Investigating the adsorption of oxalic acid onto Cu(1 1 0) to create a chemically functionalised surface

The adsorption of oxalic acid onto the Cu(1 1 0) surface has been investigated using reflection absorption infrared spectroscopy (RAIRS) and reflection anisotropy spectroscopy (RAS). The molecule adsorbs as a mono-oxalate species, bonding via the carboxylate group. For low coverage the oxalate is oriented broadly perpendicular to the surface and tilted in the plane of the molecule. With further coverage the molecule re-orients into an upright configuration with both O atoms of the carboxylate group equidistant from the Cu surface. The upright orientation of the mono-oxalate presents the carboxylic acid group at the vacuum interface, creating a chemically functionalised surface. The presence and absence of intramolecular hydrogen bonding distinguishes between two surface species of mono-oxalate. The RA spectrum of the first mono-oxalate layer is found to be similar to RA spectra observed from aromatic mono- and di-carboxylic acids. The behaviour of the RA response at 4.2 eV is consistent with the known sensitivity of this RA peak to the formation of the Cu–carboxylate bond. The formation of dimers is found at 370 K which generates an RA spectrum distinct from that observed from the first mono-oxalate layer.