Vibration spectroscopy of water on stepped gold surfaces

The vibration spectrum of H2O (ice) adsorbed at low temperatures on Au(1 0 0), Au(1 11 1), and Au(1 1 5) is studied using electron energy loss spectroscopy. On the Au(1 0 0) surface, the spectra show the presence of the typical H-bonded network of water molecules for all coverages from the submonolayer into the multilayer range. The absence of a non-H-bonded OH-stretching mode is indicative for the “H-down bilayer”. On stepped surfaces, on the other hand, a considerable fraction of the H-atoms remains in the non-H-bonded state; surprisingly even in the multilayer range, and even after annealing. The fraction of non-H-bonded hydrogen atoms scales with the step density. Spectral features of water adsorbed at step-sites are isolated after annealing a surface exposed to small doses of H2O. The results are discussed in the context of recent theoretical studies as well as in conceivable relation to the experimentally found reduction of the Helmholtz-capacitance on stepped Au(1 1 n) electrodes.