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In this paper, we used five different grain boundary (GB) structures including two twists, two symmetric tilts and one asymmetric tilt for α-Fe, in order to study the influence of different GB structures on the production and time evolution of defects. Energetic behavior of point defects near GBs is investigated and analyzed using Molecular Static (MS) method to calculate and compare the “defect absorbency” of each structure. The primary radiation damage state near each GB structure is simulated using Molecular Dynamic (MD) method for 3 keV and 6 keV primary-knocked on atom (PKA) with velocity vector perpendicular to the GB plane at various distances in 300 K. We found that all five GB structures can decrease the defect number in bulk region, if cascade center locates on the GB plane (prefect overlap) and increase the vacancy number, if the overlap is imperfect. This depends on the energy of PKA and its distance from GB plane. Also, the results proved that the magnitude of the observed variations depends on the atomic structure of GB. Furthermore, the GBs that have stronger “interstitial absorbency” produce an excess concentration of vacancies in the bulk region, while the edge of the cascades overlaps with GB plane. This is the result of bigger “interstitial absorbency” of GBs in comparison with vacancies.

We investigate theoretically the effects of Dresselhaus spin–orbit coupling (DSOC) on the spin-dependent current and shot noise through II–VI diluted magnetic semiconductor/nonmagnetic semiconductor (DMS/NMS) barrier structures. The calculation of transmission probability is based on an effective mass quantum-mechanical approach in the presence of an external magnetic field applied along the growth direction of the junction and also applied voltage. We also study the dependence of spin-dependent properties on external magnetic field and relative angle between the magnetizations of two DMS layers in CdTe/CdMnTe heterostructures by including the DSOC effect. The results show that the DSOC has great different influence on transport properties of electrons with spin up and spin down in the considered system and this aspect may be utilized in designing new spintronics devices.

In this work, XOR and OR gate responses are investigated theoretically in a benzene molecule threaded by a magnetic flux. The molecule is attached to two semi-infinite one dimensional metallic electrodes. In addition, there are two gate voltages applied to the molecule as the two inputs of the logical gates. The calculations are based on the tight-binding model and generalized Green's function method within the phase coherent transport regime. The hopping integral between two neighboring atoms in the benzene molecule is quantitatively estimated using fully self-consistence DFT based calculations as implemented in SIESTA package. Our numerical study predicts that the XOR and OR responses are explored through our molecular junction for a typical value of the magnetic flux ϕ = ϕ 0 / 2 . The application of these results can be a base for the designing of molecular electronics devices.

Theoretical studies on the electronic and optoelectronic properties of silicon hexagonal nanotubes (Si-h NTs) are carried out in the low energy region by including the effect of intrinsic geometry curvature. The effect of curvature changes the hopping matrix between nearest sites in the tube. Based on the tight-binding method in the nearest-neighbor approximation and electric-dipole vector, we obtain an analytical expression for optical matrix elements as a function of wavevector and subband index for the incident polarized light parallel to the tube axis. Our results show that the degeneracy of the bands is broken by introducing the curvature effect in the calculations leading to a change in the transition dipole matrix. Also, the resonance peaks in the absorption spectrum and the maximum absolute values in the dipole matrix elements of the tubes appear in the Van-Hove singularities for each band. Our results provide the fundamental information for developing new designs of nano- electronic and nano- optoelectronic devices.

Using a tight-binding model up to the second nearest-neighbor (2NN) interactions, an analytic expression for the selection rule and the optical dipole matrix elements have been derived as a function of optical energy of some single-walled silicon hexagonal nanotubes (Si h-NTs). For this purpose, the energy dispersion, dipole matrix elements and optical absorption obtained up to the 2NN are compared with those obtained for the first nearest-neighbors (1NN) for incident light polarized parallel to the tube axis. By concerning more distant-neighbors, in general, the 1NN model can be improved. The results show that there is a shift in the dispersion energy including second neighbors in comparison with first neighbors, which it depends on the subband index. One can also see that the absorption intensity is increased for both metallic and semiconducting nanotubes. The numerical result may be useful in designing nano-optoelectronic devices.

