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Papers by Ruishen Meng

Two-dimensional (2D) ferromagnetic materials are considered to be promising candidates for future... more Two-dimensional (2D) ferromagnetic materials are considered to be promising candidates for future generations of spintronic devices. Yet, 2D materials with intrinsic ferromagnetism are scarce. High-throughput first-principles simulations are performed in order to screen 2D materials that present a non-magnetic to a ferromagnetic transition upon hole doping. A global evolutionary search is subsequently performed, in order to identify alternative possible atomic structures of the eligible candidates, and 122 materials exhibiting hole-doping induced ferromagnetism are identified. Their energetic and dynamic stability, as well as their magnetic properties under hole doping, are investigated systematically. Half of these 2D materials are metal halides, followed by chalcogenides, oxides, and nitrides, some of them having predicted Curie temperatures above 300 K. The exchange interactions responsible for the ferromagnetic order in these 2D materials are also discussed. This work not only p...

Advanced Materials Interfaces, 2021

Large‐area epitaxy of layered materials is one of the cornerstones for a successful exploitation ... more Large‐area epitaxy of layered materials is one of the cornerstones for a successful exploitation of van der Waals (vdW) materials in the semiconductor industry. The formation of 60° twin stacking faults and 60° grain boundaries is of major concern for the defect‐free epitaxial growth. Although strategies to overcome the occurrence of these defects are being considered, more fundamental understanding on the origin of these defects is highly essential. This work focuses on understanding the formation of 60° twins in (quasi‐)vdW epitaxy of 2D chalcogenides. Molecular beam epitaxy (MBE) experiments reveal the striking difference in 60° twin occurrence between WSe2 and Bi2Se3 in both quasi‐vdW heteroepitaxy and vdW homoepitaxy. Density functional theory (DFT) calculations link this difference to the interlayer vdW coupling strength at the unit cell level. The stronger interlayer vdW coupling in Bi2Se3 unit cells compared to WSe2 unit cells is explained to result in a reduced twin occurre...

arXiv: Materials Science, 2020

Defect-free epitaxial growth of 2D materials is one of the holy grails for a successful integrati... more Defect-free epitaxial growth of 2D materials is one of the holy grails for a successful integration of van der Waals (vdW) materials in the semiconductor industry. The large-area (quasi-)vdW epitaxy of layered 2D chalcogenides is consequently carefully being researched since these materials hold very promising properties for future nanoelectronic applications. The formation of defects such as stacking faults like 60o twins and consequently 60o grain boundaries is still of major concern for the defect-free epitaxial growth of 2D chalcogenides. Although growth strategies to overcome the occurrence of these defects are currently being considered, more fundamental understanding on the origin of these defects at the initial stages of the growth is highly essential. Therefore this work focuses on the understanding of 60o twin formation in (quasi-)vdW epitaxy of 2D chalcogenides relying on systematic molecular beam epitaxy (MBE) experiments supported by density functional theory (DFT) calc...

npj 2D Materials and Applications, 2021

The possibility of dissipationless chiral edge states without the need of an external magnetic fi... more The possibility of dissipationless chiral edge states without the need of an external magnetic field in the quantum anomalous Hall effect (QAHE) offers a great potential in electronic/spintronic applications. The biggest hurdle for the realization of a room-temperature magnetic Chern insulator is to find a structurally stable material with a sufficiently large energy gap and Curie temperature that can be easily implemented in electronic devices. This work based on first-principle methods shows that a single atomic layer of V2O3 with honeycomb–kagome (HK) lattice is structurally stable with a spin-polarized Dirac cone which gives rise to a room-temperature QAHE by the existence of an atomic on-site spin–orbit coupling (SOC). Moreover, by a strain and substrate study, it was found that the quantum anomalous Hall system is robust against small deformations and can be supported by a graphene substrate.

Journal of Applied Physics, 2020

There has been tremendous research effort in hunting for novel two-dimensional (2D) materials wit... more There has been tremendous research effort in hunting for novel two-dimensional (2D) materials with exotic properties, showing great promise for various potential applications. Here, we report the findings about a new hexagonal phase of 2D Ga2O3 and In2O3, with high energetic stability, using a global searching method based on an evolutionary algorithm, combined with density functional theory calculations. Their structural and thermal stabilities are investigated by the calculations of their phonon spectra and by ab initio molecular dynamics simulations. They are predicted to be intrinsically non-magnetic stable semiconductors, with a flatband edge around the valence band top, leading to itinerant ferromagnetism and half-metallicity upon hole doping. Bilayer Ga2O3 is also studied and found to exhibit ferromagnetism without extra hole doping. The Curie temperature of these materials, estimated using Monte Carlo simulations based on the Heisenberg model, is around 40–60 K upon a modera...

