Jing Zhang

Nature Nanotechnology, Published online: 11 March 2021; doi:10.1038/s41565-021-00873-9

While two-dimensional semiconductors enable the investigation of light–matter interactions in low dimensions, a link to magnetic order has so far remained elusive. Now, the antiferromagnetic insulator NiPS3 is found to exhibit excitons with strong linear polarization that are coupled to the zigzag antiferromagnetic order.

Nature Nanotechnology, Published online: 12 March 2021; doi:10.1038/s41565-021-00876-6

Selective growth of nanoporous metal–organic framework nanocrystals in the stacking defects of graphene oxide layers improves the mechanical integrity and water–solute selectivity of graphene oxide membranes.

Next-generation spintronic devices will benefit from low-dimensionality, ferromagnetism, and half–metallicity, possibly controlled by electric fields. We find these technologically–appealing features to be combined with an exotic microscopic origin of magnetism in doped CdOHCl, a van der Waals material from which 2D layers may be exfoliated. By means of first principles simulations, we predict homogeneous hole–doping to give rise to p -band magnetism in both the bulk and monolayer phases and interpret our findings in terms of Stoner instability: as the Fermi level is tuned via hole–doping through singularities in the 2D-like density of states, ferromagnetism develops with large saturation magnetization of 1 µ B per hole, leading to a half-metallic behaviour for layer carrier densities of the order of 10 14 cm −2 . Furthermore, we put forward electrostatic doping as an additional handle to induce magnetism in monolayers and bila...

The emergence of various exciton-related effects in transition metal dichalcogenides (TMDC) and their heterostructures has inspired a significant number of studies and brought forth several possible applications. Often, standard photoluminescence (PL) with microscale lateral resolution is utilized to identify and characterize these excitonic phenomena, including interlayer excitons (IEXs). We studied the local PL signatures of van der Waals heterobilayers composed of exfoliated monolayers of the (Mo, W)(S, Se) 2 TMDC family with high spatial resolution (down to 30 nm) using tip-enhanced photoluminescence (TEPL) with different orders (top/bottom) and on different substrates. We evidence that in MoS 2 –WSe 2 heterobilayers, other PL signals may appear near the reported energy of the IEX transitions, possibly interfering in the interpretation of the results. The extra signals are only observed locally in small areas where the topography looks distorted....

Accessing the metastable phases in a controlled fashion can further expand the applications of atomically thin transition metal dichalcogenides (TMDs). Although top-down approaches based on ion intercalation exfoliation have shown to be an effective route to transform 2H phase into 1T and/or 1T′ polytype phases, a bottom-up growth strategy could be more suitable for device integration. Herein, we show that by assisting the atmospheric pressure chemical vapor deposition (APCVD) growth with a specific alkali metal halide (AMH), it possible to induce the direct synthesis of 1T phase domains coexisting with 2H phase structure in micrometer-sized MoS 2 monolayer flakes. The photoluminescence emission and structural properties of three different AMH (NaCl, KBr and KCl) MoS 2 crystals are compared. Both NaCl and KBr assisted MoS 2 monolayers displayed the semiconducting 2H-phase. On the other hand, we demonstrate that KCl promotes the formation of a 1T–2H ...

The valley-pseudospin in monolayered transition metal dichalcogenides (TMDs) provides an alternative degree of freedom for manipulating carriers to encode and store information, which has attracted wide attention. This review focuses on the investigations of TMDs valley-emission modulated by plasmonics in recent years and discusses possible directions for future applications of valleytronic devices.

Abstract

Monolayered transition metal dichalcogenides (TMDs) are one kind of hexagonal 2D semiconductors with a direct bandgap structure. Due to the property of natural broken inversion symmetry in the lattice, the strong spin–orbit coupling of electrons in TMDs can induce degenerate levels with antiparallel spins in K and K′ valleys, which selectively respond with external light excitations. Surface plasmon resonance with efficient electromagnetic enhancement and near-field coupling provides excellent potential opportunities to modulate valley emission of TMDs. Efforts have been devoted to investigating the interaction principles and applications of this research field. This review focuses on plasmonic modulation of valleytronic emission in TMDs with surface plasmon polaritons (SPP) and localized surface plasmons (LSP) based on different modulation principles, respectively, and discusses possible research directions for future device applications.

This is a comprehensive review of flexible MXene-based composites for various applications as wearable devices in sensors, supercapacitors, and electromagnetic interference shielding materials. The preparation strategies, working mechanisms, performances, and applications of flexible MXene-based composites are highlighted. Additional work is suggested to be conducted to improve the performance of the flexible MXene-based composites for wearable devices.

