The future development of optoelectronic devices will require an advanced control technology in electronic properties, for example by an external electric field (Efield). Here we demonstrate an approach that the heterostructure based on van der Waals (vdW) heterobilayer built by monolayer SnS2 and PbI2 has a well-controlled electronic properties with Efield. A type-II staggered-gap band alignment is achieved from the SnS2/PbI2 vdW heterostructure with which SnS2 dominated the lowest energy holes as well as the lowest energy electrons are separated in PbI2. The charge redistribution with an Efield is mainly on the surface of SnS2 layer and PbI2 and the numbers of polarized electrons on the monolayers display a linear evaluation with external Efield. The band structure under different Efield experiences not only a transition from semiconductor to metal but also conversions between type-I straddling-band alignment and type-II staggered-gap, which results in different spatial distribution of the lowest energy electrons and holes. Moreover, when the Efield is between −0.06 V Å−1 and −0.34 V Å−1, the material manifests a varied direct bandgap which is more favor to optoelectronics and solar cell. Consequently, this vdW heterobilayer with well-controlled manner shows expectation for huge potential in optics and electronics.

Using a first-principles method, based on the Vienna Ab-initio Simulation Package (VASP), we have studied the electronic structure, formation energy and transition level of a MoSe2 monolayer doped with V and VII atoms. The numerical results show that the dopant atoms can induce magnetism, except for in the case of the As-doped system. Specifically, N- and F-doped systems exhibit magnetic nanomaterial properties, P- and As-doped systems display metallic features, and in the cases of Cl-, Br- and I-doped systems, the systems exhibit half-metallic ferromagnetism (HMF). The formation energy calculations indicate that this can be more effective for achieving n-type and p-type doped MoSe2 under Mo-rich experimental conditions. However, for the systems doped with group V atoms, the transition level decreases with increasing atomic radius, but that of those doped with VII atoms increases with increasing atomic radius. By comparing the results, we find that the transition level is only 31 meV in F-doped MoSe2 monolayers, which indicates that F impurities can offer effective n-type carriers in MoSe2 monolayers.

Using a first-principles method, based on the Vienna Ab-initio Simulation Package (VASP), we have studied the electronic structure, formation energy and transition level of a MoSe2 monolayer doped with V and VII atoms. The numerical results show that the dopant atoms can induce magnetism, except for in the case of the As-doped system. Specifically, N- and F-doped systems exhibit magnetic nanomaterial properties, P- and As-doped systems display metallic features, and in the cases of Cl-, Br- and I-doped systems, the systems exhibit half-metallic ferromagnetism (HMF). The formation energy calculations indicate that this can be more effective for achieving n-type and p-type doped MoSe2 under Mo-rich experimental conditions. However, for the systems doped with group V atoms, the transition level decreases with increasing atomic radius, but that of those doped with VII atoms increases with increasing atomic radius. By comparing the results, we find that the transition level is only 31 meV in F-doped MoSe2 monolayers, which indicates that F impurities can offer effective n-type carriers in MoSe2 monolayers.

By performing first-principles calculations, we explore the structural, electronic and magnetic properties of 3d transition metal (TM) atom-doped 1T-HfSe2 monolayers. The results show that it is energetically favorable and relatively easier to incorporate 3d TM atoms into the HfSe2 under Se-rich experimental conditions. Electronic structures and magnetism can be tuned effectively for V, Cr, Mn, Fe, and Cu doping. We find that the V, Cr, Mn, Fe impurity atoms prefer to stay together in the nearest neighboring (NN) configuration and show ferromagnetism (FM) coupling. Moreover, V-doped HfSe2 shows the characteristics of FM half-metallic properties, and it has lower formation energy. The strong p–d hybridization mechanism is used to explain the magnetism of TM-doped HfSe2 structures. Thus, we can conclude that 3d TM doping can induce the change of electronic structures and magnetism of 1T-HfSe2 monolayers, which is important for applications in semiconductor spintronics.