Physical Review B, 2021

Recent experimental success in the realization of two-dimensional (2D) magnetism has stimulated t... more Recent experimental success in the realization of two-dimensional (2D) magnetism has stimulated the search for new magnetic 2D materials with strong magnetic anisotropy and high Curie temperature. One promising subgroup of 2D magnetic systems are Dirac half-metals (DHM) which have gained a lot of interest recently, as they host a high-temperature quantum anomalous Hall effect (QAHE). This article discusses predictions for intrinsic DHMs and identifies them as realizations of the Kane-Mele Hubbard model at quarter filling. This proposed unification contributes to a firmer understanding of these materials and suggests pathways for the discovery of new DHM systems.

Applied Sciences, 2020

The high contact resistance at metal/two-dimensional (2D) semiconductor junctions is a major issu... more The high contact resistance at metal/two-dimensional (2D) semiconductor junctions is a major issue for the integration of 2D materials in nanoelectronic devices. We review here recent theoretical results on the contact resistance at lateral heterojunctions between graphene or 1T-MoS2 with 2H-MoS2 monolayers. The transport properties at these junctions are computed using density functional theory and the non-equilibrium Green’s function method. The contact resistance is found to strongly depend on the edge contact symmetry/termination at graphene/2H-MoS2 contacts, varying between about 2 × 102 and 2 × 104 Ω∙μm. This large variation is correlated to the presence or absence of dangling bond defects and/or polar bonds at the interface. On the other hand, the large computed contact resistance at pristine 1T/2H-MoS2 junctions, in the range of 3–4 × 104 Ω.μm, is related to the large electron energy barrier (about 0.8 eV) at the interface. The functionalization of the metallic 1T-MoS2 conta...

ACS Applied Materials & Interfaces, 2020

Applied Physics Letters, 2019

The contact resistance at two-dimensional graphene/MoS2 lateral heterojunctions is theoretically ... more The contact resistance at two-dimensional graphene/MoS2 lateral heterojunctions is theoretically studied, using first-principles simulations based on density functional theory and the nonequilibrium Green's function method. The computed contact resistance lies in the range of 102 to 104 Ω μm, depending on the contact edge symmetry (armchair or zigzag) and termination (Mo and/or S terminated). This large variation in the contact resistance arises from the variation in the interface barrier height, which is sensitive to the presence of polar C-Mo bonds or sulfur dangling bonds at the interface. These results highlight that the control of the edge symmetry and/or edge termination is crucial to achieve a low contact resistance (in the range of a few hundred ohms micrometer) at graphene/MoS2 lateral heterojunctions for 2D material-based field-effect devices.

IEEE Sensors Journal, 2017

In this paper, the interaction of atmospheric gas molecules (NH3, NO2, SO2, CO, CO2, CH4, O2, and... more In this paper, the interaction of atmospheric gas molecules (NH3, NO2, SO2, CO, CO2, CH4, O2, and NO) with monolayer graphene-like hexagonal ZnS (g-ZnS) is studied with first-principle calculations to explore its potential application as gas sensor. Among all the gas molecules, NH3, and SO2, NO2 act as a strong donor and acceptor with apparent charge transfer of 0.200,-0.121 and-0.115 e. We further calculated the current-voltage (I−V) relation using the nonequilibrium Green's function (NEGF) formalism. It can be indicated from the results that a mark change of the I−V relation before and after the adsorption of NH3, which makes monolayer g-ZnS a prospective gas sensor for NH3. In addition, under the mechanical strain the adsorption is substantially enhanced with significant impact on the properties of adsorbates and g-ZnS layer, especially for the NH3, NO2, and NO-monolayer g-ZnS configurations. The results presented herein demonstrate that monolayer g-ZnS can be the potential gas sensor of NH3 with high sensitivity and selectivity.

