Sharif Digital Repository

Nanostructured aluminum titanate (AT) was synthesized by the sol-gel method. The calcination temperature was selected as a processing variable to obtain different phase ratios of AT and its parent phases i.e. TiO2 and Al2O3. The main aim behind the present work was to cast light on the photocatalytic performance of AT-based nanocomposites and evaluate their capability to serve as a novel photocatalyst. X-ray diffraction (XRD) analysis and field-emission scanning electron microscopy (FE-SEM) studies were conducted to evaluate the microstructure-sensitive properties of the synthesized powders. Diffuse reflectance spectroscopy (DRS) and the methylene blue degradation test were carried out to... 

In the band structure analysis of photonic crystals it is normally assumed that the full photonic gaps could be found by scanning high-symmetry paths along the edges of Irreducible Brillouin Zones (IBZ). We have recently shown [1] that this assumption is wrong in general for sufficiently symmetry breaking geometries, so that the IBZ is exactly half of the complete BZ. That minimal required symmetry arises from the requirement on time-reversal symmetry. In this paper we show that even that requirement might be broken by using gyro-magnetic materials in the composition of photonic structures we can observe that the IBZ extends fully to the boundaries of the complete BZ, that is IBZ must be as... 

Using tight binding theory the effect of topological ripples on the electronic band structure, density of states (DOS), and Fermi velocity of graphene are studied. The results show that by an increase in the ripple height the graphene Fermi velocity decreases and its DOS increases.- Moreover, we show that an increase in the ripple period causes the graphene band gap and DOS to decrease and its Fermi velocity to increase  

We report the results of our numerical investigation on the temperature dependence of the characteristics of the cylindrical gate-all-around Si nanowire field effect transistor (Si-NW-FET). Assuming the effect of temperature on the energy band structure of Si just like the effect of strain, we simulate the transistor characteristics at various temperatures (50 K ≤ T ≤ 300 K). In this investigation, we demonstrate the temperature dependence of the transistor sub-threshold swing and the threshold voltage are both linear functions of the temperature, represented by 61.5 × (T/300) + 63.4 (mV/decade) and 220140 × (T/300-1) (mV). By calculating the IDS - T characteristics for VDS = 0.4 V and... 

We generalize an already proposed protocol for quantum state transfer to spin chains of arbitrary spin. An arbitrary unknown d -level state is transferred through a chain with rather good fidelity by the natural dynamics of the chain. We compare the performance of this protocol for various values of d. A by-product of our study is a much simpler method for picking up the state at the destination as compared with the one proposed previously. We also discuss entanglement distribution through such chains and show that the quality of entanglement transition increases with the number of levels d. © 2007 The American Physical Society  

The electronic structure of high temperature superconductor YBCO is calculated by pseudopotential density functional theory using VASP code for different values of ZO(4). Comparison of the results of equilibrium ZO(4) with other calculation techniques indicates the capability of pseudopotential VASP code in energy band structure calculations for HTSCs. Both charge distribution and band structure calculations indicate the transfer of hole carriers from the CuO chains to the CuU2 planes with the increase of ZO(4). It is resulted that the increase of Cu(1)-0(4) bond lengths causes the creation of holes in the CuO2 planes. The redistribution of charge density confirms the charge transfer... 

We present an analytical method for solution of one-dimensional optical systems, based on the differential transfer matrices. This approach can be used for exact calculation of various functions including reflection and transmission coefficients, band structures, and bound states. We show the consistency of the WKB method with our approach and discuss improvements for even symmetry and infinite periodic structures. Moreover, a general variational representation of bound states is introduced. As application examples, we consider the reflection from a sinusoidal grating and the band structure of an infinite exponential grating. An excellent agreement between the results from our differential... 

We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-II superconductors forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and obtaining the band structure from the permittivity for both orthogonal polarizations, which depends on the above parameters and the frequency. This is while the characteristics of such crystals highly vary with an externally applied... 

We show a methodology for how to construct Dirac points that occur at the corners of Brillouin zone as the Photonic counterparts of graphene. We use a triangular lattice with circular holes on a silicon substrate to create a Coupled Photonic Crystal Resonator Array (CPCRA) which its cavity resonators play the role of carbon atoms in graphene. At first we draw the band structure of our CPCRA using the tight-binding method. For this purpose we first designed a cavity which its resonant frequency is approximately at the middle of the first H-polarization band gap of the basis triangular lattice. Then we obtained dipole modes and magnetic field distribution of this cavity using the Finite... 

