WorldWideScience

Sample records for amorphous hydrogenated carbon

  1. Rapid Annealing Of Amorphous Hydrogenated Carbon

    Science.gov (United States)

    Alterovitz, Samuel A.; Pouch, John J.; Warner, Joseph D.

    1989-01-01

    Report describes experiments to determine effects of rapid annealing on films of amorphous hydrogenated carbon. Study represents first efforts to provide information for applications of a-C:H films where rapid thermal processing required. Major finding, annealing causes abrupt increase in absorption and concomitant decrease in optical band gap. Most of change occurs during first 20 s, continues during longer annealing times. Extend of change increases with annealing temperature. Researchers hypothesize abrupt initial change caused by loss of hydrogen, while gradual subsequent change due to polymerization of remaining carbon into crystallites or sheets of graphite. Optical band gaps of unannealed specimens on silicon substrates lower than those of specimens on quartz substrates.

  2. 13C NMR spectroscopy of amorphous hydrogenated carbon and amorphous hydrogenated boron carbide

    International Nuclear Information System (INIS)

    We report the 13C NMR spectrum of amorphous hydrogenated carbon and boron carbide. The amorphous hydrogenated carbon spectra consist primarily of an sp3 line at 40 ppm and an sp2 line at 140 ppm and are in reasonable agreement with the recent theoretical calculations of Mauri, Pfrommer, and Louie, but there are some notable discrepancies. The amorphous hydrogenated boron carbide spectra are very different from those of amorphous hydrogenated carbon, being dominated by one line at 15 ppm. We interpret this line as due to carbon bound in boron carbide icosahedra, because polycrystalline boron carbide with boron carbide icosahedra as the unit cell gives very similar NMR spectra. copyright 1999 The American Physical Society

  3. Recombination of atomic oxygen and hydrogen on amorphous carbon

    International Nuclear Information System (INIS)

    Deposit buildup and fuel entrapment due to amorphous carbon are relevant issues in fusion devices with carbon based plasma facing components. Neutral atomic species play a significant role – atomic hydrogen facilitates the formation of amorphous carbon while atomic oxygen could be used to remove carbon deposits. The kinetics of either reaction depends on the density of neutral species, which in turn is influenced by recombination on the vessel walls. In this work, we measured the probability of heterogeneous recombination of atomic hydrogen and oxygen on amorphous carbon deposits. The recombination coefficients were determined by observing density profiles of atomic species in a closed side-arm of a plasma vessel with amorphous carbon deposit-lined walls. Density profiles were measured with fiber optics catalytic probes. The source of atomic species was inductively coupled radiofrequency plasma. The measured recombination coefficient values were of the order of 10−3 for both species

  4. Nanomechanical characterization of amorphous hydrogenated carbon thin films

    International Nuclear Information System (INIS)

    Amorphous hydrogenated carbon (a-C:H) thin films deposited on a silicon substrate under various mixtures of methane-hydrogen gas by electron cyclotron resonance microwave plasma chemical vapor deposition (ECR-MPCVD) was investigated. Microstructure, surface morphology and mechanical characterizations of the a-C:H films were analyzed using Raman spectroscopy, atomic force microscopy (AFM) and nanoindentation technique, respectively. The results indicated there was an increase of the hydrogen content, the ratio of the D-peak to the G-peak (I D/I G) increased but the surface roughness of the films was reduced. Both hardness and Young's modulus increased as the hydrogen content was increased. In addition, the contact stress-strain analysis is reported. The results confirmed that the mechanical properties of the amorphous hydrogenated carbon thin films improved using a higher H2 content in the source gas

  5. Inelastic Neutron-Scattering Of Molecular-Hydrogen In Amorphous Hydrogenated Carbon.

    OpenAIRE

    Honeybone, P.J.R.; Newport, Robert J; Howells, W. S.; Tomkinson, John; Bennington, S.M.; Revell, P.J.

    1991-01-01

    We have, by use of inelastic neutron scattering, detected the presence of molecular hydrogen in amorphous hydrogenated car-bon. We have found the hydrogen to be in a high-pressure, asymmetric environment formed by the compressive stresses in the a-C: H films. On comparing two samples, we have also found that the sample with higher molecular hydrogen concentration has a lower total hydrogen composition. This is caused by a higher network density, trapping the molecular hydrogen during network ...

  6. Growth, characterisation and electronic applications of amorphous hydrogenated carbon

    CERN Document Server

    Paul, S

    2000-01-01

    temperature on GaAs, has been studied and concluded to be satisfactory on the basis of good adherence and low leakage currents. Such a structure was motivated by the applicability in Metal Insulator Semiconductor Field Effect Transistors (MISFET). My thesis proposes solutions to a number of riddles associated with the material, hydrogenated amorphous carbon, (a-C:H). This material has lately generated interest in the electronic engineering community, owing to some remarkable properties. The characterisation of amorphous carbon films, grown by radio frequency plasma enhanced chemical vapour deposition has been reported. The coexistence of multiple phases in the same a-C:H film manifests itself in the inconsistent electrical behaviour of different parts of the film, thus rendering it difficult to predict the nature of films. For the first time, in this thesis, a reliable prediction of Schottky contact formation on a-C:H films is reported. A novel and simple development on a Scanning Electron Microscope, configu...

  7. Electrical characteristics of nitrogen incorporated hydrogenated amorphous carbon

    International Nuclear Information System (INIS)

    Nitrogen incorporation into hydrogenated amorphous carbon (a-C:H) films has recently attracted a wide range of interest due to its contribution in reducing film stress and improving field emission properties. In this work we characterize the electrical properties of nitrogen containing a-C:H films. The a-C:H films were prepared by plasma enhanced chemical vapor deposition in an acetylene (C2H2) environment with a range of bias voltages. Nitrogen incorporation was achieved by exposing the films to an atomic nitrogen flux from a rf plasma with up to 40% dissociation and atomic nitrogen fluxes of up to 0.85x1018 atoms s-1. Raman results indicate that the doping process is accompanied by some structural changes seen by the G-band peak shifts. X-ray photoelectron spectroscopy spectra suggest that the dopant levels exceed those previously reported. Capacitance probe and I-V techniques showed a decrease in contact potential difference and density of states for doped films, indicating a rise in the Fermi level

  8. Studies of nanostructured copper/hydrogenated amorphous carbon multilayer films

    International Nuclear Information System (INIS)

    Research highlights: → Multilayer coatings have been grown by RF-PECVD and RF-sputtering techniques under varied bilayers from one to four. → After deposition these coatings were characterized for stress, hardness, elastic modulus, SEM, AFM, XPS, EDAX, SIMS, PL, transmission, and conductivity. → Observed results were correlated fairly with each other. - Abstract: Nanostructured copper/hydrogenated amorphous carbon (a-C:H) multilayer grown in a low base vacuum (1 x 10-3 Torr) system combining plasma-enhanced chemical vapor deposition and sputtering techniques. These nanostructured multilayer were found to exhibit improved electrical, optical, surface and structural properties, compared to that of monolayer a-C:H films. The residual stresses of such multilayer structure were found well below 1 GPa. Scanning electron microscopy and atomic force microscopy results revealed a nanostructured surface morphology and low surface roughnesses values. X-ray photoelectron spectroscopy, secondary ion mass spectroscopy and energy dispersive X-ray analysis confirmed a very small amount of copper in these films. These structures exhibited very high optical transparency in the near infrared region (∼90%) and the optical band gap varied from 1.35 to 1.7 eV. It was noticed that the temperature dependent conductivity improved due to the presence of both copper and the nano-structured morphology.

  9. The Ammount of Interstellar Carbon Locked in Solid Hydrogenated Amorphous Carbon

    OpenAIRE

    Furton, D. G.; Laiho, J. W.; Witt, A. N.

    1999-01-01

    We review the literature and present new experimental data to determine the amount of carbon likely to be locked in form of solid hydrogenated amorphous carbon (HAC) grains. We conclude on the basis of a thorough analysis of the intrinsic strength of the C-H stretching band at 3.4 micron that between 10 and 80 ppM H of carbon is in the form of HAC grains. We show that it is necessary to know the level of hydrogenation (H/C) of the interstellar HAC to determine more precisely the amount of car...

  10. Tribological studies of amorphous hydrogenated carbon films in a vacuum, spacelike environment

    Science.gov (United States)

    Miyoshi, Kazuhisa

    1991-01-01

    Recent work on the adhesion and friction properties of plasma-deposited amorphous hydrogenated carbon films and their dependence on preparation conditions are reviewed. The results of the study indicate that plasma deposition enables one to deposit a variety of amorphous hydrogenated carbon (a-C:H) exhibiting diamondlike friction behavior. The plasma-deposited a-C:H films can be effectively used as hard lubricating films on ceramic materials such as silicon nitride in vacuum.

  11. The Ammount of Interstellar Carbon Locked in Solid Hydrogenated Amorphous Carbon

    CERN Document Server

    Furton, D G; Witt, A N

    1999-01-01

    We review the literature and present new experimental data to determine the amount of carbon likely to be locked in form of solid hydrogenated amorphous carbon (HAC) grains. We conclude on the basis of a thorough analysis of the intrinsic strength of the C-H stretching band at 3.4 micron that between 10 and 80 ppM H of carbon is in the form of HAC grains. We show that it is necessary to know the level of hydrogenation (H/C) of the interstellar HAC to determine more precisely the amount of carbon it ties up. We present optical constants, photoluminescence spectroscopy, and IR absorption spectroscopy for a particular HAC sample that is shown to have a 3.4 micron absorption feature that is quantatively consistent with that observed in the diffuse interstellar medium.

  12. Photoluminescence of amorphous carbon films fabricated by layer-by-layer hydrogen plasma chemical annealing method

    Institute of Scientific and Technical Information of China (English)

    徐骏; 黄晓辉; 李伟; 王立; 陈坤基

    2002-01-01

    A method in which nanometre-thick film deposition was alternated with hydrogen plasma annealing (layer-by-layermethod) was applied to fabricate hydrogenated amorphous carbon films in a conventional plasma-enhanced chemicalvapour deposition system. It was found that the hydrogen plasma treatment could decrease the hydrogen concentrationin the films and change the sp2/sp3 ratio to some extent by chemical etching. Blue photoluminescence was observed atroom temperature, as a result of the reduction of sp2 clusters in the films.

  13. The effect of relatively low hydrogen dilution on the properties of carbon-rich hydrogenated amorphous silicon carbide films

    International Nuclear Information System (INIS)

    Carbon-rich hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films were deposited by plasma enhanced chemical vapor deposition (PECVD) using silane, ethylene and hydrogen as gas sources. The effect of relatively low hydrogen dilution on the properties of as-deposited samples was investigated. A variety of techniques including Scanning Electron Microscope (SEM), Fourier transform infrared spectroscopy (FTIR), Raman scattering (RS), UV-VIS spectrophotometer and photoluminescence (PL) spectroscopy were used to characterize the grown films. The deposition rate decreases with hydrogen dilution. The silicon to carbon ratio increases slightly with the addition of hydrogen. The phenomenon can be attributed to the dissipation of power density caused by hydrogen dilution. Raman G peak position shifting to a lower wave number indicates that hydrogen dilution reduces the size and concentration of sp2 carbon clusters, which is caused by the etching effect by atomic hydrogen. The optical band gap, which is controlled by the sp2 carbon clusters and Si/C ratio, changes unmonotonously. The as-deposited samples exhibited a blue-green room-temperature (RT) PL well visible to the naked eye with UV excitation. The PL band can be attributed to the radiative recombination of electron-hole pairs within small sp2 clusters containing C=C and C-H units in a sp3 amorphous matrix.

  14. Amorphous Hydrogenated Carbon-Nitrogen Alloy Thin Films for Solar Cell Application

    Institute of Scientific and Technical Information of China (English)

    ZHOU Zhi-Bin; DING Zheng-Ming; PANG Qian-Jun; CUI Rong-Qiang

    2001-01-01

    Amorphous hydrogenated carbon-nitrogen alloy (a-CNx :H) thin films have been deposited on silicon substratesby improved dc magnetron sputtering from a graphite target in nitrogen and hydrogen gas discharging. Thefilms are investigated by using Raman spectroscopy, x-ray photoelectron spectroscopy, spectral ellipsometer and electron spin resonance techniques. The optimized process condition for solar cell application is discussed. Thephotovoltaic property of a-CNx:H/silicon heterojunctions can be improved by the adjustment of the pressureratio of hydrogen to nitrogen and unbalanced magnetic field intensity. Open-circuit voltage and short-circuitcurrent reach 300mV and 5.52 Ma/cm2, respectively.

  15. Synergistic etch rates during low-energetic plasma etching of hydrogenated amorphous carbon

    International Nuclear Information System (INIS)

    The etch mechanisms of hydrogenated amorphous carbon thin films in low-energetic (2 and pure H2 plasmas, although a contribution of swift chemical sputtering to the total etch rate is not excluded. Furthermore, ions determine to a large extent the surface morphology during plasma etching. A high influx of ions enhances the etch rate and limits the surface roughness, whereas a low ion flux promotes graphitization and leads to a large surface roughness (up to 60 nm).

  16. Plasma deposition of amorphous hydrogenated carbon films on III-V semiconductors

    Science.gov (United States)

    Pouch, John J.; Warner, Joseph D.; Liu, David C.; Alterovitz, Samuel A.

    1988-01-01

    Amorphous hydrogenated carbon films were grown on GaAs, InP and fused silica substrates using plasmas generated from hydrocarbon gases. Methane and n-butane sources were utilized. The effects of flow rate and power density on film growth were investigated. Carbon was the major constituent in the films. The degree of asymmetry at the carbon-semiconductor interface was approximately independent of the power density. Different H-C bonding configurations were detected by the technique of secondary-ion mass spectrometry. Band gaps up to 3 eV were obtained from optical absorption studies. Breakdown strengths as high as 600 MV/m were measured.

  17. Wettability and biocompatibility of nitrogen-doped hydrogenated amorphous carbon films: Effect of nitrogen

    International Nuclear Information System (INIS)

    Amorphous carbon films have been applied in biomedical fields as potential biocompatible materials with wettability that can be adjusted by doping with other elements, including F, Si, Ti, O and N. In this study, nitrogen-doped hydrogenated amorphous carbon (a-C:H:N) films were deposited by PIII-D using C2H2 + N2 gas mixtures. The biocompatibility and anti-thrombotic properties of the films were assessed in vitro. The surface morphology and surface wettability of the films were characterized using atomic force microscopy (AFM) and a contact angle method. The results show no cytotoxicity for all films, and films with appropriate nitrogen doping possess much better endothelial cell growth and anti-thrombotic properties

  18. Photoelectron spectroscopy study of metallic nanocluster arrangement at the surface of reactively sputtered amorphous hydrogenated carbon

    International Nuclear Information System (INIS)

    We report on the results of the arrangement of isolated surface metallic nanoclusters embedded in amorphous hydrogenated carbon (a-C:H) thin films, studied by photoelectron spectroscopy. As a model system we used gold-containing amorphous hydrogenated carbon (a-C:H/Au), due to the lack of reactivity between carbon and gold. The a-C:H/Au samples are obtained by simultaneous magnetron sputtering of Au target by argon and plasma-enhanced chemical vapor deposition of methane. Photoelectron spectroscopy with x-ray and ultraviolet excitation has been employed for surface studies that comprise as-deposited sample spectra recordings, measurements at off-normal takeoff angle, in situ in-depth profiling by Ar+ ion etching, and thiophene adsorption at the sample surface. The results of these extended studies firmly support previously drawn conclusions [I. R. Videnovic, V. Thommen, P. Oelhafen, D. Mathys, M. Dueggelin, and R. Guggenheim, Appl. Phys. Lett 80, 2863 (2002)] that by deposition on electrically grounded substrates one obtains samples with topmost Au clusters covered with a thin layer of a-C:H. Introducing a dc substrate bias voltage results in bald Au clusters on the surface and increased sp2/sp3 coordinated carbon ratio in the a-C:H matrix

  19. Surface morphology, cohesive and adhesive properties of amorphous hydrogenated carbon nanocomposite films

    International Nuclear Information System (INIS)

    In this work, amorphous hydrogenated carbon (a-C:H), SiOx containing a-C:H (a-C:H/SiOx) and nitrogen-doped a-C:H/SiOx (a-C:H:N/SiOx) thin films were deposited on chromium thin film coated glass using a closed drift ion beam source. Acetylene gas, hexamethyldisiloxane and hydrogen or 20% nitrogen/hydrogen mixture were used as precursors. Resulting hydrogenated carbon thin film surface morphology as well as their cohesive and adhesive properties were studied using progressive loading scratch tests followed by optical microscopy analysis. Surface analysis was also performed using atomic force microscopy via topography, surface morphology parameter, height distribution histogram and bearing ratio curve based hybrid parameter measurements. The a-C:H/SiOx and a-C:H:N/SiOx thin films showed better mechanical strength as compared to the conventional a-C:H films. X-ray photoelectron spectroscopy was used to determine the chemical composition of these films. It showed increased amounts of silicon and absence of terminal oxygenated carbon bonds in a-C:H:N/SiOx thin film which was attributed to its improved mechanical properties.

  20. Understanding the hydrogen and oxygen gas pressure dependence of the tribological properties of silicon oxide-doped hydrogenated amorphous carbon coatings

    OpenAIRE

    Koshigan, KD; Mangolini, F; McClimon, JB; Vacher, B.; Bec, S; Carpick, RW; Fontaine, J

    2015-01-01

    Silicon oxide-doped hydrogenated amorphous carbons (a–C:H:Si:O) are amorphous thin films used as solid lubricants in a range of commercial applications, thanks to its increased stability in extreme environments, relative to amorphous hydrogenated carbons (a–C:H). This work aims to develop a fundamental understanding of the environmental impact on the tribology of a–C:H:Si:O. Upon sliding an a–C:H:Si:O film against a steel counterbody, two friction regimes develop: high friction in high vacuum...

  1. Electronic Sputtering of Nanodimensional Hydrogenated Amorphous Carbon and Copper Oxide Thin Films

    Directory of Open Access Journals (Sweden)

    S. Ghosh

    2009-07-01

    Full Text Available Electronic sputtering of carbon from hydrogenated amorphous carbon (a-C:H/Si film and oxygen from copper oxide (CuO/Si film at different electronic energy loss (Se value is reported. The sputtering is monitored by online elastic recoil detection analysis (ERDA technique and the yield (sputtered atoms/incident ion is determined. Two important results emerging out from this study are: (i much higher yield of C and O from a-C:H and CuO films as compared to conventional kinetic sputtering and (ii sputtering yield increases with increase in Se in both the cases. These observations are understood on the basis of thermal spike model of ion-solid interaction.Defence Science Journal, 2009, 59(4, pp.370-376, DOI:http://dx.doi.org/10.14429/dsj.59.1536

  2. Structural changes of hydrogenated amorphous carbon films deposited on steel rods

    Science.gov (United States)

    Choi, Junho; Hatta, Tetsuya

    2015-12-01

    In this study, hydrogenated amorphous carbon (a-C:H) films were deposited on steel rods of various radii by using bipolar-type plasma based ion implantation and deposition, and the film structure and mechanical properties have been investigated. Furthermore, the behavior of plasma surrounding the steel rods (i.e., flux and energy of incident ions and electrons) was investigated using the particle-in-cell Monte Carlo collision (PIC-MCC) method to examine the mechanism behind the structural changes of the a-C:H films. Three kinds of amorphous carbon films with different microstructures were prepared by changing the negative pulse voltages from -1 kV to -5 kV: one polymer-like carbon film and two diamond-like carbon films that possess the maximum FWHM(G) (full width at half maximum of Raman G-peak) and maximum hardness. The structure of the a-C:H films was evaluated through Raman spectroscopy, and the hardness of the films was measured using nanoindentation. It was found that the structures of a-C:H films deposited on the steel-rod surfaces are quite different from those on flat surfaces, and the film structures are directly affected by the curvature of the rod. It was also determined from the plasma simulation that the incident electron flux and ion flux become more intense as the curvature increases, resulting in the structural changes of the a-C:H films due to hydrogen evolution and thermal relaxation in the films.

  3. Platinum containing amorphous hydrogenated carbon (a-C:H/Pt) thin films as selective solar absorbers

    International Nuclear Information System (INIS)

    We have investigated a double-cermet structured thin film in which an a-C:H thin film was used as an anti-reflective (AR) layer and two platinum-containing amorphous hydrogenated carbon (a-C:H/Pt) thin films were used as the double cermet layers. A reactive co-sputter deposition method was used to prepare both the anti-reflective and cermet layers. Effects of the target power and heat treatment were studied. The obtained films were characterized using X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy. The optical absorptance and emittance of the as deposited and annealed films were determined using UV–vis-NIR spectroscopy. We show that the optical absorptance of the resulting double-cermet structured thin film is as high as 96% and remains to be 91% after heat treatment at 400 °C, indicating the thermal stability of the film

  4. Rapid thermal annealing of Amorphous Hydrogenated Carbon (a-C:H) films

    Science.gov (United States)

    Alterovitz, Samuel A.; Pouch, John J.; Warner, Joseph D.

    1987-01-01

    Amorphous hydrogenated carbon (a-C:H) films were deposited on silicon and quartz substrates by a 30 kHz plasma discharge technique using methane. Rapid thermal processing of the films was accomplished in nitrogen gas using tungsten halogen light. The rapid thermal processing was done at several fixed temperatures (up to 600 C), as a function of time (up to 1800 sec). The films were characterized by optical absorption and by ellipsometry in the near UV and the visible. The bandgap, estimated from extrapolation of the linear part of a Tauc plot, decreases both with the annealing temperature and the annealing time, with the temperature dependence being the dominating factor. The density of states parameter increases up to 25 percent and the refractive index changes up to 20 percent with temperature increase. Possible explanations of the mechanisms involved in these processes are discussed.

  5. Platinum containing amorphous hydrogenated carbon (a-C:H/Pt) thin films as selective solar absorbers

    Energy Technology Data Exchange (ETDEWEB)

    Lan, Yung-Hsiang; Brahma, Sanjaya [Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan (China); Tzeng, Y.H. [Department of Electrical Engineering, National Cheng Kung University, Tainan 701, Taiwan (China); Ting, Jyh-Ming, E-mail: jting@mail.ncku.edu.tw [Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan (China); Research Center for Energy Technology and Strategy, National Cheng Kung University, Tainan 701, Taiwan (China)

    2014-10-15

    We have investigated a double-cermet structured thin film in which an a-C:H thin film was used as an anti-reflective (AR) layer and two platinum-containing amorphous hydrogenated carbon (a-C:H/Pt) thin films were used as the double cermet layers. A reactive co-sputter deposition method was used to prepare both the anti-reflective and cermet layers. Effects of the target power and heat treatment were studied. The obtained films were characterized using X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy. The optical absorptance and emittance of the as deposited and annealed films were determined using UV–vis-NIR spectroscopy. We show that the optical absorptance of the resulting double-cermet structured thin film is as high as 96% and remains to be 91% after heat treatment at 400 °C, indicating the thermal stability of the film.

  6. Structural and Electrical Properties of Amorphous Hydrogen Carbon-Nitrogen Films

    Institute of Scientific and Technical Information of China (English)

    SUO Da-Cheng; LIU Yi-Chun; LIU Yan; QI Xiu-Ying; ZHONG Dian-Qiang

    2004-01-01

    @@ Amorphous hydrogenated carbon-nitrogen (a-C:H:(N)) films with different nitrogen contents have been deposited by using rf-sputtering of a high purity graphite target in an Ar-H2-N2 atmosphere. Transmittance and reflectance spectra are used to characterize the Tauc gap and absorption coefficients in the wavelength range 0.185-3.2μm.The temperature dependence of conductivity demonstrates a hopping mechanism of the Fermi level in the temperature range of 77-300K. The density of state at the Fermi level is derived from the direct current conductivity.The photoluminescence properties of a-C:H:N films were investigated. The photoluminescence peak has a blue shift with increasing excitation energy. These results are discussed on the basis of a model in which the different sp2 clusters dispersed in sp3 matrices.

  7. Improved adhesion and tribological properties of fast-deposited hard graphite-like hydrogenated amorphous carbon films

    NARCIS (Netherlands)

    Zaharia, T.; Kudlacek, P.; Creatore, M.; Groenen, R.; Persoone, P.; M. C. M. van de Sanden,

    2011-01-01

    Graphite-like hard hydrogenated amorphous carbon (a-C:H) was deposited using an Ar-C(2)H(2) expanding thermal plasma chemical vapour deposition (ETP-CVD) process. The relatively high hardness of the fast deposited a-C:H material leads to high compressive stress resulting in poor adhesion between the

  8. Amorphous Molybdenum Sulfide on Graphene-Carbon Nanotube Hybrids as Highly Active Hydrogen Evolution Reaction Catalysts.

    Science.gov (United States)

    Pham, Kien-Cuong; Chang, Yung-Huang; McPhail, David S; Mattevi, Cecilia; Wee, Andrew T S; Chua, Daniel H C

    2016-03-01

    In this study, we report on the deposition of amorphous molybdenum sulfide (MoSx, with x ≈ 3) on a high specific surface area conductive support of Graphene-Carbon Nanotube hybrids (GCNT) as the Hydrogen Evolution Reaction (HER) catalysts. We found that the high surface area GCNT electrode could support the deposition of MoSx at much higher loadings compared with simple porous carbon paper or flat graphite paper. The morphological study showed that MoSx was successfully deposited on and was in good contact with the GCNT support. Other physical characterization techniques suggested the amorphous nature of the deposited MoSx. With a typical catalyst loading of 3 mg cm(-2), an overpotential of 141 mV was required to obtain a current density of 10 mA cm(-2). A Tafel slope of 41 mV decade(-1) was demonstrated. Both measures placed the MoSx-deposited GCNT electrode among the best performing molybdenum sulfide-based HER catalysts reported to date. The electrode showed a good stability with only a 25 mV increase in overpotential required for a current density of 10 mA cm(-2), after undergoing 500 potential sweeps with vigorous bubbling present. The current density obtained at -0.5 V vs SHE (Standard Hydrogen Electrode potential) decreased less than 10% after the stability test. The deposition of MoSx on high specific surface area conductive electrodes demonstrated to be an efficient method to maximize the catalytic performance toward HER. PMID:26864503

  9. Reactivity of lithium containing amorphous hydrogenated carbon films towards oxygen: an in situ photoelectron spectroscopy study

    International Nuclear Information System (INIS)

    Amorphous hydrogenated carbon coatings (a-C : H) containing different amounts of lithium have been prepared by a modified radio frequency-plasma assisted chemical vapour deposition (rf-PACVD) technique. They have been characterized in situ by X-ray (XPS) and ultraviolet photoelectron spectroscopy (UPS). The samples have been exposed to molecular oxygen as well as an oxygen plasma in order to obtain information about the reactivity of the coatings. The effect of the oxygen plasma on pure a-C : H is found to be a mere etching, the structure of the surface itself remaining essentially unchanged. In contrast, a transition from the carbidic carbon-lithium phase to a metal-carbonate like configuration, i.e. Li2CO3 or LiHCO3, occurs in the lithium containing samples. These differences result in a much larger oxygen uptake at the surface of the lithium containing samples as compared to the pure a-C : H. Furthermore the rate of etching by the oxygen plasma is substantially lower for the lithium containing films. ((orig.))

  10. The Use Of Neutron-Scattering Experiments For Studying Molecular-Hydrogen In Amorphous Hydrogenated Carbon

    OpenAIRE

    Howells, W.S.; Honeybone, P.J.R.; Newport, Robert J; Bennington, S.M.; Revell, P.J.

    1992-01-01

    The presence of molecular hydrogen in a-C:H has been demonstrated by a series of neutron scattering experiments. Neutron diffraction gives a peak in the pair correlation function corresponding to the H-H bond distance. Inelastic neutron scattering experiments have shown peaks consistent with the H-2 rotation and stretch, and revealed details of the hydrogen environment.

  11. Characterization of amorphous hydrogenated carbon films deposited by MFPUMST at different ratios of mixed gases

    Indian Academy of Sciences (India)

    Haiyang Dai; Changyong Zhan; Hui Jiang; Ningkang Huang

    2012-12-01

    Amorphous hydrogenated carbon films (-C:H) on -type (100) silicon wafers were prepared with a middle frequency pulsed unbalanced magnetron sputtering technique (MFPUMST) at different ratios of methane–argon gases. The band characteristics, mechanical properties as well as refractive index were measured by Raman spectra, X-ray photoelectron spectroscopy (XPS), nano-indentation tests and spectroscopic ellipsometry. It is found that the 3 fraction increases with increasing Ar concentration in the range of 17–50%, and then decreases when Ar concentration exceeds 50%. The nano-indentation tests reveal that nano-hardness and elastic modulus of the films increase with increasing Ar concentration in the range of 17–50%, while decreases with increasing Ar concentration from 50% to 86%. The variations in the nano-hardness and the elastic modulus could be interpreted due to different 3 fractions in the prepared -C:H films. The variation of refractive index with wavelength have the same tendency for the -C:H films prepared at different Ar concentrations, they decrease with increasing wavelength from 600 to 1700 nm. For certain wavelengths within 600–1700 nm, refractive index has the highest value at the Ar concentration of 50%, and it is smaller at the Ar concentration of 86% than at 17%. The results given above indicate that ratio of mixed gases has a strong influence on bonding configuration and properties of -C:H films during deposition. The related mechanism is discussed in this paper.

  12. Hydrogenated amorphous carbon coatings on implants drastically reduce biofilm formation and water permeation

    International Nuclear Information System (INIS)

    Inflammations and crystalline bacterial biofilms (encrustations) remain a major complication in long-term artificial urinary tract drainage. To solve this problem we present urological implants with coatings made of amorphous hydrogenated carbon (a-C:H) that show excellent protection from encrustation in-vitro as well as in-vivo. Part of the success of a-C:H coatings is attributed to their ability to act as a diffusion barrier between an implant and the body, which prevents leaching of solvents from polymeric implants. To further enhance their barrier properties a-C:H coatings are combined with parylene coatings to develop diffusion-barrier multilayer coatings with a total thickness between 0.2 μm and 0.8 μm. The combination of the two types of coatings leads to a reduction of water diffusion by a factor of up to ten with respect to uncoated 25 μm thick polyimide sub-strates. The diffusion of water vapour from a controlled atmospheric pressure chamber through coated foils to a vacuum chamber is measured in a custom-built device

  13. Time-Resolved Observation of Deposition Process of Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films in Pulsed Laser Deposition

    OpenAIRE

    Kunihito Nagayama; Tsuyoshi Yoshitake; Takashi Nishiyama; Kenji Hanada

    2009-01-01

    Optical emission spectroscopy was used to study pulsed laser ablation of graphite in a hydrogen atmosphere wherein ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite films were grown on heated substrates. Time-resolved photographs of a plume that expanded from a laser-irradiation spot toward a substrate were taken using a high-speed ICCD camera equipped with narrow-bandpass filters. While the emissions from C atoms and C2 dimers lasted above the laser-irradi...

  14. Hydrogen reverses the clustering tendency of carbon in amorphous silicon oxycarbide

    OpenAIRE

    Hepeng Ding; Demkowicz, Michael J.

    2015-01-01

    Amorphous silicon oxycarbide (SiOC) is of great technological interest. However, its atomic-level structure is not well understood. Using density functional theory calculations, we show that the clustering tendency of C atoms in SiOC is extremely sensitive to hydrogen (H): without H, the C-C interaction is attractive, leading to enrichment of aggregated SiC[subscript 4] tetrahedral units; with hydrogen, the C-C interaction is repulsive, leading to enrichment of randomly distributed SiCO[subsc...

  15. The influence of radio frequency power on the characteristics of carbon-rich hydrogenated amorphous silicon carbide films

    International Nuclear Information System (INIS)

    A series of carbon-rich hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films were prepared at different radio frequency (RF) powers from silane-ethylene-hydrogen plasma. The effect of the RF power on the bonding configurations and microstructures has been investigated. The grown films were characterized by a collection of techniques including Scanning Electron Microscope, Fourier transform infrared(FTIR) spectroscopy, Raman scattering and photoluminescence spectroscopy. The deposition rate increases upon RF power due to the enhancement of chemical reactivity of plasma. The carbon to silicon ratio increases, for more C2H4 molecules decompose with the enhancement of RF power and more carbon atoms are bonded into the films. Raman G peak position shifts to a higher wavenumber, which indicates that the size and concentration of sp2 carbon clusters increase as the RF power becomes stronger. Blue-green photoluminescence is detected at room temperature. The PL band can be attributed to the existence of the amorphous carbon clusters in films with high carbon concentrations.

  16. Amorphous iron (II) carbonate

    DEFF Research Database (Denmark)

    Sel, Ozlem; Radha, A.V.; Dideriksen, Knud;

    2012-01-01

    Abstract The synthesis, characterization and crystallization energetics of amorphous iron (II) carbonate (AFC) are reported. AFC may form as a precursor for siderite (FeCO3). The enthalpy of crystallization (DHcrys) of AFC is similar to that of amorphous magnesium carbonate (AMC) and more...

  17. A study of the chemical, mechanical, and surface properties of thin films of hydrogenated amorphous carbon

    Energy Technology Data Exchange (ETDEWEB)

    Vandentop, G.J.

    1990-07-01

    Amorphous hydrogenated carbon (a-C:H) films were studied with the objective of elucidating the nucleation and growth mechanisms, and the origin of their unique physical properties. The films were deposited onto Si(100) substrates both on the powered (negatively self-biased) and on the grounded electrodes from methane in an rf plasma (13.56 MHz) at 65 mTorr and 300 to 370 K. The films produced at the powered electrode exhibited superior mechanical properties, such as high hardness. A mass spectrometer was used to identify neutral species and positive ions incident on the electrodes from the plasma, and also to measure ion energies. The effect of varying ion energy flux on the properties of a-C:H films was investigated using a novel pulsed biasing technique. It was demonstrated that ions were not the dominant deposition species as the total ion flux measured was insufficient to account for the observed deposition rate. The interface between thin films of a-C:H and silicon substrates was investigated using angle resolved x-ray photoelectron spectroscopy. A silicon carbide layer was detected at the interface of a hard a-C:H film formed at the powered electrode. At the grounded electrode, where the kinetic energy is low, no interfacial carbide layer was observed. Scanning tunneling microscopy and high energy electron energy loss spectroscopy was used to investigate the initial stages of growth of a-C:H films. On graphite substrates, films formed at the powered electrode were observed to nucleate in clusters approximately 50 {Angstrom} in diameter, while at the grounded electrode no cluster formation was observed. 58 figs.

  18. Hydrogen reverses the clustering tendency of carbon in amorphous silicon oxycarbide.

    Science.gov (United States)

    Ding, Hepeng; Demkowicz, Michael J

    2015-01-01

    Amorphous silicon oxycarbide (SiOC) is of great technological interest. However, its atomic-level structure is not well understood. Using density functional theory calculations, we show that the clustering tendency of C atoms in SiOC is extremely sensitive to hydrogen (H): without H, the C-C interaction is attractive, leading to enrichment of aggregated SiC4 tetrahedral units; with hydrogen, the C-C interaction is repulsive, leading to enrichment of randomly distributed SiCO3 tetrahedral units. Our results suggest that conflicting experimental characterizations of C distributions may be due to differing amounts of H present in the samples investigated. Our work also opens a path for tailoring the properties of SiOC by using the total H content to control the C distribution. PMID:26269200

  19. Synthesis and characterization of hydrogenated amorphous carbon-based tribological coatings

    Science.gov (United States)

    Zhao, Bo

    The development of low friction surfaces is needed to improve performance and energy efficiency for macroscopic and microscopic mechanical systems. Minimizing unwanted friction and wear can lead to dramatic economic and environmental benefits. Such research is an important approach to addressing the world's increasing energy concerns. Hydrogenated amorphous carbon (CHx) thin films are ideal for some tribological applications because of their low wear rates and low coefficients of friction. The primary goal of this research is to develop and characterize modified CHx coatings so that they can be used in a variety of applications in humid environments and under higher contact loads. Doping CHx films with a small amount of sulfur (CHx+S) enables them to achieve ultralow coefficients of friction in ambient humidity. Temperature-programmed desorption and quartz crystal microbalance were used to determine that sulfur reduces water adsorption onto the film surface. Sulfur-doped films showed a decrease in the activation energy for desorption of water, or weaker film-water bonding. This decrease causes a shorter residence time of water on the surface and less equilibrium water adsorption. At a given relative humidity, sulfur-doped films adsorbed less water than undoped films. Even at 90% relative humidity, sulfur-doped films adsorbed less than 1 monolayer of water. Sulfur acts to passivate dangling bonds at the film surface susceptible to oxidation and reduces the number of surface dipoles available to attract water. This enhanced hydrophobicity increases the contact angle of adsorbed water islands, which lowers the likelihood of coalescence into a water meniscus on the film surface. The decreased quantity and discontinuity of adsorbed water molecules are responsible for CHx+S being able to achieve lower friction in humid environments. Adding titanium diboride (TiB2) to the CHx coatings yielded films with improved mechanical properties. TiB2 and CH x were synthesized in

  20. Amorphous flower-like molybdenum-sulfide-@-nitrogen-doped-carbon-nanofiber film for use in the hydrogen-evolution reaction.

    Science.gov (United States)

    Zhang, Xiaoyan; Li, Libo; Guo, Yaxiao; Liu, Dong; You, Tianyan

    2016-06-15

    A novel amorphous flower-like molybdenum sulfides@nitrogen doped carbon nanofibers (MoSx@NCNFs) films are successfully synthesized by combining electrospinning, carbonization and a mild hydrothermal process. NCNFs, as a conductive substrate, can accelerate the electron transfer rate and depress the aggregation of MoSx nanoparticles. The resultant amorphous flower-like MoSx on NCNFs exposes abundant S(2-)/S2(2-) active edge sites which is of great importance for hydrogen evolution reaction (HER) catalytic performance. Electrochemical measurements demonstrate the superior electrocatalytic activity of MoSx@NCNFs toward HER deriving from the synergistic effect between NCNFs and amorphous MoSx. The overpotential is only 137mV to reach the current density of 10mAcm(-2) with a Tafel slope of 41mVdecade(-1) at MoSx@NCNFs. Meanwhile, MoSx@NCNFs exhibits satisfactory long-time stability for HER. Noteworthy, the obtained composites show a free-standing structure which can be directly used as electrode materials. This work provides a feasible way to design promising noble-metal free electrocatalysts in the aspect of energy conversion. PMID:27015391

  1. Excitation of the aromatic infrared emission bands: Chemical energy in hydrogenated amorphous carbon particles?

    CERN Document Server

    Duley, Walter W

    2011-01-01

    We outline a model for the heating of hydrogenated amorphous (HAC) dust via the release of stored chemical energy and show that this energy (~12 kJ/mole) is sufficient to heat dust grains of classical size (50-1000 {\\AA}) to temperatures at which they can emit at 3.3 {\\mu}m and other "UIR" wavelengths. Using laboratory data, we show that this heating process is consistent with a concentration of a few percent of dangling bonds in HAC and may be initiated by the recombination of trapped H atoms. We suggest that the release of chemical energy from dust represents an additional source of excitation for the UIR bands relaxing the previous requirement that only stochastically heated molecules having fewer than ~ 50 atoms can produce emission at 3.3 {\\mu}m.

  2. Structural and Physical Characteristics of Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films Deposited Using a Coaxial Arc Plasma Gun

    Science.gov (United States)

    Yoshitake, Tsuyoshi; Nakagawa, You; Nagano, Akira; Ohtani, Ryota; Setoyama, Hiroyuki; Kobayashi, Eiichi; Sumitani, Kazushi; Agawa, Yoshiaki; Nagayama, Kunihito

    2010-01-01

    Ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) films were formed without initial nucleation using a coaxial arc plasma gun. The UNCD crystallite diameters estimated from the X-ray diffraction peaks were approximately 2 nm. The Fourier transform infrared absorption spectrum exhibited an intense sp3-CH peak that might originate from the grain boundaries between UNCD crystallites whose dangling bonds are terminated with hydrogen atoms. A narrow sp3 peak in the photoemission spectrum implied that the film comprises a large number of UNCD crystallites. Large optical absorption coefficients at photon energies larger than 3 eV that might be due to the grain boundaries are specific to the UNCD/a-C:H films.

  3. Comparative Study on Hydrogenated and Deuterated Amorphous Carbon Films Deposited by RF PECVD

    Czech Academy of Sciences Publication Activity Database

    Buršíková, V.; Stoica, A.; Peřina, Vratislav; Mikšová, Romana; Slavíček, P.; Mocanu, V.

    Innsbruck: Innsbruck univesity press, 2012, s. 242-246. ISBN 978-3-902719-52-2. [XVIIIth Symposium on Atomic, cluster and Surface Physics 2012 (SAPS 2012). Alpe d´Huez (FR), 22.01.2012-27.01.2012] R&D Projects: GA ČR GA202/07/1669 Institutional support: RVO:61389005 Keywords : hydrogenated carbon thin films * deuterated carbon thin films * PECVD * RBS * ERDA * OES * coating properties Subject RIV: BL - Plasma and Gas Discharge Physics http://www.uibk.ac.at/iup/buch_pdfs/it_sasp_2012sw_131211.pdf

  4. Stress relief patterns of hydrogenated amorphous carbon films grown by dc-pulse plasma chemical vapor deposition

    International Nuclear Information System (INIS)

    Hydrogenated amorphous carbon films were prepared on Si (1 0 0) substrates by dc-pulse plasma chemical vapor deposition. The nature of the deposited films was characterized by Raman spectra and the stress relief patterns were observed by scanning electron microscope. Besides the well-known sinusoidal type and flower type patterns, etc., two different stress relief patterns, ring type and peg-top shape with exiguous tine on the top, were observed. The ring type in this paper was a clear ridge-cracked buckle and unusual. Two competing buckle delamination morphologies ring and sinusoidal buckling coexist. The ridge-cracked buckle in ring type was narrower than the sinusoidal buckling. Meanwhile peg-top shape with exiguous tine on the top in this paper was unusual. These different patterns supported the approach in which the stress relief forms have been analyzed using the theory of plate buckling.

  5. Thin films of hydrogenated amorphous carbon (a-C:H) obtained through chemical vapor deposition assisted by plasma

    International Nuclear Information System (INIS)

    Films of hydrogenated amorphous carbon (a-C:H) were deposited using one source of microwave plasma with magnetic field (type ECR), using mixtures of H2/CH4 in relationship of 80/20 and 95/05 as precursory gases, with work pressures of 4X10-4 to 6x10-4 Torr and an incident power of the discharge of microwaves with a constant value of 400 W. It was analyzed the influence among the properties of the films, as the deposit rate, the composition and the bonding types, and the deposit conditions, such as the flow rates of the precursory gases and the polarization voltage of the sample holders. (Author)

  6. Production and characterization of hydrogenated amorphous carbon thin films deposited in methane plasmas diluted by noble gases

    International Nuclear Information System (INIS)

    The dilution effects of the precursor methane atmosphere by three noble gases (Ar, Ne and He) on the mechanical properties and the microstructure of hydrogenated amorphous carbon films deposited by rf-PECVD were studied. The chemical composition and atomic density of the films were determined by ion beam analysis. The film microstructure was probed by means of Raman spectroscopy. The internal stress was determined through the measurement of the changing of the substrate curvature by a profilometer, while nanoindentation experiments provided the film hardness. The results show that the precursor atmosphere dilution by different noble gases did not induce substantial modifications in the microstructure or in the mechanical properties of the films. On the other hand, the composition, the microstructure and the mechanical properties of the films are strongly dependent on the self-bias voltage. The results confirm the importance of the ion bombardment during film growth on the mechanical properties of the films

  7. Gas barrier properties of hydrogenated amorphous carbon films coated on polymers by surface-wave plasma chemical vapor deposition

    International Nuclear Information System (INIS)

    Gas barrier characteristics of hydrogenated amorphous carbon (a-C:H) thin films coated on polymer sheets using the large-area surface-wave plasma (SWP) were studied. With SWP in He and CH4 gas mixture, a-C:H films were deposited over about 100 mm in diameter on high density polyethylene or polyethylene terephthalate (PET) sheets at temperature less than 70 deg. C. Experimental results show that gas permeation in the case of a-C:H film coating on PET sheet was reduced by a factor of more than 150 (0.27 cm3/m2 day atm), compared with that before coating. Plasma characteristics of SWP, such as electron density and electron energy distribution functions, and other film characteristics measured with Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and atomic force microscope are presented and discussed

  8. Removal of a hydrogenated amorphous carbon film from the tip of a micropipette electrode using direct current corona discharge.

    Science.gov (United States)

    Kakuta, Naoto; Okuyama, Naoki; Yamada, Yukio

    2010-02-01

    Micropipette electrodes are fabricated by coating glass micropipettes first with metal and then with hydrogenated amorphous carbon (a-C:H) as an electrical insulator. Furthermore, at the tip of the micropipette electrode, the deposited a-C:H film needs to be removed to expose the metal-coated surface and hollow for the purposes of electrical measurement and injection. This paper describes a convenient and reliable method for removing the a-C:H film using direct current corona discharge in atmospheric air. The initial film removal occurred at an applied voltage of 1.5-2.0 kV, accompanied by an abrupt increase in the discharge current. The discharge current then became stable at a microampere level in the glow corona mode, and the removed area gradually extended. PMID:20192514

  9. Effects of prolonged illumination with white light on the photo-response of carbon-doped hydrogenated amorphous silicon photo-detectors

    International Nuclear Information System (INIS)

    A study of the photo-response behaviour of carbon-doped hydrogenated amorphous silicon photo-detectors over 2800 h of continuous illumination with white light is presented. Both direct and inverse Staebler–Wronski effects are observed in the data.

  10. Structural stability of hydrogenated amorphous carbon overcoats used in heat-assisted magnetic recording investigated by rapid thermal annealing

    KAUST Repository

    Wang, N.

    2013-01-01

    Ultrathin amorphous carbon (a-C) films are extensively used as protective overcoats of magnetic recording media. Increasing demands for even higher storage densities have necessitated the development of new storage technologies, such as heat-assisted magnetic recording (HAMR), which uses laser-assisted heating to record data on high-stability media that can store single bits in extremely small areas (∼1 Tbit/in.2). Because HAMR relies on locally changing the coercivity of the magnetic medium by raising the temperature above the Curie temperature for data to be stored by the magnetic write field, it raises a concern about the structural stability of the ultrathin a-C film. In this study, rapid thermal annealing (RTA) experiments were performed to examine the thermal stability of ultrathin hydrogenated amorphous carbon (a-C:H) films deposited by plasma-enhanced chemical vapor deposition. Structural changes in the a-C:H films caused by RTA were investigated by x-ray photoelectron spectroscopy, Raman spectroscopy, x-ray reflectivity, and conductive atomic force microscopy. The results show that the films exhibit thermal stability up to a maximum temperature in the range of 400-450 °C. Heating above this critical temperature leads to hydrogen depletion and sp 2 clustering. The critical temperature determined by the results of this study represents an upper bound of the temperature rise due to laser heating in HAMR hard-disk drives and the Curie temperature of magnetic materials used in HAMR hard disks. © 2013 American Institute of Physics.

  11. Surface morphology and grain analysis of successively industrially grown amorphous hydrogenated carbon films (a-C:H) on silicon

    Energy Technology Data Exchange (ETDEWEB)

    Catena, Alberto [Department of Physics, University of Koblenz-Landau, 56070 Koblenz (Germany); McJunkin, Thomas [Department of Physics, The Ohio State University, 43210 Columbus, Ohio (United States); Agnello, Simonpietro; Gelardi, Franco M. [Department of Physics and Chemistry, University of Palermo, 90100 Palermo (Italy); Wehner, Stefan [Department of Physics, University of Koblenz-Landau, 56070 Koblenz (Germany); Fischer, Christian B., E-mail: chrbfischer@uni-koblenz.de [Department of Physics, University of Koblenz-Landau, 56070 Koblenz (Germany)

    2015-08-30

    Graphical abstract: - Highlights: • Two different a-C:H coatings in various thicknesses on Si (1 0 0) have been studied. • For both types no significant difference in surface morphology is detectable. • The grain number with respect to their height appears randomly distributed. • In average no grain higher than 14 nm and larger than 0.05 μm{sup 2} was observed. • A height to area correlation confines all detected grains to a limited region. - Abstract: Silicon (1 0 0) has been gradually covered by amorphous hydrogenated carbon (a-C:H) films via an industrial process. Two types of these diamond-like carbon (DLC) coatings, one more flexible (f-DLC) and one more robust (r-DLC), have been investigated. Both types have been grown by a radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique with acetylene plasma. Surface morphologies have been studied in detail by atomic force microscopy (AFM) and Raman spectroscopy has been used to investigate the DLC structure. Both types appeared to have very similar morphology and sp{sup 2} carbon arrangement. The average height and area for single grains have been analyzed for all depositions. A random distribution of grain heights was found for both types. The individual grain structures between the f- and r-type revealed differences: the shape for the f-DLC grains is steeper than for the r-DLC grains. By correlating the average grain heights to the average grain areas for all depositions a limited region is identified, suggesting a certain regularity during the DLC deposition mechanisms that confines both values. A growth of the sp{sup 2} carbon entities for high r-DLC depositions is revealed and connected to a structural rearrangement of carbon atom hybridizations and hydrogen content in the DLC structure.

  12. Surface morphology and grain analysis of successively industrially grown amorphous hydrogenated carbon films (a-C:H) on silicon

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Two different a-C:H coatings in various thicknesses on Si (1 0 0) have been studied. • For both types no significant difference in surface morphology is detectable. • The grain number with respect to their height appears randomly distributed. • In average no grain higher than 14 nm and larger than 0.05 μm2 was observed. • A height to area correlation confines all detected grains to a limited region. - Abstract: Silicon (1 0 0) has been gradually covered by amorphous hydrogenated carbon (a-C:H) films via an industrial process. Two types of these diamond-like carbon (DLC) coatings, one more flexible (f-DLC) and one more robust (r-DLC), have been investigated. Both types have been grown by a radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique with acetylene plasma. Surface morphologies have been studied in detail by atomic force microscopy (AFM) and Raman spectroscopy has been used to investigate the DLC structure. Both types appeared to have very similar morphology and sp2 carbon arrangement. The average height and area for single grains have been analyzed for all depositions. A random distribution of grain heights was found for both types. The individual grain structures between the f- and r-type revealed differences: the shape for the f-DLC grains is steeper than for the r-DLC grains. By correlating the average grain heights to the average grain areas for all depositions a limited region is identified, suggesting a certain regularity during the DLC deposition mechanisms that confines both values. A growth of the sp2 carbon entities for high r-DLC depositions is revealed and connected to a structural rearrangement of carbon atom hybridizations and hydrogen content in the DLC structure

  13. Vacuum ultraviolet photolysis of hydrogenated amorphous carbons. III. Diffusion of photo-produced H2 as a function of temperature

    CERN Document Server

    Martín-Doménech, Rafael; Caro, Guillermo M Muñoz

    2016-01-01

    Hydrogenated amorphous carbon (a-C:H) has been proposed as one of the carbonaceous solids detected in the interstellar medium. Energetic processing of the a-C:H particles leads to the dissociation of the C-H bonds and the formation of hydrogen molecules and small hydrocarbons. Photo-produced H2 molecules in the bulk of the dust particles can diffuse out to the gas phase and contribute to the total H2 abundance. We have simulated this process in the laboratory with plasma-produced a-C:H and a-C:D analogs under astrophysically relevant conditions to investigate the dependence of the diffusion as a function of temperature. Plasma-produced a-C:H analogs were UV-irradiated using a microwave-discharged hydrogen flow lamp. Molecules diffusing to the gas-phase were detected by a quadrupole mass spectrometer, providing a measurement of the outgoing H2 or D2 flux. By comparing the experimental measurements with the expected flux from a one-dimensional diffusion model, a diffusion coefficient D could be derived for expe...

  14. Vacuum ultraviolet photolysis of hydrogenated amorphous carbons. III. Diffusion of photo-produced H2 as a function of temperature

    Science.gov (United States)

    Martín-Doménech, R.; Dartois, E.; Muñoz Caro, G. M.

    2016-06-01

    Context. Hydrogenated amorphous carbon (a-C:H) has been proposed as one of the carbonaceous solids detected in the interstellar medium. Energetic processing of the a-C:H particles leads to the dissociation of the C-H bonds and the formation of hydrogen molecules and small hydrocarbons. Photo-produced H2 molecules in the bulk of the dust particles can diffuse out to the gas phase and contribute to the total H2 abundance. Aims: We have simulated this process in the laboratory with plasma-produced a-C:H and a-C:D analogs under astrophysically relevant conditions to investigate the dependence of the diffusion as a function of temperature. Methods: Experimental simulations were performed in a high-vacuum chamber, with complementary experiments carried out in an ultra-high-vacuum chamber. Plasma-produced a-C:H and a-C:D analogs were UV-irradiated using a microwave-discharged hydrogen flow lamp. Molecules diffusing to the gas-phase were detected by a quadrupole mass spectrometer, providing a measurement of the outgoing H2 or D2 flux. By comparing the experimental measurements with the expected flux from a one-dimensional diffusion model, a diffusion coefficient D could be derived for experiments carried out at different temperatures. Results: Dependence on the diffusion coefficient D with the temperature followed an Arrhenius-type equation. The activation energy for the diffusion process was estimated (ED(H2) = 1660 ± 110 K, ED(D2) = 2090 ± 90 K), as well as the pre-exponential factor (D0(H2) = 0.0007 cm2 s-1, D0(D2) = 0.0045 cm2 s-1). Conclusions: The strong decrease of the diffusion coefficient at low dust particle temperatures exponentially increases the diffusion times in astrophysical environments. Therefore, transient dust heating by cosmic rays needs to be invoked for the release of the photo-produced H2 molecules in cold photon-dominated regions, where destruction of the aliphatic component in hydrogenated amorphous carbons most probably takes place.

  15. Effect of pressure on the deposition of hydrogen-free amorphous carbon and carbon nitride films by the pulsed cathodic arc discharge method

    International Nuclear Information System (INIS)

    Hydrogen-free amorphous carbon (a-C) and carbon nitride (a-C:N) films were deposited using the pulsed cathodic arc discharge at different argon and nitrogen pressures. The surface and mechanical properties of these films were found to strongly depend on the gas pressure. The tetrahedral amorphous carbon and hard a-C:N films with smooth surfaces (rms roughness: 0.15 nm) were prepared at lower gas pressures (-2 Pa). Incorporation of an increasing amount of nitrogen in a-C:N films caused a decrease in film hardness. All the films were covered with the thin (0.3-2 nm) graphite-like surface layers. The film hardness was correlated to the soft surface layer thickness, and the films with thinner surface layers exhibit higher hardness. The mean energies of pulsed plasma beams were measured as the functions of argon and nitrogen pressures. The mean energies of plasma beams decrease in an exponential fashion with increasing gas pressure due to the carbon ion collisions with the neutral gas species. The effects of mean energies of deposited species on the film deposition were explained in terms of the thermal spike migration of surface atoms. The formation of graphite-like surface layers is associated with the low-energy deposition process. The low-energy (10 eV) species may produce the strong thermal spike at film surface, and contribute to the formation of sp3 bonded structure at a sp3 bonded matrix

  16. Mechanical properties of amorphous hydrogenated carbon films fabricated on polyethylene terephthalate foils by plasma immersion ion implantation and deposition

    International Nuclear Information System (INIS)

    Amorphous hydrogenated carbon (a-C:H) films have been deposited on polyethylene terephthalate by plasma immersion ion implantation and deposition. The influence of deposition parameters such as gas pressure, bias voltage, and nitrogen incorporation on the mechanical properties of the a-C:H films are investigated. X-ray photoelectron spectroscopy reveals that the ratio of sp3 to sp2 is 0.24 indicating that the film is mainly composed of graphitelike carbon. Nanoindentation tests disclose enhanced surface hardness of ∼6 GPa. The friction coefficient of the film deposited at higher gas pressure, for instance, 2.0 Pa, is lower than that of the film deposited at a lower pressure such as 0.5 Pa. The films deposited using a low bias voltage tend to fail easily in the friction tests and nitrogen incorporation into the a-C:H films decreases the friction coefficient. Mechanical folding tests show that deformation failure is worse on a thinner a-C:H film

  17. Dynamics of hydrogen in hydrogenated amorphous silicon

    Indian Academy of Sciences (India)

    Ranber Singh; S Prakash

    2003-07-01

    The problem of hydrogen diffusion in hydrogenated amorphous silicon (a-Si:H) is studied semiclassically. It is found that the local hydrogen concentration fluctuations-induced extra potential wells, if intense enough, lead to the localized electronic states in a-Si:H. These localized states are metastable. The trapping of electrons and holes in these states leads to the electrical degradation of the material. These states also act as recombination centers for photo-generated carriers (electrons and holes) which in turn may excite a hydrogen atom from a nearby Si–H bond and breaks the weak (strained) Si–Si bond thereby apparently enhancing the hydrogen diffusion and increasing the light-induced dangling bonds.

  18. Thermal instability of the microstructure and surface mechanical properties of hydrogenated amorphous carbon films

    International Nuclear Information System (INIS)

    The thermal stability of the microstructure and surface mechanical properties of two types of hydrogenated carbon film (''hard'' and ''soft'' versions, both about 2000 A thick) deposited from methane onto Si(100) wafers by a r.f.-plasma-assisted chemical vapour deposition process have been investigated. Whilst Raman spectroscopy indicates the presence of some degree of sp3 bonding in the hard film, the soft coating luminesced and burned away easily in the laser beam. IR reflectance shows the presence of CHx in both films but the amount, and whether it is CH2 or CH3, could not be deduced owing to the strong IR absorbance of the silicon substrate. On annealing in air (in the temperature range 20-600degC), scanning electron microscopy and energy-dispersive X-ray analysis show that both films are completely oxidized by 500degC. On annealing in vacuum (at 10-6 Torr or less) a system of bubbles forms in the hard film at about 530degC, owing to the liberation of trapped argon, and leads to a decohesion of the coating-substrate interface. Also, after annealing in vacuum, transmission electron microscopy shows further marked changes in the nanostructure of the films at elevated temperatures. As expected from these microstructural changes, the microhardness and contact damage resistance of both films are drastically degraded at only relatively modest temperatures. Further, the hard composite exhibits thermal hysteresis of hardness, suggesting the presence of significant compressive residual stress in the film. These results are presented and discussed alongside further insights gained from surface displacement experiments with a nanoindenter. (orig.)

  19. Characterization of hydrogenated amorphous carbon nitride particles and coatings obtained in a CH4/N2 radiofrequency discharge

    International Nuclear Information System (INIS)

    Hydrogenated amorphous carbon nitride (a-CN x:H) particles and coatings have been prepared in a CH4/N2 13.56 MHz radiofrequency discharge. Particles and films have been examined by Scanning Electron Microscopy (SEM) and by infrared (IR) absorption spectroscopy for different nitrogen contents. SEM micrographs show that the dust particles are spherical with diameters in the range 0.2-4 μm. The surface morphology of the particles is strongly modified with the increase of the nitrogen content in the gas mixture. In the particle and film IR spectra, four predominant absorption bands have been observed. They reveal the presence of C-H, C=C, C=N and/or N-H (1300-1800 cm-1), -C≡N and -N≡C (2000-2300 cm-1), C-H (2800-3100 cm-1) and N-H and/or O-H (3200-3600 cm-1) bonds. These absorption bands are studied in order to determine the influence of the nitrogen incorporation

  20. Studies of pure and nitrogen-incorporated hydrogenated amorphous carbon thin films and their possible application for amorphous silicon solar cells

    International Nuclear Information System (INIS)

    Hydrogenated amorphous carbon (a-C:H) and nitrogen-incorporated a-C:H (a-C:N:H) thin films were deposited using radio frequency-plasma-enhanced chemical vapor deposition technique and studied for their electrical, optical, and nano-mechanical properties. Introduction of nitrogen and increase of self bias enhanced the conductivity of a-C:H and a-C:N:H films, whereas current-voltage measurement reveals heterojunction formation due to their rectifying behavior. The bandgap of these films was changed over wide range from 1.9 eV to 3.45 eV by varying self bias and the nitrogen incorporation. Further, activation energy was correlated with the electronic structure of a-C:H and a-C:N:H films, and conductivity was discussed as a function of bandgap. Moreover, a-C:N:H films exhibited high hardness and elastic modulus, with maximum values as 42 GPa and 430 GPa, respectively, at -100 V. Observed fascinating electrical, optical, and nano-mechanical properties made it a material of great utility in the development of optoelectronic devices, such as solar cells. In addition, we also performed simulation study for an a-Si:H solar cell, considering a-C:H and C:N:H as window layers, and compared their performance with the a-Si:H solar cell having a-SiC:H as window layer. We also proposed several structures for the development of a near full-spectrum solar cell. Moreover, due to high hardness, a-C:N:H films can be used as a protective and encapsulate layer on solar cells, especially in n-i-p configuration on metal substrate. Nevertheless, a-C:H and a-C:N:H as a window layer can avoid the use of additional hard and protective coating and, hence, minimize the cost of the product.

  1. Hydrogenation effects on carrier transport in boron-doped ultrananocrystalline diamond/amorphous carbon films prepared by coaxial arc plasma deposition

    International Nuclear Information System (INIS)

    Boron-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were deposited by coaxial arc plasma deposition with a boron-blended graphite target at a base pressure of <10−3 Pa and at hydrogen pressures of ≤53.3 Pa. The hydrogenation effects on the electrical properties of the films were investigated in terms of chemical bonding. Hydrogen-scattering spectrometry showed that the maximum hydrogen content was 35 at. % for the film produced at 53.3-Pa hydrogen pressure. The Fourier-transform infrared spectra showed strong absorptions by sp3 C–H bonds, which were specific to the UNCD/a-C:H, and can be attributed to hydrogen atoms terminating the dangling bonds at ultrananocrystalline diamond grain boundaries. Temperature-dependence of the electrical conductivity showed that the films changed from semimetallic to semiconducting with increasing hydrogen pressure, i.e., with enhanced hydrogenation, probably due to hydrogenation suppressing the formation of graphitic bonds, which are a source of carriers. Carrier transport in semiconducting hydrogenated films can be explained by a variable-range hopping model. The rectifying action of heterojunctions comprising the hydrogenated films and n-type Si substrates implies carrier transport in tunneling

  2. Effect of Hydrogen on the Properties of Amorphous Carbon Nitride Films

    Czech Academy of Sciences Publication Activity Database

    Mikmeková, Eliška; Urbánek, Michal; Fořt, Tomáš; Di Mundo, R.

    Chengdu : Institute of Electrical and Electronics Engineers, Inc, 2010, s. 291-295. ISBN 978-1-4244-8759-2. [International Conference on Manufacturing Science and Technology - ICMST 2010. Kuala Lumpur (MY), 26.11.2010-28.11.2010] Institutional research plan: CEZ:AV0Z20650511 Keywords : hydrogenated alfa-CNx films * ressidal stress * r. f. magnetron sputtering * SLEEM * XPS * TDMS * AFM Subject RIV: JI - Composite Materials

  3. Amorphous carbon for photovoltaics

    Science.gov (United States)

    Risplendi, Francesca; Grossman, Jeffrey C.

    2015-03-01

    All-carbon solar cells have attracted attention as candidates for innovative photovoltaic devices. Carbon-based materials such as graphene, carbon nanotubes (CNT) and amorphous carbon (aC) have the potential to present physical properties comparable to those of silicon-based materials with advantages such as low cost and higher thermal stability.In particular a-C structures are promising systems in which both sp2 and sp3 hybridization coordination are present in different proportions depending on the specific density, providing the possibility of tuning their optoelectronic properties and achieving comparable sunlight absorption to aSi. In this work we employ density functional theory to design suitable device architectures, such as bulk heterojunctions (BHJ) or pn junctions, consisting of a-C as the active layer material.Regarding BHJ, we study interfaces between aC and C nanostructures (such as CNT and fullerene) to relate their optoelectronic properties to the stoichiometry of aC. We demonstrate that the energy alignment between the a-C mobility edges and the occupied and unoccupied states of the CNT or C60 can be widely tuned by varying the aC density to obtain a type II interface.To employ aC in pn junctions we analyze the p- and n-type doping of a-C focusingon an evaluation of the Fermi level and work function dependence on doping.Our results highlight promising features of aC as the active layer material of thin-film solar cells.

  4. Preparation of hydrogenated amorphous silicon tin alloys

    OpenAIRE

    Vergnat, M.; Marchal, G.; Piecuch, M.

    1987-01-01

    This paper describes a new method to obtain hydrogenated amorphous semiconductor alloys. The method is reactive co-evaporation. Silicon tin hydrogenated alloys are prepared under atomic hydrogen atmosphere. We discuss the influence of various parameters of preparation (hydrogen pressure, tungsten tube temperature, substrate temperature, annealing...) on electrical properties of samples.

  5. Study of Synchrotron Radiation Near-Edge X-Ray Absorption Fine-Structure of Amorphous Hydrogenated Carbon Films at Various Thicknesses

    Directory of Open Access Journals (Sweden)

    Sarayut Tunmee

    2015-01-01

    Full Text Available The compositions and bonding states of the amorphous hydrogenated carbon films at various thicknesses were evaluated via near-edge X-ray absorption fine-structure (NEXAFS and elastic recoil detection analysis combined with Rutherford backscattering spectrometry. The absolute carbon sp2 contents were determined to decrease to 65% from 73%, while the hydrogen contents increase from 26 to 33 at.% as the film thickness increases. In addition, as the film thickness increases, the π⁎ (C=C, σ⁎ (C–H, σ⁎ (C=C, and σ⁎ (C≡C bonding states were found to increase, whereas the π⁎ (C≡C and σ⁎ (C–C bonding states were observed to decrease in the NEXAFS spectra. Consequently, the film thickness is a key factor to evaluate the composition and bonding state of the films.