IEEE Electron Device Letters, 2017

Applied Surface Science, 2017

First-principles calculations based on density-functional theory reveal some superior physical pr... more First-principles calculations based on density-functional theory reveal some superior physical properties of hydrogen and fluorine co-decorated silicene (HSiF) monolayer and bilayer. Our simulated results reveal that the HSiF monolayer is a large direct band gap semiconductor greatly differing from the gapless semi-metallic silicene. There exists strong interlayer coupling in HSiF bilayer, leading to the good stabilities of HSiF bilayer even beyond bilayer graphene. The proposed HSiF bilayer exhibits a moderate direct band gap of 0.296 eV which is much lower than that of HSiF monolayer. Encouragingly, HSiF layers all have a direct band gap nature, irrespective of stacking pattern, thickness and external electric fields, which is an advantage over MoS 2 layers. Furthermore, an out-of-plane electric field has an evident impact on the band structures of the HSiF monolayer and bilayer. Especially, the band gap of HSiF bilayer can be effectively tuned by external electric field, even a semiconductor-metal transition occurs. More importantly, the HSiF bilayer exhibits a significant improved visible light adsorption peak with respect to that of HSiF monolayer, and the superior optical properties is robust, independent of stacking pattern. The complete electron-hole separation also enhances the photocatalytic efficiency of HSiF bilayer. In a word, the moderate band gap, effective band gap modification by external electric field, robust direct band gap nature, suitable band edge positions, electron-hole separation, and fascinating visible light adsorption, which enable HSiF bilayer to have great potential applications in the field of solar energy conversion, high performance photocatalysis and nanoelectronic devices, and we call for more concern over this kind of 2D Janus materials which possesses excellent properties.

Advanced Materials Interfaces, 2017

ZnO also has a multitude of 1D nanomorphologies, [3,4] for example, nanowires, [5] nanotubes, [6]... more ZnO also has a multitude of 1D nanomorphologies, [3,4] for example, nanowires, [5] nanotubes, [6] nanorods, [7] nanoribbons, [8] etc. This versatile functional material has attracted significant research attention because of its excellent properties such as sizable direct band gap of ≈3.3 eV and large exciton binding energy of 60 meV and so on, which make it an excellent candidate for a variety of applications like piezoelectric devices, [9] light emitting diodes, [10] biosensors, [11] catalysis, [12] etc. Apart from those applications, ZnO has also been extensively investigated as gas sensors, in particular, the 1D ZnO nanostructures exhibit much higher sensitivity than the polycrystalline bulk ones owing to the high surface-to-volume ratio. [13-17] Recently, another type of nanostructure of ZnO, namely, the atomic-thinned g-ZnO monolayer, was theoretically predicted [18,19] and experimentally realized. [20-22] It has the honeycomb structure very similar to that of single-layered hexagonal boron nitride (h-BN), with the band gap predicted to be 3.57-5.64 eV, larger than the one of the bulk wurtzite ZnO. [23] As the mutual merit shared by the 2D materials, [24-30] monolayer g-ZnO has even larger surface area than its 1D counterparts with the same volume. Inspired by the previous researches of unique gas adsorption performance of various 2D materials, [26,31-43] it is of scientific interests to investigate the gas adsorption performance of g-ZnO and explore its suitability to be gas sensing materials. However, relevant systematical investigations of gas adsorption performance of pristine g-ZnO are relatively scarce. [44,45] In this paper, we employ first principle calculations based on the density functional theory (DFT) to gain fundamental insights into the interaction between gas molecules and pristine g-ZnO. This study mainly focuses on the following questions: (i) What is the adsorption behavior of the common atmospheric (CO 2 , H 2 O, and O 2) and toxic (CO, H 2 S, NH 3 , SO 2 , NO, and NO 2) gas molecules on g-ZnO? (ii) Will the adsorption strength be affected by the gas concentration? (iii) What is the impact of the layer numbers of g-ZnO on the adsorption? (iv) Do the heterolayers or substrates have effects on the adsorption? To solve the issues above, we utilized different supercell sizes of g-ZnO to simulate the gas concentration effect, that is, a large supercell gives rise to lower gas density. Besides, we also 2D layered materials have gained tremendous research interests for gas sensing applications because of their ultrahigh theoretical specific surface areas and unique electronic properties, which are prone to be influenced by external factors. Here, using first principle calculations, the adsorption of several common gas molecules on graphene-like ZnO (g-ZnO) is systematically studied by taking the gas concentration, homolayer number, and heterolayers into considerations. The calculation results show that the adsorption energies of all the selected gas molecules are susceptible to the concentration and the homolayer number, and they incline to gradually increase with the decreasing of the gas concentration or they dramatically increase with the raising in g-ZnO layer number combined with elevated charge transfers. Besides, choosing graphene (MoS 2) as a heterolayer material to stack with g-ZnO can enhance (weaken) the interaction with NH 3 (NO 2) while weakening (enhance) that of NO 2 (NH 3), thus facilitating the selectivity to some extent. Further, Hirshfeld charge analysis and visualization of the charge density differences between the layers reveal the different charge transfers and adsorption mechanisms before and after gas adsorption. The results indicate that g-ZnO and its homolayer and hetero-bilayer structures can be promising candidates as gas sensing materials and catalysis.

