Low-energy electron diffraction, X-ray photoelectron spectroscopy, and CO-temperature-programmed desorption characterization of bimetallic ruthenium-platinum surfaces prepared by chemical vapor deposition

Low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), and CO-temperature-programmed desorption (TPD) were used to characterize ruthenium-modified Pt(100) surfaces of very high purity and controlled stoichiometry prepared in ultrahigh vacuum (UHV) by irradiating Ru ₃ (CO) ₁₂ films condensed on cold Pt substrates at 150 K with X-rays, and subsequent annealing at ca. 620 K. The presence of Ru on Pt(100) lifted the (5 × 20) reconstruction characteristic of the bare clean substrate; however, the reconstruction reappeared as the bimetallic surfaces were briefly annealed to ca. 900 K. Exposure of nonannealed Ru(θ _Ru ≥ 0.22)/Pt(100), where θ _Ru represents the Ru coverage in monolayers, to large exposures of CO at ca. 200 K yielded smaller θ _CO , as well as TPD peaks with onset desorption temperatures, T _des (CO), ca. 50 K lower than those observed for bare Pt(100). More strikingly, however, the CO-TPD spectra of CO-saturated Ru(θ _Ru = 0.42)/Pt(100), which had been briefly annealed to 900 K, displayed T _des (CO) as low as 250 K, very similar to desorption temperatures reported for Pt-modified Ru(0001) by de Mongeot et al. (Surf. Sci. 1998, 411, 249).