Infrared Reflection Absorption Study for Carbon Monoxide Adsorption on Chromium Deposited Cu(100) Surfaces

Abstract

This study investigates carbon monoxide (CO) adsorption and desorption behaviors on 0.1–0.6-nm-thick Cr-deposited Cu(100) surfaces using infrared reflection absorption (IRRAS) and temperature-programmed desorption (TPD) spectroscopic methods. The low-energy electron diffraction (LEED) pattern for the 0.1-nm-thick Cr-deposited Cu(100) surface indicates that distorted bcc-Cr(110) grows on fcc-Cu(100). The CO exposure to a clean Cu(100) at 90 K produces a single and sharp IR absorption band at 2090 cm⁻¹ that is attributable to adsorbed CO on the on-top site of the Cu atoms’ on the surface. Two absorption bands are located at 2085 and 2105 cm⁻¹ on the IRRAS spectrum for the CO-saturated 0.1-nm-thick Cr/Cu(110) surface. The former might originate from linearly bonded CO on the uncovered Cu substrate surface. With increasing Cr thickness, the latter high-frequency band becomes prominent. For the 0.3-nm-thick Cr surface, the band at 2117 cm⁻¹ dominates all spectra through CO exposure. The TPD spectra of the Cr-deposited Cu surfaces show two remarkable features at 220–250 and 320–390 K, which are ascribable respectively to Cu-CO and Cr-CO bonds. Lower desorption peaks shift to higher temperatures with increasing Cr thickness. Based on TPD and IRRAS results, adsorption–desorption behaviors of CO on the Cr-deposited Cu(100) surfaces are discussed herein.