CHEMISORPTION AND KINETICS OF SB ON SI(001)

We study the room temperature chemisorption of Sb4 molecules on Si(001) by scanning tunneling microscopy (STM). Most of these molecules dissociate into two Sb2 dimers. Each dimer binds on top of a Si dimer row by bonding to four unsaturated dangling bonds. The two dimers always remain closely spaced after the chemisorption process. A small fraction of the Sb4 molecules chemisorbs differently: the resulting atomic configuration images as a rhombus in a filled-state STM micrograph. The mobility of the Sb2 dimers is studied and an activation energy barrier to diffusion of 1.3 +/- 0.2 eV is estimated assuming an attempt frequency of 10(13) Hz. The mobile Sb2 dimers tend to form strings which act as nuclei for growth of Sb islands. The Sb islands are composed of Sb dimer rows similar to Si islands on Si(001). We do not find preferential incorporation of Sb in Si step edges.