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Motivated by recent experimental and theoretical research on a monolayer of boron atoms, borophene, the transmission probability and current-voltage characteristics of β12-borophene nanoribbons (BNRs) with zigzag and armchair edges have been calculated using the five-band tight-binding calculation, the Green's function approach, and the Landauer-Buttiker formalism. We focus on the effects of the geometrical parameters, perpendicular electric field, and external strain on the electronic transport properties of β12-BNRs by considering the effects of the substrate. Our calculations show that the transmission coefficient and current of the system decrease by increasing the channel length, whereas increasing ribbon width leads to an increment in the transmission probability as well as the I-V characteristic of β12-BNRs. Besides, the application of tensile strain causes a decrement in the current of the inversion symmetric model of the armchair β12-BNR, whereas the current increases in the presence of compressive strain. We also observed a dip in the transmission spectrum of the biased β12-BNR along the armchair direction which shows a metal-to-n-doped semiconductor phase transition in the device when applying a strong enough electric field. Moreover, the current of the inversion symmetric model of the β12-BNR with zigzag and armchair edges increases with the application of a perpendicular electric field, while in the case of the homogeneous model, the application of an electric field enhances the current of the β12-BNR only in the zigzag direction. These results provide insights for future experimental research and show that β12-BNRs are potential candidates for next-generation electronic devices.

Tuning the physical properties of nanoribbons is increasing for real applications. We here focus on magnetic and electronic effects to contribute to this matter. We particularly investigate the effects of a Zeeman magnetic field and dilute charged impurities on the quantum transport properties of β12-borophene nanoribbons (BNRs), both in the armchair and zigzag directions, by considering substrate effects. Calculations are done using the five-band tight-binding Hamiltonian, the Green's function approach (for density of states), the Landauer–Buttiker formalism (for quantum transport quantities), and the self-consistent Born approximation (for impurity effects). Our findings show that both electronic transmission probability and current–voltage characteristics of the system can be significantly adjusted in the presence of Zeeman splitting and charged dilute impuritiesy. Interestingly, the Zeeman splitting effect leads to an enhancement of the current that flows through the channel, whereas a reduction is observed in the electrical current of charged impurity-imbrued β12-BNR. Moreover, through a detailed analysis of armchair and zigzag directions, we found that the transport characteristics of impurity-induced armchair β12-BNRs are much more strongly tuned than those of zigzag ones. These results provide useful information for logic nanoelectronics.

Magnetism in atomically thin functional materials can be an important phenomenon for exploring two-dimensional magneto-optics. Magneto-optical experimental data have revealed significant Kerr signals in insulator thin films. Here, the magneto-optical Kerr effect of oxygen functionalized and doped hexagonal boron nitride (hBN) has been investigated by performing first-principles calculations. We calculated Kerr angle and Kerr ellipticity for functionalized hBN as an attention-drawn material. Moreover, increasing of oxygen doping percentage leads to the introduction of surface plasmon to hBN. Our findings show that the functionalized hBN can tolerate high-temperature conditions, keeping oxygen atoms bridge-bonded. These giant opto/magnetic responses of insulating 2D materials provide a platform for the potential designing of magneto-optical devices.

We theoretically address the electronic structure of mono- and simple bi-layer armchair graphene nanoribbons (AGNRs) when they are infected by extrinsic charged dilute impurity. This is done with the aid of the modified tight-binding method considering the edge effects and the Green’s function approach. Also, the interplay of host and guest electrons are studied within the full self-consistent Born approximation. Given that the main basic electronic features can be captured from the electronic density of states (DOS), we focus on the perturbed DOS of lattices corresponding to the different widths. The modified model says that there is no metallic phase due to the edge states. We found that the impurity effects lead to the emergence of midgap states in DOS of both systems so that a semiconductor-to-semimetal phase transition occurs at strong enough impurity concentrations and/or impurity scattering potentials. The intensity of semiconductor-to-semimetal phase transition in monolayer (bilayer) ultra-narrow (realistic) ribbons is sharper than bilayers (monolayers). In both lattices, electron-hole symmetry breaks down as a result of induced-impurity states. The findings of this research would provide a base for future experimental studies and improve the applications of AGNRs in logic semiconductor devices in industry.

In the present paper, we study the impacts of possible uni-, bi-, and tri-axial strains on the electronic band gap of phosphorene using the density of states (DOS) quantity through the Harrison relation. To reach this goal, we use a tight-binding Hamiltonian model and the Green’s function method. The findings report that the electronic phase of phosphorene can be adjustable in the presence of strain. The band gap increases (decreases) when applying the tensile uniaxial strains along the { x , y } (z) direction, while it decreases (increases) when the compressive uniaxial ones are applied. Interestingly, due to the inherent highly anisotropic structure of phosphorene, there is a semiconductor-to-metal phase transition along the z direction as the tensile strain is increased. Furthermore, we found that among all possible configurations for uniform biaxial strains, a flat band emerges at e x = e y = - 15 % , which is a quite new outcome. In addition, phosphorene supports different phase transitions when the triaxial strains are applied, introducing new electro-optical features. Hence, these findings can provide insights into the future experimental research and improve the applications of phosphorene in the real industry such as field-effect transistors.