  6. NMR INVESTIGATIONS OF HYDROGENATED AMORPHOUS SILICON

    OpenAIRE

    J. Reimer

    1981-01-01

    A review is presented of the N.M.R. (Nuclear Magnetic Resonance) studies to date of hydrogenated amorphous silicon-hydrogen films. Structural features of proton N.M.R. lineshapes, dynamics of hydrogen containing defect sites, and the promise of quantitative determinations of local silicon-hydrogen bonding environments are discussed in detail. Finally, some comments are given on future directions for N.M.R. studies of hydrogenated thin films.

  7. Room temperature photoluminescence from nanostructured amorphous carbon

    OpenAIRE

    Henley, SJ; Carey, JD; Silva, SRP

    2004-01-01

    Visible room-temperature photoluminescence (PL) was observed from hydrogen-free nanostructured amorphous carbon films deposited by pulsed laser ablation in different background pressures of argon (PAr). By varying PAr from 5 to 340 mTorr, the film morphology changed from smooth to rough and at the highest pressures, low-density filamentary growth was observed. Over the same pressure regime an increase in the ordering of sp2 bonded C content was observed using visible Raman spectroscopy. Th...

  8. Near-Edge X-Ray Absorption Fine Structure of Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Films Prepared by Pulsed Laser Deposition

    Directory of Open Access Journals (Sweden)

    Shinya Ohmagari

    2009-01-01

    Full Text Available The atomic bonding configuration of ultrananocrystalline diamond (UNCD/hydrogenated amorphous carbon (a-C:H films prepared by pulsed laser ablation of graphite in a hydrogen atmosphere was examined by near-edge X-ray absorption fine structure spectroscopy. The measured spectra were decomposed with simple component spectra, and they were analyzed in detail. As compared to the a-C:H films deposited at room substrate-temperature, the UNCD/a-C:H and nonhydrogenated amorphous carbon (a-C films deposited at a substrate-temperature of 550∘C exhibited enhanced π∗ and σ∗C≡C peaks. At the elevated substrate-temperature, the π∗ and σ∗C≡C bonds formation is enhanced while the σ∗C–H and σ∗C–C bonds formation is suppressed. The UNCD/a-C:H film showed a larger σ∗C–C peak than the a-C film deposited at the same elevated substrate-temperature in vacuum. We believe that the intense σ∗C–C peak is evidently responsible for UNCD crystallites existence in the film.

  9. Influence of Fe-doped on structural, electronic structural and optical properties of hydrogenated amorphous carbon films prepared by plasma enhanced chemical vapor deposition

    International Nuclear Information System (INIS)

    Fe-doped hydrogenated amorphous carbon (a-C:H:Fe) films were deposited from an isobutene/ferrocene/H2 gas mixture by plasma enhanced chemical metal organic vapor deposition. Raman spectra were used to characterize the bonding structure of the a-C:H:Fe films and hydrogenated amorphous carbon (a-C:H) films. Optical properties were investigated by the UV-vis spectroscopy and the photoluminescence spectra. The number of six-numbered rings of the a-C:H films increases and sp2 clustering of the films decreases after Fe-doping. The Tauc optical gap of the a-C:H:Fe films becomes narrower by 0.15-0.23 eV relative to the value of the a-C:H films. The narrowing of the optical gap after doping is attributed primarily to the extended state around the Fe deep level in the band gap and the narrowing of the π and π* band edge states because of the increase of the number of six-numbered rings in the a-C:H films. Fe deep level defects of the a-C:H:Fe films contribute chiefly to non-radiative recombination.

  10. Structure, mechanical, and frictional properties of hydrogenated fullerene-like amorphous carbon film prepared by direct current plasma enhanced chemical vapor deposition

    Science.gov (United States)

    Wang, Yongfu; Gao, Kaixiong; Zhang, Junyan

    2016-07-01

    In this study, fullerene like carbon (FL-C) is introduced in hydrogenated amorphous carbon (a-C:H) film by employing a direct current plasma enhanced chemical vapor deposition. The film has a low friction and wear, such as 0.011 and 2.3 × 10-9mm3/N m in the N2, and 0.014 and 8.4 × 10-8mm3/N m in the humid air, and high hardness and elasticity (25.8 GPa and 83.1%), to make further engineering applications in practice. It has several nanometers ordered domains consisting of less frequently cross-linked graphitic sheet stacks. We provide new evidences for understanding the reported Raman fit model involving four vibrational frequencies from five, six, and seven C-atom rings of FL-C structures, and discuss the structure evolution before or after friction according to the change in the 1200 cm-1 Raman band intensity caused by five- and seven-carbon rings. Friction inevitably facilitates the transformation of carbon into FL-C nanostructures, namely, the ultra low friction comes from both such structures within the carbon film and the sliding induced at friction interface.

  11. Structure and gas-barrier properties of amorphous hydrogenated carbon films deposited on inner walls of cylindrical polyethylene terephthalate by plasma-enhanced chemical vapor deposition

    Science.gov (United States)

    Li, Jing; Gong, Chunzhi; Tian, Xiubo; Yang, Shiqin; Fu, Ricky K. Y.; Chu, Paul K.

    2009-01-01

    The influence of radio-frequency (RF) power on the structure and gas permeation through amorphous hydrogenated carbon films deposited on cylindrical polyethylene terephthalate (PET) samples is investigated. The results show that a higher radio-frequency power leads to a smaller sp 3/sp 2 value but produces fewer defects with smaller size. The permeability of PET samples decreases significantly after a-C:H deposition and the RF only exerts a small influence. However, the coating uniformity, color, and wettability of the surface are affected by the RF power. A higher RF power results in to better uniformity and it may be attributed to the combination of the high-density plasma and sample heating.

  12. Structure and gas-barrier properties of amorphous hydrogenated carbon films deposited on inner walls of cylindrical polyethylene terephthalate by plasma-enhanced chemical vapor deposition

    International Nuclear Information System (INIS)

    The influence of radio-frequency (RF) power on the structure and gas permeation through amorphous hydrogenated carbon films deposited on cylindrical polyethylene terephthalate (PET) samples is investigated. The results show that a higher radio-frequency power leads to a smaller sp3/sp2 value but produces fewer defects with smaller size. The permeability of PET samples decreases significantly after a-C:H deposition and the RF only exerts a small influence. However, the coating uniformity, color, and wettability of the surface are affected by the RF power. A higher RF power results in to better uniformity and it may be attributed to the combination of the high-density plasma and sample heating.

  13. Gas barrier properties of hydrogenated amorphous carbon films coated on polyethylene terephthalate by plasma polymerization in argon/n-hexane gas mixture

    International Nuclear Information System (INIS)

    Hydrogenated amorphous carbon thin films were deposited by RF plasma polymerization in argon/n-hexane gas mixture on polyethylene terephthalate (PET) foils. It was found that such deposited films may significantly improve the barrier properties of PET. It was demonstrated that the principal parameter that influences barrier properties of such deposited films towards oxygen and water vapor is the density of the coatings. Moreover, it was shown that for achieving good barrier properties it is advantageous to deposit coatings with very low thickness. According to the presented results, optimal thickness of the coating should not be higher than several tens of nm. - Highlights: • a-C:H films were prepared by plasma polymerization in Ar/n-hexane atmosphere. • Barrier properties of coatings are dependent on their density and thickness. • Highest barrier properties were observed for films with thickness 15 nm

  14. Electrical properties of pulsed UV laser irradiated amorphous carbon

    OpenAIRE

    Y. Miyajima; Adikaari, AADT; Henley, SJ; Shannon, JM; Silva, SRP

    2008-01-01

    Amorphous carbon films containing no hydrogen were irradiated with a pulsed UV laser in vacuum. Raman spectroscopy indicates an increase in the quantity of sp(2) clustering with the highest laser energy density and a commensurate reduction in resistivity. The reduction of resistivity is explained to be associated with thermally induced graphitization of amorphous carbon films. The high field transport is consistent with a Poole-Frenkel type transport mechanism via neutral trapping centers rel...

  15. Intrinsic graphene field effect transistor on amorphous carbon films

    OpenAIRE

    Tinchev, Savcho

    2013-01-01

    Fabrication of graphene field effect transistor is described which uses an intrinsic graphene on the surface of as deposited hydrogenated amorphous carbon films. Ambipolar characteristic has been demonstrated typical for graphene devices, which changes to unipolar characteristic if the surface graphene was etched in oxygen plasma. Because amorphous carbon films can be growth easily, with unlimited dimensions and no transfer of graphene is necessary, this can open new perspective for graphene ...

  16. Growth and Characterization of Hydrogenated Amorphous Silicon and Hydrogenated Amorphous Silicon Carbide with Liquid Organometallic Sources.

    Science.gov (United States)

    Gaughan, Kevin David

    The growth and characterization of hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon -carbon (rm a-rm Si _{1-X}C_{X}: H) alloys employing liquid organometallic sources are described. N -type a-Si:H films were grown using a mixture of silane and tertiarybutylphosphine (TBP-rm C_4H _9P_2) vapor in a plasma enhanced chemical vapor deposition system. Impurity levels from parts per million to about 5 at. % phosphorus have been incorporated into the film with this method. Tertiarybutylphosphine is less toxic and less pyrophoric than phosphine which is usually used in n-type doping of a-Si:H films. Optical and electronic properties were characterized by room temperature as well as temperature dependent dark conductivity, photothermal deflection spectroscopy, infrared vibrational spectroscopy, electron spin resonance, and electron microprobe analysis. The gross doping properties of a-Si:H doped with TBP are the same as those obtained with phosphine. The experimental results are compared with the predictions of several models that describe the chemical equilibrium between active dopants and deep defects. A pronounced decrease in the effects of doping, such as an increase in the activation energy of electrical conductivity and an decrease in the conductivity of the sample, were seen in heavily doped films (TBP/SiH _4> 0.5%), perhaps influenced by the increased carbon and/or phosphorus concentrations. Amorphous silicon-carbide alloys have been grown by the plasma decomposition of ditertiarybutylsilane ( rm DTBS-rm SiH_2(C _4H_9)_2). The optical bandgaps, which varied from 2.2 to 3.3 eV, are strongly dependent upon the deposition conditions. The carbon concentrations in these films varied from 60 to 95 at. %. The optical band-edge is very broad compared to that which is found in a-Si:H and this breadth is essentially independent of the deposition conditions. The plasma decomposition of admixtures of DTBS and silane has produced rm a- rm Si_{1-X

  17. The effect of temperature on the tribological mechanisms and reactivity of hydrogenated, amorphous diamond-like carbon coatings under oil-lubricated conditions

    International Nuclear Information System (INIS)

    In this work we present the wear and friction behaviour of boundary-lubricated, hydrogenated, amorphous, diamond-like carbon coatings (a-C:H), in self-mated a-C:H/a-C:H contacts, at three different testing temperatures: 20, 80, 150 deg. C. We present results from Auger electron spectroscopy, X-ray photoelectron spectroscopy and Raman analyses relating to the chemical and structural changes in the diamond-like carbon coatings during sliding in the presence of mineral oil, with and without additives. We show, that chemical reactions between the a-C:H coatings and the oil additives take place, which are dependent on the temperature, on the presence of additives and the type of additives used. At high temperatures the extreme pressure additive interacts with the diamond-like carbon surface and forms a tribochemical layer with a four-times lower sulphur/phosphorous ratio than the additive formulation. In the absence of additives, however, graphitisation of the coating occurs under these conditions, which results in high-wear and low-friction behaviour. Another result from this study is that a-C:H coatings can oxidise during room-temperature experiments, suggesting that some interactions and adsorptions are also possible at lower temperatures

  18. Stable Transistors in Hydrogenated Amorphous Silicon

    OpenAIRE

    J. M. Shannon

    2004-01-01

    Thin-film field-effect transistors in hydrogenated amorphous silicon are notoriously unstable due to the formation of silicon dangling bond trapping states in the accumulated channel region during operation. Here, we show that by using a source-gated transistor a major improvement in stability is obtained. This occurs because the electron quasi-Fermi level is pinned near the center of the band in the active source region of the device and strong accumulation of electrons is prevented. The use...

  19. Amorphous Silicon-Carbon Nanostructure Solar Cells

    Science.gov (United States)

    Schriver, Maria; Regan, Will; Loster, Matthias; Zettl, Alex

    2011-03-01

    Taking advantage of the ability to fabricate large area graphene and carbon nanotube networks (buckypaper), we produce Schottky junction solar cells using undoped hydrogenated amorphous silicon thin films and nanostructured carbon films. These films are useful as solar cell materials due their combination of optical transparency and conductance. In our cells, they behave both as a transparent conductor and as an active charge separating layer. We demonstrate a reliable photovoltaic effect in these devices with a high open circuit voltage of 390mV in buckypaper devices. We investigate the unique interface properties which result in an unusual J-V curve shape and optimize fabrication processes for improved solar conversion efficiency. These devices hold promise as a scalable solar cell made from earth abundant materials and without toxic and expensive doping processes.

  20. Structural characteristics of copper/hydrogenated amorphous carbon composite films prepared by microwave plasma-assisted deposition processes from methane-argon and acetylene-argon gas mixtures

    International Nuclear Information System (INIS)

    Copper/hydrogenated amorphous carbon (Cu/a-C:H) composite films have been deposited on silicon substrates by a hybrid technique combining microwave plasma-assisted chemical vapor deposition and sputter-deposition from methane-argon and acetylene-argon gas mixtures. The major objective of this work was to investigate the effect of the carbon gas precursor on the structural characteristics of Cu/a-C:H composite films deposited at ambient temperature. The major characteristics of CH4-argon and C2H2-argon plasmas were analyzed by Langmuir probe measurements. The composition of films was determined by Rutherford backscattering spectroscopy, energy recoil detection analyses and nuclear reaction analyses. The carbon content in the films was observed to vary in the range 20-77 at.% and 7.5-99 at.% as the CH4 and C2H2 concentrations in the gas phase increased from 10 to 100%, respectively. The atom number ratio H/C in the films was scattered approximately 0.4 whatever the carbon gas precursor used. The crystallographic structure and the size of copper crystallites incorporated in the a-C were determined by X-ray diffraction techniques. The copper crystallite size decreased from 20 nm in pure copper films to less than 5 nm in Cu/a-C:H films containing more than 40 at.% of carbon. Grazing incidence small angle X-ray scattering measurements were performed to investigate the size distribution and distance of copper crystallites as functions of the deposition parameters. The structural characteristics of copper crystallites were dependent on the hydrocarbon gas precursor used. The crystallite size and the width of the size distribution were homogeneous in films deposited from CH4. Copper crystallites with an anisotropic shape were found in films deposited from C2H2. The major radicals formed in the plasma and condensed on the surface of growing films, namely CH and C2H radicals for films produced from CH4 and C2H2, respectively, play probably a crucial role in the growth

  1. Amorphous carbon and its surfaces

    International Nuclear Information System (INIS)

    Graphical abstract: Some examples of 2.0 g/cm3 surfaces. The cell contained 64 atoms. The top figure shows some tube-like formation, the central figure is an example of a wave-like surface, and the bottom figure is an example of the bending over of the carbons at the surface to form a surface sheet when the sheets in the bulk are not parallel to the surface. - Abstract: We have investigated bulk amorphous carbon at three densities (3.2, 2.6, and 2.0 g/cm3) using density functional theory (DFT). The variation in the structure with density is discussed. The bulk structures are used to create surface structures. If the surfaces are relaxed at 700 K, the surface structures, as a function of density, are more similar than the analogous bulk structures. The relaxed surfaces appear to be graphene sheets with defects, sizable distortions, and have covalently bonded carbon chains holding the sheets together.

  2. Hydrogen, microstructure and defect density in hydrogenated amorphous silicon

    OpenAIRE

    Roca I Cabarrocas, Pere; Djebbour, Z.; Kleider, J.; Longeaud, C.; Mencaraglia, D.; Sib, J.; Bouizem, Y.; Thèye, M.; Sardin, G.; Stoquert, J.

    1992-01-01

    It is well established that by bonding with the dangling bonds of silicon, hydrogen reduces the density of states of amorphous silicon and renders this material suitable to electronic applications. For so-called “standard” a-Si : H films deposited by the RF glow discharge decomposition of silane at low deposition rates (≈1 Å/s) and over a large range of deposition temperatures, we observed the usual correlation between the hydrogen bonding and the defect density in the as-deposited material o...

  3. Properties of Erbium Doped Hydrogenated Amorphous Carbon Layers Fabricated by Sputtering and Plasma Assisted Chemical Vapor Deposition

    Directory of Open Access Journals (Sweden)

    V. Prajzler

    2008-01-01

    Full Text Available We report about properties of carbon layers doped with Er3+ ions fabricated by Plasma Assisted Chemical Vapor Deposition (PACVD and by sputtering on silicon or glass substrates. The structure of the samples was characterized by X-ray diffraction and their composition was determined by Rutherford Backscattering Spectroscopy and Elastic Recoil Detection Analysis. The Absorbance spectrum was taken in the spectral range from 400 nm to 600 nm. Photoluminescence spectra were obtained using two types of Ar laser (λex=514.5 nm, lex=488 nm and also using a semiconductor laser (λex=980 nm. Samples fabricated by magnetron sputtering exhibited typical emission at 1530 nm when pumped at 514.5 nm. 

  4. Experimentally Constrained Molecular Relaxation: The case of hydrogenated amorphous silicon

    OpenAIRE

    Biswas, Parthapratim; Atta-Fynn, Raymond; Drabold, David A.

    2007-01-01

    We have extended our experimentally constrained molecular relaxation technique (P. Biswas {\\it et al}, Phys. Rev. B {\\bf 71} 54204 (2005)) to hydrogenated amorphous silicon: a 540-atom model with 7.4 % hydrogen and a 611-atom model with 22 % hydrogen were constructed. Starting from a random configuration, using physically relevant constraints, {\\it ab initio} interactions and the experimental static structure factor, we construct realistic models of hydrogenated amorphous silicon. Our models ...

  5. Tribological Performance of Hydrogenated Amorphous Carbon (a-C: H DLC Coating when Lubricated with Biodegradable Vegetal Canola Oil

    Directory of Open Access Journals (Sweden)

    H.M. Mobarak

    2014-06-01

    Full Text Available Increasing environmental awareness and demands for lowering energy consumptions are strong driving forces behind the development of the vehicles of tomorrow. Without the advances of lubricant chemistry and adequate lubricant formulation, expansion of modern engines would not have been possible. Considering environmental awareness factors as compared to mineral oils, vegetal oil based biolubricants are renewable, biodegradable, non-toxic and have a least amount of greenhouse gases. Furthermore, improvement in engine performance and transmission components, which were impossible to achieve by applying only lubricants design, is now possible through diamond like carbon (DLC coatings. DLC coatings exhibit brilliant tribological properties, such as good wear resistance and low friction. In this regard, tribological performance of a-C: H DLC coating when lubricated with Canola vegetal oil has been investigated by the help of a ball-on-flat geometry. Experimental results demonstrated that the a-C: H DLC coating exhibited better performance with Canola oil in terms of friction and wear as compared to the uncoated materials. Large amount of polar components in the Canola oil significantly improved the tribological properties of the a-C:H coating. Thus, usage of a-C: H DLC coating with Canola oil in the long run may have a positive impact on engine life.

  6. Amorphous Carbon-Boron Nitride Nanotube Hybrids

    Science.gov (United States)

    Kim, Jae Woo (Inventor); Siochi, Emilie J. (Inventor); Wise, Kristopher E. (Inventor); Lin, Yi (Inventor); Connell, John (Inventor)

    2016-01-01

    A method for joining or repairing boron nitride nanotubes (BNNTs). In joining BNNTs, the nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation to form well bonded hybrid a-C/BNNT structures. In repairing BNNTs, the damaged site of the nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation to form well bonded hybrid a-C/BNNT structures at the damage site.

  7. Proton NMR studies of PECVD hydrogenated amorphous silicon films and HWCVD hydrogenated amorphous silicon films

    Science.gov (United States)

    Herberg, Julie Lynn

    This dissertation discusses a new understanding of the internal structure of hydrogenated amorphous silicon. Recent research in our group has included nuclear spin echo double resonance (SEDOR) measurements on device quality hydrogenated amorphous silicon photovoltaic films. Using the SEDOR pulse sequence with and without the perturbing 29Si pulse, we obtain Fourier transform spectra for film at 80K that allows us to distinguish between molecular hydrogen and hydrogen bonded to silicon. Using such an approach, we have demonstrated that high quality a-Si:H films produced by Plasma Enhanced Chemical Vapor Deposition (PECVD) from SiH 4 contains about ten atomic percent hydrogen, nearly 40% of which is molecular hydrogen, individually trapped in the amorphous equivalent of tetragonal sites (T-sites). The main objective of this dissertation is to examine the difference between a-Si:H made by PECVD techniques and a-Si:H made by Hot Wire Chemical Vapor Deposition (HWCVD) techniques. Proton NMR and 1H- 29Si SEDOR NMR are used to examine the hydrogen structure of HWCVD a-Si:H films prepared at the University of Utrecht and at the National Renewable Energy Laboratory (NREL). Past NMR studies have shown that high quality PECVD a-Si:H films have geometries in which 40% of the contained hydrogen is present as H2 molecules individually trapped in the amorphous equivalent of T-sites. A much smaller H2 fraction sometimes is physisorbed on internal surfaces. In this dissertation, similar NMR methods are used to perform structural studies of the two HWCVD aSi:H samples. The 3kHz resonance line from T-site-trapped H2 molecules shows a hole-burn behavior similar to that found for PECVD a-Si:H films as does the 24kHz FWHM line from clustered hydrogen bonded to silicon. Radio frequency hole-burning is a tool to distinguish between inhomogenous and homogeneous broadening. In the hole-burn experiments, the 3kHz FWHM resonance line from T-site-trapped H2 molecules shows a hole

  8. Synthesis of hydrogen-carbon clathrate material and hydrogen evolution therefrom at moderate temperatures and pressures

    Science.gov (United States)

    Lueking, Angela; Narayanan, Deepa

    2011-03-08

    A process for making a hydrogenated carbon material is provided which includes forming a mixture of a carbon source, particularly a carbonaceous material, and a hydrogen source. The mixture is reacted under reaction conditions such that hydrogen is generated and/or released from the hydrogen source, an amorphous diamond-like carbon is formed, and at least a portion of the generated and/or released hydrogen associates with the amorphous diamond-like carbon, thereby forming a hydrogenated carbon material. A hydrogenated carbon material including a hydrogen carbon clathrate is characterized by evolution of molecular hydrogen at room temperature at atmospheric pressure in particular embodiments of methods and compositions according to the present invention.

  9. Ion beam deposition of amorphous carbon films with diamond like properties

    Science.gov (United States)

    Angus, John C.; Mirtich, Michael J.; Wintucky, Edwin G.

    1982-01-01

    Carbon films were deposited on silicon, quartz, and potassium bromide substrates from an ion beam. Growth rates were approximately 0.3 micron/hour. The films were featureless and amorphous and contained only carbon and hydrogen in significant amounts. The density and carbon/hydrogen ratio indicate the film is a hydrogen deficient polymer. One possible structure, consistent with the data, is a random network of methylene linkages and tetrahedrally coordinated carbon atoms.

  10. Structure-property relations in amorphous carbon for photovoltaics

    OpenAIRE

    Risplendi, Francesca; Bernardi, Marco; Cicero, Giancarlo; Grossman, Jeffrey C.

    2014-01-01

    Carbon is emerging as a material with great potential for photovoltaics (PV). However, the amorphous form (a-C) has not been studied in detail as a PV material, even though it holds similarities with amorphous Silicon (a-Si) that is widely employed in efficient solar cells. In this work, we correlate the structure, bonding, stoichiometry, and hydrogen content of a-C with properties linked to PV performance such as the electronic structure and optical absorption. We employ first-principles mol...

  11. Thermal decomposition of silane to form hydrogenated amorphous Si

    Science.gov (United States)

    Strongin, M.; Ghosh, A.K.; Wiesmann, H.J.; Rock, E.B.; Lutz, H.A. III

    Hydrogenated amorphous silicon is produced by thermally decomposing silane (SiH/sub 4/) or other gases comprising H and Si, at elevated temperatures of about 1700 to 2300/sup 0/C, in a vacuum of about 10/sup -8/ to 10/sup -4/ torr. A gaseous mixture is formed of atomic hydrogen and atomic silicon. The gaseous mixture is deposited onto a substrate to form hydrogenated amorphous silicon.

  12. 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

    Science.gov (United States)

    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.

  13. Generation of correlated photons in hydrogenated amorphous-silicon waveguides

    OpenAIRE

    Clemmen, S.; Perret, A; Selvaraja, Shankar Kumar; Bogaerts, Wim; Van Thourhout, Dries; Baets, Roel; Emplit, Ph.; Massar, S.

    2011-01-01

    We report the first (to our knowledge) observation of correlated photon emission in hydrogenated amorphous- silicon waveguides. We compare this to photon generation in crystalline silicon waveguides with the same geome- try. In particular, we show that amorphous silicon has a higher nonlinearity and competes with crystalline silicon in spite of higher loss.

  14. GHz-rate optical parametric amplifier in hydrogenated amorphous silicon

    International Nuclear Information System (INIS)

    We demonstrate optical parametric amplification operating at GHz-rates at telecommunications wavelengths using a hydrogenated amorphous silicon waveguide through the nonlinear optical process of four-wave mixing. We investigate how the parametric amplification scales with repetition rate. The ability to achieve amplification at GHz-repetition rates shows hydrogenated amorphous silicon’s potential for telecommunication applications and a GHz-rate optical parametric oscillator. (paper)

  15. Hydrogenated amorphous silicon deposited by ion-beam sputtering

    Science.gov (United States)

    Lowe, V. E.; Henin, N.; Tu, C.-W.; Tavakolian, H.; Sites, J. R.

    1981-01-01

    Hydrogenated amorphous silicon films 1/2 to 1 micron thick were deposited on metal and glass substrates using ion-beam sputtering techniques. The 800 eV, 2 mA/sq cm beam was a mixture of argon and hydrogen ions. The argon sputtered silicon from a pure (7.6 cm) single crystal wafer, while the hydrogen combined with the sputtered material during the deposition. Hydrogen to argon pressure ratios and substrate temperatures were varied to minimize the defect state density in the amorphous silicon. Characterization was done by electrical resistivity, index of refraction and optical absorption of the films.

  16. Formation of molecular hydrogen on amorphous silicate surfaces

    CERN Document Server

    Li, Ling; Congiu, Emanuele; Roser, Joe; Swords, Sol; Perets, Hagai B; Lederhendler, Adina; Biham, Ofer; Brucato, John Robert; Pirronello, Valerio; Vidali, Gianfranco

    2007-01-01

    Experimental results on the formation of molecular hydrogen on amorphous silicate surfaces are presented and analyzed using a rate equation model. The energy barriers for the relevant diffusion and desorption processes are obtained. They turn out to be significantly higher than those obtained for polycrystalline silicates, demonstrating the importance of grain morphology. Using these barriers we evaluate the efficiency of molecular hydrogen formation on amorphous silicate grains under interstellar conditions. It is found that unlike polycrystalline silicates, amorphous silicate grains are efficient catalysts of H_2 formation in diffuse interstellar clouds.

  17. Heteroatom-doped hydrogenated amorphous carbons, a-C:H:X 'Volatile' silicon, sulphur and nitrogen depletion, blue photoluminescence, diffuse interstellar bands and ferro-magnetic carbon grain connections (Research Note)

    CERN Document Server

    Jones, A P

    2014-01-01

    Context. Hydrogenated amorphous carbons, a-C:H, can incorporate a variety of heteroatoms, which can lead to interesting effects. Aims. To investigate the doping of interstellar a-C:H grains with, principally, Si, O, N and S atoms within the astrophysical context. Methods. A search of the literature on doped a-C:H reveals a number of interesting phenomena of relevance to astrophysics. Results. X dopants in a-C:H:X materials can affect the sp3/sp2 ratio (X = Si, O and N), lead to blue photoluminescence (undoped or X = N), induce ferromagnetic-like behaviour (X = N and S) or simply be incorporated (depleted) into the structure (X = Si, O, N and S). Si and N atoms could also incorporate into fullerenes, possibly forming colour-centres that could mimic diffuse interstellar bands. Conclusions. Doped a-C:H grains could explain several dust-related conundrums, such as: 'volatile' Si in photo-dissociation regions, S and N depletion in molecular clouds, blue luminescence, some diffuse interstellar bands and ferromagnet...

  18. 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

    International Nuclear Information System (INIS)

    Highlights: • We tested a-C:H and ta-C DLC coatings as a function of temperature. • Jatropha oil contains large amounts of polar components that enhanced the lubricity of coatings. • CoF decreases with increasing temperature for both contacts. • Wear rate increases with increasing temperature in a-C:H and decreases in ta-C DLC. • At high temperature, ta-C coatings confer more protection than a-C:H coatings. - Abstract: 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

  19. 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

    Energy Technology Data Exchange (ETDEWEB)

    Mobarak, H.M., E-mail: mobarak.ho31@yahoo.com; Masjuki, H.H.; Mohamad, E. Niza, E-mail: edzrol@um.edu.my; Kalam, M.A.; Rashedul, H.K.; Rashed, M.M.; Habibullah, M.

    2014-10-30

    Highlights: • We tested a-C:H and ta-C DLC coatings as a function of temperature. • Jatropha oil contains large amounts of polar components that enhanced the lubricity of coatings. • CoF decreases with increasing temperature for both contacts. • Wear rate increases with increasing temperature in a-C:H and decreases in ta-C DLC. • At high temperature, ta-C coatings confer more protection than a-C:H coatings. - Abstract: 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.

  20. Atomistic models of hydrogenated amorphous silicon nitride from first principles

    NARCIS (Netherlands)

    Jarolimek, K.; De Groot, R.A.; De Wijs, G.A.; Zeman, M.

    2010-01-01

    We present a theoretical study of hydrogenated amorphous silicon nitride (a-SiNx:H), with equal concentrations of Si and N atoms (x=1), for two considerably different densities (2.0 and 3.0 g/cm3). Densities and hydrogen concentration were chosen according to experimental data. Using first-principle

  1. Atomistic models of hydrogenated amorphous silicon nitride from first principles

    NARCIS (Netherlands)

    Jarolimek, K.; Groot, R.A. de; Wijs, G.A. de; Zeman, M.

    2010-01-01

    We present a theoretical study of hydrogenated amorphous silicon nitride (a-SiNx:H), with equal concentrations of Si and N atoms (x=1), for two considerably different densities (2.0 and 3.0 g/cm3). Densities and hydrogen concentration were chosen according to experimental data. Using first-principle

  2. Polyvinylpyrrolidone surface modification with SiOx containing amorphous hydrogenated carbon (a-C:H/SiOx) and nitrogen-doped a-C:H/SiOx films using Hall-type closed drift ion beam source

    International Nuclear Information System (INIS)

    In this study SiOx containing amorphous hydrogenated carbon (a-C:H/SiOx) and nitrogen-doped a-C:H/SiOx (a-C:H:N/SiOx) films were deposited on polyvinylpyrrolidone (PVP) templates of variable thickness using a Hall-type closed drift ion beam source with constant irradiation parameters. A detailed surface characterization was followed using atomic force microscopy (AFM) topography images, surface morphology parameters, height distribution histograms and bearing ratio curves with hybrid parameters. The AFM analysis directly showed that the a-C:H/SiOx/PVP and a-C:H:N/SiOx/PVP composite films represent different morphologies with characteristic surface textures. Surface adhesive properties were evaluated by measuring the force required to separate the AFM tip from the surface by means of AFM force-distance curves. The variance in adhesion force detected was lower for a-C:H/SiOx/PVP composite films due to lower structural homogeneity of the surfaces. Fourier transform infrared spectroscopy analysis was performed to study the blend behavior of PVP upon a-C:H/SiOx and a-C:H:N/SiOx direct ion beam deposition. It was determined that interfacial interactions of PVP with the direct ion beam induced changes in the carbonyl group of the PVP and are dependent on the carrier gas used for the synthesis of the amorphous hydrogenated carbon films. - Highlights: ► Polyvinylpyrrolidone (PVP) surface was modified with diamond-like carbon (DLC). ► Hall-type closed drift ion beam source was used for synthesis of DLC films. ► Surface morphological, adhesive properties and blend behavior were studied. ► Depending on thickness of PVP different surface textures were obtained. ► Changes in carbonyl group of PVP upon modification with DLC were observed

  3. Influence of microstructure and hydrogen concentration on amorphous silicon crystallization

    International Nuclear Information System (INIS)

    Hydrogenated amorphous silicon samples were deposited on glass substrates at different temperatures by high frequency plasma-enhanced chemical vapor deposition. In this way, samples with different hydrogen concentrations and structures were obtained. The transition from an amorphous to a crystalline material, induced by a four-step thermal annealing sequence, has been followed. Effusion of hydrogen from the films plays an important role in the nucleation and growth mechanisms of crystalline silicon grains. Measurements of hydrogen concentrations, Raman scattering, X-ray diffraction and UV reflectance showed that an enhanced crystallization was obtained on samples deposited at lower substrate temperatures. A correlation between these measurements allows to analyze the evolution of structural properties of the samples. The presence of voids in the material, related to disorder in the amorphous matrix, results in a better quality of the resulting nanocrystalline silicon thin films.

  4. Influence of microstructure and hydrogen concentration on amorphous silicon crystallization

    Energy Technology Data Exchange (ETDEWEB)

    Budini, N., E-mail: nbudini@intec.unl.edu.a [Instituto de Desarrollo Tecnologico para la Industria Quimica, UNL-CONICET, Gueemes 3450, S3000GLN Santa Fe (Argentina); Rinaldi, P.A. [Instituto de Desarrollo Tecnologico para la Industria Quimica, UNL-CONICET, Gueemes 3450, S3000GLN Santa Fe (Argentina); Schmidt, J.A.; Arce, R.D.; Buitrago, R.H. [Instituto de Desarrollo Tecnologico para la Industria Quimica, UNL-CONICET, Gueemes 3450, S3000GLN Santa Fe (Argentina); Facultad de Ingenieria Quimica, UNL, Santiago del Estero 2829, S3000AOM Santa Fe (Argentina)

    2010-07-01

    Hydrogenated amorphous silicon samples were deposited on glass substrates at different temperatures by high frequency plasma-enhanced chemical vapor deposition. In this way, samples with different hydrogen concentrations and structures were obtained. The transition from an amorphous to a crystalline material, induced by a four-step thermal annealing sequence, has been followed. Effusion of hydrogen from the films plays an important role in the nucleation and growth mechanisms of crystalline silicon grains. Measurements of hydrogen concentrations, Raman scattering, X-ray diffraction and UV reflectance showed that an enhanced crystallization was obtained on samples deposited at lower substrate temperatures. A correlation between these measurements allows to analyze the evolution of structural properties of the samples. The presence of voids in the material, related to disorder in the amorphous matrix, results in a better quality of the resulting nanocrystalline silicon thin films.

  5. Gas and pressure effects on the synthesis of amorphous carbon nanotubes

    Institute of Scientific and Technical Information of China (English)

    ZHAO Tingkai; LIU Yongning; ZHU Jiewu

    2004-01-01

    The effects of gas, pressure and temperature on the production of amorphous carbon nanotubes were investigated using an arc discharging furnace at controlled temperature. Co/Ni alloy powder was used as catalyst.The discharge current was 80 A and voltage was 32 V. The optimal parameters were obtained: 600℃ temperature, hydrogen gas and 500 torr pressure. The productivity and purity of amorphous carbon nanotubes are 6.5 gram per hour and 80%, respectively. The diameter of the amorphous carbon nanotubes is about 7-20 nm.

  6. In-situ doping of erbium in hydrogenated amorphous carbon by low temperature metalorganic radio frequency plasma enhanced chemical vapor deposition

    International Nuclear Information System (INIS)

    A significant improvement in the photoluminescence of erbium doped amorphous carbon (a-C:H(Er)) is reported. The effects of the RF power on the anode and cathode a-C:H films were investigated in terms of the microstructural and local bonding features. It was determined that Er doped a-C:H films should be placed on the anode to obtain wider bandgap and lower percentage of sp2 carbon bonding. The metalorganic compound, tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate) Erbium(+ III) or Er(fod)3, was incorporated in-situ into an a-C:H host by metalorganic rf plasma enhanced chemical vapor deposition. This technique provides the capability of doping Er in a vertically uniform profile. The high erbium concentration (3.9 at.%), partial fluorination of the surrounding ligands, and the large optical bandgap of the host a-C:H are the primary factors that enable enhancement of the photoluminescence. - Highlights: • High and uniform Er concentration (3.9 at.%) in a-C:H(Er) films is achieved. • Room-temperature photoluminescence peaking at 1.54 μm is demonstrated. • Optically active Er3+ ions are preserved in as-grown samples at low growth temperature. • Non-radiative C-H vibrational quenching is reduced by fluorination of a-C host. • Metalorganic-RF-PECVD provides the potential of doping Er in vertically uniform profiles

  7. Laser annealing of hydrogen implanted amorphous silicon

    International Nuclear Information System (INIS)

    Amorphous silicon, prepared by silicon bombardment at energies of 200 to 250 keV, was implanted with 40 keV H2+ to peak concentrations up to 15 at .% and recrystallized in air by single 20 nsec pulses at 1.06 μm from a Nd:glass laser. Amorphous layer formation and recrystallization were verified using Raman spectroscopy and ion backscattering/channeling analysis

  8. Hydrogen-free amorphous silicon with no tunneling states.

    Science.gov (United States)

    Liu, Xiao; Queen, Daniel R; Metcalf, Thomas H; Karel, Julie E; Hellman, Frances

    2014-07-11

    The ubiquitous low-energy excitations, known as two-level tunneling systems (TLSs), are one of the universal phenomena of amorphous solids. Low temperature elastic measurements show that e-beam amorphous silicon (a-Si) contains a variable density of TLSs which diminishes as the growth temperature reaches 400 °C. Structural analyses show that these a-Si films become denser and more structurally ordered. We conclude that the enhanced surface energetics at a high growth temperature improved the amorphous structural network of e-beam a-Si and removed TLSs. This work obviates the role hydrogen was previously thought to play in removing TLSs in the hydrogenated form of a-Si and suggests it is possible to prepare "perfect" amorphous solids with "crystal-like" properties for applications. PMID:25062205

  9. Investigations on silicon/amorphous-carbon and silicon/nanocrystalline palladium/ amorphous-carbon interfaces.

    Science.gov (United States)

    Roy, M; Sengupta, P; Tyagi, A K; Kale, G B

    2008-08-01

    Our previous work revealed that significant enhancement in sp3-carbon content of amorphous carbon films could be achieved when grown on nanocrystalline palladium interlayer as compared to those grown on bare silicon substrates. To find out why, the nature of interface formed in both the cases has been investigated using Electron Probe Micro Analysis (EPMA) technique. It has been found that a reactive interface in the form of silicon carbide and/silicon oxy-carbide is formed at the interface of silicon/amorphous-carbon films, while palladium remains primarily in its native form at the interface of nanocrystalline palladium/amorphous-carbon films. However, there can be traces of dissolved oxygen within the metallic layer as well. The study has been corroborated further from X-ray photoelectron spectroscopic studies. PMID:19049221

  10. Thin films of hydrogenated amorphous carbon (a-C:H) obtained through chemical vapor deposition assisted by plasma; Peliculas delgadas de carbono amorfo hidrogenado (a-C:H) obtenidas mediante deposito quimico de vapores asistido por plasma

    Energy Technology Data Exchange (ETDEWEB)

    Mejia H, J.A.; Camps C, E.E.; Escobar A, L.; Romero H, S.; Chirino O, S. [ININ, 52045 Ocoyoacac, Estado de Mexico (Mexico); Muhl S, S. [IIM-UNAM, 04510 Mexico D.F. (Mexico)

    2004-07-01

    Films of hydrogenated amorphous carbon (a-C:H) were deposited using one source of microwave plasma with magnetic field (type ECR), using mixtures of H{sub 2}/CH{sub 4} in relationship of 80/20 and 95/05 as precursory gases, with work pressures of 4X10{sup -4} to 6x10{sup -4} Torr and an incident power of the discharge of microwaves with a constant value of 400 W. It was analyzed the influence among the properties of the films, as the deposit rate, the composition and the bonding types, and the deposit conditions, such as the flow rates of the precursory gases and the polarization voltage of the sample holders. (Author)

  11. Amorphous carbon film deposition on inner surface of tubes using atmospheric pressure pulsed filamentary plasma source

    OpenAIRE

    Pothiraja, Ramasamy; Bibinov, Nikita; Awakowicz, Peter

    2011-01-01

    Uniform amorphous carbon film is deposited on the inner surface of quartz tube having the inner diameter of 6 mm and the outer diameter of 8 mm. A pulsed filamentary plasma source is used for the deposition. Long plasma filaments (~ 140 mm) as a positive discharge are generated inside the tube in argon with methane admixture. FTIR-ATR, XRD, SEM, LSM and XPS analyses give the conclusion that deposited film is amorphous composed of non-hydrogenated sp2 carbon and hydrogenated sp3 carbon. Plasma...

  12. Interaction of hydrogenated amorphous silicon films with transparent conductive films

    OpenAIRE

    Kitagawa, M.; Mori, K; Ishihara, S.; Ohno, M.; Hirao, T.; Yoshioka, Y.; Kohiki, S

    1983-01-01

    The effects of the deposition temperature on the interaction of the hydrogenated amorphous silicon films with indium-tin-oxide and tin-oxide films have been investigated in the temperature range 150-300 degrees C, using Auger electron spectroscopy, secondary ion mass spectrometry, and scanning electron microscopy. It was found that the constituent atoms such as indium and tin are detected in the thin amorphous silicon films deposited. Around the interface between the transparent conductive fi...

  13. Hydrogen evolution from a copper(I) oxide photocathode coated with an amorphous molybdenum sulphide catalyst

    OpenAIRE

    Morales-Guio, Carlos G.; Tilley, S. David; Vrubel, Heron; Graetzel, Michael; HU, Xile

    2014-01-01

    Concerns over climate change resulting from accumulation of anthropogenic carbon dioxide in the atmosphere and the uncertainty in the amount of recoverable fossil fuel reserves are driving forces for the development of renewable, carbon-neutral energy technologies. A promising clean solution is photoelectrochemical water splitting to produce hydrogen using abundant solar energy. Here we present a simple and scalable technique for the deposition of amorphous molybdenum sulphide films as hydrog...

  14. Amorphous Molybdenum Phosphide Nanoparticles for Electrocatalytic Hydrogen Evolution

    OpenAIRE

    McEnaney, Joshua M.; Crompton, J. Chance; Callejas, Juan F.; Popczun, Eric J.; Biacchi, Adam J.; Nathan S. Lewis; Schaak, Raymond E.

    2014-01-01

    Amorphous molybdenum phosphide (MoP) nanoparticles have been synthesized and characterized as electrocatalysts for the hydrogen-evolution reaction (HER) in 0.50 M H_2SO_4 (pH 0.3). Amorphous MoP nanoparticles (having diameters of 4.2 ± 0.5 nm) formed upon heating Mo(CO)6 and trioctylphosphine in squalane at 320 °C, and the nanoparticles remained amorphous after heating at 450 °C in H_2(5%)/Ar(95%) to remove the surface ligands. At mass loadings of 1 mg cm^–2, MoP/Ti electrodes exhibited overp...

  15. Molecular Hydrogen Formation on Amorphous Silicates Under Interstellar Conditions

    CERN Document Server

    Perets, H B; Biham, O; Vidali, G; Li, L; Swords, S; Congiu, E; Roser, J; Manico, G; Brucato, J R; Pirronello, V; Perets, Hagai B.; Lederhendler, Adina; Biham, Ofer; Vidali, Gianfranco; Li, Ling; Swords, Sol; Congiu, Emanuele; Roser, Joe; Manico, Giulio; Brucato, John Robert; Pirronello, Valerio

    2007-01-01

    Experimental results on the formation of molecular hydrogen on amorphous silicate surfaces are presented for the first time and analyzed using a rate equation model. The energy barriers for the relevant diffusion and desorption processes are obtained. They turn out to be significantly higher than those obtained earlier for polycrystalline silicates, demonstrating the importance of grain morphology. These barriers are used in order to evaluate the efficiency of molecular hydrogen formation on amorphous silicate grains under interstellar conditions. It is found that unlike polycrystalline silicates, amorphous silicate grains are efficient catalysts of H_2 formation within a temperature range which is relevant to diffuse interstellar clouds (but not to photo-dissociation regions, where grain temperatures are higher). The results also indicate that the hydrogen molecules are thermalized with the surface and desorb with low kinetic energy. Thus, they are unlikely to occupy highly excited states.

  16. Polymeric amorphous carbon as p-type window within amorphous silicon solar cells

    NARCIS (Netherlands)

    Khan, R.U.A.; Silva, S.R.P.; Van Swaaij, R.A.C.M.M.

    2003-01-01

    Amorphous carbon (a-C) has been shown to be intrinsically p-type, and polymeric a-C (PAC) possesses a wide Tauc band gap of 2.6 eV. We have replaced the p-type amorphous silicon carbide layer of a standard amorphous silicon solar cell with an intrinsic ultrathin layer of PAC. The thickness of the p

  17. Effects of H2 gas addition into process and H ion implantation on the microstructure of hydrogenated amorphous carbon films prepared by bipolar-type plasma based ion implantation

    International Nuclear Information System (INIS)

    Hydrogenated amorphous carbon films are deposited on Si(1 0 0) and SiO2 glass substrates by a bipolar-type plasma based ion implantation system. The films are prepared using toluene gas at a constant flow rate of 2 sccm. The effects of H2 gas addition during deposition on the microstructure of the films are examined by electrical conductivity measurements, Raman spectroscopy, elastic recoil detection analysis (ERDA) and optical spectroscopy. In addition, H implantation is also carried out using H2 plasma discharge. Thickness of the films is approximately 60 nm for all samples. It is found that electrical conductivity slightly increases with increasing additive H2 flow rate. However, the conductivity drastically decreases after H implantation. Raman analysis reveals that H2 gas addition slightly causes the film graphitization, but the H implantation does it amorphization. The results of ERDA show that the H concentration in the films slightly decreases with increasing H2 gas addition, but increases by H implantation. In spite of H2 gas addition, the optical band gap is not changed and kept approximately 0.7 eV. However, H implantation makes it increase up to approximately 1.0 eV

  18. Study on stability of hydrogenated amorphous silicon films

    Institute of Scientific and Technical Information of China (English)

    Zhu Xiu-Hong; Chen Guang-Hua; Zhang Wen-Li; Ding Yi; Ma Zhan-Jie; Hu Yue-Hui; He Bin; Rong Yan-Dong

    2005-01-01

    Hydrogenated amorphous silicon (a-Si:H) films with high and same order of magnitude photosensitivity (~105) but different stability were prepared by using microwave electron cyclotron resonance chemical vapour deposition system under the different deposition conditions. It was proposed that there was no direct correlation between the photosensitivity and the hydrogen content (CH) as well as H-Si bonding configurations, but for the stability, they were the critical factors. The experimental results indicated that higher substrate temperature, hydrogen dilution ratio and lower deposition rate played an important role in improving the microstructure of a-Si:H films. We used hydrogen elimination model to explain our experimental results.

  19. Barkhausen effect during hydrogen interaction with amorphous alloy 2NSR

    International Nuclear Information System (INIS)

    The Barkhausen effect electromotive force measurements by the two-side saturation of the 2NSR (Fe78B12Si19Ni1) alloy amorphous band through hydrogen is carried out. The multiple increase in the Barkhausen effect electromotive force by hydrogen saturation is determined. It is assumed that in the metallic alloy over-saturated by hydrogen there originates a special structural state providing for decrease in the potential barrier by transition of the 180 deg boundary of the magnetic domain from the equilibrium state to another one. The value of the Barkhausen effect link with the hydrogen content in the material is indicated

  20. Amorphous Alloy Membranes for High Temperature Hydrogen Separation

    Energy Technology Data Exchange (ETDEWEB)

    Coulter, K

    2013-09-30

    At the beginning of this project, thin film amorphous alloy membranes were considered a nascent but promising new technology for industrial-scale hydrogen gas separations from coal- derived syngas. This project used a combination of theoretical modeling, advanced physical vapor deposition fabricating, and laboratory and gasifier testing to develop amorphous alloy membranes that had the potential to meet Department of Energy (DOE) targets in the testing strategies outlined in the NETL Membrane Test Protocol. The project is complete with Southwest Research Institute® (SwRI®), Georgia Institute of Technology (GT), and Western Research Institute (WRI) having all operated independently and concurrently. GT studied the hydrogen transport properties of several amorphous alloys and found that ZrCu and ZrCuTi were the most promising candidates. GT also evaluated the hydrogen transport properties of V, Nb and Ta membranes coated with different transition-metal carbides (TMCs) (TM = Ti, Hf, Zr) catalytic layers by employing first-principles calculations together with statistical mechanics methods and determined that TiC was the most promising material to provide catalytic hydrogen dissociation. SwRI developed magnetron coating techniques to deposit a range of amorphous alloys onto both porous discs and tubular substrates. Unfortunately none of the amorphous alloys could be deposited without pinhole defects that undermined the selectivity of the membranes. WRI tested the thermal properties of the ZrCu and ZrNi alloys and found that under reducing environments the upper temperature limit of operation without recrystallization is ~250 °C. There were four publications generated from this project with two additional manuscripts in progress and six presentations were made at national and international technical conferences. The combination of the pinhole defects and the lack of high temperature stability make the theoretically identified most promising candidate amorphous alloys

  1. Structural morphology of amorphous conducting carbon film

    Indian Academy of Sciences (India)

    P N Vishwakarma; V Prasad; S V Subramanyam; V Ganesan

    2005-10-01

    Amorphous conducting carbon films deposited over quartz substrates were analysed using X-ray diffraction and AFM technique. X-ray diffraction data reveal disorder and roughness in the plane of graphene sheet as compared to that of graphite. This roughness increases with decrease in preparation temperature. The AFM data shows surface roughness of carbon films depending on preparation temperatures. The surface roughness increases with decrease in preparation temperature. Also some nucleating islands were seen on the samples prepared at 900°C, which are not present on the films prepared at 700°C. Detailed analysis of these islands reveals distorted graphitic lattice arrangement. So we believe these islands to be nucleating graphitic. Power spectrum density (PSD) analysis of the carbon surface indicates a transition from the nonlinear growth mode to linear surface-diffusion dominated growth mode resulting in a relatively smoother surface as one moves from low preparation temperature to high preparation temperature. The amorphous carbon films deposited over a rough quartz substrate reveal nucleating diamond like structures. The density of these nucleating diamond like structures was found to be independent of substrate temperature (700–900°C).

  2. Nanostructural activated carbons for hydrogen storage

    Science.gov (United States)

    Li, Suoding

    A series of nanostructured activated carbons have been synthesized from poly(ether ether ketone) (PEEK), and its derivatives. These carbons, with surface area exceeding 3000 m2/g and with average pore diameters of ≤ 20 A, are proven to be superior hydrogen storage materials, with hydrogen storage capacities up to 5.5 wt% at 77 K and 45 atm. The porous texture of these carbons was controlled via optimizing three synthetic steps: thermo-oxidation of PEEK in air, pyrolysis or carbonization of the oxidized PEEK in an inert atmosphere, and activation of the pre-carbonized PEEK with metal hydroxide. Thermo-oxidation of PEEK and carbonization process were thoroughly studied. These processes have been investigated by MDSC, FTIR, TGA and Py-MS. The pyrolysis or carbonization of PEEK involves the degradation of PEEK chains in three stages. Carbon morphology, including crystallinity and porous texture, is readily controlled by adjusting carbonization temperature. Activation of PEEK carbons, using inorganic bases and other activation agents, produces microporous carbons having a very narrow pore size distribution and an average pore diameter of ≤ 20 A. The activation control parameters including activation agent, activation temperature, time and carbon morphology have been investigated extensively. High surface area activated carbon is obtained by activating a highly amorphous carbon with a high activation agent/carbon ratio at 800°C. Theoretical calculations show that the pores with smaller diameter, especially smaller than 7 A, favor hydrogen adsorption. The experimental results confirm this fact and show that: (1) the hydrogen adsorption capacity per unit surface area at 77 K and 1 bar is larger in the smaller pores, (2) gravimetric hydrogen storage capacity (W(H2)) is directly proportional to the ultramicropore (< 7 A) volume; and (3) the volumetric hydrogen storage capacity is directly proportional to the volume fraction of ultramicropores in carbon. Hydrogen

  3. Thermally stimulated H emission and diffusion in hydrogenated amorphous silicon

    OpenAIRE

    Abtew, T. A.; Inam, F.; Drabold, D. A.

    2006-01-01

    We report first principles ab initio density functional calculations of hydrogen dynam- ics in hydrogenated amorphous silicon. Thermal motion of the host Si atoms drives H diffusion, as we demonstrate by direct simulation and explain with simple models. Si-Si bond centers and Si ring centers are local energy minima as expected. We also describe a new mechanism for break- ing Si-H bonds to release free atomic H into the network: a fluctuation bond center detachment (FBCD) assisted diffusion. H...

  4. Raman and ellipsometric characterization of hydrogenated amorphous silicon thin films

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Hydrogenated amorphous silicon (a-Si:H) thin films were deposited by plasma-enhanced vapor deposition (PECVD) at different silane temperatures (Tg) before glow-discharge. The effect of Tg on the amorphous network and optoelectronic properties of the films has been investigated by Raman scattering spectra, ellipsometric transmittance spectra, and dark conductivity measurement, respectively. The results show that the increase in Tg leads to an improved ordering of amorphous network on the short and intermediate scales and an increase of both refractive index and absorption coefficient in a-Si:H thin films. It is indicated that the dark conductivity increases by two orders of magnitude when Tg is raised from room temperature (RT) to 433 K. The continuous ordering of amorphous network of a-Si:H thin films deposited at a higher Tg is the main cause for the increase of dark conductivity.

  5. Raman and ellipsometric characterization of hydrogenated amorphous silicon thin films

    Institute of Scientific and Technical Information of China (English)

    LIAO NaiMan; LI Wei; KUANG YueJun; JIANG YaDong; LI ShiBin; WU ZhiMing; QI KangCheng

    2009-01-01

    Hydrogenated amorphous silicon (a-Si:H) thin films were deposited by plasma-enhanced vapor depo-sition (PEOVD) at different silane temperatures (Tg) before glow-discharge. The effect of Tg on the amorphous network and optoelectronic properties of the films has been investigated by Raman scat-tering spectra, ellipsometric transmittance spectra, and dark conductivity measurement, respectively. The results show that the increase in Tg leads to an improved ordering of amorphous network on the short and intermediate scales and an increase of both refractive index and absorption coefficient in a-Si:H thin films. It is indicated that the dark conductivity increases by two orders of magnitude when Tg is raised from room temperature (RT) to 433 K. The continuous ordering of amorphous network of a-Si:H thin films deposited at a higher Tg is the main cause for the increase of dark conductivity.

  6. First-principles study of hydrogenated amorphous silicon

    NARCIS (Netherlands)

    Jarolimek, K.; Groot, R.A. de; Wijs, G.A. de; Zeman, M.

    2009-01-01

    We use a molecular-dynamics simulation within density-functional theory to prepare realistic structures of hydrogenated amorphous silicon. The procedure consists of heating a crystalline structure of Si64H8 to 2370 K, creating a liquid and subsequently cooling it down to room temperature. The effect

  7. Pyrolytic transformation from polydihydrosilane to hydrogenated amorphous silicon film

    International Nuclear Information System (INIS)

    The fabrication of thin film silicon devices based on solution processes rather than on conventional vacuum processes is of substantial interest since cost reductions may result. Using a solution process, we coated substrates with polydihydrosilane solution and studied the pyrolytic transformation of the material into hydrogenated amorphous silicon (a-Si:H). From thermal gravimetry and differential thermal analysis data a significant reduction in weight of the material and a construction of Si-Si bonds are concluded for the pyrolysis temperature Tp = 270 to 360 °C. The appearance of amorphous silicon phonon bands in Raman spectra for films prepared at Tp ≥ 330 °C suggests the construction of a three-dimensional amorphous silicon network. Films prepared at Tp ≥ 360 °C exhibit a hydrogen content near 10 at.% and an optical gap near 1.6 eV similar to device-grade vacuum processed a-Si:H. However, the infrared microstructure factor, the spin density, and the photosensitivity require significant improvements. - Highlights: ► We fabricate hydrogenated amorphous silicon (a-Si:H) films by a solution process. ► The a-Si:H films are prepared by pyrolytic transformation in polysilane solution. ► We investigate basic properties in relation to the pyrolysis temperature. ► Raman spectra, hydrogen content, and optical gap are similar to device-grade a-Si:H. ► Microstructure factor, spin density, and photoconductivity show poor quality.

  8. Structure-property relations in amorphous carbon for photovoltaics

    Science.gov (United States)

    Risplendi, Francesca; Bernardi, Marco; Cicero, Giancarlo; Grossman, Jeffrey C.

    2014-07-01

    Carbon is emerging as a material with great potential for photovoltaics (PV). However, the amorphous form (a-C) has not been studied in detail as a PV material, even though it holds similarities with amorphous Silicon (a-Si) that is widely employed in efficient solar cells. In this work, we correlate the structure, bonding, stoichiometry, and hydrogen content of a-C with properties linked to PV performance such as the electronic structure and optical absorption. We employ first-principles molecular dynamics and density functional theory calculations to generate and analyze a set of a-C structures with a range of densities and hydrogen concentrations. We demonstrate that optical and electronic properties of interest in PV can be widely tuned by varying the density and hydrogen content. For example, sunlight absorption in a-C films can significantly exceed that of a same thickness of a-Si for a range of densities and H contents in a-C. Our results highlight promising features of a-C as the active layer material of thin-film solar cells.

  9. Structure-property relations in amorphous carbon for photovoltaics

    International Nuclear Information System (INIS)

    Carbon is emerging as a material with great potential for photovoltaics (PV). However, the amorphous form (a-C) has not been studied in detail as a PV material, even though it holds similarities with amorphous Silicon (a-Si) that is widely employed in efficient solar cells. In this work, we correlate the structure, bonding, stoichiometry, and hydrogen content of a-C with properties linked to PV performance such as the electronic structure and optical absorption. We employ first-principles molecular dynamics and density functional theory calculations to generate and analyze a set of a-C structures with a range of densities and hydrogen concentrations. We demonstrate that optical and electronic properties of interest in PV can be widely tuned by varying the density and hydrogen content. For example, sunlight absorption in a-C films can significantly exceed that of a same thickness of a-Si for a range of densities and H contents in a-C. Our results highlight promising features of a-C as the active layer material of thin-film solar cells.

  10. Surface bioactivity of plasma implanted silicon and amorphous carbon

    Institute of Scientific and Technical Information of China (English)

    Paul K CHU

    2004-01-01

    Plasma immersion ion implantation and deposition (PⅢ&D) has been shown to be an effective technique to enhance the surface bioactivity of materials. In this paper, recent progress made in our laboratory on plasma surface modification single-crystal silicon and amorphous carbon is reviewed. Silicon is the most important material in the integrated circuit industry but its surface biocompatibility has not been investigated in details. We have recently performed hydrogen PⅢ into silicon and observed the biomimetic growth of apatite on its surface in simulated body fluid. Diamond-like carbon (DLC) is widely used in the industry due to its excellent mechanical properties and chemical inertness. The use of this material in biomedical engineering has also attracted much attention. It has been observed in our laboratory that doping DLC with nitrogen by means of PⅢ can improve the surface blood compatibility. The properties as well as in vitro biological test results will be discussed in this article.

  11. Light-induced metastable structural changes in hydrogenated amorphous silicon

    Energy Technology Data Exchange (ETDEWEB)

    Fritzsche, H. [Univ. of Chicago, IL (United States)

    1996-09-01

    Light-induced defects (LID) in hydrogenated amorphous silicon (a-Si:H) and its alloys limit the ultimate efficiency of solar panels made with these materials. This paper reviews a variety of attempts to find the origin of and to eliminate the processes that give rise to LIDs. These attempts include novel deposition processes and the reduction of impurities. Material improvements achieved over the past decade are associated more with the material`s microstructure than with eliminating LIDs. We conclude that metastable LIDs are a natural by-product of structural changes which are generally associated with non-radiative electron-hole recombination in amorphous semiconductors.

  12. Coaxial carbon plasma gun deposition of amorphous carbon films

    International Nuclear Information System (INIS)

    A unique plasma gun employing coaxial carbon electrodes was used in an attempt to deposit thin films of amorphous diamond-like carbon. A number of different structural, compositional, and electrical characterization techniques were used to characterize these films. These included scanning electron microscopy, scanning transmission electron microscopy, X ray diffraction and absorption, spectrographic analysis, energy dispersive spectroscopy, and selected area electron diffraction. Optical absorption and electrical resistivity measurements were also performed. The films were determined to be primarily amorphous, with poor adhesion to fused silica substrates. Many inclusions of particulates were found to be present as well. Analysis of these particulates revealed the presence of trace impurities, such as Fe and Cu, which were also found in the graphite electrode material. The electrodes were the source of these impurities. No evidence of diamond-like crystallite structure was found in any of the film samples. Details of the apparatus, experimental procedure, and film characteristics are presented

  13. Coaxial carbon plasma gun deposition of amorphous carbon films

    Science.gov (United States)

    Sater, D. M.; Gulino, D. A.; Rutledge, S. K.

    1984-01-01

    A unique plasma gun employing coaxial carbon electrodes was used in an attempt to deposit thin films of amorphous diamond-like carbon. A number of different structural, compositional, and electrical characterization techniques were used to characterize these films. These included scanning electron microscopy, scanning transmission electron microscopy, X ray diffraction and absorption, spectrographic analysis, energy dispersive spectroscopy, and selected area electron diffraction. Optical absorption and electrical resistivity measurements were also performed. The films were determined to be primarily amorphous, with poor adhesion to fused silica substrates. Many inclusions of particulates were found to be present as well. Analysis of these particulates revealed the presence of trace impurities, such as Fe and Cu, which were also found in the graphite electrode material. The electrodes were the source of these impurities. No evidence of diamond-like crystallite structure was found in any of the film samples. Details of the apparatus, experimental procedure, and film characteristics are presented.

  14. Pyrolytic transformation from polydihydrosilane to hydrogenated amorphous silicon film

    Energy Technology Data Exchange (ETDEWEB)

    Masuda, Takashi, E-mail: mtakashi@jaist.ac.jp [Japan Science and Technology Agency, ERATO, Shimoda Nano-Liquid Process Project, 2-13 Asahidai, Nomi, Ishikawa, 923-1211 (Japan); Matsuki, Yasuo [Japan Science and Technology Agency, ERATO, Shimoda Nano-Liquid Process Project, 2-13 Asahidai, Nomi, Ishikawa, 923-1211 (Japan); Yokkaichi Research Center, JSR Corporation, 100 Kawajiri-cho, Yokkaichi, Mie, 510-8552 (Japan); Shimoda, Tatsuya [Japan Science and Technology Agency, ERATO, Shimoda Nano-Liquid Process Project, 2-13 Asahidai, Nomi, Ishikawa, 923-1211 (Japan); School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa, 923-1292 (Japan)

    2012-08-31

    The fabrication of thin film silicon devices based on solution processes rather than on conventional vacuum processes is of substantial interest since cost reductions may result. Using a solution process, we coated substrates with polydihydrosilane solution and studied the pyrolytic transformation of the material into hydrogenated amorphous silicon (a-Si:H). From thermal gravimetry and differential thermal analysis data a significant reduction in weight of the material and a construction of Si-Si bonds are concluded for the pyrolysis temperature T{sub p} = 270 to 360 Degree-Sign C. The appearance of amorphous silicon phonon bands in Raman spectra for films prepared at T{sub p} {>=} 330 Degree-Sign C suggests the construction of a three-dimensional amorphous silicon network. Films prepared at T{sub p} {>=} 360 Degree-Sign C exhibit a hydrogen content near 10 at.% and an optical gap near 1.6 eV similar to device-grade vacuum processed a-Si:H. However, the infrared microstructure factor, the spin density, and the photosensitivity require significant improvements. - Highlights: Black-Right-Pointing-Pointer We fabricate hydrogenated amorphous silicon (a-Si:H) films by a solution process. Black-Right-Pointing-Pointer The a-Si:H films are prepared by pyrolytic transformation in polysilane solution. Black-Right-Pointing-Pointer We investigate basic properties in relation to the pyrolysis temperature. Black-Right-Pointing-Pointer Raman spectra, hydrogen content, and optical gap are similar to device-grade a-Si:H. Black-Right-Pointing-Pointer Microstructure factor, spin density, and photoconductivity show poor quality.

