Tahmineh Jalali, Abdolrasoul Gharaati and Mohammad Rastegar
In this paper, employing of one-dimensional magnetophotonic crystals in infrared wavelengths range is considered. For this purpose, magnetophotonic multilayer structures, composed of magnetic defect layer surrounded by dielectric and MO Bragg mirrors, have been proposed. Ce:YIG with an optical thickness in the range of 0 to λs was used as a magnetic material. By using four by four transfer matrix method, the transmittance values and Faraday rotation (FR) angles of these structures were computed. The electric field distribution was obtained by Finite Element Method (FEM). By investigation of transmittance and FR angle of magnetophotonic crystals, it was possible to design the optimized structures with a rotation larger than 30 degrees and high transmittance. Such structures with a few micrometer thickness and fast magneto-optical (MO) responses have the potential to be used in MO devices like integrated photonic elements and sensors.
Nanostructures of copper (II) oxide were synthesized through chemical reduction of copper (II) sulfate pentahydrate using phytochemicals present in leaf extracts of Leucas aspera. The crystalline phases and size were assessed by X-ray diffraction data analysis. From the Bragg reflection peaks, existence of monoclinic end-centered phase of copper (II) oxide along with presence of cubic primitive phase of copper (I) oxide and traces of cubic face centered lattices of zero valent copper was revealed. The three Raman active modes corresponding to CuO phase were identified in the sample with permissible merging of characteristic bands due to nanostructuring and organic capping. The surface topography measurement using field emission scanning electron microscope evidenced the occurrence of cylindrical rod shaped morphological structures along with a number of unshaped aggregates in the sample. The effective crystallite size and lattice strain were estimated from Williamson-Hall analysis of Bragg reflection data. Tauc plot analysis of UV-Vis-NIR absorption data in direct transition mode provided an estimation of band gap, viz. 1.83 eV and 2.06 eV respectively, for copper (II) oxide and copper (I) oxide. Thermal degradation study using thermogravimetric curve analysis could reveal the amount of moisture content, volatile components as well as the polymer capping over nanorods present in the sample. It could be seen that upon heating, inorganic core crystals undergo oxidation process and at temperature above 464 °C, the sample was found to be composed solely of inorganic crystallite phase of copper (II) oxide.
Potassium iodide (KI) doped potassium hydrogen phthalate (KHP) single crystals were grown by slow evaporation technique using millipore water as a solvent. The grown single crystals were analyzed by powder X-ray diffraction and the analysis confirmed that KI-doped KHP crystallizes in orthorhombic system with space group Pca21. The functional groups were identified by FT-IR technique which showed slight shift in vibrational frequencies, indicating inclusion of dopant into the crystal lattice. The UV-Vis spectral studies revealed the optical transparency of the doped crystals in the entire visible region. The optical band gap values were estimated from Tauc plots. Kurtz-Perry powder test was employed for second harmonic generation efficiency studies of the grown crystals.
An organic single crystal of 4-chloroanilinium hydrogen (2R,3R)-tartrate monohydrate (4CAHT) was grown by slow evaporation solution growth technique at room temperature. Single crystal XRD study confirmed that the crystal belongs to monoclinic system with the space group P21. Powder XRD analysis confirmed the crystalline nature of the compound. The presence of various functional groups in the compound was revealed by FT-IR analysis. UV studies showed the absence of absorption in the entire visible region. To determine the thermal stability of the grown crystals it was subjected to thermogravimetric and differential thermal analyses. Microhardness and etching studies were also carried out for the crystal. The powder second harmonic generation efficiency of 4CAHT was tested by Kurtz and Perry powder technique and the relative SHG efficiency of 4CAHT was found to be 1.44 times greater than that of standard KDP.
A. Sadoun, S. Mansouri, M. Chellali, N. Lakhdar, A. Hima and Z. Benamara
In this work, we have presented a theoretical study of Au/Ni/GaN Schottky diode based on current-voltage (I-V) measurement for temperature range of 120 K to 400 K. The electrical parameters of Au/Ni/GaN, such as barrier height (Φb), ideality factor and series resistance have been calculated employing the conventional current-voltage (I-V), Cheung and Chattopadhyay method. Also, the variation of Gaussian distribution (P (Φb)) as a function of barrier height (Φb) has been studied. Therefore, the modified
relation has been extracted from (I-V) characteristics, where the values of ΦB0 and
have been found in different temperature ranges. The obtained results have been compared to the existing experimental data and a good agreement was found.
