Jing Zhang

Nature Nanotechnology, Published online: 07 June 2021; doi:10.1038/s41565-021-00932-1

Van der Waals heterostructures serve as a platform for memory devices with ultra-fast writing speeds and non-volatile retention times, motivating their use in integrated circuits and systems.

Nature Nanotechnology, Published online: 03 June 2021; doi:10.1038/s41565-021-00921-4

MoS2/hBN/graphene van der Waals heterostructures with a clean interface and optimized barrier height and gate coupling ratio enable the realization of ultrafast non-volatile flash memory.

Nature Nanotechnology, Published online: 07 June 2021; doi:10.1038/s41565-021-00925-0

Among the candidates for large-scale quantum computing devices, silicon-based spin qubits offer an outstanding nanofabrication capability for scaling-up. In an array of three spin qubits in silicon, high-fidelity state preparation and control enable the creation of a three-qubit Greenberger–Horne–Zeilinger state with 88% state fidelity.

Nature Nanotechnology, Published online: 10 June 2021; doi:10.1038/s41565-021-00922-3

Persistent luminescence is a promising bioimaging technique that is not affected by background autofluorescence, but its in vivo application is challenged by the fact that the materials currently available are activated by high-energy light, with emission in the ultraviolet and visible spectral windows. In this paper the authors engineer X-ray activated, lanthanide-based nanoparticles with a tunable emission in the biologically relevant NIR-II spectral region, which allows high-contrast, multimodal in vivo deep-tissue organ imaging.

The decoration of atomically thin metal flakes on two-dimensional (2D) material membranes to impart intriguing properties for applications such as sensors and catalysis has attracted tremendous interest. Here, we report the formation of atomically thin Mo nanoflakes on a molybdenum disulfide monolayer (ML-MoS 2 ) via a ‘self-feeding’ process using in situ transmission electron microscopy. Driven by energetic e-beam irradiation and thermal excitation, metallic Mo atoms preferentially segregate out and aggregate around mirror twin boundaries in the host MoS 2 ML, which then assemble into metallic nanoflakes: the associated dynamic process captured at the atomic scale. The Mo atoms constituting the nanoflakes tend to sit on the Mo-top and S-top sites if they are viewed as absorbed atoms with respect to the ML-MoS 2 substrate, which is further confirmed by theoretical calculations. Density functional theory calculations reveal that the entire syst...

2D van der Waals heterostructures (vdWHs) based metal-insulator-semiconductor (MIS) photodetectors are currently attracting enormous research interest. The control of barrier height in vdWHs MIS photodetectors is investigated here to break the photodetection limit of high barrier height. The graphene/h-BN/SnS₂ device with ignorable barrier height shows the best photodetection performance compared to the other common 2D semiconductors devices.

Abstract

The vertical metal-insulator-semiconductor (MIS) photodetectors based on van der Waals heterostructures (vdWHs), fabricated by rationally stacking different layers without the limit of lattice-match, have attracted broad interest due to their wide wavelength monitoring range, high responsivity, high detectivity, and fast response. Here, for the first time, the control of barrier height in vdWHs MIS photodetectors is systematically investigated. Optimizing semiconducting and insulating layers enables lowering the hole barrier height to achieve a high performance of the device. Graphene/hexagonal boron nitride (h-BN)/SnS₂ device shows the best photodetection performance compared to the other common 2D semiconductors. The lowest barrier height ensures that the photo-induced holes transfer efficiently to the graphene electrode and the dark current is highly suppressed by the h-BN layers. Consequently, the graphene/h-BN/SnS₂ MIS photodetectors have a high photoresponsivity of 2 A W⁻¹, a high detectivity of 10¹³ Jones, and a photocurrent/dark current ratio of 5.2 × 10⁵ at a low applied bias of −0.6 V. The highest detectivity reaches 9.6 × 10¹³ Jones which is 100–1000 times greater than previously reported vdWHs MIS photodetectors.

2D van der Waals (vdW) magnets provide a unique platform for engineering Néel/Bloch-type skyrmions with the addition/exclusion of heavy metal capping layers. However, the unambiguous identification of the Néel/Bloch-type twists inherent to vdW magnets remains elusive. This work measures different magnetic domain q -vector alignments under in-plane magnetic fields and identifies the Néel- and Bloch-type twists existing in the heterostructure Fe₃GeTe₂ and the FGT thin plate, respectively.

