New Research in Physics

Abstract Synthesis of nano scale materials with required size has been fascinating for many researchers and different methods have been developed for controlling the dimensions of particles during synthesis phase. In this paper, the role of ultrasonic irradiations on synthesis of zinc oxide nano particles and the consequent changes of their dimensions are investigated. Primary colloid of zinc oxide was produced using magnetic stirrer and then the colloid was exposed to ultrasonic probe irradiations. For a certain time called optimum time, exposure to ultrasound improves the output of the synthesized ZnO to double the value of the initially produced one. This increase in production of ZnO nano particles is measured by amount of absorption edge. Before and after the optimum time, mean radius of the produced nanoparticles are smaller than the primary one, and linearly reduces along with increasing the exposure time to ultrasound. Similar result is previously reported partially. These experimentation on ZnO show time rate of reaction of particle size depends on pulse time and intensity of the ultrasound exposed.

Abstract In this paper electronic structure, magnetic and optical properties of pure SnO₂ and Sn_1-xCo_xO₂ (x= 6.25%, 12.5%, 18.75% and 25%) samples and effect of Oxygen vacancies on those were investigated using density functional theory (DFT). Density of states and band structure curves show Co doping causes increase in energy surfaces near to the Fermi level. The results of this study showed the ground states of the 12.5% and 25% samples were ferromagnetic. The study of the effects of Oxygen vacancy on 12.5%Co doped- sample revealed that the introducing of vacancies causes increase in magnetic moment of the Co ions. The results were also showed that by increasing the Co concentration up to 12.5% the optical band gap decreases and then by more increasing of Co it increases. The intensity of the first peak in absorption curve increases and the intensity of the other peak above the 6eV decreases. The red shift of peak positions was also observed on absorption curves with increasing Co concentration to 12.5%.

Abstract SmBa₂Cu₃O_7-δ (SBCO) superconductor is synthesized through the solid state reaction method and also the alumina (γ-Al₂O₃) nanoparticles with the average size of 70 nm were made through the sol-gel self-combustion method and they were compared with the SIGMA Al₂O₃ nanoparticles. Then the SBCO superconductor was doped with different percentage of the alumina nanoparticles and its properties were studied and also the oxygen content of the samples was measured by iodometric titration. It was found that the oxygen content and critical temperature of the doped samples reduced. The study of resistivity versus temperature of the samples showed a semiconducting behavior in the normal state; i.e. by increasing the temperature, the resistivity decreased. The critical current density of 0.1 percent doped sample increased significantly, but it decreased by further doping. X-ray diffraction patterns of the doped samples showed that the alumina nanoparticles did not inter into the crystal structure of the superconductor. Also, a few peaks of the X-ray diffraction patterns of the doped samples were absent and the width of the peaks was broadened compared with the undoped sample. SEM images showed that the alumina nanoparticles spread on the surface of the grains and boundaries of the doped samples.

Abstract In this paper reflection index, absorption coefficient and optical constants of p-type silicon wafer with (100) orientation have been experimentally studied by using reflection spectrum from silicon surface. This wafer has been used as a substrate for fabrication of waveguide, so its optical properties have certain importance. In this paper, optical constants of Si wafer is calculated by using Kramers-Kronig method and reflection spectrum experimental data and then our results are compared with some references. The results have good agreement between optical constants of the references and reflection spectrum experimental data and calculated for existence sample in the Lab by using Kramers-Kronig method.

Abstract In this article, the electronic and structural properties of MgAl₂O₄ such as lattice constant, bulk modulus, compressibility, density; and optical propertieshave been investigated . Calculations were performed using the Full-Potential-Linearized Argument Plane Wave (FP-LAPW) method in the density functional theory framework by Wien2k code. Structural properties and band gap have been studied with different approximations. Compared to experimental results,the results of structural properties withGGA-WCapproximation and the results of band gap withLDA approximation have been better compatibility, therefor; the MBJ method along with two mentioned approximations has been used later. The effect of pressure on MgAl₂O₄ have been investigated withMBJ+GGA(WC)approximation. The optical properties such as dielectric function, refraction index, extinction coefficient and energyloss function have been studied. The obtained results from band structure shows that MgAl₂O₄is an insulator and the band gap is equal to 7.67 eV. Therefraction indexis equal to 1.55. The obtained results have been in good agreement with other theory and experimental results.

Abstract In this paper, heat reflecting nanometric multilayer of ZrO₂/Ag/ZrO₂ (ZAZ) for optimizing energy consumption has been designed. The optimum thickness of ZrO₂ and Ag layers was calculated by using the Film Wizard code. In optimized sample, ZrO₂and Ag films were deposited by RF sputtering and thermal evaporation technique, respectively. Electrical and optical properties of optimized ZAZ system such as sheet resistance, figure of merit, optical transmittance and reflectance were investigated and compared with the theoretical predictions. According to the results, there is well coincidence between them. The measured value for optical transmittance in visible region and optical reflectance in infrared region was found to be 93% and 90%, respectively. Also, the sheet resistance of ZAZ system was 13.1((□/Ω, which is suitable amount for this coating. The optical transmission and reflection of this coating demonstrate that this structure has good performance for optimization energy consumption in warm climate.

Abstract In this paper, we study the electronic conductance of armchair and zigzag graphene nanoribbons in the presence of a local magnetic field by using Green’s function technique at the nearest neighbor tight-binding approach. The results show that the existence of magnetic flux in an armchair nanoribbon causes that the intrinsic gap of the nanoribbon becomes smaller and two anti-resonances are created in the conductance spectrum. Whenever, all rings contain the uniform magnetic flux, a part of resonance region can be converted to a tunneling region which represent a new gap energy. Moreover, in a zigzag nanoribbon which is connected to two simple leads through the trans connection, some Fano resonances can exist at the conductance spectrum in the absence of magnetic flux.