Hexagonal boron nitride (h-BN) monolayer is an isostructural analogue to graphene and promising dielectric. Inspired by recent experimental reports, we focus on suspended and corrugated boron nitride nanoribbons (BNRs) as model systems, and report an intriguing flexoelectric polar effect using a series of ab initio-based density functional theory and tight binding calculations. Our results decode various synergies of the complex flexoelectrical properties including the role of corrugation height, structural deformation, and orbital mixing in corrugated BNRs. We demonstrate structural deformation of BNRs significantly contribute to the magnitude of electric dipole moment and bandgap closing, converting the insulating BNRs to semiconductors. This important finding, combined with the fundamental insights into the nature of electromechanical coupling, provides key hypotheses for design and modulation of novel nanoelectronic and nanophotonic devices.

Using the synergy between the tight-binding model and the Green's function approach, this paper deals with the linear magneto-electron-light interaction in ultranarrow armchair graphene and boronitrene nanoribbons theoretically. In particular, we study the effect of ribbon width and the magnetic field on the refractive index, the absorption coefficient, and the extinction coefficient of abovementioned structures. Here, we reveal that there exists an increasing behavior for static refractive index of both structures when the ribbon width and the magnetic field are increased, whereas the dynamical refractive index increases (oscillates) in average with the ribbon width (magnetic field) at different light frequencies. We further show that the effect of ribbon width (magnetic field) on the absorption coefficient is generally increasing (oscillating) when the photon energy is altered. No refraction and absorption is reported at high enough photon frequencies independent of the ribbon width and the magnetic field strength. In addition, we find that the scattering process in the presence of the magnetic field manifests itself in the extinction coefficient. This information provides insights into the engineers in determining which ribbon width and magnetic field strength to use in the solar cell designs.

With the aid of the two-dimensional tight-binding effective model in combination with effective models for perpendicular electric and magnetic fields, we describe the dynamics of carriers in Bernal bilayer phosphorene. Both electric and magnetic fields are in reliable ranges. We study the electronic phase transition beyond the continuum approximation focusing on the electronic band structure and density of states. In the present work, it is shown that the system subjected to the perpendicular electric field takes a semiconductor-semimetal phase transition with linear- and quadra-like bands along the Γ − X and Γ − Y direction, respectively when the magnetic field is absent. However, turning on the magnetic field shows again the semiconductor-semimetal phase transition for electric field-induced bilayer phosphorene but with only a linear-like band along the Γ − Y direction. Furthermore, we found that by varying the magnetic field, the Landau levels exhibit different treatments in the absence and presence of the electric field. Concisely, we argue that these tunable phase transitions with new rich features give proper motivations to experimentalists to tune the electro-optical properties of bulk phosphorus.

Topological crystalline insulators (TCIs) possess linearly dispersed metallic surface states, which are protected by crystal point group symmetries. The ability to fine-tune the effective mass of surface Dirac fermions by breaking their crystalline symmetry is highly desirable for thermoelectric applications. Given that the signatures of SnTe and its family originate from the (001) surface states, a natural question is: how does the thermoelectric performance of these states change due to the emergence of massive Dirac fermions? Herein, various physical perturbations, subjects of lively discussions, have been uncovered to improve the thermoelectric power factor (PF) of SnTe (001) and related alloys. Furthermore, orientation-dependent charge and heat currents are explored in detail. The surface-state Onsager transport calculations are performed using the Kubo–Greenwood approach. Highly dispersive and degenerate energy bands originating from the band gap opening are responsible for the enhancement of PF. While the x-direction has contributed mostly to the PF of the system, we report exceptional 74.65%, 121.67% and 110% enhancement of the PF compared with the pristine case at a temperature of 540 K when we perturb the crystalline mirror symmetry by strain, exchange field (stemming from proximity coupling to a ferromagnet, or the electric field, or Zeeman magnetic field) and Rashba spin–orbit coupling, respectively. The predicted PFs propose a new research direction to experimentalists to save time and to focus only on the thermal conductivity of SnTe (001) to achieve the highest thermoelectric efficiency.

In this work, based on the Kubo-Greenwood formalism and the k . p Hamiltonian model, the impact of Rashba spin-orbit coupling on electronic band structure and electrical conductivity of spin-up and spin-down subbands in counterparts of graphene, including silicene, stanene, and germanene nanosheets has been studied. When Rashba coupling is considered, the effective mass of Dirac fermions decreases significantly and no significant change is caused by this coupling for the subband gaps. All these nanosheets are found to be in topological insulator quantum phase at low staggered on-site potentials due to the applied perpendicular external electric field. We point out that the electrical conductivity of germanene increases gradually with Rashab coupling, while silicene and stanene have some fluctuations due to their smaller Fermi velocity. Furthermore, some critical temperatures with the same electrical conductivity values for jumping to the higher energy levels are observed at various Rashba coupling strengths. For all structures, a broad peak appears at low temperatures in electrical conductivity curves corresponding to the large entropy of systems when the thermal energy reaches to the difference between the energy states. Finally, we have reported that silicene has the larger has the larger electrical conductivity than two others.

Motivated by the recent nanophotonic community, in this work, we address the behavior of quantized charge-density fluctuations of doped and gated semiconductor armchair-type graphene nanoribbons within the tight-binding model and the Green’s function technique. In particular, we study the behavior of frequency-dependent susceptibility, when the system is exposed to photons or electrons. Injecting electrons by doping or ejecting ones by gating lead to different treatments in response function. Doping offers new collective modes due to added states between the valence and conduction bands (provided by the density of states) corresponding to intraband transitions, while gating distributes intraband modes. The results show that both ribbon width and doping concentrations affect the intraband transitions in electro-optical devices. Another remarkable point is the strong sensitivity of intraband plasmons to the direction of incoming photons or electrons. We found that the susceptibility of doped nanoribbons vanishes at perpendicular angles due to the distribution of intraband modes.

