Search

In this work, we systematically investigate the electronic and optical properties of surface-functionalized GeC monolayer with F and Cl using density functional theory. Our calculations indicate that the surface functionalization of the GeC with F and C atoms leads to the disruption of the planar structure of the GeC monolayer and the surface-functionalized GeC monolayer has a low-bucking structure. At equilibrium, all four configurations of surface-functionalized GeC monolayer with F and Cl, i.e., F–GeC–F, F–GeC–Cl, Cl–GeC–F, and Cl–GeC–Cl, are direct semiconductors. Their band gaps vary from 2.839 eV to 3.175 eV which are calculated using Heyd–Scuseria–Ernzerhof (HSE) hybrid functional. Compared to the other configurations, the formation energy of F–GeC–F is the smallest, − 9 . 097 eV , which implies that this configuration is the most likely to occur. We also used the Mulliken population analysis to estimate the internal charge distribution and transferred charge in the systems. The functionalization of the surface leads to the shifting the first optical gap of the material. The fully chlorination of GeC causes its absorption coefficient to increase significantly, up to 14 . 912 × 1 0 4 cm−1 at the incident light energy of 13.173 eV. Besides, surface-functionalized GeC monolayer with F and Cl strongly absorbs light in the near ultraviolet region. Our calculation results provide detailed information on how to change the electronic and optical properties of monolayer GeC by surface functionalization, which has promising applications in opto-electronic devices.

Using the augmented plane wave + local orbitals method with different approximation functionals, we investigate systematically the electronic, optical and elastic properties of stannite-type Cu2CdGeSe4. Among different approximation functionals, the modified Becke–Johnson (mBJ) potential with Hubbard-corrected parameter U (mBJ + U) gives the most reliable results on the electronic properties of Cu2CdGeSe4 in comparison with the experimental data. Elastic modulus, elastic constants and the Poisson’s ratio of Cu2CdGeSe4 were calculated using the Elastic software package. Optical properties such as wide spectrum of absorbed photon energy, namely 1.3–27.2 eV, high absorption coefficient (above 104 cm−1) and optical anisotropy suggest the application of Cu2CdGeSe4 in solar cells.

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.

Using density functional theory, we have studied the structural, electronic and optical properties of two-dimensional graphene-like $$\hbox {C}_2\hbox {N}$$ nanosheet under in-plane strains. Our results indicate that the $$\hbox {C}_2\hbox {N}$$ nanosheet is a semiconductor with a direct band gap of 1.70 eV at the equilibrium state opening between the highest valence band and lowest conduction band located at the $$\varGamma $$ point. The band gap of the $$\hbox {C}_2\hbox {N}$$ nanosheet decreases with the increasing of both uniaxial/biaxial strains. In the presence of the strain, we found band shift and band splitting of the occupied and unoccupied energy states of the valence and conduction bands, resulting in a decrease of the band gap. Furthermore, the absorption and reflectance spectra for the $$\hbox {C}_2\hbox {N}$$ nanosheet have a broad peak around 2.6 eV, where a maximum absorption value is up to $$3.2 \times 10^{-5}\,\hbox {cm}^{-1}$$ and reflectance is about 0.27%. Moreover, our calculations also show that the optical properties of the $$\hbox {C}_2\hbox {N}$$ nanosheets can be controlled by applying the biaxial and uniaxial strains. The obtained results might provide potential applications for the $$\hbox {C}_2\hbox {N}$$ nanosheets in nanoelectronics and optoelectronics.

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.

The stacking of monolayers in the form of van der Waals heterostructures is a useful strategy for band gap engineering and the control of dynamics of excitons for potential nano-electronic devices. We performed first-principles calculations to investigate the structural, electronic, optical and photocatalytic properties of the SiC–MX2 (M = Mo, W and X = S, Se) van der Waals heterostructures. The stability of most favorable stacking is confirmed by calculating the binding energy and phonon spectrum. SiC–MoS2 is found to be a direct band gap type-II semiconducting heterostructure. Moderate in-plane tensile strain is used to achieve a direct band gap with type-II alignment in the SiC–WS2, SiC–MoSe2 and SiC–WSe2 heterostructures. A difference in the ionization potential of the corresponding monolayers and interlayer charge transfer further confirmed the type-II band alignment in these heterostructures. Furthermore, the optical behaviour is investigated by calculation of the absorption spectra in terms of e2(ω) of the heterostructures and the corresponding monolayers. The photocatalytic response shows that the SiC–Mo(W)S2 heterostructures can oxidize H2O to O2. An enhanced photocatalytic performance with respect to the parent monolayers makes the SiC–Mo(W)Se2 heterostructures promising candidates for water splitting.