We investigate the influence of doping concentration on band structures of electrons and electrical transmission in a typical aperiodic semiconductor superlattice consisting of quantum well and barrier layers, theoretically. For this purpose, we assume that each unit cell of the superlattice contains alternately two types of material GaAs (as a well) and GaAlAs (as a barrier) with six sublayers of two materials. Our calculations are based on the generalized Kronig–Penny (KP) model and the transfer matrix method within the framework of the parabolic conductance band effective mass approximation in the coherent regime. This model reduces the numerical calculation time and enables us to use the transfer matrix method to investigate transport in the superlattices. We show that by varying the doping concentration and geometrical parameters, one can easily block the transmission of the electrons. The numerical results may be useful in designing of nanoenergy filter devices.

The optical properties are investigated in a new type of one-dimensional photonic crystal, which consists of two-layer unit cells. The first layer consists of a material with a negative refractive index (NIM) and the other is made of AlxGa1−xAs with a positive refractive index (x is content of Al in GaAs slab). Based on the transfer matrix method (TMM) and the Maxwell’s equation the dependence of photonic bandgaps (PBGs) and omni-directional photonic bandgaps (OPBGs) on the geometrical structure, characteristic of incident light and the content parameter are studied theoretically, in both TE and TM polarization modes. The bandgap in the transmission spectrum originate from the Bragg’s condition in the superlattice, while the existence of the defect layer gives rise to defect modes in the photonic bandgaps. Our results may be useful to better control the position of bandgaps in the optical filters and sensors designing.

A nanoscale logic NOR gate has been theoretically designed by magnetic flux inputs in a Z-shaped graphene nanoribbon composed of an armchair ribbon device sandwiched between two semi-infinite metallic zigzag ribbon leads. The calculations are based on the tight-binding model and iterative Green's function method, in which the conductance as well as current–voltage characteristics of the nanosystem are calculated, numerically. We show that the current and conductance are highly sensitive to both the magnetic fluxes subject to the device and the size of the system. Our results may have important applications for building blocks in the nanoelectronic devices based on graphene nanoribbons.

We investigate spin-dependent current and shot noise, taking into account the Rashba spin–orbit coupling (RSOC) effect in double diluted magnetic semiconductor (DMS) barrier resonant tunneling diodes. The calculation is based on an effective mass approach. The magnetization of DMS is calculated by the mean-field approximation in low magnetic field. The spin-splitting of DMS depends on the sp–d exchange interaction. We also examine the dependence of transport properties of CdTe/CdMnTe heterostructures on applied voltage and relative angle between the magnetization of two DMS layers. It is found that the RSOC has great different influence on the transport properties of tunneling electrons with spin-up and spin-down, which have different contributions to the current and the shot noise. Also, we can see that the RSOC enhances the spin polarization of the system, which makes the nanostructure a good candidate for new spin filter devices. Thus, these numerical results may shed light on the next applications of quantum multilayer systems and make them a good choice for future spintronics devices.

In this work, we study electronic and optical properties of two (5,5) armchair carbon nanotube (CNT) and gallium nitride nanotube (GaNNT) using fully self-consistence density functional theory (DFT) based calculations as implemented in SIESTA package. The generalized gradient approximation (GGA) is considered for the exchange-correlation functional. The results show that the armchair CNT is a metal, whereas the armchair GaNNT is a semiconductor with an indirect band gap. We can find the optical properties strongly depending on direction of polarization of light, hence the dielectric function and the optical absorption spectra are different for light polarized parallel and perpendicular to tubes axis. The significant peaks in the considered parameters are related to the ultraviolet to infrared (UV-IR) spectral region, and their intensities depend on the tubular morphology of the tubes. Our results can serve as a base for developments in designing nano-electronic and nano-optoelectronics devices.

In this work, we present a recursive Green’s function method to calculate electronic transport of armchair graphene nanoribbon (AGNR) and zigzag graphene nanoribbons (ZGNRs) quantum wires with randomly adsorption of monatomic gas molecules, which attached to two semi-infinite metallic leads. This model reduces numerical calculations time and enables us to use Green’s function method to investigate transport in a supperlattice device. The calculations based on the Landauer-type formula within the tight-binding approximation, which the recursive Green’s function method is used to solve inhomogeneous differential equations. The effects of monatomic gas molecules adsorption on electronic conductance properties are studied for various length and wide size of wire. Our numerical results show that the transport properties are strongly affected by the quantum interference effect, the lead interface geometry to the device and also adsorption of gas molecules on GNR sheets. By controlling the type of contact and wire geometry, this kind of system can explain the antiresonance states at the Fermi energy. The results can be used to control and engineer the graphene-based systems.

