Defect microstructure in heavy-ion-bombarded (0 0 0 1) ZnO

Radiation defects in oxides are complex and remain poorly understood. Here, we use transmission electron microscopy to study ZnO crystals bombarded at room temperature with heavy ions (500 keV Xe). Results reveal that the damage evolution proceeds via the formation of a band of cavities centered on ∼7 nm from the sample surface. With further irradiation, a layered structure is formed, with alternating near-stoichiometric and Zn-rich layers. The anomalous intermediate peak and step in ion channeling spectra are attributed to a Zn-rich defect band and an interface between stoichiometric and Zn-rich layers, respectively. To explain these observations, we propose a damage build-up scenario involving vacancy clustering, loss of O from the surface, and peculiarities of point-defect transport through a Zn-rich defect band toward the surface.