مجله پژوهش فیزیک ایران
سال بیست و دوم شماره 1 (بهار 1401)

In the first part of the present article, the important and main methods of photolithography are reviewed and discussed. Then we introduce the ways to improve the images created on the photoresist, which is the main material of lithography. Lithography with high-energy particle and soft lithography are then described. In the second part, the contact-photolithography method and its improvement process, which we use in our laboratory, are introduced and described in detail. We used this method for lithography to make diffraction optical elements on a glass substrate, doped by silver nanoparticles, using a helium ion beam. Light diffraction from the created lithography masks prevents access to very small images. To reduce the diffraction influence on the quality of the produced elements, we adapted and optimized the contact-lithography method for our project. Our solution, presented in this article, is practical and available for other researchers in Iran

In this paper, the NixMg1-x O (0.1 ≤ x ≤ 0.4) solid solution nano-powder was synthesized by new and soft non-alkoxide sol-gel self-combustion method. In this method, Ni(NO3)3·6H2O, Mg(CH3COO)2·4H2O and Citric acid (CA), were used as Ni2+, Mg2+ ion and gelling and combusting source, respectively. Then, by thermal gravimetric analysis (TGA) the chemical reaction and the appropriate temperature to form a stable compound were determined. The influences of molar ratio of component (x) on structural and optical properties of samples have been investigated by X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and Fourier transform infrared (FTIR) analysis. By increasing in x, all the samples are shown decreasing ecreasing in lattice parameter (a) and crystallite size (D), which indicates the contamination of magnesium oxide with nickel and the formation of NixMg1-xO solid solution. The Band gap was decreased by increasing in x which shows that Ni2+ ions in MgO structure causes some modifications in the energy levels and the optical absorbance characteristics associated with F centers due to oxygen defect centers.

In this paper we obtain the conservation equations of momentum-energy of a relativistic fluid in the flat space-time. Three mechanisms for energy and momentum transferring are considered, which are: perfect fluid, stress viscosity and heat transfer mechanisms. The effect of magnetic field is ignored in this paper. Also, the connection of relativistic and non-relativistic equations are seen in this paper, so, the non-relativistic equations can be modified with the relativistic influences. The method of deriving energy and momentum conservation equations and connection of relativistic and non-relativistic conservation equations of this paper, is available to use for a variety of energy and momentum transfer mechanisms, also, applicable to all metrics.

In this work, the photoluminescence emission properties of CH3NH3PbBr3 perovskite crystals which encapsulated among the porous thin films of aluminum oxide are studied. These porous layers are made by electrochemical anodizing method. First, aluminum thin film has been deposited by magnetron sputtering deposition method and then by changing anodic voltage, different patterns of porous aluminum oxide films are fabricated. Finally, CH3NH3PbBr3 nanocrystals are synthesized on the Al2O3 porous thin film by one step spin coating method. Morphological studies of porousaluminum oxide thin films are investigated by field emission scanning electron microscopy images and Atomic Force Microscope results. In order to study optical response of  CH3NH3PbBr3 erovskite pto structural characteristics of  porousthin films, photoluminescence spectroscopy has been employed too. By structural characterization, it is found that the number and the average diameter of the nano-pores are increased by anodic voltage raising. Also, the dependence of the emission properties of the encapsulated crystals on the size of the pores has been determined by the photoluminescence spectroscopy. So that, blue-shifted photoluminescence emission has been observed by the pores diameter reduction. Eventually, by comparing the results of structural and optical characterizations with Bruce model, the fabrication of  CH3NH3PbBr3 perovskite nanocrystals within the patterned aluminum oxide mold is confirmed.

In this paper, using Arnowitt-Deser-Misner (ADM) decomposition formalism, we first obtain a neutral black hole solution for consistent $D\to 4$ Gauss-Bonnet gravity. Then, we study its thermodynamic properties near the critical point by employing new formalism of thermodynamic geometry (NTG). More precisely, critical exponents of the number density difference $\Delta n$, the isothermal compressibility ${{\kappa }_{T}}{{P}_{c}}$, the normalized intrinsic and the normalized extrinsic ${{K}_{N}}$ curvatures are calculated near the critical point for the small/large black holes phase. Our findings show that the critical amplitude of the normalized thermodynamic curvatures are independent of the Gauss-Bonnet coupling values that indicates their universal feature.

