Structural and spectroscopic modifications of nanocrystalline zinc oxide films induced by swift heavy ions

Structural and spectroscopic modifications of nanocrystalline (nc) ZnO films induced by Swift heavy ion (SHI) irradiation is reported. Films were irradiated at incremented ion fluences. Structural study reveals that the nanocrystals become more oriented at low fluences, while a release of strain and decrease in grain size is observed at high fluence. The surface morphology study also shows a decrease in crystallite size and agglomeration of grains at high fluence. On the other hand micro-Raman and Fourier transform infrared (FTIR) results show that the longitudinal optical (LO) mode is strengthened and red shifted, while the transverse optical (TO) mode get dampened at high fluence. But the amorphization of crystallites was not observed under the used irradiation conditions. The observed structural and spectroscopic modifications are explained in terms of high density of lattice defects and disorder created by dense electronic excitations induced by SHI irradiation.