Abstract
The dissociative chemisorption of HCl on clean and oxidized Cu(100) surfaces has been investigated using x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Whereas the dissociation of HCl at the clean surface is limited to the formation of a (√2×√2)-R45° Cl(a) monolayer, the presence of surface oxygen removes this barrier, leading to chlorine coverages up to twice that obtained at the clean surface. Additional features in the STM images that appear at these coverages are tentatively assigned to the nucleation of CuCl islands. The rate of reaction of the HCl was slightly higher on the oxidized surface but unaffected by the initial oxygen concentration or the availability of clean copper sites. Of the two distinct domains of adsorbed oxygen identified at room temperature on the Cu(100) surfaces, the (√2×√2)-R45° structure reacts slightly faster with HCl than the missing row (√2×2√2)-R45° O(a) structure. The results address the first stages in the formation of a copper chloride and present an interesting comparison with the HCl/O(a) reaction at Cu(110) surfaces, where oxygen also increased the extent of HCl reactions. The results emphasize the importance of the exothermic reaction to form water in the HCl/O(a) reaction on copper.
Highlights
Madix has made many seminal contributions to the area of surface science and to our understanding of the role of oxygen in reactions at surfaces in particular [1,2,3,4,5,6]
They showed that ammonia oxidation at the b100N ends of oxygen islands was at least 100 times faster than oxidation at the b110 N sides, confirming earlier predictions based on Monte Carlo modeling of x-ray photoelectron spectroscopy (XPS) data [13]
The concentration of chlorine calculated from the Cl (2p) region of the XP spectra after each individual dose is plotted against total exposure in Fig. 1, together with the equivalent experiment for oxygen
Summary
Madix has made many seminal contributions to the area of surface science and to our understanding of the role of oxygen in reactions at surfaces in particular [1,2,3,4,5,6]. One factor influencing reaction kinetics and even reaction pathways has been shown to be the local atomic structure of oxygen at surfaces [12,13,14] and in 1996 Madix and Guo explored this issue with an STM study of ammonia oxidation at Cu(110) surfaces [15]. They showed that ammonia oxidation at the b100N ends of oxygen islands was at least 100 times faster than oxidation at the b110 N sides, confirming earlier predictions based on Monte Carlo modeling of XPS data [13]. These were chosen because they represent reproducible surface states with distinct oxygen structures
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