thin films, it is presently unknown how a residual depolarizing field affects the electrocaloric properties of such films. Application of state-of-the-art computational methods to investigate the electrocaloric effect in ferroelectric films with partial surface charge compensation led to the prediction that the residual depolarizing field can perform a dual role in the electrocaloric effect in these films. When the depolarizing field creates competition between the monodomain and nanodomain states, we predict an enhancement of the electrocaloric effect due to the frustration that increases the entropy of the state and therefore the electrocaloric temperature change. On the other hand, when the depolarizing field leads to a formation of nanodomains, thin films either exhibit a small electrocaloric effect or lose their electrocaloric properties altogether to the irreversible nanodomain motion. When the residual depolarizing field is weak enough to permit the formation of monodomain phases, the electrocaloric effect is significantly reduced as compared to bulk. We believe that our findings could potentially reveal additional opportunities to optimize solid state cooling technology. While the electrocaloric effect has been a popular topic of interest in recent years [12], there still exists numerous gaps in the fundamental understanding of the effect. In particular, it is presently unknown whether the scaling laws, known to exist for magnetocaloric materials, can be applied to ferroelectric and antiferroelectric electrocalorics. We predict the existence of scaling laws for low-field electrocaloric temperature change in antiferroelectric and ferroelectric materials. With the help of first-principles-based simulations, we showed computationally that the scaling laws exist for antiferroelectric PbZrO3 along with ferroelectrics PbTiO3, BaTiO 3 and KNbO3. Additional evidence of the scaling laws existence are provided using experimental data from the literature. Interestingly, our studies on ferroelectric films predicted the existence of antiferroelectric behavior in ultrathin films with partial surface charge compensation. One may wonder whether it is possible to stabilize the ferroelectric phase in antiferroelectric films and what role the surface charge screening would play in such a transition. Motivated to address these fundamental questions, we used computational experiments to study antiferroelectric ultrathin films with a residual depolarizing field. Our studies led to the following predictions. We found that PbZrO3 thin films exhibit the ferroelectric phase upon scaling down and under the condition of efficient surface charge compensation. We also found a strong competition between the antiferroelectric and ferroelectric phases for the thin films of the critical size associated with antiferroelectric-ferroelectric phase transition. This finding motivated us to study the electrocaloric effect in PbZrO3 thin films with antiferroelectric-ferroelectric phase competition. We found that high tunability of the phase transition by the electric field leads to a wide range of temperatures associated with a strong electrocaloric effect. In addition, we found that epitaxial strain provides further tunability to the electrocaloric properties. In summary, our studies led to a broader and deeper understanding of the abundantly many roles surface charge compensation plays in ultrathin ferroelectrics and antiferroelectrics.

Tribological performance of polycrystalline tantalum-carbide-incorporated diamond films on silicon substrates

NASA Astrophysics Data System (ADS)

Ullah, Mahtab; Rana, Anwar Manzoor; Ahmed, E.; Malik, Abdul Sattar; Shah, Z. A.; Ahmad, Naseeb; Mehtab, Ujala; Raza, Rizwan

2018-05-01

Polycrystalline tantalum-carbide-incorporated diamond coatings have been made on unpolished side of Si (100) wafer by hot filament chemical vapor deposition process. Morphology of the coatings has been found to vary from (111) triangular-facetted to predominantly (111) square-faceted by increasing the concentration of tantalum carbide. The results have been compared to those of a diamond reference coating with no tantalum content. An increase in roughness has been observed with the increase of tantalum carbide (TaC) due to change in morphology of the diamond films. It is noticed that roughness of the coatings increases as grains become more square-faceted. It is found that diamond coatings involving tantalum carbide are not as resistant as diamond films with no TaC content and the coefficient of friction for such coatings with microcrystalline grains can be manipulated to 0·33 under high vacuum of 10-7 Torr. Such a low friction coefficient value enhances tribological behavior of unpolished Si substrates and can possibly be used in sliding applications.

In situ monitoring of thermal crystallization of ultrathin tris(8-hydroxyquinoline) aluminum films using surface-enhanced Raman scattering.

PubMed

Muraki, Naoki

2014-01-01

Thermal crystallization of 3, 10, and 60 nm-thick tris(8-hydroxyquinoline)aluminum (Alq3) films is studied using surface-enhanced Raman scattering with a constant heating rate. An abrupt higher frequency shift of the quinoline-stretching mode is found to be an indication of a phase transition of Alq3 molecules from amorphous to crystalline. While the 60 nm-thick film shows the same crystallization temperature as a bulk sample, the thinner films were found to have a lower crystallization temperature and slower rate of crystallization. Non-isothermal kinetics analysis is performed to quantify kinetic properties such as the Avrami exponent constants and crystallization rates of ultrathin Alq3 films.

Magnetic and structural characterization of ultra-thin Fe (222) films

NASA Astrophysics Data System (ADS)

Loving, Melissa G.; Brown, Emily E.; Rizzo, Nicholas D.; Ambrose, Thomas F.

2018-05-01

Varied thickness body centered cubic (BCC) ultrathin Fe films (10-50Å) have been sputter deposited onto Si (111) substrates. BCC Fe with the novel (222) texture was obtained by H- terminating the Si (111) starting substrate then immediately depositing the magnetic films. Structural results derived from grazing incidence x-ray diffraction and x-ray reflectivity confirm the crystallographic texture, film thickness, and interface roughness. Magnetic results indicate that Fe (222) exhibits soft magnetic switching (easy axis), high anisotropy (hard axis), which is maintained across the thickness range, and a positive magnetostriction (for the thicker film layers). The observed soft magnetic switching in this system makes it an ideal candidate for future magnetic memory development as well as other microelectronics applications that utilize magnetic materials.

Negative differential resistance in electron tunneling in ultrathin films near the two-dimensional limit

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

Batabyal, R.; Abdul Wasey, A. H. M.; Mahato, J. C.

We report on our observation of negative differential resistance (NDR) in electron tunneling conductance in atomic-scale ultrathin Ag films on Si(111) substrates. NDR was observed by scanning tunneling spectroscopy measurements. The tunneling conductance depends on the electronic local density of states (LDOS) of the sample. We show that the sample bias voltage, at which negative differential resistance and peak negative conductance occur, depends on the film thickness. This can be understood from the variation in the LDOS of the Ag films as a function of film thickness down to the two-dimensional limit of one atomic layer. First principles density functionalmore » theory calculations have been used to explain the results.« less

Interfacial and electrical properties of InGaAs metal-oxide-semiconductor capacitor with TiON/TaON multilayer composite gate dielectric

NASA Astrophysics Data System (ADS)

Wang, L. S.; Xu, J. P.; Liu, L.; Lu, H. H.; Lai, P. T.; Tang, W. M.

2015-03-01

InGaAs metal-oxide-semiconductor (MOS) capacitors with composite gate dielectric consisting of Ti-based oxynitride (TiON)/Ta-based oxynitride (TaON) multilayer are fabricated by RF sputtering. The interfacial and electrical properties of the TiON/TaON/InGaAs and TaON/TiON/InGaAs MOS structures are investigated and compared. Experimental results show that the former exhibits lower interface-state density (1.0 × 1012 cm-2 eV-1 at midgap), smaller gate leakage current (9.5 × 10-5 A/cm2 at a gate voltage of 2 V), larger equivalent dielectric constant (19.8), and higher reliability under electrical stress than the latter. The involved mechanism lies in the fact that the ultrathin TaON interlayer deposited on the sulfur-passivated InGaAs surface can effectively reduce the defective states and thus unpin the Femi level at the TaON/InGaAs interface, improving the electrical properties of the device.

Formation and prevention of fractures in sol-gel-derived thin films.

PubMed

Kappert, Emiel J; Pavlenko, Denys; Malzbender, Jürgen; Nijmeijer, Arian; Benes, Nieck E; Tsai, Peichun Amy

2015-02-07

Sol-gel-derived thin films play an important role as the functional coatings for various applications that require crack-free films to fully function. However, the fast drying process of a standard sol-gel coating often induces mechanical stresses, which may fracture the thin films. An experimental study on the crack formation in sol-gel-derived silica and organosilica ultrathin (submicron) films is presented. The relationships among the crack density, inter-crack spacing, and film thickness were investigated by combining direct micrograph analysis with spectroscopic ellipsometry. It is found that silica thin films are more prone to fracturing than organosilica films and have a critical film thickness of 300 nm, above which the film fractures. In contrast, the organosilica films can be formed without cracks in the experimentally explored regime of film thickness up to at least 1250 nm. These results confirm that ultrathin organosilica coatings are a robust silica substitute for a wide range of applications.

Measurement and modeling of short and medium range order in amorphous Ta 2O 5 thin films

DOE PAGES

Shyam, Badri; Stone, Kevin H.; Bassiri, Riccardo; ...

2016-08-26

Here, amorphous films and coatings are rapidly growing in importance. Yet, there is a dearth of high-quality structural data on sub-micron films. Not understanding how these materials assemble at atomic scale limits fundamental insights needed to improve their performance. Here, we use grazing-incidence x-ray total scattering measurements to examine the atomic structure of the top 50–100 nm of Ta 2O 5 films; mirror coatings that show high promise to significantly improve the sensitivity of the next generation of gravitational-wave detectors. Our measurements show noticeable changes well into medium range, not only between crystalline and amorphous, but also between as-deposited, annealedmore » and doped amorphous films. It is a further challenge to quickly translate the structural information into insights into mechanisms of packing and disorder. Here, we illustrate a modeling approach that allows translation of observed structural features to a physically intuitive packing of a primary structural unit based on a kinked Ta-O-Ta backbone. Our modeling illustrates how Ta-O-Ta units link to form longer 1D chains and even 2D ribbons, and how doping and annealing influences formation of 2D order. We also find that all the amorphousTa 2O 5 films studied in here are not just poorly crystalline but appear to lack true 3D order.« less

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

PubMed

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

2002-08-19

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

Nanostructured Ti-Ta thin films synthesized by combinatorial glancing angle sputter deposition

NASA Astrophysics Data System (ADS)

Motemani, Yahya; Khare, Chinmay; Savan, Alan; Hans, Michael; Paulsen, Alexander; Frenzel, Jan; Somsen, Christoph; Mücklich, Frank; Eggeler, Gunther; Ludwig, Alfred

2016-12-01

Ti-Ta alloys are attractive materials for applications in actuators as well as biomedical implants. When fabricated as thin films, these alloys can potentially be employed as microactuators, components for micro-implantable devices and coatings on surgical implants. In this study, Ti100-x Ta x (x = 21, 30) nanocolumnar thin films are fabricated by glancing angle deposition (GLAD) at room temperature using Ti73Ta27 and Ta sputter targets. Crystal structure, morphology and microstructure of the nanostructured thin films are systematically investigated by XRD, SEM and TEM, respectively. Nanocolumns of ˜150-160 nm in width are oriented perpendicular to the substrate for both Ti79Ta21 and Ti70Ta30 compositions. The disordered α″ martensite phase with orthorhombic structure is formed in room temperature as-deposited thin films. The columns are found to be elongated small single crystals which are aligned perpendicular to the (20\\bar{4}) and (204) planes of α″ martensite, indicating that the films’ growth orientation is mainly dominated by these crystallographic planes. Laser pre-patterned substrates are utilized to obtain periodic nanocolumnar arrays. The differences in seed pattern, and inter-seed distances lead to growth of multi-level porous nanostructures. Using a unique sputter deposition geometry consisting of Ti73Ta27 and Ta sputter sources, a nanocolumnar Ti-Ta materials library was fabricated on a static substrate by a co-deposition process (combinatorial-GLAD approach). In this library, a composition spread developed between Ti72.8Ta27.2 and Ti64.4Ta35.6, as confirmed by high-throughput EDX analysis. The morphology over the materials library varies from well-isolated nanocolumns to fan-like nanocolumnar structures. The influence of two sputter sources is investigated by studying the resulting column angle on the materials library. The presented nanostructuring methods including the use of the GLAD technique along with pre-patterning and a combinatorial materials library fabrication strategy offer a promising technological approach for investigating Ti-Ta thin films for a range of applications. The proposed approaches can be similarly implemented for other materials systems which can benefit from the formation of a nanocolumnar morphology.

Development of Biopolymer Composite Films Using a Microfluidization Technique for Carboxymethylcellulose and Apple Skin Particles

PubMed Central

Choi, Inyoung; Chang, Yoonjee; Shin, So-Hyang; Joo, Eunmi; Song, Hyun Ju; Eom, Haeyoung; Han, Jaejoon

2017-01-01

Biopolymer films based on apple skin powder (ASP) and carboxymethylcellulose (CMC) were developed with the addition of apple skin extract (ASE) and tartaric acid (TA). ASP/CMC composite films were prepared by mixing CMC with ASP solution using a microfluidization technique to reduce particle size. Then, various concentrations of ASE and TA were incorporated into the film solution as an antioxidant and an antimicrobial agent, respectively. Fourier transform infrared (FTIR), optical, mechanical, water barrier, and solubility properties of the developed films were then evaluated to determine the effects of ASE and TA on physicochemical properties. The films were also analyzed for antioxidant effect on 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity and antimicrobial activities against Listeria monocytogenes, Staphylococcus aureus, Salmonella enterica, and Shigella flexneri. From the results, the ASP/CMC film containing ASE and TA was revealed to enhance the mechanical, water barrier, and solubility properties. Moreover, it showed the additional antioxidant and antimicrobial properties for application as an active packaging film. PMID:28617325

Photoluminescence of Ta2O5 films formed by the molecular layer deposition method

NASA Astrophysics Data System (ADS)

Baraban, A. P.; Dmitriev, V. A.; Prokof'ev, V. A.; Drozd, V. E.; Filatova, E. O.

2016-04-01

Ta2O5 films of different thicknesses (20-100 nm) synthesized by the molecular layer deposition method on p-type silicon substrates and thermally oxidized silicon substrates have been studied by the methods of high-frequency capacitance-voltage characteristics and photoluminescence. A hole-conduction channel is found to form in the Si-Ta2O5-field electrode system. A model of the electronic structure of Ta2O5 films is proposed based on an analysis of the measured PL spectra and performed electrical investigations.

Process for obtaining multiple sheet resistances for thin film hybrid microcircuit resistors

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

Norwood, D.P.

1989-01-31

A standard thin film circuit containing Ta/sub 2/N (100 ohms/square) resistors is fabricated by depositing on a dielectric substrate successive layers of Ta/sub 2/N, Ti and Pd, with a gold layer to provide conductors. The addition of a few simple photoprocessing steps to the standard TFN manufacturing process enables the formation of Ta/sub 2/N + Ti (10 ohms/square) and Ta/sub 2/N + Ti + Pd (1 ohm/square) resistors in the same otherwise standard thin film circuit structure.

Process for obtaining multiple sheet resistances for thin film hybrid microcircuit resistors

DOEpatents

Norwood, David P.

1989-01-01

A standard thin film circuit containing Ta.sub.2 N (100 ohms/square) resirs is fabricated by depositing on a dielectric substrate successive layers of Ta.sub.2 N, Ti and Pd, with a gold layer to provide conductors. The addition of a few simple photoprocessing steps to the standeard TFN manufacturing process enables the formation of Ta.sub.2 N+Ti (10 ohms/square) and Ta.sub.2 N+Ti+Pd (1 ohm/square) resistors in the same otherwise standard thin film circuit structure.

Ferroelectric, piezoelectric, and leakage current properties of (K0.48Na0.48Li0.04)(Nb0.775Ta0.225)O3 thin films grown by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Wang, D. Y.; Lin, D. M.; Kwok, K. W.; Chan, N. Y.; Dai, J. Y.; Li, S.; Chan, H. L. W.

2011-01-01

Lead-free (K0.48Na0.48Li0.04)(Nb0.775Ta0.225)O3 (KNLNT) thin films were deposited on Pt(111)/Ti/SiO2/Si(001) substrates using pulsed laser deposition. The film exhibited a well-defined ferroelectric hysteresis loop with a remnant polarization 2Pr of 22.6 μC/cm2 and a coercive field Ec of 10.3 kV/mm. The effective piezoelectric coefficient d33,f of the KNLNT thin films was found to be about 49 pm/V by piezoelectric force microscope. The dominant conduction mechanisms of Au/KNLNT/Pt thin film capacitor were determined to be bulk-limited space-charge-limited-current and Poole-Frenkle emission at low and high electric field strengths, respectively, within a measured temperature range of 130-370 K.

Effect of manganese doping on remnant polarization and leakage current in (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 epitaxial thin films on SrTiO3

NASA Astrophysics Data System (ADS)

Abazari, M.; Akdoǧan, E. K.; Safari, A.

2008-05-01

Single phase, epitaxial, ⟨001⟩ oriented, undoped and 1mol% Mn-doped (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films of 400nm thickness were synthesized on SrRuO3 coated SrTiO3. Such films exhibit well saturated hysteresis loops and have a spontaneous polarization (Ps) of 10μC /cm2, which is a 150% higher over the Ps of the undoped composition. The coercive field of 1mol% Mn doped films is 13kV/cm. Mn-doping results in three orders of magnitude decrease in leakage current above 50kV/cm electric field, which we attribute to the suppression of intrinsic p-type conductivity of undoped films by Mn donors.

Metal oxide multilayer hard mask system for 3D nanofabrication

NASA Astrophysics Data System (ADS)

Han, Zhongmei; Salmi, Emma; Vehkamäki, Marko; Leskelä, Markku; Ritala, Mikko

2018-02-01

We demonstrate the preparation and exploitation of multilayer metal oxide hard masks for lithography and 3D nanofabrication. Atomic layer deposition (ALD) and focused ion beam (FIB) technologies are applied for mask deposition and mask patterning, respectively. A combination of ALD and FIB was used and a patterning procedure was developed to avoid the ion beam defects commonly met when using FIB alone for microfabrication. ALD grown Al2O3/Ta2O5/Al2O3 thin film stacks were FIB milled with 30 keV gallium ions and chemically etched in 5% tetramethylammonium hydroxide at 50 °C. With metal evaporation, multilayers consisting of amorphous oxides Al2O3 and Ta2O5 can be tailored for use in 2D lift-off processing, in preparation of embedded sub-100 nm metal lines and for multilevel electrical contacts. Good pattern transfer was achieved by lift-off process from the 2D hard mask for micro- and nano-scaled fabrication. As a demonstration of the applicability of this method to 3D structures, self-supporting 3D Ta2O5 masks were made from a film stack on gold particles. Finally, thin film resistors were fabricated by utilizing controlled stiction of suspended Ta2O5 structures.

Electromigration in epitaxial Cu(001) lines

NASA Astrophysics Data System (ADS)

Ramanath, G.; Kim, H.; Goindi, H. S.; Frederick, M. J.; Shin, C.-S.; Goswami, R.; Petrov, I.; Greene, J. E.

2002-04-01

We report the electromigration (EM) response of single-domain epitaxial Cu(001) lines on layers of Ta, TaN, and TiN. Epitaxial Cu(001) lines on nitride layers exhibit nearly two orders of magnitude higher mean-time-to-failure (MTTF) values than those on Ta, indicating the strong influence of the underlayer. The activation energy of EM for Cu on the nitrides is ˜0.8-1.2 eV, and that of Cu on Ta is ˜0.2 eV, for 200-300 °C. Our results also indicate that the MTTF values correlate inversely to the crystal quality of the Cu layers measured by X-ray diffraction. The EM resistance of epitaxial Cu lines with different crystal quality on TaN were measured to separate the effects of interface chemistry and crystal quality. While higher quality epitaxial films reveal a higher EM resistance, the magnitude of the change is smaller than that obtained by changing the interface chemistry. Epitaxial lines exhibit more than 3-4 orders of magnitude higher MTTF than polycrystalline lines on the same underlayer. Based upon our results, we propose that the Cu/underlayer interface chemistry and presence of grain boundary diffusion play important roles in unpassivated Cu films.

Surface Morphology of Vapor-Deposited Chitosan: Evidence of Solid-State Dewetting during the Formation of Biopolymer Films.

PubMed

Retamal, Maria Jose; Corrales, Tomas P; Cisternas, Marcelo A; Moraga, Nicolas H; Diaz, Diego I; Catalan, Rodrigo E; Seifert, Birger; Huber, Patrick; Volkmann, Ulrich G

2016-03-14

Chitosan is a useful and versatile biopolymer with several industrial and biological applications. Whereas its physical and physicochemical bulk properties have been explored quite intensively in the past, there is a lack of studies regarding the morphology and growth mechanisms of thin films of this biopolymer. Of particular interest for applications in bionanotechnology are ultrathin films with thicknesses under 500 Å. Here, we present a study of thin chitosan films prepared in a dry process using physical vapor deposition and in situ ellipsometric monitoring. The prepared films were analyzed with atomic force microscopy in order to correlate surface morphology with evaporation parameters. We find that the surface morphology of our final thin films depends on both the optical thickness, i.e., measured with ellipsometry, and the deposition rate. Our work shows that ultrathin biopolymer films can undergo dewetting during film formation, even in the absence of solvents and thermal annealing.

Tantalum oxide/silicon nitride: A negatively charged surface passivation stack for silicon solar cells

NASA Astrophysics Data System (ADS)

Wan, Yimao; Bullock, James; Cuevas, Andres

2015-05-01

This letter reports effective passivation of crystalline silicon (c-Si) surfaces by thermal atomic layer deposited tantalum oxide (Ta2O5) underneath plasma enhanced chemical vapour deposited silicon nitride (SiNx). Cross-sectional transmission electron microscopy imaging shows an approximately 2 nm thick interfacial layer between Ta2O5 and c-Si. Surface recombination velocities as low as 5.0 cm/s and 3.2 cm/s are attained on p-type 0.8 Ω.cm and n-type 1.0 Ω.cm c-Si wafers, respectively. Recombination current densities of 25 fA/cm2 and 68 fA/cm2 are measured on 150 Ω/sq boron-diffused p+ and 120 Ω/sq phosphorus-diffused n+ c-Si, respectively. Capacitance-voltage measurements reveal a negative fixed insulator charge density of -1.8 × 1012 cm-2 for the Ta2O5 film and -1.0 × 1012 cm-2 for the Ta2O5/SiNx stack. The Ta2O5/SiNx stack is demonstrated to be an excellent candidate for surface passivation of high efficiency silicon solar cells.

Integration of perovskite oxide dielectrics into complementary metal-oxide-semiconductor capacitor structures using amorphous TaSiN as oxygen diffusion barrier

NASA Astrophysics Data System (ADS)

Mešić, Biljana; Schroeder, Herbert

2011-09-01

The high permittivity perovskite oxides have been intensively investigated for their possible application as dielectric materials for stacked capacitors in dynamic random access memory circuits. For the integration of such oxide materials into the CMOS world, a conductive diffusion barrier is indispensable. An optimized stack p++-Si/Pt/Ta21Si57N21/Ir was developed and used as the bottom electrode for the oxide dielectric. The amorphous TaSiN film as oxygen diffusion barrier showed excellent conductive properties and a good thermal stability up to 700 °C in oxygen ambient. The additional protective iridium layer improved the surface roughness after annealing. A 100-nm-thick (Ba,Sr)TiO3 film was deposited using pulsed laser deposition at 550 °C, showing very promising properties for application; the maximum relative dielectric constant at zero field is κ ≈ 470, and the leakage current density is below 10-6 A/cm2 for fields lower then ± 200 kV/cm, corresponding to an applied voltage of ± 2 V.

Time-resolved atomic force microscopy imaging studies of asymmetric PS-b-PMMA ultrathin films: Dislocation and disclination transformations, defect mobility, and evolution of nanoscale morphology

NASA Astrophysics Data System (ADS)

Hahm, J.; Sibener, S. J.

2001-03-01

Time-sequenced atomic force microscopy (AFM) studies of ultrathin films of cylinder-forming polystyrene-block-polymethylmethacrylate (PS-b-PMMA) copolymer are presented which delineate thin film mobility kinetics and the morphological changes which occur in microphase-separated films as a function of annealing temperature. Of particular interest are defect mobilities in the single layer (L thick) region, as well as the interfacial morphological changes which occur between L thick and adjacent 3L/2 thick layers, i.e., structural changes which occur during multilayer evolution. These measurements have revealed the dominant pathways by which disclinations and dislocations transform, annihilate, and topologically evolve during thermal annealing of such films. Mathematical combining equations are given to better explain such defect transformations and show the topological outcomes which result from defect-defect encounters. We also report a collective, Arrhenius-type flow of defects in localized L thick regions of the film; these are characterized by an activation energy of 377 kJ/mol. These measurements represent the first direct investigation of time-lapse interfacial morphological changes including associated defect evolution pathways for polymeric ultrathin films. Such observations will facilitate a more thorough and predictive understanding of diblock copolymer thin film dynamics, which in turn will further enable the utilization of these nanoscale phase-separated materials in a range of physical and chemical applications.

'One-component' ultrathin multilayer films based on poly(vinyl alcohol) as stabilizing coating for phenytoin-loaded liposomes.

PubMed

Zasada, Katarzyna; Łukasiewicz-Atanasov, Magdalena; Kłysik, Katarzyna; Lewandowska-Łańcucka, Joanna; Gzyl-Malcher, Barbara; Puciul-Malinowska, Agnieszka; Karewicz, Anna; Nowakowska, Maria

2015-11-01

Ultrathin "one-component" multilayer polymeric films for potential biomedical applications were designed based on polyvinyl alcohol,-a non-toxic, fully degradable synthetic polymer. Good uniformity of the obtained film and adequate adsorption properties of the polymeric layers were achieved by functional modification of the polymer, which involved synthesis of cationic and anionic derivatives. Synthesized polymers were characterized by FTIR, NMR spectroscopy, dynamic light scattering measurements and elemental analysis. The layer by layer assembly technique was used to build up a multilayer film and this process was followed using UV-Vis spectroscopy and ellipsometry. The morphology and thickness of the obtained multilayered film material was evaluated by atomic force microscopy (AFM). Preliminary studies on the application of the obtained multilayer film for coating of liposomal nanocarriers containing phenytoin, an antiarrhythmic drug, were performed. The coating effectively stabilizes liposomes and the effect increases with an increasing number of deposited layers until the polymeric film reaches the optimal thickness. The obtained release profiles suggest that bilayer-coated liposomes release phenytoin less rapidly than uncoated ones. The cytotoxicity studies performed for all obtained nanocarriers confirmed that none of them has negative effect on cell viability. All of the performed experiments suggest that liposomes coated with ultrathin film obtained from PVA derivatives can be attractive drug nanocarriers. Copyright © 2015 Elsevier B.V. All rights reserved.

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.

Metal Adatoms and Clusters on Ultrathin Zirconia Films

PubMed Central

2016-01-01

Nucleation and growth of transition metals on zirconia has been studied by scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. Since STM requires electrical conductivity, ultrathin ZrO2 films grown by oxidation of Pt3Zr(0001) and Pd3Zr(0001) were used as model systems. DFT studies were performed for single metal adatoms on supported ZrO2 films as well as the (1̅11) surface of monoclinic ZrO2. STM shows decreasing cluster size, indicative of increasing metal–oxide interaction, in the sequence Ag < Pd ≈ Au < Ni ≈ Fe. Ag and Pd nucleate mostly at steps and domain boundaries of ZrO2/Pt3Zr(0001) and form three-dimensional clusters. Deposition of low coverages of Ni and Fe at room temperature leads to a high density of few-atom clusters on the oxide terraces. Weak bonding of Ag to the oxide is demonstrated by removing Ag clusters with the STM tip. DFT calculations for single adatoms show that the metal–oxide interaction strength increases in the sequence Ag < Au < Pd < Ni on monoclinic ZrO2, and Ag ≈ Au < Pd < Ni on the supported ultrathin ZrO2 film. With the exception of Au, metal nucleation and growth on ultrathin zirconia films follow the usual rules: More reactive (more electropositive) metals result in a higher cluster density and wet the surface more strongly than more noble metals. These bind mainly to the oxygen anions of the oxide. Au is an exception because it can bind strongly to the Zr cations. Au diffusion may be impeded by changing its charge state between −1 and +1. We discuss differences between the supported ultrathin zirconia films and the surfaces of bulk ZrO2, such as the possibility of charge transfer to the substrate of the films. Due to their large in-plane lattice constant and the variety of adsorption sites, ZrO2{111} surfaces are more reactive than many other oxygen-terminated oxide surfaces. PMID:27213024

Investigation of amorphous RuMoC alloy films as a seedless diffusion barrier for Cu/ p-SiOC:H ultralow- k dielectric integration

NASA Astrophysics Data System (ADS)

Jiao, Guohua; Liu, Bo; Li, Qiran

2015-08-01

Ultrathin RuMoC amorphous films prepared by magnetron co-sputtering with Ru and MoC targets in a sandwiched scheme Si/ p-SiOC:H/RuMoC/Cu were investigated as barrier in copper metallization. The evolution of final microstructure of RuMoC alloy films show sensitive correlation with the content of doped Mo and C elements and can be easily controlled by adjusting the sputtering power of the MoC target. There was no signal of interdiffusion between the Cu and SiOC:H layer in the sample of Cu/RuMoC/ p-SiOC:H/Si, even annealing up to 500 °C. Very weak signal of oxygen have been confirmed in the RuMoC barrier layer both as-deposited and after being annealed, and a good performance on preventing oxygen diffusion has been proved. Leakage current and resistivity evaluations also reveal the excellent thermal reliability of this Si/ p-SiOC:H/RuMoC/Cu film stack at the temperatures up to 500 °C, indicating its potential application in the advanced barrierless Cu metallization.