Very recently, two-dimensional (2D) iodinene, a novel layered and buckled structure has been successfully fabricated (Qian et al 2020 Adv. Mater. 32 2004835). Motivated by this latest experimental accomplishment, for the first time we conduct density functional theory, first-principles calculations to explore the structural, electronic, and optical properties of monolayer, few-layer and bulk iodinene. Unlike the majority of monoelemental 2D lattices, iodinene is predicted to be an intrinsic semiconductor. On the basis of calculations using the generalized gradient approximation of Perdew–Burke–Ernzerhof for the exchange-correlation functional and the Heyd-Scuseria-Ernzerhof (HSE06) functional, it is shown that the electronic bandgap of iodinene decreases with increasing the number of atomic layers. Our HSE06 results reveal that the bandgap of iodinene decreases from 2.08 to 1.28 eV as the number of atomic layers change from one to five, highlighting the finely tunable bandgap. The optical study shows the monolayer has the ability to absorb a wide range of ultraviolet light, more than multilayers and bulk iodinene. As the number of layers increases, the absorption spectra exhibits a blue shift relative to monolayer iodinene. This study confirms the remarkable prospect for the application of iodinene in nanoelectronics and optoelectronics owing to its intrinsic semiconducting nature.

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.

We investigate the peculiar electronic and optical properties of zigzag graphene nanoribbons (GNRs) under the effects of uniform and modulated electric fields. The hybridization between the four atomic orbitals ( s , p x , p y , p z ) is considered by means of the tight-binding model calculations. Both the π bands originating from the p z orbital and σ bands arising from the ( s , p x , p y ) orbitals play critical roles in the electronic structure and thus the absorption spectra. They determine the Fermi level and the available excitation channels between the occupied and unoccupied states. We show that an in-plane electric field in the form of modulated potential can significantly modify the electronic and optical properties of zigzag GNRs. The field-induced modification in energy dispersion, band-edge states, and band gap gives rise to rich absorption spectra with diverse structures. Our theoretical prediction could be verified by angle-resolved photoemission spectroscopies and optical spectroscopies.

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.

An ab initio simulation of the adsorption of atomic oxygen on the low-defect titanium carbide (110) surface reconstructed by laser radiation was performed. The relaxed atomic structures of the (110) surface of the O/TixCy system with Ti and C vacancies observed during the thermal treatment were studied in terms of the density functional theory. DFT calculations of their structural, thermodynamic, and electronic properties were performed. The bond lengths and adsorption energies were determined for various reconstructions of the atomic structure of the O/TixCy(110) surface. The effects of the oxygen adatom on the band and electronic spectra of the O/TixCy(110) surface were studied. The effective charges on the titanium and carbon atoms surrounding the oxygen atom in various reconstructions were determined. The charge transfer from titanium to oxygen and carbon atoms was found, which is determined by the reconstruction of the local atomic and electronic structures and correlates with chemisorption processes. The potential mechanisms of laser nanostructuring of the titanium carbide surface were suggested.

In this work, we consider the effect of out-plane strain on the electronic properties of AB-stacked bilayer armchair graphene nanoribbons (BAGNRs) using density functional theory. At equilibrium, the interlayer distance of BAGNRs is $$d_0=3.326$$ A. Our DFT calculations show that while the dependence of the band gap of 11-BAGNR on interlayer distance d is insignificant, especially in the case of the $$d

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, the effect of Peierls distortion on the electronic properties of armchair graphene nanoribbons is theoretically studied in a tight-binding approximation. As a consequence of Peierls distortion, when the Kekule-type bond alternation is introduced, the band gap of armchair nanoribbons strongly depends on the difference in bond length between short and long bonds in the honeycomb lattice. We can control the band gap of a nanoribbon by its uniaxial strain and a semiconductor–metal phase transition can occur at certain elongations.

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.

