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In this paper, we present a computational method to investigate optical properties of materials using a combination of density functional theory (DFT) calculations and finite-difference time-domain (FDTD) method. We show our method in the framework of an example for analyzing the effect of Au doping on optical transmission behavior of TiN compounds with a given geometry. First, DFT is employed based on generalized gradient approximation (GGA) exchange-correlation potential to investigate the electronic properties as well as dielectric function of TiN with respect to different percentages of doped Au. Our results reveal a growth in the imaginary part of dielectric function for energies below 4 eV by increasing Au doping level due to compression of Ti1−xAuxN DOS into the Fermi energy. In order to clarify the impact of Au doping on the optical behavior of Ti1−xAuxN with a given geometry, the optical dielectric function calculated from DFT was used as an input data for FDTD method to simulate a perforated surface plasmon system originated from Ti1−xAuxN-dielectric configuration via Optiwave package. It is observed that an increase in the Au level decreases the transmission intensity of excited modes of the perforated surface plasmon system, which is in agreement with the observed behavior for the imaginary part of dielectric function from DFT calculations. This implies that an enhanced imaginary part of dielectric function leads to more energy dissipation and finally less transmitted wave. The proposed method enables us to simulate optical properties of a wide range of compounds with arbitrary geometries and material-specific properties.

In this study, rGO − TiO 2 nanocomposites were prepared by means of a simple hydrothermal approach using TiO 2 powder and GO nanosheets as starting materials. The TiO 2 / GO weight ratio varied from 0.25 to 2 wt%. The prepared samples were characterized using AFM, SEM and TEM microscopy as well as XRD, EDX, Raman, FTIR and UV–Vis spectroscopies. BET and BJH measurements were also performed to obtain the specific surface area and pore diameter size of the synthesized samples. It was found that the samples with TiO 2 / GO weight ratio below one have high effective surface area about 124 g/m2 and pore size of 6 nm. Photocatalyst evaluation revealed that only 0.06 mg/ml of prepared composite degraded 90% of 20 ppm Methylene blue (MB) in 15 min under 50 mW / cm 2 UV light intensity. The linear kinetic rate constant (k) of the samples promoted from 22 × 10 − 3 min−1 for TiO 2 under UV exposure up to 153 × 10 − 3 min − 1 and 65 × 10 − 3 min − 1 for composites under UV and visible irradiation, respectively. More detailed analyses showed that the photocatalytic activity of samples obtained figure of merit below unity. To the best of our knowledge this seems to be an impressive result. Impedance spectroscopy analysis revealed that the enhancement of charge transfer in composites as well as high effective surface area and their mesoporous structure are mainly responsible for the significant enhancement of MB photodegradation. The reactive species trapping experiments were performed by a series of radical scavengers. On the basis of the experimental results, the electrons and superoxide ions species play the main role in degradation of MB.

In this work, combination of halides and MA, FA, Cesium (Cs) and Sodium (Na) cations were considered. The main structure of the cell absorbing layers was NaCsMAFAPb (IBr)3. The formulation of CsMAFAPb(IBr)3 without Na was used as a reference (control). Compositional cell cation by the mixture of MA0.2FA0.7Na0.05Cs0.05Pb (I5/6Br1/6)3 was used for comparison. Different characterization scheme such as IV measurements, Scanning Electron Microscopy, and X-ray Diffraction (XRD) were prepared to compare the performance of these two types of perovskite cell structures. SEM patterns showed the samples containing combined Na-Cs cations have a more compact surface with fewer pinholes. Also they exhibited higher efficiency compared to the reference sample. This was mainly due to the less defects of the interface surface. Moreover, better crystallinity was observed for the perovskite samples having Na-Cs combined cations from XRD pattern, which resulted in increase in charge transfer and also cell efficiency.

