مهدی اردیانیان

In this work, the structural, optical and photocatalytic properties of Cu1-3xNixZn2xFe2O4 ferrites prepared by citrate-nitrate method were investigated. The samples were characterized by X-ray diffraction (XRD) and UV-Vis spectrometer at room temperature. Examining the XRD patterns indicates the presence of a spinel structural phase transition from a tetragonal to cubic structure, which shows an increase in symmetry with the co-substitution of Ni and Zn in the copper ferrite. The bandgap values of the samples show a minimum value of 1.43 eV for x = 0.05. The highest catalytic activity of 95% in the degradation of methylene blue is obtained for the x = 0.05 sample due to its smaller energy gap.

In this research, semiconductor nanoparticles of Aluminum doped zinc oxide (AZO) were synthesized using zinc nitride as a precursor and ethylene-glicol as complexing agent  with Aluminum molar ratio of 0, 2, 4, 6, 8 and 10% by solvo-thermal method.  Crystal structure and surface morphology of the samples were studied by X-ray diffraction analysis (XRD), Field Effect Scanning Electron Microscopy (FESEM) and Tunneling Electron Microscopy (TEM). XRD Results describes the Hexagonal wurtzite structure of zinc oxide with preferred peaks corresponding to (100), (001), (101), (102), (110) and (103) planes. Also by increasing of Aluminum concentration, the preferred peaks shift to higher angles, hence lattice constants have a decreasing trend. While, nano-crystallite sizes have an increasing trend and the sizes were found between 17.5 to 25.2 nm. FESEM and TEM images show that increase of Aluminum concentration causes increase of the nanoparticles size. The optical band gap of the samples was found between 2.03 to 2.66 eV. By increasing Aluminum content from 0 to 4%, band gap decreases and then increases for higher concentrations from 4 to 10%. Investigation of the Acetone gas sensor properties for the sample of 4% impurity shows that maximum response time is for 2300 ppm density which is 60 s and the minimum is 42 s for 3600 ppm.

In this study, Zinc Oxide ZnO semiconductor nanoparticles were synthesized by solvo thermal method using Zinc nitrate as the precursor; the effect of different complexing agents as Urea, citric acid, ethylene glycol and ammonium fluoride on physical properties of nanoparticles was studied. Crystal structure and surface morphology of the samples were characterized by X-ray diffraction XRD and field emission scanning electron microscopy FESEM. Results of XRD patterns describe the preferred peaks corresponding 100, 002, 101, 102, 110 and 103 planes with hexagonal wurtzite structure of Zinc Oxide. Nano crystallite sizes were calculated in the range of 14 to 32 nm. FESEM images show uniform shapes of the samples. Absorbance curves based on UV-Vis spectroscopy describe a shift in absorption edge This shift could be attributed to change in Optical gap of the nanoparticles in the range of 2.13 to 2.95 eV. as a function of the kind of complexing agent.

Germanium nanostructures were generated in the post annealed germanium oxide thin films. Visible and near infrared photoluminescence bands were observed in the samples annealed at 350°C and 400°C, respectively. These different luminescence ranges are attributed to the presence of the defects in oxide matrix and quantum confinement effect in the germanium nanostructures, respectively. Decay time and temperature dependence of the luminescence for different bands were investigated, which confirmed our idea about the origin of the luminescence.

Amorphous GeOx/SiO2 multilayers (12 and SiO2 powders onto the Si substrates maintained at 100°C. Structural study by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared-absorption (FTIR) spectrometry, and transmission electron microscopy (TEM) was carried out. These techniques allowed us to follow the structural evolution, and phase decomposition due to annealing in the GeOx thin films and the multilayers annealed up to 900°C, and appearance of amorphous and crystallized germanium aggregates. For Ta≥ 400°C, the photoluminescence band around 1eV attributed to confinement effect in amorphous germanium aggregates was observed. Comparison of the luminescence in multilayer and GeOx thin film showed that in multilayer, although the control of the nanocrystals size isnt complete, the SiO2 barriers tend to enhance the intensity and reduce FWHM of the luminescence bands. This means that the confinement effect in the germanium aggregates in GeOx matrix is enhanced in multilayer system.