Quasi-One-Dimensional Free-Electron-Like States Selected by Intermolecular Hydrogen Bonds at the Glycine/Cu(100) Interface

We carry out ab initio density functional theory calculations to study manipulation of electronic structures of self-assembled molecular nanostructures on metal surfaces by investigating the geometric and electronic properties of glycine molecules on Cu(100). It is shown that a glycine monolayer on Cu(100) forms a two-dimensional hydrogen-bonding network between the carboxyl and amino groups of glycine using a first principles atomistic calculation on the basis of a recently found structure. This network includes at least two hydrogen-bonding chains oriented roughly perpendicular to each other. Through molecule–metal electronic hybridization, these two chains selectively hybridized with the two isotropic degenerate Cu(100) surface states, leading to two anisotropic quasi-one-dimensional surface states. Electrons occupying these two states can near-freely move from a molecule to its adjacent molecules directly through the intermolecular hydrogen bonds, rather than mediated by the substrate. This results in the experimentally observed anisotropic free-electron-like behavior. Our results suggest that hydrogen-bonding chains are likely candidates for charge conductors.