Softening of phonons by lattice defects and structural strain in heavy ion irradiated nanocrystalline zinc oxide films

Abstract

Origin of the Raman mode in nanocrystalline zinc oxide in the vicinity of A(1) (LO) phonon mode induced by energetic heavy ions is reported. The evolution of this mode in the irradiated films is ascribed to the effect of disorder and the high density of lattice defects induced by irradiation. The presence of such defects is confirmed by the reduction in the intensity of E(2) (high) mode and band bending of the near band edge absorption. A softening of the evolved Raman mode with increasing in ion fluence is also observed. This softening cannot be attributed to spatial confinement of phonons, as the sizes of the crystallites are large. Therefore, it is explained in terms of the combined effects of phonon localization by lattice defects and the structural strain in the lattice induced by electronic energy loss transferred by energetic heavy ions

Effect of swift heavy ion on structural and optical properties of highly transparent zinc oxide films

“…Value of c/a of ZnO is very close to the value of 1.633, which is the ideal value for an hcp structure [19,20]. This variation in crystallite size and lattice parameters are well reported by [8], and it is due to the stress created by defects in the lattice induced by SHI irradiation. The value of stress in the film is also calculated using the formula [21] r Pa ð Þ ¼ À233…”

“…Calculated values of stress are shown in Table 1. This change in nature of stress is originated from the lattice defects introduced by SHI irradiation [8]. As the irradiation fluence increases, the density of such lattice defects also increases which in turn enhances the stress value in system.…”

“…In last few years, ZnO has attracted research activities because of their potential applications such as transparent electronics [1], light-emitting diode [2], laser [3] and solar cell [3][4][5]. Annealing [6], doping [7] and irradiation [8,9] can modify the properties of ZnO thin film. But the irradiation with swift heavy ion (SHI) is unique technique that can modify the structural-optical and transport properties of materials [10][11][12][13].…”

Anomalous behavior of B1g mode in highly transparent anatase nano-crystalline Nb-doped Titanium Dioxide (NTO) thin films

“…13,[24][25][26] Moreover, the lattice defects and lattice strain also play an important role for softening, stiffening and broadening of Raman phonon modes. [27][28][29] Firstly, to understand our observations the phonon confinement model (PCM) is applied to study the stiffening and broadening of the most intense E g(1) mode. In the bulk, the phonon contribution comes from the center of the Brillouin zone (BZ) corresponding to wave vector, q = 0.…”

Pre and Post Effect of Swift Heavy Ion Irradiation on Infrared Spectral Evolution of Y₃₊<i>_x</i>Fe_5-<i>_x</i>O₁₂ (<i>x</i> = 0.0 - 1.0) System

“…Recent reports show that these techniques have been widely used for studying the irradiation induced effects on various class and different properties of materials [6][7][8]. Available reports indicate that various vibrational modes exhibit different sensitivity towards irradiation [9][10][11][12][13] but no discussion has been made on possible cause for such modifications [14].…”