Abstract

In recent decades, flexible and wearable devices have been extensively investigated due to their promising applications in portable mobile electronics and human motion monitoring. MXene, a novel growing family of 2D nanomaterials, demonstrates superiorities such as outstanding electrical conductivity, abundant terminal groups, unique layered-structure, large surface area, and hydrophilicity, making it to be a potential candidate material for flexible and wearable devices. Numerous pioneering works are devoted to develop flexible MXene-based composites with various functions and designed structures. Therefore, the latest progress of the flexible MXene-based composites for wearable devices is summarized in this review, focusing on the preparation strategies, working mechanisms, performances, and applications in sensors, supercapacitors, and electromagnetic interference shielding materials. Moreover, the current challenges and future outlooks are also discussed.

By applying in situ TEM, a dynamic evolution of the crystalline structure and the strain fields during Cu₂Se phase transformation have been studied. The instant generation and release of a large elastic strain is identified as one of the main origins of the abnormal thermoelectric behavior of Cu₂Se in the moment of phase transition.

Abstract

The superionic conductor Cu₂Se is a promising thermoelectric material due to its low thermal conductivity. An abnormal but clear change in the thermoelectric parameters has been observed during the phase transformation from the ordered and non-cubic α-Cu₂Se to the disordered and cubic β-Cu₂Se. However, the microstructural origin of the abnormal change and its implications for thermoelectric applications remain largely unknown. Herein, by mimicking the real working conditions of thermoelectrics, the phase transition from α- to β-Cu₂Se induced by the rising temperature has been carefully investigated by in situ transmission electron microscopy. It is observed that an abrupt and anisotropic volume-change in the Se-sublattice occurs when the temperature is raised to the phase transition point. The abnormal change in the crystalline volume versus temperature, which is caused by the local migration of Cu-ions, induces an instant and uncommon strain-field, which reduces the carrier's mobility and increases the electrical resistance. Local migration of Cu-ions is responsible for a quite low thermal conductivity. Such effects exist only at the instance of the phase transition. Observing the thermoelectric response of the structure during the phase transition may provide insights into the development of high performance thermoelectric materials, which fall beyond the traditional approaches.

The influence of the different characteristics of graphene‐based films on the growth and maturation of primary cortical neurons is investigated. The results suggest that high electrical conductivity by itself is not a necessary condition for the realization of an efficient neuronal interface, while other physical–chemical characteristics of the graphene‐based film, such as the atomic structure, are to be considered.

Abstract

Graphene‐based materials represent a useful tool for the realization of novel neural interfaces. Several studies have demonstrated the biocompatibility of graphene‐based supports, but the biological interactions between graphene and neurons still pose open questions. In this work, the influence of graphene films with different characteristics on the growth and maturation of primary cortical neurons is investigated. Graphene films are grown by chemical vapor deposition progressively lowering the temperature range from 1070 to 650 °C to change the lattice structure and corresponding electrical conductivity. Two graphene‐based films with different electrical properties are selected and used as substrate for growing primary cortical neurons: i) highly crystalline and conductive (grown at 1070 °C) and ii) highly disordered and 140‐times less conductive (grown at 790 °C). Electron and fluorescence microscopy imaging reveal an excellent neuronal viability and the development of a mature, structured, and excitable network onto both substrates, regardless of their microstructure and electrical conductivity. The results underline that high electrical conductivity by itself is not fundamental for graphene‐based neuronal interfaces, while other physico–chemical characteristics, including the atomic structure, should be also considered in the design of functional, bio‐friendly templates. This finding widens the spectrum of carbon‐based materials suitable for neuroscience applications.

The ability of atomically thin InSe to conduct heat is probed by scanning thermal microscopy. This reveals an anomalous low thermal conductivity that decreases with reducing the lateral size and thickness of InSe, under strain and in layers weakly coupled to a substrate. These properties are critical for future emerging technologies.

Abstract

The ability of a material to conduct heat influences many physical phenomena, ranging from thermal management in nanoscale devices to thermoelectrics. Van der Waals 2D materials offer a versatile platform to tailor heat transfer due to their high surface‐to‐volume ratio and mechanical flexibility. Here, the nanoscale thermal properties of 2D indium selenide (InSe) are studied by scanning thermal microscopy. The high electrical conductivity, broad‐band optical absorption, and mechanical flexibility of 2D InSe are accompanied by an anomalous low thermal conductivity (κ). This can be smaller than that of low‐κ dielectrics, such as silicon oxide, and it decreases with reducing the lateral size and/or thickness of InSe. The thermal response is probed in free‐standing InSe layers as well as layers supported by a substrate, revealing the role of interfacial thermal resistance, phonon scattering, and strain. These thermal properties are critical for future emerging technologies, such as field‐effect transistors that require efficient heat dissipation or thermoelectric energy conversion with low‐κ, high electron mobility 2D materials, such as InSe.