  15. Pyrolytic transformation from polydihydrosilane to hydrogenated amorphous silicon film

    OpenAIRE

    Masuda, Takashi; Matsuki, Yasuo; Shimoda, Tatsuya

    2012-01-01

    The fabrication of thin film silicon devices based on solution processes rather than on conventional vacuum processes is of substantial interest since cost reductions may result. Using a solution process, we coated substrates with polydihydrosilane solution and studied the pyrolytic transformation of the material into hydrogenated amorphous silicon (a-Si:H). From thermal gravimetry and differential thermal analysis data a significant reduction in weight of the material and a construction of S...

  16. Deposition-induced defect profiles in amorphous hydrogenated silicon

    OpenAIRE

    Hata, N.; Wagner, S.; Roca i Cabarrocas, P.; Favre, M.

    2008-01-01

    The thickness dependence of the subgap optical absorption in plasma-deposited hydrogenated amorphous silicon is carefully studied by photothermal deflection spectroscopy. The deep-level defect concentration decays from the top surface into the bulk where it approaches the thermal equilibrium defect density. This defect profile is interpreted in terms of the annealing, during growth, of growth-induced surface defects. It is also shown that this defect profile is compatible with the known growt...

  17. First-principles study of hydrogenated amorphous silicon

    OpenAIRE

    Jarolimek, K.; de Groot, R. A.; de Wijs, G. A.; Zeman, M.

    2009-01-01

    We use a molecular-dynamics simulation within density-functional theory to prepare realistic structures of hydrogenated amorphous silicon. The procedure consists of heating a crystalline structure of Si64H8 to 2370 K, creating a liquid and subsequently cooling it down to room temperature. The effect of the cooling rate is examined. We prepared a total of five structures which compare well to experimental data obtained by neutron-scattering experiments. Two structures do not contain any struct...

  18. Temperature dependence of hydrogenated amorphous silicon solar cell performances

    OpenAIRE

    Riesen, Y.; Stuckelberger, M.; Haug, F. -J.; Ballif, C.; N. Wyrsch

    2016-01-01

    Thin-film hydrogenated amorphous silicon solar (a-Si:H) cells are known to have better temperature coefficients than crystalline silicon cells. To investigate whether a-Si:H cells that are optimized for standard conditions (STC) also have the highest energy yield, we measured the temperature and irradiance dependence of the maximum power output (Pmpp), the fill factor (FF), the short-circuit current density (Jsc), and the open-circuit voltage (Voc) for four series of cells fabricated with dif...

  19. ENHANCING ADHESION OF TETRAHEDRAL AMORPHOUS CARBON FILMS

    Institute of Scientific and Technical Information of China (English)

    Zhao Yuqing; Lin Yi; Wang Xiaoyan; Wang Yanwu; Wei Xinyu

    2005-01-01

    Objective The high energy ion bombardment technique is applied to enhancing the adhesion of the tetrahedral amorphous carbon (TAC) films deposited by the filtered cathode vacuum arc (FCVA). Methods The abrasion method, scratch method, heating and shaking method as well as boiling salt solution method is used to test the adhesion of the TAC films on various material substrates. Results The test results show that the adhesion is increased as the ion bombardment energy increases. However, if the bombardment energy were over the corresponding optimum value, the adhesion would be enhanced very slowly for the harder material substrates and drops quickly, for the softer ones. Conclusion The optimum values of the ion bombardment energy are larger for the harder materials than that for the softer ones.

  20. Atomistic models of hydrogenated amorphous silicon nitride from first principles

    OpenAIRE

    Jarolimek, K.; de Groot, R. A.; de Wijs, G. A.; Zeman, M.

    2010-01-01

    We present a theoretical study of hydrogenated amorphous silicon nitride (a-SiNx:H), with equal concentrations of Si and N atoms (x=1), for two considerably different densities (2.0 and 3.0 g/cm3). Densities and hydrogen concentration were chosen according to experimental data. Using first-principles molecular-dynamics within density-functional theory the models were generated by cooling from the liquid. Where both models have a short-range order resembling that of crystalline Si3N4 because o...

  1. INFRARED VIBRATIONAL SPECTRA OF CHLORINATED AND HYDROGENATED AMORPHOUS SILICON

    OpenAIRE

    Kalem, S; Chevallier, J.; Al Dallal, S.; Bourneix, J.

    1981-01-01

    The infrared spectra of chlorinated and hydrogenated amorphous silicon have been measured. In addition to the hydrogen induced bands at 2110, 1990, 885, 840 and 640 cm-1, we observe two new modes at 545 cm-1 (Si-Cl stretching) and 500 cm-1 ( Si TO modes induced by chlorine). Observation of the 545 cm-1 band proves that chlorine acts as a dangling bond terminator. Upon annealing, some of the Si-Cl groups transform into SiCl4 molecules (SiCl4 stretching at 615 cm-1). A good agreement is found b...

  2. Microstructural analyses of amorphic diamond, i-C, and amorphous carbon

    DEFF Research Database (Denmark)

    Collins, C. B.; Davanloo, F.; Jander, D.R.;

    1992-01-01

    comparative examinations of the microstructures of samples of amorphic diamond, i-C, and amorphous carbon. Four distinct morphologies were found that correlated closely with the energy densities used in preparing the different materials. Journal of Applied Physics is copyrighted by The American Institute of...... Physics....

  3. Filtered pulsed carbon cathodic arc: Plasma and amorphous carbon properties

    Science.gov (United States)

    Liu, Dongping; Benstetter, Günther; Lodermeier, Edgar; Zhang, Jialiang; Liu, Yanhong; Vancea, Johann

    2004-06-01

    The carbon plasma ion energies produced by the filtered pulsed cathodic arc discharge method were measured as a function of filter inductance. The energy determination is based on the electro-optical time-of-flight method. The average ion energies of the pulsed ion beams were found to depend upon the rise time and duration of pulsed arc currents, which suggests that a gain of ion kinetic energy mainly arises from the electric plasma field from the ambipolar expansion of both electrons and ions, and an electron drag force because of the high expansion velocity of the electrons. The tetrahedral amorphous carbon (ta-C) films with a sp3 fraction of ˜70% were deposited on silicon substrates at the average ion energies of >6 eV in the highly ionized plasmas. The ta-C films were found to be covered with a few graphitelike atomic layers. The surface properties of ultrathin carbon films, such as nanoscale friction coefficients, surface layer thickness, and silicon contents were strongly dependent on the ion energies. The growth of amorphous carbon films was explained in terms of the thermal spike migration of surface carbon atoms. In terms of this model, the thermal spike provides the energy required to release surface atoms from their metastable positions and leads to the formation of the sp3 bonded carbon on a sp3 bonded matrix. The experimental results indicate that the low-energy (<3 eV) carbon ions have insufficient energies to cause the rearrangement reaction within the film and they form graphitelike structures at film surface.

  4. Filtered pulsed carbon cathodic arc: Plasma and amorphous carbon properties

    International Nuclear Information System (INIS)

    The carbon plasma ion energies produced by the filtered pulsed cathodic arc discharge method were measured as a function of filter inductance. The energy determination is based on the electro-optical time-of-flight method. The average ion energies of the pulsed ion beams were found to depend upon the rise time and duration of pulsed arc currents, which suggests that a gain of ion kinetic energy mainly arises from the electric plasma field from the ambipolar expansion of both electrons and ions, and an electron drag force because of the high expansion velocity of the electrons. The tetrahedral amorphous carbon (ta-C) films with a sp3 fraction of ∼70% were deposited on silicon substrates at the average ion energies of >6 eV in the highly ionized plasmas. The ta-C films were found to be covered with a few graphitelike atomic layers. The surface properties of ultrathin carbon films, such as nanoscale friction coefficients, surface layer thickness, and silicon contents were strongly dependent on the ion energies. The growth of amorphous carbon films was explained in terms of the thermal spike migration of surface carbon atoms. In terms of this model, the thermal spike provides the energy required to release surface atoms from their metastable positions and leads to the formation of the sp3 bonded carbon on a sp3 bonded matrix. The experimental results indicate that the low-energy (<3 eV) carbon ions have insufficient energies to cause the rearrangement reaction within the film and they form graphitelike structures at film surface

  5. Gas desorption during friction of amorphous carbon films

    Science.gov (United States)

    Rusanov, A.; Fontaine, J.; Martin, J.-M.; Mogne, T. L.; Nevshupa, R.

    2008-03-01

    Gas desorption induced by friction of solids, i.e. tribodesorption, is one of the numerous physical and chemical phenomena, which arise during friction as result of thermal and structural activation of material in a friction zone. Tribodesorption of carbon oxides, hydrocarbons, and water vapours may lead to significant deterioration of ultra high vacuum conditions in modern technological equipment in electronic, optoelectronic industries. Therefore, knowledge of tribodesorption is crucial for the performance and lifetime of vacuum tribosystems. Diamond-like carbon (DLC) coatings are interesting materials for vacuum tribological systems due to their high wear resistance and low friction. Highly hydrogenated amorphous carbon (a-C:H) films are known to exhibit extremely low friction coefficient under high vacuum or inert environment, known as 'superlubricity' or 'superlow friction'. However, the superlow friction period is not always stable and then tends to spontaneous transition to high friction. It is supposed that hydrogen supply from the bulk to the surface is crucial for establishing and maintaining superlow friction. Thus, tribodesorption can serve also as a new technique to determine the role of gases in superlow friction mechanisms. Desorption of various a-C:H films, deposited by PECVD, ion-beam deposition and deposition using diode system, has been studied by means of ultra-high vacuum tribometer equipped with a mass spectrometer. It was found that in superlow friction period desorption rate was below the detection limit in the 0-85 mass range. However, transition from superlow friction to high friction was accompanied by desorption of various gases, mainly of H2 and CH4. During friction transition, surfaces were heavily damaged. In experiments with DLC films with low hydrogen content tribodesorption was significant during the whole experiment, while low friction was not observed. From estimation of maximum surface temperature during sliding contact it was

  6. Source Molecular Effect on Amorphous Carbon Film Deposition

    OpenAIRE

    Kawazoe, Hiroki; Inayoshi, Takanori; Shinohara, Masanori; Matsuda, Yoshinobu; Fujiyama, Hiroshi; Nitta, Yuki; Nakatani, Tatsuyuki

    2009-01-01

    We investigated deposition process of amorphous carbon films using acetylene and methane as a source molecule, by using infrared spectroscopy in multiple internal reflection geometry (MIR-IRAS). We found that deposited film structures were different due to source molecules.

  7. Laser annealing of amorphous carbon films

    International Nuclear Information System (INIS)

    Amorphous (a-C) Carbon thin films were deposited, using pulsed laser deposition (PLD) with a Nd:YAG laser (1064 nm, 7 ns), from a pyrolytic graphite target, on silicon and refractory metal (Mo) substrates to a film thickness of 55, 400 and 500 nm. Samples were grown at RT and then annealed by a laser annealing technique, to reduce residual stress and induce a locally confined 'graphitization' process. The films were exposed to irradiation, in vacuum, by a Nd:YAG pulsed laser, operating at different wavelengths (VIS, N-UV) and increasing values of energy from 6-100 mJ/pulse. The thinner films were completely destroyed by N-UV laser treatment also at lower energies, owing to the almost direct propagation of heat to the Si substrate with melting and ruinous blistering effects. For thicker films the Raman micro-analysis evidenced the influence of laser treatments on the sp3/sp2 content evolution, and established the formation of aromatic nano-structures of average dimension 4.1-4.7 nm (derived from the ID/IG peak ratio), at fluence values round 50 mJ/cm2 for N-UV and 165 mJ/cm2 for VIS laser irradiation. Higher fluences were not suitable for a-Carbon 'graphitization', since a strong ablation process was the prominent effect of irradiation. Grazing incidence XRD (GI-XRD) used to evaluate the dimension and texturing of nano-particles confirmed the findings of Raman analysis. The effects of irradiation on surface morphology were studied by SEM analysis

  8. Dielectric relaxation and hydrogen diffusion in amorphous silicon

    Energy Technology Data Exchange (ETDEWEB)

    Phillips, J.C. (AT and T Bell Labs., Murray Hill, NJ (United States))

    1994-04-01

    Hydrogen diffusion is technologically critical to the processing of amorphous Si for solar cell applications. It is shown that this diffusion belongs to a broad class of dielectric relaxation mechanisms which were first studied by Kohlrausch in 1847. A microscopic theory of the Kohlrausch relaxation constant [beta][sub K] is also constructed. This theory explains the values of [beta] observed in many electronic, molecular and polymeric relaxation processes. It is based on two novel concepts: Wiener sausages, from statistical mechanics, and the magic wand, from axiomatic set theory

  9. Eigenmode Splitting in all Hydrogenated Amorphous Silicon Nitride Coupled Microcavity

    Institute of Scientific and Technical Information of China (English)

    ZHANG Xian-Gao; HUANG Xin-Fan; CHEN Kun-Ji; QIAN Bo; CHEN San; DING Hong-Lin; LIU Sui; WANG Xiang; XU Jun; LI Wei

    2008-01-01

    Hydrogenated amorphous silicon nitride based coupled optical microcavity is investigated theoretically and experimentally. The theoretical calculation of the transmittance spectra of optical microcavity with one cavity and coupled microcavity with two-cavity is performed.The optical eigenmode splitting for coupled microcavity is found due to the interaction between the neighbouring localized cavities.Experimentally,the coupled cavity samples are prepared by plasma enhanced chemical vapour deposition and characterized by photoluminescence measurements.It is found that the photoluminescence peak wavelength agrees well with the cavity mode in the calculated transmittance spectra.This eigenmode splitting is analogous to the electron state energy splitting in diatom molecules.

  10. Fabrication of C60/amorphous carbon superlattice structures

    International Nuclear Information System (INIS)

    The nitrogen doping effects in C60 films by RF plasma source was investigated, and it was found that the nitrogen ion bombardment broke up C60 molecules and changed them into amorphous carbon. Based on these results, formation of C60/amorphous carbon superlattice structure was proposed. The periodic structure of the resulted films was confirmed by XRD measurements, as the preliminary results of fabrication of the superlattice structure

  11. Amorphous carbon film deposition on inner surface of tubes using atmospheric pressure pulsed filamentary plasma source

    CERN Document Server

    Pothiraja, Ramasamy; Awakowicz, Peter

    2011-01-01

    Uniform amorphous carbon film is deposited on the inner surface of quartz tube having the inner diameter of 6 mm and the outer diameter of 8 mm. A pulsed filamentary plasma source is used for the deposition. Long plasma filaments (~ 140 mm) as a positive discharge are generated inside the tube in argon with methane admixture. FTIR-ATR, XRD, SEM, LSM and XPS analyses give the conclusion that deposited film is amorphous composed of non-hydrogenated sp2 carbon and hydrogenated sp3 carbon. Plasma is characterized using optical emission spectroscopy, voltage-current measurement, microphotography and numerical simulation. On the basis of observed plasma parameters, the kinetics of the film deposition process is discussed.

  12. Hydrogenated amorphous silicon thin film anode for proton conducting batteries

    Science.gov (United States)

    Meng, Tiejun; Young, Kwo; Beglau, David; Yan, Shuli; Zeng, Peng; Cheng, Mark Ming-Cheng

    2016-01-01

    Hydrogenated amorphous Si (a-Si:H) thin films deposited by chemical vapor deposition were used as anode in a non-conventional nickel metal hydride battery using a proton-conducting ionic liquid based non-aqueous electrolyte instead of alkaline solution for the first time, which showed a high specific discharge capacity of 1418 mAh g-1 for the 38th cycle and retained 707 mAh g-1 after 500 cycles. A maximum discharge capacity of 3635 mAh g-1 was obtained at a lower discharge rate, 510 mA g-1. This electrochemical discharge capacity is equivalent to about 3.8 hydrogen atoms stored in each silicon atom. Cyclic voltammogram showed an improved stability 300 mV below the hydrogen evolution potential. Both Raman spectroscopy and Fourier transform infrared spectroscopy studies showed no difference to the pre-existing covalent Si-H bond after electrochemical cycling and charging, indicating a non-covalent nature of the Si-H bonding contributing to the reversible hydrogen storage of the current material. Another a-Si:H thin film was prepared by an rf-sputtering deposition followed by an ex-situ hydrogenation, which showed a discharge capacity of 2377 mAh g-1.

  13. Amorphous Calcium Carbonate Based-Microparticles for Peptide Pulmonary Delivery.

    Science.gov (United States)

    Tewes, Frederic; Gobbo, Oliviero L; Ehrhardt, Carsten; Healy, Anne Marie

    2016-01-20

    Amorphous calcium carbonate (ACC) is known to interact with proteins, for example, in biogenic ACC, to form stable amorphous phases. The control of amorphous/crystalline and inorganic/organic ratios in inhalable calcium carbonate microparticles may enable particle properties to be adapted to suit the requirements of dry powders for pulmonary delivery by oral inhalation. For example, an amorphous phase can immobilize and stabilize polypeptides in their native structure and amorphous and crystalline phases have different mechanical properties. Therefore, inhalable composite microparticles made of inorganic (i.e., calcium carbonate and calcium formate) and organic (i.e., hyaluronan (HA)) amorphous and crystalline phases were investigated for peptide and protein pulmonary aerosol delivery. The crystalline/amorphous ratio and polymorphic form of the inorganic component was altered by changing the microparticle drying rate and by changing the ammonium carbonate and HA initial concentration. The bioactivity of the model peptide, salmon calcitonin (sCT), coprocessed with alpha-1-antitrypsin (AAT), a model protein with peptidase inhibitor activity, was maintained during processing and the microparticles had excellent aerodynamic properties, making them suitable for pulmonary aerosol delivery. The bioavailability of sCT after aerosol delivery as sCT and AAT-loaded composite microparticles to rats was 4-times higher than that of sCT solution. PMID:26692360

  14. Some aspects of hydrogen interaction with amorphous metallic materials

    International Nuclear Information System (INIS)

    For the first time is considered change of some properties of amorphous metallic materials (AMM) directly in the process of hydrogenation. A supposition is made that many found effects are consequence of accumulation and relief of internal stresses during hydrogenation, exposure or following annealing of AMM. Fe81B14Si15, Fe52Co20Si15B13, Fe5Co70Si15B10, Fe5Co58Ni10Si11B16, Co67Fe4Cr7Si8B1484KChSP, Ni60Nb35Ti5, Ni60Nb40 and Pd17,5Cu6Si16.5 AMM were investigated. 24 refs.; 4 figs

  15. Properties and application of hydrogenated amorphous silicon films

    Energy Technology Data Exchange (ETDEWEB)

    Geiger, J.

    1985-04-12

    Hydrogenated amorphous silicon (a-Si:H) films have found increasing applications in the last few years, in particular for thin film solar cells. Efficiencies of around 10% have been achieved and the field is still rapidly developing. Three main methods are used to deposite a-Si:H, i.e. the decomposition of silane in a glow discharge, the reactive sputtering of silicon in an Ar-H2 atmosphere and the reactive evaporation of silicon in atomic hydrogen. The basic properties of the film, i.e. structure, electrical and photoelectrical properties and the density of states in the gap, are reviewed. Advantages and disadvantages of the three methods are discussed, also with regard to the applications. (orig.).

  16. Polymeric amorphous carbon as p-type window within amorphous silicon solar cells

    OpenAIRE

    Khan, R U A; Silva, S. R. P.; Van Swaaij, R.A.C.M.M.

    2003-01-01

    Amorphous carbon (a-C) has been shown to be intrinsically p-type, and polymeric a-C (PAC) possesses a wide Tauc band gap of 2.6 eV. We have replaced the p-type amorphous silicon carbide layer of a standard amorphous silicon solar cell with an intrinsic ultrathin layer of PAC. The thickness of the p layer had to be reduced from 9 to 2.5 nm in order to ensure sufficient conduction through the PAC film. Although the resulting external parameters suggest a decrease in the device efficiency from 9...

  17. Hydrogen adsorption in carbon materials

    Energy Technology Data Exchange (ETDEWEB)

    David, P.; Piquero, T.; Metenier, K.; Pierre, Y. [CEA Centre d' Etudes du Ripault, 37 - Tours (France); Demoment, J.; Lecas-Hardit, A. [CEA Valduc, 21 - Is-sur-Tille (France)

    2003-09-01

    The development of new technologies for energy is a necessity for both economic and environmental aspects. Hydrogen is expected to be, in the future, an important energy vector. However its storage, for mobile applications (fuel cell for automotive for example), represents a major difficulty. Several solutions have been used for demonstration (liquid hydrogen, high pressure vessel, hydride) but do not meet the requirements. Hydrogen adsorption in carbon materials also represents a potential solution which is currently discussed. (O.M.)

  18. Hydrogen distribution in amorphous silicon and silicon based alloys

    International Nuclear Information System (INIS)

    The results of hydrogen evolution experiments on amorphous silicon alloys prepared by high frequency PECVD of gas mixtures containing SiH4, NH3, PH2, B2H6 are compared. Using a very low heating rate of 5 degree/min it is possible to resolve fine structure on the exodiffusion spectra. Three evolution processes are observed: (a) low temperature effusion due to included gas (b) mid temperature effusion due to 'clustered' hydrogen bonds (c) high temperature effusion due to 'isolated' hydrogen bonds In addition it is possible to oberve very fine structure 'puffing' due to the release of molecular hydrogen at mid to high temperature. Silicon and silicon nitride films have been annealed at low temperatures before the exodiffusion experiments and changes in the evolution spectra are observed, dependent on the annealing process. A scanning electron microscope study of the effect of high temperature heat treatment has also been undertaken. These results are correlated with infra-red absorption measurements and the influence of doping concentration and substrate character discussed. Under certain preparation conditions the films blister on heating and finally burst forming circular craters, and these effects are shown to be dependent on substrate material and intrinsic stress of the as-grown films

  19. Photodecomposition of Hg - Photo - CVD monosilane. Application to hydrogenated amorphous silicon thin films

    International Nuclear Information System (INIS)

    The construction of a Hg-photo-CVD device is discussed. The system enables the manufacturing of hydrogenous thin films of amorphous silicon from monosilane compound. The reaction mechanisms taking place in the gaseous phase and at the surface, and the optimal conditions for the amorphous silicon film growth are studied. The analysis technique is based on the measurement of the difference between the condensation points of the gaseous components of the mixture obtained from the monosilane photolysis. A kinetic simplified model is proposed. Conductivity measurements are performed and the heat treatment effects are analyzed. Trace amounts of oxygen and carbon are found in the material. No Hg traces are detected by SIMS analysis

  20. Excellent Silicon Surface Passivation Achieved by Industrial Inductively Coupled Plasma Deposited Hydrogenated Intrinsic Amorphous Silicon Suboxide

    Directory of Open Access Journals (Sweden)

    Jia Ge

    2014-01-01

    Full Text Available We present an alternative method of depositing a high-quality passivation film for heterojunction silicon wafer solar cells, in this paper. The deposition of hydrogenated intrinsic amorphous silicon suboxide is accomplished by decomposing hydrogen, silane, and carbon dioxide in an industrial remote inductively coupled plasma platform. Through the investigation on CO2 partial pressure and process temperature, excellent surface passivation quality and optical properties are achieved. It is found that the hydrogen content in the film is much higher than what is commonly reported in intrinsic amorphous silicon due to oxygen incorporation. The observed slow depletion of hydrogen with increasing temperature greatly enhances its process window as well. The effective lifetime of symmetrically passivated samples under the optimal condition exceeds 4.7 ms on planar n-type Czochralski silicon wafers with a resistivity of 1 Ωcm, which is equivalent to an effective surface recombination velocity of less than 1.7 cms−1 and an implied open-circuit voltage (Voc of 741 mV. A comparison with several high quality passivation schemes for solar cells reveals that the developed inductively coupled plasma deposited films show excellent passivation quality. The excellent optical property and resistance to degradation make it an excellent substitute for industrial heterojunction silicon solar cell production.

  1. Optical determination of the mass density of amorphous and microcrystalline silicon layers with different hydrogen contents

    OpenAIRE

    Remeš, Z.; Vaněček, Milan; Torres, Pedro; Kroll, U.; Mahan, A. H.; Crandall, R. S.

    2008-01-01

    We have measured the density of amorphous and microcrystalline silicon films using an optical method. The mass density decreases with increasing hydrogen content, consistent with a hydrogenated di-vacancy model that fits the data for amorphous silicon. Material produced by hot wire assisted chemical vapour deposition, with low hydrogen content, has a higher density and is structurally different from glow discharge material with hydrogen content around 10 at.%. The lower density microcrystalli...

  2. SISGR - Hydrogen Caged in Carbon-Exploration of Novel Carbon-Hydrogen Interactions

    Energy Technology Data Exchange (ETDEWEB)

    Lueking, Angela [Pennsylvania State Univ., State College, PA (United States); Badding, John [Pennsylvania State Univ., State College, PA (United States); Crespi, Vinent [Pennsylvania State Univ., State College, PA (United States)

    2015-12-01

    Hydrogen trapped in a carbon cage, captured through repulsive interactions, is a novel concept in hydrogen storage. Trapping hydrogen via repulsive interactions borrows an idea from macroscale hydrogen storage (i.e. compressed gas storage tanks) and reapplies these concepts on the nanoscale in specially designed molecular containers. Under extreme conditions of pressure, hydrogen solubility in carbon materials is expected to increase and carbon is expected to restructure to minimize volume via a mixed sp2/sp3 hydrogenated state. Thermodynamics dictate that pre-formed C-H structures will rearrange with increased pressure, yet the final carbon-hydrogen interactions may be dependent upon the mechanism by which hydrogen is introduced. Gas “trapping” is meant to denote gas present in a solid in a high density, adsorbed-like state, when the external pressure is much less than that necessary to provide a comparable fluid density. Trapping thus denotes a kinetically metastable state rather than thermodynamic equilibrium. This project probed mechanochemical means to polymerize select hydrocarbons in the presence of gases, in an attempt to form localized carbon cages that trap gases via repulsive interactions. Aromatic, polyaromatic, and hydroaromatic molecules expected to undergo cyclo-addition reactions were polymerized at high (~GPa) pressures to form extended hydrogenated amorphous carbon networks. Notably, aromatics with a pre-existing internal free volume (such as Triptycene) appeared to retain an internal porosity upon application of pressure. However, a high photoluminescence background after polymerization precluded in situ identification of trapped gases. No spectroscopic evidence was found after depressurization that would be indicative of pockets of trapped gases in a localized high-pressure environment. Control studies suggested this measurement may be insensitive to gases at low pressure. Similarly, no spectral fingerprint was found for gas-imbued spherical

  3. Investigation of hydrogen plasma treatment for reducing defects in silicon quantum dot superlattice structure with amorphous silicon carbide matrix.

    Science.gov (United States)

    Yamada, Shigeru; Kurokawa, Yasuyoshi; Miyajima, Shinsuke; Konagai, Makoto

    2014-01-01

    We investigate the effects of hydrogen plasma treatment (HPT) on the properties of silicon quantum dot superlattice films. Hydrogen introduced in the films efficiently passivates silicon and carbon dangling bonds at a treatment temperature of approximately 400°C. The total dangling bond density decreases from 1.1 × 1019 cm-3 to 3.7 × 1017 cm-3, which is comparable to the defect density of typical hydrogenated amorphous silicon carbide films. A damaged layer is found to form on the surface by HPT; this layer can be easily removed by reactive ion etching. PMID:24521208

  4. Investigation of hydrogen plasma treatment for reducing defects in silicon quantum dot superlattice structure with amorphous silicon carbide matrix

    OpenAIRE

    Yamada, Shigeru; Kurokawa, Yasuyoshi; Miyajima, Shinsuke; KONAGAI, MAKOTO

    2014-01-01

    We investigate the effects of hydrogen plasma treatment (HPT) on the properties of silicon quantum dot superlattice films. Hydrogen introduced in the films efficiently passivates silicon and carbon dangling bonds at a treatment temperature of approximately 400°C. The total dangling bond density decreases from 1.1 × 1019 cm-3 to 3.7 × 1017 cm-3, which is comparable to the defect density of typical hydrogenated amorphous silicon carbide films. A damaged layer is found to form on the surface by ...

  5. Investigation of hydrogen plasma treatment for reducing defects in silicon quantum dot superlattice structure with amorphous silicon carbide matrix

    Science.gov (United States)

    Yamada, Shigeru; Kurokawa, Yasuyoshi; Miyajima, Shinsuke; Konagai, Makoto

    2014-02-01

    We investigate the effects of hydrogen plasma treatment (HPT) on the properties of silicon quantum dot superlattice films. Hydrogen introduced in the films efficiently passivates silicon and carbon dangling bonds at a treatment temperature of approximately 400°C. The total dangling bond density decreases from 1.1 × 1019 cm-3 to 3.7 × 1017 cm-3, which is comparable to the defect density of typical hydrogenated amorphous silicon carbide films. A damaged layer is found to form on the surface by HPT; this layer can be easily removed by reactive ion etching.

  6. Novel Carbon Nanotubes-supported NiB Amorphors Alloy Catalyst for Benzene Hydrogenation

    Institute of Scientific and Technical Information of China (English)

    Mei Hua YANG; Rong Bin ZHANG; Feng Yi LI

    2004-01-01

    The NiB amorphous alloy catalysts supported on CNTs and alumina were prepared by impregnation and chemical reduction. The gas-phase benzene hydrogenation was used as a probe reaction to evaluate the catalytic activity. The result showed that the NiB amorphous alloy catalyst supported on carbon nanotubes exhibited higher activity than that supported on alumina.

  7. Elimination of residual stress in hydrogenated amorphous silicon films

    Energy Technology Data Exchange (ETDEWEB)

    Jones, P.L.; Korhonen, A.S.; Dimmey, L.J.; Cocks, F.H.; Pollock, J.T.A.

    1982-02-01

    Residual stresses were measured in hydrogenated amorphous silicon films produced by glow discharge decomposition of silane and deposited onto aluminium, Invar (36Ni-64Fe), copper and nickel substrates. The substrate temperatures were in the range 54-295/sup 0/C during deposition. For low deposition temperatures, all films irrespective of substrate exhibited compressive room temperature residual stresses ranging from -60 to -120 mPa. A major fraction of this residual stress is found to come from the intrinsic deposition stress, which has complex origins relating to deposition and substrate conditions. With aluminium substrates, increasing the deposition temperature increased the compressive residual stress, primarily because of the difference between the thermal expansion coefficients of silicon and aluminium. However, with Invar substrates, films deposited at 225/sup 0/C exhibited a zero residual stress at room temperature because of a balancing of the compressive intrinsic deposition stress with the tensile stress produced during cooling by the low thermal expansion of the Invar.

  8. Optical limiting in hydrogenated amorphous silicon-selenium thin films

    Energy Technology Data Exchange (ETDEWEB)

    Manaa, Hacene, E-mail: hmanaa@gmail.co [Physics Department, Kuwait University, P.O. Box 5969, Safat 13060 (Kuwait); Al-Mulla, Abdullah; Al-Jamal, Noor [Physics Department, Kuwait University, P.O. Box 5969, Safat 13060 (Kuwait); Al-Dallal, Shawqi; Al-Alawi, Saleh [Physics Department, University of Bahrain, P.O. Box 32038 (Bahrain)

    2010-05-03

    Hydrogenated amorphous silicon-selenium alloy thin films grown by capacitively coupled radio-frequency glow-discharge are investigated. Nonlinear absorptive effects are evaluated with the help of open aperture z-scan technique in the 525 to 580 nm spectral range. The nonlinear absorption coefficient is found to be very large and reaching the value of 5.14 x 10{sup -3} cm/W at 525 nm. The origin of the optical nonlinearities is studied and found to be due mainly to two photon absorption in the case of pulsed excitation, whereas thermal effects are thought to be dominant when the sample is excited with a continuous wave laser. Optical limiting potentialities of the thin film are experimentally observed and their thresholds are found to be very low.

  9. Light-induced metastability in pure and hydrogenated amorphous silicon

    Science.gov (United States)

    Queen, D. R.; Liu, X.; Karel, J.; Wang, Q.; Crandall, R. S.; Metcalf, T. H.; Hellman, F.

    2015-10-01

    Light soaking is found to increase the specific heat C and internal friction Q-1 of pure (a-Si) and hydrogenated (a-Si:H) amorphous silicon. At the lowest temperatures, the increases in C and Q-1 are consistent with an increased density of two-level systems (TLS). The light-induced increase in C persists to room temperature. Neither the sound velocity nor shear modulus change with light soaking indicating that the Debye specific heat is unchanged which suggests that light soaking creates localized vibrational modes in addition to TLS. The increase can be reversibly added and removed by light soaking and annealing, respectively, suggesting that it is related to the Staebler-Wronski effect (SWE), even in a-Si without H, and involves a reversible nanoscale structural rearrangement that is facilitated by, but does not require, H to occur.

  10. Friction and wear of plasma-deposited amorphous hydrogenated films on silicon nitride

    Science.gov (United States)

    Miyoshi, Kazuhisa

    1991-01-01

    An investigation was conducted to examine the friction and wear behavior of amorphous hydrogenated carbon (a-C:H) films in sliding contact with silicon nitride pins in both dry nitrogen and humid air environments. Amorphous hydrogenated carbon films approximately 0.06 micron thick were deposited on silicon nitride flat substrates by using the 30 kHz ac glow discharge of a planar plasma reactor. The results indicate that an increase in plasma deposition power gives an increase in film density and hardness. The high-density a-C:H films deposited behaved tribologically much like bulk diamond. In the dry nitrogen environment, a tribochemical reaction produced a substance, probably a hydrocarbon-rich layer, that decreased the coefficient of friction. In the humid air environment, tribochemical interactions drastically reduced the wear life of a-C:H films and water vapor greatly increased the friction. Even in humid air, effective lubrication is possible with vacuum-annealed a-C:H films. The vacuum-annealed high-density a-C:H film formed an outermost superficial graphitic layer, which behaved like graphite, on the bulk a-C:H film. Like graphite, the annealed a-C:H film with the superficial graphitic layer showed low friction when adsorbed water vapor was present.

  11. Infrared Insight into the Network of Hydrogenated Amorphous and Polycrystalline Silicon thin Films

    OpenAIRE

    Jarmila Mullerova

    2006-01-01

    IR measurements were carried out on both amorphous and polycrystalline silicon samples deposited by PECVD on glass substrate. The transition from amorphous to polycrystalline phase was achieved by increasing dilution of silane plasma at the deposition process. The samples were found to be mixed phase materials. Commonly, infrared spectra of hydrogenated silicon thin films yield information about microstructure, hydrogen content and hydrogen bonding to silicon. In this paper, addit...

  12. Hydrogen evolution from a copper(I) oxide photocathode coated with an amorphous molybdenum sulphide catalyst.

    Science.gov (United States)

    Morales-Guio, Carlos G; Tilley, S David; Vrubel, Heron; Grätzel, Michael; Hu, Xile

    2014-01-01

    Concerns over climate change resulting from accumulation of anthropogenic carbon dioxide in the atmosphere and the uncertainty in the amount of recoverable fossil fuel reserves are driving forces for the development of renewable, carbon-neutral energy technologies. A promising clean solution is photoelectrochemical water splitting to produce hydrogen using abundant solar energy. Here we present a simple and scalable technique for the deposition of amorphous molybdenum sulphide films as hydrogen evolution catalyst onto protected copper(I) oxide films. The efficient extraction of excited electrons by the conformal catalyst film leads to photocurrents of up to -5.7 mA cm(-2) at 0 V versus the reversible hydrogen electrode (pH 1.0) under simulated AM 1.5 solar illumination. Furthermore, the photocathode exhibits enhanced stability under acidic environments, whereas photocathodes with platinum nanoparticles as catalyst deactivate more rapidly under identical conditions. The work demonstrates the potential of earth-abundant light-harvesting material and catalysts for solar hydrogen production. PMID:24402352

  13. Ion beam effects on the hydrogenated bonds of amorphous silicon carbide

    International Nuclear Information System (INIS)

    Ion irradiation of amorphous hydrogenated silicon carbide films introduces additional disorder into the films and leads to chemical modifications. These effects were monitored using Infrared, UV-visible optical and Raman spectroscopies. Samples were prepared by plasma enhanced chemical vapour deposition (PECVD), then irradiated with 300 keV Ar+ to fluences ranging from 5x1013 to 1x1015 cm-2. The hydrogen concentration was determined by elastic recoil detection analysis using 2.0 MeV He+ beam. After ion irradiation, the absorption coefficient in the UV-visible energy range was observed to increase by an order of magnitude, while the optical energy gap decreases from 3.2 eV to 2.0 eV. These changes are due to the formation of carbon clusters, as evidenced by the carbon yield in Raman measurements. Infrared spectra indicate that this excess of carbon atoms results from the breaking of CHn bonds in the as-grown film and by a concomitant decrease in the hydrogen concentration. In addition, defects created by ion bombardment change the oscillator strength of the Si-H vibrational modes

  14. STUDY ON MAXIMUM HYDROGEN CAPACITY FOR Zr-Ni AMORPHOUS ALLOY

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    To design the amorphous hydrogen storage alloy efficiently, the maximum hydrogen capacities for Zr-Ni amorphous alloy were calculated. Based on the Rhomb Unit Structure Model(RUSM) for amorphous alloy and the experimental result that hydrogen atoms exist in 3Zr1Ni and 4Zr tetrahedron interstices in Zr-Ni amorphous alloy, the numbers of 3Zr-1Ni and 4Zr tetrahedron interstices in a RUSM were calculated which correspond to the hydrogen capacity. The two extremum Zr distribution states were calculated, such as highly heterogeneous Zr distribution and homogeneous Zr distribution. The calculated curves of hydrogen capacity with different Zr contents at two states indicate that the hydrogen capacity increases with increasing Zr content and reaches its maximum when Zr is 75%. The theoretical maximum hydrogen capacity for Zr-Ni amorphous alloy is 2.0(H/M). Meanwhile, the hydrogen capacity of heterogeneous Zr distribution alloy is higher than that of homogenous one at the same Zr content. The experimental results prove the calculated results reasonable, and accordingly, the experimental results that the distribution of Zr atom in amorphous alloy occur heterogeneous after a few hydrogen absorption-desorption cycles can be explained.

  15. Temperature dependence of hydrogenated amorphous silicon solar cell performances

    Science.gov (United States)

    Riesen, Y.; Stuckelberger, M.; Haug, F.-J.; Ballif, C.; Wyrsch, N.

    2016-01-01

    Thin-film hydrogenated amorphous silicon solar (a-Si:H) cells are known to have better temperature coefficients than crystalline silicon cells. To investigate whether a-Si:H cells that are optimized for standard conditions (STC) also have the highest energy yield, we measured the temperature and irradiance dependence of the maximum power output (Pmpp), the fill factor (FF), the short-circuit current density (Jsc), and the open-circuit voltage (Voc) for four series of cells fabricated with different deposition conditions. The parameters varied during plasma-enhanced chemical vapor deposition (PE-CVD) were the power and frequency of the PE-CVD generator, the hydrogen-to-silane dilution during deposition of the intrinsic absorber layer (i-layer), and the thicknesses of the a-Si:H i-layer and p-type hydrogenated amorphous silicon carbide layer. The results show that the temperature coefficient of the Voc generally varies linearly with the Voc value. The Jsc increases linearly with temperature mainly due to temperature-induced bandgap reduction and reduced recombination. The FF temperature dependence is not linear and reaches a maximum at temperatures between 15 °C and 80 °C. Numerical simulations show that this behavior is due to a more positive space-charge induced by the photogenerated holes in the p-layer and to a recombination decrease with temperature. Due to the FF(T) behavior, the Pmpp (T) curves also have a maximum, but at a lower temperature. Moreover, for most series, the cells with the highest power output at STC also have the best energy yield. However, the Pmpp (T) curves of two cells with different i-layer thicknesses cross each other in the operating cell temperature range, indicating that the cell with the highest power output could, for instance, have a lower energy yield than the other cell. A simple energy-yield simulation for the light-soaked and annealed states shows that for Neuchâtel (Switzerland) the best cell at STC also has the best energy

  16. Neutron scattering studies of hydrogenated, deuterated and fluorinated amorphous silicon

    International Nuclear Information System (INIS)

    A comprehensive neutron scattering study has been performed of hydrogenated (Si0.78H0.22), deuterated (Si0.77D0.23) and partially fluorinated deuterated (Si0.725D0.120F0.155) amorphous silicon, prepared by the glow-discharge technique. The measurements performed include diffraction, small-angle neutron scattering (SANS) and inelastic neutron scattering, and the data obtained are discussed in terms of various structural models in the literature. The real-space correlation function for Si0.77D0.23 exhibits sharp peaks at 1.49 and 2.36 A, due to Si-D and Si-Si covalent bonds, respectively, while peaks centred at 3.2 and 3.8 A are due to Si-D and Si-Si second-neighbour distances. High-energy resolution inelastic scattering measurements for Si0.78H0.22 show that there are approximately equal numbers of ≡SiH and = SiH2 groupings, there being no indication of excitations corresponding to -SiH3 groupings. The presence of molecular hydrogen is demonstrated unambiguously by the observation of the ortho-to-para conversion, via molecular rotation modes at 14.5 and 29.4 meV. The shift in the Si-H stretch modes introduced by deuteration is slightly less than the value of √2 expected for free hydrogen, indicating a small but observable influence of the amorphous silicon matrix. The size of the cages containing the H2 molecules has been investigated via SANS, which yields a mean Guinier radius of ∼5-6 A. In addition, the use of the H-D SANS contrast technique indicates that each cage contains on average about 60 H2 (D2) molecules. The data for the Si0.725D0.120F0.155 sample are consistent with a previously suggested model of network cages predominantly containing molecular SiF4

  17. Growth and defect chemistry of amorphous hydrogenated silicon

    Science.gov (United States)

    Scott, Bruce A.; Reimer, Jeffrey A.; Longeway, Paul A.

    1983-12-01

    Magnetic resonance (NMR,EPR) and infrared studies are presented of amorphous hydrogenated silicon (a-Si:H) films prepared by homogeneous chemical vapor deposition (HOMOCVD) and rf plasma decomposition using silane and disilane. Hydrogen incorporation occurs with a small activation energy (˜0.06 eV) for all films, while the barrier for changes in spin defect density is almost an order of magnitude larger and comparable to that measured in defect annealing studies. Films deposited by rf(Si2H6) plasma exhibit the greatest hydrogen contents, followed by HOMOCVD and rf(SiH4) plasma material. NMR measurements suggest that HOMOCVD films are less disordered than plasma-deposited a-Si:H. Previous work and recent kinetic studies of plasma and thermal environments are extensively analyzed, along with thermodynamic and kinetic data, to determine a a-Si:H growth mechanisms most consistent with the experimental results. The model presented to explain compositional and defect changes with substrate temperature emphasizes plasma deposition by monoradical precursors and HOMOCVD growth by diradicals, resulting initially in a similar surface-bound intermediate in all cases. Plasma growth from Si2H6 involves the surface attachment of longer radical chains, compared to SiH4, while oligomeric diradicals could be present in HOMOCVD. The possibility that reactions at the hot reactor wall, as well as in the gas, create monoradicals in HOMOCVD is also explored in detail. Finally, film dehydrogenation and crosslinking reactions are examined, and experiments proposed to determine the channels most relevant for each deposition environment.

  18. Field Emission Properties of Nitrogen-doped Amorphous Carbon Films

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Nitrogen-doped amorphous carbon thin films are deposited on the ceramic substrates coated with Ti film by using direct current magnetron sputtering technique at N2 and Ar gas mixture atmosphere during deposition. The field emission properties of the deposited films have been investigated. The threshold field as low as 5.93V/μm is obtained and the maximum current density increases from 4μA/cm2 to 20.67μA/cm2 at 10.67V/μm comparing with undoped amorphous film. The results show that nitrogen doping plays an important role in field emission of amorphous carbon thin films.

  19. Hydrogen diffusion in Zr35Ni55V10 amorphous alloy

    Institute of Scientific and Technical Information of China (English)

    CHENG Xiao-ying; WAHG Fang

    2007-01-01

    Hydrogen diffusion in Zr35Ni55V10 amorphous alloy was measured by chronopotentiometry. The results show that at lower molar ratio of hydrogen (x<0.06, x=n(H)/n(M)), the diffusivity of hydrogen increases rapidly with increasing the molar ratio of hydrogen. However, when x(H)>0.1, the diffusivity of hydrogen decreases slightly with increasing the molar ratio of hydrogen, which is similar to the change in crystalline alloy. It is proposed that hydrogen atoms mainly occupy the sites corresponding to tetrahedra with 4 Zr atoms at lower molar ratio of hydrogen. When the molar ratio of hydrogen is higher, the additional hydrogen atoms are in sites with higher energy and these sites in amorphous state are similar to these in crystalline states.

  20. Role of amorphous silicon domains on Er3+ emission in the Er-doped hydrogenated amorphous silicon suboxide film

    Institute of Scientific and Technical Information of China (English)

    陈长勇; 陈维德; 李国华; 宋淑芳; 丁琨; 许振嘉

    2003-01-01

    An investigation on the correlation between amorphous Si (a-Si) domains and Er3+ emission in the Er-doped hydrogenated amorphous silicon suboxide (a-Si:O:H) film is presented. On one hand, a-Si domains provide sufficient carriers for Er3+ carrier-mediated excitation which has been proved to be the highest excitation path for Er3+ ion; on the other hand, hydrogen diffusion from a-Si domains to amorphous silicon oxide (a-SiOx) matrix during annealing has been found and this possibly decreases the number of nonradiative centres around Er3+ ions. This study provides a better understanding of the role of a-Si domains on Er3+ emission in a-Si:O:Hfilms.

  1. Role of amorphous silicon domains of Er3+ emission in the Er—doped hydrogenated amorphous silicon suboxide film

    Institute of Scientific and Technical Information of China (English)

    ChenChang-Yong; ChenWei-De; LeGuo-Hua; SongShu-Fang; DingKun; XuZhen-Jia

    2003-01-01

    An investigation on the correlation between amorphous Si(a-Si) domains and Er3+ emission in the Er-doped hydrogenated amorphous silicon suboxide (a-Si:O:H) film is presented. On one hand, a-Si domains provide sufficient carrlers for Er3+ carrier-mediated excitation which has been proved to be the highest excitation path for Er3+ ion; on the other hand, hydrogen diffusion from a-Si domains to amorphous silicon oxide (a-SiOx) matrix during annealing has been found and this possibly decreases the number of nonradiative centres around Er3+ ions. This study provides a better understanding of the role of a-Si domains on Er3+ emission in a-Si:O:H films.

  2. Amorphous carbon contamination monitoring and process optimization for single-walled carbon nanotube integration

    International Nuclear Information System (INIS)

    We detail the monitoring of amorphous carbon deposition during thermal chemical vapour deposition of carbon nanotubes and propose a contamination-less process to integrate high-quality single-walled carbon nanotubes into micro-electromechanical systems. The amorphous content is evaluated by confocal micro-Raman spectroscopy and by scanning/transmission electron microscopy. We show how properly chosen process parameters can lead to successful integration of single-walled nanotubes, enabling nano-electromechanical system synthesis

  3. Surface passivation and boundary lubrication of self-mated tetrahedral amorphous carbon asperities under extreme tribological conditions

    OpenAIRE

    Romero, A. P.; Pastewka, L.; Lautz, J.; Moseler, M.

    2014-01-01

    Tetrahedral amorphous carbon coatings have the potential to significantly reduce friction and wear between sliding components. Here, we provide atomistic insights into the evolution of the sliding interface between naked and hydrogen-passivated ta-C sliding partners under dry and lubricated conditions. Using reactive classical atomistic simulations we show that sliding induces a sp3 to sp2 rehybridization and that the shear resistance is reduced by hydrogen-passivation and hexadecane-lubricat...

  4. High Pressure Chemical Vapor Deposition of Hydrogenated Amorphous Silicon Films and Solar Cells.

    Science.gov (United States)

    He, Rongrui; Day, Todd D; Sparks, Justin R; Sullivan, Nichole F; Badding, John V

    2016-07-01

    Thin films of hydrogenated amorphous silicon can be produced at MPa pressures from silane without the use of plasma at temperatures as low as 345 °C. High pressure chemical vapor deposition may open a new way to low cost deposition of amorphous silicon solar cells and other thin film structures over very large areas in very compact, simple reactors. PMID:27174318

  5. Structural analysis of amorphous and hydrogen absorption alloys by neutron diffraction

    International Nuclear Information System (INIS)

    Structural studies of amorphous alloys and hydrogen absorption amorphous alloys by taking advantage of neutron and X-ray diffractions and using the reverse Monte Carlo (RMC) modeling for getting information of the three dimensional atom configuration are reviewed. Voronoi analysis of the RMC models is powerful to elucidate the structural origin of the stability of amorphous state, since Ni-Zr amorphous alloys are unstable in comparison with Cu-Zr ones. The polyhedra around Ni atoms are dominated by trigonal prism-like polyhedra. In contrast, icosahedron-like polyhedra are preferred for Cu. The Ni-Zr amorphous alloys have been reported to stabilize by adding Al. The Voronoi analysis informs us that trigonal prism-like polyhedra decreased in number by adding Al to the Ni-Zr system. On the contrary, the number of icosahedron-like polyhedra was found to increase. The results apparently indicate that the icosahedron-like polyhedra play an important role to stabilize the amorphous state. Moreover, neutron diffraction is a powerful tool to clarify the location of hydrogen atoms in the hydrogen absorption materials. For TbFe2D3.8 and TbNi2D2.4 amorphous alloys, the RMC model structure based on the diffraction data teach us that about 98% of hydrogen atoms occupy tetrahedral sites formed by metal atoms and stabilize the amorphous state. (author)

  6. Raman spectroscopy of PIN hydrogenated amorphous silicon solar cells

    Science.gov (United States)

    Keya, Kimitaka; Torigoe, Yoshihiro; Toko, Susumu; Yamashita, Daisuke; Seo, Hyunwoong; Itagaki, Naho; Koga, Kazunori; Shiratani, Masaharu

    2015-09-01

    Light-induced degradation of hydrogenated amorphous silicon (a-Si:H) is a key issue for enhancing competitiveness in solar cell market. A-Si:H films with a lower density of Si-H2 bonds shows higher stability. Here we identified Si-H2 bonds in PIN a-Si:H solar cells fabricated by plasma CVD using Raman spectroscopy. A-Si:H solar cell has a structure of B-doped μc-SiC:H (12.5 nm)/ non-doped a-Si:H (250nm)/ P-doped μc-Si:H (40 nm) on glass substrates (Asahi-VU). By irradiating HeNe laser light from N-layer, peaks correspond to Si-H2 bonds (2100 cm-1) and Si-H bonds (2000 cm-1) have been identified in Raman scattering spectra. The intensity ratio of Si-H2 and Si-H ISiH2/ISiH is found to correlate well to light induced degradation of the cells Therefore, Raman spectroscopy is a promising method for studying origin of light-induced degradation of PIN solar cells.

  7. Nanohole Structuring for Improved Performance of Hydrogenated Amorphous Silicon Photovoltaics.

    Science.gov (United States)

    Johlin, Eric; Al-Obeidi, Ahmed; Nogay, Gizem; Stuckelberger, Michael; Buonassisi, Tonio; Grossman, Jeffrey C

    2016-06-22

    While low hole mobilities limit the current collection and efficiency of hydrogenated amorphous silicon (a-Si:H) photovoltaic devices, attempts to improve mobility of the material directly have stagnated. Herein, we explore a method of utilizing nanostructuring of a-Si:H devices to allow for improved hole collection in thick absorber layers. This is achieved by etching an array of 150 nm diameter holes into intrinsic a-Si:H and then coating the structured material with p-type a-Si:H and a conformal zinc oxide transparent conducting layer. The inclusion of these nanoholes yields relative power conversion efficiency (PCE) increases of ∼45%, from 7.2 to 10.4% PCE for small area devices. Comparisons of optical properties, time-of-flight mobility measurements, and internal quantum efficiency spectra indicate this efficiency is indeed likely occurring from an improved collection pathway provided by the nanostructuring of the devices. Finally, we estimate that through modest optimizations of the design and fabrication, PCEs of beyond 13% should be obtainable for similar devices. PMID:27227369

  8. Electrical characterization of hydrogenated amorphous silicon oxide films

    Science.gov (United States)

    Itoh, Takashi; Katayama, Ryuichi; Yamakawa, Koki; Matsui, Kento; Saito, Masaru; Sugiyama, Shuhichiroh; Sichanugrist, Porponth; Nonomura, Shuichi; Konagai, Makoto

    2015-08-01

    The electrical characterization of hydrogenated amorphous silicon oxide (a-SiOx:H) films was performed by electron spin resonance (ESR) and electrical conductivity measurements. In the ESR spectra of the a-SiOx:H films, two ESR peaks with g-values of 2.005 and 2.013 were observed. The ESR peak with the g-value of 2.013 was not observed in the ESR spectra of a-Si:H films. The photoconductivity of the a-SiOx:H films decreased with increasing spin density estimated from the ESR peak with the g-value of 2.005. On the other hand, photoconductivity was independent of spin density estimated from the ESR peak with the g-value of 2.013. The optical absorption coefficient spectra of the a-SiOx:H films were also measured. The spin density estimated from the ESR peak with the g-value of 2.005 increased proportionally with increasing optical absorption owing to the gap-state defect.

  9. Fracture properties of hydrogenated amorphous silicon carbide thin films

    International Nuclear Information System (INIS)

    The cohesive fracture properties of hydrogenated amorphous silicon carbide (a-SiC:H) thin films in moist environments are reported. Films with stoichiometric compositions (C/Si ≈ 1) exhibited a decreasing cohesive fracture energy with decreasing film density similar to other silica-based hybrid organic–inorganic films. However, lower density a-SiC:H films with non-stoichiometric compositions (C/Si ≈ 5) exhibited much higher cohesive fracture energy than the films with higher density stoichiometric compositions. One of the non-stoichiometric films exhibited fracture energy (∼9.5 J m−2) greater than that of dense silica glasses. The increased fracture energy was due to crack-tip plasticity, as demonstrated by significant pileup formation during nanoindentation and a fracture energy dependence on film thickness. The a-SiC:H films also exhibited a very low sensitivity to moisture-assisted cracking compared with other silica-based hybrid films. A new atomistic fracture model is presented to describe the observed moisture-assisted cracking in terms of the limited Si-O-Si suboxide bond formation that occurs in the films.

  10. Structural and electrical properties of metastable defects in hydrogenated amorphous silicon

    NARCIS (Netherlands)

    Melskens, J.; Schnegg, A.; Baldansuren, A.; Lips, K.; Plokker, M.P.; Eijt, S.W.H.; Schut, H.; Fischer, M.; Zeman, M.; Smets, A.H.M.

    2015-01-01

    The structural and electrical properties of metastable defects in various types of hydrogenated amorphous silicon have been studied using a powerful combination of continuous wave electron-paramagnetic resonance spectroscopy, electron spin echo (ESE) decay measurements, and Doppler broadening positr

  11. Damage at hydrogenated amorphous/crystalline silicon interfaces by indium tin oxide overlayer sputtering

    OpenAIRE

    Demaurex, Bénédicte; De Wolf, Stefaan; Descoeudres, Antoine; Charles Holman, Zachary; Ballif, Christophe

    2012-01-01

    Damage of the hydrogenated amorphous/crystalline silicon interface passivation during transparent conductive oxide sputtering is reported. This occurs in the fabrication process of silicon heterojunction solar cells. We observe that this damage is at least partially caused by luminescence of the sputter plasma. Following low-temperature annealing, the electronic interface properties are recovered. However, the silicon-hydrogen configuration of the amorphous silicon film is permanently changed...

  12. Molecular Dynamics Simulation of Chemical Vapor Deposition of Amorphous Carbon: Dependence on H/C Ratio of Source Gas

    OpenAIRE

    Ito, Atsushi M.; Takayama, Arimichi; Saito, Seiki; Ohno, Noriyasu; Kajita, Shin; Nakamura, Hiroaki

    2010-01-01

    By molecular dynamics simulation, the chemical vapor deposition of amorphous carbon onto graphite and diamond surfaces was studied. In particular, we investigated the effect of source H/C ratio, which is the ratio of the number of hydrogen atoms to the number of carbon atoms in a source gas, on the deposition process. In the present simulation, the following two source gas conditions were tested: one was that the source gas was injected as isolated carbon and hydrogen atoms, and the other was...

  13. Etching characteristics of hydrogenated amorphous silicon and poly crystalline silicon by hydrogen hyperthermal neutral beam

    International Nuclear Information System (INIS)

    A hydrogen hyperthermal neutral beam (HNB) generated by an inclined slot-excited antenna electron cyclotron resonance plasma source has been used to etch hydrogenated amorphous silicon (a-Si:H) and polycrystalline silicon (poly-Si) films. In this work, we present selective etching of a-Si:H with respect to poly-Si by hydrogen plasma and hydrogen HNB under various substrate temperatures, gas pressures, and bias voltages of the neutralizer. We have observed that the etch rate of a-Si:H is considerably higher than that of poly-Si. The etch rate is largely dependent upon the substrate temperature. In this experiment, the optimal substrate temperature for improving the etch rate is approximately at 150 °C. The root mean square surface roughness of the etched material reaches a maximum at 150 °C and decreases rapidly. The etch rate of poly-Si is not sensitive to changes in the experimental condition, such as the substrate temperatures and gas pressures. However, as the hydrogen HNB energy is increased, the etch rate of poly-Si also increases gradually. The hydrogen HNB energy contributes in improving the etch rate of a-Si:H and poly-Si films. - Highlights: • The highest etch rate is shown to be at the substrate temperature of 150 °C. • We investigated the effects of hydrogen hyperthermal neutral beam (HNB) energy. • Increasing HNB energy shows an increase in the etch rate of the poly-Si and a-Si:H

  14. Etching characteristics of hydrogenated amorphous silicon and poly crystalline silicon by hydrogen hyperthermal neutral beam

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Seung Pyo; Kim, Jongsik; Park, Jong-Bae; Oh, Kyoung Suk; Kim, Young-Woo; Yoo, Suk Jae; Kim, Dae Chul, E-mail: dchcharm@nfri.re.kr

    2015-03-31

    A hydrogen hyperthermal neutral beam (HNB) generated by an inclined slot-excited antenna electron cyclotron resonance plasma source has been used to etch hydrogenated amorphous silicon (a-Si:H) and polycrystalline silicon (poly-Si) films. In this work, we present selective etching of a-Si:H with respect to poly-Si by hydrogen plasma and hydrogen HNB under various substrate temperatures, gas pressures, and bias voltages of the neutralizer. We have observed that the etch rate of a-Si:H is considerably higher than that of poly-Si. The etch rate is largely dependent upon the substrate temperature. In this experiment, the optimal substrate temperature for improving the etch rate is approximately at 150 °C. The root mean square surface roughness of the etched material reaches a maximum at 150 °C and decreases rapidly. The etch rate of poly-Si is not sensitive to changes in the experimental condition, such as the substrate temperatures and gas pressures. However, as the hydrogen HNB energy is increased, the etch rate of poly-Si also increases gradually. The hydrogen HNB energy contributes in improving the etch rate of a-Si:H and poly-Si films. - Highlights: • The highest etch rate is shown to be at the substrate temperature of 150 °C. • We investigated the effects of hydrogen hyperthermal neutral beam (HNB) energy. • Increasing HNB energy shows an increase in the etch rate of the poly-Si and a-Si:H.

  15. Bivalves build their shells from amorphous calcium carbonate

    Science.gov (United States)

    Jacob, D. E.; Wirth, R.; Soldati, A. L.; Wehrmeister, U.

    2012-04-01

    One of the most common shell structures in the bivalve class is the prism and nacre structure. It is widely distributed amongst both freshwater and marine species and gives cultured pearls their sought-after lustre. In freshwater bivalves, both shell structures (prism and nacre) consist of aragonite. Formation of the shell form an amorphous precursor phase is a wide-spread strategy in biomineralization and presents a number of advantages for the organisms in the handling of the CaCO3 material. While there is already evidence that larval shells of some mollusk species use amorphous calcium carbonate (ACC) as a transient precursor phase for aragonite, the use of this strategy by adult animals was only speculated upon. We present results from in-situ geochemistry, Raman spectroscopy and focused-ion beam assisted TEM on three species from two different bivalve families that show that remnants of ACC can be found in shells from adult species. We show that the amorphous phase is not randomly distributed, but is systematically found in a narrow zone at the interface between periostracum and prism layer. This zone is the area where spherulitic CaCO3- structures protrude from the inner periostracum to form the initial prisms. These observations are in accordance with our earlier results on equivalent structures in freshwater cultured pearls (Jacob et al., 2008) and show that the original building material for the prisms is amorphous calcium carbonate, secreted in vesicles at the inner periostracum layer. Quantitative temperature calibrations for paleoclimate applications using bivalve shells are based on the Mg-Ca exchange between inorganic aragonite (or calcite) and water. These calibrations, thus, do not take into account the biomineral crystallization path via an amorphous calcium carbonate precursor and are therefore likely to introduce a bias (a so-called vital effect) which currently is not accounted for. Jacob et al. (2008) Geochim. Cosmochim. Acta 72, 5401-5415

  16. Electonic properties of hydrogenated amorphous silicon-germanium alloys

    Energy Technology Data Exchange (ETDEWEB)

    Bullot, J.; Galin, M.; Gauthier, M. (Universite de Paris-Sud, Orsay (France)); Bourdon, B. (CIT-Alcatel Transmission, Marcoussis (France))

    1983-06-01

    The electronic properties of some binary hydrogenated amorphous silicon-germanium alloys a-Sisub(x)Gesub(1-x):H in the silicon rich region (x > 0.6) are investigated. Experimental evidence is presented of photo-induced effects similar to those described in Si:H (Staebler-Wronski effect). The electronic properties are then studied from the dual point of view of the germanium content dependence and of the photo and thermal histories of the films. The dark conductivity changes between the annealed state and the light-soaked state are interpreted in terms of the variation of the temperature coefficient of the Fermi level. The photoconductivity efficiency is shown to remain close to that of a-Si:H for 1 > x >= 0.9 and to strongly decrease when the germanium content is further increased: the photoresponse of the Sisub(0.62)Gesub(0.38) alloy is 10/sup 4/ times smaller than that of a-Si:H. This deterioration of the photoconductive properties is explained in terms of the increase of the density of gap states following Ge substitution. This conclusion is based on the study of the width of the exponential absorption edge and on the results of photoconductivity time response studies. The latter data are interpreted by means of the model of Rose of trapping and recombination kinetics and it is found that for x approximately 0.6 the density of states at 0.4-0.5 eV below the mobility edge is 7 x 10/sup 17/ eV/sup -1/ cm/sup -3/ as compared to 2.4 x 10/sup 16/ eV/sup -1/ cm/sup -3/ for x = 0.97.

  17. Dynamics of hydrogenated amorphous silicon flexural resonators for enhanced performance

    Science.gov (United States)

    Mouro, J.; Chu, V.; Conde, J. P.

    2016-04-01

    Hydrogenated amorphous silicon thin-film flexural resonators with sub-micron actuation gaps are fabricated by surface micromachining on glass substrates. Experimentally, the resonators are electrostatically actuated and their motion is optically detected. Three different configurations for the electrostatic excitation force are used to study the dynamics of the resonators. In the first case, a dc voltage (Vdc) is added to an ac voltage with variable excitation frequency (Vac(ω)) and harmonic, superharmonic, and subharmonic resonances of different orders are observed. The second case consists on mixing the dc voltage (Vdc) with an ac voltage applied at a fixed frequency of twice the natural frequency of the resonator (V(2ω0)). High-amplitude parametric resonance is excited at the natural frequency of the system, ω0. This configuration allows a separation between the frequencies of the excitation and the mechanical motion. Finally, in the third case, the dc voltage (Vdc) is combined with both ac voltages, Vac(ω) and V(2ω0), and parametric resonance is excited and emerges from the fundamental harmonic resonance peak. The single-degree-of-freedom equation of motion is modeled and discussed for each case. The nonlinearity inherent to the electrostatic force is responsible for modulating the spring constant of the system at different frequencies, giving rise to parametric resonance. These equations of motion are simulated in the time and frequency domains, providing a consistent explanation of the experimentally observed phenomena. A wide variety of possible resonance modes with different characteristics can be used advantageously in MEMS device design.

  18. X-ray and neutron scattering from amorphous diamondlike carbon and hydrocarbon films

    International Nuclear Information System (INIS)

    In this report amorphous, diamondlike, carbon and hydrocarbon films are investigated by two different methods, namely, X-ray scattering and a combination of X-ray and neutron reflectivity. As specular reflectivity probes the scattering length density profile of a sample perpendicular to its surface, the combination of X-ray and neutron reflectivity reveals the nuclei density of both carbon and hydrogen separately. This allows to calculate the concentration of hydrogen in the films, which varies in the presented experiments between 0 and 36 atomic %. This method is a new and nondestructive technique to determine the concentration of hydrogen within an error of about ±1 at. % in samples with sharp interfaces. It is well suited for thin diamondlike carbon films. X-ray scattering is used to obtain structural information on the atomic scale, especially the average carbon-carbon distance and the average coordination number of the carbon atoms. As grazing incidence diffraction experiments were not successful, free-standing films are used for the scattering experiments with synchrotron light. However, the scattered intensity for large scattering vectors is, in spite of the intense primary beam, very weak, and therefore the accuracy of the obtained structural parameter is not sufficient to prove the diamondlike properties also on the atomic scale. (au) (10 tabs., 76 ills., 102 refs.)

