The observation of in situ and ex situ oxidation processes for ZnTe surfaces by high-resolution electron microscopy

The oxidation of ZnTe surfaces, both in situ and ex situ, is studied by high-resolution electron microscopy. The in situ oxidation is induced by the incident electron beam inside the microscope column, and the process is followed in real time by atomic-resolution electron microscopy. The ex situ oxidation studies involve heating ZnTe crystals up to 260 0C in air for various periods, with subsequent observation by electron microscopy. In both cases, optical diffractograms are used to identify the phases present in the surface layers, using the lattice spacings of bulk ZnTe as an internal reference. For in situ oxidation, the oxidation sequence involved amorphization of the ZnTe crystal as Te is removed by a non-thermal electron stimulated process, with subsequent formation of hexagonal ZnO by oxygen diffusion into the sample. In ex situ oxidation, the main phases present are crystals of ZnO and Te metal, which usually give rise to layered surface regions, in the sequence ZnTe/Te/ZnO, with the large crystals (up to 100 nm) of Te in an epitaxial relationship with the bulk ZnTe and the small ZnO crystals (5 nm) in random orientations. This process involves the diffusion of Zn from the bulk ZnTe to the surface followed by reaction with oxygen in air to form ZnO. (author)