Effect Of Interlayer Coupling Research Articles

Tunable electronic properties of two-dimensional type-I 1T-SN2/hBN and type-II 1T-XN2/hBN (X = Se, Te) van der Waals heterostructures from first-principle study

Layer-by-layer integration of two-dimensional atomically thin materials provides an effective approach to the customized engineering of heteromaterials. Herein, first-principle calculations are employed to investigate the geometrical configurations and the electronic characteristics of 1T-XN2(X = S, Se, Te)/hBN van der Waals heterostructures (vdWHs). Our results demonstrate that the SN2/hBN vdWH possesses an obviously type-I band alignment. Whereas the 1T-XN2(X = Se, Te)/hBN vdWHs have a desired type-II band alignment, which may facilitate the spontaneous photogenerated electron-hole charge separation. The strain-induced semiconductor–metal transition can be realized in all the heterostructures. An intriguing type-II to type-I band alignment and indirect-direct bandgap transition takes place in 1T-TeN2/hBN under strain effect, which is a result of the different response behaviors of band-edge states with strain. The band alignment transition can be explained by the analysis of wave function topologies of band-edge states. The interlayer-coupling-tunable bandgap of 1T-XN2(X = S, Se)/hBN can also be found, and all the vdWHs always maintain their intrinsic band alignment type with the interlayer coupling effect. Overall, these findings will provide an avenue for applications of 1T-XN2(X = S, Se, Te)/hBN heterostructures in future electronic and optoelectronic devices, and strain engineering strategy can be utilized to regulate the carrier separation of the vdWHs.

Exploring the thickness dependent photocatalytic oxygen evolution performance for Bi4TaO8Cl two-dimensional semiconductor

The utilization of solar energy for water splitting has great potential to alleviate the worsening environmental issues. Two-dimensional (2D) materials, possessing tunable band gap, large surface area with more active sites, and short photogenerated carriers migrating distance, have attracted massive research interests as promising photocatalysts. In the water splitting reaction, compared with the hydrogen evolution reaction, the four elementary steps of oxygen evolution reaction (OER) is a complex and difficult reaction. Among 2D materials, Bi4TaO8Cl exhibits great potential for the OER. It is worth noting that the thicknesses of 2D materials is a significant factor for modifying physicochemical properties. However, the thickness dependence of OER performance remains unclear in Bi4TaO8Cl. Here, we systematically studied the effects of thicknesses on photocatalytic performance. Interestingly, we found that the few-layer Bi4TaO8Cl possesses more remarkable photocatalytic properties than monolayer Bi4TaO8Cl deriving from interlayer coupling effect. Compared with monolayer Bi4TaO8Cl, the few-layer exhibits broader range of light absorption accompanied with larger transition dipole moment, stronger reduction potential to drive the OER, and lower recombination probability of photogenerated electron and hole. The interlayer coupling interaction improves the photocatalytic properties, which promotes the progress of 2D material at photocatalytic water splitting reaction.

Atomic-Scale Studies of Overlapping Grain Boundaries between Parallel and Quasi-Parallel Grains in Low-Symmetry Monolayer ReS2

Summary Grain boundaries (GBs) are significant microstructures that dominate properties of polycrystalline two-dimensional (2D) materials. Low-symmetry rhenium disulfide monolayers provide an ideal platform to investigate diverse configurations of GBs and their orientation-dependent characteristics. Here, we utilize the preferential deposition of platinum-based nanoparticles on grain edges to rapidly locate nanoscale-wide overlapping GBs during microscopic-scale observation. Atomic-resolution investigations by aberration-corrected annular dark-field scanning transmission electron microscopy reveal diverse overlapping GBs constructed by parallel grains with transversal displacement. They prefer to align along several primary lattice directions with different interlayer atomic registries. Calculations show that the electronic band structures of overlapping GBs are strongly direction dependent, suggesting their potential in tunable electronic and photonic devices. Incommensurate overlapping GBs formed by quasi-parallel grains with ultrasmall twist angles are also observed. These results unveil the rich polymorphism of GBs and new opportunities to tailor properties of anisotropic 2D materials via GB engineering.

