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MoS 2 can exist in many different polytypes, such as trigonal prismatic, distorted octahedral, or octahedral. The 2 H -phase of MoS 2 has been extensively studied in recent times, but there are very few studies focusing on the remaining phases, especially the distorted octahedral T ′)-phase. Here, we design the MoS 2 monolayer and Janus MoSSe structure in the 1 T ′ phase and study their electronic properties within the framework of first-principles calculations. Both 1 T ′ -MoS 2 and 1 T ′ -MoSSe monolayers are confirmed to have structural stability and anisotropic mechanical characteristics. Interestingly, while the 1 T ′ -MoS 2 monolayer exhibits metallic characteristics, Janus MoSSe in the 1 T ′ phase is a semiconductor with a small band gap of 0.04 eV. More interestingly, a tiny bandgap of 0.05 eV has opened up in the 1 T ′ -MoS 2 monolayer due to the spin–orbit coupling effect. We also study the mobility of carriers in the semiconductor Janus 1 T ′ -MoSSe monolayer. 1 T ′ -MoSSe monolayer exhibits a high anisotropic carrier mobility due to its high anisotropic crystal structure. Surprisingly, 1 T ′ -MoSSe monolayer possesses extremely high electron mobility, up to 4. 58 × 1 0 3 cm 2 V−1 s−1. Our findings give a deeper insight into the 1 T ′ -phase of transition metal dichalcogenide and its Janus structure. • MoS 2 and MoSSe monolayers are structurally stable in the 1T' crystal phase. • 1T' -MoS 2 and 1T' -MoSSe monolayers exhibit anisotropic mechanical characteristics. • A small band gap of 0.05 eV has opened up in 1T' -MoS 2 due to the spin–orbit coupling effect. • 1T' -MoSSe monolayer possesses anisotropic transport characteristics with electron mobility exceeding 4 × 103 cm2 V−1 s−1. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 Å 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. [ABSTRACT FROM AUTHOR]

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/WSe 2 van der Waals heterobilayer using the first-principle calculations. Our results demonstrate that the intrinsic electronic properties of graphene and WSe 2 monolayer are quite well preserved due to the weak van der Waals interactions. We find that the graphene/WSe 2 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/WSe 2 heterobilayer can be tailored by inserting WSe 2 monolayers to form graphene/WSe 2 /WSe 2 and WSe 2 /graphene/WSe 2 heterotrilayers or by applying electric field perpendicular to the heterobilayer. The p -type Schottky barrier decreases with the insertion of the WSe 2 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. [ABSTRACT FROM AUTHOR]

Abstract 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 TiB 2 (0001) surface without and with vacancies of titanium and boron atoms using the density functional theory (DFT). Local atomic structures of the surfaces R/TiB 2 (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/TiB 2 (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 TiB 2 (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. Highlights • Adsorption, electronic and thermodynamic properties of W, N, O atoms on TiB 2 (0001) surfaces with vacancies were investigated. • Reconstructions of the TiB 2 surfaces with different adsorbate coverage are examined. • Charges are transferred from the Ti atom to the adsorbate and B atoms due to the reconstruction. • Chemisorption mechanisms in the N/TiB 2-y (0001) system are 1.5 times more intense than in the O/TiB 2-y (0001) system. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. • MoSSe and WSSe monolayers exhibit a direct-indirect bandgap transition at a specific strain ratio. • Semiconductor-metal phase transition can be found at large biaxial strain ratio. • Effective mass of the charge carriers and band gaps can be significantly modulated by the biaxial strain. • Optical properties of the Janus MoSSe and WSSe monolayers depend strongly on the biaxial strain. [ABSTRACT FROM AUTHOR]

