Abstract
The Au(110) surface offers unique advantages for atomically-resolved model studies of catalytic oxidation processes on gold. We investigate the adsorption of oxygen on Au(110) using a combination of scanning tunneling microscopy (STM) and density functional theory (DFT) methods. We identify the typical (empty-states) STM contrast resulting from adsorbed oxygen as atomic-sized dark features of electronic origin. DFT-based image simulations confirm that chemisorbed oxygen is generally detected indirectly, from the binding-induced electronic structure modification of gold. STM images show that adsorption occurs without affecting the general structure of the pristine Au(110) missing-row reconstruction. The tendency to form one-dimensional structures is observed already at low coverage (<0.05ML), with oxygen adsorbing on alternate sides of the reconstruction ridges. Consistently, calculations yield preferred adsorption on the (111) facets of the reconstruction, on a 3-fold coordination site, with increased stability when adsorbed in chains. Gold atoms with two oxygen neighbors exhibit enhanced electronic hybridization with the O states. Finally, the species observed are reactive to CO oxidation at 200K and desorption of CO2 leaves a clean and ordered gold surface.
Highlights
Visualization of reactive adsorbed species is a powerful tool for understanding how chemical reactions occur on surfaces, especially in heterogeneous catalysis.[1]
We find that O is generally imaged indirectly through the electronic perturbations induced in its gold nearest neighbors and this result is corroborated by simulated scanning tunneling microscopy (STM) images
The Au(110) single crystal was purchased from Princeton Sci. and cleaned via cycles of sputtering and annealing at ~900K until no impurity trace was detected by Auger electron spectroscopy, and STM showed a uniform Au(110)(1x2) surface
Summary
Visualization of reactive adsorbed species is a powerful tool for understanding how chemical reactions occur on surfaces, especially in heterogeneous catalysis.[1]. Madix, who is being honored by this special issue, was a pioneer in the application of scanning tunneling microscopy (STM) to the investigation of chemical reactions on surfaces, including coinage metals.[2] Because gold is an efficient and selective catalyst for oxidation processes[3,4,5,6,7,8,9] there is considerable interest in imaging reactant species, including adsorbed oxygen (Oads), on its surfaces. If a more wellordered system state of adsorbed O were accessible that had the same reactivity, the high spatial resolution offered by STM could be used to probe the details of adsorbate organization and overall reactivity
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