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In the present study, the effects of the strain engineering and electric field on electronic properties of the GaS monolayer are investigated by ab initio investigations. Our calculated results demonstrate that the GaS monolayer is a semi-conductor with a large indirect bandgap of 2.568 eV at the equilibrium. In the presence of a biaxial strain, the band structure of the GaS monolayer, especially the conduction band, changes significantly. However, while the effect of compressive strain on the energy gap of the GaS monolayer is quite weak, its energy gap depends strongly on the tensile strain. On the other hand, external electric fields can cause the semiconductor–metal transition in the monolayer. Being able to control electronic properties, especially the occurrence of the semiconductor–metal phase transition, makes the GaS monolayer a prospective material for nanoelectromechanical and nanospintronic applications.

In this study, we investigate systematically the effect of strain engineering and electric field on electronic properties of single-layer SnSe 2 using density functional theory . Our calculated results indicate that the single-layer SnSe2 is a semiconductor with a small band gap of 0.715 eV at the equilibrium state. The electronic states near the Fermi level are mainly contributed by Sn- d and Se-p orbitals, especially the contribution of the Se-p orbital to the valence band is dominant. Under biaxial strain, the band gap of the single-layer SnSe2 changes abnormally. While compressive biaxial strain reduces band gap rapidly, the band gap of the single-layer SnSe2 only increases slightly when increasing the tensile biaxial strain. In contrast to the strain-dependence case, the influence of the external electric field on the electronic properties of the single-layer SnSe2 is quite small and the energy gap of the single-layer SnSe2 does not depend on the direction of the perpendicular electric field. Our calculated results can provide more information for application possibility of the single-layer SnSe2 in nanoelectronic devices.

We theoretically study the combined effect of Al-concentration, hydrostatic pressure, and temperature on the magneto-optical absorption properties of a semi-parabolic quantum well (SPQW) by investigating the magneto-optical absorption coefficient (MOAC) and the full-width at half-maximum (FWHM). The expression of MOAC is expressed by the second-order golden rule approximation where the electron–longitudinal-optical (LO) phonon interaction is taken into account while the FWHM is obtained from the profile of the curves. The numerical calculations are made for a typical GaAs/GaAlAs quantum well. Our results showed that the Al-concentration, hydrostatic pressure, and temperature affect the magneto-optical absorption properties strongly. Threshold energy and the resonant peaks are non-monotonic functions of the Al-concentration. Moreover, it has been revealed that the magneto-optical absorption properties of SPQW can be controlled by changing these parameters.

The vertical stacking and influence of external electric field are good techniques to tune the electronic properties of two-dimensional materials for potential nanoelectronics and optoelectronic devices. The structural and electronic properties of P-ZnO and SiC-ZnO van der Waals (vdW) heterostructures are investigated by first principles calculations. P-ZnO (SiC-ZnO) heterostructure exhibits an indirect type-I (direct type-II) semiconducting band character. The effect of perpendicular applied external electric field on the electronic properties of the most stable vdW heterostructure has also been systematically discussed. Remarkable variations in the band gap nature are induced by increasing field strength from 0.1 to 1.0 V/A (for P-ZnO) and 0.1 to 0.8 V/A (for SiC-ZnO). The intrinsic indirect type-I is modulated to type-II semiconducting band gap in P-ZnO by applying electric field strength 0.1 V/A. More interestingly, reduction in the size with transition from an indirect-to-direct type-II semiconductor band gap nature is noted at 0.5 V/A. However, a direct type-II semiconductor to metallic character is found at 1.0 V/A (for P-ZnO) and 0.8 V/A (for SiC-ZnO). Our results suggests that these vdW heterostructures are promising candidates for electronic and optoelectronic device applications.

In this letter, we systematically investigate the electronic properties of the PtS2/InSe heterostructure using first-principle calculations. At the equilibrium interlayer distance D = 3.23 A, the PtS2/InSe heterostructure displays a semiconducting character with an indirect band gap. Moreover, it forms a type-II band alignment, making the PtS2/InSe heterostructure a potential material for efficient separation of photogenerated electron-hole pairs. More interestingly, by applying vertical strain and electric field, the electronic properties of the PtS2/InSe heterostructure can be effectively controlled, and a semiconductor-to-metal transition even emerges. These findings suggest attractive potential application for PtS2/InSe heterostructure as a novel optolectronic nanodevices, along with a potential pholocatalyst.

We investigate the combined effects of hydrostatic pressure, Al-concentration, temperature, and well-width parameter on the magneto-optical absorption properties (MOAPs) of a hyperbolic-type quantum well (HTQW). The results covered all possible processes: both phonon absorption and emission as well as both one- and two-photon. Our results show that the MOAPs of the HTQW significantly depend on the pressure, the Al-concentration, the temperature, and the well-width. We also suggest two new expressions for the dependence of the full-width at half-maximum on the pressure and concentration which need an experimental study to evaluate their validity. Our study provides a systematic results of the combined effects of pressure, Al-concentration, temperature, electron-phonon scattering, and the two-photon absorption on the nonlinear optical properties of such two-dimensional semiconductors, which would be useful for the applications in photonic devices.

