Sharif Digital Repository

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 superprism effects of higher bands, i.e., for normal frequencies of higher than one, in two-dimensional (2D) polymer photonic crystals (PCs) are investigated. It is shown that in a polymer PC of triangular symmetry with filling factor of about 31%, the gradual transition of the hexagonal into triangular equi-frequency dispersion contours leads to a strong superprism in the 6th band at a normal frequency of 1.2. This dispersion is more prominent than those observed in the lower bands in 2D PCs. Also, this requires a lattice constant longer than the concerned wavelength. Furthermore, in a 2D polymer PC with a filling factor of about 83% a strong discontinuous superprism effect occurs at... 

The classical methods utilized for modeling nano-scale systems are not practical because of the enlarged surface e ects that appear at small dimensions. Contrarily, implementing more accurate methods is followed by prolonged computations as these methods are highly dependent on quantum and atomistic models, and they can be employed for very small sizes in brief time periods. In order to speed up the Molecular Dynamics (MD) simulations of the silicon structures, Coarse-Graining (CG) models are put forward in this research. The procedure involves establishing a map between the main structure's atoms and the beads comprising the CG model and modifying the parameters of the system so that the... 

Growth of thin layers of compound semiconductors such as GaAs and Al x Ga1-x As was obtained by Liquid Phase Epitaxy (LPE) at 838-828 ° C in thickness range of 0.1-4.3 μm which was estimated by Scanning Electron Microscopy (SEM). By Secondary Ion Mass Spectroscopy (SIMS) measurements, type of impurity atoms and their density and uniformity with respect to thickness were measured. In this way we are sure that variation of impurity atoms such as Si, Te, Sn and Ge indicates that epilayers were formed uniformly and it demonstrated that the LPE growth was a suitable way to obtain a good quality of epitaxy layers. Amount of composition parameter x in the compound semiconductor AlxGa1-xAs was... 

The effect of milling time on the magnetic properties of FINEMET amorphous ribbons has been investigated using X-ray diffraction, Mössbauer spectroscopy, thermo-magnetic measurements, transmission electron microscopy and SQUID magnetometery. Ribbons were melt-spun at a wheel speed of 38 ms-1 and then mechanically milled for different periods up to 45 min. The results showed that the partially crystallization of the amorphous powder occurs during milling. TEM observations confirmed the formation of small volume fraction of the crystalline phase with ∼9 nm crystallite size in the amorphous matrix for the ribbon milled for 45 min. Thermo-magnetic measurements indicated the enhancement of the... 

We performed density functional calculations aimed at identifying the atomistic and electronic structure origin of the valence and conduction band, and band gap tunability of halide perovskites ABX3 upon variations of the monovalent and bivalent cations A and B and the halide anion X. We found that the two key ingredients are the overlap between atomic orbitals of the bivalent cation and the halide anion, and the electronic charge on the metal center. In particular, lower gaps are associated with higher negative antibonding overlap of the states at the valence band maximum (VBM), and higher charge on the bivalent cation in the states at the conduction band minimum (CBM). Both VBM orbital... 

Controlled growth of atomic monolayers of IV-VII transition metal dichalcogenides (TMDs) has provided unprecedented opportunities to fabricate modern optoelectronic nanodevices. However, synthesis of large-area and high quality two-dimensional TMDs is still challenging. We have synthesized WS2 and MoS2 nanosheets by atmospheric pressure chemical vapor deposition (APCVD) at wide-range of processing conditions. The nanostructures were analyzed by optical and confocal microscopy, atomic force microscopy, Raman spectroscopy, and X-ray diffraction to determine the thickness, lateral size and structure of the deposits. Through designing and performing of a set of controlled experiments as well as... 

In this paper, a hierarchical multi-scale technique is developed to investigate the thermo-mechanical behavior of nano-crystalline structures in the presence of edge dislocations. The primary edge dislocations are generated by proper adjustment of atomic positions to resemble discrete dislocations. The interatomic potential used to perform atomistic simulation is based on the Finnis-Sinclair embedded-atom method as many-body potential and, the Nose-Hoover thermostat is employed to control the effect of temperature. The strain energy density function is obtained for various representative volume elements under biaxial and shear loadings by fitting a fourth order polynomial in the atomistic... 

In this work, a GaN-based quantum well LED is theoretically analyzed in a multi-layer structure composed of a quantum well embedded in a waveguide core surrounded by photonic crystal slab and a sapphire substrate. The electromagnetic eigenmodes are obtained throughout above structure via revised plane wave-scattering matrix method. The omnidirectional transmission and reflection are investigated for both TE and TM polarizations from diffraction channels in Ewald construction. Then, we introduced angular power density and calculated radiative modes extraction efficiency. All structural parameters, such as lattice geometry, lattice constant, photonic crystal thickness and filling factor, are... 

Low power operation and high speed have always been desirable in applications such as data processing and telecommunications. While achieving these two goals simultaneously, however, one encounters the well-known powerbandwidth trade-off. This is here discussed in a typical bistable switch based on a two-dimensional photonic crystal with Kerr type nonlinearity. The discussion is supported by the nonlinear finite difference time domain (FDTD) simulation of a direct coupled structure with a home-developed code. Two cases of working near resonant and off- resonant are simulated to compare the power and the speed of the device in the two cases. It is shown that working nearresonance reduces the... 

Recently, aluminum titanate (Al2TiO5)-based nanostructures have been proved to serve as an efficient photocatalytic material with satisfactory photodegradation capacity. In this study, the citrate sol–gel method was used to synthesize these nanostructures and inspect the significant impacts of nitrogen-doping-originated crystalline defects on their photocatalytic performance in some details for the first time. The results indicated that the penetration of nitrogen atoms into AT crystal lattice, depending on the nitriding time and temperature, can induce a great deal of the residual stress and result in propagating the existing cracks and breaking down the particles. The XPS and FTIR results... 