In this paper, we analytically investigate the electronic density of states (DOS) of bilayer Bernal black phosphorus (BBP) in order to study the anisotropic electronic phase transition. We employ the Green's function approach, the Born approximation, and the tight-binding Hamiltonian model including ten intra-layer and four inter-layer hopping energies. BBP consisting of two coupled layers of black phosphorus is a suitable candidate for studying the layer-dependent electronic properties of few-layer black phosphorus. We examine the electronic properties of BBP under conditions in which only one layer and both layers are subjected to a dilute charged impurity and a perpendicular electric field. Our findings show that there is no phase transition when the impurity is doped on only one layer, whereas in the case of both layers, BBP suffers a phase transition from semiconductor to semimetal at strong impurity scattering potentials. Also, applying the electric field on one layer of BBP leads to an increase in the band gap, whereas in the case of both layers, the band gap decreases with the electric field and eventually, a phase transition appears at a bias voltage of more than 1.8 eV. Consequently, the band gap of BBP can be tuned by applying an electric field and a charged impurity, and thereby these findings provide insights for future experimental research on black phosphorus.

In this paper, we theoretically address the strain and electric field effects on the electronic heat capacity of TCI SnTe (001) thin film with the aid of low-energy Dirac theory, the Green's function technique, and the semi-classical Boltzmann approach. We found that the Schottky anomaly in TCI SnTe (001) thin films decreases with both uniaxial and biaxial strains and the electric field with different decreasing rates. Furthermore, the Schottky temperature does not change with strain, while it fluctuates with the electric field. Our results show that before and after a critical low-temperature, the electronic heat capacity behaves differently. Finally, the results confirm that the electronic heat capacity does not change significantly with strain and electric field at high temperatures due to the thermal effects (quantum effects are quite weak at high enough temperatures). The results may help to understand the exotic thermal phenomena in practical applications.

In present work, p-type CdTe nanostructure thin films successfully synthesized on transparent conductive fluorine-doped SnO2-coated (FTO) substrate from acidic bath using three-electrode electrodeposition technique. Influence of applied potential and electrodeposition time on the structural, morphology and opto-electrical properties of the deposited films has been systematically investigated. Raman spectroscopy, low angle XRD, and HR-TEM analysis suggest that electrodeposited thin films have zinc blende cubic crystal structure. At optimized deposition conditions, we have found that CdTe thin films have direct band gap in the range 1.42–1.53 eV with a blue shift in absorption edge which may caused by quantum confinement effects in the CdTe thin films. The Hot probe experiment and Hall coefficient (RH) values confirmed the p-type semiconducting behavior of CdTe thin films. The ease of deposition of p-type CdTe nanostructure with different morphologies at room temperature provides a new insight for potential applications in hetero-junction solar cells technology.

The k.p Hamiltonian model at low-energy regime and Green’s function technique are carried out to study the effect of Rashba spin-orbit coupling (RSOC) on the spin-dependent thermodynamic properties in monolayer molybdenum disulphide. In particular, we have studied electronic band structure (EBS), electronic heat capacity (EHC), and magnetic susceptibility (MS) of spin-up and spin-down subbands by variation of RSOC strength. An enhancement of the spin splitting can be achieved by increasing the Rashba coupling strength. Electronic subband structure shows that the effective mass of carriers decreases with Rashba coupling while the spin-up and spin-down subband gaps remain constant. The reduced effective mass leads to the increase of both EHC and MS as reasonable results. Spin splitting can be also obtained from the EHC and MS findings. At very strong Rashba couplings, two Dirac-like points appear for spin-up subbands which we can claim that the system gets a new quantum anomalous Hall phase.

By applying the full π-band Holstein model, we analytically have calculated the electronic density of states (DOS) and optical conductivity of doped gapped graphene-like structures including silicon carbide (SiC), boron nitride (BN), and beryllium monoxide (BeO) beyond the Dirac cone approximation. We have implemented the Kubo linear response formalism which is established to get the retarded self-energy here. For strong electron-phonon (e-ph) coupling strengths, an addition peak in the optical conductivity has been found, associated with transitions between the midgap states and the Van Hove singularities of the main π-bands. Optical conductivity (optical absorption) decreases (increases) with the gap which is useful in the fabrication of low-dimensional-based solar cells. At large gaps, a clean sheet of doped graphene has a zero optical conductivity at low energies because of the optically interband excitations through the Dirac points. Also, the Drude weight remains unchanged for all cases at low energy regimes. Consequently, DOS and optical conductivity remain constant with temperature at low e-ph interaction strengths.

Dirac theory and Green's function technique are carried out to compute the spin dependent band structures and corresponding electronic heat capacity (EHC) of monolayer (ML) and AB-stacked bilayer (BL) molybdenum disulfide ( MoS 2 ) two-dimensional (2D) crystals. We report the influence of induced exchange magnetic field (EMF) by magnetic insulator substrates on these quantities for both structures. The spin-up (down) subband gaps are shifted with EMF from conduction (valence) band to valence (conduction) band at both Dirac points in the ML because of the spin-orbit coupling (SOC) which leads to a critical EMF in the K point and EHC returns to its initial states for both spins. In the BL case, EMF results split states and the decrease (increase) behavior of spin-up (down) subband gaps has been observed at both K and K ′ valleys which is due to the combined effect of SOC and interlayer coupling. For low and high EMFs, EHC of BL MoS 2 does not change for spin-up subbands while increases for spin-down subbands.

