Structural investigation of glycine on Cu(100) and comparison to glycine on Cu(110)

Abstract

New O 1s and N 1s scanned-energy mode photoelectron diffraction (PhD) measurements and low energy electron diffraction observations from the Cu(100)(2×4)pg phase formed by deprotonated glycine, glycinate (NH2CH2COO–) have been used to determine the local structure of this adsorbed phase. The favored model involves bonding of both O atoms of the carboxylate and the N atom of the amino group in near atop sites with Cu–N and Cu–O distances of 2.05 Å. This bonding geometry is similar to that of glycinate on Cu(110), but in this case the fact that the C–C backbone is aligned along 〈100〉 straggling the more widely spaced Cu atoms rows leads to a larger offset from atop of the O atoms. A reanalysis of O 1s PhD data from the Cu(110)(3×2)pg-glycinate surface shows that the two O atoms are inequivalent, with one O being offset by 0.29 Å more than the other, leading to a twist of the molecule. The results are discussed in the light of other measurements on these surfaces and recent theoretical total energy calculations, in order to obtain models of the long-range ordered phases. These favor models for both surfaces involving only heterochiral structures in which the unit mesh contains one glycinate species with each chirality, defined by the side of the C–C backbone on which the amino group bonds to the surface.