In this work, we study quantum transport properties of a defective graphene nanoribbon (DGNR) attached to two semi-infinite metallic armchair graphene nanoribbon (AGNR) leads. A line of defects is considered in the GNR device with different configurations, which affects on the energy spectrum of the system. The calculations are based on the tight-binding model and Green’s function method, in which localization length of the system is investigated, numerically. By controlling disorder concentration, the extended states can be separated from the localized states in the system. Our results may have important applications for building blocks in the nano-electronic devices based on GNRs.

In this work, we introduce a recursive Green’s function method for investigating electronic transport in a graphene nanoribbons (GNRs) quantum wire with armchair (AGNR) and zigzag (ZGNR) edges which attached to two semi-infinite square lattice leads. This model reduces numerical calculations time and enables us to use Green’s function method to investigate transport in a supperlattice device. Therefore, we consider AGNR and ZGNR devices attached to metallic semi-infinite square lattice leads, taking into account the effects of longitudinal and wide of the wire. Our calculations are based on the tight-binding model, which the recursive Green’s function method is used to solve inhomogeneous differential equations. We concentrate on the electrical conductance and current for various length and wide size of the wire. Our numerical results show that the transport properties are strongly affected by the quantum interference effect and the lead interface geometry to the device. By controlling the type of contact and wire geometry, this kind of system can explain the antiresonance states at the Fermi energy. Our results can serve as a base for developments in designing nano-electronic devices.

In this work, we report a theoretical investigation of parasitic capacitance in FeCo/MgO/FeCo magnetic tunnel junctions (MTJs). The electronic structures needed for accomplishment of this work are computed within the density functional theory using the full-potential linearized augmented plane-wave method (FLAPW) as implemented in Wien2k. Fixed-spin-moment (FSM) calculations are used to simulate the interfacial effects on the electronic structure of the electrodes. It is discussed that the charge screening at surfaces of the electrodes alters their local electric permittivities. The relative electric permittivities of the electrodes are calculated and their effects on the overall capacitance of the MTJ are estimated. Finally, capacitive properties of the MTJ are investigated and it is resulted that its capacitance, especially for the Co-ending electrodes, is not considerably dependent on an externally applied magnetic field.

We use the transfer matrix method to study spin-dependent tunneling transmission through the NM/EuS/NM/EuS/NM junction which affected by random corrugation interfacial roughness. The temperature dependence of spin-splitting energy is calculated for EuS magnetic barrier within the mean-field approximation. We perform several calculations to study the effect of random nonplanar interfacial on transmission probability for several widths of quantum well at different temperatures. Our results show that the scattering process due to random roughness open the new conduction channels (the dip and peak resonance energies). The results may be useful in designing spintronic devices.

The original version of this article unfortunately contains an error in Equation 3.

In this paper, we use the transfer matrix method to study the effect of roughness with nonplanar interfaces on spin-dependent transport properties in a magnetic tunnel junction, which consists of two ferromagnetic semiconductor barriers separated by a nonmagnetic (NM) layer. This trilayer is sandwiched between two NM electrodes. The roughness is modeled as a periodic corrugation interface. Based on the effective mass approximation, the spin-dependent transmission probability, and also the dependence of tunnel magnetoresistance (TMR) and electron spin polarization (SP) on the center nonmagnetic layer quantum well width are studied, theoretically, at several different temperatures. The numerical results show that the SP and TMR have an oscillatory behavior as a function of NM layer thickness and the interface roughness/islands degrade the transmission probability. Our results may be useful for the development of nanoelectronic devices.

Electronic transport properties of superlattice-carbon nanotubes (SCNTs) attached to semi-infinite clean metallic carbon nanotube (CNT) leads are investigated in the framework of a simple model based on mode (momentum)-space within the tight-binding approximation. This model reduces the numerical calculation time and enables us to use the transfer matrix method to investigate transport in an SCNT. We calculate the localization length and density of states (DOS) for various strengths of boron defect. Our numerical results indicate that the localization length decreases with increasing boron concentration, showing the tendency of the system towards the insulating behavior. Also, we observe a nearly stepwise dependence of the localization length on energy at small boron concentration. By controlling the layered boron concentration, the system can be tuned to yield either localized or extended states. These calculations can be generalized to the magnetic defects embedded in the device, which can act as a spin-filter. Our results can serve as a base for developments in designing nano-electronic devices.

