M. Rashad

CuO and Co 3 O 4 nanoparticles: synthesis, characterizations, and Raman spectroscopy

Copper oxide and cobalt oxide (CuO, Co3O4) nanocrystals (NCs) have been successfully prepared in a short time using microwave irradiation without any postannealing treatment. Both kinds of nanocrystals (NCs) have been prepared using copper nitrate and cobalt nitrate as the starting materials and distilled water as the solvent. The resulted powders of nanocrystals (NCs) were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) measurements. The obtained results confirm the presence of the both of oxides nanopowders produced during chemical precipitation using microwave irradiation. A strong emission under UV excitation is obtained from the prepared CuO and Co3O4 nanoparticles. The results show that the nanoparticles have high dispersion and narrow size distribution. The line scans of atomic force microscopy (AFM) images of the nanocrystals (NCs) sprayed on GaAs substrates confirmthe results of both X-ray diffraction and transmission electron microscopy. Furthermore, vibrational studies have been carried out using Raman spectroscopic technique. Specific Raman peaks have been observed in the CuO and Co3O4 nanostructures, and the full width at half maximum (FWHM) of the peaks indicates a small particle size of the nanocrystals.

Direct precipitation and characterization of ZnO nanoparticles

ZnO nanoparticles are prepared through hydrolysis and condensation of zinc acetate dihydrate by potassium hydroxide in alcoholic medium at low temperatures. Thermal gravimetric analysis (TGA) of the precursor is made in order to specify the temperature range over which the weight loss and thermal effect are significant. X-ray diffraction of the as-prepared specimens shows that the hexagonal (a = 3.2459 A, c = 5.1999 A) structure is the predominant crystallographic structure. According to Scherers formula, the average size of the nanoparticles is 22.4 ± 0.6 nm. The structural properties of the synthesized ZnO nanoparticles have been confirmed using the TEM micrographs. The optical energy gap of the ZnO nanoparticles, as obtained from applying Taucs equation, is equal to 3.52 eV, which is higher than that of the bulk material. Absorption peak of the as-prepared sample is 298nm which is highly blue shifted as compared to the bulk (360 nm). Large optical energy gap and highly blue shifted absorption edge confirm that the prepared ZnO nanoparticle exhibits strong quantum confinement effect.

Photo-induced changes in arsenic selenide films

The spectral dependence of the transmittance and reflectance of thermally-evaporated amorphous AsxSe100−x (where x = 20 and 40 at.%) films was measured in the wavelength range of 190–900 nm. A procedure was given for accurate determination of the film thickness using a standard method of numerical differences from the experimental data. The process of indirect electronic transitions was found to be responsible for the photon absorption. The variation of the energy band gap with the exposure time was investigated. Amorphous-crystalline transformations occurring as a result of photoexposure have been confirmed by the structural studies of the As20Se80 specimens using the scanning electron microscope and transmission electron microscope. Photodarkening relaxation under light exposure of the well annealed films was studied and the relaxation process has been described by the stretched exponential function (SEF).

Synthesis and characterization of some metal oxide nanocrystals by microwave irradiation

Copper oxide and cobalt oxide (CuO, Co3O4) nanocrystals (NCs) have been successfully prepared in a short time using microwave irradiation. The resulted powders of nanocrystals (NCs) were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thermogravimetric analysis (TGA) measurements are also studied. Fourier-transform infrared (FT-IR) and UV–visible absorption spectroscopy of both kind of nanoparticels are illustrated. Optical absorption analysis indicated the direct band gap for both kinds of nanocrystals.