The electronic structure and optical properties of three different groups of full-Heusler alloys, X MnSi (X= Fe, Co, Ni), Fe YSi (Y= V, Cr, Mn), and Fe MnZ (Z= Si, Ge, Sn), were investigated using density functional theory (DFT). Our results reveal that the half-metallicity properties can be controlled by changing the atomic contributions at the X, Y, and Z positions. Additionally, we considered both intraband and interband transitions to investigate the optical properties of these compounds. Due to the partially occupied d orbitals of transition metal atoms around the Fermi level, the optical absorption peak of these compounds is located in the visible range of light. Meanwhile, intraband transition plays the main role in the infrared range of light. Our findings suggest that full-Heusler alloys can be promising candidates for optoelectronic applications.

Heusler compounds as an impressive group of materials with a vast potential for different applications such as future energy, thermoelectric and spintronics are great interest to materials scientists. Dynamical, electronic and optical properties of Fe 2 TaAl and Fe 2 TaGa full-Heusler alloys have been studied in the framework of the density functional theory (DFT). The main goal of this manuscript is tuning of the electronic and optical properties of compounds by applying hydrostatic pressure. The electronic results show that both compounds are semiconductors with energy gap about 0.84 and 0.64 eV, respectively. Also, an indirect to direct gap transition occurs for Fe 2 TaAl and Fe 2 TaGa at 5 and 80 GPa pressure, respectively. Calculated phonon dispersion illustrates that both compounds are stable at the range of applied pressure. Also, a blue shift can be observed for optical conductivity spectra by increasing …

Strong spin–orbit coupling and lack of inversion symmetry in monolayer transition metal dechalcogenides has made these materials as a promising candidate for both spintronic and valleytronic applications. We investigate the effect of adjustable parameters on quantum transmission of electrons through a magnetic barrier on MoS 2 monolayer and introduce selection rules for generation of perfectly polarized spin-valley beams in various directions. These selection rules provide an efficient tool for versatile electrical manipulation of spin-valley beams in two-dimensional structures.

In order to implement the Heusler alloys in spintronic devices, the half-metallic property should be preserved at the surfaces even with contamination elements that may be present in the residue gas during the deposition processes. Therefore, we have considered the bulk and surface properties of NaCrAs with contamination H elements using DFT+ U approximation. It is found that NaCrAs is a half-metal with the magnetic moment of 4 μ B. Much of the magnetic moment arises from Cr atoms and the hybridization between the d orbitals of Cr with the p orbitals of As gives rise to the half-metallic property. The Curie temperature is estimated to be well above the room temperature and the half-metallicity is preserved in a rather wide range of the lattice parameter. The vibrational properties of the specimen are also considered by phonon spectrum calculation, which confirms the stability of the sample. The electronic and …

The structural, electronic and magnetic properties of the bulk and (001) surfaces of CsXNO (X= Mg, Ca and Sr) quaternary Heusler alloys are investigated. It is found that all of the compounds are half-metallic ferromagnets with a magnetic moment of 2 μ B which obeys the Slater–Pauling rule. The half-metallic gaps are calculated to be 0.84, 0.80 and 0.82 eV for CsMgNO, CsCaNO and CsSrNO, respectively. It seems that the shift of the bands due to the rather strong p–p exchange interaction leads to half-metallic ferromagnetism in these compounds. They can also maintain their half-metallic properties under great stresses and the calculated Curie temperatures are 705.14, 504.85 and 488.82 K for CsMgNO, CsCaNO and CsSrNO, respectively. The (001) surfaces of the compounds are also simulated using the symmetric slab model. The results of the calculation of surface energies indicate that NO-terminated surface …