Constructing van der Waals heterostructures (vdWHs) based on different two-dimensional materials could afford many interesting properties, which may not hold for single-layered materials. In this study, we design a novel vdWH-GaSe/MoSe2 and investigate its electronic properties using first-principles calculations. It has a type-II band alignment with an indirect bandgap. Moreover, we found that the band alignment transformation of the GaSe/MoSe2 vdWH from type-II to type-I can be realized by decreasing the interlayer distance or by applying a positive electric field. Our findings could provide fundamental insights into the GaSe/MoSe2 vdWH for designing high-performance optoelectronic nanodevices.

Strain effects on the electronic and optical properties of monolayer SnSe is studied by APW + lo method in DFT framework. The applied strains cause direct-indirect transition of SnSe band gap which is mainly constructed by s / p hybridization. The armchair e ac and zigzag e zz reduce the unstrained band gap of 1.05 eV down to 0 eV at 12% compression, but at 12% tension, the band gap decreases to 0.726–0.804 eV. The band gap always increases under biaxial strain e b at 12% compression to 12% tension. We observe an enhancement of real e 1 ( ω ) and imaginary e 2 ( ω ) parts of dielectric function by 14%–30% of magnitude, wider peak distribution to infrared and ultra-violet regions, and appearance of new peaks in the e 1 ( ω ) and e 2 ( ω ) spectrums. As a consequence, the light absorption α ( ω ) is significantly enhanced in the ultra-violet region and the absorption even starts at lower energy at infrared region.

Graphene based two-dimensional layered materials are attracting wide attention both experimentally and theoretically and show many superior properties that individual layers may not hold. In this work, we study theoretically the electronic properties of the graphene/WSe2 van der Waals heterobilayer using the first-principle calculations. Our results demonstrate that the intrinsic electronic properties of graphene and WSe2 monolayer are quite well preserved due to the weak van der Waals interactions. We find that the graphene/WSe2 heterobilayer forms a p-type Schottky contact with the Schottky barrier height of 0.60 eV and shows a good thermoelectric material with high Seebeck coefficient at room temperature. Moreover, the p-type Schottky contact of the graphene/WSe2 heterobilayer can be tailored by inserting WSe2 monolayers to form graphene/WSe2/WSe2 and WSe2/graphene/WSe2 heterotrilayers or by applying electric field perpendicular to the heterobilayer. The p-type Schottky barrier decreases with the insertion of the WSe2 layers, whereas it can be transformed to the n-type one when the negative electric field of −1.5 V/nm is applied. The results reveal the physical nature of the van der Waals heterostructures based on graphene and other two-dimensional transition metal dichalcogenides, which are helpful in providing a route to design graphene-based high-performance optoelectronic nanodevices, such as Schottky diodes and interlayer tunneling field-effect transistors.

In this paper, van der Waals heterostructures consisting of MX2 (M = Zr, Hf and X = S, Se) monolayers are modeled. The favorable stacking and stability of the modeled monolayer heterostructures are confirmed through binding energy and phonon dispersion calculations. After confirming stability, the electronic and thermoelectric properties of these compounds are explored using the first-principles calculations combined with semiclassical Boltzmann transport theory. It is found that type-II band alignment in ZrS2 HfSe2 facilitates charge separation for optoelectronics and solar energy conversion. All studied heterostructures show remarkably higher electrical conductivity than corresponding monolayers, responsible for large power factor values, especially at 1200 K. These findings indicate that the creation of van der Waals heterostructures from MX2 may be promising for efficient optoelectronic and thermoelectric devices.

In the present work, we consider electronic properties of WX2 (X = S, Se) monolayers under a biaxial strain e b using the first principles study. Our calculations indicate that, at equilibrium, the WS2 and WSe2 monolayers are semiconductors with a direct band gap of respectively 1.800 eV and 1.566 eV while their bulk structures are indirect semiconductors. The electronic properties of the WX2 monolayers are very sensitive with the biaxial strain, especially compression strain. The biaxial strain e b is the cause of the band gap of the WX2 monolayers and especially the semiconductor-metal phase transition has occurred in the WS2 monolayer at e b = - 10 % . In addition, the direct-indirect band gap transition was observed in both WS2 and WSe2 monolayers at a certain elongation of biaxial strain e b . The phase transitions in these monolayers can be very useful for their applications in nanoelectromechanical devices.

Transition-metal dichalcogenide monolayers recently have attracted much attention motivated by their exotic physical properties. In this paper, we theoretically investigate the optical absorption in the monolayer MoS2 which is subjected to a uniform static magnetic field and an electromagnetic wave. The magneto-optical absorption power (MOAP) is calculated using the projection operator technique in the linear response scheme, taking account of the electron–optical phonon interaction at high temperature. Both phonon emission and phonon absorption processes are included. The cyclotron–phonon resonance (CPR) is observed in the photon energy dependence of the MOAP. Numerical analyses show that the photon energy satisfying CPR condition depends linearly on the strength of magnetic field, which is similar to that in conventional low-dimensional semiconductors but different from that in graphene. The increase of the full width at half maximum (FWHM) of CPR peaks with increasing magnetic field shows a similar behaviour to that in graphene. In addition, FWHM increases slightly with temperature, which is different from that in graphene where the FWHM is temperature independent. Our investigation provides basic information about the magneto-optical properties of the monolayer MoS2 that are useful for further experiments and applications.

