Adsorption and desorption of S on and off Si(001) studied
by Ab initio Density Functional Theory
School of Physics, University of Exeter, Stocker Road, Exeter
EX4 4QL, UK
Abstract
We present detailed ab initio density functional calculations of
equilibrium atomic geometry, electronic states and chemical bonding
for the adsorption of elemental S on Si(001). Following recently
reported room temperature LEED, AES, TDS and WF measurements by
Papageorgopoulos et al, three different adsorption models have
been studied: hemisulfide-(2 x 1) structure,
monosulfide-(1 x 1) structure, and disulfide-(1 x 1)
structure. For hemisulfide and monosulfide structures, the calculated
location of S above the Si(001) surface is in excellent agreement with
experiment. An analysis of surface free energy suggests that, in the
allowed range of S chemical potential, the monosulfide structure is
more stable than the hemisulfide and disulfide structures. A signature
of desorption of SiS unit is obtained from the study of the
disulfide structure.