  19. Presence of Amorphous Carbon Nanoparticles in Food Caramels

    OpenAIRE

    Md Palashuddin Sk; Amit Jaiswal; Anumita Paul; Siddhartha Sankar Ghosh; Arun Chattopadhyay

    2012-01-01

    We report the finding of the presence of carbon nanoparticles (CNPs) in different carbohydrate based food caramels, viz. bread, jaggery, sugar caramel, corn flakes and biscuits, where the preparation involves heating of the starting material. The CNPs were amorphous in nature; the particles were spherical having sizes in the range of 4–30 nm, depending upon the source of extraction. The results also indicated that particles formed at higher temperature were smaller than those formed at lower ...

  20. Simulation of swift boron clusters traversing amorphous carbon foils

    OpenAIRE

    Heredia Ávalos, Santiago; Abril Sánchez, Isabel; Denton Zanello, Cristian D.; García Molina, Rafael

    2007-01-01

    We use a simulation code to study the interaction of swift boron clusters (Bn+, n=2–6, 14) with amorphous carbon foils. We analyze different aspects of this interaction, such as the evolution of the cluster structure inside the target, the energy and angle distributions at the detector or the stopping power ratio. Our simulation code follows in detail the motion of the cluster fragments through the target and in the vacuum until reaching a detector, taking into account the following interacti...

  1. Computational investigation of the mechanical and tribological responses of amorphous carbon nanoparticles

    Science.gov (United States)

    Bucholz, Eric W.; Sinnott, Susan B.

    2013-02-01

    Nanoparticles are a class of materials that have seen increasing use as friction and wear reducers in tribological applications. Amorphous carbon (a-C) films have been the subject of significant scientific and industrial interest for use as solid-state lubricants. Here, we present classical molecular dynamics simulations to investigate the mechanical and tribological responses of a-C nanoparticles that are subjected to external forces between hydrogen-terminated diamond surfaces. Over the range of a-C nanoparticle diameters (2-5 nm) and hydrogenation (0%-50%) considered, the simulations predict a consistent mechanical response where each nanoparticle is highly elastic. The simulations predict that the transition from elastic to plastic response is directly related to an increase in the percentage of carbon-carbon crosslinking within the individual nanoparticles. Contrarily, the simulations also predict that the tribological response is noticeably impacted by changes in diameter and hydrogenation. This is because during friction, hydrogen passivates the unsaturated carbon atoms near the nanoparticle's surface, which prevents interfacial bond formation and allows the nanoparticle to roll within the interface. From these findings, it is demonstrated that a-C nanoparticles are able to provide good tribological performance only when sufficient chemical passivation of the nanoparticles is maintained.

  2. Magnetically stabilized bed reactor for selective hydrogenation of olefins in reformate with amorphous nickel alloy catalyst

    Institute of Scientific and Technical Information of China (English)

    Xuhong; Mu; Enze; Min

    2007-01-01

    A magnetically stabilized bed (MSB) reactor for selective hydrogenation of olefins in reformate was developed by combining the advantages of MSB and amorphous nickel alloy catalyst. The effects of operating conditions, such as temperature, pressure, liquid space velocity, hydrogen-to-oil ratio, and magnetic field intensity on the reaction were studied. A mathematical model of MSB reactor for hydrogenation of olefins in reformate was established. A reforming flow scheme with a post-hydrogenation MSB reactor was proposed. Finally, MSB hydrogenation was compared with clay treatment and conventional post-hydrogenation.

  3. The magnetic properties and the Barkhausen noise of the hydrogenated Fe-V-B amorphous alloy

    International Nuclear Information System (INIS)

    As a consequence of hydrogenation-dehydrogenation process, in the present paper the study of structural changes which could be followed by measuring structure sensitive magnetic properties as the stress induced anisotropy, coercive force, demagnetizing factor and the Barkhausen noise parameters of the as-cast and hydrogenated Fe80V5B15 amorphous alloys is performed. (author)

  4. Solid state photochemistry. Subpanel A-2(b): Metastability in hydrogenated amorphous silicon

    Energy Technology Data Exchange (ETDEWEB)

    Carlson, D. [Solarex Corporation, Newton, PA (United States)

    1996-09-01

    All device quality amorphous silicon based materials exhibit degradation in electronic properties when exposed to sunlight. The photo-induced defects are associated with Si dangling bonds that are created by the recombination and/or trapping of photogenerated carriers. The defects are metastable and can be annealed out at temperatures of about 150 to 200 degrees Centigrade. The density of metastable defects is larger in films that are contaminated with > 10{sup 19} per cubic cm of impurities such as oxygen, carbon and nitrogen. However, recent experimental results indicate that some metastable defects are still present in films with very low impurity concentrations. The photo-induced defects typically saturate after 100 to 1000 hours of exposure to one sun illumination depending on the deposition conditions. There is also experimental evidence that photo-induced structural changes are occurring in the amorphous silicon based materials and that hydrogen may be playing an important role in both the photo-induced structural changes and in the creation of metastable defects.

  5. HRTEM study of Popigai impact diamond: heterogeneous diamond nanostructures in native amorphous carbon matrix

    Science.gov (United States)

    Kis, Viktoria K.; Shumilova, Tatyana; Masaitis, Victor

    2016-07-01

    High-resolution transmission electron microscopy was applied for the detailed nanostructural investigation of Popigai impact diamonds with the aim of revealing the nature of the amorphous carbon of the matrix. The successful application of two complementary specimen preparation methods, focused ion beam (FIB) milling and mechanical cleavage, allowed direct imaging of nanotwinned nanodiamond crystals embedded in a native amorphous carbon matrix for the first time. Based on its stability under the electron beam, native amorphous carbon can be easily distinguished from the amorphous carbon layer produced by FIB milling during specimen preparation. Electron energy loss spectroscopy of the native amorphous carbon revealed the dominance of sp 2-bonded carbon and the presence of a small amount of oxygen. The heterogeneous size distribution and twin density of the nanodiamond crystals and the structural properties of the native amorphous carbon are presumably related to non-graphitic (organic) carbon precursor material.

  6. Catalytic hydrogenation of carbon monoxide

    International Nuclear Information System (INIS)

    Focus of this project is on developing new approaches for hydrogenation of carbon monoxide to produce organic oxygenates at mild conditions. The strategies to accomplish CO reduction are based on favorable thermodynamics manifested by rhodium macrocycles for producing a series of intermediates implicated in the catalytic hydrogenation of CO. Metalloformyl complexes from reactions of H2 and CO, and CO reductive coupling to form metallo α-diketone species provide alternate routes to organic oxygenates that utilize these species as intermediates. Thermodynamic and kinetic-mechanistic studies are used in guiding the design of new metallospecies to improve the thermodynamic and kinetic factors for individual steps in the overall process. Electronic and steric effects associated with the ligand arrays along with the influences of the reaction medium provide the chemical tools for tuning these factors. Non-macrocyclic ligand complexes that emulate the favorable thermodynamic features associated with rhodium macrocycles, but that also manifest improved reaction kinetics are promising candidates for future development

  7. Amorphous nickel/cobalt tungsten sulfide electrocatalysts for high-efficiency hydrogen evolution reaction

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Amorphous nickel/cobalt tungsten sulfides were synthesized by a thermolytic process. • Amorphous NiWS and CoWS could realize hydrogen evolution efficiently. • Ni/Co promotion and annealing alter the porous structure and chemical bonding states. • Active sites on the surface of amorphous WSx are increased with Ni or Co doping. • Amorphous NiWS and CoWS have immense potentials in water splitting devices. - Abstract: The hydrogen evolution reaction (HER), an appealing solution for future energy supply, requires efficient and inexpensive electrocatalysts with abundant active surface sites. Although crystalline MoS2 and WS2 are promising candidates, their activity is dominated by edge sites. Amorphous tungsten sulfide prepared so far lacks the required active sites and its application has thus been hampered. In this work, nickel and cobalt incorporated amorphous tungsten sulfide synthesized by a thermolytic process is demonstrated to enhance the HER efficiency dramatically. The amorphous nickel tungsten sulfide (amorphous NiWS) annealed at 210 °C delivers the best HER performance in this system boasting a Tafel slope of 55 mV per decade and current density of 8.6 mA cm−2 at 250 mV overpotential in a sustained test for 24 h. The introduction of Ni or Co into the catalyst and subsequent thermal treatment alters the porous structure and chemical bonding states thereby increasing the density of active sites on the surface

  8. Combined HRTEM and PEELS analysis of nanoporous and amorphous carbon

    International Nuclear Information System (INIS)

    Both the mass density (1.37 kgm/m3) and sp2+sp3 bonding fraction (0.15) were determined for an unusual nanoporous amorphous carbon consisting of curved single graphitic sheets. A combination of high-resolution transmission electron microscopy (HRTEM) and parallel electron energy loss spectroscopy (PEELS) was used. The values of these two parameters provide important constraints for the determination of the structure of this relatively low density variety of nanoporous carbon. The results are relevant also in the search for negatively-curved Schwarzite-related carbon structures. New date are also presented for highly-oriented pyrollytic graphite (HOPG), chemically vapour deposited (CVD) diamond, C60, glassy carbon (GC) and evaporated amorphous carbon (EAC); these are compared with the results for NAC. Kramers-Kronig analysis (KKA) of the low-loss PEELS data shows that the band gaps of both NAC and EAC are collapsed relative to that of CVD diamond. 18 refs., 2 tabs., 3 figs

  9. In situ ultraviolet treatment in an Ar ambient upon p-type hydrogenated amorphous silicon-carbide windows of hydrogenated amorphous silicon based solar cells

    International Nuclear Information System (INIS)

    We proposed an in situ postdeposition ultraviolet treatment in an Ar ambient (UTA) to improve the p/i interface of amorphous silicon based solar cell. We have increased the conversion efficiency by ∼16% by improving the built-in potential and reducing recombination at the p/i interface. Through spectroscopic ellipsometry and Fourier-transform infrared measurements, it is concluded that the UTA process induces structural modification of the p-type hydrogenated amorphous silicon-carbide (p-a-SiC:H) window layer. An ultrathin p-a-SiC:H contamination layer formed during the UTA process acts as a buffer layer at the interface

  10. Structural,Optical and Electrical Properties of Hydrogen-Doped Amorphous GaAs Thin Films

    Institute of Scientific and Technical Information of China (English)

    YAO Yan-Ping; LIU Chun-Ling; QIAO Zhong-Liang; LI Mei; GAO Xin; BO Bao-Xue

    2008-01-01

    @@ Amorphous GaAs films are deposited on substrates of quartz glass and silicon by rf magnetron sputtering technique in different gas ambient.First,the amorphous structure of the prepared samples is identified by x-ray diffraction.Second,analysis by radial distribution function and pair correlation function method is established to characterize the microstructure of the samples.Then,the content and bond type of hydrogen are analysed using Fourier transform infrared absorption spectroscopy.

  11. Calorimetry of dehydrogenation and dangling-bond recombination in several hydrogenated amorphous silicon materials

    OpenAIRE

    Roura Grabulosa, Pere; Farjas Silva, Jordi; Rath, Chandana; Serra-Miralles, J.; Bertrán Serra, Enric; Roca I Cabarrocas, Pere

    2006-01-01

    Differential scanning calorimetry (DSC) was used to study the dehydrogenation processes that take place in three hydrogenated amorphous silicon materials: nanoparticles, polymorphous silicon, and conventional device-quality amorphous silicon. Comparison of DSC thermograms with evolved gas analysis (EGA) has led to the identification of four dehydrogenation processes arising from polymeric chains (A), SiH groups at the surfaces of internal voids (A'), SiH groups at interfaces (B), and in the b...

  12. Spectroscopic Ellipsometry Studies of n-i-p Hydrogenated Amorphous Silicon Based Photovoltaic Devices

    OpenAIRE

    Laxmi Karki Gautam; Maxwell M. Junda; Hamna F. Haneef; Collins, Robert W.; Nikolas J. Podraza

    2016-01-01

    Optimization of thin film photovoltaics (PV) relies on characterizing the optoelectronic and structural properties of each layer and correlating these properties with device performance. Growth evolution diagrams have been used to guide production of materials with good optoelectronic properties in the full hydrogenated amorphous silicon (a-Si:H) PV device configuration. The nucleation and evolution of crystallites forming from the amorphous phase were studied using in situ near-infrared to u...

  13. Correlation of magnetic and mechanical properties of hydrogenated, compositionally modulated, amorphous Fe80Zr20 films (abstract)

    International Nuclear Information System (INIS)

    Recent research has demonstrated that large amounts of hydrogen can be electrolytically incorporated in amorphous, compositionally modulated (CM) FeZr films. The first irreversible changes in the magnetic state of an electrolytically hydrogenated iron-rich amorphous alloy were observed. The hydrogen-induced changes in the magnetization were interpreted in terms of specific structural rearrangements. In this work, simultaneous measurements of the variations in the magnetization and mechanical properties of these films were measured as a function of hydrogen charging to further clarify the hydrogen-induced structure changes. The Young close-quote s moduli E and internal friction d of as-deposited, and as-hydrogenated CM Fe80Zr20 thin films were calculated from the displacements of a vibrating composite cantilever, measured using a laser heterodyne interferometer (LHI) having a displacement sensitivity of ∼0.01 A. E and d were measured using the resonant frequency method. CM films with thickness 1390 A and modulation wavelength ∼10 A were deposited on glass cantilevers (5 mm long, 2 mm wide, and 150 μm thick) by sequentially sputtering (rf diode) elemental Fe and Zr targets. The samples were electrolytically hydrogenated for various times in 2 N phosphoric acid with a current density of 26.3 mA/cm2. The maximum change in magnetization of the film (from 71.5 to 551 emu/cm3) was observed after 5 min. During this time, E increased 18-fold from 535 GPa to 9.63 TPa. The unusually high Young close-quote s modulus of the as-deposited CM film is comparable to those previously observed in other CM films. The change is three times larger than the change in the E of carbon steel at the martensitic transformation, and nine times larger than the hydrogen induced increase in E of pure single crystals of iron. (Abstract Truncated)

  14. NATO Advanced Study Institute on Hydrogen in Disordered and Amorphous Solids

    CERN Document Server

    Bowman, Robert

    1986-01-01

    This is the second volume in the NATO ASI series dealing with the topic of hydrogen in solids. The first (V. B76, Metal Hydrides) appeared five years ago and focussed primarily on crystalline phases of hydrided metallic systems. In the intervening period, the amorphous solid state has become an area of intense research activity, encompassing both metallic and non-metallic, e.g. semiconducting, systems. At the same time the problem of storage of hydrogen, which motivated the first ASI, continues to be important. In the case of metallic systems, there were early indications that metallic glasses and disordered alloys may be more corrosion resistant, less susceptible to embrittlement by hydrogen and have a higher hydrogen mobility than ordered metals or intermetallics. All of these properties are desirable for hydrogen storage. Subsequent research has shown that thermodynamic instability is a severe problem in many amorphous metal hydrides. The present ASI has provided an appropriate forum to focus on these issu...

  15. Formation of Ultrananocrystalline Diamond/Amorphous Carbon Composite Films in Vacuum Using Coaxial Arc Plasma Gun

    Science.gov (United States)

    Hanada, Kenji; Yoshida, Tomohiro; Nakagawa, You; Yoshitake, Tsuyoshi

    2010-12-01

    Ultrananocrystalline diamond (UNCD)/nonhydrogenated amorphous carbon (a-C) composite films were grown in vacuum using a coaxial arc plasma gun. From the X-ray diffraction measurement, the UNCD crystallite size was estimated to be 1.6 nm. This size is dramatically reduced from that (2.3 nm) of UNCD/hydrogenated amorphous carbon (a-C:H) composite films grown in a hydrogen atmosphere. The sp3/(sp3 + sp2) value, which was estimated from the X-ray photoemission spectrum, was also reduced to be 41%. A reason for it might be the reduction in the UNCD crystallite size. From the near-edge X-ray absorption fine-structure (NEXAFS) spectrum, it was found that the π*C=C and π*C≡C bonds are preferentially formed instead of the σ*C-H bonds in the UNCD/a-C:H films. Since the extremely small UNCD crystallites (1.6 nm) correspond to the nuclei of diamond, we consider that UNCD crystallite formation should be due predominantly to nucleation. The supersaturated condition required for nucleation is expected to be realized in the deposition using the coaxial arc plasma gun.

  16. Superconductivity in Sulfur-Doped Amorphous Carbon Films

    OpenAIRE

    Felner, I.; Wolf, O; Millo, O.

    2013-01-01

    Following our previous investigations on superconductivity in amorphous carbon (aC) based systems; we have prepared thin composite aC-W films using electron-beam induced deposition. The films did not show any sign for superconductivity above 5 K. However, local, non-percolative, superconductivity emerged at Tc = 34.4 K after treatment with sulfur at 250 C for 24 hours. The superconducting features in the magnetization curves were by far sharper compared to our previous results, and the shield...

  17. Superconductivity and unusual magnetic behavior in amorphous carbon

    OpenAIRE

    Felner, Israel

    2013-01-01

    Traces of superconductivity (SC) at elevated temperatures (up to 65 K) were observed by magnetic measurements in three different inhomogeneous sulfur doped amorphous carbon (a-C) systems: (a) in commercial and (b) synthesized powders and (c) in a-C thin films. (a) Studies performed on commercial (a-C) powder which contains 0.21% of sulfur, revealed traces of non-percolated superconducting phases below Tc = 65 K. The SC volume fraction is enhanced by the sulfur doping. (b) a-C powder obtained ...

  18. A percolation theory approach to the implantation induced diamond to amorphous-carbon transition

    International Nuclear Information System (INIS)

    The physical fact that diamond is electrically insulating while amorphous carbon and graphite are conducting is used in the present work to study the local damage that each implanted ion creates around its track and to conclude about the processes through which implanted diamond turns amorphous. Experimental data for the conductivity of Sb implanted diamond for various geometries, energies and doses are analyzed by the use of percolation theory. It seems that the amorphization of implanted diamond proceeds gradually with no well defined amorphous regions formed around the ion track. Amorphization in implanted diamond seems to occur in a way different than is believed to be the case for implanted silicon, where some direct amorphization around an ion track is suggested. This major difference can be attributed to the abnormally large change in densities between diamond and amorphous carbon or graphite which suppresses the growth of local amorphous regions in diamond. (author)

  19. Hydrogen gas permeation through amorphous and partially crystallized Fe40Ni38Mo4B18

    Directory of Open Access Journals (Sweden)

    Rafaella Martins Ribeiro

    2012-10-01

    Full Text Available Samples of amorphous and partially crystallized Fe40Ni38Mo4B18 alloy were submitted to hydrogen gas permeation from 523 to 643 K. The hydrogen permeation curves exhibited a single sigmoidal shape, typical of tests where no hydride formation occurs. It was observed that the hydrogen diffusivity increases for the amorphous samples and partially crystallized alloy with the temperature increase. The hydrogen diffusion coefficient as a function of temperature was found to be D = 5.1 ± 0.5 × 10-12 exp (-11.0 ± 3.5/RT (m².s-1 for amorphous condition and D = 3.6 ± 0.5 × 10-11 exp (-19.8 ± 3.3/RT (m².s-1 for the partially crystallized condition. This suggests that the annihilation of defects in the amorphous structure and the crystalline phase precipitate contributes to the increase of the hydrogen diffusion.

  20. Development of carbon membranes for hydrogen recovery

    OpenAIRE

    Grainger, David

    2007-01-01

    The recovery of hydrogen from gas mixtures with hydrocarbons may provide a commercial niche for carbon molecular sieve membranes (CMSMs). Previous work has shown that carbon membranes achieve excellent performance, with respect to hydrogen permeability and selectivity, in the separation of hydrogen from light hydrocarbons, such as CH4, and CO2. The intent of this work was to screen CMSMs derived from cellulose-hemicellulose for H2 recovery and to generate performance data so that commercial a...

  1. Nuclear reaction analysis of hydrogen in amorphous silicon and silicon carbide films

    International Nuclear Information System (INIS)

    The 1H(11B, α)αα nuclear reaction is used to determine the H content and the density of amorphous semiconductor Si1-sub(x)Csub(x)H2 and SiHsub(z) thin films. Rutherford backscattering is used to determine the x values and infrared transmission to study the hydrogen bonds. We have observed a transfer or/and a release of hydrogen under bombardment by various ions and we show that this last effect must be taken into account for a correct determination of the hydrogen content. An attempt is made to correlate the hydrogen release with electronic and nuclear energy losses. (orig.)

  2. Chemical bonding modifications of tetrahedral amorphous carbon and nitrogenated tetrahedral amorphous carbon films induced by rapid thermal annealing

    Energy Technology Data Exchange (ETDEWEB)

    McCann, R. [NIBEC, School of Electrical and Mechanical Engineering, University of Ulster at Jordanstown, Newtownabbey, Co. Antrim, BT37 OQB, N. Ireland (United Kingdom); Roy, S.S. [NIBEC, School of Electrical and Mechanical Engineering, University of Ulster at Jordanstown, Newtownabbey, Co. Antrim, BT37 OQB, N. Ireland (United Kingdom)]. E-mail: s.sinha-roy@ulster.ac.uk; Papakonstantinou, P. [NIBEC, School of Electrical and Mechanical Engineering, University of Ulster at Jordanstown, Newtownabbey, Co. Antrim, BT37 OQB, N. Ireland (United Kingdom); Bain, M.F. [Queens University of Belfast, School of Elect and Elect Engineering, Belfast, Antrim, N. Ireland (United Kingdom); Gamble, H.S. [Queens University of Belfast, School of Elect and Elect Engineering, Belfast, Antrim, N. Ireland (United Kingdom); McLaughlin, J.A. [NIBEC, School of Electrical and Mechanical Engineering, University of Ulster at Jordanstown, Newtownabbey, Co. Antrim, BT37 OQB, N. Ireland (United Kingdom)

    2005-06-22

    Tetrahedral amorphous carbon (ta-C) and nitrogenated tetrahedral amorphous carbon films (ta-CN {sub x}), deposited by double bend off plane Filtered Vacuum Cathodic Arc were annealed up to 1000 deg. C in flowing argon for 2 min. Modifications on the chemical bonding structure of the rapidly annealed films, as a function of temperature, were investigated by NEXAFS, X-ray photoelectron and Raman spectroscopies. The interpretation of these spectra is discussed. The results demonstrate that the structure of undoped ta-C films prepared at floating potential with an arc current of 80 A remains stable up to 900 deg. C, whereas that of ta-CN {sub x} containing 12 at.% nitrogen is stable up to 700 deg. C. At higher temperatures, all the spectra indicated the predominant formation of graphitic carbon. Through NEXAFS studies, we clearly observed three {pi}* resonance peaks at the {sup '}N K edge structure. The origin of these three peaks is not well established in the literature. However our temperature-dependant study ascertained that the first peak originates from C=N bonds and the third peak originates from the incorporation of nitrogen into the graphite like domains.

  3. Erosion of thin hydrogenated carbon films in oxygen, oxygen/hydrogen and water plasmas

    International Nuclear Information System (INIS)

    The erosion of amorphous hydrogenated carbon films in oxygen, oxygen/hydrogen and water electron cyclotron resonance plasmas was investigated by in situ ellipsometry. The erosion was measured as a function of the energy of the impinging ions and the substrate temperature. Erosion is most effective in pure oxygen plasmas. The erosion rate rises with increasing ion energy and substrate temperature, in the latter case however only at low ion energies. The reaction layer at the surface of the eroded film is further analyzed by X-ray photoelectron spectroscopy (XPS). The C ls peak of the XPS spectra shows, that oxygen is implanted in the films and forms double and single bonds to the carbon atoms. This modification, however, is limited to a few atomic layers. (orig.)

  4. The Urbach focus and optical properties of amorphous hydrogenated SiC thin films

    Science.gov (United States)

    Guerra, J. A.; Angulo, J. R.; Gomez, S.; Llamoza, J.; Montañez, L. M.; Tejada, A.; Töfflinger, J. A.; Winnacker, A.; Weingärtner, R.

    2016-05-01

    We report on the optical bandgap engineering of sputtered hydrogenated amorphous silicon carbide (a-SiC:H) thin films under different hydrogen dilution conditions during the deposition process and after post-deposition annealing treatments. The Tauc-gap and Urbach energy are calculated from ultraviolet-visible optical transmittance measurements. Additionally, the effect of the thermal annealing temperature on the hydrogen out-diffusion is assessed through infra-red absorption spectroscopy. A new model for the optical absorption of amorphous semiconductors is presented and employed to determine the bandgap as well as the Urbach energy from a single fit of the absorption coefficient. This model allowed the discrimination of the Urbach tail from the Tauc region without any external bias. Finally, the effect of the hydrogen dilution on the band-edge and the Urbach focus is discussed.

  5. Nanoparticles embedded in hydrogenated amorphous silicon thin layers

    Czech Academy of Sciences Publication Activity Database

    Remeš, Zdeněk; Stuchlík, Jiří; Stuchlíková, The-Ha; Purkrt, Adam; Fajgar, Radek; Dřínek, Vladislav; Zhuravlev, K.; Galkin, N.G.

    Aachen : ICANS26, 2015 - (Carius, R.). s. 196-197 [International Conference on Amorphous and Nanocrystalline Semiconductors /26./ (ICANS26). 13.09.2015-18.09.2015, Aachen] R&D Projects: GA ČR(CZ) GA14-05053S; GA MŠk(CZ) LD14011; GA MŠk LH12236 Institutional support: RVO:68378271 ; RVO:67985858 Keywords : a-Si:H * LED * RLA * RDE Subject RIV: BM - Solid Matter Physics ; Magnetism

  6. Properties and local structure of plasma-deposited amorphous silicon-carbon alloys

    International Nuclear Information System (INIS)

    Hydrogenated amorphous silicon-carbon alloy films were plasma-deposited from methane and silane, varying gas ratio, R.F. power and substrate temperature. Carbon addition increases the optical gap, but also raises the dangling bond density while decreasing conductivity. Low C alloys can be gas-phase doped both p and n type. In the IR spectra the various Si-C stretching modes observed between 650 and 780 cm/sup -1/ are explained by back bonding variations. A tentative method of assigning this shift to back bonding of C to the Si is given. A distribution of modes is observed for all alloys, with each mode appearing even at 2% C. The distribution is sensitive to substrate temperature, but is stable after vacuum annealing to 4000C

  7. Electron transport in W-containing amorphous carbon-silicon diamond-like nanocomposites

    International Nuclear Information System (INIS)

    The electron transport in amorphous hydrogenated carbon-silicon diamond-like nanocomposite films containing tungsten over the concentration range 12-40 at.% was studied in the temperature range 80-400 K. The films were deposited onto polycrystalline substrates, placed on the RF-biased substrate holder, by the combination of two methods: PECVD of siloxane vapours in the stimulated dc discharge and dc magnetron sputtering of tungsten target. The experimental dependences of the conductivity on the temperature are well fitted by the power-law dependences over the entire temperature range. The results obtained are discussed in terms of the model of inelastic tunnelling of the electrons in amorphous dielectrics. The average number of localized states (n) in the conducting channels between metal clusters calculated in the framework of this model is characterized by the non-monotonic dependence on the tungsten concentration in the films. The qualitative explanation of the results on the basis of host carbon-silicon matrix structural modifications is proposed. The evolution of the carbon-silicon matrix microstructure by the increase in the tungsten concentration is confirmed by the Raman spectroscopy data

  8. CORRELATION BETWEEN ELECTRICAL AND VIBRATIONAL PROPERTIES OF CHLORINATED AND HYDROGENATED AMORPHOUS SILICON PREPARED BY GLOW DISCHARGE

    OpenAIRE

    Al Dallal, S.; Chevallier, J.; Kalem, S; Bourneix, J.

    1982-01-01

    Electrical conductivity and infrared transmission measurements have been carried out on chlorinated and hydrogenated amorphous silicon films prepared by glow discharge. Upon increasing the plasma power, we observed a change of transport mechanism, accompanied by an evolution of hydrogen and chlorine related bands. From this correlation between the transport and the infrared data we suggest that the evolution of SiCl2 species with the plasma power is mainly responsible for the change in bandga...

  9. Fabrication of solution-processed hydrogenated amorphous silicon single junction solar cells

    OpenAIRE

    Masuda, Takashi; Sotani, Naoya; Hamada, Hiroki; Matsuki, Yasuo; Shimoda, Tatsuya

    2012-01-01

    Hydrogenated amorphous silicon solar cells were fabricated using solution-based processes. All silicon layers of the p-i-n junction were stacked by a spin-cast method using doped and non-doped polydihydrosilane solutions. Further, a hydrogen-radical treatment under vacuum conditions was employed to reduce spin density in the silicon films. Following this treatment, the electric properties of the silicon films were improved, and the power conversion efficiency of the solar cells was also incre...

  10. Structural and optical properties of hydrogenated amorphous silicon carbide films by helicon wave plasma-enhanced chemical vapour deposition

    International Nuclear Information System (INIS)

    Hydrogenated amorphous silicon carbide (a-Si1-xCx : H) films with different carbon concentrations have been deposited using the helicon wave plasma-enhanced chemical vapour deposition technique under the condition of strong hydrogen dilution. The a-Si1-xCx:H films with carbon content x up to 0.64 have been deposited. Their structural and optical properties are investigated using Fourier transform infrared spectroscopy, Raman scattering, ultraviolet-visible transmittance spectroscopy and x-ray photoelectron spectroscopy. The deposition rate, optical band gap and B factor related to structural disorder are found to monotonically change in the investigated range with methane-silane gas flow ratios. It is found that the deposited films exist with the structure of Si-like clusters and Si-C networks when silicon content is high, while they consist mainly of C-like clusters and Si-C networks for carbon-rich samples. A large optical band gap is obtained in high carbon concentration samples, which is attributed to the high density characteristic of helicon wave plasmas and the strong hydrogen dilution condition

  11. A Comparison of Photo-Induced Hysteresis Between Hydrogenated Amorphous Silicon and Amorphous IGZO Thin-Film Transistors.

    Science.gov (United States)

    Ha, Tae-Jun; Cho, Won-Ju; Chung, Hong-Bay; Koo, Sang-Mo

    2015-09-01

    We investigate photo-induced instability in thin-film transistors (TFTs) consisting of amorphous indium-gallium-zinc-oxide (a-IGZO) as active semiconducting layers by comparing with hydrogenated amorphous silicon (a-Si:H). An a-IGZO TFT exhibits a large hysteresis window in the illuminated measuring condition but no hysteresis window in the dark condition. On the contrary, a large hysteresis window measured in the dark condition in a-Si:H was not observed in the illuminated condition. Even though such materials possess the structure of amorphous phase, optical responses or photo instability in TFTs looks different from each other. Photo-induced hysteresis results from initially trapped charges at the interface between semiconductor and dielectric films or in the gate dielectric which possess absorption energy to interact with deep trap-states and affect the movement of Fermi energy level. In order to support our claim, we also perform CV characteristics in photo-induced hysteresis and demonstrate thermal-activated hysteresis. We believe that this work can provide important information to understand different material systems for optical engineering which includes charge transport and band transition. PMID:26716230

  12. Selective Oxidation of Amorphous Carbon Layers without Damaging Embedded Single Wall Carbon Nanotube Bundles

    Science.gov (United States)

    Choi, Young Chul; Lim, Seong Chu

    2013-11-01

    Single wall carbon nanotubes (SWCNTs) were synthesized by arc discharge, and then purified by selective oxidation of amorphous carbon layers that were found to encase SWCNT bundles and catalyst metal particles. In order to remove selectively the amorphous carbon layers with SWCNTs being intact, we have systematically investigated the thermal treatment conditions; firstly, setting the temperature by measuring the activation energies of SWCNTs and amorphous carbon layers, and then, secondly, finding the optimal process time. As a consequence, the optimal temperature and time for the thermal treatment was found to be 460 °C and 20 min, respectively. The complete elimination of surrounding amorphous carbon layers makes it possible to efficiently disperse the SWCNT bundles, resulting in high absorbance of SWCNT-ink. The SWCNTs which were thermal-treated at optimized temperature (460 °C) and duration (20 min) showed much better crystallinity, dispersibility, and transparent conducting properties, compared with as-synthesized and the nanotubes thermal-treated at different experimental conditions.

  13. Stable, high-efficiency amorphous silicon solar cells with low hydrogen content

    Science.gov (United States)

    Fortmann, C. M.; Hegedus, S. S.

    1992-12-01

    Results and conclusions obtained during the investigation of amorphous silicon, amorphous silicon based alloy materials, and solar cells fabricated by photo-chemical vapor and glow discharge depositions are reported. Investigation of the effects of the hydrogen content in a-Si:H i-layers in amorphous silicon solar cells show that cells with lowered hydrogen content i-layers are more stable. A classical thermodynamic formulation of the Staebler-Wronski effect has been developed for standard solar cell operating temperatures and illuminations. Methods have been developed to extract a lumped equivalent circuit from the current voltage characteristic of a single junction solar cell in order to predict its behavior in a multijunction device.

  14. Infrared Insight into the Network of Hydrogenated Amorphous and Polycrystalline Silicon thin Films

    Directory of Open Access Journals (Sweden)

    Jarmila Mullerova

    2006-01-01

    Full Text Available IR measurements were carried out on both amorphous and polycrystalline silicon samples deposited by PECVDon glass substrate. The transition from amorphous to polycrystalline phase was achieved by increasing dilution of silaneplasma at the deposition process. The samples were found to be mixed phase materials. Commonly, infrared spectra ofhydrogenated silicon thin films yield information about microstructure, hydrogen content and hydrogen bonding to silicon. Inthis paper, additional understanding was retrieved from infrared response. Applying standard optical laws, effective mediatheory and Clausius-Mossoti approach concerning the Si-Si and Si-H bonds under IR irradiation as individual oscillators,refractive indices in the long wavelength limit, crystalline, amorphous and voids volume fractions and the mass density of thefilms were determined. The mass density was found to decrease with increasing crystalline volume fraction, which can beattributed to the void-dominated mechanism of network formation.

  15. Amorphous nickel/cobalt tungsten sulfide electrocatalysts for high-efficiency hydrogen evolution reaction

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Lun [Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics and Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Wu, Xinglong, E-mail: hkxlwu@nju.edu.cn [Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics and Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Department of Physics, NingBo University, NingBo 315001 (China); Zhu, Xiaoshu [Center for Analysis and Testing, Nanjing Normal University, Nanjing 210093 (China); He, Chengyu; Meng, Ming; Gan, Zhixing [Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics and Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Chu, Paul K. [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China)

    2015-06-30

    Graphical abstract: - Highlights: • Amorphous nickel/cobalt tungsten sulfides were synthesized by a thermolytic process. • Amorphous NiWS and CoWS could realize hydrogen evolution efficiently. • Ni/Co promotion and annealing alter the porous structure and chemical bonding states. • Active sites on the surface of amorphous WS{sub x} are increased with Ni or Co doping. • Amorphous NiWS and CoWS have immense potentials in water splitting devices. - Abstract: The hydrogen evolution reaction (HER), an appealing solution for future energy supply, requires efficient and inexpensive electrocatalysts with abundant active surface sites. Although crystalline MoS{sub 2} and WS{sub 2} are promising candidates, their activity is dominated by edge sites. Amorphous tungsten sulfide prepared so far lacks the required active sites and its application has thus been hampered. In this work, nickel and cobalt incorporated amorphous tungsten sulfide synthesized by a thermolytic process is demonstrated to enhance the HER efficiency dramatically. The amorphous nickel tungsten sulfide (amorphous NiWS) annealed at 210 °C delivers the best HER performance in this system boasting a Tafel slope of 55 mV per decade and current density of 8.6 mA cm{sup −2} at 250 mV overpotential in a sustained test for 24 h. The introduction of Ni or Co into the catalyst and subsequent thermal treatment alters the porous structure and chemical bonding states thereby increasing the density of active sites on the surface.

  16. Preliminary radiation tests of 32 μm thick hydrogenated amorphous silicon films

    International Nuclear Information System (INIS)

    Preliminary radiation tests of hydrogenated amorphous silicon n-i-p photodiodes deposited on a coated glass substrate are presented in this paper. These tests have been performed using a 24 GeV proton beam. We report results on the fluence dependence of the diode dark current and of the signal induced by a proton spill

  17. Preliminary radiation tests of 32 {mu}m thick hydrogenated amorphous silicon films

    Energy Technology Data Exchange (ETDEWEB)

    Despeisse, M. [CERN, 1211 Geneva 23 (Switzerland)]. E-mail: matthieu.despeisse@cern.ch; Jarron, P. [CERN, 1211 Geneva 23 (Switzerland); Johansen, K.M. [CERN, 1211 Geneva 23 (Switzerland); Moraes, D. [CERN, 1211 Geneva 23 (Switzerland); Shah, A. [IMT, rue A.L Breguet 2, CH-2000 Neuchatel (Switzerland); Wyrsch, N. [IMT, rue A.L Breguet 2, CH-2000 Neuchatel (Switzerland)

    2005-10-21

    Preliminary radiation tests of hydrogenated amorphous silicon n-i-p photodiodes deposited on a coated glass substrate are presented in this paper. These tests have been performed using a 24 GeV proton beam. We report results on the fluence dependence of the diode dark current and of the signal induced by a proton spill.

  18. Thermal ideality factor of hydrogenated amorphous silicon p-i-n solar cells

    NARCIS (Netherlands)

    Kind, R.; Van Swaaij, R.A.C.M.M.; Rubinelli, F.A.; Solntsev, S.; Zeman, M.

    2011-01-01

    The performance of hydrogenated amorphous silicon (a-Si:H) p-i-n solar cells is limited, as they contain a relatively high concentration of defects. The dark current voltage (JV) characteristics at low forward voltages of these devices are dominated by recombination processes. The recombination rate

  19. Nonlinear properties of and nonlinear processing in hydrogenated amorphous silicon waveguides

    DEFF Research Database (Denmark)

    Kuyken, B.; Ji, Hua; Clemmen, S.;

    2011-01-01

    We propose hydrogenated amorphous silicon nanowires as a platform for nonlinear optics in the telecommunication wavelength range. Extraction of the nonlinear parameter of these photonic nanowires reveals a figure of merit larger than 2. It is observed that the nonlinear optical properties of these...

  20. High quality crystalline silicon surface passivation by combined intrinsic and n-type hydrogenated amorphous silicon

    NARCIS (Netherlands)

    Schuttauf, J.A.; van der Werf, C.H.M.; Kielen, I.M.; van Sark, W.G.J.H.M.; Rath, J.K.

    2011-01-01

    We investigate the influence of thermal annealing on the passivation quality of crystalline silicon (c-Si) surfaces by intrinsic and n-type hydrogenated amorphous silicon (a-Si:H) films. For temperatures up to 255 C, we find an increase in surface passivation quality, corresponding to a decreased da

  1. Friction reduction in powertrain and engine components by coating with diamond-like, amorphous carbon; Reibungsminderung an Antriebs- und Motorkomponenten durch Beschichtungen mit diamantaehnlichem amorphen Kohlenstoff

    Energy Technology Data Exchange (ETDEWEB)

    Schork, Willi Sebastian

    2010-07-01

    The author investigated inhowfar coatings with diamond-like amorphous carbon (ta-C) in combination with suitable lubricants may help to reduce friction in selected powertrain and engine components. The influence of the microstructure on the stresses on layers in tribological contact was investigated using simulations. By varying the parameters of the background gas in the coating plant, hydrogen-free amorphous carbon layers of different elasticities and compositions were deposited reproducibly using a pulsed arc technology. For selective analyses of damage mechanisms in high-wear conditions, a novel tribometer for increasing loads was designed and constructed, with oscillating sliding contact and dynamic load. Failure models were established for various stress-related damge mechanisms of layered systems measured by the new tribometer. Practical tests with engines with ta-C coated piston rings proved the applicability of hydrogen-free amorphous carbon in engine applications.

  2. A high-porosity carbon molybdenum sulphide composite with enhanced electrochemical hydrogen evolution and stability

    DEFF Research Database (Denmark)

    Laursen, Anders B.; Vesborg, Peter C. K.; Chorkendorff, Ib

    2013-01-01

    This work describes a highly active and stable acid activated carbon fibre and amorphous MoSx composite hydrogen evolution catalyst. The increased electrochemical-surface area is demonstrated to cause increased catalyst electrodeposition and activity. These composite electrodes also show an...

  3. Molecular dynamics study of hydrogen isotopes migration in amorphous silica

    International Nuclear Information System (INIS)

    Full text of publication follows: Fused silica is a material of interest due to its increasing number of applications in many different technology fields. In thermonuclear fusion it is a key component in a number of diagnostics of the Safety and Control Systems of the ITER machine as well as in the final focusing optics of lasers for NIF. Materials properties of interest (optical absorption, radioluminescence, mechanical properties, oe) are closely related to the presence of defects. These defects can be generated directly by irradiation or by the presence of impurities in the material. Hydrogen is an ubiquitous impurity in this material and, moreover in a fusion reactor environment this material will be exposed to energetic hydrogen isotopes. Hydrogen isotopes will be deposited also on the surface of the fused silica components coming from the reaction chamber. On the other hand, some experimental results show that radiation damage can be different depending on hydrogen content, indicating that a detailed knowledge of the hydrogen role in fused silica should be fully understood. In this work we present molecular dynamics simulations to study the effects of different hydrogen isotopes in this material and their interaction with defects. The interatomic potential developed by Feuston and Garofallini has been used in these studies. The diffusion coefficients and mechanisms of H mobility in fused silica has been calculated and compared with those existing in the literature. (authors)

  4. Molecular dynamics study of hydrogen isotopes migration in amorphous silica

    International Nuclear Information System (INIS)

    Fused silica is a material of interest due to its increasing number of applications in many different technology fields. In thermonuclear fusion it is a key component in a number of diagnostics of the Safety and Control Systems of the ITER machine as well as in the final focusing optics of lasers for NIF. Materials properties of interest (optical absorption, radioluminescence, mechanical properties, ...) are closely related to the presence of defects. These defects can be generated directly by irradiation or by the presence of impurities in the material. Hydrogen is an ubiquitous impurity in this material and, moreover in a fusion reactor environment this material will be exposed to energetic hydrogen isotopes. Hydrogen isotopes will be deposited also on the surface of the fused silica components coming from the reaction chamber. On the other hand, some experimental results show that radiation damage can be different depending on hydrogen content, indicating that a detailed knowledge of the hydrogen role in fused silica should be fully understood. In this work we present molecular dynamics simulations to study the effects of different hydrogen isotopes in this material and their interaction with the defects. The interatomic potential developed by Feuston and Garofallini will be used in these studies. The diffusion coefficients and mechanisms of H mobility in fused silica will be calculated and compared with those existing in the literature. (author)

  5. Evidence of chemical ordering in amorphous hydrogenated silicon carbide

    International Nuclear Information System (INIS)

    Amorphous Si/sub 0.68/C/sub 0.32/:H prepared by radio frequency glow discharge from a mixture of methane and silane was studied by means of the complementary techniques of electron energy-loss spectroscopy and electron diffraction. The experimental results are consistent with Si and C forming a tetrahedral network with nearest neighbor distances similar to those in crystalline Si and crystalline SiC. There is evidence that the C atoms tend to be surrounded by four Si atoms rather than a random distribution of C and Si on the tetrahedral network

  6. Hydrogen attack - Influence of hydrogen sulfide. [on carbon steel

    Science.gov (United States)

    Eliezer, D.; Nelson, H. G.

    1978-01-01

    An experimental study is conducted on 12.5-mm-thick SAE 1020 steel (plain carbon steel) plate to assess hydrogen attack at room temperature after specimen exposure at 525 C to hydrogen and a blend of hydrogen sulfide and hydrogen at a pressure of 3.5 MN/sq m for exposure times up to 240 hr. The results are discussed in terms of tensile properties, fissure formation, and surface scales. It is shown that hydrogen attack from a high-purity hydrogen environment is severe, with the formation of numerous methane fissures and bubbles along with a significant reduction in the room-temperature tensile yield and ultimate strengths. However, no hydrogen attack is observed in the hydrogen/hydrogen sulfide blend environment, i.e. no fissure or bubble formation occurred and the room-temperature tensile properties remained unchanged. It is suggested that the observed porous discontinuous scale of FeS acts as a barrier to hydrogen entry, thus reducing its effective equilibrium solubility in the iron lattice. Therefore, hydrogen attack should not occur in pressure-vessel steels used in many coal gasification processes.

  7. Carbon nanotube materials from hydrogen storage

    Energy Technology Data Exchange (ETDEWEB)

    Dillon, A.C.; Bekkedahl, T.A.; Cahill, A.F. [National Renewable Energy Laboratory, Golden, CO (United States)

    1995-09-01

    The lack of convenient and cost-effective hydrogen storage is a major impediment to wide scale use of hydrogen in the United States energy economy. Improvements in the energy densities of hydrogen storage systems, reductions in cost, and increased compatibility with available and forecasted systems are required before viable hydrogen energy use pathways can be established. Carbon-based hydrogen adsorption materials hold particular promise for meeting and exceeding the U.S. Department of Energy hydrogen storage energy density targets for transportation if concurrent increases in hydrogen storage capacity and carbon density can be achieved. These two goals are normally in conflict for conventional porous materials, but may be reconciled by the design and synthesis of new adsorbent materials with tailored pore size distributions and minimal macroporosity. Carbon nanotubes offer the possibility to explore new designs for adsorbents because they can be fabricated with small size distributions, and naturally tend to self-assemble by van der Waals forces. This year we report heats of adsorption for hydrogen on nanotube materials that are 2 and 3 times greater than for hydrogen on activated carbon. The hydrogen which is most strongly bound to these materials remains on the carbon surface to temperatures greater than 285 K. These results suggest that nanocapillary forces are active in stabilizing hydrogen on the surfaces of carbon nanotubes, and that optimization of the adsorbent will lead to effective storage at higher temperatures. In this paper we will also report on our activities which are targeted at understanding and optimizing the nucleation and growth of single wall nanotubes. These experiments were made possible by the development of a unique feedback control circuit which stabilized the plasma-arc during a synthesis run.

  8. Study of some structural properties of hydrogenated amorphous silicon thin films prepared by radiofrequency cathodic sputtering

    International Nuclear Information System (INIS)

    In this work, we have used the grazing X-rays reflectometry technique to characterise hydrogenated amorphous silicon thin films deposited by radio-frequency cathodic sputtering. Relfectometry measurements are taken immediately after films deposition as well as after having naturally oxidised their surfaces during a more or less prolonged stay in the ambient. For the films examined just after deposition, the role of hydrogen appears in the increase of their density. For those analysed after a short stay in the ambient, hydrogen plays a protective role against the oxidation of their surfaces. This role disappears when the stay in the ambient is so long. (author)

  9. Electroless deposition and characterization of Pd thin films on hydrogenated amorphous silicon

    International Nuclear Information System (INIS)

    This paper reports on electroless palladium thin films deposited on hydrogenated amorphous Si from a palladium-ammine bath. The d.c. magnetron reactive sputtered 18% hydrogenated amorphous silicon (a-Si:H) possessed a hydrogen passivated surface, using an activation step prior to the electroless deposition to obtain a film with good uniformity. The specially prepared hypophosphite-based dilute metal ion bath exhibited good stability as low operating temperatures of 35--50 degrees C. The morphology and microstructure of the Pd aggregates were characterized by scanning transmission electron microscopy (STEM) and energy dispersive x-ray spectroscopy (EDX), while the Pd aggregates and as-deposited films from the citrate and NH3/NH4Cl baths were examined by scanning electron microscopy (SEM). Marked differences in morphology and distribution of the Pd aggregates on activated a-Si:H and c-Si substrates were observed and discussed

  10. Carbon compound used in hydrogen storage

    International Nuclear Information System (INIS)

    In the present work it is studied the activated carbon of mineral origin for the sorption of hydrogen. The carbon decreased of particle size by means of the one alloyed mechanical. The time of mill was of 10 hours. The characterization one carries out by scanning electron microscopy and X-ray diffraction. The hydrogen sipped in the carbon material it was determined using the Thermal gravimetric method (TGA). The conditions of hydrogenation went at 10 atm of pressure and ambient temperature during 18 hours. They were also carried out absorption/desorption cycles of hydrogen in the same one system of thermal gravimetric analysis. The results showed percentages of sorption of 2% approximately in the cycles carried out in the system TGA and of 4.5% in weight of hydrogen at pressure of 10 atmospheres and ambient temperature during 18 hours. (Author)

  11. Development of radiation detectors based on hydrogenated amorphous silicon and its alloys

    International Nuclear Information System (INIS)

    Hydrogenated amorphous silicon and related materials have been applied to radiation detectors, utilizing their good radiation resistance and the feasibility of making deposits over a large area at low cost. Effects of deposition parameters on various material properties of a-Si:H have been studied to produce a material satisfying the requirements for specific detection application. Thick(-∼50 μm), device quality a-Si:H p-i-n diodes for direct detection of minimum ionizing particles have been prepared with low internal stress by a combination of low temperature growth, He-dilution of silane, and post annealing. The structure of the new film contained voids and tiny crystalline inclusions and was different from the one observed in conventional a-Si:H. Deposition on patterned substrates was attempted as an alternative to controlling deposition parameters to minimize substrate bending and delamination of thick a-Si:H films. Growth on an inversed-pyramid pattern reduced the substrate bending by a factor of 3∼4 for the same thickness film. Thin (0.1 ∼ 0.2 μm) films of a-Si:H and a-SiC:H have been applied to microstrip gas chambers to control gain instabilities due to charges on the substrate. Light sensitivity of the a-Si:H sheet resistance was minimized and the surface resistivity was successfully' controlled in the range of 1012 ∼ 1017 Ω/□ by carbon alloying and boron doping. Performance of the detectors with boron-doped a-Si:C:H layers was comparable to that of electronic-conducting glass. Hydrogen dilution of silane has been explored to improve electrical transport properties of a-Si:H material for high speed photo-detectors and TFT applications

  12. Chemical and Phase Evolution of Amorphous Molybdenum Sulfide Catalysts for Electrochemical Hydrogen Production.

    Science.gov (United States)

    Lee, Sang Chul; Benck, Jesse D; Tsai, Charlie; Park, Joonsuk; Koh, Ai Leen; Abild-Pedersen, Frank; Jaramillo, Thomas F; Sinclair, Robert

    2016-01-26

    Amorphous MoSx is a highly active, earth-abundant catalyst for the electrochemical hydrogen evolution reaction. Previous studies have revealed that this material initially has a composition of MoS3, but after electrochemical activation, the surface is reduced to form an active phase resembling MoS2 in composition and chemical state. However, structural changes in the MoSx catalyst and the mechanism of the activation process remain poorly understood. In this study, we employ transmission electron microscopy (TEM) to image amorphous MoSx catalysts activated under two hydrogen-rich conditions: ex situ in an electrochemical cell and in situ in an environmental TEM. For the first time, we directly observe the formation of crystalline domains in the MoSx catalyst after both activation procedures as well as spatially localized changes in the chemical state detected via electron energy loss spectroscopy. Using density functional theory calculations, we investigate the mechanisms for this phase transformation and find that the presence of hydrogen is critical for enabling the restructuring process. Our results suggest that the surface of the amorphous MoSx catalyst is dynamic: while the initial catalyst activation forms the primary active surface of amorphous MoS2, continued transformation to the crystalline phase during electrochemical operation could contribute to catalyst deactivation. These results have important implications for the application of this highly active electrocatalyst for sustainable H2 generation. PMID:26624225

  13. Hydrogenated amorphous silicon radiation detectors: Material parameters, radiation hardness, charge collection

    International Nuclear Information System (INIS)

    For nearly two decades now hydrogenated amorphous silicon has generated considerable interest for its potential use in various device applications namely, solar cells, electrolithography, large-area electronics etc. The development of efficient and economic solar cells has been on the forefront of this research. This interest in hydrogenated amorphous silicon has been motivated by the fact that amorphous silicon can be deposited over a large area at relatively low cost compared to crystalline silicon. Hydrogenated amorphous silicon, frequently abbreviated as a-Si:H, used in solar-cell applications is a micron or less thick. The basic device structure is a p-i-n diode where the i layer is the active layer for radiation to interact. This is so because intrinsic a-Si:H has superior electrical properties in comparison to doped a-Si:H which serves the purpose of forming a potential barrier on either end of the i layer. The research presented in this dissertation was undertaken to study the properties of a-Si:H for radiation detection applications in physics and medicine

  14. Designing Microporus Carbons for Hydrogen Storage Systems

    Energy Technology Data Exchange (ETDEWEB)

    Alan C. Cooper

    2012-05-02

    An efficient, cost-effective hydrogen storage system is a key enabling technology for the widespread introduction of hydrogen fuel cells to the domestic marketplace. Air Products, an industry leader in hydrogen energy products and systems, recognized this need and responded to the DOE 'Grand Challenge' solicitation (DOE Solicitation DE-PS36-03GO93013) under Category 1 as an industry partner and steering committee member with the National Renewable Energy Laboratory (NREL) in their proposal for a center-of-excellence on Carbon-Based Hydrogen Storage Materials. This center was later renamed the Hydrogen Sorption Center of Excellence (HSCoE). Our proposal, entitled 'Designing Microporous Carbons for Hydrogen Storage Systems,' envisioned a highly synergistic 5-year program with NREL and other national laboratory and university partners.

  15. Pulsed laser deposition of amorphous carbon/silver nanocomposites

    International Nuclear Information System (INIS)

    Metal/amorphous carbon (a-C:M) composite films are emerging as a category of very important engineering materials for surface protection. We implement pulsed laser deposition (PLD) to grow pure a-C and a-C:Ag nanocomposites. Our PLD process is assisted by a static electric field. We investigate the structural features of the a-C:Ag nanocomposites and the bonding configuration of the a-C matrix with respect to the electric field and the composition of the PLD target. For this study we use Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS) and X-ray diffraction (XRD). We show that the Ag mean grain size and the sp2 content of the a-C matrix are increasing with increasing Ag content in the films

  16. Pulsed laser deposition of amorphous carbon/silver nanocomposites

    Science.gov (United States)

    Matenoglou, G.; Evangelakis, G. A.; Kosmidis, C.; Foulias, S.; Papadimitriou, D.; Patsalas, P.

    2007-07-01

    Metal/amorphous carbon (a-C:M) composite films are emerging as a category of very important engineering materials for surface protection. We implement pulsed laser deposition (PLD) to grow pure a-C and a-C:Ag nanocomposites. Our PLD process is assisted by a static electric field. We investigate the structural features of the a-C:Ag nanocomposites and the bonding configuration of the a-C matrix with respect to the electric field and the composition of the PLD target. For this study we use Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS) and X-ray diffraction (XRD). We show that the Ag mean grain size and the sp 2 content of the a-C matrix are increasing with increasing Ag content in the films.

  17. Pulsed laser deposition of amorphous carbon/silver nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Matenoglou, G. [University of Ioannina, Department of Materials Science and Engineering, GR-45110 Ioannina (Greece); Evangelakis, G.A. [University of Ioannina, Department of Physics, GR-45110 Ioannina (Greece); Kosmidis, C. [University of Ioannina, Department of Physics, GR-45110 Ioannina (Greece); Foulias, S. [University of Ioannina, Department of Physics, GR-45110 Ioannina (Greece); Papadimitriou, D. [University of Ioannina, Department of Physics, GR-45110 Ioannina (Greece); Patsalas, P. [University of Ioannina, Department of Materials Science and Engineering, GR-45110 Ioannina (Greece)]. E-mail: ppats@cc.uoi.gr

    2007-07-31

    Metal/amorphous carbon (a-C:M) composite films are emerging as a category of very important engineering materials for surface protection. We implement pulsed laser deposition (PLD) to grow pure a-C and a-C:Ag nanocomposites. Our PLD process is assisted by a static electric field. We investigate the structural features of the a-C:Ag nanocomposites and the bonding configuration of the a-C matrix with respect to the electric field and the composition of the PLD target. For this study we use Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS) and X-ray diffraction (XRD). We show that the Ag mean grain size and the sp{sup 2} content of the a-C matrix are increasing with increasing Ag content in the films.

  18. Presence of Amorphous Carbon Nanoparticles in Food Caramels

    Science.gov (United States)

    Palashuddin, Sk; Jaiswal, Amit; Paul, Anumita; Ghosh, Siddhartha Sankar; Chattopadhyay, Arun

    2012-04-01

    We report the finding of the presence of carbon nanoparticles (CNPs) in different carbohydrate based food caramels, viz. bread, jaggery, sugar caramel, corn flakes and biscuits, where the preparation involves heating of the starting material. The CNPs were amorphous in nature; the particles were spherical having sizes in the range of 4-30 nm, depending upon the source of extraction. The results also indicated that particles formed at higher temperature were smaller than those formed at lower temperature. Excitation tuneable photoluminescence was observed for all the samples with quantum yield (QY) 1.2, 0.55 and 0.63%, for CNPs from bread, jaggery and sugar caramels respectively. The present discovery suggests potential usefulness of CNPs for various biological applications, as the sources of extraction are regular food items, some of which have been consumed by humans for centuries, and thus they can be considered as safe.

  19. Resistance switching at the nanometre scale in amorphous carbon

    International Nuclear Information System (INIS)

    The electrical transport and resistance switching mechanism in amorphous carbon (a-C) is investigated at the nanoscale. The electrical conduction in a-C thin films is shown to be captured well by a Poole-Frenkel transport model that involves nonisolated traps. Moreover, at high electric fields a field-induced threshold switching phenomenon is observed. The following resistance change is attributed to Joule heating and subsequent localized thermal annealing. We demonstrate that the mechanism is mostly due to clustering of the existing sp2 sites within the sp3 matrix. The electrical conduction behaviour, field-induced switching and Joule-heating-induced rearrangement of atomic order resulting in a resistance change are all reminiscent of conventional phase-change memory materials. This suggests the potential of a-C as a similar nonvolatile memory candidate material.

  20. Si-H bond dynamics in hydrogenated amorphous silicon

    Science.gov (United States)

    Scharff, R. Jason; McGrane, Shawn D.

    2007-08-01

    The ultrafast structural dynamics of the Si-H bond in the rigid solvent environment of an amorphous silicon thin film is investigated using two-dimensional infrared four-wave mixing techniques. The two-dimensional infrared (2DIR) vibrational correlation spectrum resolves the homogeneous line shapes ( 4ps waiting times. The Si-H stretching mode anharmonic shift is determined to be 84cm-1 and decreases slightly with vibrational frequency. The 1→2 linewidth increases with vibrational frequency. Frequency dependent vibrational population times measured by transient grating spectroscopy are also reported. The narrow homogeneous line shape, large inhomogeneous broadening, and lack of spectral diffusion reported here present the ideal backdrop for using a 2DIR probe following electronic pumping to measure the transient structural dynamics implicated in the Staebler-Wronski degradation [Appl. Phys. Lett. 31, 292 (1977)] in a-Si:H based solar cells.

  1. Radiative processes of amorphization and hydrogenation in monocrystalline silicon

    CERN Document Server

    Dovbnya, A N; Dyomin, V S

    2001-01-01

    The processes described will form the H-concentration at the required depth of Si semiconductor due spin splitting of Si:H compounds with the intensive electron beams and processes of the photo stimulation of the volume diffusion. This will provide a continuous migration of hydrogen into the bulk material.

  2. Effect of ambient gaseous environment on the properties of amorphous carbon thin films

    International Nuclear Information System (INIS)

    Amorphous carbon films have been deposited by filtered cathodic jet carbon arc technique under different gaseous environments. Scanning electron microscope and atomic force microscope studies have been performed on the deposited films for the surface morphological studies. The morphology of the deposited film changes with the change in gas environment. X-ray photoelectron spectroscopic (XPS) and Raman studies have been carried out on the deposited samples for the evaluation of the chemical bonding of carbon atoms with the ambient gas atoms. The sp3 and sp2 contents have been evaluated from the XPS studies and found to be dependent on the gaseous environment. The film deposited under hydrogen environment has the highest value of the sp3 content (54.6 at.%) whereas the film deposited under helium environment has the lowest value of sp3 content (37 at.%). For the evaluation of the electrical and mechanical properties of the deposited films, the electrical conductivity and nanoindentation measurements have been performed on the deposited films. It has been observed that the film deposited under helium environment has the highest electrical conductivity and the lowest hardness (∼15 GPa) value whereas film deposited under hydrogen environment has the highest hardness (∼21 GPa) and the lowest conductivity.

  3. Low-temperature graphitization of amorphous carbon nanospheres

    Institute of Scientific and Technical Information of China (English)

    Katia Barbera; Leone Frusteri; Giuseppe Italiano; Lorenzo Spadaro; Francesco Frusteri; Siglinda Perathoner; Gabriele Centi

    2014-01-01

    The investigation by SEM/TEM, porosity, and X-ray diffraction measurements of the graphitization process starting from amorphous carbon nanospheres, prepared by glucose carbonization, is re-ported. Aspects studied are the annealing temperature in the 750-1000 °C range, the type of inert carrier gas, and time of treatment in the 2-6 h range. It is investigated how these parameters influ-ence the structural and morphological characteristics of the carbon materials obtained as well as their nanostructure. It is shown that it is possible to maintain after graphitization the round-shaped macro morphology, a high surface area and porosity, and especially a large structural disorder in the graphitic layers stacking, with the presence of rather small ordered domains. These are charac-teristics interesting for various catalytic applications. The key in obtaining these characteristics is the thermal treatment in a flow of N2. It was demonstrated that the use of He rather than N2 does not allow obtaining the same results. The effect is attributed to the presence of traces of oxygen, enough to create the presence of oxygen functional groups on the surface temperatures higher than 750 °C, when graphitization occurs. These oxygen functional groups favor the graphitization pro-cess.

  4. Field emission from amorphous-carbon nanotips on copper

    International Nuclear Information System (INIS)

    Amorphous-carbon (a-C) nanotips were directly grown on copper substrates by microwave plasma-enhanced chemical-vapor deposition. The length of a typical a-C nanotip is ∼250 nm and its tip diameter is ∼25 nm. The in-plane correlation length La, equivalent to the size of the sp2 clusters, is determined to be 1.2 nm through the intensity ratio of the D and G peaks in the Raman spectrum, which is about in the optimum range for field emission. A low turn-on field of 1.6 V/μm at 10 μA/cm2, a threshold field of 3.8 V/μm at 10 mA/cm2, and a high current density of 32.42 mA/cm2 at 4.0 V/μm are achieved. The field emission characteristics of a-C nanotips are close to those of carbon nanotubes, and much better than what has been reported for flat diamond-like carbon or a-C:H coated cathodes. The roles of the sp2 cluster size, electron confinement and conductivity in the field emission of a-C nanotips are discussed

  5. Research Update: Direct conversion of amorphous carbon into diamond at ambient pressures and temperatures in air

    International Nuclear Information System (INIS)

    We report on fundamental discovery of conversion of amorphous carbon into diamond by irradiating amorphous carbon films with nanosecond lasers at room-temperature in air at atmospheric pressure. We can create diamond in the form of nanodiamond (size range <100 nm) and microdiamond (>100 nm). Nanosecond laser pulses are used to melt amorphous diamondlike carbon and create a highly undercooled state, from which various forms of diamond can be formed upon cooling. The quenching from the super undercooled state results in nucleation of nanodiamond. It is found that microdiamonds grow out of highly undercooled state of carbon, with nanodiamond acting as seed crystals

  6. Carbon nanotube materials for hydrogen storage

    Energy Technology Data Exchange (ETDEWEB)

    Dillon, A.C.; Jones, K.M.; Heben, M.J. [National Renewable Energy Lab., Golden, CO (United States)

    1996-10-01

    Hydrogen burns pollution-free and may be produced from renewable energy resources. It is therefore an ideal candidate to replace fossil fuels as an energy carrier. However, the lack of a convenient and cost-effective hydrogen storage system greatly impedes the wide-scale use of hydrogen in both domestic and international markets. Although several hydrogen storage options exist, no approach satisfies all of the efficiency, size, weight, cost and safety requirements for transportation or utility use. A material consisting exclusively of micropores with molecular dimensions could simultaneously meet all of the requirements for transportation use if the interaction energy for hydrogen was sufficiently strong to cause hydrogen adsorption at ambient temperatures. Small diameter ({approx}1 mm) carbon single-wall nanotubes (SWNTs) are elongated micropores of molecular dimensions, and materials composed predominantly of SWNTs may prove to be the ideal adsorbent for ambient temperature storage of hydrogen. Last year the authors reported that hydrogen could be adsorbed on arc-generated soots containing 12{Angstrom} diameter nanotubes at temperatures in excess of 285K. In this past year they have learned that such adsorption does not occur on activated carbon materials, and that the cobalt nanoparticles present in their arc-generated soots are not responsible for the hydrogen which is stable at 285 K. These results indicate that enhanced adsorption forces within the internal cavities of the SWNTs are active in stabilizing hydrogen at elevated temperatures. This enhanced stability could lead to effective hydrogen storage under ambient temperature conditions. In the past year the authors have also demonstrated that single-wall carbon nanotubes in arc-generated soots may be selectively opened by oxidation in H{sub 2}O resulting in improved hydrogen adsorption, and they have estimated experimentally that the amount of hydrogen stored is {approximately}10% of the nanotube weight.

