Fig. 6: Characteristics and role of quasi-liquid layer in dissociative evaporation of ZnO (0001).
From: Vacancy driven surface disorder catalyzes anisotropic evaporation of ZnO (0001) polar surface
a Ab initio MD simulation snapshots showing the disordering of Zn-deficient Zn1-xO (top three bilayers above the dash line). VZn were introduced to the top three Zn layers to make the composition the same as that of the quasi-liquid layer. Oxygen molecules (O2) desorbed from the surface are indicated. Detailed results of MD simulation are given in Supplementary Figs. 17, 18, Supplementary Movie 9. b RDF of each Zn and O bilayer of the simulated structure in a. The disordered quasi-liquid layer surface (red) shows a characteristic short range order of liquid state. The dash line differentiates the quasi-liquid (VZn) from the bulk region. c, Experimental (Exp.) EEL spectra of O-K edge (blue and red line) and calculated unoccupied oxygen density of states (DOS) from DFT (blue and red area). The quasi-liquid layer in both experimental EELS O-K and calculated unoccupied oxygen DOS shows additional peak at around 544 eV (black arrow), which does not exist in bulk ZnO. d Layer-by-layer DOS of each Zn and O bilayers. The quasi-liquid Zn1-xO layers (red) show a metallic character (dashed circles) whereas bulk ZnO layers (blue) show an insulating character. e Calculated desorption energy of Zn, O and O2 in ZnO and ZnO2 by DFT. The cubic and orthorhombic ZnO2 are represented as blue and red, respectively. Desorption energy of O in form of O2 molecule is reduced dramatically below 1 eV in the crystalline ZnO2 phases (Supplementary Figs. 20).
