Mesoporous Hollow Sb/ZnS@C Core–Shell Heterostructures as Anodes for High‐Performance Sodium‐Ion Batteries

Combining the advantage of metal, metal sulfide, and carbon, mesoporous hollow core–shell Sb/ZnS@C hybrid heterostructures composed of Sb/ZnS inner core and carbon outer shell are rationally designed based on a robust template of ZnS nanosphere, as anodes for high‐performance sodium‐ion batteries (SIBs). A partial cation exchange reaction based on the solubility difference between Sb₂S₃ and ZnS can transform mesoporous ZnS to Sb₂S₃/ZnS heterostructure. To get a stable structure, a thin contiguous resorcinol‐formaldehyde (RF) layer is introduced on the surface of Sb₂S₃/ZnS heterostructure. The effectively protective carbon layer from RF can be designed as the reducing agent to convert Sb₂S₃ to metallic Sb to obtain core–shell Sb/ZnS@C hybrid heterostructures. Simultaneously, the carbon outer shell is beneficial to the charge transfer kinetics, and can maintain the structure stability during the repeated sodiation/desodiation process. Owing to its unique stable architecture and synergistic effects between the components, the core–shell porous Sb/ZnS@C hybrid heterostructure SIB anode shows a high reversible capacity, good rate capability, and excellent cycling stability by turning the optimized voltage range. This novel strategy to prepare carbon‐layer‐protected metal/metal sulfide core–shell heterostructure can be further extended to design other novel nanostructured systems for high‐performance energy storage devices.     

Wrap‐Around Core–Shell Heterostructures of Layered Crystals

Engineered heterostructures create new functionality by integrating dissimilar materials. Combining different 2D crystals naturally produces two distinct classes of heterostructures, vertical van der Waals (vdW) stacks or 2D sheets bonded laterally by covalent line interfaces. When joining thicker layered crystals, the arising structural and topological conflicts can result in more complex geometries. Phase separation during one‐pot synthesis of layered tin chalcogenides spontaneously creates core–shell structures in which large orthorhombic SnS crystals are enclosed in a wrap‐around shell of trigonal SnS₂, forcing the coexistence of parallel vdW layering along with unconventional, orthogonally layered core–shell interfaces. Measurements of the optoelectronic properties establish anisotropic carrier separation near type II core–shell interfaces and extended long‐wavelength light harvesting via spatially indirect interfacial absorption, making multifunctional layered core–shell structures attractive for energy‐conversion applications.     

Chemical Vapor Deposition Growth of High Crystallinity Sb2Se3 Nanowire with Strong Anisotropy for Near‐Infrared Photodetectors

Low‐dimensional semiconductors have attracted considerable attention due to their unique structures and remarkable properties, which makes them promising materials for a wide range of applications related to electronics and optoelectronics. Herein, the preparation of 1D Sb₂Se₃ nanowires (NWs) with high crystal quality via chemical vapor deposition growth is reported. The obtained Sb₂Se₃ NWs have triangular prism morphology with aspect ratio range from 2 to 200, and three primary lattice orientations can be achieved on the sixfold symmetry mica substrate. Angle‐resolved polarized Raman spectroscopy measurement reveals strong anisotropic properties of the Sb₂Se₃ NWs, which is also developed to identify its crystal orientation. Furthermore, photodetectors based on Sb₂Se₃ NW exhibit a wide spectral photoresponse range from visible to NIR (400–900 nm). Owing to the high crystallinity of Sb₂Se₃ NW, the photodetector acquires a photocurrent on/off ratio of about 405, a responsivity of 5100 mA W^?1, and fast rise and fall times of about 32 and 5 ms, respectively. Additionally, owing to the anisotropic structure of Sb₂Se₃ NW, the device exhibits polarization‐dependent photoresponse. The high crystallinity and superior anisotropy of Sb₂Se₃ NW, combined with controllable preparation endows it with great potential for constructing multifunctional optoelectronic devices.     