The recently predicted penta-RuS4 monolayer with high stability, large nontrivial band gap and robustness against oxidation is promising for applications in nanoelectronics. The band structure of this material exhibits unique characteristics under the uniaxial strains and we show that this feature provides the possibility of generating the controllable charge and spin beams. We calculate the transport coefficients for the strain barrier in this monolayer, generally, in the presence of a magnetic filed and an applied voltage. Charge transport through the strain barrier shows that we can generate electron beams which their directions are adjusted by the strain and the external voltage. Also, we show that by addition of a magnetic field, we can generate fully spin polarized electron beams, emerging at angles determined by the applied voltage. These features can be of great importance in designing splitters and spin lenses …

Although the existence of four valley degrees of freedom in the (0 0 1) surface of IV–VI semiconductor topological crystalline insulators (TCIs) provides the opportunity to multiply the valleytronic functionality, it makes the generation of highly polarized valley currents less plausible. We investigate quantum adiabatic valley pumping in (0 0 1) surface of these TCIs and show that applying shear strains and exchange field gives the possibility of control and manipulation of the valley resolved currents with high polarizations. Interchange of polarizations, simply by turning the tensile strain into compressive mode and vice versa, highlights the potential application for valleytronic switching process. Furthermore, since the surface states are robust against disorders, we can increase the lengths of driving regions and pump significantly larger currents without breaking the coherency of the quantum transport regime.

Previous studies of electronic transport in molybdenum disulfide (MoS2) are restricted to the first order approximation of the Hamiltonian. In this paper, to obtain more exact results, we firstly present an analytical solution for the Hamiltonian of MoS2 when terms up to the second order (quadratic k-dependent) of the Hamiltonian are taken into account. Our analytical solution is easily applicable to study the transport properties of any single and multi-junctions of MoS2. Then, we propose a device composed of two ferromagnetic barriers with anti-parallel exchange fields and we show that this device has interesting properties such as spin and valley filtering with perfect spin and valley polarizations. Using this device, we can easily switch both spin and valley polarizations to their opposite polarizations only by using electric voltage, which is of fundamental importance in quantum computation and the next generation of …

We have investigated the electronic and optical properties of AlN hexagonal nanosheets under different kinds of strains, using the band structure results obtained through the full potential linearized augmented plane wave method within the density functional theory. The results show that 10% uniaxial strain along the zig-zag direction induces an indirect to direct band-gap transition. The dielectric tensor and corresponding optical properties are derived within the random phase approximation. Specifically, the dielectric function, reflectivity and refractive index of AlN nanosheets are calculated for both parallel ( ) and perpendicular ( ) electric field polarizations.

In this work, we calculated the phonon dispersion of GaNNTs (4,0) and (4,4) by quantum ESPRESSO package using Density Functional Theory (DFT), pseudo potentials, and plane wave self-consistent field (PWscf) method. For the purpose of lattice-dynamical calculation and phononic properties, we used PWscf and Phonon codes. The former produces the self-consistent electronic and all related computations (forces, stresses, structural optimization). The latter solves the DFPT equations and calculates dynamical matrices for a single wave-vector or for a uniform grid of wave-vectors. The stability of these nanotubes was studied by phonon curves. According to the calculations, the breathing mode was distinguished for both nanotubes. The mechanical properties of these nanotubes were characterized by the results obtained for phonon dispersion curves. Finally, a quantitative comparison was made between the …

In this study the structural and electronic properties of III-nitride monolayers XN (X=B, Al, Ga and In) under different percentages of homogeneous and shear strain are investigated using the full potential linearized augmented plane wave within the density functional theory. Geometry optimizations indicate that GaN and InN monolayers get buckled under compressive strain. Our calculations show that the free-strains of these four monolayers have an indirect band gap. By applying compressive biaxial strain, a transition from indirect to direct band gap occurs for GaN and InN, while the character of band gap for BN and AlN is not changed. Under tensile strain, only BN monolayer behaves as direct band gap semiconductor. In addition, when the shear strain is applied, only InN undergoes an indirect to direct band gap transition. Furthermore, the variations of band gap versus strain for III-nitride monolayers have …

