نشریه پژوهش سیستم های بس ذره ای
سال ششم شماره 1 (پیاپی 11، تابستان 1395)

In this paper, we study the electronic conductance of a nanowire including vibrating surface atoms which is embedded between two simple rigid chains by using Green’s function technique at the tight-binding and linear response approaches. We use the Fock space to consider the effect of electron-phonon interaction on the electronic transmission coefficient. The results show that by increasing of the strength of electron-phonon interaction, the positions of resonance peaks of the conductance curve will be shifted to the lower energies. Some new peaks will be appeared in the conductance spectrum, too. It can be seen that at a fixed the electron-phonon coupling strength by decreasing of the electron hopping energies of contacts, the resonance peaks become sharper and the valleys become deeper.

Today, exclusive optical properties of monolayer Molybdenum disulfide (MoS2) as a two-dimensional semiconductor has found upsurge attention. In this paper, Fresnel equations are used to determine optical properties, i.e. absorbance, reflectance and transmittance of MoS2 layer in the THz range. The whole structure includes two semi-infinite SiO2 and air with monolayer MoS2 in between. We found that the maximum absorption to be as low as 2.5×10-6 which appears in internal reflection for TE mode closed to the critical angle. Such low amount of absorption suggests application of such layer in opto-electronics devices especially in transparent electrodes and other electronics elements.

In this paper, we study the electronic conductance of a simple chain -as well as a polyacetylene oligomer- which is connected to three one-dimensional metallic leads. The calculations are based on Green’s function technique within the nearest neighbor tight-binding approach. Two types of conductances, one which is measured between left and right leads and another which is measured between left and top leads, are calculated as functions of energy; and their behaviors are investigated with respect to the position of the top lead connection in the center wire. The results show that the existence and the position of third lead in the center wire strongly effects on the values and behaviors of the mentioned electronic conductances. For polyacetylene case, the value of each conductance at zero energy can be tuned by variation of third lead position.

In this research we tried to make Zeolite Y by using hydrothermal method and also characterized by x-ray diffraction (XRD) and FTIR, SEM and EDAX we investigated dielectric properties of zeolite Y that it is in Artificial group and it has Faujstie structure. That is we tried to measure dielectric permittivity ε', and loss factor ε", conductivity and catalytic behaviour in rang of 10KHz until 200KHz frequency at (24°C, 120°C, 170°C, 200°C) firing temperature. Measurement of electrical and dielectric Properties is one of the best method for investigation of catalytic behaviour of sample. Analysis of XRD pattern of sample by XPert software confirmed the formation of zeolite Y. Dielectric characteristics of the samples were measured with using LCR-meter.

This paper has focused on the potential of the negative refractive index materials in order to improve the optical and magneto-optical characteristics of one dimensional magnetophotonic crystals (MPCs). We have investigated the capability of double-negative materials (DNGs) in comparison with conventional materials in MPCs. As a result, we found that broadening in optical and magneto-optical spectra of the MPCs comprising DNGs can be occurred. indeed, the results show that the use of DNGs in MPC structures always leads to a spectral broadening, but a usefull broadening and it's amount depend on the structure and the refractive indices of the used materials inside the structure.

In this paper, we obtain electronic transport of a linear triatomic molecule which is located between two semi-infinite simple leads by using the standard Green's function at the tight binding approach. Also, we investigate the effect of electron–phonon interaction and temperature on electronic transport of molecule in the adiabatic regime. The results show that by increasing the strength of e-ph interaction, the rate of the electron scattering increases due to the vibration of atoms so the transmission coefficient decreases for all energies except the edges of the energy band. Also by decreasing the temperature and reducing in atomic vibration, electron scattering declines, then electron conductance increases.