High‐Responsivity Graphene/InAs Nanowire Heterojunction Near‐Infrared Photodetectors with Distinct Photocurrent On/Off Ratios

Graphene is a promising candidate material for high‐speed and ultra‐broadband photodetectors. However, graphene‐based photodetectors suffer from low photoreponsivity and I_light/I_dark ratios due to their negligible‐gap nature and small optical absorption. Here, a new type of graphene/InAs nanowire (NW) vertically stacked heterojunction infrared photodetector is reported, with a large photoresponsivity of 0.5 AW^?1 and I_light/I_dark ratio of 5 × 10², while the photoresponsivity and I_light/I_dark ratio of graphene infrared photodetectors are 0.1 mAW^?1 and 1, respectively. The Fermi level (E_F ) of graphene can be widely tuned by the gate voltage owing to its 2D nature. As a result, the back‐gated bias can modulate the Schottky barrier (SB) height at the interface between graphene and InAs NWs. Simulations further demonstrate the rectification behavior of graphene/InAs NW heterojunctions and the tunable SB controls charge transport across the vertically stacked heterostructure. The results address key challenges for graphene‐based infrared detectors, and are promising for the development of graphene electronic and optoelectronic applications.     

Ultrathin CsPbX3 Nanowire Arrays with Strong Emission Anisotropy

1D nanowires of all‐inorganic lead halide perovskites represent a good architecture for the development of polarization‐sensitive optoelectronic devices due to their high absorption efficient, emission yield, and dielectric constants. However, among as‐fabricated perovskite nanowires with the lateral dimensions of hundreds nanometers so far, the optical anisotropy is hindered and rarely explored owing to the invalidating of electrostatic dielectric mismatch in the physical dimensions. Here, well‐aligned CsPbBr₃ and CsPbCl₃ nanowires with thickness T down to 15 and 7 nm, respectively, are synthesized using a vapor phase van der Waals epitaxial method. Strong emission anisotropy with polarization ratio up to ≈0.78 is demonstrated in the nanowires with T < 40 nm due to the electrostatic dielectric confinement. With the increasing of thickness, the polarization ratio remarkably reduces monotonously to ≈0.17 until T ≈140 nm; and further oscillates in a small amplitude owing to the wave characteristic of light. These findings not only represent a demonstration of perovskite‐based polarization‐sensitive light sources, but also advance fundamental understanding of their polarization properties of perovskite nanowires.     

Anisotropic Broadband Photoresponse of Layered Type‐II Weyl Semimetal MoTe2

Photodetectors based on Weyl semimetal promise extreme performance in terms of highly sensitive, broadband and self‐powered operation owing to its extraordinary material properties. Layered Type‐II Weyl semimetal that break Lorentz invariance can be further integrated with other two‐dimensional materials to form van der Waals heterostructures and realize multiple functionalities inheriting the advantages of other two‐dimensional materials. Herein, we report the realization of a broadband self‐powered photodetector based on Type‐II Weyl semimetal T_d‐MoTe₂. The prototype metal–MoTe₂–metal photodetector exhibits a responsivity of 0.40 mA W^?1 and specific directivity of 1.07 × 10⁸ Jones with 43 μs response time at 532 nm. Broadband responses from 532 nm to 10.6 μm are experimentally tested with a potential detection range extendable to far‐infrared and terahertz. Furthermore, we identify the response of the detector is polarization angle sensitive due to the anisotropic response of MoTe₂. The anisotropy is found to be wavelength dependent, and the degree of anisotropy increases as the excitation wavelength gets closer to the Weyl nodes. In addition, with power and temperature dependent photoresponse measurements, the photocurrent generation mechanisms are investigated. Our results suggest this emerging class of materials can be harnessed for broadband angle sensitive, self‐powered photodetection with decent responsivities.     

Tunneling Diode Based on WSe2/SnS2 Heterostructure Incorporating High Detectivity and Responsivity

van der Waals (vdW) heterostructures based on atomically thin 2D materials have led to a new era in next‐generation optoelectronics due to their tailored energy band alignments and ultrathin morphological features, especially in photodetectors. However, these photodetectors often show an inevitable compromise between photodetectivity and photoresponsivity with one high and the other low. Herein, a highly sensitive WSe₂/SnS₂ photodiode is constructed on BN thin film by exfoliating each material and manually stacking them. The WSe₂/SnS₂ vdW heterostructure shows ultralow dark currents resulting from the depletion region at the junction and high direct tunneling current when illuminated, which is confirmed by the energy band structures and electrical characteristics fitted with direct tunneling. Thus, the distinctive WSe₂/SnS₂ vdW heterostructure exhibits both ultrahigh photodetectivity of 1.29 × 10¹³ Jones (I_ph/I_dark ratio of ≈10⁶) and photoresponsivity of 244 A W^?1 at a reverse bias under the illumination of 550 nm light (3.77 mW cm^?2).     

