Carbon Monoxide Adsorption on Ni/Pt(111) Surfaces Investigated by Infrared Reflection Absorption Spectroscopy

Infrared reflection absorption spectroscopic (IRRAS) measurements were conducted for carbon monoxide (CO) adsorption on Pt(111) bimetallic surfaces with various thicknesses of deposited Ni, i.e., Ni (x) /Pt(111) (x, Ni thickness in nanometer units), which were fabricated using molecular beam epitaxy at substrate temperatures of 343-473 K. The reflection high-energy electron diffraction (RHEED) patterns for the 343-K-deposited Ni(0.1)n(m)- (0.6nm)/Pt(111) reveal Ni epitaxial growth on Pt(111). The CO exposure to the clean Pt(111) surface at 323 K engenders linearly bonded and bridge-bonded CO-Pt bands at 2093 and 1858 cm(-1). The 343-K-deposited Ni-0.1nm/Pt(111) gives rise to a new band at 2070 cm(-1) in addition to the CO-Pt(111) bands. T he new band is most prominent for the Ni-0.3nm/Pt(111), on which the bridge-bonded CO on the Ni admetal layer appears at 1874 cm(-1). For the Ni-0.3nm/Pt(111), the 2070 cm(-1) band decreases in intensity and the bridge-bonded CO on the Ni admetal-layer dominates the spectrum, with accompanying weak absorption at 2035 cm(-1) caused by linearly adsorbed CO on the Ni layer. The low-energy electron diffraction (LEED) pattern for the 343-K-deposited Ni-0.3nm/Pt(111) shows incommensurate higher-order extra spots surrounding integer spots. In contrast, the incommensurate pattern changes to its original six-fold symmetry for the 473-K-deposited Ni-0.3nm/Pt(111). In contrast, the RHEED pattern for the 473-K-deposited Ni-0.3nm/Pt(111) revealed streaks having slightly wider separations than those for the clean Pt(111). The IRRAS spectrum for the 1.0-L-CO exposed 473-K-deposited Ni-0.3nm/Pt(111) reveals single-absorption at 2074 cm(-1). We discuss the CO adsorption behavior of Ni-x /Pt(111).