DIHYDRIDE 1 X-1 STRUCTURES ON GROUP-IV (100) SURFACES

In the formation of dihydride structures on elemental group IV (100) surfaces the hydrogen atoms saturate dangling bonds and cause the 2 x 1 clean surface reconstructions to reduce to 1 x 1 topologies. It has also been suggested that repulsion between hydrogen atoms on adjacent dihydride groups may produce large deviations in the hydrogen bond angles from those of tetrahedral geometry. In this communication we first illustrate the features of these dihydride systems by calculating the structure of the Si(100) 1 x 1 : 2H systems. The effect of hydrogen repulsion is then examined by comparing the dihydride surface structure corresponding to substrates of different lattice constant. For this purpose we have employed the C(100) surface, the carbon-terminated beta-SiC(100) surface, and an adsorbed layer on Si(100). In each case the optimum surface topology has been determined by minimising the total energy of the system with respect to variations in the atomic co-ordinates of the hydrogen and the first four layers of the substrate. The results clearly show that the H-C-H bond angle decreases sharply with decreasing C-C internuclear distance.