Raman scattering from irradiated nanocrystalline zinc oxide thin films: Perspective view on effects of energy loss, ion fluence, and ion flux

Raman scattering were used to study lattice damage in nanocrystalline zinc oxide (nc-ZnO) thin films implanted with 300 keV Ar and 1.2 MeV Xe ions at different ion fluences and ion fluxes. Raman spectra of all of the implanted samples show a broad Raman band at the lower Raman shift side along with A(1) (LO) phonon mode. The A(1) (LO) phonon modes get evolved with an increase in ion fluence with the reduction in the intensity of E-2 (high) mode which is the characteristic mode of the wurtzite phase of ZnO. The implanted films show broadening and softening of A(1) (LO) phonon mode upon an increase in ion fluences and observed to be more prominent in the case of 1.2 MeV Xe ions as compared to 300 keV Ar ions. The evolution of A(1) (LO) phonon mode and broadening of Raman band assigned to the damage induced in the system upon ion-implantation and correlated well with the damage profile, while the peak broadening and softening could be assigned to the stress-induced into the films due to implantation. Thus, for a better understanding, the Raman tensor of first-order optical Raman modes in back-scattering geometry is also presented in the manuscript.