An STM study of the growth behaviour of the oxidation of the Ge(1 1 1) surface

The initial steps of the oxidation of the Ge(1 1 1) surface have been studied at the atomic scale using scanning tunnelling microscopy (STM). It has been found that the oxidation starts at defects sites and that with successive exposures to oxygen, islands of oxidised surface are formed. The defects that react are the result of surface rearrangements that disrupt the clean c(2×8) reconstruction creating localised changes in the electron density which promote the oxidation process. Other defects resulting from the adsorption of hydrogen from the residual gas also act as nucleation sites for the oxidation. In addition, hydrogen is able to displace whole rows of surface atoms producing so called “zip” sites which create new defect sites reactive to oxygen. Dislocated rows can spontaneously change length and even disappear thus giving the impression that oxidation has occurred without the prior existence of a defect.