In this paper, we study the electronic conductance of a poly-para-phenylene oligomer which is embedded between two simple metallic leads within the tight-binding approach and by considering the nearest and next neighbor electron hopping energies. At the first, the Hamiltonian of the poly-para-phenylene oligomer is converted to the Hamiltonian of a polyacetylene-like chain. Then, with help of Green’s function method, an analytic formula is given in order to calculate the electronic transmission coefficient. The numerical results show that the second neighbor interaction destroys the symmetry of the electron transmission as a function of energy with respect to zero energy. Moreover, due to the destructive quantum interference effect, in the conductance spectra we see more anti-resonances and also a Fano resonance will be observed.

In this work, lead spinel ferrite nanoparticles (PbFe2O4) was synthesized by sol-gel method. A gel of metal nitrates with proper molar ratios was firstly prepared and the effect annealing temperature on their structural and magnetic properties have been investigated. The annealing temperature of samples was determined by thermal analysis (TG/DTA). The structural and magnetic properties of samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectrophotometer (FT-IR), and vibrating sample magnetometer (VSM). The results of x-ray diffraction patterns showed that by increasing annealing temperature, lead spinel phase percentage of samples increase and impurity phases such as lead oxide and hematite have been decreased. Also, the results of field emission scanning electron microscope showed that the particles size is nano, but particles are bounded together. Also nanoparticles size increases with annealing temperature and well-defined shape. The Hysteresis loops of samples show that by increasing annealing temperature the coercivity was increased. The results of Fourier transform infrared spectrometry annealed samples show that structure of samples at temperatures of 650 and 700°C is spinel.

In this article, plasmonic waveguides aimed to controlling the colloidal quantum dot spontaneous emission rate have been designed. To this end, with considering aluminum and silver waveguides, the dependence of plasmonic emission rate to the dimension, material, and the place of quantum dots have been investigated. The results show that for a quantum dot with a distance of 5 nm from the edge of a silver waveguide with a gap of 20 nm and width of 30 nm, the plasmonic emission rate enhancement reaches 209 at the wavelength of 480 nm. This value for aluminum is 30. This waveguide is appropriate for ZnCdS/ZnS colloidal quantum dot with a photoluminescence peak at cyan wavelength.

In this work, the optical absorption enhancement of the organic (P3HT:PCBM) solar cells in the presence of silver nanopyramids was investigated with a finite-difference time-domain method. The nanopyramids’ base lengths were changed from 40 to 160 nm. The results show for nanopyramids with a base length of 100 nm, the surface plasmon polariton as well as the effective forward scattering modes are excited effectively, which significantly contribute in enhancement of optical and electrical properties of organic solar cells. Due to the better light concentration in the absorption layer by nanopyramids, which are located under the ITO layer, this design is showed to be more influential in increasing the optical and electrical properties of the cells. The results show that for nanopyramids with a base length of 100 nm, the highest short-circuit current density enhancement are achieved.

In this paper, the electronic properties and topological phase of Li2AgSn nanolayer are investigated. The calculation is done based on the density functional theory within generalized gradient approximation (GGA) using full potential Linearized Augmented Plane Waves plus local orbitals . The electron density of states of this nanolayer is calculated using GGA approximation. The linear electron specific heat coefficient of Li2AgSn nanolayer is calculated. The xx and zz compounds of dielectric constant, reflection, absorption, refraction, extinction coefficients and energy loss function of this nanolayer are investigated. The topological phase and band order of this nanolayer are investigated by using the band structure.

Carbon ceramic electrodes were prepared by sol–gel processing of a hydrophobic precursor methyltrimethoxysilane (MTMOS) together with dispersed graphite microparticles according to a literature procedure. The electrochemical behavior of L-cysteine at the surface of a carbon ceramic electrode (CCE) modified with gold nanoparticles (GNPs) is described. The modified electrode showed excellent catalytic activity toward L-cysteine reduction and can be used successfully for amperometric detection of L-cysteine. Under the optimized conditions, the calibration plots are linear in the concentration range 0.165 mM- 2.64 mM. Detection limit (signal to noise is 3) and sensitivity were found to be 0.053 mM and 1769 nA / mM, respectively.

