Adsorption Sequence of Multifunctional Groups: A Study on the Reaction Pathway and the Adsorption Structure of Homocysteine on the Ge(100) Surface

Abstract

We investigated the adsorption mechanism of homocysteine (HS - CH2 - CH2 - CH(NH2) - COOH) on the Ge(100) surface along with its electronic structures and adsorption geometries to determine the sequence of adsorption of this amino acid's functional groups using core-level photoemission spectroscopy (CLPES) in conjunction with density functional theory (DFT) calculations. We found that the " SH-dissociated OH-dissociated Ndative- bonded structure" and the " SH-dissociated OH-dissocia-tion-bonded structure" were preferred at a monolayer (ML) coverage of 0.30 (lower coverage) and 0.60 (higher coverage), respectively. The " SH-dissociated OH-dissociated N-dativebonded structure" was the most stable structure. Moreover, we systematically confirmed the sequence of adsorption of the functional groups of the homocysteine molecule on the Ge(100) surface, which is thiol group (- SH), carboxyl group (- COOH), and amine group (-NH2).