IEEE Electron Device Letters, 2016

The adsorption behaviors of sulfur dioxide (SO 2) gas molecule over pristine, boron-, silicon-, s... more The adsorption behaviors of sulfur dioxide (SO 2) gas molecule over pristine, boron-, silicon-, sulfur-, and nitrogen-doped phosphorenes are theoretically studied using first-principles approach based on density-functional theory (DFT). The adsorption energy (E a), adsorption distance (d) and Mulliken charge (Q) of SO 2 molecules adsorbed on the different phosphorenes are calculated. The simulation results demonstrate that pristine phosphorene is sensitive to SO 2 gas molecule with a moderate adsorption energy and an excellent charge transfer, while evidence of negative effect is observed during doping with S and N. We also observe that B-or Si-doped phosphorene exhibits extremely high reactivity towards SO 2 with a stronger adsorption energy, indicating that they are not suitable for use as SO 2 sensors, but have potential applications in the development of metal-free catalysts for SO 2. Therefore, we suggest that pristine phosphorene could be an excellent candidate as sensor for the polluting gas SO 2 .

IEEE Electron Device Letters, 2017

The gas-adsorption behaviors of the pristine antimonene are investigated by first principles calc... more The gas-adsorption behaviors of the pristine antimonene are investigated by first principles calculations to exploit its potential for high-performance gas sensing. The results show that the atmospheric gas molecules (N2, CO2, O2, and H2O) presented ubiquitously in the sensing environments weakly binds to antimonene, while the polluted gas adsorbates (NH3, SO2, NO, and NO2) show stronger affinity towards antimonene with considerable adsorption energies and elevated charge transfers. Considering the susceptibility of the electronic properties of antimonene induced by the adsorbed molecules, we suggest that single-layered antimonene could be an eligible sensing material for polluted gases detection.

Journal of Materials Chemistry C, 2016

The structure along with the electronic and optical properties of a SiGe/BN monolayer heterostruc... more The structure along with the electronic and optical properties of a SiGe/BN monolayer heterostructure were theoretically researched using density functional theory calculations.

Journal of Materials Chemistry C, 2016

By means of comprehensive first-principles calculations, we investigate the stability, electronic... more By means of comprehensive first-principles calculations, we investigate the stability, electronic and optical properties of an AlAs/germanene heterostructure.

Journal of Materials Chemistry C, 2016

In this work, the structural, electronic and optical properties of novel atomically thin systems ... more In this work, the structural, electronic and optical properties of novel atomically thin systems based on germanene and antimonene nanocomposites have been investigated by means of density functional theory.

Nanoscale, 2017

Ferromagnetic character and biocompatible properties have become key factors for developing next-... more Ferromagnetic character and biocompatible properties have become key factors for developing next-generation spintronic devices and show potential in biomedical applications. Unfortunately, the Mn-containing monolayer is not biocompatible though it has been extensively studied, and the Cr-containing monolayer is not environmental friendly, although these monolayers are ferromagnetic. Herein, we systematically investigated new types of 2D ferromagnetic monolayers Nb3X8 (X = Cl, Br or I) by means of first principles calculations together with mean field approximation based on the classical Heisenberg model. The small cleavage energy and high in-plane stiffness have been calculated to evaluate the feasibility of exfoliating the monolayers from their layered bulk phase. Spin-polarized calculations together with self-consistently determined Hubbard U were utilized to assess a strong correlation energy, which demonstrated that Nb3X8 (X = Cl, Br or I) monolayers are ferromagnetic. The calculated Curie temperatures for Nb3Cl8, Nb3Br8 and Nb3I8 were 31, 56 and 87 K, respectively, which may be increased by external strain, or electron or hole doping. Moreover, the Nb3X8 (X = Cl, Br or I) monolayers exhibited strong visible and infrared light absorption. The biocompatibility, ferromagnetism and considerable visible and infrared light absorption render the Nb3X8 (X = Cl, Br or I) monolayers with great potential application in next-generation biocompatible spintronic and optoelectronic devices.

The Journal of Physical Chemistry C, 2016

A comprehensive first-principles study has been employed to investigate the geometric structures,... more A comprehensive first-principles study has been employed to investigate the geometric structures, electrical properties, and optical properties of two-dimensional (2D) Ge/BeO heterostructure. The results show that there is weak interaction between germanene and BeO monolayer via van der Waals force without any site selectivity. Therefore, most of the outstanding properties of germanene are conserved, especially a linear band dispersion near the K point. The energy gap of ∼49 meV can be opened for the heterostructure, which is a pretty large value for the gap opening at room temperature. Meanwhile, the band gap can be tuned by the interlayer distance, external strain, as well as external electric field, and the electric field has been found to be the most effective way (14–382 meV). All of these methods for band gap modulation can maintain the characteristics of a Dirac cone with a linear band dispersion relationship of germanene. Moreover, the enhanced optical properties are also observed after the format...

