The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
J. Robertson - One of the best experts on this subject based on the ideXlab platform.
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interpretation of infrared and raman spectra of Amorphous Carbon nitrides
Physical Review B, 2003Co-Authors: Andrea Ferrari, S E Rodil, J. RobertsonAbstract:A general framework for the interpretation of infrared and Raman spectra of Amorphous Carbon nitrides is presented. In the first part of this paper we examine the infrared spectra. The peaks around 1350 and 1550 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ found in the infrared spectrum of Amorphous Carbon nitride or hydrogenated and hydrogen-free Amorphous Carbon are shown to originate from the large dynamic charge of the more delocalized \ensuremath{\pi} bonding which occurs in more ${\mathrm{sp}}^{2}$ bonded networks. The IR absorption decreases strongly when the \ensuremath{\pi} bonding becomes localized, as in tetrahedral Amorphous Carbon. Isotopic substitution is used to assign the modes to $\mathrm{C}=\mathrm{C}$ skeleton modes, even those modes around 1600 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ which become strongly enhanced by the presence of hydrogen. The infrared spectrum of Carbon nitride may resemble the Raman spectrum at some excitation energy, but the infrared activity does not primarily result from nitrogen breaking the symmetry. In the second part we examine the Raman spectra. A general model is presented for the interpretation of the Raman spectra of Amorphous Carbon nitrides measured at any excitation energy. The Raman spectra can be explained in terms of an Amorphous Carbon based model, without need of extra peaks due to CN, NN, or NH modes. We classify Amorphous Carbon nitride films in four classes, according to the corresponding N-free film: $a\ensuremath{-}\mathrm{C}:\mathrm{N},$ $a\ensuremath{-}\mathrm{C}:\mathrm{H}:\mathrm{N},$ $ta\ensuremath{-}\mathrm{C}:\mathrm{H}:\mathrm{N},$ and $ta\ensuremath{-}\mathrm{C}:\mathrm{N}.$ We analyze a wide variety of samples for the four classes and present the Raman spectra as a function of N content, ${\mathrm{sp}}^{3}$ content, and band gap. In all cases, a multiwavelength Raman study allows a direct correlation of the Raman parameters with the N content, which is not generally possible for single wavelength excitation. The G peak dispersion emerges as a most informative parameter for Raman analysis. UV Raman enhances the ${\mathrm{sp}}^{1}$ CN peak, which is usually too faint to be seen in visible excitation. As for N-free samples, UV Raman also enhances the C-C ${\mathrm{sp}}^{3}$ bonds vibrations, allowing the ${\mathrm{sp}}^{3}$ content to be quantified.
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Diamond-like Amorphous Carbon
Materials Science and Engineering: R: Reports, 2002Co-Authors: J. RobertsonAbstract:Diamond-like Carbon (DLC) is a metastable form of Amorphous Carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).
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interpretation of raman spectra of disordered and Amorphous Carbon
Physical Review B, 2000Co-Authors: Andrea Ferrari, J. RobertsonAbstract:The model and theoretical understanding of the Raman spectra in disordered and Amorphous Carbon are given. The nature of the G and D vibration modes in graphite is analyzed in terms of the resonant excitation of \ensuremath{\pi} states and the long-range polarizability of \ensuremath{\pi} bonding. Visible Raman data on disordered, Amorphous, and diamondlike Carbon are classified in a three-stage model to show the factors that control the position, intensity, and widths of the G and D peaks. It is shown that the visible Raman spectra depend formally on the configuration of the ${\mathrm{sp}}^{2}$ sites in ${\mathrm{sp}}^{2}$-bonded clusters. In cases where the ${\mathrm{sp}}^{2}$ clustering is controlled by the ${\mathrm{sp}}^{3}$ fraction, such as in as-deposited tetrahedral Amorphous Carbon (ta-C) or hydrogenated Amorphous Carbon (a-C:H) films, the visible Raman parameters can be used to derive the ${\mathrm{sp}}^{3}$ fraction.
William I. Milne - One of the best experts on this subject based on the ideXlab platform.
