Rocksalt ZnO nanocrystal formation by beam irradiation of wurtzite ZnO in a transmission electron microscope

•Beam irradiation in a TEM of wurtzite ZnO produces rocksalt-ZnO nanocrystals.•The nanocrystal formation appears to occur by electron-beam-induced charging.•The result supports a possibility that there is a size effect for rocksalt ZnO.

Under ambient conditions, ZnO crystallizes in a hexagonal wurtzite structure, but undergoes a phase transformation into a rocksalt structure with increasing hydrostatic pressure. However, in the present study, I have successfully demonstrated that intense beam irradiation of a wurtzite ZnO specimen in a transmission electron microscope produces nanoparticles of rocksalt ZnO as well as wurtzite ZnO, suggesting that the application of pressures is not a necessary condition for the formation of rocksalt ZnO.