Two-dimensional (2D) ferromagnetic materials are considered to be promising candidates for future... more Two-dimensional (2D) ferromagnetic materials are considered to be promising candidates for future generations of spintronic devices. Yet, 2D materials with intrinsic ferromagnetism are scarce. High-throughput first-principles simulations are performed in order to screen 2D materials that present a non-magnetic to a ferromagnetic transition upon hole doping. A global evolutionary search is subsequently performed, in order to identify alternative possible atomic structures of the eligible candidates, and 122 materials exhibiting hole-doping induced ferromagnetism are identified. Their energetic and dynamic stability, as well as their magnetic properties under hole doping, are investigated systematically. Half of these 2D materials are metal halides, followed by chalcogenides, oxides, and nitrides, some of them having predicted Curie temperatures above 300 K. The exchange interactions responsible for the ferromagnetic order in these 2D materials are also discussed. This work not only p...

Advanced Materials Interfaces, 2021

Large‐area epitaxy of layered materials is one of the cornerstones for a successful exploitation ... more Large‐area epitaxy of layered materials is one of the cornerstones for a successful exploitation of van der Waals (vdW) materials in the semiconductor industry. The formation of 60° twin stacking faults and 60° grain boundaries is of major concern for the defect‐free epitaxial growth. Although strategies to overcome the occurrence of these defects are being considered, more fundamental understanding on the origin of these defects is highly essential. This work focuses on understanding the formation of 60° twins in (quasi‐)vdW epitaxy of 2D chalcogenides. Molecular beam epitaxy (MBE) experiments reveal the striking difference in 60° twin occurrence between WSe2 and Bi2Se3 in both quasi‐vdW heteroepitaxy and vdW homoepitaxy. Density functional theory (DFT) calculations link this difference to the interlayer vdW coupling strength at the unit cell level. The stronger interlayer vdW coupling in Bi2Se3 unit cells compared to WSe2 unit cells is explained to result in a reduced twin occurre...

arXiv: Materials Science, 2020

Defect-free epitaxial growth of 2D materials is one of the holy grails for a successful integrati... more Defect-free epitaxial growth of 2D materials is one of the holy grails for a successful integration of van der Waals (vdW) materials in the semiconductor industry. The large-area (quasi-)vdW epitaxy of layered 2D chalcogenides is consequently carefully being researched since these materials hold very promising properties for future nanoelectronic applications. The formation of defects such as stacking faults like 60o twins and consequently 60o grain boundaries is still of major concern for the defect-free epitaxial growth of 2D chalcogenides. Although growth strategies to overcome the occurrence of these defects are currently being considered, more fundamental understanding on the origin of these defects at the initial stages of the growth is highly essential. Therefore this work focuses on the understanding of 60o twin formation in (quasi-)vdW epitaxy of 2D chalcogenides relying on systematic molecular beam epitaxy (MBE) experiments supported by density functional theory (DFT) calc...

npj 2D Materials and Applications, 2021

The possibility of dissipationless chiral edge states without the need of an external magnetic fi... more The possibility of dissipationless chiral edge states without the need of an external magnetic field in the quantum anomalous Hall effect (QAHE) offers a great potential in electronic/spintronic applications. The biggest hurdle for the realization of a room-temperature magnetic Chern insulator is to find a structurally stable material with a sufficiently large energy gap and Curie temperature that can be easily implemented in electronic devices. This work based on first-principle methods shows that a single atomic layer of V2O3 with honeycomb–kagome (HK) lattice is structurally stable with a spin-polarized Dirac cone which gives rise to a room-temperature QAHE by the existence of an atomic on-site spin–orbit coupling (SOC). Moreover, by a strain and substrate study, it was found that the quantum anomalous Hall system is robust against small deformations and can be supported by a graphene substrate.

Journal of Applied Physics, 2020

There has been tremendous research effort in hunting for novel two-dimensional (2D) materials wit... more There has been tremendous research effort in hunting for novel two-dimensional (2D) materials with exotic properties, showing great promise for various potential applications. Here, we report the findings about a new hexagonal phase of 2D Ga2O3 and In2O3, with high energetic stability, using a global searching method based on an evolutionary algorithm, combined with density functional theory calculations. Their structural and thermal stabilities are investigated by the calculations of their phonon spectra and by ab initio molecular dynamics simulations. They are predicted to be intrinsically non-magnetic stable semiconductors, with a flatband edge around the valence band top, leading to itinerant ferromagnetism and half-metallicity upon hole doping. Bilayer Ga2O3 is also studied and found to exhibit ferromagnetism without extra hole doping. The Curie temperature of these materials, estimated using Monte Carlo simulations based on the Heisenberg model, is around 40–60 K upon a modera...

