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

The coverage-dependent attachment of multifunctional groups included in alanine and leucine molecules adsorbed to the Ge(100)-2×1 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 DFT 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.