مجله فیزیک کاربردی
سال دوازدهم شماره 1 (پیاپی 28، بهار 1401)

In this paper, structural properties such as structure parameters, energy band structure, the density of state, and charge density of LaGaO3 are calculated from the cubic phase. The calculations have been performed using the pseudopotential and a plane wave method in the framework of density functional theory (DFT) with generalized gradient approximation (GGA) by the Quantum Espresso package. The results are in good agreement with the results of others.

In this study, the photonic band structure of two-dimensional photonic crystals with square and honeycomb lattices consisting of air holes in the Kerr nonlinear material background has been investigated. We assumed that the holes with different geometrical shapes are filled with plasma. The numerical results based on the finite difference time method show that most of the designed structures represent a complete photonic bandgap with noticeable width at optimum values of structural parameters for low-intensity incident waves, in which the width can be changed through varying the incident light intensity. The calculations show that when the shape of the plasma-filled holes is the same as the shape of the unit cell of the structures, the most change in the total photonic bandgap is visible in the frequency range as  the light intensity of the incident light changes. Furthermore, the maximum width of the photonic gap in these structures was reached , which has increased approximately  in comparison with similar previously studied structures. The obtained result can be used for designing tunable optical devices.

The purpose of this paper is an optimization of high reflection mirrors in the infrared wavelength. Infrared mirrors, in addition to being one of the main components of carbon dioxide lasers, are widely used in the flexible optical path or beam conduction. In the structure of these high reflection infrared mirrors, metal, dielectric and quasi-metal are used as Glass / Metal / Dielectric / Quasi metal / Air. Separately the design of the high reflection mirror was investigated for each of the metals, dielectric and quasi-metal layers with different materials. In each step, the best type of material is selected based on the highest percentage of reflection. These layers are Silver (with a reflection of 99.87% in the structure of Glass / Metal / Air), magnesium fluoride (with a reflection of 98.31% in the structure of Glass / Ag / MgF 2/ Air), and Germanium (with a reflection of 99.88% in Structure Glass / Ag / MgF 2 / Ge / Air) for metal, dielectric and quasi-metal, respectively. Then, by changing the thickness of each layer, the optimal thicknesses for silver, magnesium fluoride, and germanium were determined to be 100, 550, and 200 nm, respectively. Examining the effect of angles of light incidence, it was observed that the highest average reflection is related to the angle of zero and 99.88%. The coating designs were done by McLeod coating software.

In this paper, we are going to study the fluid around nanoparticles and their hydrodynamic size, completely. First, we obtain the complete set of relations of the velocity equations and the velocity vector field around a spherical nanoparticle. For this, we use Stokes' analytical method with boundary conditions. Using the velocity vector field equations, we obtain the stress tensor components on the sphere surface and the fluid resistance force on the nanoparticle. In the next step, we consider the hydrodynamic diameter of the particle to be the diameter at which the fluid no longer moves effectively with the particle, and we obtain a description for this quantity from the equations of velocity. We will examine and find a significant correlation between these values. In the experimental part, gold nanoparticles with a diameter of 12 nm are synthesized and characterized by the Turkevich method. The diameter and hydrodynamic diameter of particles are measured using an electron microscope (TEM) and dynamic light scattering (DLS). By numerical fitting the Fortran 90 programming code and using experimental data, we were able to estimate the relative velocity of the particles relative to the fluid. These studies can be a useful method for the experimental and theoretical study of resistance force and dispersion of nanoparticles in colloidal media and have many applications in experimental applications of nano colloids such as nanoparticle drug delivery.

This research focuses on the effect of cadmium doping on the crystal lattice of the tin oxide (IV) nanofibrous layer. This nanofibrous layer was prepared using the electrospinning method which had no beads and had a circular cross-section. The effects of cadmium doping of these nanofibers on the crystal lattice were studied using X-ray diffraction patterns. The values of tin oxide (IV) lattice parameters and in turn, the unit cells volume and its density increased very little. This change can be related to the entry of cadmium into the crystal structure of tin oxide (IV). However, doping with cadmium had no effect on unit cell angles and the same tetragonal structure was preserved. It should be noted that the peaks shifted slightly toward larger angles which were attributed to the formation of voids at the location of anions (oxygen).

In this paper, the titanium dioxide thin films were electrodeposited on the aluminum substrate. In electrodeposition, a pure or alloy material is deposited on a conductive or a semiconductor substrate from a solution by the passage of an electric current via two or three electrodes. The structure of TiO2 thin film with 1000 nm thickness was studied by X-ray diffraction. The crystallite size of the thin film was obtained about 41 nm via Debye– Scherrer equation. Also, the crystallite size and strain of lattice calculated by Williamson– Hall equation were about 46 nm and 0.004, respectively. The film surface roughness was investigated using an atomic force microscope (AFM). The logarithmic plots of roughness as a function of scan length for titanium dioxide films indicate that the film roughness increases as the film thickness increases. The electrodeposited TiO2 films exhibit anomalous scaling roughness behavior on the film thickness. The photocatalyst properties of TiO2 thin films were investigated via photodegradation of two azo dyes, acid blue and acid black, under ultraviolet irradiation. The absorbance spectra indicated that the titanium dioxide thin film with 1000 nm thickness degradation 94 % both acid blue and acid black in 60 min. Also, the increasing film thickness increased degradation at the same time.