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  • 1
    Electronic Resource
    Electronic Resource
    Study of defects in GaN grown by the two-flow metalorganic chemical vapor deposition technique using monoenergetic positron beams (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 181-186 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Defects in GaN grown using metalorganic chemical vapor deposition were studied through the use of monoenergetic positron beams. For Mg-doped GaN, no large change in the diffusion length of positrons was observed before and after activation of Mg. This was attributed to the scattering of positrons by potentials caused by electric dipoles of Mg–hydrogen pairs. For Si-doped GaN, the line-shape parameter S increased as carrier density increased, suggesting an introduction of Ga vacancy due to the Fermi level effect. Based on these results, we discuss the effects of the growth polar direction of GaN on optical properties in this article. Although the optical properties of a GaN film grown toward the Ga face direction exhibited excitonic features, a film grown toward the N face (−c) direction exhibited broadened photoluminescence and transmittance spectra, and a Stokes shift of about 20 meV was observed. This difference was attributed to extended band-tail states introduced by high concentrations of donors and acceptor-type defects in −c GaN. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1372163
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  • 2
    Electronic Resource
    Electronic Resource
    Modification of exchange interaction parameters by wire width in Cd0.95Mn0.05Te/Cd0.90Mg0.10Te quantum wires (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6701-6703 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magneto-photoluminescence from mesa-shaped Cd0.95Mn0.05Te/Cd0.90Mg0.10Te quantum wires were studied. The Zeeman shift of the excitonic photoluminescence from the quantum wires in a magnetic field is significantly decreased, compared to that from quantum wells. This decrease results from the possible reduction of the exchange interaction of electrons and holes with Mn ions in low dimensional structures. In the excitonic photoluminescence of the quantum wires with the width of 50–100 nm, the transient relaxation of the luminescence peak energy due to the excitonic magnetic polaron formation is remarkably less than that in the quantum well. This result shows the suppressed excitonic magnetic polaron effect in the narrower quantum wires. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1357143
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  • 3
    Electronic Resource
    Electronic Resource
    Patterning of sp3- and sp2-bonded carbon by atomic-force microscopy (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 3619-3621 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the pattering of sp3- and sp2-bonded carbon by using conducting atomic-force microscopy (AFM) working in the noncontact mode. A ta-C film with ∼80% sp3 bonds was scanned by the conducting AFM with a biased tip. A current image that clearly shows gray/white and black features was obtained while scanning in the noncontact mode. These features were proposed to be the result of the different electron emission abilities of the sp3- and sp2-bonded carbon in the film. The result not only enables us to image the distribution of the sp3 and sp2 bonds of a-C, but also extends the AFM to provide the electron emission information of a-C on a nanometer scale. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1354654
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of temperature on carbon nitride films synthesized by ion-beam-assisted pulsed laser deposition (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 7060-7066 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Carbon nitride thin films were deposited by pulsed laser deposition with nitrogen ion beam assistance at a substrate temperature varying from room temperature to 800 °C. The effect of the substrate temperature on the nitrogen content, surface morphology, structure, and electrical property of the carbon nitride films was investigated. The deposited films were characterized by atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and four-probe resistance. The nitrogen content of the deposited films reached its maximum value of 25% at a substrate temperature of 400 °C. AFM images revealed that an island structure occurred and developed on the surface of the films deposited at the high substrate temperature. FTIR and XPS spectra showed the existence of sp3C–N and sp2C(Double Bond)N bonds in the deposited films. The deposited carbon nitride films had an amorphous structure with two carbon nitride phases inclusions, which had a stoichiometry near C3N4 and a variable stoichiometry from C5N to C2N, respectively. With the increase in substrate temperature, the relative content of the sp3C–N bonds, i.e., the C3N4 phase, increased and the crystallization degree of the deposited films enhanced, which were confirmed by the Raman analysis. Very few C(Triple Bond)N bonds in the films were found as compared to other carbon–nitrogen bonds. Electrical resistivity exhibited the highest value for the film deposited at 400 °C. Investigation results indicated that the high substrate temperature could promote the formation of C3N4 phase. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1326474
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  • 5
    Electronic Resource
    Electronic Resource
    Irradiation effect of low energy nitrogen-ion beam during pulsed laser deposition process on the structural and bonding properties of carbon–nitride thin films (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 1580-1587 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Carbon–nitride thin films were deposited by pulsed laser ablation of graphite with assistance of low energy nitrogen-ion-beam irradiation. The nitrogen to carbon (N/C) atomic ratio, bonding state, microstructure, surface morphology, and electrical property of the deposited carbon–nitride films were characterized by x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, micro-Raman spectroscopy, x-ray diffraction (XRD), atomic force microscopy, and four-probe resistance. The irradiation effect of low energy nitrogen-ion beam on the synthesis of carbon–nitride films was investigated. The N/C atomic ratio of the carbon–nitride films reached the maximum at the ion energy of ∼200 eV. The energy of ∼200 eV was proposed to promote the desired sp3-hybridized carbon and the C3N4 phase. Electrical resistivity of the deposited films was also influenced by the low energy nitrogen-ion-beam irradiation. However, the low energy irradiation had little effect on the surface morphology of the films. XRD results revealed the coexistence of the α- and β-C3N4 phases in the deposited thin films. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1335643
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  • 6
    Electronic Resource
    Electronic Resource