•Mn-doped HfS2 monolayer is magnetic nanomaterial without strain.•The doped system transforms from semiconductor to half-metallic when the tensile strain is equal or greater than 5%.•The largest half-metallic gap is 1.307 eV at 5% tensile strain and the magnetic moment always keeps about 3μB.•TC of NN configuration of 8% concentration closes to the room temperature.Using the first-principles calculations, we investigated electronic and magnetic properties of Mn-doped HfS2 monolayer for 4% and 8% Mn concentration. We study the strain tuning of electronic and magnetic properties of 4% Mn-doped HfS2 monolayer firstly. Our results show that the Mn-doped HfS2 monolayer is magnetic nanomaterial without strain. It keeps this character until the compressive strain comes to −8%, and the magnetism disappear with lager compressive strain. With the increasing tensile strain, the doped system transforms from semiconductor to half-metallic when the tensile strain is equivalent to or greater than 5%. The largest half-metallic gap is 1.307 eV at 5% tensile strain and the magnetic moment always keeps about 3μB, which indicates that Mn-doped HfS2 monolayer can be a candidate for superior half-metallic namomaterial. Furthermore, we find two Mn dopants couple ferromagnetically via antiferromagnetic (AFM) p-d exchange interaction at the environment of 8% concentration. It keeps the properties of magnetic semiconductor under two Mn-doped configurations with different Mn-Mn separations. Our studies predict Mn-doped HfS2 monolayer under strain to be candidates for dilute magnetic semiconductors.

•Cr does not induce magnetism in the WSe2 monolayer at 0% strain.•The doped system shows n-type doping semiconductor feature without strain.•Effect of strain on magnetic properties is inappreciable in Cr-doped WSe2.•Tensile strain is more effective in reducing the band gap of the doped system.Using first-principles calculations based on the density functional theory, we study the effect of strain on the electronic and magnetic properties of Cr-doped WSe2 monolayer. The results show that no magnetic moment is induced in the Cr-doped WSe2 monolayer without strain. For the Cr substitutions, the impurity states are close to the conduction bands, which indicate n-type doping occurs in this case. Then we applied strain (from −10% to 10%) to the doped system, and find that a little magnetic moment is induced with tensile strain from 6% to 9% and negligible. We find that the influence of strain on the magnetic properties is inappreciable in Cr-doped WSe2. Moreover, the tensile strain appears to be more effective in reducing the band gap of Cr-doped WSe2 monolayer than the compressive strain.

•Ni doping induces magnetism in the WSe2 monolayer.•The doped system shows half-metal feature from −2% to −7% strain.•The largest half-metallic gap is 89 meV at −5% tensile strain.•The biggest magnetic moment is 3.280 μBat-3% compressive strain.We study the effect of strain on electronic and magnetic properties of Ni-doped monolayer WSe2 by using a method of plane wave potential technique based on the density function theory. We find that Ni-doped monolayer WSe2 becomes a magnetic metal material, and the magnetic moment is 1.466 μB. When we apply different compressive strain, Ni-doped WSe2 shows half-metallic from magnetic properties firstly. With increasing compressive strain, Ni-doped WSe2 shows magnetic metal properties from −8% to −10%. The magnetic moment also increases firstly and then decreases with increasing compressive strains, the biggest magnetic moment is 3.280 μB at −3% compressive strain and the minimum magnetic moment is 0.658μB at −10% compressive strain. While, the magnetic moment increases slowly with increasing tensile strain and comes to 1.812μB at 10% tensile strain. By comparison, we find that there is stronger effect of compressive strain on electronic and magnetic properties of this doped system than that of tensile strain.

•N, P, F, Br and I substitutions can induce magnetic moment.•N and P atoms p orbitals play an important role in the total magnetic moment.•W2 atom d orbitals play an important role in the total magnetic moment in F-doped case.•W atoms d orbitals play an important role in the case of Br- and I-doped.We have investigated electronic and magnetic properties of n- and p-type impurities by means of group V and VII atoms substituting selenium in WSe2 monolayer based on density functional theory. Our results show that N, P and As substitutions indicate p-type doping and F, Cl, Br and I substitutions indicate n-type doping. Moreover, some atoms of group V and VII can induce magnetic moment, and the magnetic moment mainly originates from p orbital of the dopant and d orbital of the neighbor W atoms. N-, P-, F- (or Br-doped) WSe2 exhibit magnetic nanomaterial (or magnetic metallic) features, Cl- and As-doped systems show no-magnetic metal and I-doped system exhibits half-metallic (HM) properties. The biggest magnetic moment is 0.846 μB of F-doped system. The formation energy calculations also indicate that it is energetically favorable and relatively easier to incorporate group V and VII atoms into WSe2 monolayer under W-rich experimental conditions. The formation energy of the F-doped system is the lowest and the next lowest formation energy is obtained in the N-doped system. These results are useful for understand characteristics of n- and p-doped WSe2 nanostructures.