Metal-insulator transition of SrVO3 ultrathin films embedded in SrVO3/SrTiO3 superlattices

The metal-insulator transition (MIT) in strongly correlated oxides is a topic of great interest for its potential applications, such as Mott field effect transistors and sensors. We report that the MIT in high quality epitaxial SrVO3 (SVO) thin films is present as the film thickness is reduced, lowering the dimensionality of the system, and electron-electron correlations start to become the dominant interactions. The critical thickness of 3 u.c is achieved by avoiding effects due to off-stoichiometry using optimal growth conditions and excluding any surface effects by a STO capping layer. Compared to the single SVO thin films, conductivity enhancement in SVO/STO superlattices is observed. This can be explained by the interlayer coupling effect between SVO sublayers in the superlattices. Magnetoresistance and Hall measurements indicate that the dominant driving force of MIT is the electron–electron interaction.

Tunable valley polarization, magnetic anisotropy and dipole moment for layered Janus 2H–VSSe with intrinsic room temperature ferromagnetism

Effects of strain, interlayer coupling and electric field on the valley polarization, magnetocrystalline anisotropy and dipole moment of layered Janus 2H–VSSe are systematically investigated by first-principles calculations. A unique V 3 d1 electronic configuration and strong electron coupling interaction guarantee the stable in-plane ferromagnetic ground states with Tc of 512 K. By considering spin-orbit coupling (SOC) and exchange interaction based on the effective Hamiltonian k•p model, a large valley splitting of 94.8 meV is observed, which is mainly contributed by the spontaneous magnetic exchange field and not SOC effect. Under various bi-axis strains, Janus 2H–VSSe monolayer still maintains intrinsic in-plane ferromagnetism, but exhibits tunable valley polarization and magnetocrystalline anisotropy, which are associated with the in-plane dx2-y2/dxy orbitals of V atoms. Importantly, stacking patterns can influence the spatial inversion symmetry and further alter the valley polarization for the layered Janus 2H–VSSe. Applied external electric-field can effectively control intrinsic built-in electric-field by charge redistribution in the vertical direction, which can remarkably change the dipole moments and slightly adjust the valley polarization. The layered Janus 2H–VSSe possesses intrinsic ferromagnetism, robust valley-contrasting physics and outfield-dependent dipole moment, making them competitive materials for practical applications in spin-valleytronics, optoelectronics and piezoelectric sensor.

Monte Carlo study on the compensation behavior and hysteresis properties of a ferrimagnetic superlattice with alternate layers

Based on Monte Carlo simulation, the magnetic properties of a mixed spin-1 and spin-3/2 Ising superlattice with alternate layers are studied. The effects of interlayer coupling and external magnetic field on the compensation behavior and hysteresis properties for the ferrimagnetic superlattice are investigated. The occurrence of a compensation point is found to be greatly affected by the interlayer coupling. In particular, various multiple hysteresis loops can be observed under certain system parameters. The calculated results agree well with available experimental and theoretical works.

Blue Phosphorus-MoX2 (X=S/Se/Te) heterobilayers with strain enhanced photovoltaic properties: A first-principle study

Two-dimensional (2D) structural materials have suggested promising photonic applications for their prominent physicochemical properties. In this work, blue phosphorous (BP) and MoX 2 (X = S/Se/Te) were combined by van der Waals force (vdW) interaction to construct stable and efficient functional materials with well-defined type-II formalization. First-principles calculations were conducted to investigate the electronic properties and potential applications of the mentioned three heterostructures . Several aspects were considered to determine the effects of interlayer coupling and bands characteristic on the BP-MoX 2 heterogeneous interface after introducing the strain. In order to design potential photovoltaic cell materials with high efficiency or for the application of degrading pollutants, numerous studies have proved the exploitation of 2D materials as a practicable method. In the present study, BP and MoX 2 with different angles were distorted to lay a theoretical basis for the rearrangement of energy bands. As indicated from the results, the electronic properties of BP and MoX 2 with freestanding are basically preserved in the corresponding heterostructures. After the strain is applied, the energy band arrangement can be effectively adjusted by altering the strain. Specifically, the three heterostructures can maintain the type-II band structure within a certain strain, thus the electron-hole pairs in space could be significantly separate. Under the applied external strain, the mentioned heterostructures will transfer between type-II and type-I band alignment. This work presents more insights into the construction of heterostructures as well as demonstrating new possibilities for the application of nanomaterials with a flexible and feasible method of strain engineering. • The electronic properties of BP-MoX 2 are studied via first-principles calculations. • BP-MoX 2 exhibit a typical type-II heterostructure with a certain strain. • The strain can enhance photovoltaic properties of BP-MoX 2 though tuning bandstructure. • The BP-MoX 2 can be a candidate for photovoltaic devices with 17% PCE value.

