Relaxation of the adsorption geometry of Sb and K on Si(001) surface induced by an electric field

The electric field-induced relaxation of the adsorption geometry of Sb and K atoms on Si(001)2 x 1 surface was studied using ab initio cluster calculations. We have found that the adsorption geometry changes considerably due to field. The difference in the response to the applied field of the different adatoms and the underlying Si layer is remarkable. The relaxation of the Sb dimer is less than that of the clean surface dimers, whereas the changes in K atom positions are an order of magnitude larger than those of the clean surface. In addition, there are drastic changes in the geometry of the Si dimers on the K-covered surface. The buckling of the dimers increases greatly for a positive field; for a negative field the increase in buckling is smaller. In both surfaces the relaxation of the Si dimers, to which the adsorbed atom is bonded, is defined by the elastic interactions with the adsorbed atom and differs from that of clean surface. The distribution of the field does not affect significantly the changes in adsorption geometry. However, for the field-sensitive surfaces, an extremely sharp tip may cause a selective desorption of the adsorbed atoms. [S0163-1829(98)01215-6].