Interaction of Hydrogen with ZnO: Surface Adsorption versus Bulk Diffusion

The interaction of hydrogen (H) and a ZnO(000 (1) over bar)-O surface has been investigated using a temperature programmed desorption (TPD) technique. When the surface is exposed to atomic hydrogen below 400 K, hydrogen is adsorbed on the surface. As the hydrogen exposure increases, bulk diffusion of hydrogen takes place. The existence of surface and bulk hydrogen has been confirmed using X-ray photoelectron spectroscopy (XPS). When the ZnO surface dosed with hydrogen is heated, surface hydrogen is desorbed at 432 K and bulk hydrogen is evolved at similar to 539 K. Diffusion of hydrogen into the ZnO bulk is an activated process, and the activation energy is estimated to be 0.19 eV.