HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY OF STRUCTURAL-CHANGES AT AND NEAR SURFACES OF ZNTE CRYSTALS

Structural changes on and near surfaces of ZnTe crystals were observed by the surface profile imaging method in a high-resolution transmissi on electron microscope (HRTEM) with 200 kV accelerating voltage. It wa s found that ZnO particles form under electron irradiation on surfaces originally covered with a thin amorphous layer. For amorphous coverag es thicker than about 7 nm, ZnO particles were not observed. Under the ZnO particles, 2X1 and 2x2 superstructures (about 10 nm in size) were often found in the ZnTe matrix. These superstructures can be describe d as a metastable Zn2Te3 having a structure similar to the ordered Ga2 Te3 structure. This change can be accomplished by Considering the diff usion of zinc from the ZnTe matrix to the surface to form the oxide an d evaporation of tellurium out of the surface, leaving behind a matrix with an altered stoichiometry. The HRTEM computer-simulated images fo r the proposed Zn2Te3 superstructure matched very well the experimenta l images. The 2x1 and 2x2 superstructures corresponded to the HRTEM im ages of the new Zn2Te3 structure viewed along its [211] and [100] dire ctions, respectively. (C) 1996 American Institute of physics,