Jing Zhang

The transformation of a subwavelength nanostructured metasurface with an electric and magnetic response to a photonic bulk material is investigated from morphological and optical perspectives. Departing from a periodic structure, a randomized orientation and arrangement of the meta‐atoms is forced that preserves their magnetic and electric response. The material combines the advantages of materials fabricated with both top‐down and bottom‐up techniques.

Abstract

Artificial photonic nanomaterials made from densely packed scatterers are frequently realized either by top‐down or bottom‐up techniques. While top‐down techniques offer unprecedented control over achievable geometries for the scatterers, by trend they suffer from being limited to planar and periodic structures. In contrast, materials fabricated with bottom‐up techniques do not suffer from such disadvantages but, unfortunately, they offer only little control on achievable geometries for the scatterers. To overcome these limitations, a nanofabrication strategy is introduced that merges both approaches. A large number of scatterers are fabricated with a tailored optical response by fast character projection electron‐beam lithography and are embedded into a membrane. By peeling‐off this membrane from the substrate, scrambling, and densifying it, a bulk material comprising densely packed and randomly arranged scatterers is obtained. The fabrication of an isotropic material from these scatterers with a strong electric and magnetic response is demonstrated. The approach of this study unlocks novel opportunities to fabricate nanomaterials with a complex optical response in the bulk but also on top of arbitrarily shaped surfaces.

Charge-order–driven ferroelectrics are an emerging class of functional materials, distinct from conventional ferroelectrics, where electron-dominated switching can occur at high frequency. Despite their promise, only a few systems exhibiting this behavior have been experimentally realized thus far, motivating the need for new materials. Here, we use density-functional theory to study...

Seeding promoters facilitate the nucleation and growth of transition metal dichalcogenides in chemical vapor deposition (CVD). However, sophisticated roles of seeding promoter remain unclear. Here, adopting triangular-shaped crystal violet (CV) consisting of nonpolar and polar parts as the seeding promoter, we study the role of seeding promoter for the growth of molybdenum disulfide (MoS 2 ). We systematically control the geometrical configuration of CV on SiO 2 /Si substrate by changing the solvent polarity and find that it strongly affects the growth of monolayer or multilayer MoS 2 domains via CVD. Monolayer MoS 2 domains were predominantly grown on randomly lying-down CV configurations on SiO 2 /Si substrate, whereas multilayer MoS 2 domains are synthesized at concentrated polar parts in CV micelle on the substrate. Density functional theory calculations reveal that the initial nucleation step for the MoS 2 g...

The chemical and thermal stability of PdTe₂ is assessed by experiments and theory, with successive implementation in electronics. Remarkably, the responsivity of a PdTe₂‐based millimeter‐wave receiver is 13 and 21 times higher than similar devices based on black phosphorus and graphene in the same operational conditions, respectively. Moreover, the PdTe₂ surface is stable for one year, with only a sub‐nanometric TeO₂ skin formed after air exposure.

Abstract

Palladium ditelluride (PdTe₂) is a novel transition‐metal dichalcogenide exhibiting type‐II Dirac fermions and topological superconductivity. To assess its potential in technology, its chemical and thermal stability is investigated by means of surface‐science techniques, complemented by density functional theory, with successive implementation in electronics, specifically in a millimeter‐wave receiver. While water adsorption is energetically unfavorable at room temperature, due to a differential Gibbs free energy of ≈+12 kJ mol⁻¹, the presence of Te vacancies makes PdTe₂ surfaces unstable toward surface oxidation with the emergence of a TeO₂ skin, whose thickness remains sub‐nanometric even after one year in air. Correspondingly, the measured photocurrent of PdTe₂‐based optoelectronic devices shows negligible changes (below 4%) in a timescale of one month, thus excluding the need of encapsulation in the nanofabrication process. Remarkably, the responsivity of a PdTe₂‐based millimeter‐wave receiver is 13 and 21 times higher than similar devices based on black phosphorus and graphene in the same operational conditions, respectively. It is also discovered that pristine PdTe₂ is thermally stable in a temperature range extending even above 500 K, thus paving the way toward PdTe₂‐based high‐temperature electronics. Finally, it is shown that the TeO₂ skin, formed upon air exposure, can be removed by thermal reduction via heating in vacuum.

The proposed interconnection weakening strategy can effectively increase the sensitivity of graphene‐polymer composite fiber‐based strain sensors by replacing the panel‐inserting structure with a nanoball‐decorating frame. The obtained fibers show a high gauge factor of 87 and low detection limit of 0.01%, which also allows for the fabrication of wearable electronic fabrics with excellent performance.