In the first part of this manuscript, two OLED devices composed of Alq3:DCM–TPA organic material as doped emitting layer, have been simulated. In the first device, the reduced mobility property of this doped layer and in the second device, trapping effects of this dopant are considered. With comparison of the simulation results obtained for these devices, the approximated values of the traps concentration and Gaussian width of traps is obtained. In the second part, the OLED devices with considering of the NPB:Alq3 organic material as mixed host emitting layer have been simulated for obtaining optimal thickness of the emitting layer. In the final part, an OLED device composed of (NPB:Alq3):DCM–TPA organic material as mixed host-doped emitting layer has been simulated for studying the influence of DCM–TPA dopant on the performance of this device.

In this study, the effect of magneto-impedance (MI) in three-layer structures was studied. Ni/Cu/Fe sandwiched films were prepared by thermal evaporation on glass substrates. MI sensor impedance as a function of external magnetic field and the driving frequency was measured. MI ratios were obtained as large as 68% and 95% at 5 MHz and 15 MHz, respectively. The results showed that the three-layer structures had a dramatic increase in performance with respect to the single-layer magneto-impedance films.

Spin dependent transport of transition metals doped Zigzag Silicene Nano-Ribbons (ZSiNR) are investigated through the Density Functional Theory (DFT) and Non-Equilibrium Green's Functions (NEGF) formalism. The edge dangling bonds are passivated with hydrogen atoms. The DOS and Transmission functions are calculated and the resulting I-V curves show a behavior characteristics of spin polarized currents. These facts results in Negative Differential Resistance (NDR) and a reasonable Spin-Filtering Effect (SFE) in doped ZSiNRs compared to the pristine ZSiNR which shows the applicability of the considered structures in spintronic devices.

Using first-principles plane-wave calculations in the framework of density functional theory, we calculated the coefficients of elasticity, piezoelectric strain and stress tensors for the buckled V-structure group III-V monolayer materials (GaP, GaAs, InP, InAs). We demonstrated that these compounds have four independent elastic coefficients (c11, c21, c22, c66) and three piezoelectric coefficients (d11, d12, d26). Our analysis shows that the InAs (d11 = 64.47 p.m./V) and the GaAs (d11 = 35.39 p.m./V) monolayers exhibit much stronger piezoelectricity than reported two-dimensional materials such as the h-BN and the MoS2 monolayers. These nanomaterials that have simultaneously piezoelectricity and semiconducting behavior are promising candidates for piezotronics and piezo-phototronics applications.

Metal cation doping is an established strategy to increase the efficiency of perovskite solar cells. However, the underlying mechanism is less discussed regarding the doping site. In this paper, the effect of rubidium/potassium as dopant has been evaluated on the CH3NH3PbI3 (MAPbI3) perovskite lattice. At the 5% doping level, K cations have significantly improved photovoltaic properties by promoting crystallinity, releasing the strain, reducing the trap states, and boosting all key photovoltaic parameters. Moreover, this study provides a rough description of Rb/K doping mechanisms in the MAPbI3 lattice, where K cations occupy the interstitial sites while both interstitial and substitutional occupancies may occur for Rb cations. Our findings help to adjust the properties of perovskite layers to design new materials with better photovoltaic performance.

The importance of applying DNA sequencing in different fields, results in looking for fast and cheap methods. Nanotechnology helps this development by introducing nanostructures used for DNA sequencing. In this work we study the interaction between zigzag silicene nanoribbon and DNA nucleobases using DFT and non equilibrium Green's function approach, to investigate the possibility of using zigzag silicene nanoribbons as a biosensor for DNA sequencing.

In this present paper, the non-equilibrium Green function (NEGF) method along with the density functional theory (DFT) were used to investigate the effect of doping a single transition-metal atom on transport and electronic properties of armchair graphyne (γ-graphyne) nanoribbons. It can be deduced from the results that among the doped TM atoms, Mn and Fe cause stronger polarized currents comparing to Co and Ni. Mn-AGyNR represents the features of a half-semiconductor and behaves like a semiconductor in both up and down spin channels. On the other hand, Fe-AGyNR shows a great potential in spintronic applications due to its half-metal properties. Also our results show the promising application of armchair graphyne nanoribbons in nano-electrical devices.

