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  • 1
    Electronic Resource
    Electronic Resource
    Pressure and temperature effects on the kinetics and quality of diamond films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5026-5032 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Quantitative measurements of the effects of pressure on the kinetics and quality of diamond films grown with hot-filament chemical-vapor deposition are reported. Pressure affects growth kinetics largely because it affects transport of precursors to the growing surface. H and CH3 concentrations at the growth surfaces are determined with a recombination enthalpy technique combined with appropriate transport analyses. The growth rate rises and then falls with increasing pressure, although the concentrations of CH3 and atomic hydrogen at the surface are nearly constant. Both the rise and the fall in growth rate at higher pressure are explained with a chemical kinetics model as due in large part to an increase in substrate temperature at higher pressures. The fall at higher pressure (temperature) is due to the rate of thermal desorption of the CH3 precursor increasing more rapidly with temperature than the competing rate of its incorporation: Once these rates become comparable, higher substrate temperatures lower the incorporation rates, and the growth rate decreases. Previously measured Arrhenius plots for diamond-growth kinetics are explained quantitatively. The quality of the diamond, as determined using Raman and scanning electron micrograph data, falls with increasing pressure and substrate temperature. For the first time, this decline in quality is correlated with experimental temperature, H:CH3 ratio, and C2H2 concentration measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355744
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  • 2
    Electronic Resource
    Electronic Resource
    Diamond film quality: Effects of gas phase concentrations on the Raman spectra (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2187-2194 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of diamond films have been grown, all at Tsub=1110 K and atomic H concentrations [H]=3×10−10 mol/cm3. The acetylene and methyl radical concentrations at the substrate surface were varied independently by factors of up to 4 and 10, respectively, by adjusting the pressure and the input methane concentration, and the effects of these variations on the Raman spectra were examined. The linewidth of the 1332 cm−1 diamond feature, the sp2 nondiamond carbon feature, and the luminescence yields all increased with increased [CH3]sub, but varying the [C2H2] had no observable impact. A quantitative relationship is provided between the sp2 content and [CH3]sub. The luminescence peak, which is the most sensitive feature to [CH3]sub, is due to an impurity from the filament. Using micro-Raman spectroscopy, large variations are found in the Raman spectra of adjacent crystals and within a single crystal. We attribute these fluctuations to inhomogeneous and anisotropic strains. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363111
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  • 3
    Electronic Resource
    Electronic Resource
    Gas-phase kinetics during diamond growth: CH4 as-growth species (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 3044-3048 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used a one-dimensional kinetic analysis to model the gas-phase chemistry that occurred during the diamond growth experiments of Chauhan, Angus, and Gardner [J. Appl. Phys. 47, 4746 (1976)]. In those experiments the weight of diamond seed crystals heated by lamps in a CH4/H2 environment was monitored by a microbalance. No filament or electric discharge was present. Our analysis shows that diamond growth occurred in this system by direct reaction of CH4 on the diamond surface. C2H2 and CH3, which have been proposed as diamond growth species, played no significant role there, although our results do not address their possible contributions in other systems such as filament- or plasma-assisted diamond growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342696
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  • 4
    Electronic Resource
    Electronic Resource
    Diamond formation on platinum (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 5353-5359 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have made in situ mass spectral measurements and x-ray photoelectron spectroscopy (XPS) measurements at the surface of a diamond film growing on a platinum substrate. We measured the concentrations of CH4, C2H4, and C2H2 and detected additional species with from three to ten carbon atoms. The gas-phase chemical kinetics controlling the concentrations of the C1 and C2 species was modeled, and agreement between the calculated and measured concentrations was good. The presence or absence of the platinum foil had no effect on the measured concentrations, showing that heterogeneous chemistry on platinum did not affect the gas-phase environment. XPS spectra were taken during the course of the diamond growth without exposing the platinum foil to air. After exposure to a room-temperature CH4/H2 mixture but before any growth, the platinum surface was mostly covered with graphitic carbon. Once growth was initiated the graphitic layer was gradually replaced by 1–3 monolayers of hydrocarbon material, which did not thicken with time. Finally, the hydrocarbons were replaced or covered by a diamond film. CO titration experiments demonstrated that practically no active platinum atoms were exposed to the gas-phase reactants during growth. This fact explains the lack of activity of the platinum foil.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343729
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  • 5
    Electronic Resource
    Electronic Resource
