Defect engineering for enhanced optical and photocatalytic properties of ZnS nanoparticles synthesized by hydrothermal method.

Defect engineering is a promising method for improving light harvesting in photocatalytic materials like Zinc sulphide (ZnS). By altering the S/Zn molar ratio during hydrothermal processes, Zn and S defects are successfully introduced into the ZnS crystal. The band structures can be modified by adding defects to the crystal structure of ZnS samples. During the treatment process, defects are formed on the surface. XRD and Raman studies are used for the confirmation of the crystallinity and phase formation of the samples. Using an X-ray peak pattern assessment based on the Debye Scherer model, the Williamson-Hall model, and the size strain plot, it was possible to study the influence of crystal defect on the structural characteristics of ZnS nanoparticles. The band gap (Eg) values were estimated using UV-Vis diffuse spectroscopy (UV-Vis DRS) and found that the Eg is reduced from 3.28 to 3.49 eV by altering the S/Zn molar ratio. Photoluminescence study (PL) shows these ZnS nanoparticles emit violet and blue radiations. In keeping with the results of XRD, TEM demonstrated the nanoscale of the prepared samples and exhibited a small agglomeration of homogenous nanoparticles. Scanning electron microscopy (SEM) was used to examine the surface morphology of the ZnS particles. Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and X-ray photoelectron spectroscopy (XPS) were used to evaluate and validate the elemental composition. XPS results indicate the presence of defects on the prepared ZnS nanoparticles. For the investigation of vacancy-dependent catalytic activity under exposure to visible light, defective ZnS with different quantities of Zn and S voids are used as catalysts. The lowest S/Zn sample, ZnS0.67 and the highest S/Zn sample, ZnS3, show superior photocatalytic activity.

Growth of InN nanocrystalline films by activated reactive evaporation.

InN films are grown on silicon and glass substrates by radio frequency (rf) activated reactive evaporation. High purity indium (99.99) is evaporated by resistive heating in the presence of nitrogen plasma. X-ray diffraction shows that the film deposited at low rf plasma powers (< or =100 W) are indium rich and further increase in the rf power formation of InN take place. The average crystallite size was found varying from 8 nm to 20 nm as the power increases from 200 to 400 W. The diffraction pattern shows the polycrystalline nature of InN films. The band gap obtained from the transmission spectra show an increase in the band gap with the increase in rf power which can be attributed to variation of nitrogen: indium stoichiometry. The Raman spectra shows wurtzite nature of the film and the photoluminescence measurements show a weak peak around 1.81 eV for the film grown at 400 W. Plasma diagnostics has been carried out in order to understand the role of active species in the process. The large shift in the band gap is attributed to Moss-Burstein shift and presence of residual oxygen in the film.