Facile fabrication of network film electrodes with ultrathin Au nanowires for nonenzymatic glucose sensing and glucose/O2 fuel cell.

PubMed

Yang, Lu; Zhang, Yijia; Chu, Mi; Deng, Wenfang; Tan, Yueming; Ma, Ming; Su, Xiaoli; Xie, Qingji; Yao, Shuozhuo

2014-02-15

We report here on the facile fabrication of network film electrodes with ultrathin Au nanowires (AuNWs) and their electrochemical applications for high-performance nonenzymatic glucose sensing and glucose/O2 fuel cell under physiological conditions (pH 7.4, containing 0.15M Cl(-)). AuNWs with an average diameter of ~7 or 2 nm were prepared and can self-assemble into robust network films on common electrodes. The network film electrode fabricated with 2-nm AuNWs exhibits high sensitivity (56.0 μA cm(-2)mM(-1)), low detection limit (20 μM), short response time (within 10s), excellent selectivity, and good storage stability for nonenzymatic glucose sensing. Glucose/O2 fuel cells were constructed using network film electrodes as the anode and commercial Pt/C catalyst modified glassy carbon electrode as cathode. The glucose/O2 fuel cell using 2-nm AuNWs as anode catalyst output a maximum power density of is 126 μW cm(-2), an open-circuit cell voltage of 0.425 V, and a short-circuit current density of 1.34 mA cm(-2), respectively. Due to the higher specific electroactive surface area of 2-nm AuNWs, the network film electrode fabricated with 2-nm AuNWs exhibited higher electrocatalytic activity toward glucose oxidation than the network film electrode fabricated with 7-nm AuNWs. The network film electrode exhibits high electrocatalytic activity toward glucose oxidation under physiological conditions, which is helpful for constructing implantable electronic devices. © 2013 Elsevier B.V. All rights reserved.

Dynamics of ultrathin metal films on amorphous substrates under fast thermal processing

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

Favazza, Christopher; Kalyanaraman, Ramki; Sureshkumar, Radhakrishna

A mathematical model is developed to analyze the growth/decay rate of surface perturbations of an ultrathin metal film on an amorphous substrate (SiO{sub 2}). The formulation combines the approach of Mullins [W. W. Mullins, J. Appl. Phys. 30, 77 (1959)] for bulk surfaces, in which curvature-driven mass transport and surface deformation can occur by surface/volume diffusion and evaporation-condensation processes, with that of Spencer et al. [B. J. Spencer, P. W. Voorhees, and S. H. Davis, Phys. Rev. Lett. 67, 26 (1991)] to describe solid-state transport in thin films under epitaxial strain. Modifications of the Mullins model to account for thin-filmmore » boundary conditions result in qualitatively different dispersion relationships especially in the limit as kh{sub o}<<1, where k is the wavenumber of the perturbation and h{sub o} is the unperturbed film height. The model is applied to study the relative rate of solid-state mass transport as compared to that of liquid phase dewetting in a thin film subjected to a fast thermal pulse. Specifically, we have recently shown that multiple cycles of nanosecond (ns) pulsed laser melting and resolidification of ultrathin metal films on amorphous substrates can lead to the formation of various types of spatially ordered nanostructures [J. Trice, D. Thomas, C. Favazza, R. Sureshkumar, and R. Kalyanaraman, Phys. Rev. B 75, 235439 (2007)]. The pattern formation has been attributed to the dewetting of the thin film by a hydrodynamic instability. In such experiments the film is in the solid state during a substantial fraction of each thermal cycle. However, results of a linear stability analysis based on the aforementioned model suggest that solid-state mass transport has a negligible effect on morphological changes of the surface. Further, a qualitative analysis of the effect of thermoelastic stress, induced by the rapid temperature changes in the film-substrate bilayer, suggests that stress relaxation does not appreciably contribute to surface deformation. Hence, surface deformation caused by liquid phase instabilities is rapidly quenched-in during the cooling phase. This deformed state is further evolved by subsequent laser pulses. These results have implications to developing accurate computer simulations of thin-film dewetting by energetic beams aimed at the manufacturing of optically active nanoscale materials for applications including information processing, optical devices, and solar energy harvesting.« less

CH3Br adsorption on MgO/Mo ultrathin films: A DFT study

NASA Astrophysics Data System (ADS)

Cipriano, Luis A.; Tosoni, Sergio; Pacchioni, Gianfranco

2018-06-01

The adsorption of methyl bromide on MgO ultrathin films supported on Mo(100) was studied by means of density functional theory calculations, in comparison to the MgO(100) and Mo(100) surfaces. The adsorption energy and geometry were shown to depend on the thickness of the supported oxide film. MgO films as thick as 2ML (or more) display adsorptive properties similar to MgO(100), i.e. the adsorption of CH3Br is mostly due to dispersion and the molecule lies in a tilted geometry almost parallel to the surface. The CH3Br HOMO-LUMO gap is almost unaltered with respect to the gas phase. On metallic Mo(100) surfaces the bonding is completely different with the CH3Br molecule strongly bound and the C-Br bond axis almost vertical with respect to the metal surface. The MgO monolayer supported on Mo exhibits somehow intermediate properties: the tilt angle is larger and the bonding is stronger than on MgO(100), due to the effect of the supporting metal. In this case, a small reduction of the HOMO-LUMO gap of the adsorbed molecule is reported. The results help to rationalize the observed behavior in photodissociation of CH3Br supported on different substrates.

Superstructures and Electronic Properties of Manganese-Phthalocyanine Molecules on Au(110) from Submonolayer Coverage to Ultrathin Molecular Films.

PubMed

Topyła, M; Néel, N; Kröger, J

2016-07-12

The adsorption of manganese-phthalocyanine molecules on Au(110) was investigated using a low-temperature scanning tunneling microscope. A rich variety of commensurate superstructures was observed upon increasing the molecule coverage from submonolayers to ultrathin films. All structures were associated with reconstructions of the Au(110) substrate. Molecules adsorbed in the second molecular layer exhibited negative differential conductance occurring symmetrically around zero bias voltage. A double-barrier tunneling model rationalized this observation in terms of a peaked molecular resonance at the Fermi energy together with a voltage drop across the molecular film.

Multiscale Relaxation Dynamics in Ultrathin Metallic Glass-Forming Films

NASA Astrophysics Data System (ADS)

Bi, Q. L.; Lü, Y. J.; Wang, W. H.

2018-04-01

The density layering phenomenon originating from a free surface gives rise to the layerlike dynamics and stress heterogeneity in ultrathin Cu-Zr glassy films, which facilitates the occurrence of multistep relaxations in the timescale of computer simulations. Taking advantage of this condition, we trace the relaxation decoupling and evolution with temperature simply via the intermediate scattering function. We show that the β relaxation hierarchically follows fast and slow modes in films, and there is a β -relaxation transition as the film is cooled close to the glass transition. We provide the direct observation of particle motions responsible for the β relaxation and reveal the dominant mechanism varying from the thermal activated to the cooperative jumps across the transition.

Resistive switching of organic–inorganic hybrid devices of conductive polymer and permeable ultra-thin SiO2 films

NASA Astrophysics Data System (ADS)

Yamamoto, Shunsuke; Kitanaka, Takahisa; Miyashita, Tokuji; Mitsuishi, Masaya

2018-06-01

We propose a resistive switching device composed of conductive polymer (PEDOT:PSS) and SiO2 ultra-thin films. The SiO2 film was fabricated from silsesquioxane polymer nanosheets as a resistive switching layer. Devices with metal (Ag or Au)∣SiO2∣PEDOT:PSS architecture show good resistive switching performance with set–reset voltages as low as several hundred millivolts. The device properties and the working mechanism were investigated by varying the electrode material, surrounding atmosphere, and SiO2 film thickness. Results show that resistive switching is based on water and ion migration at the PEDOT:PSS∣SiO2 interface.

Surface Acoustic Wave Monitor for Deposition and Analysis of Ultra-Thin Films

NASA Technical Reports Server (NTRS)

Hines, Jacqueline H. (Inventor)

2015-01-01

A surface acoustic wave (SAW) based thin film deposition monitor device and system for monitoring the deposition of ultra-thin films and nanomaterials and the analysis thereof is characterized by acoustic wave device embodiments that include differential delay line device designs, and which can optionally have integral reference devices fabricated on the same substrate as the sensing device, or on a separate device in thermal contact with the film monitoring/analysis device, in order to provide inherently temperature compensated measurements. These deposition monitor and analysis devices can include inherent temperature compensation, higher sensitivity to surface interactions than quartz crystal microbalance (QCM) devices, and the ability to operate at extreme temperatures.

Resistive switching of organic-inorganic hybrid devices of conductive polymer and permeable ultra-thin SiO2 films.

PubMed

Yamamoto, Shunsuke; Kitanaka, Takahisa; Miyashita, Tokuji; Mitsuishi, Masaya

2018-06-29

We propose a resistive switching device composed of conductive polymer (PEDOT:PSS) and SiO 2 ultra-thin films. The SiO 2 film was fabricated from silsesquioxane polymer nanosheets as a resistive switching layer. Devices with metal (Ag or Au)∣SiO 2 ∣PEDOT:PSS architecture show good resistive switching performance with set-reset voltages as low as several hundred millivolts. The device properties and the working mechanism were investigated by varying the electrode material, surrounding atmosphere, and SiO 2 film thickness. Results show that resistive switching is based on water and ion migration at the PEDOT:PSS∣SiO 2 interface.

Intrinsic stress evolution during amorphous oxide film growth on Al surfaces

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

Flötotto, D., E-mail: d.floetotto@is.mpg.de; Wang, Z. M.; Jeurgens, L. P. H.

2014-03-03

The intrinsic stress evolution during formation of ultrathin amorphous oxide films on Al(111) and Al(100) surfaces by thermal oxidation at room temperature was investigated in real-time by in-situ substrate curvature measurements and detailed atomic-scale microstructural analyses. During thickening of the oxide a considerable amount of growth stresses is generated in, remarkably even amorphous, ultrathin Al{sub 2}O{sub 3} films. The surface orientation-dependent stress evolutions during O adsorption on the bare Al surfaces and during subsequent oxide-film growth can be interpreted as a result of (i) adsorption-induced surface stress changes and (ii) competing processes of free volume generation and structural relaxation, respectively.

Amorphous alumina coatings: processing, structure and remarkable barrier properties.

PubMed

Samélor, Diane; Lazar, Ana-Maria; Aufray, Maëlenn; Tendero, Claire; Lacroix, Loïc; Béguin, Jean-Denis; Caussat, Brigitte; Vergnes, Hugues; Alexis, Joël; Poquillon, Dominique; Pébère, Nadine; Gleizes, Alain; Vahlas, Constantin

2011-09-01

Amorphous aluminium oxide coatings were processed by metalorganic chemical vapour deposition (MOCVD); their structural characteristics were determined as a function of the processing conditions, the process was modelled considering appropriate chemical kinetic schemes, and the properties of the obtained material were investigated and were correlated with the nanostructure of the coatings. With increasing processing temperature in the range 350 degrees C-700 degrees C, subatmospheric MOCVD of alumina from aluminium tri-isopropoxide (ATI) sequentially yields partially hydroxylated amorphous aluminium oxides, amorphous Al2O3 (415 degrees C-650 degrees C) and nanostructured gamma-Al2O3 films. A numerical model for the process allowed reproducing the non uniformity of deposition rate along the substrate zone due to the depletion of ATI. The hardness of the coatings prepared at 350 degrees C, 480 degrees C and 700 degrees C is 6 GPa, 11 GPa and 1 GPa, respectively. Scratch tests on films grown on TA6V titanium alloy reveal adhesive and cohesive failures for the amorphous and nanocrystalline ones, respectively. Alumina coating processed at 480 degrees C on TA6V yielded zero weight gain after oxidation at 600 degrees C in lab air. The surface of such low temperature processed amorphous films is hydrophobic (water contact angle 106 degrees), while the high temperature processed nanocrystalline films are hydrophilic (48 degrees at a deposition temperature of 700 degrees C). It is concluded that amorphous Al2O3 coatings can be used as oxidation and corrosion barriers at ambient or moderate temperature. Nanostructured with Pt or Ag nanoparticles, they can also provide anti-fouling or catalytic surfaces.

Time-dependent changes in the growth of ultrathin ionic liquid films on Ag(111).

PubMed

Lexow, Matthias; Talwar, Timo; Heller, Bettina S J; May, Benjamin; Bhuin, Radha G; Maier, Florian; Steinrück, Hans-Peter

2018-05-09

Various amounts of the ionic liquids (ILs) [C1C1Im][Tf2N] and [C8C1Im][Tf2N] were deposited in vacuo by physical vapour deposition (PVD) on single crystalline Ag(111) at room temperature and subsequently monitored by angle-resolved X-ray photoelectron spectroscopy (ARXPS) as a function of time. For very low coverages of up to one closed molecular layer, an initial wetting layer was rapidly formed for both ILs. Deposition of higher amounts of [C1C1Im][Tf2N] revealed an initial three-dimensional film morphology. On the time scale of hours, characteristic changes of the XPS signals were observed. These are interpreted as island spreading and a transformation towards a nearly two dimensional [C1C1Im][Tf2N] film as the final state. In contrast, a film morphology close to 2D was found from the very beginning for [C8C1Im][Tf2N] deposited on Ag(111) demonstrating the influence of the alkyl chain length on the growth kinetics. These studies also highlight the suitability of time-resolved ARXPS for the investigation of IL/solid interfaces, which play a crucial role in IL thin film applications such as in catalysis, sensor, lubrication, and coating technologies.

Promising Ta-Ti-Zr-Si metallic glass coating without cytotoxic elements for bio-implant applications

NASA Astrophysics Data System (ADS)

Lai, J. J.; Lin, Y. S.; Chang, C. H.; Wei, T. Y.; Huang, J. C.; Liao, Z. X.; Lin, C. H.; Chen, C. H.

2018-01-01

Tantalum (Ta) is considered as one of the most promising metal due to its high corrosion resistance, excellent biocompatibility and cell adhesion/in-growth capabilities. Although there are some researches exploring the biomedical aspects of Ta and Ta based alloys, systematic characterizations of newly developed Ta-based metallic glasses in bio-implant applications is still lacking. This study employs sputtering approach to produced thin-film Ti-based metallic glasses due to the high melting temperature of Ta (3020 °C). Two fully amorphous Ta-based metallic glasses composed of Ta57Ti17Zr15Si11 and Ta75Ti10Zr8Si7 are produced and experimentally characterized in terms of their mechanical properties, bio-corrosion properties, surface hydrophilic characteristics, and in-vitro cell viability and cells attachment tests. Compare to conventional pure Ti and Ta metals, the developed Ta-based metallic glasses exhibit higher hardness and lower modulus which are better match to the mechanical properties of bone. MTS assay results show that Ta-based metallic glasses show comparable cell viability and cell attachment rate compared to that of pure Ti and Ta surface in a 72 h in-vitro test.

Flux-mediated syntheses, structural characterization and low-temperature polymorphism of the p-type semiconductor Cu2Ta4O11

NASA Astrophysics Data System (ADS)

King, Nacole; Sullivan, Ian; Watkins-Curry, Pilanda; Chan, Julia Y.; Maggard, Paul A.

2016-04-01

A new low-temperature polymorph of the copper(I)-tantalate, α-Cu2Ta4O11, has been synthesized in a molten CuCl-flux reaction at 665 °C for 1 h and characterized by powder X-ray diffraction Rietveld refinements (space group Cc (#9), a=10.734(1) Å, b = 6.2506(3) Å, c=12.887(1) Å, β = 106.070(4)°). The α-Cu2Ta4O11 phase is a lower-symmetry monoclinic polymorph of the rhombohedral Cu2Ta4O11 structure (i.e., β-Cu2Ta4O11 space group R 3 ̅ c (#167), a = 6.2190(2) Å, c=37.107(1) Å), and related crystallographically by ahex=amono/√3, bhex=bmono, and chex=3cmonosinβmono. Its structure is similar to the rhombohedral β-Cu2Ta4O11 and is composed of single layers of highly-distorted and edge-shared TaO7 and TaO6 polyhedra alternating with layers of nearly linearly-coordinated Cu(I) cations and isolated TaO6 octahedra. Temperature dependent powder X-ray diffraction data show the α-Cu2Ta4O11 phase is relatively stable under vacuum at 223 K and 298 K, but reversibly transforms to β-Cu2Ta4O11 by at least 523 K and higher temperatures. The symmetry-lowering distortions from β-Cu2Ta4O11 to α-Cu2Ta4O11 arise from the out-of-center displacements of the Ta 5d0 cations in the TaO7 pentagonal bipyramids. The UV-vis diffuse reflectance spectrum of the monoclinic α-Cu2Ta4O11 shows an indirect bandgap transition of ∼2.6 eV, with the higher-energy direct transitions starting at ∼2.7 eV. Photoelectrochemical measurements on polycrystalline films of α-Cu2Ta4O11 show strong cathodic photocurrents of ∼1.5 mA/cm2 under AM 1.5 G solar irradiation.

Periodically pulsed wet annealing approach for low-temperature processable amorphous InGaZnO thin film transistors with high electrical performance and ultrathin thickness

PubMed Central

Kim, Ye Kyun; Ahn, Cheol Hyoun; Yun, Myeong Gu; Cho, Sung Woon; Kang, Won Jun; Cho, Hyung Koun

2016-01-01

In this paper, a simple and controllable “wet pulse annealing” technique for the fabrication of flexible amorphous InGaZnO thin film transistors (a-IGZO TFTs) processed at low temperature (150 °C) by using scalable vacuum deposition is proposed. This method entailed the quick injection of water vapor for 0.1 s and purge treatment in dry ambient in one cycle; the supply content of water vapor was simply controlled by the number of pulse repetitions. The electrical transport characteristics revealed a remarkable performance of the a-IGZO TFTs prepared at the maximum process temperature of 150 °C (field-effect mobility of 13.3 cm2 V−1 s−1; Ion/Ioff ratio ≈ 108; reduced I-V hysteresis), comparable to that of a-IGZO TFTs annealed at 350 °C in dry ambient. Upon analysis of the angle-resolved x-ray photoelectron spectroscopy, the good performance was attributed to the effective suppression of the formation of hydroxide and oxygen-related defects. Finally, by using the wet pulse annealing process, we fabricated, on a plastic substrate, an ultrathin flexible a-IGZO TFT with good electrical and bending performances. PMID:27198067

Periodically pulsed wet annealing approach for low-temperature processable amorphous InGaZnO thin film transistors with high electrical performance and ultrathin thickness.

PubMed

Kim, Ye Kyun; Ahn, Cheol Hyoun; Yun, Myeong Gu; Cho, Sung Woon; Kang, Won Jun; Cho, Hyung Koun

2016-05-20

In this paper, a simple and controllable "wet pulse annealing" technique for the fabrication of flexible amorphous InGaZnO thin film transistors (a-IGZO TFTs) processed at low temperature (150 °C) by using scalable vacuum deposition is proposed. This method entailed the quick injection of water vapor for 0.1 s and purge treatment in dry ambient in one cycle; the supply content of water vapor was simply controlled by the number of pulse repetitions. The electrical transport characteristics revealed a remarkable performance of the a-IGZO TFTs prepared at the maximum process temperature of 150 °C (field-effect mobility of 13.3 cm(2) V(-1) s(-1); Ion/Ioff ratio ≈ 10(8); reduced I-V hysteresis), comparable to that of a-IGZO TFTs annealed at 350 °C in dry ambient. Upon analysis of the angle-resolved x-ray photoelectron spectroscopy, the good performance was attributed to the effective suppression of the formation of hydroxide and oxygen-related defects. Finally, by using the wet pulse annealing process, we fabricated, on a plastic substrate, an ultrathin flexible a-IGZO TFT with good electrical and bending performances.

Enhanced Hydrogen Transport over Palladium Ultrathin Films through Surface Nanostructure Engineering.

PubMed

Abate, Salvatore; Giorgianni, Gianfranco; Gentiluomo, Serena; Centi, Gabriele; Perathoner, Siglinda

2015-11-01

Palladium ultrathin films (around 2 μm) with different surface nanostructures are characterized by TEM, SEM, AFM, and temperature programmed reduction (TPR), and evaluated in terms of H2 permeability and H2-N2 separation. A change in the characteristics of Pd seeds by controlled oxidation-reduction treatments produces films with the same thickness, but different surface and bulk nanostructure. In particular, the films have finer and more homogeneous Pd grains, which results in lower surface roughness. Although all samples show high permeo-selectivity to H2 , the samples with finer grains exhibit enhanced permeance and lower activation energy for H2 transport. The analysis of the data suggests that grain boundaries between the Pd grains at the surface favor H2 transfer from surface to subsurface. Thus, the surface nanostructure plays a relevant role in enhancing the transport of H2 over the Pd ultrathin film, which is an important aspect to develop improved membranes that function at low temperatures and toward new integrated process architectures in H2 and syngas production with enhanced sustainability. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of nanoconfinement on the sputter yield in ultrathin polymeric films: Experiments and model

NASA Astrophysics Data System (ADS)

Cristaudo, Vanina; Poleunis, Claude; Delcorte, Arnaud

2018-06-01

This fundamental contribution on secondary ion mass spectrometry (SIMS) polymer depth-profiling by large argon clusters investigates the dependence of the sputter yield volume (Y) on the thickness (d) of ultrathin films as a function of the substrate nature, i.e. hard vs soft. For this purpose, thin films of polystyrene (PS) oligomers (∼4,000 amu) are spin-coated, respectively, onto silicon and poly (methyl methacrylate) supports and, then, bombarded by 10 keV Ar3000+ ions. The investigated thickness ranges from 15 to 230 nm. Additionally, the influence of the polymer molecular weight on Y(d) for PS thin films on Si is explored. The sputtering efficiency is found to be strongly dependent on the overlayer thickness, only in the case of the silicon substrate. A simple phenomenological model is proposed for the description of the thickness influence on the sputtering yield. Molecular dynamics (MD) simulations conducted on amorphous films of polyethylene-like oligomers of increasing thickness (from 2 to 20 nm), under comparable cluster bombardment conditions, predict a significant increase of the sputtering yield for ultrathin layers on hard substrates, induced by energy confinement in the polymer, and support our phenomenological model.

Integration of amorphous tantalum silicon nitride (TaSiN) films as diffusion barriers in a Cu/SiLK(TM) metallization scheme

NASA Astrophysics Data System (ADS)

Padiyar, Sumant Devdas

2003-09-01

Current and future performance requirements for high- speed integrated circuit (IC) devices have placed great emphasis on the introduction of novel materials, deposition techniques and improved metrology techniques. The introduction of copper interconnects and more currently low-k dielectric materials in IC fabrication are two such examples. This introduction necessitates research on the compatibility of these materials and process techniques with adjacent diffusion barrier materials. One candidate, which has attracted significant attention is tantalum-silicon-nitride (TaSiN) on account of its superior diffusion barrier performance and high recrystallization temperature1. The subject of this dissertation is an investigation of the integration compatibility and performance of TaSiN barrier layers with a low-k dielectric polymer (SiLK ®2). A plasma- enhanced chemical vapor deposition (PECVD) approach is taken for growth of TaSiN films in this work due to potential advantages in conformal film coverage compared to more conventional physical vapor deposition methods. A Design of Experiment (DOE) methodology was introduced for PECVD of TaSiN on SiLK to optimize film properties such as film composition, resistivity, growth rate and film roughness with respect to the predictors viz. substrate temperature, precursor gas flow and plasma power. The first pass study determined the response window for optimized TaSiN film composition, growth rate and low halide contamination and the compatibility of the process with an organic polymer substrate, i.e. SiLK. Second-pass studies were carried out to deposit ultra- thin (10nm) films on: (a)blanket SiLK to investigate the performance of TaSiN films against copper diffusion, and (b)patterned SiLK to evaluate step coverage and conformality. All TaSiN depositions were carried out on SiO2 substrates for baseline comparisons. A second purpose of the diffusion barrier in IC processing is to improve interfacial adhesion between the barrier and the adjacent dielectric material; especially important for an organic polymer like SiLK. Hence, a detailed study was undertaken to evaluate the interfacial adhesion of TaSiN with SiLK and SiO2 and study the dependence of the adhesion with the film composition. The results of diffusion barrier performance studies, conformality studies, and interfacial adhesion studies of TaSiN films are discussed in relation to the elemental compositions of the films. 1J. S. Reid, M. Nicolet, J. Appl. Phys. 79 (2) p. 1109 (1996). 2SiLK is a low-k dielectric candidate registered by Dow Chemical Company, MI.

Layered ultra-thin coherent structures used as electrical resistors having low-temperature coefficient of resistivity

DOEpatents

Werner, T.R.; Falco, C.M.; Schuller, I.K.

1982-08-31

A thin film resistor having a controlled temperature coefficient of resistance (TCR) ranging from negative to positive degrees kelvin and having relatively high resistivity. The resistor is a multilayer superlattice crystal containing a plurality of alternating, ultra-thin layers of two different metals. TCR is varied by controlling the thickness of the individual layers. The resistor can be readily prepared by methods compatible with thin film circuitry manufacturing techniques.

Magneto-optical Kerr rotation and color in ultrathin lossy dielectric

NASA Astrophysics Data System (ADS)

Zhang, Jing; Wang, Hai; Qu, Xin; Zhou, Yun song; Li, Li na

2017-05-01

Ultra-thin optical coating comprising nanometer-thick silicon absorbing films on iron substrates can display strong optical interference effects. A resonance peak of ∼1.6^\\circ longitudinal Kerr rotation with the silicon thickness of ∼47 \\text{nm} was found at the wavelength of 660 nm. The optical properties of silicon thin films were well controlled by the sputtering power. Non-iridescence color exhibition and Kerr rotation enhancement can be manipulated and encoded individually.

Multi-Layer Coating of Ultrathin Polymer Films on Nanoparticles of Alumina by a Plasma Treatment

DTIC Science & Technology

2001-01-01

Proc. Vol. 635 © 2001 Materials Research Society Multi-Layer Coating of Ultrathin Polymer Films on Nanoparticles of Alumina by a Plasma Treatment Donglu...interconnected organic and inorganic networks results in coatings with a very low permeability for gases and liquids. Hybrid materials are very suitable for... materials consist of a clear alcoholic solution that can easily be processed by classical application techniques such as dipping, spraying, or spin coating

Polar phase transitions in heteroepitaxial stabilized La0.5Y0.5AlO3 thin films

NASA Astrophysics Data System (ADS)

Liu, Shenghua; Zhang, Chunfeng; Zhu, Mengya; He, Qian; Chakhalian, Jak; Liu, Xiaoran; Borisevich, Albina; Wang, Xiaoyong; Xiao, Min

2017-10-01

We report on the fabrication of epitaxial La0.5Y0.5AlO3 ultrathin films on (001) LaAlO3 substrates. Structural characterizations by scanning transmission electron microscopy and x-ray diffraction confirm the high quality of the film with a - b + c - AlO6 octahedral tilt pattern. Unlike either of the nonpolar parent compound, LaAlO3 and YAlO3, second harmonic generation measurements on the thin films suggest a nonpolar-polar phase transition at T c near 500 K, and a polar-polar phase transition at T a near 160 K. By fitting the angular dependence of the second harmonic intensities, we further propose that the two polar structures can be assigned to the Pmc2 1 and Pmn2 1 space group, while the high temperature nonpolar structure belongs to the Pbnm space group.

Fine-grained BaZr0.2Ti0.8O3 thin films for tunable device applications

NASA Astrophysics Data System (ADS)

Ying, Z.; Yun, P.; Wang, D. Y.; Zhou, X. Y.; Song, Z. T.; Feng, S. L.; Wang, Y.; Chan, H. L. W.

