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In this paper, the structural, electronic, and transport properties of Janus GaInX3 (X = S, Se, Te) single-layers are investigated by a first-principles calculations.

The generation of layered heterostructures with type-II band alignment is considered to be an effective tool for the design and fabrication of a highly efficient photocatalyst.

Due to the broken vertical symmetry, the Janus material possesses many extraordinary physico-chemical and mechanical properties that cannot be found in original symmetric materials. In this paper, we study in detail the structural, electronic, and transport properties of 1T Janus PdXO monolayers (X = S, Se, Te) by means of density functional theory. PdXO monolayers are observed to be stable based on the analysis of the vibrational characteristics and molecular dynamics simulations. All three PdXO structures exhibit semiconducting characteristics with indirect bandgap based on evaluations with hybrid functional Heyd-Scuseria-Ernzerhof (HSE06). The influences of the spin-orbit coupling (SOC) on the band diagram of PdXO are strong. Particularly, when the SOC is included, PdTeO is calculated to be metallic by the HSE06+SOC approach. With high electron mobility, Janus PdXO structures have good potential for applications in future nanodevices.

In this work, we propose novel two-dimensional Janus XCrSiN2 (X = S, Se, and Te) single-layers and comprehensively investigate their crystal structure, electronic properties, and carrier mobility by using a first-principles method.

The shape of energy dispersions near the band-edges plays a decisive role in the transport properties, especially the carrier mobility, of semiconductors. In this work, we design and investigate the γ phase of tin monoxide and monochalcogenides γ-SnX (X = O, S, Se, and Te) through first-principles simulations. γ-SnX is found to be dynamically stable with phonon dispersions containing only positive phonon frequencies. Due to the hexagonal atomic lattice, the mechanical properties of γ-SnX single-layers are directionally isotropic and their elastic constants meet Born's criterion for mechanical stability. Our calculation results indicate that all four single-layers of γ-SnX are semiconductors with the Mexican-hat dispersions. The biaxial strain not only greatly changes the electronic structures of the γ-SnX single-layers, but also can cause a phase transition from semiconductor to metal. Meanwhile, the effects of an electric field on the electron states of γ-SnX single-layers are insignificant. γ-SnX structures have high electron mobility and their electron mobility is highly directional isotropic along the two transport directions

Surface functionalization is one of the useful techniques for modulating the mechanical and electronic properties of two-dimensional systems. In the present study, we investigate the structural, elastic, and electronic properties of hexagonal boron phosphide monolayer functionalized by Br and Cl atoms using first-principles predictions. Once surface-functionalized with Br/Cl atoms, the planar structure of BP monolayer is transformed to the low-buckled lattice with the bucking constant of about 0.6 A for all four configurations of functionalized boron phosphide, i.e., Cl–BP–Cl, Cl–BP–Br, Br–BP–Cl, and Br–BP–Br. The stability of functionalized BP monolayers is confirmed via their phonon spectra analysis and ab initio molecular dynamics simulations. Our calculations indicate that the functionalized BP monolayers possess a fully isotropic elastic characteristic with the perfect circular shape of the angle-dependent Young's modulus and Poisson's ratio due to the hexagonal symmetry. The Cl–BP–Cl is the most stiff with the Young's modulus C2D = 43.234 N m−1. All four configurations of the functionalized boron phosphide are direct semiconductors with a larger band gap than that of a pure BP monolayer. The outstanding stability, isotropic elastic properties, and moderate band gap make functionalized boron phosphide a very intriguing candidate for next-generation nanoelectromechanical devices.