The β-Ga2O3 (100) surface, with or without defects, as a robust photocatalyst for water decomposition was studied on the basis of density functional theory (DFT). The surface defects considered, herein, were oxygen vacancies and doping with higher chalcogens, such as S, Se and Te. Narrowed bandgaps of the defective surfaces, leading to a high utilization of solar energy with respect to pure Ga2O3, were observed. By optimizing the geometrical structures of the initial molecular adsorption states (IS), the transition states (TS) and the final dissociative adsorption states (FS), the reaction activation energy and the adsorption energy of each species in the reaction pathway were obtained. Water acts as a Lewis base and provides electrons to the surfaces. The presence of water on the surfaces more likely preferred the molecular modes. The reaction results demonstrate that the surface is robust for water decomposition, where the defects, both vacancies and doping with high chalcogens, have no evident influence on the reaction parameters. The reaction pathway can be improved by vacancies or Se doping. These findings for water decomposition on Ga2O3 (100) surfaces can be used in synthesis of photocatalysts and for understanding the interactions across the reaction pathway.

•Pristine 1T-HfS2 is a semiconductor with indirect gaps of 1.252 eV.•Magnetism cannot be observed for 1T-HfS2 under strain.•Compressive strain is more effective in band engineering of pristine 1T-HfS2 monolayer than the tensile strain.•The band gap of 1T-HfS2 comes to zero when the compressive strain is above −7%.We perform first-principles based on the density function theory to investigate electronic and magnetic properties of 1T-HfS2 monolayer with biaxial tensile strain and compressive strain. The results show that HfS2 monolayer under strains doesn’t display magnetic properties. When the strain is 0%, the HfS2 monolayer presents an indirect band gap semiconductor with the band gap is about 1.252 eV. The band gap of HfS2 monolayer decreases quickly with increasing compressive strain and comes to zero when the compressive strain is above −7%, the HfS2 monolayer system turns from semiconductor to metal. While the band gap increases slowly with increasing tensile strain and comes to 1.814 eV when the tensile strain is 10%. By comparison, we find that the compressive strain is more effective in band engineering of pristine 1T-HfS2 monolayer than the tensile strain. And we notice that the extent of band gap variation is different under tensile strain. The change of band gap with strain from 1% to 5% is faster than that of the strain 6–10%. To speak of, the conduction band minimum (CBM) is all located at M point with different strains. While the valence band maximum (VBM) turns from Γ point to K point when the strain is equal to and more than 6%.

•Conduction band minimum (CBM) and valence band maximum (VBM) are changed under the variation of isotropic strain.•ZrS2 monolayer turns to metal at −8% compressive strain.•The biggest band gap of 1T-ZrS2 monolayer is 1.577 eV at tensile strain 6%.•Compression strain is more effective than tensile strain in modulating band-gap of ZrS2 monolayer.We report electronic structure of 1T-ZrS2 monolayer with biaxial strain from −10% to 15%, basing the first principles calculations. Our calculation results indicate that the band structure of ZrS2 monolayer was changed clearly. The location of conduction band minimum (CBM) and valence band maximum (VBM) changed with the variation of isotropic strain. At compressive strain, the location of CBM and VBM retains at M and Γ point, respectively. The band gap of ZrS2 monolayer decreases from 1.111 eV to 0 eV when compressive strain increases from 0% to −8%, which means that the ZrS2 monolayer turns to metal at −8% compressive strain. Under the tensile strain, the ZrS2 monolayer also retains be an indirect band gap semiconductor. The location of CBM moves from M to Γ point and the location of VBM moves along Γ-A-K-Γ direction. The band gap of ZrS2 monolayer firstly increases and then decreases and the biggest band gap is 1.577 eV at tensile strain 6%. We can see the compression strain is more effective than tensile strain in modulating band gap of 1T-ZrS2 monolayer.