• Janus Al 2 SSe monolayer is dynamically and thermally stable at room temperature. • Al 2 SSe monolayer is an indirect semiconductor with band gap of 2.079 eV. • Electronic properties of Al2SSe monolayer depend strongly on biaxial strain. • Al 2 SSe monolayers can strongly absorb the near-ultraviolet light. • Optical absorbance intensity of Al2SSe can be enhanced by strain. Motivated by the successful experimental fabrication of Janus structures recently, a systematic study of the structural, electronic, and optical properties of the Janus Al 2 SSe monolayer has been done through first-principles approach. Through phonon spectrum and ab initio molecular dynamics analysis, Al 2 SSe was confirmed to be dynamically and thermally stable. The Janus Al 2 SSe 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 Al 2 SSe 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 Al 2 SSe monolayer by strain engineering. [ABSTRACT FROM AUTHOR]

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. • Doping effects of La and Ce atoms on electronic and optical properties of Janus MoSSe monolayer are investigated. • CFV. • Increasing the doping concentration, Janus MoSSe monolayer switched from semiconductor to metal. • La and Ce doped MoSSe systems possess high absorption ability in the visible and infrared regions. • La and Ce doped MoSSe monolayer are potential candidate for spintronics, nanoelectronics and optoelectronics. [ABSTRACT FROM AUTHOR]

• A single layer Janus MoSSe possesses a semiconducting character with a direct band gap. • Janus MoSSe monolayer has been proved to be energetically stable with no imaginary frequency. • Tensile and compressive strains can transform Janus MoSSe monolayer from direct to indirect band gap semiconductor. • The tensile strain gives rise to an existence of blue shift, while compressive strain is responsible for the formation of a red shift. • Janus MoSSe monolayer with 4% or 6% strained could be a catalyst for the H 2 O oxidation. 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 H 2 O oxidation, making it suitable for water splitting applications. [ABSTRACT FROM AUTHOR]

• Electronic and interface characteristics of BlueP/ZrSSe heterostructure are investigated. • Stacking and electric field effects on the interface characters of BlueP/ZrSSe heterostructure are also considered. • BlueP/ZrSSe heterostructure possesses indirect semiconductor and exhibit type-I band alignment. • Electric field can tune the band edge positions and switch the BlueP/ZrSSe heterostructure from semiconductor to metal. • These findings could provide a helpful guidance for using BlueP/ZrSSe heterostructure in practical applications of nanoelectronics and optoelectronics. Electronic structure, optical, and photocatalytic properties of SnS, SnSe and their van der Waals heterostructures are investigated by first-principle calculations. Thermal stability confirmed that SnS, SnSe and SnS-SnSe van der Waals heterostructure are thermodynamically stable. The calculated band structure shows that SnS, SnSe and SnS-SnSe van der Waals heterostructure are indirect band nature while the heterostructure are confirmed for type-II band alignment. Bader charge analysis shows that the charges are transfer from SnS layer to SnSe layer. Furthermore, absorption spectra are calculated to understand the optical behavior of these systems, where the lowest energy transitions are lies in visible region. The valence and conduction band edges straddle the standard redox potentials in SnS, SnSe and their van der Waals heterostructures van der Waals heterostructures, making them promising candidates for water splitting in the acidic solution. [ABSTRACT FROM AUTHOR]

In this work, we construct the BlueP/ZrSSe heterostructure and explore systematically its electronic characteristics and interface features in the framework of first principles calculations. The stacking and electric field effects on the interface characters of BlueP/ZrSSe heterostructure are also considered. We find that the BlueP layer interacts with Janus ZrSSe layer via the weak van der Waals forces, which keeps the BlueP/ZrSSe heterostructure feasible. Both the BlueP/SZrSe and BlueP/SeZrS heterostructures possess indirect semiconductor and exhibits type-I band alignment. Furthermore, electric field can tune the band alignment and switch the BlueP/ZrSSe heterostructure from semiconductor to metal. These findings could provide a helpful guidance for using BlueP/ZrSSe heterostructure in practical applications of nanoelectronics and optoelectronics. • BlueP layer interacts with Janus ZrSSe layer via vdW forces, keeping BlueP/ZrSSe heterostructure feasible. • BlueP/ZrSSe heterostructure possesses indirect semiconductor and exhibit type-I band alignment. • Electric field can tune the band edge positions and switch the BlueP/ZrSSe heterostructure from semiconductor to metal. [ABSTRACT FROM AUTHOR]