Recently, hybrid organic-inorganic perovskite (HOIP) solar cells with AMX3-perovskite-based photovoltaics have opened up a new paradigm in solar cell fabrication. Among numerous studies on these novel materials, there are limited researches that compare theoretical and experimental results simultaneously. Here, we have investigated the most feasible structures – MAPbI3 and FAPbI3 – utilized as efficient active layers in HOIP solar cells. To this end, the proposed structures were evaluated experimentally and theoretically through dark I-V characterization and quantum-transport approach, respectively; which have been rarely discussed in previous reports. While trap density and ideality factor are determined through dark I-V characterization, geometrical and electrical properties are studied via first-principle density-functional theory. Moreover, quantum transport and I-V characteristics have been calculated …

We have investigated the electronic structures and optical properties of pristine and full-fluorinated SnC nanosheets using the full potential linearized augmented plane wave [FP-LAPW] technique based on the first principles density-functional theory (DFT). The random phase approximation (RPA), the reflectivity, absorption coefficient, energy-loss function, and refraction index of the nanosheets for parallel and perpendicular electric field polarizations are well described via using the calculated dielectric function. The electronic structure calculations of the study have confirmed that the nanosheets are nonmagnetic semiconductors. The main results of the investigation illustrate that the optical properties of full-fluorinated SnC nanosheet are different with the pristine SnC nanosheet. The results of the comparison represent that the values of static refractive index and static dielectric constant of full-fluorinated …

Generation of large currents, versatile functionality, and simple structures are of fundamental importance in the development of adiabatic quantum pump devices with nanoscale dimensions. In the present study, we propose an adiabatic quantum pump with a simple structure based on molybdenum disulfide, MoS2, to generate large spin and valley resolved currents. We show that pure and fully polarized spin and valley currents can be easily generated by employing two potential gates and using an exchange magnetic field. Unlike graphene and silicene, in order to induce a valley resolved current in MoS2, one does not need to induce strain and apply an electric field. The spin and valley resolved currents are completely coupled together, so that the spin up (down) current is exactly equal to the valley K(K′) current. Hence, we can detect the valley resolved current by utilizing more straightforward and simple …

Based on first-principles calculations with generalized gradient approximation as exchange-correlation functional, the structural, electronic, mechanical, thermal, and phonon properties of III-phosphide binary compounds, namely BP, AlP, GaP, and InP, with cubic zincblende structure have been investigated. The calculations were performed in the framework of density functional theory and density functional perturbation theory (DFPT) implemented in the Quantum ESPRESSO package. The results obtained for the structural and electronic properties are in good agreement with available theoretical and experimental results. The results of our electronic calculations indicate semiconducting properties for these binary compounds. Furthermore, the frequency bandgaps and phonon density of states were also investigated. The computed mechanical constants predict that BP, AlP, GaP, and InP are elastically …

The electronic structures and optical properties of XC (X = Ge, Sn, Si) nanosheets are investigated in the present study using the full potential linearized augment plane wave (FP-LAPW) technique based on the first principles density-functional theory (DFT). Using the calculated dielectric function within the random phase approximation (RPA), the reflectivity, absorption coefficient, energy-loss function and refraction index of these nanosheets for parallel and perpendicular electric field polarizations are well described. Our electronic structure calculations for XC (X = Ge, Sn, Si) nanosheets confirmed the semiconductor property of these compounds. To ensure the accuracy of our work, we have also calculated the energy gap and optical constants of XC (X = Ge, Sn, Si) bulks in Zinc-blende structure and compared our obtained results with the previous works. The results of our comparison study show that the …

Using spin-polarized density functional theory calculations, we demonstrated that carbon doped boron nitride nanowire (C-doped BNNW) has diverse electronic and magnetic properties depending on position of carbon atoms and their percentages. Our results show that only when one carbon atom is situated on the edge of the nanowire, C-doped BNNW is transformed into half-metal. The calculated electronic structure of the C-doped BNNW suggests that doping carbon can induce localized edge states around the Fermi level, and the interaction among localized edge states leads to semiconductor to half-metal transition. Overall, the bond reconstruction causes of appearance of different electronic behavior such as semiconducting, half-metallicity, nonmagnetic metallic, and ferromagnetic metallic characters. The formation energy of the system shows that when a C atom is doped on surface boron site, system is …

