ADSORPTION AND DECOMPOSITION OF CF3I ON CLEAN AND IODINE-PRECOVERED AG(111)

To enhance our understanding of the thermal interactions of fluorocarbons with transition-metal surfaces, CF3I was adsorbed on clean and iodine-precovered Ag(111) and studied by temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and Auger electron spectroscopy (AES). On clean Ag(111) at 105 K, dissociative adsorption dominates at low coverages and molecular adsorption at high coverages. Dissociation involves C-I bond cleavage; there is no evidence for C-F cleavage, even during TPD. While multilayer desorption peaks near 118 K, chemisorbed CF3I desorbs in a sharp peak at 126 K with a high-temperature shoulder near 145 K. The only other detectable desorption products are CF3(g) and I(g), which desorb at 300 and 830 K, respectively. In the presence of low coverages of I(a), less CF3 and more CF3I desorbs. When the surface I/Ag ratio is 0.33 (square-root 3 X square-root 3 R30-degrees structure), the dissociation channel is completely suppressed. The influence of atomic iodine is discussed in terms of combined electronic and site blocking effects.