Effect of Plasma Irradiation on CdI2Cd I_2 films

The effect of plasma irradiation is studied systematically on a 4H polytype (002) oriented ${\rm CdI_2}$ stoichiometric film having compressive residual stress. Plasma irradiation was found to change the orientation to (110) of the film at certain moderate irradiation distances. A linear decrease in grain size and residual stress was observed with decreasing irradiation distance (or increasing ion energy) consistent with both structural and morphological observations. The direct optical energy gap ${\rm E_g}$ was found to increase linearly at the rate ${\rm 15\mu eV/atm}$ with the compressive stress. The combined data of present compressive stress and from earlier reported tensile stress show a consistent trend of ${\rm E_g}$ change with stress. The iodine-iodine distance in the unit cell could be responsible for the observed change in ${\rm E_g}$ with stress.Comment: 13 pages and 10 fi

Grain size dependent optical properties of CdI

The optical properties (refractive index and optical energy gap) were studied as a function of film thickness, substrate temperature and heat-treatment temperature for structurally, compositionally and morphologically well characterized CdI2 films grown by thermal evaporation. The variation of residual stress in the film (determined by X-ray diffraction), grain size (D), refractive index (n) and optical energy gap (Eg) was observed to be different in the above three cases. Combining the results of all three experiments, the grain size dependence of n and Eg was derived. Variation of n with grain size may be attributed to the changing packing density of crystallites with grain size and its distribution consistent with SEM results. Eg was found to decrease with D non-linearly and the data fits well with the equation of the type either $E_{\rm g}(D)=3.61-0.023D-0.0034D^2$ or $E_{\rm g}(D)=3.59-\frac{0.075 D^2}{(2+D)}\cdot$ The variation of Eg with D could be attributed as due to the defect densities in the film

Flux trapping in hafnium-doped Y-Ba-Cu-O ceramics: the microwave-loss-signal analysis

Studies of microwave absorption at low fields in zero-field-cooled (ZFC) and field-cooled (FC) samples of Hf-doped Y-Ba-Cu-O are presented. Flux trapping during the FC process is clearly demonstrated. Results show that the superconducting glass phase appears in ceramics for fields greater than or equal to Hm (where Hm is the field at which the signal is maximum), where the difference between ZFC and FC signals starts. The results can be explained quite satisfactorily in terms of a percolation description and the superconducting cluster model