In this work, the spin-dependent electronic band structure and magnetic susceptibility (MS) of two graphene’s analogue, monolayer and AB-stacked bilayer MoS 2, are investigated in the presence of induced magnetization by magnetic insulators. Here, we have assumed that the type of magnetic insulators can change the magnetization strength. By focusing on the Dirac points of Brillouin zone and using the Dirac theory within the Green’s function approach, band structures and MSs of two systems are compared. In the bilayer case, gate voltage produces an electric field in order to have spin-orbit coupling (SOC) for spintronic applications. Our results represent the Stark and Zeeman effects because of the spin splitting states by electric and magnetic fields. We have found that the MS has marvelous behaviors before and after a critical magnetization in the monolayer MoS 2 while it increases slightly in bilayer lattice. Up (down) spin band gaps in bilayer MoS 2 decreases (increases) at both Dirac points due to the combined SOC and interlayer hopping potentials.

The Kane-Mele model and Green’s function technique help us to describe and survey the influences of electric and exchange magnetic fields (EF and EMF) on the dynamics of Dirac fermions in the monolayer silicene by studying the energy dispersion (ED), electronic heat capacity (EHC) and Pauli magnetic susceptibility (MS). Spin band gaps show three phases including topological insulator (TI), valley-spin polarized metal (VSPM) and band insulator (BI) in the presence of external EF. The maximum value for EHC and MS have been observed in the VSPM phase. Also, ED evolution with EMF shows that the Fermi level decreases. Interestingly, two critical temperatures have been found in the VSPM regime of 0.5 and 2 in terms of spin-orbit coupling (SOC) strength in the EHC and MS curves, respectively. In addition, remarkable point in the VSPM regime is the observed phase transition from antiferromagnetic to paramagnetic in MS curves. Competition between thermal and quantum effects is the main reason of these critical points which these findings can control the thermal properties of silicene-based devices.

Using the Green’s function technique and tight-binding (TB) Hamiltonian method for π-electrons within a ladder model of long DNA double-strands acting as semiconducting nanowires, the temperature and sequence dependency of the Pauli paramagnetic susceptibility (PMS) and electronic heat capacity (EHC) of some selected configurations are investigated. The results show the explicit reliance of the two quantities on the arrangement of the DNA base-pairs (BPs). The notable result of this study is the appearance of three temperature points for which the EHC (PMS) curves of the ordered systems converge (diverge) at the lowest and highest points, while they diverge (converge) at the middle point. Disordered systems exhibit a deviation from the trend of the ordered ones and this is more significant around the higher temperature points. Over a wide range of temperatures, the responses of the poly(GC) and poly(AT) double-helices limit the behavior of the random DNA chains. Our finding could inspire the design of experiments to assess the order of randomness in BP sequencing and also to better set the TB parameters of the model.

Topological crystalline insulators (TCIs) are particularly one of the most fascinating materials in current research. The gapless surface states protected by the crystal point group symmetries in TCIs entail the emergence of nontrivial physics and can be tailored by controlling the external perturbations. This paper is devoted to a detailed analysis of the perturbation effects on the quantum phase of SnTe(001) surface states. Generically, surface states are gradually perturbed so that the gapless phase dies out. In doing so, a numerical study of the perturbed k[combining right harpoon above]·p[combining right harpoon above] model is accomplished by the linear response theory and the Green's function technique. The model is experimentally accessible. The system displays a commensurate breaking of the mirror invariance imposed by external perturbations such as strain, magnetic proximity effect/electric field/Zeeman magnetic field, Rashba spin-orbit coupling, and dilute charged impurity. The interesting behaviors are explained by the variation of the gap with the above-mentioned perturbations (invoking the opening of the gap) at Dirac cones corresponding to the TCI phase. For suitably tuned parameters, SnTe(001) surface states realize gapped phases. The synergy of perturbations is responsible for breaking down the topologically non-trivial character of SnTe and related alloys. Further, the conditions under which the variations of the parameters maintain the topological properties are discussed. These findings and predictions report that, besides a vast number of TCI applications, TCIs are versatile candidates for topological transistors with tunable ON and OFF states if appropriate tuning of the surface band gap can be performed experimentally.

Tin disulfide can be a good electrode material in supercapacitors due to the presence of significant interlayer space in crystalline structures and large surface area. However, there are only a few reports of its supercapacitor applications. In this study, we report flower-like pure SnS2 and alkali metals (Li, Na, K and Cs) doped-SnS2 nanostructures synthetized by simple single-step solvothermal method without use of any surfactants. Results show that due to the presence of dopants, with increasing radius of the dopant element, the interlayer distance and dislocation intensity increase. This leads to an increase in the expanded space between interlayer and electro-active sites, and therefore, it is possible to intercalate more ions from the electrolyte. But due to the higher conductivity of Na than the other alkali metals, Na doped-SnS2 shows higher current density at constant voltage and thus better capacitance performance than the others. Na doped-SnS2 exhibits higher supercapacitor performance with a high capacitance of 269 Fg−1 at a current density of 1 Ag−1. The significant electrochemical performance of Na doped-SnS2 can be attributed to its particularly good surface area due to the expansion of interlayer space, increasing of electro-active sites and greater conductivity due to the presence of Na.

