Interlayer Transition Research Articles

Infrared Photodetector Based on van der Waals MoS2/MoTe2 Hetero‐Bilayer Modulated by Photogating

AbstractPhotodetectors based on 2D hetero‐bilayers can overcome the bandgap limitations of individual 2D monolayers and operate at relatively long wavelengths. However, ultra‐low light absorptions within hetero‐bilayers result in extremely weak photoresponsivity. Here, an infrared photodetector based on the MoS2/MoTe2 type‐II hetero‐bilayer is demonstrated to reach a photoresponsivity of 0.55 A W−1 at 1550 nm, well beyond energy band cut‐offs of monolayer MoS2 and MoTe2, primarily resulted from the photogating effect. Raman and photoluminescence (PL) spectroscopy reveal strong interlayer couplings in the hetero‐bilayer, and a broad PL peak around 1550 nm is observed that is ascribed to interlayer transitions of carriers. The photodetector showcases a broadband detection capability from 1100 to 1700 nm, with a peak at 1550 nm corresponding to the interlayer absorption. Electrical characterization of the hetero‐bilayer‐based field‐effect transistor and kelvin probe force microscopy reveal efficient interlayer hole transfer. The highly responsive MoS2/MoTe2 infrared photodetector offers a large photo‐gain of ≈103 and a time constant of 130 ms. The research illuminates how interlayer transitions affect 2D hetero‐bilayer‐based photodetectors and advances the utilization of layered semiconductor heterostructures.

Protons intercalation induced hydrogen bond network in δ-MnO2 cathode for high-performance aqueous zinc-ion batteries

Birnessite-type MnO2 (δ-MnO2) exhibits great potential as a cathode material for aqueous zinc-ion batteries (AZIBs). However, the structural instability and sluggish reaction kinetics restrict its further application. Herein, a unique protons intercalation strategy was utilized to simultaneously modify the interlayer environment and transition metal layers of δ-MnO2. The intercalated protons directly form strong O H bonds with the adjacent oxygens, while the increased H2O molecules also establish a hydrogen bond network (O H···O) between H2O molecules or bond with adjacent oxygens. Based on the Grotthuss mechanism, these bondings ultimately enhance the stability of layered structures and facilitate the rapid diffusion of protons. Moreover, the introduction of protons induces numerous oxygen vacancies, reduces steric hindrance, and accelerates ion transport kinetics. Consequently, the protons intercalated δ-MnO2 (H-MnO2-x) demonstrates exceptional specific capacity of 401.7 mAh/g at 0.1 A/g and a fast-charging performance over 1000 cycles. Density functional theory analysis confirms the improved electronic conductivity and reduced diffusion energy barrier. Most importantly, electrochemical quartz crystal microbalance tests combining with ex-situ characterizations verify the inhibitory effect of the interlayer proton environment on basic zinc sulfate formation. Protons intercalation behavior provides a promising avenue for the development of MnO2 as well as other cathodes in AZIBs.

Stratified water columns: homogenization and interface evolution

Stratified water columns are often found in lakes and oceans. Stratifications result from differences in density due to salt concentration, temperature, solid content and oxygenation. The stability of stratifications affects bioactivity, sedimentation, contaminant transport and environmental remediation. This study investigates the evolution of 6 stratified water columns created by differences in salinity, suspended minerals and the presence of a bottom heat source. We use acoustic wave reflection, photography, and both electrical conductivity and temperature profiles to track changes in stratification. Results show that multiple concurrent processes emerge across layers in otherwise quiescent water bodies. Dissimilar chemo-thermo conditions give rise to chemical and thermal diffusion, convection, and double-diffusion convection. When stratification involves suspended particles, interlayer processes include diffusiophoresis, flocculation/aggregation, sedimentation, osmosis, and chemo-consolidation; in this case, the specific surface and surface charge of suspended particles, and the salt concentration in contiguous layers determine aggregation-sedimentation-consolidation patterns. The interlayer transition zone acts as a high-pass filter that preferentially reflects low-frequency long-wavelength P-waves; invasive thermal and electrical conductivity probes provide complementary information and may identify stratification even when it is undetected by acoustic signals.