The field of molecular electronics is a branch of science, which can have a variety of semiconductor technologies that extend beyond the silicon-based technology for the future. This branch of science may solve the limitations on size, high power usage and low speed in semiconductor technology. Rapid improvements in molecular electronics require modeling in the design of molecular devices. In this regard, we examine a three-leg molecule as a molecular transistor model and an indicator of methyl molecule as a resistance, in which the linkage of these abilities is carried out using LTspice simulation software. In order to investigate the effect of gated molecular on transport properties of the device, we design the half-adder molecular circuit and full-adder molecular circuit with them. The feasibility of building a prototype molecular transistor is illustrated using three-leg molecules directly contacted to gold electrodes, which the transmitted current from the structure is calculated using the Landauer formula. The application of the predicted results can be a base for designing moletronics devices.

In this work, we study quantum transport properties of superlattice-graphene nanoribbons (SGNRs) attached to two semi-infinite metallic armchair graphene nanoribbon (AGNR) leads. The calculations are based on the tight-binding model and Green's function method, in which localization length, density of states (DOS) and conductance of the system are calculated, numerically. By controlling the layered boron concentration, this kind of system can separate the extended states from the localized states. Our results may have important applications for building blocks in the nano-electronic devices based on GNRs.

Our aim is to study theoretically, the sensitivity of a hydrogen sulfide gas sensor, with regard to electrical conductance behavior. Our senor consists of a semiconductor single-wall carbon nanotube (SWCNT), functionalized with palladium nanoclusters, sandwiched between two gold electrodes. Initially, we have computed the optimized structure of the sensor, via molecular dynamic simulations. Then by using non-equilibrium Green’s function method, combined with density functional theory, the electronic and transport properties of the sensor were calculated, and compared before and after adsorption of H2S gas, at different bias voltages. The highest sensitivity is achieved at 40 mV bias voltage. In this bias voltage, H2S gas adsorption causes a significant decrease of current, because as a result of charge transfer from the CNT and palladium nanoclusters, to H2S gas, majority carriers (electrons) decrease. The results show that CNT decorated with palladium nanoclusters can be a promising candidate in gas-sensorics.

Spin-dependent transport properties are investigated in a single-crystal magnetic tunnel junction (MTJ) which consists of two Fe electrodes separated by an MgO insulating barrier. Our calculations are based on the first-principle density functional theory including the metal–oxide interface. Modifications are observed in the electronic and magnetic structure of the interface as a result of oxidation. Spin polarizations (SPs) more than 80% and −86% are obtained at zero temperature for clean interfaces in the parallel and anti-parallel alignments of the ferromagnetic electrodes, respectively, when a 7 monolayer MgO is used as the barrier. In the parallel alignment, the zero-bias SP is observed to be positive throughout the barrier reaching to a maximum at the central point. On the other hand, in the anti-parallel alignment, the SP of the electrodes is seen to penetrate deep into the barrier. The effects of interface oxidation on the band structure of the electrode surfaces are simulated using the fixed-spin-moment calculations. Also, we study dependence of the tunneling magnetoresistance on the barrier thickness and applied voltage in the trilayer within the effective mass approximation. It is shown that the TMR ratio decreases rapidly with increasing the barrier thickness and applied voltage. Our calculations explain qualitatively the main features of the recent experimental observations. Our results may be useful for the development of spintronic devices.

In this work, we study electronic quantum transport properties of a quasi-one-dimensional inhomogeneous quantum wire attached to semi-infinite clean metallic leads, taking into account the influence of hopping parameter. The calculations are based on the tight-binding model and transfer matrix method, which the electron transmission probability of the system is analytically calculated. We then concentrate on localization length and density of states (DOS) with additional diagonal disorder for various strengths of the hopping parameters. Our results show that the transmission decreases when the wire length increases, or the hopping parameter reduces. Furthermore, we investigate the concentration influence of disorder on the localization properties in quasi-one-dimensional systems. Also, we found that the localization length is almost independent of the wire size, while it increases with the higher hopping parameter. By controlling the relevant parameters, such as disorder concentration, wire length and hopping parameters, the system can be tuned to yield either localized or extended states. The application of the predicted results may be useful in designing nano-electronic devices.