A simple method for the controllable synthesis of ultrathin charge transfer complexes (CT) nanosheets on graphdiyne (CTNS/GDY) is reported. This catalyst shows a record‐high oxygen evolution reaction activity with only 155 mV of overpotential to deliver 10 mA cm⁻² in the basic electrolyte.

Abstract

Graphdiyne (GDY) is an emerging 2D carbon material that exhibits unusual structures and properties. Therefore, growing heterogeneous materials on the surface of GDY is very attractive to achieve efficient energy utilization. Here, a simple method for the controllable synthesis of ultrathin charge‐transfer complexes (CTs) of nickel with terephthalic acid nanosheets on GDY is reported. This catalyst shows record‐high oxygen evolution reaction (OER) activity with an overpotential of only 155 mV to deliver a current density of 10 mA cm⁻² in an alkaline electrolyte. Density functional theory calculations reveals that a strong p–d coupling effect in the GDY–CT interface region enhances the overall electronic activity, resulting in fast reversible redox‐switching with a low electron‐transfer barrier. Experimental characterization confirms that GDY plays a key role in modulating the morphological and electronic structures to accelerate the OER rate. These findings are expected to contribute to the design of more efficient catalysts for the realization of efficient hydrogen energy technologies.

Photonic printing of invisible patterns based on a wettability‐controlled strategy is realized by a cellulose‐liquid‐crystal/polycation composite film with a counteranion‐controlled swelling behavior and reversible printability, enabling multi‐dimensional encryptions including wettability responses, polarization decoding, fluorescent watermarks, and miniature patterns.

Abstract

The construction of invisible patterns via high‐resolution printing and the independent encoding/decoding of complex information can lead to promising applications in steganography and watermarking for optical encryption. Herein, a rewritable chiral photonic paper formed by cholesteric cellulose nanocrystals and polycation is reported. The chemically crosslinked polycation network interpenetrates in the cholesteric structure while retaining the optical properties of the photonic crystals. The film exhibits controllable wettability via anion exchange, leading to extremely low contrast in the dry state but high contrast by a rapid wetting response. Triple invisible information is independently encoded on the films, including invisible patterns caused by reversible counterion‐controlled wettability, permanent fluorescent labels based on fluorescent counterions, and polarization‐dependent structural colors based on cholesteric structures. Full color patterns can be reversibly constructed via inkjet printing, with a high resolution of 100 µm. In addition, the circular polarization characteristics of the cellulose nanocrystals, liquid crystals, endow the system with complex and independent responses, realizing a wetting/polarization double‐key decryption. This work provides a simple and effective optical technique for coding complex information on a single material platform and expands the techniques available to achieve invisible patterns for sensing and anti‐counterfeiting.

This review presents the state of the art of 2D‐nanomaterial‐based triboelectric nanogenerators (2D‐TENGs). Basic classifications, enhancement mechanisms, and special advantages of 2D nanomaterials for 2D‐TENGs are reviewed. The output performances and applications in energy harvesting and self‐powered sensing of 2D‐TENGs are also summarized. Several challenges for the development and application of 2D‐TENGs are proposed.

Abstract

The integration of triboelectric nanogenerators (TENGs) and 2D nanomaterials brings about 2D‐nanomaterial‐based TENGs (2D‐TENGs) that promote the rapid development of self‐powered sensing systems and wearable electronics. Extraordinary physical, electronic, chemical, and optical properties of 2D nanomaterials endow 2D‐TENGs with improved output performance. This review presents the state of the art of 2D‐TENGs with respect to basic classifications, enhancement mechanisms, special advantages, output performances, and applications in energy harvesting and self‐powered sensing. Furthermore, several challenges that can impede applications of 2D‐TENGs are discussed.

The ultraviolet/laser irradiation is employed for reversible functionalization on 2D rhenium disulfide and rhenium diselenide evidenced by Raman spectroscopy, dynamic force microscopy, transmission electron microscopy, and X‐ray photoelectron spectroscopy. This photochemical approach without atomic defects is highly controllable and can effectively modulate the electrical, optical, and chemical properties of these 2D semiconductors.