Vertical stacking of ultrathin two-dimensional materials via weak van der Waals (vdW) interactions is identified as an important technique for tuning the physical properties and designing viable products for nanoelectronics, spintronics, and renewable energy source applications. The geometry, electronic, and photocatalytic properties of vdW heterostructures of GeC and Janus transition metal dichalcogenides $M\mathrm{SSe}$ ($M$ = Mo, W) monolayers are investigated by performing first-principles calculations. Two different possible models of GeC-$M\mathrm{SSe}$ heterostructures are presented with an alternative order of chalcogen atoms at opposite surfaces in $M\mathrm{SSe}$. The most favorable stacking pattern of both models is dynamically and energetically feasible. A direct type-II band alignment is obtained in both models of understudy heterobilayer systems. The spin orbit coupling (SOC) effect causes considerable Rashba spin splitting in both $M\mathrm{SSe}$ monolayers. In particular, a greater Rashba spin polarization is demonstrated in model 1 (GeC-WSSe) than model 2 (GeC-MoSSe) caused by the alternative order of chalcogen atoms and larger SOC effect of heavier W than Mo atoms, which provides a platform for experimental and theoretical understanding of designing two-dimensional spintronic devices. More interestingly, the appropriate band alignments of model 1 with the standard water redox potentials enable its capability to dissociate water into ${\text{H}}^{+}/{\text{H}}_{2}$ and ${\text{O}}_{2}/{\text{H}}_{2}\text{O}$. In contrast to model 1, model 2 can only oxidize water into ${\text{O}}_{2}/{\text{H}}_{2}\text{O}$. The simulated design of GeC-$M\mathrm{SSe}$ is predicted for promising use in future electronic, spintronics, and photocatalytic water splitting.

Vertical heterostructures from two or more than two two-dimensional materials are recently considered as an effective tool for tuning the electronic properties of materials and for designing future high-performance nanodevices. Here, using first principles calculations, we propose a GeC/C

In this paper, the potential of engineering and manipulating the electronic heat capacity and Pauli susceptibility of pristine and perturbed hydrogenated AA-stacked graphene, SiC (silicon carbide), and h-BN (hexagonal boron nitride) bilayers is studied using a designed transverse Zeeman magnetic field and the dilute charged impurity. The tight-binding Hamiltonian model, the Born approximation and the Green’s function method describe the carrier dynamics up to a certain degree. The unperturbed results show that the heat capacity and susceptibility of all bilayers increase with different hydrogenation doping configurations. We also found that the maximum heat capacity and susceptibility relates to the chair-like and table-like configurations. Also, the graphene possesses the highest activity compared to SiC and h-BN lattices due to its zero on-site energies. For the Zeeman magnetic field-induced Schottky anomaly and the Neel temperature corresponding to the maximum electronic heat capacity, EHCMax., and Pauli spin paramagnetic susceptibility, PSPSMax., respectively, the pristine EHCMax. (PSPSMax.) decreases (increases) with the Zeeman field. On the other hand, the corresponding results for reduced table-like and reduced chair-like lattices illustrate that both EHCMax. and PSPSMax. decrease with the Zeeman field, on average. However, under the influence of the dilute charged impurity, the pristine EHCMax. of graphene (SiC and h-BN) decreases (increases) with impurity concentration for all configurations while the corresponding PSPSMax. fluctuates (decreases) for the pristine (reduced table-like and reduced chair-like) case. These findings introduce hydrogenated AA-stacked bilayers as versatile candidates for real applications.

van der Waals heterostructures (vdWHs), obtained by vertically stacking different two-dimensional (2D) layered materials are being considered intensively as potential materials for nanoelectronic and optoelectronic devices because they can show the most potential advantages of individual 2D materials. Here, we construct the SnSe2/MoS2 vdWH and investigate its electronic and optical properties using first-principles calculations. We find that the band structures of both MoS2 and SnSe2 monolayers are well kept in the SnSe2/MoS2 vdWH because of their weakly interacting features via vdW interaction. The SnSe2/MoS2 vdWH forms a type-I band alignment and exhibits an indirect semiconductor band gap of 0.45 eV. The type-I band alignment makes the SnSe2/MoS2 vdWH a promising material for optoelectronic nanodevices, such as light emitting diodes because of ultra-fast recombination of electrons and holes. Moreover, the band gap and band alignment of the SnSe2/MoS2 vdWH can be tailored by the electric field and the insertion of a graphene sheet. After applying an electric field, type-I to type-II and semiconductor to metal transitions can be achieved in the SnSe2/MoS2 vdWH. Besides, when a graphene sheet is inserted into the SnSe2/MoS2 vdWH to form three stacking types of G/SnSe2/MoS2, SnSe2/G/MoS2 and SnSe2/MoS2/G, the p-type semiconductor of the SnSe2/MoS2 vdWH is converted to an n-type Ohmic contact. These findings provide theoretical guidance for designing future nanoelectronic and optoelectronic devices based on the SnSe2/MoS2 vdWH.

