The ability to grow thin MgO(100) films of quality approaching that of vacuum-cleaved MgO(100) is demonstrated using low-energy electron diffraction and temperature-programmed desorption (TPD) of CO. Highly ordered MgO(100) surfaces are used to study the adsorption and desorption of CO. A linearly increasing sticking coefficient from 0.47 ( 0.03 to 0.90 is observed for relative CO coverages, θ, less than 0.8 monolayer (ML). For this coverage range, the total sticking coefficient is given by S MgO (1 -P CO ) + S CO P CO , where S MgO (S CO ) is the sticking on the bare (CO-covered) MgO and P CO is the probability of striking the CO-covered surface. In TPD, the desorption of CO is dominated at very low coverages by desorption from sites influenced by defects. At intermediate coverages (0.25-0.8 ML) the CO desorbs via first-order desorption. At 0.8 ML where the monolayer peak saturates, the desorption energy is 17 ( 2 kJ/mol and the preexponential factor is 1 × 10 15(2 s -1 . The desorption energy increases linearly as coverage decreases due to repulsive interactions between adsorbed CO molecules. Above θ ) 0.8 ML the adsorption occurs on fully-CO-covered MgO(100) surfaces, and further increases in θ are achieved by compression of the CO layer. The compression results in a sharp decrease in desorption energy, which, upon saturation of the first CO layer (θ ) 1 ML) and the formation of a c(4×2) ordered phase, has a value of ∼9 kJ/mol. † Part of the special issue "John T. Yates, Jr. Festschrift".

Pt:SnO2 thin films for gas sensor characterized by atomic force microscopy and xray photoemission spectromicroscopy J.

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