Abstract

Wearable textile strain sensors that can perceive and respond to human stimuli are an essential part of wearable electronics. Yet, the detection of subtle strains on the human body suffers from the low sensitivity of many existing sensors. Generally, the inadequate sensitivity originates from the strong structural integrity of the sensors because tiny external strains cannot trigger enough variation in the conducting network. Inspired by the rolling friction where the interaction is weakened by decreasing interface area, porous fibers made of graphene decorated with nanoballs are prepared via a prolonged phase‐separation process. This novel structure confers the graphene fibers with high gauge factors (51 in 0–5% and 87 in 5–8%), which is almost 10 times larger than the same structures without nanoballs. A low detection limit (0.01% strain) and good durability (over 6000 circles) are obtained. By the virtue of these qualities, these fiber‐based textile sensors can recognize a pulse wave and eyeball movement in real‐time while keeping comfortable wearing sense. Moreover, by weaving such fibers, the electronic fabrics with a specially designed structure can distinguish the multilocation in real time, which shows great potential as wearable electronics.

An all‐inorganic flexible ferroelectric field effect transistor (FeFET) based on an epitaxial Pb(Zr_0.1Ti_0.9)O₃/ZnO heterostructure on a mica substrate is developed, which not only operates under a small voltage and thus consumes low power, but also shows robust FeFET performance under large bending deformation, extended bending cycling cycles, and high temperature operation at 200 °C.

Abstract

Flexible ferroelectric field effect transistors (FeFETs) with multiple functionalities and tunable properties are attractive for low power sensing, nonvolatile data storage, as well as emerging memristor applications such as artificial synapses, though the state‐of‐art flexible FeFETs based on organic materials possess low polarization, large coercivity, and high operating voltage, and suffer from poor thermal stability. Here, developed is an all‐inorganic flexible FeFET based on epitaxial Pb(Zr_0.1Ti_0.9)O₃/ZnO heterostructure on a mica substrate, which not only operates under a small voltage (±6 V) and thus consumes low power with an excellent on/off ratio of 10⁴ as well as retention characteristics, but also shows robust FeFET performance under large bending deformation (4 mm), extended bending cycling (500 cycles), and high temperature operation at 200 °C. Importantly, the FeFET characteristics depend on temperature, but not on temperature history, critical for operation under repeated thermal loading. The excellent mechanical flexibility and functional robustness of the flexible FeFET originate from the unique van der Waals bonded layer structure of mica, facilitating a small bending radius yet modest strain. This work demonstrates the great promise of mica as a universal platform to integrate complicated functional devices for flexible electronics, especially under harsh environment.

Nature Nanotechnology, Published online: 18 November 2019; doi:10.1038/s41565-019-0571-2

Synthesis of MoS2 on a silicon surface pre-treated with phosphine enables the growth of one-dimensional MoS2 nanocrystals with tunable dimensions and optical properties.

Nature Nanotechnology, Published online: 11 November 2019; doi:10.1038/s41565-019-0565-0

A comprehensive understanding of the magnetic phase diagram of atomically thin layered antiferromagnets is obtained by combining systematic tunnelling magnetoconductance measurements with theoretical modelling.

Nitrogen‐doped MoSe₂/graphene composites prepared via a biotemplated strategy are employed as highly effective anodes for potassium‐ion hybrid capacitors, manifesting high energy/power density (119 Wh kg⁻¹/7212 W kg⁻¹) and long lifespan.

Abstract

Potassium‐ion hybrid capacitors (KICs) reconciling the advantages of batteries and supercapacitors have stimulated growing attention for practical energy storage because of the high abundance and low cost of potassium sources. Nevertheless, daunting challenge remains for developing high‐performance potassium accommodation materials due to the large radius of potassium ions. Molybdenum diselenide (MoSe₂) has recently been recognized as a promising anode material for potassium‐ion batteries, achieving high capacity and favorable cycling stability. However, KICs based on MoSe₂ are scarcely demonstrated by far. Herein, a diatomite‐templated synthetic strategy is devised to fabricate nitrogen‐doped MoSe₂/graphene (N‐MoSe₂/G) composites with favorable pseudocapacitive potassium storage targeting a superior anode material for KICs. Benefiting from the unique biomorphic structure, high electron/K‐ion conductivity, enriched active sites, and the conspicuous pseudocapacitive effect of N‐MoSe₂/G, thus‐derived KIC full‐cell manifests high energy/power densities (maximum 119 Wh kg⁻¹/7212 W kg⁻¹), outperforming those of recently reported KIC counterparts. Furthermore, the potassium storage mechanism of N‐MoSe₂/G composite is systematically explored with the aid of first‐principles calculations in combination of in situ X‐ray diffraction and ex situ Raman spectroscopy/transmission electron microscopy/X‐ray photoelectron spectroscopy.