Dichalcogenides of transition metals are attractive material due to its unique properties. In this work, it has been investigated the electronic band structure, phonon spectrum and heat capacity of MoS2 under the applied tensile and compressive biaxial strain using the density functional theory. The Molybdenum disulfide under compressive (tensile) strain up to 6% (10%) has stable atomic structure without any negative frequency in the phonon dispersion curves. The tensile biaxial strain reduces the energy gap in the electronic band structure and the optical-acoustic gap in phonon dispersion curves. The tensile biaxial strain also increases the specific heat capacity. On the other hand, the compressive biaxial strain in this material increases phonon gap and reduces the heat capacity and the electronic band gap. The phonon softening/hardening is reported for tensile/compressive biaxial strain in MoS2. We report phonon hardening for out of plane ZA mode in the presence of both tensile and compressive strains. Results show that the linear variation of specific heat with strain (CV ∝ e) and square dependency of specific heat with the temperature (CV ∝ T2) for low temperature regime. The results demonstrate that the applied biaxial strain tunes the electronic energy gap and modifies the phonon spectrum of MoS2.

First principle calculations based on density functional theory using GW approximation and two particle Bethe–Salpeter equation with electron-hole effect were performed to investigate electronic structure and optical properties of two-layered hydrogenated AlN. According to many body green function due to decrease in dimension and considering electron-electron effect, direct (indirect) band gap change from 2 (1.01) eV to 4.83 (3.62) eV. The first peak in imaginary part of dielectric function was observed in parallel direction to a plane obtaining 3.4 was achieved by bound exciton states possess 1.39 eV. The first absorption peak was seen in two parallel and perpendicular directions to a plane which are in UV region.

Silicene, a hexagonal buckled 2D allotrope of silicon, shows potential for numerous new applications, and may allow for easier integration with existing silicon-based microelectronics than graphene. The possibility of the application of silicene as a biosensor is discussed. The interaction between a hydrogen-passivated zigzag silicene nanoribbon (ZSiNR) and the nucleic acid bases, adenine (A), guanine (G), cytosine (C) and thymine (T), is investigated by density functional theory. The binding energy of the nucleobase-stacked nanoribbons shows the following order: G > C > A > T.

In a recent paper [(2017) Mol. Cryst. Liq. Cryst., 658, 186–197], Kumari et al. studied the optical, photoluminescence and dielectric properties of the benzoyl valine acentric crystal. The refracti...

In the present study, we have explored the interaction of five distinct kinds of amino acid molecules namely, arginine (Arg), aspartic acid (Asp), alanine (Ala), asparagine (Asn) and histidine (His) with graphene and germanene monolayers employing dispersion-corrected density functional theory. The dispersion correction incorporated in the computational methodology improves the accuracy of the results by taking into account the long range van der Waals interactions between the adsorbent and adsorbate. Using this method, the equilibrium configuration, energetic, electronic and optical properties of amino acids adsorbed on substrate have systematically been found. It is also found that arginine makes the most stable complexes with graphene and germanene in comparison to the other amino acids used in this study. Compared to graphene, germanene shows higher sensitivity to amino acids indicating that germanene monolayers can be useful for bio-integrated electronic devices.

An ab-initio study on the spin-polarized transport properties of H-passivated Fe-doped graphyne nanoribbons is presented. All the calculations were based on density functional theory (DFT). Doping single magnetic atom on graphyne nanoribbons leads to metallicity which can significantly improve the conductivity. The currents are not degenerate for both up and down spin electrons and they are considerably spin-polarized. Therefore a relatively good spin-filtering can be expected. For configurations with geometric symmetry spin-rectifying is also observed. Therefore they can be applied as a dual spin-filter or a dual spin-diode in spintronic equipment.

First-principle calculations within Eliashberg theory framework have been utilized to investigate theoretically the effect of hole-doping along with applying strain on superconductivity in α-graphyne and graphene as a benchmark. We show how the electronic properties, electron-phonon interaction strength and superconducting critical temperature T C of α -graphyne and graphene are affected by hole-doping and biaxial tensile strain. Although, intrinsic α -graphyne is semi-metal but it is found that increasing hole-doped concentration of 12.5–25% changes its electronic properties from metal to semiconductor with a band gap energy of 0.46 eV. Furthermore, we demonstrate that it is not possible to induce superconductivity in α -graphyne by the conspiracy of 12.5% hole-doping and critical strain (8%) contrary to 12.5% hole-doped graphene under critical strain (12%) which becomes superconductor with T C ∼ 12 K . It seems that the presence of C C bond suppresses the effect of strain significantly and hole-doping slightly on improving electron-phonon coupling constant and T C in contrast to graphene.

