Effect of surface treatment on the γ-WO3(001) surface: A comprehensive study of oxidation and reduction by scanning tunneling microscopy and low-energy electron diffraction

摘要: The structure of the (001) surface monoclinic γ-WO3 was characterized using scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), and low-energy diffraction (LEED). depended strongly on preparation conditions. Oxidizing by heating in O2 removed carbonaceous impurities resulted large atomically rough terraces. Subsequent lower pressures led to metastable superstructures c(2×2) Continued progressively reduced surface, resulting a series reconstructions. Each could be explained terms ordered oxygen vacancies. First, regions reconstruction grew. This corresponds WO2 plane which half W6+ sites are covered terminal O. Since all W atoms 6+ oxidation state, this is considered “fully oxidized.” Certain STM images terraces revealed pseudo-primitive-(2×2) periodicity that can related distortion from cubic symmetry. It shown always present but ability detect it depends tip. also caused twinning lead spot splitting LEED patterns. disappeared 785 K when bulk converted orthorhombic reduction produced areas with (2×2), (6×2), c(4×2) periodicities. These reconstructions formed further O removed, total W5+. Sputtering ultrahigh vacuum annealing ultimately leading reduced” (1×1) no only W5+ cations. structural transformations were reversible: at any stage during reduction, ⩾10−4 Torr reoxidized regenerating original morphology.