The lacking of the vertical mirror symmetry in Janus structures compared to their conventional metal monochalcogenides/dichalcogenides leads to their characteristic properties, which are predicted to play significant roles for various promising applications. In this framework, we systematically examine the structural, mechanical, electronic, and optical properties of the two-dimensional 2H Janus CrXO (X = S, Se, Te) monolayers by using first-principles calculation method based on density functional theory. The obtained results from optimization, phonon spectra, and elastic constants demonstrate that all three Janus monolayers present good structural and mechanical stabilities. The calculated elastic constants also indicate that the Janus CrTeO monolayer is much mechanically flexible than the other two monolayers due to its low Young's modulus value. The metallic behavior is observed at the ground state for the Janus CrSeO and CrTeO monolayers in both PBE and HSE06 levels. Meanwhile, the Janus CrSO monolayer exhibits a low indirect semiconducting characteristic. The bandgap of CrSO after the correction of HSE06 hybrid functional is the average value of its binary transition metal dichalcogenides. The broad absorption spectrum of CrSO reveals the wide activated range from the visible to near-ultraviolet region. Our findings not only present insight into the brand-new Janus CrXO monolayers but can also motivate experimental research for several applications in optoelectric and nanoelectromechanical devices.

Constructing van der Waals (vdW) heterostructures is an exciting method for tuning the electronic and optical properties and the photocatalytic performances of two-dimensional materials. In this work, we investigated the electronic, optical and photocatalytic properties of a blue phosphorene–BAs (BlueP–BAs) vdW heterostructure using first-principles calculations. We found that the most energetically favorable stacking pattern of the BAs–BlueP vdW heterostructure possesses a direct band gap with type-I band alignment. The absorption spectrum of the BAs–BlueP vdW heterostructure showed that the lower energy transitions are dominated by excitons. Furthermore, the photocatalytic performance of the BAs–BlueP vdW heterostructure makes it suitable for water splitting at pH = 0. Our findings demonstrated that the BlueP–BAs heterostructure is a good candidate for optoelectronic and photocatalytic devices.

Designing van der Waals (vdW) heterostructures of two-dimensional materials is an efficient way to realize amazing properties as well as open up opportunities for applications in solar energy conversion, nanoelectronic and optoelectronic devices. The electronic structures and optical and photocatalytic properties of SiS, P and SiC van der Waals (vdW) heterostructures are investigated by (hybrid) first-principles calculations. Both binding energy and thermal stability spectra calculations confirm the stability of these heterostructures. Similar to the corresponding parent monolayers, SiS-P (SiS-SiC) vdW heterostructures are found to be indirect type-II bandgap semiconductors. Furthermore, absorption spectra are calculated to understand the optical behavior of these systems, where the lowest energy transitions lie in the visible region. The valence and conduction band edges straddle the standard redox potentials of SiS, P and SiC vdW heterostructures, making them promising candidates for water splitting in acidic solution.

Graphene-based van der Waals (vdW) heterostructures have attracted much attention because they can enhance the properties of separated materials, possess numerous new phenomena and unusual properties and improve the performance of devices. Motivated by the successful fabrication of single-layer transition metal nitrides (TMNs) [Science, 2020, 369, 670], we investigate the interfacial properties of heterostructures formed by stacking graphene (GR) on two different TMN monolayers, MoGe2N4 (MGN) and MoSi2N4 (MSN). Both the GR/MGN and GR/MSN heterostructures are characterized by weak vdW interactions, which preserve the intrinsic electronic properties of both the GR and TMN monolayers. The GR/MGN heterostructure forms an n-type Schottky contact, while a p-type Schottky contact is formed at the GR/MSN interface. Both the barrier and contact types in the GR/MGN heterostructure are sensitive to the electric gating and interlayer coupling. The transformation from an n-type Schottky contact to a p-type one or to an n-type ohmic contact can be achieved in the GR/MGN heterostructure by applying electric gating. In addition, adjusting the interlayer spacings between the GR and MGN layers leads to a transition from n-type to p-type Schottky contact. Our findings demonstrate that the GR/TMN heterostructures can be considered as promising high-performance nanodevices.

The World Wide Web is a large, wealthy, and accessible information system whose users are increasing rapidly nowadays. To retrieve information from the web as per users’ requests, search engines are built to access web pages. As search engine systems play a significant role in cybernetics, telecommunication, and physics, many efforts were made to enhance their capacity.However, most of the data contained on the web are unmanaged, making it impossible to access the entire network at once by current search engine system mechanisms. Web Crawler, therefore, is a critical part of search engines to navigate and download full texts of the web pages. Web crawlers may also be applied to detect missing links and for community detection in complex networks and cybernetic systems. However, template-based crawling techniques could not handle the layout diversity of objects from web pages. In this paper, a web crawler module was designed and implemented, attempted to extract article-like contents from 495 websites. It uses a machine learning approach with visual cues, trivial HTML, and text-based features to filter out clutters. The outcomes are promising for extracting article-like contents from websites, contributing to the search engine systems development and future research gears towards proposing higher performance systems.

