The adsorption and bonding of chlorine at silicon(100) investigated using ESD/ESDIAD with Cl+ and Cl- ions

The adsorption of chlorine on Si(100) 2x1 surface has been studied using electron stimulated desorption (ESD) and electron stimulated desorption ion angular distribution (ESDIAD) in conjunction with AES and gas uptake techniques. ESDIAD and ESD measurements were performed on negative as well as positive atomic chlorine species, and the responses with the different polarity of charged species are not seen as complementary. Gas uptake at the surface proceeds initially with a high sticking probability with the atomic chlorine resulting from dissociation not being limited to single dimer sites. ESDIAD studies with positive Cl+ ions reveal normal and off-normal beams associated with symmetric and asymmetric dimers, with relative contributions depending on surface coverage and temperature. Transformations between bonding configurations seen in positive ion ESDIAD are linked with lateral interactions in the adsorbate layer, and their influence is also evident in the forms of the ion yields of both polarity of species with changing coverage. Negative chlorine ions exhibit a predominance of emission around the surface normal, and are produced via a dipolar dissociation process. Missing atom defect sites with an associated high electron density are postulated as playing a central role in their production. The desorption of positive chlorine ions follows mainly from a two-hole, one-electron (2h1e) repulsive state initiated by the ionisation of the C1 3s level.