In this paper, by using density functional theory, Mg and Nb-Mg co-doping of TiO2 anatase (101) surfaces are studied. By studying the formation energy of the defects and the bond length distribution of the surface, it is shown that Mg defects tend to stay as far as possible to induce least possible lattice distortion while Nb and Mg defects stay close to each other to cause less stress to the surface. By investigating band structure of the surface and changes stemmed from the defects, potential effects of Mg and Mg-Nb co-doping of TiO2 surface on dye-sensitized solar cells are investigated. In this study, it is shown that the Nb-Mg co-doping could increase JSC of the surface while slightly decreasing VOC compared to Mg doped surface, which might result in an increase in efficiency of the DSSCs compared to Nb or Mg doped surfaces.

In axially coordinated DSSCs the dye is attached to the surface via linker and the linker play a role of a conductor of electron and a bridge to the surface which has a very important effect on the efficiency of the cell. It has been shown that using one particular dye with different linkers could result in different efficiencies. In this paper, using density functional theory, different carboxylic acid (CA) linkers, and different phosphonic acid (PA) linkers are studied and their effects on the electronic structure of the surface and changes in the HOMO and LUMO of the linkers due to adsorption on the surface are investigated. For each family of linkers, based on calculations, the best one to be used in axially coordinated DSSCs is suggested. Comparing these two families, carboxylic acid linkers show superior properties in terms of cell efficiencies. phosphonic acid linkers, however, are shown to strongly bond to surface while resulting in lower conversion efficiencies compared to the carboxylic acid linkers the reason of which is still a question. Based on calculation of the changes in properties of the surface and properties of phosphonic acid linkers some reasons behind their low performances are suggested.

In this work, effects of Niobium (Nb) defects on TiO 2 surface using density functional theory (DFT) are investigated. Based on formation energy of the defects, their occurrences in two different extreme conditions, O-rich and O-poor conditions, are evaluated. Effects of Nb defects on surface and its electronic structure are studied and it is demonstrated that Nb doping widens valence band in deep energy level leaving the band gap without any change and it also lowers oxygen vacancy defect concentration due to the stronger bonding of Nb sub defect with oxygen atoms specially bridging oxygen (most probable defect site for Oxygen vacancy). Higher density of Nb substitutional defects (Nb sub ) are examined and it is shown that higher density doping of TiO 2 surface leads to uniform distribution of defects over the anatase structure as a result of interaction of Nb defects when they are close and this fact prevents segregation of Nb atoms in Nb-doped TiO 2 .

The self-assembly of fibrils is a subject of intense interest, primarily due to its relevance to the formation of pathological structures. Some fibrils develop branches via the so-called secondary nucleation. In this paper, we use the master equation approach to model the kinetics of formation of branched fibrils. In our model, a branched fibril consists of one mother branch and several daughter branches. We consider five basic processes of fibril formation, namely, nucleation, elongation, branching, fragmentation, and dissociation of the primary nucleus of fibrils into free monomers. Our main focus is on the effect of the directionality of growth on the kinetics of fibril formation. We consider several cases. At first, the mother branch may elongate from one or from both ends, while the daughter branch elongates only from one end. We also study the case of branched fibrils with bidirectionally growing daughter branches, tangentially to the main stem, which resembles the intertwining process. We derive a set of ordinary differential equations for the moments of the number concentration of fibrils, which can be solved numerically. Assuming that the primary nucleus of fibrils dissociates with the fragmentation rate, in the limit of the zero branching rate, our model reproduces the results of a previous model that considers only the three basic processes of nucleation, elongation, and fragmentation. We also use the experimental parameters for the fibril formation of Huntingtin fragments to investigate the effect of unidirectional vs bidirectional elongation of the filaments on the kinetics of fibrillogenesis.

The gap modulation is an intriguing feature of the single-layer black phosphorene (BP) in optoelectronics. In this paper, the uniaxial and biaxial strain effects are systematically investigated to tailor the band gap, Fermi velocity, and effective mass along both armchair (AC) and zigzag (ZZ) directions in BP. The tight-binding model and the Harrison rule propose the electronic phase transitions. In the presence of uniaxial strains, in-plane strains keep the semiconducting phase, while the semiconductor-to-insulator and semiconductor-to-semimetal phase transitions emerge for biaxial strains. Although the anisotropic Fermi velocity introduces critical strains for which the concavity inversion occurs, Fermi velocity increases (decreases) with in-plane (out-of-plane) strain along the AC direction, while it remains constant along the ZZ direction. Further, we found that the heavy (light)-effective mass is related to the ZZ (AC) direction. Moreover, both in-plane and out-of-plane strains lead to effective mass sign-changing due to the concavity inversion of bands. Additionally, the heaviest effective masses are dedicated to critical strains corresponding to the phase transitions after which the concavity inversion of bands emerges. Our results propose interesting information for the strain tuning of electronic properties in BP.

The evolution of the electron energy loss spectrum (EELS) of ultranarrow armchair boron nitride nanoribbons (aBNNRs) during low and high photon energy transfers has been studied theoretically when a magnetic field and temperature gradient are applied. In order to achieve this goal, the widely used linear response theory within the Green’s function theory was employed. Here, using the EELS we show that σ ↦ σ* or π ↦ π* and σ ↦ π* or π ↦ σ* excitations corresponding to the intraband and interband transitions, respectively, can be tuned by ribbon width, magnetic field, wave vector transfer, and temperature. A comparison with experimental studies reveals that for realistic ribbon widths, i.e. 10–100 nm, both excitations are weak. However, we observe that only transitions between the same states, i.e. σ ↦ σ* or π ↦ π* can be controlled with a magnetic field due to the localized highest occupied and lowest unoccupied states at low-energy regions and different states are not influenced when the magnetic field is applied. Interestingly, the detailed shape of the magneto-EELS of the 7-aBNNR indicates a direct-to-indirect band gap transition when the wave vector transfer is perpendicular to the 7-aBNNR plane. Finally, we discover that there is an anomalous behavior for the temperature dependence of the magneto-EELS in general. The present work brings forward the understanding of the magneto-EELS of ultranarrow aBNNRs under different environmental conditions for logic applications in nanoplasmonics.