In this paper, a multilayer electromagnetic absorber is proposed in X band (8-12.4 GHz) frequencies. In the investigated absorber the electromagnetic characteristics of Nano-composite materials are obtain from previous studies. The analytical method of the transmission line method (TLM) is used to design of the proposed absorber. Performance of the proposed absorber is influenced by the properties of layers such as number of the layers, thickness of each layer, material of them, the layer arrangement and electromagnetic coefficients. Further, the modified local particle swarm optimization (MLPSO) method and non-dominated sorting genetic algorithm type two (NSGA-II) are employed to enhance absorption value and absorption bandwidth of the proposed structure with thin profile. The proposed multilayer configuration with 3mm thickness shows more than -18.5 dB absorption in X band frequencies. In this band, the maximum absorption value is about -57 dB for the proposed structure. Furthermore, the return loss of the proposed absorber is calculated by use of the numerical method of finite integration technique (FIT) in CST Microwave Studio (MWS). Finally, an error function is defined for comparison the analytical results with the numerical. According to this function,differences between these results are less than 5 percent over the X band frequencies.

The present article is devoted to first-principles investigation of methane-sensing properties of (8, 0) carbon nanotube decorated with nickel atom using density functional theory. As we shall show the pure (8, 0) carbon nanotube is a weak methane sensor with very low adsorption energy whereas nickel decoration increases methane adsorption energy in this system and significantly affects its electronic structure. Our results also show that nickel decoration of (8, 0) carbon nanotube enhances the band gap energy as well as density of states near the valance band, indicating the feasibility of nickel-decorated (8, 0) carbon nanotube as a methane gas sensor.

Cadmium Selenide quantum dots are synthesized by a chemical method in various sizes. These CdSe quantum dots can be used in adsorption of wide range of solar spectrum. The optical properties of these QDs are characterized by ultraviolet-visible and photoluminescence (PL) spectroscopies. The results of absorption and emission spectroscopies show a red shift by increasing the size of QDs. Moreover, transmission electron microscopy (TEM) is applied for investigation on morphology of the nanoparticles. Then CdSe QDs are coated on a Si PV cell with a specific efficiency by drop casting method for I-V characterization. It is found that the CdSe QDs can enhance the efficiency of Si PV cells depending on the nanoparticle size. Studies show that these QDs can increase the efficiency of solar cells about 18.78 % compared to uncoated cell.

In this research zinc oxide (ZnO) Nanostructures were grown using Carbothermal Reduction method on Si substrate with magnetron sputter deposited Nano sheet .The structural and morphology of ZnO nanostructures were studied by x- ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) . Photoluminescence and optical absorption were measured by UV excitation and UV-Vis-Near IR spectrophotometer.With the help of X-ray energy loss spectroscopy density was determined. Visible Luminescence was observed. Substrate temperature, deposition time and Cu Nano-sheet thickness affect nanostructure dimension and optical properties. The presence of copper increases the band gap of ZnO occurs as well as the spectrum would shift toward the red (Red Shift).x -Ray diffraction pattern show Vrtzayt hexagonal structure for zinc oxid structures

Due to the capability of tuning the electric conductivity of Graphene, this two dimensional material can be used in designing tunable metamaterials. In this article, two different metamaterials with unit cells in the form of slit ring resonators (SRR) and its complimentary (CSRR) are introduced and their effective electric permittivity modification with changing the chemical potential of graphene, dimension of the structure and incident light polarization is investigated. Comparing the effect of changing the dimension of the structure with chemical potential modification, shows that the first changes maximum of the effective permittivity in a more limited frequency range relative to the letter. Resonant frequency displacement of 16THz is achieved by changing the chemical potential of graphene from 0.3 to 0.45ev. Changing the polarization of the incident light will modify the charge and current distribution and the frequency range of maximum effective permittivity will be changed. Introduced structure in this article is an effective step in controlling the electromagnetic wave in the terahertz frequency range.