Designing van der Waals (vdW) heterostructures of two-dimensional materials is an efficient way to realize amazing properties as well as opening opportunities for applications in solar energy conversion and nanoelectronic and optoelectronic devices. In this work, we investigate the electronic, optical, and photocatalytic properties of a boron phosphide–SiC (BP–SiC) vdW heterostructure using first-principles calculations. The relaxed configuration is obtained from the binding energies, inter-layer distance, and thermal stability. We show that the BP–SiC vdW heterostructure has a direct band gap with type-II band alignment, which separates the free electrons and holes at the interface. Furthermore, the calculated absorption spectra demonstrate that the optical properties of the BP–SiC heterostructure are enhanced compared with those of the constituent monolayers. The intensity of optical absorption can reach up to about 105 cm−1. The band edges of the BP–SiC heterostructure are located at energetically favourable positions, indicating that the BP–SiC heterostructure is able to split water under working conditions of pH = 0–3. Our theoretical results provide not only a fascinating insight into the essential properties of the BP–SiC vdW heterostructure, but also helpful information for the experimental design of new vdW heterostructures.

In this paper, we investigate the electronic, optical, and thermoelectric properties of Ga2SSe monolayer by using density functional theory. Via analysis of the phonon spectrum and ab initio molecular dynamics simulations, Ga2SSe is confirmed to be stable at room temperature. Our calculations demonstrate that Ga2SSe exhibits indirect semiconductor characteristics and the spin–orbit coupling (SOC) effect has slightly reduced its band gap. Besides, the band gap of Ga2SSe depends tightly on the biaxial strain. When the SOC effect is included, small spin–orbit splitting energy of 90 meV has been found in the valence band. However, the spin–orbit splitting energy dramatically changes in the presence of biaxial strain. Ga2SSe exhibits high optical absorption intensity in the near-ultraviolet region, up to 8.444 × 104 cm−1, which is needed for applications in optoelectronic devices. By using the Boltzmann transport equations, the electronic transport coefficients of Ga2SSe are comprehensively investigated. Our calculations reveal that Ga2SSe exhibits a very low lattice thermal conductivity and high figure of merit ZT and we can enhance its ZT by temperature. Our findings provide further insight into the physical properties of Ga2SSe as well as point to prospects for its application in next-generation high-performance devices.

The electrical contacts formed between the channel materials and the electrodes play a vital role in the design and fabrication of high-performance optoelectronic and nanoelectronic devices. In this work we propose combining metallic single-layer graphene (SLG) and a Janus SMoSiN2 semiconductor and investigate the electronic properties and contact types of the combined heterostructures (HTSs) using first-principles calculations. The effects of electric fields and interlayer coupling are also examined. The combined SLG/SMoSiN2 and SLG/N2SiMoS HTSs are both structurally and thermodynamically stable at equilibrium interlayer coupling. The combination between SLG and a Janus SMoSiN2 semiconductor generates a p-type or n-type Schottky contact, depending on the stacking configuration. The SLG/SMoSiN2 HTS generates a p-type Schottky contact while the SLG/N2SiMoS HTS forms an n-type one. Furthermore, applied electric field and strain can adjust the electronic features and contact types of the HTSs. An applied negative electric field and tensile strain lead to conversion from a p-type to an n-type Schottky contact in the SLG/SMoSiN2 stacking configuration, whereas a positive electric field and compressive strain give a transformation from an n-type to a p-type Schottky contact in the SLG/N2SiMoS stacking configuration. Our findings provide rational evidence for the fabrication and design of electrical and optical devices based on SLG/SMoSiN2 HTSs.

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.

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 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.

