Interaction of hydrogen with metal oxides:: the case of the polar ZnO(0001) surface

The formation and structure of hydrogen adlayers on the Zn-terminated ZnO(0 0 0 1) surface have been investigated by various analytical techniques. Whereas low energy electron diffraction data showed virtually no change upon H-atom adsorption, the highly surface sensitive method of He-atom scattering revealed for small H-coverages the formation of a H(1 x 1) overlayer. Surprisingly, for larger exposures to hydrogen (both atomic and molecular) the surface becomes highly unstable. Even before completion of the H(1 x 1) overlayer the polar Zn=ZnO-surface restructures, most likely as a consequence of subsurface OH-formation. The defects formed in this restructuring process are found to strongly increase the sticking coefficient of hydrogen molecules. (C) 2001 Elsevier Science B.V. All rights reserved.