Jing Zhang

Few-layer CrI 3 is the most known example among two-dimensional (2D) ferromagnets, which have attracted growing interest in recent years. Despite considerable efforts and progress in understanding the properties of 2D magnets both from theory and experiment, the mechanism behind the formation of in-plane magnetic ordering in chromium halides is still under debate. Here, we propose a microscopic orbitally-resolved description of ferromagnetism in monolayer CrI 3 . Starting from first-principles calculations, we construct a low-energy model for the isotropic Heisenberg exchange interactions. We find that there are two competing contributions to the long-range magnetic ordering in CrI 3 : (i) Antiferromagnetic Anderson’s superexchange between half-filled t 2 g orbitals of Cr atoms; and (ii) Ferromagnetic exchange governed by the Kugel–Khomskii mechanism, involving the transitions between half-filled t 2 g ...

Nature Nanotechnology, Published online: 02 March 2020; doi:10.1038/s41565-020-0654-0

Grouping all carbon nanotubes into a single substance category is scientifically unjustified

The isolation of air-sensitive two-dimensional (2D) materials and the race to achieve a better control of the interfaces in van der Waals heterostructures has pushed the scientific community towards the development of experimental setups that allow to exfoliate and transfer 2D materials under inert atmospheric conditions. These systems are typically based on over pressurized N 2 of Ar gloveboxes that require the use of very thick gloves to operate within the chamber or the implementation of several motorized micro-manipulators. Here, we set up a deterministic transfer system for 2D materials within a gloveless anaerobic chamber. Unlike other setups based on over-pressurized gloveboxes, in our system the operator can manipulate the 2D materials within the chamber with bare hands. This experimental setup allows us to exfoliate 2D materials and to deterministically place them at a desired location with accuracy in a controlled O 2 -free and very low humidity (

Two-dimensional (2D) van der Waals (vdW) heterostructures with pre-determined properties are key ingredients for the success of advanced electronics and optoelectronics. The construction of vdW heterostructures is a prerequisite to obtain the desired performance with high quality. A typical dry/wet transfer technique is a promising route to physically stack vdW heterostructures via a gentle-energy fabrication procedure, allowing the fabrication of atomically sharp and thin heterointerfaces. This strategy has gained considerable attention for intriguing physics phenomena such as superconductivity, topological insulator, valleytronics, and interweaving proximity effect. It also offers various possibilities to construct sophisticated electrical, optical, energy harvesting, and memory devices. Here, we review the state-of-the-art transfer techniques and describe their advantages and drawbacks. We also discuss the transfer methodologies of particular purposes, which are extremely des...

The outstanding thermoelectric performance of pristine half‐filled p‐bonded chalcogenides with octahedral arrangements can be understood from a chemical bonding perspective, where different bonding mechanisms can be separated in a map depicting the electrons transferred and/or shared between adjacent atoms. Metavalent bonding is responsible for the large band degeneracy, the band anisotropy, and the low lattice thermal conductivity, giving rise to a promising thermoelectric performance.

Abstract

Thermoelectric materials have attracted significant research interest in recent decades due to their promising application potential in interconverting heat and electricity. Unfortunately, the strong coupling between the material parameters that determine thermoelectric efficiency, i.e., the Seebeck coefficient, electrical conductivity, and thermal conductivity, complicates the optimization of thermoelectric energy converters. Main‐group chalcogenides provide a rich playground to alleviate the interdependence of these parameters. Interestingly, only a subgroup of octahedrally coordinated chalcogenides possesses good thermoelectric properties. This subgroup is also characterized by other outstanding characteristics suggestive of an exceptional bonding mechanism, which has been coined metavalent bonding. This conclusion is further supported by a map that separates different bonding mechanisms. In this map, all octahedrally coordinated chalcogenides with good performance as thermoelectrics are located in a well‐defined region, implying that the map can be utilized to identify novel thermoelectrics. To unravel the correlation between chemical bonding mechanism and good thermoelectric properties, the consequences of this unusual bonding mechanism on the band structure are analyzed. It is shown that features such as band degeneracy and band anisotropy are typical for this bonding mechanism, as is the low lattice thermal conductivity. This fundamental understanding, in turn, guides the rational materials design for improved thermoelectric performance by tailoring the chemical bonding mechanism.