In this work, detailed investigations of the electronic and optical properties of a Janus Ga 2 STe monolayer under a biaxial strain and electric field have been performed using density functional theory. Via the phonon spectrum and ab-initio molecular dynamics simulations, the dynamical and thermal stabilities of the Janus Ga 2 STe monolayer are verified. Our obtained results showed that the Janus Ga 2 STe exhibits a direct semiconducting characteristic and its band gap depends greatly on the biaxial strain. While both the electronic and optical properties are very weakly dependent on the electric field, strain engineering can cause a direct–indirect band gap transitions in the Janus Ga 2 STe. At equilibrium, the optical absorbance of the Janus Ga 2 STe monolayer is activated in the infrared light region of about 0.9 eV, which is close to its band gap value. The main peak of the optical absorbance spectrum is located in the ultraviolet light region with an absorbance intensity of 11.914 × 104 cm−1 may be increased by compression strain. In particular, the absorbance intensity of the Janus Ga 2 STe monolayer increases rapidly in the visible light region, reaching 4.810 × 104 cm−1 and can be altered by strain. Our results not only show that the Janus Ga 2 STe monolayer has many promising applications in opto-electronic devices but also motivates experimental works on Janus structures in near future. • Janus Ga 2 STe monolayer is dynamically and thermal stable at room temperature. • Janus Ga 2 STe is a direct semiconductor and its band gap can be strongly altered by strain. • The direct-indirect gap transitions were found in strained Janus Ga 2 STe monolayer. • Electronic and optical properties of Ga 2 STe depend weakly on external electric field. • Ga 2 STe has wide absorption spectrum, stretching from infrared to ultraviolet light region. [ABSTRACT FROM AUTHOR]

Combining different two-dimensional materials into layered van der Waals heterostructures are recently considered as an effective route to enhance the electronic properties of the constituent materials and to extend the application range in next-generation nanodevices. Here, the GeC/GaSe heterostructure and its electronic properties controlled by electric field have been constructed and systematically investigated using first-principles calculations. Five different stacking patterns of the GeC/GaSe heterostructure are constructed to consider the stacking effects on the electronic properties. We find that the GeC/GaSe heterostructure is mainly characterized by the weak van der Waals forces, dominating between GeC and GaSe layers, preserving their intrinsic properties in GeC/GaSe heterostructure. The GeC/GaSe heterostructure exhibits the type-II band alignment, where the electron–hole pairs are separated, making it suitable for fabricating next-generation optoelectronic nanodevices. Moreover, the stacking configurations have little affect the structural and electronic properties of the GeC/GaSe heterostructures. The pattern-I stacking configuration has the lowest binding energy and shortest interlayer distance as compared with other stacking patterns of the GeC/GaSe heterostructure. Furthermore, our results demonstrate that the electric field is considered as an effective route to modulate the electronic properties of GeC/GaSe heterostructure from semiconductor to metal. This finding makes the GeC/GaSe heterostructure promising material for optoelectronic nanodevices. • GeC/GaSe heterostructure is mainly characterized by the weak van der Waals forces. • GeC/GaSe heterostructure exhibits the type-II band alignment. • Stacking configurations have little affect electronic properties of heterostructures. • Electric field is an effective way to tune the electronic properties of heterostructure from semiconductor to metal. [ABSTRACT FROM AUTHOR]

