Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 387, 15 November 2016, Pages 1–9
Himanshu Narayan, Department of Physics & Electronics, National University of Lesotho, Roma 180, Lesotho
Smita Survase, Thin Film Research Laboratory, Department of Physics, Birla College (Affiliated to University of Mumbai), Kalyan 421 304, India
Sulaniac, Madhavi Thakurdesai, Inter University Accelerator Centre, Aruna Asaf Ali Road, New Delhi 110 067, India
Swift Heavy Ion (SHI) irradiation is a unique technique for nanograin formation through grain fragmentation. Contrary to the generally reported SHI irradiation induced grain growth on CdTe thin films, we report fragmentation leading to nanograin formation.
Thermally evaporated polycrystalline CdTe thin films were irradiated with 100 MeV 197Au, 107Ag and 58Ni ions beams up to a fluence of 5 × 1012 ions/cm2. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) were carried out for surface analysis before and after irradiation. SEM micrographs indicate that the larger grains in the as-deposited films were fragmented into smaller grains due to irradiation.
The extent of fragmentation was found to increase with increasing electronic energy loss (Se). AFM pictures also supported the irradiation induced fragmentation. Structural characterization was done using X-ray Diffraction (XRD) technique. The ion induced strain and dislocation density were calculated from the XRD data.
Both the strain and dislocation density were found to increase with increasing Se. The observed grain fragmentation is explained on the basis of a combined effect of strain induced disintegration of grains after the Coulomb explosion, and an ‘incomplete’ re-crystallization of the molten thermal spikes. Moreover, the optical band gap Eg (1.5 eV for as-deposited film), determined from UV–vis spectroscopy, increased with Se, and possibly because of ion induced strain and defect annealing.