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  • 1990-1994  (14)
  • 1
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.349546
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  • 2
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.354948
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  • 3
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.349379
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  • 4
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.462033
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  • 5
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.355744
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  • 6
    Digitale Medien
    Digitale Medien
    Mechanism for diamond growth from methyl radicals (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2298-2300 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We use a 9-carbon model compound to describe a proposed mechanism for homoepitaxial growth of diamond from methyl radicals on a hydrogenated, electrically neutral (100) surface. We estimate enthalpy and entropy changes for each step in the mechanism using group additivity methods, taking into account the types of bonding and steric repulsions found on the (100) surface. Rate constants are estimated based on analogous reactions for hydrocarbon molecules, while gas phase species concentrations are taken from our previous measurements. The rate equations are then integrated. The method, which contains no adjustable parameters or phenomenological constants, predicts a growth rate of between 0.06 and 0.6 μm/h, depending on the local details of the surface. Uncertainties related to the use of a model compound rather than diamond are discussed. The analysis demonstrates that the proposed mechanism is feasible.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.102946
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  • 7
    Digitale Medien
    Digitale Medien
    Does benzene inhibit diamond film growth? (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 1911-1913 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Experiments were conducted to test the hypothesis that aromatic molecules inhibit the growth of diamond thin films. Small amounts of benzene vapor were added to a flowtube system for diamond film growth. In this system, diamonds are grown by adding methane or acetylene to a flow of atomic hydrogen at 800 °C. Mass spectrometric measurements verified that the benzene passed through the flowtube. No inhibition of the growth rate or decrease in the quality of the diamonds due to the presence of benzene was observed for either methane or acetylene.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.106186
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  • 8
    Digitale Medien
    Digitale Medien
    Filament activated chemical vapor deposition of boron carbide coatings (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 1757-1759 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In this study, we have demonstrated that boron carbide, an extremely hard and wear-resistant material, can be deposited with hot filament-activated chemical vapor deposition (HFCVD). There are several benefits to using a hot filament system, including a high deposition rate and a relatively low substrate temperature with a process that is not line-of-sight. High purity, apparently amorphous boron carbide films were obtained by the use of a chlorine based precursor (which is less toxic than diborane). This indicates that either the hot filament helps in complete decomposition of BCl3 or the presence of high concentration of atomic hydrogen in a HFCVD environment helps in scavenging the chlorine. © 1994 American Institue of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.112909
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  • 9
    Digitale Medien
    Digitale Medien
    Thermochemistry on a fluorinated diamond (111) surface (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 1949-1951 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have performed calculations to evaluate mechanisms for growth of diamond on fluorinated diamond surfaces. These surfaces are very hard and have excellent tribological properties. Our calculations show that steric repulsion between neighboring F atoms on the fully fluorinated surface studied is small, which−given the strength of C—F bonds−implies that this surface should be chemically very stable. Our analysis also shows that in the absence of hydrogen, growth of diamond on a fluorinated surface is thermodynamically so unfavorable that it will not occur. Finally, diamond growth on fluorinated surfaces could be quite favorable in the presence of hydrogen and hydrocarbons.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.106145
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  • 10
    Digitale Medien
    Digitale Medien
    Thermochemistry of BHmCln Calculated at the G-2 Level of Theory (1994)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 11178-11180 
    Details
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1021/j100094a028
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