2007-04-01

A study of the structure and in-plane dielectric properties of BaZr0.2Ti0.8O3 thin film epitaxially grown on (LaAlO3)0.3(Sr2AlTaO6)0.35 (001) single-crystal substrates through pulsed-laser deposition has been carried out. X-ray diffraction measurements revealed a good crystallinity and tensile in-plane stress in the film. Fine grains with an average size of ˜20 nm were observed using atomic force microscopy. Curie temperature of the film was found to be ˜120 °C, which is 100 °C higher than that of the ceramic. Butterfly-shaped C-V curve confirmed the in-plane ferroelectric state in the film. A large dielectric tunability of ˜50% was found in the film.

Ultra-thin passivating film induced by vinylene carbonate on highly oriented pyrolytic graphite negative electrode in lithium-ion cell

NASA Astrophysics Data System (ADS)

Matsuoka, O.; Hiwara, A.; Omi, T.; Toriida, M.; Hayashi, T.; Tanaka, C.; Saito, Y.; Ishida, T.; Tan, H.; Ono, S. S.; Yamamoto, S.

We investigated the influence of vinylene carbonate, as an additive molecule, on the decomposition phenomena of electrolyte solution [ethylene carbonate (EC)—ethyl methyl carbonate (EMC) (1:2 by volume) containing 1 M LiPF 6] on a highly oriented pyrolytic graphite (HOPG) negative electrode by using cyclic voltammetry (CV) and atomic force microscopy (AFM). Vinylene carbonate deactivated reactive sites (e.g. radicals and oxides at the defects and the edge of carbon layer) on the cleaved surface of the HOPG negative electrode, and prevented further decomposition of the other solvents there. Further, vinylene carbonate induced an ultra-thin film (less than 1.0 nm in thickness) on the terrace of the basal plane of the HOPG negative electrode, and this film suppressed the decomposition of electrolyte solution on the terraces of the basal plane. We consider that this ultra-thin passivating film is composed of a reduction product of vinylene carbonate (VC), and might have a polymer structure. These induced effects might explain how VC improves the life performance of lithium-ion cells.

Effects of annealing on arrays of Ge nanocolumns formed by glancing angle deposition

NASA Astrophysics Data System (ADS)

Khare, C.; Gerlach, J. W.; Höche, T.; Fuhrmann, B.; Leipner, H. S.; Rauschenbach, B.

2012-10-01

Post-deposition thermal annealing of glancing angle deposited Ge nanocolumn arrays was carried out in a continuous Ar-flow at temperatures ranging from TA = 300 to 800 °C for different annealing durations. Morphological alterations and the recrystallization process induced by the thermal annealing treatment were investigated for the Ge nanocolumns deposited on planar and pre-patterned Si substrates. From X-ray diffraction (XRD) measurements, the films annealed at TA ≥ 500 °C were found to be polycrystalline. On planar Si substrates, at TA = 600 °C nanocolumns exhibited strong coarsening and merging, while a complete disintegration of the nanocolumns was detected at TA = 700 °C. The morphology of nanostructures deposited on pre-patterned substrates differs substantially, where the merging or column-disintegration effect was absent at elevated annealing temperatures. The two-arm-chevron nanostructures grown on pre-patterned substrates retained their complex shape and morphology, after extended annealing intervals. Investigations by transmission electron microscopy revealed nanocrystalline domains of the order of 5-30 nm (in diameter) present within the chevron structures after the annealing treatment.

High performance top-gated ferroelectric field effect transistors based on two-dimensional ZnO nanosheets

NASA Astrophysics Data System (ADS)

Tian, Hongzheng; Wang, Xudong; Zhu, Yuankun; Liao, Lei; Wang, Xianying; Wang, Jianlu; Hu, Weida

2017-01-01

High quality ultrathin two-dimensional zinc oxide (ZnO) nanosheets (NSs) are synthesized, and the ZnO NS ferroelectric field effect transistors (FeFETs) are demonstrated based on the P(VDF-TrFE) polymer film used as the top gate insulating layer. The ZnO NSs exhibit a maximum field effect mobility of 588.9 cm2/Vs and a large transconductance of 2.5 μS due to their high crystalline quality and ultrathin two-dimensional structure. The polarization property of the P(VDF-TrFE) film is studied, and a remnant polarization of >100 μC/cm2 is achieved with a P(VDF-TrFE) thickness of 300 nm. Because of the ultrahigh remnant polarization field generated in the P(VDF-TrFE) film, the FeFETs show a large memory window of 16.9 V and a high source-drain on/off current ratio of more than 107 at zero gate voltage and a source-drain bias of 0.1 V. Furthermore, a retention time of >3000 s of the polarization state is obtained, inspiring a promising candidate for applications in data storage with non-volatile features.

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.

Nanoscale control of reversible chemical reaction between fullerene C60 molecules using scanning tunneling microscope.

PubMed

Nakaya, Masato; Kuwahara, Yuji; Aono, Masakazu; Nakayama, Tomonobu

2011-04-01

The nanoscale control of reversible chemical reactions, the polymerization and depolymerization between C60 molecules, has been investigated. Using a scanning tunneling microscope (STM), the polymerization and depolymerization can be controlled at designated positions in ultrathin films of C60 molecules. One of the two chemical reactions can be selectively induced by controlling the sample bias voltage (V(s)); the application of negative and positive values of V(s) results in polymerization and depolymerization, respectively. The selectivity between the two chemical reactions becomes extremely high when the thickness of the C60 film increases to more than three molecular layers. We conclude that STM-induced negative and positive electrostatic ionization are responsible for the control of the polymerization and depolymerization, respectively.

Fully transparent conformal organic thin-film transistor array and its application as LED front driving.

PubMed

Cui, Nan; Ren, Hang; Tang, Qingxin; Zhao, Xiaoli; Tong, Yanhong; Hu, Wenping; Liu, Yichun

2018-02-22

A fully transparent conformal organic thin-film field-effect transistor array is demonstrated based on a photolithography-compatible ultrathin metallic grid gate electrode and a solution-processed C 8 -BTBT film. The resulting organic field-effect transistor array exhibits a high optical transparency of >80% over the visible spectrum, mobility up to 2 cm 2 V -1 s -1 , on/off ratio of 10 5 -10 6 , switching current of >0.1 mA, and excellent light stability. The transparent conformal transistor array is demonstrated to adhere well to flat and curved LEDs as front driving. These results present promising applications of the solution-processed wide-bandgap organic semiconductor thin films in future large-scale transparent conformal active-matrix displays.

Annealing temperature and thickness dependencies of structural and magnetic properties of Co2FeAl thin films

NASA Astrophysics Data System (ADS)

Belmeguenai, M.; Gabor, M. S.; Zighem, F.; Roussigné, Y.; Faurie, D.; Tiusan, C.

2016-09-01

Co2FeAl (CFA) thin films, of various thicknesses (3 nm≤t ≤50 nm ), have been grown by sputtering on (001) MgO single-crystal substrates and annealed at different temperatures (RT≤Ta≤600 ∘C , where RT is the room temperature). The influence of the CFA thickness (t ), as well as ex situ annealing temperature (Ta), on the magnetic and structural properties has been investigated by x-ray diffraction (XRD), vibrating sample magnetometry, and broadband microstrip ferromagnetic resonance (MS-FMR). The XRD revealed an epitaxial growth of the films with the cubic [001] CFA axis normal to the substrate plane and that the chemical order varies from the B 2 phase to the A 2 phase when decreasing t or Ta. The deduced lattice parameters showed an in-plane tetragonal distortion and in-plane and out-plane strains that increase with Ta and 1 /t . For all Ta values, the variation of the effective magnetization, deduced from the fit of MS-FMR measurements, shows two different regimes separated by a critical thickness, which is Ta dependent. It decreases (increases) linearly with the inverse thickness (1 /t ) in the first (second) regime due to the contribution of the magnetoelastic anisotropy to surface (to volume) anisotropy. The observed behavior has been analyzed through a model allowing for the separation of the magnetocrystalline, magnetoelastic, and Néel-type interface anisotropy constants to the surface and the volume anisotropies. Similar behavior has been observed for the effective fourfold anisotropy field which governs the in-plane anisotropy present in all the samples. Finally, the MS-FMR data also allow one to conclude that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with Ta.

A general strategy for hybrid thin film fabrication and transfer onto arbitrary substrates.

PubMed

Zhang, Yong; Magan, John J; Blau, Werner J

2014-04-28

The development of thin film-based structures/devices often requires thin films to be transferred onto arbitrary substrates/surfaces. Controllable and non-destructive transfer method, although highly desired, remains quite challenging. Here we report a general method for fabrication and transfer of hybrid (ultra)thin films. The proposed solution-based in-situ transfer method shows not only its robust ability for thin film transfer onto arbitrary substrates but also its highly controlled and non-destructive characteristic. With a hole structure as the support, fully-stretched free-standing thin film is prepared. The successful transfer to a curved surface demonstrates the possibility for production of thin film-coated complex optical components. Ultrathin (35 nm) hybrid film transferred onto PET (50 μm thick) shows high transparency (>90% in visible range), conductivity (1.54 × 10(4) S/m), and flexibility (radius of curvature down to mm scale). The reported transfer method would provide a powerful route towards complex thin film-based structures/devices.

A General Strategy for Hybrid Thin Film Fabrication and Transfer onto Arbitrary Substrates

PubMed Central

Zhang, Yong; Magan, John J.; Blau, Werner J.

2014-01-01

The development of thin film-based structures/devices often requires thin films to be transferred onto arbitrary substrates/surfaces. Controllable and non-destructive transfer method, although highly desired, remains quite challenging. Here we report a general method for fabrication and transfer of hybrid (ultra)thin films. The proposed solution-based in-situ transfer method shows not only its robust ability for thin film transfer onto arbitrary substrates but also its highly controlled and non-destructive characteristic. With a hole structure as the support, fully-stretched free-standing thin film is prepared. The successful transfer to a curved surface demonstrates the possibility for production of thin film-coated complex optical components. Ultrathin (35 nm) hybrid film transferred onto PET (50 μm thick) shows high transparency (>90% in visible range), conductivity (1.54 × 104 S/m), and flexibility (radius of curvature down to mm scale). The reported transfer method would provide a powerful route towards complex thin film-based structures/devices. PMID:24769689

Effects of addition of Ta and Y ions to InZnO thin film transistors by sol-gel process.

PubMed

Son, Dae-Ho; Kim, Dae-Hwan; Kim, Jung-Hye; Park, Si-Nae; Sung, Shi-Joon; Kang, Jin-Kyu

2013-06-01

We have investigated the effects of the addition of tantalum (Ta) and yttrium (Y) ions to InZnO thin film transistors (TFTs) using the sol-gel process. TaInZnO and YInZnO TFTs had significantly lower off current and higher on-to-off current ratio than InZnO TFTs. Ta and Y ions have strong affinity to oxygen and so suppress the formation of free electron carriers in thin films; they play an important role in enhancing the electrical characteristic due to their high oxygen bonding ability. The optimized TaInZnO and YInZnO TFTs showed high on/off ratio and low subthreshold swing.

Probing of the interfacial Heisenberg and Dzyaloshinskii-Moriya exchange interaction by magnon spectroscopy.

PubMed

Zakeri, Khalil

2017-01-11

This Topical Review presents an overview of the recent experimental results on the quantitative determination of the magnetic exchange parameters in ultrathin magnetic films and multilayers grown on different substrates. The experimental approaches for probing both the symmetric Heisenberg and the antisymmetric Dzyaloshinskii-Moriya exchange interaction in ultrathin magnetic films and at interfaces are discussed in detail. It is explained how the experimental spectrum of magnetic excitations can be used to quantify the strength of these interactions.

Evidence for stable grain boundary melt films in experimentally deformed olivine-orthopyroxene rocks

NASA Astrophysics Data System (ADS)

de Kloe, R.; Drury, M. R.; van Roermund, H. L. M.

The microstructure of olivine-olivine grain boundaries has been studied in experimentally deformed (1200-1227°C, 300MPa) partially molten olivine and olivine-orthopyroxene rocks. In-situ melting produced 1vol% melt in all samples studied. Grain boundary analyses were carried out using a number of transmission electron microscopy techniques. The grain boundary chemistry in undeformed olivine-orthopyroxene starting material showed evidence for the presence of an intergranular phase along some, but not all, of the olivine-olivine boundaries. In the deformed samples, ultrathin Si-rich, Al- and Ca-bearing amorphous films have been observed along all investigated olivine-olivine grain boundaries. The chemistry of the grain boundaries, which is considered to be indicative for the presence of a thin film, was measured with energy-dispersive X-ray spectroscopy (EDX) and energy-filtering imaging. The amorphous nature of the films was confirmed with diffuse dark field imaging, Fresnel fringe imaging, and high-resolution electron microscopy. The films range in thickness from 0.6 to 3.0nm, and EDX analyses show that the presence of Al and Ca is restricted to this ultrathin film along the grain boundaries. Because thin melt films have been observed in all the samples, they are thought to be stable features of the melt microstructure in deformed partially molten rocks. The transition from the occasional presence of films in the undeformed starting material to the general occurrence of the films in deformed materials suggests that deformation promotes the formation and distribution of the films. Alternatively, hot-pressing may be too short for films to develop along all grain boundaries. A difference in creep strength between the studied samples could not be attributed to grain boundary melt films, as these have been found in all deformed samples. However, a weakening effect of grain boundary melt films on olivine rheology could not be ruled out due to the lack of confirmed melt-film free experiments.

Direct evidence on Ta-Metal Phases Igniting Resistive Switching in TaOx Thin Film

PubMed Central

Kyu Yang, Min; Ju, Hyunsu; Hwan Kim, Gun; Lee, Jeon-Kook; Ryu, Han-Cheol

2015-01-01

A Ta/TaOx/Pt stacked capacitor-like device for resistive switching was fabricated and examined. The tested device demonstrated stable resistive switching characteristics including uniform distribution of resistive switching operational parameters, highly promising endurance, and retention properties. To reveal the resistive switching mechanism of the device, micro structure analysis using high-resolution transmission electron microscope (HR-TEM) was performed. From the observation results, two different phases of Ta-metal clusters of cubic α-Ta and tetragonal β-Ta were founded in the amorphous TaOx mother-matrix after the device was switched from high resistance state (HRS) to low resistance state (LRS) by externally applied voltage bias. The observed Ta metal clusters unveiled the origin of the electric conduction paths in the TaOx thin film at the LRS. PMID:26365532

Direct evidence on Ta-Metal Phases Igniting Resistive Switching in TaOx Thin Film

NASA Astrophysics Data System (ADS)

Kyu Yang, Min; Ju, Hyunsu; Hwan Kim, Gun; Lee, Jeon-Kook; Ryu, Han-Cheol

2015-09-01

A Ta/TaOx/Pt stacked capacitor-like device for resistive switching was fabricated and examined. The tested device demonstrated stable resistive switching characteristics including uniform distribution of resistive switching operational parameters, highly promising endurance, and retention properties. To reveal the resistive switching mechanism of the device, micro structure analysis using high-resolution transmission electron microscope (HR-TEM) was performed. From the observation results, two different phases of Ta-metal clusters of cubic α-Ta and tetragonal β-Ta were founded in the amorphous TaOx mother-matrix after the device was switched from high resistance state (HRS) to low resistance state (LRS) by externally applied voltage bias. The observed Ta metal clusters unveiled the origin of the electric conduction paths in the TaOx thin film at the LRS.

The Ultrathin Limit and Dead-layer Effects in Local Polarization Switching of BiFeO3

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

Maksymovych, Petro; Huijben, Mark; Pan, Minghu

Using piezoresponse force microscopy in ultra-high vacuum, polarization switching has been detected and quantified in epitaxial BiFeO3 films from 200 down to ~ 4 unit cells. Local remnant piezoresponse was used to infer the applied electric field inside the ferroelectric volume, and account for the elusive effect of dead-layers in ultrathin films. The dead-layer manifested itself in the slower than anticipated decrease of the switching bias with film thickness, yielding apparent Kay-Dunn scaling of the switching field, while the statistical analysis of hysteresis loops revealed lateral variation of the dead-layer with sub-10 nm resolution.

Preparation of Ferroelectric Thin Films of Bismuth Layer Structured Compounds

NASA Astrophysics Data System (ADS)

Watanabe, Hitoshi; Mihara, Takashi; Yoshimori, Hiroyuki; Araujo, Carlos

1995-09-01

Ferroelectric thin films of bismuth layer structured compounds, SrBi2Ta2O9, SrBi2Nb2O9, SrBi4Ti4O15 and their solid solutions, were formed onto a sputtered platinum layer on a silicon substrate using spin-on technique and metal-organic decomposition (MOD) method. X-ray diffraction (XRD) analysis and some electrical measurements were performed on the prepared thin films. XRD results of SrBi2(Ta1- x, Nb x)2O9 films (0≤x≤1) showed that niobium ions substitute for tantalum ions in an arbitrary ratio without any change of the layer structure and lattice constants. Furthermore, XRD results of SrBi2 xTa2O9 films (0≤x≤1.5) indicated that the formation of the bismuth layer structure does not always require an accurate bismuth content. The layer structure was formed above 50% of the stoichiometric bismuth content in the general formula. SrBi2(Ta1- x, Nb x)2O9 films with various Ta/Nb ratios have large enough remanent polarization for nonvolatile memory application and have shown high fatigue resistance against 1011 cycles of full switching of the remanent polarization. Mixture films of the three compounds were also investigated.

Development and Characterization of Novel Polyurethane Films Impregnated with Tolfenamic Acid for Therapeutic Applications

PubMed Central

Sheraz, Muhammad Ali; Rehman, Ihtesham ur

2013-01-01

The present study deals with the preparation of polyurethane (PU) films impregnated with a nonsteroidal anti-inflammatory drug, tolfenamic acid (TA). Solvent evaporation technique has been employed for the preparation of TA-PU films in two different ratios of 1 : 2 and 1 : 5 in Tetrahydrofuran (THF) or THF-ethanol mixtures. The prepared films were characterized using X-Ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and release studies. The results indicate transformation of crystalline TA to its amorphous form. The degree of crystallinity changes both by increasing the polymer concentration and solvent used for the film preparations. The release profiles of TA were also found to be affected, showing a decrease from approximately 50% to 25% from 1 : 2 to 1 : 5 ratios, respectively. PMID:24073394

High-rate deposition of LiNb 1- xTa xO 3 films by thermal plasma spray CVD

NASA Astrophysics Data System (ADS)

Majima, T.; Yamamoto, H.; Kulinich, S. A.; Terashima, K.

2000-12-01

LiNb 1- xTa xO 3 films were prepared by a thermal plasma spray CVD method using liquid source materials. Preferentially (0 0 1)-oriented LiNb 1- xTa xO 3 films with satisfactory in-plane and out-of-plane alignment were fabricated on sapphire (0 0 1) substrates. The full-width at half-maximum (FWHM) of the (0 0 6) rocking curve could achieve 0.12°, which was comparable with those of LiNbO 3 and LiTaO 3 films prepared by other conventional vapor-phase deposition methods. The deposition rate was up to 0.07 μm/min, which was 5-40 times faster than those for most other conventional vapor-phase deposition methods. From inductively coupled plasma atomic emission spectroscopy analysis, x values of these films were estimated to be 0.36-0.49.

Monolayer-Mediated Growth of Organic Semiconductor Films with Improved Device Performance.

PubMed

Huang, Lizhen; Hu, Xiaorong; Chi, Lifeng

2015-09-15

Increased interest in wearable and smart electronics is driving numerous research works on organic electronics. The control of film growth and patterning is of great importance when targeting high-performance organic semiconductor devices. In this Feature Article, we summarize our recent work focusing on the growth, crystallization, and device operation of organic semiconductors intermediated by ultrathin organic films (in most cases, only a monolayer). The site-selective growth, modified crystallization and morphology, and improved device performance of organic semiconductor films are demonstrated with the help of the inducing layers, including patterned and uniform Langmuir-Blodgett monolayers, crystalline ultrathin organic films, and self-assembled polymer brush films. The introduction of the inducing layers could dramatically change the diffusion of the organic semiconductors on the surface and the interactions between the active layer with the inducing layer, leading to improved aggregation/crystallization behavior and device performance.

Conducting ion tracks generated by charge-selected swift heavy ions

NASA Astrophysics Data System (ADS)

Gupta, Srashti; Gehrke, H. G.; Krauser, J.; Trautmann, C.; Severin, D.; Bender, M.; Rothard, H.; Hofsäss, H.

2016-08-01

Conducting ion tracks in tetrahedral amorphous carbon (ta-C) thin films were generated by irradiation with swift heavy ions of well-defined charge state. The conductivity of tracks and the surface topography of the films, showing characteristic hillocks at each track position, were investigated using conductive atomic force microscopy measurements. The dependence of track conductivity and hillock size on the charge state of the ions was studied using 4.6 MeV/u Pb ions of charge state 53+, 56+ and 60+ provided by GANIL, as well as 4.8 MeV/u Bi and Au ions of charge state from 50+ to 61+ and 4.2 MeV/u 238U ions in equilibrium charge state provided by UNILAC of GSI. For the charge state selection at GSI, an additional stripper-foil system was installed at the M-branch that now allows routine irradiations with ions of selected charge states. The conductivity of tracks in ta-C increases significantly when the charge state increases from 51+ to 60+. However, the conductivity of individual tracks on the same sample still shows large variations, indicating that tracks formed in ta-C are either inhomogeneous or the conductivity is limited by the interface between ion track and Si substrate.

Development and ultra-structure of an ultra-thin silicone epidermis of bioengineered alternative tissue.

PubMed

Wessels, Quenton; Pretorius, Etheresia

2015-08-01

Burn wound care today has a primary objective of temporary or permanent wound closure. Commercially available engineered alternative tissues have become a valuable adjunct to the treatment of burn injuries. Their constituents can be biological, alloplastic or a combination of both. Here the authors describe the aspects of the development of a siloxane epidermis for a collagen-glycosaminoglycan and for nylon-based artificial skin replacement products. A method to fabricate an ultra-thin epidermal equivalent is described. Pores, to allow the escape of wound exudate, were punched and a tri-filament nylon mesh or collagen scaffold was imbedded and silicone polymerisation followed at 120°C for 5 minutes. The ultra-structure of these bilaminates was assessed through scanning electron microscopy. An ultra-thin biomedical grade siloxane film was reliably created through precision coating on a pre-treated polyethylene terephthalate carrier. © 2013 The Authors. International Wound Journal © 2013 Medicalhelplines.com Inc and John Wiley & Sons Ltd.

Effects of copolymer composition, film thickness, and solvent vapor annealing time on dewetting of ultrathin block copolymer films.

PubMed

Huang, Changchun; Wen, Gangyao; Li, Jingdan; Wu, Tao; Wang, Lina; Xue, Feifei; Li, Hongfei; Shi, Tongfei

2016-09-15

Effects of copolymer composition, film thickness, and solvent vapor annealing time on dewetting of spin-coated polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) films (<20nm thick) were mainly investigated by atomic force microscopy. Surface chemical analysis of the ultrathin films annealed for different times were performed using X-ray photoelectron spectroscopy and contact angle measurement. With the annealing of acetone vapor, dewetting of the films with different thicknesses occur via the spinodal dewetting and the nucleation and growth mechanisms, respectively. The PS-b-PMMA films rupture into droplets which first coalesce into large ones to reduce the surface free energy. Then the large droplets rupture into small ones to increase the contact area between PMMA blocks and acetone molecules resulting from ultimate migration of PMMA blocks to droplet surface, which is a novel dewetting process observed in spin-coated films for the first time. Copyright © 2016 Elsevier Inc. All rights reserved.

Ultrathin ZnS and ZnO Interfacial Passivation Layers for Atomic-Layer-Deposited HfO2 Films on InP Substrates.

PubMed

Kim, Seung Hyun; Joo, So Yeong; Jin, Hyun Soo; Kim, Woo-Byoung; Park, Tae Joo

2016-08-17

Ultrathin ZnS and ZnO films grown by atomic layer deposition (ALD) were employed as interfacial passivation layers (IPLs) for HfO2 films on InP substrates. The interfacial layer growth during the ALD of the HfO2 film was effectively suppressed by the IPLs, resulting in the decrease of electrical thickness, hysteresis, and interface state density. Compared with the ZnO IPL, the ZnS IPL was more effective in reducing the interface state density near the valence band edge. The leakage current density through the film was considerably lowered by the IPLs because the film crystallization was suppressed. Especially for the film with the ZnS IPL, the leakage current density in the low-voltage region was significantly lower than that observed for the film with the ZnO IPL, because the direct tunneling current was suppressed by the higher conduction band offset of ZnS with the InP substrate.

Effects of background oxygen pressure on dielectric and ferroelectric properties of epitaxial (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films on SrTiO3

NASA Astrophysics Data System (ADS)

Abazari, M.; Akdoǧan, E. K.; Safari, A.

2008-11-01

Oxygen partial pressure (PO_2) in pulsed laser deposition significantly influences the composition, microstructure, and electrical properties of epitaxial misfit strain-relieved 450nm ⟨001⟩ oriented epitaxial (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films on SrRuO3 coated SrTiO3. Films deposited at 400mTorr exhibit high remnant and saturated polarization of 7.5 and 16.5μC /cm2, respectively, which is ˜100% increase over the ones grown at 100mTorr. The dielectric constant linearly increases from 220 to 450 with increasing PO2. The observed changes in surface morphology of the films and their properties are shown to be due to the suppression of volatile A-site cation loss.

Confined Transformation Derived Ultrathin Titanate Nanosheets/ Graphene Films for Excellent Na/K Ion Storage.

PubMed

Zeng, Cheng; Xie, Fangxi; Yang, Xianfeng; Jaroniec, Mietek; Zhang, Lei; Qiao, Shizhang

2018-05-02

Confined transformation of assembled two-dimensional MXene (titanium carbide) and reduced graphene oxide (rGO) nanosheets was employed to prepare the free-standing films of the integrated ultrathin sodium titanate (NTO)/potassium titanate (KTO) nanosheets sandwiched between graphene layers. The ultrathin Ti-based nanosheets reduce the diffusion distance while rGO layers enhance conductivity. Incorporation of graphene into the titanate films produced efficient binder-free anodes for ion storage. The resulting NTO/rGO electrode for sodium ion batteries exhibited an excellent rate performance and long cycling stability characterized by reversible capacity of 72 mA h g-1 at 5 A g-1 after 10000 cycles. Moreover, flexible KTO/rGO electrode for potassium ion batteries maintained a reversible capacity of 75 mA h g-1 after 700 cycles at 2 A g-1. These results demonstrate the superiority of the unique sandwich-type electrodes. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Restoring the magnetism of ultrathin LaMn O3 films by surface symmetry engineering

NASA Astrophysics Data System (ADS)

Peng, J. J.; Song, C.; Li, F.; Gu, Y. D.; Wang, G. Y.; Pan, F.

2016-12-01

The frustration of magnetization and conductivity properties of ultrathin manganite is detrimental to their device performance, preventing their scaling down process. Here we demonstrate that the magnetism of ultrathin LaMn O3 films can be restored by a SrTi O3 capping layer, which engineers the surface from a symmetry breaking induced out-of-plane orbital occupancy to the recovered in-plane orbital occupancy. The stabilized in-plane orbital occupancy would strengthen the intralayer double exchange and thus recovers the robust magnetism. This method is proved to be effective for films as thin as 2 unit cells, greatly shrinking the critical thickness of 6 unit cells for ferromagnetic LaMn O3 as demonstrated previously [Wang et al., Science 349, 716 (2015), 10.1126/science.aaa5198]. The achievement made in this work opens up new perspectives to an active control of surface states and thereby tailors the surface functional properties of transition metal oxides.

Magnetoresistance of antiferromagnetic Ir22Mn78-pinned spin filter specular spin valves

NASA Astrophysics Data System (ADS)

Hwang, J. Y.; Kim, M. Y.; Rhee, J. R.; Lee, S. S.; Hwang, D. G.; Yu, S. C.; Lee, H. B.