Physical Review B, 2021

Recent experimental success in the realization of two-dimensional (2D) magnetism has stimulated t... more Recent experimental success in the realization of two-dimensional (2D) magnetism has stimulated the search for new magnetic 2D materials with strong magnetic anisotropy and high Curie temperature. One promising subgroup of 2D magnetic systems are Dirac half-metals (DHM) which have gained a lot of interest recently, as they host a high-temperature quantum anomalous Hall effect (QAHE). This article discusses predictions for intrinsic DHMs and identifies them as realizations of the Kane-Mele Hubbard model at quarter filling. This proposed unification contributes to a firmer understanding of these materials and suggests pathways for the discovery of new DHM systems.

Applied Sciences, 2020

The high contact resistance at metal/two-dimensional (2D) semiconductor junctions is a major issu... more The high contact resistance at metal/two-dimensional (2D) semiconductor junctions is a major issue for the integration of 2D materials in nanoelectronic devices. We review here recent theoretical results on the contact resistance at lateral heterojunctions between graphene or 1T-MoS2 with 2H-MoS2 monolayers. The transport properties at these junctions are computed using density functional theory and the non-equilibrium Green’s function method. The contact resistance is found to strongly depend on the edge contact symmetry/termination at graphene/2H-MoS2 contacts, varying between about 2 × 102 and 2 × 104 Ω∙μm. This large variation is correlated to the presence or absence of dangling bond defects and/or polar bonds at the interface. On the other hand, the large computed contact resistance at pristine 1T/2H-MoS2 junctions, in the range of 3–4 × 104 Ω.μm, is related to the large electron energy barrier (about 0.8 eV) at the interface. The functionalization of the metallic 1T-MoS2 conta...

ACS Applied Materials & Interfaces, 2020

Applied Physics Letters, 2019

The contact resistance at two-dimensional graphene/MoS2 lateral heterojunctions is theoretically ... more The contact resistance at two-dimensional graphene/MoS2 lateral heterojunctions is theoretically studied, using first-principles simulations based on density functional theory and the nonequilibrium Green's function method. The computed contact resistance lies in the range of 102 to 104 Ω μm, depending on the contact edge symmetry (armchair or zigzag) and termination (Mo and/or S terminated). This large variation in the contact resistance arises from the variation in the interface barrier height, which is sensitive to the presence of polar C-Mo bonds or sulfur dangling bonds at the interface. These results highlight that the control of the edge symmetry and/or edge termination is crucial to achieve a low contact resistance (in the range of a few hundred ohms micrometer) at graphene/MoS2 lateral heterojunctions for 2D material-based field-effect devices.

IEEE Sensors Journal, 2017

In this paper, the interaction of atmospheric gas molecules (NH3, NO2, SO2, CO, CO2, CH4, O2, and... more In this paper, the interaction of atmospheric gas molecules (NH3, NO2, SO2, CO, CO2, CH4, O2, and NO) with monolayer graphene-like hexagonal ZnS (g-ZnS) is studied with first-principle calculations to explore its potential application as gas sensor. Among all the gas molecules, NH3, and SO2, NO2 act as a strong donor and acceptor with apparent charge transfer of 0.200,-0.121 and-0.115 e. We further calculated the current-voltage (I−V) relation using the nonequilibrium Green's function (NEGF) formalism. It can be indicated from the results that a mark change of the I−V relation before and after the adsorption of NH3, which makes monolayer g-ZnS a prospective gas sensor for NH3. In addition, under the mechanical strain the adsorption is substantially enhanced with significant impact on the properties of adsorbates and g-ZnS layer, especially for the NH3, NO2, and NO-monolayer g-ZnS configurations. The results presented herein demonstrate that monolayer g-ZnS can be the potential gas sensor of NH3 with high sensitivity and selectivity.

