Adsorption on an Oxidized Cu(111) Single Crystal as Characterized by STM*

Copper oxide based catalysts have the promising capability to selectively reduce CO₂ into useful products, however the details of the mechanism are not well understood. Scanning tunneling microscopy (STM) studies performed on oxidized Cu(111) single crystal surfaces allow for the investigation of the fundamentals of this process on an atomic scale. Oxidized copper surfaces were generated via annealing under ambient conditions, and then subsequently annealed in ultra-high vacuum under a range of temperatures from 100 °C to 500 °C. After a low temperature vacuum anneal to remove adsorbates, STM revealed an oxidized structure characterized by grains tens of nanometers in size. Additional high temperature vacuum annealing led to STM imaging of flat atomically resolved oxide surfaces, which do not correspond to the “29” or “44” reconstructions in the literature. Differential conductance spectroscopy indicates a thin oxide layer with a gap-like feature of roughly 500 mV. After STM characterization of the surfaces, CO₂ was dosed in situ under cryogenic (5K) conditions. Individual CO₂ molecules were not observed, however scratchiness in the imaging following deposition indicates physisorbed CO₂ being perturbed by the apex of the tip.