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  • 1
    Electronic Resource
    Electronic Resource
    Nitrogen doping of tetrahedral amorphous carbon films: Scanning tunneling spectroscopy (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 1619-1624 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous nitrogenated carbon films with nitrogen atomic concentration between 12% and 29% were deposited using a filtered cathodic vacuum arc and a Kaufman-type ion source. The surface topography of the samples has been investigated by scanning tunneling microscopy in ultrahigh vacuum, showing that the roughness of the film surface decreases with nitrogen concentration. Scanning tunneling spectroscopy is employed to understand the role of nitrogen in the change of the surface microstructure and electronic structure near the Fermi level. The tunneling current (I)–bias voltage (V) curve is flat at low bias regions indicating a finite gap for the sample with low (12%) nitrogen concentration. An increase of tunneling current and its nonlinearity along with the decrease of energy gap occurs in the samples with increase of N concentration. The observed surface density of states [(dI/dV)/(I/V)] has been fitted as a square-root function of bias voltage. An improvement of the quality of these fits in the films with the increase of nitrogen concentration suggests that a depletion of defect density of states near the Fermi level (EF) takes place. These analyses could be attributed to the modification of the structure of amorphous carbon by a large concentration of nitrogen. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1339854
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  • 2
    Electronic Resource
    Electronic Resource
    Valence band spectra of nitrogen incorporated amorphous carbon films (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 2414-2421 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tetrahedral amorphous carbon (ta-C) films were deposited in a filtered cathodic vacuum arc chamber. Nitrogen, of atomic concentration up to 30%, was introduced in the films during deposition by a Kaufmann-ion source. Change of the film structure and the valence band (VB) spectra of ta-C film due to nitrogen incorporation was studied by ultraviolet photoelectron spectroscopy (UPS) using He I and He II excitations as well as x-ray photoelectron spectroscopy (XPS). A comparative study of the electronic structure between ta-C and the nitrogenated films was demonstrated by decomposition of their VB spectra into several bands and from the intensity difference of these spectra. An additional density of states close to the Fermi level (EF), representing the nitrogen lone pair state, has been detected from both UPS and XPS VB spectra of nitrogenated samples. From the shift of the VB relative to the EF nitrogen doping of ta-C is demonstrated. The change of the density of states at the edge of VB and especially the C 2s and N 2s states is thoroughly explained. The modification of the structure of nitrogenated films prepared by applying the substrate bias and temperature was also studied through comparison of the VB spectra. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1337602
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  • 3
    Electronic Resource
    Electronic Resource
    Near edge x-ray absorption fine structure of thermally annealed amorphous nitrogenated carbon films (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 5043-5049 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The change of structure of tetrahedral amorphous carbon (ta-C) films after nitrogen incorporation, particularly at a high concentration, was studied by near edge x-ray absorption fine structure (NEXAFS) spectroscopy and it was found to be very close to pyridine. The π* peak at the N K (nitrogen K) edge was decomposed into three components corresponding to different resonances. From a detailed analysis of N K edge by NEXAFS spectroscopy it was revealed that as the nitrogen concentration in the films increases, the σ*/π* intensity ratio decreases, indicating that there is an increase of the amount of C(Double Bond)N relative to the C–N bonds. By thermal annealing at different temperatures, up to 800 °C, the nitrogen concentration in the films is reduced. Intensity as well as the position of the π* peak at the C K edge changed with annealing temperature. At the same time, a decrease of the intensity of the π* peak at the N K edge and a very interesting change of the relative intensities of the three split components of this π* peak have been observed. The possible changes of structure of nitrogenated carbon films by annealing and thermal stability of the films have been thoroughly emphasized. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1318389
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  • 4
    Electronic Resource
    Electronic Resource
    Growth, microstructure and electronic properties of amorphous carbon nitride films investigated by plasma diagnostics (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 4668-4676 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous nitrogenated carbon films are prepared in a dual electron cyclotron resonance-radio frequency plasma from a mixture of methane and nitrogen gas. A marked variation of electronic properties and microstructure of the films as a function of nitrogen concentration is observed from Fourier transform infrared (FTIR) spectra, electron energy loss spectra, optical absorption spectra, x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and electrical conductivity. From the variation of intensity of different positive ions and neutral radicals, using quadrupole mass spectroscopy and optical emission spectroscopy, the growth rate, structure and properties of the films are investigated. The density of methyl (CH3) radicals and the film growth rate are found to decrease with the increase of nitrogen concentration. A correlation between the C/N atomic ratio in the films and CH/CN and also CH/N ratio in the plasma is noticed. Also, the CH radical intensity in the plasma and the amount of CH bonds in the films, observed from FTIR spectra, vary in a similar fashion as a function of nitrogen concentration. A model describing film growth and nitrogen incorporation in the films is proposed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371419
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  • 5
    Electronic Resource
    Electronic Resource
