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 $\left\{0001\right\}$ 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 ($a_{\mathrm{Zn}}\sim 2.72\AA$) compared with its bulk counterpart ($a_{\mathrm{Zn}}\sim 2.66\AA$), and exhibits an unreported relationship with ZnO: ${\left[0001\right]}_{\mathrm{Zn}}\parallel {\left[0001\right]}_{\mathrm{ZnO}},(01\overline{1}0{)}_{\mathrm{Zn}}\parallel (1\underline{25}\underline{\overline{26}}0{)}_{\mathrm{ZnO}}$. It is interesting to note that the enlarged value of $a_{\mathrm{Zn}}\sim 2.72\AA$ 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.

• Received 8 December 2017

DOI:https://doi.org/10.1103/PhysRevMaterials.2.060402