Cadmium telluride (CdTe) nanoparticles were deposited on glass substrates coated by indium tin oxide (ITO) and fluorine doped tin oxide (FTO) as transparent conducting films at 200 °C under pressure of 2×10-5 mbar. The thickness of the prepared films prepared was about 200 nm. The structure, optical, electrical, and morphological properties of the layers were analyzed by x-ray diffraction (XRD), ultraviolet-visible (UV-Vis) spectroscopy, current-voltage (IV) characterization, and scanning electron microscopy (SEM), respectively. XRD patterns show the cubic structure of the deposited CdTe thin film on both ITO and FTO substrates. The preferred orientation of deposited films also changed from (111) for ITO substrate to (220) for FTO substrate. The crystallite size of films on ITO and FTO in these orientations were about 23.41 and 34.84 nm, respectively. The thin-film transmittance spectra were determined using UV-Vis spectroscopy in the wavelength range of 200-1200 nm. The optical energy bandgap of thin films on ITO and FTO substrates was calculated to be 1.60 and 1.63 eV, respectively. The I-V curve shows more electrical conductivity of the CdTe thin film on the FTO compared to the ITO. The surface morphology images show homogeneity and uniformity of the surface.

In this research, the coupling of surface plasmon-polariton and surface exciton-polariton in a multilayer structure of metallic medium and columnar dielectric thin film with excitonic spacer in Kretschmann configuration theoretically is investigated; using transfer matrix method. The effect of structural parameters such as the length of columns of columnar thin film and the rise angle of them, the refractive index of prism, the void fractions of columnar thin film and the thickness of excitonic medium on coupling are studied. The results showed that the coupling becomes strength by decreasing the length of columns of dialectic medium and refractive index of prism. Also, by reducing the volume fraction of air in columnar thin film, the coupling becomes stronger as the thickness of the excitonic medium increases and the ultra- strong coupling was obtained at fv=0.2. The energy spectrum of plexciton branches in terms of detuning frequency indicates the anti-crossover behavior of plexciton modes, which includes the coupling strength of the modes from the medium to ultra-strong region.

In this research, the effect of exposure time on the phenomenon of multicolor photochromism in silver-silver chloride thin film has been investigated. The effect of multicolor photochromism in the silver-silver chloride layer is created by continuous-beam laser radiation in a short time. Irradiating the subwavelength silver-silver chloride layer by monochromatic and linear polarized laser beam in the visible light region, creates multicolor photochromism phenomenon and induced anisotropy simultaneously. Anisotropy in these layers is due to the alignment of silver nanoparticles along the polarization of light; whereas multicolor photochromism due to the resizing of silver nanoparticles is proportional to the wavelength of the incident light. An interesting phenomenon in silver-silver chloride thin films is the possibility of removing both effects by ultraviolet radiation. Also, in this study, we showed that although the phenomenon of multicolor photochromism is caused by laser writing in a short time, the complete removal of this effect by irradiation of ultraviolet light is not instantaneous and is done over time. Therefore, the use of silver-silver chloride thin films is not only useful for multiple color printing, it also has the potential to be used for dosimetry of ultraviolet light.

In this study, we have investigated the form of velocity and pressure functions of a fluid oscillating between two parallel glass sheets that form a circular Hele-Shaw cell. The flow has been considered to be radial, incompressible and laminar. The time-dependent Navier-Stokes equation has been solved in cylindrical coordinates using Fourier transform, and the oscillating flow velocity across the thickness of the cell has been obtained at different times.  The flow velocity function in the unsteady state is related to the vertical component of the coordinates in the form of parabolic functions and also to the inverse of the radial component. The time dependence appears as a simple harmonic with a frequency equal to the oscillation frequency. The velocity of the flow is maximum at the middle of the cell along its height and gradually decreases from the middle towards the top or bottom plane and reaches zero. Pressure does not depend on the height and changes logarithmically with the radius. The dependence of pressure on time is also a simple harmonic with the external frequency, but it has a phase shift with respect to the velocity.