One-dimensional TiO2/SiO2 core-shell nanofibers were fabricated using a single-nozzle co-electrospinning process with phase-separated, mixed polymer composite solution. The core and shell are composed of Polyvinylpyrrolidone (PVP) and Polyacrylonitrile (PAN) polymers with uniform distribution of TiO2 and SiO2 nanoparticles (NPs), respectively. The NPs were synthesized via sol-gel reaction, simultaneously, in the respective polymer solutions. The morphologies and structures of the fabricated TiO2/SiO2 core-shell nanofibers were investigated by XRD, FTIR, SEM, EDS and TEM images. The influence of different amounts of TiO2 and SiO2 precursors on the photocatalytic and UV-shielding performance of TiO2/SiO2 core-shell nanofibers were studied. Photocatalytic activity of the nanofibers evaluated by observing photodegradation of Methyl Orange (MO) aqueous solution under irradiation of ultraviolet (UV) light. Our results on the TiO2/SiO2 core-shell nanofibers indicate good potential for superior applications in photocatalytic and UV shielding devices.

In this work, the structural and electronic properties of armchair and zigzag graphdiyne nanotubes (GDYNTs) have been investigated using the density functional theory (DFT). All the nanotubes under investigation exhibited semiconducting behavior. The edge configuration and diameter effects on the electrical transport of graphdiyne nanotubes are studied using non-equilibrium Green's function (NEGF) method. Our results showed that the currents in the zigzag graphdiyne nanotubes are remarkably higher comparing to the armchair nanotubes.

In present paper, the non-equilibrium Green function (NEGF) method along with the density functional theory (DFT) are used to investigate the effect of width on transport and electronic properties of armchair graphyne (γ-graphyne) nanoribbons. The results show that all the studied nanoribbons are semiconductor and their band gaps decrease as the widths of nanoribbons increase, which will result in increasing current at a certain voltage. Also our results show the promising application of armchair graphyne nanoribbons in nano-electrical devices.

The fast growing application of inorganic nanostructures for biomedical purposes has led to an increasing demand for further studies to obtain deeper understanding on the interactions between biomolecules and nanostructures at the atomic level. In this regard, a group of amino acids (AA) are the subject of the present study; in which density functional theory (DFT) is employed to investigate the interaction between aromatic amino acids (AAs) and Zinc oxide single walled nanotubes (SWNT) to identify the effective parameters for the biomedical applications. The structural changes and site specific binding nature of the bio-conjugated system are examined in detail. The results show that nanotube’s curvature is an effective factor in the magnitude of binding energy, since by decrease of nanotubes’ curvature the binding energy increases. Examination of the interactions between ZnO SWNTs and different binding sites of aromatic AAs indicates that the charge-solvent structure involving aromatic ring site of AAs is energetically more favorable. In this configuration the bonding is mediated by hybridization of π orbitals in aromatic ring and the d orbitals of Zinc atoms. The results of this study support the possible capability of ZnO SWNTs in detection of amino acids which shows the promising application of ZnO SWNTs in biosensing purposes.