In this work, we construct the C2N/InSe heterostructure and investigate its electronic properties as well as the effect of strain and electric field. Our results demonstrate that the weak van der Waals interactions are dominated in such heterostructure. It forms the type-II band alignment and implies the spatial separation of photogenerated electron-hole pairs. The type-II band alignment can be switched to type-I one and an indirect to direct band gap transition can be achieved by applying the electric field or vertical strain. Our findings demonstrate that the C2N/InSe heterostructure can be considered to be a good candidate for optoelectronic and nanoelectronic devices.

In this work, the structure, electronic properties, and the Schottky barrier of the van der Waals heterostructure (vdWH) based on graphene and gallium sulfide (GaS) have been theoretically considered using density functional theory. We found that the graphene/GaS vdWH keeps the extraordinary intrinsic properties of both the graphene and GaS monolayer. Moreover, an n-type Schottky contact with a small Schottky barrier of 0.51 eV was formed in the ground state of the heterostructure. Especially, our results demonstrated that applying an electric gating can tune effectively the Schottky barrier and contact types. The transformations from the n-type Schottky contact to the p-type one and from the Schottky to the Ohmic contacts were observed in the vdWH under electric gating. These results propose a great potential for the van der Waals heterostructure in future nanoelectronic and optoelectronic devices.

In this work, we consider systematically the influence of uniaxial strain and external electric field E on electronic properties of a monolayer InSe using ab initio approach based on density functional theory. Our calculations indicate that the monolayer InSe has a medium indirect energy bandgap of 1.38 eV at equilibrium. The calculated results also demonstrate that we can adjust the bandgap of the monolayer InSe by strain engineering or electric field. The bandgap of the monolayer InSe changes dramatically when the uniaxial strain is applied. Especially, under the compressed uniaxial strain, an indirect–direct bandgap transition has been observed at certain elongations. Within the electric field magnitude E range from 0 to 5 V/nm, the calculated results show that the negative electric field changes the bandgap of the monolayer InSe up to 23% while the positive electric field effect on its bandgap is negligible.

In this paper, we study the difference in electronic and optical properties of bulk and monolayer zirconium sulfide by applying the APW + lo method in the framework of density functional theory. All calculation is performed at the energy level of visual light and higher ranging from 0 eV to 15 eV. Our results demonstrates that except for the underestimated band gap like other GGA calculation, the remain properties like dielectric function, the reflectivity, absorption and loss energy are close to experiment. The valence band is constructed by mainly sulfur s/p-states and the lower portion of zirconium s/p/d-states. The conduction band is mostly donated by zirconium d-state. In contrast with bulk structure, the valence band maximum in monolayer has the triple peak at Γ point, making its monolayer be more sensitive to light absorption. The dielectric function has the highest peak at about 1.5–2.5 eV with remarkable anisotropy, beyond this level to the ultraviolet region the anisotropy decreases and almost disappears at energy larger than 10 eV. The absorption is at 106 x 10 4 cm -1 for energy range 5–10 eV, while the reflectivity is at its highest value of 30 %–50 % in the energy range from 0 to 8 eV. The energy loss of monolayer is higher than those of bulk. For optical and electronic properties, the monolayer show sharper peaks and their clear separation indicate the progressive application of monolayer zirconium sulfide.

The magneto-optical transport properties in monolayer silicene subjected simultaneously to a perpendicular magnetic field and an electromagnetic wave (optical field) are theoretically studied. The nonlinear absorption coefficient is calculated using perturbation theory taking account of the electron–impurity scattering. The cyclotron–impurity resonance (CIR) is observed through the absorption spectrum. The photon energy at resonances is found to be proportional to the square root of magnetic field. This behaviour is similar to that in graphene but different from that in conventional low-dimensional semiconductors. The full width at half maximum (FWHM) of CIR peaks increases with increasing magnetic field by the laws FWHM [meV] ≈ 0.432 B [ T ] and FWHM [meV] ≈ 0.215 B [ T ] for one- and two-photon absorption, respectively. The obtained FWHM is about one order of magnitude smaller than it is in graphene monolayers. Moreover, the temperature dependence of the FWHM is similar to that in graphene but different from that in conventional low-dimensional semiconductors.

The magneto-optical absorption coefficients (MOAC) and the full-width at half-maximum (FWHM) in a quasi-zero-dimensional quantum dot (QD) via two-photon process are theoretically studied in which the electron–phonon (e–p) interaction is involved. It is found that the best range of the magnetic field to observe the MOAC is from B = 3.49 T to B = 15.77 T. As the magnetic field enhances, the peaks intensities firstly enhance, reach the maximum value at B = 5.38 T, and then start reducing if the magnetic field continues increases further, while the peaks positions give a blue-shift. Besides, the magneto-optical absorption properties are found to be significantly affected not only by the quantum dot parameter but also by the temperature. The FWHM rises nonlinearly with the enhance of the magnetic field, the confinement frequency, and the temperature. The two-photon process makes an appreciable amount of the total absorption process.