Abstract

The advent of ferromagnetism in 2D van der Waals (vdW) magnets has stimulated high interest in exploring topological magnetic textures, such as skyrmions for use in future skyrmion-based spintronic devices. To engineer skyrmions in vdW magnets by transforming Bloch-type magnetic bubbles into Néel-type skyrmions, a heavy metal/vdW magnetic thin film heterostructure has been made to induce interfacial Dzyaloshinskii–Moriya interaction (DMI). However, the unambiguous identification of the magnetic textures inherent to vdW magnets, for example, whether the magnetic twists (skyrmions/domain walls) are Néel- or Bloch-type, is unclear. Here we demonstrate that the magnetic twists can be tuned between Néel and Bloch-type in the vdW magnet Fe₃GeTe₂ (FGT) with/without interfacial DMI. We use an in-plane magnetic field to align the modulation wavevector q of the magnetizations in order to distinguish the Néel- or Bloch-type magnetic twists. We observe that q is perpendicular to the in-plane field in the heterostructure (Pt/oxidized-FGT/FGT/oxidized-FGT), while q aligns at a rotated angle with respect to the field direction in the FGT thin plate thinned from bulk. We find that the aligned domain wall twists hold fan-like modulations, coinciding qualitatively with our computational results.

2D transition metal borides (MBenes) have emerged as promising post-MXene materials. This work provides signposts for the rational design and development of novel MBene-based biotechnological solutions. Latest milestones are discussed as an inspiration for future research approaches using MBenes. A detailed understanding of MBenes’ bio-recognition, responses, and material-property relationship is essential to explore their biological potential and ensure their safe application.

Abstract

2D transition metal borides (MBenes) have emerged as promising post-MXene materials with potential application in various biotechnological fields. Although they possess prospective bioactive properties due to boron in their structure, the experience gained from MXenes shows that an in-depth understanding of their biological recognition and response as well as the exploration of their biological applications are highly challenging. This makes the identification of the most promising 2D MBenes for future biological research and final industrial applications rather complicated. Herein, MBenes are differentiated from MXenes and further untangled for their bioactivity-generating features. It is expected that MBenes’ positive or negative biological impact on living organisms and different types of cells connect with their morphological, structural and physicochemical features in the context of relevant environments. Necessary toxicological data are also highlighted, which are key aspects to enable MBenes’ safe application in biotechnology and nanomedicine. Furthermore, a perspective for the rational development and design of novel biotechnological solutions based on MBenes is provided, which will meet the legal safety requirements for nanomaterials. In this regard, this work is an unprecedented contribution toward strategies for regulatory development for MBene/MXene-type nanomaterials. It provides an inspiration for future biotechnological and nanotoxicological approaches using MBenes.

In article number 2011083, Congli He, Guangyu Zhang, and co-workers report an all-2D materials two-terminal floating-gate memory as an artificial synapse device for high energy-efficient neuromorphic computing. It exhibits linear and symmetric weight update behaviors with high reliability and tunability. A large number of states up to 3000, high switching speed of 40 ns, and low energy consumption of 18 fJ for a single pulse event are realized, demonstrating great potential for high-speed and low-power neuromorphic computing applications.

A novel scheme for a chiral detector based on GaAsN is demonstrated allowing for the simultaneous detection of the light intensity and degree of circular polarization at room temperature. It relies on the engineering of deep paramagnetic defects displaying a giant spin dependent recombination, effectively providing chirality to these conventional compounds and removing the need for any additional optical elements.

Abstract

The detection of light helicity is key for various applications, from drug production to optical communications. However, the light helicity direct measurement is inherently impossible with conventional photodetectors based on III–V or IV–VI non-chiral semiconductors. The prior polarization analysis by often moving optical elements is necessary before light is sent to the detector. A method is here presented to effectively give the conventional dilute nitride GaAs-based semiconductor epilayer a chiral photoconductivity. The detection scheme relies on the giant spin-dependent recombination of conduction electrons and the accompanying spin polarization of the engineered defects to control the conduction band. As the conduction electron spin polarization is, in turn, intimately linked to the excitation light polarization, the light polarization state and intensity can be determined by a simple conductivity measurement. This approach, removing the need for any optical elements in front of a non-chiral detector, could offer easier integration and miniaturization. This new chiral photodetector could potentially operate in a spectral range from the visible to the infra-red using (InGaAl)AsN alloys or ion-implanted nitrogen-free III–V compounds.