Due to association of protein tyrosine nitration (PTN) with development of some serious human disorders and diseases, in this paper, the possible applications of ZnO-based nanobiosensors in nitrated tyrosine (nTyr) detection were explored within the density functional framework. With this motivation, the interaction of nTyr with ZnO single walled nanotubes via all possible active sites of nTyr was investigated. The results show the tendency of nTyr to interact through its nitro site (forming nitro-site configuration) with ZnO SWNTs as it has the highest binding energy; while, the charge–solvent configuration involving the interaction of nTyr's phenolic ring has the second place in terms of binding energy magnitude. Regardless of which active site contributes in interaction, the binding energies exhibit an ascending trend with decrease of SWNTs' curvature. Electronic properties analysis indicates that nTyr interaction via its nitro group results in formation of some flat bands inside the band gap region leading to significant reduction of overall band gap energy. Similar behavior is also observed in charge–solvent configuration but the band gap energy is larger. These red shifts are mainly attributed to contribution of 2p orbitals of species present in nTyr. Also, the hybridization of 3d orbital of Zn atom with 2p orbitals of nitro group atomic species is found responsible for bonding formation in bioconjugated system possessing the highest binding energy. Comparison of the electronic band structure of ZnO SWNT–Tyr with that of ZnO SWNT–nTyr indicates the sensitivity of ZnO SWNTs toward tyrosine nitration hence, a considerable change in its optical spectra is expectable. This introduces ZnO SWNTs as a promising candidate for PTN detection.

The electronic, vibrational and thermal properties of germanene and stanene have been investigated based on density functional theory (DFT) and density functional perturbation theory (DFPT). The electronic band structure, total and partial density of states and phonon dispersion spectrum and states are analyzed. The phonon spectrum is positive for all modes in the first Brillouin zone and there is a phonon energy band gap between acoustic and optical modes which is around 50 cm−1 for both structure. The constant-volume specific heats of two structures are calculated by using phonon spectrum and density of states. The spin–orbit coupling (SOC) opens a direct energy band gap at the Dirac point, softens phonon spectrum and decreases phonon group velocity of ZA mode.

In a recent paper [Opt. Laser. Technol. 112 (2019) 207–214] Manthrammel et al. studied the optical properties of nanostructured rose bengal thin films. The refractive index and extinction coefficient of samples were calculated based on the reflectance and phase angle between the incident and reflected signals for a particular wavenumber. It is showed in this comment that they have used a wrong relation to calculate the extinction coefficient and the calculated optical parameters based on the extinction coefficient such as dielectric constant, dielectric loss, optical conductivity and electrical conductivity are incorrect.

In a recent paper [Physica B 552 (2019) 62–70] Assiri et al. studied the optical properties of the spin-coated nanostructured methyl violet-10B (MV-10B) thin films. The refractive index and extinction coefficient of samples were calculated based on the reflectance and phase angle between the incident and reflected signals for a particular wavenumber. It is shown in this comment that they have used a wrong relation to calculate the extinction coefficient and the calculated optical parameters based on the extinction coefficient such as absorption coefficient, band gap energy, dielectric constant, dielectric loss, optical conductivity and electrical conductivity are incorrect.

In this study, structural and electronic properties of the single-layer structure of Graphene, the single-layer structure of blue Phosphorene, the two-layer structure of blue Phosphorene/Graphene, the three-layer structure of blue-Phosphorene/Graphene/blue-Phosphorene and the three-layer structure of Graphene/blue-Phosphorene/Graphene have been investigated. The calculations are conducted based on the density functional theory (DFT) and using SIESTA code and generalized gradient approximation (GGA). The results show that the single-layer structure of Graphene reveals quasi-metallic behavior, and the single-layer structure of blue Phosphorene exhibit semiconducting behavior. Two - and three-layer structures of Graphene and blue Phosphorene have a metallic behavior. Total energy and structural stability have also been investigated.

This paper reports electromagnetic interference (EMI) shielding effectiveness (SE) and UV-shielding performance of polyvinylpyrrolidone (PVP)– $$\hbox {TiO}_{2}$$ /polyacrylonitrile (PAN)– $$\hbox {SiO}_{2}$$ nanofibre nanocomposites synthesized via the single nozzle co-electrospinning method. Herein, three samples with different average diameters were fabricated using 0.3, 0.4 and 0.5 ml h $$^{-1}$$ flow rates during the electrospinning process. Morphological characterization confirmed that a core–shell structure of nanofibre nanocomposites was formed successfully. The EMI SE of the as-prepared nanofibre nanocomposites was studied using a vector network analyser over the full X-band (8–12 GHz) frequency at room temperature. The experimental results demonstrate excellent microwave absorption properties for all samples. PVP– $$\hbox {TiO}_{2}$$ /PAN– $$\hbox {SiO}_{2}$$ nanofibres with 596.67 nm average diameter show maximum total EMI (110 dB at about 9 GHz) and 98% UV-shielding performance.

