Effect Of Interlayer Coupling Research Articles

Twisted Stacking Metasurface for Complete Amplitude and Phase Control of Circularly Polarized Terahertz Waves

AbstractTerahertz (THz) metasurfaces have emerged as a powerful tool for manipulating THz wavefronts, typically achieved by adjusting various geometric parameters. In this study, an approach is introduced by incorporating interlayer coupling into twisted stacking metasurface design to completely control the amplitude and phase of circularly polarized THz waves. By leveraging the interlayer coupling effect and the Pancharatnam–Berry phase, the study achieves efficient control over transmission phase and amplitude by simply adjusting the relative twist angle between paired C‐shaped split‐ring resonators. To validate the concept, a holographic metasurface is fabricated and characterized, providing experimental evidence of its THz wavefront manipulation capabilities. This design strategy presents a versatile and tunable solution for THz wave control, promising applications in a wide range of functional devices.

Double Superconducting Dome of Quasi Two-Dimensional TaS2 in Non-Centrosymmetric van der Waals Heterostructure.

Two-dimensional van der Waals heterostructures (2D-vdWHs) based on transition metal dichalcogenides (TMDs) provide unparalleled control over electronic properties. However, the interlayer coupling is challenged by the interfacial misalignment and defects, which hinders a comprehensive understanding of the intertwined electronic orders, especially superconductivity and charge density wave (CDW). Here, by using pressure to regulate the interlayer coupling of non-centrosymmetric 6R-TaS2 vdWHs, we observe an unprecedented phase diagram in TMDs. This phase diagram encompasses successive suppression of the original CDW states from alternating H-layer and T-layer configurations, the emergence and disappearance of a new CDW-like state, and a double superconducting dome induced by different interlayer coupling effects. These results not only illuminate the crucial role of interlayer coupling in shaping the complex phase diagram of TMD systems but also pave a new avenue for the creation of a novel family of bulk heterostructures with customized 2D properties.

Toward Broadband Photodetection: Band Alignment and Interlayer Charge Transfer in 2D Transition Metal Dichalcogenides/3D-Ga2O3 Hybrid-Dimensional Heterostructures.

Recently, various transition metal dichalcogenides (TMDs)/Ga2O3 heterostructures have emerged as excellent candidates for the development of broadband photodetection, exhibiting various merits such as broadband optical absorption, efficient interlayer carrier transfer, a relatively simple fabrication process, and potential for flexibility. In this work, vertically stacked MoSe2/Ga2O3, WS2/Ga2O3, and WSe2/Ga2O3 heterostructures were experimentally synthesized, all exhibiting broadband light absorption, spanning at least from 200 to 800 nm. The absorption coefficients of these TMDs/Ga2O3 heterostructures are significantly improved compared to those of individual Ga2O3 films. The superior performance can be attributed to the type-I band alignment and efficient interlayer carrier transfer, which result from various band offsets along with the different doping conditions of the TMD layers, leading to distinct photoluminescence (PL) emission properties. Through a detailed analysis of the excitation-power-dependent PL spectra, we offer an in-depth discussion of the interlayer carrier transfer mechanism in the TMDs/Ga2O3 heterostructures. Regarding interlayer coupling effects, the shift of the EF of TMD layers plays a crucial role in modulating their trion emission properties. These findings suggest that these three TMDs/Ga2O3 heterostructures have great potential in broadband photodetection, and our in-depth physical mechanism analysis lays a solid foundation for a new device design.

Three-Dimensional Reconfigurable Optical Singularities in Bilayer Photonic Crystals.

Metasurfaces and photonic crystals have revolutionized classical and quantum manipulation of light and opened the door to studying various optical singularities related to phases and polarization states. However, traditional nanophotonic devices lack reconfigurability, hindering the dynamic switching and optimization of optical singularities. This paper delves into the underexplored concept of tunable bilayer photonic crystals (BPhCs), which offer rich interlayer coupling effects. Utilizing silicon nitride-based BPhCs, we demonstrate tunable bidirectional and unidirectional polarization singularities, along with spatiotemporal phase singularities. Leveraging these tunable singularities, we achieve dynamic modulation of bound-state-in-continuum states, unidirectional guided resonances, and both longitudinal and transverse orbital angular momentum. Our work paves the way for multidimensional control over polarization and phase, inspiring new directions in ultrafast optics, optoelectronics, and quantum optics.

Enhancing the Carrier Transport in Monolayer MoS2 through Interlayer Coupling with 2D Covalent Organic Frameworks.