Graphene-based two-dimensional van der Waals heterostructures (vdWH) have recently shown a great potential for high-performance nanodevices. Here, we design a novel vdWH, consisting of the graphene and a noble transition metal dichalcogenide $${\mathrm{{PtS}}_2}$$ monolayer and investigate its electronic properties as well as the effect of electric field. We find that the key intrinsic characteristics of both the graphene and $${\mathrm{{PtS}}_2}$$ monolayers are well preserved due to the weak vdW interactions. The graphene is found to form an n-type Schottky contact with the $${\mathrm{{PtS}}_2}$$ monolayer with a small barrier height of 0.11 eV. Moreover, this small barrier height of the $$\mathrm{{G}}/{\mathrm{{PtS}}_2}$$ vdWH is known to be very sensitive to the external electric field. It can be controlled and turned to the Ohmic contact under electric field. These findings could provide significant knowledge for designing novel electronic and optoelectronic devices of such heterostructure.

We study the two-photon-induced cyclotron–phonon resonance (CPR) effect resulting from the interaction between electrons and phonons in a quantum well with the modified-Poschl–Teller (MPT) potential. The CPR is considered via the magneto-optical absorption coefficient (MOAC) and the full-width at half-maximum (FWHM). Numerical results are presented for a typical GaAs MPT quantum well. It is found that the quantum well parameters, such as well-depth and well-width, the magnetic field, and the temperature affect significantly the energy separation, the MOAC, and the FWHM. Obtained results agree well with previous theoretical and experimental results. Especially, we found two new rules of the well-depth and well-width-dependent FWHM, which should be tested by experimental works to examine their validities.

We theoretically study the magneto-optical transport properties of monolayer molybdenum disulfide (MoS_2) on polar substrates in the presence of a perpendicular magnetic field. The magneto-optical absorption coefficient (MOAC) is investigated as a function of the incident photon energy when carriers are scattered by three different types of phonons: the intrinsic MoS_2 acoustic, optical phonons, and the surface optical (SO) phonons induced by polar substrates. Among the substrates considered, the largest magnitude of MOAC and full-width at half maximum (FWHM) are observed for a SiO_2 substrate over the entire temperature and magnetic field range considered due to its strongest electron-SO phonon scattering, while an h-BN substrate displays the lowest one. The piezoelectric (PE) coupling to the transverse (TA) phonon is shown to dominate the MOAC and FWHM due to intrinsic acoustic phonon scattering. Meanwhile, these properties for intrinsic optical phonons are dominated by zero-order deformation potential (DP) couplings and the Fröhlich interaction. The dependence of the MOAC and FWHM on temperature, magnetic field, and the effective MoS_2-substrate distance is also examined. The present results for monolayer MoS_2 are compared with those in conventional two-dimensional systems as well as in graphene. Our results show that SO phonons play a crucial role at high temperature depending on the substrates and have a non-negligible effect on the magneto-optical transport properties of monolayer MoS_2, which could be further experimentally and theoretically investigated in the future. This research is funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) under Grant No. 103.01-2015.93 and the Belarusian scientific program “Convergence”.

In the present work, we consider systematically the electronic and optical properties of two-dimensional monolayer germanium monosulfide (GeS) under uniaxial strains along armchair (AC-strain) and zigzag (ZZ-strain) directions. Our calculations show that, at the equilibrium state, the monolayer GeS is a semiconductor with an indirect band gap of 1.82 eV. While monolayer GeS is still an indirect band gap semiconductor under ZZ-strain, an indirect–direct energy gap transition can be found in the monolayer GeS when the AC-strain is applied. The optical spectra of the monolayer GeS have strong anisotropy in the investigated energy range from 0 eV to 8 eV. Based on optical properties, we believe that the monolayer GeS is a potential candidate for applications in energy conversion and optoelectronic technologies. This research is funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) under Grant Number 103.01-2017.309 and the Belarusian Scientific Program ‘‘Convergence’’.