•Pristine 1T-ZrSe2 is a semiconductor with indirect gaps of 0.439eV.•Magnetism can be observed for V, Cr, Mn, and Fe doped systems.•Strong p–d hybridization was found between TM 3d orbitals and Se 3p orbitals.•Hubbard potential Ueff can manipulate effectively the magnetic moment and electronic structure of TM-doped 2D nanostructure.Zirconium diselenide (ZrSe2) is one of many members of the layer-structured transition-metal dichalcogenide family. We report a systematic study of the magnetic properties of 1T-ZrSe2 doped with 3d transition metals (TM) using the first-principles calculation. The calculations show that the pristine 1T-ZrSe2 is semiconductors with indirect gaps of 0.439eV. The magnetism can be obtained for V, Cr, Mn, and Fe doping. The reduced total magnetic moment is 1.027μB, 1.841μB, 3.062μB, 0.249μB, respectively, and mainly comes from the transition metal 3d orbitals. The strong p–d hybridization was found between the 3d orbital of TM and 4p orbital of Se. We further performed DFT + U calculations with U on the TM impurities 6eV to describe the strong electron-electron correlation, we found that the magnetic moment of dopants were been increased to 2.791μB, 3.152μB, 4.348μB, 4.600μB, respectively, which indicates a transition from the low to high spin state. The electronic structure analysis reveals that the V, Cr, Mn, and Fedoped systems turn into magnetic metal. These results can provide useful guidance to engineer the magnetic properties of 1T-ZrSe2 in future experiments.

•An atomically type-II heterobilayer which is suitable for optoelectronics and solar cell with wide bandgap was formed.•The charge redistribution is mainly on the surface and the amount of electrons depends on the strength of Efield.•The bandgaps varying with Efield can be divided into three ranges indicating different Efield-sensitive which may possess potential in sensor.•Increasing the Efield upon 0.07 V/Å, the band alignment converts from type-II to type-I heterojunction.The interfacial electronic properties of PbI2 and BN van der Waals (vdW) heterobilayer are explored by using density functional theory (DFT) method. An intrinsic type-II heterostructure with a wide bandgap is demonstrated. The spatial separation of the lowest energy electron-hole pairs can be actualised and make PbI2/BN heterostructure as a good candidate for applications in optoelectronics and solar cell. A simulation of Efield is actualized to modify its electronic properties. Band alignment converts from type-II to type-I heterostructure separated by a forward voltage with the value of about 0.07 V/Å. Three regions implying different Efield-sensitive properties are obtained from the variations of bandgap with Efield. The charge redistribution with an Efield is mainly on the surface of PbI2 and BN layers as well as the amount of electrons depends on the strength of Efield. In addition, the PbI2/BN heterobilayer exhibits more outstanding optical conductivity capability. Our results could bring forward a new perspective on sensor and shed light on the design of novel nano- and optoelectronics based on the PbI2/BN vdW heterostructure.Download high-res image (109KB)Download full-size image

•One X-doped (X = Ti, Zr, Hf) WS2 monolayer is non-magnetic.•Two next nearest neighbor X-doped WS2 is ferromagnetic.•The p(d)–d(d) hybridizations induce to magnetism of the two nearest neighbor X-doped WS2.•It is easier to incorporate X atom into the WS2 monolayer under S-rich experimental conditions.Based on density functional theory, we investigated electronic and magnetic properties of X-doped (Group 4) WS2 monolayer for 6.25% and 12.5% X concentration. Numerical results show that one X-doped WS2 monolayer is non-magnetic, while two X-doped systems of the next nearest neighbor configuration are ferromagnetic (FM). The hybridization between the X dopant and its neighboring W and S atoms results in the splitting of the energy levels near the Fermi energy. These results suggest the p(d)–d(d) hybridization mechanism for the magnetism of the X-doped WS2 monolayer structures. The asymmetric charge density distribution induces to magnetism for two next nearest neighbor X-doped WS2 systems. The studies find that the two next nearest X-doped WS2 monolayers to be candidates for magnetic metallic material. Moreover, the formation energy calculations also indicate that it is energy favorably and relatively easier to incorporate X atom into the WS2 monolayer under S-rich experimental conditions. Our results show that substitutional doping from IVB group is an effective way to modulate electronic and magnetic properties of tungsten disulphide monolayer.