In this paper the band structure of spin polarized zigzag graphene nanoribbons(ZGNRs) and armchair graphene nanoribons(AGNRs) with Stone-Wales defect are investigated. The results show when the spin effect is considered, the band structures of ZGNRs and AGNRs will be changed and modified. A larger gap will be created and the degenerate bands in ZGNRs will become far from each other. Tight-binding and hubard model were used to simulate the band structures  

Nonequilibrium dynamics induced by rapid changes of external parameters is relevant for a wide range of scenarios across many domains of physics. For waves in spatially periodic systems, quenches will alter the band structure and generate new excitations. In the case of topological band structures, defect modes at boundaries can be generated or destroyed when quenching through a topological phase transition. Here, we show that optomechanical arrays are a promising platform for studying such dynamics, as their band structure can be tuned temporally by a control laser. We study the creation of nonequilibrium optical and mechanical excitations in one-dimensional arrays, including a bosonic... 

We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-II superconductors forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and obtaining the band structure from the permittivity, which depends on the above parameters and the frequency. This is while the characteristics of such crystals highly vary with an externally applied static normal magnetic field,... 

We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-11 superconductors forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and obtaining the band structure from the permittivity, which depends on the above parameters and the frequency. This is while the characteristics of such crystals highly vary with an externally applied static normal magnetic field,... 

Using polynomial expansion of electromagnetic fields has been already reported for extraction of E polarized defect modes in two-dimensional photonic crystals. This approach is now applied to straight single-line defect optical waveguides, where H polarized defect modes are analytically extracted for the first time. Electromagnetic fields are expanded in accordance with the Floquet theorem, where each Floquet order is itself expanded in terms of Hermite polynomials and finally a new set of linear ordinary differential equations with non-constant coefficients is obtained. This set of equations is handled by employing differential transfer matrix method. In this fashion, algebraic and easy to... 

Ab initio frozen-phonon calculations have been performed for k = 0 A g Raman modes of two superconducting systems Y123 and Y124. We have used the local density approximation pseudopotential method in our calculations by VASP code. Results have been compared with other computational and experimental data for similar systems. Then we present changes of electronic band structure with the change of ionic positions in each Ag mode for both systems. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA  

Ab initio frozen-phonon calculations have been performed for k = 0 A g Raman modes of superconducting GdBa2Cu3O 7 and insulating PrBa2Cu3O7. We have used the generalized gradient approximation full-potential linear augmented plane-wave method in our calculations by Wien2k code. Results have been compared with other computational and experimental data for similar systems. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA  

A Legendre polynomial expansion of electromagnetic fields for analysis of layers with an inhomogeneous refractive index profile is reported. The solution of Maxwell's equations subject to boundary conditions is sought in a complete space spanned by Legendre polynomials. Also, the permittivity profile is interpolated by polynomials. Different cases including computation of reflection-transmission coefficients of inhomogeneous layers, band-structure extraction of one-dimensional photonic crystals whose unit-cell refractive index profiles are inhomogeneous, and inhomogeneous planar waveguide analysis are investigated. The presented approach can be used to obtain the transfer matrix of an... 

Electronic and phonon structures of the BaFe2As2 superconductor in the magnetic-orthorhombic phase have been investigated by the ab-initio density functional theory using the pseudopotential Quantum Espresso code. Density of state and electronic band structure for this phase has been studied, but phonon dispersion has been obtained only for the nonmagnetic-orthorhombic phase. Electronic band structure and density of states are in good agreement with other calculations in the literature. The electronic state near the Fermi energy are essentially made from Fe3d and As4p orbital that indicate in-plane conductivity in FeAs layers in this system. Comparing calculated phonon dispersions with... 

We propose a new method to extract the modes of photonic crystal slabs and, thus, obtain their band structures. These slabs, which are 2-D periodic structures with finite thickness, can completely confine light and have the important advantage of simple construction for applications in integrated optic devices. In this paper, reflection pole method (RPM) is utilized to analyze photonic crystal slabs. Modes are poles of reflection and transmission coefficients of multilayered structures. According to this principle, modes can be detected by only pursuing phase variations of transmission coefficients that are equal to π rad. Therefore, extraction of modes becomes fast and simple through...