Variation of Coverage-Dependent Attachment of Multifunctional Groups in Alanine and Leucine to the Ge(100)-2 x 1 Surface: Bonding Configuration and Adsorption Stability

Abstract

The coverage-dependent attachment of multifunctional groups included in alanine and leucine molecules adsorbed to the Ge(100)-2 x 1 surface was investigated and compared using core-level photoemission spectroscopy (CLPES) and density functional theory (DFT) calculations. The bonding configuration, stability, and adsorption energies were evaluated for two different coverage levels. In both molecules, the core-level spectra at a low coverage indicated that both the carboxyl and amine groups participated in the bonding with the Ge(100) surface by "O-H dissociated and N-dative bonded structure". This is consistent with the D FT calculation results showing that such adsorption geometry is the most stable and follows the minimum reaction pathway. However, at high coverage level, an additional adsorption geometry of "O-H dissociation bonded structure" appeared possibly to minimize the steric hindrance between adsorbed molecules.