In this paper, we systematically investigate the adsorption properties, atomic structures, electronic, and thermodynamic properties of tungsten, nitrogen, and oxygen atoms on the Ti-terminated TiB2(0001) surface without and with vacancies of titanium and boron atoms using the density functional theory (DFT). Local atomic structures of the surfaces R/TiB2(0001) (R = W, N, O) of adsorption models and their thermodynamic and electronic properties are studied by DFT. The bond lengths and the adsorption energy for different reconstructions of the atomic surface of the R/TiB2(0001) systems are established. The role of the degree of coverage of W, N and O atoms on the electronic structure and mechanisms of their adsorption on the surface (0001) of titanium diboride is investigated. We also consider the mechanisms of possible nucleation of tungsten on the surface of TiB2(0001). Effective charges on the tungsten atom (N and O) and nearest-neighbor atoms in the studied reconstructions are estimated. Our calculations show that the charges are transferred from the titanium atom to the W, N, and O atoms, which are due to the reconstruction of the local atomic and electronic structures and correlates with the electronegativity of the nearest-neighbor atoms.

Graphene-based van der Waals heterostructures by stacking graphene on other two-dimensional materials have recently attracted much attention due to their extraordinary properties and greatly extend the applications of the parent materials. By means of the density functional theory from first-principles calculations, in this work, the electronic properties and Schottky contact of the Graphene/InSe heterostructure, together with the effect of strain, are investigated systematically. Our results show that in the graphene/InSe heterostructure, graphene is very weakly bound to the InSe monolayer. Furthermore, we find that due to the sublattice symmetry breaking, a tiny band gap of 5 meV is opened in the graphene/InSe heterostructure, making it suitable for applications in electronic and optoelectronic devices. Moreover, we also find that the n-type Schottky contact is formed in the graphene/InSe heterostructure with a very small Schottky barrier height of 0.05 eV. The Schottky barrier height as well as Schottky contact types in the graphene/InSe heterostructure could be controlled by vertical strain applied perpendicularly to the heterostructure. When the interlayer distance between graphene and the topmost InSe monolayer is smaller than 2.40 A, one can observe a transformation of the Schottky contact of the graphene/InSe heterostructure. Our results may provide helpful information for designing novel high-performance graphene-based van der Waals heterostructures and explore their potential applications in future nanoelectronic and optoelectronic devices.

In this paper, we design novel ultra-thin graphene/MoSeS and graphene/MoSSe heterostructures and investigate systematically their structural and electronic properties as well as the effect due to perpendicularly applied electric field on the heterostructure. Our results show that the electronic properties of both the graphene (Gr) and Janus MoSeS monolayer are well kept in the Gr/MoSeS and Gr/MoSSe heterostructures due to weak interaction between them. The interlayer distance between the Gr and Janus MoSeS monolayer is derived to be 3.34 A, whereas the binding energy in the heterostructure is found to be - 3 meV per carbon atom, indicating the weak interactions between the Gr and Janus MoSeS layers. We find that in both Gr/MoSeS and Gr/MoSSe heterostructures, the Gr becomes a semiconductor with a tiny band gap of about 3 meV, forming between the π and π ∗ bands at the high symmetry K point. The appearance of the fundamental band gap in the Gr makes it suitable for application in electronics and optoelectronics like as field effect transistors. Furthermore, the Gr/MoSeS heterostructure forms an n-type Schottky contact with the Schottky barrier height of 0.53 eV at the equilibrium state. Our results also indicate that the electric field applied perpendicularly to the heterostructure could control not only the Schottky barrier height, but also the Schottky contact type from the n-type to p-type. Based on these extraordinary electronic properties of ultra-thin Gr/MoSeS heterostructures, which are expected to be with applications in nanoelectronic and optoelectronic devices in the future experiments.

In this work, by means of density functional theory, we systematically investigate the geometric structure and electronic properties of the vertical heterostructure by stacking graphene on top of single-layered hexagonal boron nitride and molybdenum diselenide (Gr/h-BN/MoSe2). Our results show that the interlayer coupling in the heterostructure is mainly governed by the weak van der Waals interactions. We find that in the heterostructure, a tiny band gap of 82 meV is opened around the Dirac K point of graphene due to sublattice symmetry breaking, and a minigap of 39 meV is opened between the π band of graphene and the vertical orbitals of MoSe2 due to their hybridization. This band gap opening in graphene makes it suitable for application in novel high-performance nanoeclectronic devices. Furthermore, the Gr/h-BN/MoSe2 heterostructure with inserting insulated h-BN layer forms an n-type Schottky contact with a small Schottky barrier height of 0.1 eV. These findings could provide helpful information for designing novel nanoelectronic devices by stacking graphene on top of single-layered h-BN and MoSe2.

In this work, we consider the effect of biaxial ɛb and uniaxial ɛac∕zz strains on electronic properties and optical parameters of monolayer SnS using first-principles calculations. Our calculations show that the monolayer SnS is a semiconductor with an indirect energy gap of 1.63 eV at the equilibrium state. While an effect of tensile strains on bandgap is quite small, the bandgap of monolayer SnS depends strongly on the compressive strains, especially a semiconductor-metal phase transition is occurred due to the uniform compressive biaxial strain at −14% elongation. The optical spectra of the monolayer are high anisotropic, and the absorption coefficient of monolayer SnS tends to increase in the presence of compression strains, while the tensile strains reduce the absorption coefficient of the monolayer SnS. We believe that the phase transition and extraordinary optical properties of the strained monolayer SnS will make it become a useful material in nanoelectromechanical devices and optoelectronic applications.

