مجله فیزیک کاربردی
سال نهم شماره 4 (پیاپی 19، زمستان 1398)

In this research, cadmium sulphide (CdS) nanoparticles were prepared by sol-gel chemical method. After reaching the appropriate synthesis method, the reaction time of these nanoparticles were studied.  Three samples were synthesized with different reaction times of 60, 100 and 140 minutes, and analyzed with X-ray diffraction (XRD). According to the results, the sample with the reaction time of 140 minutes was recognized as the best sample. These samples (with a reaction time of 140 min) are calcinated at temperatures 500, 600, 700 and 800˚C and their properties are compared. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) were used for characterization of the samples. SEM and XRD were used to investigate the morphology and crystal structures. X-ray diffraction results showed that the purity of cadmium sulfide nanoparticles and their crystallinity and the size of crystallites were increased with increasing calcination temperature and stronger scattering pattern peaks, which was predictable. The structure of nanoparticles was also hexagonal. The SEM images depicted the spherical shape of nanoparticles. It also measured the average size of nanoparticles about 67nm, which was increased with increasing temperature. The EDS results also showed the atomic percentage and the weight percentage correctly.

Second harmonic generation of Nd:YAG laser, as one of the most applicable and popular solid-state lasers, has been widely used in different fields of military applications and in diverse fields of medicine and industry etc., in last few decades. Non-linear crystals are mentioned as one of the most efficient and common methods for harmonic generating of lasers. In this research, we performed the simulation of the second and fourth harmonic generation of pulsed Nd:YAG laser with characteristics of 1064nm wavelength, 1joule/cm2 energy density, and 10ns pulse width, and considering the effects of temperature and divergence angle of the incident beam. The conversion efficiency of the second harmonic generation of this laser was investigated using KTP, BBO and LBO crystals. The simulation results suggested the KTP crystal as the most efficient crystal with 89.59% conversion efficiency. Formerly, achieving 80% efficiency using Nd: YAG laser with similar characteristics of the simulated specifications presented in this paper by using KTP crystal in an experimental configuration had been presented. In addition, the conversion efficiency of the fourth harmonic generation of this laser was investigated using BBO, CLBO and DKDP crystals. The simulation results suggested the BBO crystal as the most efficient crystal with 19.21% conversion efficiency. For the sake of comparison, 12% efficiency in the experimental layout with similar Nd:YAG laser specifications, presented in this article, had been presented in another article.

plasma Torch is widely used in industry and it is very important for determination of the properties of plasma formed in it. Accurate determination of the plasma properties, such as its velocity and temperature profiles, can greatly help to improve plasma torch structure for use for future purposes. Since, experimental testing of plasma properties is very costly and time consuming, simulation of the plasma is utilized. In this paper, the three-dimensional, time-dependent, and non- equilibrium model of plasma torch is simulated and properties of the plasma are investigated. Comparison with the results of similar works shows that the model works well. The effect of change in inlet gas velocity on plasma has also been studied. The results show that with increasing gas velocity at the inlet, the plasma velocity increases, while its temperature decreases. Changing the velocity of the inlet gas also causes the deviation from the thermodynamic equilibrium near the walls.

Optical properties of the yttrium oxide, such as the dielectric function, refractive index and electron energy loss spectroscopy (EELS), are studied. Calculations are done by full-potential augmented plane waves (FP-LAPW) in density functional theory (DFT) framework by Wien2k package. According to EELS curve, the plasmon energy is estimated about 13eV. The obtained static refractive index is 1.92. In addition, optical conductivity diagrams show that due to the band gap at 4 eV, it is not able to excite the conduction band. The results are in good agreement with that of other theoretical and experimental works.

In this study, within the tight-binding Hamiltonian model, the Green’s function approach, and the Kubo formula, the density of states and the electrical conductivity (EC) of armchair carbon and boron nitride (BN) nanotubes with different diameters are investigated and the results are compared with graphene and BN monolayers. The results show that, contrary tographene, which is a semimetal, armchair carbon nanotubes of any diameter are conductors, while armchair BN nanotubes similar to a BN monolayer are all semiconductors. Also, since it is a semimetal, the EC of graphene is observed to be higher than BN monolayer at all temperatures. In addition, it can be seen that the ECs of both types of nanotubes decrease with increasing diameter and approaches the EC of graphene and BN monolayer becausethe increase in the cross sectionsize provides more lateral ways for electrons to move in transverse directions with respect to the longitudinal axis, and this in turn reduces their mobility along that longitudinal axis. It is also observed that by increasing the diameter, the behaviors of carbon and boron nitride nanotubes respectively approach those of graphene and boron nitride plane.

A cylindrical PA cell is designed and constructed; also the Q factor, thermal and viscous loss depths and resonance frequencies are calculated for each buffer gas. The NO2 sample gas and Ar buffer are inserted to the cell and minimum concentration is detected 47.5 ppm at 700 mbar. In this experiment the cell is illuminated with a chopped CW CO2 laser beam. Then the buffer gas is replaced by N2 in the same pressure and minimum detectable concentration is obtained to be 62.2 ppm. The output of another CW Nd:YAG laser after passing through the chopper illuminates the cell in the same experimental condition giving 32.8 and 16.2 ppm minimum detectable concentration for Ar and N2 buffers, respectively. For these four experiments, the magnitude of PA signals are plotted against pressure and it is shown that the slope of the graph when using Nd:YAG laser and N2 buffer gas is approximately 2 times greater than the others.