Abstract

Despite the van der Waals (vdW) surfaces are usually chemically inert, un‐destructive, scalable, and reversible redox reactions are introduced on the vdW surfaces of 2D anisotropic semiconductors ReX₂ (X = S or Se) facilitated by simple photochemistry. Ultraviolet (UV) light (with humid) and laser exposure can reversibly oxidize and reduce rhenium disulfide (ReS₂) and rhenium diselenide (ReSe₂), respectively, yielding a pronounced doping effect with good control. Evidenced by Raman spectroscopy, dynamic force microscopy, transmission electron microscopy, and X‐ray photoelectron spectroscopy, the grafting and removal of covalently functionalized oxygen groups on the perfect vdW surfaces are confirmed. The optical and electrical properties can be thereby reversibly tunable in wide ranges. Such optical direct‐writing and rewritable capability via solvent/contaminant‐free approach for chemical doping are compelling in the coming era of 2D materials.

Efficient electrochemical exfoliation of MoS₂ is realized through a lateral inward oxidation reaction starting from a typical layer edge with a rapid depth penetration, ultimately forming a stable stacked few‐layer (two/three layers) structure. This stacked atomically thin MoS₂ shows enhanced electrocatalysis performance and surface‐enhanced Raman spectroscopy sensitivity.

Abstract

The production of atomically thin transition‐metal dichalcogenides (TMDs) has been investigated through various top‐to‐down exfoliation methods, such as mechanical and chemical exfoliation, while large‐scale chemical exfoliation is sluggish and needs over ten hours to achieve atomically thin TMDs. Herein, a new strategy is reported for exfoliating bulk MoS₂ into two/three‐layer flakes within tens of seconds through a mild electrochemical treatment. This exfoliation method is driven by a lateral inward oxidation reaction starting from the typical layer edge with a rapid depth penetration, whereby a stacked few‐layer (two/three layers) structure is ultimately formed. This efficient reaction process is monitored based on an individual MoS₂ on‐chip device combined with in situ Raman and cross‐sectional scanning transmission electron microscopy, and the uniformity of thickness is demonstrated. This preferentially initiated method can be also extended to produce few‐layer MoSe₂ and the selective extraction mechanism is assumed to be related to intrinsic layer‐dependent energy band properties. Moreover, the special reassembled few‐layer MoS₂ possesses great performance as functional materials in electrocatalysis (127 mV overpotential for hydrogen evolution reaction) and surface‐enhanced Raman spectroscopy (10⁵ enhancement factor). These results illustrate the broad prospects of the reassembled few‐layer MoS₂ for optics, catalysis, and sensors.

A 2D zinc‐based metal–organic frameworks (MOFs) with plenty of active sites are prepared through a molecular self‐assembly strategy and used to solve the incompatibility between MOFs and perovskite films. The tunable crystallographic orientation and functionalized framework of this material are considered for regulating the photovoltaic performance and stability of perovskite solar cells.

Abstract

Perovskite degradation induced by surface defects and imperfect grain boundaries of films seriously damages the performance of perovskite solar cells (PSCs). Meanwhile, conventional organic molecules cannot maintain the long‐time passivation effects under the stimulation of external environmental factors. Here, efficient and stable grain passivation in perovskite films is realized by preparing formic acid‐functionalized 2D metal–organic frameworks (MOFs) as the terminated agent. Through robust interactions between exposed active sites and PbI₂, the 2D MOFs tightly caps the surface of PbI₂‐terminated perovskite grains to stabilize the perovskite phases and aids the adhesion of adjacent grains. The MOFs mainly distributed at the grain boundaries of the perovskite film is directly observed at the microscopic scale. The modified perovskite films have regular morphology, lower defect density, and superior optoelectronic properties. Benefiting from the suppressed charge recombination and faster charge extraction, a power conversion efficiency of 21.28% is achieved for the best‐performing PSC device. The unencapsulated PSCs with the MOFs modification maintain 88% and 81% of their initial efficiency after 750 h heating at 85 °C under N₂ atmosphere and more than 1000 h storage in ambient environment (25 °C, RH ≈ 40%), respectively.

Atomic‐scale engineering of 2D layered catalysts via a heteroepitaxial conversion process using metal‐organic chemical vapor deposition has proven to be very efficient in enhancing the quality of the electrocatalysts. The out‐of‐plane deformation of the 2D WS₂/WTe₂ heterostructure driven by lattice coherency could enhance intrinsic catalytic activity and long‐term durability of the electrocatalysts under continuous operation.

