P. Mallick

Anomalous x-ray diffraction peak broadening and lattice strains in Zn1?xCoxO dilute magnetic semiconductors

Nanocrystalline powders of Zn(1-x)Co(x)O synthesized by the coprecipitation technique show anomalous anisotropic broadening for x>0.05. This peak broadening is shown to be not only due to a reduction in the particle size but also due to a significant strain contribution, as confirmed by Williamson-Hall analysis. The presence of grouped Co(2+) ions, revealing the presence of clusters of high spin Co(2+) with antiferromagnetically coupled spins, as indicated by magnetization studies, seems to be responsible for the strain.

UV-Vis studies of 800 keV Ar ion irradiated NiO thin films

Abstract We report the evolution of optical absorption properties of 800 keV Ar ion irradiated NiO thin films through UV-Vis characterization. Our results indicate the existence of both Mott-Hubbard (d → d transition) and charge-transfer (p → d transition) characteristic of NiO. The optical band gap of NiO increases from 3.58 to 3.75 eV when irradiated at the fluence of 5 × 1014 ions cm-2 but it does not show any remarkable variation upon 800 keV Ar ion irradiation at higher fluences. The refractive index and electron polarizability at different ion fluences have been determined from the optical band gap. Both refractive index and electron polarizability follow an opposite trend to that of the energy gap as a function of ion fluence.

Evolution of Crystallinity and Texturing on 120 MeV Au Ion Irradiation on NiO Thin Films

NiO thin films grown on Si(100) substrate by electron beam evaporation and sintered at 500 °C and 700 °C were irradiated with 120 MeV 197Au9+ ions. The FCC structure of the sintered films was retained up to the highest fluence (3 × l013 ions.cm−2) of irradiation. As against the expected amorphization due to ion irradiation when electronic energy loss exceeds certain threshold value, we observe an improvement of crystallinity and grain orientation at certain fluences of irradiation.