2D ferromagnetic Fe₃GeTe₃ has the potential to be an excellent oxygen evolution reaction (OER) electrocatalyst, as demonstrated in this article. The self‐reduction of surface hydroxyl into water plays a crucial role in lowering the overpotential. This work not only reveals new mechanisms for OER, but also opens the door for utilizing 2D ferromagnets in the field of energy storage and conversion.

Abstract

Fe₃GeTe₂ is a water‐ and air‐stable, metallic, and layered material. Very recently, few‐layer and single‐layer Fe₃GeTe₂ have been successfully exfoliated from its bulk and revealed as 2D ferromagnets (Nature 2018, 563, 94; Nat. Mater. 2018, 17, 778). Here, the basal plane of Fe₃GeTe₂ is demonstrated to be of high electrocatalytic activity towards oxygen evolution reaction (OER) without resorting to any chemical modifications, by means of systematic density functional theory computations. The Fe₃GeTe₂ nanosheet preserves the metallic character of the bulk, and its 2D layered structure provides abundant exposed active sites to catalyze OER. All these unique characteristics suggest that the Fe₃GeTe₂ nanosheet may be an excellent catalyst for electrochemical OER. More importantly, it is found that the self‐reduction of surface hydroxyl into water can significantly reduce the overpotential for OER, which greatly boosts the OER activity. This work not only reveals new mechanisms for OER but also opens the door for the application of emerging 2D ferromagnets in the field of energy storage and conversion.

Ultrathin 2D‐layered polymeric macrocycle membranes consisting of amino‐cyclodextrin are prepared via interfacial polymerization in mild condition. The membrane is chemically robust and exhibits excellent separation performance for organic solvent nanofiltration, both with nonpolar and polar solvents. Interestingly, this new membrane type can discriminate between molecules with nearly identical molecular weights but different shapes.

Abstract

Synthetic membranes with a high selectivity for demanding molecular separations and high permeance have a large potential for the reduction of energy consumption in separation processes. Herein, for the first time, the fabrication of an ultrathin layered macrocycle membrane for molecular separation in organic solvent nanofiltration using per‐6‐amino‐β‐cyclodextrin as a monomer for membrane manufacturing by interfacial polymerization is reported. Compared to a regular nonfunctionalized cyclodextrin, a higher reactivity is observed, enabling a very fast membrane formation under mild conditions. The formed membrane is composed of a layered structure of polymerized cyclodextrin, which shows high stability in different organic solvents. The membrane exhibits excellent separation performance for organic solvent nanofiltration, both with nonpolar and polar solvents. Most importantly, this new membrane type can discriminate between molecules with nearly identical molecular weights but different shapes. The unmatched high permeance and shape selectivity of the membranes can be attributed to the ultralow thickness, controlled microporosity, as well as the layered macrocycle structure, which makes the membranes promising for high‐performance molecular separation in the chemical and biochemistry industry.

Heterojunction tunnel field effect transistors (TFETs) based on MoS₂/MoTe₂ are fabricated by placing individual gates below the contact regions to suppress the Schottky barrier's influence on band‐to‐band tunneling current. The work reports a detailed study on the influence of source/drain contacts, gate architecture, and impact of multiple layers in conjunction with quantum transport simulations on 2D TFET performance.

Abstract

2D transition metal dichalcogenide based van der Waals materials are promising candidates to realize tunnel field effect transistors (TFETs) with a steep subthreshold swing (SS) for low‐power applications. Their atomically flat, self‐passivated layers offer potentially defect free interlayer tunneling. There are still several issues that need to be addressed to experimentally achieve a steep SS, e.g., the Schottky contacts, impact of thick layers, and device architecture with respect to gate configuration. This paper resolves these challenges by experimentally demonstrating MoS₂/MoTe₂ TFETs and their electrical characteristics, in conjunction with ab initio simulations and surface Kelvin probe microscopy. The Schottky barrier's effect at the contact regions are isolated by fabricating individual buried gates below the contacts. Devices with different top and bottom gate configurations are produced to understand the impact of gate placement on the heterostructure characteristics. Quantum transport simulations are performed on MoS₂/MoTe₂ multilayer stack to evaluate the impact of multiple layers on TFET performance, effect of gate placement, and the mechanism behind indirect tunneling over the heterojunction region. This work highlights the influence of the Schottky contacts, multiple layers and the role of different gate configurations on the band‐to‐band tunneling phenomenon in 2D heterojunction TFETs.

The proposed interconnection weakening strategy can effectively increase the sensitivity of graphene‐polymer composite fiber‐based strain sensors by replacing the panel‐inserting structure with a nanoball‐decorating frame. The obtained fibers show a high gauge factor of 87 and low detection limit of 0.01%, which also allows for the fabrication of wearable electronic fabrics with excellent performance.