2004-06-01

Specular spin valves (SSVs) having the spin filter layer (SFL) in contact with the ultrathin free layer of composition Ta3/NiFe2/IrMn7/CoFe1/(NOL1)/CoFe2/Cu1.8/CoFe(tF)/Cu(tSF)/(NOL2)/Ta3.5 (in nm) deposited by magnetron sputtering were studied. For these antiferromagnetic Ir22Mn78-pinned spin filter specular spin valve (SFSSV) films, an optimal magnetoresistance (MR) ratio of 11.9% was obtained when both the free layer thickness (tF) and the SFL thickness (tSF) were 1.5 nm, and a MR ratio higher than 11% was maintained even when tF was reduced to 1.0 nm. This was due to an increase of specular electrons by the nano-oxide layer (NOL) and of current shunting through the SFL. Moreover, the interlayer coupling field (Hint) between the free layer and pinned layer could be explained by considering the RKKY and magnetostatic coupling. The coercivity of the free layer (Hcf) was significantly reduced as compared to traditional spin valves (TSV), and remained as low as 4 Oe when tF varied from 1 to 4 nm. It was found that the SFL made it possible to reduce the free layer thickness and enhance the MR ratio without degrading the soft magnetic property of the free layer.

Chain and mirophase-separated structures of ultrathin polyurethane films

NASA Astrophysics Data System (ADS)

Kojio, Ken; Uchiba, Yusuke; Yamamoto, Yasunori; Motokucho, Suguru; Furukawa, Mutsuhisa

2009-08-01

Measurements are presented how chain and microphase-separated structures of ultrathin polyurethane (PU) films are controlled by the thickness. The film thickness is varied by a solution concentration for spin coating. The systems are PUs prepared from commercial raw materials. Fourier-transform infrared spectroscopic measurement revealed that the degree of hydrogen bonding among hard segment chains decreased and increased with decreasing film thickness for strong and weak microphase separation systems, respectively. The microphase-separated structure, which is formed from hard segment domains and a surrounding soft segment matrix, were observed by atomic force microscopy. The size of hard segment domains decreased with decreasing film thickness, and possibility of specific orientation of the hard segment chains was exhibited for both systems. These results are due to decreasing space for the formation of the microphase-separated structure.

On the persistence of polar domains in ultrathin ferroelectric capacitors.

PubMed

Zubko, Pavlo; Lu, Haidong; Bark, Chung-Wung; Martí, Xavi; Santiso, José; Eom, Chang-Beom; Catalan, Gustau; Gruverman, Alexei

2017-07-19

The instability of ferroelectric ordering in ultra-thin films is one of the most important fundamental issues pertaining realization of a number of electronic devices with enhanced functionality, such as ferroelectric and multiferroic tunnel junctions or ferroelectric field effect transistors. In this paper, we investigate the polarization state of archetypal ultrathin (several nanometres) ferroelectric heterostructures: epitaxial single-crystalline BaTiO 3 films sandwiched between the most habitual perovskite electrodes, SrRuO 3 , on top of the most used perovskite substrate, SrTiO 3 . We use a combination of piezoresponse force microscopy, dielectric measurements and structural characterization to provide conclusive evidence for the ferroelectric nature of the relaxed polarization state in ultrathin BaTiO 3 capacitors. We show that even the high screening efficiency of SrRuO 3 electrodes is still insufficient to stabilize polarization in SrRuO 3 /BaTiO 3 /SrRuO 3 heterostructures at room temperature. We identify the key role of domain wall motion in determining the macroscopic electrical properties of ultrathin capacitors and discuss their dielectric response in the light of the recent interest in negative capacitance behaviour.

Observations on Si-based micro-clusters embedded in TaN thin film deposited by co-sputtering with oxygen contamination

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

Lee, Young Mi; Jung, Min-Sang; Choi, Duck-Kyun, E-mail: duck@hanyang.ac.kr, E-mail: mcjung@oist.jp

2015-08-15

Using scanning electron microscopy (SEM) and high-resolution x-ray photoelectron spectroscopy with the synchrotron radiation we investigated Si-based micro-clusters embedded in TaSiN thin films having oxygen contamination. TaSiN thin films were deposited by co-sputtering on fixed or rotated substrates and with various power conditions of TaN and Si targets. Three types of embedded micro-clusters with the chemical states of pure Si, SiO{sub x}-capped Si, and SiO{sub 2}-capped Si were observed and analyzed using SEM and Si 2p and Ta 4f core-level spectra were derived. Their different resistivities are presumably due to the different chemical states and densities of Si-based micro-clusters.

Spin dynamics and frequency dependence of magnetic damping study in soft ferromagnetic FeTaC film with a stripe domain structure

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

Samantaray, B., E-mail: iitg.biswanath@gmail.com; Ranganathan, R.; Mandal, P.

Perpendicular magnetic anisotropy (PMA) and low magnetic damping are the key factors for the free layer magnetization switching by spin transfer torque technique in magnetic tunnel junction devices. The magnetization precessional dynamics in soft ferromagnetic FeTaC thin film with a stripe domain structure was explored in broad band frequency range by employing micro-strip ferromagnetic resonance technique. The polar angle variation of resonance field and linewidth at different frequencies have been analyzed numerically using Landau-Lifshitz-Gilbert equation by taking into account the total free energy density of the film. The numerically estimated parameters Landé g-factor, PMA constant, and effective magnetization are foundmore » to be 2.1, 2 × 10{sup 5} erg/cm{sup 3} and 7145 Oe, respectively. The frequency dependence of Gilbert damping parameter (α) is evaluated by considering both intrinsic and extrinsic effects into the total linewidth analysis. The value of α is found to be 0.006 at 10 GHz and it increases monotonically with decreasing precessional frequency.« less

Fabrication of (K0.5Na0.5)(Nb0.7Ta0.3)O3 thick films by electrophoretic deposition

NASA Astrophysics Data System (ADS)

Vineetha, P.; Saravanan, K. Venkata

2018-05-01

(K0.5Na0.5)(Nb0.7Ta0.3)O3 (KNNT) thick films were prepared by electrophoretic deposition method on copper plates (substrates). Prior to the deposition, stable suspensions of KNNT powder were prepared in isopropyl alcohol medium with and without adding triethanolamine (TEA) as dispersant. The optical transmittance spectra with time for both the suspensions were recorded and compared. Suspensions with dispersant has shown low transmittance, which indicate that the particles were dispersed very well in isopropyl alcohol. Fourier Transform Infrared (FTIR) spectroscopy was used to analyze the adsorption of TEA on KNNT particles. Suspension with dispersant was used for electrophoretic deposition. The depositions were carried out at various d.c voltages, keeping the deposition duration and inter electrode distance constant. X-Ray diffraction was used for the phase analysis of the films.

Ultrathin Composite Polymeric Membranes for CO2 /N2 Separation with Minimum Thickness and High CO2 Permeance.

PubMed

Benito, Javier; Sánchez-Laínez, Javier; Zornoza, Beatriz; Martín, Santiago; Carta, Mariolino; Malpass-Evans, Richard; Téllez, Carlos; McKeown, Neil B; Coronas, Joaquín; Gascón, Ignacio

2017-10-23

The use of ultrathin films as selective layers in composite membranes offers significant advantages in gas separation for increasing productivity while reducing the membrane size and energy costs. In this contribution, composite membranes have been obtained by the successive deposition of approximately 1 nm thick monolayers of a polymer of intrinsic microporosity (PIM) on top of dense membranes of the ultra-permeable poly[1-(trimethylsilyl)-1-propyne] (PTMSP). The ultrathin PIM films (30 nm in thickness) demonstrate CO 2 permeance up to seven times higher than dense PIM membranes using only 0.04 % of the mass of PIM without a significant decrease in CO 2 /N 2 selectivity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Atomic layer deposited TaCy metal gates: Impact on microstructure, electrical properties, and work function on HfO2 high-k dielectrics

NASA Astrophysics Data System (ADS)

Triyoso, D. H.; Gregory, R.; Schaeffer, J. K.; Werho, D.; Li, D.; Marcus, S.; Wilk, G. D.

2007-11-01

TaCy has been reported to have the appropriate work function for negative metal-oxide semiconductor metal in high-k metal-oxide field-effect transistors. As device size continues to shrink, a conformal deposition for metal gate electrodes is needed. In this work, we report on the development and characterization of a novel TaCy process by atomic layer deposition (ALD). Detailed physical properties of TaCy films are studied using ellipsometry, a four-point probe, Rutherford backscattering spectrometry (RBS), x-ray photoelectron spectroscopy (XPS), and x-ray diffraction (XRD). RBS and XPS analysis indicate that TaCy films are near-stoichiometric, nitrogen free, and have low oxygen impurities. Powder XRD spectra showed that ALD films have a cubic microstructure. XPS carbon bonding studies revealed that little or no glassy carbon is present in the bulk of the film. Excellent electrical properties are obtained using ALD TaCy as a metal gate electrode. Well-behaved capacitance-voltage characteristics with ALD HfO2 gate dielectrics are demonstrated for TaCy thicknesses of 50, 100, and 250 Å. A low fixed charge (˜2-4×10-11 cm-2) is observed for all ALD HfO2/ALD TaCy devices. Increasing the thickness of ALD TaCy results in a decrease in work function (4.77 to 4.54 eV) and lower threshold voltages.

Oxygen related recombination defects in Ta{sub 3}N{sub 5} water splitting photoanode

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

Fu, Gao; Yu, Tao, E-mail: yscfei@nju.edu.cn, E-mail: yutao@nju.edu.cn; Zou, Zhigang

2015-10-26

A key route to improving the performance of Ta{sub 3}N{sub 5} photoelectrochemical film devices in solar driving water splitting to hydrogen is to understand the nature of the serious recombination of photo-generated carriers. Here, by using the temperature-dependent photoluminescence (PL) spectrum, we confirmed that for the Ta{sub 3}N{sub 5} films prepared by nitriding Ta{sub 2}O{sub 5} precursor, one PL peak at 561 nm originates from deep-level defects recombination of the oxygen-enriched Ta{sub 3}N{sub 5} phases, and another one at 580 nm can be assigned to band recombination of Ta{sub 3}N{sub 5} itself. Both of the two bulk recombination processes may decrease themore » photoelectrochemical performance of Ta{sub 3}N{sub 5}. It was difficult to remove the oxygen-enriched impurities in Ta{sub 3}N{sub 5} films by increasing the nitriding temperatures due to their high thermodynamically stability. In addition, a broadening PL peak between 600 and 850 nm resulting from oxygen related surface defects was observed by the low-temperature PL measurement, which may induce the surface recombination of photo-generated carriers and can be removed by increasing the nitridation temperature. Our results provided direct experimental evidence to understand the effect of oxygen-related crystal defects in Ta{sub 3}N{sub 5} films on its photoelectric performance.« less

Continuous Ultra-Thin MOS2 Films Grown by Low-Temperature Physical Vapor Deposition (Postprint)

DTIC Science & Technology

2014-07-01

MoS2 target of 99.95% purity. The SiO2 and highly oriented pyrolitic graphite (HOPG) substrates were intro- duced via a vacuum load- lock and mounted on...im- mediately prior insertion into a sample vacuum load- lock . In this work, the samples were heated to 350 C and allowed to rotate at approximately...136805 (2010). 6H. Terrones, F. Lopez-Urias, and M. Terrones, Sci. Rep. 3(203), 1549 (2013). 7H. Li, Q. Zhang, C. C. R. Yap, B. K. Tay, T. H. T. Edwin

High resolution electron energy loss spectroscopy of spin waves in ultra-thin film - The return of the adiabatic approximation?

NASA Astrophysics Data System (ADS)

Ibach, Harald

2014-12-01

The paper reports on recent considerable improvements in electron energy loss spectroscopy (EELS) of spin waves in ultra-thin films. Spin wave spectra with 4 meV resolution are shown. The high energy resolution enables the observation of standing modes in ultra-thin films in the wave vector range of 0.15 Å- 1 < q|| < 0.3 Å- 1. In this range, Landau damping is comparatively small and standing spin wave modes are well-defined Lorentzians for which the adiabatic approximation is well suited, an approximation which was rightly dismissed by Mills and collaborators for spin waves near the Brillouin zone boundary. With the help of published exchange coupling constants, the Heisenberg model, and a simple model for the spectral response function, experimental spectra for Co-films on Cu(100) as well as for Co films capped with further copper layers are successfully simulated. It is shown that, depending on the wave vector and film thickness, the most prominent contribution to the spin wave spectrum may come from the first standing mode, not from the so-called surface mode. In general, the peak position of a low-resolution spin wave spectrum does not correspond to a single mode. A discussion of spin waves based on the "dispersion" of the peak positions in low resolution spectra is therefore subject to errors.

Combined three-axis surface magneto-optical Kerr effects in the study of surface and ultrathin-film magnetism

NASA Astrophysics Data System (ADS)

Yang, Z. J.; Scheinfein, M. R.

1993-12-01

Surface and ultrathin-film magnetocrystalline anisotropy in epitaxial fcc Fe thin films grown on room-temperature Cu(100) single crystals has been investigated, in situ, by the combined surface magneto-optical Kerr effects (SMOKE). In polar, longitudinal, and transverse Kerr effects, the direction of the applied magnetic field must be distinguished from the direction of magnetization during the switching process. For arbitrary orientations of the magnetization and field axis relative to the optical scattering plane, any of the three Kerr effects may contribute to the detected signal. A general expression for the normalized light intensity sensed by a photodiode detector, involving all three combined Kerr effects, is obtained both in the ultrathin-film limit and for bulk, at general oblique incidence angles and with different orientations of the polarizer, modulator, and analyzer. This expression is used to interpret the results of fcc Fe/Cu(100) SMOKE measurements. For films grown at room temperature, polar and longitudinal Kerr-effect magnetization loops show that the easy axis of magnetization rotates from the (canted) out-of-plane direction to the in-plane direction at a thickness of about 4.7 monolayers. Transverse Kerr-effect measurements indicate that the in-plane easy axes are biaxial.

Ultrathin Nanocrystalline Diamond Films with Silicon Vacancy Color Centers via Seeding by 2 nm Detonation Nanodiamonds.

PubMed

Stehlik, Stepan; Varga, Marian; Stenclova, Pavla; Ondic, Lukas; Ledinsky, Martin; Pangrac, Jiri; Vanek, Ondrej; Lipov, Jan; Kromka, Alexander; Rezek, Bohuslav

2017-11-08

Color centers in diamonds have shown excellent potential for applications in quantum information processing, photonics, and biology. Here we report chemical vapor deposition (CVD) growth of nanocrystalline diamond (NCD) films as thin as 5-6 nm with photoluminescence (PL) from silicon-vacancy (SiV) centers at 739 nm. Instead of conventional 4-6 nm detonation nanodiamonds (DNDs), we prepared and employed hydrogenated 2 nm DNDs (zeta potential = +36 mV) to form extremely dense (∼1.3 × 10 13 cm -2 ), thin (2 ± 1 nm), and smooth (RMS roughness < 0.8 nm) nucleation layers on an Si/SiO x substrate, which enabled the CVD growth of such ultrathin NCD films in two different and complementary microwave (MW) CVD systems: (i) focused MW plasma with an ellipsoidal cavity resonator and (ii) pulsed MW plasma with a linear antenna arrangement. Analytical ultracentrifuge, infrared and Raman spectroscopies, atomic force microscopy, and scanning electron microscopy are used for detailed characterization of the 2 nm H-DNDs and the nucleation layer as well as the ultrathin NCD films. We also demonstrate on/off switching of the SiV center PL in the NCD films thinner than 10 nm, which is achieved by changing their surface chemistry.

78 FR 19647 - Initiation of Five-Year (“Sunset”) Review

Federal Register 2010, 2011, 2012, 2013, 2014

2013-04-02

... 731-TA-933....... India Polyethylene Dana Mermelstein Terephthalate (Pet) (202) 482-1391. Film (2nd...-1391. Film (2nd Review). A-583-837 731-TA-934....... Taiwan Polyethylene Dana Mermelstein Terephthalate (Pet) (202) 482-1391. Film (2nd Review). With respect to the orders on Light-Walled Rectangular Pipe...

Interfacial stability of ultrathin films of magnetite Fe3O4 (111) on Al2O3(001) grown by ozone-assisted molecular-beam epitaxy

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

Hong, Hawoong; Kim, Jongjin; Fang, Xinyue

Thin films of iron oxides including magnetite (Fe3O4) and hematite (α-Fe2O3) have many important applications. Both forms of oxide can occur naturally during film growth by iron deposition under various oxidation environment; an important issue is to understand and control the process resulting in a single-phase film. We have performed in-situ real-time studies using x-ray diffraction of such film growth on sapphire (001) under pure ozone by monitoring the (00L) rod. Stable magnetite growth can be maintained at growth temperatures below 600° C up to a certain critical film thickness, beyond which the growth becomes hematite. The results demonstrate themore » importance of interfacial interaction in stabilizing the magnetite phase.« less

Uncovering the Fundamental Nature of Tribological Interfaces: High Resolution Tribology and Spectroscopy of Ultrahard Nanostructured Diamond Films for MEMS and Beyond

DTIC Science & Technology

2007-12-31

Wisconsin-Madison) for 2? ol !> o "S \\ % M 31 Statement of Objectives The original objectives of the proposal were as follows: 1. Obtain high-quality...performed multiple PEEM experiments on wear tracks on carbon-based films and polysilicon micro-electro mechanical systems (MEMS) devices, a comprehensive... polysilicon MEMS device known as the "nanotractor", and studies of the structure and composition of UNCD, ta-C, and nanocrystalline diamond (NCD) films. They

Partially Reduced Graphene Oxide Modified Tetrahedral Amorphous Carbon Thin-Film Electrodes as a Platform for Nanomolar Detection of Dopamine

DOE PAGES

Wester, Niklas; Sainio, Sami; Palomäki, Tommi; ...

2017-03-16

Here, we present for the first time tetrahedral amorphous carbon (ta-C)—a partially reduced graphene oxide (PRGO) hybrid electrode nanomaterial platform for electrochemical sensing of dopamine (DA). Graphene oxide was synthesized with the modified Hummer’s method. Before modification of ta-C by drop casting, partial reduction of the GO was carried out to improve electrochemical properties and adhesion to the ta-C thin film. A facile nitric acid treatment that slightly reoxidized the surface and modified the surface chemistry was subsequently performed to further improve the electrochemical properties of the electrodes. The largest relative increase was seen in carboxyl groups. The HNO 3more » treatment increased the sensitivity toward DA and AA and resulted in a cathodic shift in the oxidation of AA. The fabricated hybrid electrodes were characterized with scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and electrochemical impedance spectroscopy (EIS). Moreover, compared to the plain ta-C electrode the hybrid electrode was shown to exhibit superior sensitivity and selectivity toward DA in the presence of ascorbic acid (AA), enabling simultaneous sensing of AA and DA close to the physiological concentrations by cyclic voltammetry (CV) and by differential pulse voltammetry (DPV). Two linear ranges of 0–1 μM and 1–100 μM and a detection limit (S/N = 3.3) of 2.6 nM for DA were determined by means of cyclic voltammetry. Thus, the current work provides a fully CMOS-compatible carbon based hybrid nanomaterial that shows potential for in vivo measurements of DA.« less

Partially Reduced Graphene Oxide Modified Tetrahedral Amorphous Carbon Thin-Film Electrodes as a Platform for Nanomolar Detection of Dopamine

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

Wester, Niklas; Sainio, Sami; Palomäki, Tommi

Here, we present for the first time tetrahedral amorphous carbon (ta-C)—a partially reduced graphene oxide (PRGO) hybrid electrode nanomaterial platform for electrochemical sensing of dopamine (DA). Graphene oxide was synthesized with the modified Hummer’s method. Before modification of ta-C by drop casting, partial reduction of the GO was carried out to improve electrochemical properties and adhesion to the ta-C thin film. A facile nitric acid treatment that slightly reoxidized the surface and modified the surface chemistry was subsequently performed to further improve the electrochemical properties of the electrodes. The largest relative increase was seen in carboxyl groups. The HNO 3more » treatment increased the sensitivity toward DA and AA and resulted in a cathodic shift in the oxidation of AA. The fabricated hybrid electrodes were characterized with scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and electrochemical impedance spectroscopy (EIS). Moreover, compared to the plain ta-C electrode the hybrid electrode was shown to exhibit superior sensitivity and selectivity toward DA in the presence of ascorbic acid (AA), enabling simultaneous sensing of AA and DA close to the physiological concentrations by cyclic voltammetry (CV) and by differential pulse voltammetry (DPV). Two linear ranges of 0–1 μM and 1–100 μM and a detection limit (S/N = 3.3) of 2.6 nM for DA were determined by means of cyclic voltammetry. Thus, the current work provides a fully CMOS-compatible carbon based hybrid nanomaterial that shows potential for in vivo measurements of DA.« less

Enhanced light absorption in an ultrathin silicon solar cell utilizing plasmonic nanostructures

NASA Astrophysics Data System (ADS)

Xiao, Sanshui; Mortensen, Niels A.

2012-10-01

Nowadays, bringing photovoltaics to the market is mainly limited by high cost of electricity produced by the photovoltaic solar cell. Thin-film photovoltaics offers the potential for a significant cost reduction compared to traditional photovoltaics. However, the performance of thin-film solar cells is generally limited by poor light absorption. We propose an ultrathin-film silicon solar cell configuration based on SOI structure, where the light absorption is enhanced by use of plasmonic nanostructures. By placing a one-dimensional plasmonic nanograting on the bottom of the solar cell, the generated photocurrent for a 200 nm-thickness crystalline silicon solar cell can be enhanced by 90% in the considered wavelength range. These results are paving a promising way for the realization of high-efficiency thin-film solar cells.

Local variation of fragility and glass transition temperature of ultra-thin supported polymer films.

PubMed

Hanakata, Paul Z; Douglas, Jack F; Starr, Francis W

2012-12-28

Despite extensive efforts, a definitive picture of the glass transition of ultra-thin polymer films has yet to emerge. The effect of film thickness h on the glass transition temperature T(g) has been widely examined, but this characterization does not account for the fragility of glass-formation, which quantifies how rapidly relaxation times vary with temperature T. Accordingly, we simulate supported polymer films of a bead-spring model and determine both T(g) and fragility, both as a function of h and film depth. We contrast changes in the relaxation dynamics with density ρ and demonstrate the limitations of the commonly invoked free-volume layer model. As opposed to bulk polymer materials, we find that the fragility and T(g) do not generally vary proportionately. Consequently, the determination of the fragility profile--both locally and for the film as a whole--is essential for the characterization of changes in film dynamics with confinement.

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.

Tribological properties of amorphous hydrogenated (a-C:H) and hydrogen-free tetrahedral (ta-C) diamond-like carbon coatings under jatropha biodegradable lubricating oil at different temperatures

NASA Astrophysics Data System (ADS)

Mobarak, H. M.; Masjuki, H. H.; Mohamad, E. Niza; Kalam, M. A.; Rashedul, H. K.; Rashed, M. M.; Habibullah, M.

2014-10-01

The application of diamond-like carbon (DLC) coatings on automotive components is emerging as a favorable strategy to address the recent challenges in the industry. DLC coatings can effectively lower the coefficient of friction (CoF) and wear rate of engine components, thereby improving their fuel efficiency and durability. The lubrication of ferrous materials can be enhanced by a large amount of unsaturated and polar components of oils. Therefore, the interaction between nonferrous coatings (e.g., DLC) and vegetable oil should be investigated. A ball-on-plate tribotester was used to run the experiments. Stainless steel plates coated with amorphous hydrogenated (a-C:H) DLC and hydrogen-free tetrahedral (ta-C) DLC that slide against 440C stainless steel ball were used to create a ball-on-plate tribotester. The wear track was investigated through scanning electron microscopy. Energy dispersive and X-ray photoelectron spectroscopies were used to analyze the tribofilm inside the wear track. Raman analysis was performed to investigate the structural changes in the coatings. At high temperatures, the CoF in both coatings decreased. The wear rate, however, increased in the a-C:H but decreased in the ta-C DLC-coated plates. The CoF and the wear rate (coated layer and counter surface) were primarily influenced by the graphitization of the coating. Tribochemical films, such as polyphosphate glass, were formed in ta-C and acted as protective layers. Therefore, the wear rate of the ta-C DLC was lower than that of the-C:H DLC.

Comparative analysis of the effects of tantalum doping and annealing on atomic layer deposited (Ta2O5)x(Al2O3)1-x as potential gate dielectrics for GaN/AlxGa1-xN/GaN high electron mobility transistors

NASA Astrophysics Data System (ADS)

Partida-Manzanera, T.; Roberts, J. W.; Bhat, T. N.; Zhang, Z.; Tan, H. R.; Dolmanan, S. B.; Sedghi, N.; Tripathy, S.; Potter, R. J.

2016-01-01

This paper describes a method to optimally combine wide band gap Al2O3 with high dielectric constant (high-κ) Ta2O5 for gate dielectric applications. (Ta2O5)x(Al2O3)1-x thin films deposited by thermal atomic layer deposition (ALD) on GaN-capped AlxGa1-xN/GaN high electron mobility transistor (HEMT) structures have been studied as a function of the Ta2O5 molar fraction. X-ray photoelectron spectroscopy shows that the bandgap of the oxide films linearly decreases from 6.5 eV for pure Al2O3 to 4.6 eV for pure Ta2O5. The dielectric constant calculated from capacitance-voltage measurements also increases linearly from 7.8 for Al2O3 up to 25.6 for Ta2O5. The effect of post-deposition annealing in N2 at 600 °C on the interfacial properties of undoped Al2O3 and Ta-doped (Ta2O5)0.12(Al2O3)0.88 films grown on GaN-HEMTs has been investigated. These conditions are analogous to the conditions used for source/drain contact formation in gate-first HEMT technology. A reduction of the Ga-O to Ga-N bond ratios at the oxide/HEMT interfaces is observed after annealing, which is attributed to a reduction of interstitial oxygen-related defects. As a result, the conduction band offsets (CBOs) of the Al2O3/GaN-HEMT and (Ta2O5)0.16(Al2O3)0.84/GaN-HEMT samples increased by ˜1.1 eV to 2.8 eV and 2.6 eV, respectively, which is advantageous for n-type HEMTs. The results demonstrate that ALD of Ta-doped Al2O3 can be used to control the properties of the gate dielectric, allowing the κ-value to be increased, while still maintaining a sufficient CBO to the GaN-HEMT structure for low leakage currents.

Ocular Protection from Laser Hazards. Phase 2

DTIC Science & Technology

1993-10-31

including optics,electronics and surface protection. Physical vapor deposition ( PVD ) is the commonly used method to produce thin film coatings . Standard...control computer. In this part of the program, we intended to investigate various binary combinations of the following coating materials: SiC 2, Ta2O5 ...80 [ o Ta2O5 60 40 U 20 0 i I I Thickness [nm] 0 50 100 150 200 250 Figure 2. Dependence of the temperature in the coating chamber as a function of

Rutherford forward scattering and elastic recoil detection (RFSERD) as a method for characterizing ultra-thin films

DOE PAGES

Lohn, Andrew J.; Doyle, Barney L.; Stein, Gregory J.; ...

2014-04-03

We present a novel ion beam analysis technique combining Rutherford forward scattering and elastic recoil detection (RFSERD) and demonstrate its ability to increase efficiency in determining stoichiometry in ultrathin (5-50 nm) films as compared to Rutherford backscattering. In the conventional forward geometries, scattering from the substrate overwhelms the signal from light atoms but in RFSERD, scattered ions from the substrate are ranged out while forward scattered ions and recoiled atoms from the thin film are simultaneously detected in a single detector. Lastly, the technique is applied to tantalum oxide memristors but can be extended to a wide range of materialsmore » systems.« less

Insulator at the ultrathin limit: MgO on Ag(001).

PubMed

Schintke, S; Messerli, S; Pivetta, M; Patthey, F; Libioulle, L; Stengel, M; De Vita, A; Schneider, W D

2001-12-31

The electronic structure and morphology of ultrathin MgO films epitaxially grown on Ag(001) were investigated using low-temperature scanning tunneling spectroscopy and scanning tunneling microscopy. Layer-resolved differential conductance (dI/dU) measurements reveal that, even at a film thickness of three monolayers, a band gap of about 6 eV is formed corresponding to that of the MgO(001) single-crystal surface. This finding is confirmed by layer-resolved calculations of the local density of states based on density functional theory.

Nanopatterning of magnetic domains: Fe coverage of self-assembled alumina nanostructure

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

Wu, Qibin; Wang, Bo -Yao; Lin, Wen -Chin

2015-08-19

Nanosized ultrathin magnetic films were prepared by controlling the deposition of Fe onto an oxidized NiAl(001) surface with an alumina nanostructure on it. Because the ultrathin ferromagnetic Fe films on the bare NiAl(001) surface are separated by paramagnetic Fe nanoparticles on the alumina stripes, as determined by scanning electron microscopy with spin analysis, they form rectangular domains with sizes ranging from tens of nanometer to larger than a micrometer. Furthermore, magnetic domain patterning can thus be achieved by controlling the Fe coverage and nanostructured template.