In the present work we study the spin polarization effects on the ground-state energy of an interacting two-dimensional electron gas in the presence of disorder scattering (impurity scattering) at arbitrarily spin polarization for various electron densities. For this purpose we employ the modified density-density correlation function at small values of wave-vector and frequency in the framework of linear response theory to calculate the exchange, correlation and ground-state energy for a spin polarized two-dimensional disordered electron gas. Our results show that the effect of spin polarization on the exchange, correlation and ground-state energy becomes considerable at high densities. We also conclude that the two-dimensional disordered electron system becomes unstable by increasing the spin polarization degree.

We propose an efficient scheme for the generation and control of both pure and fully polarized valley currents in a silicene-based junction, using adiabatic quantum pumping. The pure and fully polarized valley currents are induced using ferromagnetic proximity and the application of a perpendicular electric field. We show that the valley polarized current can easily be switched from valley K to valley and vice versa, simply by reversing the direction of the electric field. Thus, the valley current is controllable electrically. Compared to the methods proposed for generation of valley current by quantum pumping in graphene, which are based on inducing strain on its sheet, our method is very simple and can be easily utilized in practical applications. Also, we show that the magnitude of pumped current in a silicene-based junction is roughly one order of magnitude greater than that of graphene. In addition to valley …

In this work we use density functional theory based on the ultra-soft pseudo-potential to calculate the structural, mechanical and thermal properties of narrow single walled BN, AlN and GaN nanotubes. The electron-electron interactions were expressed within the local density approximation (LDA). We have also obtained the Phonon dispersion and elastic constants of these nanotubes using the density functional perturbation theory. Furthermore the values of Young’s modulus, radial breathing mode frequencies and phononic band gaps for BN, AlN and GaN nanotubes (4, 0) are reported. Finally it is demonstrated that the behavior of heat capacity of these nanotubes strongly depends on the mass of cations.

We have studied the electronic structure and magnetic properties of Nitrogen and Carbon codoped ZnO (5,0) single-walled zigzag nanotube using first-principle calculations based on the density functional theory. We performed our calculations for N- and C- codoping ZnO nanotube in two different configurations. For the first configuration in which the two impurity atoms (N or C) are on first nearest-neighbor sites in the plane of codoping, our calculation predicts that the N- and C-codoped ZnO nanotubes are antiferromagnetic material with no net magnetization. On the other hand, it is found that for the configuration in which the two impurity atoms are next nearest-neighbors, a spin polarization results in a magnetic moment in the N- and C-codoped ZnO nanotubes.

Nitinol as a superelastic shape memory alloy (SMA) has been the focus of physical-chemical studies in recent decades in respect to functionality of biocompatibility in the body. Superelastic properties of nitinol are the direct results of the electronic structure of this material while dealing with the ab initio behavior of microstructure. In the present work, the elastic properties and electronic structure of B2-phase binary TiNi(1-x)Cux (x = 0, 0.25 and 0.75) shape memory alloys are discussed aiming at understanding of the physical properties underlying superelastic behavior. The calculations have been performed with the program package WIEN2K, in the framework of first-principle, all-electron density functional theory (DFT) within the scheme of the generalized gradient approximation (GGA). The optimized lattice parameters and independent elastic constants are obtained for use in the calculation of the bulk and shear …

The elastic, electronic and optical properties of the cubic fluoro-perovskite KCaF 3 have been calculated using the full potential linearized augmented plane wave based on density functional theory. Exchange and correlation effects are taken into account by a generalized gradient approximation and an orbital independent modified Becke–Johnson potential coupled with generalized gradient approximation. The equilibrium lattice parameter, bulk modulus and its pressure derivative have been obtained using optimization method. The results are in good agreement with the available theoretical and experimental data. The elastic properties such as elastic constants, shear modulus, Young modulus, Poisson’s ratio, ratio, sound velocities for longitudinal and shear waves, Debye average velocity, Debye temperature and specific heat have been calculated. The pressure dependence of the elastic moduli has been also …