Nature Nanotechnology, Published online: 01 July 2021; doi:10.1038/s41565-021-00934-z

A single or multilayer graphene veil grown by chemical vapour deposition can be used to protect artworks against colour fading, with a protection factor of up to 70%.

The imitation of synaptic plasticity in artificial neuromorphic devices has been widely realized based on memristors, transistors and ion devices. This development of artificial synaptic devices is expected to open up a new era for neuromorphic computing. However, the complicated functions in biological synapse are dependent on the dynamic neural activities with modulated plasticity, which is still very difficult to emulate at the device level. Here, an artificial synaptic transistor based on WSe 2 /graphene van der Waals heterojunction is demonstrated with both electrically and optically modulated synaptic plasticity. By changing the polarity of applied V gs and V ds as well as superimposed gate voltage spikes, both excitatory and inhibitory synaptic plasticity can be realized in a single device. Moreover, due to the asymmetric optical response of WSe 2 /graphene heterojunction, optical modulation on hysteretic behaviors is ...

Van der Waals (vdW) integration based on 2D materials provides a new solution for high-performance infrared photodetectors. In this review, recent progress in vdW integration-based infrared photodetectors is presented, focusing on 2D/nD (n = 0, 1, 2, 3) vdW integration, and the band engineering and performance of the photodetectors are discussed in detail.

Abstract

Infrared photodetectors have been widely applied in various fields, including thermal imaging, biomedical imaging, and communication. Van der Waals (vdW) integration based on 2D materials provides a new solution for high-performance infrared photodetectors due to the versatile device configurations and excellent photoelectric properties. In recent years, great progress has been made in infrared photodetectors based on vdW integration. In this review, recent progress in vdW integration-based infrared photodetectors is presented. First, the working mechanisms and advantages of photodetectors with different structures and band alignments are presented. Then, the recent progress of vdW integration-based infrared photodetectors is reviewed, focusing on 2D/nD (n = 0, 1, 2, 3) vdW integration, and the band engineering as well as the performance of the photodetectors are discussed in detail. Finally, a summary is delivered, and the challenges and future directions of vdW integration-based infrared photodetectors are provided.

Two Xene heterostructures based on two well-established configurations, silicene-on-Ag(111) and stanene-on-Ag(111), are presented. Various in situ and ex situ analysis, along with theoretical studies, confirm that one Xene layer can act as a suitable template for the other reciprocal Xene layer. This demonstration of the Xene heterostructure opens a door to a new atomic-scale materials engineering.

Abstract

The synthesis of new Xenes and their potential applications prototypes have achieved significant milestones so far. However, to date the realization of Xene heterostructures in analogy with the well known van der Waals heterostructures remains an unresolved issue. Here, a Xene heterostructure concept based on the epitaxial combination of silicene and stanene on Ag(111) is introduced, and how one Xene layer enables another Xene layer of a different nature to grow on top is demonstrated. Single-phase (4 × 4) silicene is synthesized using stanene as a template, and stanene is grown on top of silicene on the other way around. In both heterostructures, in situ and ex situ probes confirm layer-by-layer growth without intercalations and intermixing. Modeling via density functional theory shows that the atomic layers in the heterostructures are strongly interacting, and hexagonal symmetry conservation in each individual layer is sequence selective. The results provide a substantial step toward currently missing Xene heterostructures and may inspire new paths for atomic-scale materials engineering.

Ti₃C₂T _x MXene nanosheets are used as a fast electron/potassium-ion dual-conductor to construct the framework of all-integrated graphite nanoflake/MXene (GNFM) electrodes with improved electrochemical performances by exploiting unique MXene properties such as 2D morphology, metallic conductivity, and good flexibility. All-integrated GNFM electrodes designed with MXene as multifunctional frameworks provide a new paradigm for producing efficient potassium storage anodes.