    Methyl radical and H-atom concentrations during diamond growth (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6520-6526 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The gas-phase composition at the surface of a growing diamond film was measured as a function of the initial methane (CH4) fraction and, for a 2% methane fraction, as a function of added oxygen (O2). The results were modeled with a one-dimensional reactor flow code that includes diffusion and detailed chemical kinetics. We found that most of the ethylene (C2H4) and ethane (C2H6) that was detected was actually not present in the growth chamber but was instead formed in the probe by recombination of methyl radicals (CH3) that were present in the gas phase. Thus, C2H4 and C2H6 acted as surrogates for CH3 in our system, and measurement of those two stable species allowed us to estimate the mole fraction of the CH3 radical. We then took advantage of the fact that CH3, CH4, H2, and H were in partial equilibrium in the diamond growth chamber in order to estimate the concentration of H. A comparison between the mole fractions of CH3 and H, as determined from our experiments, and the mole fractions calculated from the model shows very good agreement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345128
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  • 6
    Electronic Resource
    Electronic Resource
    Thermochemistry on the hydrogenated diamond (111) surface (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2654-2659 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: As part of our effort to control the growth of diamond films by chemical vapor deposition, we are studying the chemical mechanism for conversion of gas phase hydrocarbons into diamond. In this work we analyze the thermochemistry of a number of structures on the hydrogenated diamond (111) surface. We use the MM2 molecular mechanics force field to calculate strain energies, which are due to crowding of adsorbed species on the surface, and we use a group additivity scheme to estimate bond enthalpies and entropies. These data allow calculation of equilibrium structures on the surface and, together with estimates for rate constants, will permit a prediction for the kinetics of diamond formation as a function of growth conditions. We find that a straightforward abstraction/addition mechanism using either CH3 or C2H2 to grow on a hydrogenated (111) surface cannot account for experimentally measured growth rates. We suggest that experimental measurements of growth rates on (111) surfaces are strongly influenced by growth at steps, kinks, and edges on those surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349379
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  • 7
    Electronic Resource
    Electronic Resource
    A gas phase chemical etchant for boron nitride films (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2314-2316 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have demonstrated that boron nitride films deposited on silicon and tantalum can be etched in a hot filament environment with an input gas composition of 1% methane in hydrogen. Etching experiments were carried out at around 800 K on a tantalum foil and at somewhat higher temperatures on silicon substrates. If the etchant is atomic hydrogen or methyl radical, then we estimate etching efficiencies (atoms etched per collision) of ∼10−5 or 10−4 for these species, respectively. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115137
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  • 8
    Electronic Resource
    Electronic Resource
    Reaction kinetics on diamond: Measurement of H atom destruction rates (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 1022-1026 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: There is presently a considerable effort to understand the chemistry of diamond film growth by chemical-vapor deposition. The first measurements of reaction kinetics between diamond and a gas-phase species—H atoms—involved in its formation are described. A remarkably simple method to measure H atom concentrations is developed and the method is used to measure γd, the destruction probability of H atoms on diamond at 20 Torr and 1200 K. It is found that γd=0.12, with an estimated uncertainty of a factor of 2. This value is about half that estimated from gas-phase alkane rate constants and very close to that predicted by molecular-dynamics/Monte Carlo calculations. The agreement to within the estimated uncertainty supports the assumption that gas-phase alkane rate constants are essentially transferable to reactions between a diamond surface and gas-phase species. The H atom measurement technique could be useful for studying growth in other chemical-vapor-deposition systems in which hydrogen is in high concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354948
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  • 9
    Electronic Resource
    Electronic Resource
    Filament-assisted diamond growth kinetics (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 1385-1391 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the growth rate of chemical vapor deposition diamond films under filament-assisted conditions using a microbalance. The pressure was varied from 20 to 200 Torr, and the ratio R of CH4 to H2 was varied from 0.2% to 1%. Raman spectra showed only diamond features for our films. We found that for R(approximately-greater-than)0.2%, where filament carburization was not an issue, the growth rate scaled as Rα, where α is an empirical constant that varies from about 1 at 20 Torr to about 0.5 at 200 Torr. A comparison of these results to predictions of our gas-phase/gas-surface model for diamond growth shows that the model accurately predicts both the value of α and how α varies with pressure. Reasons for the success of our very simple model are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349546
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  • 10
    Electronic Resource
    Electronic Resource
    A mechanism for growth on diamond (110) from acetylene (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 2371-2377 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have proposed a detailed chemical kinetics mechanism for the addition of C2H2 to a (110) diamond surface, which is the fastest growing face. The model contains no adjustable parameters and is based on the hypothesis that diamond surface chemistry may be understood in analogy with gas-phase hydrocarbon chemistry. We calculated a growth rate of 0.03 μm/h, which gives order-of-magnitude agreement with experiments and suggests we have a feasible mechanism for growth on (110) surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462033
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