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Bernard J. Feldman - One of the best experts on this subject based on the ideXlab platform.
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13C NMR spectroscopy of Amorphous Hydrogenated Carbon — further evidence of inhomogeneity
Solid State Communications, 2001Co-Authors: Janet Braddock-wilking, Shu-han Lin, Bernard J. FeldmanAbstract:Abstract We report the 13C NMR spectra of Amorphous Hydrogenated Carbon grown at various substrate temperatures and deconvolute these spectra into a contribution from hydrogen-bonded Carbon and one from non-hydrogen bonded Carbon. We interpret this deconvolution as evidence that this material is inhomogeneous and consists of hydrogen-rich and hydrogen-poor regions. As the substrate temperature is increased, the films have fewer hydrogen-rich regions, but the composition and structure of the hydrogen-rich regions do not change. Our results are in agreement with inhomogeneity model of Jager, Gottwald, Spiess and Newport.
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13 C NMR spectroscopy of Amorphous Hydrogenated Carbon and Amorphous Hydrogenated boron carbide
Physical Review B, 1999Co-Authors: Janet Braddock-wilking, Shu-han Lin, Bernard J. FeldmanAbstract:We report the {sup 13}C NMR spectrum of Amorphous Hydrogenated Carbon and boron carbide. The Amorphous Hydrogenated Carbon spectra consist primarily of an sp{sup 3} line at 40 ppm and an sp{sup 2} 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} {ital 1999} {ital The American Physical Society}
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13C NMR spectroscopy of Amorphous Hydrogenated Carbon nitride
Solid State Communications, 1999Co-Authors: J. Lamanna, Shu-han Lin, Janet Braddock-wilking, Bernard J. FeldmanAbstract:Abstract The 13 C NMR spectra of chemical vapor deposited Amorphous Hydrogenated Carbon nitride thin films were measured and a number of sharp lines superimposed on top of a broad peak were observed. These sharp lines have been interpreted as arising from nanocrystals of nitrogen-containing aromatic rings terminated by amino groups. The concentration of these nanocrystals increases with increasing nitrogen concentration and decreases with thermal annealing. These nanocrystals are responsible for the increased structural order in these films. Similar nanocrystals are probably present in sputtered Carbon nitride thin films. There is no 13 C NMR evidence of any phase of crystalline Carbon nitride in either the chemical vapor deposited or sputtered films.
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13C NMR Spectroscopy of Amorphous Hydrogenated Carbon and Amorphous Hydrogenated Boron Carbide
MRS Proceedings, 1998Co-Authors: Janet Braddock-wilking, Shiu-han Lin, Bernard J. FeldmanAbstract:We report the 13 C NMR spectra of Amorphous Hydrogenated Carbon and boron carbide. The Amorphous Hydrogenated Carbon spectra consist primarily of a sp 2 Carbon peak at 40 ppm and a sp 3 Carbon peak at 140 ppm and are in reasonable agreement with recent theoretical calculations of Mauri, Pfrommer, and Louie, but there are some noteable discrepancies. The Amorphous Hydrogenated boron carbide spectra are very different from that of Amorphous Hydrogenated Carbon, showing two sharp lines at 135 and 170 ppm at low boron concentrations and an intense, broader line at 15 ppm at high boron concentrations. We suggest the two sharp lines at 135 and 170 ppm could be due to Carbon atoms in boron-containing aromatic rings, and the broader line at 15 ppm as due to Carbon atoms in boron carbide icosahedra. These lines provide evidence of nanocrystalline structure imbedded in an Amorphous Hydrogenated boron carbide matrix.
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The role of hydrogen in the growth of Amorphous Hydrogenated Carbon
Solid State Communications, 1993Co-Authors: David Revelle, Shu-han Lin, L. Mulestagno, Bernard J. FeldmanAbstract:Abstract We have investigated the role of hydrogen atoms, ions, and molecules in the growth of Amorphous Hydrogenated Carbon by plasma chemical vapor deposition. By varying the ratio of CH 4 to H 2 in the feedstock, we varied the concentration of hydrogen atoms, ions, and molecules in the plasma. We observed that with increasing hydrogen concentrations in the plasma, the film growth rate decreases, the hydrogen concentration in the grown film decreases, and the optical bandgap decreases. We interpret these results in term of increased hydrogen etching of the Carbon-hydrogen bonds that terminate the growing graphite-like crystallites. This leads to larger graphite-like crystallites, lower hydrogen concentrations in the growing film, and consequently, smaller optical bandgaps.
Peter Oelhafen - One of the best experts on this subject based on the ideXlab platform.
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Photoelectron spectroscopy study of metallic nanocluster arrangement at the surface of reactively sputtered Amorphous Hydrogenated Carbon
Journal of Applied Physics, 2005Co-Authors: Ivan R. Videnovic, Peter OelhafenAbstract: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. Duggelin, and R. Guggenheim, Appl. Phys. Lett 80, 2863 (2002)] that by deposition on electrically grounded sub...