Abstract

Wearable textile strain sensors that can perceive and respond to human stimuli are an essential part of wearable electronics. Yet, the detection of subtle strains on the human body suffers from the low sensitivity of many existing sensors. Generally, the inadequate sensitivity originates from the strong structural integrity of the sensors because tiny external strains cannot trigger enough variation in the conducting network. Inspired by the rolling friction where the interaction is weakened by decreasing interface area, porous fibers made of graphene decorated with nanoballs are prepared via a prolonged phase‐separation process. This novel structure confers the graphene fibers with high gauge factors (51 in 0–5% and 87 in 5–8%), which is almost 10 times larger than the same structures without nanoballs. A low detection limit (0.01% strain) and good durability (over 6000 circles) are obtained. By the virtue of these qualities, these fiber‐based textile sensors can recognize a pulse wave and eyeball movement in real‐time while keeping comfortable wearing sense. Moreover, by weaving such fibers, the electronic fabrics with a specially designed structure can distinguish the multilocation in real time, which shows great potential as wearable electronics.

A greatly enhanced photocatalytic performance is mainly attributed to the zinc vacancy (V_Zn) and unique 3D hierarchical structure. Introducing V_Zn into 3D hierarchical ZnIn₂S₄ increases the light response range, accelerates carrier separation and transport, provides more surface active sites, so‐called "hitting three birds with one stone" to enhance photocatalytic efficiency.

Abstract

Zinc vacancy (V_Zn) is successfully introduced into 3D hierarchical ZnIn₂S₄ (3D‐ZIS). The photo‐electrochemical experiments demonstrate that the charge separation and carrier transfer are more efficient in the 3D‐ZIS with rich V_Zn. Of note, for the first time, it is found that V_Zn can decrease the carrier transport activation energy (CTAE), from 1.14 eV for Bulk‐ZIS (Bulk ZnIn₂S₄) to 0.93 eV for 3D‐ZIS, which may provide a feasible platform for further understanding the mechanism of photocatalytic CO₂ reduction. In situ Fourier transform infrared (FT‐IR) results reveal that the presence of rich V_Zn ensures CO₂ chemical activation, promoting single‐electron reduction of CO₂ to CO₂ ⁻. In addition, in situ FT‐IR and CO₂ temperature programmed desorption results show that V_Zn can promote the formation of surface hydroxyl. To the best of current knowledge, there are no reports on the photoreduction of CO₂ simply by virtue of 3D‐ZIS with V_Zn and few literature reports on the photocatalytic reduction of CO₂ concerned with CTAE. Additionally, this work finds that surface hydroxyl may play a crucial role in the process of CO₂ photoreduction. The work may provide some novel ways to ameliorate solar energy conversion performance and a better understanding of photoreaction mechanisms.

Polymer‐based organic field‐effect transistors (OFETs) with enhanced field‐effect mobility are successfully fabricated with small device‐to‐device variation using highly hydrophobic nanogrooved gate dielectric surfaces. The OFETs exhibit potential high operational stability. Spin coating of polymeric semiconductor solution onto the highly hydrophobic channel regions is enabled by appropriate patterning of hydrophobic–hydrophilic surface regions.

Abstract

In this study, polymer‐based organic field‐effect transistors (OFETs) that exhibit alignment‐induced mobility enhancement, very small device‐to‐device variation, and high operational stability are successfully fabricated by a simple coating method of semiconductor solutions on highly hydrophobic nanogrooved surfaces. The highly hydrophobic nanogrooved surfaces (water contact angle >110°) are effective at inducing unidirectional alignment of polymer backbone structures with edge‐on orientation and are advantageous for realizing high operational stability because of their water‐repellent nature. The dewetting of the semiconductor solution is a critical problem in the thin film formation on highly hydrophobic surfaces. Dewetting during spin coating is suppressed by surrounding the hydrophobic regions with hydrophilic ones under appropriate designs. For the OFET array with an aligned terrace‐phase active layer of poly(2,5‐bis(3‐hexadecylthiophene‐2‐yl)thieno[3,2‐b]thiophene), the hole mobility in the saturation regime of 30 OFETs with channel current direction parallel to the nanogrooves is 0.513 ± 0.018 cm² V⁻¹ s⁻¹, which is approximately double that of the OFETs without nanogrooves, and the intrinsic operational stability is comparable to the operational stability of amorphous‐silicon field‐effect transistors. In other words, alignment‐induced mobility enhancement and high operational stability are successfully achieved with very small device‐to‐device variation. This coating method should be a promising means of fabricating high‐performance OFETs.