Highly Flexible and Transparent Ag Nanowire Electrode Encapsulated with Ultra-Thin Al2O3: Thermal, Ambient, and Mechanical Stabilities

PubMed Central

Hwang, Byungil; An, Youngseo; Lee, Hyangsook; Lee, Eunha; Becker, Stefan; Kim, Yong-Hoon; Kim, Hyoungsub

2017-01-01

There is an increasing demand in the flexible electronics industry for highly robust flexible/transparent conductors that can withstand high temperatures and corrosive environments. In this work, outstanding thermal and ambient stability is demonstrated for a highly transparent Ag nanowire electrode with a low electrical resistivity, by encapsulating it with an ultra-thin Al2O3 film (around 5.3 nm) via low-temperature (100 °C) atomic layer deposition. The Al2O3-encapsulated Ag nanowire (Al2O3/Ag) electrodes are stable even after annealing at 380 °C for 100 min and maintain their electrical and optical properties. The Al2O3 encapsulation layer also effectively blocks the permeation of H2O molecules and thereby enhances the ambient stability to greater than 1,080 h in an atmosphere with a relative humidity of 85% at 85 °C. Results from the cyclic bending test of up to 500,000 cycles (under an effective strain of 2.5%) confirm that the Al2O3/Ag nanowire electrode has a superior mechanical reliability to that of the conventional indium tin oxide film electrode. Moreover, the Al2O3 encapsulation significantly improves the mechanical durability of the Ag nanowire electrode, as confirmed by performing wiping tests using isopropyl alcohol. PMID:28128218

Influence of tantalum underlayer on magnetization dynamics in Ni{sub 81}Fe{sub 19} films

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

Kwon, Jae Hyun; Deorani, Praveen; Yoon, Jungbum

2015-07-13

The effect of tantalum (Ta) underlayer is investigated in Ni{sub 81}Fe{sub 19} thin films for magnetization dynamics. The damping parameters extracted from spin wave measurements increase systematically with increasing Ta thickness, whereas the damping parameters from ferromagnetic resonance measurements are found to be weakly dependent on the Ta thickness. The difference is attributed to propagating properties of spin wave and short spin diffusion length in Ta. The group velocity of spin waves is found to be constant for different Ta thicknesses, and nonreciprocity of spin waves is not affected by the Ta thickness. The experimental observations are supported by micromagneticmore » simulations.« 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.

Ultrathin IBAD MgO films for epitaxial growth on amorphous substrates and sub-50 nm membranes

DOE PAGES

Wang, Siming; Antonakos, C.; Bordel, C.; ...

2016-11-07

Here, a fabrication process has been developed for high energy ion beam assisted deposition (IBAD) biaxial texturing of ultrathin (~1 nm) MgO films, using a high ion-to-atom ratio and post-deposition annealing instead of a homoepitaxial MgO layer. These films serve as the seed layer for epitaxial growth of materials on amorphous substrates such as electron/X-ray transparent membranes or nanocalorimetry devices. Stress measurements and atomic force microscopy of the MgO films reveal decreased stress and surface roughness, while X-ray diffraction of epitaxial overlayers demonstrates the improved crystal quality of films grown epitaxially on IBAD MgO. The process simplifies the synthesis ofmore » IBAD MgO, fundamentally solves the “wrinkle” issue induced by the homoepitaxial layer on sub-50 nm membranes, and enables studies of epitaxial materials in electron/X-ray transmission and nanocalorimetry.« less

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.

Fabrication and stability investigation of ultra-thin transparent and flexible Cu-Ag-Au tri-layer film on PET

NASA Astrophysics Data System (ADS)

Prakasarao, Ch Surya; D'souza, Slavia Deeksha; Hazarika, Pratim; Karthiselva N., S.; Ramesh Babu, R.; Kovendhan, M.; Kumar, R. Arockia; Joseph, D. Paul

2018-04-01

The need for transparent conducting electrodes with high transmittance, low sheet resistance and flexibility to replace Indium Tin Oxide is ever growing. We have deposited and studied the performance of ultra-thin Cu-Ag-Au tri-layer films over a flexible poly-ethylene terephthalate substrate. Scotch tape test showed good adhesion of the metallic film. Transmittance of the tri-layer was around 40 % in visible region. Optical profiler measurements were done to study the surface features. The XRD pattern revealed that film was amorphous. Sheet resistance measured by four probe technique was around 7.7 Ohm/Δ and was stable up to 423 K. The transport parameters by Hall effect showed high conductivity and carrier concentration with a mobility of 5.58 cm2/Vs. Tests performed in an indigenously designed bending unit indicated the films to be stable both mechanically and electrically even after 50,000 bending cycles.

Composite membranes from photochemical synthesis of ultrathin polymer films

NASA Astrophysics Data System (ADS)

Liu, Chao; Martin, Charles R.

1991-07-01

THERE has recently been a resurgence of interest in synthetic membranes and membrane-based processes1-12. This is motivated by a wide variety of technological applications, such as chemical separations1-7, bioreactors and sensors8,9, energy conversion10,11 and drug-delivery systems12. Many of these technologies require the ability to prepare extremely thin, defect-free synthetic (generally polymeric) films, which are supported on microporous supports to form composite membranes. Here we describe a method for producing composite membranes of this sort that incorporate high-quality polymer films less than 50-nm thick. The method involves interfacial photopolymerization of a thin polymer film on the surface of the microporous substrate. We have been able to use this technique to synthesize a variety of functionalized ultrathin films based on electroactive, photoactive and ion-exchange polymers. We demonstrate the method here with composite membranes that show exceptional gas-transport properties.

Image potential states at transition metal oxide surfaces: A time-resolved two-photon photoemission study on ultrathin NiO films

NASA Astrophysics Data System (ADS)

Gillmeister, K.; Kiel, M.; Widdra, W.

2018-02-01

For well-ordered ultrathin films of NiO(001) on Ag(001), a series of unoccupied states below the vacuum level has been found. The states show a nearly free electron dispersion and binding energies which are typical for image potential states. By time-resolved two-photon photoemission (2PPE), the lifetimes of the first three states and their dependence on oxide film thickness are determined. For NiO film thicknesses between 2 and 4 monolayers (ML), the lifetime of the first state is in the range of 28-42 fs and shows an oscillatory behavior with increasing thickness. The values for the second state decrease monotonically from 88 fs for 2 ML to 33 fs for 4 ML. These differences are discussed in terms of coupling of the unoccupied states to the layer-dependent electronic structure of the growing NiO film.

CdO nanosheet film with a (200)-preferred orientation with sensitivity to liquefied petroleum gas (LPG) at low-temperatures.

PubMed

Cui, Guangliang; Li, Zimeng; Gao, Liang; Zhang, Mingzhe

2012-12-21

CdO nanosheet film can be synthesized by electrochemical deposition in an ultra-thin liquid layer by using Cd(NO(3))(2) and HNO(3) as source materials for Cd and oxygen respectively. HNO(3) is also used to adjust the pH of the electrolyte. Studies on the detailed structure indicate that the synthesized CdO nanosheet film has a face-centered cubic structure with (200)-preferred orientation. The response of the CdO nanosheet film to liquefied petroleum gas (LPG) at low temperature has been significantly improved by the novel structure of film. It has exhibited excellent sensitivity and selectivity to LPG at low temperature. A new growth mechanism of electrochemical deposition has been proposed to elaborate the formation of nanosheet in an ultra-thin liquid layer. The self-oscillation of potential in the growth interface and intermediate hydroxide are responsible for the formation of nanosheets.

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.

Static and dynamic properties of Co2FeAl thin films: Effect of MgO and Ta as capping layers

NASA Astrophysics Data System (ADS)

Husain, Sajid; Barwal, Vineet; Kumar, Ankit; Behera, Nilamani; Akansel, Serkan; Goyat, Ekta; Svedlindh, Peter; Chaudhary, Sujeet

2017-05-01

The influence of MgO and Ta capping layers on the static and dynamic magnetic properties of Co2FeAl (CFA) Heusler alloy thin films has been investigated. It is observed that the CFA film deposited with MgO capping layer is preeminent compared to the uncapped or Ta capped CFA film. In particular, the magnetic inhomogeneity contribution to the ferromagnetic resonance line broadening and damping constant are found to be minimal for the MgO capped CFA thin film i.e., 0.12±0.01 Oe and 0.0074±0.00014, respectively. The saturation magnetization was found to be 960±25emu/cc.

Microstructure, Surface Characterization, and Electrochemical Behavior of New Ti-Zr-Ta-Ag Alloy in Simulated Human Electrolyte

NASA Astrophysics Data System (ADS)

Vasilescu, Cora; Drob, Silviu Iulian; Osiceanu, Petre; Moreno, Jose Maria Calderon; Prodana, Mariana; Ionita, Daniela; Demetrescu, Ioana; Marcu, Maria; Popovici, Ion Alexandru; Vasilescu, Ecaterina

2017-01-01

A new Ti-20Zr-5Ta-2Ag alloy was elaborated and characterized regarding its microstructure, its native passive film composition and thickness, its surface wettability, its electrochemical behavior in Ringer solution of different pH values, and its ion release. The new alloy has a bi-phase, α + β, acicular, homogeneous microstructure (scanning electron microscopy (SEM)). Its native passive film (12-nm thicknesses) consists of the protective TiO2, ZrO2, and Ta2O5 oxides, Ti and Ta suboxides, and metallic Ag (X-ray photoelectron spectroscopy (XPS) data). The alloy possesses high hydrophilic properties. The main electrochemical parameters of the new alloy are superior to those of Ti as a result of the beneficial influence of Zr, Ta, and Ag alloying elements, which reinforce its native passive film. Electrochemical impedance spectroscopy (EIS) spectra in Ringer solutions for the new alloy displayed better values of impedances and phase angles, proving a more insulate passive film than that on the Ti surface. The main corrosion parameters for the new Ti-20Zr-5Ta-2Ag alloy are more favorable by about 25 to 38 times than those of Ti, confirming extremely resistant passive film. The new Ti-20Zr-5Ta-2Ag alloy releases into Ringer solution low quantities of Ti4+, Zr4+ metallic ions (inductively coupled plasma-mass spectroscopy (ICP-MS)). The Ag+ ions are released in low quantity, conferring to this alloy's low antibacterial activity. All experimental results show that the new Ti-20Zr-5Ta-2Ag alloy fulfills the requirements for biocompatibility, corrosion resistance, and antibacterial protection.

Comparisons of immersion and electrochemical properties of highly biocompatible Ti-15Zr-4Nb-4Ta alloy and other implantable metals for orthopedic implants

NASA Astrophysics Data System (ADS)

Okazaki, Yoshimitsu; Nagata, Hiroyuki

2012-12-01

Metal release from implantable metals and the properties of oxide films formed on alloy surfaces were analyzed, focusing on the highly biocompatible Ti-15Zr-4Nb-4Ta alloy. The thickness and electrical resistance (Rp) of the oxide film on such an alloy were compared with those of other implantable metals. The quantity of metal released during a 1-week immersion test was considerably smaller for the Ti-15Zr-4Nb-4Ta than the Ti-6Al-4V alloy. The potential (E10) indicating a current density of 10 μA cm-2 estimated from the anodic polarization curve was significantly higher for the Ti-15Zr-4Nb-4Ta than the Ti-6Al-4V alloy and other metals. Moreover, the oxide film (4-7 nm thickness) formed on the Ti-15Zr-4Nb-4Ta surface is electrochemically robust. The oxide film mainly consisted of TiO2 with small amounts of ZrO2, Nb2O5 and Ta2O5 that made the film electrochemically stable. The Rp of Ti-15Zr-4Nb-4Ta was higher than that of Ti-6Al-4V, i.e. 0.9 Ω cm2 in 0.9% NaCl and 1.3 Ω cm2 in Eagle's medium. This Rp was approximately five-fold higher than that of stainless steel, which has a history of more than 40 years of clinical use in the human body. Ti-15Zr-4Nb-4Ta is a potential implant material for long-term clinical use. Moreover, E10 and Rp were found to be useful parameters for assessing biological safety.

Correlation between the transport mechanisms in conductive filaments inside Ta2O5-based resistive switching devices and in substoichiometric TaOx thin films

NASA Astrophysics Data System (ADS)

Rosário, Carlos M. M.; Thöner, Bo; Schönhals, Alexander; Menzel, Stephan; Wuttig, Matthias; Waser, Rainer; Sobolev, Nikolai A.; Wouters, Dirk J.

2018-05-01

Conductive filaments play a key role in redox-based resistive random access memory (ReRAM) devices based on the valence change mechanism, where the change of the resistance is ascribed to the modulation of the oxygen content in a local region of these conductive filaments. However, a deep understanding of the filaments' composition and structure is still a matter of debate. We approached the problem by comparing the electronic transport, at temperatures from 300 K down to 2 K, in the filaments and in TaOx films exhibiting a substoichiometric oxygen content. The filaments were created in Ta (15 nm)/Ta2O5 (5 nm)/Pt crossbar ReRAM structures. In the TaOx thin films with various oxygen contents, the in-plane transport was studied. There is a close similarity between the electrical properties of the conductive filaments in the ReRAM devices and of the TaOx films with x ˜ 1, evidencing also no dimensionality difference for the electrical transport. More specifically, for both systems there are two different conduction processes: one in the higher temperature range (from 50 K up to ˜300 K), where the conductivity follows a √{ T } dependence, and one at lower temperatures (<50 K), where the conductivity follows the exp(-1 / √{ T } ) dependence. This suggests a strong similarity between the material composition and structure of the filaments and those of the substoichiometric TaOx films. We also discuss the temperature dependence of the conductivity in the framework of possible transport mechanisms, mainly of those normally observed for granular metals.

Release properties of tannic acid from hydrogen bond driven antioxidative cellulose nanofibrous films.

PubMed

Zhou, Bin; Hu, Xiaoqian; Zhu, Jinjin; Wang, Zhenzhen; Wang, Xichang; Wang, Mingfu

2016-10-01

Layer-by-layer (LBL) assembled films have been exploited for surface-mediated bioactive compound delivery. Here, an antioxidative hydrogen-bonded multilayer electrospun nanofibrous film was fabricated from tannic acid (TA), acting as a polyphenolic antioxidant, and poly(ethylene glycol) (PEG) via layer-by-layer assembly. It overcame the burst release behavior of nanofibrous carrier, due to the reversible/dynamic nature of hydrogen bond, which was responded to external stimuli. The PEG/TA nanofibrous films disassembled gradually and released TA to the media, when soaked in aqueous solutions. The release rate of TA increased with increasing bilayer number, pH and temperature, but decreased with enhancing ionic strength. The surface morphology of the nanofibrous mats was observed by scanning electron microscopy (SEM). The following antioxidant activity assay revealed that it could scavenge DPPH free radicals and ABTS(+) cation radicals, a major biological activity of polyphenols. This technology can be used to fabricate other phenolic-containing slowly releasing antioxidative nanofibrous films. Copyright © 2016 Elsevier B.V. All rights reserved.

Surface chirality of CuO thin films.

PubMed

Widmer, Roland; Haug, Franz-Josef; Ruffieux, Pascal; Gröning, Oliver; Bielmann, Michael; Gröning, Pierangelo; Fasel, Roman

2006-11-01

We present X-ray photoelectron spectroscopy (XPS) and X-ray photoelectron diffraction (XPD) investigations of CuO thin films electrochemically deposited on an Au(001) single-crystal surface from a solution containing chiral tartaric acid (TA). The presence of enantiopure TA in the deposition process results in a homochiral CuO surface, as revealed by XPD. On the other hand, XPD patterns of films deposited with racemic tartaric acid or the "achiral" meso-tartaric acid are completely symmetric. A detailed analysis of the experimental data using single scattering cluster calculations reveals that the films grown with l(+)-TA exhibit a CuO(1) orientation, whereas growth in the presence of d(-)-TA results in a CuO(11) surface orientation. A simple bulk-truncated model structure with two terminating oxygen layers reproduces the experimental XPD data. Deposition with alternating enantiomers of tartaric acid leads to CuO films of alternating chirality. Enantiospecifity of the chiral CuO surfaces is demonstrated by further deposition of CuO from a solution containing racemic tartaric acid. The pre-deposited homochiral films exhibit selectivity toward the same enantiomeric deposition pathway.

Raman Scattering from Tin

DTIC Science & Technology

2015-09-01

ARL-TR-7448 ● SEP 2015 US Army Research Laboratory Raman Scattering from Tin by Patrick A Folkes, Patrick Taylor, Charles Rong...REPORT TYPE 3. DATES COVERED 00-00-2015 to 00-00-2015 4. TITLE AND SUBTITLE Raman Scattering from Tin 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c... tin as an analytical tool for discerning specific allotropic differences in ultra-thin tin films, and discerning differences between the tin and the

Understanding the doping effects on the structural and electrical properties of ultrathin carbon nanotube networks

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

Zhou, Ying, E-mail: y-shuu@aist.go.jp; Shimada, Satoru; Azumi, Reiko

Similar to other semiconductor technology, doping of carbon nanotube (CNT) thin film is of great significance for performance improvement or modification. However, it still remains a challenge to seek a stable and effective dopant. In this paper, we unitize several spectroscopic techniques and electrical characterizations under various conditions to investigate the effects of typical dopants and related methods. Nitric acid (HNO{sub 3}) solution, I{sub 2} vapor, and CuI nanoparticles are used to modify a series of ultrathin CNT networks. Although efficient charge transfer is achieved initially after doping, HNO{sub 3} is not applicable because it suffers from severe reliability problemsmore » in structural and electrical properties, and it also causes a number of undesired structural defects. I{sub 2} vapor doping at 150 °C can form some stable C-I bonding structures, resulting in relatively more stable but less efficient electrical performances. CuI nanoparticles seem to be an ideal dopant. Photonic curing enables the manipulation of CuI, which not only results in the construction of novel CNT-CuI hybrid structures but also encourages the deepest level of charge transfer doping. The excellent reliability as well as processing feasibility identify the bright perspective of CNT-CuI hybrid film for practical applications.« less

Dry etching technologies for the advanced binary film

NASA Astrophysics Data System (ADS)

Iino, Yoshinori; Karyu, Makoto; Ita, Hirotsugu; Yoshimori, Tomoaki; Azumano, Hidehito; Muto, Makoto; Nonaka, Mikio

2011-11-01

ABF (Advanced Binary Film) developed by Hoya as a photomask for 32 (nm) and larger specifications provides excellent resistance to both mask cleaning and 193 (nm) excimer laser and thereby helps extend the lifetime of the mask itself compared to conventional photomasks and consequently reduces the semiconductor manufacturing cost [1,2,3]. Because ABF uses Ta-based films, which are different from Cr film or MoSi films commonly used for photomask, a new process is required for its etching technology. A patterning technology for ABF was established to perform the dry etching process for Ta-based films by using the knowledge gained from absorption layer etching for EUV mask that required the same Ta-film etching process [4]. Using the mask etching system ARES, which is manufactured by Shibaura Mechatronics, and its optimized etching process, a favorable CD (Critical Dimension) uniformity, a CD linearity and other etching characteristics were obtained in ABF patterning. Those results are reported here.

Comparison of the cohesive and delamination fatigue properties of atomic-layer-deposited alumina and titania ultrathin protective coatings deposited at 200 °C

PubMed Central

Sadeghi-Tohidi, Farzad; Samet, David; Graham, Samuel; Pierron, Olivier N

2014-01-01

The fatigue properties of ultrathin protective coatings on silicon thin films were investigated. The cohesive and delamination fatigue properties of 22 nm-thick atomic-layered-deposited (ALD) titania were characterized and compared to that of 25 nm-thick alumina. Both coatings were deposited at 200 °C. The fatigue rates are comparable at 30 °C, 50% relative humidity (RH) while they are one order of magnitude larger for alumina compared to titania at 80 °C, 90% RH. The improved fatigue performance is believed to be related to the improved stability of the ALD titania coating with water compared to ALD alumina, which may in part be related to the fact that ALD titania is crystalline, while ALD alumina is amorphous. Static fatigue crack nucleation and propagation was not observed. The underlying fatigue mechanism is different from previously documented mechanisms, such as stress corrosion cracking, and appears to result from the presence of compressive stresses and a rough coating–substrate interface. PMID:27877645

Highly efficient ultrathin-film amorphous silicon solar cells on top of imprinted periodic nanodot arrays

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

Yan, Wensheng, E-mail: yws118@gmail.com; Gu, Min, E-mail: mgu@swin.edu.au; Tao, Zhikuo

2015-03-02

The addressing of the light absorption and conversion efficiency is critical to the ultrathin-film hydrogenated amorphous silicon (a-Si:H) solar cells. We systematically investigate ultrathin a-Si:H solar cells with a 100 nm absorber on top of imprinted hexagonal nanodot arrays. Experimental evidences are demonstrated for not only notable silver nanodot arrays but also lower-cost ITO and Al:ZnO nanodot arrays. The measured external quantum efficiency is explained by the simulation results. The J{sub sc} values are 12.1, 13.0, and 14.3 mA/cm{sup 2} and efficiencies are 6.6%, 7.5%, and 8.3% for ITO, Al:ZnO, and silver nanodot arrays, respectively. Simulated optical absorption distribution shows high lightmore » trapping within amorphous silicon layer.« less

Layer thickness dependence of the current-induced effective field vector in Ta|CoFeB|MgO.

PubMed

Kim, Junyeon; Sinha, Jaivardhan; Hayashi, Masamitsu; Yamanouchi, Michihiko; Fukami, Shunsuke; Suzuki, Tetsuhiro; Mitani, Seiji; Ohno, Hideo

2013-03-01

Current-induced effective magnetic fields can provide efficient ways of electrically manipulating the magnetization of ultrathin magnetic heterostructures. Two effects, known as the Rashba spin orbit field and the spin Hall spin torque, have been reported to be responsible for the generation of the effective field. However, a quantitative understanding of the effective field, including its direction with respect to the current flow, is lacking. Here we describe vector measurements of the current-induced effective field in Ta|CoFeB|MgO heterostructrures. The effective field exhibits a significant dependence on the Ta and CoFeB layer thicknesses. In particular, a 1 nm thickness variation of the Ta layer can change the magnitude of the effective field by nearly two orders of magnitude. Moreover, its sign changes when the Ta layer thickness is reduced, indicating that there are two competing effects contributing to it. Our results illustrate that the presence of atomically thin metals can profoundly change the landscape for controlling magnetic moments in magnetic heterostructures electrically.

Modulation of strain, resistance, and capacitance of tantalum oxide film by converse piezoelectric effect

NASA Astrophysics Data System (ADS)

Jia, Yanmin; Tian, Xiangling; Si, Jianxiao; Huang, Shihua; Wu, Zheng; Zhu, Chenchen

2011-07-01

We deposited tantalum oxide film on a laminate structure composed of a Si substrate and a piezoelectric 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 single crystal and achieved in situ modulation of the resistance and capacitance of the Ta2O5 film. The modulation arises from the induced lattice strain in the Ta2O5 film, which is induced by the electric-field-induced strain in the piezoelectric crystal. Under an external electric field of ˜2 kV/cm, the longitudinal gauge factor of the Ta2O5 film is ˜3300. The control of the strain using the converse piezoelectric effect may be further extended to tune the intrinsic strain of other oxide thin films.

Deposition and characterization of magnetron sputtered bcc tantalum

NASA Astrophysics Data System (ADS)

Patel, Anamika

The goal of this thesis was to provide scientific and technical research results for developing and characterizing tantalum (Ta) coatings on steel substrates deposited by DC magnetron sputtering. Deposition of tantalum on steel is of special interest for the protection it offers to surfaces, e.g. the surfaces of gun barrels against the erosive wear of hot propellant gases and the mechanical damage caused by the motion of launching projectiles. Electro-plated chromium is presently most commonly used for this purpose; however, it is considered to be carcinogenic in its hexavalent form. Tantalum is being investigated as non-toxic alternative to chromium and also because of its superior protective properties in these extreme environments. DC magnetron sputtering was chosen for this investigation of tantalum coatings on steel substrates because it is a versatile industrial proven process for deposition of metals. Sputter deposited Ta films can have two crystallographic structures: (1) body center cubic (bcc) phase, characterized by high toughness and high ductility and (2) a tetragonal beta phase characterized by brittleness and a tendency to fail under stress. It was found in this work that the bcc Ta coatings on steel can be obtained reliably by either of two methods: (1) depositing Ta on a submicron, stoichiometric TaN seed layer reactively sputtered on unheated steel and (2) depositing Ta directly on steel heated above a critical temperature. For argon sputtering gas this critical temperature was found to be 400°C at a pressure of 5 mtorr. With the heavier krypton gas, this critical temperature is reduced to 350°C. X-ray diffraction (XRD) was used to investigate the structure of tantalum and nitride films, and the composition of the nitride films was measured by nuclear reaction analyses (NRA), which were used to study in detail the enhancement of the bcc phase of Ta on steel. The scratch adhesion tests performed with a diamond hemispherical tip of radius 200 mum under increasing loads revealed high critical load values for failure (>15 N) for the bcc coatings versus the low load values (<9 N) for the beta coatings. The coating deposited on TaN interlayers on sputter-etched steel had better adhesion than those on steel surface without sputter etching. The results for this work have demonstrated that by controlling the various process parameters of do magnetron sputtering, high quality bcc Ta coatings of multi-micron thickness with excellent adhesion to steel can be made. An important contribution of this dissertation is in the enhancing an understanding of this process. The impact of this research will be in a number of fields where superior protective castings are needed. These include military applications, electronic components, chemical processing, and others.

Ultrathin free-standing close-packed gold nanoparticle films: Conductivity and Raman scattering enhancement

NASA Astrophysics Data System (ADS)

Yu, Qing; Huang, Hongwen; Peng, Xinsheng; Ye, Zhizhen

2011-09-01

A simple filtration technique was developed to prepare large scale free-standing close-packed gold nanoparticle ultrathin films using metal hydroxide nanostrands as both barrier layer and sacrificial layer. As thin as 70 nm, centimeter scale robust free-standing gold nanoparticle thin film was obtained. The thickness of the films could be easily tuned by the filtration volumes. The electronic conductivities of these films varied with the size of the gold nanoparticles, post-treatment temperature, and thickness, respectively. The conductivity of the film prepared from 20 nm gold nanoparticles is higher than that of the film prepared from 40 nm gold nanoparticle by filtering the same filtration volume of their solution, respectively. Their conductivities are comparable to that of the 220 nm thick ITO film. Furthermore, these films demonstrated an average surface Raman scattering enhancement up to 6.59 × 105 for Rhodamine 6 G molecules on the film prepared from 40 nm gold nanoparticles. Due to a lot of nano interspaces generated from the close-packed structures, two abnormal enhancements and relative stronger intensities of the asymmetrical vibrations at 1534 and 1594 cm-1 of R6G were observed, respectively. These robust free-standing gold nanoparticle films could be easily transferred onto various solid substrates and hold the potential application for electrodes and surface enhanced Raman detectors. This method is applicable for preparation of other nanoparticle free-standing thin films.A simple filtration technique was developed to prepare large scale free-standing close-packed gold nanoparticle ultrathin films using metal hydroxide nanostrands as both barrier layer and sacrificial layer. As thin as 70 nm, centimeter scale robust free-standing gold nanoparticle thin film was obtained. The thickness of the films could be easily tuned by the filtration volumes. The electronic conductivities of these films varied with the size of the gold nanoparticles, post-treatment temperature, and thickness, respectively. The conductivity of the film prepared from 20 nm gold nanoparticles is higher than that of the film prepared from 40 nm gold nanoparticle by filtering the same filtration volume of their solution, respectively. Their conductivities are comparable to that of the 220 nm thick ITO film. Furthermore, these films demonstrated an average surface Raman scattering enhancement up to 6.59 × 105 for Rhodamine 6 G molecules on the film prepared from 40 nm gold nanoparticles. Due to a lot of nano interspaces generated from the close-packed structures, two abnormal enhancements and relative stronger intensities of the asymmetrical vibrations at 1534 and 1594 cm-1 of R6G were observed, respectively. These robust free-standing gold nanoparticle films could be easily transferred onto various solid substrates and hold the potential application for electrodes and surface enhanced Raman detectors. This method is applicable for preparation of other nanoparticle free-standing thin films. Electronic supplementary information (ESI) available: Figure S1, the SEM images and photograph of the films prepared from 10 ml, 20 nm gold nanoparticles. Scheme S1, the vibrations of 1534 and 1594 cm-1 of R6G. See DOI: 10.1039/c1nr10578g

Vacancy-mediated fcc/bcc phase separation in Fe1 -xNix ultrathin films

NASA Astrophysics Data System (ADS)

Menteş, T. O.; Stojić, N.; Vescovo, E.; Ablett, J. M.; Niño, M. A.; Locatelli, A.