Recent Modification Strategies of MoS2 towards Electrocatalytic Hydrogen Evolution

Hydrogen production by the electrolysis of water is a green and efficient method, which is of great significance for achieving sustainable development. Molybdenum disulfide (MoS2) is a promising electrocatalyst for hydrogen evolution reaction (HER) due to its high electrochemical activity, low cost, and abundant reserves. In comparison to the noble metal Pt, MoS2 has poorer hydrogen evolution performance in water electrolysis. Therefore, further modifications of MoS2 need to be developed aiming at improving its catalytic performance. The present work summarizes the modification strategies that have been developed in the past three years on hydrogen evolution from water electrolysis by utilizing MoS2 as the electrocatalyst and following the two aspects of internal and external modifications. The former includes the strategies of interlayer spacing, sulfur vacancy, phase transition, and element doping, while the latter includes the heterostructure and conductive substrate. If the current gap in this paper’s focus on modification strategies for electrocatalytic hydrogen evolution in water electrolysis is addressed, MoS2 will perform best in acidic or alkaline media. In addition to that, the present work also discusses the challenges and future development directions of MoS2 catalysts.

Novel BiOI/LaOXI〈IX〉 heterojunction with enhanced visible-light driven photocatalytic performance: unveiling the mechanism of interlayer electron transition.

Improving visible light absorption plays an important role in the utilization of solar power for photocatalysis. Using first-principles calculations within the HSE06 functional, we propose that the semiconductor heterojunction BiOI/LaOXI〈IX〉 extends the optical absorption to the near-infrared range, boosts the absorption coefficient from 1.28 × 105 cm-1 to above 2.20 × 105 cm-1 in the visible light range, and increases the conversion efficiency of solar power up to 9.48%. The enhanced optical absorption derives from the significant interlayer transition and excitonic effect which benefit from polarized LaOXI with a flat band in the highest valence band (VB). In BiOI/LaOClI〈ICl 〉, the electrostatic potential difference (ΔΦ) modifies the band edge positions to meet the requirements for photocatalytic overall water splitting, while the polarized electric field (Ep) accelerates the separation of photogenerated carriers and regulates the overpotentials of photogenerated carriers following a direct Z-scheme strategy. In addition, BiOI/LaOXI〈IX〉 is dynamically and thermodynamically stable. Furthermore, only a low external potential is needed to drive the redox reaction. Our theoretical results suggest that BiOI/LaOXI〈IX〉 could be a potential photocatalyst for overall water splitting with enhanced visible light absorption.

Carrier-recirculating broadband photodetector with high gain based on van der Waals In2Se3/MoS2 heterostructure

Two-dimensional (2D) materials present enormous potential in photoelectric detection, medical imaging, and neuromorphic vision applications due to their superior electronic and optoelectronic properties. Nevertheless, the photoelectric performance is restricted by the short lifetime of photogenerated carriers and weak optical absorption attributed to the atomic-scale thickness. This work demonstrates a novel high-gain photodetector based on van der Waals β-In2Se3/MoS2 heterostructure induced by carrier recirculation. In this structure, the photoexcited holes are trapped in the charge traps of MoS2 driven by the built-in electric field, which suppresses the recombination of photogenerated carriers, thus the electrons are repeatedly recycled across the In2Se3 channel after the generation of electron-hole pairs, achieving the high optical gain of 2.95 × 103. The responsivity, external quantum efficiency and specific detectivity of In2Se3/MoS2 photodetector can reach 616.77 A/W, 125900 %, and 1.03 × 1012 Jones at 638 nm, respectively, which are significantly higher than those of individual In2Se3 and MoS2 photodetector. More significantly, due to the enhanced optical absorption and interlayer transition, the photoresponse spectrum of In2Se3/MoS2 heterojunction is further extended to 1310 nm, which can be applied to broadband photodetection. Therefore, the In2Se3/MoS2 vdWs heterojunction photodetector provides a feasible approach to fabricate high-performance broadband photodetectors.