Highly‐Anisotropic Dion–Jacobson Hybrid Perovskite by Tailoring Diamine into CsPbBr3 for Polarization‐Sensitive Photodetection

2D materials with inherent attributes of structural anisotropy have been well applied in the field of polarization‐sensitive photodetection. However, to explore new 2D members with strong polarized‐light responses still remains a challenge. Herein, by alloying diamine molecule into the 3D prototype of CsPbBr₃, a new Dion–Jacobson (DJ) type 2D perovskite of (HDA)CsPb₂Br₇ ( 1 , where HDA²⁺ is 1,6‐hexamethylenediammonium), containing both inorganic Cs metal and organic cations is designed. The natural anisotropy characteristics of 1 are solidly elucidated by analyzing crystal structure, electric conductivity, and optical properties. Strikingly, distinct polarization‐sensitive responses are observed in 1 , owing to its strong anisotropy of optical absorption (the ratio of α_c/α_b ≈ 2.2). Consequently, crystal‐based detectors of 1 exhibit fascinating photo‐activities to polarized‐light, including high detectivity (1.5 × 10⁹ Jones), large dichroism ratio (I_ph^c/I_ph^b ≈ 1.6) and fast responding rate (200 µs). All these polarization‐sensitive performances along with intriguing phase stability make 1 a potential candidate for polarized‐light detection. This work paves a pathway toward new functionalities of DJ‐type 2D hybrid perovskites for their future optoelectronic device applications.     

Thermally Phase‐Transformed In2Se3 Nanowires for Highly Sensitive Photodetectors

The photoresponse characteristics of In₂Se₃ nanowire photodetectors with the κ‐phase and α‐phase structures are investigated. The as‐grown κ‐phase In₂Se₃ nanowires by the vapor‐liquid‐solid technique are phase‐transformed to the α‐phase nanowires by thermal annealing. The photoresponse performances of the κ‐phase and α‐phase In₂Se₃ nanowire photodetectors are characterized over a wide range of wavelengths (300–900 nm). The phase of the nanowires is analyzed using a high‐resolution transmission microscopy equipped with energy dispersive X‐ray spectroscopy and X‐ray diffraction. The electrical conductivity and photoresponse characteristics are significantly enhanced in the α‐phase due to smaller bandgap structure compared to the κ‐phase nanowires. The spectral responsivities of the α‐phase devices are 200 times larger than those of the κ‐phase devices. The superior performance of the thermally phase‐transformed In₂Se₃ nanowire devices offers an avenue to develop highly sensitive photodetector applications.     

Highly Anisotropic Sb2Se3 Nanosheets: Gentle Exfoliation from the Bulk Precursors Possessing 1D Crystal Structure

2D materials, particularly those bearing in‐plane anisotropic optical and electrical properties such as black phosphorus and ReS₂, have spurred great research interest very recently as promising building blocks for future electronics. However, current progress is limited to layered compounds that feature atomic arrangement asymmetry within the covalently bonded planes. Herein, a series of highly anisotropic nanosheets (Sb₂Se₃, Sb₂S₃, Bi₂S₃, and Sb₂(S, Se)₃), which are composed of 1D covalently linked ribbons stacked together via van der Waals force, is introduced as a new member to the anisotropic 2D material family. These unique anisotropic nanosheets are successfully fabricated from their polymer‐like bulk counterparts through a gentle water freezing‐thawing approach. Angle‐resolved polarized Raman spectroscopy characterization confirms the strong in‐plane asymmetry of Sb₂Se₃ nanosheets, and photodetection study reveals their high responsivity and anisotropic in‐plane transport. This work can enlighten the synthesis and application of new anisotropic 2D nanosheets that can be potentially applied for future electronic and optoelectronic devices.     