We have theoretically investigated the effect of Dresselhaus spin–orbit coupling on spin-transport properties of ferromagnet/insulator/semiconductor/insulator/ferromagnet (Fe/Al2O3/SM/Al2O3/Fe) heterostructure. Based on the two band model and nearly-free-electron apptoximation, tunnel current and magnetoresistance are calculated as a function of bias voltage. Our calculations are carried out for three different semiconductors such as InAs, AlAs and InP. It is shown that the Dresselhaus spin–orbit interaction, in general, leads to enhancement of tunneling magnetoresistance. It is also shown that it strongly depends on the thickness of layers, bias voltage and electron effective mass in semiconductor layers.

Electronic, structural and optical properties of the cubic perovskite BaSnO 3 have been calculated using the full potential linearized augmented plane wave (FP-LAPW) based on density functional theory (DFT). Exchange and correlation effects are taken into account by a generalized gradient approximation (GGA) and an orbital independent modified Becke–Johanson (MBJ) potential as coupled with GGA. The structural properties including the lattice constant, the bulk modulus and the pressure derivative of the bulk modulus are calculated. The results of our calculations are in good agreement with available theoretical and experimental data. We have also calculated the energy band gap using MBJGGA. The calculated indirect band gap (R→ Γ) is 2.65 eV, while the smallest direct band gap (Γ→ Γ) is 3.0 eV. The real and imaginary parts of dielectric function, refractive index, real part of optical conductivity, optical …

The quantum vacuum fluctuation i.e., Casimir attraction can induce mechanical instability in ultra-small devices. Previous researchers have focused on investigating the instability in structures with planar or rectangular cross-section. However, to the best knowledge of the authors, no attention has been paid for modeling this phenomenon in the structures made of nanowires with cylindrical geometry. In this regard, present work is dedicated to simulate the Casimir force-induced instability of freestanding nanoactuator and nanotweezers made of conductive nanowires with circular cross-section. To compute the quantum vacuum fluctuations, two approaches i.e., the proximity force approximation (for small separations) and scattering theory approximation (for large separations), are considered. The Euler-beam model is employed, in conjunction with the size-dependent modified couple stress continuum theory, to derive …

We use density functional perturbation theory based on the pseudo-potential to calculate the phonon spectrum, phonon density of states, specific heat capacity and mechanical properties of pristine and cobalt doped (5, 0) single wall carbon nanotube (CNT). In the calculations, we consider one Co atom in the center of the unit cell of the tube and it is shown that the pristine (5, 0) CNT is nonmagnetic while the Co-doped tube becomes magnetic. Young’s modulus for both systems is about 1TPa (after Co-doping it goes slightly higher) and the Poisson ratio for the pristine tube becomes quite a bit larger than the doped one. On the other hand, the calculated value of radial breath mode for the pristine CNT is in good agreement with the experimental reports while after Co-doping it is increased. In addition, heat capacity of the doped CNT is reduced, which leads to some important empirical applications.

Pseudo-potential method under frame work of density functional perturbation theory (DFPT) has been utilized to calculate the phonon spectrum, phonon DOS, specific heat capacity and mechanical properties of narrow armchair and zigzag single walled carbon nanotubes (SWCNTs). Our calculations show that although their Young modulus are about 1 TPa, but armchair SWCNTs have greater compressive modulus than the zigzag tubes while the situation would be vice versa for tensile modulus. On the other hand, it was found out that specific heat capacity of narrow tubes shows chirality independence and decreases by increasing the radius of nanotube whereas, this is not the case for the wider ones. In addition, chirality dependence of the radial breadth mode (RBM) frequency of narrow SWCNTs has been shown.