2016-08-01

The phase separation occurring in Fe-Ni thin films near the Invar composition is studied by using high-resolution spectromicroscopy techniques and density functional theory calculations. Annealed at temperatures around 300 ∘C ,Fe0.70Ni0.30 films on W(110) break into micron-sized bcc and fcc domains with compositions in agreement with the bulk Fe-Ni phase diagram. Ni is found to be the diffusing species in forming the chemical heterogeneity. The experimentally determined energy barrier of 1.59 ±0.09 eV is identified as the vacancy formation energy via density functional theory calculations. Thus, the principal role of the surface in the phase separation process is attributed to vacancy creation without interstitials.

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

NASA Astrophysics Data System (ADS)

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

2017-11-01

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

Phase formation and morphological stability of ultrathin Ni-Co-Pt silicide films formed on Si(100)

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

Xu, Peng; Wu, Dongping, E-mail: dongpingwu@fudan.edu.cn; Kubart, Tomas

Ultrathin Ni, Co, and Pt films, each no more than 4 nm in thickness, as well as their various combinations are employed to investigate the competing growth of epitaxial Co{sub 1-y}Ni{sub y}Si{sub 2} films against polycrystalline Pt{sub 1-z}Ni{sub z}Si. The phase formation critically affects the morphological stability of the resulting silicide films, with the epitaxial films being superior to the polycrystalline ones. Any combination of those metals improves the morphological stability with reference to their parent individual metal silicide films. When Ni, Co, and Pt are all included, the precise initial location of Pt does little to affect the final phasemore » formation in the silicide films and the epitaxial growth of Co{sub 1-x}Ni{sub x}Si{sub 2} films is always perturbed, in accordance to thermodynamics that shows a preferential formation of Pt{sub 1-z}Ni{sub z}Si over that of Co{sub 1-y}Ni{sub y}Si{sub 2}.« less

Computational Study of In-Plane Phonon Transport in Si Thin Films

PubMed Central

Wang, Xinjiang; Huang, Baoling

2014-01-01

We have systematically investigated the in-plane thermal transport in Si thin films using an approach based on the first-principles calculations and lattice dynamics. The effects of phonon mode depletion induced by the phonon confinement and the corresponding variation in interphonon scattering, which may be important for the thermal conductivities of ultra-thin films but are often neglected in precedent studies, are considered in this study. The in-plane thermal conductivities of Si thin films with different thicknesses have been predicted over a temperature range from 80 K to 800 K and excellent agreements with experimental results are found. The validities of adopting the bulk phonon properties and gray approximation of surface specularity in thin film studies have been clarified. It is found that in ultra-thin films, while the phonon depletion will reduce the thermal conductivity of Si thin films, its effect is largely offset by the reduction in the interphonon scattering rate. The contributions of different phonon modes to the thermal transport and isotope effects in Si films with different thicknesses under various temperatures are also analyzed. PMID:25228061

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

NASA Astrophysics Data System (ADS)

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

2017-03-01

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

An ultrathin wide-band planar metamaterial absorber based on a fractal frequency selective surface and resistive film

NASA Astrophysics Data System (ADS)

Fan, Yue-Nong; Cheng, Yong-Zhi; Nie, Yan; Wang, Xian; Gong, Rong-Zhou

2013-06-01

We propose an ultrathin wide-band metamaterial absorber (MA) based on a Minkowski (MIK) fractal frequency selective surface and resistive film. This absorber consists of a periodic arrangement of dielectric substrates sandwiched with an MIK fractal loop structure electric resonator and a resistive film. The finite element method is used to simulate and analyze the absorption of the MA. Compared with the MA-backed copper film, the designed MA-backed resistive film exhibits an absorption of 90% at a frequency region of 2 GHz-20 GHz. The power loss density distribution of the MA is further illustrated to explain the mechanism of the proposed MA. Simulated absorptions at different incidence cases indicate that this absorber is polarization-insensitive and wide-angled. Finally, further simulated results indicate that the surface resistance of the resistive film and the dielectric constant of the substrate can affect the absorbing property of the MA. This absorber may be used in many military fields.

Stabilization of ultrathin (hydroxy)oxide films on transition metal substrates for electrochemical energy conversion

DOE PAGES

Zeng, Zhenhua; Chang, Kee-Chul; Kubal, Joseph; ...

2017-05-08

Design of cost-effective electrocatalysts with enhanced stability and activity is of paramount importance for the next generation of energy conversion systems, including fuel cells and electrolyzers. However, electrocatalytic materials generally improve one of these properties at the expense of the other. Here, using Density Functional Theory calculations and electrochemical surface science measurements, we explore atomic-level features of ultrathin (hydroxy)oxide films on transition metal substrates and demonstrate that these films exhibit both excellent stability and activity for electrocatalytic applications. The films adopt structures with stabilities that significantly exceed bulk Pourbaix limits, including stoichiometries not found in bulk and properties that aremore » tunable by controlling voltage, film composition, and substrate identity. Using nickel (hydroxy)oxide/Pt(111) as an example, we further show how the films enhance activity for hydrogen evolution through a bifunctional effect. Finally, the results suggest design principles for a new class of electrocatalysts with simultaneously enhanced stability and activity for energy conversion.« less

Stabilization of ultrathin (hydroxy)oxide films on transition metal substrates for electrochemical energy conversion

NASA Astrophysics Data System (ADS)

Zeng, Zhenhua; Chang, Kee-Chul; Kubal, Joseph; Markovic, Nenad M.; Greeley, Jeffrey

2017-06-01

Design of cost-effective electrocatalysts with enhanced stability and activity is of paramount importance for the next generation of energy conversion systems, including fuel cells and electrolysers. However, electrocatalytic materials generally improve one of these properties at the expense of the other. Here, using density functional theory calculations and electrochemical surface science measurements, we explore atomic-level features of ultrathin (hydroxy)oxide films on transition metal substrates and demonstrate that these films exhibit both excellent stability and activity for electrocatalytic applications. The films adopt structures with stabilities that significantly exceed bulk Pourbaix limits, including stoichiometries not found in bulk and properties that are tunable by controlling voltage, film composition, and substrate identity. Using nickel (hydroxy)oxide/Pt(111) as an example, we further show how the films enhance activity for hydrogen evolution through a bifunctional effect. The results suggest design principles for this class of electrocatalysts with simultaneously enhanced stability and activity for energy conversion.

Transport properties of ultra-thin VO2 films on (001) TiO2 grown by reactive molecular-beam epitaxy

NASA Astrophysics Data System (ADS)

Paik, Hanjong; Moyer, Jarrett A.; Spila, Timothy; Tashman, Joshua W.; Mundy, Julia A.; Freeman, Eugene; Shukla, Nikhil; Lapano, Jason M.; Engel-Herbert, Roman; Zander, Willi; Schubert, Jürgen; Muller, David A.; Datta, Suman; Schiffer, Peter; Schlom, Darrell G.

2015-10-01

We report the growth of (001)-oriented VO2 films as thin as 1.5 nm with abrupt and reproducible metal-insulator transitions (MIT) without a capping layer. Limitations to the growth of thinner films with sharp MITs are discussed, including the Volmer-Weber type growth mode due to the high energy of the (001) VO2 surface. Another key limitation is interdiffusion with the (001) TiO2 substrate, which we quantify using low angle annular dark field scanning transmission electron microscopy in conjunction with electron energy loss spectroscopy. We find that controlling island coalescence on the (001) surface and minimization of cation interdiffusion by using a low growth temperature followed by a brief anneal at higher temperature are crucial for realizing ultrathin VO2 films with abrupt MIT behavior.

Structure of periodic crystals and quasicrystals in ultrathin films of Ba-Ti-O

DOE PAGES

Cockayne, Eric; Mihalkovič, Marek; Henley, Christopher L.

2016-01-07

Here, we model the remarkable thin-film Ba-Ti-O structures formed by heat treatment of an initial perovskite BaTiO 3 thin film on a Pt(111) surface. All structures contain a rumpled Ti-O network with all Ti threefold coordinated with O, and with Ba occupying the larger. mainly Ti 7O 7, pores. The quasicrystal structue is a simple decoration of three types of tiles: square, triangle and 30° rhombus, with edge lengths 6.85 Å, joined edge-to-edge in a quasicrystalline pattern; observed periodic crystals in ultrathin film Ba-Ti-O are built from these and other tiles. Simulated STM images reproduce the patterns seen experimentally, andmore » identify the bright protrusions as Ba atoms. The models are consistent with all experimental observations.« less

Biopolymers for Sample Collection, Protection, and Preservation

DTIC Science & Technology

2015-05-19

biopolymer. The cured polymer results in a solid protective film that is stable to many organic solvents, but quickly removed by the application of the water...the biopolymer. The cured polymer results in a solid protective film that is stable to many organic solvents, but quickly removed by the appli- cation...frozen after that. RNAlater® has been demonstrated to Ta bl e 1 C om pa ri so n of ce ll an d nu cl ei c ac id pr es er va tio n te ch ni qu es Sy st

Small temperature coefficient of resistivity of graphene/graphene oxide hybrid membranes.

PubMed

Sun, Pengzhan; Zhu, Miao; Wang, Kunlin; Zhong, Minlin; Wei, Jinquan; Wu, Dehai; Zhu, Hongwei

2013-10-09

Materials with low temperature coefficient of resistivity (TCR) are of great importance in some areas, for example, highly accurate electronic measurement instruments and microelectronic integrated circuits. In this work, we demonstrated the ultrathin graphene-graphene oxide (GO) hybrid films prepared by layer-by-layer assembly with very small TCR (30-100 °C) in the air. Electrical response of the hybrid films to temperature variation was investigated along with the progressive reduction of GO sheets. The mechanism of electrical response to temperature variation of the hybrid film was discussed, which revealed that the interaction between graphene and GO and the chemical doping effect were responsible for the tunable control of its electrical response to temperature variation. The unique properties of graphene-GO hybrid film made it a promising candidate in many areas, such as high-end film electronic device and sensor applications.

Mixed-Penetrant Sorption in Ultrathin Films of Polymer of Intrinsic Microporosity PIM-1.

PubMed

Ogieglo, Wojciech; Furchner, Andreas; Ghanem, Bader; Ma, Xiaohua; Pinnau, Ingo; Wessling, Matthias

2017-11-02

Mixed-penetrant sorption into ultrathin films of a superglassy polymer of intrinsic microporosity (PIM-1) was studied for the first time by using interference-enhanced in situ spectroscopic ellipsometry. PIM-1 swelling and the concurrent changes in its refractive index were determined in ultrathin (12-14 nm) films exposed to pure and mixed penetrants. The penetrants included water, n-hexane, and ethanol and were chosen on the basis of their significantly different penetrant-penetrant and penetrant-polymer affinities. This allowed studying microporous polymer responses at diverse ternary compositions and revealed effects such as competition for the sorption sites (for water/n-hexane or ethanol/n-hexane) or enhancement in sorption of typically weakly sorbing water in the presence of more highly sorbing ethanol. The results reveal details of the mutual sorption effects which often complicate comprehension of glassy polymers' behavior in applications such as high-performance membranes, adsorbents, or catalysts. Mixed-penetrant effects are typically very challenging to study directly, and their understanding is necessary owing to a broadly recognized inadequacy of simple extrapolations from measurements in a pure component environment.

Numerical experiments on evaporation and explosive boiling of ultra-thin liquid argon film on aluminum nanostructure substrate

NASA Astrophysics Data System (ADS)

Wang, Weidong; Zhang, Haiyan; Tian, Conghui; Meng, Xiaojie

2015-04-01

Evaporation and explosive boiling of ultra-thin liquid film are of great significant fundamental importance for both science and engineering applications. The evaporation and explosive boiling of ultra-thin liquid film absorbed on an aluminum nanostructure solid wall are investigated by means of molecular dynamics simulations. The simulated system consists of three regions: liquid argon, vapor argon, and an aluminum substrate decorated with nanostructures of different heights. Those simulations begin with an initial configuration for the complex liquid-vapor-solid system, followed by an equilibrating system at 90 K, and conclude with two different jump temperatures, including 150 and 310 K which are far beyond the critical temperature. The space and time dependences of temperature, pressure, density number, and net evaporation rate are monitored to investigate the phase transition process on a flat surface with and without nanostructures. The simulation results reveal that the nanostructures are of great help to raise the heat transfer efficiency and that evaporation rate increases with the nanostructures' height in a certain range.

Numerical experiments on evaporation and explosive boiling of ultra-thin liquid argon film on aluminum nanostructure substrate.

PubMed

Wang, Weidong; Zhang, Haiyan; Tian, Conghui; Meng, Xiaojie

2015-01-01

Evaporation and explosive boiling of ultra-thin liquid film are of great significant fundamental importance for both science and engineering applications. The evaporation and explosive boiling of ultra-thin liquid film absorbed on an aluminum nanostructure solid wall are investigated by means of molecular dynamics simulations. The simulated system consists of three regions: liquid argon, vapor argon, and an aluminum substrate decorated with nanostructures of different heights. Those simulations begin with an initial configuration for the complex liquid-vapor-solid system, followed by an equilibrating system at 90 K, and conclude with two different jump temperatures, including 150 and 310 K which are far beyond the critical temperature. The space and time dependences of temperature, pressure, density number, and net evaporation rate are monitored to investigate the phase transition process on a flat surface with and without nanostructures. The simulation results reveal that the nanostructures are of great help to raise the heat transfer efficiency and that evaporation rate increases with the nanostructures' height in a certain range.

Electronic-Reconstruction-Enhanced Tunneling Conductance at Terrace Edges of Ultrathin Oxide Films.

PubMed

Wang, Lingfei; Kim, Rokyeon; Kim, Yoonkoo; Kim, Choong H; Hwang, Sangwoon; Cho, Myung Rae; Shin, Yeong Jae; Das, Saikat; Kim, Jeong Rae; Kalinin, Sergei V; Kim, Miyoung; Yang, Sang Mo; Noh, Tae Won

2017-11-01

Quantum mechanical tunneling of electrons across ultrathin insulating oxide barriers has been studied extensively for decades due to its great potential in electronic-device applications. In the few-nanometers-thick epitaxial oxide films, atomic-scale structural imperfections, such as the ubiquitously existed one-unit-cell-high terrace edges, can dramatically affect the tunneling probability and device performance. However, the underlying physics has not been investigated adequately. Here, taking ultrathin BaTiO 3 films as a model system, an intrinsic tunneling-conductance enhancement is reported near the terrace edges. Scanning-probe-microscopy results demonstrate the existence of highly conductive regions (tens of nanometers wide) near the terrace edges. First-principles calculations suggest that the terrace-edge geometry can trigger an electronic reconstruction, which reduces the effective tunneling barrier width locally. Furthermore, such tunneling-conductance enhancement can be discovered in other transition metal oxides and controlled by surface-termination engineering. The controllable electronic reconstruction can facilitate the implementation of oxide electronic devices and discovery of exotic low-dimensional quantum phases. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fabrication of Ta2O5/GeNx gate insulator stack for Ge metal-insulator-semiconductor structures by electron-cyclotron-resonance plasma nitridation and sputtering deposition techniques

NASA Astrophysics Data System (ADS)

Otani, Yohei; Itayama, Yasuhiro; Tanaka, Takuo; Fukuda, Yukio; Toyota, Hiroshi; Ono, Toshiro; Mitsui, Minoru; Nakagawa, Kiyokazu

2007-04-01

The authors have fabricated germanium (Ge) metal-insulator-semiconductor (MIS) structures with a 7-nm-thick tantalum pentaoxide (Ta2O5)/2-nm-thick germanium nitride (GeNx) gate insulator stack by electron-cyclotron-resonance plasma nitridation and sputtering deposition. They found that pure GeNx ultrathin layers can be formed by the direct plasma nitridation of the Ge surface without substrate heating. X-ray photoelectron spectroscopy revealed no oxidation of the GeNx layer after the Ta2O5 sputtering deposition. The fabricated MIS capacitor with a capacitance equivalent thickness of 4.3nm showed excellent leakage current characteristics. The interface trap density obtained by the modified conductance method was 4×1011cm-2eV-1 at the midgap.

Comparative Study of HfTa-based gate-dielectric Ge metal-oxide-semiconductor capacitors with and without AlON interlayer

NASA Astrophysics Data System (ADS)

Xu, J. P.; Zhang, X. F.; Li, C. X.; Chan, C. L.; Lai, P. T.

2010-04-01

The electrical properties and high-field reliability of HfTa-based gate-dielectric metal-oxide-semiconductor (MOS) devices with and without AlON interlayer on Ge substrate are investigated. Experimental results show that the MOS capacitor with HfTaON/AlON stack gate dielectric exhibits low interface-state/oxide-charge densities, low gate leakage, small capacitance equivalent thickness (˜1.1 nm), and high dielectric constant (˜20). All of these should be attributed to the blocking role of the ultrathin AlON interlayer against interdiffusions of Ge, Hf, and Ta and penetration of O into the Ge substrate, with the latter effectively suppressing the unintentional formation of unstable poor-quality low- k GeO x and giving a superior AlON/Ge interface. Moreover, incorporation of N into both the interlayer and high- k dielectric further improves the device reliability under high-field stress through the formation of strong N-related bonds.

Improvement in surface conditions of electroplated Fe-Pt thick-film magnets

NASA Astrophysics Data System (ADS)

Yanai, T.; Honda, J.; Hamamura, R.; Omagari, Y.; Yamada, H.; Fujita, N.; Takashima, K.; Nakano, M.; Fukunaga, H.

2018-05-01

Fe-Pt thick-films were electroplated on Ta, Ti, Co, Ni, and Cu plates (substrates) using a direct current, and the surface morphology, the magnetic properties, and the crystal structure of the films were evaluated. The films plated on the Co, Ni, and Cu substrates showed much smooth surface compared with those for the Ta and Ti ones, and we confirmed that the Cu plate was the most attractive substrate due to very small cracks after an annealing for L10 ordering. High coercivity (>800 kA/m) for the Cu substrate is almost the same as that for our previous study in which we employed the Ta substrate, and we found that the Cu plate is a hopeful substrate to improve the surface conditions of electroplated Fe-Pt thick-film magnets.

Thin film integrated capacitors with sputtered-anodized niobium pentoxide dielectric for decoupling applications

NASA Astrophysics Data System (ADS)

Jacob, Susan

Electronics system miniaturization is a major driver for high-k materials. High-k materials in capacitors allow for high capacitance, enabling system miniaturization. Ta2O5 (k˜24) has been the dominant high-k material in the electronic industry for decoupling capacitors, filter capacitors, etc. In order to facilitate further system miniaturization, this project has investigated thin film integrated capacitors with Nb2O5 dielectric. Nb2O 5 has k˜41 and is a potential candidate for replacing Ta2O5. But, the presence of suboxides (NbO2 and NbO) in the dielectric deteriorates the electrical properties (leakage current, thermal instability of capacitance, etc.). Also, the high oxygen solubility of niobium results in oxygen diffusion from the dielectric to niobium metal, if any is present. The major purpose of this project was to check the ability of NbN as a diffusion barrier and fabricate thermally stable niobium capacitors. As a first step to produce niobium capacitors, the material characterizations of reactively sputtered Nb2O5 and NbN were done. Thickness and film composition, and crystal structures of the sputtered films were obtained and the deposition parameters for the desired stoichiometry were found. Also, anodized Nb2O5 was characterized for its stoichiometry and thickness. To study the effect of nitrides on capacitance and thermal stability, Ta2O5 capacitors were initially fabricated with and without TaN. The results showed that the nitride does not affect the capacitance, and that capacitors with TaN are stable up to 150°C. In the next step, niobium capacitors were first fabricated with anodized dielectric and the oxygen diffusion issues associated with capacitor processing were studied. Reactively sputtered Nb2O5 was anodized to form complete Nb2O5 (with few oxygen vacancies) and NbN was used to sandwich the dielectric. The capacitor fabrication was not successful due to the difficulties in anodizing the sputtered dielectric. Another method, anodizing reactively sputtered Nb2O5 and a thin layer of sputtered niobium metal yielded high yield (99%) capacitors. Capacitors were fabricated with and without NbN and the results showed 93% decrease in leakage for a capacitor with ˜2000 A dielectric when NbN was present in the structure. These capacitors could withstand 20 V and showed 2.7 muA leakage current at 5 V. These results were obtained after thermal storage at 100°C and 150°C in air for 168 hours at each temperature. Two set of experiments were performed using Ta2O5 dielectric: one to determine the effect of anodization end point on the thickness (capacitance) and the second to determine the effect of boiling the dielectric on functional yield. The anodization end point experiment showed that the final current of anodization along with the anodizing voltage determines the anodic oxide thickness. The lower the current, the thicker the films produced by anodization. Therefore, it was important to specify the final current along with the anodization voltage for oxide growth rate. The capacitors formed with boiled wafers showed better functional yield 3 out of 5 times compared with the unboiled wafer. Niobium anodization was studied for the Nb--->Nb 2O5 conversion ratio and the effect of anodization bath temperature on the oxide film; a color chart was prepared for thicknesses ranging from 1900 A - 5000 A. The niobium metal to oxide conversion ratio was found to change with temperature.

Atomistic study of ternary oxides as high-temperature solid lubricants

NASA Astrophysics Data System (ADS)

Gao, Hongyu

Friction and wear are important tribological phenomena tightly associated with the performance of tribological components/systems such as bearings and cutting machines. In the process of contact and sliding, friction and wear lead to energy loss, and high friction and wear typically result in shortened service lifetime. To reduce friction and wear, solid lubricants are generally used under conditions where traditional liquid lubricants cannot be applied. However, it is challenging to maintain the functionality of those materials when the working environment becomes severe. For instance, at elevated temperatures (i.e., above 400 °C), most traditional solid lubricants, such as MoS2 and graphite, will easily oxidize or lose lubricity due to irreversible chemical changes. For such conditions, it is necessary to identify materials that can remain thermally stable as well as lubricious over a wide range of temperatures. Among the currently available high-temperature solid lubricants, Ag-based ternary metal oxides have recently drawn attention due to their low friction and ability to resist oxidation. A recent experimental study showed that the Ag-Ta-O ternary exhibited an extremely low coefficient of friction (0.06) at 750 °C. To fully uncover the lubricious nature of this material as a high-temperature solid lubricant, a series of tribological investigations were carried out based on one promising candidate - silver tantalate (AgTaO3). The study was then extended to alternative materials, Cu-Ta-O ternaries, to accommodate a variety of application requirements. We aimed to understand, at an atomic level, the effects of physical and chemical properties on the thermal, mechanical and tribological behavior of these materials at high temperatures. Furthermore, we investigated potassium chloride films on a clean iron surface as a representative boundary lubricating system in a nonextreme environment. This investigation complemented the study of Ag/Cu-Ta-O and enhanced the understanding of lubricious mechanisms of solid lubricants in general. Molecular dynamics (MD) simulations was used as the primary tool in this research, complemented by density-functional theory and experiments from our colleagues. In this research, we first developed empirical potential parameters for AgTaO3 and later Cu- Ta-O ternaries using the modified embedded-atom method (MEAM) formalism. With those parameters, we explored the sliding mechanisms of AgTaO3, CuTaO3 and CuTa2O6 at elevated temperatures. Particularly on AgTaO3, we investigated the effects of applied loads as well as surface terminations on friction and wear as functions of temperature. In addition, to optimize the tribological performance of AgTaO3, film reconstruction mechanisms were investigated on Ta2O5/Ag films with varying amounts of Ag. For the potassium chloride-iron system, we studied the effect of contact pressure on interfacial structure, based on which the origin of the commonly observed pressure-dependent shear strengths was explored. We hope this research will benefit the design and development of solid lubricant materials for a wide range of applications.

Mechanical behavior of Ti-Ta-based surface alloy fabricated on TiNi SMA by pulsed electron-beam melting of film/substrate system

NASA Astrophysics Data System (ADS)

Meisner, S. N.; Yakovlev, E. V.; Semin, V. O.; Meisner, L. L.; Rotshtein, V. P.; Neiman, A. A.; D'yachenko, F.

2018-04-01

The physical-mechanical properties of the Ti-Ta based surface alloy with thickness up to ∼2 μm fabricated through the multiple (up to 20 cycles) alternation of magnetron deposition of Ti70Ta30 (at.%) thin (50 nm) films and their liquid-phase mixing with the NiTi substrate by microsecond low-energy, high current pulsed electron beam (LEHCPEB: ≤15 keV, ∼2 J/cm2) are presented. Two types of NiTi substrates (differing in the methods of melting alloys) were pretreated with LEHCPEB to improve the adhesion of thin-film coating and to protect it from local delimitation because of the surface cratering under pulsed melting. The methods used in the research include nanoindentation, transmission electron microscopy, and depth profile analysis of nanohardness, Vickers hardness, elastic modulus, depth recovery ratio, and plasticity characteristic as a function of indentation depth. For comparison, similar measurements were carried out with NiTi substrates in the initial state and after LEHCPEB pretreatment, as well as on "Ti70Ta30(1 μm) coating/NiTi substrate" system. It was shown that the upper surface layer in both NiTi substrates is the same in properties after LEHCPEB pretreatment. Our data suggest that the type of multilayer surface structure correlates with its physical-mechanical properties. For NiTi with the Ti-Ta based surface alloy ∼1 μm thick, the highest elasticity falls on the upper submicrocrystalline layer measuring ∼0.2 μm and consisting of two Ti-Ta based phases: α‧‧ martensite (a = 0.475 nm, b = 0.323 nm, c = 0.464 nm) and β austenite (a = 0.327 nm). Beneath the upper layer there is an amorphous sublayer followed by underlayers with coarse (>20 nm) and fine (<20 nm) average grain sizes which provide a gradual transition of the mechanical parameters to the values of the NiTi substrate.

Selection and Manufacturing of Membrane Materials for Solar Sails

NASA Technical Reports Server (NTRS)

Bryant, Robert G.; Seaman, Shane T.; Wilkie, W. Keats; Miyaucchi, Masahiko; Working, Dennis C.

2013-01-01

Commercial metallized polyimide or polyester films and hand-assembly techniques are acceptable for small solar sail technology demonstrations, although scaling this approach to large sail areas is impractical. Opportunities now exist to use new polymeric materials specifically designed for solar sailing applications, and take advantage of integrated sail manufacturing to enable large-scale solar sail construction. This approach has, in part, been demonstrated on the JAXA IKAROS solar sail demonstrator, and NASA Langley Research Center is now developing capabilities to produce ultrathin membranes for solar sails by integrating resin synthesis with film forming and sail manufacturing processes. This paper will discuss the selection and development of polymer material systems for space, and these new processes for producing ultrathin high-performance solar sail membrane films.

Fabrication of ultrathin film capacitors by chemical solution deposition

DOE PAGES

Brennecka, Geoff L.; Tuttle, Bruce A.

2007-10-01

We present that a facile solution-based processing route using standard spin-coating deposition techniques has been developed for the production of reliable capacitors based on lead lanthanum zirconate titanate (PLZT) with active areas of ≥1 mm 2 and dielectric layer thicknesses down to 50 nm. With careful control of the dielectric phase development through improved processing, ultrathin capacitors exhibited slim ferroelectric hysteresis loops and dielectric constants of >1000, similar to those of much thicker films. Furthermore, it has been demonstrated that chemical solution deposition is a viable route to the production of capacitor films which are as thin as 50 nmmore » but are still macroscopically addressable with specific capacitance values >160 nF/mm 2.« less

Silicon nanomembranes as a means to evaluate stress evolution in deposited thin films

Treesearch

Anna M. Clausen; Deborah M. Paskiewicz; Alireza Sadeghirad; Joseph Jakes; Donald E. Savage; Donald S. Stone; Feng Liu; Max G. Lagally

2014-01-01

Thin-film deposition on ultra-thin substrates poses unique challenges because of the potential for a dynamic response to the film stress during deposition. While theoretical studies have investigated film stress related changes in bulk substrates, little has been done to learn how stress might evolve in a film growing on a compliant substrate. We use silicon...