The nonequilibrium Green’s function (NEGF) on the basis of unitary transformation is used to study the effects of phonon scattering on the electron transport and photocurrent of rectangular Armchair graphene quantum dots (GQD) in different lengths and widths. Applying the Landauer–Buttiker formalism, the electron current and photocurrent is calculated. The noninteracting Hamiltonian is interpreted as nearest neighbor tight-binding model, and electron–phonon interaction contribution to the earlier Hamiltonian is written using the Holstein model. The obtained results show that electron–phonon coupling has three major effects: (i) phonon-assisted and phonon-restricted effect on the electron transport and photocurrent, (ii) increasing the band gap in the absence of photon radiation, and (iii) increasing and decreasing the band gap in the presence of photon radiation.

In this work, we study the effects of electron-phonon and electron-photon interaction on the electronic and optoelectronic properties of nano systems consisting of graphene nano-flakes (small length armchair graphene nanoribbons) connected to two semi-infinite metal electrodes. Our calculations are based on the use of non-equilibrium Green's function formalism. The non-interacting Hamiltonian is written within the nearest neighbor tight binding approximation. The full interacting Hamiltonian is then obtained by addition the electron-phonon and electron –photon interaction to the above non-interacting Hamiltonian. Using unitary transformations the interacting Hamiltonian is renormalized into a non-interacting tight-binding form with effective onsite energy and hopping parameter which contain the interacting effects. The Landuer-Buttiker formalism can now be used for the system with renormalized non-interacting Hamiltonian for calculating the electronic current. Within the above framework, we calculate the electron current, density of states (DOS) and photocurrent in the presence and absence of electron-phonon interaction in a nano-system consisting of graphene nano-flake with different width as central molecule. Our results show that electron-phonon interaction leads to decreasing the number of peaks in the DOS. Also the photocurrent has oscillatory behavior versus electron-photon coupling for different widths of the nano-flake. Finally, incident photon energy dependence of threshold electron-photon coupling (i.e photocurrent becomes larger than Ballistic case) and its increasing trend versus photon energy are studied.

In order to explore the possibility of using 2D nanostructures as biosensors , we have studied the adsorption characteristics of nucleotide bases on armchair germanene nanoribbon (AGeNR) using density functional theory with several approximations of exchange-correlation functionals with the addition of dispersion correction. It has been found that the dispersion interactions have the key role in characterizing adsorption phenomena through the non-covalent interactions. The structural and electronic properties of the nucleobase-nanoribbon complexes have been investigated along with the study of the dependence of binding energies on ribbon widths and hence the edge (armchair or zigzag) effects. A physisorption process with binding energies in the range of about 0.83–1.37 eV has been found for 10-AGeNR, which alters the electronic and structural properties of the subsystems indicating the potential use of these complexes as biosensors.

With a convenient surfactant-assisted sol-gel technique, we can assert that single-phase Pseudowollastonite (PWS) nanoparticles are synthesized at low temperature for the first time. Synthesized powders have been characterized by Fourier Transform Infrared spectroscopy, X-ray fluorescence spectrometer, X-ray diffraction (XRD) analysis and transmission electron microscopy. Effect of calcination temperature on crystallite size and lattice strain is studied from XRD data. Results indicate that single-phase PWS nanoparticles were successfully synthesized at 775 °C by the surfactant-assisted sol-gel method and increasing calcination temperature causes the rise of crystallite size and lattice strain.

In this study, the structural and electronic properties of armchair graphdiyne nanoribbons, which have different widths are studied using the first principle calculation. The results indicate that all studied AGDYNRs show semiconducting behavior in which the band gap values decrease with the increase of nanoribbons width. The electronic and electrical properties of the graphdiyne sandwiched between two graphene nanoribbons are also investigated. The findings of our study indicate that among 4 investigated n-G-GDY-G-NR structures, the highest current is calculated for n = 3 (3-G-GDY-G-NR), due to phase transition.