Controlling Magnetic and Optical Properties of the van der Waals Crystal CrCl3−xBrx via Mixed Halide Chemistry

Magnetic van der Waals (vdW) materials are the centerpiece of atomically thin devices with spintronic and optoelectronic functions. Exploring new chemistry paths to tune their magnetic and optical properties enables significant progress in fabricating heterostructures and ultracompact devices by mechanical exfoliation. The key parameter to sustain ferromagnetism in 2D is magnetic anisotropy—a tendency of spins to align in a certain crystallographic direction known as easy‐axis. In layered materials, two limits of easy‐axis are in‐plane (XY) and out‐of‐plane (Ising). Light polarization and the helicity of topological states can couple to magnetic anisotropy with promising photoluminescence or spin‐orbitronic functions. Here, a unique experiment is designed to control the easy‐axis, the magnetic transition temperature, and the optical gap simultaneously in a series of CrCl_3?xBr_x crystals between CrCl₃ with XY and CrBr₃ with Ising anisotropy. The easy‐axis is controlled between the two limits by varying spin–orbit coupling with the Br content in CrCl_3?x Br_x. The optical gap, magnetic transition temperature, and interlayer spacing are all tuned linearly with x. This is the first report of controlling exchange anisotropy in a layered crystal and the first unveiling of mixed halide chemistry as a powerful technique to produce functional materials for spintronic devices.     

Dirac Semimetal Heterostructures: 3D Cd3As2 on 2D Graphene

Dirac semimetal is an emerging class of quantum matters, ranging from 2D category, such as, graphene and surface states of topological insulator to 3D category, for instance, Cd₃As₂ and Na₃Bi. As 3D Dirac semimetals typically possess Fermi‐arc surface states, the 2D–3D Dirac van der Waals heterostructures should be promising for future electronics. Here, graphene–Cd₃As₂ heterostructures are fabricated through direct layer‐by‐layer stacking. The electronic coupling results in a notable interlayer charge transfer, which enables us to modulate the Fermi level of graphene through Cd₃As₂. A planar graphene p–n–p junction is achieved by selective modification, which demonstrates quantized conductance plateaus. Moreover, compared with the bare graphene device, the graphene–Cd₃As₂ hybrid device presents large nonlocal signals near the Dirac point due to the charge transfer from the spin‐polarized surface states in the adjacent Cd₃As₂. The results enrich the family of van der Waals heterostructure and should inspire more studies on the application of Dirac/Weyl semimetals in spintronics.     

High Detectivity and Transparent Few‐Layer MoS2/Glassy‐Graphene Heterostructure Photodetectors

Layered van der Waals heterostructures have attracted considerable attention recently, due to their unique properties both inherited from individual two‐dimensional (2D) components and imparted from their interactions. Here, a novel few‐layer MoS₂/glassy‐graphene heterostructure, synthesized by a layer‐by‐layer transfer technique, and its application as transparent photodetectors are reported for the first time. Instead of a traditional Schottky junction, coherent ohmic contact is formed at the interface between the MoS₂ and the glassy‐graphene nanosheets. The device exhibits pronounced wavelength selectivity as illuminated by monochromatic lights. A responsivity of 12.3 mA W^?1 and detectivity of 1.8 × 10¹⁰ Jones are obtained from the photodetector under 532 nm light illumination. Density functional theory calculations reveal the impact of specific carbon atomic arrangement in the glassy‐graphene on the electronic band structure. It is demonstrated that the band alignment of the layered heterostructures can be manipulated by lattice engineering of 2D nanosheets to enhance optoelectronic performance.     

2D Lead Dihalides for High‐Performance Ultraviolet Photodetectors and their Detection Mechanism Investigation

2D halide semiconductors, a new family of 2D materials in addition to transition metal dichalcogenides, present ultralow dark current and high light conversion yield, which hold great potential in photoconductive detectors. Herein, a facile aqueous solution method is developed for the preparation of large‐scale 2D lead dihalide nanosheets (PbF_2‐xI_x). High‐performance UV photodetectors are successfully implemented based on 2D PbF_2‐xI_x nanosheets. By modulating the components of halogens, the bandgap of PbF_2‐xI_x nanosheets can be tuned to meet varied detection spectra. The photoresponse dependence on incident power density, wavelength, detection environment, and temperature are systematically studied to investigate their detection mechanism. For PbI₂ photodetectors, they are dominantly driven by a photoconduction mechanism and show a fast response speed and a low noise current density. A high normalized detectivity of 1.5 × 10¹² Jones and an I_ON/I_OFF ratio up to 10³ are reached. On the other hand, PbFI photodetectors demonstrate a photogating mechanism mediated by trap states showing high responsivity. The novel 2D halide materials with wide bandgaps, superior detection performance, and facile synthesis process can enrich the Van der Waals solids family and hold great potential for a wide variety of applications in advanced optoelectronics.     