Improved extra capacitance is observed due to enlarged ion storage space from a synergistically interplayed effect in 1T‐MoS₂/Ti₃C₂ MXene 3D interconnected networks. Outstanding rate performance is realized due to ultrafast electron transport originating from Ti₃C₂ MXene. This work paves the way for investigating the electrochemical energy storage mechanism of supercapacitors in 2D/2D heterostructures.

Abstract

2D/2D heterostructures can combine the collective advantages of each 2D material and even show improved properties from synergistic effects. 2D Transition metal carbide Ti₃C₂ MXene and 2D 1T‐MoS₂ have emerged as attractive prototypes in electrochemistry due to their rich properties. Construction of these two 2D materials, as well as investigation about synergistic effects, is absent due to the instability of 1T‐MoS₂. Here, 3D interconnected networks of 1T‐MoS₂/Ti₃C₂ MXene heterostructure are constructed by magneto‐hydrothermal synthesis, and the electrochemical storage mechanisms are investigated. Improved extra capacitance is observed due to enlarged ion storage space from a synergistically interplayed effect in 3D interconnected networks. Outstanding rate performance is realized because of ultrafast electron transport originating from Ti₃C₂ MXene. This work provides an archetype to realize excellent electrochemical properties in 2D/2D heterostructures.

A hierarchical bimetallic Bi₂S₃/MoS₂ heterogeneous is fabricated for sodium‐ion storage. The full understanding of self‐generated phase boundaries on enhanced electrochemical properties is unraveled by combining theoretical analyses and in situ results, which can induce the interior self‐built‐in electric field with boosted charge transfer. Moreover, the Bi/Na₂S interface is well‐maintained by the homogeneously distributed phase boundaries, effectively improving conversion/alloying reversibility.

Abstract

Regulating nanocrystal composition with multiphase compounds is considered an efficient approach to enhance electrochemical performance and structure stability. Nevertheless, the thorough understanding of significant reaction mechanisms and insight into the reason of enhanced performance is still urgent. In this work, the bimetallic sulfide Bi₂S₃/MoS₂ heterogeneous with abundant phase boundaries is successfully fabricated. The in situ investigation of Na⁺‐storage mechanism confirms that enormous phase boundaries are self‐generated by composition optimization and rational structural design. More importantly, the full understanding of abundant phase boundaries on the enhanced electrochemical properties is explicitly unraveled by combining theoretical analysis and experimental results. It confirms that the interior self‐built‐in electric‐field induced by phase boundaries can enhance the reaction kinetics and boost the charge transfer. Besides, the Bi/Na₂S interface is well‐maintained by the homogeneously distributed phase boundaries, effectively improving the conversion/alloying reversibility and keeping integrity without agglomeration and pulverization. As expected, the Bi₂S₃/MoS₂ composite exhibits superior rate capability and long‐cycling stability (323.4 mAh g⁻¹ after long‐term 1200 cycles at ultrahigh rate of 10 A g⁻¹). This strategy of constructing sufficient phase boundaries sheds light on the enhancement of reversibility and stability for other advanced conversion/alloying‐type anode materials.

A two‐step chemical functionalization method is developed to enhance the contact behavior of metal/MoS₂ interfaces. After the two‐step chemical treatment, the unintentional defect states at the metal/MoS₂ junctions are removed, resulting in facilitated injection of electron from metal to channels. Moreover, the present chemical method employs simple processes, enabling integration of this functionalization into conventional semiconductor processing.