The one-dimensional quantum Ising model is used to describe many physical systems, therefore the calculation of ground and excited state energies of Ising model that has many applications in statistical mechanics, has been paid attention.  We obtain the ground and excited states of this model by using the Quantum Approximate Optimization Algorithm(QAOA), which is a kind of hybrid quantum-classical algorithms. For this purpose, first, we find the ground state with quantum approximate optimization algorithm, then we generalize this algorithm by adding an overlap term to obtain excited states. We calculated ground state energy and excited states energies for different coupling coefficients which is compatible with exact calculation.

In this research, the CoZn alloy nanowire arrays were deposited in a porous aluminum oxide template by alternative current pulse electrodeposition. The aluminum oxide template was fabricated through two-step soft anodization of pure aluminum foils and its morphology was determined using a scanning electron microscope.In order to systematically study the constructed sample, non-destructive ion beam analysis techniques were used. Among these methods, Rutherford backscattering spectrum analysis was performed by interaction of proton ions with energy of 2000 keV and 2500 keV and helium ions with energy of 2500 keV with the sample. Analysis of the RBS spectrum of the sample along with simulations performed by SIMNRA code made it possible to determine the concentration, depth profile of the elements in the sample, and determination of stoichiometry of the alumina template at different depths. The best results are related to a proton with energy 2500 keV, which reported the depth of 10 to 14 μm for CoZn alloy nanowire. Also, for validation of the results, FE-SEM images were prepared from the sample, which confirms the agreement with the results obtained from the RBS method.

We study the entanglement of purification in a field theory with momentum relaxation using gauge/gravity duality. The dual geometry is an asymptotically AdS spacetime which is a solution to Einestein-Hilbert action coupled to axionic fields. Our study show that the critical separation for the transition of entanglement of purification decreases as we increase the dissipation parameter, hence the total correlation between the subsystems decreases.

Knowledge of distribution and emission pattern of natural and artificial radioactive elements and their radiation level in the environment is very important to assess its effects on human health and living organisms. In this study, the specific activity of natural and artificial radioactive elements for 30 soil and sediment samples collected from upstream and the outlet of Qarasu River to Gorgan Bay as well as sediments in the eastern part of Gorgan Bay were measured using High-Purity Germanium detector and their distribution map with using SURFER and GIS software was drawn. Specific activity of 226Ra, 232Th, 40K and 137Cs was obtained from 8.80 to 31.92, from 11.16 to 43.19, from 183.77 to 562.88 and from 0.83 to 12.72 in Bq/kg respectively.  Upstream of the Qarasu River, the average concentration of 226Ra, 232Th, 40K and 137Cs in the soil samples beside the Qarasu River was higher than the sediments of the river, which indicates the washing of sediments and the transport of radioactive elements by water flow and transfer of these elements to lower areas. In Qarasu estuary and Gorgan Bay, 232Th and 40K distribution patterns are almost similar and the highest concentrations of 226Ra, 232Th and 40K elements are related to Qarasu estuary sediments. The concentration of 137Cs in the mouth of Qarasu River has the lowest value and increases with its distance from the mouth to the middle parts of Gorgan Bay, which indicates a high mobility and a tendency to sediment in calmer places for 137Cs. The measured values for radiological parameters and risk indices due to nuclear radiation in this study are within the allowable range and the amount of available nuclear radiation does not threaten the health of the inhabitants of the region‎‎‎.‎

Atomic spectral line filter is a narrow band pass optical filter which has many applications in quantum and laser systems. By engineering the system parameters like gas temperature and intensity of magnetic field, the filter with desired characteristics could be obtained. In this work, an atomic spectral line filter for Cesium D1 line (894.6nm) is implemented and characterized. The effect of system parameters on the filter transmission and its bandwidth is investigated. It is observed that by applying a magnetic field of 390 Gauss and adjusting the gas cell temperature on 40°C, a single peak filter with maximum filter transmission and FWHM of 0.24 GHz could be obtained.