The coupling of different 2D materials (2DMs) to form van der Waals heterostructures (vdWHs) is a powerful strategy for adjusting the electronic properties of 2D semiconductors, for applications in opto-electronics and quantum computing. 2D molybdenum disulfide (MoS2 ) represents an archetypical semiconducting, monolayer thick versatile platform for the generation of hybrid vdWH with tunable charge transport characteristics through its interfacing with molecules and assemblies thereof. However, the physisorption of (macro)molecules on 2D MoS2 yields hybrids possessing a limited thermal stability, thereby jeopardizing their technological applications. Herein, the rational design and optimized synthesis of 2D covalent organic frameworks (2D-COFs) for the generation of MoS2 /2D-COF vdWHs exhibiting strong interlayer coupling effects are reported. The high crystallinity of the 2D-COF films makes it possible to engineer an ultrastable periodic doping effect on MoS2 , boosting devices' field-effect mobility at room temperature. Such a performance increase can be attributed to the synergistic effect of the efficient interfacial electron transfer process and the pronounced suppression of MoS2 's lattice vibration. This proof-of-concept work validates an unprecedented approach for the efficient modulation of the electronic properties of 2D transition metal dichalcogenides toward high-performance (opto)electronics for CMOS digital circuits.

Large interlayer Dzyaloshinskii-Moriya interactions across Ag-layers

Seeking to enhance the strength of the interlayer Dzyaloshinskii-Moriya interaction (IL-DMI) through a combination of atomic and Rashba type spin-orbit coupling (SOC) we studied the strength and the thickness evolution of effective interlayer coupling in Co/Ag/Co trilayers by means of surface sensitive magneto-optical measurements that take advantage of the light penetration depth. Here, we report the observation of oscillatory, thickness-dependent chiral interaction between ferromagnetic layers. Despite the weakness of the Ag atomic SOC, the IL-DMI in our trilayers is orders of magnitude larger than that of known systems using heavy metals as a spacer except of recently reported −0.15 mJ/m2 in Co/Pt/Ru(t)/Pt/Co and varies between ≈ ±0.2 mJ/m2. In contrast to known multilayers Co/Ag/Co promotes in-plane chirality between magnetic layers. The strength of IL-DMI opens up new routes for design of three-dimensional chiral spin structures combining intra- and interlayer DMI and paves the way for enhancements of the DMI strength.

Effects of electric field and interlayer coupling on Schottky barrier of germanene/MoSSe vertical heterojunction

Effects of electric field and interlayer coupling on Schottky barrier of germanene/MoSSe vertical heterojunction

Directly Imaging and Regulating the Nanoscale Inhomogeneity of S‐Vacancies in Molybdenum Disulfide Monolayer during Electrocatalytic Hydrogen Evolution

AbstractThe study of electron transfer event on two‐dimensional (2D) layered transition metal dichalcogenides has attracted tremendous attentions attributing to their promising applications in electrochemical devices. Herein, we demonstrate an opto‐electrochemical strategy to directly map and regulate electron transfer event on molybdenum disulfide (MoS2) monolayer by combining bright field (BF) imaging technique with electrochemical modulation. The heterogeneity of electrochemical activity on MoS2 monolayer down to nanoscale is resolved spatiotemporally. The thermodynamics of MoS2 monolayer is measured during electrocatalytic hydrogen evolution, and the Arrhenius correlations are obtained. We validate that the defect generation engineered by oxygen plasma bombardment dramatically enhances the local electrochemical activity of MoS2 monolayer, which can be attributed to point defects of S‐vacancies as evidenced. Furthermore, by comparing the difference of electron transfer event on MoS2 with various layers, the interlayer coupling effect is uncovered. This study represents a facile method to image the heterogeneity of electrochemical properties for nanomaterials with atomic thickness and regulate the local activity within the plane by extrinsic factors. It also has potential applications in the design and evaluation of high‐performance layered electrochemical systems down to nanoscale.

Directly Imaging and Regulating the Nanoscale Inhomogeneity of S-Vacancies in Molybdenum Disulfide Monolayer during Electrocatalytic Hydrogen Evolution.

