Surface-dependent formation of Zn clusters in ZnO single crystals by electron irradiation

SF Jia and L Li and LL Zhao and H Zheng and PL Zhao and XX Guan and GJ Chen and JB Wu and SY Zhou and JB Wang, PHYSICAL REVIEW MATERIALS, 2, UNSP 060402 (2018).

DOI: 10.1103/PhysRevMaterials.2.060402

In sharp contrast to the well-documented irradiation-hardness property of ZnO, in situ transmission electron microscopy investigations reveal an unexpected nucleation and rotation of Zn clusters in single-crystal ZnO nanosheets (enclosed by the 0001 planes) subjected to the 200-keV electron beam irradiation. Detailed classical molecular dynamics simulations mirror the experimental findings and suggest that the nucleation of Zn clusters is dependent on the surface planes. More importantly, a Schottky barrier may form at the Zn/ZnO interface, whereas the Zn can act as an electron sink and thus may facilitate the p-type doping of the ZnO, consistent with the former experimental findings. In addition, the as-nucleated Zn cluster shows a transient hexagonal phase with an expansion in the a-b plane (a(Zn) similar to 2.72 angstrom) compared with its bulk counterpart (a(Zn) similar to 2.66 angstrom), and exhibits an unreported relationship with ZnO: 0001(Zn) parallel to 0001(ZnO), (01 (1) over bar0)(Zn) parallel to (1<(25<(26)over bar>)under bar>0)(ZnO). It is interesting to note that the enlarged value of a(Zn) similar to 2.72 angstrom has been predicted by the theoretical calculation N. Gaston et al., Phys. Rev. Lett. 100, 226404 (2008), while never reported in the experiments. Our results contribute to the basic understanding of point defects behavior in ZnO and shed light on controllable structural modification of Zn/ZnO heterostructures for industrial applications.

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