Controlling the dynamic responses of different ordered phases has stimulated extensive research interests. Here, the implementation of a charge‐density‐wave (CDW) for terahertz detection is reported and its extremely high sensitivity driven by CDW distortion is demonstrated. The collective excitation combined with the strong interaction with long‐wavelength photons opens up novel feasibility toward realistic exploration of many‐body states for imaging and sensing applications.

Abstract

The quantum behavior of carriers in solid is the foundation of modern electronic and optoelectronic technology, but it is still facing huge challenges within inherited single‐particle quantum processes working at the millimeter wave/terahertz (THz) band. Here, a straightforward strategy for the direct detection of millimeter wave/THz photons in a sub‐wavelength metal‐TaSe₂‐metal structure under strong interaction with a localized field of surface plasmon is proposed. By breaking the inversion symmetry under the perturbations of electric field and atomic reconstruction from van der Waals integration, the nonequilibrium electronic states under a radiant field can be manipulated in a collective fashion, leading to a large photocurrent responsivity over 40 A W⁻¹ and noise equivalent power less than 1 pW Hz^−1/2 even at room temperature. A more than 40‐fold enhancement in responsivity is achieved when transitioning from the normal phase to the CDW phase. The findings shed fresh light on the understanding of the delicate balance in the charge‐ordered phase, and facilitate the exploitation of a correlated electron system for optoelectronic applications in fields of security, remote sensing, and imaging.

Liquid metal droplets are tailored to remain liquid at temperatures as low as −85 °C. Their polymer composites are soft and stretchable even at extreme cold conditions and show exceptional thermal and electrical performance. This unique combination of properties is enabling for emerging technologies, including self‐powered electronics, deep‐sea underwater robots, and space applications.

Abstract

Elastomers embedded with droplets of liquid metal (LM) alloy represent an emerging class of soft multifunctional composites that have potentially transformative impact in wearable electronics, biocompatible machines, and soft robotics. However, for these applications it is crucial for LM alloys to remain liquid during the entire service temperature range in order to maintain high mechanical compliance throughout the duration of operation. Here, LM‐based functional composites that do not freeze and remain soft and stretchable at extremely low temperatures are introduced. It is shown that the confinement of LM droplets to micro‐/nanometer length scales significantly suppresses their freezing temperature (down to −84.1 from −5.9 °C) and melting point (down to −25.6 from +17.8 °C) independent of the choice of matrix material and processing conditions. Such a supercooling effect allows the LM inclusions to preserve their fluidic nature at low temperatures and stretch with the surrounding polymer matrix without introducing significant mechanical resistance. These results indicate that LM composites with highly stabilized droplets can operate over a wide temperature range and open up new possibilities for these emerging materials, which are demonstrated with self‐powered wearable thermoelectric devices for bio‐sensing and personal health monitoring at low temperatures.

Au–Fe₃O₄ heterogeneous nanoparticles (NPs) and Au@Fe₃O₄ core/shell NPs are selectively prepared and directly adopted as ideal model electrocatalysts to evaluate N₂ electroreduction for the first time, where the Au–Fe₃O₄ heterogeneous NPs have a unique synergistic effect between the high electrochemical performance of Au and the strong N₂ fixation capacity of Fe₃O₄, resulting in enhanced nitrogen reduction reaction activity.

Abstract

Electrochemical nitrogen reduction reaction (NRR) is a promising approach to convert earth‐adundant N₂ into highly value‐added NH₃. Herein, it is demonstrated that the heterogeneous Au–Fe₃O₄ nanoparticles (NPs) can be adopted as highly efficient catalysts for NRR. Due to the synergistic effect of the strong N₂ fixation ability of Fe₃O₄ and the charge transfer capability of Au, the Au–Fe₃O₄ NPs show excellent performance with a high yield (NH₃: 21.42 µg mg_cat ⁻¹ h⁻¹) and a favorable faradaic efficiency (NH₃: 10.54%) at −0.2 V (vs reversible hydrogen electrode), both of which are much better than those of the Au NPs, Fe₃O₄ NPs, as well as core@shell Au@Fe₃O₄ NPs. It also exhibits good stability with largely maintained performance after six cycles. The N₂ temperature‐programmed desorption, surface valance band spectra, and X‐ray photoelectron spectroscopy collectively confirm that Au–Fe₃O₄ NPs have a strong adsorption capacity for the reaction species and suitable surface structure for electronic transfer. The theoretical calculations reveal that Fe provides the active site to fix N₂ into *N₂H while introducing Au optimizes the adsorption of NRR intermediates, making the NRR pathway on Au–Fe₃O₄ along an energetic‐favorable process and enhancing the NRR.

We show that it is possible to construct foam-based heterostructures with complete photonic band gaps. Three-dimensional foams are promising candidates for the self-organization of large photonic networks with combinations of physical characteristics that may be useful for applications. The largest band gap found is based on 3D Weaire–Phelan foam, a...