The study of electron transfer event on two-dimensional (2D) layered transition metal dichalcogenides has attracted tremendous attentions attributing to their promising applications in electrochemical devices. Herein, we demonstrate an opto-electrochemical strategy to directly map and regulate electron transfer event on molybdenum disulfide (MoS2 ) monolayer by combining bright field (BF) imaging technique with electrochemical modulation. The heterogeneity of electrochemical activity on MoS2 monolayer down to nanoscale is resolved spatiotemporally. The thermodynamics of MoS2 monolayer is measured during electrocatalytic hydrogen evolution, and the Arrhenius correlations are obtained. We validate that the defect generation engineered by oxygen plasma bombardment dramatically enhances the local electrochemical activity of MoS2 monolayer, which can be attributed to point defects of S-vacancies as evidenced. Furthermore, by comparing the difference of electron transfer event on MoS2 with various layers, the interlayer coupling effect is uncovered. This study represents a facile method to image the heterogeneity of electrochemical properties for nanomaterials with atomic thickness and regulate the local activity within the plane by extrinsic factors. It also has potential applications in the design and evaluation of high-performance layered electrochemical systems down to nanoscale.

Ultrafast charge transfer in mixed-dimensional WO3-x nanowire/WSe2 heterostructures for attomolar-level molecular sensing

Developing efficient noble-metal-free surface-enhanced Raman scattering (SERS) substrates and unveiling the underlying mechanism is crucial for ultrasensitive molecular sensing. Herein, we report a facile synthesis of mixed-dimensional heterostructures via oxygen plasma treatments of two-dimensional (2D) materials. As a proof-of-concept, 1D/2D WO3-x/WSe2 heterostructures with good controllability and reproducibility are synthesized, in which 1D WO3-x nanowire patterns are laterally arranged along the three-fold symmetric directions of 2D WSe2. The WO3-x/WSe2 heterostructures exhibited high molecular sensitivity, with a limit of detection of 5 × 10−18 M and an enhancement factor of 5.0 × 1011 for methylene blue molecules, even in mixed solutions. We associate the ultrasensitive performance to the efficient charge transfer induced by the unique structures of 1D WO3-x nanowires and the effective interlayer coupling of the heterostructures. We observed a charge transfer timescale of around 1.0 picosecond via ultrafast transient spectroscopy. Our work provides an alternative strategy for the synthesis of 1D nanostructures from 2D materials and offers insights on the role of ultrafast charge transfer mechanisms in plasmon-free SERS-based molecular sensing.

Tuning electronic structures and optical properties of Ti2CO2 MXenes by applying stress

Functionalized MXenes have attracted great interest due to their unique electrical, magnetic, optical, and electrochemical properties. In this paper, the effect of interlayer coupling on the electronic structures of Ti2CO2 MXenes is investigated by using density functional theory. Due to the interlayer coupling, the band structures of Ti2CO2 nanosheet are split, generating an indirect band gap of 0.869 eV, which is smaller than that of Ti2CO2 monolayer (1.044 eV). Biaxial strain can be used to achieve the transitions of direct-indirect-negative band gaps semiconductor. The interlayer interaction effectively inhibits the structural changes under stress, resulting that the band gap of nanosheet be adjusted in a large stress range. Furthermore, the change trend of imaginary part ε2 of the dielectric function indicates that stress has an obvious regulatory effect on the optical transition. The different responses of monolayer and nanosheet under stress provides more choice for the optical devices of Ti2CO2 MXenes.

A type-II MnPSe3/GeC heterostructure with tunable spin and valley splitting

The ternary chalcogenide MnPSe3 monolayer recently gets a lot of attention because of its two nonequivalent energy valleys. The existence of spin–orbit coupling (SOC) effect can cause the valley splitting of around 24 meV. However, the spin degeneracy is still kept in MnPSe3 monolayer owing to the antiferromagnetic coupling between Mn2+ ions. The interlayer coupling effect in the van der Waals (vdW) heterostructures can break the symmetry of MnPSe3 and induce the spin splitting. Here, we simulate the MnPSe3/GeC vdW heterostructure and investigate the effects of the stacking and interlayer coupling effect on both spin and valley splitting. The excitation mode of valley excitons is greatly related to the stacking of heterostructures. The interlayer excitons can only be formed in one of the configurations with C3 symmetry according to optical selection transition rule. The interlayer coupling effect is modulated by changing interlayer distance. With vertical compressive strain (−20%), the spin and valley splitting higher than 50 meV and 30 meV can be obtained in MnPSe3/GeC vdW heterostructures, respectively. This study suggests that the stacking and vertical strain are both efficient approaches to modulate the spin and valley splitting through the interlayer coupling effect in the vdW heterostructures.