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.

van der Waals heterostructures can be effectively used to enhance the electronic and optical properties and extend the application range of two-dimensional materials. Here, we construct for the first time MoSeTe/X(OH)2 (X = Ca, Mg) heterostructures and investigate their electronic and optical properties as well as the relative orientation of these layers with respect to each other and the effects of an electric field. Our results show that in the MoSeTe/X(OH)2 heterostructures, the Janus MoSeTe monolayer is bonded to the X(OH)2 layer via weak van der Waals forces. Owing to different kinds of chalcogen Se and Te atoms in both sides of Janus MoSeTe, there exist two main stacking types of the MoSeTe/X(OH)2 heterostructures, that are MoSeTe-Se/X(OH)2 and MoSeTe-Te/X(OH)2 heterostructures. Interestingly, the Se- and Te-interface can induce straddling type-II and type-I band alignments. The MoSeTe-Se/X(OH)2 heterostructure exhibits a type-II band alignment, thus endowing it with a potential ability to separate photogenerated electrons and holes. Whereas, the MoSeTe-Te/Ca(OH)2 heterostructure displays a type-I band alignment, which may result in an ultrafast recombination between electrons and holes, making the MoSeTe-Te/Ca(OH)2 heterostructure a suitable material for optoelectronic applications. The MoSeTe/X(OH)2 heterostructures show an isotropic behavior in the low energy region while an anisotropic behaviour in the high photon energy region. The dielectric function of the MoSeTe-Te/Ca(OH)2 heterostructure is high at low photon energy relative to other heterostructures verifying it to have a good optical absorption. Furthermore, the band gap values and band alignment of the MoSeTe/X(OH)2 heterostructures can be modulated by applying an electric field, which induces semiconductor-to-metal and type-I(II) to type-II(I) band alignment. These results demonstrate that the MoSeTe/X(OH)2 heterostructures are promising candidates for optoelectronic and photovoltaic nanodevices.

The breaking of the vertical symmetry in Janus monochalcogenides gave rise to many properties that were not present in the original monochalcogenide monolayers. However, recent papers have often focused only on Janus monochalcogenides containing S, Se, and Te elements despite that O is also one of the group VI chalcogen elements. In this paper, we systematically investigate the electronic, transport, optical, and thermoelectric properties of Janus monolayers ${\mathrm{In}}_{2}X\mathrm{O}$ ($X=\mathrm{S},\mathrm{Se},\mathrm{Te}$) using first-principles calculations. Based on phonon spectrum analysis and ab initio molecular dynamics simulations at room temperature, ${\mathrm{In}}_{2}X\mathrm{O}$ monolayers were reported to be stable. Our calculations reveal that, while ${\mathrm{In}}_{2}\mathrm{SO}$ is an indirect semiconductor, ${\mathrm{In}}_{2}\mathrm{SeO}$ exhibits a direct semiconducting characteristic, and biaxial strain can lead to the semiconductor-metal phase transition in ${\mathrm{In}}_{2}\mathrm{SeO}$. Monolayer ${\mathrm{In}}_{2}\mathrm{TeO}$ is metal at equilibrium, and its metallic characteristics are prevented under biaxial strains. Calculations for transport properties show that the carrier mobilities of ${\mathrm{In}}_{2}\mathrm{SO}$ and ${\mathrm{In}}_{2}\mathrm{SeO}$ monolayers are highly anisotropic, and electron mobility of ${\mathrm{In}}_{2}\mathrm{SO}$ exceeds $3\ifmmode\times\else\texttimes\fi{}{10}^{3}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{2}/\mathrm{Vs}$. In this paper, the optical and thermoelectric properties of ${\mathrm{In}}_{2}\mathrm{SO}$ and ${\mathrm{In}}_{2}\mathrm{SeO}$ monolayers are also investigated and discussed in detail. Finally, the electronic properties of all four possible stacking configurations of the Janus bilayers are briefly calculated. Our findings not only contribute to a more general view of the physical properties of the Janus group III monochalcogenides but also recommend them as potential nanomaterials for applications in optoelectronic and thermal devices.