  7. Fabrication And Determination Of Coefficient Absorption Of Hydrogenated Amorphous Silicon By Direct Evaporation Method

    International Nuclear Information System (INIS)

    Fabrication and characterization of hydrogenated amorphous silicon produced by direct evaporation method have been done. The experiment was carried out at pressure conditions of 2 x 10-5 torr, RF frequency of 13.56 MHz, hydrogen gas flow of 0,8 1/minute, electrode distance of 2.48 cm. voltage electrode of 700 volt and evaporation time 1.45 minute. Using UV-VIS spectrophotometer, it is found that at wavelength of 359 nm, the absorbance degree of material that was by direct hydrogenated method was 0,886. This means that more hydrogen are absorbed by direct method While, if the hydrogenation is carried out by means of indirect method, the degree of absorbance at the wavelength of 359 nm is 0,103. From this result, it can be concluded that the direct methods is better than indirect method

  8. Hot wire deposited hydrogenated amorphous silicon solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Mahan, A.H.; Iwaniczko, E.; Nelson, B.P.; Reedy, R.C. Jr.; Crandall, R.S. [National Renewable Energy Lab., Golden, CO (United States)

    1996-05-01

    This paper details the results of a study in which low H content, high deposition rate hot wire (HW) deposited amorphous silicon (a-Si:H) has been incorporated into a substrate solar cell. The authors find that the treatment of the top surface of the HW i layer while it is being cooled from its high deposition temperature is crucial to device performance. They present data concerning these surface treatments, and correlate these treatments with Schottky device performance. The authors also present first generation HW n-i-p solar cell efficiency data, where a glow discharge (GD) {mu}c-Si(p) layer was added to complete the partial devices. No light trapping layer was used to increase the device Jsc. Their preliminary investigations have yielded efficiencies of up to 6.8% for a cell with a 4000 {Angstrom} thick HW i-layer, which degrade less than 10% after a 900 hour light soak. The authors suggest avenues for further improvement of their devices.

  9. Sintering furnace with hydrogen carbon dioxide atmosphere

    International Nuclear Information System (INIS)

    A heated furnace for sintering structures of uranium oxide containing composition being introduced to the furnace is described. The furnace receives an atmosphere comprising a mixture of hydrogen and carbon dioxide as initially introduced to the furnace, and this mixture reacts in the furnace to give the presence of water vapor and carbon monoxide

  10. Study of SEY degradation of amorphous carbon coatings

    CERN Document Server

    Bundaleski, N; Santos, A; Teodoro, O M N D; Silva, A G

    2013-01-01

    Deposition of low secondary electron yield (SEY) carbon coatings by magnetron sputtering onto the inner walls of the accelerator seems to be the most promising solution for suppressing the electron cloud problem. However, these coatings change their electron emission properties during long term exposure to air. The ageing process of carbon coated samples with initial SEY of about 0.9 received from CERN is studied as a function of exposure to different environments. It is shown that samples having the same initial SEY may age with different rates. The SEY increase can be correlated with the surface concentration of oxygen. Annealing of samples in air at 100-200 {\\deg}C reduces the ageing rate and even recovers previously degraded samples. The result of annealing is reduction of the hydrogen content in the coatings by triggering its surface segregation followed by desorption.

  11. The Interplay of Quantum Confinement and Hydrogenation in Amorphous Silicon Quantum Dots

    OpenAIRE

    Askari, Sadegh; Svrcek, Vladmir; Maguire, Paul; Mariotti, Davide

    2015-01-01

    Hydrogenation in amorphous silicon quantum dots (QDs) has a dramatic impact on the corresponding optical properties and band energy structure, leading to a quantum‐confined composite material with unique characteristics. The synthesis of a‐Si:H QDs is demonstrated with an atmospheric‐pressure plasma process, which allows for accurate control of a highly chemically reactive non‐equilibrium environment with temperatures well below the crystallization temperature of Si QDs.

  12. The Interplay of Quantum Confinement and Hydrogenation in Amorphous Silicon Quantum Dots.

    Science.gov (United States)

    Askari, Sadegh; Svrcek, Vladmir; Maguire, Paul; Mariotti, Davide

    2015-12-22

    Hydrogenation in amorphous silicon quantum dots (QDs) has a dramatic impact on the corresponding optical properties and band energy structure, leading to a quantum-confined composite material with unique characteristics. The synthesis of a-Si:H QDs is demonstrated with an atmospheric-pressure plasma process, which allows for accurate control of a highly chemically reactive non-equilibrium environment with temperatures well below the crystallization temperature of Si QDs. PMID:26523743

  13. The boron-tailing myth in hydrogenated amorphous silicon solar cells

    OpenAIRE

    Stuckelberger, M.; Park, B.-S.; Bugnon, G.; Despeisse, M; Schüttauf, J.-W.; Haug, F.-J.; Ballif, C.

    2015-01-01

    The boron-tailing effect in hydrogenated amorphous silicon (a-Si:H) solar cells describes the reduced charge collection specifically in the blue part of the spectrum for absorber layers deposited above a critical temperature. This effect limits the device performance of state-of-the art solar cells: For enhanced current density (reduced bandgap), the deposition temperature should be as high as possible, but boron tailing gets detrimental above 200°C. To investigate this limitation and to show...

  14. Nonlinear properties of and nonlinear processing in hydrogenated amorphous silicon waveguides

    OpenAIRE

    Kuyken, B.; Ji, H.; Clemmen, S.; Selvaraja, S. K.; Hu, H; Pu, M; Galili, M; Jeppesen, P; Morthier, G; Massar, S.; Oxenløwe, L. K.; Roelkens, G.; Baets, R.

    2011-01-01

    We propose hydrogenated amorphous silicon nanowires as a platform for nonlinear optics in the telecommunication wavelength range. Extraction of the nonlinear parameter of these photonic nanowires reveals a figure of merit larger than 2. It is observed that the nonlinear optical properties of these waveguides degrade with time, but that this degradation can be reversed by annealing the samples. A four wave mixing conversion efficiency of + 12 dB is demonstrated in a 320 Gbit/s serial optical w...

  15. THE ELECTRONIC STRUCTURE OF A MODEL DEFECT IN HYDROGENATED AMORPHOUS SILICON

    OpenAIRE

    DiVincenzo, D.; Bernholc, J.; Brodsky, M.

    1981-01-01

    We calculate the electronic properties of a model defect for hydrogen in hydrogenated amorphous Si. Our model is a vacancy in crystal Si with four H's satisfying the dangling bonds. Using a Green's function technique, we find the change in the density of states caused by the defect, as well as the local density of states for the Si-H bond and surrounding bonds. From several approaches, we extract information on band edge localization. Each approach gives a mobility edge of order tenths of an ...

  16. Hydrogen effect on properties of iron and cobalt base amorphous alloys

    International Nuclear Information System (INIS)

    Stress relaxation studies were carried out for amorphous alloys 71KNSR (AS-1), 82k3KhSR (AS-2) and Fe78Nb3.5Cu1Si13.5 (AS-3) in their annealing and hydrogenation. Reversible change of elastic properties on hydrogenation is revealed. The restoration of elastic properties is observed in the process of holding at the temperature of 295 K. It is shown that elastic properties vary synchronously with electric conductivity and magnetic susceptibility. On the basis of electric and magnetic variables measurements as well as X-ray diffraction studies possible reasons for phenomena observed are discussed

  17. In situ probing of surface hydrides on hydrogenated amorphous silicon using attenuated total reflection infrared spectroscopy

    CERN Document Server

    Kessels, W M M; Sanden, M C M; Aydil, E S

    2002-01-01

    An in situ method based on attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) is presented for detecting surface silicon hydrides on plasma deposited hydrogenated amorphous silicon (a-Si:H) films and for determining their surface concentrations. Surface silicon hydrides are desorbed by exposing the a-Si:H films to low energy ions from a low density Ar plasma and by comparing the infrared spectrum before and after this low energy ion bombardment, the absorptions by surface hydrides can sensitively be separated from absorptions by bulk hydrides incorporated into the film. An experimental comparison with other methods that utilize isotope exchange of the surface hydrogen with deuterium showed good agreement and the advantages and disadvantages of the different methods are discussed. Furthermore, the determination of the composition of the surface hydrogen bondings on the basis of the literature data on hydrogenated crystalline silicon surfaces is presented, and quantification of the h...

  18. Carbon: Hydrogen carrier or disappearing skeleton?

    International Nuclear Information System (INIS)

    The use of liquid hydrocarbons as energy carriers implies the use of carbon as a carrier for hydrogen to facilitate hydrogen transport and storage. The current trend for liquid energy carriers used in the transport sector is to maximize the load of hydrogen on the carbon carrier. The recently developed Shell Middle Distillate Hydrogenation process for the manufacture of high quality diesel from aromatic refinery streams fits this picture. In the future, the hydrogen required to raise the product H/C ratio will be increasingly produced via gasification of large amounts of heavy residues. In the light of the strong preference towards using liquid fuels in the transport sector, the Shell Middle Distillate Synthesis process to convert natural gas into diesel of very high quality is discussed. Finally, a few comments on the use of hydrogen without a carbon carrier are made. Long lead times and the likelihood of producing the 'first' hydrogen from fossil fuel are highlighted. 13 figs., 6 tabs., 5 refs

  19. Optical Waveform Sampling of a 320 Gbit/s Serial Data Signal using a Hydrogenated Amorphous Silicon Waveguide

    DEFF Research Database (Denmark)

    Ji, Hua; Hu, Hao; Pu, Minhao;

    2011-01-01

    We propose using a hydrogenated amorphous silicon waveguide for ultra-high-speed serial data waveform sampling. 320 Gbit/s serial optical data sampling is experimentally demonstrated with +12 dB intrinsic four wave mixing conversion efficiency.......We propose using a hydrogenated amorphous silicon waveguide for ultra-high-speed serial data waveform sampling. 320 Gbit/s serial optical data sampling is experimentally demonstrated with +12 dB intrinsic four wave mixing conversion efficiency....

  20. Microstructure from joint analysis of experimental data and ab initio interactions: Hydrogenated amorphous silicon

    Energy Technology Data Exchange (ETDEWEB)

    Biswas, Parthapratim, E-mail: Partha.Biswas@usm.edu [Department of Physics and Astronomy, The University of Southern Mississippi, Hattiesburg, MS 39406 (United States); Department of Physics and Astronomy, Condensed Matter and Surface Science Program, Ohio University, Ohio 45701 (United States); Drabold, D. A., E-mail: drabold@ohio.edu [Department of Physics and Astronomy, Condensed Matter and Surface Science Program, Ohio University, Ohio 45701 (United States); Atta-Fynn, Raymond, E-mail: attafynn@uta.edu [Department of Physics, The University of Texas, Arlington, Texas 76019 (United States)

    2014-12-28

    A study of the formation of voids and molecular hydrogen in hydrogenated amorphous silicon is presented based upon a hybrid approach that involves inversion of experimental nuclear magnetic resonance data in conjunction with ab initio total-energy relaxations in an augmented solution space. The novelty of this approach is that the voids and molecular hydrogen appear naturally in the model networks unlike conventional approaches, where voids are created artificially by removing silicon atoms from the networks. Two representative models with 16 and 18 at. % of hydrogen are studied in this work. The result shows that the microstructure of the a-Si:H network consists of several microvoids and few molecular hydrogen for concentration above 15 at. % H. The microvoids are highly irregular in shape and size, and have a linear dimension of 5–7 Å. The internal surface of a microvoid is found to be decorated with 4–9 hydrogen atoms in the form of monohydride Si–H configurations as observed in nuclear magnetic resonance experiments. The microstructure consists of (0.9–1.4)% hydrogen molecules of total hydrogen in the networks. These observations are consistent with the outcome of infrared spectroscopy, nuclear magnetic resonance, and calorimetry experiments.

  1. Effect of radio-frequency bias voltage on the optical and structural properties of hydrogenated amorphous silicon carbide

    International Nuclear Information System (INIS)

    Hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films have been deposited using the electron cyclotron resonance chemical vapor deposition process under varying negative rf-bias voltage at the substrate. The optical and structural properties of these films are characterized using Rutherford backscattering spectroscopy, transmittance/reflectance spectrophotometry, photothermal deflection spectroscopy, Fourier transform infrared absorption, Raman scattering, and room temperature photoluminescence (PL). These films deposited using a gas mixture of silane, methane, and hydrogen at a constant gas flow ratio showed a slight increase in the carbon fraction x, but very obvious structural transformation, at increasing rf induced bias voltage from -20 to -120 V. Near stoichiometric a-Si1-xCx:H films with a carbon fraction x of almost 0.5 are achieved at low bias voltage range from -20 to -60 V. Visible PL with relatively low efficiency can be observed from such films at room temperature. For larger bias voltages from -80 to -120 V, slightly C-rich a-Si1-xCx:H films (x>0.5) with larger optical gaps are obtained. These films have relatively higher PL efficiency, and the relative quantum efficiency was also found to depend strongly on the optical gap. Structurally, it was found that there is an increase in the hydrogen content and carbon sp2 bonding in the films at larger bias voltages. The latter leads to an increase in the disorder in the films. The linear relationship observed between the Urbach energy E0 and B factor in the Tauc equation suggests that the local defects related to microstructural disorder resulting from alloying with carbon dominate the overall defect structure of the films. Substrate biasing is noted to be crucial for the formation of Si - C bonds, as deduced from the Raman scattering results. [copyright] 2001 American Institute of Physics

  2. Controlled epitaxial graphene growth within removable amorphous carbon corrals

    Science.gov (United States)

    Palmer, James; Kunc, Jan; Hu, Yike; Hankinson, John; Guo, Zelei; Berger, Claire; de Heer, Walt A.

    2014-07-01

    We address the question of control of the silicon carbide (SiC) steps and terraces under epitaxial graphene on SiC and demonstrate amorphous carbon (aC) corrals as an ideal method to pin SiC surface steps. aC is compatible with graphene growth, structurally stable at high temperatures, and can be removed after graphene growth. For this, aC is first evaporated and patterned on SiC, then annealed in the graphene growth furnace. There at temperatures above 1200 °C, mobile SiC steps accumulate at the aC corral that provide effective step flow barriers. Aligned step free regions are thereby formed for subsequent graphene growth at temperatures above 1330 °C. Atomic force microscopy imaging supports the formation of step-free terraces on SiC with the step morphology aligned to the aC corrals. Raman spectroscopy indicates the presence of good graphene sheets on the step-free terraces.

  3. Fabrication of hydrogenated amorphous silicon carbide films by decomposition of hexamethyldisilane with microwave discharge flow of Ar

    Science.gov (United States)

    Ito, Haruhiko; Kumakura, Motoki; Suzuki, Tsuneo; Niibe, Masahito; Kanda, Kazuhiro; Saitoh, Hidetoshi

    2016-06-01

    Hydrogenated amorphous silicon carbide films have been fabricated by the decomposition of hexamethyldisilane with a microwave discharge flow of Ar. Mechanically hard films were obtained by applying radio-frequency (RF) bias voltages to the substrate. The atomic compositions of the films were analyzed by a combination of Rutherford backscattering and elastic recoil detection, X-ray photoelectron spectroscopy (XPS), and glow discharge optical emission spectroscopy. The chemical structure was analyzed by carbon-K near-edge X-ray absorption fine structure spectroscopy, high-resolution XPS, and Fourier transform infrared absorption spectroscopy. The structural changes upon the application of RF bias were investigated, and the concentration of O atoms near the film surface was found to play a key role in the mechanical hardness of the present films.

  4. Amorphous Alloy Membranes Prepared by Melt-Spin methods for Long-Term use in Hydrogen Separation Applications

    Energy Technology Data Exchange (ETDEWEB)

    Chandra, Dhanesh; Kim, Sang-Mun; Adibhatla, Anasuya; Dolan, Michael; Paglieri, Steve; Flanagan, Ted; Chien, Wen-Ming; Talekar, Anjali; Wermer, Joseph

    2013-02-28

    Amorphous Ni-based alloy membranes show great promise as inexpensive, hydrogenselective membrane materials. In this study, we developed membranes based on nonprecious Ni-Nb-Zr alloys by adjusting the alloying content and using additives. Several studies on crystallization of the amorphous ribbons, in-situ x-ray diffraction, SEM and TEM, hydrogen permeation, hydrogen solubility, hydrogen deuterium exchange, and electrochemical studies were conducted. An important part of the study was to completely eliminate Palladium coatings of the NiNbZr alloys by hydrogen heattreatment. The amorphous alloy (Ni0.6Nb0.4)80Zr20 membrane appears to be the best with high hydrogen permeability and good thermal stability.

  5. Micromachining of large area amorphous carbon membranes prepared by filtered cathodic vacuum arc technique

    Science.gov (United States)

    Liujiang, Yu; Tay, B. K.; Sheeja, D.; Fu, Y. Q.; Miao, J. M.

    2004-02-01

    Currently, there is a strong drive to make micro-electro-mechanical system (MEMS) devices from higher performance materials such as diamond-like carbon or amorphous carbon (a-C) films, due to their excellent tribological properties, low-stiction (hydrophobic) surfaces, chemical inertness and high elastic modulus, compared to that of Si. The hydrogen free a-C films prepared, by Nanyang Technological University's (NTUs) patented filtered cathodic vacuum arc (FCVA) technique, at 100 eV exhibits high fraction of tetrahedral (sp 3 bonded) carbon atoms. These films exhibit relatively high hardness, stiffness and wear resistance in addition to low friction and stiction behaviour. However, the primary problem lies in the large intrinsic compressive stress induced during the deposition process. By making use of high substrate pulse bias, we have successfully produced low stress, thick a-C films. The films were then characterised using different equipments to evaluate the stress, microstructure and morphological roughness. Large area a-C membranes, of 2 mm×2 mm in size, have also been fabricated using the low stress, thick film deposited by the above method.

  6. Micromachining of large area amorphous carbon membranes prepared by filtered cathodic vacuum arc technique

    Energy Technology Data Exchange (ETDEWEB)

    Liujiang, Yu; Tay, B.K.; Sheeja, D.; Fu, Y.Q.; Miao, J.M

    2004-02-29

    Currently, there is a strong drive to make micro-electro-mechanical system (MEMS) devices from higher performance materials such as diamond-like carbon or amorphous carbon (a-C) films, due to their excellent tribological properties, low-stiction (hydrophobic) surfaces, chemical inertness and high elastic modulus, compared to that of Si. The hydrogen free a-C films prepared, by Nanyang Technological University's (NTUs) patented filtered cathodic vacuum arc (FCVA) technique, at 100 eV exhibits high fraction of tetrahedral (sp{sup 3} bonded) carbon atoms. These films exhibit relatively high hardness, stiffness and wear resistance in addition to low friction and stiction behaviour. However, the primary problem lies in the large intrinsic compressive stress induced during the deposition process. By making use of high substrate pulse bias, we have successfully produced low stress, thick a-C films. The films were then characterised using different equipments to evaluate the stress, microstructure and morphological roughness. Large area a-C membranes, of 2 mmx2 mm in size, have also been fabricated using the low stress, thick film deposited by the above method.

  7. Femtosecond laser induced crystallization of hydrogenated amorphous silicon for photovoltaic applications

    International Nuclear Information System (INIS)

    Femtosecond laser assisted crystallization is used to produce nanocrystalline silicon from hydrogenated amorphous silicon. Changes in structural, optical, electrical and photoelectric properties of laser modified amorphous silicon were investigated. Laser treated films were characterized using atomic force microscopy, Raman spectroscopy, constant photocurrent method and current measurements. Crystalline volume fraction as well as conductivity of laser irradiated films increased with the applied laser fluence, while hydrogen concentration in the films was found to decrease with the fluence. Spectral dependences of absorption coefficient, measured by constant photocurrent method, are discussed in terms of hydrogen out-effusion and additional defect state formation in silicon films during the laser treatment. - Highlights: • Structural, optical and electrical properties of laser modified a-Si:H were studied. • Volume fraction of Si nanocrystals in a-Si:H increased with applied laser fluence. • Laser modification is accompanied by hydrogen effusion from a-Si:H film. • Laser modification of a-Si:H leads to increase of dangling bond concentration. • Conductivity of laser modified a-Si:H increases by about 6 orders of magnitude

  8. Characteristics of Disorder and Defect in Hydrogenated Amorphous Silicon Nitride Thin Films Containing Silicon Nanograins

    Institute of Scientific and Technical Information of China (English)

    DING Wen-ge; YU Wei; ZHANG Jiang-yong; HAN Li; FU Guang-sheng

    2006-01-01

    The hydrogenated amorphous silicon nitride (SiNx) thin films embedded with nano-structural silicon were prepared and the microstructures at the interface of silicon nano-grains/SiNx were identified by the optical absorption and Raman scattering measurements. Characterized by the exponential tail of optical absorption and the band-width of the Raman scattering TO mode, the disorder in the interface region increases with the gas flow ratio increasing. Besides, as reflected by the sub-gap absorption coefficients, the density of interface defect states decreases, which can be attributed to the structural mismatch in the interface region and also the changes of hydrogen content in the deposited films. Additional annealing treatment results in a significant increase of defects and degree of disorder, for which the hydrogen out-diffusion in the annealing process would be responsible.

  9. Analysis of IV characteristics of solar cells made of hydrogenated amorphous, polymorphous and microcrystalline silicon

    International Nuclear Information System (INIS)

    The IV characteristics of pin solar cells made of amorphous, polymorphous and microcrystalline silicon were investigated. The temperature dependence was measured in the temperature range between 150 K and 395 K. This range covers the most terrestrial applications condition. Using simplex procedure, the IV parameter of the cells were deduce using line fitting. It has been shown that polymorphous silicon shows electrical properties that are close to properties of microcrystalline silicon but as it is well known, polymorphous silicon shows higher absorption similar to amorphous silicon. The polymorphous silicon solar cells showed higher efficiencies, lower shunting and higher filling factors. In the above mentioned temperature range, polymorphous silicon is the better material for the manufacturing of thin film hydrogenated silicon pin solar cells. More investigations concerning the structural properties are necessary to make stronger conclusions in regards to the stability of the material, what we hope to do in the future. (author)

  10. Superconductivity and unusual magnetic behavior in amorphous carbon

    Science.gov (United States)

    Felner, Israel

    2014-03-01

    Traces of superconductivity (SC) at elevated temperatures (up to 65 K) were observed by magnetic measurements in three different inhomogeneous sulfur doped amorphous carbon (a-C) systems: (a) in commercial and (b) synthesized powders and (c) in a-C thin films. (a) Studies performed on a commercial (a-C) powder, which contains 0.21% sulfur, revealed traces of non-percolated superconducting phases below T c = 65 K. The SC volume fraction is enhanced by the sulfur doping. (b) The a-C powder obtained by pyrolytic decomposition of sucrose did not show any sign of SC above 5 K. This powder was mixed with sulfur and synthesized at 400 °C (a-CS). The inhomogeneous products obtained show traces of SC phases at T c = 17 and 42 K. (c) Non-superconducting composite a-C-W thin films were grown by electron-beam induced deposition. SC emerged at T c = 34.4 K only after heat treatment with sulfur. Other parts of the pyrolytic a-CS powder show unusual magnetic features. (i) Pronounced irreversible peaks around 55-75 K appear in the first zero-field-cooled (ZFC) sweep only. Their origin is not known. (ii) Unexpectedly, these peaks are totally suppressed in the second ZFC runs measured a few minutes later. (iii) Around the peak position the field-cooled (FC) curves cross the ZFC plots (ZFC > FC). These peculiar magnetic observations are also ascribed to an a-CS powder prepared from the commercial a-C powder and are connected to each other. All SC and magnetic phenomena observed are intrinsic properties of the sulfur doped a-C materials. It is proposed that the a-CS systems behave similarly to well-known high T c curates and/or pnictides in which SC emerges from magnetic states.

  11. Superconductivity and unusual magnetic behavior in amorphous carbon

    International Nuclear Information System (INIS)

    Traces of superconductivity (SC) at elevated temperatures (up to 65 K) were observed by magnetic measurements in three different inhomogeneous sulfur doped amorphous carbon (a-C) systems: (a) in commercial and (b) synthesized powders and (c) in a-C thin films. (a) Studies performed on a commercial (a-C) powder, which contains 0.21% sulfur, revealed traces of non-percolated superconducting phases below T c = 65 K. The SC volume fraction is enhanced by the sulfur doping. (b) The a-C powder obtained by pyrolytic decomposition of sucrose did not show any sign of SC above 5 K. This powder was mixed with sulfur and synthesized at 400 °C (a-CS). The inhomogeneous products obtained show traces of SC phases at T c = 17 and 42 K. (c) Non-superconducting composite a-C-W thin films were grown by electron-beam induced deposition. SC emerged at T c = 34.4 K only after heat treatment with sulfur. Other parts of the pyrolytic a-CS powder show unusual magnetic features. (i) Pronounced irreversible peaks around 55–75 K appear in the first zero-field-cooled (ZFC) sweep only. Their origin is not known. (ii) Unexpectedly, these peaks are totally suppressed in the second ZFC runs measured a few minutes later. (iii) Around the peak position the field-cooled (FC) curves cross the ZFC plots (ZFC > FC). These peculiar magnetic observations are also ascribed to an a-CS powder prepared from the commercial a-C powder and are connected to each other. All SC and magnetic phenomena observed are intrinsic properties of the sulfur doped a-C materials. It is proposed that the a-CS systems behave similarly to well-known high T c curates and/or pnictides in which SC emerges from magnetic states. (papers)

  12. Effect of hydrogen on dynamic charge transport in amorphous oxide thin film transistors

    Science.gov (United States)

    Kim, Taeho; Nam, Yunyong; Hur, Ji-Hyun; Park, Sang-Hee Ko; Jeon, Sanghun

    2016-08-01

    Hydrogen in zinc oxide based semiconductors functions as a donor or a defect de-activator depending on its concentration, greatly affecting the device characteristics of oxide thin-film transistors (TFTs). Thus, controlling the hydrogen concentration in oxide semiconductors is very important for achieving high mobility and minimizing device instability. In this study, we investigated the charge transport dynamics of the amorphous semiconductor InGaZnO at various hydrogen concentrations as a function of the deposition temperature of the gate insulator. To examine the nature of dynamic charge trapping, we employed short-pulse current‑voltage and transient current‑time measurements. Among various examined oxide devices, that with a high hydrogen concentration exhibits the best performance characteristics, such as high saturation mobility (10.9 cm2 v‑1 s‑1), low subthreshold slope (0.12 V/dec), and negligible hysteresis, which stem from low defect densities and negligible transient charge trapping. Our finding indicates that hydrogen atoms effectively passivate the defects in subgap states of the bulk semiconductor, minimizing the mobility degradation and threshold voltage instability. This study indicates that hydrogen plays a useful role in TFTs by improving the device performance and stability.

  13. Effect of hydrogen on dynamic charge transport in amorphous oxide thin film transistors.

    Science.gov (United States)

    Kim, Taeho; Nam, Yunyong; Hur, Ji-Hyun; Park, Sang-Hee Ko; Jeon, Sanghun

    2016-08-12

    Hydrogen in zinc oxide based semiconductors functions as a donor or a defect de-activator depending on its concentration, greatly affecting the device characteristics of oxide thin-film transistors (TFTs). Thus, controlling the hydrogen concentration in oxide semiconductors is very important for achieving high mobility and minimizing device instability. In this study, we investigated the charge transport dynamics of the amorphous semiconductor InGaZnO at various hydrogen concentrations as a function of the deposition temperature of the gate insulator. To examine the nature of dynamic charge trapping, we employed short-pulse current-voltage and transient current-time measurements. Among various examined oxide devices, that with a high hydrogen concentration exhibits the best performance characteristics, such as high saturation mobility (10.9 cm(2) v(-1) s(-1)), low subthreshold slope (0.12 V/dec), and negligible hysteresis, which stem from low defect densities and negligible transient charge trapping. Our finding indicates that hydrogen atoms effectively passivate the defects in subgap states of the bulk semiconductor, minimizing the mobility degradation and threshold voltage instability. This study indicates that hydrogen plays a useful role in TFTs by improving the device performance and stability. PMID:27363543

  14. Immobilized Ruthenium Catalyst for Carbon Dioxide Hydrogenation

    Institute of Scientific and Technical Information of China (English)

    Ying Min YU; Jin Hua FEI; Yi Ping ZHANG; Xiao Ming ZHENG

    2006-01-01

    Three kinds of cross linked polystyrene resin (PS) supported ruthenium complexes were developed as catalysts for the synthesis of formic acid from carbon dioxide hydrogenation. Many factors, such as the functionalized supports, solvents and ligands, could influence their activities and reuse performances greatly. These immobilized catalysts also offer the industrial advantages such as easy separation.

  15. Hydrogenation catalyst based on modified carbon nanofibers

    International Nuclear Information System (INIS)

    The aim of this work was to study the palladium-carboxylated carbon nanofibers (CNF) as a catalyst for the hydrogenation of nitrobenzene model reaction. It is shown that the efficiency of the catalyst obtained more than 6 times higher than that of the industrial counterpart (Pd/C).

  16. Roughening transition in nanoporous hydrogenated amorphous germanium: Roughness correlation to film stress

    Science.gov (United States)

    Carroll, M. S.; Verley, J. C.; Sheng, J. J.; Banks, J.

    2007-03-01

    Hydrogenated amorphous germanium (a-Ge:H) is a material of interest for optoelectronic applications such as solar cells and radiation detectors because of the material's potential to extend the wavelength sensitivity of hydrogenated amorphous silicon (a-Si:H). An increase in porosity is observed in amorphous germanium compared to a-Si :H, and this increase in porosity has been correlated with a degradation of the electrical performance. Improved understanding of the mechanisms of porous formation in a-Ge :H films is therefore desirable in order to better control it. In this paper we describe a correlation between film stress and surface roughness, which evolves with increasing thickness of a-Ge :H. A roughening transition from planar two-dimensional growth to three-dimensional growth at a critical thickness less than 800Å results in a network of needlelike nanotrench cavities which stretch from the transition thickness to the surface in films up to 4000Å thick. Surface roughness measurements by atomic force microscope and transmission electron microscopy indicate that the transition is abrupt and that the roughness increases linearly after the transition thickness. The roughening transition thickness is, furthermore, found to correlate with the maxima of the integrated compressive stress. The compressive stress is reduced after this transition thickness due to the incorporation of nanovoids into the film that introduce tensile stress as the islands coalesce together. The roughening transition behavior is similar to that found in a general class of Volmer-Weber mode thin film deposition (e.g., Cu, Ag, and nonhydrogenated amorphous silicon), which offers additional insight into the underlying mechanisms of the stress and roughening in these a-Ge :H films. The suppression of the roughening transition by changing the kinetics of the deposition rates (e.g., slowing the deposition rate with a weak sputtering bias) is also observed and discussed.

  17. Hydrogen storage in carbon derived from solid endosperm of coconut

    OpenAIRE

    Dixit, Viney; Bhatnagar, Ashish; Shahi, R. R.; Yadav, T. P.; O.N. Srivastava

    2014-01-01

    Carbons are being widely investigated as hydrogen storage material owing to their light weight, fast hydrogen adsorption kinetics and cost effectiveness. However, these materials suffer from low hydrogen storage capacity, particularly at room temperature. The aim of the present study is to develop carbon-based material from natural bio-precursor which shows at least moderate hydrogen storage at room temperature. For this purpose, hydrogenation characteristics of carbon derived from solid endo...

  18. Solar hydrogen hybrid system with carbon storage

    International Nuclear Information System (INIS)

    A complete solar hydrogen hybrid system has been developed to convert, store and use energy from renewable energy sources. The theoretical model has been implemented in a dynamic model-based software environment and applied to real data to simulate its functioning over a one-year period. Results are used to study system design and performance. A photovoltaic sub-system directly drives a residential load and, if a surplus of energy is available, an electrolyzer to produce hydrogen which is stored in a cluster of nitrogen-cooled tanks filled with AX-21 activated carbons. When the power converted from the sun is not sufficient to cover load needs, hydrogen is desorbed from activated carbon tanks and sent to the fuel-cell sub-system so to obtain electrical energy. A set of sub-systems (bus-bar, buck- and boost-converters, inverter, control circuits), handle the electrical power according to a Programmable Logic Control unit so that the load can be driven with adequate Quality of Service. Hydrogen storage is achieved through physisorption (weak van der Waals interactions) between carbon atoms and hydrogen molecules occurring at low temperature (77 K) in carbon porous solids at relatively low pressures. Storage modeling has been developed using a Langmuir-Freundlich 1st type isotherm and experimental data available in literature. Physisorption storage provides safer operations along with good gravimetric (10.8% at 6 MPa) and volumetric (32.5 g/l at 6 MPa) storage capacities at costs that can be comparable to, or smaller than, ordinary storage techniques (compression or liquefaction). Several test runs have been performed on residential user data-sets: the system is capable of providing grid independence and can be designed to yield a surplus production of hydrogen which can be used to recharge electric car batteries or fill tanks for non-stationary uses. (author)

  19. Single walled carbon nanotube network—Tetrahedral amorphous carbon composite film

    International Nuclear Information System (INIS)

    Single walled carbon nanotube network (SWCNTN) was coated by tetrahedral amorphous carbon (ta-C) using a pulsed Filtered Cathodic Vacuum Arc system to form a SWCNTN—ta-C composite film. The effects of SWCNTN areal coverage density and ta-C coating thickness on the composite film properties were investigated. X-Ray photoelectron spectroscopy measurements prove the presence of high quality sp3 bonded ta-C coating on the SWCNTN. Raman spectroscopy suggests that the single wall carbon nanotubes (SWCNTs) forming the network survived encapsulation in the ta-C coating. Nano-mechanical testing suggests that the ta-C coated SWCNTN has superior wear performance compared to uncoated SWCNTN

  20. Single walled carbon nanotube network—Tetrahedral amorphous carbon composite film

    Energy Technology Data Exchange (ETDEWEB)

    Iyer, Ajai, E-mail: ajai.iyer@aalto.fi; Liu, Xuwen; Koskinen, Jari [Department of Materials Science and Engineering, School of Chemical Technology, Aalto University, POB 16200, 00076 Espoo (Finland); Kaskela, Antti; Kauppinen, Esko I. [NanoMaterials Group, Department of Applied Physics, School of Science, Aalto University, POB 15100, 00076 Espoo (Finland); Johansson, Leena-Sisko [Department of Forest Products Technology, School of Chemical Technology, Aalto University, POB 16400, 00076 Espoo (Finland)

    2015-06-14

    Single walled carbon nanotube network (SWCNTN) was coated by tetrahedral amorphous carbon (ta-C) using a pulsed Filtered Cathodic Vacuum Arc system to form a SWCNTN—ta-C composite film. The effects of SWCNTN areal coverage density and ta-C coating thickness on the composite film properties were investigated. X-Ray photoelectron spectroscopy measurements prove the presence of high quality sp{sup 3} bonded ta-C coating on the SWCNTN. Raman spectroscopy suggests that the single wall carbon nanotubes (SWCNTs) forming the network survived encapsulation in the ta-C coating. Nano-mechanical testing suggests that the ta-C coated SWCNTN has superior wear performance compared to uncoated SWCNTN.

  1. Skeletal Amorphous Nickel Based Alloy Catalysts and Magnetically Stabilized Bed Hydrogenation Technology

    Institute of Scientific and Technical Information of China (English)

    Min Enze

    2004-01-01

    Looking toward 21 century, smaller, cleaner and more energy-efficient technology will be an important trend in the development of chemical industry. In light of the new process requirements,a number of technology breakthroughs have occurred. One of these discoveries, the magnetically stabilized bed (MSB), has been proven a powerful process for intensification. Since its initial research in the late 1980's at Research Institute of Petroleum Processing (RIPP), the MSB technology and related catalytic material have matured rapidly through an intensive research and engineering program, primarily focused on its scaling-up.In this paper, we report the discovery of a novel skeletal amorphous nickel-based alloy and its use in magnetically stabilized bed (MSB). Amorphous alloys are new kinds of catalytic materials with short-range order but long-range disorder structure. In comparison with Raney Ni, the skeletal amorphous nickel-based alloy has an increasingly higher activity in the hydrogenation of reactive groups and compounds including nitro, nitrile, olefin, acetylene, aromatics, etc. Up to now, the amorphous nickel based alloy catalysts, SRNA series catalyst, one with high Ni ratio have been commercially manufactured more than four year. The new SRNA catalyst has been successfully implemented for hydrogenation applications in slurry reactor at Balin Petrochemical, SINOPEC.SRNA catalyst with further improvement in catalytic activity and stability raise its relative stability to 2~4 times of that of conventional catalyst. In the course of the long-cycle operation of SRNA-4 the excellent catalyst activity and stability can bring about such advantage as low reaction temperature, good selectivity and low catalyst resumption.Magnetically stabilized bed (MSB), a fluidized bed of magnetizable particles by applying a spatially uniform and time-invariant magnetic field oriented axially relative to the fluidizing fluid flow, had many advantages such as the low pressure drop and

  2. Storage of hydrogen on carbons; Stockage de l'hydrogene sur les carbones

    Energy Technology Data Exchange (ETDEWEB)

    Conard, J. [Centre National de la Recherche Scientifique, CNRS-CRMD, 45 - Orleans-la-Source (France)

    2000-07-01

    The storage of hydrogen on carbons, with densities above 10% hydrogen weight, can be used in the sector of transport. However, only the physical-sorption of this gas (which is almost perfect and boils at 20 K under atmospheric pressure) cannot explain this performance. A study of the possible sites for one hydrogen, which can take very different forms, is presented, in order to better understand the rational development of this storage mode which could reach about ten weight %. (O.M.)

  3. Dependence of Structure and Haemocompatibility of Amorphous Carbon Films on Substrate Bias Voltage

    Institute of Scientific and Technical Information of China (English)

    GUO Yang-Ming; MO Dang; LI Zhe-Yi; LIU Yi; HE Zhen-Hui; CHEN Di-Hu

    2004-01-01

    @@ Tetrahedral amorphous hydrogenated carbon (ta-C:H) films on Si(100) substrates were prepared by using a magnetic-field-filter plasma stream deposition system. Samples with different ratios of spa-bond to sp2-bond were obtained by changing the bias voltage applied to the substrates. The ellipsometric spectra of various carbon films in the photon energy range of 1.9-5.4eV were measured. The refractive index n and the relative sp3 C ratio of these films were obtained by simulating their ellipsometric spectra using the Forouhi-Bloomer model and by using the Bruggeman effective medium approximation, respectively. The haemocompatibility of these ta-C:H films was analysed by observation of platelet adhesion and measurement of kinetic clotting time. The results show that the sp3 C fraction is dependent on the substrate bias voltage, and the haemocompatibility is dependent on the ratio of sp3-bond to sp2-bond. A good haemocompatibility material of ta-C:H films with a suitable sp3 C fraction can be prepared by changing the substrate bias voltage.

  4. Structural evolutions in polymer-derived carbon-rich amorphous silicon carbide.

    Science.gov (United States)

    Wang, Kewei; Ma, Baisheng; Li, Xuqin; Wang, Yiguang; An, Linan

    2015-01-29

    The detailed structural evolutions in polycarbosilane-derived carbon-rich amorphous SiC were investigated semiquantitatively by combining experimental and analytical methods. It is revealed that the material is comprised of a Si-containing matrix phase and a free-carbon phase. The matrix phase is amorphous, comprised of SiC4 tetrahedra, SiCxOx-4 tetrahedra, and Si-C-C-Si/Si-C-H defects. With increasing pyrolysis temperature, the amorphous matrix becomes more ordered, accompanied by a transition from SiC2O2 to SiCO3. The transition was completed at 1250 °C, where the matrix phase started to crystallize by forming a small amount of β-SiC. The free-carbon phase was comprised of carbon nanoclusters and C-dangling bonds. Increasing pyrolysis temperature led to the transition of the free carbon from amorphous carbon to nanocrystalline graphite. The size of the carbon clusters decreased first and then increased, while the C-dangling bond content decreased continuously. The growth of carbon clusters was attributed to Ostwald ripening and described using a two-dimensional grain growth model. The calculated activation energy suggested that the decrease in C-dangling bonds is directly related to the lateral growth of the carbon clusters. PMID:25490064

  5. Hydrogenated Amorphous Silicon Sensor Deposited on Integrated Circuit for Radiation Detection

    OpenAIRE

    Despeisse, M; Anelli, G.; Jarron, P.; Kaplon, J; Moraes, D.; A. Nardulli(Institute for Particle Physics, ETH Zurich, Zurich, Switzerland); Powolny, F; Wyrsch, N

    2008-01-01

    Radiation detectors based on the deposition of a 10 to 30 μm thick hydrogenated amorphous silicon (a-Si:H) sensor directly on top of integrated circuits have been developed. The performance of this detector technology has been assessed for the first time in the context of particle detectors. Three different circuits were designed in a quarter micron CMOS technology for these studies. The so-called TFA (Thin-Film on ASIC) detectors obtained after deposition of a-Si:H sensors on the developed c...

  6. Picosecond all-optical switching in hydrogenated amorphous silicon microring resonators

    CERN Document Server

    Pelc, Jason S; Vo, Sonny; Santori, Charles; Fattal, David A; Beausoleil, Raymond G

    2014-01-01

    We utilize cross-phase modulation to observe all-optical switching in microring resonators fabricated with hydrogenated amorphous silicon (a-Si:H). Using 2.7-ps pulses from a mode-locked fiber laser in the telecom C-band, we observe optical switching of a cw telecom-band probe with full-width at half-maximum switching times of 14.8 ps, using approximately 720 fJ of energy deposited in the microring. In comparison with telecom-band optical switching in crystalline silicon microrings, a-Si:H exhibits substantially higher switching speeds due to reduced impact of free-carrier processes.

  7. Hydrogen-induced rupture of strained Si─O bonds in amorphous silicon dioxide

    OpenAIRE

    El-Sayed, Al-Moatasem; Watkins, Matthew B.; Grasser, Tibor; Afanas'ev, Valery; Shluger, Alexander L

    2015-01-01

    Using ab initio modeling we demonstrate that H atoms can break strained Si─O bonds in continuous amorphous silicon dioxide (a-SiO(2)) networks, resulting in a new defect consisting of a threefold-coordinated Si atom with an unpaired electron facing a hydroxyl group, adding to the density of dangling bond defects, such as E' centers. The energy barriers to form this defect from interstitial H atoms range between 0.5 and 1.3 eV. This discovery of unexpected reactivity of atomic hydrogen may hav...

  8. Nano-structural Modification of Amorphous Carbon Thin Films by Low-energy Electron Beam Irradiation

    Institute of Scientific and Technical Information of China (English)

    EijiIwamura; MasanoriYamaguchi

    2004-01-01

    A new approach using a low-energy electron beam radiation system was investigated to synthesize carbon hybrid structures in amorphous carbon thin films. Two types of amorphous carbon films, which were 15at% iron containing film and with column/inter-column structures, were deposited onto Si substrates by a sputtering technique and subsequently exposed to an electron shower of which the energy and dose rate were much smaller compared to an intense electron beam used in a transmission electron microscopy. As a result of the low-energy and low-dose electron irradiation process, graphitic structures formed in amorphous matrix at a relatively low temperature up to 450 K. Hybrid carbon thin films containing onion-like structures in an amorphous carbon matrix were synthesized by dynamic structural modification of iron containing amorphous carbon thin films. It was found that the graphitization progressed more in the electron irradiation than in annealing at 773K, and it was attributed to thermal and catalytic effects which are strongly related to grain growth of metal clusters. On the other hand, a reversal of TEM image contrast was observed in a-C films with column/inter-column structures. It is presumed that preferable graphitization occurred in the inter-column regions induced by electron irradiation.

  9. Nano-structural Modification of Amorphous Carbon Thin Films by Low-energy Electron Beam Irradiation

    Institute of Scientific and Technical Information of China (English)

    Eiji Iwamura; Masanori Yamaguchi

    2004-01-01

    A new approach using a low-energy electron beam radiation system was investigated to synthesize carbon hybrid structures in amorphous carbon thin films. Two types of amorphous carbon films, which were 15at% iron containing film and with column/inter-column structures, were deposited onto Si substrates by a sputtering technique and subsequently exposed to an electron shower of which the energy and dose rate were much smaller compared to an intense electron beam used in a transmission electron microscopy. As a result of the low-energy and low-dose electron irradiation process,graphitic structures formed in amorphous matrix at a relatively low temperature up to 450 K. Hybrid carbon thin films containing onion-like structures in an amorphous carbon matrix were synthesized by dynamic structural modification of iron containing amorphous carbon thin films. It was found that the graphitization progressed more in the electron irradiation than in annealing at 773K, and it was attributed to thermal and catalytic effects which are strongly related to grain growth of metal clusters. On the other hand, a reversal of TEM image contrast was observed in a-C films with column/inter-column structures. It is presumed that preferable graphitization occurred in the inter-column regions induced by electron irradiation.

  10. The effect of empirical potential functions on modeling of amorphous carbon using molecular dynamics method

    International Nuclear Information System (INIS)

    Empirical potentials have a strong effect on the hybridization and structure of amorphous carbon and are of great importance in molecular dynamics (MD) simulations. In this work, amorphous carbon at densities ranging from 2.0 to 3.2 g/cm3 was modeled by a liquid quenching method using Tersoff, 2nd REBO, and ReaxFF empirical potentials. The hybridization, structure and radial distribution function G(r) of carbon atoms were analyzed as a function of the three potentials mentioned above. The ReaxFF potential is capable to model the change of the structure of amorphous carbon and MD results are in a good agreement with experimental results and density function theory (DFT) at low density of 2.6 g/cm3 and below. The 2nd REBO potential can be used when amorphous carbon has a very low density of 2.4 g/cm3 and below. Considering the computational efficiency, the Tersoff potential is recommended to model amorphous carbon at a high density of 2.6 g/cm3 and above. In addition, the influence of the quenching time on the hybridization content obtained with the three potentials is discussed.

  11. Synchrotron radiation photoemission study of metal overlayers on hydrogenated amorphous silicon at room temperature

    Energy Technology Data Exchange (ETDEWEB)

    Pi, J.

    1990-09-21

    In this dissertation, metals deposited on a hydrogenated amorphous silicon (a-Si:H) film at room temperature are studied. The purpose of this work is mainly understanding the electronic properties of the interface, using high-resolution synchrotron radiation photoemission techniques as a probe. Atomic hydrogen plays an important role in passivating dangling bonds of a-Si:H films, thus reducing the gap-state distribution. In addition, singly bonded hydrogen also reduces states at the top of the valence band which are now replaced by deeper Si-H bonding states. The interface is formed by evaporating metal on an a-Si:H film in successive accumulations at room temperature. Au, Ag, and Cr were chosen as the deposited metals. Undoped films were used as substrates. Since some unique features can be found in a-Si:H, such as surface enrichment of hydrogen diffused from the bulk and instability of the free surface, we do not expect the metals/a-Si:H interface to behave exactly as its crystalline counterpart. Metal deposits, at low coverages, are found to gather preferentially around regions deficient in hydrogen. As the thickness is increased, some Si atoms in those regions are likely to leave their sites to intermix with metal overlayers like Au and Cr. 129 refs., 30 figs.

  12. Structural, hydrogen bonding and in situ studies of the effect of hydrogen dilution on the passivation by amorphous silicon of n-type crystalline (100) silicon surfaces

    OpenAIRE

    Meddeb, H.; Bearda, T.; Abdelraheem, Y.; Ezzaouia, H.; Gordon, I.; Szlufcik, J.; Poortmans, Jef

    2015-01-01

    Hydrogenated amorphous silicon (a-Si : H) layers deposited by chemical vapour deposition provide an attractive route to achieve high-performance crystalline silicon (c-Si) solar cells due to their deposition at low temperatures and their superior passivation quality. Hydrogen certainly plays an additional crucial role by passivating the dangling bonds, and thus improving the electrical and optical properties. In this work, we present the variation of the effective lifetime with the hydrogen d...

  13. Hydrogen adsorption in doped porous carbons

    International Nuclear Information System (INIS)

    Full text of publication follows: Hydrogen is a clean fuel that will be used in automotive transport when the problem of storage will be solved. The difficulties of H2 storage (available space, security and performance, etc...) require a material that can store 5 weight % of hydrogen. Research is focused on new materials that can assume the constraints imposed by the automotive applications. Among these materials, the nano-structured carbons (nano-fibers and single walled carbon nano-tubes) were claimed to be promising by numerous authors [1-3]. The more promising carbon materials for hydrogen adsorption are those having micropores (i. e. single walled carbon nano-tubes and activated carbon), for which the energy of sorption of hydrogen molecules is theoretically higher [7- 8]. Presently, the best performance of hydrogen adsorption was found in super-activated micro-porous carbons sorbing 5 weight % at 77 K, and almost 0.5 % at room temperature and 6 MPa [9]. Up to now, the performance of these materials can still be improved as the known mechanism of sorption in these carbon materials: physisorption controlled by Van der Waals attractive forces through London interaction is efficient at cryogenic temperatures (77 K) where the interaction between adsorbent and adsorbate becomes stronger. One way to improve the attractive interaction between adsorbent and molecule is to increase the forces due to the interaction of electrical field and induced dipole of the molecule. This can be theoretically tailored in carbon materials through the electron charge transfer by electron donors who can provide an increase in the electrical field al the surface of the adsorbent. Then, the doping of carbon substrates, appearing to be a promising method to increase the energy of adsorption has been proposed in recent papers as a solution to obtain good hydrogen adsorption properties at appropriate temperatures close to room temperatures [10-12]. Thus, we have studied the adsorption

  14. Hydrogen adsorption in doped porous carbons

    International Nuclear Information System (INIS)

    Full text of publication follows: Hydrogen is a clean fuel that will be used in automotive transport when the problem of storage will be solved. The difficulties of H2 storage (available space, security and performance, etc...) require a material that can store 5 weight % of hydrogen. Research is focused on new materials that can assume the constraints imposed by the automotive applications. Among these materials, the nano-structured carbons (nano-fibers and single walled carbon nano-tubes) were claimed to be promising by numerous authors [1-3]. The more promising carbon materials for hydrogen adsorption are those having micropores (i. e. single walled carbon nano-tubes and activated carbon), for which the energy of sorption of hydrogen molecules is theoretically higher [7-8]. Presently, the best performance of hydrogen adsorption was found in super-activated microporous carbons sorbing 5 weight % at 77 K, and almost 0.5 % at room temperature and 6 MPa [9]. Up to now, the performance of these materials can still be improved as the known mechanism of sorption in these carbon materials: physi-sorption controlled by Van der Waals attractive forces through London interaction is efficient at cryogenic temperatures (77 K) where the interaction between adsorbent and adsorbate becomes stronger. One way to improve the attractive interaction between adsorbent and molecule is to increase the forces due to the interaction of electrical field and induced dipole of the molecule. This can be theoretically tailored in carbon materials through the electron charge transfer by electron donors who can provide an increase in the electrical field at the surface of the adsorbent. Then, the doping of carbon substrates, appearing to be a promising method to increase the energy of adsorption has been proposed in recent papers as a solution to obtain good hydrogen adsorption properties at appropriate temperatures close to room temperatures [10-12]. Thus, we have studied the adsorption

  15. Crystalline and amorphous carbon nitride films produced by high-energy shock plasma deposition

    International Nuclear Information System (INIS)

    High-energy shock plasma deposition techniques are used to produce carbon-nitride films containing both crystalline and amorphous components. The structures are examined by high-resolution transmission electron microscopy, parallel-electron-energy loss spectroscopy and electron diffraction. The crystalline phase appears to be face-centered cubic with unit cell parameter approx. a=0.63nm and it may be stabilized by calcium and oxygen at about 1-2 at % levels. The carbon atoms appear to have both trigonal and tetrahedral bonding for the crystalline phase. There is PEELS evidence that a significant fraction of the nitrogen atoms have sp2 trigonal bonds in the crystalline phase. The amorphous carbon-nitride film component varies from essentially graphite, containing virtually no nitrogen, to amorphous carbon-nitride containing up to 10 at % N, where the fraction of sp3 bonds is significant. 15 refs., 5 figs

  16. Recent progress in the synthesis and characterization of amorphous and crystalline carbon nitride coatings

    CERN Document Server

    Widlow, I

    2000-01-01

    This review summarizes our most recent findings in the structure and properties of amorphous and crystalline carbon nitride coatings, synthesized by reactive magnetron sputtering. By careful control of the plasma conditions via proper choice of process parameters such as substrate bias, target power and gas pressure, one can precisely control film structure and properties. With this approach, we were able to produce amorphous carbon nitride films with controlled hardness and surface roughness. In particular, we can synthesize ultrathin (1 nm thick) amorphous carbon nitride films to be sufficiently dense and uniform that they provide adequate corrosion protection for hard disk applications. We demonstrated the strong correlation between ZrN (111) texture and hardness in CN sub x /ZrN superlattice coatings. Raman spectroscopy and near-edge X-ray absorption show the predominance of sp sup 3 -bonded carbon in these superlattice coatings.

  17. Amorphization and recrystallization of single-crystalline hydrogen titanate nanowires by N+ ion irradiation

    International Nuclear Information System (INIS)

    We report on the phase transformation of hydrogen titanate (H2Ti3O7) nanowires induced by 50 keV N+ ion irradiation at room temperature with fluences of 1 × 1015 ions/cm2 and 1 × 1016 ions/cm2, respectively. Using transmission electron microscopy, the internal structure of the ion irradiated nanowires is analyzed. At low fluence, a transformation from crystalline H2Ti3O7 to amorphous TiO2 is observed. However, at higher fluence, a remarkable crystalline-amorphous TiO2 core-shell structure is formed. At this higher fluence, the recrystallization occurs in the core of the nanowire and the outer layer remains amorphous. The phase transformation and formation of core-shell structure are explained using the thermal spike model, radiation enhanced diffusion, and classical theory of nucleation and growth under non-equilibrium thermodynamics. X-ray photoelectron spectroscopy and Raman scattering reveal further insight into the structure of the nanowires before and after ion irradiation.

  18. Properties of Amorphous Carbon Microspheres Synthesised by Palm Oil-CVD Method

    International Nuclear Information System (INIS)

    Amorphous carbon microspheres were synthesized using a dual-furnace chemical vapour deposition method at 800-1000 deg. C. Palm oil-based cooking oil (PO) and zinc nitrate solution was used as a carbon source and catalyst precursor, respectively with PO to zinc nitrate ratio of 30:20 (v/v) and a silicon wafer as the sample target. Regular microsphere shape of the amorphous carbons was obtained and a uniform microsphere structure improved as the carbonization temperature increased from 800 to 1000 deg. C. At 800 deg. C, no regular microspheres were formed but more uniform structure is observed at 900 deg. C. Generally the microspheres size is uniform when the heating temperature was increased to 1000 deg. C, but the presence of mixed sizes can still be observed. X-ray diffraction patterns show the presence of oxide of carbon, ZnO phase together with Zn oxalate phase. Raman spectra show two broad peaks characteristic to amorphous carbon at 1344 and 1582 cm-1 for the D and G bands, respectively. These bands become more prominent as the preparation temperature increased from 800 to 1000 deg. C. This is in agreement with the formation of amorphous carbon microspheres as shown by the FESEM study and other Zn-based phases as a result of the oxidation process of the palm oil as the carbon source and the zinc nitrate as the catalyst precursor, respectively.

  19. Large-deformation and high-strength amorphous porous carbon nanospheres

    Science.gov (United States)

    Yang, Weizhu; Mao, Shimin; Yang, Jia; Shang, Tao; Song, Hongguang; Mabon, James; Swiech, Wacek; Vance, John R.; Yue, Zhufeng; Dillon, Shen J.; Xu, Hangxun; Xu, Baoxing

    2016-04-01

    Carbon is one of the most important materials extensively used in industry and our daily life. Crystalline carbon materials such as carbon nanotubes and graphene possess ultrahigh strength and toughness. In contrast, amorphous carbon is known to be very brittle and can sustain little compressive deformation. Inspired by biological shells and honeycomb-like cellular structures in nature, we introduce a class of hybrid structural designs and demonstrate that amorphous porous carbon nanospheres with a thin outer shell can simultaneously achieve high strength and sustain large deformation. The amorphous carbon nanospheres were synthesized via a low-cost, scalable and structure-controllable ultrasonic spray pyrolysis approach using energetic carbon precursors. In situ compression experiments on individual nanospheres show that the amorphous carbon nanospheres with an optimized structure can sustain beyond 50% compressive strain. Both experiments and finite element analyses reveal that the buckling deformation of the outer spherical shell dominates the improvement of strength while the collapse of inner nanoscale pores driven by twisting, rotation, buckling and bending of pore walls contributes to the large deformation.

  20. Depth profiling of hydrogen in amorphous media and applicable to quartz air filters

    International Nuclear Information System (INIS)

    We have explored the use of proton-proton coincidence, at proton energy of 6.35 MeV, for hydrogen determination and depth profiling in amorphous media. The method has been applied to quartz air filters. This non-destructive method is highly specific to hydrogen, depending only on the energy-loss distribution in p-p scattering events. The method, combined with other techniques, can be used to measure the total amount and depth distribution of particulate organic matter in aerosols on quartz air. The results for ambient air quartz filters show that the technique can separate several kinds of gaseous organic artifact, one of which cannot be corrected through the standard use of tandem quartz filters. (Copyright (c) 1998 Elsevier Science B.V., Amsterdam. All rights reserved.)

  1. Visible Absorption Properties of Retinoic Acid Controlled on Hydrogenated Amorphous Silicon Thin Film

    Science.gov (United States)

    Tsujiuchi, Yutaka; Masumoto, Hiroshi; Goto, Takashi

    2008-02-01

    Langmuir-Blodgett (LB) films of retinoic acid and LB films of retinoic acid mixed with a peptide that contains an alanine-lysine-valine (AKV) amino acid sequence deposited on a hydrogenated amorphous silicon (a-Si:H) film prepared by electron cyclotron resonance (ECR) plasma sputtering were fabricated, and their light absorption spectrums were compared. A specific visible light absorption at approximately 500 nm occurred in a film that had a film thickness of more than 80 nm and a hydrogen concentration of more than 20% in the sputtering process gas. Mixing the AKV sequence peptide with retinoic acid caused a 6 nm blueshift, from 363 to 357 nm, of the absorption maximum of the composite LB film on a SiO2 substrate. Using the same peptide, a large 30 nm blueshift, from 500 to 470 nm, was induced in the composite LB film on the a-Si:H film.

  2. Properties of hydrogenated amorphous silicon (a-Si:H) deposited using a microwave Ecr plasma

    International Nuclear Information System (INIS)

    Hydrogenated amorphous silicon (a-Si:H) films have been widely applied to semiconductor devices, such as thin film transistors, solar cells and photosensitive devices. In this work, the first Si-H-Cl alloys (obtained at the National Institute for Nuclear Research of Mexico) were formed by a microwave electron cyclotron resonance (Ecr) plasma CVD method. Gaseous mixtures of silicon tetrachloride (Si Cl4), hydrogen and argon were used. The Ecr plasma was generated by microwaves at 2.45 GHz and a magnetic field of 670 G was applied to maintain the discharge after resonance condition (occurring at 875 G). Si and Cl contents were analyzed by Rutherford Backscattering Spectrometry (RBS). It was found that, increasing proportion of Si Cl4 in the mixture or decreasing pressure, the silicon and chlorine percentages decrease. Optical gaps were obtained by spectrophotometry. Decreasing temperature, optical gap values increase from 1.4 to 1.5 eV. (Author)

  3. Activation of extended red emission photoluminescence in carbon solids by exposure to atomic hydrogen and UV radiation

    Science.gov (United States)

    Furton, Douglas G.; Witt, Adolf N.

    1993-01-01

    We report on new laboratory results which relate directly to the observation of strongly enhanced extended red emission (ERE) by interstellar dust in H2 photodissociation zones. The ERE has been attributed to photoluminescence by hydrogenated amorphous carbon (HAC). We are demonstrating that exposure to thermally dissociated atomic hydrogen will restore the photoluminescence efficiency of previously annealed HAC. Also, pure amorphous carbon (AC), not previously photoluminescent, can be induced to photoluminesce by exposure to atomic hydrogen. This conversion of AC into HAC is greatly enhanced by the presence of UV irradiation. The presence of dense, warm atomic hydrogen and a strong UV radiation field are characteristic environmental properties of H2 dissociation zones. Our results lend strong support to the HAC photoluminescence explanation for ERE.

  4. From amorphous to microcrystalline silicon films prepared by hydrogen dilution using the VHF (70 MHz) GD technique

    OpenAIRE

    Kroll, U.; Meier, Johannes; Torres, Pedro; Pohl, J.; Shah, Arvind

    2008-01-01

    The amorphous and microcrystalline silicon films have been prepared by hydrogen dilution from pure silane to silane concentrations ≥1.25%. At silane concentrations of less than 10%, a transition from the amorphous phase to the microcrystalline phase can be observed. X-ray diffraction spectroscopy indicates a preferential growth of the crystallites in the [220] direction. Additionally, the transition into the microcrystalline regime is accompanied by a shrinking of the optical gap, a reduction...

  5. Crystallization mechanism of silicon quantum dots upon thermal annealing of hydrogenated amorphous Si-rich silicon carbide films

    International Nuclear Information System (INIS)

    We have investigated the crystallization process of silicon quantum dots (QDs) imbedded in hydrogenated amorphous Si-rich silicon carbide (a-SiC:H) films. Analysis reveals that crystallization of silicon QDs upon thermal annealing of the samples can be explained in terms of bonding configuration and evolution of microstructure. The precursor gases were dissociated via electron impact reactions in the plasma-enhanced chemical vapor deposition, where the hydrogenated silicon radicals and reactive SiHn species lead to the formation of primary Si nuclei. With increasing annealing temperature, the breaking of SiHn bonds and decomposition of Si-rich SiC were progressively enhanced, allowing the formation of crystalline silicon QDs inside the a-SiC:H matrix. The results help clarify a probable mechanism for the growth of silicon QDs and provide the possibility to optimize the microstructure of silicon QDs in a-SiC:H films. - Highlights: • Si-rich SiC samples are grown by plasma-enhanced chemical vapor deposition. • Silicon radicals and reactive SiHn (n = 1,2,3) exist in the as-grown samples. • Annealing temperature induces the growth of crystalline silicon quantum dots. • Carbon atoms are incorporated in the formation of Si-C and C-H bonds in the matrix

  6. Label-free photonic biosensors fabricated with low-loss hydrogenated amorphous silicon resonators

    Science.gov (United States)

    Lipka, Timo; Wahn, Lennart; Trieu, Hoc Khiem; Hilterhaus, Lutz; Müller, Jörg

    2013-01-01

    The precise detection of chemicals and biomolecules is of great interest in the areas of biotechnology and medical diagnostics. Thus, there is a need for highly sensitive, small area, and low-cost sensors. We fabricated and optically characterized hydrogenated amorphous silicon photonic resonators for label-free lab-on-chip biosensors. The sensing was performed with small-footprint microdisk and microring resonators that detect a refractive-index change via the evanescent electric field. Homogeneous sensing with NaCl and surface-sensing experiments with immobilized bovine serum albumin (BSA) were carried out. A sensitivity as high as 460 nm/RIU was measured for NaCl dissolved in deionized water for the disk, whereas about 50 nm/RIU was determined for the ring resonator. The intrinsic limits of detection were calculated to be 3.3×10 and 3.2×10 at 1550-nm wavelength. We measured the binding of BSA to functionalized ring resonators and found that molecular masses can be detected down to the clinically relevant femtogram regime. The detection and quantification of related analytes with hydrogenated amorphous silicon photonic sensors can be used in medical healthcare diagnostics like point-of-care-testing and biotechnological screening.