In this paper, we have used density functional perturbation theory (DFPT) and Pseudo-potential method to calculate the phonon spectrum, phonon density of states (DOS), specific heat capacity and mechanical properties of (5,5) armchair and (9,0) zigzag Single Wall Carbon Nanotubes (SWCNTs). Our calculations show that Young’s modulusfor (5,5) and (9,0) nanotubesare higher than 1TPa. We have also shown that the value of compressive Young’s modulus for (5,5) nanotube isgreater thanthat for (9,0) nanotube while thevalue of tensile Young’s modulus for (9,0) nanotubeisgreater than that for(5,5) nanotube. The result of our calculations shows that thespecific heat capacity of (5,5) and (9,0) nanotubes coincides, therefore we may conclude that thespecific heat capacity of nanotubes is independent of their chirality. Furthermore we have found that the atoms in the armchair nanotubes are positioned as close as possible in the direction of the nanotube axis, therefore they could have more resistant against compressive pressure

We study the effect of spin polarization on spin-drag transresistivity in a two-dimensional (2D) electron gas at temperature T beyond the random phase approximation (RPA). We make use of spin resolved static local field factors for 2D spin polarized electron gas to take into account the many-body electronic correlation beyond the RPA. The main result of our work is that the reduction in spin Coulomb drag (SCD), due to the spin polarization of the system, is significantly compensated by the inclusion of the many-body local field corrections. We also calculate the temperature behavior of spin diffusion constant based on SCD theory for a spin polarized electron system.

Using density functional theory, a systematic study of the elastic properties of CaN, SrN, and BaN compounds is performed. As a result, the optimized lattice parameters and independent elastic constants are calculated within the generalized gradient approximation. We have also derived bulk and shear moduli, Young’s moduli, Poisson’s ratio, and brittle/ductile behavior for CaN, SrN, and BaN. The estimated anisotropy parameter, A, shows that SrN has higher degree of elastic isotropy in comparison to CaN and BaN.

In this paper, the electronic, phononic and mechanical properties of zinc-blende and wurtzite phases of GaN compound are studied by Density Functional Theory (DFT), generalized gradient approximation (GGA) and pseudo potentials. Results show both phases are semiconductors. The calculated band gaps are 2 and 2.2 eV for zinc-blende and wurtzite phases correspondingly. Bulk modules are obtained by fitting the variation of energy vs. the lattice constants data to the murnaghan equation of state. The phonon dispersion curves are obtained in high symmetry directions. The elastic constants are calculated by the slope of the phonon acoustic modes in different directions. These constants are =272, =122 and =127 GPa in zinc-blende phase and =301, =380, =85, =88, =125, =153 GPa in wurtzite phase. Our results are compared with other calculation and are in good agreement with them. Young modules are …

The structural and electronic properties of isolated and bundled of (8, 0) Beryllium monoxide nanotube (BeONT) have been studied by the first principles calculations in the framework of the density functional theory (DFT). Results show that the inter-tube interaction in nanotube bundle changes the structural and electronic properties of nanotubes. The effects of H2 molecule gas adsorption on the electronic properties of BeONT bundle are investigation. Adsorption of H2 molecules in BeONT bundle reduced the semiconductor energy gap. Our results show that the BeONT bundle has a good candidate for hydrogen storage and a gas sensor.

We report results of [sup. 75] As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) experiments as well as [sup. 7] Li NMR on different samples of self flux grown LiFeAs and 5% Co doped LiFeAs single crystals, and a polycrystalline LiFeAs sample. We were able to distinguish the samples by their slightly different quadrupole frequencies,[v. sub. Q], which is a direct measure of the electric field gradient (EFG) at the As site. Interestingly, samples with a large quadrupole frequency appear to show a different Knight shift and spin lattice relaxation in the superconducting state from those with a lower [V. sub. Q], yet all the samples are clearly superconducting. For sample S1 which has the largest [v. sub. Q], we find constant Knight shift K across [T. sub. c] for a certain direction of the magnetic field and a peculiar upturn of the NQR spin lattice relaxation rate [([T. sub. 1] T). sup.-1] below [T. sub. c …