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Optical properties of titanium containing Amorphous Hydrogenated Carbon films (a-C:H/Ti)
Journal of Applied Physics, 2000Co-Authors: Andreas Schüler, Peter Oelhafen, C. Ellenberger, Christian Haug, Rüdiger BrennAbstract:Titanium containing Amorphous Hydrogenated Carbon films have been deposited by reactive magnetron sputtering. Real time laser reflectometry and ex situ spectrophotometry have served as a means for the determination of the optical constants index of refraction n and extinction coefficient k. The experimental results are being compared to effective medium theories, modeling the optical constants of the composite material from the ones of Amorphous Hydrogenated Carbon and TiC. We have used the effective medium theories to estimate the bulk stoichiometries which agree with Rutherford backscattering experiments but deviate from the surface stoichiometries determined by in situ photoelectron spectroscopy. These deviations can be explained by surface diffusion and three dimensional cluster growth.
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In situ photoelectron spectroscopy of titanium-containing Amorphous Hydrogenated Carbon films
Physical Review B, 1999Co-Authors: Andreas Schueler, R. Gampp, Peter OelhafenAbstract:Titanium-containing Amorphous Hydrogenated Carbon films (a-C:H/Ti) have been deposited by a medium-frequency-driven physical vapor deposition plasma-enhanced chemical-vapor deposition process at 40 kHz. Core-level photoelectron spectroscopy and valence-band photoelectron spectroscopy have served as means for the characterization of these films. The spectroscopic data are interpreted by a structural model on the basis of a nanocomposite containing titanium carbide clusters embedded in an Amorphous Hydrogenated Carbon matrix. Within this model parallel energy shifts in the measured positions of the Ti 2p core levels and of the Fermi edge can be explained by a one-electron charging effect of nanometer-sized TiC clusters due to the photoemission process.
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Electronic structure and electron emission of lithium-containing Amorphous Hydrogenated Carbon films
Journal of Vacuum Science & Technology A: Vacuum Surfaces and Films, 1997Co-Authors: J.-u. Thiele, P. Kania, Peter OelhafenAbstract:Amorphous Hydrogenated Carbon films were prepared by ion beam deposition. The degree of sp3 coordination and the density of the films were determined from ultraviolet photoelectron valence band spectra and electron energy loss spectra. The films prepared can be described as highly sp3 coordinated (about 80%) and of relatively high density (about 2.3 g/cm3). An indication of a negative electron affinity is found in the valence band spectra. In an attempt to lower the work function, lithium-containing a-C:H films were deposited by lithium evaporation from dispensers during deposition of the a-C:H films. Photoelectron spectra of these films reveal parallel shifts of the core levels and valence band to higher binding energies with respect to the spectra of pure Amorphous Hydrogenated Carbon. These shifts can be attributed to a shift of the Fermi level due to a charge transfer from the lithium to the Carbon matrix. From the onset of the valence band spectra at low kinetic energy and from total photoyield spect...
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Interaction of energetic oxygen ions with lithium-containing Amorphous Hydrogenated Carbon: an in-situ photoelectron spectroscopy study
Journal of Nuclear Materials, 1996Co-Authors: J.-u. Thiele, Peter OelhafenAbstract:Abstract Pure and Li-containing Amorphous Hydrogenated Carbon films were deposited using an ion beam deposition technique. Depending on Li content and deposition conditions, differences in chemical structure are detected. Samples were irradiated at room temperature with energetic oxygen ions of 100 eV to 1 keV. Transient time during which layers retain oxygen is significantly longer for Li-containing as compared to pure Amorphous Hydrogenated Carbon films. Oxygen uptake is found to be mainly determined by Li content. For lower contents (cLi 50 at.%) Carbon is almost completely removed upon irradiation and the resulting composition of the films is found to be close to the stochiometry of Li oxide.
Shu-han Lin - One of the best experts on this subject based on the ideXlab platform.
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13C NMR spectroscopy of Amorphous Hydrogenated Carbon — further evidence of inhomogeneity
Solid State Communications, 2001Co-Authors: Janet Braddock-wilking, Shu-han Lin, Bernard J. FeldmanAbstract:Abstract We report the 13C NMR spectra of Amorphous Hydrogenated Carbon grown at various substrate temperatures and deconvolute these spectra into a contribution from hydrogen-bonded Carbon and one from non-hydrogen bonded Carbon. We interpret this deconvolution as evidence that this material is inhomogeneous and consists of hydrogen-rich and hydrogen-poor regions. As the substrate temperature is increased, the films have fewer hydrogen-rich regions, but the composition and structure of the hydrogen-rich regions do not change. Our results are in agreement with inhomogeneity model of Jager, Gottwald, Spiess and Newport.