High‐Gain 200 ns Photodetectors from Self‐Aligned CdS–CdSe Core–Shell Nanowalls

1D core–shell heterojunction nanostructures have great potential for high‐performance, compact optoelectronic devices owing to their high interface area to volume ratio, yet their bottom‐up assembly toward scalable fabrication remains a challenge. Here the site‐controlled growth of aligned CdS–CdSe core–shell nanowalls is reported by a combination of surface‐guided vapor–liquid–solid horizontal growth and selective‐area vapor–solid epitaxial growth, and their integration into photodetectors at wafer‐scale without postgrowth transfer, alignment, or selective shell‐etching steps. The photocurrent response of these nanowalls is reduced to 200 ns with a gain of up to 3.8 × 10³ and a photoresponsivity of 1.2 × 10³ A W^?1, the fastest response at such a high gain ever reported for photodetectors based on compound semiconductor nanostructures. The simultaneous achievement of sub‐microsecond response and high‐gain photocurrent is attributed to the virtues of both the epitaxial CdS–CdSe heterojunction and the enhanced charge‐separation efficiency of the core–shell nanowall geometry. Surface‐guided nanostructures are promising templates for wafer‐scale fabrication of self‐aligned core–shell nanostructures toward scalable fabrication of high‐performance compact photodetectors from the bottom‐up.     

Orientation Engineering in Low‐Dimensional Crystal‐Structural Materials via Seed Screening

The orientation of low‐dimensional crystal‐structural (LDCS) films significantly affects the performance of photoelectric devices, particularly in vertical conducting devices such as solar cells and light‐emitting diodes. According to film growth theory, the initial seeds determine the final orientation of the film. Ruled by the minimum energy principle, lying (chains or layers parallel to the substrate) seeds bonding with the substrate through van der Waals forces are easier to form than standing (chains or layers perpendicular to the substrate) seeds bonding with the substrate by a covalent bond. Utilizing high substrate temperature to re‐evaporate the lying seeds and preserve the standing seeds, the orientation of 1D crystal‐structural Sb₂Se₃ is successfully controlled. Guided by this seed screening model, highly [211]‐ and [221]‐oriented Sb₂Se₃ films on an inert TiO₂ substrate are obtained; consequently, a record efficiency of 7.62% in TiO₂/Sb₂Se₃ solar cells is achieved. This universal model of seed screening provides an effective method for orientation control of other LDCS films.     

Ultrathin Single‐Crystalline CdTe Nanosheets Realized via Van der Waals Epitaxy

Due to the novel physical properties, high flexibility, and strong compatibility with Si‐based electronic techniques, 2D nonlayered structures have become one of the hottest topics. However, the realization of 2D structures from nonlayered crystals is still a critical challenge, which requires breaking the bulk crystal symmetry and guaranteeing the highly anisotropic crystal growth. CdTe owns a typical wurtzite crystal structure, which hinders the 2D anisotropic growth of hexagonal‐symmetry CdTe. Here, for the first time, the 2D anisotropic growth of ultrathin nonlayered CdTe as thin as 4.8 nm via an effective van der Waals epitaxy method is demonstrated. The anisotropic ratio exceeds 10³. Highly crystalline nanosheets with uniform thickness and large lateral dimensions are obtained. The in situ fabricated ultrathin 2D CdTe photodetector shows ultralow dark current (≈100 fA), as well as high detectivity, stable photoswitching, and fast photoresponse speed (τ_rising = 18.4 ms, τ_decay = 14.7 ms). Besides, benefitting from its 2D planar geometry, CdTe nanosheet exhibits high compatibility with flexible substrates and traditional microfabrication techniques, indicating its significant potential in the applications of flexible electronic and optoelectronic devices.     

