The reflectivity change induced by adsorbates on Cu(100) at (lambda) equals 632.8 nm is investigated. It is found that physisorbed molecules (water, methanol, acetone) induce no observable reflectivity change, while chemisorbed molecules (carbon monoxide, oxygen, acetylene) do. The magnitude of the reflectivity change is such that submonolayer sensitivity is obtained for chemisorbed species. Furthermore, the change is found to vary linearly with coverage. The results show that this technique is a versatile, inexpensive, and straightforward optical probe of the surface coverage, and as such is applicable to many different surface investigations.
Transient IR reflection-absorption spectroscopy with diode lasers has been used to characterize the adsorption kinetics and the nature of the bonding of CO on Cu(100). Although the strong dynamic dipole coupling between the CO molecules adversely affect the absorption intensity and frequency, it can be used to reveal the interadsorbate interactions. It was found that the adsorption of CO on Cu is correlated, resulting from a repulsive interaction between the first and second nearest neighboring sites. A model based on static screening of the charge transferred from CO to Cu is proposed to account for all the observations. Furthermore, a nonresonant reflectivity change, which results only from chemisorption, but not physisorption, was identified in both the IR and visible regions.
Conference Committee Involvement (1)
Physical Chemistry of Interfaces and Nanomaterials II
6 August 2003 | San Diego, California, United States