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13 C NMR spectroscopy of Amorphous Hydrogenated Carbon and Amorphous Hydrogenated boron carbide
Physical Review B, 1999Co-Authors: Janet Braddock-wilking, Shu-han Lin, Bernard J. FeldmanAbstract:We report the {sup 13}C NMR spectrum of Amorphous Hydrogenated Carbon and boron carbide. The Amorphous Hydrogenated Carbon spectra consist primarily of an sp{sup 3} line at 40 ppm and an sp{sup 2} 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} {ital 1999} {ital The American Physical Society}
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13C NMR spectroscopy of Amorphous Hydrogenated Carbon nitride
Solid State Communications, 1999Co-Authors: J. Lamanna, Shu-han Lin, Janet Braddock-wilking, Bernard J. FeldmanAbstract:Abstract The 13 C NMR spectra of chemical vapor deposited Amorphous Hydrogenated Carbon nitride thin films were measured and a number of sharp lines superimposed on top of a broad peak were observed. These sharp lines have been interpreted as arising from nanocrystals of nitrogen-containing aromatic rings terminated by amino groups. The concentration of these nanocrystals increases with increasing nitrogen concentration and decreases with thermal annealing. These nanocrystals are responsible for the increased structural order in these films. Similar nanocrystals are probably present in sputtered Carbon nitride thin films. There is no 13 C NMR evidence of any phase of crystalline Carbon nitride in either the chemical vapor deposited or sputtered films.
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The role of hydrogen in the growth of Amorphous Hydrogenated Carbon
Solid State Communications, 1993Co-Authors: David Revelle, Shu-han Lin, L. Mulestagno, Bernard J. FeldmanAbstract:Abstract We have investigated the role of hydrogen atoms, ions, and molecules in the growth of Amorphous Hydrogenated Carbon by plasma chemical vapor deposition. By varying the ratio of CH 4 to H 2 in the feedstock, we varied the concentration of hydrogen atoms, ions, and molecules in the plasma. We observed that with increasing hydrogen concentrations in the plasma, the film growth rate decreases, the hydrogen concentration in the grown film decreases, and the optical bandgap decreases. We interpret these results in term of increased hydrogen etching of the Carbon-hydrogen bonds that terminate the growing graphite-like crystallites. This leads to larger graphite-like crystallites, lower hydrogen concentrations in the growing film, and consequently, smaller optical bandgaps.
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Luminescence study of Amorphous Hydrogenated Carbon grown with varying self-bias voltages
Solid State Communications, 1992Co-Authors: Jeremy Viehland, Shu-han Lin, Bernard J. Feldman, Kimberly Kilgore, M.t. JonesAbstract:As a function of increasing self-bias voltage across the plasma, the following changes are observed in the grown Amorphous Hydrogenated Carbon thin films: the photoluminescence intensity decreases while the peak position shifts only silightly to lower energy; the optical bandgap decreases; the hydrogen concentration decreases; and the Carbon dangling bond electron spin resonance signal increases. We explain all these trends in terms of increased number of electron collisions in the plasma that break more Carbon-hydrogen bonds in precursor ions and molecules, leading to larger clusters of graphite-like cores coated with hydrogen in the grown films.
M.t. Jones - One of the best experts on this subject based on the ideXlab platform.
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Luminescence study of Amorphous Hydrogenated Carbon grown with varying self-bias voltages
Solid State Communications, 1992Co-Authors: Jeremy Viehland, Shu-han Lin, Bernard J. Feldman, Kimberly Kilgore, M.t. JonesAbstract:As a function of increasing self-bias voltage across the plasma, the following changes are observed in the grown Amorphous Hydrogenated Carbon thin films: the photoluminescence intensity decreases while the peak position shifts only silightly to lower energy; the optical bandgap decreases; the hydrogen concentration decreases; and the Carbon dangling bond electron spin resonance signal increases. We explain all these trends in terms of increased number of electron collisions in the plasma that break more Carbon-hydrogen bonds in precursor ions and molecules, leading to larger clusters of graphite-like cores coated with hydrogen in the grown films.
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Electrical and electron spin resonance measurements of Amorphous Hydrogenated Carbon nitride
Solid State Communications, 1991Co-Authors: Shu-han Lin, Bernard J. Feldman, Kevin Noonan, Dong Min, M.t. JonesAbstract:Abstract The electrical conductivity and electron spin resonance spectra of Amorphous Hydrogenated Carbon nitride and Amorphous Hydrogenated Carbon are reported. Both measurements present evidence that the addition of nitrogen significantly decreases the density of dangling bonds, similar to the role of hydrogen in Amorphous hudrogenated silicon. These results are also consistent with previously reported optical absorption and photoluminescence measurements.