ZnO/TiO2 core/shell nanorod arrays were deposited on indium tin oxide (ITO) substrate via a facile sol–gel dip-coating process. Effects of solution pH for ZnO, annealing temperature, growth time and temperature on the physical properties of nanorods have been investigated. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) were employed to characterize the structural and morphological properties of the prepared composite nanorods. XRD result revealed wurtzite structure of ZnO with a mixed anatase and rutile structure phase for TiO2. Energy-dispersive X-ray (EDX) and UV–vis spectroscopy were used to study the chemical composition and optical properties of the films, respectively. Electrical resistivity of the films was also investigated. The optical and electrical properties of the bare TiO2 thin film and core/shell composite were compared together. The results showed that owing to smaller band gap and lower resistivity, the core/shell structure as an electron transport layer for inverted photovoltaic devices is more suitable than bare TiO2 thin film.

Lead sulfide (PbS) quantum dots were prepared by successive ion layer adsorption and reaction technique based on spin-coating (spin-SILAR). The effect of molar concentration of solution on optical and photovoltaic properties was studied. Optimized PbS quantum dot sensitized solar cell demonstrated maximum power conversion efficiency of 3.29% with short-circuit current of 10.06 mA/cm 2 and open-circuit voltage of 0.59 V under 1 sun illumination (AM1.5). The results showed that PbS QD layer fabricated by a solution with molar concentration of 5 mM can be used as a highly efficient sensitizer for solar cells. PbS QD layer acts as light absorber and recombination blocking layer in the ITO/ZnO film/PbS QD/P3HT/PCBM/Ag structure.

TiO2 nanotube arrays were grown on glass substrate by ZnO nanorod sol–gel template process. XRD analysis and FESEM microscopy were employed to characterize the structural and morphological properties of the prepared nanotube. EDX and UV–Vis spectroscopy were used to assess the chemical composition and study the optical properties of the film. An optical model has been performed to simulate the optical constants and thicknesses of the films from transmittance data using the Levenberg–Marquardt algorithm via Drude model. The simulated transmittance is in good agreement with the measured spectrum in the whole measurement wavelength range. The refractive index and extinction coefficient, thickness and dielectric function of TiO2 nanotube films were calculated by Drude model. Also, the related absorption coefficient, optical bandgap and porosity were determined.

An inverted structure of polymer solar cells based on Poly(3-hexylthiophene)(P3HT):[6-6] Phenyl-(6) butyric acid methyl ester (PCBM) with thin films of sol-gel derived Cesium doped ZnO (Cs:ZnO) was developed as an efficient cathode buffer layer. Doped and undoped thin films were deposited using a less studied method, doctor blade, which was compatible with Roll-2-Roll printing method. By comparing the effect of Cs:ZnO thin films with various dopant ratio on the performance of inverted polymer solar cells, 0.5% Cs doped ZnO was found as the most effective doping level among the selected doping ratios. Using 30 nm thickness of 0.5% Csn:ZnO thin film as an electron transport layer led to the average efficiency which was significantly higher than (9%) that of similar devices employing the same thickness of undoped ZnO film. Results showed that the devices fabricated with 1% and 2% cesium doped ZnO yielded lower power conversion efficiency, which could be due to the lower FF. Also, the influence of dopant incorporation on the optical transmittance and electrical conductivity of ZnO films was investigated.

Improved power conversion efficiency of hybrid solar cells with ITO/ZnO seed layer/ZnO NRs/ZnS QDs/P3HT/PCBM/Ag structure was obtained by optimizing the growth period of ZnO nanorods (NRs). ZnO NRs were grown using a hydrothermal method on ZnO seed layers, while ZnS quantum dots (QDs) (average thickness about 24 nm) were fabricated on the ZnO NRs by the successive ionic layer adsorption and reaction (SILAR) technique. Morphology, crystalline structure and optical absorption of layers were analyzed by a scanning electron microscope (SEM), X-ray diffraction (XRD) and UV-Visible absorption spectra, respectively. The XRD results implied that ZnS QDs were in the cubic phase (sphalerite). Other experimental results showed that the maximum power conversion efficiency of 4.09% was obtained for a device based on ZnO NR10 under an illumination of one Sun (AM 1.5G, $100mW/cm^2$ ).

In this work, the structural and electronic structure of CuInS 2 nanowires have been computed via density functional theory by using numerical atomic orbital bases set with local-density approximation. The norm-conserving pseudopotentials of Troullier and Martins are used. In our calculation we used nanowires in two shapes of hexagonal and triangular with their diameters ranging from 8 to 19 A in (1–10) growth direction for both cases of unsaturated and saturated with hydrogen. The geometrical parameters like equilibrium lattice constant and anion displacement are in reasonable agreement with the experimental data and other theoretical results. We show that for the unsaturated nanowires there is a significant contraction of the Cu–S and In–S bond lengths at the edge of the wires of 0.17–3.70%, as for saturated wires at the edge, it is 0.7%. Also electronic properties like band structures and atom-projected density of states have been studied. The band structures confirm that CuInS 2 nanowires are semiconductors with a direct band gap and there is hybridization between Cu-d with S-p states in the uppermost valance sub-bands of the CuInS 2 nanowires. We show that for saturated nanowires, as the diameter of the nanowire increases, its relative band gap (Δ E g ) decreases. But for the unsaturated nanowires, the band gap remains constant with varying diameter and from projected density of states of atoms, the peaks are decreasing from edge to center of nanowires. Also the highest valence bands involve atoms located at the surface. And finally we can see that for all atoms the peaks are increased when the size of nanowires increases.