    Persistent photoconductivity on ion irradiated carbon films prepared by plasma assisted chemical vapor deposition and determination of traps in the pseudo-gap region (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2079-2081 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The defects created by ion beam irradiation in disordered conducting carbon films have been studied by the photoconductivity technique. A very complex distribution of traps created mostly by random displacement of carbon atoms by energetic ion beam from its polymeric matrix showed a persistent photoconductivity at low temperature. The decay time constant estimated from the photocurrent is around 15 s at 10 K. From the time constant and the intensity of photocurrent the density of traps and the corresponding activation energies are calculated. This report shows how slow decay of photocurrent can be applied to probe distribution of traps in the amorphous carbon due to ion bombardment in the most general case. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115590
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  • 6
    Electronic Resource
    Electronic Resource
    Spectroscopic determination of the structure of amorphous nitrogenated carbon films (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 4491-4500 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Studies on structure and electronic properties of amorphous nitrogenated carbon films prepared in dual electron cyclotron resonance–radio frequency plasma from a mixture of methane and nitrogen are presently reported. These films are characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, x-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), electrical conductivity measurement, and optical absorption spectroscopy. Symmetry breaking of aromatic rings are at a very small amount of nitrogen incorporation is understood from FTIR spectra. The relative contribution of C(Double Bond)N and C–N bonds is found to change with the variation of the nitrogen content in the samples, which shows a similar trend with the shift of the G peak to a higher wave number and the increase of the ID/IG ratio. From decomposition of XPS C 1s and N 1s peaks a three-phase model of CN bonds is proposed. UPS valence band spectra obtained by using a Helium II source, are decomposed into p-π, p-σ, 2s bands and a mixture of s-p band. The intensity of p-π band increases as a function of nitrogen concentration, confirming the increase of sp2 bonds in the samples. An enhancement of the room temperature electrical conductivity and a decrease of the optical gap are observed with the addition of nitrogen in the films. The effect of nitrogen doping in carbon films is also emphasized. Our analyses establish an interrelationship between the microstructure and electronic structure of nitrogenated carbon films, which helps to understand the change in electronic properties of the carbon films due to a low amount of nitrogen incorporation. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367211
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  • 7
    Electronic Resource
    Electronic Resource
    Structure of nitrogenated carbon films prepared from acetylene and nitrogen mixture in electron cyclotron resonance plasma (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 7524-7532 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous nitrogenated carbon (a-CNx) films have been prepared from a mixture of acetylene and nitrogen gas in an electron cyclotron resonance plasma and characterized by electron energy-loss spectroscopy (EELS), spectroscopic ellipsometry (SE), Fourier transformed infrared (FTIR) spectroscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy. From EELS and SE, a significant change in the π plasmon peak position and a reduction of its area is observed in the carbon films after nitrogen introduction, which suggest that there is no further development of graphitic structure. The features of D and G peaks observed from Raman as well as FTIR spectra support a decrease in the amount of sp2 bonded carbon in the a-CNx films. Valence band spectra using He I and He II excitations show that the p-π band becomes less intense upon nitrogen addition. A comparative study between the characteristics of these films and the films deposited from a methane-nitrogen mixture using an identical procedure is also presented. It is found that the structural changes in these films upon nitrogen incorporation are different, indicating a definite role of the precursors on the film structure. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373018
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  • 8
    Electronic Resource
    Electronic Resource
    Metallic conductivity of amorphous carbon films under high pressure (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 632-634 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous carbon films are prepared by plasma-assisted chemical vapor deposition. Resistivity of the films is measured from 300 down to 8 K showing a negative temperature coefficient of resistivity. An increase of room temperature conductivity from 102 S cm−1 to a value of about 104 S cm−1 is found at a pressure of 2 GPa. At a fixed pressure of 0.5 GPa, the films show a positive temperature coefficient of conductivity in the range from 300 to 200 K, followed by a very weak dependence of temperature down to 15 K. At a pressure of 2 GPa a positive temperature coefficient of resistivity is observed in the range between 300 and 15 K. The metallic behavior of the carbon films under high pressure is explained using electronic structure. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120425
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  • 9
    Electronic Resource
    Electronic Resource
    Thermoelectric power of nitrogen-incorporated tetrahedral amorphous-carbon films (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 4157-4159 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tetrahedral amorphous-carbon (ta-C) films were deposited using a filtered cathodic vacuum arc in which nitrogen was incorporated up to an atomic fraction (fN) of 30%. Electrical conductivity and specially thermoelectric power (S) have been performed over a wide range of temperature. The room-temperature conductivity of these samples initially increases with fN up to several orders of magnitude compared to that of ta-C, followed by no dramatic change at higher nitrogen concentration. The sign of the S is negative in the samples with fN below ∼17%, then changes to a positive value with a higher fN. From thermal annealing of the nitrogenated samples a change of the sign of S and its dependence on fN has been analyzed. The small values of both room-temperature S and small variation of conductivity at high fN in all the samples suggest that electrical properties of these films are controlled by compensation of defects. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1426696
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  • 10
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    Thermoelectric power of nitrogen-incorporated tetrahedral amorphous-carbon films (2001)
    American Institute of Physics
    Details
    Publication Date: 2001-12-17
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics
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