Expanding the adiabatic design toolbox – more modes, parameters and versatility

Adiabatic design principles can be used to improve the performance of many photonic components. The recently published adiabatic optimization method, MODALL, relies on a design rule that guarantees adiabaticity and enables optimization of adiabatic photonic components against multiple dimensions and radiation modes. In this work, MODALL is extended to enable optimization of multi-mode components, optimization against an extra degree of freedom and optimization of modal crosstalk. We present a derivation of these extensions starting from MODALL theory and verify them via the design, fabrication and characterization of a mode multiplexer with ultra-low crosstalk: worst-case <−38 dB and median <−45 dB. These design extensions will aid the adiabatic design optimization of many photonic components including splitters, polarization rotators, interlayer transitions and edge couplers.

Partially reduced-linked covalent organic frameworks: A new approach for heterogeneous catalysis and naked-eye HCl sensing

Compared to the traditionally made imine-linked covalent organic frameworks (COFs), amine-linked COFs provided by in-situ reduction of the linkages represent significant potential for advanced applications, including catalysis and sensing. The current paper deals with preparing a partially reduced COF with secondary amine groups (IR-COF) via in-situ reduction of imine linkages as a dual-functional material adopted for heterogeneous catalysis and acid-sensing. This COF was synthesized using formic acid as a reductant and catalyst in a solvothermal reaction between 2,4,6-tris-(4-formyl-phenoxy)-1,3,5-triazine and p-phenylenediamine. The IR-COF was used as a basic organocatalyst for the efficient synthesis of tetrahydro-4H-chromenes through the Knoevenagel-Michael cyclocondensation. Excellent yields, short reaction times, easy workup, absence of toxic organic solvents, easy recovery, and reusability of the catalyst are outstanding aspects of this catalytic method, making it convenient and useful for fine chemical synthesis. Moreover, the immediate naked-eye color change of IR-COF upon exposure to the hydrochloric acid by protonating the secondary amine groups was investigated. The (time-dependent) density functional theory (TD)DFT PBE/DNP+ method was used to investigate the mechanism of color change during the sensing. The appearance of a new absorption band at higher wavelengths upon protonation is proved to be due to intermolecular or interlayer electron transitions.

Hydrogen storage in MXenes: Controlled adjustment of sorption by interlayer distance and transition metal elements

MXene is an attractive solid-state material for high-capacity, secure hydrogen storage under ambient conditions. Controlled adjustment of hydrogen sorption in MXene is essential to improve the storage capability and reversibility at room temperature. This study employed first-principles calculations to investigate the hydrogen sorption properties of multilayered MXenes at the electron level. The strong physical adsorption (Kubas type) of hydrogen was observed in MXene. The interlayer distance and the transition metal elements of MXenes allowed adjustment of the sorption energy of hydrogen. The narrow interlayer space benefited the adsorption of hydrogen molecules, instead of hydrogen atoms. Group 4B elements enhanced the chemical absorption, while Hf2C and Ta2C MXenes possessed relatively strong physical adsorption of hydrogen molecules. Furthermore, the density of states, d-band center, and electron density difference were used to reveal the electronic properties of MXene-hydrogen system.

Operando structural analysis of phase transition of graphite electrode during Li de-intercalation process using neutron and synchrotron radiation X-ray diffraction

Graphite is widely used as a negative electrode material for lithium-ion batteries. Although it is well known lithium ions are inserted between the graphene layers, the details of the structural transition they undergo are not well understood. In this study, we performed operando structural analyses of graphite electrode during the discharge process using neutron diffraction and synchrotron radiation X-ray diffraction and established a solid foundation to clarify the relationship among the LiCx composition, discharging profile, and phase evolution of lithium-intercalated graphite (LIG). The operando analyses enabled us to assess simultaneously the structural changes of LIG along the ab plane (in-plane structure) and the c-axis direction (stage structure). In the de-lithiation process, the intralayer transition was observed on the ab plane from the LiC6-type to the LiC9-type arrangement near the LiC18 composition. The LiC9-type arrangement was retained in the Li-poorer phases such as LiC27, LiC36, LiC54, and LiC72, where the Li de-lithiation proceeded with the interlayer transition to higher-order stages. The phase transition of LIG involves a rapid switchover between the LiC6-type and the LiC9-type intralayer arrangement along with the changes in the interlayer stage structure. A reaction mechanism for the configurational transition on the intralayer and interlayer structure was updated.