One of the most powerful and popular quantum entanglement-based computation methods for the simulation of one-dimensional and quasi-two-dimensional strongly correlated materials is the Density Matrix Renormalization Group (DMRG) technique. A lower quantum entanglement between the system’s degrees of freedom will result in a higher accuracy of the method. However, quantum entanglement between two complementary subsystems of a closed system depends on how the degrees of freedom have been distributed between them, and therefore, it is not in general invariant under arbitrary unitary transformations. Entanglement is invariant only under those unitary transformations which do not mix the degrees of freedom associated with the two subsystems. Consequently, a fundamental question is that if it is possible to construct, algorithmically, unitary transformations which minimize entanglement between degrees of freedom of the system and therefore maximize the DMRG technique? A general solution to this problem is highly nontrivial in general. In this paper, we study interacting fermionic models and by considering single-particle unitary transformations only. We define a novel and efficient method to find the optimal single-particle unitary transformations. In this framework, we show that using our algorithm, the accuracy of the DMRG method at a given bond dimension is increased and the ground-state energy is decreased and approaches to its exact value. Our method paves the way toward finding more general (many-particle) optimized unitary transformations and helps us to better understand the behavior of fermions in strongly correlated materials.

In this paper, by using of laser induced breakdown spectroscopy (LIBS) method, the elemental concentrations existed in standard aluminum alloys are measured quantitatively. Pulse laser of Nd:YAG at 1064 nm is irradiated on Al standard samples and analysis is performed by created plasma. Among different methods for estimation of concentration of existed elements in aluminum samples, artificial neural network (ANN), Support vector regression, autoregressive integrated moving average model (ARIMA), kernelized support vector regression (KSVR) and combined method of KSVR-ARIMA are utilized for prediction of element concentrations of Fe, Cu, Zn, Mg, Mn, and Si and obtained results from these methods are compared together. The extracted results show that the combined method of KSVR-ARIMA reports the best prediction values by the least error for the most of the elements.

The aim of this paper is to investigate dynamical properties of a harmonic oscillator coupled to a non-equilibrium bath without the rotating wave approximation. At first, we investigate the theory of this model and obtain the Heisenberg equations of motion for the oscillator and bath annihilation operators in the absence and in the presence of a rotating wave approximation. Then, we obtain the fluctuation and fluctuation-dissipation relations in the absence and in the presence of a rotating wave approximation for the non-equilibrium bath annihilation operator, respectively. After that, we study the decay of system modes using the Wigner-Weisskopf approximation. Finally, we calculate the time-dependent spectrum of a cavity field mode coupled to a non-equilibrium reservoir. We show that even under the condition in which the RWA is considered to be valid (weak interaction), there are significant effects of virtual-photon field on the diffusion coefficient, the energy density, line width and the shift frequency.

Guides play a key role in concentrating the neutron beam and increasing the flux for a neutron guide system. In this research, the role of a radius of curvature and length parameters on neutron intensity on the sample for the S-shape guide has been investigated and the results have been analyzed for three different types of geometry. In this work, the Monte Carlo simulation method is used with McStas software. The results show that at a constant radius with increasing length, the guide moves more towards bending and passes neutrons with less energy. Conversely, at a constant length with increasing radius, the guide gradually deviates from the curved state and it leads directly to the straight guide, all of the neutron energy spectra passes. A radius of curvature of 70 m and a length of 4 m were chosen for the S-shaped guide due to the passage of a larger range of thermal neutron fluxes. The guide radius can lead to a cut-off wavelength for neutrons. This guide can also eliminate fast neutrons and gamma rays..

In this paper, mobility and thermoelectric properties of diamanes C2X (X = H, F, Cl) are studied using quantum espresso and Boltztrap computational package based on density functional theory. In all structures of C2X (X = H, F, Cl), the mobility of holes is smaller than the mobility of the electrons, which is due to the shape of the band structure of each structure. Maximum of Seebeck coefficient is 2733, 2811, 2201 µV/K for n-type C2H, C2Fand C2Cl and it is -2767, -2696 and -2269 µV/K for p-type C2H, C2Fand C2Cl, respectively. In all structures, thermoelectric parameters such as electrical conductivity, electrical thermal conductivity and power factor are maximum in positive values of chemical potential. As a result, these materials can be more suitable thermoelectric materials with n-type doping. Also, all three structures have a maximum power factor in the temperature range of 200-500 Kelvin.