This paper is devoted to the study of the phonon-assisted cyclotron resonance (PACR) in a special asymmetric hyperbolic-type (SAsH) quantum well, in which the two-photon absorption process and the electron–LO-phonon interaction have been included. The PACR effect has been investigated through considering the magneto-optical absorption coefficient (MOAC) and the full-width at half maximum (FWHM). Our results showed that it is better to investigate MOAC and FWHM when the a-parameter value of the quantum well is in the range from 9.72 nm to 37.14 nm. The threshold energy decreases non-linearly with the a-parameter but increases linearly with the magnetic field. The resonant peaks caused by the emission phonon process are observed significantly. MOAC gives red-shift with the increase of a-parameter, gives blue-shift with the rise of magnetic field, but unchanged with the change of temperature, while MOAC's intensities increase with the increase of these three parameters. FWHM decreases with the rise of a-parameter but increases with the growth of temperature and magnetic field in both the emission and absorption phonon processes.

In the present work, using density functional theory (DFT), we investigate the influence of biaxial strain e b on electronic and optical properties of single-layer GeS. Our DFT calculations show that single-layer GeS is a semiconducting material at equilibrium and semiconductor-metal phase transition may occur at large compression biaxial strain. The optical absorption of single-layer GeS is high in the range of the middle ultraviolet lights. Besides, the biaxial has a great impact on the optical spectra of single-layer GeS in the high energy domains. The semiconductor-metal phase transition and the computational results of the absorption of GeS can provide more useful information for applications in nanoelectromechanical and optoelectronic devices.

The effect of strain on the structural and electronic properties of monolayer phosphorene is studied by using first-principle calculations based on the density functional theory. The intra- and inter-bond length and bond angle for monolayer phosphorene is also evaluated. The intra- and inter-bond length and the bond angle for phosphorene show an opposite tendency under different directions of the applied strain. At the equilibrium state, monolayer phosphorene is a semiconductor with a direct band gap at the Γ -point of 0.91 eV. A direct-indirect band gap transition is found in monolayer phosphorene when both the compression and tensile strain are simultaneously applied along both zigzag and armchair directions. Under the applied compression strain, a semiconductor-metal transition for monolayer phosphorene is observed at −13% and −10% along armchair and zigzag direction, respectively. The direct-indirect and phase transition will largely constrain application of monolayer phosphorene to electronic and optical devices.

Graphene-based van der Waals heterostructures are expected recently to design and fabricate many novel electronic and optoelectronic devices. The combination of the electronic structures of graphene and graphene-like GaSe monolayer (g-GaSe) in an ultrathin heterostructure has been realized experimentally, such as graphene/g-GaSe field effect transistor and dual Schottky diode device. In the present work, we investigate the electronic properties of the graphene/g-GaSe heterostructures under the applied electric field, in-plane strains, and interlayer coupling. Our results show that the electronic properties of the graphene/g-GaSe heterostructures are well preserved owing to a weak vdW interaction. Especially, a tiny band gap of 13 meV has opened in the presence of the g-GaSe monolayer. We found that the n-type Schottky contact is formed in the graphene/g-GaSe heterostructure with a Schottky barrier height of 0.86 eV, which can be efficiently modulated by applying the electric field, in-plane strains, and interlayer coupling. Furthermore, a transformation from the n-type to p-type Schottky contact is observed when the applied electric field is larger than 0.1 V/A or the interlayer distance is smaller than 3.2 A. Our results may provide helpful information to design and fabricate the future graphene-based vdW heterostructures, such as graphene/g-GaSe heterostructure and understand the physics mechanism in the graphene-based 2D vdW heterostructures.

In this paper, we investigate systematically the structural, electronic, magnetic and adsorption properties of Bernal–stacked bilayer graphene on MnO(111) surface terminated by an oxygen atom, as a function of nonstoichiometric composition of the BLG/MnOx(111) interface. For additional functionalization of the BLG/MnOx(111) system, we also studied the adsorption properties of oxygen adsorbed on the BLG/MnOx(111) interface. Our results showed that the BLG is bound to the MnOx(111) substrate by the weak interaction for both spin-up and spin-down. Furthermore, we found that BLG adsorbed on the MnOx(111) substrate with a reduced oxygen symmetry in the interface is accompanied with a downshift of the Fermi level, which identifies the band structure of BLG as a p-type semiconductor. Upon interaction between BLG and MnOx(111) substrate, a forbidden gap of about 350 meV was opened between its bonding and antibonding π bands. A forbidden gap and the local magnetic moments in bilayer graphene can be controlled by changing the oxygen nonstoichometry or by oxygen adsorption. Additionally, magnetism has been predicted in the bilayer graphene adsorbed on the polar MnOx(111) surface with oxygen vacancies in the BLG/MnOx(111) interface, and its nature has also been discussed in this work. These results showed that the adsorption of bilayer graphene on the MnO(111) substrate can be used for developing novel generation of electronic and spintronic devices.