Hafnium oxide films for application as gate dielectrics

NASA Astrophysics Data System (ADS)

Hsu, Shuo-Lin

The deposition and characterization of HfO2 films for potential application as a high-kappa gate dielectric in MOS devices has been investigated. DC magnetron reactive sputtering was utilized to prepare the HfO2 films. Structural, chemical, and electrical analyses were performed to characterize the various physical, chemical and electrical properties of the sputtered HfO2 films. The sputtered HfO2 films were annealed to simulate the dopant activation process used in semiconductor processing, and to study the thermal stability of the high-kappa, films. The changes in the film properties due to the annealing are also discussed in this work. Glancing angle XRD was used to analyse the atomic scale structure of the films. The as deposited films exhibit an amorphous, regardless of the film thickness. During post-deposition annealing, the thicker films crystallized at lower temperature (< 600°C), and ultra-thin (5.8 nm) film crystallized at higher temperature (600--720°C). The crystalline phase which formed depended on the thickness of the films. The low temperature phase (monoclinic) formed in the 10--20 nm annealed films, and high temperature phase (tetragonal) formed in the ultra-thin annealed HfO2 film. TEM cross-section studies of as deposited samples show that an interfacial layer (< 1nm) exists between HfO2/Si for all film thicknesses. The interfacial layer grows thicker during heat treatment, and grows more rapidly when grain boundaries are present. XPS surface analysis shows the as deposited films are fully oxidized with an excess of oxygen. Interfacial chemistry analysis indicated that the interfacial layer is a silicon-rich silicate layer, which tends to transform to silica-like layer during heat treatment. I-V measurements show the leakage current density of the Al/as deposited-HfO 2/Si MOS diode is of the order of 10-3 A/cm 2, two orders of magnitude lower than that of a ZrO2 film with similar physical thickness. Carrier transport is dominated by Schottky emission at lower electric fields, and by Frenkel-Poole emission in the higher electric field region. After annealing, the leakage current density decreases significantly as the structure remains amorphous structure. It is suggested that this decrease is assorted with the densification and defect healing which accures when the porous as-deposited amorphous structure is annealed. The leakage current density increases of the HfO2 layer crystallizes on annealing, which is attributed to the presence of grain boundaries. C-V measurements of the as deposited film shows typical C-V characteristics, with negligible hystersis, a small flat band voltage shift, but great frequency dispersion. The relative permittivity of HfO2/interfacial layer stack obtained from the capacitance at accumulation is 15, which corresponds to an EOT (equivalent oxide thickness) = 1.66 nm. After annealing, the frequency dispersion is greatly enhanced, and the C-V curve is shifted toward the negative voltage. Reliability tests show that the HfO2 films which remain amorphous after annealing possess superior resistance to constant voltage stress and ambient aging. This study concluded that the sputtered HfO 2 films exhibit an amorphous as deposited. Postdeposition annealing alters the crystallinity, interfacial properties, and electrical characteristics. The HfO2 films which remain amorphous structure after annealing possess the best electrical properties.

Real-time monitoring of the structure of ultrathin Fe3O4 films during growth on Nb-doped SrTiO3(001)

NASA Astrophysics Data System (ADS)

Kuschel, O.; Spiess, W.; Schemme, T.; Rubio-Zuazo, J.; Kuepper, K.; Wollschläger, J.

2017-07-01

In this work, thin magnetite films were deposited on SrTiO3 via reactive molecular beam epitaxy at different substrate temperatures. The growth process was monitored in-situ during deposition by means of x-ray diffraction. While the magnetite film grown at 400 °C shows a fully relaxed vertical lattice constant already in the early growth stages, the film deposited at 270 °C exhibits a strong vertical compressive strain and relaxes towards the bulk value with increasing film thickness. Furthermore, a lateral tensile strain was observed under these growth conditions although the inverse behavior is expected due to the lattice mismatch of -7.5%. Additionally, the occupancy of the A and B sublattices of magnetite with tetrahedral and octahedral sites was investigated showing a lower occupancy of the A sites compared to an ideal inverse spinel structure. The occupation of A sites decreases for a higher growth temperature. Thus, we assume a relocation of the iron ions from tetrahedral sites to octahedral vacancies forming a deficient rock salt lattice.

Energy deposition in ultrathin extreme ultraviolet resist films: extreme ultraviolet photons and keV electrons

NASA Astrophysics Data System (ADS)

Kyser, David F.; Eib, Nicholas K.; Ritchie, Nicholas W. M.

2016-07-01

The absorbed energy density (eV/cm3) deposited by extreme ultraviolet (EUV) photons and electron beam (EB) high-keV electrons is proposed as a metric for characterizing the sensitivity of EUV resist films. Simulations of energy deposition are used to calculate the energy density as a function of the incident aerial flux (EUV: mJ/cm2, EB: μC/cm2). Monte Carlo calculations for electron exposure are utilized, and a Lambert-Beer model for EUV absorption. The ratio of electron flux to photon flux which results in equivalent energy density is calculated for a typical organic chemically amplified resist film and a typical inorganic metal-oxide film. This ratio can be used to screen EUV resist materials with EB measurements and accelerate advances in EUV resist systems.

How Do Organic Vapors Swell Ultrathin Films of Polymer of Intrinsic Microporosity PIM-1?

PubMed

Ogieglo, Wojciech; Rahimi, Khosorov; Rauer, Sebastian Bernhard; Ghanem, Bader; Ma, Xiaohua; Pinnau, Ingo; Wessling, Matthias

2017-07-27

Dynamic sorption of ethanol and toluene vapor into ultrathin supported films of polymer of intrinsic microporosity PIM-1 down to a thickness of 6 nm are studied with a combination of in situ spectroscopic ellipsometry and in situ X-ray reflectivity. Both ethanol and toluene significantly swell the PIM-1 matrix and, at the same time, induce persistent structural relaxations of the frozen-in glassy PIM-1 morphology. For ethanol below 20 nm, three effects were identified. First, the swelling magnitude at high vapor pressures is reduced by about 30% as compared to that of thicker films. Second, at low penetrant activities (below 0.3p/p 0 ), films below 20 nm are able to absorb slightly more penetrant as compared with thicker films despite a similar swelling magnitude. Third, for the ultrathin films, the onset of the dynamic penetrant-induced glass transition P g has been found to shift to higher values, indicating higher resistance to plasticization. All of these effects are consistent with a view where immobilization of the superglassy PIM-1 at the substrate surface leads to an arrested, even more rigid, and plasticization-resistant, yet still very open, microporous structure. PIM-1 in contact with the larger and more condensable toluene shows very complex, heterogeneous swelling dynamics, and two distinct penetrant-induced relaxation phenomena, probably associated with the film outer surface and the bulk, are detected. Following the direction of the penetrant's diffusion, the surface seems to plasticize earlier than the bulk, and the two relaxations remain well separated down to 6 nm film thickness, where they remarkably merge to form just a single relaxation.

Multiferroic YCrO3 thin films grown on glass substrate: Resistive switching characteristics

NASA Astrophysics Data System (ADS)

Seo, Jeongdae; Ahn, Yoonho; Son, Jong Yeog

2016-01-01

Polycrystalline YCrO3 thin films were deposited on (111) Pt/Ta/glass substrates by pulsed laser deposition. The YCrO3 thin films exhibited good ferroelectric properties with remnant polarization of about 5 µC/cm2. Large leakage current was observed by I- V curve and ferroelectric hysteresis loop. The YCrO3 resistive random access memory (RRAM) capacitor showed unipolar switching behaviors with SET and RESET voltages higher than those of general NiO RRAM capacitors. [Figure not available: see fulltext.

A novel interferometric method for the study of the viscoelastic properties of ultra-thin polymer films determined from nanobubble inflation

NASA Astrophysics Data System (ADS)

Chapuis, P.; Montgomery, P. C.; Anstotz, F.; Leong-Hoï, A.; Gauthier, C.; Baschnagel, J.; Reiter, G.; McKenna, G. B.; Rubin, A.

2017-09-01

Glass formation and glassy behavior remain as the important areas of investigation in soft matter physics with many aspects which are still not completely understood, especially at the nanometer size-scale. In the present work, we show an extension of the "nanobubble inflation" method developed by O'Connell and McKenna [Rev. Sci. Instrum. 78, 013901 (2007)] which uses an interferometric method to measure the topography of a large array of 5 μ m sized nanometer thick films subjected to constant inflation pressures during which the bubbles grow or creep with time. The interferometric method offers the possibility of making measurements on multiple bubbles at once as well as having the advantage over the AFM methods of O'Connell and McKenna of being a true non-contact method. Here we demonstrate the method using ultra-thin films of both poly(vinyl acetate) (PVAc) and polystyrene (PS) and discuss the capabilities of the method relative to the AFM method, its advantages and disadvantages. Furthermore we show that the results from experiments on PVAc are consistent with the prior work on PVAc, while high stress results with PS show signs of a new non-linear response regime that may be related to the plasticity of the ultra-thin film.

Operando SXRD of E-ALD deposited sulphides ultra-thin films: Crystallite strain and size

NASA Astrophysics Data System (ADS)

Giaccherini, Andrea; Russo, Francesca; Carlà, Francesco; Guerri, Annalisa; Picca, Rosaria Anna; Cioffi, Nicola; Cinotti, Serena; Montegrossi, Giordano; Passaponti, Maurizio; Di Benedetto, Francesco; Felici, Roberto; Innocenti, Massimo

2018-02-01

Electrochemical Atomic Layer Deposition (E-ALD), exploiting surface limited electrodeposition of atomic layers, can easily grow highly ordered ultra-thin films and 2D structures. Among other compounds CuxZnyS grown by means of E-ALD on Ag(111) has been found particularly suitable for the solar energy conversion due to its band gap (1.61 eV). However its growth seems to be characterized by a micrometric thread-like structure, probably overgrowing a smooth ultra-thin films. On this ground, a SXRD investigation has been performed, to address the open questions about the structure and the growth of CuxZnyS by means of E-ALD. The experiment shows a pseudo single crystal pattern as well as a powder pattern, confirming that part of the sample grows epitaxially on the Ag(111) substrate. The growth of the film was monitored by following the evolution of the Bragg peaks and Debye rings during the E-ALD steps. Breadth and profile analysis of the Bragg peaks lead to a qualitative interpretation of the growth mechanism. This study confirms that Zn lead to the growth of a strained Cu2S-like structure, while the growth of the thread-like structure is probably driven by the release of the stress from the epitaxial phase.

Omnidirectional, broadband light absorption using large-area, ultrathin lossy metallic film coatings

NASA Astrophysics Data System (ADS)

Li, Zhongyang; Palacios, Edgar; Butun, Serkan; Kocer, Hasan; Aydin, Koray

2015-10-01

Resonant absorbers based on nanostructured materials are promising for variety of applications including optical filters, thermophotovoltaics, thermal emitters, and hot-electron collection. One of the significant challenges for such micro/nanoscale featured medium or surface, however, is costly lithographic processes for structural patterning which restricted from industrial production of complex designs. Here, we demonstrate lithography-free, broadband, polarization-independent optical absorbers based on a three-layer ultrathin film composed of subwavelength chromium (Cr) and oxide film coatings. We have measured almost perfect absorption as high as 99.5% across the entire visible regime and beyond (400-800 nm). In addition to near-ideal absorption, our absorbers exhibit omnidirectional independence for incidence angle over ±60 degrees. Broadband absorbers introduced in this study perform better than nanostructured plasmonic absorber counterparts in terms of bandwidth, polarization and angle independence. Improvements of such “blackbody” samples based on uniform thin-film coatings is attributed to extremely low quality factor of asymmetric highly-lossy Fabry-Perot cavities. Such broadband absorber designs are ultrathin compared to carbon nanotube based black materials, and does not require lithographic processes. This demonstration redirects the broadband super absorber design to extreme simplicity, higher performance and cost effective manufacturing convenience for practical industrial production.

Rapid amperometric detection of trace metals by inhibition of an ultrathin polypyrrole-based glucose biosensor.

PubMed

Ayenimo, Joseph G; Adeloju, Samuel B

2016-02-01

A sensitive and reliable inhibitive amperometric glucose biosensor is described for rapid trace metal determination. The biosensor utilises a conductive ultrathin (55 nm thick) polypyrrole (PPy) film for entrapment of glucose oxidase (GOx) to permit rapid inhibition of GOx activity in the ultrathin film upon exposure to trace metals, resulting in reduced glucose amperometric response. The biosensor demonstrates a relatively fast response time of 20s and does not require incubation. Furthermore, a complete recovery of GOx activity in the ultrathin PPy-GOx biosensor is quickly achieved by washing in 2mM EDTA for only 10s. The minimum detectable concentrations achieved with the biosensor for Hg(2+), Cu(2+), Pb(2+) and Cd(2+) by inhibitive amperometric detection are 0.48, 1.5, 1.6 and 4.0 µM, respectively. Also, suitable linear concentration ranges were achieved from 0.48-3.3 µM for Hg(2+), 1.5-10 µM for Cu(2+), 1.6-7.7 µM for Pb(2+) and 4-26 µM for Cd(2+). The use of Dixon and Cornish-Bowden plots revealed that the suppressive effects observed with Hg(2+) and Cu(2+) were via non-competitive inhibition, while those of Pb(2+) and Cd(2+) were due to mixed and competitive inhibition. The stronger inhibition exhibited by the trace metals on GOx activity in the ultrathin PPy-GOx film was also confirmed by the low inhibition constant obtained from this analysis. The biosensor was successfully applied to the determination of trace metals in tap water samples. Copyright © 2015 Elsevier B.V. All rights reserved.

High electron mobility and quantum oscillations in non-encapsulated ultrathin semiconducting Bi2O2Se

NASA Astrophysics Data System (ADS)

Wu, Jinxiong; Yuan, Hongtao; Meng, Mengmeng; Chen, Cheng; Sun, Yan; Chen, Zhuoyu; Dang, Wenhui; Tan, Congwei; Liu, Yujing; Yin, Jianbo; Zhou, Yubing; Huang, Shaoyun; Xu, H. Q.; Cui, Yi; Hwang, Harold Y.; Liu, Zhongfan; Chen, Yulin; Yan, Binghai; Peng, Hailin

2017-07-01

High-mobility semiconducting ultrathin films form the basis of modern electronics, and may lead to the scalable fabrication of highly performing devices. Because the ultrathin limit cannot be reached for traditional semiconductors, identifying new two-dimensional materials with both high carrier mobility and a large electronic bandgap is a pivotal goal of fundamental research. However, air-stable ultrathin semiconducting materials with superior performances remain elusive at present. Here, we report ultrathin films of non-encapsulated layered Bi2O2Se, grown by chemical vapour deposition, which demonstrate excellent air stability and high-mobility semiconducting behaviour. We observe bandgap values of ˜0.8 eV, which are strongly dependent on the film thickness due to quantum-confinement effects. An ultrahigh Hall mobility value of >20,000 cm2 V-1 s-1 is measured in as-grown Bi2O2Se nanoflakes at low temperatures. This value is comparable to what is observed in graphene grown by chemical vapour deposition and at the LaAlO3-SrTiO3 interface, making the detection of Shubnikov-de Haas quantum oscillations possible. Top-gated field-effect transistors based on Bi2O2Se crystals down to the bilayer limit exhibit high Hall mobility values (up to 450 cm2 V-1 s-1), large current on/off ratios (>106) and near-ideal subthreshold swing values (˜65 mV dec-1) at room temperature. Our results make Bi2O2Se a promising candidate for future high-speed and low-power electronic applications.

Seeds screening aqueous synthesis, multiphase interfacial separation and in situ optical characterization of invisible ultrathin silver nanowires.

PubMed

Zhang, Xiao-Yang; Xue, Xiao-Mei; Zhou, Huan-Li; Zhao, Ning; Shan, Feng; Su, Dan; Liu, Yi-Ran; Zhang, Tong

2018-06-21

We report a multi-step synthetic method to obtain ultrathin silver nanowires (Ag NWs) from an aqueous solution with a ∼17 nm diameter average, and where some of them decreased down to 9 nm. Carefully designed seed screening processes including LED irradiation at high temperature for a short time, and then continuous H2O2 etching, and relative growth mechanisms of high-yield five-twinned pentagonal seeds and ultrathin Ag NWs in aqueous environment are detailed. Then, a rapid and simple multiphase interfacial assembly method particularly suitable for the separation of ultrathin Ag NWs from various by-products was demonstrated with a clear mechanism explanation. Next, a unique optical interaction between light and individual AG NWs, as well as feature structures in the AG NWs film, was investigated by a micro-domain optical confocal microscope measurement in situ together with a theoretical explanation using modal transmission theory. That revealed that the haze problem of AG NWs films was not only arising from the interaction between light and individual or crossed Ag NWs but was also greatly dependent on a weak coupling effect of leaky modes supported by adjacent Ag NWs with large distances which had not been considered before. We then provided direct experimental evidence and concluded how to obtain haze-free films with 100% transparency in the whole visible range based on ultrathin Ag NWs. This breakthrough in diameter confinement and purification of Ag NWs is a highly expected step to overcome the well-focused light diffusion and absorption problems of Ag NWs-based devices applied in various fields such as flexible electronics, high-clarity displays, visible transparent heaters, photovoltaics and various optoelectronic technologies.

EDMOS in ultrathin FDSOI: Impact of the drift region properties

NASA Astrophysics Data System (ADS)

Litty, Antoine; Ortolland, Sylvie; Golanski, Dominique; Dutto, Christian; Cristoloveanu, Sorin

2016-11-01

The development of high-voltage MOSFET (HVMOS) is necessary for including power management or radiofrequency functionalities in CMOS technology. In this paper, we investigate the fabrication and optimization of an Extended Drain MOSFET (EDMOS) directly integrated in the ultra-thin SOI film (7 nm) of the 28 nm FDSOI CMOS technology node. Thanks to TCAD simulations, we analyse in detail the device behaviour as a function of the doping level and length of the drift region. The influence of the back-plane doping type and of the back-biasing schemes is discussed. DC measurements of fabricated EDMOS samples reveal promising performances in particular in terms of specific on-resistance versus breakdown voltage trade-off. The experimental results indicate that, even in an ultrathin film, the engineering of the drift region could be a lever to obtain integrated HVMOS (3.3-5 V).

Spatially and momentum resolved energy electron loss spectra from an ultra-thin PrNiO{sub 3} layer

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

Kinyanjui, M. K., E-mail: michael.kinyanjui@uni-ulm.de; Kaiser, U.; Benner, G.

2015-05-18

We present an experimental approach which allows for the acquisition of spectra from ultra-thin films at high spatial, momentum, and energy resolutions. Spatially and momentum (q) resolved electron energy loss spectra have been obtained from a 12 nm ultra-thin PrNiO{sub 3} layer using a nano-beam electron diffraction based approach which enabled the acquisition of momentum resolved spectra from individual, differently oriented nano-domains and at different positions of the PrNiO{sub 3} thin layer. The spatial and wavelength dependence of the spectral excitations are obtained and characterized after the analysis of the experimental spectra using calculated dielectric and energy loss functions. The presentedmore » approach makes a contribution towards obtaining momentum-resolved spectra from nanostructures, thin film, heterostructures, surfaces, and interfaces.« less

Ultra-thin multilayer capacitors.

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

Renk, Timothy Jerome; Monson, Todd C.

2009-06-01

The fabrication of ultra-thin lanthanum-doped lead zirconium titanate (PLZT) multilayer ceramic capacitors (MLCCs) using a high-power pulsed ion beam was studied. The deposition experiments were conducted on the RHEPP-1 facility at Sandia National Laboratories. The goal of this work was to increase the energy density of ceramic capacitors through the formation of a multilayer device with excellent materials properties, dielectric constant, and standoff voltage. For successful device construction, there are a number of challenging requirements including achieving correct stoichiometric and crystallographic composition of the deposited PLZT, as well as the creation of a defect free homogenous film. This report detailsmore » some success in satisfying these requirements, although 900 C temperatures were necessary for PLZT perovskite phase formation. These temperatures were applied to a previously deposited multi-layer film which was then post-annealed to this temperature. The film exhibited mechanical distress attributable to differences in the coefficient of thermal expansion (CTE) of the various layers. This caused significant defects in the deposited films that led to shorts across devices. A follow-on single layer deposition without post-anneal produced smooth layers with good interface behavior, but without the perovskite phase formation. These issues will need to be addressed in order for ion beam deposited MLCCs to become a viable technology. It is possible that future in-situ heating during deposition may address both the CTE issue, and result in lowered processing temperatures, which in turn could raise the probability of successful MLCC formation.« less

Oxidation of the Ru(0001) surface covered by weakly bound, ultrathin silicate films

DOE PAGES

Emmez, Emre; Anibal Boscoboinik, J.; Tenney, Samuel; ...

2015-06-30

Bilayer silicate films grown on metal substrates are weakly bound to the metal surfaces, which allows ambient gas molecules to intercalate the oxide/metal interface. In this work, we studied the interaction of oxygen with Ru(0001) supported ultrathin silicate and aluminosilicate films at elevated O 2 pressures (10 -5–10 mbar) and temperatures (450–923 K). The results show that the silicate films stay essentially intact under these conditions, and oxygen in the film does not exchange with oxygen in the ambient. O 2 molecules readily penetrate the film and dissociate on the underlying Ru surface underneath. Also, the silicate layer does howevermore » strongly passivate the Ru surface towards RuO 2(110) oxide formation that readily occurs on bare Ru(0001) under the same conditions. Lastly, the results indicate considerable spatial effects for oxidation reactions on metal surfaces in the confined space at the interface. Moreover, the aluminosilicate films completely suppress the Ru oxidation, providing some rationale for using crystalline aluminosilicates in anti-corrosion coatings.« less

Ultra-thin solid oxide fuel cells: Materials and devices

NASA Astrophysics Data System (ADS)

Kerman, Kian

Solid oxide fuel cells are electrochemical energy conversion devices utilizing solid electrolytes transporting O2- that typically operate in the 800 -- 1000 °C temperature range due to the large activation barrier for ionic transport. Reducing electrolyte thickness or increasing ionic conductivity can enable lower temperature operation for both stationary and portable applications. This thesis is focused on the fabrication of free standing ultrathin (<100 nm) oxide membranes of prototypical O 2- conducting electrolytes, namely Y2O3-doped ZrO2 and Gd2O3-doped CeO2. Fabrication of such membranes requires an understanding of thin plate mechanics coupled with controllable thin film deposition processes. Integration of free standing membranes into proof-of-concept fuel cell devices necessitates ideal electrode assemblies as well as creative processing schemes to experimentally test devices in a high temperature dual environment chamber. We present a simple elastic model to determine stable buckling configurations for free standing oxide membranes. This guides the experimental methodology for Y 2O3-doped ZrO2 film processing, which enables tunable internal stress in the films. Using these criteria, we fabricate robust Y2O3-doped ZrO2 membranes on Si and composite polymeric substrates by semiconductor and micro-machining processes, respectively. Fuel cell devices integrating these membranes with metallic electrodes are demonstrated to operate in the 300 -- 500 °C range, exhibiting record performance at such temperatures. A model combining physical transport of electronic carriers in an insulating film and electrochemical aspects of transport is developed to determine the limits of performance enhancement expected via electrolyte thickness reduction. Free standing oxide heterostructures, i.e. electrolyte membrane and oxide electrodes, are demonstrated. Lastly, using Y2O3-doped ZrO2 and Gd2O 3-doped CeO2, novel electrolyte fabrication schemes are explored to develop oxide alloys and nanoscale compositionally graded membranes that are thermomechanically robust and provide added interfacial functionality. The work in this thesis advances experimental state-of-the-art with respect to solid oxide fuel cell operation temperature, provides fundamental boundaries expected for ultrathin electrolytes, develops the ability to integrate highly dissimilar material (such as oxide-polymer) heterostructures, and introduces nanoscale compositionally graded electrolyte membranes that can lead to monolithic materials having multiple functionalities.

Molecular dynamics simulations of disjoining pressure effects in ultra-thin water films on a metal surface

NASA Astrophysics Data System (ADS)

Hu, Han; Sun, Ying

2013-11-01

Disjoining pressure, the excess pressure in an ultra-thin liquid film as a result of van der Waals interactions, is important in lubrication, wetting, flow boiling, and thin film evaporation. The classic theory of disjoining pressure is developed for simple monoatomic liquids. However, real world applications often utilize water, a polar liquid, for which fundamental understanding of disjoining pressure is lacking. In the present study, molecular dynamics (MD) simulations are used to gain insights into the effect of disjoining pressure in a water thin film. Our MD models were firstly validated against Derjaguin's experiments on gold-gold interactions across a water film and then verified against disjoining pressure in an argon thin film using the Lennard-Jones potential. Next, a water thin film adsorbed on a gold surface was simulated to examine the change of vapor pressure with film thickness. The results agree well with the classic theory of disjoining pressure, which implies that the polar nature of water molecules does not play an important role. Finally, the effects of disjoining pressure on thin film evaporation in nanoporous membrane and on bubble nucleation are discussed.

Structural, electronic and chemical properties of metal/oxide and oxide/oxide interfaces and thin film structures

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

Lad, Robert J.

1999-12-14

This project focused on three different aspects of oxide thin film systems: (1) Model metal/oxide and oxide/oxide interface studies were carried out by depositing ultra-thin metal (Al, K, Mg) and oxide (MgO, AlO{sub x}) films on TiO{sub 2}, NiO and {alpha}-Al{sub 2}O{sub 3} single crystal oxide substrates. (2) Electron cyclotron resonance (ECR) oxygen plasma deposition was used to fabricate AlO{sub 3} and ZrO{sub 2} films on sapphire substrates, and film growth mechanisms and structural characteristics were investigated. (3) The friction and wear characteristics of ZrO{sub 2} films on sapphire substrates in unlubricated sliding contact were studied and correlated with filmmore » microstructure. In these studies, thin film and interfacial regions were characterized using diffraction (RHEED, LEED, XRD), electron spectroscopies (XPS, UPS, AES), microscopy (AFM) and tribology instruments (pin-on-disk, friction microprobe, and scratch tester). By precise control of thin film microstructure, an increased understanding of the structural and chemical stability of interface regions and tribological performance of ultra-thin oxide films was achieved in these important ceramic systems.« less

Acoustic Phonons and Mechanical Properties of Ultra-Thin Porous Low-k Films: A Surface Brillouin Scattering Study

NASA Astrophysics Data System (ADS)

Zizka, J.; King, S.; Every, A.; Sooryakumar, R.

2018-04-01

To reduce the RC (resistance-capacitance) time delay of interconnects, a key development of the past 20 years has been the introduction of porous low-k dielectrics to replace the traditional use of SiO2. Moreover, in keeping pace with concomitant reduction in technology nodes, these low-k materials have reached thicknesses below 100 nm wherein the porosity becomes a significant fraction of the film volume. The large degree of porosity not only reduces mechanical strength of the dielectric layer but also renders a need for non-destructive approaches to measure the mechanical properties of such ultra-thin films within device configurations. In this study, surface Brillouin scattering (SBS) is utilized to determine the elastic constants, Poisson's ratio, and Young's modulus of these porous low-k SiOC:H films (˜ 25-250 nm thick) grown on Si substrates by probing surface acoustic phonons and their dispersions.

Conformal surface plasmons propagating on ultrathin and flexible films

PubMed Central

Shen, Xiaopeng; Cui, Tie Jun; Martin-Cano, Diego; Garcia-Vidal, Francisco J.

2013-01-01

Surface plasmon polaritons (SPPs) are localized surface electromagnetic waves that propagate along the interface between a metal and a dielectric. Owing to their inherent subwavelength confinement, SPPs have a strong potential to become building blocks of a type of photonic circuitry built up on 2D metal surfaces; however, SPPs are difficult to control on curved surfaces conformably and flexibly to produce advanced functional devices. Here we propose the concept of conformal surface plasmons (CSPs), surface plasmon waves that can propagate on ultrathin and flexible films to long distances in a wide broadband range from microwave to mid-infrared frequencies. We present the experimental realization of these CSPs in the microwave regime on paper-like dielectric films with a thickness 600-fold smaller than the operating wavelength. The flexible paper-like films can be bent, folded, and even twisted to mold the flow of CSPs. PMID:23248311

Water Vapor Uptake of Ultrathin Films of Biologically Derived Nanocrystals: Quantitative Assessment with Quartz Crystal Microbalance and Spectroscopic Ellipsometry.

PubMed

Niinivaara, Elina; Faustini, Marco; Tammelin, Tekla; Kontturi, Eero

2015-11-10

Despite the relevance of water interactions, explicit analysis of vapor adsorption on biologically derived surfaces is often difficult. Here, a system was introduced to study the vapor uptake on a native polysaccharide surface; namely, cellulose nanocrystal (CNC) ultrathin films were examined with a quartz crystal microbalance with dissipation monitoring (QCM-D) and spectroscopic ellipsometry (SE). A significant mass uptake of water vapor by the CNC films was detected using the QCM-D upon increasing relative humidity. In addition, thickness changes proportional to changes in relative humidity were detected using SE. Quantitative analysis of the results attained indicated that in preference to being soaked by water at the point of hydration each individual CNC in the film became enveloped by a 1 nm thick layer of adsorbed water vapor, resulting in the detected thickness response.