Tuning magnetism by electric field in MnPS3/Sc2CO2 van der Waals heterostructure

Combining a two-dimensional (2D) antiferromagnetic (AFM) material, MnPS3 and a 2D ferroelectric material, Sc2CO2, we propose 2D van der Waals (vdW) heterostructure multiferroics to realize strong magnetoelectric coupling, which is important for designing high-performance magnetoelectric devices. By using first-principles simulations, it is found that the transition from an AFM state to a ferromagnetic (FM) state of a MnPS3 layer could be realized by reversing the polarization direction of a Sc2CO2 layer. We further reveal that such strong magnetoelectric effects originate from the large inter-layer charge transfer due to the competitive interaction between the difference of the interface work functions between MnPS3 and Sc2CO2 and the strong electronegativity of the O atom interface in the Sc2CO2 layer. Our results suggest a feasible scheme for constructing 2D vdW heterostructure multiferroics with very strong inter-layer magnetoelectric coupling effect.

The effects of intercalated environmental gas molecules on carrier dynamics in WSe2/WS2 heterostructures.

Effective tuning of carrier dynamics in two-dimensional (2D) materials is significant for multi-scene device applications. Using first-principles and ab initio nonadiabatic molecular dynamics calculations, the kinetics of O2, H2O, and N2 intercalation into 2D WSe2/WS2 van der Waals heterostructures and its effect on carrier dynamics have been comprehensively explored. It is found that the O2 molecule prefers to dissociate into atomic O atoms spontaneously after intercalation of WSe2/WS2 heterostructures, whereas H2O and N2 molecules remain intact. O2 intercalation significantly speeds up the electron separation process, while H2O intercalation largely speeds up the hole separation process. The lifetime of excited carriers can be prolonged by O2 or H2O or N2 intercalations. These intriguing phenomena can be attributed to the effect of interlayer coupling, and the underlying physical mechanism for tuning the carrier dynamics is fully discussed. Our results provide useful guidance for the experimental design of 2D heterostructures for optoelectronic applications in photocatalysts and solar energy cells.

Revealing the Modulation Effects on the Electronic Band Structures and Exciton Properties by Stacking Graphene/h-BN/MoS2 Schottky Heterostructures.

Stacking two dimensional tunneling heterostructures has always been an important strategy to improve the optoelectronic device performance. However, there are still many disputes about the blocking ability of monolayer (1L-) h-BN on the interlayer coupling. Graphene/h-BN/MoS2 optoelectronic devices have been reported for superior device results. In this study, starting with graphene/h-BN/MoS2 heterostructures, we report experimental evidence of 1L-h-BN barrier layer modulation effects about the electronic band structures and exciton properties. We find that 1L-h-BN insertion only partially blocks the interlayer carrier transfer. In the meantime, the 1L-h-BN barrier layer weakens the interlayer coupling effect, by decreasing the efficient dielectric screening and releasing the quantum confinement. Consequently, the optical conductivity and plasmon excitation slightly improve, and the electronic band structures remain unchanged in graphene/h-BN/MoS2, explaining their fascinating optoelectronic responses. Moreover, the excitonic binding energies of graphene/h-BN/MoS2 redshift with respect to the graphene/MoS2 counterparts. Our results, as well as the broadband optical constants, will help better understand the h-BN barrier layers, facilitating the developing progress of h-BN-based tunneling optoelectronic devices.

Tunable Schottky contact at the graphene/Janus SMoSiN2 interface for high-efficiency electronic devices

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

Conversion of MoS2 to ternary alloyed MoS2−xSex for resistive NO2 sensors

The inert basal planes and strong quantum confinement of 2D materials usually lead to the reduction of carrier transport efficiency and device performance. In this work, a ternary alloyed MoS2-xSex nanocomposites has been prepared by converting few-layered MoS2 nanomaterials through a selenization process to boost the gas sensing performance of gas sensors at room temperature. The selenization process makes the MoS2-xSex nanocomposites generate weak interlayer coupling effect, rich surface defects (states), moderate surface strains, local built-in electric field, and can effectively eliminate oxide impurities in MoS2. Moreover, the band gap of the samples can be tuned from 1.74 eV for MoS2 nanomaterials to 1.49 eV for MoS2−xSex nanocomposites. Owing to the modified surface and electronic structures, the MoS2−xSex nanocomposites exhibit excellent NO2 sensing performance at room temperature in terms of response, repeatability, selectivity, and detection limit. The responses of the best MoS2−xSex nanocomposites are about 2–3 times that of the MoS2 nanomaterials, and its theoretical detection limit reaches 4.0 ppb. This study reveals that ternary alloyed TMDs have better development potential than their binary TMD counterparts in the field of gas sensors.