  7. Monitor for hydrogen, oxygen, carbon and hydrocarbons

    International Nuclear Information System (INIS)

    Monitors are described of the activity of hydrogen, oxygen and hydrocarbon mixtures designed for use in technological sodium cooling channels of fast reactor power plants. The hydrogen monitor consists of an iron diffusion membrane and an ion pump which maintains a pressure gradient on the membrane. Its supply current is proportional to hydrogen concentration. The oxygen monitor uses the principle of a concentration galvanic element with a solid ceramic electrolyte. The carbon activity monitor is based on a diffusion membrane and the modified chromatographic unit SU-2 with a flame ionization detector. An identical unit is also used for determining hydrocarbons in the cover gas. For these purposes, the unit is provided with a diffusion standard. The results are described of tests of the said analyzers. (author)

  8. High-rate, low-temperature synthesis of composition controlled hydrogenated amorphous silicon carbide films in low-frequency inductively coupled plasmas

    International Nuclear Information System (INIS)

    It is commonly believed that in order to synthesize high-quality hydrogenated amorphous silicon carbide (a-Si1-xCx : H) films at competitive deposition rates it is necessary to operate plasma discharges at high power regimes and with heavy hydrogen dilution. Here we report on the fabrication of hydrogenated amorphous silicon carbide films with different carbon contents x (ranging from 0.09 to 0.71) at high deposition rates using inductively coupled plasma (ICP) chemical vapour deposition with no hydrogen dilution and at relatively low power densities (∼0.025 W cm-3) as compared with existing reports. The film growth rate Rd peaks at x = 0.09 and x = 0.71, and equals 18 nm min-1 and 17 nm min-1, respectively, which is higher than other existing reports on the fabrication of a-Si1-xCx : H films. The extra carbon atoms for carbon-rich a-Si1-xCx : H samples are incorporated via diamond-like sp3 C-C bonding as deduced by Fourier transform infrared absorption and Raman spectroscopy analyses. The specimens feature a large optical band gap, with the maximum of 3.74 eV obtained at x = 0.71. All the a-Si1-xCx : H samples exhibit low-temperature (77 K) photoluminescence (PL), whereas only the carbon-rich a-Si1-xCx : H samples (x ≥ 0.55) exhibit room-temperature (300 K) PL. Such behaviour is explained by the static disorder model. High film quality in our work can be attributed to the high efficiency of the custom-designed ICP reactor to create reactive radical species required for the film growth. This technique can be used for a broader range of material systems where precise compositional control is required

  9. 低碳含量a-Si1-xCx∶H薄膜的Raman和荧光特性%Raman and Photoluminescence Characterization of Hydrogenated Amorphous Silicon Carbide Alloys with Low Carbon Concentrations

    Institute of Scientific and Technical Information of China (English)

    王燕; 岳瑞峰

    2001-01-01

    The network disorder of the a-Si1-xCx∶H films with carbon concentration lower than 20 at.% has been studied with Raman spectroscopy and photoluminescence spectroscopy (PL).Two different laser irradiation wavelengths were employed to excite the materials,one with a wavelength of 647.1 nm and an energy close to the optical gap of the material,can penetrate fairly deep into the material,whereas the other with a wavelength of 488.0 nm and an energy higher than the optical gap,can be almost completely absorbed by the surface of the materials.The variations in penetration depth result in significant differences between Raman spectra and PL spectra.These results indicate that there exist high density defects in the layers close to the surface,and that the spatial fluctuation of the gap due to variation in bulk concentrations.The complex microstructures of the films are responsible for the marked red-shift and broadening of the frequency and width of the TO mode of the Raman spectra and a small blue-shift and broadening of the PL peak when the sample was excited with a high laser energy.These observations show that in the a-Si1-xCx∶H sample,irradiation energies may strongly affect the results of Raman spectroscopy and PL measurements because of the complexity of the microstructures of the films.%采用Raman和荧光测量研究了低碳含量a-Si1-xCx∶H(x≤20%(原子比))薄膜的结构特征,并选用两种不同波长的激光来激发这些材料。采用647.1 nm光激发时,由于激发光能量接近于各样品的光学带隙,因而在样品中具有较大的透射深度,而488.0 nm光激发时则被样品表面强烈吸收。探测深度的变化造成了Raman谱和荧光谱有较大的差异,这些结果一方面表明样品的表面存在一层高浓度的缺陷层,同时也证明样品体内存在着带隙的空间起伏,这两种空间的不均性造成了高能激发时Raman谱的TO模频率和半高宽比低能激发时有大的红移和

  10. Room Temperature Growth of Hydrogenated Amorphous Silicon Films by Dielectric Barrier Discharge Enhanced CVD

    Institute of Scientific and Technical Information of China (English)

    GUO Yu; ZHANG Xiwen; HAN Gaorong

    2007-01-01

    Hydrogenated amorphous silicon (a-Si:H) films were deposited on Si (100) and glass substrates by dielectric barrier discharge enhanced chemical vapour deposition (DBD-CVD)in (SiH4+H2) atmosphere at room temperature.Results of the thickness measurement,SEM (scanning electron microscope),Raman,and FTIR (Fourier transform infrared spectroscopy) show that with the increase in the applied peak voltage,the deposition rate and network order of the films increase,and the hydrogen bonding configurations mainly in di-hydrogen (Si-H2) and poly hydrogen (SiH2)n are introduced into the films.The UV-visible transmission spectra show that with the decrease in Sill4/ (SiH4+H2) the thin films'band gap shifts from 1.92 eV to 2.17 eV.These experimental results are in agreement with the theoretic analysis of the DBD discharge.The deposition of a-Si:H films by the DBD-CVD method as reported here for the first time is attractive because it allows fast deposition of a-Si:H films on large-area low-melting-point substrates and requires only a low cost of production without additional heating or pumping equipment.

  11. Corrosion resistance of amorphous hydrogenated SiC and diamond-like coatings deposited by r.f.-plasma-enhanced chemical vapour deposition

    International Nuclear Information System (INIS)

    This paper reports on the properties and corrosion resistance of amorphous hydrogenated carbon and amorphous hydrogenated SiC films deposited by r.f.-plasma-enhanced chemical vapour deposition at low temperatures (below 200 C). SiC coatings were prepared from SiH4-CH4 gas mixtures. Hydrogenated diamond-like coatings were deposited from classical CH4-H2 mixtures. The influence of various deposition parameters was investigated. Microstructural and mechanical properties of the films were studied (density, hydrogen content, nanohardness, internal stress, critical load and friction coefficient). Two examples of corrosion resistance are given: (1) the corrosion resistance and biocompatibility of SiC and diamond-like coatings deposited on metal implants (Ti alloy) (the corrosion resistance is evaluated through potentiodynamic polarization tests in biological media; the biocompatibility of coated and uncoated metals is compared using differentiated human cell cultures); and (2) the corrosion resistance of SiC-coated magnesium in chloride-containing boric borate buffer at pH = 9.3 evaluated from anodic polarization curves and scanning electron microscopy studies. (orig.)

  12. Mechanical and tribological properties of amorphous carbon films deposited on implanted steel substrates

    International Nuclear Information System (INIS)

    Hydrogen-free amorphous carbon (a-C) films were deposited using unbalanced magnetron sputtering technique from graphite targets on AISI 440C steel substrates implanted with (1) carbon (C), (2) titanium (Ti), and (3) titanium followed by carbon (Ti+C), respectively. After deposition, the adhesion strength of the films was examined by scratch test and Rockwell-C indentation test. The tribological performance of the films was evaluated by a typical ball-on-disk tribometer and a reciprocating wear tester. A dynamic impact tester was also carried out to study the fatigue strength of the films. In order to study the effect of the pre-treatment of steel substrates by means of ion implantation on the actual performance of a-C films, the implanted substrates were investigated by using X-ray photoelectron spectroscopy and nano-indentation, from which the composition depth profile as well as the hardness (H) and elastic modulus (E) depth profiles could be accurately obtained. As a result, due to higher contents of carbide bonds appeared at the outmost surface of the C and Ti+C implanted substrates, a critical load over 65 N was obtained, indicating good scratch resistance of the films. The combination of high interfacial strength and high plastic deformation resistance (H3/E2) of the Ti+C implanted substrates led to a higher load-carrying capacity and longer duration lifetime in the sliding wear test. In the dynamic impact test, the good adhesion strength and high toughness of C and Ti+C implanted substrates improved the impact resistance of the films

  13. Computational Evaluation of Amorphous Carbon Coating for Durable Silicon Anodes for Lithium-Ion Batteries

    OpenAIRE

    Jeongwoon Hwang; Jisoon Ihm; Kwang-Ryeol Lee; Seungchul Kim

    2015-01-01

    We investigate the structural, mechanical, and electronic properties of graphite-like amorphous carbon coating on bulky silicon to examine whether it can improve the durability of the silicon anodes of lithium-ion batteries using molecular dynamics simulations and ab-initio electronic structure calculations. Structural models of carbon coating are constructed using molecular dynamics simulations of atomic carbon deposition with low incident energies (1–16 eV). As the incident energy decrease...

  14. Amorphous Silicon Carbide Photoelectrode for Hydrogen Production from Water using Sunlight

    OpenAIRE

    Zhu, Feng; Hu, Jian; Matulionis, Ilvydas; Deutsch, Todd; Gaillard, Nicolas; Miller, Eric; Madan, Arun

    2010-01-01

    State-of-the-art a-SiC:H films have been prepared using RF-PECVD deposition technique. Incorporation of carbon in amorphous silicon network increases the bandgap to >2.0eV and adding H2 during fabrication has led to a material with low defects. A-SiC:H with Eg=2.0eV used as the active layer in single junction solar cell led to an efficiency of ~7%, which also indicated that a-SiC:H is high-quality and that it has potential to be used as photoelectrode. Immersing in pH2 sulphamic acid electrol...

  15. Amorphous carbon for structured step bunching during graphene growth on SiC

    Science.gov (United States)

    Palmer, James; Kunc, Jan; Hu, Yike; Hankinson, John; Guo, Zelei; Berger, Claire; de Heer, Walt

    2014-03-01

    Structured growth of high quality graphene is necessary for technological development of carbon based materials. Specifically, control of the bunching and placement of surface steps under epitaxial graphene on SiC is an important consideration for graphene device production. We demonstrate lithographically patterned evaporated amorphous carbon as a method to pin SiC surface steps. Evaporated amorphous carbon is an ideal step-flow barrier on SiC due to its chemical compatibility with graphene growth and its structural stability at high temperatures, as well as its patternability. The amorphous carbon is deposited in vacuum on SiC prior to graphene growth. In the graphene furnace at temperatures above 1200°C, mobile SiC steps accumulate at these amorphous carbon barriers, forming an aligned step free region for graphene growth at temperatures above 1330°C. AFM imaging and Raman spectroscopy support the formation of quality step-free graphene sheets grown on SiC with the step morphology aligned to the carbon grid.

  16. The influence of hydrogen on the chemical, mechanical, optical/electronic, and electrical transport properties of amorphous hydrogenated boron carbide

    Science.gov (United States)

    Nordell, Bradley J.; Karki, Sudarshan; Nguyen, Thuong D.; Rulis, Paul; Caruso, A. N.; Purohit, Sudhaunshu S.; Li, Han; King, Sean W.; Dutta, Dhanadeep; Gidley, David; Lanford, William A.; Paquette, Michelle M.

    2015-07-01

    Because of its high electrical resistivity, low dielectric constant (κ), high thermal neutron capture cross section, and robust chemical, thermal, and mechanical properties, amorphous hydrogenated boron carbide (a-BxC:Hy) has garnered interest as a material for low-κ dielectric and solid-state neutron detection applications. Herein, we investigate the relationships between chemical structure (atomic concentration B, C, H, and O), physical/mechanical properties (density, porosity, hardness, and Young's modulus), electronic structure [band gap, Urbach energy (EU), and Tauc parameter (B1/2)], optical/dielectric properties (frequency-dependent dielectric constant), and electrical transport properties (resistivity and leakage current) through the analysis of a large series of a-BxC:Hy thin films grown by plasma-enhanced chemical vapor deposition from ortho-carborane. The resulting films exhibit a wide range of properties including H concentration from 10% to 45%, density from 0.9 to 2.3 g/cm3, Young's modulus from 10 to 340 GPa, band gap from 1.7 to 3.8 eV, Urbach energy from 0.1 to 0.7 eV, dielectric constant from 3.1 to 7.6, and electrical resistivity from 1010 to 1015 Ω cm. Hydrogen concentration is found to correlate directly with thin-film density, and both are used to map and explain the other material properties. Hardness and Young's modulus exhibit a direct power law relationship with density above ˜1.3 g/cm3 (or below ˜35% H), below which they plateau, providing evidence for a rigidity percolation threshold. An increase in band gap and decrease in dielectric constant with increasing H concentration are explained by a decrease in network connectivity as well as mass/electron density. An increase in disorder, as measured by the parameters EU and B1/2, with increasing H concentration is explained by the release of strain in the network and associated decrease in structural disorder. All of these correlations in a-BxC:Hy are found to be very similar to those

  17. Multiwavelength Raman analysis of SiOx and N containing amorphous diamond like carbon films

    International Nuclear Information System (INIS)

    In the current research SiOx and N containing amorphous diamond like carbon (a-C:H) films were deposited on crystalline silicon from hexamethyldisiloxane and hexamethyldisilazane compounds respectively, using closed drift ion beam source and different ion beam energy in a range 300–800 eV. Hydrogen was used as a carrier gas of the precursors. Composition of the films was studied by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The structure of these films was studied employing multiwavelength (325 nm–785 nm) Raman analysis. From the Raman spectra analysis, the characteristic parameters such as the position of G peak, D/G peak intensity ratio as well as dispersion of G (Disp(G)) peak showing topological disorder of sp2 phase in doped a-C:H films were determined. Analysis of Disp (G) and D/G intensity ratio revealed that in both types of films increase of ion beam energy gives higher sp3/sp2 ratio in the films. - Highlights: • Siloxanes are used to incorporate Si, O and N into a-C:H films. • Closed drift ion beam source at varying ion beam energy was used. • Multiwavelength Raman spectroscopy analysis (325–785 nm) was performed. • Dispersion of G peak shows that sp3/sp2 ratio rises with increasing ion beam energy

  18. Strength and Fracture Resistance of Amorphous Diamond-Like Carbon Films for MEMS

    Directory of Open Access Journals (Sweden)

    K. N. Jonnalagadda

    2009-01-01

    Full Text Available The mechanical strength and mixed mode I/II fracture toughness of hydrogen-free tetrahedral amorphous diamond-like carbon (ta-C films, grown by pulsed laser deposition, are discussed in connection to material flaws and its microstructure. The failure properties of ta-C were obtained from films with thicknesses 0.5–3 μm and specimen widths 10–20 μm. The smallest test samples with 10 μm gage section averaged a strength of 7.3 ± 1.2 GPa, while the strength of 20-μm specimens with thicknesses 0.5–3 μm varied between 2.2–5.7 GPa. The scaling of the mechanical strength with specimen thickness and dimensions was owed to deposition-induced surface flaws, and, only in the smallest specimens, RIE patterning generated specimen sidewall flaws. The mode I fracture toughness of ta-C films is KIc=4.4±0.4 MPam, while the results from mixed mode I/II fracture experiments with cracks arbitrarily oriented in the plane of the film compared very well with theoretical predictions.

  19. Energy loss of electrons impinging upon glassy carbon, amorphous carbon, and diamond: Comparison between two different dispersion laws

    International Nuclear Information System (INIS)

    In this paper, we compare and discuss calculated inelastic mean free path, stopping power, range, and reflection electron energy loss spectra obtained using two different and popular dispersion laws. We will present and discuss the results we obtained investigating the interaction of electron beams impinging upon three allotropic forms of carbon, i.e. solid glassy carbon, amorphous carbon, and diamond. We will compare numerical results with experimental reflection electron energy loss spectra

  20. Carbon nanotube materials for hydrogen storage

    Energy Technology Data Exchange (ETDEWEB)

    Dillon, A.C.; Parilla, P.A.; Jones, K.M.; Riker, G.; Heben, M.J. [National Renewable Energy Lab., Golden, CO (United States)

    1998-08-01

    Carbon single-wall nanotubes (SWNTs) are essentially elongated pores of molecular dimensions and are capable of adsorbing hydrogen at relatively high temperatures and low pressures. This behavior is unique to these materials and indicates that SWNTs are the ideal building block for constructing safe, efficient, and high energy density adsorbents for hydrogen storage applications. In past work the authors developed methods for preparing and opening SWNTs, discovered the unique adsorption properties of these new materials, confirmed that hydrogen is stabilized by physical rather than chemical interactions, measured the strength of interaction to be {approximately} 5 times higher than for adsorption on planar graphite, and performed infrared absorption spectroscopy to determine the chemical nature of the surface terminations before, during, and after oxidation. This year the authors have made significant advances in synthesis and characterization of SWNT materials so that they can now prepare gram quantities of high-purity SWNT samples and measure and control the diameter distribution of the tubes by varying key parameters during synthesis. They have also developed methods which purify nanotubes and cut nanotubes into shorter segments. These capabilities provide a means for opening the tubes which were unreactive to the oxidation methods that successfully opened tubes, and offer a path towards organizing nanotube segments to enable high volumetric hydrogen storage densities. They also performed temperature programmed desorption spectroscopy on high purity carbon nanotube material obtained from collaborator Prof. Patrick Bernier and finished construction of a high precision Seivert`s apparatus which will allow the hydrogen pressure-temperature-composition phase diagrams to be evaluated for SWNT materials.

  1. Reduction of tail state on boron doped hydrogenated amorphous silicon oxide films prepared at high hydrogen dilution.

    Science.gov (United States)

    Park, Jinjoo; Iftiquar, S M; Lee, Sunwha; Park, Hyeongsik; Shin, Chonghoon; Jung, Junhee; Lee, Youn-Jung; Balaji, Nagarajan; Yi, Junsin

    2013-12-01

    In this report, we have investigated on the defect state of diborane (B2H6) doped wide bandgap hydrogenated amorphous silicon oxide (p-type a-SiO:H) films prepared using silane (SiH4), hydrogen (H2) and nitrous oxide (N2O) in a radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) system with different hydrogen dilutions. The films prepared with higher hydrogen dilution show lower Urbach energy (Eu), lower microstructure (R*), lower short and medium range disorder (omegaTO, Gamma(TO), I(TA)/I(TO), I(LA)/I(TO)), higher dark conductivity (sigma d) and higher refractive index (n) with high optical gap (Eg). Eu decreases from 248 meV to 153 meV, and R* decreases from 0.46 to 0.26, Raman peak omegaTO-TO mode position shifts from 480.24 to 483.28, GammaTO-full width half maximum of omegaTO decreases from 78.16 to 63.87, I(TA)/I(TO)-the ratio of integrated area of TA and TO mode decreases from 0.624 to 0.474, I(LA)/I(TO)-the ratio of integrated area of LA and TO mode deceases from 0.272 to 0.151, sigma d increases from 4.6 x 10(-7) S/cm to 1.1 x 10(-6) S/cm, n increases from 3.70 to 3.86. Reduced Nd, Eu and R* at wide Eg indicates that the films are more useful for solar cell window layer. Applying this layer to a single junction solar cell shows open circuit voltage (Voc) = 0.80 V, short circuit current density (Jsc) = 16.3 mA/cm2, fill factor (FF) = 72%, efficiency (eta) = 9.4%. PMID:24266147

  2. Functionalized carbon nanostructures for hydrogen catalysis

    Science.gov (United States)

    Hu, Lung-Hao

    Sodium borohydride, NaBH4, is widely used as a source of pure hydrogen. Hydrogen is of interest because it is a source of clean energy. It can be converted directly into electrical energy by means of fuel cells. One of the objectives of this thesis was to develop a new catalytic process to (i) enhance the rate of hydrogen generation, and (ii) to achieve hydrogen generation equal to 100% of the theoretically expected value. The catalyst investigated in this research is constructed by starting from single wall carbon nanotubes (SWNT). This material has a very high specific surface area and good conductivity. The SWNT were formed into a paper by a special filtration process. Polysilazane, a polymeric precursor (Ceraset(TM)-SN from KiON Corp., Wiesbaden, Germany) was diluted by acetone and then layered onto SWNT paper. The Ceraset coated SWNT was then pyrolyzed at 1100°C for three hours to form a silicon carbonitride (SiCN), polymer derived ceramic (PDC), layer on the surface of SWNT filtered paper. This functionalized SiCN carbon nanotube paper (SiCN/CNT) was used as the substrate for catalyst dispersions. The catalyst consisted of transition metals, Pt/Pd/Ru. Suspension solutions of Pt, Pd and Ru were impregnated onto the SiCN/CNT paper with the expectation of creating a monolayer of these transition metals on surface of the SiCN/CNT substrate. It is likely that an interaction could occur between the transition metals and the silicon atoms present in the SiCN layer on the surface of the carbon nanotubes. It is known that transition metals and silicon react to form silicides, suggesting the formation of a strong Si-transition metal bond. Therefore, it is possible that this bond could provide good wetting of metal atoms on SiCN functionalized carbon nanotube substrate. In the limit a monolayer of the transition metals may be achieved, which would correspond to a near zero dihedral angle between the substrate and the cluster of transition metals. In such a scenario a

  3. Amorphous Interface Layer in Thin Graphite Films Grown on the Carbon Face of SiC

    Energy Technology Data Exchange (ETDEWEB)

    Colby, R.; Stach, E.; Bolen, M.L.; Capano, M.A.

    2011-09-05

    Cross-sectional transmission electron microscopy (TEM) is used to characterize an amorphous layer observed at the interface in graphite and graphene films grown via thermal decomposition of C-face 4H-SiC. The amorphous layer does not cover the entire interface, but uniform contiguous regions span microns of cross-sectional interface. Scanning transmission electron microscopy (STEM) images and electron energy loss spectroscopy (EELS) demonstrate that the amorphous layer is a carbon-rich composition of Si/C. The amorphous layer is clearly observed in samples grown at 1600 C for a range of growth pressures in argon, but not at 1500 C, suggesting a temperature-dependent formation mechanism.

  4. Photobiological hydrogen production and carbon dioxide sequestration

    Science.gov (United States)

    Berberoglu, Halil

    Photobiological hydrogen production is an alternative to thermochemical and electrolytic technologies with the advantage of carbon dioxide sequestration. However, it suffers from low solar to hydrogen energy conversion efficiency due to limited light transfer, mass transfer, and nutrient medium composition. The present study aims at addressing these limitations and can be divided in three parts: (1) experimental measurements of the radiation characteristics of hydrogen producing and carbon dioxide consuming microorganisms, (2) solar radiation transfer modeling and simulation in photobioreactors, and (3) parametric experiments of photobiological hydrogen production and carbon dioxide sequestration. First, solar radiation transfer in photobioreactors containing microorganisms and bubbles was modeled using the radiative transport equation (RTE) and solved using the modified method of characteristics. The study concluded that Beer-Lambert's law gives inaccurate results and anisotropic scattering must be accounted for to predict the local irradiance inside a photobioreactor. The need for accurate measurement of the complete set of radiation characteristics of microorganisms was established. Then, experimental setup and analysis methods for measuring the complete set of radiation characteristics of microorganisms have been developed and successfully validated experimentally. A database of the radiation characteristics of representative microorganisms have been created including the cyanobacteria Anabaena variabilis, the purple non-sulfur bacteria Rhodobacter sphaeroides and the green algae Chlamydomonas reinhardtii along with its three genetically engineered strains. This enabled, for the first time, quantitative assessment of the effect of genetic engineering on the radiation characteristics of microorganisms. In addition, a parametric experimental study has been performed to model the growth, CO2 consumption, and H 2 production of Anabaena variabilis as functions of

  5. Microstructural tuning of polycrystalline silicon films from hydrogen diluted amorphous silicon films by AIC

    Energy Technology Data Exchange (ETDEWEB)

    Prathap, P.; Tuzun, O.; Roques, S.; Schmitt, S.; Slaoui, A. [InESS, CNRS-UdS, Strasbourg Cedex-2 (France); Maurice, C. [SMS Centre, UMR CNRS 5146, Ecole des Mines de Saint Etienne, 158 Cours Fauriel, 42023 Saint Etienne Cedex 2 (France)

    2011-03-15

    In the present study, the effect of hydrogen dilution in amorphous silicon on its crystallization kinetics and defect distribution using AIC has been studied. The a -Si films were deposited at different ratios of H{sub 2}/(H{sub 2}+SiH{sub 4}) using plasma enhanced chemical vapour deposition (ECR-PECVD) on glass-ceramic substrates. The thicknesses of aluminium and a -Si:H films were 0.20 {mu}m and 0. 37 {mu}m, respectively. The bi-layer structures were annealed in a tube furnace at 475 C for 8 hours in a nitrogen atmosphere. The results indicated that as the hydrogen dilution for a -Si:H films increased from 0% to 85%, the AIC grown poly-Si films were more stressed compressively, while the Raman peak broadened from 6.7 cm{sup -1} to 8.6 cm{sup -1}. It was found that the initiation of crystallization temperature as well as microstructure of poly-Si films was dramatically influenced by the hydrogen content in precursor a -Si films. The distribution of microstructural defects analysed by Electron Back Scattering Diffraction (EBSD) method indicated that frequency of low angle grain boundaries (LAGB) were more at higher hydrogen dilution ratios while coincident site lattice boundaries (CSL) of first order ({sigma}3), second order ({sigma}9) and third order ({sigma}27) were less sensitive to the hydrogen dilutions/content (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  6. X-ray photoelectron spectroscopic study of nitrogen incorporated amorphous carbon films embedded with nanoparticles

    International Nuclear Information System (INIS)

    The effect of substrate bias on X-ray photoelectron spectroscopy (XPS) study of nitrogen incorporated amorphous carbon (a-C:N) films embedded with nanoparticles deposited by filtered cathodic jet carbon arc technique is discussed. High resolution transmission electron microscope exhibited initially the amorphous structure but on closer examination the film was constituted of amorphous phase with the nanoparticle embedded in the amorphous matrix. X-ray diffraction study reveals dominantly an amorphous nature of the film. A straight forward method of deconvolution of XPS spectra has been used to evaluate the sp3 and sp2 contents present in these a-C:N films. The carbon (C 1s) peaks have been deconvoluted into four different peaks and nitrogen (N 1s) peaks have been deconvoluted into three different peaks which attribute to different bonding state between C, N and O. The full width at half maxima (FWHM) of C 1s peak, sp3 content and sp3/sp2 ratio of a-C:N films increase up to -150 V substrate bias and beyond -150 V substrate bias these parameters are found to decrease. Thus, the parameters evaluated are found to be dependent on the substrate bias which peaks at -150 V substrate bias.

  7. Measurement of hydrogen content in carbon steel exposed to hydrogen gas environment

    International Nuclear Information System (INIS)

    Carbon steel overpacks for high level radioactive waste disposal would be attacked corrosion due to water reduction under reducing condition and the hydrogen would be generated by the corrosion reaction. When the hydrogen is absorbed into metal in the solution or in the hydrogen gas environment, the metal is sometimes damaged by the hydrogen embrittlement. In this study, hydrogen content in carbon steel specimens were measured after the exposure to hydrogen gas environment of 10 MPa, 100degC which is regarded as the most severe case under repository condition. As the results of measurement, the absorbed hydrogen concentration in carbon steel was 0.02∼0.03 ppm and it was concluded that the hydrogen embrittlement due to the contact with hydrogen gas would not be likely to occur on carbon steel overpack under the repository condition. (author)

  8. Strong Metal-Support Interaction: Growth of Individual Carbon Nanofibers from Amorphous Carbon Interacting with an Electron Beam

    DEFF Research Database (Denmark)

    Zhang, Wei; Kuhn, Luise Theil

    2013-01-01

    The article discusses the growth behavior of carbon nanofibers (CNFs). It mentions that CNFs can be synthesized using methods such as arc-discharge, laser ablation and chemical vapor deposition. It further states that CNFs can be grown from a physical mixing of amorphous carbon and CGO/Ni nanopar......The article discusses the growth behavior of carbon nanofibers (CNFs). It mentions that CNFs can be synthesized using methods such as arc-discharge, laser ablation and chemical vapor deposition. It further states that CNFs can be grown from a physical mixing of amorphous carbon and CGO....../Ni nanoparticles, devoid of any gaseous carbon source and external heating and stimulated by an electron beam in a 300 kilo volt transmission electron microscope....

  9. Hydrogenated Amorphous Silicon Sensor Deposited on Integrated Circuit for Radiation Detection

    CERN Document Server

    Despeisse, M; Jarron, P; Kaplon, J; Moraes, D; Nardulli, A; Powolny, F; Wyrsch, N

    2008-01-01

    Radiation detectors based on the deposition of a 10 to 30 mum thick hydrogenated amorphous silicon (a-Si:H) sensor directly on top of integrated circuits have been developed. The performance of this detector technology has been assessed for the first time in the context of particle detectors. Three different circuits were designed in a quarter micron CMOS technology for these studies. The so-called TFA (Thin-Film on ASIC) detectors obtained after deposition of a-Si:H sensors on the developed circuits are presented. High internal electric fields (104 to 105 V/cm) can be built in the a-Si:H sensor and overcome the low mobility of electrons and holes in this amorphous material. However, the deposited sensor's leakage current at such fields turns out to be an important parameter which limits the performance of a TFA detector. Its detailed study is presented as well as the detector's pixel segmentation. Signal induction by generated free carrier motion in the a-Si:H sensor has been characterized using a 660 nm pul...

  10. Annealing optimization of hydrogenated amorphous silicon suboxide film for solar cell application

    International Nuclear Information System (INIS)

    We investigate a passivation scheme using hydrogenated amorphous silicon suboxide (a-SiOx:H) film for industrial solar cell application. The a-SiOx:H films were deposited using plasma-enhanced chemical vapor deposition (PECVD) by decomposing nitrous oxide, helium and silane at a substrate temperature of around 250 deg. C. An extensive study has been carried out on the effect of thermal annealing on carrier lifetime and surface recombination velocity, which affect the final output of the solar cell. Minority carrier lifetimes for the deposited a-SiOx:H films without and with the thermal annealing on 4 Ω·cm p-type float-zone silicon wafers are 270 μs and 670 μs, respectively, correlating to surface recombination velocities of 70 cm/s and 30 cm/s. Optical analysis has revealed a distinct decrease of blue light absorption in the a-SiOx:H films compared to the commonly used intrinsic amorphous silicon passivation used in solar cells. This paper also reports that the low cost and high quality passivation fabrication sequences employed in this study are suitable for industrial processes. (semiconductor physics)

  11. Boron doping compensation of hydrogenated amorphous and polymorphous germanium thin films for infrared detection applications

    Energy Technology Data Exchange (ETDEWEB)

    Moreno, M., E-mail: mmoreno@inaoep.mx [National Institute of Astrophysics, Optics and Electronics, INAOE, P.O. Box 51 and 216, Puebla, Z. P. 72840 Puebla (Mexico); Delgadillo, N. [Universidad Autónoma de Tlaxcala, Av. Universidad No. 1, Z. P. 90006 Tlaxcala (Mexico); Torres, A. [National Institute of Astrophysics, Optics and Electronics, INAOE, P.O. Box 51 and 216, Puebla, Z. P. 72840 Puebla (Mexico); Ambrosio, R. [Technology and Engineering Institute, Ciudad Juarez University UACJ, Av. Del Charro 450N, Z. P. 32310 Chihuahua (Mexico); Rosales, P.; Kosarev, A.; Reyes-Betanzo, C.; Hidalga-Wade, J. de la; Zuniga, C.; Calleja, W. [National Institute of Astrophysics, Optics and Electronics, INAOE, P.O. Box 51 and 216, Puebla, Z. P. 72840 Puebla (Mexico)

    2013-12-02

    In this work we have studied boron doping of hydrogenated amorphous germanium a-Ge:H and polymorphous germanium (pm-Ge:H) in low regimes, in order to compensate the material from n-type (due to oxygen contamination that commonly occurs during plasma deposition) to intrinsic, and in this manner improve the properties that are important for infrared (IR) detection, as activation energy (E{sub a}) and temperature coefficient of resistance (TCR). Electrical, structural and optical characterization was performed on the films produced. Measurements of the temperature dependence of conductivity, room temperature conductivity (σ{sub RT}), E{sub a} and current–voltage characteristics under IR radiation were performed in the compensated a-Ge:H and pm-Ge:H films. Our results demonstrate that, effectively, the values of E{sub a}, TCR and IR detection are improved on the a-Ge:H/pm-Ge:H films, using boron doping in low regimes, which results of interest for infrared detectors. - Highlights: • We reported boron doping compensation of amorphous and polymorphous germanium. • The films were deposited by plasma enhanced chemical vapor deposition. • The aim is to use the films as thermo-sensing elements in un-cooled microbolometers. • Those films have advantages over boron doped a-Si:H used in commercial detectors.

  12. Operando spectroscopic analysis of an amorphous cobalt sulfide hydrogen evolution electrocatalyst.

    Science.gov (United States)

    Kornienko, Nikolay; Resasco, Joaquin; Becknell, Nigel; Jiang, Chang-Ming; Liu, Yi-Sheng; Nie, Kaiqi; Sun, Xuhui; Guo, Jinghua; Leone, Stephen R; Yang, Peidong

    2015-06-17

    The generation of chemical fuel in the form of molecular H2 via the electrolysis of water is regarded to be a promising approach to convert incident solar power into an energy storage medium. Highly efficient and cost-effective catalysts are required to make such an approach practical on a large scale. Recently, a number of amorphous hydrogen evolution reaction (HER) catalysts have emerged that show promise in terms of scalability and reactivity, yet remain poorly understood. In this work, we utilize Raman spectroscopy and X-ray absorption spectroscopy (XAS) as a tool to elucidate the structure and function of an amorphous cobalt sulfide (CoSx) catalyst. Ex situ measurements reveal that the as-deposited CoSx catalyst is composed of small clusters in which the cobalt is surrounded by both sulfur and oxygen. Operando experiments, performed while the CoSx is catalyzing the HER, yield a molecular model in which cobalt is in an octahedral CoS2-like state where the cobalt center is predominantly surrounded by a first shell of sulfur atoms, which, in turn, are preferentially exposed to electrolyte relative to bulk CoS2. We surmise that these CoS2-like clusters form under cathodic polarization and expose a high density of catalytically active sulfur sites for the HER. PMID:26051104

  13. Depth profile study on Raman spectra of high-energy-electron-irradiated hydrogenated amorphous silicon films

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    According to the different penetration depths for the incident lights of 472 nm and 532 nm in hydrogenated amorphous silicon (a-Si:H) thin films, the depth profile study on Raman spectra of a-Si:H films was carried out. The network ordering evolution in the near surface and interior region of the unirradiated and irradiated a-Si:H films was investigated. The results show that there is a structural improvement in the shortand intermediate-range order towards the surface of the unirradiated a-Si:H films. The amorphous silicon network in the near and interior region becomes more disordered on the shortand intermediate-range scales after being irradiated with high energy electrons. However, the surface of the irradiated films becomes more disordered in comparison with their interior region, indicating that the created defects caused by electron irradiation are concentrated in the near surface of the irradiated films. Annealing eliminates the irradiation effects on a-Si:H thin films and the structural order of the irradiated films is similar to that of the unirradiated ones after being annealed. There exists a structural improvement in the shortand intermediate-range order towards the surface of the irradiated a-Si:H films after being annealed.

  14. High sp~3 content hydrogen-free amorphous diamond: an excellent electron field emission material

    Institute of Scientific and Technical Information of China (English)

    茅东升; 赵俊; 李炜; 王曦; 柳襄怀; 诸玉坤; 李琼; 徐静芳

    1999-01-01

    Details are given of a study of the characteristics of field-induced electron emission from hydrogen-free high sp~3 content (>90 % ) amorphous diamond (a-D) film deposited on heavily doped (p<0.01 Ω·cm) n-type monoerystalline Si (111 ) substrate. It is demonstrated that a-D film has excellent electron field emission properties. The emission current can reach 0.9 μA at applied field as low as 1 V/μm, and the emission current density can be ahout several mA/cm~2 under 20 V/μm. The emission current is stable when the beginning current is at 50 μA within 72 h. Uniform fluorescence display of electron emission from the whole face of the a-D film under the electric field of 10-12 V/μm is also observed. The contribution of excellent electron emission property results from the smooth, uniform, amorphous surface and high sp~3 content of the a-D film.

  15. Acoustically induced optical second harmonic generation in hydrogenated amorphous silicon films

    CERN Document Server

    Ebothe, J; Cabarrocas, P R I; Godet, C; Equer, B

    2003-01-01

    Acoustically induced second harmonic generation (AISHG) in hydrogenated amorphous silicon (a-Si : H) films of different morphology has been observed. We have found that with increasing acoustical power, the optical SHG of Gd : YAB laser light (lambda = 2.03 mu m) increases and reaches its maximum value at an acoustical power density of about 2.10 W cm sup - sup 2. With decreasing temperature, the AISHG signal strongly increases below 48 K and correlates well with the temperature behaviour of differential scanning calorimetry indicating near-surface temperature phase transition. The AISHG maxima were observed at acoustical frequencies of 10-11, 14-16, 20-22 and 23-26 kHz. The independently performed measurements of the acoustically induced IR spectra have shown that the origin of the observed phenomenon is the acoustically induced electron-phonon anharmonicity in samples of different morphology.

  16. Electroless chemical grafting of nitrophenyl groups on n-doped hydrogenated amorphous silicon surfaces.

    Science.gov (United States)

    Kim, Chulki; Oh, Kiwon; Han, Seunghee; Kim, Kyungkon; Kim, Il Won; Kim, Heesuk

    2014-08-01

    The direct spontaneous grafting of 4-nitrophenyl molecules onto n-doped hydrogenated amorphous silicon (a-Si:H) surfaces without external ultraviolet, thermal, or electrochemical energy was invegtigated. Clean n-doped a-Si:H thin films were dipped in a solution of 4-nitrobenzenediazonium salts (PNBD) in acetonitrile. After the modified surfaces were rinsed, they were analyzed qualitatively and quantitatively by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). XPS and AFM results show that the reaction of an n-doped a-Si:H thin film with PNBD self-terminates without polymerization, after 5 h, and the surface number density of 4-nitrophenyl molecules is 4.2 x 10(15)/cm2. These results demonstrate that the spontaneous grafting of nitrophenyl layers onto n-doped a-Si:H thin films is an attractive pathway toward forming interfaces between a-Si:H and organic layers under ambient conditions. PMID:25936109

  17. Hydrogen-induced rupture of strained Si─O bonds in amorphous silicon dioxide.

    Science.gov (United States)

    El-Sayed, Al-Moatasem; Watkins, Matthew B; Grasser, Tibor; Afanas'ev, Valery V; Shluger, Alexander L

    2015-03-20

    Using ab initio modeling we demonstrate that H atoms can break strained Si─O bonds in continuous amorphous silicon dioxide (a-SiO(2)) networks, resulting in a new defect consisting of a threefold-coordinated Si atom with an unpaired electron facing a hydroxyl group, adding to the density of dangling bond defects, such as E' centers. The energy barriers to form this defect from interstitial H atoms range between 0.5 and 1.3 eV. This discovery of unexpected reactivity of atomic hydrogen may have significant implications for our understanding of processes in silica glass and nanoscaled silica, e.g., in porous low-permittivity insulators, and strained variants of a-SiO(2). PMID:25839289

  18. AFM and STM investigations of hydrogenated amorphous silicon: topography and barrier heights

    Energy Technology Data Exchange (ETDEWEB)

    Herion, J. [Forschungszentrum Juelich GmbH (Germany). Inst. fuer Schicht- und Ionentechnik; Szot, K. [Silesian Univ., Katowice (Poland); Barzen, S. [Colorado Univ., Boulder, CO (United States). Joint Inst. for Laboratory Astrophysics; Siebke, F. [Forschungszentrum Juelich GmbH (Germany). Inst. fuer Schicht- und Ionentechnik; Teske, M. [Forschungszentrum Juelich GmbH (Germany). Inst. fuer Grenzflaechenforschung und Vakuumphysik

    1997-05-01

    As-grown films of hydrogenated amorphous silicon (a-Si : H, highly phosphorous-doped) were investigated by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Hills up to 10 nm in height and 10 to 20 nm in diameter have been observed by AFM. By using STM in a new high-sensitivity mode, (1) atomically smooth areas (roughness about 0.3 A rms) which occur at the top of the hills, (2) subnanometer structures several A in height which cover large parts of the surface have been identified. Simultaneous measurements of the local apparent barrier heights (LABH) show a clear correlation to the topography. Areas showing subnanometer structures have always low LABHs while the highest values of the LABH occur on the smooth areas. (orig.). With 5 figs.

  19. Characterization of defects in hydrogenated amorphous silicon deposited on different substrates by capacitance techniques

    Energy Technology Data Exchange (ETDEWEB)

    Darwich, R., E-mail: rdarwich@aec.org.sy [Physics Department, Atomic Energy Commission of Syria, P. O. Box 6091, Damascus (Syrian Arab Republic); Roca i Cabarrocas, P. [Laboratoire de physique des interfaces et des couches minces, CNRS, Ecole Polytechnique, 91128 Palaiseau France (France)

    2011-06-01

    Hydrogenated amorphous silicon (a-Si:H) thin films deposited on crystalline silicon and Corning glass substrate were analyzed using different capacitance techniques. The distribution of localized states and some electronic properties were studied using the temperature, frequency and bias dependence of the Schottky barrier capacitance and deep level transient spectroscopy. Our results show that the distribution of the gap states depends on the type of substrate. We have found that the films deposited on c-Si substrate represent only one positively charged or prerelaxed neutral deep state and one interface state, while the films deposited on glass substrate have one interface state and three types of deep defect states, positively or prerelaxed neutral, neutral and negatively charged.

  20. Characterization of defects in hydrogenated amorphous silicon deposited on different substrates by capacitance techniques

    International Nuclear Information System (INIS)

    Hydrogenated amorphous silicon (a-Si:H) thin films deposited on crystalline silicon and Corning glass substrate were analyzed using different capacitance techniques. The distribution of localized states and some electronic properties were studied using the temperature, frequency and bias dependence of the Schottky barrier capacitance and deep level transient spectroscopy. Our results show that the distribution of the gap states depends on the type of substrate. We have found that the films deposited on c-Si substrate represent only one positively charged or pre relaxed neutral deep state and one interface state, while the films deposited on glass substrate have one interface state and three types of deep defect states, positively or pre relaxed neutral, neutral and negatively charged. (author)

  1. Characterization of defects in hydrogenated amorphous silicon deposited on different substrates by capacitance techniques

    International Nuclear Information System (INIS)

    Hydrogenated amorphous silicon (a-Si:H) thin films deposited on crystalline silicon and Corning glass substrate were analyzed using different capacitance techniques. The distribution of localized states and some electronic properties were studied using the temperature, frequency and bias dependence of the Schottky barrier capacitance and deep level transient spectroscopy. Our results show that the distribution of the gap states depends on the type of substrate. We have found that the films deposited on c-Si substrate represent only one positively charged or prerelaxed neutral deep state and one interface state, while the films deposited on glass substrate have one interface state and three types of deep defect states, positively or prerelaxed neutral, neutral and negatively charged.

  2. Broadband, stable and highly coherent supercontinuum generation at telecommunication wavelengths in an hydrogenated amorphous silicon waveguide

    CERN Document Server

    Leo, F; Kuyken, B; Roelkens, G; Gorza, S -P

    2014-01-01

    Hydrogenated amorphous silicon (a:Si-H) has recently been recognized as a highly nonlinear CMOS compatible photonic platform. We experimentally demonstrate the generation of a supercontinuum (SC) spanning over 500 nm in a-Si:H photonic wire waveguide at telecommunication wavelengths using femtosecond input pulse with energy lower than 5 pJ. Numerical modeling of pulse propagation in the waveguide, based on the experimentally characterized dispersion profile, shows that the supercontinuum is the result of soliton fission and dispersive wave generation. It is demonstrated that the SC is highly coherent and that the waveguides do not suffer from material degradation under femtosecond pulse illumination. Finally, a direct comparison of SC generation in c-Si and a-Si:H waveguides confirms the higher performances of a-Si:H over c-Si for broadband low power SC generation at telecommunication wavelengths.

  3. Hydrogen plasma treatment for improved conductivity in amorphous aluminum doped zinc tin oxide thin films

    Directory of Open Access Journals (Sweden)

    M. Morales-Masis

    2014-09-01

    Full Text Available Improving the conductivity of earth-abundant transparent conductive oxides (TCOs remains an important challenge that will facilitate the replacement of indium-based TCOs. Here, we show that a hydrogen (H2-plasma post-deposition treatment improves the conductivity of amorphous aluminum-doped zinc tin oxide while retaining its low optical absorption. We found that the H2-plasma treatment performed at a substrate temperature of 50 °C reduces the resistivity of the films by 57% and increases the absorptance by only 2%. Additionally, the low substrate temperature delays the known formation of tin particles with the plasma and it allows the application of the process to temperature-sensitive substrates.

  4. Surface structure and optical property of amorphous carbon nanotubes hybridized with cadmium selenide quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Tan, Kim Han, E-mail: kimhan8419@gmail.com; Johan, Mohd Rafie [University of Malaya, Nanomaterials Engineering Research Group, Advanced Materials Research Laboratory, Department of Mechanical Engineering (Malaysia)

    2013-09-15

    Amorphous carbon nanotubes ({alpha}-CNTs) were synthesized by a chemical reaction between ferrocene and ammonium chloride at low temperature. The as-synthesized {alpha}-CNTs were then hybridized with cadmium selenide quantum dots (CdSe QDs) through a simple chemical process. Raman spectra reveal the amorphous nature of the {alpha}-CNTs surface. X-ray diffraction pattern confirmed the amorphous phase of carbon and the formation of CdSe QDs crystalline phase. Field emission scanning electron microscopy and transmission electron microscopy (TEM and HRTEM) indicate that the successfully formed hybridized {alpha}-CNTs-CdSe QDs possess an average outer diameter in the range of 110-130 nm. The CdSe QDs fall in the size range of 15-40 nm. UV-visible spectroscopy showed quantum confinement effect due to the attachment of CdSe QDs on the surface of {alpha}-CNTs.

  5. Charge deep-level transient spectroscopy study of high-energy-electron-beam-irradiated hydrogenated amorphous silicon

    NARCIS (Netherlands)

    Klaver, A.; Nádaždy, V.; Zeman, M.; Swaaiij, R.A.C.M.M.

    2006-01-01

    We present a study of changes in the defect density of states in hydrogenated amorphous silicon (a-Si:H) due to high-energy electron irradiation using charged deep-level transient spectroscopy. It was found that defect states near the conduction band were removed, while in other band gap regions the

  6. Estimation of the impact of electrostatic discharge on density of states in hydrogenated amorphous silicon thin-film transistors

    NARCIS (Netherlands)

    Tosic Golo, Natasa; Wal, van der Siebrigje; Kuper, F.G.; Mouthaan, A.J.

    2002-01-01

    The objective of this letter is to give an estimation of the impact of an electrostatic discharge (ESD) stress on the density of states (DOS) within the energy gap of hydrogenated amorphous silicon (a-Si:H) thin-film transistors. ESD stresses were applied by means of a transmission line model tester

  7. Effect of hydrogen on the properties of amorphous alloys 'finemet' type: PEN-X effect

    Energy Technology Data Exchange (ETDEWEB)

    Spivak, L.V.; Skryabina, N.Ye. [Perm State Univ. (Russian Federation)

    1999-09-01

    Elastic properties of the amorphous metallic alloys based on iron and cobalt were found to decrease after hydrogenation, and to recover upon subsequent storage at 295 K. The possible causes for this unusual behaviour are discussed on the basis of measurements of electrical resistance and magnetic susceptibility, as well as X-ray diffraction data.

  8. Residual stresses and mechanical properties of amorphous carbon films on 40 CAD 6-12 plasma nitrided steel

    International Nuclear Information System (INIS)

    Full text.An investigation has been carried out to study the effect of deposition time and benzene flow rate on residual stresses level, morphological, hardness, adhesion strength and friction coefficient of carbon films. Amorphous hydrogenated carbon a-c:H films were deposited on plasma nitrided layers (ε+γ') of 40 CAD 6-12 steel substrate using Microwave Electron Cyclotron Resonance Plasma Assisted Chemical Vapour Deposition nethod with benzene/Argon gas as precursor. The coatings have been deposited at different temperatures 350 and 520 degree celsius for times 3,5,60 and 120 minutes under different pressures ranging from 10-3 to 10-5 mbar. A wide range of thickness values of the amorphous carbon layers (0.4 up 15 μm) was formed as function of the deposition conditions and precursors, when the bias voltage (-200V) and microwave power (300 W) were kept constant. Stress behavior in carbon films has been investigated by x-ray diffraction measurement using the sin2Ψ technique. The type and the value of stress have shown a strong dependence of film thickness and the benzene flow rate (σ= -259 ÷ 5 MPa). Scratch tests revealed that they possess excellent adhesion strength and exhibit both low values of friction coefficient and roughness. The has been concluded than the micro hardness measurements results are not influenced by the coating thickness. The hardness of the coatings is normally below 30 GPa for coatings with 7 sccm of benzene flow rate. The carbon films were characterized by SEM and Raman spectroscopy

  9. Silicon and aluminum doping effects on the microstructure and properties of polymeric amorphous carbon films

    Science.gov (United States)

    Liu, Xiaoqiang; Hao, Junying; Xie, Yuntao

    2016-08-01

    Polymeric amorphous carbon films were prepared by radio frequency (R.F. 13.56 MHz) magnetron sputtering deposition. The microstructure evolution of the deposited polymeric films induced by silicon (Si) and aluminum(Al) doping were scrutinized through infrared spectroscopy, multi-wavelength Raman spectroscopy, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The comparative results show that Si doping can enhance polymerization and Al doping results in an increase in the ordered carbon clusters. Si and Al co-doping into polymeric films leads to the formation of an unusual dual nanostructure consisting of cross-linked polymer-like hydrocarbon chains and fullerene-like carbon clusters. The super-high elasticity and super-low friction coefficients (amorphous carbon films with different elements doping are also discussed in detail.

  10. Opto-electrical properties of amorphous carbon thin film deposited from natural precursor camphor

    Energy Technology Data Exchange (ETDEWEB)

    Pradhan, Debabrata [Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400 076 (India)]. E-mail: dpradhan@sciborg.uwaterloo.ca; Sharon, Maheshwar [Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400 076 (India)

    2007-06-30

    A simple thermal chemical vapor deposition technique is employed for the pyrolysis of a natural precursor 'camphor' and deposition of carbon films on alumina substrate at higher temperatures (600-900 deg. C). X-ray diffraction measurement reveals the amorphous structure of these films. The carbon films properties are found to significantly vary with the deposition temperatures. At higher deposition temperature, films have shown predominately sp{sup 2}-bonded carbon and therefore, higher conductivity and lower optical band gap (Tauc gap). These amorphous carbon (a-C) films are also characterized with Raman and X-ray photoelectron spectroscopy. In addition, electrical and optical properties are measured. The thermoelectric measurement shows these as-grown a-C films are p-type in nature.

  11. A solvothermal method for synthesizing monolayer protected amorphous calcium carbonate clusters.

    Science.gov (United States)

    Sun, Shengtong; Gebauer, Denis; Cölfen, Helmut

    2016-05-19

    A solvothermal method was developed for synthesizing organic monolayer protected amorphous calcium carbonate clusters using 10,12-pentacosadiynoic acid as ligand, ethanol as solvent and NaHCO3 decomposition as CO2 source, which can be extended to synthesize other monolayer protected mineral clusters. PMID:27161807

  12. Interfacial electrical properties of ion-beam sputter deposited amorphous carbon on silicon

    Science.gov (United States)

    Khan, A. A.; Woollam, J. A.; Chung, Y.; Banks, B.

    1983-01-01

    Amorphous, 'diamond-like' carbon films have been deposited on Si substrates, using ion-beam sputtering. The interfacial properties are studied using capacitance and conductance measurements. Data are analyzed using existing theories for interfacial electrical properties. The density of electronic states at the interface, along with corresponding time constants are determined.

  13. A transparent hybrid of nanocrystalline cellulose and amorphous calcium carbonate nanoparticles

    OpenAIRE

    Gebauer, Denis; Oliynyk, Vitaliy; Salajkova, Michaela; Sort, Jordi; Zhou, Qi; Bergström, Lennart; Salazar-Alvarez, German

    2011-01-01

    Nanocellulose hybrids are promising candidates for biodegradable multifunctional materials. Hybrids of nanocrystalline cellulose (NCC) and amorphous calcium carbonate (ACC) nanoparticles were obtained through a facile chemical approach over a wide range of compositions. Controlling the interactions between NCC and ACC results in hard, transparent structures with tunable composition, homogeneity and anisotropy.

  14. Citrate effects on amorphous calcium carbonate (ACC) structure, stability, and crystallization

    DEFF Research Database (Denmark)

    Tobler, Dominique Jeanette; Rodriguez Blanco, Juan Diego; Dideriksen, Knud;

    2015-01-01

    Understanding the role of citrate in the crystallization kinetics of amorphous calcium carbonate (ACC) is essential to explain the formation mechanisms, stabilities, surface properties, and morphologies of CaCO3 biominerals. It also contributes to deeper insight into fluid-mineral inte...

  15. Electrochemical Tuning of Amorphous Carbon Amount and Surface Oxidation Degree of Graphitic Quantum Dots.

    Science.gov (United States)

    Wang, Jun; Li, Yan; Zhang, Bo-Ping; Ma, Ning; Ge, Juan; Li, Ling; Li, Ting; Liu, Qian-Qian

    2016-04-01

    Graphitic quantum dots (GQDs) have attracted much interesting of researchers because of its amazing optical properties and its ability to be used for many applications. Now, there are various methods have been reported for preparation of GQDs. Among them electrochemical method is simple technology, while it can afford various conditions to realize controllable prepared of GQDs. In this study, we tuned the PH values of electrolyte to probe the relationship of electrolyte environment and GQDs' optical properties as well as to seek the effective controllable condition for GQDs' preparation. It is found that the density of oxygen-related functional groups and the amount of amorphous carbon of GQDs were related to the PH values of electrolyte. The amount of amorphous carbon decreased as the PH values increased in the region of 6.6 to 7.1. Although, the positions of photoluminescence (PL) peak almost no changed of GQDs with different density of oxygen-related functional groups, GQDs with the lowest amount of amorphous carbon achieved the maximum PL intensity. Therefore, controlling amorphous carbon's amount by electrochemical method may afford a new direction to improve the fluorescence (FL) emission of GQDs. PMID:27451661

  16. The effect of temperature on the tribological mechanisms and reactivity of hydrogenerated, amorphous diamond-like carbon coatings under oil-lubricated conditions

    OpenAIRE

    Roman, E.; Kalin, Mitjan; Vižintin, Jože

    2015-01-01

    In this work we present the wear and friction behaviour of boundary-lubricated, hydrogenated, amorphous, diamond-like carbon coatings (a-C:H), in self-mated a-C:H/a-C:H contacts, at three different testing temperaturesČ 20, 80, 150 °C. We present results from Auger electron spectroscopy, X-ray photoelectron spectroscopy and Raman analyses relating to the chemical and structural changes in the diamond-like carbon coatings duringsliding in the presence of mineral oil, with and without additives...

  17. Effects of Atomic-Scale Structure on the Fracture Properties of Amorphous Carbon - Carbon Nanotube Composites

    Science.gov (United States)

    Jensen, Benjamin D.; Wise, Kristopher E.; Odegard, Gregory M.

    2015-01-01

    The fracture of carbon materials is a complex process, the understanding of which is critical to the development of next generation high performance materials. While quantum mechanical (QM) calculations are the most accurate way to model fracture, the fracture behavior of many carbon-based composite engineering materials, such as carbon nanotube (CNT) composites, is a multi-scale process that occurs on time and length scales beyond the practical limitations of QM methods. The Reax Force Field (ReaxFF) is capable of predicting mechanical properties involving strong deformation, bond breaking and bond formation in the classical molecular dynamics framework. This has been achieved by adding to the potential energy function a bond-order term that varies continuously with distance. The use of an empirical bond order potential, such as ReaxFF, enables the simulation of failure in molecular systems that are several orders of magnitude larger than would be possible in QM techniques. In this work, the fracture behavior of an amorphous carbon (AC) matrix reinforced with CNTs was modeled using molecular dynamics with the ReaxFF reactive forcefield. Care was taken to select the appropriate simulation parameters, which can be different from those required when using traditional fixed-bond force fields. The effect of CNT arrangement was investigated with three systems: a single-wall nanotube (SWNT) array, a multi-wall nanotube (MWNT) array, and a SWNT bundle system. For each arrangement, covalent bonds are added between the CNTs and AC, with crosslink fractions ranging from 0-25% of the interfacial CNT atoms. The SWNT and MWNT array systems represent ideal cases with evenly spaced CNTs; the SWNT bundle system represents a more realistic case because, in practice, van der Waals interactions lead to the agglomeration of CNTs into bundles. The simulation results will serve as guidance in setting experimental processing conditions to optimize the mechanical properties of CNT

  18. Chemical bonding in hard and elastic amorphous carbon-nitride films

    Science.gov (United States)

    Gammon, Wesley Jason

    In this study, the chemical bonding in hard and elastic amorphous carbon nitride (a-CNx) films is investigated with x-ray photoelectron spectroscopy (XPS) and 15N, 13C, and 1H nuclear magnetic resonance (NMR) spectroscopy. The films were deposited by DC Magnetron sputtering in a pure nitrogen discharge on Si(001) substrates at 300--400°C. Nanoindentation measurements reveal an elastic modulus of ˜50 GPa and a hardness of ˜5 GPa, thus confirming our films are highly elastic but resist plastic deformation. Our 13C NMR study demonstrates the absence of sp 3-bonded carbon in this material. Collectively, our N(1s) XPS, 13C NMR, and 15N NMR data suggest a film-bonding model that has an aromatic carbon structure with sp2-hybridized nitrogen incorporated in heterocyclic rings. We demonstrate that the nitrogen bonding is predominantly in configurations similar to those in pyridine and pyrrole. In addition, the data indicate that the a-CNx films prepared for this study have low hydrogen content, but are hydrophilic. Specifically, results from 15N and 13C cross polarization (CP) and 1H magic angle spinning (MAS) NMR experiments suggest that nitrogen sites are susceptible to protonation from water absorbed during sample preparation for the NMR experiments. The sensitivity of the surface of a-CNx to water absorption may impact tribological applications for this material. In accord with our XPS and NMR spectroscopic studies on a-CN x films, we propose a film-structure model consisting of buckled graphitic planes that are cross-linked together by sp2 hybridized carbons. The curvature and cross-linking is attributed to a type of compound defect, which is formed by placing a pentagon next to single-atom vacancy in a graphite layer. Our proposed film structure is called the pentagon-with-vacancy-defect (5VD) model. Using Hartree-Fock calculations, we show that the 5VD, film-structure model is compatible with our XPS, NMR, and nanoindentation measurements and with previous

  19. Transformation from amorphous to nano-crystalline SiC thin films prepared by HWCVD technique without hydrogen dilution

    Indian Academy of Sciences (India)

    F Shariatmadar Tehrani

    2015-09-01

    Silicon carbide (SiC) thin films were deposited on Si(111) by the hot wire chemical vapour deposition (HWCVD) technique using silane (SiH4) and methane (CH4) gases without hydrogen dilution. The effects of SiH4 to CH4 gas flow ratio (R) on the structural properties, chemical composition and photoluminescence (PL) properties of the films deposited at the different gas flow ratios were investigated and compared. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra revealed a structural transition from amorphous SiC to cubic nano-crystalline SiC films with the increase in the gas flow ratio. Raman scattering confirmed the multi-phased nature of the films. Auger electron spectroscopy showed that the carbon incorporation in the film structure was strongly dependent on the gas flow ratio. A similar broad visible room-temperature PL with two peaks was observed for all SiC films. The main PL emission was correlated to the band to band transition in uniform a-SiC phase and the other lower energy emission was related to the confined a-Si : H clusters in a-SiC matrix. SiC nano-crystallites exhibit no significant contribution to the radiative recombination.

  20. Local structure reconstruction in hydrogenated amorphous silicon from angular correlation and synchrotron diffraction studies

    International Nuclear Information System (INIS)

    Hydrogenated amorphous silicon (a-Si:H) is a widely used thin film semiconductor material which is still incompletely understood. It is generally assumed to form a continuous random network, with a high concentration of coordination defects (dangling bonds), which are hydrogen terminated. Neither the exact nature of these sites nor the degree of medium range order has been fully determined. In this paper, we present the first results for the local structure, from a combined study using angular correlation of positron annihilation radiation (ACAR) and synchrotron radiation diffraction. Reciprocal space information is obtained directly, for the mesoscale structure and the local defect structure, from the orientation dependent diffraction and 2D-ACAR patterns, respectively. Furthermore, inversion of both patterns yields a comparison of real space information through maps of the silicon-silicon pair correlation function and the electron-positron autocorrelation function B 2γ(r). From this information, it is possible to identify the dominant structural defect as a vacancy-size dangling bond cluster, around which the network strain is fully relaxed

  1. [The Influence of Deposition Pressure on the Properties of Hydrogenated Amorphous Silicon Thin Films].

    Science.gov (United States)

    Yuan, Jun-bao; Yang, Wen; Chen, Xiao-bo; Yang, Pei-zhi; Song, Zhao-ning

    2016-02-01

    Hydrogenated amorphous silicon (a-Si:H) thin films on soda-lime glass substrates were deposited by plasma enhanced chemical vapor deposition (PECVD) using disilane and hydrogen as source gases. To study the influence of deposition pressure on the deposition rate, optical band gap and structure factor, a surface profilometer, an ultraviolet-visible spectrometer, a Fourier transform infrared (FTIR) spectrometer and a scanning electron microscopy (SEM) were used to characterize the deposited thin films. It is found that the deposition rate firstly increased and then decreased and the optical band gap monotonically decreased with the increasing deposition pressure. Moreover, the formation of SiH bond was preferable to the formation of SH₂ or SiH₃ bond when the deposition pressure was less than 210 Pa, while it was opposite when the deposition pressure is higher than 210 Pa. Finally, the deposition pressure in the range of 110~210 Pa was found to be more suitable for the preparation of high quality a-Si:H thin films. PMID:27209724

  2. Confinement of hydrogen at high pressure in carbon nanotubes

    Science.gov (United States)

    Lassila, David H.; Bonner, Brian P.

    2011-12-13

    A high pressure hydrogen confinement apparatus according to one embodiment includes carbon nanotubes capped at one or both ends thereof with a hydrogen-permeable membrane to enable the high pressure confinement of hydrogen and release of the hydrogen therethrough. A hydrogen confinement apparatus according to another embodiment includes an array of multi-walled carbon nanotubes each having first and second ends, the second ends being capped with palladium (Pd) to enable the high pressure confinement of hydrogen and release of the hydrogen therethrough as a function of palladium temperature, wherein the array of carbon nanotubes is capable of storing hydrogen gas at a pressure of at least 1 GPa for greater than 24 hours. Additional apparatuses and methods are also presented.

  3. TEM-simulation of amorphous carbon films: influence of supercell packaging.

    Science.gov (United States)

    Schultrich, H; Schultrich, B

    2001-07-01

    Recent developments in thin film technology allow to prepare deliberately amorphous carbon films with structures widely varying between graphite-like (sp2) and diamond-like (sp3) atomic bonds. This leads to amorphous structures with correspondingly varying densities. By periodically changing deposition conditions, nanometer multilayers may be prepared consisting of carbon layers of different density. Simulation of the electron microscopic imaging allows to differentiate between such real structural details (on the nanometer scale) and artefacts induced by the imaging procedure. But it must be assured that the modeled structure reflects the real one with sufficient accuracy. Thorough comparison of different simulation strategies shows that for the adequate simulation of TEM imaging of amorphous materials, the thickness of the layer with independently distributed atoms has to exceed a certain limit. Then, the statistical scattering of the randomly distributed atoms will be averaged. Otherwise, if the model of the transmission electron microscopy sample is constructed as iteration of thin identical supercells, the superposition of scattering waves with constant phase differences results in enhanced local fluctuations burying the multilayer structure. For thicker packages of supercells with independent random distributions, the effect of statistical atomic arrangements is more and more leveled off. Hence, nanometer structures based on regions with different density will be visible more distinctively in the random background. For carbon, this critical thickness amounts to about 4 nm. This is of special importance for the visualization of nanoscaled heterogeneities like multilayers or nanotube-like inclusions in amorphous matrices. PMID:11419873

  4. The influence of hydrogen on the chemical, mechanical, optical/electronic, and electrical transport properties of amorphous hydrogenated boron carbide

    Energy Technology Data Exchange (ETDEWEB)

    Nordell, Bradley J.; Karki, Sudarshan; Nguyen, Thuong D.; Rulis, Paul; Caruso, A. N.; Paquette, Michelle M., E-mail: paquettem@umkc.edu [Department of Physics and Astronomy, University of Missouri-Kansas City, Kansas City, Missouri 64110 (United States); Purohit, Sudhaunshu S. [Department of Chemistry, University of Missouri-Kansas City, Kansas City, Missouri 64110 (United States); Li, Han; King, Sean W. [Logic Technology Development, Intel Corporation, Hillsboro, Oregon 97124 (United States); Dutta, Dhanadeep; Gidley, David [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States); Lanford, William A. [Department of Physics, University at Albany, Albany, New York 12222 (United States)

    2015-07-21

    Because of its high electrical resistivity, low dielectric constant (κ), high thermal neutron capture cross section, and robust chemical, thermal, and mechanical properties, amorphous hydrogenated boron carbide (a-B{sub x}C:H{sub y}) has garnered interest as a material for low-κ dielectric and solid-state neutron detection applications. Herein, we investigate the relationships between chemical structure (atomic concentration B, C, H, and O), physical/mechanical properties (density, porosity, hardness, and Young's modulus), electronic structure [band gap, Urbach energy (E{sub U}), and Tauc parameter (B{sup 1/2})], optical/dielectric properties (frequency-dependent dielectric constant), and electrical transport properties (resistivity and leakage current) through the analysis of a large series of a-B{sub x}C:H{sub y} thin films grown by plasma-enhanced chemical vapor deposition from ortho-carborane. The resulting films exhibit a wide range of properties including H concentration from 10% to 45%, density from 0.9 to 2.3 g/cm{sup 3}, Young's modulus from 10 to 340 GPa, band gap from 1.7 to 3.8 eV, Urbach energy from 0.1 to 0.7 eV, dielectric constant from 3.1 to 7.6, and electrical resistivity from 10{sup 10} to 10{sup 15} Ω cm. Hydrogen concentration is found to correlate directly with thin-film density, and both are used to map and explain the other material properties. Hardness and Young's modulus exhibit a direct power law relationship with density above ∼1.3 g/cm{sup 3} (or below ∼35% H), below which they plateau, providing evidence for a rigidity percolation threshold. An increase in band gap and decrease in dielectric constant with increasing H concentration are explained by a decrease in network connectivity as well as mass/electron density. An increase in disorder, as measured by the parameters E{sub U} and B{sup 1/2}, with increasing H concentration is explained by the release of strain in the network and associated decrease in

  5. Development of amorphous carbon protective coatings on poly(vinyl)chloride

    International Nuclear Information System (INIS)

    The great versatility of polymers has promoted their application in a series of ordinary situations. The development of specific devices from polymers, however, requires modifications to fit specific stipulations. In this work the surface properties of thin films grown onto polyvinylchloride (PVC) were investigated. Hydrogenated amorphous carbon films were deposited onto commercial PVC plates from acetylene and argon plasmas excited by radiofrequency (13.56 MHz, 70 W) power. The proportion of acetylene in the gas feed was varied against that of argon, keeping the total pressure constant at 2.5 Pa. Deposition time was 1800 s. Film elemental composition was analyzed by X-ray photoelectron spectroscopy, XPS. Water contact angle measurements were performed using the sessile drop technique. The root mean squared roughness was derived from 50 x 50 μm2 surface topographic images, acquired by scanning probe microscopy. Nanoindentation and pin-on-disk techniques were employed on the determination of film hardness and sliding wear, respectively. Oxidation resistance was obtained through the etching rate of the samples in oxygen radiofrequency (1.3 Pa, 50 W) plasmas. From XPS analysis it was detected oxygen and nitrogen contamination in all the samples. It was also found that sp3/sp2 ratio depends on the proportion of argon in the plasma. At lower argon concentrations, hardness, wear and oxidation resistances were all improved with respect to the uncoated PVC. In such conditions, the surface wettability is low indicating a moderate receptivity to water. This combination of properties, ascribed to a balance between the ion bombardment and deposition processes, is suitable for materials exposed to rigorous weathering conditions.

