Abstract
Infrared reflection−absorption spectroscopy (IRRAS) was used to investigate carbon monoxide (CO) adsorption on sub-monolayer (ML)-thick to 1.0 ML-thick Fe deposited Pt(111) bimetallic surfaces, that is, Fex/Pt(111) (x, Fe thickness in ML units), fabricated using molecular beam epitaxy at substrate temperatures of 343, 403, and 473 K. The 1.0 L CO exposure to a clean Pt(111) at room temperature yielded linearly bonded and bridge-bonded CO−Pt bands at 2093 and 1855 cm−1. The CO−Pt band intensities for the CO-exposed surfaces of the Fex/Pt(111) decreased with increasing Fe thickness. The CO−Pt bands almost disappeared, and the bridge-bonded CO−Fe band at 1950 cm−1 dominated the spectra for the Fe1.0ML/Pt(111) deposited at 343 K. In addition, the Fe deposition brought about a new absorption band at around 2060 cm−1; this band is predominant for the Fe0.5ML/Pt(111) deposited at 473 K. The 1 ML-thick Fe deposition onto the 473 K Pt(111) engenders less-intense, rather broad absorption at 2050 cm−1, accompanied by a weak band attributable to bridge adsorption of CO on the surface Fe atoms. The IRRAS spectra for CO adsorption on the 0.6 nm and 0.3 nm-thick Pt grown on the Fe1.0ML/Pt(111), that is, Pty/Fe1.0ML/Pt(111) (y, Pt thickness in nm units), respectively, showed single absorption bands at 2080 and 2070 cm−1. The reflection high-energy electron diffraction (RHEED) patterns for the Fe1.0ML/Pt(111) deposited at 343 K gave rise to new RHEED streaks, outside the original streaks, attributable to the substrate Pt(111). In contrast, for Pty/Fe1.0ML/Pt(111) “sandwich” structures, the new streaks disappeared, leaving streaks that had slightly wider separation than that of the clean Pt(111). The Fe0.5ML/Pt(111) deposited at 473 K showed similar streaks to those of the Pt/Fe1.0ML/Pt(111). The temperature-programmed desorption (TPD) spectrum of adsorbed CO on the Fe0.5ML/Pt(111) deposited at 473 K revealed a 40% weaker and 10 K lower desorption signal than those for the clean Pt(111). We discuss the CO adsorption behavior on the well-defined Fe deposited Pt(111) bimetallic surfaces.
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