•The formation energy is lower under Hf-rich conditions.•N-doped system owns the lowest formation energy compared with other atoms.•The transition level of N-doping in HfS2 is 119 meV.•The magnetism is observed for P and As doping.We explored the characteristics of n- and p-type impurities by means of group V and VII atoms substituting sulfur in 1T-HfS2 monolayer using the first-principles calculation. Numerical results show that the formation energy increases with the increasing impurity atom size for each considered doping case, and the formation energy calculations also indicate that it is energy favorably and relatively easier to incorporate these atoms into the HfS2 under Hf-rich experimental conditions. Meanwhile, with increasing atomic size, the transition energy levels increase for group V atoms substitution. While the transition energy levels decrease with increasing atomic size for group VII atoms substitution. The calculations of the transition energy level indicate that the N-doped HfS2 monolayer has the lowest formation energy and the shallowest transition level among the p-doped HfS2 monolayer systems.

We investigate the electronic and magnetic properties of an Fe-doped single-layer WSe2 sheet with strain from −10% to 10% using first-principles methods based on density functional theory. In our calculation, an Fe-doped WSe2 monolayer is a magnetic semiconductor without strain. With the tensile strain increasing, its magnetic moment increases slightly, and the system shows a half-metal feature from 4% to 9% and transforms to a metal at 10% strain. The largest half-metallic gap is 0.183 eV at 4% tensile strain. However, with compressive strain increasing, its magnetic moment decreases slightly and disappears from −5% to −10%, and the system transforms from half-metallic to metallic. Fe-doped WSe2 can endure strain from −4% to 10%. Our studies predict Fe-doped WSe2 monolayers under strain to be candidates for dilute magnetic semiconductors. Moreover, the formation energy calculations also indicate that it is energy favorable and relatively easier to incorporate Fe atom into the WSe2 monolayer under Se-rich experimental conditions.

The electronic and magnetic properties of n- and p-type impurities by means of group V and VII atoms substituting sulfur in a MoS2 monolayer were investigated using first-principles methods based on density functional theory. Numerical results show that group V and VII atoms can induce magnetic properties, and the magnetic moment mainly originates from the dopant’s p orbital and neighbor Mo atoms’ d orbital. N-, P-, F-, and I-doped (or As-doped) MoS2 exhibits magnetic nanomaterial (or metallic) features, and Cl- and Br-doped systems exhibit half-metallic ferromagnetism (HMF). Moreover, the formation energy calculations also indicate that it is energetically favorable and relatively easier to incorporate group V and VII atoms into a MoS2 monolayer under Mo-rich experimental conditions. The formation energy of the F-doped system is the lowest, the next lowest formation energy is obtained in the Cl-doped system. By comparison, Cl-doped MoS2 is more suitable for spin injection. This finding is important for the achievement of spin devices on MoS2 nanostructures.

•WSe2 monolayer retains direct band gap when tensile strain is less than 13%.•WSe2 monolayer turns to indirect gap semiconductor with compressive strain (less than −7%).•Strain can reduce the band gap of the WSe2 monolayer.In this paper, we study the electronic properties of WSe2 monolayer with biaxial tensile strain and compressive strain by using first principles based on the density function theory. Under the biaxial tensile strain, WSe2 monolayer retains direct band gap with increasing strain and the band gap of WSe2 continuously decreases with increasing strain, eventually turn to metal when strain is equal to or more than 13%. Under the biaxial compressive strain, WSe2 monolayer turns to indirect gap and the band gap continuously decreases with increasing strain, finally turn to metal when strain is up to −7%. The strain can reduce the band gap of the WSe2 monolayer regardless of the strain direction. By comparison, we can see that the tensile strain appears to be more effective in reducing the band gap of pristine WSe2 monolayer than the compressive strain from −5% to 5%. But the band gap turns to zero quickly from −6% to −7% under compressive strain, however for tensile strain from 5% to 13%, the band gap decreases slowly. Based on the further analysis of the projected charge density for WSe2 monolayer, the fundamental reason of the change of band structure under biaxial tensile strain is revealed.