Abstract

Graphite anodes show great potential for potassium storage, however, their capacity fades quickly owing to substantial interlayer expansion/shrinkage (i.e., up to 60%) induced structural degradation. Here, Ti₃C₂T _x MXene nanosheets are used as a fast electron/potassium-ion dual-function conductor to construct the framework of all-integrated graphite nanoflake (GNF)/MXene (GNFM) electrodes. The continuous MXene framework constructs a 3D channel for fast electron/potassium-ion transfer and endows GNFM electrodes with a high structural stability. Owing to this unique MXene framework, GNFM electrodes exhibit much enhanced potassium storage performances than that of the conventional polymer-bonded electrodes even at high mass loadings. Moreover, GNFM electrodes also show impressive cyclability in non-flammable electrolytes and are further used as anodes to assemble novel non-flammable potassium-ion capacitors that show an excellent cyclability and high energy/power densities (113.1 Wh kg^–1 and 12.2 kW kg^–1). New insights into phase transition mechanism in GNFM electrodes are verified by operando XRD. Density functional theory calculations demonstrate that MXene can promote electron transfer and potassium diffusion in the heterointerface between GNF and MXene. Therefore, the results demonstrate that all-integrated GNFM electrodes designed with MXene as multifunctional frameworks provide a new paradigm for producing efficient potassium storage anodes.

In article number 2010104, Eben Alsberg and co-workers report the engineering of 4D high cell density constructs (1.0 × 10⁸ cells mL⁻¹) that change their shape over time by exploiting temporal differences in swelling rates between two biodegradable and cytocompatible materials. This strategy presents a paradigm changing platform technology that could significantly impact 4D tissue-engineered therapeutics for the treatment of damaged tissues, investigation of questions in developmental biology, and formation of tissue models for drug testing.

2D arsenic-phosphorus (AsP) nanosheets are constructed for photoacoustic (PA) imaging-guided synergistic hyperthermia and photo-chemotherapy of tumors. Strong photothermal-conversion efficiency (37.6%) in NIR-II of AsP nanosheets not only bestows them with desirable contrast-enhanced PA properties, but also achieves high-performance tumor hyperthermia, which further synergistically triggers in-situ transformation from low toxic/nontoxic AsP nanosheets into highly toxic arsenic species, exerting a strong anti-cancer effect.

Abstract

As an anticancer drugs, arsenic trioxide (ATO) has been certified to efficiently treat refractory acute promyelocytic leukemia (APL). Unfortunately it suffers from limited therapeutic potency for solid tumors due to its in vivo restricted administration dose and rapid renal clearance. Herein, distinct 2D arsenic-phosphorus (AsP) nanosheets are engineered by adopting an alloy strategy followed by exfoliation, which can confine toxic arsenic into AsP crystals, thus significantly improving the biosafety and biocompatibility of arsenic-based chemotherapeutic drugs. Of particular note, the high light absorption and strong photothermal-conversion efficiency (37.6%) in the second near infrared biowindow (NIR-II) of AsP nanosheets not only endow them with desirable contrast-enhanced photoacoustic imaging properties, but also achieve efficient local tumor hyperthermia, which further synergistically triggers the in-situ transformation from low toxic/nontoxic AsP crystals into highly toxic arsenic species, exerting a strong arsenic-mediated antineoplastic effect. Both in vitro and in vivo data verify the synergy between photonic therapy in NIR-II and enhanced chemotherapy as enabled by AsP nanosheets, paving the way for efficient nanomedicine-enabled arsenic-based chemotherapeutic tumor treatment.

This work provides a facile strategy for efficient high-temperature thermal camouflage using ultrathin MXene films/coatings; the performance of the MXene films/coatings is almost comparable to that of stainless steel and superior to that of other 2D nanomaterials as well as other reported film-/coating-based thermal camouflage materials/systems. The results of this work demonstrate the great promise of MXene materials for thermal camouflage, infrared stealth, counter-surveillance, and security protection.