We introduce a simple method for investigating electronic transport in pure and superlattice-like disordered carbon nanotubes (SDCNTs). This model reduces the numerical calculation time and enables us to use the transfer matrix method to investigate transport in a carbon nanotube (CNT). Therefore, we consider an SDCNT device attached to metallic CNT leads, taking into account the disorder effect. Our calculations are based on the tight-binding model and the transfer matrix method. We concentrate on the localization length and density of sates (DOS) for various strengths of disorder. Our numerical results show a nearly steplike dependence of the localization length on energy at small disorder concentration. By controlling the disorder concentration and wire length, this kind of system can explain the extended states from the localized states. Our results can serve as a base for developments in designing nano-electronic devices.

The spin-dependent electrical conductance and magnetoresistance (MR) of a one-dimensional system are calculated with disorder paramagnetic impurities. The system contains a quasi-paramagnetic quantum wire (QPQW) device attached between two non-magnetic semi-infinite leads. The calculations are based on the tight-binding model and generalized Green’s function method within the phase coherent transport regime. In order to investigate spin-filtering effect of QPQW, we study the spin-polarized electrical transmission as a function of impurity concentration and molecular field acting on paramagnetic impurities. It is assumed that in the absence of the external field, magnetic moments of the impurities are compensated (oriented at random), whereas the magnetic field creates finite net magnetization. It is found that the spin-dependent transport and MR depend strongly on the concentration of magnetic disorder, the size of the system and the Fermi energy. It is shown that MR has an oscillating behavior with respect to the magnetic molecular field at a fixed disorder concentration. The application of the predicted results can be a base for the designing of spintronics and moletronics devices.

By using a hydrochemical simulation, the effect of host liquid, acoustic pressure and noble gas on the parameters in water for the single bubble Sonoluminescence, N-methylformamide and Sulfuric Acid with 65 wt %, is described. The results show, with the viscosity increment of the host liquid, the SL temperature and intensity are increased. Furthermore, numerical calculation shows that, increase in the amplitude of the driving pressure from 1.3 to 1.45 atm and increase in the atomic mass of the noble gas from Ar to Xe in N-methylformamide leads to increase in the bubble intensity by about one and two order of magnitude, respectively. The results are in excellent agreement with the experimental measurements.

Theoretical studies on spin-dependent transport in magnetic tunnel heterostructures consisting of two diluted magnetic semiconductors (DMS) separated by a nonmagnetic semiconductor (NMS) barrier, are carried in the limit of coherent regime by including the effect of angular dependence of the magnetizations in DMS. Based on parabolic valence band effective mass approximation and spontaneous magnetization of DMS electrodes, we obtain an analytical expression of angular dependence of transmission for DMS/NMS/DMS junctions. We also examine the dependence of spin polarization and tunneling magnetoresistance (TMR) on barrier thickness, temperature, applied voltage and the relative angle between the magnetizations of two DMS layers in GaMnAs/GaAs/GaMnAs heterostructures. We discuss the theoretical interpretation of this variation. Our results show that TMR of more than 65% are obtained at zero temperature, when one GaAs monolayer is used as a tunnel barrier. It is also shown that the TMR decreases rapidly with increasing barrier width and applied voltage; however at high voltages and low thicknesses, the TMR first increases and then decreases. Our calculations explain the main features of the recent experimental observations and the application of the predicted results may prove useful in designing nano spin-valve devices.

