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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 440-447 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The origin and interpretation of the Raman features of amorphous (hydrogenated) carbon films deposited at room temperature in the region of 1000–1700 cm−1 is discussed in this paper. Possible interpretations of the linewidths, positions of the "G'' graphite peak and "D'' disordered peak, and their intensity ratios are examined using results obtained from magnetron sputtered and magnetic field enhanced plasma deposited films. It is shown that even small "clusters'' of condensed benzene rings (cluster size below 20 A(ring)) in carbon films can explain the observed Raman scattering. Besides the care that should be taken in the correct interpretation of Raman results, the utility of Raman scattering in obtaining an estimate of cluster sizes in amorphous (hydrogenated) carbon films is discussed. Carbon films prepared by magnetron sputtering show two additional Raman features at 1180 and 1490 cm−1 in addition to the G and D peaks. It is shown that a correlation exists between the 1180 cm−1 peak and the sp3 content in the films. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4137-4140 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hexagonal and cubic GaN layers are grown on (001) GaAs substrates by means of molecular beam epitaxy. First order Raman spectra are taken from these layers at various incident laser wavelengths and temperatures. The T2 transverse-optical (TO) and longitudinal-optical (LO) frequencies of cubic GaN are determined, as well as the A1 TO and LO, E1 TO, and E2 frequencies of hexagonal GaN. The T2 TO frequency of cubic GaN lies between the A1 and E1 TO frequencies of hexagonal GaN as one expects comparing the lattice dynamics of zincblende and wurtzite type crystals. The T2 TO frequency is close to the calculated value but disagrees with a recently reported experimental value. For the hexagonal layer, all frequencies are close to those previously measured. A broad Raman structure below the A1 LO peak is interpreted in terms of a disturbed long range order of the hexagonal layer. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7227-7233 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optical emission spectra (OES) from CH4/N2 rf plasmas, which are used for the deposition of nitrogen-containing hydrogenated amorphous carbon (a-C:H:N) thin films, have been characterized. Previously unidentified spectral lines have been assigned to atomic N. Further identified species include CH, H, H2, N2, N+2, N, and CN. Variations between spectra from the pure CH4 or N2 plasmas and the mixed CH4/N2 plasma are discussed. The enhancement of excited nitrogen species, with the addition CH4, is attributed to Penning ionization. The observed OES variations of the CH4/N2 plasma with power, pressure, and CH4/N2 ratio are explained in terms of possible reaction mechanisms and their activation, and correlated with preliminary film growth characteristics. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7234-7240 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion energy, controlled by the substrate bias, is an important parameter in determining properties of films deposited by the filtered cathodic vacuum arc technique. The substrate bias determines the ion energy distribution of the growth species. The ion energy is varied, while keeping the other deposition conditions constant, in order to study the effect of ion energy on the film properties. The films were characterized by their optical and mechanical parameters using an ellipsometer, surface profilometer, optical spectrometer, and nanoindenter. Electron energy-loss spectroscopy and Raman spectroscopy were used for structural analysis of the films. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4044-4048 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thermal annealings of amorphous gallium antimonide films were accompanied using Raman spectroscopy, both for stoichiometric and nonstoichiometric compositions. The films were prepared by flash evaporation on silicon substrates. Structural changes were induced by the heat treatments: an increasing degree of crystallization as a function of the annealing temperature is observed. Sb clusters are found to crystallize before GaSb does, and the dependence of the corresponding Raman peak intensity with the annealing temperature (occurring in two regimes) is explained. A mechanism for the crystallization of the amorphous GaSb is proposed, based on the prior migration of the Sb excess outside the GaSb region to be crystallized. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Raman spectroscopy indicates the formation of extended intermixture alloy regions at the interfaces in the GaSb/AlSb superlatttices, which suppress the optical confined modes. A misfit strain was found to be responsible for the high-frequency shift of the optical phonons confined in the AlSb layers. It turned out that, in the ultrathin layer GaSb/AlSb superlattices with layer thicknesses less than 7 monolayers, the strain was completely relaxed in the alloy interface regions. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 2626-2634 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of nitrogen addition on the structural and electronic properties of hydrogenated amorphous carbon (a-C:H) films has been characterized in terms of its composition, sp3 bonding fraction, infrared and Raman spectra, optical band gap, conductivity, and paramagnetic defect. The variation of conductivity with nitrogen content suggests that N acts as a weak donor, with the conductivity first decreasing and then increasing as the Fermi level moves up in the band gap. Compensated behavior is found at about 7 at. % N, for the deposition conditions used here, where a number of properties show extreme behavior. The paramagnetic defect density and the Urbach tailwidth are each found to decrease with increasing N content. It is unusual to find alloy additions decreasing disorder in this manner. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 1416-1422 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Highly tetrahedral, dense amorphous carbon (ta-C) films have been deposited using rf sputtering of graphite by an unbalanced magnetron with intense dc Ar-ion plating at low temperatures (〈70 °C). The ratio of the argon ion flux to neutral carbon flux Φi/Φn is about 5. The film density and compressive stress are found to pass through a maximum of 2.7 g/cm3 and 16 GPa, respectively, at an ion plating energy of about 100 eV. Experiments with higher ion flux ratios of Φi/Φn=10 show that it is possible to deposit carbon films with densities up to 3.1 g/cm3 and sp3 contents up to 87%. Deposition of ta-C in this experiment when the energetic species is Ar appears to require a minimum stress of 14 GPa to create significant sp3 bonding, which contrasts with the continuous increase in sp3 content with stress when the energetic species is C ions themselves. These results are used to discuss possible deposition mechanisms. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 1819-1827 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Study has been initiated of the deposition of thin films using cluster ions in differing abundances generated in a pulsed inductively coupled plasma. A pulse unit controlling the "on" and "off" timing ratio of a 13.56 MHz rf power supply is used to alter systematically the composition of the contents of the plasma. Adamantane (C10H16) vapor, in argon or nitrogen, was selected as precursor for the deposition of CxHy or CxNyHz thin films using this pulsed source. The effect of varying the relative abundances of the cluster ions present in the resultant plasmas on the films produced, by changing driving power on/off ratio, is investigated. The mass-energy diagnostic data recorded under 50/150 and 150/50 μs on/off pulse sequences showed that fragmentation of C10H16 is a function of the switching ratio selected, i.e., clusters of different sizes and abundances are thus produced. Langmuir probe data also suggest that the electrical characteristics of the plasma generated under these regimes can be monitored. Postdeposition x-ray photoelectron spectroscopy (XPS) analysis of specimen films deposited under the same on/off regimes, within a 200 μs cycle, indicate clear differences are present in these films in terms of the atomic concentration, the C 1s envelope bandwidths, and profiles. Contact angle measurements and optical data performed were found to reflect the variations in the differently deposited films already indicated in the XPS data. For example, specimens deposited under a 50/150 on/off ratio show a high contact angle (low surface energy) and lower refractive index, whereas those deposited under a 150/50 ratio exhibit a low contact angle (high surface energy). Films prepared using the same precursor streams but with the further on/off ratios, 20/180, 100/100, and 20/180 μs, were also considered. Postdeposition analyses confirmed the same tends in the fragmentation behavior of C10H16. Finally, the significance of such a cluster ions selection technique is discussed. © 2002 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 5175-5179 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mechanism of photoluminescence (PL) in hydrogenated amorphous carbon (a-C:H), and nitrogenated and hydrogenated amorphous carbon (a-C:H:N) thin films grown by radio frequency driven plasma enhanced chemical vapor deposition is still a subject of much debate. In this work, we investigate the PL signal obtained from a-C:H and a-C:H:N films, paying particular attention to the effect of nitrogen flow rate during growth, and postgrowth, ex situ annealing on the PL properties of the films. We also correlate the PL spectra to the electronic structure of the films. The films had a low paramagnetic defect density (1017 cm−3). The PL spectra were obtained using the 488 nm (2.54 eV) line of an argon ion laser, as the excitation source. It was observed that the nitrogenation of the films leads to the creation of new bands in the PL signal, which were correlated to the bond fraction of CN triple bonds, as measured by infrared spectroscopy. © 2000 American Institute of Physics.
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