    Optical and electrical properties of nitrogen incorporated amorphous carbon films (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 2874-2879 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nitrogen incorporated amorphous carbon (a-C:N) films on silicon (111) wafer, quartz, and Ti/C substrates with nitrogen concentration up to 20 at. % are prepared by filtered arc deposition. The nitrogen concentration and area density of the films were measured by Rutherford backscattering. The electrical properties of the films were investigated by Hall electrical measurements. The optical properties of the films were characterized by ultraviolet–visible and infrared reflection spectrometry. Results indicate that the optical band gap and area density of a-C:N films decrease with increasing nitrogen pressure, accompanied with an increase of nitrogen concentration and reflectivity of the films. Furthermore, the influence of nitrogen concentration on the optical band gap of the films is discussed. The dielectric constant, refractive index and absorption coefficient of a-C:N films in infrared region were investigated. The results indicate that the optical constants of a-C:N show considerable variation with wave number and nitrogen content. The variation of optical properties and optical constants of a-C:N films may be due to the development of graphite-like structure with the increasing of nitrogen content in these films. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372271
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  • 7
    Electronic Resource
    Electronic Resource
    Structural and bonding properties of carbon nitride films synthesized by low energy nitrogen-ion-beam-assisted pulsed laser deposition with different laser fluences (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 1634-1640 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Carbon nitride films were deposited by pulsed Nd:yttrium–aluminum–garnet laser ablation of graphite with assistance of low energy nitrogen-ion-beam bombardment. The nitrogen to carbon (N/C) atomic ratio, surface morphology, bonding state, and microstructure of the deposited carbon nitride films were characterized by x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, micro-Raman spectroscopy, atomic force microscopy (AFM), and x-ray diffraction. The influence of laser fluence on the synthesis of carbon nitride films was investigated. The N/C atomic ratio of the carbon nitride films can reach the maximum at the highest laser fluence. XPS and FTIR analyses indicated that the bonding state between the carbon and nitrogen in the deposited films was significantly influenced by the laser fluence during deposition. The carbon–nitrogen bonding of C–N and C=N were observed in the films. In addition, α and β C3N4 phases were found to coexist in the carbon nitride films with relative low degree of ordering in the crystal lattice. AFM results indicated that the laser fluence also had a critical effect on the surface structure of the carbon nitride films. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1334643
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  • 8
    Electronic Resource
    Electronic Resource
    Observation of sp3 bonding in tetrahedral amorphous carbon using visible Raman spectroscopy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 2305-2308 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Visible Raman spectroscopy excited at 532 nm was used to characterize the carbon bonding in tetrahedral amorphous carbon (ta-C) films. The vibrational modes of the sp3 bonding in ta-C films were revealed directly. An additional Raman band occurring below 1350 cm−1 was observed. It consisted of two features centered on ∼1270 and ∼1170 cm−1, which were associated with sp3 bond stretching. The observed sp3 related Raman spectrum approached the vibrational density of states of amorphous diamond. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288160
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  • 9
    Electronic Resource
    Electronic Resource
    Optical constants of tetrahedral amorphous carbon films in the infrared region and at a wavelength of 633 nm (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4268-4273 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optical constants of tetrahedral amorphous carbon (ta-C) films in the infrared region and at a wavelength of 633 nm were investigated. The ta-C films were prepared by the filtered arc deposition technique under different carbon ion energies of 22–320 eV. The ta-C films contained high sp3 bonding of 82%–93% and had very smooth surfaces. The optical band gap was found to be controlled essentially by the presence and arrangement of the sp2 sites in the ta-C films. The real and imaginary parts, ε1 and ε2, of the dielectric constant, refractive index, n, and extinction coefficient, k, of ta-C films were determined from measurements of infrared reflection and spectroscopic ellipsometry. The results indicated that in our region of investigation ta-C films exhibited a fine transparency at a wavelength of 633 nm, especially in the infrared region. Both n and k, and consequently, ε1 and ε2, showed considerable variation in ion energy, and had minimum values approaching those of diamond for film prepared at an ion energy around 220 eV. The dependence of the optical constants on the sp3 content of ta-C films indicated that with increased sp3 content, ta-C film possessed a dielectric constant, refractive index and extinction coefficient much closer to that of diamond. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373064
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  • 10
    Electronic Resource
    Electronic Resource
    Electron field emission from tetrahedral amorphous carbon films with multilayer structure (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 8098-8102 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A multilayer structure with alternating metal and semiconductor layers is proposed to occur in tetrahedral amorphous carbon (ta-C) films prepared by using an intermittent layer-by-layer deposition method. In this model, the multilayers can be represented as A/B/A/B/.../A/B/A stacks, in which A is considered to be a semimetallic sp2-rich graphite-like layer with B being a semiconducting sp3-rich diamond-like layer. According to the proposed structural model, the electron field emission properties of the ta-C multilayers that could be modulated by adjusting the total number of layers, layer thickness and sp3 content of each layer have been predicted. Correspondingly, three kinds of ta-C multilayers were designed and deposited to confirm this model by enabling us to measure the electron field emission properties. Agreement between the prediction and the experimental results has been observed. It was found that field emission from ta-C multilayers can be optimized by changing the number of layers, layer thickness and sp3 content of each layer. In our experiments, a threshold electric field (Eth) as low as ∼5 V/μm has been obtained for field emission from ta-C multilayers with a total of 20 layers and with a 10 nm layer thickness. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373504
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