| ZnO (10(')10), (40(')41), (50(')51) and (0001) surfaces were prepared under ultra high vacuum conditions and characterized by Auger electron spectroscopy and low energy electron diffraction. Regular steps with zinc edge atoms and single step height of about 2,80 (ANGSTROM) were observed on the (40(')41) and (50(')51) surfaces. The presence of stepped arrays with step height equal to two double layers on the (0001) surface was shown to be dependent on the annealing temperature. The properties of these surfaces were investigated by flash desorption of CO(,2), O(,2) and CO and decomposition of methanol.; Four CO(,2) chemisorption states were observed on ZnO surfaces. Binding energies of CO(,2) increase with decreasing coordination number of cations. Coordination heterogeneity is induced by the presence of anion vacancies and steps in the surface.; Oxygen and CO(,2) bond to ZnO with induced charge transfer from the specimen. The net charges of adsorbed CO(,2)((alpha)), ((beta)) and ((gamma)) were estimated to be about -5 x 10('-3), -1.5 x 10('-2) and -6 x 10('-3) respectively.; Only CO desorbs following room temperature chemisorption of CO on the stepped nonpolar surfaces and the (0001) surface. CO(,2) is the desorbing molecules from the stoichiometric (10(')10) surface.; Methanol decomposition occurs at geometric anion vacancies which include nonstoichiometric oxygen vacancies, defects at the steps and the polar cation surface. The reactivity correlates qualitatively with the concentration of anion vacancies. CO, CO(,2) and D(,2) were common decomposition products from CD(,3) OD on these surfaces. CD(,4) was found only from the (10(')10), (40(')41) and (50(')51) surfaces. D(,2)O and CD(,2)O were observed from the (0001) surface. Different reaction mechanisms are proposed.; The initial sticking coefficient of CO(,2) ((alpha)) and the total amount of charge transferred to CO(,2) or O(,2) on the (50(')51) surface were twice and half, respectively the values on the reduced (10(')10) surface. This was explained by the step facilitated surface atom relaxation and the creation of electron-trapped surface states respectively on the (50(')51) surface. |
