Real-time scanning tunneling microscopy observations of the oxidation of a Ti∕Pt(111)-(2×2) surface alloy using O2 and NO2a)

The authors have used scanning tunneling microscopy (STM), low energy electron diffraction (LEED), and Auger electron spectroscopy (AES) to study the nascent oxidation of an ordered Ti∕Pt(111)-(2×2) surface alloy exposed to oxygen (O2) or nitrogen dioxide (NO2) under ultrahigh vacuum conditions. The Ti∕Pt(111)-(2×2) surface alloy was formed by depositing an ultrathin Ti film on Pt(111) and annealing to 1050K. This produces an alloy film in which the surface layer is pure Pt and the second layer contains Ti atoms in a (2×2) structure, which causes the pattern observed by STM and LEED. Real-time imaging of the surface at 300K was carried out by continuously scanning with the STM while either O2 or NO2 was introduced into the chamber. O2 exposures did not cause any gross structural changes; however oxygen was detected on the surface afterward using AES. Annealing this surface to 950K resulted in the formation of an ordered TiOx overlayer as characterized by both LEED and STM. In contrast, NO2 exposures cause...

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