Vibrational spectroscopy of a Au(hkl)-electrolyte interface by in situ visible-infrared difference frequency generation

We demonstrate a significant decrease in the non-resonant response of gold substrates in IR-VIS nonlinear optical spectroscopy by switching from sum- to difference-frequency generation. This has allowed DFG spectroscopy to show the significant effect of the surface orientation on the adsorption strength of CN−, which decreases from (110) to (100) and (111). Both the linewidth and the potential tuning rate of the DFG resonances are independent of the electrode structure, pointing to CN− being tightly and linearly bound to each nearest surface gold atom.