We have studied the collective excitations (spin-wave energies) in the ground state of a two-dimensional (2D) electron system using the random phase approximation (RPA). To do so, we have calculated the magnetic transverse susceptibility in 2D electron system by Hartree-Fock (HF) approximation of Hubbard model at T= 0 which is generally referred to as the Stoner model. The spin-waves dispersion of three-dimensional (3D) electron system due to its quadratic behavior starts from zero at q0 while our numerical results show that the spin-waves dispersion of 2D electron system starts from the value Δ, known as exchange splitting energy, even at q= 0.

We calculate the TMR of a quantum nanowire with circle cross section consisting of two ferromagnetic electrodes separated by an insulator based on the nearly-free-electron approximation. The dependence of TMR to applied voltage by different cross-sections of nanowire and different electron effective mass of nanowire are studied theoretically.

Among the various academic awards in the field of physics, the Nobel Prize is considered the most prestigious international award. Since 1901 the Nobel Prize in Physics is awarded once a year by the Royal Swedish Academy of Sciences. There have been a few years in which the Nobel Prize was not awarded, particularly during World War I and II. The Nobel Prize in Physics was not awarded on six occasions: in 1916, 1931, 1934, 1940, 1941, and 1942. It has been awarded 105 times to 192 Nobel Laureates between 1901 and 2011. John Bardeen is the only Nobel Laureate who has been awarded the Nobel Prize in Physics twice, in 1956 and 1972. The youngest Nobel Laureate in Physics is Lawrence Bragg, who was 25 years old when he was awarded the Nobel Prize with his father in 1915. Bragg is not only the youngest Physics Laureate; he is also the youngest Nobel Laureate in any Nobel Prize area. The …

The electronic and optical properties of the nonstoicheiometric Heusler alloys Fe3− xMnxSi with (x= 0, 0.75, 1, 1.25, 2) have been studied by the first principles study in the framework of the density functional theory (DFT). Optical properties including the dielectric function, refractive index, energy-loss spectra, absorption spectra, optical conductivity and reflectivity were also calculated. Results show that the electronic structure of Fe3− xMnxSi alloys have half-metallic property for (x= 0.75, 1, 1.25). The real part of dielectric function has two main peaks in high energies. From absorption spectra it can be seen that absorption curves in low energy are broadened with respect to higher energies. The refractive index has a nonlinear dispersion in the energy range of 45–55 eV. The energy of plasmon peaks obtained from electron energy loss function (ELF) are about 25 eV.

The electrical behaviour of porous silicon layers has been investigated on one side of p-type silicon with various anodization currents, electrolytes, and times. Electron microscopy reveals the evolution of porous silicon layer morphology with variation in anodization time. In this work electrical conductivity of bulk silicon and porous layer which is formed by electrochemical etching is compared due to I-V measurements and calculation of activation energy. We have also studied the dependence of porous silicon conductivity on fabrication conditions. Also the effect of the temperature on conduction of porous silicon at different frequencies is investigated. At last dependence of capacitance on the temperature was probed at Hz frequency range.

We use the constructed spin-dependent static local field functions to calculate the plasmon dispersion of two dimensional spin polarized electron gas (2D SPEG) over a range of electron densities at arbitrarily spin polarization. We also investigate how the finite width of electron layer will affect the plasmon frequency and inverse static dielectric function of 2D SPEG. Our results show that the effect of finite thickness on plasmon dispersion and inverse dielectric function becomes considerable even at high densities in 2D SPEG.

We have studied the charge-density oscillations (plasmons) of a two-dimensional electron gas within the framework of finite temperature and frequency independent (static) version of Singwi, Tosi, Land and Sjölander approximation. We have shown that even at high densities the finite temperature and layer thickness have non-negligible impact on plasma dispersion of the two-dimensional electron system.

