Low-energy electron diffraction study of the surface structures of adsorbed amino acid monolayers and ordered films deposited on copper crystal surfaces

Abstract

Monolayer structures and ordered multilayer films of several amino acids on single-crystal substrates were studied using low-energy electron diffraction. At monolayer coverage, ordered layers of glycine, alanine, D- and L-tryptophan were observed on both Cu(100) and Cu(111). With increasing film thickness, ordered multilayer structures of the tryptophans were also seen on both substrates. The monolayer structures are considered in terms of molecular size and packing. The optically isomeric D- and L-tryptophans yielded surface structures which were related by mirror inversion. Ordered multilayer films, apparently unlike the bulk crystals, were obtained only for tryptophan. Electron beam damage was serious for both glycine and alanine multilayer films while tryptophan films remained unaffected in agreement with previously observed stabilization by conjugated electron systems.