IRRAS and TPD investigations of carbon monoxide adsorption on MBE grown Fe on Pt(100)

Infrared reflection absorption spectroscopy (IRRAS) and temperature programmed desorption (TPD) were used to investigate carbon monoxide (CO) adsorption on 0.25-1.0 monolayer (ML)-thick Fe deposited Pt(100) (Fe _{∞(∞=0:25-1:0ML)}/Pt(100)). The cleaned Pt(100) surface shows 5×20 reconstruction (Pt(100)-hex). The 1.0-LCO exposure to the Pt(100)-hex at 300 K yields linearly bonded CO-Pt bands at 2089 and 2081 cm _-1. They are ascribable respectively to adsorbed CO on 1×1 and hex domains. Low-energy electron diffraction (LEED) patterns for the 343-K-deposited Fe_∞/Pt(100) change from blurred hex (0.25 ML) to 1×1 (>0.5 ML), indicating that the outermost surface structures changed through Fe thickness. Regarding the Fe_0:25ML/Pt(100), two bands are located at 2082 and 2069 cm^-1 for the 1.0-L-CO exposed surface. The Fe_0:5ML/Pt(100), however, reveals a single absorption band at 2050 cm^-1. The CO exposure to the Fe_1:0ML/Pt(100) generates a broad and more red-shifted band at 2027 cm^-1. In contrast, the LEED pattern for Fe_0:5ML/Pt(100) fabricated at 873 K shows hex reconstruction. The IRRAS spectrum recorded after 1.0-L-CO exposure for the 873 K deposited Fe_0:5ML/Pt(100) shows an absorption band at 2073 cm_-1 with narrow bandwidth. The CO desorption temperature for the Pt(100)-hex (about 520 K) was shifted to a lower temperature by Fe deposition: the temperatures are about 470 and 430 K for the Fe _0:5ML/Pt(100) fabricated substrate temperatures of 343 and 873 K. Based on IRRAS and TPD results, CO adsorption behavior on the Fex/Pt(100) is discussed.