For accessing to higher speed and more densities in packaging, FET structures have become small increasing from day to day. Devices as small as 18nm can still exhibit acceptable transistor characteristics but At such small sizes, the nature of carrier transport in the device begins to change. In such MOSFETs that the device size becomes smaller than the carrier scattering length, it is statistically very probable for carriers to traverse the channel from the source to drain electrodes without encountering a scattering event. Such transport is called ballistic transport technically. In this article, we have conducted a survey on the electron transport in nanotransistor and using the semi-classical approach based on Boltzmann Equations for ballistic regimes, the electrical currents for a two dimensional structure as well as a quantum wire have been calculated that this calculations are based on model that is indicated by A …

In this paper, we investigate the Tunneling Magneto Resistance (TMR) in magnetic multilayers. Keldish Non Equilibrium Green’s Functions (KNEGF) have been calculated via solving Schrodinger equation in WKB approximation.

THEORETICALLY INVESTIGATED THE INFLUENCE OF IMPURITIES EMBEDDED INTO THE INSULATING BARRIER (I) SEPARATING THE TWO FERROMAGNETIC ELECTRODES (F) ON THE IV CHARACTERISTICS AND TUNNEL MAGNETO RESISTANCE (TMR). IT IS SHOWN THAT THE CURRENT AND TMR ARE STRONGLY ENHANCED IN THE VICINITY OF IMPURITY. IF THE POSITION OF IMPURITY INSIDE THE BARRIER IS ASYMMETRIC, THE IV CHARACTERISTIC EXHIBITS A QUASIDIODE BEHAVIOR.

The influence on the characteristics and tunnel magnetoresistance (TMR) of impurities embedded into the insulating barrier separating the two ferromagnetic electrodes of a magnetic tunnel junction was theoretically investigated. When the energy of the electron bound state at the impurity site is close to the Fermi energy, the current and TMR are strongly enhanced in the vicinity of the impurity. If the position of the impurity inside the barrier is asymmetric, e.g., closer to one of the interfaces, the characteristic exhibits a quasidiode behavior. The cases of a single impurity and of a planar random distribution of impurities were both studied.

The conductance and tunnel magneto-resistance (TMR) of the double barrier magnetic tunnel junction with spin-valve sandwich (F/P/F) inserted between two insulating barrier, are theoretically investigated. It is shown, that resonant tunnelling, due to the quantum well states of the electron confined between two barriers, sharply depends on the mutual orientation of the magnetizations of ferromagnetic layers F. The calculated optimistic value of TMR exceeds 2000%.

The influence of impurities, embedded into the isolating spacer (I) between two ferromagnetic electrodes (F), on the I-V curve and tunnel magnetoresistance (TMR), is theoretically investigated. It is shown, that the current and TMR are strongly enhanced in the vicinity of the impurity under the condition that the energy of the electron’s bound state on the impurity is close to the Fermi energy. If the position of the impurity inside the barrier is asymmetric, e.g. closer to the one of the interfaces F/I the I-V curve exhibits quasidiode behavior.

The influence on the I-V characteristics and tunnel magnetoresistance (TMR), of impurities embedded into the insulating barrier I separating the two ferromagnetic electrodes F of a magnetic tunnel junction, was theoretically investigated. When the energy of the electron’s bound state at the impurity site is close to the Fermi energy, it is shown that the current and TMR are strongly enhanced in the vicinity of the impurity. If the position of the impurity inside the barrier is asymmetric, e.g. closer to one of the interfaces F/I, the I-V characteristic exhibits a quasidiode behavior. The case of a single impurity and of a random distribution of impurities within a plane were both studied.

In this paper we have investigated the properties of CrAs in NiAs structure. The calculations are based on the Density Functional Perturbation Theory (DFPT) with the generalized gradient approximation (GGA). We have calculated Young module by using Murnaghan method and spring model which obey Hooke, s law.. Also the phonon spectrum, elastic constants and thermodynamic properties are obtained.