Carbon monoxide adsorption on cobalt-deposited platinum single crystal surfaces investigated by IR reflection-absorption and low-energy electron diffraction

Infrared reflection absorption spectroscopy (IRRAS) was used to investigate carbon monoxide (CO) adsorption on Co deposited Pt(111) (Co/Pt(111)) and Pt(100) (Co/Pt(100)) (Co thickness = 0.15, 0.3 and 0.6 nm) bimetallic surfaces. The 1.0-L-CO exposure to a clean Pt(111) at room temperature yielded linear-bonded and bridgebonded CO-Pt bands at 2092 and 1850 cm^-1. The Co depositions onto the Pt(111) at 333 K brought about the small hexagons of satellites on the low-energy electron diffraction (LEED) patterns, even for the Co thickness of 0.15 nm. The CO-Pt IRRAS band intensities for the 333-K-fabricated Co/Pt(111) surfaces decreased with increasing Co thickness. The CO-Pt bands almost disappeared for the 6nm-thick-Co/Pt(111) surface and the band at 2000 cm^-1 that ascribable to CO-Co bonds dominated the spectra. The results indicated that the deposited Co grows epitaxially on the 333-K-Pt(111) substrate. In contrast, the 693-K-fabricated 0.3nm-thick-Co/ Pt(111) which showed a clear p(1×1) LEED pattern yielded a single absorption band at 2067 cm^-1 originated from adsorbed CO on the Pt site influenced by neighbored Co atoms. As for the cleaned Pt(100) substrate surface, the LEED pattern showed a hex-reconstructed pattern and the 1.0-L-CO exposed surface arose two absorption bands at 2086 and 2076 cm^-1, which can be ascribed respectively to linearly bonded CO on Pt in the 1×1 and hex domains. The Co depositions onto the 333-K-Pt(100)-hex substrate surface lift the hex reconstruction. The adsorbed CO on the 333-K-fabricated 0.3nm-thick-Co/Pt(100)-hex revealed a single absorption band at 2059 cm ^-1. In contrast to the 333-K-fabricated surface, the 693-K-fabricated 0.3nm-thick-Co/Pt(100)-hex showed the hex-like reconstruction: the 1.0-L-CO exposure to the 693-K-fabricated surface resulted in an adsorbed CO band at 2073 cm^-1 accompanied with a shoulder at 2059 cm^-1. The results obtained suggest that the deposited Co atoms are easy to incorporated into the Pt(100)-hex substrate surface in comparison to the Pt(111).