Oxidation of Au nanoparticles on HOPG using atomic oxygen

Various Au nanostructures prepared on highly ordered pyrolytic graphite (HOPG) were oxidized using atomic oxygen under ultrahigh-vacuum conditions, and the oxygen species formed in the Au nanostructures were characterized using X-ray photoelectron spectroscopy (XPS). For an Au thin film, only a single oxygen species could be identified in the O 1s spectrum, which can be attributed to Au-oxide. For Au nanoparticles smaller than ∼10 nm, in contrast, two different oxygen species were detected, which are suggested to be Au-oxide and subsurface oxygen (or dissolved oxygen), respectively. CO titration experiments confirm the formation of different oxygen species depending on the particle size.