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Nitrogenation of highly sp2 bonded Amorphous Carbon
Journal of the Korean Physical Society, 2004Co-Authors: Sunglyul Maeng, Soonil Lee, Alberto Tagliaferro, John Robertson, William I. MilneAbstract:Amorphous Carbon with a high sp bonding content is considered to be a poor electronic material due to its very narrow band gap and its excessive density of defect states in the gap, both of which pin the Fermi level. This paper describes the ability of nitrogen to improve the semiconducting properties of highly sp bonded (∼ 80 ∼ 90 % sp) Amorphous Carbon. The electron spin resonance shows a reduction in the density of gap states in nitrogenated Amorphous Carbon (a-C : N) with increasing nitrogen content. Photo-thermal deflection spectroscopy and ultraviolet-visual spectroscopy measurements show that the opening of the gap and clearing of the gap states occur through nitrogen incorporation into the Amorphous Carbon film.
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Photoconductivity and electronic transport in tetrahedral Amorphous Carbon and hydrogenated tetrahedral Amorphous Carbon
Journal of Applied Physics, 1998Co-Authors: Adelina Ilie, John Robertson, B. Kleinsorge, Nmj Conway, William I. MilneAbstract:The photoconductivity of tetrahedral Amorphous Carbon (ta-C) and hydrogenated tetrahedral Amorphous Carbon (ta-C:H) has been studied as a function of temperature, photon energy, and light intensity in order to understand the transport and recombination processes. ta-C and ta-C:H are found to be low mobility solids with μτ products of order 10−11–10−12 cm2/V at room temperature because of their relatively high defect densities. Deep defects tend to be the dominant recombination centers, but at high and moderate temperatures only a fraction of these centers or even tail states can act as recombination centers because the carrier demarcation levels do not always span the gap. For excitation by high energy UV photons, a peak in the photoconductivity is found at 200 K, similar to the thermal quenching effect found in a-Si:H, and attributed to competitive recombination between two classes of centers with very different capture cross sections.
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Nanocrystallites in tetrahedral Amorphous Carbon films
Applied Physics Letters, 1996Co-Authors: S. Ravi, P. Silva, B. X. Tay, H.s. Tan, William I. MilneAbstract:The microstructure of filtered cathodic vacuum arc deposited tetrahedral Amorphous Carbon films is studied as a function of ion energy. An optimum energy window in the density and C–C sp3 content at an ion energy of ∼90 eV observed in this study. It is shown that the density of the Amorphous Carbon films are closely related to the sp3 content. The observation of nanocrystals embedded in the Amorphous Carbon matrix is reported. Most of the crystals observed by transmission electron microscopy can be indexed to graphite, but some of the crystals can be indexed to cubic diamond. The chemical composition of the crystals is analyzed using electron energy loss spectroscopy (EELS). The only discernible EELS edge is that of C at an energy of 285 eV.
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Tetrahedrally bonded Amorphous Carbon
Journal of Non-crystalline Solids, 1996Co-Authors: William I. MilneAbstract:This paper will review the work currently being carried out on tetrahedrally bonded Amorphous Carbon (ta-C). It will include a brief description of the deposition technique and will discuss in some detail the structural, optical and electrical properties of the material and its application to electronic devices.
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Tetrahedral Amorphous Carbon Thin Film Transistors
MRS Proceedings, 1996Co-Authors: Fj Clough, William I. Milne, B. Kleinsorge, John RobertsonAbstract:This paper describes the design and fabrication of a Carbon based thin film transistor (TFT). The active layer is formed from a novel form of Amorphous Carbon (a-C) known as tetrahedrally bonded Amorphous Carbon (ta-C) which can be deposited at room temperature using a filtered cathodic vacuum arc (FCVA) technique. In its ‘as grown’ condition, ta-C is p-type and the devices described here, produced using undoped material, exhibit p-channel operation.
Holger Lüthje - One of the best experts on this subject based on the ideXlab platform.