We theoretically study the magneto-optical absorption coefficients (MOACs) and the refractive index changes (RICs) due to both intra- and inter-band transitions in topological insulator (TI) thin films. The interplay between Zeeman energy and hybridization contribution leads to a transition between the normal insulator phase and the TI phase. The difference in the optical response in these two phases as well as at the phase transition point has been analyzed. The influence of the electron density, magnetic field, and temperature on the MOACs and RICs in both intra- and inter-band transitions is investigated. Our results show that the electron density affects directly the threshold energy. At a finite temperature, the thermal excitation causes the triggering of some new transitions which do not appear at T = 0 K. Evidence of the half-peak feature of the first inter-band transition is also found in TI thin films.

In this paper, we investigate the electronic, optical, and thermoelectric properties of Ga

It is complicated to distinguish among thousands of plant species in the natural ecosystem, and many efforts have been investigated to address the issue. In Vietnam, the task of identifying one from 12,000 species requires specialized experts in flora management, with thorough training skills and in-depth knowledge. Therefore, with the advance of machine learning, automatic plant identification systems have been proposed to benefit various stakeholders, including botanists, pharmaceutical laboratories, taxonomists, forestry services, and organizations. The concept has fueled an interest in research and application from global researchers and engineers in both fields of machine learning and computer vision. In this paper, the Vietnamese plant image dataset was collected from an online encyclopedia of Vietnamese organisms, together with the Encyclopedia of Life, to generate a total of 28,046 environmental images of 109 plant species in Vietnam. A comparative evaluation of four deep convolutional feature extraction models, which are MobileNetV2, VGG16, ResnetV2, and Inception Resnet V2, is presented. Those models have been tested on the Support Vector Machine (SVM) classifier to experiment with the purpose of plant image identification. The proposed models achieve promising recognition rates, and MobilenetV2 attained the highest with 83.9%. This result demonstrates that machine learning models are potential for plant species identification in the natural environment, and future works need to examine proposing higher accuracy systems on a larger dataset to meet the current application demand., 7 pages, 8 figures, 2 tables, Published with International Journal of Engineering Trends and Technology (IJETT)

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.

Computer Automated Tomography has been shown to be a valuable tool in production research because it provides a non-destructive method to identify and evaluate the internal structural characteristics of reservoir rock. In CT scan, Hounsfield Unit (HU) is proportional to the degree of X-ray attenuation by the tissue. The aim of the present study was to introduce the method to estimate porosity which is one of physical parameters of reservoir rock though HU data. In this study, an Image J software was used to extract Hounsfield Unit data and calibrate by standard material’s density. This method provides the ability of using CT Scanner in advanced reservoir characterization and flow test experiments.

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 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

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.

We propose a new approach to calculate the photodetachment cross section of the atom using the Green’s function for summation over the final states of the system. In the present work, we approbate this approach for calculation of the photodetachment cross section for the two electron atomic system, namely, the negatively charged hydrogen ion H− using the two-electron Coulomb Green’s function. The analytical form of this function is obtained by convolution of the one-particle Coulomb Green’s functions in the framework of the regular perturbation theory. Our results are in a good agreement with available experimental data.

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’’.

We comprehensively study the electronic and optical properties of InTe monolayer in the presence of biaxial strain and electric field using density functional theory. Via analysis phonon spectrum, InTe monolayer is confirmed to be dynamically stable. InTe monolayer has an indirect semiconducting characteristic with a band gap of 1.25 eV at equilibrium and can be controlled by strain or electric field. The semiconductor–metal phase transition has been found in InTe monolayer at a large electric field of E = 5 V/nm. The optical attributes of InTe monolayer depend strongly on the polarization direction of the incident light. The optical absorption coefficient is activated in the infrared region and increases rapidly in the visible light region. While optical properties are independent of the electric field, strain engineering alters not only the intensity of optical peaks but also their position.

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.