Population growth, industrial development as well as limited fossil fuel resources have motivated the study of other energies, especially nuclear energy. Small modular reactors have been introduced as an efficient energy source due to their greater safety, easy transport, electricity generation and water desalination, even in remote areas. Optimization in the nuclear fuel management to improve performance and save energy leads to cost-effective design with higher efficiency and better safety. In this research, core loading pattern optimization of system-integrated modular advanced reactor (SMART) has been considered using the new dragonfly algorithm. In addition to the selected algorithm, the efficiency of optimizing loading pattern also depends on the definition of the objective function. Two-objective functions including flattening the power distribution and maximizing the effective multiplication factor are considered. Simulations of the reactor fuel assemblies and reactor core were performed by DRAGON lattice calculation and PARCS core calculation codes, respectively. According to the final results, the cycle length and effective multiplication factor are increased for 185 days and 582 pcm, respectively. Also the fitness function is decreased from 0.905931 to 0.194527.

Sheath formation and its characteristics are studied in collisional magnetized plasma consisting of nonextensive electrons and thermal ions. Using two-fluid model, the Bohm criterion for ion velocity is deduced as a function of plasma parameters and shown that ion-neutral collisions impose an upper limit for the Bohm criterion. It is also found that deviation from the standard Maxwellian distribution significantly affects the sheath characteristics. Sheath potential and ion density are considered under the effects of magnetic field, ion temperature, nonextensivity and ion-neutral collision frequency. The results indicate that by applying an external magnetic field, it is possible to control the sheath thickness.

In Maxwell electrostatics the electrostatic potential of a point charge is singular at the position of the point charge. In this paper, a nonsingular model for a point charge potential is presented in the presence of a momentum cutoff pmax based on a one-parameter deformation of the Heisenberg algebra in a 2D-dimensional phase space. For pmax→∞, the results of this paper reduce to the results of ordinary Maxwell electrostatics for a point charge.

In the framework of different theories of quantum gravity, such as string theory, dual special relativity, and the physics of black holes, the existence of a minimal length is proposed. It is necessary to modify and generalize the usual Heisenberg principle of uncertainty to incorporate the minimal length into the ordinary quantum mechanics. In this scenario, the momentum of the system is modified, and the Hamiltonian obtains additional terms. It is expected that the energy spectrum of any physical system is modified under the hypothesis of minimal length. In this article, these effects on the spectra of the exponential potential for the ground state are studied by applying a perturbation method. As a popular application of the exponential potential, the deuteron bound state can be explained by using this potential. Here, the modification of the energy spectrum of deuteron under the supposition of the existence of a minimal length is calculated.

In this letter, the random matrix theory representation of a bond-percolation model on square lattice is presented. The behavior of random matrix model can be determined only by its two largest eigenvalues. The second largest eigenvalue sits exactly on the edge of semicircle part of eigenvalue’s distribution and its position is a function of p, on the other hand the first largest eigenvalue is disjointed from other eigenvalues and its distribution is Gaussian. Also the first largest eigenvalue is responsible for scaling properties near criticality. Numerical simulations show power-law divergences emerged from coalescence of two largest eigenvalues near critical point at the thermodynamic limit. In this letter a scaling formalism is presented which describes complete scaling behavior of largest eigenvalue’s fluctuations with a set of scaling exponents in finite-size systems.

We have studied the intrinsic contribution to anomalous Hall conductivity in presence of the normal magnetic field. A semiclassical approach for calculating the Hall conductivity in presence of the nontrivial Berry phase is used. This method is based on the semiclassical equations of motion with anomalous velocity correction and the Boltzmann transport equation. We present the formulation of anomalous Hall conductivity in this approach. We perform explicit calculations for a two-dimensional system which is described by Dirac Hamiltonian. At zero magnetic field, our results coincide with previous results which are obtained both using the semiclassical method and Kubo formalism. For the strong magnetic field, Hall conductivity decreases as a power-law. The exponent of the power-law behavior for the infinite energy band is 1/3 and for the finite energy band, there is a crossover from 1/3 to1.