Localized Control of Curie Temperature in Perovskite Oxide Film by Capping-Layer-Induced Octahedral Distortion

DOE PAGES

Thomas, S.; Kuiper, B.; Hu, J.; ...

2017-10-27

With reduced dimensionality, it is often easier to modify the properties of ultrathin films than their bulk counterparts. Strain engineering, usually achieved by choosing appropriate substrates, has been proven effective in controlling the properties of perovskite oxide films. An emerging alternative route for developing new multifunctional perovskite is by modification of the oxygen octahedral structure. Here we report the control of structural oxygen octahedral rotation in ultrathin perovskite SrRuO 3 films by the deposition of a SrTiO 3 capping layer, which can be lithographically patterned to achieve local control. Here, using a scanning Sagnac magnetic microscope, we show an increasemore » in the Curie temperature of SrRuO 3 due to the suppression octahedral rotations revealed by the synchrotron x-ray diffraction. Lastly, this capping-layer-based technique may open new possibilities for developing functional oxide materials.« less

Transport properties of ultra-thin VO{sub 2} films on (001) TiO{sub 2} grown by reactive molecular-beam epitaxy

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

Paik, Hanjong; Tashman, Joshua W.; Moyer, Jarrett A.

2015-10-19

We report the growth of (001)-oriented VO{sub 2} films as thin as 1.5 nm with abrupt and reproducible metal-insulator transitions (MIT) without a capping layer. Limitations to the growth of thinner films with sharp MITs are discussed, including the Volmer-Weber type growth mode due to the high energy of the (001) VO{sub 2} surface. Another key limitation is interdiffusion with the (001) TiO{sub 2} substrate, which we quantify using low angle annular dark field scanning transmission electron microscopy in conjunction with electron energy loss spectroscopy. We find that controlling island coalescence on the (001) surface and minimization of cation interdiffusion bymore » using a low growth temperature followed by a brief anneal at higher temperature are crucial for realizing ultrathin VO{sub 2} films with abrupt MIT behavior.« less

Localized Control of Curie Temperature in Perovskite Oxide Film by Capping-Layer-Induced Octahedral Distortion.

PubMed

Thomas, S; Kuiper, B; Hu, J; Smit, J; Liao, Z; Zhong, Z; Rijnders, G; Vailionis, A; Wu, R; Koster, G; Xia, J

2017-10-27

With reduced dimensionality, it is often easier to modify the properties of ultrathin films than their bulk counterparts. Strain engineering, usually achieved by choosing appropriate substrates, has been proven effective in controlling the properties of perovskite oxide films. An emerging alternative route for developing new multifunctional perovskite is by modification of the oxygen octahedral structure. Here we report the control of structural oxygen octahedral rotation in ultrathin perovskite SrRuO_{3} films by the deposition of a SrTiO_{3} capping layer, which can be lithographically patterned to achieve local control. Using a scanning Sagnac magnetic microscope, we show an increase in the Curie temperature of SrRuO_{3} due to the suppression octahedral rotations revealed by the synchrotron x-ray diffraction. This capping-layer-based technique may open new possibilities for developing functional oxide materials.

Acoustic Phonons and Mechanical Properties of Ultra-Thin Porous Low- k Films: A Surface Brillouin Scattering Study

NASA Astrophysics Data System (ADS)

Zizka, J.; King, S.; Every, A.; Sooryakumar, R.

2018-07-01

To reduce the RC (resistance-capacitance) time delay of interconnects, a key development of the past 20 years has been the introduction of porous low- k dielectrics to replace the traditional use of SiO2. Moreover, in keeping pace with concomitant reduction in technology nodes, these low- k materials have reached thicknesses below 100 nm wherein the porosity becomes a significant fraction of the film volume. The large degree of porosity not only reduces mechanical strength of the dielectric layer but also renders a need for non-destructive approaches to measure the mechanical properties of such ultra-thin films within device configurations. In this study, surface Brillouin scattering (SBS) is utilized to determine the elastic constants, Poisson's ratio, and Young's modulus of these porous low- k SiOC:H films (˜ 25-250 nm thick) grown on Si substrates by probing surface acoustic phonons and their dispersions.

In Vitro Biocompatibility of Si Alloyed Multi-Principal Element Carbide Coatings

PubMed Central

Vladescu, Alina; Titorencu, Irina; Dekhtyar, Yuri; Jinga, Victor; Pruna, Vasile; Balaceanu, Mihai; Dinu, Mihaela; Pana, Iulian; Vendina, Viktorija

2016-01-01

In the current study, we have examined the possibility to improve the biocompatibility of the (TiZrNbTaHf)C through replacement of either Ti or Ta by Si. The coatings were deposited on Si and 316L stainless steel substrates by magnetron sputtering in an Ar+CH4 mixed atmosphere and were examined for elemental composition, chemical bonds, surface topography, surface electrical charge and biocompatible characteristics. The net surface charge was evaluated at nano and macroscopic scale by measuring the electrical potential and work function, respectively. The biocompatible tests comprised determination of cell viability and cell attachment to the coated surface. The deposited coatings had C/(metal+Si) ratios close to unity, while a mixture of metallic carbide, free-carbon and oxidized species formed on the film surface. The coatings’ surfaces were smooth and no influence of surface roughness on electrical charge or biocompatibility was found. The biocompatible characteristics correlated well with the electrical potential/work function, suggesting a significant role of surface charge in improving biocompatibility, particularly cell attachment to coating's surface. Replacement of either Ti or Ta by Si in the (TiZrNbTaHf)C coating led to an enhanced surface electrical charge, as well as to superior biocompatible properties, with best results for the (TiZrNbSiHf)C coating. PMID:27571361

Qualitative and quantitative differentiation of gases using ZnO thin film gas sensors and pattern recognition analysis.

PubMed

Pati, Sumati; Maity, A; Banerji, P; Majumder, S B

2014-04-07

In the present work we have grown highly textured, ultra-thin, nano-crystalline zinc oxide thin films using a metal organic chemical vapor deposition technique and addressed their selectivity towards hydrogen, carbon dioxide and methane gas sensing. Structural and microstructural characteristics of the synthesized films were investigated utilizing X-ray diffraction and electron microscopy techniques respectively. Using a dynamic flow gas sensing measurement set up, the sensing characteristics of these films were investigated as a function of gas concentration (10-1660 ppm) and operating temperature (250-380 °C). ZnO thin film sensing elements were found to be sensitive to all of these gases. Thus at a sensor operating temperature of ~300 °C, the response% of the ZnO thin films were ~68, 59, and 52% for hydrogen, carbon monoxide and methane gases respectively. The data matrices extracted from first Fourier transform analyses (FFT) of the conductance transients were used as input parameters in a linear unsupervised principal component analysis (PCA) pattern recognition technique. We have demonstrated that FFT combined with PCA is an excellent tool for the differentiation of these reducing gases.

Surface temperature determination in surface analytic systems by infrared optical pyrometry

NASA Technical Reports Server (NTRS)

Wheeler, Donald R.; Jones, William R., Jr.; Pepper, Stephen V.

1988-01-01

An IR pyrometric technique for measuring the surface temperatures of metal specimens in an ultrahigh-vacuum analytic chamber is described and demonstrated. The experimental setup comprises a commercial IR microscope with a long-working-distance right-angle objective (focal spot diameter 1 mm at 53 cm), a metal-coated glass vacuum chamber with a Ta-mesh-covered quartz viewport, an Mo specimen stub with an internal heating element, and a Ta disk test specimen with a flat side coated with a high-emissivity graphite film. The results of an initial calibration test are presented graphically and briefly characterized. The measurement error at 450 C is found to be less than 10 C.

Clay induced aggregation of a tetra-cationic metalloporphyrin in Layer by Layer self assembled film

NASA Astrophysics Data System (ADS)

Banik, Soma; Bhattacharjee, J.; Hussain, S. A.; Bhattacharjee, D.

2015-12-01

Porphyrins have a general tendency to form aggregates in ultrathin films. Also electrostatic adsorption of cationic porphyrins onto anionic nano clay platelets results in the flattening of porphyrin moieties. The flattening is evidenced by the red-shifting of Soret band with respect to the aqueous solution. In the present communication, we have studied the clay induced aggregation behaviour of a tetra-cationic metalloporphyrin Manganese (III) 5, 10, 15, 20-tetra (4 pyridyl)-21 H, 23 H-porphine chloride tetrakis (methochloride) (MnTMPyP) in Layer-by-Layer (LbL) self assembled film. The adsorption of dye molecules onto nano clay platelets resulted in the flattening of the meso substituent groups of the dye chromophore. In Layer-by-Layer ultrathin film, the flattened porphyrin molecules tagged nano clay platelets were further associated to form porphyrin aggregates. This has been clearly demonstrated from the UV-vis absorption spectroscopic studies. Atomic Force Microscopic (AFM) studies gave visual evidence of the association of organo-clay hybrid molecules in the LbL film.

Chemical vapor deposition of anisotropic ultrathin gold films on optical fibers: real-time sensing by tilted fiber Bragg gratings and use of a dielectric pre-coating

NASA Astrophysics Data System (ADS)

Mandia, David J.; Zhou, Wenjun; Ward, Matthew J.; Joress, Howie; Giorgi, Javier B.; Gordon, Peter; Albert, Jacques; Barry, Seán. T.

2014-09-01

Tilted fiber Bragg gratings (TFBGs) are refractometry-based sensor platforms that have been employed herein as devices for the real-time monitoring of chemical vapour deposition (CVD) in the near-infrared range (NIR). The coreguided light launched within the TFBG core is back-reflected off a gold mirror sputtered onto the fiber-end and is scattered out into the cladding where it can interact with a nucleating thin film. Evanescent fields of the growing gold nanostructures behave differently depending on the polarization state of the core-guided light interrogating the growing film, therefore the resulting spectral profile is typically decomposed into two separate peak families for the orthogonal S- and P-polarizations. Wavelength shifts and attenuation profiles generated from gold films in the thickness regime of 5-100 nm are typically degenerate for deposition directly onto the TFBG. However, a polarization-dependence can be imposed by adding a thin dielectric pre-coating onto the TFBG prior to using the device for CVD monitoring of the ultrathin gold films. It is found that addition of the pre-coating enhances the sensitivity of the P-polarized peak family to the deposition of ultrathin gold films and renders the films optically anisotropic. It is shown herein that addition of the metal oxide coating can increase the peak-to-peak wavelength separation between orthogonal polarization modes as well as allow for easy resonance tracking during deposition. This is also the first reporting of anisotropic gold films generated from this particular gold precursor and CVD process. Using an ensemble of x-ray techniques, the local fine structure of the gold films deposited directly on the TFBG is compared to gold films of similar thicknesses deposited on the Al2O3 pre-coated TFBG and witness slides.

Materials science and integration bases for fabrication of (BaxSr1-x)TiO3 thin film capacitors with layered Cu-based electrodes

NASA Astrophysics Data System (ADS)

Fan, W.; Kabius, B.; Hiller, J. M.; Saha, S.; Carlisle, J. A.; Auciello, O.; Chang, R. P. H.; Ramesh, R.

2003-11-01

The synthesis and fundamental material properties of layered TiAl/Cu/Ta electrodes were investigated to achieve the integration of Cu electrodes with high-dielectric constant (κ) oxide thin films for application to the fabrication of high-frequency devices. The Ta layer is an excellent diffusion barrier to inhibit deleterious Cu diffusion into the Si substrate, while the TiAl layer provides an excellent barrier against oxygen diffusion into the Cu layer to inhibit Cu oxidation during the growth of the high-κ layer in an oxygen atmosphere. Polycrystalline (BaxSr1-x)TiO3 (BST) thin films were grown on the Cu-based bottom electrode by rf magnetron sputtering at temperatures in the range 400-600 °C in oxygen, to investigate the performance of BST/Cu-based capacitors. Characterization of the Cu-based layered structure using surface analytical methods showed that two amorphous oxide layers were formed on both sides of the TiAl barrier, such that the oxide layer on the free surface of the TiAl layer correlates with TiAlOx, while the oxide layer at the TiAl/Cu interface is an Al2O3-rich layer. This double amorphous barrier layer structure effectively prevents oxygen penetration towards the underlying Cu and Ta layers. The TiAlOx interfacial layer, which has a relatively low dielectric constant compared with BST, reduced the total capacitance of the BST thin film capacitors. In addition, the layered electrode-oxide interface roughening observed during the growth of BST films at high temperature, due to copper grain growth, resulted in large dielectric loss on the fabricated BST capacitors. These problems were solved by growing the BST layer at 450 °C followed by a rapid thermal annealing at 700 °C. This process significantly reduced the thickness of the TiAlOx layer and interface roughness resulting in BST capacitors exhibiting properties suitable for the fabrication of high-performance high-frequency devices. In summary, relatively high dielectric constant (280), low dielectric loss (0.007), and low leakage current (<2×10-8 A/cm2 at 100 kV/cm) were achieved for BST thin film capacitors with Cu-based electrodes.

The Effect of Film Thickness on the Gas Sensing Properties of Ultra-Thin TiO₂ Films Deposited by Atomic Layer Deposition.

PubMed

Wilson, Rachel L; Simion, Cristian Eugen; Blackman, Christopher S; Carmalt, Claire J; Stanoiu, Adelina; Di Maggio, Francesco; Covington, James A

2018-03-01

Analyte sensitivity for gas sensors based on semiconducting metal oxides should be highly dependent on the film thickness, particularly when that thickness is on the order of the Debye length. This thickness dependence has previously been demonstrated for SnO₂ and inferred for TiO₂. In this paper, TiO₂ thin films have been prepared by Atomic Layer Deposition (ALD) using titanium isopropoxide and water as precursors. The deposition process was performed on standard alumina gas sensor platforms and microscope slides (for analysis purposes), at a temperature of 200 °C. The TiO₂ films were exposed to different concentrations of CO, CH₄, NO₂, NH₃ and SO₂ to evaluate their gas sensitivities. These experiments showed that the TiO₂ film thickness played a dominant role within the conduction mechanism and the pattern of response for the electrical resistance towards CH₄ and NH₃ exposure indicated typical n -type semiconducting behavior. The effect of relative humidity on the gas sensitivity has also been demonstrated.

Love-type surface acoustic wave on Y-X LiTaO3 with amorphous Ta2O5 thin film

NASA Astrophysics Data System (ADS)

Kakio, Shoji; Fukasawa, Haruka; Hosaka, Keiko

2015-07-01

In this study, to obtain a substrate structure with a lower phase velocity, the propagation properties of a Love-type surface acoustic wave (Love SAW) on Y-X LiTaO3 (LT) with an amorphous tantalum pentoxide (a-Ta2O5) thin film were investigated using a simple delay line and a resonator with a wavelength λ of 8 µm. The insertion loss of a simple delay line was decreased markedly by loading with an a-Ta2O5 film owing to a transformation from a leaky SAW (LSAW) to a non-leaky Love SAW. A phase velocity of 3,340 m/s, a coupling factor of 5.8%, and a propagation loss of 0.03 dB/λ were obtained for a normalized thickness h/λ of 0.120. Moreover, the resonance properties of the Love SAW were almost equal or superior to those for an LSAW on Al/36° Y-X LT, except for the fractional bandwidth.

Dynamics of ultra-thin polystyrene with and without a (artificial) dead layer studied by resonance enhanced dynamic light scattering

NASA Astrophysics Data System (ADS)

Vianna, S. D. B.; Lin, F. Y.; Plum, M. A.; Duran, H.; Steffen, W.

2017-05-01

Using non-invasive, marker-free resonance enhanced dynamic light scattering, the dynamics of capillary waves on ultrathin polystyrene films' coupling to the viscoelastic and mechanical properties have been studied. The dynamics of ultrathin polymer films is still debated. In particular the question of what influence either the solid substrate and/or the fluid-gas interface has on the dynamics and the mechanical properties of films of glass forming liquids as polymers is in the focus of the present research. As a consequence, e.g., viscosity close to interfaces and thus the average viscosity of very thin films are prone to change. This study is focused on atactic, non-entangled polystyrene thin films on the gold surface. A slow dynamic mode was observed with Vogel-Fulcher-Tammann temperature dependence, slowing down with decreasing film thickness. We tentatively attribute this relaxation mode to overdamped capillary waves because of its temperature dependence and the dispersion with a wave vector which was found. No signs of a more mobile layer at the air/polymer interface or of a "dead layer" at the solid/polymer interface were found. Therefore we investigated the influence of an artificially created dead layer on the capillary wave dynamics by introducing covalently bound polystyrene polymer brushes as anchors. The dynamics was slowed down to a degree more than expected from theoretical work on the increase of density close to the solid liquid interface—instead of a "dead layer" of 2 nm, the interaction seems to extend more than 10 nm into the polymer.

Bias current dependence of resistivity in Co0.4Fe0.4B0.2 ultrathin film prepared by RF magnetron sputtering

NASA Astrophysics Data System (ADS)

Mandal, Snehal; Mazumdar, Dipak; Das, I.

2018-04-01

Ultrathin film of Co0.4Fe0.4B0.2 was prepared on p-type Si (100) substrate by RF magnetron sputtering. X-Ray Reflectivity and Atomic Force Microscopy measurements were performed to estimate the thickness and surface roughness of the film. Electrical transport measurements were performed by four-probe method in a current-in-plane (CIP) geometry. Presence of non-linearity in the current-voltage (I-V) characteristics was observed at higher current range. The electrical resistivity was found to change by several orders of magnitude (105) by changing the bias current from nano-ampere (nA) to milli-ampere (mA) range. This bias current dependence of the resistivity has been explained by different transport mechanisms.

Formation of silicon nanodots via ion beam sputtering of ultrathin gold thin film coatings on Si

PubMed Central

2011-01-01

Ion beam sputtering of ultrathin film Au coatings used as a physical catalyst for self-organization of Si nanostructures has been achieved by tuning the incident particle energy. This approach holds promise as a scalable nanomanufacturing parallel processing alternative to candidate nanolithography techniques. Structures of 11- to 14-nm Si nanodots are formed with normal incidence low-energy Ar ions of 200 eV and fluences above 2 × 1017 cm-2. In situ surface characterization during ion irradiation elucidates early stage ion mixing migration mechanism for nanodot self-organization. In particular, the evolution from gold film islands to the formation of ion-induced metastable gold silicide followed by pure Si nanodots formed with no need for impurity seeding. PMID:21711934

Quantum-Fluctuation Effects in the Transport Properties of Ultrathin Films of Disordered Superconductors above the Paramagnetic Limit

NASA Astrophysics Data System (ADS)

Khodas, M.; Levchenko, A.; Catelani, G.

2012-06-01

We study the transport in ultrathin disordered film near the quantum critical point induced by the Zeeman field. We calculate corrections to the normal state conductivity due to quantum pairing fluctuations. The fluctuation-induced transport is mediated by virtual rather than real quasiparticle excitations. We find that at zero temperature, where the corrections come from purely quantum fluctuations, the Aslamazov-Larkin paraconductivity term, the Maki-Thompson interference contribution, and the density of states effects are all of the same order. The total correction leads to the negative magnetoresistance. This result is in qualitative agreement with the recent transport observations in the parallel magnetic field of the homogeneously disordered amorphous films and superconducting two-dimensional electron gas realized at the oxide interfaces.

Tantalum oxide/silicon nitride: A negatively charged surface passivation stack for silicon solar cells

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

Wan, Yimao, E-mail: yimao.wan@anu.edu.au; Bullock, James; Cuevas, Andres

2015-05-18

This letter reports effective passivation of crystalline silicon (c-Si) surfaces by thermal atomic layer deposited tantalum oxide (Ta{sub 2}O{sub 5}) underneath plasma enhanced chemical vapour deposited silicon nitride (SiN{sub x}). Cross-sectional transmission electron microscopy imaging shows an approximately 2 nm thick interfacial layer between Ta{sub 2}O{sub 5} and c-Si. Surface recombination velocities as low as 5.0 cm/s and 3.2 cm/s are attained on p-type 0.8 Ω·cm and n-type 1.0 Ω·cm c-Si wafers, respectively. Recombination current densities of 25 fA/cm{sup 2} and 68 fA/cm{sup 2} are measured on 150 Ω/sq boron-diffused p{sup +} and 120 Ω/sq phosphorus-diffused n{sup +} c-Si, respectively. Capacitance–voltage measurements reveal a negativemore » fixed insulator charge density of −1.8 × 10{sup 12 }cm{sup −2} for the Ta{sub 2}O{sub 5} film and −1.0 × 10{sup 12 }cm{sup −2} for the Ta{sub 2}O{sub 5}/SiN{sub x} stack. The Ta{sub 2}O{sub 5}/SiN{sub x} stack is demonstrated to be an excellent candidate for surface passivation of high efficiency silicon solar cells.« less

Peripheral Ferroelectric Domain Switching and Polarization Fatigue in Nonvolatile Memory Elements of Continuous Pt/SrBi2Ta2O9/Pt Thin-Film Capacitors

NASA Astrophysics Data System (ADS)

Chen, Min-Chuan; Jiang, An-Quan

2011-07-01

We verify the domain sideway motion around the peripheral regions of the crossed capacitors of top and bottom electrode bars without electrode coverage. To avoid the crosstalk problem between adjacent memory cells, the safe distance between adjacent elements of Pt/SrBi2Ta2O9/Pt thin-film capacitors is estimated to be 0.156 μm. Moreover, the fatigue of Pt/SrBi2Ta2O9/Pt thin-film capacitors is independent of the individual memory size due to the absence of etching damage.

Multilevel Dual Damascene copper interconnections

NASA Astrophysics Data System (ADS)

Lakshminarayanan, S.

Copper has been acknowledged as the interconnect material for future generations of ICs to overcome the bottlenecks on speed and reliability present with the current Al based wiring. A new set of challenges brought to the forefront when copper replaces aluminum, have to be met and resolved to make it a viable option. Unit step processes related to copper technology have been under development for the last few years. In this work, the application of copper as the interconnect material in multilevel structures with SiO2 as the interlevel dielectric has been explored, with emphasis on integration issues and complete process realization. Interconnect definition was achieved by the Dual Damascene approach using chemical mechanical polishing of oxide and copper. The choice of materials used as adhesion promoter/diffusion barrier included Ti, Ta and CVD TiN. Two different polish chemistries (NH4OH or HNO3 based) were used to form the interconnects. The diffusion barrier was removed during polishing (in the case of TiN) or by a post CMP etch (as with Ti or Ta). Copper surface passivation was performed using boron implantation and PECVD nitride encapsulation. The interlevel dielectric way composed of a multilayer stack of PECVD SiO2 and SixNy. A baseline process sequence which ensured the mechanical and thermal compatibility of the different unit steps was first created. A comprehensive test vehicle was designed and test structures were fabricated using the process flow developed. Suitable modifications were subsequently introduced in the sequence as and when processing problems were encountered. Electrical characterization was performed on the fabricated devices, interconnects, contacts and vias. The structures were subjected to thermal stressing to assess their stability and performance. The measurement of interconnect sheet resistances revealed lower copper loss due to dishing on samples polished using HNO3 based slurry. Interconnect resistances remained stable upto 400oC, 500oC and 600oC for Ti, TiN and Ta barriers respectively. Via resistivity on the order of 10-9/ /Omegacm2 was measured for Cu/Ta/Cu interfaces and no degradation in the via resistance was observed upto 600oC on the 2 μm and 3 μm wide contact windows. Characterization of diode leakage and subthreshold currents of CMOS transistors fabricated with Ta adhesion layers, showed the failure of the Ta barrier at 450oC. Despite the good barrier performance of the CVD TiN films, obtaining low contact resistivity may be a concern. The potential use of Cu-Mg alloy as the backend metallization has also been studied. Fully encapsulated wiring has been fabricated by causing the Mg to out- diffuse towards the Cu/SiO2 interfaces and the free copper surface. The inter-connects exhibited good stability and oxidation resistance, but via resistances were extremely high, probably due to the presence of insulating films like MgO or MgF2 at the interface between the two metal levels. It may be possible to decrease the via resistance to values comparable to Cu/Ta/Cu by altering the process flow and using a suitable via clean. When used at the contact level, undesirable interaction with the CoSi2 film was observed at temperatures as low as 350oC. Another problem was the high contact resistance at the Cu-Mg/CoSi2 interface. Hence the use of this alloy as a contact fill material is not feasible at this time. An additional barrier layer may be required between the Cu-Mg and CoSi2 films to protect the integrity of the silicide and provide low contact resistance.

Interparticle coupling effect of silver-gold heterodimer to enhance light harvesting in ultrathin perovskite solar cell

NASA Astrophysics Data System (ADS)

Hu, Zhaosheng; Ma, Tingli; Hayase, Shuzi

2018-01-01

Thin perovskite solar cells are under intensive interest since they reduce the amount of absorber layer, especially toxic lead in methylammonium lead iodide (MAPbI3) devices and have wide application in semitransparent and tandem solar cells. However, due to the decrease of the layer thickness, thin perovskite devices with weak light-harvesting have poor performance. Moreover, the performance of plasmonic thin perovskite devices by incorporating noncoupling metal NPs cannot give comparable performance with normal devices. In this perspective, we discuss the implication of employing random silver-gold heterodimers in MAPbI3 solar cells with the aim of establishing some guidelines for the efficient ultrathin perovskite solar cells. This method induces an extraordinarily high light-harvesting for ultrathin perovskite film. And the underlying physical mechanism behind the enhanced absorption is deeply investigated by plasmon hybridization, dipolar-dipolar coupling method and FDTD simulation. We notice that perovskite embedded silver-gold heterodimer overcomes the vanished antibonding plasmon resononse (σ * ) in nonjunction area of gold/silver homodimer. A 150-nm perovskite film with embedded random silver-gold heterodimers with 80 nm size and 25 nm gap distance processes 28.15% absorption enhancement compared to the reference film, which is higher than the reported 10% for gold homodimers. And we also predict a realistic solution-processed, easy, and low-cost fabrication method, which provide a means to realize highly efficient ultrathin perovskite solar cell including other absorber-based photovoltaics.

A cost-effective nanoporous ultrathin film electrode based on nanoporous gold/IrO2 composite for proton exchange membrane water electrolysis

NASA Astrophysics Data System (ADS)

Zeng, Yachao; Guo, Xiaoqian; Shao, Zhigang; Yu, Hongmei; Song, Wei; Wang, Zhiqiang; Zhang, Hongjie; Yi, Baolian

2017-02-01

A cost-effective nanoporous ultrathin film (NPUF) electrode based on nanoporous gold (NPG)/IrO2 composite has been constructed for proton exchange membrane (PEM) water electrolysis. The electrode was fabricated by integrating IrO2 nanoparticles into NPG through a facile dealloying and thermal decomposition method. The NPUF electrode is featured in its 3D interconnected nanoporosity and ultrathin thickness. The nanoporous ultrathin architecture is binder-free and beneficial for improving electrochemical active surface area, enhancing mass transport and facilitating releasing of oxygen produced during water electrolysis. Serving as anode, a single cell performance of 1.728 V (@ 2 A cm-2) has been achieved by NPUF electrode with a loading of IrO2 and Au at 86.43 and 100.0 μg cm-2 respectively, the electrolysis voltage is 58 mV lower than that of conventional electrode with an Ir loading an order of magnitude higher. The electrolysis voltage kept relatively constant up to 300 h (@250 mA cm-2) during the course of durability test, manifesting that NPUF electrode is promising for gas evolution.

Improved interfacial and electrical properties of atomic layer deposition HfO2 films on Ge with La2O3 passivation

NASA Astrophysics Data System (ADS)

Li, Xue-Fei; Liu, Xiao-Jie; Cao, Yan-Qiang; Li, Ai-Dong; Li, Hui; Wu, Di

2013-01-01

We report the characteristics of HfO2 films deposited on Ge substrates with and without La2O3 passivation at 250 °C by atomic layer deposition (ALD) using La[N(SiMe3)2]3 and Hf[N(CH3)(C2H5)]4 as the precursors. The HfO2 is observed to form defective HfGeOx at its interface during 500 °C postdeposition annealing. The insertion of an ultrathin La2O3 interfacial passivation layer effectively prevents the Ge outdiffusion and improves interfacial and electrical properties. Capacitance equivalent thickness (CET) of 1.35 nm with leakage current density JA of 8.3 × 10-4 A/cm2 at Vg = 1 V is achieved for the HfO2/La2O3 gate stacks on Ge substrates.