Structure, Bonding Nature, and Binding Energy of Alkanethiolate on As-Rich GaAs (001) Surface: A Density Functional Theory Study

Chemisorption of alkanethiols on As-rich GaAs (001) surface under a low coverage condition was studied
using first principles density functional calculations in a periodic supercell approach. The thiolate adsorption
site, tilt angle and its direction are dictated by the high directionality of As dangling bond and sulfur 3p
orbital participating in bonding and steric repulsion of the first three CH2 units from the surface. Small charge
transfer between thiolate and surface, strong dependence of total energy on tilt angle, and a relatively short
length of 2.28 Å of the S−As bond indicate the highly covalent nature of the bonding. Calculated binding
energy of 2.1 eV is consistent with the available experimental data.