Strain and electric-field induced tunable electronic properties of blue phosphorus-GeS/SnS/SnSe (orthorhombic) vdW heterostructures

In this work, we composite blue phosphorous (blueP) and monolayer GeS/SnS/SnSe through van der Waals (vdW) force interaction. It is found that blueP-GeS/SnS heterostructures are stable and form type-II band alignments, which can effectively promote the separation of photoinduced carriers. We perform a systematic theoretical study of interlayer coupling effects and band realignment of blueP-GeS/SnS/SnSe heterostructures after the strain and electric-field are imposed. BlueP and GeS/SnS/SnSe are twisted with different angles, and the theoretical framework of bands alignment and carriers' separation are established. The results show that the electronic properties of independent blueP and GeS/SnS/SnSe can be roughly maintained. When strain is applied, the band alignment shows significant adjustability by changing the external strain. Besides, the blueP-SnSe heterostructure show type-II characteristic in the range from -0.25 V/Å to -0.1 V/Å. Our theoretical calculation proves that strain and electric field engineering are two useful methods to design novel electronic devices.

Remarkable Band-Gap Renormalization via Dimensionality of the Layered Material C3B

Layer-dependent electronic and structural properties of emerging graphitic carbon boron compound C3B are investigated using both density functional theory and the GW approximation. We discover that, in contrast to a moderate quasiparticle band gap of 2.55 eV for monolayer C3B, the calculated quasiparticle band gap of perfectly stacked bulk phase C3B is as small as 0.17 eV. Therefore, our results suggest that layered material C3B exhibits a remarkably large band gap renormalization of over 2.3 eV due to the interlayer coupling and screening effects, providing a single material with an extraordinary band gap tunability. The quasiparticle band gap of monolayer C3B is also over 1.0 eV larger than that of C3N, a closely related two-dimensional semiconductor. Detailed inspections of the near-edge electronic states reveal that the conduction and valence band edges of C3B are formed by out-of-plane and in-plane electronic states, respectively, suggesting an interesting possibility of tuning the band edges of such layered material separately by modulating the in-plane and out-of-plane interactions.

Stacking angle dependent multiple excitonic resonances in bilayer tungsten diselenide

Abstract We report on multiple excitonic resonances in bilayer tungsten diselenide (BL-WSe2) stacked at different angles and demonstrate the use of the stacking angle to control the occurrence of these excitations. BL-WSe2 with different stacking angles were fabricated by stacking chemical vapour deposited monolayers and analysed using photoluminescence measurements in the temperature range 300–100 K. At reduced temperatures, several excitonic features were observed and the occurrences of these exitonic resonances were found to be stacking angle dependent. Our results indicate that by controlling the stacking angle, it is possible to excite or quench higher order excitations to tune the excitonic flux in optoelectronic devices. We attribute the presence/absence of multiple higher order excitons to the strength of interlayer coupling and doping effect from SiO2/Si substrate. Understanding interlayer excitations will help in engineering excitonic devices and give an insight into the physics of many-body dynamics.

Insights into the photocatalytic mechanism of the C4N/MoS2 heterostructure: A first-principle study

Constructing heterostructures by combining COFs and TMD is a new strategy to design efficient photocatalysts for CO2 reduction reaction (CO2RR) due to their good stability, tunable band gaps and efficient charge separation. Based on the synthesis of completely novel C4N−COF in our previous reported work, a new C4N/MoS2 heterostructure was constructed and then the related structural, electronic and optical properties were also studied using first principle calculations. The interlayer coupling effect and charge transfer between the C4N and MoS2 layer are systematically illuminated. The reduced band gap of the C4N/MoS2 heterostructure is beneficial to absorb more visible light. For the formation of type-II band alignment, a built-in electric field appears which separates the photogenerated electrons and holes into different layers efficiently and produces redox active sites. The band alignment of the heterostructure ensures its photocatalytic activities of the whole CO2 reduction reaction. Furthermore, the charge density difference and charge carrier mobility confirm the existence of the built-in electric field at the interface of the C4N/MoS2 heterostructure directly. Finally, the high optical absorption indicates it is an efficient visible light harvesting photocatalyst. Therefore, this work could provide strong insights into the internal mechanism and high photocatalytic activity of the C4N/MoS2 heterostructure and offer guiding of designing and synthesizing COF/TMD heterostructure photocatalysts.

