Diamond surface atomic geometry

Articles dealing with the structure and chemistry of solid and crystal surfaces include Tabor (1981) and Forty (1983), who discusses metals and catalysts in particular. The surface of diamond is discussed by Pate (1986), metal oxides by Henrich (1985), transition-metal compounds by Langell and Bernasek (1979), and transition-metal oxides by Henrich (1983). Some of these articles deal with the electronic structures of the surfaces as well as the surface atom geometry the volume edited by Rhodin and Ertl (1979) on the nature of the surface chemical bond and the review paper by Tsukada et al. (1983) on the electronic structure of oxide surfaces concentrate on this aspect. One of the few reviews directed specifically towards minerals is that of Berry (1985). 

With these newly developed 0(N) TBMD algorithms, simulations with more than 1000 atoms can be performed on sequential computers such as the IBM RISC-6000 workstation or vector computers such as the Cray. Qiu et al. have applied the 0 N) method to study the structure and energetics of giant fullerenes. Shown in Fig. 26 is the optimized geometry of a 1620-atom fullerene obtained using an IBM RISC-6000 workstation. Mauri and Galli have applied the 0 N) TBMD to study the structure and dynamic of C q striking a diamond surface [131] 1140 carbon atoms have been used in their simulation. 

Hydrogen termination of the diamond (110) surface maintains the 1x1 geometry [63] but reduces the relaxation of the clean surface considerably. The distance between surface atoms is now smaller by only 1.7% compared to the bulk-terminated structure. All other atomic distances that deviate by less than 0.6% form the corresponding bulk values [60]. No occupied (donorlike) surface states are found in the gap (compare Table 10.2), neither by band structure calculations [60] nor by photoemission [64]. Unoccupied (acceptorlike) surface states are predicted by theory, ranging from 2.0 eV above the VBM to the CBM and extending as pronounced surface resonances up to 2.8 eV above the CBM [60]. As for the other diamond surfaces, hydrogen can thus provide a successful passivation of the (110) surface for p-type bulk material, but leaves electronically active surface states on -type diamond. 

It appears that diamond is not essentially the same to metals in the process of reaction. In fact, factors dominating the oxidation of a solid surface are as follows (1) the difference in electronegativity, (2) the scale and geometry of the lattice, and (3) the temperature and oxygen pressure, disregarding the host atom. Electronegativity determines the nature of the bond or the easiness and amount of charge... 

A surface is created by breaking interatomic bonds-for brittle materials, quite often literally by cleavage of a bulk crystal. This picture works especially well for semiconductors with their almost directional covalent bonds. When creating a surface of a certain orientation the directional bonds are truncated. In the case of bulk termination, the sp hybridized orbitals are directed out of the surface and remain unbonded. The orientation of the broken bonds at the surface is determined by the tetrahedral bonding geometry of the bulk atoms of the diamond structure crystal. These unsaturated orbitals are called dangling bonds. 

Figure 10.6 Schematic image (top and side view) of the three topmost iayers of carbon atoms of the ordered diamond (100) surface, (a) The buik-terminated, unreconstructed 1x1 geometry. A (primitive) unit mesh, the main c staiiographic directions paraiiei to the surface and the two mirror pianes (iightly yellow shaded) are indicated in the top view. On the right hand side the...

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