The formation of the graphene-based van der Waals (vdW) heterostructures has shown great potential for designing novel electronic and optoelectronic nanodevices. Here, we construct the Graphene/WSeTe heterostructure and investigate its structural, electronic, optical and transport properties through first-principles calculations. We find that the electronic properties of both graphene and Janus WSeTe are well preserved in Graphene/WSeTe heterostructure because of the weak vdW interactions. The optical absorption of the Graphene/WSeTe heterostructure is enhanced in both regions of the visible and UV lights in comparison with that of the graphene and Janus WSeTe monolayers. The absorption coefficient of the Graphene/WSeTe heterostructure for the visible light can reach 5 × 104 cm−1, which is as twice as that of Janus WSeTe monolayer. Whereas, for the UV light, the absorption coefficient of such heterostructure can reach up to 105 cm−1. Moreover, the Graphene/WSeTe heterostructure tends to own a high carrier mobility for both electrons and holes as compared with single-layered Graphene. Especially, a band gap of about 10 meV at the Dirac cone of graphene in such heterostructures can be opened. Depending on the stacking configurations, the Graphene/WSeTe heterostructure can form the p-type Ohmic contact or p-type Schottky contact with a small Schottky barrier of 0.35 eV. Furthermore, our results demonstrate that the electric fields and vertical strains can be effectively used to tune both the contact types and the Schottky barrier height of Graphene/WSeTe heterostructure from the p-type Schottky contact to n-type one or to p-type Ohmic contact. Our results could provide a significant guidance for understanding the physical properties of the Graphene/WSeTe heterostructure towards nanoelectronic and optoelectronic devices.

In this work, we investigate the electronic and optical properties of monolayer GeSe and the possibility of enhancement the photocatalytic activities for the water splitting of monolayer GeSe through strain engineering using first-principles calculations. Our calculations indicate that monolayer GeSe is a semiconductor with a moderate indirect gap of 1.13 eV at equilibrium and we can control its band gap by biaxial strain. In the presence of biaxial strain e b , the semiconductor-metal phase transition happens at large compressive strain of - 10 % and the indirect-direct gap transition occurs at e b = 4 % . The optical spectrum of monolayer GeSe are highly anisotropic and biaxial strain can increase the absorption coefficient of monolayer GeSe up to about 6 × 10 5 cm−1. Our calculations demonstrate that monolayer GeSe possesses photocatalytic properties for water splitting at e b = 5 % and we can enhance its photocatalytic activity by strain.

In this work, we investigate theoretically the structural and electronic properties of the monolayer Ti2CO2 MXene using first-principles calculations. At the ground state, the monolayer Ti2CO2 MXene structure is dynamically stable and is a semiconductor with an indirect band gap of 0.75 eV, which can be controlled by strain engineering and electric field. We find that the indirect band gap of the monolayer Ti2CO2 MXene could be transformed into a direct one. Whereas, a semiconductor–metal transition can be achieved by applying the compressive biaxial strain of −10%. Our results demonstrate that the monolayer Ti2CO2 MXene can be a potential material for designing optical nanodevices with the strain engineering and electric field tunable of the band gap.

In the present work, we consider the electronic properties of graphene with Kekule structure formed from two different C–C bonds in its hexagonal lattice. When the C–C bond alternation was introduced, a small band gap has been opened in the band structure of graphene and it increases linearly by a difference in the bond lengths δ. While the applied strain along the zigzag or armchair direction causes band gap to decrease rapidly to zero, the strain in the other directions can increase the band gap. Interestingly, when the graphene with Kekule structure is strained, its band gap is inversely proportional to the bond length difference δ. Opening a band gap in graphene due to bond alternation and strain can open up new applications in nanoelectronic devices.

In this paper, we study the structural and electronic properties of graphene adsorbed on MoS2 monolayer (G/MoS2) with different stacking configurations using dispersion-corrected density functional theory. Our calculations show that the interaction between graphene and MoS2 monolayer is a weak van der Waals interaction in all four stacking configurations with the binding energy per carbon atom of −30 meV. In the presence of MoS2 monolayer, the linear bands on the Dirac cone of graphene at the interfaces are slightly split. A band gap about 3 meV opens in G/MoS2 interfaces due to the breaking of sublattice symmetry by the intrinsic interface dipole, and it could be effectively modulated by the stacking configurations. Furthermore, we found that an n-type Schottky contact is formed at the G/MoS2 interface in all four stacking configurations with a small Schottky barrier about 0.49 eV. The appearance of the non-zero band gap in graphene has opened up new possibilities for its application in electronic devices such as graphene field-effect transistors.