•Co induces magnetism in the WSe2 monolayer.•The doped system is a magnetic semiconductor nanomaterial without strain.•The doped system transforms to half-metallic material under strain.•The largest half-metallic gap is 0.147 eV at 8% tensile strain.We perform first-principles calculation to investigate electronic and magnetic properties of Co-doped WSe2 monolayer with strains from −10% to 10%. We find that Co can induce magnetic moment about 0.894 μB, the Co-doped WSe2 monolayer is a magnetic semiconductor material without strain. The doped system shows half-metallic properties under tensile strain, and the largest half-metal gap is 0.147 eV at 8% strain. The magnetic moment (0.894 μB) increases slightly from 0% to 6%, and jumps into about 3 μB at 8% and 10%, which presents high-spin state configurations. When we applied compressive strain, the doped system shows a half-metallic feature at −2% strain, and the magnetic moment jumps into 1.623 μB at −4% strain, almost two times as the original moment 0.894 μB at 0% strain. The magnetic moment vanishes at −7% strain. The Co-doped WSe2 can endure strain from −6% to 10%. Strain changes the redistribution of charges and magnetic moment. Our calculation results show that the Co-doped WSe2 monolayer can transform from magnetic semiconductor to half-metallic material under strain.

•The transition level is dependent highly on the atom number in the periodic table.•Group V atom can create deep acceptor impurity level inside the band gap.•Group VII atom can create shallow transition level under Sn-rich growth conditions.•Group VII atom substituting S atom may serve as a promising n-type doping.Based on density functional theory, the electronic structure, formation energy and transition level of group V and VII atoms-doped SnS2 are investigated by means of first-principles methods. Numerical results show that the formation energy and transition level are dependent highly on the atom number in the periodic table. Group V atom substituting S atom has high formation energy and can create deep acceptor impurity level inside the band gap of SnS2. However, our calculations also show that group VII atom substituting S atom may serve as a promising n-type doping in the SnS2 due to its negative formation energy and shallow transition level under the Sn-rich growth conditions.

•V3W, V6S and V1W+2S can induce to spin magnetic moment.•One and two sulfurs vacancy show spin magnetic moment.•Total magnetic moment of Mn-doped WS2 system is increased with sulfur vacancy defects.•W atoms display antiferromagnetic coupling to the dopant.We investigate electronic and magnetic properties of pristine and Mn-doped monolayer WS2 with vacancy defects using the first-principles methods based on density functional theory. The results show that intrinsic three-tungsten vacancy (V3W), six-sulfur vacancy (V6S) and 1W+2S vacancy (V1W+2S) can induce to total spin magnetic moment of 0.169μB, 0.608μB and 0.981μB, respectively. One and two sulfurs vacancy show spin magnetic moment up to 1.048μB and 1.172μB in Mn-doped monolayer WS2. Sulfur vacancy defects (V1S and V2S) can induce to the increase of the total magnetic moment in Mn-doped monolayer WS2 system. Several of the W atoms in the immediate vicinity of the Mn atom display antiferromagnetic coupling to the dopant with the increase of sulfur vacancy defects. This finding indicates an immediate significance of pristine and Mn-doped 1L WS2 with vacancy defects for new spintronic applications.

•Mn dopants are shown to couple ferromagnetically.•The formation energy is low under S-rich experimental conditions.•A possible Mn clustering behavior may be formed.We investigate the electronic and magnetic properties of Mn-doped monolayer WS2 for 6.25% and 8% Mn concentration using the first-principles methods based on the density functional theory. Mn dopants are shown to couple ferromagnetically via a double-exchange mechanism. Our studies predict Mn-doped WS2 monolayers to be candidates for thin dilute magnetic semiconductors. Moreover, the formation energy calculations also indicate that it is energy favorably and relatively easier to incorporate Mn atom into the WS2 monolayer under S-rich experimental conditions. For all possible Mn-doped configurations, a possible Mn clustering behavior may be formed in the Mn-doped WS2 monolayer systems.