Titanium nitride (TiN) thin films were grown onto 316 stainless steel substrate at 350 ° C by hollow cathode discharge ion plating technique. Since microstructure and mechanical properties of the samples were strongly affected by bias voltage, different bias voltages from 0 to | − 120| V were applied to the substrate. Rutherford back-scattering spectroscopy showed that the film thickness decreased when the bias voltage increased. X-ray diffraction patterns showed that the as-prepared TiN thin films were preferentially grown in the (200) direction with a satisfactory crystal quality at −30 V. The spatial scaling behavior of the TiN films grown by ion coating have been investigated by using the atomic force microscopy as well as a kinetic roughening model for the film thickness ranging from 380 to 590nm. The roughness and dynamic scaling exponents have been independently measured (α = 0.7 ± 0.05 and Z = 3.03 ± 0.05) and they exhibited a smooth surface growth. Nanohardness showed formation of a film with 30GPa hardness and 285 GPa Young modulus at −30 V bias voltage.

We have explored logical AND and NOR gate responses of a 1,4-2-phenyl-dithiolate molecule threaded by a magnetic flux ϕ in two-terminal junctions by using the Green’s function method in the framework of a nearest-neighbor tight-binding approximation. Here, we put emphasis on the logical gate voltages, and obtain the electrical transmission and current-voltage characteristics with metal-molecule-metal (m-M-m) tunnel junctions. The hopping integral among two neighboring atoms in the molecule was quantitatively estimated by means of density functional theory (DFT) calculations. Our results show that the AND and NOR responses are explored through our molecular junction for a typical value of the magnetic flux. The numerical results may shed light on the next applications of molecular systems and make them a good, promising candidate for field-effect transistors.

In this work, the influence of boron atom impurity is investigated on the electronic properties of a single-wall carbon nanotube superlattice which is connected by pentagon–heptagon topological defects along the circumference of the heterojunction of these superlattices. Our calculation is based on tight-binding [Formula: see text]-electron method in nearest-neighbor approximation. The density of states (DOS) and electronic band structure in presence of boron impurity has been calculated. Results show that when boron atom impurity and nanotube atomic layers have increased, electronic band structure and the DOS have significant changes around the Fermi level.

In this work, we investigate electron transport across a carbon molecular junction consisting of a C60 molecule attached to two semi-infinite metallic open-end CNT leads in the coherent regime. Here, we put emphasis on topology of the molecular-electrode interface and gate voltage, and obtain the electrical transmission through the CNT/C60/CNT structure, using the Green’s function method in the framework of a nearest neighbor tight-binding approximation. To this end, three different ways of coupling C60 fullerene through one, five, and six carbon atoms to the CNT-leads in the direction of the longitudinal axis of the tube have been considered. Also, the current-voltage characteristic is calculated in the Landauer-Buttiker formalism at room temperature. It is shown that the number of contact points between the electrodes and the molecule can play an important role in the electrical transport. Also, the bond dimerization and a gate voltage shift the molecular levels, where by adjusting the related parameter...

A theoretical investigation on capacitive properties of Fe/MgO/Fe trilayers is presented where there is a dc coupling between the two conductors. It is discussed that capacities of the nanoscale metal/insulator/metal contacts are mainly determined by the electronic charge screening at surfaces of their electrodes. The interface effects are simulated using fixed spin moment calculations. In order to have a comparison between the capacities for the parallel and antiparallel alignments of the trilayer, it is assumed that the charge induction across the junction occurs in two independent channels corresponding to the up- and down-spin electrons. The calculations give a larger capacitance for the antiparallel alignment of the electrodes, even though the stable phase of the tunnel junction in the absence of any externally applied magnetic field is calculated to be ferromagnetic.

In this work, spin-dependent current and shot noise transport in double magnetic barrier resonant tunnelling diodes is theoretically investigated. All components of the junctions, including external and central (spacer) electrodes are non-magnetic semiconductor, which have been separated by two II-VI diluted magnetic semiconductors (II-IV DMSs) layers. Our calculations are based on parabolic energy band approximation and transfer matrix method in the presence of external magnetic field and also applied voltage, within the phase coherent transport regime. In order to calculate the magnetisation of DMS, we have used the mean-field approximation in low magnetic field (B < 5T). We also examine the dependence of shot noise and tunnelling current densities on applied voltage and the relative angle between the magnetisations of two DMS layers in CdTe/CdMnTe heterostructures. All current and shot-noise components show a negative differential resistor (NDR), which originates from the resonant states tunnelling through quantum well. Also, the produced high spin polarisation makes the nanostructure a good candidate for new spin filter devices. Thus, these numerical results may shed light on the next applications of the quantum multilayer systems and make them convenient for future spintronics devices.