In this paper, the electronic properties and Schottky contact in graphene/MoS2 (G/MoS2) heterostructure under an applied electric field are investigated by means of the density functional theory. It can be seen that the electronic properties of the G/MoS2 heterostructure are preserved upon contacting owing to the weak van der Waals interaction. We found that the n-type Schottky contact is formed in the G/MoS2 heterostructure with the Schottky barrier height of 0.49 eV. Furthermore, both Schottky contact and Schottky barrier height in the G/MoS2 heterostructure could be controlled by the applied electric field. If a positive electric field of 4 V/nm is applied to the system, a transformation from the n-type Schottky contact to the p-type one was observed, whereas the system keeps an n-type Schottky contact when a negative electric field is applied. Our results may provide helpful information to design, fabricate, and understand the physics mechanism in the graphene-based two-dimensional van der Waals heterostructures like as G/MoS2 heterostructure.

In this paper, we study the electronic properties of graphene/phosphorene (G/P) heterostructure under applied electric field. The interlayer distance between graphene and topmost phosphorene is 3.50 A and the binding energy per carbon atom is 28.2 meV, which is indicated that graphene is bound to phosphorene via vdW interaction. The appearance of an energy gap of 33 meV in graphene is due to the dominant influence exerted by the phosphorene on graphene and sublattice symmetry broken between graphene and substrate. The G/P heterostructure forms a p-type Schottky contact with Φ B p = 0.34 eV. By applying the negative electric field, the G/P heterostructure keeps a p-type Schottky contact. Whereas with the positive electric field of E ≥ +0.25 V/A, Φ B p becomes larger than Φ B n , resulting in a transformation from p-type to n-type Schottky contact. The present results may open up a new avenue for application of the G/P vdW heterostructure in electronic devices.

In the present work, electronic properties and Schottky contact of graphene adsorbed on the MoS 2 monolayer under applied out-plane strain are studied using density functional theory calculations. Our calculations show that weak van derpp Waals interactions between graphene and monolayer MoS 2 are dominated at the interlayer distance of 3.34 A and the binding energy per C atom of − 25.1 meV. A narrow band gap of 3.6 meV has opened in G/MoS 2 heterointerface, and it can be modulated by the out-plane strain. Furthermore, the Schottky barrier and Schottky contact types in the G/MoS 2 heterointerface can be controlled by the out-plane strain. At the equilibrium state ( d = 3.34 A), the intrinsic electronic structure of G/MoS 2 heterointerface is well preserved and forms an n -type Schottky barrier of 0.49 eV. When the interlayer distance decreases, the transition from n -type to p -type Schottky contact occurs at d = 2.74 A. Our studies promote the application of ultrathin G/MoS 2 heterointerface in the next-generation nanoelectronic and photonic devices such as van-der-Waals-based field effect transistors.

We used ab initio calculations to systematically investigate the atomic structure, electronic and thermodynamic properties of oxygen-adsorbed TiC(111) surface affecting its potential reconstructions. Using the density functional theory, we study various degrees of coverage with the oxygen of TiC(111) surface in fcc position, which is in reconstructions of TiC(111)–( 3 × 3 )R30–O and TiC(111)–(1 × 1)–O. A considerable rearrangement has been established in the local atomic structure of O/TiC(111) surface depending upon the degree of its coverage with atomic oxygen in fcc stacking position. We demonstrated that the distance between adsorbate and TiC(111) surface decreases with the increase of its coverage with oxygen. We also examined the effects of the oxygen adatom upon the band and electron spectra of the O/TiC(111) surface in its various reconstructions. Effective charges of titanium and carbon atoms surrounding the oxygen adatom in various reconstructions have been identified. We established charge transfer from titanium atom to oxygen and carbon atoms determined by the reconstruction of local atomic and electron structures and correlating with their electronegativity values and chemisorption processes. Potential mechanisms for laser nanostructuring of titanium carbide surface have been suggested.

In this paper, the electronic properties of graphene/monolayer antimonene (G/m-Sb) heterostructure have been studied using the density functional theory (DFT). The effects of out-of-plane strain (interlayer coupling) and electric field on the electronic properties and Schottky contact of the G/m-Sb heterostructure are also investigated. The results show that graphene is bound to m-Sb layer by a weak van-der-Waals interaction with the interlayer distance of 3.50 A and the binding energy per carbon atom of −39.62 meV. We find that the n-type Schottky contact is formed at the G/m-Sb heterostructure with the Schottky barrier height (SBH) of 0.60 eV. By varying the interlayer distance between graphene and the m-Sb layer we can change the n-type and p-type SBH at the G/m-Sb heterostructure. Especially, we find the transformation from n-type to p-type Schottky contact with decreasing the interlayer distance. Furthermore, the SBH and the Schottky contact could be controlled by applying the perpendicular electric field. With the positive electric field, electrons can easily transfer from m-Sb to graphene layer, leading to the transition from n-type to p-type Schottky contact.

In this paper, we systematically investigate the atomic structure, electronic and thermodynamic properties of adsorbed W atoms on the polar Ti-terminated Ti x C y (111) surface with different configurations of adsorptions using first principle calculations. The bond length, adsorption energy, and formation energy for different reconstructions of the atomic structure of the W/ Ti x C y (111) systems were established. The effect of the tungsten coverage on the electronic structure and the adsorption mechanism of tungsten atom on the Ti x C y (111) are also investigated. We also suggest the possible mechanisms of W nucleation on the Ti x C y (111) surface. The effective charges on W atoms and nearest-neighbor atoms in the examined reconstructions were identified. Additionally, we have established the charge transfer from titanium atom to tungsten and carbon atoms which determine by the reconstruction of the local atomic and electronic structures. Our calculations showed that the charge transfer correlates with the electronegativity of tungsten and nearest-neighbor atoms. We also determined the effective charge per atom of titanium, carbon atoms, and neighboring adsorbed tungsten atom in different binding configurations. We found that, with reduction of the lattice symmetry associated with titanium and carbon vacancies, the adsorption energy increases by 1.2 times in the binding site A of W/ Ti x C y systems.