We investigated the effects of external electric and magnetic fields on the electronic and transport properties of corrugated stanene. We match density functional calculations with the effective Dirac model and applied external fields in the Dirac model. We calculate both the Fermi velocity and the strength of spin–orbit interaction in stanene within the framework of density functional theory. In the presence of intrinsic spin–orbit interaction accompanying with external electric field splits spin-up and down states. We also study the spin-dependent Landau levels and transport for stanene in the presence of periodically modulated electric and tilted magnetic fields with corrugation. Additionally, the Weiss and spin-polarization oscillations with inverse of magnetic field in stanene are reported.

In this article we study the effect of applied strain on the electronic and mechanical properties of stanene, the Tin counterpart of graphene. Due to the relatively large intrinsic spin–orbit coupling we used the fully-relativistic pseudo-potentials to consider the effect of spin–orbit in the density functional calculations. The spin–orbit interaction opens a 70 meV energy gap in the K point but by applying strain the energy gap in the band structure is closed. The density functional theory and simple molecular mechanic models are used to estimate the Young’s modulus of stanene. According to our calculations we estimate the in-plane stiffness of stanene Y s = 40 N/m. By matching DFT and molecular mechanic results of stanene, we investigate the size and chirality effects on the in-plane stiffness of stanene nano ribbons.

In this paper, we investigate the electronic structure of both armchair and zigzag α-graphyne nanoribbons. We use a simple tight binding model to study the variation of the electronic band gap in α-graphyne nanoribbon. The effects of ribbon width, transverse electric field and edge shape on the electronic structure have been studied. Our results show that in the absence of external electric field, zigzag α-graphyne nanoribbons are semimetal and the electronic band gap in armchair α-graphyne nanoribbon oscillates and decreases with ribbon's width. By applying an external electric field the band gap in the electronic structure of zigzag α-graphyne nanoribbon opens and oscillates with ribbon width and electric field magnitude. Also the band gap of armchair α-graphyne nanoribbon decreases in low electric field, but it has an oscillatory growth behavior for high strength of external electric field.

Stanene is a two-dimensional (2D) buckled honeycomb structure which has been studied recently owing to its promising electronic properties for potential electronic and spintronic applications in nanodevices. In this article, we present a first-principles study of electronic properties of fluorinated bilayer stanene. The effect of tensile strain, intrinsic spin-orbit, and van der Waals interactions are considered within the framework of density functional theory. The electronic band structure shows a very small overlap between valence and conduction bands at the {\Gamma} point which is a characteristic of semimetal in fluorinated bilayer stanene. A relatively high value of tensile strain is needed to open an energy band gap in the electronic band structure and the parity analysis reveals that the strained nanostructure is a trivial insulator. According to our results, despite the monolayer fluorinated stanene, the bilayer one is not an appropriate candidate for topological insulator.

We numerically analyze the interaction of small-amplitude phonon waves with standing gap discrete breather (DB) in strained graphene. To make the system support gap DB, strain is applied to create a gap in the phonon spectrum. We only focus on the in-plane phonons and DB, so the issue is investigated under a quasi-one-dimensional setup. It is found that, for the longitudinal sound waves having frequencies below 6 THz, DB is transparent and thus no radiation of energy from DB takes place; whereas for those sound waves with higher frequencies within the acoustic (optical) phonon band, phonon is mainly transmitted (reflected) by DB, and concomitantly, DB radiates its energy when interacting with phonons. The latter case is supported by the fact that, the sum of the transmitted and reflected phonon energy densities is noticeably higher than that of the incident wave. Our results here may provide insight into energy transport in graphene when the spatially localized nonlinear vibration modes are presented.

In this article we study the role of Rashba spin–orbit coupling and electron–phonon interaction on the electronic structure of zigzag graphene nanoribbon with different width. The total Hamiltonian of nanoribbon is written in the tight binding form and the electron–electron interaction is modeled in the Hubbard term. We used a unitary transformation to reach an effective Hamiltonian for nano ribbon in the presence of electron–phonon interaction. Our results show that small Rashba spin orbit coupling annihilates the anti-ferromagnetic phase in the zigzag edges of ribbon and the electron–phonon interaction yields small polaron formation in graphene nano ribbon. Furthermore, Rashba type spin–orbit coupling increases (decreases) the polaron formation energy for up (down) spin state.