In this paper, Cd0.3Zn0.7S thin film has been electrodeposited from aqueous bath containing CdSO4, ZnSO4, Na2S2O3 and EDTA, having pH ~ 14. The structural, optical, morphological, surface wettability and photoluminescence properties of the film were investigated. The XRD pattern showed that the film consisted of mixed phases of CdS and ZnS with polycrystalline structure. The bandgap of the film was evaluated as 2.69 eV. The AFM study revealed that the Cd0.3Zn0.7S thin film contained spherical grains with root mean square roughness of 6.09 nm. The water contact angle measurement showed that the thin film was hydrophilic in nature. Moreover, the PL study revealed that the excitation wavelength was 460 nm.
The present work reports on the optimization of substrate temperature, molar concentration and volume of the solution of nickel oxide (NiO) thin films prepared by nebulizer spray pyrolysis (NSP) technique. NiO films were optimized and characterized by XRD, SEM, EDX, UV-Vis and I-V measurements. Based on XRD analysis, the molar concentration, volume of solution and substrate temperature of the prepared NiO films were optimized as 0.20 M, 5 mL and 450 °C for P-N diode applications. The XRD pattern of the optimized NiO film revealed cubic structure. The surface morphological variations and elemental composition were confirmed by SEM and EDX analysis. The optical properties were studied with UV-Vis spectrophotometer and the minimum band gap value was 3.67 eV for 450 °C substrate temperature. Using J-V characteristics, the diode parameters: ideality factor n and barrier height Φb values of p-NiO/N-Si diode prepared at optimum conditions, i.e. 450 °C, 0.2 M, 5 mL, were evaluated in dark and under illumination.
Copper oxide and cobalt oxide (Co3O4, CuO) nanocrystals (NCs) have been successfully prepared using microwave irradiation. The obtained powders of the nanocrystals (NCs) were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric (TGA) analysis and Fourier-transform infrared spectroscopy. The obtained results confirm the presence of both nanooxides which have been produced during chemical precipitation using microwave irradiation. TEM micrographs have shown that the obtained nanocrystals are characterized by high dispersion and narrow size distribution. The results of X-ray diffraction confirmed those obtained from the transmission electron microscope. Optical absorption analysis indicated the direct band gap for both kinds of the nanocrystals.
GaN thin films were deposited on p-Si(1 0 0) substrates using RF magnetron sputtering at various RF powers. Influence of RF power on morphological, optical and structural properties of GaN thin films were investigated and presented in detail. XRD results proved that the films were polycrystalline in structure with (1 0 0) and (1 1 0) planes of hexagonal GaN. It was found that increasing RF power led to deterioration of crystal structure of the films due to increased decomposition of GaN. Stress in GaN thin films was calculated from XRD measurements and the reasons for this stress were discussed. Furthermore, it was analyzed and interpreted whether the experimental measurement results support each other. E2 (high) optical phonon mode of hexagonal GaN was obtained from the analysis of Raman results. UV-Vis spectroscopy results showed that optical band gap of the films varied by changing RF power. The reasons of this variation were discussed. AFM study of the surfaces of the GaN thin films showed that some of them were grown in Stranski-Krastanov mode and others were grown in Frank-Van der Merwe mode. AFM measurements revealed almost homogeneous, nanostructured, low-roughness surface of the GaN thin films. SEM analysis evidenced agglomerations in some regions of surface of the films and their possible causes have been discussed. It has been inferred that morphological, optical, structural properties of GaN thin film can be changed by controlling RF power, making them a potential candidate for LED, solar cell, diode applications.
In the present study, nanocrystalline undoped and Fe (5 wt.%) doped ZnO powder has been synthesized by soft chemical route. The structural, nano/microstructural, vibrational and magnetic properties of these samples have been studied as a function of calcination temperature (400 °C to 1100 °C). X-ray diffraction analysis of Fe doped ZnO powder has shown the major nanocrystalline wurtzite (ZnO) phase and the minor cubic spinel-like secondary nanocrystalline phase at 700 °C. At calcination temperature of 700 °C, the magnetization and coercivity have been enhanced in Fe doped ZnO. As the calcination temperature increased to 1100 °C, the major phase of ZnO and minor cubic spinel-like secondary phase turned into bulk in doped ZnO. Interestingly, the reduced magnetization and zero coercivity have been observed in this case. These changes are attributed to the conversion of secondary nanocrystalline ferromagnetic spinel phase to its bulk paramagnetic phase. The degree of inversion i.e. the occupancy of both sites with different symmetry by ferric ions is proposed to be solely responsible for the unusual behavior.