With the help of a high‐resolution polymer mask, for the first time, top‐contact monolayer organic field‐effect transistors on pure polymer dielectrics are fabricated. More significantly, charge density redistribution occurs at the interface between the pentacene and poly (amic acid) (PAA) caused by electron transfer from pentacene to the PAA dielectric layer, which leads to highly efficient charge transport.

Abstract

The study of monolayer organic field‐effect transistors (MOFETs) provides an effective way to investigate the intrinsic charge transport of semiconductors. To date, the research based on organic monolayers on polymeric dielectrics lays far behind that on inorganic dielectrics and the realization of a bulk‐like carrier mobility on pure polymer dielectrics is still a formidable challenge for MOFETs. Herein, a quasi‐monolayer coverage of pentacene film with orthorhombic phase is grown on the poly (amic acid) (PAA) dielectric layer. More significantly, charge density redistribution occurs at the interface between the pentacene and PAA caused by electron transfer from pentacene to the PAA dielectric layer, which is verified by theoretical simulations and experiments. As a consequence, an enhanced hole accumulation layer is formed and pentacene‐based MOFETs on pure polymer dielectrics exhibit bulk‐like carrier mobilities of up to 13.7 cm² V⁻¹ s⁻¹ from the saturation region at low V _GS, 9.1 cm² V⁻¹ s⁻¹ at high V _GS and 7.6 cm² V⁻¹ s⁻¹ from the linear region, which presents one of the best results of previously reported MOFETs so far and indicates that the monolayer semiconductor growing on pure polymer dielectric could produce highly efficient charge transport.

The remarkable mechanical robustness and excellent electrical/thermal properties make graphene a promising candidate for future flexible, stretchable and bio-integrated electronics. In practice, many soft electronics such as the graphene electronic tattoos (GETs) demand the chemical vapor deposited (CVD) graphene to be supported by a deformable substrate. Moreover, various conductive overlayers need to directly laminate on graphene to make electrical contacts. To investigate the mechanical reliability of CVD graphene in these situations, we fabricated CVD monolayer graphene supported by ultrathin poly(methyl methacrylate) (PMMA) substrate and also placed gold/polyethylene terephthalate (Au/PET) and graphene/PMMA (Gr/PMMA) overlayers on graphene. The stretchability of the Gr/PMMA and the overlayer-Gr/PMMA interface was characterized by electrical resistance change during uniaxial tensile tests. Combined with in situ microstructure and Raman investigation, we identified fou...

Van der Waals epitaxy holds great promise in producing high-quality films of 2D materials. However, scalable van der Waals epitaxy processes operating at low temperatures and low vacuum conditions are lacking. Herein, atomic layer deposition is used for van der Waals epitaxy of continuous multilayer films of 2D materials HfS 2 , MoS 2 , SnS 2 , and ZrS 2 on muscovite mica and PbI 2 on sapphire at temperatures between 75 °C and 400 °C. For the metal sulfides on mica, the main epitaxial relation is ##IMG## [http://ej.iop.org/images/2053-1583/7/1/011003/tdmab4c09ieqn001.gif] MS 2 ‖ ##IMG## [http://ej.iop.org/images/2053-1583/7/1/011003/tdmab4c09ieqn002.gif] mica. Some domains rotated by 30° are also observed corresponding to the ##IMG## [http://ej.iop.org/images/2053-1583/7/1/011003/tdmab4c09ieqn003.gif] MS 2 ‖ ##IMG## [ht...]

The recent successful fabrication of borophene sheets has prompted extensive researches. Here, the recent theoretical and experimental progress on the structure, growth, and electronic and thermal transport properties of borophene sheets is summarized. Recent theoretical studies on the thermal stability, ballistic thermal transport, diffusive thermal transport, and abnormal strain effect of borophene are discussed and compared with those of graphene.

Abstract

The structures of boron clusters, such as flat clusters and fullerenes, resemble those of carbon. Various two‐dimensional (2D) borophenes have been proposed since the production of graphene. The recent successful fabrication of borophene sheets has prompted extensive researches, and some unique properties are revealed. In this review, the recent theoretical and experimental progress on the structure, growth, and electronic and thermal transport properties of borophene sheets is summarized. The history of prediction of boron sheet structures is introduced. Existing with a mixture of triangle lattice and hexagonal lattice, the structures of boron sheets have peculiar characteristics of polymorphism and show significant dependence on the substrate. Due to the unique structure and complex BB bonds, borophene sheets have many interesting electronic and thermal transport properties, such as strong nonlinear effect, strong thermal transport anisotropy, high thermal conductance in the ballistic transport and low thermal conductivity in the diffusive transport. The growth mechanism and synthesis of borophene sheets on different metal substrates are also presented. The successful prediction and synthesis will shed light on the exploration of new novel materials. Besides, the outstanding and peculiar properties of borophene make them tempting platform for exploring novel physical phenomena and extensive applications.

