Energetics of surface reactions on (100) diamond plane

Abstract

decreased in intervals of 0.1 (to log Kb,s = -2.O), and the new steady-state current was evaluated a t each Kb,s, using the steady-state concentration profile evolved a t the previous value of Kbs as the initial condition. With this computational procedure, it was possible to generate working curves comprising 51 points in under 20 CPU minutes on a VAX 6410 mainframe computer.For simulations of the finite substrate problem, the radial coordinate in the diffusion equation (eq 3) was left untransformed over the region R = 0 to the larger of the edge of the substrate or electrode, Le., to R = h or a. Beyond this limit, the radial coordinate was transformed with an exponential function similar to that in eqn A2 in ref 1 1 I These changes required some modifications of the computational algorithm, but these should be self-evident on the basis of our earlier work." The number of grid points employed in the 2 direction for these calculations depended upon the normalized tipsubstrate separation, varying from 100 (log L = -1.2) to 200 (log L = 0.3). In the radial direction, the density and distribution of grid points depended upon the magnitude of h. For h 5 0.4, calculations employed 100 points over the substrate (and thus a total of 100/h points over the electrode). For 0.5 I h I 1, 250 points were utilized over the electrode, and for larger values of h, between 150 and 250 points were employed. Beyond the edge of the electrode (or substrate), between 100 and 200 points were necessary to give the desired level of accuracy. Registry No. Ru(NH3)P,The energetics of several possible diamond (1 00) surface growth reactions was investigated by a semiempirical quantum chemical method. These reactions included thermal and radical-driven dehydrogenation, hydrogen atom migration, and diamond growth by the addition of methyl, acetylene, carbon monoxide, and carbon atoms. Some of the major findings are as follows: the calculated potential energy barrier for H2 elimination from a (loo)-( 1 X 1) diamond dihydride forming a (2x1) surface dimer is in good agreement with experiment; diamond growth by CH3 addition on a dihydrogenated (lOO)-(lXl) surface encounters a large potential energy barrier, yet the barrier is lower for the addition of CH3 to a triplet surface diradical or to a monohydride dimer surface radical; CO addition reactions have substantial potential energy barriers; the energetics for the addition of C atoms onto a diamond (loo)-( 1 X 1) surface is very favorable; and the growth of diamond by the addition of C,H2 on a (100) surface is feasible and should be the energetically preferred channel for the growth on surface ledges and kinks.

Growth on the reconstructed diamond (100) surface

“…(Another proposed mechanism for insertion into dimer bonds [46] includes a step with a 3-center transition state. Since the barrier at that transition state is calculated [46] to be very high, it is not considered further.)…”

“…(Another proposed mechanism for insertion into dimer bonds [46] includes a step with a 3-center transition state. Since the barrier at that transition state is calculated [46] to be very high, it is not considered further.) For addition across the troughs we use the bicyclononane (BCN) mechanism, which was originally proposed [2] to explain growth on the unreconstructed (100) surface.…”

Spatial distributions of atomic hydrogen and C2 in an oxyacetylene flame in relation to diamond growth

“…It is generally believed that hydrogen atoms incident on the surface abstract hydrogen to produce vacant sites, where growth species can then stick to the diamond layer, 5 and that atomic hydrogen etches surface graphite. 6 Gas phase hydrogen atoms may also produce condensable carbon radicals by reactions with hydrocarbons, 7 and, impinging on the surface, they may create surface radicals [8][9][10] and refill vacant sites by adsorption. 8,11 Once adsorbed, atomic hydrogen may also stabilize the diamond surface structure.…”

A surface and a gas-phase mechanism for the description of growth on the diamond(100) surface in an oxy-acetylene torch reactor

“…Table III lists the enthalpy of reaction for different hydrogen abstraction reactions as estimated in this study. A complete, consistent set of thermodynamic data is now obtained by setting the enthalpy of formation H i 0 of the dimer with 2 adsorbed hydrogen atoms to 0.785 kJ/mol 25 and the entropy of formation of the dimer without adsorbed hydrogen to zero. The enthalpy and entropy of the gas-phase species were calculated at 1400 K, the typical temperature at which diamond is deposited in combustion-flame diamond CVD.…”