Tunable valley splitting in two-dimensional CrBr3/VSe2 van der Waals heterostructure under strains and electric fields

Valleytronics opens up fascinating opportunities for using the valley degree of freedom in information storage and quantum computation. Here, based on the first-principles calculations, we investigate the effects of biaxial strains and electric fields on the magnetic, electronic, and valleytronic properties of two-dimensional CrBr3/VSe2 van der Waals (vdW) heterostructure consisting of two ferromagnetic monolayers. An interlayer magnetic phase transition from parallel to antiparallel is found when a compressive strain exceeds or a tensile strain exceeds 4% is applied, while the interlayer magnetic configuration remains parallel under perpendicular electric fields. The valley splitting in the conduction bands is significantly enhanced by a compressive strain or an electric field pointing from the VSe2 to the CrBr3 layer. Specifically, a large valley splitting about 30.8 meV is obtained in the system with antiparallel interlayer magnetic configurations under a compressive strain of , which is more than three times that of pristine CrBr3/VSe2 heterostructure. Our findings provide new insights into the future valleytronic applications for two-dimensional magnetic vdW heterostructures.

Engineering Interlayer Hybridization in Energy Space via Dipolar Overlayers

The interlayer hybridization (IH) of van der Waals (vdW) materials is thought to be mostly associated with the unignorable interlayer overlaps of wavefunctions (t) in real space. Here, we develop a more fundamental understanding of IH by introducing a new physical quantity, the IH admixture ratio α. Consequently, an exotic strategy of IH engineering in energy space can be proposed, i.e., instead of changing t as commonly used, α can be effectively tuned in energy space by changing the on-site energy difference (2Δ) between neighboring-layer states. In practice, this is feasible via reshaping the electrostatic potential of the surface by deposing a dipolar overlayer, e.g., crystalline ice. Our first-principles calculations unveil that IH engineering via adjusting 2Δ can greatly tune interlayer optical transitions in transition-metal dichalcogenide bilayers, switch different types of Dirac surface states in Bi2Se3 thin films, and control magnetic phase transition of charge density waves in 1H/1T-TaS2 bilayers, opening new opportunities to govern the fundamental optoelectronic, topological, and magnetic properties of vdW systems beyond the traditional interlayer distance or twisting engineering.

Inter-layer transition in neural architecture search

Neural architecture search (NAS) attracts much research attention, contributing to its ability to identify better architectures than manually-designed ones. Recently, differential neural architecture search methods have been widely used due to their impressive effectiveness and performance. They represent the network architecture as a repetitive proxy-directed acyclic graph (DAG) and optimize the network weights and architecture weights alternatively in a differential manner. However, existing methods model the architecture weights on each edge (i.e., a layer in the network) as statistically independent variables, ignoring the dependency between edges in DAG induced by their directed topological connections. In this paper, we make the first attempt to investigate such a dependency or relationship by proposing a novel inter-layer transition NAS method. It casts the architecture optimization into a sequential decision process where the dependency between the architecture weights of connected edges is explicitly modeled. Specifically, edges are divided into inner and outer groups according to whether or not their predecessor edges are in the same cell. While the architecture weights of outer edges are optimized independently, those of inner edges are derived sequentially based on the architecture weights of their predecessor edges and the learnable transition matrices in an attentive probability transition manner. Experiments on five benchmark classification datasets, four searching spaces, and NAS-Bench-201 confirm the value of modeling inter-layer dependency and demonstrate the proposed method outperforms other methods.

Progress and Insight of Van der Waals Heterostructures Containing Interlayer Transition for Near Infrared Photodetectors

AbstractVan der Waals (vdWs) heterostructures enable bandgap engineering of different 2D materials to realize the interlayer transition via type‐II band alignment leading to broaden spectrum that is beyond the cut‐off wavelength of individual 2D materials. Interlayer transition has a significant effect on the optoelectronic performance of vdWs heterostructure devices, and strong interlayer transition in 2D vdWs heterojunction is always demandable for sufficient charge transfer and rapid speed response. Herein, a state‐of‐the‐art review is presented on recent progress on interlayer transition in vdWs heterostructures for near‐infrared (NIR) photodetectors. First, the general synthesis techniques for vdWs heterostructures, band alignments in the vdWs heterostructures are provided. Then, the mechanism of interlayer transition in vdWs heterostructure and recent progress on interlayer transition in vdWs heterostructures for NIR photodetectors are summarized. Afterward, some worthy applications of NIR photodetectors are reviewed in related areas of this topic. At the last, an outlook, challenges, and future research directions of vdWs heterostructures for photodetectors at broaden response spectrum are presented.