Graphene‐based thermal devices can be divided into four categories: uncoupled thermal devices, thermoacoustic coupling devices, thermoelectric coupling devices, and thermo‐optical coupling devices. The structure, working mechanism, and performance of these devices are discussed, as well as the coupling method of physical quantities. Finally, graphene production and graphene‐based thermal device prospects are summarized.

Abstract

Thermal energy conversion and utilization of integrated circuits is a very important research topic. Graphene is a new 2D material with superior electrical, mechanical, thermal, and optical properties, which is expected to continue Moore's law and make breakthroughs in the direction of “More than Moore.” Graphene‐based functionalized devices are applied in various aspects, including breakthroughs in thermal devices, due to their high thermal conductivity and thermal rectification. According to the coupling of different physical quantities, graphene‐based thermal devices can be divided into four categories: uncoupled thermal devices, thermoacoustic coupling devices, thermoelectric coupling devices, and thermo‐optical coupling devices. The structure, working mechanism, and performance of these devices are discussed, as well as the coupling methods of physical quantities. Moreover, scale‐up production of graphene and prospect for future graphene‐based thermal devices are summarized. In‐depth study of the development tendency of these graphene‐based thermal devices is expected to contribute to the development of new high‐performance thermal nanoelectronic devices in the future.

GaTe/InSe van der Waals heterostructure photodetectors present an extraordinary detectivity D* (10¹⁴–10¹² Jones) in a shortwave infrared spectrum of 1.0−1.55 µm forbidden by the bandgap limits of the constituent GaTe and InSe, which is attributed to the formation of the interlayer transition in the type‐II band alignment heterostructure.

Abstract

Van der Waals (vdW) heterostructures of 2D atomically thin layered materials (2DLMs) provide a unique platform for constructing optoelectronic devices by staking 2D atomic sheets with unprecedented functionality and performance. A particular advantage of these vdW heterostructures is the energy band engineering of 2DLMs to achieve interlayer excitons through type‐II band alignment, enabling spectral range exceeding the cutoff wavelengths of the individual atomic sheets in the 2DLM. Herein, the high performance of GaTe/InSe vdW heterostructures device is reported. Unexpectedly, this GaTe/InSe vdWs p–n junction exhibits extraordinary detectivity in a new shortwave infrared (SWIR) spectrum, which is forbidden by the respective bandgap limits for the constituent GaTe (bandgap of ≈1.70 eV in both the bulk and monolayer) and InSe (bandgap of ≈1.20–1.80 eV depending on thickness reduction from bulk to monolayer). Specifically, the uncooled SWIR detectivity is up to ≈10¹⁴ Jones at 1064 nm and ≈10¹² Jones at 1550 nm, respectively. This result indicates that the 2DLM vdW heterostructures with type‐II band alignment produce an interlayer exciton transition, and this advantage can offer a viable strategy for devising high‐performance optoelectronics in SWIR or even longer wavelengths beyond the individual limitations of the bandgaps and heteroepitaxy of the constituent atomic layers.

Inorganic hybrid lead perovskites have attracted worldwide attention but the toxicity of lead hinders their development. Herein, high‐performance photoresponsive transistors based on the stable lead‐free CsBi₃I₁₀ perovskites and semiconducting single‐walled carbon nanotubes are firstly reported and their multifunctional application in photodetectors and light‐stimulated synapses are demonstrated.

Abstract

Lead‐free perovskite materials are exhibiting bright application prospects in photodetectors (PDs) owing to their low toxicity compared with traditional lead perovskites. Unfortunately, their photoelectric performance is constrained by the relatively low charge conductivity and poor stability. In this work, photoresponsive transistors based on stable lead‐free bismuth perovskites CsBi₃I₁₀ and single‐walled carbon nanotubes (SWCNTs) are first reported. The SWCNTs significantly strengthen the dissociation and transportation of the photogenerated charge carriers, which lead to dramatically improved photoresponsivity, while a decent I _light/I _dark ratio over 10² can be maintained with gate modulation. The devices exhibit high photoresponsivity (6.0 × 10⁴ A W⁻¹), photodetectivity (2.46 × 10¹⁴ jones), and external quantum efficiency (1.66 × 10⁵%), which are among the best reported results in lead‐free perovskite PDs. Furthermore, the excellent stability over many other lead‐free perovskite PDs is demonstrated over 500 h of testing. More interestingly, the device also shows the application potential as a light‐stimulated synapse and its synaptic behaviors are demonstrated. In summary, the lead‐free bismuth perovskite‐based hybrid phototransistors with multifunctional performance of photodetection and light‐stimulated synapse are first demonstrated in this work.