In this work, the influence of biaxial strain on electronic, optical, and effective masses characteristics of Janus MSSe (M = Mo, W) have been investigated through first-principles calculations as implemented in WIEN2k package. From the obtained results, we remark that MoSSe and WSSe monolayers exhibit, respectively, a direct and indirect bandgap transition at equilibrium. Our achieved results demonstrate that the biaxial strain fundamentally alters the electronic states of Janus MSSe monolayers, and mainly, a semiconductor-metal transition phase has been determined to occur at a biaxial strain ratio of 12%. Moreover, it has been revealed that both electrons and holes effective masses of MSSe monolayers can be tuned by biaxial strain. For the optical properties of Janus monolayers, the polarization direction of the incident light plays a vital role in defining the light absorption domain. The MSSe Janus monolayers are shown to have a wide range of absorption spectrum , including the visible light domain with perpendicular polarized light . Furthermore, our computations of the dielectric function indicate that the optical responses of Janus monolayers MoSSe and WSSe strongly depend on the applied strain ratio; particularly, for the high photon energy domain. Overall, the findings revealed that both Janus MoSSe and WSSe monolayers could be potential materials for applications in optoelectronics.

We investigated the effects of biaxial strain on electronic structure of ZrS2, ZrSe2, HfS2, HfSe2, ZrSSe and HfSSe monolayers. Similar to ZrS2, ZrSe2, HfS2, HfSe2 monolayers, Janus ZrSSe and HfSSe monolayers are indirect bandgap semiconductors. Tensile strain of 6(8)% transform ZrSSe(HfSSe) monolayer to direct bandgap semiconductor. Based on the calculation of binding energies and interlayer distance staking-(c) is found to be the most stable configuration for ZrSSe/HfSSe vdW heterostructure. Unstrained ZrSSe/HfSSe vdW heterostructure in staking-(c) is a type-II indirect bandgap semiconductor. Valence and conduction band edges show that under tensile strain ZrSSe, HfSSe and ZrSSe/HfSSe vdW heterostructure are efficient photocatalysts.

Motivated by the successful experimental fabrication of Janus structures recently, a systematic study of the structural, electronic, and optical properties of the Janus Al2SSe monolayer has been done through first-principles approach. Through phonon spectrum and ab initio molecular dynamics analysis, Al2SSe was confirmed to be dynamically and thermally stable. The Janus Al2SSe monolayer exhibits a semiconducting characteristics with indirect band gap of 2.079 eV at equilibrium. While biaxial strain can significantly alter band gap, the influence of electric field on electronic as well as optical properties is negligible. The optical absorbance of Al2SSe is activated in the visible light region and its intensity can be enhanced by strain. Our findings only highlight the physical properties but also provide an effective way for tuning the electronic and optical properties of Al2SSe monolayer by strain engineering.

In this work, we study the magneto-optical absorption coefficients (MOACs) and refractive index changes (RICs) in monolayer graphene under a perpendicular magnetic field using the compact density matrix approach. The results are presented as functions of photon energy and external magnetic field. Our results show that there are three groups of the possible transitions: the intra-band, the mixed, and the inter-band transitions; in which the MOACs and the RICs appear as a series of peaks in both intra-band and inter-band transitions between the Landau levels. With an increase magnetic field, the resonant peaks give a blue-shift and reduce in their amplitudes. These results suggest a potential application of monolayer graphene in nanoscale electronic and magneto-optical devices.

In this work, structural, electronic and magnetic properties of graphene adsorbed on MnO(111) with O-terminated surface depending on the number of vacancies in graphene/MnOx(111) interface are investigated using density functional theory. Local atomic reconstructions of the graphene/MnOx(111) interface, and their thermodynamic, electronic and magnetic properties were also studied. Bond lengths and adsorption energy were obtained for various reconstructions of graphene/MnOx(111) interface. Influence of graphene adsorption on the electronic structure of graphene/MnOx(111) interface for various reconstructions is also discussed. The charge transfer and local magnetic moments of carbon atoms and nearest-neighbor atoms were determined for these adsorption models. The charge transfer from carbon to nearest-neighbor atoms is due to the reconstruction of the local atomic and electronic structures, correlating with the number of oxygen vacancies in the interfaces. Magnetism of undefected graphene adsorbed on insulator MnOx(111) substrate with oxygen vacancies is also focused on discussing.