We have investigated the piezoelectric response of the hydrogenated graphene oxide (H-G-SiO2) stacks both experimentally and theoretically. The piezoresponse force microscopy method and density-functional theory (DFT) calculations were used to study the piezoresponse effect of this structure from both experimental and computational point of views. A mono-layer graphene, made by chemical vapour deposition method, is deposited on Si/SiO2 substrate and its surface is then functionalized with hydrogen atoms. The vertical piezoresponse, observed by piezoresponse force microscopy, is measured to be about 2146 pC N-1, that is comparable to the reported state of the art piezoelectric materials such... 

The present research sheds new light on the development of a triple-cation quasi-two-dimensional (2D) perovskite family with the general formula of (S1−xS′x)2[Cs0.05(FA1−xMAx)0.95]3Pb4(I1−xBrx)13, in which two spacers, namely 5-ammonium valeric acid iodide (S) and tetra-n-octylammonium bromide (S′) were simultaneously incorporated. Morphology, crystal structure, optical properties, photovoltaic performance, and internal resistances of such compound were systemically studied in comparison with an analogous single-cation 2D counterpart (i.e. (S)2(FA)3Pb4I13) as a reference. X-ray diffraction set forth that the films deposited based upon these compounds had a 2D perovskite crystal structure... 

Herein, we report the synthesis, characterization and combined structural and full computational analysis of noncovalent interactions in a new hydrazine ligand and its two chlorido- and endo-nitrito-rhenium(I) tricarbonyl complexes. The analysis of crystal structures has been accompanied by comprehensive computational studies of the noncovalent interactions utilizing the quantum theory of atoms in molecules (QTAIM), natural bond orbitals (NBO), independent gradient model (IGM), and electron localization function (ELF) to shed light on the nature of the interactions. On the other hand, comprehensive energy decomposition analysis (EDA) by extended transition state coupled with natural orbitals... 

Faujasite (X, Y) zeolites are considered the main and important catalysts in hydrorefining processes. In order to obtain zeolites with higher acidity and volume of mesopores, post-synthesis modification, dealumination by different pickling techniques (using ethylenediamine tetraacetic acid [EDTA] chelating agent), and thermal treatment (calcination) were employed. The dealumination process led to the removal of the aluminum atoms from the zeolite structure and a rise in acidity while maintaining the zeolite crystalline lattice. X-ray diffraction (XRD), atomic absorption spectrometry (AAS), Fourier-transform infrared (FT-IR), field-emission scanning electron microscopy (FE-SEM),... 

Bismuth ferrite, BiFeO 3, is almost the only material that is simultaneously magnetic and a strong ferroelectric at room temperature. As a result it is the most investigated multiferroic material. In this study, bismuth ferrite thin films were deposited on silicon wafer (100) and glass by pulsed-laser deposition and their structural, optical, and electrical properties were measured. Our study indicates that Bi richness in these films can stimulate formation of oxygen vacancy in the system which in its turn leads to delocalization of carriers and a more intensified photoconductivity response. X-ray diffraction analysis revealed formation of BiFeO 3 (BFO), but it also showed formation of Bi 2O... 

The nanocrystallization process of amorphous Fe73.5Si13.5B9Nb3Cu 1 was investigated by active screen plasma nitriding (ASPN) treatment at temperatures ranging from 410 °C to 560 °C for 3 h in two gas mixtures of 75% N2-25% H2 and 25% N2-75% H2 at 5 mbar atmosphere. The amorphous ribbons were then annealed under vacuum at the same time and temperatures mentioned above. The structure of the samples was analyzed using various techniques such as X-ray diffraction (XRD), atomic force microscopy (AFM) and differential scanning calorimetry (DSC). Microhardness measurements, electrical resistivity and Vibrating Sample Magnetometer (VSM) were used to study mechanical, electrical and magnetic... 

Theoretical study of carbon monoxide adsorption on SixGe4 - x(x = 0-4) nano-clusters has been carried out using advanced hybrid meta density functional method of Truhlar (MPW1B95). MG3 semi-diffuse (MG3S) and correlation consistent valence basis sets with relativistic core potential were employed to improve the results. The agreement of the calculated ionization and dissociation energies with experimental values validates the reported structures of nano-clusters and justifies the use of hybrid meta density functional method. The geometry, adsorption energy, charge distribution, and vibrational frequency of CO adsorption on all possible structures were investigated. The maximum vibrational... 

It has been recently shown that guided modes in two-dimensional photonic crystal based structures can be fast and efficiently extracted by using the Galerkin's method with Hermite-Gauss basis functions. Although quite efficient and reliable for photonic crystal line defect waveguides, difficulties are likely to arise for more complicated geometries, e.g., for coupled resonator optical waveguides. First, unwanted numerical instability may well occur if a large number of basis functions are retained in the calculation. Second, the method could have a slow convergence rate with respect to the truncation order of the electromagnetic field expansion. Third, spurious solutions are not unlikely to... 

Highly stable, water-based barium titanate (BaTiO3) sols were developed by a low cost and straightforward sol-gel process. Nanocrystalline barium titanate thin films and powders with various Ba:Ti atomic ratios were produced from the aqueous sols. The prepared sols had a narrow particle size distribution in the range 21-23 nm and they were stable over 5 months. X-ray diffraction pattern revealed that powders contained mixture of hexagonal- or perovskite-BaTiO3 as well as a trace of Ba2Ti 13O22 and Ba4Ti2O27 phases, depending on annealing temperature and Ba:Ti atomic ratio. Highly pure barium titanate with cubic perovskite structure achieved with Ba:Ti = 50:50 atomic ratio at the high...