مجله فیزیک کاربردی
سال هشتم شماره 1 (پیاپی 14، بهار و تابستان 1397)

In this paper, we have presented the absorption spectral the sample of Rodamine 6G dye in methanol with concentration of 0.1 g l-1 mixed with a solution of aggregated silver nanoparticles (with the concentration of 1.34 ×1012cm-3) using Xecl laser (wavelength 308 nm, pulse width 15 ns and 1Hz repetition rate) irradiation. We have demonstration that by irradiating the Xecl laser on the dye-Ag aggregate mixture can change the absorption spectra. In this study the effect of the pulse energy and the exposure time of the Xecl laser on the absorption spectra have been investigated. The experiments were carried out with pulse energies 220,342mj and the exposure times 5, 15 and 30min. It was shown that, irradiation of sample with 15 min exposure time and 220 mj pulse energy is the most optimal condition for increasing the absorption spectra. Our results can be helpful in the choice of active medium concentration of dye lasers.

By studying the polarizability of a spherical metallic nanoparticle on a dielectric substrate, the optical properties of the system is investigated. Since the size of nanoparticle is much smaller than the wavelength of the incident light, by solving the Laplace equation, the electric potential at different regions is expanded in terms of multipoles. By using the polarizability tensor, expressions for the parallel and normal polarizability are derived and then numerical results discussed. In addition to the impact of the size of plasmonic nanoparticle, by defining a geometrical parameter that called the truncation parameter, the impact of this parameter on the parallel and normal components of polarizability tensor is shown. It is demonstrated that the optical dispersion and absorption strongly depends on the particle size, the type of metal particle and the truncation parameter. The type of nanoparticle is gold and silver, because these noble metals have predominately been the materials of choice for plasmonic applications around the optical frequencies.

X-ray diffraction is a very practical and useful method for characterizing crystals, viruses, including influenza viruses, microscopic particles in biological sciences etc. So, X-ray diffraction is simulated and analyzed in the paper. The calculations are performed using the Green's function by written FORTRAN codes. Also, atoms in a crystal are proposed to be the same as circular apertures and diffraction patterns of square and triangular arrays are studied. In this approach the apertures represent the core of the crystal atoms, and the X-ray diffraction pattern is simulated by passing electromagnetic waves from these apertures. The results show that the general diffraction patterns are independent of the number of crystal atoms, so they can be used as a fingerprint to examine a variety of crystal structures. Also, the increase in the atoms sizes (atomic radius) leads to raise the intensity of the diffraction pattern. The increase in the crystal lattice constant reduces divergence and higher order diffraction patterns appear.

Nematic liquid crystals doped with magnetic nanoparticles, called ferronematics, are among the new colloidal suspensions with critical magnetic properties. Dispersing magnetic nanoparticles in a cholesteric liquid crystal medium also leads to the creation of the other phase of anisotropic magnetic fluids known as ferrrocholesteric. In fact, the ordering behavior and some features of these new materials are drastically influenced by the presence of magnetic nanodopants. The transition field and orientational ordering depend on the volume fraction and magnetic moment of the dispersed particles as well as the external and material parameters such as magnetic anisotriopy and the cell thickness of a liquid crystal cell. The investigation of these new anisotropic nanomaterials is very important not only from the theoretical point of views but also practical application in nanotechnology. In this work we consider a ferrocholesteric cell with homeotropic anchoring conditions on the cell walls and soft anchoring modes on the ferrpparticle surfaces. Then, we study the stability of the system and transition to a feronematic state caused by exposure to a laser beam and under applied magnetic and electric fields.

Tungsten nitride (WXN) thin films with crystalline structure were deposited by reactive Chemical Vapor Deposition (CVD) technique at different mixture of N2 and Ar mixture gases. Experimental data demonstrated that different N2 concentration in gas mixture, strongly affect microstructure, phase formation, grain size and texture morphology of the WXN films. According to XRD spectra, growth of tungsten nitride films promoted hexagonal WN phase for lower N2 concentration in gas mixture (N2=10%, N2=30% and N2=50%) and layers have non- homogenous morphology with rough surface. At higher N2 concentration (N2=80% and N2=100%) a phase transition was happened and two hexagonal WN and cubic W2N crystalline phases were observed. It seems that nitrogen concentration has strong effect on preferred growth orientation .The layers have smooth surfaces with low roughness. SEM micrographs for deposited films at lower nitrogen concentration in gas mixture, indicated a definite dense columnar nanostructure and non-columnar at higher nitrogen amount.

Effective interfacial energy and the real contact area for contact between a hard substrate and a rough elastic solid in the case that both rough surfaces are self-similar fractal are investigated using the Persson's theory of contact mechanics and its extension for two rough surfaces. In addition, the effect of different Hurst exponents on elastic solids and the presence of non-zero compressive stress about 11 GPa has been investigated in this paper. Our purpose in this study is to compare the difference and variations between adhesion and the effective contact area of the self-similar fractal surfaces with the self-affine fractal surfaces. By solving the equations and numerical calculations, it is determined that the observed effects on the self-affine fractal surfaces are also observed in this case, and effective interfacial energy, contact area and adhesion in a larger roughness amplitude than the self-affine fractal surfaces disappears and by applying non-zero compressive stress, the surfaces remain in contact, and increasing the roughness will not eliminate the contact surface.

Most problems in physics, mathematics and engineering, including fluid mechanics (fluid flow, heat transfer, etc.), plasma physics, laser, optics, and equations are intrinsically nonlinear. Most of these problems are shaped by ordinary differential equations. Except for a limited number of these equations that are rigorous in analytical solutions, most of these problems do not resolve accurately; they need to be solved by new methods based on coding based on software such as Mapp and Matlab. In recent years, a lot of research has been done to solve these types of equations, which has led to new methods for solving these equations. In this paper, using a new generalization for the form of solutions in the convergence method, we use the Miep software to describe the new soliton solutions for the Generalized Radhakrishnan, Kundu, Lakshmanan equation. One of the advantages of this method is the variety of solutions obtained, which includes the solutions of these equations with several different methods.