The production of enantiopure chiral bio-relevant molecules is of significant importance for the development of new pharmaceuticals and the improvement of existing ones. In this context chiral surface systems, e.g. chiral molecules adsorbed on chiral single crystal surfaces, are of considerable interest as they are model systems for potential enentioselective heterogeneous catalysts or enantiomeric selection. In this study the adsorption properties of L- and D- Serine enantiomers on the intrinsically chiral Cu{531} surface were investigated. These aminoacids have four functional groups which can make bonds to the Cu{531} surface: OH, NH₂, and two oxygen atoms in the carboxyl group (-COOH). The geometry of the adsorption complex was characterised using XPS and NEXAFS. The bonding characteristics of the molecule strongly depend on the coverage. The main peak in the O1s XPS spectra, at BE 531.5eV, is assigned to be overlapping signal of the two oxygen atoms in the deprotonated carboxylate (COO) group forming bonds with Cu atoms. For the low coverages this peak has a shoulder at a lower BE (530.7 eV), as the coverage increases this shoulder disappears and a new peak appears at higher BE (532.8 eV). The low BE shoulder at low coverage is assigned to the OH group also forming a bond with the Cu surface. With increasing coverage the surface becomes more crowded and a less space-consuming configuration is assumed with a ‘dangling’ OH group, which is the origin of the high BE O1s peak.

In order to investigate the orientation of the amino acids within the surface NEXAFS spectra were recorded for different in-plane polarization angles and different coverages. These spectra show large enantiomeric differences between the orientation of D-serine and L-serine, which is also reflected in the LEED patterns, indicating different long-range ordered overlayers. These enantiomeric differences are much bigger than those previously observed for alanine on the same surface, which suggests that the size and the nature of the amino acid side group is the dominating factor for enantioselective behaviour on this surface.