Collective Magnetic Behavior in Vanadium Telluride Induced by Self-Intercalation

Self-intercalation of native magnetic atoms within the van der Waals (vdW) gap of layered two-dimensional (2D) materials provides a degree of freedom to manipulate magnetism in low-dimensional systems. Among various vdW magnets, the vanadium telluride is an interesting system to explore the interlayer order-disorder transition of magnetic impurities due to its flexibility in taking nonstoichiometric compositions. In this work, we combine high-resolution scanning transmission electron microscopy (STEM) analysis with density functional theory (DFT) calculations and magnetometry measurements, to unveil the local atomic structure and magnetic behavior of V-rich V1+xTe2 nanoplates with embedded V3Te4 nanoclusters grown by chemical vapor deposition (CVD). The segregation of V intercalations locally stabilizes the self-intercalated V3Te4 magnetic phase, which possesses a distorted 1T'-like monoclinic structure. This phase transition is controlled by the electron doping from the intercalant V ions. The magnetic hysteresis loops show that the nanoplates exhibit superparamagnetism, while the temperature-dependent magnetization curves evidence a collective superspin-glass magnetic behavior of the nanoclusters at low temperature. Using four-dimensional (4D) STEM diffraction imaging, we reveal the formation of collective diffuse magnetic domain structures within the sample under the high magnetic fields inside the electron microscope. Our results shed light on the studies of dilute magnetism at the 2D limit and on strategies for the manipulation of magnetism for spintronic applications.

Risk assessment of a layered slope considering spatial variabilities of interlayer and intralayer

While many studies have analyzed the effects of spatial variabilities of intralayer soil parameters on the probability of failure and risk of layered slopes, there is a paucity of research on the effects of interlayer variability. This paper is intended to investigate the influence of interlayer variability on the mechanical responses of a layered slope, as well as the effects of spatial variabilities of strength parameters of intralayer soils. To characterize the uncertainty of intralayer and interlayer spatial variabilities of layered geologic profiles, an integrated random field is developed using the program of FLAC based on both the two-dimensional random field theory and one-dimensional random process theory. Particularly, the random field for the interlayer transition zone is generated by a linear interpolation technique. Within the framework of Monte-Carlo simulation, a large number of stochastic calculations for a two-layered slope are conducted to evaluate the influences of spatial variabilities of both interlayer and intralayer on the stability and risk of the slope. The results show the failure mode of a two-layered slope changes greatly due to the stochastic layered boundary. It is also noted that the probability and risk of slope failure might be underestimated if ignoring the uncertainty arising from layered boundary and layered transition zone. The proposed equations can provide helpful information when investigating the probability and risk associated with layered slopes.

Laser Additive Manufacturing of TC4/AlSi12 Bimetallic Structure via Nb Interlayer.

The TC4/AlSi12 bimetallic structures (BS) with Nb interlayer transition were fabricated by laser additive manufacturing (LAM). The results showed that the TC4/AlSi12 BS with Nb interlayer prepared with optimized process parameters can be divided into three regions (the TC4 region, Nb region and the AlSi12 region) and two interfaces (the TC4/Nb interface and the Nb/AlSi12 interface). The high melting point (Ti, Nb) solid solution formed in the Nb region acted as a diffusion barrier between the TC4 alloy and the AlSi12 alloy, thereby effectively inhibiting the formation of Ti-Al intermetallic compounds (IMCs). With the decrease of the laser output power for AlSi12 deposition, the NbAl3 IMC changed from layered to dispersed distribution, while γ-TiAl and Ti5Si3 IMC disappeared, thus significantly reducing the crack susceptibility of the BS deposited layer. The tensile strength of TC4/AlSi12 BS with Nb interlayer was about 128MPa, and the fracture was located near the Nb/AlSi12 interface.