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Piezoresistive effect in Amorphous Carbon thin films
Materials Science and Technology, 2007Co-Authors: A. Tibrewala, Erwin Peiner, Ralf Bandorf, Saskia Biehl, Holger LüthjeAbstract:Abstract In this contribution Amorphous Carbon (a-C) films are integrated as strain gauges in micromachined silicon boss membranes. Sputter deposited a-C films have high hardness and
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Transport and optical properties of Amorphous Carbon and hydrogenated Amorphous Carbon films
Applied Surface Science, 2006Co-Authors: A. Tibrewala, Erwin Peiner, Ralf Bandorf, Saskia Biehl, Holger LüthjeAbstract:Abstract In this paper we report on the electrical and optical properties of Amorphous Carbon (a-C) and hydrogenated Amorphous Carbon (a-C:H) films. Resistivity of both types of films decreases with increase in temperature. At lower temperatures (60–250 K) the electron transport is due to variable range hopping for the a-C films. At higher temperatures (300–430 K) it is thermally activated for both types of films. Analysis of the heterojunction between diamond-like Carbon (DLC) and bulk silicon (Si) leads to the conclusion that our a-C films are of n-type and our a-C:H films are of p-type. The optical measurements with DLC revealed a Tauc bandgap of 0.6 eV for the a-C films and 1–1.2 eV for the a-C:H films. An Urbach energy around 170 meV could be determined for the a-C:H films. Strain versus resistance plots were measured resulting in piezoresistive gauge factors around 50 for the a-C films and in between 100 and 1200 for the a-C:H films.
Andrea Ferrari - One of the best experts on this subject based on the ideXlab platform.
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interpretation of infrared and raman spectra of Amorphous Carbon nitrides
Physical Review B, 2003Co-Authors: Andrea Ferrari, S E Rodil, J. RobertsonAbstract:A general framework for the interpretation of infrared and Raman spectra of Amorphous Carbon nitrides is presented. In the first part of this paper we examine the infrared spectra. The peaks around 1350 and 1550 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ found in the infrared spectrum of Amorphous Carbon nitride or hydrogenated and hydrogen-free Amorphous Carbon are shown to originate from the large dynamic charge of the more delocalized \ensuremath{\pi} bonding which occurs in more ${\mathrm{sp}}^{2}$ bonded networks. The IR absorption decreases strongly when the \ensuremath{\pi} bonding becomes localized, as in tetrahedral Amorphous Carbon. Isotopic substitution is used to assign the modes to $\mathrm{C}=\mathrm{C}$ skeleton modes, even those modes around 1600 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ which become strongly enhanced by the presence of hydrogen. The infrared spectrum of Carbon nitride may resemble the Raman spectrum at some excitation energy, but the infrared activity does not primarily result from nitrogen breaking the symmetry. In the second part we examine the Raman spectra. A general model is presented for the interpretation of the Raman spectra of Amorphous Carbon nitrides measured at any excitation energy. The Raman spectra can be explained in terms of an Amorphous Carbon based model, without need of extra peaks due to CN, NN, or NH modes. We classify Amorphous Carbon nitride films in four classes, according to the corresponding N-free film: $a\ensuremath{-}\mathrm{C}:\mathrm{N},$ $a\ensuremath{-}\mathrm{C}:\mathrm{H}:\mathrm{N},$ $ta\ensuremath{-}\mathrm{C}:\mathrm{H}:\mathrm{N},$ and $ta\ensuremath{-}\mathrm{C}:\mathrm{N}.$ We analyze a wide variety of samples for the four classes and present the Raman spectra as a function of N content, ${\mathrm{sp}}^{3}$ content, and band gap. In all cases, a multiwavelength Raman study allows a direct correlation of the Raman parameters with the N content, which is not generally possible for single wavelength excitation. The G peak dispersion emerges as a most informative parameter for Raman analysis. UV Raman enhances the ${\mathrm{sp}}^{1}$ CN peak, which is usually too faint to be seen in visible excitation. As for N-free samples, UV Raman also enhances the C-C ${\mathrm{sp}}^{3}$ bonds vibrations, allowing the ${\mathrm{sp}}^{3}$ content to be quantified.
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interpretation of raman spectra of disordered and Amorphous Carbon
Physical Review B, 2000Co-Authors: Andrea Ferrari, J. RobertsonAbstract:The model and theoretical understanding of the Raman spectra in disordered and Amorphous Carbon are given. The nature of the G and D vibration modes in graphite is analyzed in terms of the resonant excitation of \ensuremath{\pi} states and the long-range polarizability of \ensuremath{\pi} bonding. Visible Raman data on disordered, Amorphous, and diamondlike Carbon are classified in a three-stage model to show the factors that control the position, intensity, and widths of the G and D peaks. It is shown that the visible Raman spectra depend formally on the configuration of the ${\mathrm{sp}}^{2}$ sites in ${\mathrm{sp}}^{2}$-bonded clusters. In cases where the ${\mathrm{sp}}^{2}$ clustering is controlled by the ${\mathrm{sp}}^{3}$ fraction, such as in as-deposited tetrahedral Amorphous Carbon (ta-C) or hydrogenated Amorphous Carbon (a-C:H) films, the visible Raman parameters can be used to derive the ${\mathrm{sp}}^{3}$ fraction.