IEEE Electron Device Letters, 2017

Applied Surface Science, 2017

First-principles calculations based on density-functional theory reveal some superior physical pr... more First-principles calculations based on density-functional theory reveal some superior physical properties of hydrogen and fluorine co-decorated silicene (HSiF) monolayer and bilayer. Our simulated results reveal that the HSiF monolayer is a large direct band gap semiconductor greatly differing from the gapless semi-metallic silicene. There exists strong interlayer coupling in HSiF bilayer, leading to the good stabilities of HSiF bilayer even beyond bilayer graphene. The proposed HSiF bilayer exhibits a moderate direct band gap of 0.296 eV which is much lower than that of HSiF monolayer. Encouragingly, HSiF layers all have a direct band gap nature, irrespective of stacking pattern, thickness and external electric fields, which is an advantage over MoS 2 layers. Furthermore, an out-of-plane electric field has an evident impact on the band structures of the HSiF monolayer and bilayer. Especially, the band gap of HSiF bilayer can be effectively tuned by external electric field, even a semiconductor-metal transition occurs. More importantly, the HSiF bilayer exhibits a significant improved visible light adsorption peak with respect to that of HSiF monolayer, and the superior optical properties is robust, independent of stacking pattern. The complete electron-hole separation also enhances the photocatalytic efficiency of HSiF bilayer. In a word, the moderate band gap, effective band gap modification by external electric field, robust direct band gap nature, suitable band edge positions, electron-hole separation, and fascinating visible light adsorption, which enable HSiF bilayer to have great potential applications in the field of solar energy conversion, high performance photocatalysis and nanoelectronic devices, and we call for more concern over this kind of 2D Janus materials which possesses excellent properties.

Advanced Materials Interfaces, 2017

ZnO also has a multitude of 1D nanomorphologies, [3,4] for example, nanowires, [5] nanotubes, [6]... more ZnO also has a multitude of 1D nanomorphologies, [3,4] for example, nanowires, [5] nanotubes, [6] nanorods, [7] nanoribbons, [8] etc. This versatile functional material has attracted significant research attention because of its excellent properties such as sizable direct band gap of ≈3.3 eV and large exciton binding energy of 60 meV and so on, which make it an excellent candidate for a variety of applications like piezoelectric devices, [9] light emitting diodes, [10] biosensors, [11] catalysis, [12] etc. Apart from those applications, ZnO has also been extensively investigated as gas sensors, in particular, the 1D ZnO nanostructures exhibit much higher sensitivity than the polycrystalline bulk ones owing to the high surface-to-volume ratio. [13-17] Recently, another type of nanostructure of ZnO, namely, the atomic-thinned g-ZnO monolayer, was theoretically predicted [18,19] and experimentally realized. [20-22] It has the honeycomb structure very similar to that of single-layered hexagonal boron nitride (h-BN), with the band gap predicted to be 3.57-5.64 eV, larger than the one of the bulk wurtzite ZnO. [23] As the mutual merit shared by the 2D materials, [24-30] monolayer g-ZnO has even larger surface area than its 1D counterparts with the same volume. Inspired by the previous researches of unique gas adsorption performance of various 2D materials, [26,31-43] it is of scientific interests to investigate the gas adsorption performance of g-ZnO and explore its suitability to be gas sensing materials. However, relevant systematical investigations of gas adsorption performance of pristine g-ZnO are relatively scarce. [44,45] In this paper, we employ first principle calculations based on the density functional theory (DFT) to gain fundamental insights into the interaction between gas molecules and pristine g-ZnO. This study mainly focuses on the following questions: (i) What is the adsorption behavior of the common atmospheric (CO 2 , H 2 O, and O 2) and toxic (CO, H 2 S, NH 3 , SO 2 , NO, and NO 2) gas molecules on g-ZnO? (ii) Will the adsorption strength be affected by the gas concentration? (iii) What is the impact of the layer numbers of g-ZnO on the adsorption? (iv) Do the heterolayers or substrates have effects on the adsorption? To solve the issues above, we utilized different supercell sizes of g-ZnO to simulate the gas concentration effect, that is, a large supercell gives rise to lower gas density. Besides, we also 2D layered materials have gained tremendous research interests for gas sensing applications because of their ultrahigh theoretical specific surface areas and unique electronic properties, which are prone to be influenced by external factors. Here, using first principle calculations, the adsorption of several common gas molecules on graphene-like ZnO (g-ZnO) is systematically studied by taking the gas concentration, homolayer number, and heterolayers into considerations. The calculation results show that the adsorption energies of all the selected gas molecules are susceptible to the concentration and the homolayer number, and they incline to gradually increase with the decreasing of the gas concentration or they dramatically increase with the raising in g-ZnO layer number combined with elevated charge transfers. Besides, choosing graphene (MoS 2) as a heterolayer material to stack with g-ZnO can enhance (weaken) the interaction with NH 3 (NO 2) while weakening (enhance) that of NO 2 (NH 3), thus facilitating the selectivity to some extent. Further, Hirshfeld charge analysis and visualization of the charge density differences between the layers reveal the different charge transfers and adsorption mechanisms before and after gas adsorption. The results indicate that g-ZnO and its homolayer and hetero-bilayer structures can be promising candidates as gas sensing materials and catalysis.