Abstract

Thermal camouflage has attracted increasing attention owing to the rapid development of infrared (IR) surveillance technologies. Various materials and systems have been developed to date, but the realization of high-temperature thermal camouflage using ultrathin film/coating remains a great challenge; this is of great significance, especially for IR stealth in military equipment. This work demonstrates a series of ultrathin Ti₃C₂T _x MXene films (as low as 1 µm) with superior high-temperature indoor/outdoor thermal camouflage performance: wide camouflage temperature range (from below −10 °C to over 500 °C), large reduction in radiation temperature (exceeding 300 °C for objects with temperatures over 500 °C), long-term high-temperature or fire stability, multifunctionality including disguised Joule heating capability, and high electromagnetic interference shielding efficiency. The superior high-temperature thermal camouflage performance of the ultrathin MXene film is attributed to its low mid-IR emissivity (0.19), which is comparable to that of stainless steel but far below that of other 2D nanomaterials, such as graphene. The multifunctional ultrathin MXene films prepared through simple vacuum-assisted filtration provide a feasible method for efficient high-temperature thermal camouflage using ultrathin films, demonstrating the great promise of MXene materials for thermal camouflage, IR stealth, counter-surveillance, and security protection.

The effective reduction of band overlap with nontrivial helical edge states is realized in semimetallic monolayer 1T′-MoTe₂ with proximity to a 3D topological insulator Bi₂Te₃. The charge transfer and interlayer interactions are theoretically and experimentally verified to be vital for the enhancements of spin orbital coupling, and thus the effective opening of the quantum spin Hall band gap of monolayer 1T′-MoTe₂.

Abstract

Monolayer (ML) 1T′-MoTe₂ has attracted intensive interest as a fascinating quantum spin Hall (QSH) insulator. However, there are two critical aspects impeding its exploration and potential applications of QSH effects. One is its semimetallic feature with a negative band gap, leading to nontrivial edge channels annihilated by the bulk states. The other is its fabrication always accompanied by a mixed phase of 1T′ and 2H. Based on first-principles calculations, it is shown that the large work-function difference results in strong interlayer interactions and proximity effects in ML 1T′-MoTe₂ via interfacing a 3D topological insulator Bi₂Te₃, facilitating the realization of pure 1T′ phase and even the band gap opening. It is further verified that the epi-grown ML 1T′-MoTe₂ on Bi₂Te₃ is nearly in single phase. Furthermore, the measurements of angle resolved photoemission spectroscopy and scanning tunneling spectroscopy confirm the obvious separated-tendency of conduction and valence bands as well as the strong metallic edge states in ML 1T′-MoTe₂. The results also reveal the nontrivial band topology in ML 1T′-MoTe₂ is preserved in 1T′-MoTe₂/Bi₂Te₃ heterostructure. This work offers a promising candidate to realize QSH effects and provides guidance for controlling the nontrivial band gap opening by proximity effects in van der Waals engineering.

An investigation of the nanocrystalline structure of different 2D platinum diselenide (PtSe₂) thin films grown via thermally assisted conversion at low temperatures in a scalable manner is presented. The structural properties determined using scanning transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy exhibit a strong correlation to the electronic and piezoresistive properties extracted from fabricated devices.

Abstract

Platinum diselenide (PtSe₂) is a 2D material with outstanding electronic and piezoresistive properties. The material can be grown at low temperatures in a scalable manner, which makes it extremely appealing for many potential electronics, photonics, and sensing applications. Here, the nanocrystalline structure of different PtSe₂ thin films grown by thermally assisted conversion (TAC) is investigated and is correlated with their electronic and piezoresistive properties. Scanning transmission electron microscopy for structural analysis, X-ray photoelectron spectroscopy (XPS) for chemical analysis, and Raman spectroscopy for phase identification are used. Electronic devices are fabricated using transferred PtSe₂ films for electrical characterization and piezoresistive gauge factor measurements. The variations of crystallite size and their orientations are found to have a strong correlation with the electronic and piezoresistive properties of the films, especially the sheet resistivity and the effective charge carrier mobility. The findings may pave the way for tuning and optimizing the properties of TAC-grown PtSe₂ toward numerous applications.

Nature Nanotechnology, Published online: 17 June 2021; doi:10.1038/s41565-021-00919-y

A strain-gradient approach induced by the phase-change transition enables the observation of the flexo-photovoltaic effect in MoS2.

Nature Nanotechnology, Published online: 03 June 2021; doi:10.1038/s41565-021-00916-1

The existence of interlayer excitons with strong oscillator strength in bilayer MoS2 enables their electrical manipulation up to room temperature.