STRUCTURES OF SMALL HYDROCARBONS ADSORBED ON SI(001) AND SI TERMINATED BETA-SIC(001)

In this paper a theoretical examination of the adsorption of hydrocarbons atop Si(001) and silicon terminated beta-SiC(001) is presented. In each case the addition of a hydrocarbon species on top of each silicon dimer of the originally clean (2 x 1) silicon terminated substrate is examined. Both C2H2 and C2H4 Species are considered. The total energies of the various potential candidate structures are determined to find the preferred structure. Each structure is obtained by varying the atomic positions in the first four layers of the appropriate unit cell to obtain the minimum total energy configuration for each proposed structure. The resulting structures are then compared to see whether one particular structure is strongly preferred or whether more than one structure may coexist. The results for the two substrates are compared and show that a c(2 x 2) arrangement of carbon dimers is strongly preferred for the SiC(001) substrate. However this structure is not determined for the Si(001) substrate, where the bridging of adjacent silicon atoms by carbon pairs is found to be more energetically favourable.