Alberto Tagliaferro - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen and nitrogen effects on optical and structural properties of Amorphous Carbon
Materials Science and Engineering: C, 2008Co-Authors: R. Gharbi, M. Fathallah, N. Alzaied, Elena Maria Tresso, Alberto TagliaferroAbstract:Abstract Two series of Amorphous Carbon alloys were deposited by reactive sputtering using a graphite target and argon as a sputtering gas. The effect of hydrogen or nitrogen on the structure of Amorphous Carbon was investigated using photothermal deflection spectroscopy (PDS), UV–Vis–near infrared spectroscopy, Fourier Transform Infrared (FT-IR), Raman and Photoluminescence (PL) techniques. The change in the structure of hydrogenated Amorphous Carbon (a-C:H) is due to the fact that H incorporation favours the formation of sp 3 sites. In fact, the hydrogen incorporation relaxes the structure enough to improve electronic properties by increasing the number of terminal bonds. In the Amorphous Carbon nitride (a-CN) films, the lone pairs belonging to the nitrogen atoms are important in determining the optical properties of the films. The nitrogen alters the structure of Carbon and creates cavities to be responsible for hydroxyl (OH) inclusions.
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Nitrogenation of highly sp2 bonded Amorphous Carbon
Journal of the Korean Physical Society, 2004Co-Authors: Sunglyul Maeng, Soonil Lee, Alberto Tagliaferro, John Robertson, William I. MilneAbstract:Amorphous Carbon with a high sp bonding content is considered to be a poor electronic material due to its very narrow band gap and its excessive density of defect states in the gap, both of which pin the Fermi level. This paper describes the ability of nitrogen to improve the semiconducting properties of highly sp bonded (∼ 80 ∼ 90 % sp) Amorphous Carbon. The electron spin resonance shows a reduction in the density of gap states in nitrogenated Amorphous Carbon (a-C : N) with increasing nitrogen content. Photo-thermal deflection spectroscopy and ultraviolet-visual spectroscopy measurements show that the opening of the gap and clearing of the gap states occur through nitrogen incorporation into the Amorphous Carbon film.
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Diamond-like properties of Amorphous Carbon and hydrogenated Amorphous Carbon thin films
Surface and Coatings Technology, 1991Co-Authors: F. Demichelis, Alberto Tagliaferro, D. Das GuptaAbstract:Abstract Films of Amorphous Carbon (a-C) and hydrogenated Amorphous Carbon (a-C:H) have been prepared by r.f. magnetron sputtering of a graphite target in atmospheres without and with hydrogen respectively. These films have been studied by optical, electrical and electron spin resonance measurements. The conductivity and the optical absorption coefficient values were found to be similar for the two materials. The only relevant difference was detected in the volume density of spins. It was found to be around 10 21 cm -3 for a-C and below 10 20 cm -3 for a-C:H samples. It is shown that diamond-like a-C, having similar properties to a-C:H, can be obtained by means of this technique. As a consequence, hydrogen plays only an indirect role in determining the relevant optical and electrical parameters. However, the hydrogenated material is less defective.
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Band Edges and Gap States by Optical Absorption and Electron Spin Resonance in Amorphous Carbon (a-C) and Hydrogenated Amorphous Carbon (a-C:H)
Diamond and Diamond-like Films and Coatings, 1991Co-Authors: D. Das Gupta, F. Demichelis, C. F. Pirri, R. Spagnolo, Alberto TagliaferroAbstract:There have recently been many experimental and theoretical studies of Amorphous Carbon (a-C) and hydrogenated Amorphous Carbon (a-C:H) 1, 2. In a-C, the Carbon atoms form both fourfold (sp3) sites (diamond-like) and threefold (sp2) sites (graphite-like).