•Mn atom induces a spin-polarization with local net magnetic moments of 1.730 μB.•Mn atom breaks the local time reversal symmetry.•The Dirac cone of the top surface disappears and the Fermi level shifts up to band gaps.•The Dirac cone of the bottom surface is still alive and shifts downward.Based on first-principles calculations within density functional theory, we studied the electronic and magnetic properties of Mn-coverd Bi2Se3 film employing spin–orbit coupling (SOC) self-consistently. For the Mn monolayer on the Bi2Se3 film, the energy favored structure is that Mn atoms are buried between top surface Se atoms and the second layer Bi atoms. It induces a spin-polarization with local net magnetic moments of 1.730 μB Mn atom breaks the local time reversal symmetry and the Dirac cone of Mn-covered surface disappears. While the Dirac cone of the Mn free surface is still alive. For the substitution of Mn atom for the outmost-layer Se atom, the electronic structure is similar to the case of the ad-Mn system.

•One Cu-doped monolayer WS2 is non-magnetic.•Two Cu-doped systems of the nearest neighbor configuration are ferromagnetic.•The microscopic FM ordering originates from the p–d hybridization.We investigate magnetic properties of Cu-doped monolayer WS2 for 6.25%, 8% and 12.5% Cu concentration using the first-principles methods based on density functional theory. The results show that one Cu-doped monolayer WS2 is non-magnetic, while two Cu-doped systems of the nearest neighbor configuration are ferromagnetic (FM). The hybridization between the Cu dopant and its neighboring S atoms results in the splitting of the energy levels near the Fermi energy. These results suggest the p–d hybridization mechanism for the magnetism of the Cu-doped WS2 monolayer structures. While the magnetic moment disappears with the increasing Cu–Cu distances. Our studies predict the nearest two Cu-doped WS2 monolayers to be candidates for thin dilute magnetic semiconductors. Moreover, the formation energy calculations also indicate that it is energy favorably and relatively easier to incorporate Cu atom into the WS2 monolayer under S-rich experimental conditions.

•The effects of Cr adsorbing on Bi2Se3 are studied by first-principles calculations.•Cr atom induces a spin-polarization with total net magnetic moments of 2.157 μB.•The electronic structures change and the energy level splits.•A p-d hybridization appears between Cr 3d states and the neighboring Se 4p states.Based on first-principles calculations within density functional theory, we studied the effects of Cr adsorption on the electronic and magnetic properties of Bi2Se3 topological insulators employing spin–orbit coupling (SOC) self-consistently. Cr atom induces a spin-polarization with total net magnetic moments of 2.157 μB (spin up). There is a p-d hybridization between the Cr 3d states and the nearest neighbor Se 4p states. A peak of density of states appears at Fermi level. The electronic structures change and the energy levels split near the Fermi level. No gap opening has been found at the Dirac point of the surface state from the bottom surface.

Based on the framework of effective-mass approximation and variational approach, optical properties of exciton are investigated theoretically in ZnO/MgxZn1−xO vertically coupled quantum dots (QDs), with considering the three-dimensional confinement of electron and hole pair and the strong built-in electric field effects due to the piezoelectricity and spontaneous polarization. The exciton binding energy, the emission wavelength and the oscillator strength as functions of the different structural parameters (the dot height and the barrier thickness between the coupled wurtzite ZnO QDs) are calculated with the built-in electric field in detail. The results elucidate that structural parameters have a significant influence on the exciton state and optical properties of ZnO coupled QDs. These results show the optical and electronic properties of the quantum dot that can be controlled and also tuned through the nanoparticle size variation.