Graphical abstract: - Highlights: • TOPO-capped CuInS{sub 2} nanoparticles were synthesized by injection method. • Pure CuInS{sub 2} nanoparticle was obtained by injection in 200 °C. • The size, shape and optical properties of products were controlled. • Nanoparticles with size smaller than 10 nm and wurtzite phase was obtained. • The absorption and PL spectra of CuInS{sub 2} nanoparticles were tunable. - Abstract: In this work, synthesis of CuInS{sub 2} semiconductor nanoparticles by thermolysis of a mixed solution of CuAc, In(Ac){sub 3} and DDT in coordinating solvent and trioctylphosphine oxide (TOPO) as ligand was developed. CuInS{sub 2} nanoparticles with size of −10 nm and nanorods were obtained and optical properties controlled by adjusting the reaction parameters such as temperature and time. Also the shape of nanoparticles was controlled by various solvents elaborately. The as-prepared nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), UV–vis absorption, and photoluminescence (PL) spectroscopy. With the use of different solvent different morphology obtained. In the presence of oleylamine/octadecene rectangle-like nanorods obtained while with the use of oleic acid sphere-like nanoparticles achieved.

Highly transparent Gallium doped ZnO (GZO) thin films with different ratios of Gallium were synthesized by sol-gel process and dip coating technique. Concentration of the used solutions for dip coating was 0.09 M. Morphological investigations were done on GZO thin films with 0, 0.5, 1 and 2 at. % gallium content. Influences of doping ratio and post-annealing temperature on optical and electrical properties of the films were also studied. It was found that the film prepared from the solution containing 2 at. % Ga had improved structural properties, less electrical resistivity and biggest optical transmittance. The thickness dependence of the band gap of 2 at. % GZO thin films was also examined. Effect of Cs2CO3 nanolayer and ZnO thin film deposited on 2 at. % GZO thin film was studied. SEM images exhibited island features on the surface of GZO/Cs2CO3 bilayer.

The anisotropic frequency-dependent optical conductivity of single-layer puckered phosphorene is studied, and also its dependence on the electrostatic gating of the top and bottom sublayers. The effective Hamiltonian within the k → ⋅ p → approximation is used to obtain the electronic band structure from which the interband optical transitions are evaluated using the Kubo formula. Inherent asymmetry in the dispersion energy of carriers along the armchair and zigzag edges gives rise to anisotropic optical features. The bandgap increases with gate voltage resulting in absorption at higher optical energies along the armchair edge, which is the so-called blue shift, while along the zigzag edge such a shift is not significant. The temperature and exciton effects on the interband response are concisely discussed. These results provide new insights which render phosphorene attractive for optoelectronic devices.

We investigated the effect of employing ZnO nanorods in an inverted polymer solar cell based on Poly(3-hexylthiophene) and Indene-C60 Bis-Adduct. Hydrothermal method was chosen to growth of vertically aligned ZnO nanorods on 30 nm thick ZnO seed layer. The samples were analyzed by x-ray diffraction (XRD), scanning electron microscopy (SEM), and electrical conductivity measurements. Indene-C60 Bis-Adduct, as new acceptor with higher-lying LUMO energy level than PCBM blended with P3HT. Efficient infiltration of polymer into interspaces between nanorod arrays concluded to improved performance of the device. Photovoltaic characteristic of inverted polymer solar cell with ZnO nanorods were compared with devices employed ZnO thin film. Inverted polymer solar cell based on Poly (3-hexylthiophene) and Indene-C60 Bis-Adduct hybridized with ZnO nanorods exhibited power conversion efficiency of 4.04% that was better than a device with ZnO thin film interlayer (3.80%).

Single crystalline cesium-doped ZnO nanorods with homogeneous size and shape were hydrothermally grown on Cs–ZnO nucleated glass substrate. The effect of hydrothermal growth duration on the characteristics of Cs-doped ZnO nanorods was examined. The samples were analyzed by X-ray diffraction (XRD), energy dispersive X-ray analysis, scanning electron microscopy, and electrical conductivity, optical transmission and photoluminescence (PL) measurements. XRD analysis showed that Cs-doped ZnO nanorods are wurtzite single crystals and are grown preferentially along the c-axis. Elemental analysis confirmed the presence of 1 at.% of Cs, according to the composition of growth solution. Electrical conductivity of typical samples showed higher values for the 1 at.%-doped sample, which confirmed incorporation of the Cs dopant. The samples were optically transparent and showed two UV and visible PL peaks from which the former peak experienced a red shift and a pronounced increase in intensity with increasing growth time. The fabricated Cs-doped ZnO nanorods are suitable candidates for applications as excitonic solar cells due to their ease of fabrication, morphology control and optical properties.