  6. Hydrogen storage in single walled carbon nanotubes

    International Nuclear Information System (INIS)

    Claims have emerged recently, of high hydrogen storage capacities at room temperature and above, for carbons such as single-wall and multi-walled nanotubes. We have been unable to verify any claims of high capacities at room temperature and low pressure. For (10,10) single wall carbon nanotubes, we used a computer controlled Sievert's apparatus to measure an adsorption at RT of 0.07 wt% gravimetric density at 1 bar, typical of what is expected on the basis of BET surface area measurements for carbons. At high pressures of > 60 bar and temperatures of 80K gravimetric densities up to ∼ 8 wt% are obtained, but more typically ∼ 7 wt% after a few adsorption desorption cycles. These values and isotherm shapes can be attributed to rearrangement of the rope structure that is formed by condensed nanotubes. Certain fullerites can also exhibit adsorption/desorption cycle dependent capacity, ranging from 2.5 to 4 wt% at 80K and 120 bar. (author)

  7. Reactive Infiltration of Silicon Melt Through Microporous Amorphous Carbon Preforms

    Science.gov (United States)

    Sangsuwan, P.; Tewari, S. N.; Gatica, J. E.; Singh, M.; Dickerson, R.

    1999-01-01

    The kinetics of unidirectional capillary infiltration of silicon melt into microporous carbon preforms have been investigated as a function of the pore morphology and melt temperature. The infiltrated specimens showed alternating bands of dark and bright regions, which corresponded to the unreacted free carbon and free silicon regions, respectively. The decrease in the infiltration front velocity for increasing infiltration distances, is in qualitative agreement with the closed-form solution of capillarity driven fluid flow through constant cross section cylindrical pores. However, drastic changes in the thermal response and infiltration front morphologies were observed for minute differences in the preforms microstructure. This suggests the need for a dynamic percolation model that would account for the exothermic nature of the silicon-carbon chemical reaction and the associated pore closing phenomenon.

  8. Microtribology of Nitrogen-doped Amorphous Carbon Coatings

    Institute of Scientific and Technical Information of China (English)

    Dong F. Wang

    2004-01-01

    The friction, wear and lubrication of carbon nitride coatings on silicon substrates are studied using a spherical diamond counter-face with nano-scale asperities. The first part of this paper clarifies the coating thickness effect on frictional behavior of carbon nitride coatings. The second part of this paper reports empirical data on wear properties in repeated sliding contacts through in situ examination and post-sliding observation. The third part will concentrate on wear mechanisms for the transition from "No observable wear particles" to "Wear particle generation." In light of the above tribological study, the application of carbon nitride coatings to MicroElectroMechanical system (MEMS) is therefore discussed from view points of both microtribology and micromachining.

  9. Effect of the hydrogen dilution on the local microstructure in hydrogenated amorphous silicon films deposited by radiofrequency magnetron sputtering

    Science.gov (United States)

    Daouahi, M.; Zellama, K.; Bouchriha, H.; Elkaïm, P.

    2000-06-01

    The nature of the hydrogen bonding and content and their influence on the film microstructure have been investigated in detail, as a function of the H2 dilution and the residual pressure, in hydrogenated amorphous silicon (a-Si:H) films prepared by radiofrequency (rf) magnetron sputtering at a common substrate temperature (sim 250 °C) and pressure (5× 10^{-4} torr) and high rates (11-15 Å/s). H2 percentages in the gas phase mixture (Ar + % H2) of 5, 10, 15 and 20% have been introduced during growth. For the 20% of H2, two different pressures of 5× 10^{-4} and 50× 10^{-4} torr were used. A combination of infrared absorption, optical transmission and elastic recoil detection analysis experiments have been carried out to fully characterize the samples in their as-deposited state. The results clearly indicate that for H2 percentage equal to or lower than 15% , the total bonded H content in the films increases as the H2 percentage increases, and then reaches a saturation value or even decreases for higher H2 percentage. Moreover, the microstructure is also found to be deeply affected by the H2 dilution and pressure. In particular, for high H2 percentage (20% ) and high pressure (50× 10^{-4} torr), unbounded H as well as polyhydride (Si-H2)_n chains, possibly located in structural inhomogeneities such as voids, are also present in the films in addition to the isolated monohydride Si-H and polyhydride Si-H2 complexes. As a result, a reduction of the compactness of the film structure associated with a decrease of the refractive index n is observed. The optical gap is found to be rather controlled by the total bonded hydrogen content. The lowest proportion of isolated polyhydride Si-H2 complexes and the highest density are observed for films deposited with 10% of H2 in the gas phase and a pressure of 5× 10^{-4} torr.

  10. Synthesis, characterization and hydrogen storage studies on porous carbon

    International Nuclear Information System (INIS)

    Porous carbon sample has been prepared, using zeolite-Y as template followed by annealing at 800°C, with view to estimate the extent of hydrogen storage by the sample. Based on XRD, 13C MAS NMR and Raman spectroscopic studies it is confirmed that the porous Carbon sample contains only sp2 hybridized carbon. The hydrogen sorption isotherms have been recorded for the sample at 273, 223K and 123K and the maximum hydrogen absorption capacity is found to be 1.47wt% at 123K. The interaction energy of hydrogen with the carbon framework was determined to be ∼ 10 kJ mol−1at lower hydrogen uptake and gradually decreases with increase in hydrogen loading

  11. Synthesis, characterization and hydrogen storage studies on porous carbon

    Science.gov (United States)

    Ruz, Priyanka; Banerjee, Seemita; Pandey, M.; Sudarsan, V.

    2015-06-01

    Porous carbon sample has been prepared, using zeolite-Y as template followed by annealing at 800°C, with view to estimate the extent of hydrogen storage by the sample. Based on XRD, 13C MAS NMR and Raman spectroscopic studies it is confirmed that the porous Carbon sample contains only sp2 hybridized carbon. The hydrogen sorption isotherms have been recorded for the sample at 273, 223K and 123K and the maximum hydrogen absorption capacity is found to be 1.47wt% at 123K. The interaction energy of hydrogen with the carbon framework was determined to be ˜ 10 kJ mol-1at lower hydrogen uptake and gradually decreases with increase in hydrogen loading.

  12. Amorphous Carbon Gold Nanocomposite Thin Films: Structural and Spectro-ellipsometric Analysis

    International Nuclear Information System (INIS)

    Spectroscopic Ellipsometry was used to determine the optical and structural properties of amorphous carbon:gold nanocomposite thin films deposited by dc magnetron co-sputtering at different deposition power. The incorporation of gold as small particles distributed in the amorphous carbon matrix was confirmed by X-ray Diffraction, Rutherford Backscattering measurements and High Resolution Transmission Electron Microscopy. Based on these results, an optical model for the films was developed using the Maxwell-Garnett effective medium with the Drude-Lorentz model representing the optical response of gold and the Tauc-Lorentz model for the amorphous carbon. The gold volume fraction and particle size obtained from the fitting processes were comparable to those from the physical characterization. The analysis of the ellipsometric spectra for all the samples showed strong changes in the optical properties of the carbon films as a consequence of the gold incorporation. These changes were correlated to the structural modification observed by Raman Spectroscopy, which indicated a clustering of the sp2 phase with a subsequent decrease in the optical gap. Finally, measurements of Reflection and Transmission Spectroscopy were carried out and Transmission Electron Microscopy images were obtained in order to support the ellipsometric model results.

  13. Inprovement of Field Emission Properties of PBS Thin Films by Amorphous Carbon Coating

    Directory of Open Access Journals (Sweden)

    S. Jana

    2011-01-01

    Full Text Available Lead sulfide (PbS nanocrystalline thin films were synthesized at room temperature via chemical bath deposition on both silicon and glass substrates and coated with amorphous carbon of different thickness by varying deposition time in plasma enhanced chemical vapor deposition technique. The as prepared samples were characterized by X-ray diffraction (XRD, field emission scanning electron microscope (FESEM and atomic force microscope (AFM. XRD study reveals that coating of amorphous carbon does not change the crystal structure of PbS. From FESEM images it is seen that the average size of PbS nanoparticle does not exceed 100 nm, though sometomes small cubic particles agglomerated to form bigger particles. The coating of amorphous carbon can be clearly visible by the FESEM as well as from AFM micrographs. Field emission study show a significant betterment for the carbon coated sample as compared to the pure PbS. The effect of inter-electrode distance on the field emission characteristics of best field emitting sample has been studied for three different inter-electrode distances.

  14. Optical properties of amorphous carbons and their applications and perspectives in photonics

    Energy Technology Data Exchange (ETDEWEB)

    Patsalas, P., E-mail: ppats@cc.uoi.g

    2011-04-01

    Amorphous carbon exhibits a wide variety of optical properties and, thus, offers substantial opportunities for various applications in photonics. The main optical properties, which should be taken into account for the design of new photonic devices, are the refractive index n, the fundamental gap E{sub g} and the E{sub 04} gap. In this work, the optical properties of the various forms of amorphous carbon films grown by plasma-enhanced chemical vapor deposition, pulsed laser deposition, sputtering and vacuum cathodic arc deposition and the crucial structural and chemical factors that determine n, E{sub g}, and E{sub 04} are reviewed. The knowledge of the optical properties of such films is exploited in order to design and implement various photonic devices such as: 1) anti-reflection (AR) coatings for various uses including photovoltaic modules, 2) interferometric sensors and indicators based on carbon-based AR layers, and 3) laser patterning of amorphous carbons and study of its photosensitivity for holographic applications.

  15. Raman spectra of electrochemically hydrogenated diamond like carbon surface

    OpenAIRE

    Biswas, Hari Shankar; Datta, Jagannath; Sen, Pintu; Ghosh, Uday Chand; Ray, Nihar Ranjan

    2013-01-01

    Raman spectroscopy has been employed to distinguish between the Raman spectrum of pristine hydrogenated diamond like carbon (PHDLC) and that of electrochemically hydrogenated diamond like carbon (ECHDLC). The enhancement of the background photoluminescence (PL) in the Raman spectrum and broadening of PL spectrum of ECHDLC are identified to be due to increase of sp3 C-H density onto the PHDLC surface, during novel electrochemical process of hydrogenation of sp2 C=C into sp3 C-H.

  16. DEVELOPMENT OF DOPED NANOPOROUS CARBONS FOR HYDROGEN STORAGE

    Energy Technology Data Exchange (ETDEWEB)

    Lueking, Angela D.; Li, Qixiu; Badding, John V.; Fonseca, Dania; Gutierrez, Humerto; Sakti, Apurba; Adu, Kofi; Schimmel, Michael

    2010-03-31

    Hydrogen storage materials based on the hydrogen spillover mechanism onto metal-doped nanoporous carbons are studied, in an effort to develop materials that store appreciable hydrogen at ambient temperatures and moderate pressures. We demonstrate that oxidation of the carbon surface can significantly increase the hydrogen uptake of these materials, primarily at low pressure. Trace water present in the system plays a role in the development of active sites, and may further be used as a strategy to increase uptake. Increased surface density of oxygen groups led to a significant enhancement of hydrogen spillover at pressures less than 100 milibar. At 300K, the hydrogen uptake was up to 1.1 wt. % at 100 mbar and increased to 1.4 wt. % at 20 bar. However, only 0.4 wt% of this was desorbable via a pressure reduction at room temperature, and the high lowpressure hydrogen uptake was found only when trace water was present during pretreatment. Although far from DOE hydrogen storage targets, storage at ambient temperature has significant practical advantages oner cryogenic physical adsorbents. The role of trace water in surface modification has significant implications for reproducibility in the field. High-pressure in situ characterization of ideal carbon surfaces in hydrogen suggests re-hybridization is not likely under conditions of practical interest. Advanced characterization is used to probe carbon-hydrogen-metal interactions in a number of systems and new carbon materials have been developed.

  17. Annealing effect and stability of carbon nanotubes in hydrogen flame

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Annealing of carbon nanotubes (CNTs) by the hydrogen flame in air was investigated in this study. Raman spectroscopy and scanning electron microscopy were used to characterize the products. The peak width of Raman spectra decreased with the increase in the annealing time. The CNTs were not stable in the hydrogen flame and the etching rate of the CNTs by hydrogen flame was very high. The hydrogen flame annealing had some effects on improving the crystallinity of CNTs.

  18. Self-irradiation enhanced tritium solubility in hydrogenated amorphous and crystalline silicon

    International Nuclear Information System (INIS)

    Experimental results on tritium effusion, along with the tritium depth profiles, from hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si) tritiated in tritium (T2) gas at various temperatures and pressures are presented. The results indicate that tritium incorporation is a function of the material microstructure of the as-grown films, rather than the tritium exposure condition. The highest tritium concentration obtained is for a-Si:H deposited at a substrate temperature of 200 deg. C. The tritium content is about 20 at. % on average with a penetration depth of about 50 nm. In contrast, tritium occluded in the c-Si is about 4 at. % with penetration depth of about 10 nm. The tritium concentration observed in a-Si:H and c-Si is much higher than the reported results for the post-hydrogenation process. β irradiation appears to catalyze the tritiation process and enhance tritium dissolution in the silicon matrix. The combination of tritium decay and β-induced ionizations results in formation of reactive species of tritium (tritium atoms, radicals, and ions) that readily adsorb on silicon. The electron bombardment of the silicon surface and subsurface renders it chemically active thereby promoting surface adsorption and subsurface diffusion of tritium, thus leading to tritium occlusion in the silicon matrix. Gaussian deconvolution of tritium effusion spectra yields two peaks for a-Si:H films tritiated at high temperature (250 deg. C), one low temperature (LT) peak which is attributed to tritiated clusters and higher order tritides, and another high temperature peak which is attributed to monotritides. Activation energy of 2.6-4.0 eV for the LT peak was found.

  19. Electrochemical Hydrogen Storage in a Highly Ordered Mesoporous Carbon

    Directory of Open Access Journals (Sweden)

    Dan eLiu

    2014-10-01

    Full Text Available A highly order mesoporous carbon has been synthesized through a strongly acidic, aqueous cooperative assembly route. The structure and morphology of the carbon material were investigated using TEM, SEM and nitrogen adsorption-desorption isotherms. The carbon was proven to be meso-structural and consisted of graphitic micro-domain with larger interlayer space. AC impedance and electrochemical measurements reveal that the synthesized highly ordered mesoporous carbon exhibits a promoted electrochemical hydrogen insertion process and improved capacitance and hydrogen storage stability. The meso-structure and enlarged interlayer distance within the highly ordered mesoporous carbon are suggested as possible causes for the enhancement in hydrogen storage. Both hydrogen capacity in the carbon and mass diffusion within the matrix were improved.

  20. Ultrafast carrier dynamics in tetrahedral amorphous carbon: carrier trapping versus electron-hole recombination

    International Nuclear Information System (INIS)

    We report the investigation of the ultrafast carrier dynamics in thin tetrahedral amorphous carbon films by means of femtosecond time-resolved reflectivity. We estimated the electron-phonon relaxation time of a few hundred femtoseconds and we observed that under low optical excitation photo-generated carriers decay according to two distinct mechanisms attributed to trapping by defect states and direct electron-hole recombination. With high excitation, when photo-carrier and trap densities are comparable, a unique temporal evolution develops, as the time dependence of the trapping process becomes degenerate with the electron-hole recombination. This experimental evidence highlights the role of defects in the ultrafast electronic dynamics and is not specific to this particular form of carbon, but has general validity for amorphous and disordered semiconductors

  1. Carbon nanotube-amorphous silicon hybrid solar cell with improved conversion efficiency

    Science.gov (United States)

    Funde, Adinath M.; Nasibulin, Albert G.; Gufran Syed, Hashmi; Anisimov, Anton S.; Tsapenko, Alexey; Lund, Peter; Santos, J. D.; Torres, I.; Gandía, J. J.; Cárabe, J.; Rozenberg, A. D.; Levitsky, Igor A.

    2016-05-01

    We report a hybrid solar cell based on single walled carbon nanotubes (SWNTs) interfaced with amorphous silicon (a-Si). The high quality carbon nanotube network was dry transferred onto intrinsic a-Si forming Schottky junction for metallic SWNT bundles and heterojunctions for semiconducting SWNT bundles. The nanotube chemical doping and a-Si surface treatment minimized the hysteresis effect in current-voltage characteristics allowing an increase in the conversion efficiency to 1.5% under an air mass 1.5 solar spectrum simulator. We demonstrated that the thin SWNT film is able to replace a simultaneously p-doped a-Si layer and transparent conductive electrode in conventional amorphous silicon thin film photovoltaics.

  2. Carbon nanotube-amorphous silicon hybrid solar cell with improved conversion efficiency.

    Science.gov (United States)

    Funde, Adinath M; Nasibulin, Albert G; Syed, Hashmi Gufran; Anisimov, Anton S; Tsapenko, Alexey; Lund, Peter; Santos, J D; Torres, I; Gandía, J J; Cárabe, J; Rozenberg, A D; Levitsky, Igor A

    2016-05-01

    We report a hybrid solar cell based on single walled carbon nanotubes (SWNTs) interfaced with amorphous silicon (a-Si). The high quality carbon nanotube network was dry transferred onto intrinsic a-Si forming Schottky junction for metallic SWNT bundles and heterojunctions for semiconducting SWNT bundles. The nanotube chemical doping and a-Si surface treatment minimized the hysteresis effect in current-voltage characteristics allowing an increase in the conversion efficiency to 1.5% under an air mass 1.5 solar spectrum simulator. We demonstrated that the thin SWNT film is able to replace a simultaneously p-doped a-Si layer and transparent conductive electrode in conventional amorphous silicon thin film photovoltaics. PMID:27005494

  3. A transparent hybrid of nanocrystalline cellulose and amorphous calcium carbonate nanoparticles

    Science.gov (United States)

    Gebauer, Denis; Oliynyk, Vitaliy; Salajkova, Michaela; Sort, Jordi; Zhou, Qi; Bergström, Lennart; Salazar-Alvarez, German

    2011-09-01

    Nanocellulose hybrids are promising candidates for biodegradable multifunctional materials. Hybrids of nanocrystalline cellulose (NCC) and amorphous calcium carbonate (ACC) nanoparticles were obtained through a facile chemical approach over a wide range of compositions. Controlling the interactions between NCC and ACC results in hard, transparent structures with tunable composition, homogeneity and anisotropy.Nanocellulose hybrids are promising candidates for biodegradable multifunctional materials. Hybrids of nanocrystalline cellulose (NCC) and amorphous calcium carbonate (ACC) nanoparticles were obtained through a facile chemical approach over a wide range of compositions. Controlling the interactions between NCC and ACC results in hard, transparent structures with tunable composition, homogeneity and anisotropy. Electronic supplementary information (ESI) available: Additional experimental procedures and results. See DOI: 10.1039/c1nr10681c

  4. In Situ Mechanical Property Measurements of Amorphous Carbon-Boron Nitride Nanotube Nanostructures

    Science.gov (United States)

    Kim, Jae-Woo; Lin, Yi; Nunez, Jennifer Carpena; Siochi, Emilie J.; Wise, Kristopher E.; Connell, John W.; Smith, Michael W.

    2011-01-01

    To understand the mechanical properties of amorphous carbon (a-C)/boron nitride nanotube (BNNT) nanostructures, in situ mechanical tests are conducted inside a transmission electron microscope equipped with an integrated atomic force microscope system. The nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation. We demonstrate multiple in situ tensile, compressive, and lap shear tests with a-C/BNNT hybrid nanostructures. The tensile strength of the a-C/BNNT hybrid nanostructure is 5.29 GPa with about 90 vol% of a-C. The tensile strength and strain of the end-to-end joint structure with a-C welding is 0.8 GPa and 5.2% whereas the lap shear strength of the side-by-side joint structure with a-C is 0.25 GPa.

  5. In situ mechanical property measurements of amorphous carbon-boron nitride nanotube nanostructures

    Science.gov (United States)

    Kim, Jae-Woo; Carpena Núñez, Jennifer; Siochi, Emilie J.; Wise, Kristopher E.; Lin, Yi; Connell, John W.; Smith, Michael W.

    2012-01-01

    To understand the mechanical properties of amorphous carbon (a-C)/boron nitride nanotube (BNNT) nanostructures, in situ mechanical tests are conducted inside a transmission electron microscope equipped with an integrated atomic force microscope system. The nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation. We demonstrate multiple in situ tensile, compressive, and lap shear tests with a-C/BNNT hybrid nanostructures. The tensile strength of the a-C/BNNT hybrid nanostructure is 5.29 GPa with about 90 vol% of a-C. The tensile strength and strain of the end-to-end joint structure with a-C welding is 0.8 GPa and 5.2% whereas the lap shear strength of the side-by-side joint structure with a-C is 0.25 GPa.

  6. The boron-tailing myth in hydrogenated amorphous silicon solar cells

    Science.gov (United States)

    Stuckelberger, M.; Park, B.-S.; Bugnon, G.; Despeisse, M.; Schüttauf, J.-W.; Haug, F.-J.; Ballif, C.

    2015-11-01

    The boron-tailing effect in hydrogenated amorphous silicon (a-Si:H) solar cells describes the reduced charge collection specifically in the blue part of the spectrum for absorber layers deposited above a critical temperature. This effect limits the device performance of state-of-the art solar cells: For enhanced current density (reduced bandgap), the deposition temperature should be as high as possible, but boron tailing gets detrimental above 200 °C. To investigate this limitation and to show potential paths to overcome it, we deposited high-efficiency a-Si:H solar cells, varying the deposition temperatures of the p-type and the intrinsic absorber (i) layers between 150 and 250 °C. Using secondary ion mass spectroscopy, we study dedicated stacks of i-p-i layers deposited at different temperatures. This allows us to track boron diffusion at the p-i and i-p interfaces as they occur in the p-i-n and n-i-p configurations of a-Si:H solar cells for different deposition conditions. Finally, we prove step-by-step that the common explanation for boron tailing—boron diffusion from the p layer into the i layer leading to enhanced recombination—is not generally true and propose an alternative explanation for the experimentally observed drop in the external quantum efficiency at short wavelengths.

  7. Hydrogenated amorphous silicon sensors based on thin film on ASIC technology

    CERN Document Server

    Despeisse, M; Anelli, G; Jarron, P; Kaplon, J; Rusack, R; Saramad, S; Wyrsch, N

    2006-01-01

    The performance and limitations of a novel detector technology based on the deposition of a thin-film sensor on top of processed integrated circuits have been studied. Hydrogenated amorphous silicon (a-Si:H) films have been deposited on top of CMOS circuits developed for these studies and the resulting "thin-film on ASIC" (TFA) detectors are presented. The leakage current of the a-Si:H sensor at high reverse biases turns out to be an important parameter limiting the performance of a TFA detector. Its detailed study and the pixel segmentation of the detector are presented. High internal electric fields (in the order of 10/sup 4/-10/sup 5/ V/cm) can be built in the a-Si:H sensor and overcome the low mobility of electrons and holes in a-Si:H. Signal induction by generated carrier motion and speed in the a-Si:H sensor have been studied with a 660 nm pulsed laser on a TFA detector based on an ASIC integrating 5 ns peaking time pre- amplifiers. The measurement set-up also permits to study the depletion of the senso...

  8. Growth of hydrogenated amorphous silicon (a-Si:H) on patterned substrates for increased mechanical stability

    International Nuclear Information System (INIS)

    Residual stress in hydrogenated amorphous silicon (a-Si:H) film, which causes substrate bending and delamination, is studied. The internal stress can be reduced by controlling deposition parameters, but it is known to produce a trade-off between stress and electronic quality. Selective area deposition, in which the deposition area is reduced by making islands, reduced the stress when the lateral dimension of the islands becomes comparable to the film thickness. The overall stress is reduced by approximately 40% when the lateral dimension is decreased to 40 μm, but the adhesion was not improved much. However, substrates having a 2-dimensional array of inversed pyramids of 200 μm in lateral dimension produced overall stress 3 ∼ 4 times lower than that on the normal substrates. Such substrates were prepared by anisotropic etching of silicon wafers. The inversed pyramid structure also has other advantages including minimized delamination and increased effective thickness. Computer simulation confirmed that the overall stress can be reduced by deposition on the pyramidal structure

  9. Hydrogenated Amorphous Silicon Germanium Active Layer for Top Cell of a Multi Junction Cell Structure.

    Science.gov (United States)

    Cho, Jaehyun; Iftiquar, S M; Kim, Minbum; Park, Jinjoo; Jung, Junhee; Kim, Jiwoong; Yi, Junsin

    2016-05-01

    Intrinsic hydrogenated amorphous silicon-germanium (a-SiGe:H) alloy is generally used in the bottom cell because of its low band gap. The a-SiGe:H has a higher photo conductivity in comparison to the a-Si:H; thus, it is expected that the a-SiGe:H can show better short circuit current density than that of the a-Si:H based solar cell. Therefore, we optimized a-SiGe:H active layer that can be a suitable choice for the front cell of a multi junction.solar cell. Furthermore, we carried out a comparative study of the solar cells that have a-SiGe:H and a-Si:H as respective active layers. The a-SiGe:H based solar cells show higher short circuit current density, while the a-Si:H based cells show higheropen circuit voltage. The current-voltage characteristics of these cells are as follows: (a) V(oc) = 770 mV, J(sc) = 15.0 mA/cm2, FF = 64.5%, and η = 7.47% for a-SiGe:H based cell; and (b) V(oc) = 826 mV, J(sc) = 13.63 mA/cm2, FF = 72.0%, and η = 8.1% for a-Si:H based cell. PMID:27483837

  10. Morphological characteristics and optical properties of hydrogenated amorphous silicon thin films

    Science.gov (United States)

    Tang, Haihua; Liu, Shuang; Zhou, Xiang; Liu, Yunfei; Chen, Dejun; Liu, Yong; Zhong, Zhiyong

    2016-05-01

    Hydrogenated amorphous silicon (a-Si:H) thin films were prepared by radio frequency (RF) plasma enhanced chemical vapor deposition (RF-PECVD) technique with silane (SiH4) as reactive gas. The influence of process parameters on the morphological characteristics and optical properties of a-Si:H thin films were systematically investigated. When the RF power density was taken as the only variable, it firstly improves the smoothness of the surface with increasing the RF power density below the value of 0.17 W/cm2, and then exhibits an obvious degradation at further power density. The refractive index, extinction coefficient, optical energy gap initially increase and reach a maximum at 0.17 W/cm2, followed by a significant decrease with further RF power density. When the RF power density was taken as the only variable, the surface of a-Si:H thin films become smoother by increasing the reaction pressure in the investigated range (from 50 Pa to 140 Pa), and the refractive index, extinction coefficient, optical energy gap increase with increasing of reaction pressure. The effect of RF power density and the reaction pressure on the morphological characteristics and optical properties of a-Si:H thin films was obtained, contributing to the further studies of the performance and applications of a-Si:H thin films.

  11. Stable, high-efficiency amorphous-silicon solar cells with low hydrogen content

    Science.gov (United States)

    Hegedus, S. S.; Phillips, J. E.

    1993-08-01

    This report describes a 21-month project to demonstrate amorphous-silicon (a-Si) solar cells with high stabilized conversion efficiency. The objective was to develop a research program spanning material issues (more stable a-Si and better a-SiGe alloys) and device issues (more stable a-Si-based solar cells) with the goal of high stabilized solar cell efficiency. The Institute of Energy Conversion (IEC) produced and analyzed the stability of a-Si films and solar cells with reduced hydrogen content (2-6%). A thermodynamic model of defect formation was developed that describes the high-temperature degraded state of a solar cell. An analysis of bi-facial current voltage and quantum efficiency results for a-SiGe p-i-n devices with transparent front and back contacts provided information about the influence of alloying and band-gap grading on hole and electron collection. IEC also studied the stability of graded and ungraded a-SiGe solar cells using bifacial devices to learn about the relative degradation of hole and electron collection, and concludes that degradation of the photoconductivity of a-SiGe materials does not agree with degradation observed in solar cells.

  12. The boron-tailing myth in hydrogenated amorphous silicon solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Stuckelberger, M., E-mail: michael.stuckelberger@alumni.ethz.ch; Bugnon, G.; Despeisse, M.; Schüttauf, J.-W.; Haug, F.-J.; Ballif, C. [Ecole Polytechnique Fédérale de Lausanne (EPFL), Institute of Microengineering (IMT), Photovoltaics and Thin-Film Electronics Laboratory, Rue de la Maladière 71, CH-2000 Neuchâtel (Switzerland); Park, B.-S. [SIMS Services, Evans Analytical Group, 810 Kifer Road, Sunnyvale, California 94086 (United States)

    2015-11-16

    The boron-tailing effect in hydrogenated amorphous silicon (a-Si:H) solar cells describes the reduced charge collection specifically in the blue part of the spectrum for absorber layers deposited above a critical temperature. This effect limits the device performance of state-of-the art solar cells: For enhanced current density (reduced bandgap), the deposition temperature should be as high as possible, but boron tailing gets detrimental above 200 °C. To investigate this limitation and to show potential paths to overcome it, we deposited high-efficiency a-Si:H solar cells, varying the deposition temperatures of the p-type and the intrinsic absorber (i) layers between 150 and 250 °C. Using secondary ion mass spectroscopy, we study dedicated stacks of i-p-i layers deposited at different temperatures. This allows us to track boron diffusion at the p-i and i-p interfaces as they occur in the p-i-n and n-i-p configurations of a-Si:H solar cells for different deposition conditions. Finally, we prove step-by-step that the common explanation for boron tailing—boron diffusion from the p layer into the i layer leading to enhanced recombination—is not generally true and propose an alternative explanation for the experimentally observed drop in the external quantum efficiency at short wavelengths.

  13. The boron-tailing myth in hydrogenated amorphous silicon solar cells

    International Nuclear Information System (INIS)

    The boron-tailing effect in hydrogenated amorphous silicon (a-Si:H) solar cells describes the reduced charge collection specifically in the blue part of the spectrum for absorber layers deposited above a critical temperature. This effect limits the device performance of state-of-the art solar cells: For enhanced current density (reduced bandgap), the deposition temperature should be as high as possible, but boron tailing gets detrimental above 200 °C. To investigate this limitation and to show potential paths to overcome it, we deposited high-efficiency a-Si:H solar cells, varying the deposition temperatures of the p-type and the intrinsic absorber (i) layers between 150 and 250 °C. Using secondary ion mass spectroscopy, we study dedicated stacks of i-p-i layers deposited at different temperatures. This allows us to track boron diffusion at the p-i and i-p interfaces as they occur in the p-i-n and n-i-p configurations of a-Si:H solar cells for different deposition conditions. Finally, we prove step-by-step that the common explanation for boron tailing—boron diffusion from the p layer into the i layer leading to enhanced recombination—is not generally true and propose an alternative explanation for the experimentally observed drop in the external quantum efficiency at short wavelengths

  14. The Effect of Hybrid Photovoltaic Thermal Device Operating Conditions on Intrinsic Layer Thickness Optimization of Hydrogenated Amorphous Silicon Solar Cells

    OpenAIRE

    Pathak, M. J. M.; Girotra, K.; Harrison, S. J.; Pearce, J.M.

    2012-01-01

    Historically, the design of hybrid solar photovoltaic thermal (PVT) systems has focused on cooling crystalline silicon (c-Si)-based photovoltaic (PV) devices to avoid temperature-related losses. This approach neglects the associated performance losses in the thermal system and leads to a decrease in the overall exergy of the system. Consequently, this paper explores the use of hydrogenated amorphous silicon (a-Si:H) as an absorber material for PVT in an effort to maintain higher and more favo...

  15. Flexible Electronics: High Pressure Chemical Vapor Deposition of Hydrogenated Amorphous Silicon Films and Solar Cells (Adv. Mater. 28/2016).

    Science.gov (United States)

    He, Rongrui; Day, Todd D; Sparks, Justin R; Sullivan, Nichole F; Badding, John V

    2016-07-01

    On page 5939, J. V. Badding and co-workers describe the unrolling of a flexible hydrogenated amorphous silicon solar cell, deposited by high-pressure chemical vapor deposition. The high-pressure deposition process is represented by the molecules of silane infiltrating the small voids between the rolled up substrate, facilitating plasma-free deposition over a very large area. The high-pressure approach is expected to also find application for 3D nanoarchitectures. PMID:27442970

  16. Enhanced Photoelectrical Response of Hydrogenated Amorphous Silicon Single-Nanowire Solar Cells by Front-Opening Crescent Design

    OpenAIRE

    Yang, Zhenhai; Cao, Guoyang; Shang, Aixue; Lei, Dang Yuan; Zhang, Cheng; Gao, Pingqi; Ye, Jichun; Li, Xiaofeng

    2016-01-01

    We report an approach for substantially enhancing the light-trapping and photoconversion efficiency of hydrogenated amorphous silicon (a-Si:H) single-nanowire solar cells (SNSCs) by engineering the cross section of the nanowire from circular into a front-opening crescent shape. The proposed SNSCs show a broadband and highly tunable optical absorption compared to the conventional circular counterparts under both transverse electric and transverse magnetic incidences, enabling an enhancement ra...

  17. Room temperature photoluminescence spectrum modeling of hydrogenated amorphous silicon carbide thin films by a joint density of tail states approach and its application to plasma deposited hydrogenated amorphous silicon carbide thin films

    International Nuclear Information System (INIS)

    Room temperature photoluminescence (PL) spectrum of hydrogenated amorphous silicon carbide (a-SiCx:H) thin films was modeled by a joint density of tail states approach. In the frame of these analyses, the density of tail states was defined in terms of empirical Gaussian functions for conduction and valance bands. The PL spectrum was represented in terms of an integral of joint density of states functions and Fermi distribution function. The analyses were performed for various values of energy band gap, Fermi energy and disorder parameter, which is a parameter that represents the width of the energy band tails. Finally, the model was applied to the measured room temperature PL spectra of a-SiCx:H thin films deposited by plasma enhanced chemical vapor deposition system, with various carbon contents, which were determined by X-ray photoelectron spectroscopy measurements. The energy band gap and disorder parameters of the conduction and valance band tails were determined and compared with the optical energies and Urbach energies, obtained by UV–Visible transmittance measurements. As a result of the analyses, it was observed that the proposed model sufficiently represents the room temperature PL spectra of a-SiCx:H thin films. - Highlights: ► Photoluminescence spectra (PL) of the films were modeled. ► In the model, joint density of tail states and Fermi distribution function are used. ► Various values of energy band gap, Fermi energy and disorder parameter are applied. ► The model was applied to the measured PL of the films. ► The proposed model represented the room temperature PL spectrum of the films.

  18. Electronic state modification in laser deposited amorphous carbon films by the inclusion of nitrogen

    OpenAIRE

    Y. Miyajima; Adamopoulos, G; Henley, SJ; V.Stolojan; Tison, Y; Garcia-Caurel, E; Drevillon, B.; Shannon, JM; Silva, SRP

    2008-01-01

    In this study, we investigate the effect of the inclusion of nitrogen in amorphous carbon thin films deposited by pulsed laser deposition, which results in stress induced modifications to the band structure and the concomitant changes to the electronic transport properties. The microstructural changes due to nitrogen incorporation were examined using electron energy-loss spectroscopy and Raman scattering. The band structure was investigated using spectroscopic ellipsometry data in the range o...

  19. Facile fabrication of boron nitride nanosheets-amorphous carbon hybrid film for optoelectronic applications

    KAUST Repository

    Wan, Shanhong

    2015-01-01

    A novel boron nitride nanosheets (BNNSs)-amorphous carbon (a-C) hybrid film has been deposited successfully on silicon substrates by simultaneous electrochemical deposition, and showed a good integrity of this B-C-N composite film by the interfacial bonding. This synthesis can potentially provide the facile control of the B-C-N composite film for the potential optoelectronic devices. This journal is

  20. Ultrasound-assisted Cinnamaldehyde Hydrogenation to Cinnamyl Alcohol at Atmospheric Pressure over Ru-B Amorphous Catalyst

    Institute of Scientific and Technical Information of China (English)

    LI Hui; MA Chun-Jing; LI He-Xing

    2006-01-01

    The ultrafine Ru-B amorphous alloy catalyst was prepared by chemical reduction with KBH4. During liquid phase hydrogenation of cinnamaldehyde at atmospheric pressure, the Ru-B catalyst prepared exhibited excellent selectivity to cinnamyl alcohol. When the hydrogenation was performed with ultrasonic irradiation, the reaction rate could be greatly enhanced while the selectivity to cinnamyl alcohol remained almost unchanged. The hydrogenation rate was increased with the increase of either the ultrasonic frequency or the irradiation time. According to various characterizations, such as XRD, XPS, TEM, BET and ICP, the effect of ultrasonic irradiation on the structural and electronic characteristics of Ru-B catalyst was studied briefly. Meanwhile, the promotion effect of ultrasonication on the catalytic performance was also discussed based on the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol.

  1. Incorporation of nitrogen into amorphous carbon films produced by surface-wave plasma chemical vapor deposition

    International Nuclear Information System (INIS)

    In order to study the influence of nitrogen incorporated into amorphous carbon films, nitrogenated amorphous carbon films have been deposited by using surface wave plasma chemical vapor deposition under various ratios of N2/CH4 gas flow. Optical emission spectroscopy has been used to monitor plasma features near the deposition zone. After deposition, the samples are checked by Raman spectroscopy and x-ray photo spectroscopy (XPS). Optical emission intensities of CH and N atom in the plasma are found to be enhanced with the increase in the N2/CH4 gas flow ratio, and then reach their maximums when the N2/CH4 gas flow ratio is 5%. A contrary variation is found in Raman spectra of deposited films. The intensity ratio of the D band to the G band (ID/IG) and the peak positions of the G and D bands all reach their minimums when the N2/CH4 gas flow ratio is 5%. These show that the structure of amorphous carbon films has been significantly modified by introduction of nitrogen

  2. Hydrogenated amorphous silicon thin-film deposition by direct photo-enhanced decomposition of silane using an internal hydrogen discharge lamp

    International Nuclear Information System (INIS)

    Hydrogenated amorphous silicon (a-Si:H) thin films have been deposited from silane using a novel photo-enhanced decomposition technique. The system comprises a hydrogen discharge lamp contained within the reaction vessel; this unified approach allows high energy photon excitation of the silane molecules without absorption by window materials or the need for mercury sensitisation. The film growth rates (exceeding 4 A/s) and material properties obtained are comparable to those of films produced by plasma-enhanced CVD techniques. The reduction of energetic charged particles in the film growth region should enable the fabrication of cleaner semiconductor/insulator interfaces in thin-film transistors

  3. Synthesis of Ag-doped hydrogenated carbon thin films by a hybrid PVD–PECVD deposition process

    Indian Academy of Sciences (India)

    Majji Venkatesh; Sukru Taktak; Efstathios I Meletis

    2014-12-01

    Silver-doped hydrogenated amorphous carbon (Ag-DLC) films were deposited on Si substrates using a hybrid plasma vapour deposition–plasma enhanced chemical vapour deposition (PVD–PECVD) process combining Ag target magnetron sputtering and PECVD in an Ar–CH4 plasma. Processing parameters (working pressure, CH4/Ar ratio and magnetron current) were varied to obtain good deposition rate and a wide variety of Ag films. Structure and bonding environment of the films were obtained from transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared (FTIR) spectroscopy studies. Variation of processing parameters was found to produce Ag-doped amorphous carbon or diamond-like carbon (DLC) films with a range of characteristics with CH4/Ar ratio exercising a dominant effect. It was pointed out that Ag concentration and deposition rate of the film increased with the increase in d.c. magnetron current. At higher Ar concentration in plasma, Ag content increased whereas deposition rate of the film decreased. FTIR study showed that the films contained a significant amount of hydrogen and, as a result of an increase in the Ag content in the hydrogenated DLC film, $sp^{2}$ bond content also increased. The TEM cross sectional studies revealed that crystalline Ag particles were formed with a size in the range of 2–4 nm throughout an amorphous DLC matrix.

  4. Electron field emission from 2-induced insulating to metallic behaviour of amorphous carbon (-C) films

    Indian Academy of Sciences (India)

    Pitamber Mahanandia; P N Viswakarma; Prasad Vishnu Bhotla; S V Subramanyam; Karuna Kar Nanda

    2010-06-01

    The influence of concentration and size of 2 cluster on the transport properties and electron field emissions of amorphous carbon films have been investigated. The observed insulating to metallic behaviour from reduced activation energy derived from transport measurement and threshold field for electron emission of -C films can be explained in terms of improvements in the connectivity between 2 clusters. The connectivity is resulted by the cluster concentration and size. The concentration and size of 2 content cluster is regulated by the coalescence of carbon globules into clusters, which evolves with deposition conditions.

  5. Methane Flow Rate Effects On The Optical Properties of Amorphous Silicon Carbon (a-SiC:H Films Deposited By DC Sputtering Methods

    Directory of Open Access Journals (Sweden)

    Rosari Saleh

    2002-04-01

    Full Text Available We have investigated the refractive index (n and the optical absorption coeffi cient (α from refl ection and transmission measurements on hydrogenated amorphous silicon carbon (a-SiC:H fi lms. The a-SiC:H fi lms were prepared by dc sputtering method using silicon target in argon and methane gas mixtures. The refractive index (n decreases as the methane fl ow rate increase. The optical absorption coeffi cient (α shifts to higher energy with increasing methane fl ow rate. At higher methane fl ow rate, the fi lms tend to be more disorder and have wider optical gap. The relation of the optical properties and the disorder amorphous network with the compositional properties will be discussed.

  6. Field Emission from Amorphous carbon Nitride Films Deposited on silicon Tip Arrays

    Institute of Scientific and Technical Information of China (English)

    李俊杰; 郑伟涛; 孙龙; 卞海蛟; 金曾孙; 赵海峰; 宋航; 孟松鹤; 赫晓东; 韩杰才

    2003-01-01

    Amorphous carbon nitride films (a-CNx) were deposited on silicon tip arrays by rf magnetron sputtering in pure nitrogen atmosphere. The field emission property of carbon nitride films on Si tips was compared with that of carbon nitride on silicon wafer. The results show that field emission property of carbon nitride films deposited on silicon tips can be improved significantly in contrast with that on wafer. It can be explained that field emission is sensitive to the local curvature and geometry, thus silicon tips can effectively promote field emission property of a-CNx films. In addition, the films deposited on silicon tips have a smaller effective work function ( F = 0.024 eV)of electron field emission than that on silicon wafer ( F = 0.060 e V), which indicates a significant enhancement of the ability of electron field emission from a-CNx films.

  7. High spatial resolution radiation detectors based on hydrogenated amorphous silicon and scintillator

    International Nuclear Information System (INIS)

    Hydrogenated amorphous silicon (a-Si:H) as a large-area thin film semiconductor with ease of doping and low-cost fabrication capability has given a new impetus to the field of imaging sensors; its high radiation resistance also makes it a good material for radiation detectors. In addition, large-area microelectronics based on a-Si:H or polysilicon can be made with full integration of peripheral circuits, including readout switches and shift registers on the same substrate. Thin a-Si:H p-i-n photodiodes coupled to suitable scintillators are shown to be suitable for detecting charged particles, electrons, and X-rays. The response speed of CsI/a-Si:H diode combinations to individual particulate radiation is limited by the scintillation light decay since the charge collection time of the diode is very short (< 10ns). The reverse current of the detector is analyzed in term of contact injection, thermal generation, field enhanced emission (Poole-Frenkel effect), and edge leakage. A good collection efficiency for a diode is obtained by optimizing the p layer of the diode thickness and composition. The CsI(Tl) scintillator coupled to an a-Si:H photodiode detector shows a capability for detecting minimum ionizing particles with S/N ∼20. In such an arrangement a p-i-n diode is operated in a photovoltaic mode (reverse bias). In addition, a p-i-n diode can also work as a photoconductor under forward bias and produces a gain yield of 3--8 for shaping times of 1 micros. The mechanism of the formation of structured CsI scintillator layers is analyzed. Initial nucleation in the deposited layer is sensitive to the type of substrate medium, with imperfections generally catalyzing nucleation. Therefore, the microgeometry of a patterned substrate has a significant effect on the structure of the CsI growth

  8. Ultrafast all-optical arithmetic logic based on hydrogenated amorphous silicon microring resonators

    Science.gov (United States)

    Gostimirovic, Dusan; Ye, Winnie N.

    2016-03-01

    For decades, the semiconductor industry has been steadily shrinking transistor sizes to fit more performance into a single silicon-based integrated chip. This technology has become the driving force for advances in education, transportation, and health, among others. However, transistor sizes are quickly approaching their physical limits (channel lengths are now only a few silicon atoms in length), and Moore's law will likely soon be brought to a stand-still despite many unique attempts to keep it going (FinFETs, high-k dielectrics, etc.). This technology must then be pushed further by exploring (almost) entirely new methodologies. Given the explosive growth of optical-based long-haul telecommunications, we look to apply the use of high-speed optics as a substitute to the digital model; where slow, lossy, and noisy metal interconnections act as a major bottleneck to performance. We combine the (nonlinear) optical Kerr effect with a single add-drop microring resonator to perform the fundamental AND-XOR logical operations of a half adder, by all-optical means. This process is also applied to subtraction, higher-order addition, and the realization of an all-optical arithmetic logic unit (ALU). The rings use hydrogenated amorphous silicon as a material with superior nonlinear properties to crystalline silicon, while still maintaining CMOS-compatibility and the many benefits that come with it (low cost, ease of fabrication, etc.). Our method allows for multi-gigabit-per-second data rates while maintaining simplicity and spatial minimalism in design for high-capacity manufacturing potential.

  9. Impact of contamination on hydrogenated amorphous silicon thin films and solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Woerdenweber, Jan

    2011-09-26

    This thesis deals with atmospheric contamination and cross-contamination of boron (single-chamber process) of the intrinsic absorber layer (i-layer) of p-i-n thin film solar cells based on hydrogenated amorphous silicon. The atmospheric contaminations were introduced by means of intentional leaks. Hereby, the focus is on the influence of contamination species (oxygen and nitrogen), quantity of contamination (leak flow), source of contamination (leaks at chamber wall or in the process gas pipe), and plasma power on the properties of solar cells. Thereby, the minimum requirements for the purity of vacuum and process gas as well as leak conditions of the recipient and gas pipe system have been determined. Additionally, deposition regimes were developed, where the incorporation of impurities is significantly suppressed. For standard processes critical levels of nitrogen and oxygen contamination are determined to be {proportional_to} 4 x 10{sup 18} cm{sup -3} and {proportional_to} 2 x 10{sup 19} cm{sup -3}, respectively, for a leak situated at the chamber wall. Above these concentrations the solar cell efficiency deteriorates. In literature, incorporation of oxygen and nitrogen in doping configuration is assumed to be the reason for the cell deterioration. This assumption is supported by additional material studies of contaminated absorber layers done in this work. The difference in critical concentration is due to the higher doping efficiency of nitrogen compared to that for oxygen. Nevertheless, applying an air leak the critical concentrations of O and N are reached almost simultaneously since the incorporation probability of oxygen is about one order of magnitude higher compared to that for nitrogen. Applying a leak in the process gas pipe the critical oxygen contamination level increases to {proportional_to} 2 x 10{sup 20} cm{sup -3} whereas the critical nitrogen level remains unchanged compared to a chamber wall leak. Applying a deposition regime with a very high

  10. Physisorption of molecular hydrogen on carbon nanotube with vacant defects

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Gang; Shen, Huaze; Wang, Enge; Xu, Limei, E-mail: limei.xu@pku.edu.cn [International Center for Quantum Materials and School of Physics, Peking University, Beijing 100871 (China); Collaborative Innovation Center of Quantum Matter, Beijing (China); Tangpanitanon, Jirawat [University of Cambridge, Cambridge, Cambridgeshire CB2 1TP (United Kingdom); Wen, Bo [International Center for Quantum Materials and School of Physics, Peking University, Beijing 100871 (China); Beijing Computational Science Research Center, Heqing Street, Haidian District, Beijing 100084 (China); Xue, Jianming [State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871 (China); Center for Applied Physics and Technology, Peking University, Beijing 100871 (China)

    2014-05-28

    Physisorption of molecular hydrogen on single-walled carbon nanotubes (SWCNTs) is important for its engineering applications and hydrogen energy storage. Using molecular dynamics simulation, we study the physisorption of molecular hydrogen on a SWCNT with a vacant defect, focusing on the effect of the vacant defect size and external parameters such as temperature and pressure. We find that hydrogen can be physisorbed inside a SWCNT through a vacant defect when the defect size is above a threshold. By controlling the size of the defects, we are able to extract hydrogen molecules from a gas mixture and store them inside the SWCNT. We also find that external parameters, such as low temperature and high pressure, enhance the physisorption of hydrogen molecules inside the SWCNT. In addition, the storage efficiency can be improved by introducing more defects, i.e., reducing the number of carbon atoms on the SWCNT.

  11. Template synthesis, characterization and magnetic property of Fe nanowires-filled amorphous carbon nanotubes array

    International Nuclear Information System (INIS)

    A Fe nanowires-filled amorphous carbon nanotubes (FeNW-filled a-CNTs) array was synthesized by sequential growth of electrodeposited Fe nanowires and subsequent chemical vapour deposition of amorphous CNTs in the nanochannels of alumina template. Structural characterizations of as-prepared FeNW-filled a-CNTs were carried out via field emission scanning electron microscope (FE-SEM), x-ray diffraction (XRD), elemental mapping, high-resolution transmission electron microscope (HRTEM) and Raman scattering. The formation mechanism of such Fe/C nanoheterostructure was proposed according to the detailed HRTEM analyses. Furthermore, the room temperature magnetic property of the as-prepared FeNW-filled a-CNTs array was also investigated, and obvious anisotropic behaviour in magnetization was observed

  12. The ir emission features: Emission from PAH [Polycyclic Aromatic Hydrocarbons] molecules and amorphous carbon particles

    International Nuclear Information System (INIS)

    PAHs can have several forms in the interstellar medium. To assess the importance of each requires the availability of a collection of high quality, complete mid-ir interstellar emission spectra, a collection of laboratory spectra of PAH samples prepared under realistic conditions and a firm understanding of the microscopic emission mechanism. Given what we currently know about PAHs, the spectroscopic data suggests that there are at least two components which contribute to the interstellar emission spectrum: free molecule sized PAHs producing the narrow features and amorphous carbon particles (which are primarily made up of an irregular ''lattice'' of PAHs) contributing to the broad underlying components. An exact treatment of the ir fluorescence from highly vibrationally excited large molecules shows that species containing between 20 and 30 carbon atoms are responsible for the narrow features, although the spectra match more closely with the spectra of amorphous carbon particles. Since little is known about the spectroscopic properties of free PAHs and PAH clusters, much laboratory work is called for in conjunction with an observational program which focuses on the spatial characteristics of the spectra. In this way the distribution and evolution of carbon from molecule to particle can be traced. 38 refs., 9 figs

  13. Crystalline and Amorphous Phosphorus – Carbon Nanotube Composites as Promising Anodes for Lithium-Ion Batteries

    KAUST Repository

    Smajic, Jasmin

    2016-05-04

    Battery research has been going full steam and with that the search for alternative anodes. Among many proposed electrode materials, little attention has been given to phosphorus. Phosphorus boasts the third highest gravimetric charge capacity and the highest volumetric charge capacity of all elements. Because of that, it would be an attractive battery anode material were it not for its poor cyclability with significant capacity loss immediately after the first cycle. This is known to be the consequence of considerable volume changes of phosphorus during charge/discharge cycles. In this work, we propose circumventing this issue by mixing amorphous red phosphorus with carbon nanotubes. By employing a non-destructive sublimation-deposition method, we have synthesized composites where the synergetic effect between phosphorus and carbon nanotubes allow for an improvement in the electrochemical performance of battery anodes. In fact, it has been shown that carbon nanotubes can act as an effective buffer to phosphorus volumetric expansions and contractions during charging and discharging of the half-cells [1]. By modifying the synthesis parameters, we have also been able to change the degree of crystallinity of the phosphorus matrix in the composites. In fact, the less common phase of red phosphorus, named fibrous phosphorus, was obtained, and that explains some of the varying electrochemical performances observed in the composites. Overall, it is found that a higher surface area of amorphous phosphorus allows for a better anode material when using single-walled carbon nanotubes as fillers.

  14. Hydrogen storage capacity of some carbon nanotubes and filaments

    International Nuclear Information System (INIS)

    We have studied the sorption of hydrogen by 8 different carbon materials at pressures up to 11 MPa (1600 psi) and temperatures from -80oC to +500oC. Our samples include graphite flakes, Aldrich activated carbon, graphitized PYROGRAF vapor-grown carbon fibers (VGCF), etched PYROGRAF fibers, Showa-Denko VGCF, filaments grown from a FeNiCu alloy, and nanotubes from MER Corp. and Rice University. The results so far have been remarkably similar: very little hydrogen sorption. In fact, the sorption is so small that we must pay careful attention to calibration to get reliable answers. The largest sorption observed is less than 0.1 weight percent hydrogen at room temperature and 3.5 MPa. Furthermore, our efforts to activate these materials by reduction at high temperatures and pressures were also futile. These results cast serious doubts on any claims for large hydrogen sorption in carbon materials. (author)

  15. Ion bombardment effects in plasma deposition of hydrogenated amorphous silicon carbide films: a comparative study of d.c. and r.f. discharges

    International Nuclear Information System (INIS)

    The structure and the properties of hydrogenated amorphous silicon carbide films produced at room temperature by d.c. and r.f. glow discharge decomposition of silane and ethylene were studied with a systematic control of the ion flux at the surface of the growing film. The composition and structure of the films were monitored by measuring their IR absorption, their refractive index and their optical gap. The ion fluxes were determined from the saturation current of a small grid probe located in the substrate holder. It was found that d.c. cathodic and r.f. films show an inorganic structure with a dispersed carbon phase while d.c. anodic films exhibit mainly hydrogenated carbon clusters. These structural changes are thought to result from differences in the energies of the bombarding ions. The versatility of the r.f. and d.c. proximity discharges in comparison with d.c. discharges (anodic and cathodic films) is also emphasized. (Auth.)

  16. Hydrogen storage in carbon materials—preliminary results

    Science.gov (United States)

    Jörissen, Ludwig; Klos, Holger; Lamp, Peter; Reichenauer, Gudrun; Trapp, Victor

    1998-08-01

    Recent developments aiming at the accelerated commercialization of fuel cells for automotive applications have triggered an intensive research on fuel storage concepts for fuel cell cars. The fuel cell technology currently lacks technically and economically viable hydrogen storage technologies. On-board reforming of gasoline or methanol into hydrogen can only be regarded as an intermediate solution due to the inherently poor energy efficiency of such processes. Hydrogen storage in carbon nanofibers may lead to an efficient solution to the above described problems.

  17. Designed synthesis of tunable amorphous carbon nanotubes (a-CNTs) by a novel route and their oxidation resistance properties

    Indian Academy of Sciences (India)

    Longlong Xu; Yifu Zhang; Xiongzhi Zhang; Yu Huang; Xiaoyu Tan; Chi Huang; Xiao Mei; Fei Niu; Changgong Meng; Gongzhen Cheng

    2014-10-01

    Tunable amorphous carbon nanotubes (a-CNTs) were successfully synthesized using V3O7.H2O and glucose solution as the starting materials by a novel route for the first time. The as-obtained samples were separately characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), energy-dispersive spectrometer (EDS), elemental analysis (EA), Fourier transform infrared spectroscopy (FT–IR) and Raman spectrum. The results showed that the as-obtained a-CNTs had uniform diameters with outer diameter ranging from 140 to 250 nm and inner diameter about 28 nm on an average, and their length was up to several micrometres. No VO residues remaining in a-CNTs showed the as-obtained a-CNTs with high purity. The as-prepared a-CNTs were a kind of hydrogenated a-CNTs containing both the 3- and 2-type carbons. Furthermore, the thermal stability of the as-obtained a-CNTs in the air atmosphere were investigated by thermo-gravimetric/differential thermal analyser (TG-DTA), revealing that the as-obtained a-CNTs had good thermal stability and oxidation resistance below 300 °C in air.

  18. Monte Carlo simulations of hydrogen storage in carbon nanotubes

    International Nuclear Information System (INIS)

    The storage capacities of porous materials made up of carbon nanotubes are estimated by Monte Carlo simulations for the specific case of hydrogen in the pressure domain from 0.1 to 20 MPa at temperatures of 293, 150 and 77 K. The use of these materials in devices for hydrogen storage is discussed on the basis of the simulation results. (author)

  19. Hydrogen peroxide leaching of uranium in carbonate solutions

    International Nuclear Information System (INIS)

    The kinetics of UO2 dissolution in ammoniacal carbonate solutions were investigated with hydrogen peroxide as an oxidant. The effects of hydrogen peroxide concentration, total carbonate concentration and pH were studied. For similar conditions, the rate of dissolution was considerably faster with hydrogen peroxide than with oxygen. The reaction was found to be of 0.5 order with respect to both hydrogen peroxide and total carbonate concentrations. At pH values below approximately 10, the rate was relatively insensitive to pH. These results are consistent with an electrochemical surface reaction similar to that developed for the oxygen-leaching system. Electrochemical interpretation adequately explain the enhanced rate of dissolution observed for hydrogen peroxide leaching. The decomposition of hydrogen peroxide in alkaline solutions is discussed. Surface-electrode potentials are used to explain the catalytic activity of various solids. Hydrogen peroxide was found to decompose rapidly in the presence of freshly precipitated ferric hydroxide. The effect of pH on the rate of hydrogen peroxide decomposition was investigated in the pH range 4.3 to 11.2. Problems associated with the use of hydrogen peroxide in the in-situ leaching of uranium are considered. (author)

  20. General laws of the effect of hydrogen on the crystallization of amorphous alloys based on the quasi-binary TiNi-TiCu system

    Science.gov (United States)

    Spivak, L. V.; Shelyakov, A. V.; Shchepina, N. E.

    2014-02-01

    The crystallization processes that occur during heating of hydrogen-containing melt-quenched alloys based on the quasi-binary TiNi-TiCu system alloyed with aluminum, iron, hafnium, and zirconium are studied by high-resolution differential scanning calorimetry. The general laws of the transition of the hydrogen-containing alloys from an amorphous into a crystalline state are determined.

  1. Hydrogen effect on properties of amorphous alloy 78Fe-3.5Nb-1Cu-4B-13.5Si

    International Nuclear Information System (INIS)

    It is reported about the detection of a practically complete loss of elastic properties after hydrogenation, and about subsequent reconstruction of the latter during exposure of hydrogenated amorphous metal alloy at 275 K. Possible reasons for such an unusual phenomenon are discussed

  2. A Comprehensive Study of Hydrogen Adsorbing to Amorphous Water-Ice: Defining Adsorption in Classical Molecular Dynamics

    CERN Document Server

    Dupuy, John L; Stancil, P C

    2016-01-01

    Gas-grain and gas-phase reactions dominate the formation of molecules in the interstellar medium (ISM). Gas-grain reactions require a substrate (e.g. a dust or ice grain) on which the reaction is able to occur. The formation of molecular hydrogen (H$_2$) in the ISM is the prototypical example of a gas-grain reaction. In these reactions, an atom of hydrogen will strike a surface, stick to it, and diffuse across it. When it encounters another adsorbed hydrogen atom, the two can react to form molecular hydrogen and then be ejected from the surface by the energy released in the reaction. We perform in-depth classical molecular dynamics (MD) simulations of hydrogen atoms interacting with an amorphous water-ice surface. This study focuses on the first step in the formation process; the sticking of the hydrogen atom to the substrate. We find that careful attention must be paid in dealing with the ambiguities in defining a sticking event. The technical definition of a sticking event will affect the computed sticking ...

  3. Deposit of thin films of nitrided amorphous carbon using the laser ablation technique

    International Nuclear Information System (INIS)

    It is reported the synthesis and characterization of thin films of amorphous carbon (a-C) nitrided, deposited by laser ablation in a nitrogen atmosphere at pressures which are from 4.5 x 10 -4 Torr until 7.5 x 10 -2 Torr. The structural properties of the films are studied by Raman spectroscopy obtaining similar spectra at the reported for carbon films type diamond. The study of behavior of the energy gap and the ratio nitrogen/carbon (N/C) in the films, shows that the energy gap is reduced when the nitrogen incorporation is increased. It is showed that the refraction index of the thin films diminish as nitrogen pressure is increased, indicating the formation of graphitic material. (Author)

  4. Hydrogen storage capacity of lithium-doped KOH activated carbons

    International Nuclear Information System (INIS)

    Highlights: • The hydrogen adsorption of lithium-doped KOH activated carbons has been studied. • Lithium doping improves their hydrogen adsorption affinity. • Lithium doping is more effective for materials with micropores of 0.8 nm or smaller. • Lithium reagent can alter the pore structure, depending on the raw material. • Optimizing the pore size and functional group is needed for better hydrogen uptake. - Abstract: The authors have studied the hydrogen adsorption performance of several types of lithium-doped KOH activated carbons. In the case of activated cokes, lithium doping improves their hydrogen adsorption affinity from 5.02 kg/m3 to 5.86 kg/m3 at 303 K. Hydrogen adsorption density increases by around 17% after lithium doping, likely due to the fact that lithium doping is more effective for materials with micropores of 0.8 nm or smaller. The effects of lithium on hydrogen storage capacity vary depending on the raw material, because the lithium reagent can react with the material and alter the pore structure, indicating that lithium doping has the effect of plugging or filling the micropores and changing the structures of functional groups, resulting in the formation of mesopores. Despite an observed decrease in hydrogen uptake, lithium doping was found to improve hydrogen adsorption affinity. Lithium doping increases hydrogen uptake by optimizing the pore size and functional group composition

  5. Study of the hydrogen behavior in amorphous hydrogenated materials of type a - C:H and a - SiC:H facing fusion reactor plasma

    International Nuclear Information System (INIS)

    Plasma facing components of controlled fusion test devices (tokamaks) are submitted to several constraints (irradiation, high temperatures). The erosion (physical sputtering and chemical erosion) and the hydrogen recycling (retention and desorption) of these materials influence many plasma parameters and thus affect drastically the tokamak running. First, we will describe the different plasma-material interactions. It will be pointed out, how erosion and hydrogen recycling are strongly related to both chemical and physical properties of the material. In order to reduce these interactions, we have selected two amorphous hydrogenated materials (a-C:H and a-SiC:H), which are known for their good thermal and chemical qualities. Some samples have been then implanted with lithium ions at different fluences. Our materials have been then irradiated with deuterium ions at low energy. From our results, it is shown that both the lithium implantation and the use of an a - SiC:H substrate can be beneficial in enhancing the hydrogen retention. These results were completed with thermal desorption studies of these materials. It was evidenced that the hydrogen fixation was more efficient in a-SiC:H than in a-C:H substrate. Results in good agreement with those described above have been obtained by exposing a - C:H and a - SiC:H samples to the scrape off layer of the tokamak of Varennes (TdeV, Canada). A modelling of hydrogen diffusion under irradiation has been also proposed. (author)

  6. Hydrogen behaviour study in plasma facing a-C:H and a-SiC:H hydrogenated amorphous materials for fusion reactors

    International Nuclear Information System (INIS)

    Plasma facing components of controlled fusion test devices (tokamaks) are submitted to several constraints (irradiation, high temperatures). The erosion (physical sputtering and chemical erosion) and the hydrogen recycling (retention and desorption) of these materials influence many plasma parameters and thus affect drastically the tokamak running. Firstly, we will describe the different plasma-material interactions. It will be pointed out, how erosion and hydrogen recycling are strongly related to both chemical and physical properties of the material. In order to reduce this interactions, we have selected two amorphous hydrogenated materials (a-C:H and a-SiC:H), which are known for their good thermal and chemical qualities. Some samples have been then implanted with lithium ions at different fluences. Our materials have been then irradiated with deuterium ions at low energy. From our results, it is shown that both the lithium implantation and the use of an a-SiC:H substrate can be benefit in enhancing the hydrogen retention. These results were completed with thermal desorption studies of these materials. It was evidenced that the hydrogen fixation was more efficient in a -SiC:H than in a-C:H substrate. Results in good agreement with those described above have been obtained by exposing a-C:H and a-SiC:H samples to the scrape off layer of the tokamak of Varennes (TdeV, Canada). A modeling of hydrogen diffusion under irradiation has been also proposed. (author)

  7. X-ray diffraction study of atomic structure features of amorphous carbon containing materials of nature and synthetic origin

    International Nuclear Information System (INIS)

    The atomic structure of amorphous carbon-containing materials such as carbon glass, spectroscopically pure carbon, schungite and anthracite is investigated using X ray diffraction analysis and computerized simulation. In computerized simulation of model gratings packing into packets an interlayer distance and a number of layer in a packet varied and a gratings turn is predetermined randomly. The quantity of gratings in a packet is shown to vary between four for anthracite and six for spectroscopically pure coal. The interlayer distance for all amorphous carbonaceous materials is above 3.35 A which is typical for graphite

  8. Growth of crystalline silicon nanowires on nickel-coated silicon wafer beneath sputtered amorphous carbon

    International Nuclear Information System (INIS)

    Growth of crystalline silicon nanowire of controllable diameter directly from Si wafer opens up another avenue for its application in solar cells and optical sensing. Crystalline Si nanowire can be directly grown from Si wafer upon rapid thermal annealing in the presence of the catalyst such as nickel (Ni). However, the accompanying oxidation immediately changes the crystalline Si nanowire to amorphous SiOx. In this study, amorphous carbon layer was sputtered to on top of the catalyst Ni layer to retard the oxidation. Scanning electron microscope, transmission electron microscope, Raman spectroscopy and X-ray photoelectron spectroscopy were employed to characterize the wires and oxidation process. A model was developed to explain the growth and oxidation process of the crystalline Si nanowire. - Highlights: ► Carbon was sputtered on nickel to retard the oxidation of silicon nanowires. ► Silicon core was controlled by carbon layer thickness and annealing duration. ► An oxidation-accompanying solid–liquid–solid growth mechanism was developed

  9. Substrate temperature influence on the trombogenicity in amorphous carbon nitride thin coatings

    Science.gov (United States)

    Galeano-Osorio, D. S.; Vargas, S.; López-Córdoba, L. M.; Ospina, R.; Restrepo-Parra, E.; Arango, P. J.

