Role of Chain Length in the Adsorption Structures and Geometric Configurations of Phenylalanine Derivatives on Ge(100) Surfaces

Abstract

The variation of the adsorption structures and geometric configurations among phenylalanine derivatives (2-amino-4-phenylpropanoic acid (PhenA), 2-amino-5-phenylpropanoic acid (PhenB), and 2-amino-6-phenylpropanoic acid (PhenC)) adsorbed on Ge(100) surfaces was investigated using density functional theory (DFT) calculations. The chain length of a linker bonded to the alpha-carbon of the phenylalanine derivatives influenced the preferred adsorption structure in self-assembled monolayers (SAMs). We confirmed that the "O-H dissociated-N dative bonded structure" is the most favorable structure among the five possible adsorption structures. Interestingly, geometric differences in the adsorption configurations indicated that the phenyl rings of PhenA and PhenB were tilted with respect to the Ge(100) surface, with an angle 30 degrees from the surface normal. In contrast, the phenyl ring of PhenC was tilted with an angle of 60 degrees with respect to the surface normal. We therefore confirmed that PhenA and PhenB are available to use in SAMs considering the geometrical configurations and the adsorption energies. The theoretical results were further supported by conducting DFT calculations of the reaction pathways, leading to the favored adsorption geometries.