Adsorption kinetics and dynamics of CO on silica supported Au nanoclusters—Utilizing physical vapor deposition and electron beam lithography

Abstract

The adsorption kinetics and dynamics of CO on silica supported Au clusters have been studied by thermal desorption spectroscopy (TDS) and molecular beam scattering. Physical vapor deposition (PVD) and electron beam lithography (EBL) have been used to fabricate the samples. According to our prior study (Kadossov et al., in press [49]), a maximum in the initial adsorption probability, S 0, occurs for 3 nm Au clusters. Therefore, in the present study, we have focused on this cluster size for PVD samples. In addition, 12 nm EBL Au clusters have been studied. This is presently one of the smallest achievable cluster sizes using EBL for macroscopic samples. Auger electron spectroscopy and scanning electron microscopy have been used to further characterize the samples. TDS revealed well-known features for PVD samples; i.e., two peaks assigned to CO adsorption on different defect sites were present. Interestingly, TDS data of EBL samples were dominated solely by one CO desorption peak. The initial adsorption probability of CO, S 0, decreased as a function of impact energy, E i, and adsorption temperature, T s, for both samples, which is consistent with non-activated molecular adsorption. The coverage dependence of the adsorption probability and S 0 are discussed in the framework of the capture zone model.