Comparative Study of Blue Phosphorus–MoTe2/WTe2 van der Waals Heterostructures on Electronic Structures and Band Realignment

Herein, blue phosphorus (BP) and monolayer MoTe2/WTe2 are blended to obtain type‐II band alignment heterostructures based on the density functional theory (DFT). The first‐principles calculations are performed to explore the interlayer coupling effects and the bands realignment of BP–MoTe2/WTe2 when the external strain is imposed. It is proved that the bandgap variation of BP–MoTe2/WTe2 heterostructures exhibits interesting responses to the applied external strain compared with freestanding structures, and an obvious promoted light adsorption in solar spectrum range is observed in BP–MoTe2. The band structures reveal that the photoinduced electrons/holes are transferred to the conduction/valence band of BP from the valence/conduction band of MoTe2/WTe2, respectively. The calculations also confirm that BP–MoTe2 is more suitable for solar energy utilization in comparison with BP–WTe2, because it can realize a better response to solar energy and a prominent carriers’ separation. In brief, a convictive theoretical approach is presented to reveal the evolution of water splitting activity achieved by BP–MoTe2/WTe2 heterostructures.

Strain-tunable band alignment of blue phosphorus–WX2 (X = S/Se/Te) vertical heterostructures: from first-principles study

In the scope of two-dimensional (2D) material study, blue phosphorus (BP) is a new graphene-like layered structure that has been successfully synthesized in the experiment after it was theoretically proved to be thermostable. These 2D structured functional materials have great potential in the next-generation nanoscale electronic devices for their unique features. Here, we composite BP and monolayer WX2 (X = S/Se/Te) based on van der Waals force (vdW) interaction to obtain well-defined type-II band alignment heterostructures. A systematic theoretic study was conducted to explore the interlayer coupling effects and the bands’ re-alignment of the BP–WX2 heterostructure after the strain was applied. Nowadays, many researches have proved that 2D materials can be used to degrade pollutants or used as a potential photovoltaic cell material to obtain high performance. We here twist BP and WX2 (X = S/Se/Te) into different angles to lay a theoretical framework on the band alignment and carriers’ separation. It reveals that the electronic properties of freestanding BP and WX2 can be roughly preserved in the corresponding heterostructures. Upon applying strain, band alignment exhibits significant adjustability through varying external strain. The heterostructures are type-II in a certain strain range, within which the carriers can be effectively separated spatially. These heterostructures undergo a transition from semiconductor to metal when a certain strain is imposed. This work not only provides a deep insight into the construction of heterostructures, but presents a new possibility for strain engineering that is both flexible and feasible and can be used for diverse applications.

Effects of interlayer coupling and electric field on the electronic properties of PtSe2/ZrSe2 van der Waals heterojunctions

Using the first-principles methods based on density functional theory, the electronic characteristics of PtSe2/ZrSe2 vertical van der Waals heterojunctions and the influence of stacking pattern, interlayer coupling effect and external electric field on them have been systematically investigated. We found that the stacking pattern not only could change the band gap type, but also modulate the band alignment, such as type-II (AA and AA′ stacking patterns) and type-I (AB, AC, AB′, AC′ stacking patterns) band alignment. AA stacking pattern is the most energy favorable among all of stacking patterns and the most stable interlayer distances of it is 2.79 Å, and it exhibits the type-II band alignment, which is beneficial for the separation of carriers. Moreover, interlayer coupling effect and external electric field not only make the indirect-direct band gap transformation happen, but also can effectively turn the type of band alignment. The most promising type-II band alignment will be reserved in range of −0.06 < E-field < 0.02 V/Å and 0.17 < E-field < 0.23 V/Å. These findings in this paper make the application of 2D PtSe2/ZrSe2 vertical van der Waals heterojunction in multi-functional electronic and optoelectronic device possible.

