The reactivity of the clean and contaminated (0001̄) polar and the (101̄0) prism ZnO surfaces to chlorine

Abstract

The reactivities of the (0001̄) and (101̄O) surfaces of zinc oxide to chlorine gas have been studied by a range of techniques. In the case of the (0001̄) oxygen polar surface investigations were made with the surface both atomically clean and with a known level of carbon and calcium contamination. Comparison is made with our earlier results on the (0001) surface which showed a high level of reactivity due to the increased electrostatic stability on adsorption of the electronegative gas. Both the oxygen polar and the prism surface showed a much lower reactivity to chlorine than the zinc face: contamination by carbon and calcium on the former surface reduced the reactivities still further. This result conflicts with comparable data for oxygen adsorption where previous work has shown a greater take-up of oxygen on the oxygen face than the zinc face. Unlike the zinc face, no LEED superstructures were observed on any of, the three surfaces, but in common with the (0001) there were significant electron beam desorption effects. Two states could be identified: one was rapidly removed in ~10 μA min exposure to the beam, the other in much longer periods. Work function and ELS data were consistent with atomic adsorption of chlorine on all surfaces. An exception was the (101̄O) at high exposures where a work function decrease took place following the initial increase: this may indicate a second molecular state.