Boosting the solar conversion efficiency of MoSe2/PtX2 (X = O, S) vdW heterostructure by strain and electric field engineering

Vertically stacking two-dimensional materials via weak van der Waals (vdW) forces is an effective strategy for modulating optoelectronic performance of materials. To accelerate more novel MoSe2-based heterostructure design, the interlayer coupling effect in MoSe2/PtX2 (X = O, S) heterostructure has been systematically studied, from the atomic structure to the electronic and optical properties, on the basis of first-principles calculations and BSE model with scissor inclusion. Density functional theory (DFT) calculations unveil a type-II indirect bandgap measuring between 0.85 and 0.91 eV at HSE06 level, with Bader and charge density difference analyses suggesting occurrence of charge redistributions at the interface and electrons diffusion from MoSe2 to PtX2 layers, driven by large band offsets. The thermodynamic and thermal stabilities of the heterostructures are demonstrated by the negative binding energy and AIMD simulation. The heterostructure interface is influenced by the weak vdW coupling with an equilibrium interlayer distance of 3.01 to 3.08 Å and binding energy of −5.5 to −11.2 meV Å−2, indicating an exothermic process and steady adhesion at the interface. Reasonable lattice mismatch that ranges from 1.5 to 4.7% between the vdW heterostructure and separate monolayers suggests good structure compatibility. The optical performance of the heterostructure was examined using the real and imaginary components of dielectric function, where enhanced light absorption of 104–105 cm−1 and prominent peaks are observed encompassing the infrared to ultraviolet domains. Record high spectroscopic limited maximum efficiency (SLME) of ∼33% was also predicted. The absorption strength of MoSe2/PtO2 and MoSe2/PtS2 enhances with increasing negative external electric field (Eext) and compressive strain, individually, inferring their optical properties modulation by Eext and biaxial strain. Both heterostructures present high carrier mobility up to 1322.98 cm2 V−1 s−1 in zigzag direction.

Interlayer coupling and external electric field controllable electronic structures and Schottky contact of HfSeX (X = S, Se)/graphene van der Waals heterostructures

Graphene-based van der Waals heterostructures (vdWHs) owing to their remarkable physical properties and extensive application attract much attention. However, the Schottky barrier height (SBH) at the interface limits the charge injection effect. Here, we investigate the geometry, electronic structures, contact behavior and optical properties of the HfSeX/graphene (HfSeX/G, X = S, Se) vdWHs via first-principles calculations. The effect of interlayer coupling and external electric field (Efield) on the HfSeX/G are examined. Our results show that the Dirac cones of graphene are well preserved in all modes due to weak van der Waals interaction and a small bandgap is opened in graphene. The SBH of n-type Schottky contact types (SCT) HfSe2/G, SHfSe/G and SeHfS/G vdWHs are 0.100, 0.085 and 0.114 eV, respectively. Both the interlayer distance and Efield can induce the n-type SCT of the Janus HfSSe/G to transfer to p-type, and large Efield can cause an Ohmic contact. The HfSeX/G heterostructures enhance light absorption intensity in visible-light region compared with isolate graphene and HfSeX monolayers. The work provides a valuable theoretical guidance for designing Schottky-based devices of the HfSeX/G heterostructures, as well as indicates that the heterostructures have a flexible application prospect in further optoelectronic and field effect transistors devices.

Nonlinear Optical and Photocurrent Responses in Janus MoSSe Monolayer and MoS2-MoSSe van der Waals Heterostructure.

Two-dimensional (2D) transition metal dichalcogenides are promising materials platforms for a variety of optoelectronic device applications. Janus 2D materials are a rising class of 2D materials with low symmetry, which leads to the emergence of out-of-plane electric polarization and piezoelectricity. Using first-principles density functional theory, we show that monolayer and bilayer heterostructure Janus MoSSe moieties exhibit strong nonlinear optical responses that are vanishing in the non-Janus form. The absence of horizontal mirror plane symmetry enables a circular photocurrent as well as a large out-of-plane second harmonic generation (SHG) and shift photocurrent. Through a comparative study of the Janus heterostructure MoS2-MoSSe on five distinct stacking configurations, we find that the magnitude of the out-of-plane SHG in the Janus heterostructure is enhanced due to the interlayer coupling and interference effect compared to that of monolayer MoSSe. Thus, Janus 2D materials offer a unique opportunity for exploring nonlinear optical phenomena and designing configurable layered nonlinear optical materials.