Effects of interlayer and bi-quadratic exchange coupling on layered triangular lattice antiferromagnets

The magnetic field evolution of ground spin states of the stacked planar triangular antiferromagnet with antiferromagnetic interlayer interaction Jc is explored using a minimal 3D classical Heisenberg model. A bi-quadratic coupling is also used to mimic the effect of spin fluctuations (Zhitomirsky 2015 J. Phys.: Conf. Ser. 592 012110) which are known to stabilize the magnetization plateau. A single ion anisotropy is included and states with a magnetic field applied in the ab plane and along the c axis are determined. For -plane, an additional new state, in contrast to 2D model (Zhitomirsky 2015 J. Phys.: Conf. Ser. 592 012110), is obtained with weak interlayer interaction, while the magnetization plateau vanishes at large Jc and other new states with z components of spins emerge. For -axis, an extra state, compared with 2D model, is obtained with a weak interlayer interaction. When Jc is large enough, only the state corresponding to the Umbrella phase in 2D model exits.

The strain induced type-II band re-alignment of blue phosphorus-GeX (X = C/H/Se) heterostructures

Efforts to efficiently use of the next generation 2-dimension (2D) structured monolayers is getting a lot of attention for their excellent properties recently. In this work, we composite the blue phosphorus (BP) and monolayer GeX (X = C/H/Se) via van der Waals force (vdW) interaction to obtain well defined type-II band alignment heterostructures. A systematic theoretic study is conducted to explore the interlayer coupling effects and the bands re-alignment of BP-GeX (X = C/H/Se) heterostructure after the strain imposed. To devise usable and efficient materials to degrade pollutant or used as a potential photovoltaic cell material, previous researches have proved that using 2D materials as components is a feasible way to obtain high performance. Here, we prudently present a comprehensive investigation on the BP and GeX (X = C/H/Se) with different twisted angles via first-principles calculation to lay a theoretical framework on the band alignment and carriers' separation. It reveals that the intrinsic electronic properties of BP and GeX are roughly preserved in the corresponding heterostructures. Upon strain applied, band alignment can be flexibly manipulated by varying external imposed strain. The heterostructures can maintain type-II character within a certain strain range, and thus the carriers are spatially separated to different portions. This work not only provides a deep insight into the construction of the heterostructure, but presents a new possibility to search for a flexible and feasible approach to promote its catalytic performance. The corresponding results would provide meaningful guidelines for designing 2D structure based novel materials.

Interface-controlled band alignment transition and optical properties of Janus MoSSe/GaN vdW heterobilayers

Since the Janus MoSSe monolayer was fabricated in 2017, it has attracted increasing attention because the out-of-plane mirror symmetry is broken. Here, based on first-principles calculations, we construct theoretically 2D Janus MoSSe/GaN van der Waals (vdW) heterobilayers, and demonstrate that it has direct band structure and a broad optical absorption spectrum from visible to the UV region. Interestingly, the S- and Se-interface can induce straddling type-I and staggered type-II band alignments, and the gap values are modified. Moreover, the interlayer coupling and electronic field effects on electronic structures depend on the interface characteristics in Janus MoSSe/GaN heterobilayers. The studies provide the idea to modify the electronic characteristics using interface characteristics in the 2D materials-based vdW heterostructures.

Substrates and interlayer coupling effects on Mo1−xWxSe2 alloys

Two-dimensional (2D) transition metal dichalcogenides alloys are potential materials in the application of photodetectors over a wide spectral range due to their composition-dependent bandgaps. The study of bandgap engineering is important for the application of 2D materials in devices. Here, we grow the Mo1−xWxSe2 alloys on mica, sapphire and SiO2/Si substrates by chemical vapor deposition (CVD) method. Mo1−xWxSe2 alloys are grown on the mica substrates by CVD method for the first time. Photoluminescence (PL) spectroscopy is used to investigate the effects of substrates and interlayer coupling force on the optical bandgaps of as-grown Mo1−xWxSe2 alloys. We find that the substrates used in this work have an ignorable effect on the optical bandgaps of as-grown Mo1−xWxSe2. The interlayer coupling effect on the optical bandgaps of as-grown Mo1−xWxSe2 is larger than the substrates effect. These findings provide a new way for the future study of the growth and physical properties of 2D alloy materials.

Fabrication and the Interlayer Coupling Effect of Twisted Stacked Black Phosphorus for Optical Applications

With a new polycarbonate-film-based dry transfer method, we successfully fabricated twisted stacked black phosphorus. Optical characterization showed the overlapping area had special optical respon...

Effects of Interlayer Coupling on the Magnetic Flux of Vortices in Bi-layer Superconductors

We discuss the fractional (half-) flux quantization in bi-layer superconductors from a phenomenological point of view. In particular, it has been theoretically proved that the Josephson coupling be...