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Search for the nitrogen dangling bond in Amorphous Hydrogenated Carbon nitride
Solid State Communications, 1991Co-Authors: Jeremy Viehland, Shu-han Lin, Bernard J. Feldman, Kimberly Kilgore, M.t. JonesAbstract:Abstract Motivated by the recent observation of the nitrogen dangling bond in Amorphous Hydrogenated silicon nitride by electron spin resonance, we report our search for the nitrogen dangling bond in Amorphous Hydrogenated Carbon nitride using electron spin resonance. We searched in films as grown, annealed, irradiated with ultraviolet radiation, and with varying nitrogen concentrations. We are led to the conclusion that the nitrogen dangling bond state in Amorphous Hydrogenated Carbon nitride is always below the top of the valence band, always filled with two electrons, and consequently unobservable by electron spin resonce.
W.s. Howells - One of the best experts on this subject based on the ideXlab platform.
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A spectroscopic study of the structure of Amorphous Hydrogenated Carbon
Journal of Physics: Condensed Matter, 1995Co-Authors: J.k. Walters, Robert J. Newport, Stewart F. Parker, W.s. HowellsAbstract:A range of Amorphous Hydrogenated Carbon (a-C:H) samples have been studied using inelastic neutron spectroscopy (INS) and Fourier transform infrared (FTIR) spectroscopy. Using these complementary techniques, the bonding environments of both Carbon and hydrogen can be probed in some detail, with the INS data providing not only qualitative but also quantitative information. By comparing the data from each of the samples we have been able to examine the effects of different deposition conditions, i.e. precursor gas, deposition energy and deposition method, on the atomic-scale structure of a-C:H.
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The effect of temperature on the structure of Amorphous Hydrogenated Carbon
Physica Scripta, 1995Co-Authors: J.k. Walters, Robert J. Newport, Stewart F. Parker, Jane S. Rigden, W.s. HowellsAbstract:The results of complementary inelastic neutron scattering and infrared spectroscopy studies on the structure of Amorphous Hydrogenated Carbon (a-C: H) as a function of temperature are presented, up to a maximum temperature of 1000 °C. These complementary data show that changes in the network structure occur on heating to only 200 °C, with the Amorphous network becoming progressively aromatic even before significant hydrogen loss occurs at temperatures above 400 °C. Reference is also made to earlier, diffraction-based studies of the effects of heating a-C: H).
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Structural properties of Amorphous Hydrogenated Carbon. II. An inelastic neutron-scattering study.
Physical review. B Condensed matter, 1994Co-Authors: P.j.r. Honeybone, Robert J. Newport, W.s. Howells, J.k. Walters, John TomkinsonAbstract:Inelastic-neutron-scattering experiments have been performed on samples of Amorphous Hydrogenated Carbon, prepared from acetylene and propane, containing about 35 and 32 at. % hydrogen, respectively. In these hard Carbons, the hydrogen is predominantly bonded to ${\mathit{sp}}^{3}$ Carbon, with approximately equal concentrations of CH and ${\mathrm{CH}}_{2}$ groups. There is little hydrogen in other bonding environments, and a small amount of ${\mathrm{H}}_{2}$ is trapped in cages in the material.
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THE EFFECT OF TEMPERATURE ON THE STRUCTURE OF Amorphous Hydrogenated Carbon
The Journal of Chemical Physics, 1994Co-Authors: J.k. Walters, Robert J. Newport, Terry Burke, D.m. Fox, O.d. Weedon, W.s. HowellsAbstract:The results of a neutron diffraction study on the structure of Amorphous Hydrogenated Carbon a‐C:H are presented up to a maximum temperature of 1000 °C. The data show clearly the effect on atomic correlations of elevated temperatures, with the initial room‐temperature Amorphous network (a mixture of single bonds and olefinic double bonds) becoming progressively aromatic, then graphitic as hydrogen is evolved. Complementary x‐ray diffraction and infrared spectroscopy data are also presented, the infrared data enabling a more detailed discussion of the temperature‐dependent hydrogen environment, and the x‐ray data are used to highlight the change in the Carbon network. Comparisons have been made with previous work on similar systems and a brief summary of these results is given.
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A high-resolution neutron-diffraction study of the structure of Amorphous Hydrogenated Carbon, a-C:H
Journal of Physics: Condensed Matter, 1993Co-Authors: J.k. Walters, P.j.r. Honeybone, Robert J. Newport, D.w. Huxley, W.s. HowellsAbstract:Current structural models for Amorphous Hydrogenated Carbon (a-C:H) are called into question on the basis of neutron-diffraction experimental work carried out at the ISIS pulsed neutron source (UK) on a-C:H. The nature of the neutron source allows the collection of data over an exceptionally wide dynamic range that ensures a real-space resolution sufficient to allow direct observation, for the first time, of contributions from the principal C-C bond types. The data also reveal details of the C-H correlations, and the presence of trapped molecular hydrogen.