In this work, adsorption of graphene on polar MnO(1 1 1) surface with and without hydrogen coverage was investigated by density functional theory. Local atomic reconstructions of the graphene/H:MnO(1 1 1) interface and their thermodynamic and electronic properties were analyzed for different adsorption models. Bond length and adsorption energy were found for different reconstructions of surface atomic structure in the graphene/H:MnO(1 1 1) systems. Effect of graphene adsorption on the electronic spectrum of the graphene/H:MnO(1 1 1) interface was also studied. The effective charge of carbon atoms and nearest-neighbor atoms were determined for the considered adsorption models. Our calculations show that the charge transfer from carbon atom to nearest-neighbor atoms is due to reconstruction of the local atomic and electronic structures, correlating with the interface hydrogenation concentration. At the interface hydrogen concentration of Θ = 1.0 ML (monolayer), the p–n junction was observed in the graphene and a new state, n-type semiconductor, is qualitatively emerged.

In this work, the doping effects of rare-earth La and Ce atoms on electronic and optical properties of Janus MoSSe monolayer are investigated by means of first principles calculations. Our results imply that when one La and Ce doped to one S or Se side of Janus MoSSe monoalayer, it leads to a decrease in the band gap and results in the transition from direct to indirect. With increasing the La and Ce doping concentration, the Janus MoSSe monolayer switched from semiconductor to metal. Moreover, we find that effective masses of all the La and Ce doped Janus MoSSe systems are decreased as compared to pristine state, rendering their high carrier mobility. Furthermore, all the La and Ce doped MoSSe systems have red shift and possess high absorption ability in the visible and infrared regions. These findings suggest that rare-earth La and Ce doped MoSSe monolayer are potential candidate for spintronics, nanoelectronics and optoelectronics.

In this paper, the electronic, optical, and photocatalytic properties of GaSe/HfS2 heterostructure are studied via first-principles calculations. The stability of the vertically stacked heterobilayers is validated by the binding energy, phonon spectrum, and ab initio molecular dynamics simulation. The results reveal that the most stable GaSe/HfS2 heterobilayer retains a type-II alignment with an indirect bandgap 1.40 eV. As well, the results also show strong optical absorption intensity in the studied heterostructure (1.8 × 105 cm−1). The calculated hole mobility is 1376 cm2 V−1 s−1, while electron mobility reaches 911 cm2 V−1 s−1 along the armchair and zigzag directions. By applying an external electric field, the bandgap and band offset of the designed heterostructure can be effectively modified. Remarkably, a stronger external electric field can create nearly free electron states in the vicinity of the bottom of the conduction band, which induces indirect-to-direct bandgap transition as well as a semiconductor-to-metal transition. In contrast, the electronic properties of GaSe/HfS2 heterostructure are predicted to be insensitive to biaxial strain. The current work reveals that GaSe/HfS2 heterostructure is a promising candidate as a novel photocatalytic material for hydrogen generation in the visible range.

In present work, we study the electronic, optical and photocatalytic properties of strained MoSSe monolayer through first-principles study. A single layer Janus MoSSe possesses a semiconducting character with a direct band gap of 1.59/2.09 eV obtained by PBE/HSE06 method. The valence band maximum (VBM) of Janus MoSSe monolayer is mainly contributed by the S-p orbital, whereas the conduction band minimum (CBM) comes from the Mo- d x 2 . Furthermore, Janus MoSSe monolayer has been proved to be energetically stable with no imaginary frequency in its phonon spectrum. Interesting, both the tensile and compressive strains can transform Janus MoSSe monolayer from direct to indirect band gap nature as well as tune its band gap. The compressive strain tends to an increase in the band gap, whereas the tensile strain leads to decrease in the band gap. Optical absorption of Janus MoSSe monolayer demonstrates that the tensile strain gives rise to an existence of blue shift, while compressive strain is responsible for the formation of a red shift. Photocatalytic properties show that Janus MoSSe monolayer with 4% or 6% strained could be a catalyst for the H2O oxidation, making it suitable for water splitting applications.

A model of the oxygen adsorption on the defective surfaces (0 0 1), (1 1 1) and (1 1 0) of titanium carbide with different reconstructions is investigated by ab-initio calculations. In the framework of DFT calculations, the relaxed atomic structures of the surfaces (0 0 1), (1 1 1), and (1 1 0) of O/Ti x C y systems with titanium and carbon vacancies are studied. The structural and electronic properties of these systems are also investigated. The bond length and the adsorption energy for different reconstructions of the atomic structure of the surfaces (0 0 1), (1 1 1), and (1 1 0) of O/Ti x C y systems were established. The influence of the oxygen adatoms on the band structure and the electronic spectra of the O/Ti x C y system with different reconstructions was studied. Our calculations of effective charge per oxygen and nearest atoms show that the observed charge transfer from the titanium atoms to the oxygen and the carbon atoms is due to the reconstruction of local atomic and electronic structures and it correlates with processes of chemisorption. The physical nature and mechanisms of nanostructuring of the surfaces (0 0 1), (1 1 1) and (1 1 0) of titanium carbide are also discussed.

In this work, transport properties of armchair graphene nanoribbons (AGNRs) under uniaxial strain are considered using density functional theory. We found that carrier mobility of AGNRs depends strongly on uniaxial strain. The electron mobility of 5-AGNR is up to 38.5 × 10 4 cm 2 / V s at an elongation of 6%. However, the dependence of the effective mass of electrons and holes of AGNR on uniaxial strain can almost be described by the same function and their effective masses coincide at an elongation of 10%. The sensitivity to strain of the transport properties of AGNRs opens many ways for applications in nanoelectromechanical devices.