STM STUDY OF HYDROGEN EXPOSURE OF THE SI(111)ROOT-3X-ROOT-3-IN SURFACE

We have used scanning tunneling microscopy to study Si(111)root 3 x ro ot 3-In surfaces exposed to atomic hydrogen at temperatures in the ran ge 350-450 degrees C. For hydrogen doses as low as 2 L a considerable disorder is induced in the root 3 x root 3 structure. Increasing the d ose to 10 L results in the formation of two-dimensional islands exhibi ting 2 x 2, 4 x 1 and root 7 x root 3 reconstructions, exposing small areas of the underlying surface with the hydrogen-terminated 1 x 1 str ucture. Our data for the 4 x 1 reconstruction corroborate proposed mod els consisting of 1 ML of In atoms in two distinct layers. After 50 L exposure, most of the surface exhibits the hydrogen-terminated 1 x 1 s tructure with a small amount of isolated defects while about 15% of th e surface is covered with two-dimensional islands. For the majority of these islands, showing a weak corrugation with root 7 x root 3 period icity, we propose a structure consisting of two pseudomorphic In layer s on top of the Si(111) surface. Further increase of the hydrogen dose results in the formation of three-dimensional In islands. We observe a substantial loss of In from the surface during hydrogen exposure, wh ich increases-with increasing dose and increasing temperature. For sur faces exposed to 5000 L above 400 degrees C, al In is removed but some stacking-faulted regions have formed on the resulting hydrogen-termin ated 1 x 1 surfaces.