Fig. 2: Anisotropic evaporation of ZnO observed by in-situ HRTEM.
From: Vacancy driven surface disorder catalyzes anisotropic evaporation of ZnO (0001) polar surface
a Outlines of the polar (0001), semi-polar \((10\bar{1}1)\), \((\bar{1}011)\) and non-polar \((10\bar{1}0)\) surface edges overlaid on HRTEM image tracing their movements during evaporation at 300 °C. The outlines of the edges traced in every 20 s for total 140 s are displayed in different colors. The quasi-liquid layer (highlighted in red) starts forming at ~100 s only on the (0001) surface. Referring to Supplementary Movie 2 for the corresponding real-time process. b Plot of the moving distance, d of four major surface orientations during evaporation as a function of time, t. The black arrow marks the time when a quasi-liquid layer starts forming on the (0001) surface and the moving rate increases steeply afterwards. Before the formation of quasi-liquid layer the (0001) surface moves linearly with t. After the quasi-liquid layer formed, the (0001) surface moves with t1/2 dependence, indicating that the evaporation is limited by a diffusion process. The error bars represent the standard deviation of data points along the direction in which they were averaged. c, d, HRTEM images of the (0001) and the \((000\bar{1})\) polar surfaces during evaporation, respectively. A quasi-liquid layer (highlighted in red) forms only on the (0001) surface but not on the \((000\bar{1})\) surface. All HRTEM images and movies are taken along the \([11\bar{2}0]\) zone axis.