The pressure and temperature effects on the optical responses involving the $$1s-1p$$ intersubband transition of an exciton in a spherical quantum dot are investigated. Calculations are performed in the framework of the effective mass approximation and the energies are obtained by using a Ritz variational method. Our approach is based on the Hylleraas formalism were the correlations between the electron and hole are taken into account. Temperature, pressure and the size effects on the linear and third nonlinear optical properties are analyzed. Our results show that the temperature and pressure provide important effects on linear and nonlinear parts of the absorption coefficient (AC) and the relative refractive index change (RI) associated to the $$1s-1p$$ transition. We found that by increasing the temperature and pressure the AC and RI curves shift to lower and higher energies respectively. Calculations show also that the dot size affects considerably the AC and RI and their corresponding amplitude.

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.

Very recently, the 2D form of poly-benzimidazobenzophenanthroline (BBL) structures has been successfully fabricated [Noh et al., Nat. Commun. 369, 670 (2020)]. Motivated by these exciting experimental results on 2D layered BBL structures, herein we perform density functional theory-based first-principles calculations in order to gain insight into the structural, electronic, and optical properties of the BBL monolayer and bilayer honeycomb crystal structures (planar and vertical). Our computational structural optimization reveals that the BBL monolayer crystallizes in a puckered, anisotropic hexagonal structure, while the BBL bilayer is composed of covalently bonded shifted one with respect to the other BBL layers. Two terminations with hydrogen and fluorine atoms are considered for the BBL bilayer, namely, H-BBL and F-BBL, respectively. The direct bandgaps of H-BBLs and F-BBLs are ∼ 1 eV and ∼ 1.2 eV. The top of the valence band and the bottom of the conduction band are flat due to the localized carbon states. The BBL monolayer and bilayer can absorb a wide range of visible light. The calculated refractive index of the BBL monolayer is ∼ 1, i.e., it is smaller than the refractive index of the common natural or synthetic polymers.

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 paper, we study the effect of uniaxial and biaxial strain on the structural and electronic properties of MoS monolayers by first-principle calculations based on density functional theory. Our calculations show that the bond length between Mo and S atoms depends linearly on the strain. At the equilibrium state, MoS has a direct band gap of 1.72 eV opening at the K-point. However, an indirect–direct band gap transition has been found in MoS monolayer when the strain is introduced. MoS becomes a semiconductor with an indirect band gap when the uniaxial strain or the biaxial strain . Under biaxial strain, a metal–semiconductor transition occurs at of elongation. The indirect character and phase transition will largely constrain application of MoS monolayer to electronic and optical devices.

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.

We used ab initio calculations to systematically investigate the adsorption of atomic oxygen on non-stoichiometric polar TiC(111) and Ti x C y (111) with Ti/C vacancies surface simulating its potential tructions with laser radiation. Local atomic structures of O/Ti x C y (111) polar surfaces were studied in the selected models as well as their thermodynamic and electronic properties based on the density functional theory. The bond length and adsorption energy for various reconstructions of the O/Ti x C y (111) surface atomic structure were established. We also have examined the effects of oxygen adsorption upon the band and electron spectra of TiC(111) surface in its various reconstructions. We have established a correlation between the energy level of flat bands (− 5.1 eV and − 5.7 eV) responsible for the doublet of singular peaks corresponding to partial densities of oxygen 2 p electrons and the energy of oxygen adsorption in non-stoichiometric O/TiC y (111) systems. Effective charges of the oxygen atom and the titanium and carbon atoms nearest to it were identified in the examined adsorption models. We have established charge transfer from titanium atom to oxygen and carbon atoms determined by the reconstruction of local atomic and electronic structures. Charge transfer correlates with the electronegativity values of titanium, carbon, and oxygen atoms, and chemisorption processes. Calculated values of structural parameters in the studied models of ultrathin O/TiC(111) and O/Ti x C y (111) films correlate well with experimental findings and other theoretical results.