Emergence of atomic‐level structural information for ordered metal–solution interfaces: Some recent contributions from in situ infrared spectroscopy and scanning tunneling microscopy

The utilization of infrared reflection–absorption spectroscopy (IRAS) and scanning tunneling microscopy (STM) for extracting atomic‐resolution information for ordered metal–solution interfaces in a related (and relatable) fashion to metal‐ultrahigh vacuum (UHV) surfaces is illustrated by means of some recent results from our laboratory. Two specific topics are addressed. The first involves the potential‐dependent properties of saturated CO adlayers on low‐index platinum and rhodium electrodes in aqueous and nonaqueous media. The central role of the surface potential in controlling the CO adlayer structure is discussed on the basis of in situ IRAS data, especially in comparison with the properties of corresponding metal‐UHV interfaces. The application of in situ atomic‐resolution STM in tandem with IRAS for elucidating real‐space adsorbate structures is noted for saturated CO adlayers on Rh(111) and Rh(110) electrodes. The second topic concerns the application of in situ STM to probe potential‐induced reconstruction at gold‐aqueous interfaces. All three low‐index gold surfaces are seen to undergo reconstruction at potentials corresponding to small (∼10–15 μC cm⁻²) negative electrode charges. The subtle surface relaxation observed for Au(111) is essentially identical to that observed recently by atomic‐resolution STM in UHV. The (5×27) and (1×n) (n=2,3) symmetries observed for reconstructed Au(100) and (110) electrodes, respectively, are compatible with the structures deduced for the UHV systems by diffraction methods, although the STM data afford greater real‐space detail.