Twinned Growth of Metal‐Free,Triazine‐Based Photocatalyst Films as Mixed‐Dimensional (2D/3D) van der Waals Heterostructures

Design and synthesis of ordered, metal‐free layered materials is intrinsically difficult due to the limitations of vapor deposition processes that are used in their making. Mixed‐dimensional (2D/3D) metal‐free van der Waals (vdW) heterostructures based on triazine (C₃N₃) linkers grow as large area, transparent yellow‐orange membranes on copper surfaces from solution. The membranes have an indirect band gap (E _g,opt = 1.91 eV, E _g,elec = 1.84 eV) and are moderately porous (124 m² g^?1). The material consists of a crystalline 2D phase that is fully sp² hybridized and provides structural stability, and an amorphous, porous phase with mixed sp²–sp hybridization. Interestingly, this 2D/3D vdW heterostructure grows in a twinned mechanism from a one‐pot reaction mixture: unprecedented for metal‐free frameworks and a direct consequence of on‐catalyst synthesis. Thanks to the efficient type I heterojunction, electron transfer processes are fundamentally improved and hence, the material is capable of metal‐free, light‐induced hydrogen evolution from water without the need for a noble metal cocatalyst (34 µmol h^?1 g^?1 without Pt). The results highlight that twinned growth mechanisms are observed in the realm of “wet” chemistry, and that they can be used to fabricate otherwise challenging 2D/3D vdW heterostructures with composite properties.     

2D Perovskites with Giant Excitonic Optical Nonlinearities for High‐Performance Sub‐Bandgap Photodetection

Two‐dimensional (2D) perovskites have proved to be promising semiconductors for photovoltaics, photonics, and optoelectronics. Here, a strategy is presented toward the realization of highly efficient, sub‐bandgap photodetection by employing excitonic effects in 2D Ruddlesden–Popper‐type halide perovskites (RPPs). On near resonance with 2D excitons, layered RPPs exhibit degenerate two‐photon absorption (D‐2PA) coefficients as giant as 0.2–0.64 cm MW^?1. 2D RPP‐based sub‐bandgap photodetectors show excellent detection performance in the near‐infrared (NIR): a two‐photon‐generated current responsivity up to 1.2 × 10⁴ cm² W^?2 s^?1, two orders of magnitude greater than InAsSbP‐pin photodiodes; and a dark current as low as 2 pA at room temperature. More intriguingly, layered‐RPP detectors are highly sensitive to the light polarization of incoming photons, showing a considerable anisotropy in their D‐2PA coefficients (β_[001]/β_[011] = 2.4, 70% larger than the ratios reported for zinc‐blende semiconductors). By controlling the thickness of the inorganic quantum well, it is found that layered RPPs of (C₄H₉NH₃)₂(CH₃NH₃)Pb₂I₇ can be utilized for three‐photon photodetection in the NIR region.     

SnSe/MoS2 van der Waals Heterostructure Junction Field‐Effect Transistors with Nearly Ideal Subthreshold Slope

The minimization of the subthreshold swing (SS) in transistors is essential for low‐voltage operation and lower power consumption, both critical for mobile devices and internet of things (IoT) devices. The conventional metal‐oxide‐semiconductor field‐effect transistor requires sophisticated dielectric engineering to achieve nearly ideal SS (60 mV dec^?1 at room temperature). However, another type of transistor, the junction field‐effect transistor (JFET) is free of dielectric layer and can reach the theoretical SS limit without complicated dielectric engineering. The construction of a 2D SnSe/MoS₂ van der Waals (vdW) heterostructure‐based JFET with nearly ideal SS is reported. It is shown that the SnSe/MoS₂ vdW heterostructure exhibits excellent p–n diode rectifying characteristics with low saturate current. Using the SnSe as the gate and MoS₂ as the channel, the SnSe/MoS₂ vdW heterostructure exhibit well‐behavioured n‐channel JFET characteristics with a small pinch‐off voltage V_P of ?0.25 V, nearly ideal subthreshold swing SS of 60.3 mV dec^?1 and high ON/OFF ratio over 10⁶, demonstrating excellent electronic performance especially in the subthreshold regime.