In this paper, phonon-mediated superconductivity has been investigated in MgB 2 bulk structure and bilayer thin film by using first-principles calculations. The electronic band structure, total and partial density of states (DOS and PDOS), phonon dispersion, isotropic Eliashberg function α 2 F ( ω ), and electron–phonon coupling have been calculated within the framework of density functional theory (DFT). Our results indicate that holes at the top of boron σ bands mainly and holes in the boron π band partially contribute to formation of coupled holes in superconductivity state. The density of states at the Fermi energy level is increased for MgB 2 bilayer with respect to its bulk structure. According to the phonon dispersion and Eliashberg function curves, coupling considerably occurs between holes at the top of the boron σ band by means of optical phonon mode for both structures. This phonon mode has the E 2g symmetry at the Г point. We obtain electron–phonon coupling constants of 0.74 and 0.91 for bulk and bilayer structures, respectively. By using the Allen–Dynes formula, we estimate superconducting transition temperature T C of 40 K for bulk and 48 K for the thin film.

Using non-equilibrium Green׳s function and ab initio calculations we investigate structural, electronic, and transport properties of a junction consisting of armchair hexagonal boron phosphide nanoribbon (ABPNR) contacted by two semi-infinite electrodes composed of armchair graphene nanoribbons (AGNRs). We consider three different configurations including the pristine AGNR–BP–GNR and substitutions for Iron atoms, namely on phosphorus and boron atoms at one edge of the BP nanoribbon. The spin current polarization in all these cases is extracted for each structure and bias. Such hybrid system is found to exhibit not only significant spin-filter efficiency (SFE) but also tunable negative differential resistance (NDR).

In this study, we use the Siesta ab initio code based on Density Functional Theory (DFT) to determine the feasibility of hydrogen storage on the α-graphyne. We examined the effect of hydrogen adsorption on the structural properties, the density of states of this nano structure. Calculations were performed in the GGA and LDA approximations. We find that in the case of chemical adsorption of hydrogen, functional exchange–correlation PBE (GGA) in explaining chemical bonds have more accuracy and leads to more stable structures. Adsorption is chemical and the binding energy of single and double hydrogen adsorption is −2.28 eV and −3.48 eV, respectively. Our calculations show that the adsorption of one hydrogen atom induces a magnetic moment as 1 μB , because of breaking of π-bonds and generate unpaired electron and system find ferromagnetic configuration. Further analysis indicates that adsorption of second hydrogen eliminates magnetization and the semi metalic α-graphyne structure attains a band gap of 2 eV upon hydrogenation.

Electronic, magnetic and transport properties of a triangle graphene quantum clot have been studied in the presence of Rashba type spin-orbit coupling. The non-interacting part is written in the tight-binding model, and we use the Kene-Mele-Hubbard (KMH) Hamiltonian to describe the electron-electron and the Rashba spin-orbit interaction. While the Hubbard tel split the spin up and down states, the Rashba tel mixed these states. The competition between these two effects produces an interesting situation in a nano-device. Our results indicate that the magnetization of zigzag edge and spin coherence are decreased due to the Rashba spin-orbit interaction in the triangle graphene quantum dot It is shown that the reduction of spin coherence is non-negligible even in the case of weak Rashba spin-orbit interaction. (C) 2014 Elsevier By. All rights reserved.

Transport through a nano-device in the presence of electron–phonon interaction has been studied by using unitary-transformation scheme together with the non-equilibrium Green׳s function formalism. The non-interacting Hamiltonian is written within the tight binding model and left/right electrodes are described in wide-band approximation. The interaction between electrons is studied in the mean-field Hubbard model. Our results indicate that both phonon-restricted and phonon-assisted transport through two different configurations of graphene quantum dot occur. Also, the electron–phonon interaction screens the electron–electron interaction, and reduces the spin polarization.