Strong interlayer transition in a staggered gap GeSe/MoTe2 heterojunction diode for highly efficient visible and near‐infrared photodetection and logic inverter

AbstractTransition‐metal dichalcogenides exhibit strong light–matter interactions and unique multifunctional logic behavior. Here, the strong interlayer transition and excellent broadband photodetection of GeSe/MoTe2 van der Waals (vdW) heterojunction are demonstrated. Differential charge density and photoluminescence quenching analyses reveal a strong interlayer transition between GeSe and MoTe2. In addition, density functional theory analysis predicts the formation of staggered band alignment, which contributed to the spatial segregation of photogenerated electron–hole pairs. The diode exhibited excellent optoelectronic characteristics in the visible and near‐infrared region. A high responsivity of ~1.0 × 104 A/W, an excellent detectivity of ~8.4 × 1012 jones, and a fast rise and fall time of 458 and 498 μs, respectively. Finally, a two‐dimensional complementary inverter consisting of p‐channel GeSe and n‐channel MoTe2 is examined to analyze its application for a logic inverter. The findings of this study will play a crucial role in the stimulation and fabrication of multifunctional vdW heterostructure devices.image

Self-powered, ultra-fast and high photoresponsivity of MoTe2/HfSe2 heterostructure broadband photovoltaic device

Due to their multifunctionality and tunable properties in electronic devices, the transition-metal dichalcogenides (TMDs) based van der Waals (vdW) heterostructures have attracted much attention and are considered a potential candidate for advanced nanoelectronics. In this work, a self-powered molybdenum ditelluride (MoTe2)/hafnium diselenide (HfSe2) vdW heterostructure-based photodetector with ohmic contacts is designed. The high rectification ratio is attained as 1.9×106, rising from the clean interface and small barrier height. Photovoltaic experiments are also carried out using laser light with a wavelength of 532–1064 nm in visible and near-infrared (VNIR) regions with different power intensities ranging from 10 to 120 nW. The photoresponsivity of MoTe2/HfSe2 is enhanced remarkably up to 1.3×103A/W with detectivity 2.6 × 1013 Jones and external quantum efficiency of 68% because of band-to-band and interlayer TMDs charge transition at a longer wavelength (1064 nm). Under incoming light with an intensity of 120 nW, rapid growth (6.8 μs) and decay times (8.7 μs) are projected because of interlayer TMDs charge transition at the longer wavelength. The obtained results showed significantly higher values than the reported vdW heterostructures. The fast response time, low recombination rate and astonishing value of photoresponsivity are the key parameters to developing highly efficient TMDs-based solar devices.

Study on Water Vertical Infiltration Characteristics and Water Content Simulation of Sandstone Overlying Loess

Research on the infiltration characteristics of surface water is fundamental for understanding the entire hydrological process. Therefore, studying the water infiltration process of sandstone slopes overlaid with loess and predicting soil moisture content are of great importance for investigating hydrological processes and controlling soil erosion in the hilly and gully areas of the Loess Plateau in China. This study mainly focuses on the simulation of the vertical water infiltration characteristics and water movement patterns of four kinds of sandstone (feldspathic and argillaceous sandstone) structures covered with thin layers of loess. In the one-dimensional vertical infiltration experiment and Hydrus-1D model simulation, the interlayer transition planes of loess–feldspathic and loess–feldspathic–argillaceous sandstones were found to present two conditions: fine soil covering coarse soil and coarse soil covering fine soil. Therefore, water infiltration reduced permeability. The existence of a transition layer between loess and feldspathic sandstone decreased the water infiltration rate and infiltration amount and decelerated the speed of the wetting front, thereby further affecting the ability of water infiltration. By using the Hydrus-1D model, 15 sets of soil hydraulic parameters, including θx (0.028–0.05795 cm3/cm3), θs (0.2306–0.4786 cm3/cm3), α (0.01899–0.06071 cm−1), n (1.438–6.408), and Ks (1.96·10−4–0.0576 cm/s) were inverted and optimized for each 20 cm soil layer (total of 60 cm). The Van Genuchten model constructed using these parameters demonstrated high accuracy in the simulation of water content in the vertical infiltration process of sandstone covered by loess with the coefficient of determination R2 > 0.849 and relative error RE < 5.311.