In this work, we construct van der Waals heterostructure based on graphene and InN monolayer and analyze the interface, electronic and optical properties of formed heterostructure using first-principles calculations. Our results prove that the graphene/InN heterostructure is mainly contributed by the weak vdW interactions, which keep it feasible and thus it can be realized easily in recent experiment. Moreover, the intrinsic superior properties of both graphene and InN monolayers are well preserved in the graphene/InN heterostructure. In the graphene/InN heterostructure, InN layer becomes the electron-rich layer, while the graphene layer becomes the hole-rich layer, leading to the transportation of electrons from graphene to InN monolayer. The heterostructure possesses high performance absorption in the visible and near-infrared regions, revealing it is useful for acquiring efficient photocatalysts. The graphene/InN heterostructure at the equilibrium state form the n-type Schottky contact with a small of Schottky barrier height of 0.246 eV. More interestingly, our results predict that external electric fields can tune the graphene/InN heterostructure from n-type to p-type Schottky contact and to n-type Ohmic contact, demonstrating that such heterostructure is appreciate material for highly integrated devices, such as Schottky devices and Schottky diodes. Unlabelled Image • Interface, electronic and optical properties of graphene/InN were investigated. • Graphene/InN is contributed by weak vdW interactions. • Heterostructure possesses high performance absorption in the visible and near-infrared regions. • Graphene/InN forms the n-type Schottky contact with a Schottky barrier height of 0.246 eV. • Electric field can tune the graphene/InN from n-type to p-type Schottky contact and to n-type Ohmic contact. [ABSTRACT FROM AUTHOR]

• Structural and electronic properties of combined InSe/Ca(OH) 2 heterostructures were investigated through DFT calculations. • Combination of InSe and Ca(OH) 2 tends to a significant decrease in the band gap of heterostructure. • InSe/Ca(OH) 2 heterostructure mediates by the weak vdW interactions and possesses a type-II semiconductor. • Type-II band alignment of heterostructure can be engineered by applying electric field or vertical strains. • Semiconductor-to-metal and direct-to-indirect transitions can be emerged, which make InSe/Ca(OH) 2 heterostructure promising material. In this work, we investigate the structural and electronic properties of the combined InSe/Ca(OH) 2 heterostructure through density functional theory. It suggests that a combination of InSe and Ca(OH) 2 tends to a significant decrease in the band gap of the heterostructure, which may result from the vacuum energy difference of the monolayers. The InSe/Ca(OH) 2 heterostructure mediates by the weak vdW interactions and possesses a type-II semiconductor with a direct band gap of 0.55 eV, which can also be engineered by applying electric field or vertical strains. The semiconductor-to-metal and direct-to-indirect transitions can also emerge, which make InSe/Ca(OH) 2 heterostructure promising material for electronic nanodevices. [ABSTRACT FROM AUTHOR]

In this work, we propose an ultrathin graphene/Ca(OH) 2 van der Waals heterostructure (vdWH) and investigate its structural stability, electronic structures and Schottky contact types modulation by ab initio calculations. Our results show the preservation of graphene and Ca(OH) 2 intrinsic electronic properties in graphene/Ca(OH) 2 vdWH, which is mainly characterized by the physicoadsorption interaction with the binding energy of -33.37 meV per carbon atom. Ca(OH) 2 monolayer stacking on graphene to form the vdWH forms the p -type Schottky contact and opens a valuable graphene's band gap of 9.7 meV, suggesting its promising application in high speed nanoelectronic devices. Furthermore, electric field and vertical strain can be used to modulate the Schottky contact from the p -type to the n -type one and to Ohmic contact. These predictions demonstrate the potential candidate of the G/Ca(OH) 2 vdWH for future nanoelectronic applications. • Intrinsic electronic properties of graphene and Ca(OH) 2 monolayer are well preserved in their vdWH. • G/Ca(OH) 2 vdWH forms a p-type Schottky contact with small Schottky barrier of 0.78 eV. • A band gap of 9.7 meV has opened in graphene, making it promising application in high speed nanoelectronic devices. • Electric field and strain can tune a transformation from p-type to n-type Schottky contact and to Ohmic contact. [ABSTRACT FROM AUTHOR]