Artificial skyrmions in synthetic antiferromagnetic multilayers are robust against temperature and device size as guaranteed by the antiferromagnetic interlayer exchange coupling. These synthetic skyrmions exhibit a high tunability and are still well behaved with a size less than 100 nm. Moreover, the designable arrangement according to the functional demands can be realized with nanolithography.

Abstract

Magnetic skyrmions are topologically nontrivial spin structures, and their existence in ferromagnetically coupled multilayers has been widely reported with a disordered arrangement. Here, a nucleation scenario of ordered skyrmions in nanostructured synthetic antiferromagnetic (SAF) multilayers is proposed and experimentally demonstrated using direct magnetization imaging, indirect magnetometer and magnetoresistance measurement, and micromagnetic simulation. Instead of relying on Dzyaloshinskii–Moriya interaction, the antiferromagnetic interlayer exchange coupling in the SAF multilayers fulfills the role of nucleation and stabilization of skyrmions. The robustness of the proposed skyrmion nucleation scenario is examined against temperature from 4.5 to 300 K and device size from 400 to 1200 nm. Interestingly, these synthetic skyrmions still behave well with a size less than 100 nm. The higher stability than generic magnetic domains can be attributed to topological protection. The results thus provide an artificial skyrmion platform to meet the functional needs of high density and designable arrangement in magnonic and spintronic applications.

In article number https://doi.org/10.1002/adfm.2019038161903816, Aleksandar Matković and co‐workers employ networks of self‐assembled organic nanostructures epitaxially grown on two‐dimensional hexagonal boron nitride. The work demonstrates how the polarization direction of external light can be used to realize a “light‐gate” for switching on and off the conductivity of organic nanocrystals, and to even guide charge propagation along desired directions in self‐assembled crystallite networks.

Nanostructures of fractal β‐Bi₂O₃ are uniformly fabricated on carbon fiber paper via a one‐step hot‐aerosol synthesis. The structure then is utilized as an electrocatalyst for CO₂ reduction and has high selectivity toward formate production. The high performance is attributed to the exposure of a larger number of active sites and high electron density of the structure.

Abstract

3D Bi₂O₃ fractal nanostructures (f‐Bi₂O₃) are directly self‐assembled on carbon fiber papers (CFP) using a scalable hot‐aerosol synthesis strategy. This approach provides high versatility in modulating the physiochemical properties of the Bi₂O₃ catalyst by a tailorable control of its crystalline size, loading, electron density as well as providing exposed stacking of the nanomaterials on the porous CFP substrate. As a result, when tested for electrochemical CO₂ reduction reactions (CO₂RR), these f‐Bi₂O₃ electrodes demonstrate superior conversion of CO₂ to formate (HCOO⁻) with low onset overpotential and a high mass‐specific formate partial current density of −52.2 mA mg⁻¹, which is ≈3 times higher than that of the drop‐casted control Bi₂O₃ catalyst (−15.5 mA mg⁻¹), and a high Faradaic efficiency (FE_HCOO ⁻) of 87% at an applied potential of −1.2 V versus reversible hydrogen electrode. The findings reveal that the high exposure of roughened β‐phase Bi₂O₃/Bi edges and the improved electron density of these fractal structures are key contributors in attainment of high CO₂RR activity.

An approach to create a robust room temperature multiferroic using light element doping is demonstrated. The synthesis of self‐assembled ferrimagnetic LiFe₅O₈ nanopillars heteroepitaxially embedded in a single crystal ferroelectric BiFeO₃ matrix provides new avenues for designing multifunctional energy, sensing, and computing applications.

Abstract

Multiferroic materials have driven significant research interest due to their promising technological potential. Developing new room‐temperature multiferroics and understanding their fundamental properties are important to reveal unanticipated physical phenomena and potential applications. Here, a new room temperature multiferroic nanocomposite comprised of an ordered ferrimagnetic spinel α‐LiFe₅O₈ (LFO) and a ferroelectric perovskite BiFeO₃ (BFO) is presented. It is observed that lithium (Li)‐doping in BFO favors the formation of LFO spinel as a secondary phase during the synthesis of Li _x Bi_{1− x} FeO₃ ceramics. Multimodal functional and chemical imaging methods are used to map the relationship between doping‐induced phase separation and local ferroic properties in both the BFO‐LFO composite ceramics and self‐assembled nanocomposite thin films. The energetics of phase separation in Li doped BFO and the formation of BFO‐LFO composites are supported by first principles calculations. These findings shed light on Li's role in the formation of a functionally important room temperature multiferroic and open a new approach in the synthesis of light element doped nanocomposites for future energy, sensing, and memory applications.