In Situ Scanning Tunneling Microscopy of Well-Defined Ir(111) Surface: High-Resolution Imaging of Adsorbed Sulfate

Abstract

It is demonstrated by using in situ scanning tunneling microscopy (STM) that well-defined Ir(111) surfaces can be exposed in aqueous solutions by a flame-annealing−quenching technique. Atomically flat terrace-step structures were consistently observed in the double layer potential range in an aqueous HClO4 solution. It is shown that sulfate/bisulfate anions form highly ordered adlayers on Ir(111) in H2SO4 solution over a wide potential range. In situ STM images disclosed an Ir(111)−(√3 × √7) structure, which is identical with that found previously on Au(111), Pt(111), Rh(111), and Cu(111). High-resolution STM imaging allowed us to determine the orientation of hydrogen-bonded water molecules. Two different water molecules were clearly distinguished as separate spots along the √3 direction between neighboring rows of adsorbed sulfate.