    2010-10-01

    Carbon nitride thin films were obtained through plasma assisted physical vapor deposition technique by pulsed arc, varying the substrate temperature and investigating the influence of this parameter on the films hemocompatibility. For obtaining approaches of blood compatibility, environmental scanning electron microscopy (ESEM) was used in order to study the platelets adherence and their morphology. Moreover, the elemental chemical composition was determined by using energy dispersive spectroscopy (EDS), finding C, N and O. The coatings hemocompatibility was evaluated by in vitro thrombogenicity test, whose results were correlated with the microstructure and roughness of the films obtained. During the films growth process, the substrate temperature was varied, obtaining coatings under different temperatures, room temperature ( Troom), 100 °C, 150 °C and 200 °C. Parameters as interelectrodic distance, voltage, work pressure and number of discharges, were remained constant. By EDS, carbon and nitrogen were found in the films. Visible Raman spectroscopy was used, and it revealed an amorphous lattice, with graphitic process as the substrate temperature was increased. However, at a critical temperature of 150 °C, this tendency was broken, and the film became more amorphous. This film showed the lowest roughness, 2 ± 1 nm. This last characteristic favored the films hemocompatibility. Also, it was demonstrated that the blood compatibility of carbon nitride films obtained were affected by the ID/ IG or sp 3/sp 2 ratio and not by the absolute sp 3 or sp 2 concentration.

  10. Substrate temperature influence on the trombogenicity in amorphous carbon nitride thin coatings

    International Nuclear Information System (INIS)

    Carbon nitride thin films were obtained through plasma assisted physical vapor deposition technique by pulsed arc, varying the substrate temperature and investigating the influence of this parameter on the films hemocompatibility. For obtaining approaches of blood compatibility, environmental scanning electron microscopy (ESEM) was used in order to study the platelets adherence and their morphology. Moreover, the elemental chemical composition was determined by using energy dispersive spectroscopy (EDS), finding C, N and O. The coatings hemocompatibility was evaluated by in vitro thrombogenicity test, whose results were correlated with the microstructure and roughness of the films obtained. During the films growth process, the substrate temperature was varied, obtaining coatings under different temperatures, room temperature (Troom), 100 deg. C, 150 deg. C and 200 deg. C. Parameters as interelectrodic distance, voltage, work pressure and number of discharges, were remained constant. By EDS, carbon and nitrogen were found in the films. Visible Raman spectroscopy was used, and it revealed an amorphous lattice, with graphitic process as the substrate temperature was increased. However, at a critical temperature of 150 deg. C, this tendency was broken, and the film became more amorphous. This film showed the lowest roughness, 2 ± 1 nm. This last characteristic favored the films hemocompatibility. Also, it was demonstrated that the blood compatibility of carbon nitride films obtained were affected by the ID/IG or sp3/sp2 ratio and not by the absolute sp3 or sp2 concentration.

  11. Substrate temperature influence on the trombogenicity in amorphous carbon nitride thin coatings

    Energy Technology Data Exchange (ETDEWEB)

    Galeano-Osorio, D.S.; Vargas, S.; Lopez-Cordoba, L.M.; Ospina, R. [Laboratorio de Fisica del Plasma, Universidad Nacional de Colombia Sede Manizales, Km. 9 via al Magdalena, Manizales (Colombia); Restrepo-Parra, E., E-mail: erestrepopa@unal.edu.co [Laboratorio de Fisica del Plasma, Universidad Nacional de Colombia Sede Manizales, Km. 9 via al Magdalena, Manizales (Colombia); Arango, P.J. [Laboratorio de Fisica del Plasma, Universidad Nacional de Colombia Sede Manizales, Km. 9 via al Magdalena, Manizales (Colombia)

    2010-10-01

    Carbon nitride thin films were obtained through plasma assisted physical vapor deposition technique by pulsed arc, varying the substrate temperature and investigating the influence of this parameter on the films hemocompatibility. For obtaining approaches of blood compatibility, environmental scanning electron microscopy (ESEM) was used in order to study the platelets adherence and their morphology. Moreover, the elemental chemical composition was determined by using energy dispersive spectroscopy (EDS), finding C, N and O. The coatings hemocompatibility was evaluated by in vitro thrombogenicity test, whose results were correlated with the microstructure and roughness of the films obtained. During the films growth process, the substrate temperature was varied, obtaining coatings under different temperatures, room temperature (T{sub room}), 100 deg. C, 150 deg. C and 200 deg. C. Parameters as interelectrodic distance, voltage, work pressure and number of discharges, were remained constant. By EDS, carbon and nitrogen were found in the films. Visible Raman spectroscopy was used, and it revealed an amorphous lattice, with graphitic process as the substrate temperature was increased. However, at a critical temperature of 150 deg. C, this tendency was broken, and the film became more amorphous. This film showed the lowest roughness, 2 {+-} 1 nm. This last characteristic favored the films hemocompatibility. Also, it was demonstrated that the blood compatibility of carbon nitride films obtained were affected by the I{sub D}/I{sub G} or sp{sup 3}/sp{sup 2} ratio and not by the absolute sp{sup 3} or sp{sup 2} concentration.

  12. Anomalous interaction of longitudinal electric field with hydrogenated amorphous silicon films

    OpenAIRE

    Zhang, J.; Gecevičius, M.; Beresna, M; Kazanskii, A.G.; Kazansky, P. G.

    2013-01-01

    Cylindrically polarized beams produced by femtosecond laser written S-waveplate are used to modify amorphous silicon films. Paradoxically, no crystallization is observed in the maximum of longitudinal electric field despite the strongest light intensity

  13. Tetrahedral amorphous carbon coatings for friction reduction of the valve train in internal combustion engines

    OpenAIRE

    Götze, Andreas; Makowski, Stefan; Kunze, Tim; Hübner, Matthias; Zellbeck, Hans; Weihnacht, Volker; Leson, Andreas; Beyer, Eckhard; Joswig, Jan-Ole; Seifert, Gotthard; Abrasonis, Gintautas; Posselt, Matthias; Fassbender, Jürgen; Möller, Wolfhard; Gemming, Sibylle

    2014-01-01

    Tetrahedral amorphous carbon (ta-C) is studied as a tribological coating for the valve train's exhaust camshaft of a combustion engine. The coated camshafts were installed in a non-fired engine, tested in a computerized component test bench under practice-relevant conditions and analyzed for their frictional behavior. A notable reduction of the valve train's drive torque on the test bench is demonstrated. Namely, on a roller cam system with ta-C-coated camshaft the reduction is about 15% in a...

  14. Influence of dc bias on amorphous carbon deposited by pulse laser ablation

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Amorphous carbon films were deposited on single-crystalline silicon and K9 glass by pulse laser ablation using different negative substrate bias. Scanning electron microscope (SEM) was used to observe morphology of the surface. Thickness and refractive index of the film deposited on K9 glass were measured by ellipsometry. Micro-hardness of films was measured relatively to single crystal silicon. All films deposited on silicon were analyzed by Raman spectra. All spectra were deconvoluted to three peaks. Line-width ratios varied similarly with bias voltage when the laser energy was kept invariant.

  15. Phonon transport in amorphous carbon using Green-Kubo modal analysis

    Science.gov (United States)

    Lv, Wei; Henry, Asegun

    2016-05-01

    Amorphous carbon (a-C) is an important material often used in microelectronics. Using a recently developed approach, termed Green-Kubo modal analysis, we were able to calculate the thermal conductivity of a-C, which yielded excellent agreement with experiments, by employing a simple correction to the specific heat. The results show that the heat capacity substantially limits the thermal conductivity of a-C at room temperature and it is dominated by contributions from diffusons between 10 and 40 THz. Furthermore, the phonon relaxation times in a-C do not vary significantly with increasing temperature, which is quite unusual by comparison with the behavior observed for other materials.

  16. Soft x-ray reflectivity measurements of amorphous carbon thin films using Indus-I

    International Nuclear Information System (INIS)

    Using Indus-I synchrotron radiation source, the soft x-ray reflectivity measurements have been performed on electron beam deposited amorphous carbon thin films. The study shows that soft x-ray reflectivity is an extremely effective, accurate and non-destructive technique for measuring thickness, density and microscopic roughness. High q- space resolution at larger wavelength permits to investigate thicker films in the range of 100 to 3000 A. Our simulation study for hard x-ray region reveals that the instrumental resolution factor limits the probing thickness range. (author)

  17. Strength and tribology of bulk and electroformed nickel amorphized by implantation of titanium and carbon

    International Nuclear Information System (INIS)

    Dual ion implantation of titanium and carbon was shown to produce an amorphous layer of exceptional strength within annealed bulk Ni and electroformed Ni and Ni80Fe20 materials used in micro-electromechanical systems. The intrinsic elastic and plastic mechanical properties of the implanted region were quantified using nanoindentation testing in conjunction with finite-element modeling, and the results were interpreted in the light of microstructures observed by electron microscopy. The implantation treatment was found to produce substantial reductions in unlubricated friction and wear

  18. Reduction of Photoluminescence Quenching by Deuteration of Ytterbium-Doped Amorphous Carbon-Based Photonic Materials

    OpenAIRE

    Hui-Lin Hsu; Keith R. Leong; I-Ju Teng; Michael Halamicek; Jenh-Yih Juang; Sheng-Rui Jian; Li Qian; Nazir P. Kherani

    2014-01-01

    In situ Yb-doped amorphous carbon thin films were grown on Si substrates at low temperatures (<200 °C) by a simple one-step RF-PEMOCVD system as a potential photonic material for direct integration with Si CMOS back end-of-line processing. Room temperature photoluminescence around 1 µm was observed via direct incorporation of optically active Yb3+ ions from the selected Yb(fod)3 metal-organic compound. The partially fluorinated Yb(fod)3 compound assists the suppression of photoluminescence...

  19. Cell survival in carbon beams - comparison of amorphous track model predictions

    DEFF Research Database (Denmark)

    Grzanka, L.; Greilich, S.; Korcyl, M.;

    Introduction: Predictions of the radiobiological effectiveness (RBE) play an essential role in treatment planning with heavy charged particles. Amorphous track models ( [1] , [2] , also referred to as track structure models) provide currently the most suitable description of cell survival under i....... Amorphous track modelling of luminescence detector efficiency in proton and carbon beams. 4.Tsuruoka C, Suzuki M, Kanai T, et al. LET and ion species dependence for cell killing in normal human skin fibroblasts. Radiat Res. 2005;163:494-500.......Introduction: Predictions of the radiobiological effectiveness (RBE) play an essential role in treatment planning with heavy charged particles. Amorphous track models ( [1] , [2] , also referred to as track structure models) provide currently the most suitable description of cell survival under ion...... factors is the normalization of the energy distribution around the particle tracks to the actual LET value. Later on we check what is the effect of radial dose distribution choice on kappa parameter for different types and energy of ions. Outline References 1.Katz R, Sharma SC.Response of cells to fast...

  20. Strain-induced photoconductivity in thin films of Co doped amorphous carbon.

    Science.gov (United States)

    Jiang, Y C; Gao, J

    2014-01-01

    Traditionally, strain effect was mainly considered in the materials with periodic lattice structure, and was thought to be very weak in amorphous semiconductors. Here, we investigate the effects of strain in films of cobalt-doped amorphous carbon (Co-C) grown on 0.7PbMg(1/3)Nb(2/3)O3-0.3PbTiO3 (PMN-PT) substrates. The electric transport properties of the Co-C films were effectively modulated by the piezoelectric substrates. Moreover, we observed, for the first time, strain-induced photoconductivity in such an amorphous semiconductor. Without strain, no photoconductivity was observed. When subjected to strain, the Co-C films exhibited significant photoconductivity under illumination by a 532-nm monochromatic light. A strain-modified photoconductivity theory was developed to elucidate the possible mechanism of this remarkable phenomenon. The good agreement between the theoretical and experimental results indicates that strain-induced photoconductivity may derive from modulation of the band structure via the strain effect. PMID:25338641

  1. Study of hydrogenated amorphous silicon devices under intense electric field: application to nuclear detection

    International Nuclear Information System (INIS)

    The goal of this work was the study, development and optimization of hydrogenated amorphous silicon (a-Si:H) devices for use in detection of ionizing radiation in applications connected to the nuclear industry. Thick p-i-n devices, capable of withstanding large electric fields (up to 106 V/cm) with small currents (nA/cm2), were proposed and developed. In order to decrease fabrication time, films were made using the 'He diluted' PECVD process and compared to standard a-Si:H films. Aspects connected to specific detector applications as well as to the fundamental physics of a-Si:H were considered: the internal electric field technique, in which the depletion charge was measured as a function of the applied bias voltage; study of the leakage current of p-i-n devices permitted us to demonstrate different regimes: depletion, field-enhanced thermal generation and electronic injection across the p layer. The effect of the electric field on the thermal generation of the carriers was studied considering the Poole-Frenkel and tunneling mechanisms. A model was developed taking under consideration the statistics of the correlated states and electron-phonon coupling. The results suggest that mechanisms not included in the 'standard model' of a Si:h need to be considered, such as defect relaxation, a filed-dependent mobility edge etc...; a new metastable phenomenon, called 'forming', induced by prolonged exposure to a strong electric field, was observed and studied. It is characterized by marked decrease of the leakage current and the detector noise, and increase in the breakdown voltage, as well as an improvement of carrier collection efficiency. This forming process appears to be principally due to an activation of the dopants in the p layer; finally, the capacity of thick p-i-n a Si:H devices to detect ionizing radiation has been evaluated. We show that it is possible, with 20-50 micron thick p-i-n devices, to detect the full spectrum of alpha and beta particles. With an

  2. Charge deep-level transient spectroscopy study of high-energy-electron-beam-irradiated hydrogenated amorphous silicon

    OpenAIRE

    Klaver, A.; Nádaždy, V.; Zeman, M.; Swaaiij, R.A.C.M.M.

    2006-01-01

    We present a study of changes in the defect density of states in hydrogenated amorphous silicon (a-Si:H) due to high-energy electron irradiation using charged deep-level transient spectroscopy. It was found that defect states near the conduction band were removed, while in other band gap regions the defect-state density increased. A similar trend is observed for a-Si:H which has been subjected to light soaking, but in that case the majority of defect states are created around midgap, whereas ...

  3. Dangling bond electron spin-lattice relaxation in rf-sputtered hydrogenated amorphous silicon and silicon carbide

    International Nuclear Information System (INIS)

    Electron spin resonance methods have been used to measure the temperature dependence of the spin-lattice relaxation time T1 of dangling bond electrons in hydrogenated amorphous silicon and silicon carbide samples prepared by radio frequency sputtering. The T1 measurements were made by a combination of continuous-wave absorption mode saturation and periodic adiabatic passage methods over the temperature range 100--400 K, yielding T/sup -1/1proportionalT2 behavior consistent with relaxation by two-level systems

  4. Carbon dioxide utilization and hydrogen production by photosynthetic microorganisms

    Energy Technology Data Exchange (ETDEWEB)

    Aoyama, Katsuhiro [Tokyo Gas Co. Ltd., Frontier Technology Research Inst., Yokohama (Japan); Takasaki, Koichi [Tokyo Gas Co. Ltd., Frontier Technology Research Inst., Yokohama (Japan)]|[RITE, Project Center for CO2 Fixation and Utilization, Minato, Tokyo (Japan); Miyake, Jun; Asada, Yasuo [National Institute of Bioscience and Human-Technology, AIST/MITI, Tsukuba, Ibaraki (Japan)

    1999-07-01

    The solar energy is the largest energy source in the world. Using the photosynthesis, we will be able utilise the huge amount of carbon dioxide. Microalgae, cyanobacteria, photosynthetic bacteria belong to photosynthetic microorganisms, which assimilate carbon dioxide during the photosynthesis. One of the cyanobacteria, Spirulina platensis accumulates carbohydrate photoautotrophically up to 50% of the dry cell weight in the nitrogen-deficient condition. Under an anaerobic condition in the dark, it is degraded into organic compounds such as organic acids, alcohol and sugar. As the hydrogen gas is also evolved in this process, the participation of hydrogenase (Hydrogen producing enzyme) has been suggested in this metabolism. We have investigated several conditions of evolution of hydrogen and production of organic compounds. The bacterial concentration initial pH and temperature had significant effects on hydrogen evolution as well as production of organic compounds. When the bacterial cell concentration was high, the pH of fermentation products was reduced to acidic and the evolution of hydrogen tended to be inhibited. The profiles of fermentation products varied according to the culture condition. The increase of organic acids were remarkable in the inhibitory condition for hydrogen production, such as acidic pH and high temperature. Furthermore these fermentation products were converted into hydrogen gas by using photosynthetic bacterium Rhodobacter sphaeroides RV with light energy. The composition of evolved gas was mainly hydrogen and carbon dioxide, and their contents were 78% and 10%, respectively. The total amount of evolved hydrogen was nearly equal to the estimated, value which was calculated by the degradation of each organic acid. Combining this system with the photosynthesis of cyanobacteria, we could accomplish the production of hydrogen by solar energy, carbon dioxide and water. And we demonstrated that the evolved gas could be directly supplied to the

  5. THE MEDIUM RANGE STRUCTURE OF HYDROGENATED Cu-Ti AMORPHOUS ALLOYS STUDIED BY ANOMALOUS SMALL-ANGLE SCATTERING OF X-RAYS AND NEUTRON DIFFRACTION

    OpenAIRE

    Goudeau, P.; Naudon, A.; Rodmacq, B.; Mangin, P; Chamberod, A.

    1985-01-01

    Amorphous Cu-Ti alloys, when hydrogenated, reveal a strong small-angle scattered intensity. The anomalous X-ray scattering effect is used to analyse this SAS intensity on both copper and titanium edges. It allows to assert the presence of very small clusters of titanium hydride having the TiH2 composition. These results are in good agreement with those obtained by neutron scattering experiments when using either hydrogen (b 0) for the hydrogenation of the samples.

  6. Computational Evaluation of Amorphous Carbon Coating for Durable Silicon Anodes for Lithium-Ion Batteries

    Directory of Open Access Journals (Sweden)

    Jeongwoon Hwang

    2015-10-01

    Full Text Available We investigate the structural, mechanical, and electronic properties of graphite-like amorphous carbon coating on bulky silicon to examine whether it can improve the durability of the silicon anodes of lithium-ion batteries using molecular dynamics simulations and ab-initio electronic structure calculations. Structural models of carbon coating are constructed using molecular dynamics simulations of atomic carbon deposition with low incident energies (1–16 eV. As the incident energy decreases, the ratio of sp2 carbons increases, that of sp3 decreases, and the carbon films become more porous. The films prepared with very low incident energy contain lithium-ion conducting channels. Also, those films are electrically conductive to supplement the poor conductivity of silicon and can restore their structure after large deformation to accommodate the volume change during the operations. As a result of this study, we suggest that graphite-like porous carbon coating on silicon will extend the lifetime of the silicon anodes of lithium-ion batteries.

  7. Development of Thin Film Amorphous Silicon Tandem Junction Based Photocathodes Providing High Open-Circuit Voltages for Hydrogen Production

    Directory of Open Access Journals (Sweden)

    F. Urbain

    2014-01-01

    Full Text Available Hydrogenated amorphous silicon thin film tandem solar cells (a-Si:H/a-Si:H have been developed with focus on high open-circuit voltages for the direct application as photocathodes in photoelectrochemical water splitting devices. By temperature variation during deposition of the intrinsic a-Si:H absorber layers the band gap energy of a-Si:H absorber layers, correlating with the hydrogen content of the material, can be adjusted and combined in a way that a-Si:H/a-Si:H tandem solar cells provide open-circuit voltages up to 1.87 V. The applicability of the tandem solar cells as photocathodes was investigated in a photoelectrochemical cell (PEC measurement set-up. With platinum as a catalyst, the a-Si:H/a-Si:H based photocathodes exhibit a high photocurrent onset potential of 1.76 V versus the reversible hydrogen electrode (RHE and a photocurrent of 5.3 mA/cm2 at 0 V versus RHE (under halogen lamp illumination. Our results provide evidence that a direct application of thin film silicon based photocathodes fulfills the main thermodynamic requirements to generate hydrogen. Furthermore, the presented approach may provide an efficient and low-cost route to solar hydrogen production.

  8. The adsorption of hydrogen on nano-structured carbons

    Energy Technology Data Exchange (ETDEWEB)

    Didion, A.; Gadiou, R.; Vix-Guterl, C. [Institut de Chimie des Surfaces et Interfaces, CNRS UPR 9069, 68 - Mulhouse (France); Piquero, Th.; David, P. [CEA Centre d' Etudes du Ripault, 37 - Tours (France)

    2005-07-01

    A major key point for the development of hydrogen as an energy source is the design of a safe and compact storage device. The adsorption of molecular hydrogen on various carbon structures has been widely studied during the last two decades, and the storage capacities which are obtained are of the order of a few weight percents. Nano-structured carbons can be obtained by templating from ordered meso-porous silicas, different carbon precursors have been used such as sucrose solutions, pitch, or propylene [1-3]. Compared to conventional activated carbons, these carbon materials have specific features such as an ordered network of meso-pores and a micro-porous volume which is obtained without any activation. It has been shown that the storage capacity of these carbons materials is comparable to the one of activated carbo4], and further investigation is needed to understand the influence of the pore shape and connectivity on the adsorption. The objective of this study was to obtained more insight in the determination of the pore size distribution of nano-structured carbons, and to correlate this measurement with hydrogen adsorption capacities. Five nano-structured carbons were studied and compared to three activated carbons. For all samples, the adsorption isotherms of nitrogen at 77 K, and CO{sub 2} at 273 were measured. From these isotherms, the following textural parameters were determined: BET surface area, total porous volume, the volume of micro-pores and super-micro-pores were obtained from Dubinin-Radushkevich equation on CO{sub 2} and nitrogen isotherm respectively. The pore size distribution was obtained with a DFT analysis on the N{sub 2} adsorption isotherm. DFT analysis showed that nano-structured carbon materials have a bimodal distribution with ultra-micropores and a large volume of small meso-pores. The hydrogen capacity of these carbon materials was then measured at 77 K with a manometric device. Although hydrogen is in supercritical state in the pores

  9. Storage of hydrogen on single-walled carbon nanotubes and other carbon structures

    Energy Technology Data Exchange (ETDEWEB)

    Poirier, E.; Chahine, R.; Benard, P.; Cossement, D.; Lafi, L.; Melancon, E.; Bose, T.K. [Institut de recherche sur l' hydrogene, Universite du Quebec a Trois-Rivieres, C.P. 500, G9A 5H7, Trois-Rivieres, Quebec (Canada); Desilets, S. [R and D pour la defense Canada - Valcartier, 2459, boulevard Pie-XI Nord, G3J 1X5, Val-Belair, Quebec (Canada)

    2004-04-01

    The sorption of hydrogen on carbon structures and nanostructures offers a way to reduce the storage pressure of hydrogen with respect to compression storage while achieving interesting gravimetric storage densities. The most readily available carbon structures, activated carbons, can achieve reproducible, high gravimetric storage densities under cryogenic operating conditions: 5-6% at 35 bar and 77 K, in excess of the normal density that would be present in the pore volume under compression at the same temperature and pressure. We discuss and compare the adsorption of hydrogen on high specific surface activated carbons, nanofibres and nanotubes from experimental and theoretical considerations. In particular, we present gravimetric and volumetric hydrogen sorption measurements on single-walled carbon nanotubes (SWNTs) at (1 bar, 77 K) and (1 bar, 295 K) within the context of our ongoing work on the storage of hydrogen on activated carbon and carbon nanostructures. BET surface area and XRD characterization results on SWNTs are also presented. The experiments were performed on as received, chemically treated and metal-incorporated SWNT samples. Hydrogen sorption capacities measured on treated samples ranged from {proportional_to}0 to about 1 wt. % at 1 bar and 295 K and reached about 4 wt. % at 1 bar and 77 K. Our results show that under certain conditions, SWNTs have better hydrogen uptake performance than large surface area activated carbons. (orig.)

  10. Hydrogen storage on high-surface-area carbon monoliths for Adsorb hydrogen Gas Vehicle

    Science.gov (United States)

    Soo, Yuchoong; Pfeifer, Peter

    2014-03-01

    Carbon briquetting can increase hydrogen volumetric storage capacity by reducing the useless void volume resulting in a better packing density. It is a robust and efficient space-filling form for an adsorbed hydrogen gas vehicle storage tank. To optimize hydrogen storage capacity, we studied three fabrication process parameters: carbon-to-binder ratio, compaction temperature, and pyrolysis atmosphere. We found that carbon-to-binder ratio and pyrolysis atmosphere have influences on gravimetric excess adsorption. Compaction temperature has large influences on gravimetric and volumetric storage capacity. We have been able to optimize these parameters for high hydrogen storage. All monolith uptakes (up to 260 bar) were measured by a custom-built, volumetric, reservoir-type instrument.

  11. Hydrogenation of Furfural to Furfuryl Alcohol over Co-B Amorphous Catalysts Prepared by Chemical Reduction in Variable Media

    Institute of Scientific and Technical Information of China (English)

    LI, Hui; CHAI, Wei-Mei; LUO, Hong-Shan; LI, He-Xing

    2006-01-01

    Five Co-B amorphous alloy catalysts were prepared by chemical reduction in different media, including pure water and pure ethanol as well as the mixture of ethanol and water with variable ethanol content. Their catalytic properties were evaluated using liquid phase furfural hydrogenation to furfuryl alcohol as the probe reaction. It was found that the reaction media had no significant influence on either the amorphous structure of the Co-B catalyst or the electronic interaction between metallic Co and alloying B. This could successfully account for the fact that all the as-prepared Co-B catalysts exhibited almost the same selectivity to furfuryl alcohol and the same activity per surface area ( RSH ), which could be considered as the intrinsic activity, since the nature of active sites remained unchanged. However, the activity per gram of Co ( RmH ) of the as-prepared Co-B catalysts increased rapidly when the ethanol content in the water-ethanol mixture used as the reaction medium for catalyst preparation increased. This could be attributed to the rapid increase in the surface area possibly owing to the presence of more oxidized boron species which could serve as a support for dispersing the Co-B amorphous alloy particles.

  12. The adsorption of hydrogen on nano-structured carbons

    Energy Technology Data Exchange (ETDEWEB)

    Antoine Didion; Roger Gadiov; Cathie Vix Guterl [Institut de Chimie des Surfaces et Interfaces, CNRS UPR 9069, 15, rue Jean Starcky, BP 2488, 68093 Mulhouse cedex (France); Thierry Piquero; Patrick David [CEA Le Ripault, BP 16, 37260 Monts (France)

    2005-07-01

    A major key point for the development of hydrogen as an energy source is the design of a safe and compact storage device. The adsorption of molecular hydrogen on various carbon structures has been widely studied during the last two decades, and the storage capacities which are obtained are of the order of a few weight percents. Nano-structured carbons can be obtained by templating from ordered meso-porous silicas, different carbon precursors have been used such as sucrose solutions, pitch, or propylene. Compared to conventional activated carbons, these carbon materials have specific features such as an ordered network of meso-pores and a microporous volume which is obtained without activation. It has been shown that the storage capacity of these carbons materials is comparable to the one of activated carbons, and further investigation is needed to understand the influence of the pore shape and connectivity on the adsorption. The objective of this study was to obtained more insight in the determination of the pore size distribution of nano-structured carbons, and to correlate this measurement with hydrogen adsorption capacities. Five nano-structured carbons were studied and compared to three activated carbons. For all samples, the adsorption isotherms of nitrogen at 77 K, and CO{sub 2} at 273 K were measured. From these isotherms, the following textural parameters were determined: BET surface area, total porous volume, the volume of micropores and super-micropores were obtained from Dubinin-Radushkevich equation on CO{sub 2} and nitrogen isotherm respectively. The pore size distribution was obtained with a DFT analysis on the N{sub 2} adsorption isotherm. DFT analysis showed that nano-structured carbon materials have a bimodal distribution with ultra-micro-pores and a large volume of small meso-pores. The hydrogen capacity of these carbon materials was then measured at 77 K with a manometric device. Although hydrogen is in supercritical state in the pores, a first

  13. The adsorption of hydrogen on nano-structured carbons

    International Nuclear Information System (INIS)

    A major key point for the development of hydrogen as an energy source is the design of a safe and compact storage device. The adsorption of molecular hydrogen on various carbon structures has been widely studied during the last two decades, and the storage capacities which are obtained are of the order of a few weight percents. Nano-structured carbons can be obtained by templating from ordered meso-porous silicas, different carbon precursors have been used such as sucrose solutions, pitch, or propylene. Compared to conventional activated carbons, these carbon materials have specific features such as an ordered network of meso-pores and a microporous volume which is obtained without activation. It has been shown that the storage capacity of these carbons materials is comparable to the one of activated carbons, and further investigation is needed to understand the influence of the pore shape and connectivity on the adsorption. The objective of this study was to obtained more insight in the determination of the pore size distribution of nano-structured carbons, and to correlate this measurement with hydrogen adsorption capacities. Five nano-structured carbons were studied and compared to three activated carbons. For all samples, the adsorption isotherms of nitrogen at 77 K, and CO2 at 273 K were measured. From these isotherms, the following textural parameters were determined: BET surface area, total porous volume, the volume of micropores and super-micropores were obtained from Dubinin-Radushkevich equation on CO2 and nitrogen isotherm respectively. The pore size distribution was obtained with a DFT analysis on the N2 adsorption isotherm. DFT analysis showed that nano-structured carbon materials have a bimodal distribution with ultra-micro-pores and a large volume of small meso-pores. The hydrogen capacity of these carbon materials was then measured at 77 K with a manometric device. Although hydrogen is in supercritical state in the pores, a first computation of the

  14. Structure evolution from nanocolumns to nanoporous of nitrogen doped amorphous carbon films deposited by magnetron sputtering

    International Nuclear Information System (INIS)

    Different nitrogen doped amorphous carbon (CNx) films were obtained by magnetron sputtering of carbon target in argon and nitrogen atmosphere at the increasing negative bias voltages from 0 to 150 V. The films structures have experienced great change, from the novel column to nanoporous structure at the bias voltage of 0 V to the porous structure at 150 V. The proposed growth process was that the CNx nuclei grew at 0 V acted as the 'seeds' for the growth of the nanocolumns, and ion etching effects at 150 V induced the formation of nanoporous structures. Furthermore, a comparison study showed that the field emission properties of the CNx films were related with the introduction of the nitrogen atoms, the size and concentration of sp2 C clusters and the surface roughness. The films with rougher surface have lower threshold field.

  15. Amorphous Carbon Coatings for Mitigation of Electron Cloud in the CERN SPS

    CERN Document Server

    Yin Vallgren, Christina; Bauche, Jeremie; Calatroni, Sergio; Chiggiato, Paolo; Cornelis, Karel; Costa Pinto, Pedro; Metral, Elias; Rumolo, Giovanni; Shaposhnikova, Elena; Taborelli, Mauro; Vandoni, Giovanna

    2010-01-01

    Amorphous carbon thin films have been applied to the liners in the electron cloud monitors and to vacuum chambers of three dipole magnets in the SPS. The electron cloud is completely suppressed for LHC type beams in the liners even after 3 months of air venting and no performance deterioration is observed after more than one year of SPS operation. In stainless steel (StSt) liners upon variation of the magnetic field in the monitors the electron cloud current maintains its intensity down to weak fields of some 40 Gauss. This is in agreement with previous findings and also with dark traces observed on the RF shields made of StSt, which are located between dipoles and quadrupoles. The dynamic pressure rise has been used to monitor the behavior of the dipole magnets. It is about the same for coated and uncoated magnets, apart from a weak improvement in the carbon coated ones under conditions of intense electron cloud

  16. Stabilization of amorphous calcium carbonate by phosphate rich organic matrix proteins and by single phosphoamino acids.

    Science.gov (United States)

    Bentov, Shmuel; Weil, Simy; Glazer, Lilah; Sagi, Amir; Berman, Amir

    2010-08-01

    Stable amorphous calcium carbonate (ACC) is a unique material produced naturally exclusively as a biomineral. It was demonstrated that proteins extracted from biogenic stable ACC induce and stabilize synthetic ACC in vitro. Polyphosphate molecules were similarly shown to induce amorphous calcium carbonate formation in vitro. Accordingly, we tested the hypothesis that biogenic ACC induction and stabilization is mediated by the phosphorylated residues of phosphoproteins. We show that extracellular organic matrix extracted from gastroliths of the red claw crayfish Cherax quadricarinatus induce stable ACC formation in vitro. The proteinaceous fraction of this organic matrix is highly phosphorylated and is incorporated into the ACC mineral phase during precipitation. We have identified the major phosphoproteins of the organic matrix and showed that they have high calcium binding capacity. Based on the above, in vitro precipitation experiments with single phosphoamino acids were performed, indicating that phosphoserine or phosphothreonine alone can induce the formation of highly stable ACC. The results indicate that phosphoproteins may play a major role in the control of ACC formation and stabilization and that their phosphoamino acid moieties are key components in this process. PMID:20416381

  17. Controlled fluoridation of amorphous carbon films deposited at reactive plasma conditions

    Directory of Open Access Journals (Sweden)

    Yoffe Alexander

    2015-09-01

    Full Text Available A study of the correlations between plasma parameters, gas ratios, and deposited amorphous carbon film properties is presented. The injection of a C4F8/Ar/N2 mixture of gases was successfully used in an inductively coupled plasma system for the preparation of amorphous carbon films with different fluoride doping at room-temperature, using silicon as a substrate. This coating was formed at low-pressure and low-energy using an inductively coupled plasma process. A strong dependence between the ratios of gases during deposition and the composition of the substrate compounds was shown. The values of ratios between Ar (or Ar+N2 and C4F8 - 1:1 and between N2 and Ar - 1:2 in the N2/Ar/C4F8 mixture were found as the best for low fluoridated coatings. In addition, an example of improving the etch-passivation in the Bosch procedure was described. Scanning electron microscopy with energy dispersive spectroscopy options, X-ray diffraction, and X-ray reflectivity were used for quantitative analysis of the deposited films.

  18. Synthesis and characterization of thin films of nitrided amorphous carbon deposited by laser ablation

    International Nuclear Information System (INIS)

    The objective of this work is the synthesis and characterization of thin films of amorphous carbon (a-C) and thin films of nitrided amorphous carbon (a-C-N) using the laser ablation technique for their deposit. For this purpose, the physical properties of the obtained films were studied as function of diverse parameters of deposit such as: nitrogen pressure, power density, substrate temperature and substrate-target distance. For the characterization of the properties of the deposited thin films the following techniques were used: a) Raman spectroscopy which has demonstrated being a sensitive technique to the sp2 and sp3 bonds content, b) Energy Dispersive Spectroscopy which allows to know semi-quantitatively way the presence of the elements which make up the deposited films, c) Spectrophotometry, for obtaining the absorption spectra and subsequently the optical energy gap of the deposited material, d) Ellipsometry for determining the refraction index, e) Scanning Electron Microscopy for studying the surface morphology of thin films and, f) Profilemetry, which allows the determination the thickness of the deposited thin films. (Author)

  19. Time-Resolved Spectroscopic Observation of Deposition Processes of Ultrananocrystalline Diamond/Amorphous Carbon Composite Films by Using a Coaxial Arc Plasma Gun

    Science.gov (United States)

    Hanada, Kenji; Yoshitake, Tsuyoshi; Nishiyama, Takashi; Nagayama, Kunihito

    2010-08-01

    The deposition of ultrananocrystalline diamond (UNCD)/amorphous carbon composite films using a coaxial arc plasma gun in vacuum and, for comparison, in a 53.3 Pa hydrogen atmosphere was spectroscopically observed using a high-speed camera equipped with narrow-band-pass filters. UNCD crystallites with diameters of approximately 1.6 nm were formed even in vacuum. These extremely small crystallites imply that the formation is predominantly due to nucleation without the subsequent growth. Even in vacuum, emissions from C+ ions, C atoms, and C2 dimers lasted for approximately 100 µs, although the emission lifetimes of these species are generally 10 ns. We consider that the nucleation is due to the supersaturated environment containing excited carbon species with large number densities.

  20. Biological Characteristics of the MG-63 Human Osteosarcoma Cells on Composite Tantalum Carbide/Amorphous Carbon Films

    OpenAIRE

    Yin-Yu Chang; Heng-Li Huang; Ya-Chi Chen; Jui-Ting Hsu; Tzong-Ming Shieh; Ming-Tzu Tsai

    2014-01-01

    Tantalum (Ta) is a promising metal for biomedical implants or implant coating for orthopedic and dental applications because of its excellent corrosion resistance, fracture toughness, and biocompatibility. This study synthesizes biocompatible tantalum carbide (TaC) and TaC/amorphous carbon (a-C) coatings with different carbon contents by using a twin-gun magnetron sputtering system to improve their biological properties and explore potential surgical implant or device applications. The carbon...

  1. Transformation of Mg-bearing amorphous calcium carbonate to Mg-calcite - In situ monitoring

    Science.gov (United States)

    Purgstaller, Bettina; Mavromatis, Vasileios; Immenhauser, Adrian; Dietzel, Martin

    2016-02-01

    The formation of Mg-bearing calcite via an amorphous precursor is a poorly understood process that is of relevance for biogenic and abiogenic carbonate precipitation. In order to gain an improved insight on the controls of Mg incorporation in calcite formed via an Mg-rich amorphous calcium carbonate (Mg-ACC) precursor, the precipitation of Mg-ACC and its transformation to Mg-calcite was monitored by in situ Raman spectroscopy. The experiments were performed at 25.0 ± 0.03 °C and pH 8.3 ± 0.1 and revealed two distinct pathways of Mg-calcite formation: (i) At initial aqueous Mg/Ca molar ratios ⩽ 1:6, Mg-calcite formation occurs via direct precipitation from solution. (ii) Conversely, at higher initial Mg/Ca molar ratios, Mg-calcite forms via an intermediate Mg-rich ACC phase. In the latter case, the final product is a calcite with up to 20 mol% Mg. This Mg content is significant higher than that of the Mg-rich ACC precursor phase. Thus, a strong net uptake of Mg ions from the solution into the crystalline precipitate throughout and also subsequent to ACC transformation is postulated. Moreover, the temporal evolution of the geochemical composition of the reactive solution and the Mg-ACC has no significant effect on the obtained "solubility product" of Mg-ACC. The enrichment of Mg in calcite throughout and subsequent to Mg-ACC transformation is likely affected by the high aqueous Mg/Ca ratio and carbonate alkalinity concentrations in the reactive solution. The experimental results have a bearing on the formation mechanism of Mg-rich calcites in marine early diagenetic environments, where high carbonate alkalinity concentrations are the rule rather than the exception, and on the insufficiently investigated inorganic component of biomineralisation pathways in many calcite secreting organisms.

  2. Characterization of amorphous carbon films as total-reflection mirrors for XUV free-electron lasers

    Science.gov (United States)

    Jacobi, Sandra; Steeg, Barbara; Wiesmann, Jorg; Stormer, Michael; Feldhaus, Josef; Bormann, R.'diger; Michaelsen, Carsten

    2002-12-01

    As part of the TESLA (TeV-Energy Superconducting Linear Accelerator) project a free electron laser (FEL) in the XUV (Extreme Ultra-Violet, (6-200 eV)) and X-ray (0.5-15 keV) range is being developed at DESY (Deutsches Elektronen Synchrotron, Hamburg). At the TESLA Test Facility (TTF) a prototype FEL has recently demonstrated maximum light amplification in the range of 80 nm to 120 nm. It is expected that the FEL will provide intense, sub-picosecond radiation pulses with photon energies up to 200 eV in the next development stage. In a joint project between DESY and GKSS, thin film optical elements with very high radiation stability, as required for FEL applications, are currently being developed. Sputter-deposited amorphous carbon coatings have been prepared for use as total reflection X-ray mirrors. The optical characterization of the mirrors has been carried out using the soft X-ray reflectometer at HASYLAB (Hamburger Synchrotronstrahlungslabor) beamline G1. The reflectivity of the carbon films at 2 deg incidence angle is close to the theoretical reflectivity of 95.6 %, demonstrating the high quality of the coatings. For comparison, layers produced by different methods (e.g. Chemical vapor deposition, Pulsed laser deposition) have been characterized as well. Annealing experiments have been performed to evaluate the thermal stability of the amorphous carbon films. Further investigations concerning the radiation stability of the X-ray mirrors have also been conducted. The mirrors were irradiated in the FELIS (Free Electron Laser-Interaction with Solids) experiment at the TTF-FEL. Microscopic investigations demonstrate that the carbon mirrors are fairly stable.

  3. 3D micro- and nano-machining of hydrogenated amorphous silicon films on SiO2/Si and glass substrates

    Science.gov (United States)

    Soleimani-Amiri, S.; Zanganeh, S.; Ramzani, R.; Talei, R.; Mohajerzadeh, S.; Azimi, S.; Sanaee, Z.

    2015-07-01

    We report on the hydrogen-assisted deep reactive ion etching of hydrogenated amorphous silicon (a-Si:H) films deposited using radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD). High aspect-ratio vertical and 3D amorphous silicon features, with the desired control over the shaping of the sidewalls, in micro and nano scales, were fabricated in ordered arrays. The suitable adhesion of amorphous Si film to the underlayer allows one to apply deep micro- and nano-machining to these layers. By means of a second deposition of amorphous silicon on highly curved 3D structures and subsequent etching, the fabrication of amorphous silicon rings is feasible. In addition to photolithography, nanosphere colloidal lithography and electron beam lithography were exploited to realize ultra-small features of amorphous silicon. We have also investigated the optical properties of fabricated hexagonally patterned a-Si nanowire arrays on glass substrates and demonstrated their high potential as active layers for solar cells. This etching process presents an inexpensive method for the formation of highly featured arrays of vertical and 3D amorphous silicon rods on both glass and silicon substrates, suitable for large-area applications.

  4. Determination of carbon in amorphous carbon and uranium monocarbide by oxidation with lead(IV) oxide, copper(II) oxide or barium sulfate in an inert atmosphere

    International Nuclear Information System (INIS)

    Oxidation behavior was studied on amorphous carbon and carbon in uranium monocarbide when lead(IV) oxide, copper(II) oxide and barium sulfate were used as the oxidizing fluxes in helium. The amorphous carbon and the carbon in the carbide were completely extracted with lead oxide in 5 min at 10000C and in 8 min at 700 and 5000C, respectively. Carbon in two samples was quantitatively extracted at 10000C with copper oxide in 8 and 5 min, and with barium sulfate in 7 and 5 min, respectively. The rate of extraction of carbon with copper oxide decreased with decreasing temperature. It was found that the mixing ratio of the oxidizing flux to the amorphous carbon or carbide gave effect on the recovery of carbon. The conventional capillary-trap method which is used for the determination of carbon has a disadvantage that, when carbon dioxide is caught in a cold trap (liquid nitrogen), oxygen is also trapped. This disadvantage was eliminated when a stream of helium was used in place of oxygen. Carbon in the sample can be determined with lead oxide, copper oxide or barium sulfate by extracting carbon dioxide at 10000C for 10 min. (auth.)

  5. High Growth Rate Deposition of Hydrogenated Amorphous Silicon-Germanium Films and Devices Using ECR-PECVD

    Energy Technology Data Exchange (ETDEWEB)

    Yong Liu

    2002-05-31

    Hydrogenated amorphous silicon germanium films (a-SiGe:H) and devices have been extensively studied because of the tunable band gap for matching the solar spectrum and mature the fabrication techniques. a-SiGe:H thin film solar cells have great potential for commercial manufacture because of very low cost and adaptability to large-scale manufacturing. Although it has been demonstrated that a-SiGe:H thin films and devices with good quality can be produced successfully, some issues regarding growth chemistry have remained yet unexplored, such as the hydrogen and inert-gas dilution, bombardment effect, and chemical annealing, to name a few. The alloying of the SiGe introduces above an order-of-magnitude higher defect density, which degrades the performance of the a-SiGe:H thin film solar cells. This degradation becomes worse when high growth-rate deposition is required. Preferential attachment of hydrogen to silicon, clustering of Ge and Si, and columnar structure and buried dihydride radicals make the film intolerably bad. The work presented here uses the Electron-Cyclotron-Resonance Plasma-Enhanced Chemical Vapor Deposition (ECR-PECVD) technique to fabricate a-SiGe:H films and devices with high growth rates. Helium gas, together with a small amount of H{sub 2}, was used as the plasma species. Thickness, optical band gap, conductivity, Urbach energy, mobility-lifetime product, I-V curve, and quantum efficiency were characterized during the process of pursuing good materials. The microstructure of the a-(Si,Ge):H material was probed by Fourier-Transform Infrared spectroscopy. They found that the advantages of using helium as the main plasma species are: (1) high growth rate--the energetic helium ions break the reactive gas more efficiently than hydrogen ions; (2) homogeneous growth--heavy helium ions impinging on the surface promote the surface mobility of the reactive radicals, so that heteroepitaxy growth as clustering of Ge and Si, columnar structure are reduced

  6. Formation, Structure and Properties of Amorphous Carbon Char from Polymer Materials in Extreme Atmospheric Reentry Environments

    Science.gov (United States)

    Lawson, John W.

    2010-01-01

    Amorphous carbonaceous char produced from the pyrolysis of polymer solids has many desirable properties for ablative heat shields for space vehicles. Molecular dynamics simulations are presented to study the transformation of the local atomic structure from virgin polymer to a dense, disordered char [1]. Release of polymer hydrogen is found to be critical to allow the system to collapse into a highly coordinated char structure. Mechanisms of the char formation process and the morphology of the resulting structures are elucidated. Thermal conductivity and mechanical response of the resulting char are evaluated [2]. During reenty, the optical response and oxidative reactivity of char are also important properties. Results of ab initio computations of char optical functions [3] and char reactivity [4] are also presented.

  7. Interaction of hydrogen in carbon matrix with impurities of nickel

    International Nuclear Information System (INIS)

    This work aims to define general criteria to allow theoretical and experimental design of new materials with high hydrogen content, with a view to their potential application as moderators in reactors at high temperatures and hydrogen storage materials. To this end we study the effects of Ni impurities on the properties of pure carbon (slabs as well as nanoparticles and gels) in order to analyze the thermodynamical characteristics, and improve the behavior of alloys for Ni-metal hydride rechargeable batteries. These elements are chosen because they have a wide range of solubility of hydrogen, which from the technological point of view makes them important candidates for the search for new materials. Our results show that this kind of carbon material could be used as support for hydrogen storage improving the screening charge density and the density of available states, as analyzed by the authors in previous works (author)

  8. Hydrogen storage properties of carbon nanomaterials and carbon containing metal hydrides

    Energy Technology Data Exchange (ETDEWEB)

    Maehlen, Jan Petter

    2003-07-01

    The topic of this thesis is structural investigations of carbon containing materials in respect to their hydrogen storage properties. This work was initially triggered by reports of extremely high hydrogen storage capacities of specific carbon nanostructures. It was decided to try to verify and understand the mechanisms in play in case of the existence of such high hydrogen densities in carbon. Two different routes towards the goal were employed; by studying selected hydrides with carbon as one of its constituents (mainly employing powder diffraction techniques in combination with hydrogen absorption and desorption measurements) and by carefully conducting hydrogen sorption experiments on what was believed to be the most ''promising'' carbon nanomaterial sample. In the latter case, a lot of effort was attributed to characterisations of different carbon nanomaterial containing samples with the aid of electron microscopy. Three different carbon-containing metal hydride systems, Y2C-H, YCoC-H and Y5SiC0.2-H, were examined. A relation between hydrogen occupation and the local arrangement of metal and carbon atoms surrounding the hydrogen sites was established. Several characteristic features of the compounds were noted in addition to solving the structure of the former unknown deuterideY5Si3C0.2D2.0 by the use of direct methods. Several carbon-nanomaterial containing samples were studied by means of transmission electron microscopy and powder diffraction, thus gaining knowledge concerning the structural aspects of nanomaterials. Based on these investigations, a specific sample containing a large amount of open-ended single-wall carbon nanotubes was chosen for subsequent hydrogen storage experiments. The latter experiments revealed moderate hydrogen storage capacities of the nanotubes not exceeding the values obtained for more conventional forms of carbon. These two different routes in investigating the hydrogen storage properties of carbon and

  9. Hydrosilylation of crystalline silicon (111) and hydrogenated amorphous silicon surfaces: A comparative x-ray photoelectron spectroscopy study

    International Nuclear Information System (INIS)

    Alkene molecules were covalently bonded to hydrogen-terminated crystalline silicon (111) and hydrogenated amorphous silicon (a-Si:H) surfaces by thermally induced hydrosilylation. The resulting chemical surface structure was analyzed by x-ray photoelectron spectroscopy and compared to that of the corresponding silicon surfaces covered by a native oxide and terminated with hydrogen. Our results demonstrate successful hydrosilylation on both substrate materials. However, the presence of oxygen on the surface turns out to hinder the hydrosilylation reaction, as shown by the reduced concentration of hydrocarbons on the surface after prolonged exposure of the Si substrates prior to hydrosilylation. By monitoring both the O 1s and the Si 2p peaks, the oxidation kinetics of a-Si:H was found to be diffusion limited. Since stable hydrogen termination as a prerequisite of hydrosilylation can be achieved on a-Si:H surfaces with much less technological effort than on crystalline silicon surfaces, a-Si:H is a promising substrate for biofunctionalization procedures requiring less stringent process conditions

  10. Theoretical analysis of hydrogen spillover mechanism on carbon nanotubes

    Directory of Open Access Journals (Sweden)

    Rosalba eJuarez Mosqueda

    2015-02-01

    Full Text Available The spillover mechanism of molecular hydrogen on carbon nanotubes in the presence of catalytically active platinum clusters was critically and systematically investigated by using density-functional theory. Our simulation model includes a Pt4 cluster for the catalyst nanoparticle and curved and planar circumcoronene for two exemplary single-walled carbon nanotubes (CNT, the (10,10 CNT and one of large diameter, respectively. Our results show that the H2 molecule dissociates spontaneously on the Pt4 cluster. However, the dissociated H atoms have to overcome a barrier of more than 2 eV to migrate from the catalyst to the CNT, even if the Pt4 cluster is at full saturation with six adsorbed and dissociated hydrogen molecules. Previous investigations have shown that the mobility of hydrogen atoms on the CNT surface is hindered by a barrier. We find that instead the Pt4 catalyst may move along the outer surface of the CNT with activation energy of only 0.16 eV, and that this effect offers the possibility of full hydrogenation of the CNT. Thus, although we have not found a low-energy pathway to spillover onto the CNT, we suggest, based on our calculations and calculated data reported in the literature, that in the hydrogen-spillover process the observed saturation of the CNT at hydrogen background pressure occurs through mobile Pt nanoclusters, which move on the substrate more easily than the substrate-chemisorbed hydrogens, and deposit or reattach hydrogens in the process. Initial hydrogenation of the carbon substrate, however, is thermodynamically unfavoured, suggesting that defects should play a significant role.

  11. Increased calcium absorption from synthetic stable amorphous calcium carbonate: Double-blind randomized crossover clinical trial in post-menopausal women

    Science.gov (United States)

    Calcium supplementation is a widely recognized strategy for achieving adequate calcium intake. We designed this blinded, randomized, crossover interventional trial to compare the bioavailability of a new stable synthetic amorphous calcium carbonate (ACC) with that of crystalline calcium carbonate (C...

  12. Study on effects of carbon impurities and oxygen vacancies in amorphous alumina phosphor prepared via a solution method

    International Nuclear Information System (INIS)

    The amorphous alumina phosphors without containing expensive or toxic elements were prepared via a solution method. The obtained sample indicates bluish-white emission centered at 390–430 nm by UV excitation. According to the measurement results of Electron Spin Resonance (ESR), Fourier Transform Infrared Spectroscopy (FT-IR) and organic microanalysis, it is found that the carbon impurities exist in the sample and they are essential for luminescence. On the other hand, 27Al NMR measurements indicate the presence of Al of 5-coordination. Moreover, there is good correspondence among the excitation spectra of the emission samples, the experimental optical properties of amorphous alumina, and the calculated oxygen vacancies levels in amorphous alumina model. Therefore, the new luminescence mechanism can be proposed as follows; the electrons in valence band are excited to oxygen vacancies bands by UV light and return to ground state through the carbon impurities band, being accompanied by the bluish-white emission. - Highlights: • The amorphous alumina prepared via solution method shows bluish-white emission. • According to the ESR results, carbon impurities are necessary for luminescence. • FT-IR, NMR and UV–vis measurements of the samples were conducted. • Our results indicated that oxygen vacancies play an important role. • We proposed the new luminescence mechanism for amorphous alumina phosphor

  13. Study on effects of carbon impurities and oxygen vacancies in amorphous alumina phosphor prepared via a solution method

    Energy Technology Data Exchange (ETDEWEB)

    Wakui, Yoshinori; Takahashi, Kanako [Department of Material and Environmental Chemistry, Graduate School of Engineering, Utsunomiya University, 7-1-2 Yoto, Utsunomiya-shi, Tochigi 321-8585 (Japan); Shan, Yue Jin, E-mail: shan@cc.utsunomiya-u.ac.jp [Department of Material and Environmental Chemistry, Graduate School of Engineering, Utsunomiya University, 7-1-2 Yoto, Utsunomiya-shi, Tochigi 321-8585 (Japan); Tezuka, Keitaro; Imoto, Hideo [Department of Material and Environmental Chemistry, Graduate School of Engineering, Utsunomiya University, 7-1-2 Yoto, Utsunomiya-shi, Tochigi 321-8585 (Japan); Hosokawa, Shogo; Shinozaki, Norifumi [Tatsumori Ltd., 50 Minami-Kawada, Kami-Yukiai, Tamura-cho, Koriyama-shi, Fukushima 963-0724 (Japan); Ando, Mariko; Maekawa, Hideki [Graduate School of Engineering, Tohoku University, 6-6-04 Aramaki Aoba, Sendai-shi, Miyagi 980-8579 (Japan)

    2015-01-15

    The amorphous alumina phosphors without containing expensive or toxic elements were prepared via a solution method. The obtained sample indicates bluish-white emission centered at 390–430 nm by UV excitation. According to the measurement results of Electron Spin Resonance (ESR), Fourier Transform Infrared Spectroscopy (FT-IR) and organic microanalysis, it is found that the carbon impurities exist in the sample and they are essential for luminescence. On the other hand, {sup 27}Al NMR measurements indicate the presence of Al of 5-coordination. Moreover, there is good correspondence among the excitation spectra of the emission samples, the experimental optical properties of amorphous alumina, and the calculated oxygen vacancies levels in amorphous alumina model. Therefore, the new luminescence mechanism can be proposed as follows; the electrons in valence band are excited to oxygen vacancies bands by UV light and return to ground state through the carbon impurities band, being accompanied by the bluish-white emission. - Highlights: • The amorphous alumina prepared via solution method shows bluish-white emission. • According to the ESR results, carbon impurities are necessary for luminescence. • FT-IR, NMR and UV–vis measurements of the samples were conducted. • Our results indicated that oxygen vacancies play an important role. • We proposed the new luminescence mechanism for amorphous alumina phosphor.

  14. 非晶碳氮纳米尖端的微结构和发光机理%Microstructure and Photoluminescence Mechanism of Amorphous Carbon Nitride Nanotips

    Institute of Scientific and Technical Information of China (English)

    王必本; 谢焕玲; 陈玉安; 董国波

    2012-01-01

    利用等离子体增强热丝化学气相沉积系统,用CH4、H2和N2为反应气体,在Si衬底上制备了碳氮纳米尖端.用扫描电子显微镜和显微Raman光谱仪对其进行了表征.在室温下测试了它的发光性能,发光谱由中心约为406 nm和506 nm的两条发光带组成.根据Raman散射谱,对其微结构进行了分析.结合非晶碳氮薄膜的结构和发光机理,分析了它的发光性能.%Carbon nitride nanotips were prepared on silicon substrate in plasma-enhanced hot fila ment chemical vapor deposition system, in which methane, hydrogen and nitrogen were used as the reaction gases. The carbon nitride nanotips were characterized by scanning electron microscopy and micro-Raman spectroscopy. The photoluminescence of the carbon nitride nanotips was measured at room temperature and the photoluminescence spectrum shows two emission bands at 406 and 506 nm. Combined with the Raman spectrum, the microstructure of the carbon nitride was analyzed. Ac cording to the structure and photoluminescence mechanism of amorphous carbon nitride films, the photoluminescence of carbon nitride nanotips was studied.

  15. Carbonate leaching of uranium and hydrogen peroxide stabilizer therefor

    International Nuclear Information System (INIS)

    In the carbonate leaching process for the solution mining of subterranean uranium containing formations in which an injection well is drilled and completed within the uranium formation; alkaline carbonate uranium leaching solution and sufficient hydrogen peroxide are injected through the injection wells into the formation whereby uranium values are produced from production wells, characterized by providing in the leaching solution a mixture of 1-hydroxyethylidene-1,1-diphosphonic acid and an alkali metal pyrophosphate in a weight ratio of from 1 to 10 to 10 to 1, the amount of said mixture being sufficient to inhibit decomposition of the hydrogen peroxide in said leaching solution

  16. Scale-up activation of carbon fibres for hydrogen storage

    OpenAIRE

    Kunowsky, Mirko; Marco Lozar, Juan Pablo; Cazorla Amorós, Diego; Linares Solano, Ángel

    2009-01-01

    In a previous study, we investigated, at a laboratory scale, the chemical activation of two different carbon fibres (CF), their porosity characterization, and their optimization for hydrogen storage [1]. In the present work, this study is extended to: (i) a larger range of KOH activated carbon fibres, (ii) a larger range of hydrogen adsorption measurements at different temperatures and pressures (i.e. at room temperature, up to 20 MPa, and at 77 K, up to 4 MPa), and (iii) a scaling-up activat...

  17. Study of hydrogen diffusion in amorphous and crystalline hydrides of the alloy Zr2Ni by gamma-gamma perturbed angular correlations of 181Ta

    International Nuclear Information System (INIS)

    The diffusion of hydrogen in crystalline hydrides Zr2NiHx (x = 2.1, 3 and 4.8) and amorphous hydrides of Zr2Ni with x = 2.5 and 4.5, has been studied by Perturbed Angular Correlation spectroscopy using 181Ta as a probe in substitution for zirconium. The quadrupole relaxation of the 181Ta spins produced by hydrogen motions was observed between 170 K and 470 K. The activation energy and pre-exponential frequency factors were deduced from the temperature dependence of the quadrupole relaxation constant in both crystalline and amorphous hydrides. In crystalline hydrides our results are consistent with those previously reported from 1H NMR experiments. Combining the PAC data with the results of neutron diffraction experiments performed on crystalline deuterides, we are able to propose a mechanism for hydrogen jumps in these hydrides using a single geometrical model. In the amorphous hydrides our PAC results are consistent with the existence of a short-range ordering or microsegregation induced by the hydrogen loading process in the amorphous lattice. However, our data do not indicate the existence of broad distributions of the activation energy for hydrogen jumps

  18. Carbonate-coordinated metal complexes precede the formation of liquid amorphous mineral emulsions of divalent metal carbonates

    Science.gov (United States)

    Wolf, Stephan E.; Müller, Lars; Barrea, Raul; Kampf, Christopher J.; Leiterer, Jork; Panne, Ulrich; Hoffmann, Thorsten; Emmerling, Franziska; Tremel, Wolfgang

    2011-03-01

    During the mineralisation of metal carbonates MCO3 (M = Ca, Sr, Ba, Mn, Cd, Pb) liquid-like amorphous intermediates emerge. These intermediates that form via a liquid/liquid phase separation behave like a classical emulsion and are stabilized electrostatically. The occurrence of these intermediates is attributed to the formation of highly hydrated networks whose stability is mainly based on weak interactions and the variability of the metal-containing pre-critical clusters. Their existence and compositional freedom are evidenced by electrospray ionization mass spectrometry (ESI-MS). Liquid intermediates in non-classical crystallisation pathways seem to be more common than assumed.During the mineralisation of metal carbonates MCO3 (M = Ca, Sr, Ba, Mn, Cd, Pb) liquid-like amorphous intermediates emerge. These intermediates that form via a liquid/liquid phase separation behave like a classical emulsion and are stabilized electrostatically. The occurrence of these intermediates is attributed to the formation of highly hydrated networks whose stability is mainly based on weak interactions and the variability of the metal-containing pre-critical clusters. Their existence and compositional freedom are evidenced by electrospray ionization mass spectrometry (ESI-MS). Liquid intermediates in non-classical crystallisation pathways seem to be more common than assumed. Electronic supplementary information (ESI) available: (S1 and S5) TEM at higher magnifications and of crystallizations conducted at pH = 6.0, 9.0 and 11.3; (S2) sketch of a spreading liquid particle on a TEM grid; (S3) wide-angle scattering of BaCO3 and CdCO3; (S4 and S6-S9) ESI-MS spectra of a solution of carbon dioxide and of bicarbonates of Sr, Ba, Pb, Mn and Cd. See DOI: 10.1039/c0nr00761g

  19. Highly ordered amorphous silicon-carbon alloys obtained by RF PECVD

    CERN Document Server

    Pereyra, I; Carreno, M N P; Prado, R J; Fantini, M C A

    2000-01-01

    We have shown that close to stoichiometry RF PECVD amorphous silicon carbon alloys deposited under silane starving plasma conditions exhibit a tendency towards c-Si C chemical order. Motivated by this trend, we further explore the effect of increasing RF power and H sub 2 dilution of the gaseous mixtures, aiming to obtain the amorphous counterpart of c-Si C by the RF-PECVD technique. Doping experiments were also performed on ordered material using phosphorus and nitrogen as donor impurities and boron and aluminum as acceptor ones. For nitrogen a doping efficiency close to device quality a-Si:H was obtained, the lower activation energy being 0,12 eV with room temperature dark conductivity of 2.10 sup - sup 3 (OMEGA.cm). Nitrogen doping efficiency was higher than phosphorous for all studied samples. For p-type doping, results indicate that, even though the attained conductivity values are not device levels, aluminum doping conducted to a promising shift in the Fermi level. Also, aluminum resulted a more efficie...

  20. Carbon-assisted growth and high visible-light optical reflectivity of amorphous silicon oxynitride nanowires

    Directory of Open Access Journals (Sweden)

    Tang Zirong

    2011-01-01

    Full Text Available Abstract Large amounts of amorphous silicon oxynitride nanowires have been synthesized on silicon wafer through carbon-assisted vapor-solid growth avoiding the contamination from metallic catalysts. These nanowires have the length of up to 100 μm, with a diameter ranging from 50 to 150 nm. Around 3-nm-sized nanostructures are observed to be homogeneously distributed within a nanowire cross-section matrix. The unique configuration might determine the growth of ternary amorphous structure and its special splitting behavior. Optical properties of the nanowires have also been investigated. The obtained nanowires were attractive for their exceptional whiteness, perceived brightness, and optical brilliance. These nanowires display greatly enhanced reflection over the whole visible wavelength, with more than 80% of light reflected on most of the wavelength ranging from 400 to 700 nm and the lowest reflectivity exceeding 70%, exhibiting performance superior to that of the reported white beetle. Intense visible photoluminescence is also observed over a broad spectrum ranging from 320 to 500 nm with two shoulders centered at around 444 and 468 nm, respectively.