The effect of the crystallographic orientation of ZnO on the surface adsorption and bulk diffusion of hydrogen

The thermal reactions of surface and subsurface hydrogen atoms on ZnO have been investigated. When the (0001) and ( 10 1 ¯ 0 ) surfaces of ZnO are exposed to atomic hydrogen at 370 K, surface‐bound hydrogen atoms are formed on both surfaces. As the hydrogen exposure increases, H atoms diffuse into the bulk of ZnO. Upon heating, recombinative desorption of surface H atoms occurs at ∼450 K on both surfaces. Bulk H atoms also evolve as H 2 molecules. In the case of ZnO(0001), bulk hydrogen is completely removed below 750 K. Evolution of bulk hydrogen on the ( 10 1 ¯ 0 ) face of ZnO takes place at much higher temperatures. Our observations confirm that the migration of H atoms in the ZnO crystal lattice takes place mostly along the c ‐axis.