Doh-Yeon Kim showed also that the ZnO grains of a characteristic angular shape and surrounded by a liquid phase at low temperature become spherical with the increase of temperature.14 The only difference between this description and our case is the liquid phase present whereas we have only gas surrounding the particles. Then the atomic diffusion will be slower than for Kim’s experiments but the final state of spherical particles is the same and corresponds to the thermodynamic stable state.