GaN is a semiconductor material with promising applications in display and laser devices. GaNbased thin films have been grown by various methods and intensively investigated. Additionally, GaN nano particles have been prepared by various different methods. in this paper, we report our new finding of the structural modulation of GaN nano crystals induced by electron beam irradiation within a transmission electron microscope (TEM). The origin of the modulation structure is due to the ordering of N vacancies in the GaN nano crystals.

The GaN nano crystals were prepared by d.c arc plasma method. A Philips CM200 TEM with a field emission gun (FEG) operating at 200KV was used in this study. The GaN nano crystals normally show hexagonal shape (see Fig.la). Corresponding electron diffraction pattern along [0001] axis indicates the Wurtzite structure (see Fig. lb). It was unexpected that satellite reflections gradually appeared in the diffraction pattern after the GaN nano crystal had been exposed to the electron beam (see Fig.lc-d).