Ultraviolet-Light-Induced Bactericidal Mechanism on ZnO Single Crystal --Supplementary Material

The judgment of Zn plane and O plane of ZnO single crystal The ZnO wafers with size of 5×5×1mm and the resistance in MΩ•cm grade were purchased from HeFei KeJing Materials Technology Co., LTD, China. ZnO is a polar crystal belonging to hexagonal crystal system, and c-axis is the polar axis. The face of +c is terminated with Zn atoms, and –c is terminated with O atoms. A conventional way to define the O or Zn plane is via surface etching treatment. As to ZnO grown from hydrothermal method, the hexagonal pyramid-like etch pits could be observed in Zn plane, while the hillock-like etch pits could densely distribute on the O plane [1]. The purchased ZnO wafers were polished and rinsed by ethanol and acetone respectively for 20min, then etched by diluted HCl solution. Fig.S1 illustrates the microscopy images of ZnO crystal etched in the diluted HCl solution. The plane with hexagonal etch pits is defined as Zn plane, and the other plane is O plane.