Abstract

The structural engineering of 2D layered materials is emerging as a powerful strategy to design catalysts for high‐performance hydrogen evolution reaction (HER). However, the ultimate test of this technology under typical operating settings lies in the reduced performance and the shortened lifespan of these catalysts. Here, a novel approach is proposed to design efficient and robust HER catalysts through out‐of‐plane deformation of 2D heterojunction using metal‐organic chemical vapor deposition. High‐yield, single‐crystalline WTe₂ nanobelts are used as an epitaxial template for their coherent conversion to WS₂. During the conversion process, the WTe₂/WS₂ heterostructure containing both lateral and vertical junctions are achieved by coherent heteroepitaxial stacking despite differences in symmetry. The lattice coherency drives out‐of‐plane deformation of heteroepitaxially grown WS₂. The increase in the effective surface area and decrease in the electron‐transfer resistance across the 2D heterojunctions in turn enhances the HER performance as well as the long‐term durability of these electrocatalysts.

The two-dimensional layered material MoTe 2 has aroused extensive research interests in its rich optoelectronic properties in various phases. One property of particular interest is the circular photogalvanic effect (CPGE): a conventional second order nonlinear optical effect that is related to the chirality of materials. It has been demonstrated in T d -MoTe 2 , a type-II topological Weyl semimetal candidate, while it has been unclear so far whether it exists in the semimetallic 1T’ phase, another interesting phase that hosts a quantum spin hall state. In this article, we report a clear experimental observation of in-plane CPGE in 1T’-MoTe 2 . The observation is confirmed under various experimental designs with excitation by normally incident mid-infrared laser, and we find it to be related to an in-plane internal DC electric field. We attribute the circular photogalvanic response to a third-order nonlinear optical effect involving this DC el...

Herein, we proposed a dimension-increasing regulation strategy to realize the dimensionality engineering of perovskite from two-dimensional (2D) nanoplates (NPs) to quasi-two-dimensional (Q-2D) nanocrystals (NCs), and successfully prepared 2D (PEA) 2 PbBr 4 NPs (PEA (phenylethylammonium) = C 8 H 9 NH 3 ), Q-2D (PEA) 2 CsPb 2 Br 7 (1) and (PEA) 2 Cs 2 Pb 3 Br 10 (2) NCs. The photoluminescence dynamics changes from 2D (PEA) 2 PbBr 4 NPs to Q-2D (1), (2) NCs by performing the time-resolved nanosecond transient absorption (NTAS) measurement for our perovskites. Compared with 2D (PEA) 2 PbBr 4 NPs, we discovered for the first time that the electronic spectral redshift is intrinsic property of Q-2D NCs, which is caused by excitons transition to higher dimensionality. And the photoluminescence quantum yields (PLQYs) of Q-2D (1), (2) NCs is...

We study the stability and electronic structure of magic-angle twisted bilayer graphene on the hexagonal boron nitride (TBG/BN). Structural relaxation has been performed for commensurate supercells of the heterostructures with different twist angles ( ##IMG## [http://ej.iop.org/images/2053-1583/8/2/025025/tdmabddcbieqn1.gif] {$\theta^{^{\prime}}$} ) and stackings between TBG and BN. We find that the slightly misaligned configuration with ##IMG## [http://ej.iop.org/images/2053-1583/8/2/025025/tdmabddcbieqn2.gif] {$\theta^{^{\prime}} = 0.54^\circ$} and the AA/AA stacking has the globally lowest total energy due to the constructive interference of the moiré interlayer potentials and thus the greatly enhanced relaxation in its 1 × 1 commensurate supercell. Gaps are opened at the Fermi level ( E F ) for small supercells with the stackings that enable strong breaking of the C 2 symmetry in the atomic ...

Nature Nanotechnology, Published online: 11 February 2021; doi:10.1038/s41565-021-00848-w

The realization of atomically flat vertical 2D perovskite heterojunctions offers a novel materials platform that reveals the mechanism of anionic diffusion in 2D perovskites.

Nature Nanotechnology, Published online: 15 February 2021; doi:10.1038/s41565-021-00846-y

On-chip, long-distance entanglement of spin qubits in semiconductors could enable connectivity of quantum core units for networked quantum computing. The moving trapping potential of a surface acoustic wave can subsequently displace two entangled spins while preserving entanglement over a separation of 6 μm.

Nature Nanotechnology, Published online: 25 February 2021; doi:10.1038/s41565-021-00861-z

Interferometers can probe the wave-nature and exchange statistics of indistinguishable particles. Quantum Hall interferometers from graphite-encapsulated graphene heterostructures now enable the observation of the Aharonov–Bohm effect and of robust fractional quantum Hall states.