Based on the framework of effective-mass approximation and variational approach, optical properties of exciton are investigated theoretically in ZnO/MgxZn1−xO vertically coupled quantum dots (QDs), with considering the three-dimensional confinement of electron and hole pair and the strong built-in electric field effects. The exciton binding energy, the emission wavelength and the oscillator strength as functions of the structural parameters (the dot height, the barrier thickness between the coupled wurtzite ZnO QDs and Mg content x in the barrier layers) is calculated in detail. The results elucidate that Mg content have a significant influence on the exciton state and optical properties of ZnO coupled QDs. When Mg content x increases, the strong built-in electric field increases and leads to the redshift of the effective band gap of the MgxZn1−xO layer. These theoretical results are useful for design and application of some important photoelectronic devices constructed by using ZnO strained QDs.► Mg content have a significant influence on optical properties of ZnO coupled QDs. ► When Mg content x increases, the strong built-in electric field increases. ► The built-in electric field leads to the redshift of the effective band gap.

•One Cu-doped monolayer WS2 is non-magnetic.•Two Cu-doped systems of the nearest neighbor configuration are ferromagnetic.•The microscopic FM ordering originates from the p–d hybridization.We investigate magnetic properties of Cu-doped monolayer WS2 for 6.25%, 8% and 12.5% Cu concentration using the first-principles methods based on density functional theory. The results show that one Cu-doped monolayer WS2 is non-magnetic, while two Cu-doped systems of the nearest neighbor configuration are ferromagnetic (FM). The hybridization between the Cu dopant and its neighboring S atoms results in the splitting of the energy levels near the Fermi energy. These results suggest the p–d hybridization mechanism for the magnetism of the Cu-doped WS2 monolayer structures. While the magnetic moment disappears with the increasing Cu–Cu distances. Our studies predict the nearest two Cu-doped WS2 monolayers to be candidates for thin dilute magnetic semiconductors. Moreover, the formation energy calculations also indicate that it is energy favorably and relatively easier to incorporate Cu atom into the WS2 monolayer under S-rich experimental conditions.

•Mn dopants are shown to couple ferromagnetically.•The formation energy is low under S-rich experimental conditions.•A possible Mn clustering behavior may be formed.We investigate the electronic and magnetic properties of Mn-doped monolayer WS2 for 6.25% and 8% Mn concentration using the first-principles methods based on the density functional theory. Mn dopants are shown to couple ferromagnetically via a double-exchange mechanism. Our studies predict Mn-doped WS2 monolayers to be candidates for thin dilute magnetic semiconductors. Moreover, the formation energy calculations also indicate that it is energy favorably and relatively easier to incorporate Mn atom into the WS2 monolayer under S-rich experimental conditions. For all possible Mn-doped configurations, a possible Mn clustering behavior may be formed in the Mn-doped WS2 monolayer systems.

•Mn doping induces magnetism in the WSe2 monolayer.•The doped system is a magnetic semiconductor nanomaterial without strain.•The doped system transforms to half-metallic material under strain.•The largest half-metallic gap is 0.450 eV at −2% tensile strain.Electronic and magnetic properties of Mn-doped WSe2 monolyer subject to isotropic strain are investigated using the first-principles methods based on the density functional theory. Our results indicate that Mn-doped WSe2 monolayer is a magnetic semiconductor nanomaterial with strong spontaneous magnetism without strain and the total magnetic moment of Mn-doped system is 1.038μB. We applied strain to Mn-doped WSe2 monolayer from -10% to 10%. The doped system transforms from magnetic semiconductor to half-metallic material from −10% to −2% compressive strain and from 2% to 6% tensile strain. The largest half-metallic gap is 0.450 eV at −2% compressive strain. The doped system shows metal property from 7% to 10%. Its maximum magnetic moment comes to 1.181μB at 6% tensile strain. However, the magnetic moment of system decreases to zero sharply when tensile strain arrived at 7%. Strain changes the redistribution of charges and arises to the magnetic effect. The coupling between the 3d orbital of Mn atom, 5d orbital of W atom and 4p orbital of Se atom is analyzed to explain the strong strain effect on the magnetic properties. Our studies predict Mn-doped WSe2 monolayers under strain to be candidates for thin dilute magnetic semiconductors, which is important for application in semiconductor spintronics.