In this work, the structural, electronic structure and optical properties of CuXY2(X=In, Ga and Y=S, Se) chalcopyrite semiconductors have been computed with density functional theory using numerical atomic orbital pseudopotential method with both local-density and generalized gradient approximations. The geometrical parameters like equilibrium lattice constant and anion displacement are in reasonable agreement with the experimental data and other theoretical results. Also electronic properties like band structures and density of states have been studied. The band structures show that CuXY2 compounds are semiconductors with a direct band gap and there is hybridization between Cu (d) with S (p) orbital in CuInS2 and CuGaS2 and hybridization between Cu (d) with Se (p) orbital in CuInSe2 and CuGaSe2. Furthermore, the optical properties, real part of the dielectric function, refractive index, reflectivity and absorption coefficients are calculated from the imaginary part of the dielectric function, which are compatible with the experimental data and earlier theoretical results.

Geometries of monomers and oligomers of a platinum polyyne and its free ligands were optimized using density functional theory with B3LYP hybrid functional. The LANL2DZ basis set was used for Pt and the 6-31G* for other atoms in geometry optimizations. The electronic structures of these compounds were analyzed using Stuttgart/Dresden ECPs (SDD) basis set for metal atoms and 6-311G* for others. The polymerization has very little effect on the bond lengths and by introducing the metal, the acetylide bond length increases slightly. The strong overlap between metal spx orbitals and σpx orbitals of acetylides results in localized σ bonding. The hybridization between the ligand pπ orbitals and the platinum dπ orbital resulted in the π-conjugation enhancement. This conjugation enhancement causes some effects such as the highest-occupied molecular orbital–lowest-unoccupied molecular orbital gap reduction and charge transfer characteristic of low-energy vertical transitions. © 2013 Wiley Periodicals, Inc.

Composite of polymer with a small content of strong material, such as carbon nanotube (CNT) and metallic nanowire (NW) has interesting mechanical, thermal, optical and electrical properties. For the first time, we used molecular dynamics simulations (MD) with polymer consistent force field (PCFF) to study adsorption of polymers involving Poly(3-hexythiophene) (P3HT) and Poly[[[(2ethylhexyl)oxy]methoxy-1,4-phenylene]-1,2-ethenediyl] (MEH-PPV) on metallic NW including silver and gold. The influence of main factors such as NW radius and temperature on the interfacial adhesion of NW–polymer and radius of gyration of polymers ( R g ) were studied. We showed that the interaction energy decreases slowly with increasing temperature, thus the temperature influence is very weak. Our results showed that P3HT-Au has the strongest interaction energy, then MEH-PPV-Au, P3HT-Ag, and finally MEH-PPV-Ag. In addition, the interaction energy increased with increasing NW radius, thus the NW with large radius is the best type for reinforcement. We studied the influence of NW radius and temperature on the radius of gyration ( R g ). We found that R g oscillated slowly and no obvious trend was seen. In other words, NW radius and temperature had no influence on R g value. We showed that the R g value for P3HT was higher than MEH-PPV, thus P3HT expanded more than MEH-PPV on NW surface.

Mixtures of Single-Walled Carbon Nanotubes (SWNTs) and polymers play an important role in practical applications such as ultrastrong lightweight materials and organic solar cells. In present work, we studied the interaction between SWNTs and polymers including poly(3-hexythiophene) (P3HT), Poly(2-methoxy-5-(3-7-dimethyloctyloxy)-1,4-phenylenevinylene) (MDMO-PPV), and Poly[[[(2ethylhexyl)oxy]methoxy-1,4-phenylene]-1,2-ethenediyl] (MEH-PPV) by molecular dynamics (MD) simulation. For the first time, we use molecular dynamics simulation based on a reactive force field (ReaxFF) to study the interaction between polymers and SWNTs. Interaction energy between polymers and SWNTs was calculated. Morphology of polymers adsorbed to the surface of SWNTs was investigated by the radius of gyration ( R g ). Influence of temperature, SWNT radius, and chirality on interfacial adhesion of SWNT-polymer and R g of the polymers were studied. Our results showed that the strongest interaction between the SWNTs and these polymers was observed first for P3HT, then MDMO-PPV, and finally MEH-PPV. We found that the interaction energy is influenced by the specific monomer structure of the polymers, SWNT radius, and chirality, but the influence of temperature is very weak. The temperature, radius, and chirality have not any important effect on the radius of gyration.

Single-walled carbon nanotubes (SWNTs) have unique properties such as high electrical conductivity and high tensile strength. Their composites with polymers have a great role in new sciences such as organic solar cells and ultrastrong lightweight materials. In this article, molecular dynamic simulations with polymer consistent force field are performed to study the interaction between SWNTs and conjugated polymers including poly(2-methoxy-5-(3-7-dimethyloctyloxy)-1,4-phenylenevinylene) (MDMO-PPV), poly(3-hexythiophene) (P3HT), and poly[(9,9′-dioctylfluorenyl-2,7-diyl)-co-bis(N,N′-(4,butylphenyl))bis(N,N′-phenyl-1,4-phenylene)diamine] (PFB). We computed the interaction energy and morphology of polymers adsorbed to the surface of SWNTs was studied by the radius of gyration (Rg). The influence of important factors such as SWNT radius, chirality, and the temperature on the interfacial adhesion of SWNT–polymer and Rg of polymers were studied. We found that the strongest interaction between the SWNTs and these polymers was, first observed for P3HT, then MDMO-PPV, and finally PFB. Our results showed that the interaction energy is influenced by SWNT radius and the specific monomer structure of the polymers, but the effects of chirality and temperature are very weak. In addition, we found that the temperature, chirality, and radius have not any important effect on the radius of gyration. POLYM. COMPOS.,, 2012. © 2012 Society of Plastics Engineers