IEEE Electron Device Letters, 2016

The adsorption behaviors of sulfur dioxide (SO 2) gas molecule over pristine, boron-, silicon-, s... more The adsorption behaviors of sulfur dioxide (SO 2) gas molecule over pristine, boron-, silicon-, sulfur-, and nitrogen-doped phosphorenes are theoretically studied using first-principles approach based on density-functional theory (DFT). The adsorption energy (E a), adsorption distance (d) and Mulliken charge (Q) of SO 2 molecules adsorbed on the different phosphorenes are calculated. The simulation results demonstrate that pristine phosphorene is sensitive to SO 2 gas molecule with a moderate adsorption energy and an excellent charge transfer, while evidence of negative effect is observed during doping with S and N. We also observe that B-or Si-doped phosphorene exhibits extremely high reactivity towards SO 2 with a stronger adsorption energy, indicating that they are not suitable for use as SO 2 sensors, but have potential applications in the development of metal-free catalysts for SO 2. Therefore, we suggest that pristine phosphorene could be an excellent candidate as sensor for the polluting gas SO 2 .

IEEE Electron Device Letters, 2017

The gas-adsorption behaviors of the pristine antimonene are investigated by first principles calc... more The gas-adsorption behaviors of the pristine antimonene are investigated by first principles calculations to exploit its potential for high-performance gas sensing. The results show that the atmospheric gas molecules (N2, CO2, O2, and H2O) presented ubiquitously in the sensing environments weakly binds to antimonene, while the polluted gas adsorbates (NH3, SO2, NO, and NO2) show stronger affinity towards antimonene with considerable adsorption energies and elevated charge transfers. Considering the susceptibility of the electronic properties of antimonene induced by the adsorbed molecules, we suggest that single-layered antimonene could be an eligible sensing material for polluted gases detection.

Journal of Materials Chemistry C, 2016

The structure along with the electronic and optical properties of a SiGe/BN monolayer heterostruc... more The structure along with the electronic and optical properties of a SiGe/BN monolayer heterostructure were theoretically researched using density functional theory calculations.

Journal of Materials Chemistry C, 2016

By means of comprehensive first-principles calculations, we investigate the stability, electronic... more By means of comprehensive first-principles calculations, we investigate the stability, electronic and optical properties of an AlAs/germanene heterostructure.

Journal of Materials Chemistry C, 2016

In this work, the structural, electronic and optical properties of novel atomically thin systems ... more In this work, the structural, electronic and optical properties of novel atomically thin systems based on germanene and antimonene nanocomposites have been investigated by means of density functional theory.

Nanoscale, 2017

Ferromagnetic character and biocompatible properties have become key factors for developing next-... more Ferromagnetic character and biocompatible properties have become key factors for developing next-generation spintronic devices and show potential in biomedical applications. Unfortunately, the Mn-containing monolayer is not biocompatible though it has been extensively studied, and the Cr-containing monolayer is not environmental friendly, although these monolayers are ferromagnetic. Herein, we systematically investigated new types of 2D ferromagnetic monolayers Nb3X8 (X = Cl, Br or I) by means of first principles calculations together with mean field approximation based on the classical Heisenberg model. The small cleavage energy and high in-plane stiffness have been calculated to evaluate the feasibility of exfoliating the monolayers from their layered bulk phase. Spin-polarized calculations together with self-consistently determined Hubbard U were utilized to assess a strong correlation energy, which demonstrated that Nb3X8 (X = Cl, Br or I) monolayers are ferromagnetic. The calculated Curie temperatures for Nb3Cl8, Nb3Br8 and Nb3I8 were 31, 56 and 87 K, respectively, which may be increased by external strain, or electron or hole doping. Moreover, the Nb3X8 (X = Cl, Br or I) monolayers exhibited strong visible and infrared light absorption. The biocompatibility, ferromagnetism and considerable visible and infrared light absorption render the Nb3X8 (X = Cl, Br or I) monolayers with great potential application in next-generation biocompatible spintronic and optoelectronic devices.

The Journal of Physical Chemistry C, 2016

A comprehensive first-principles study has been employed to investigate the geometric structures,... more A comprehensive first-principles study has been employed to investigate the geometric structures, electrical properties, and optical properties of two-dimensional (2D) Ge/BeO heterostructure. The results show that there is weak interaction between germanene and BeO monolayer via van der Waals force without any site selectivity. Therefore, most of the outstanding properties of germanene are conserved, especially a linear band dispersion near the K point. The energy gap of ∼49 meV can be opened for the heterostructure, which is a pretty large value for the gap opening at room temperature. Meanwhile, the band gap can be tuned by the interlayer distance, external strain, as well as external electric field, and the electric field has been found to be the most effective way (14–382 meV). All of these methods for band gap modulation can maintain the characteristics of a Dirac cone with a linear band dispersion relationship of germanene. Moreover, the enhanced optical properties are also observed after the format...