Abstract

The performance of electronic/optoelectronic devices is governed by carrier injection through metal–semiconductor contact; therefore, it is crucial to employ low‐resistance source/drain contacts. However, unintentional introduction of extrinsic defects, such as substoichiometric oxidation states at the metal–semiconductor interface, can degrade carrier injection. In this report, controlling the unintentional extrinsic defect states in layered MoS₂ is demonstrated using a two‐step chemical treatment, (NH₄)₂S(aq) treatment and vacuum annealing, to enhance the contact behavior of metal/MoS₂ interfaces. The two‐step treatment induces changes in the contact of single layer MoS₂ field effect transistors from nonlinear Schottky to Ohmic behavior, along with a reduction of contact resistance from 35.2 to 5.2 kΩ. Moreover, the enhancement of I _ON and electron field effect mobility of single layer MoS₂ field effect transistors is nearly double for n‐branch operation. This enhanced contact behavior resulting from the two‐step treatment is likely due to the removal of oxidation defects, which can be unintentionally introduced during synthesis or fabrication processes. The removal of oxygen defects is confirmed by scanning tunneling microscopy and X‐ray photoelectron spectroscopy. This two‐step (NH₄)₂S(aq) chemical functionalization process provides a facile pathway to controlling the defect states in transition metal dichalcogenides (TMDs), to enhance the metal‐contact behavior of TMDs.

Electric‐field‐induced strain in piezoelectric materials usually provides about 1% strain. A giant and reversible deformation as large as ≈5% in BiFeO3 thin film induced by electrochemistry, where the large lattice change is caused by electrochemical reaction through absorption and desorption of oxygen, provides a new route to realize giant and reversible deformation in oxides.

Abstract

Electric‐field‐induced strain in piezoelectric materials, which has demonstrated broad applications, usually provides about 1% strain. A giant and reversible deformation as large as ≈5% in BiFeO₃ thin film induced by electrochemistry is reported, where the large lattice change is induced by electrochemical reaction through absorption and desorption of oxygen. Prior to deformation, a precursor phase with projected Fe–Fe pairs is formed first under low voltage (1 V), and then a large lattice expansion is eventually achieved under a high voltage (≈18 V), which is reversible under negative voltage. It is found that the giant strain is due to the electrochemically induced migration of oxygen ion which leads to significant out‐of‐plane lattice expansion under positive voltage, resulting in the formation of a new oxygen‐deficient phase. Interestingly, the new oxygen‐deficient phase is capable of transforming back to the pristine structure by absorbing oxygen under negative voltage. The results provide a new route to realize giant and reversible deformation in oxides by oxygen migration.

Nature Nanotechnology, Published online: 17 February 2020; doi:10.1038/s41565-020-0637-1

Dirac-point photocurrents due to the photothermoelectric effect in non-uniform graphene devices

Two-dimensional (2D) semiconductors hold promises for electronic and optoelectronic applications due to their outstanding electrical and optical properties. Despite a short research history, a wide range of ‘proof-of-concept’ devices based on 2D materials have been demonstrated, highlighting their impact in advanced technology. Here we review the unique properties 2D semiconducting materials and their applications in terms of electronic and optoelectronic devices. We summarize all the engineering issues in 2D devices, including material quality, dielectric, and contacts. We also discuss recent advances of 2D semiconductor devices in electronic and optoelectronic applications. This review would help to understand superior performance and multifunctions of 2D semiconductor devices and guide us toward new device applications of 2D semiconductors.

Nature Nanotechnology, Published online: 10 February 2020; doi:10.1038/s41565-020-0633-5

The spontaneous relaxation of misfit strain achieved on graphene-coated substrates enables the growth of heteroepitaxial single-crystalline films with reduced dislocation density.

A broad variety of defects has been observed in two-dimensional materials. Many of these defects can be created by top–down methods such as electron irradiation or chemical etching, while a few of them are created along bottom–up processes, in particular during the growth of the material itself, in which case avoiding their formation can be challenging. This occurs e.g. with dislocations, Stone–Wales defects, or atomic vacancies in graphene. Here we address a defect that has been observed repeatedly since 2007 in epitaxial graphene on metal surfaces like Ru(0 0 0 1) and Re(0 0 0 1), but whose nature h666as remained elusive thus far. This defect has the appearance of a vacant hill in the periodically nanorippled topography of graphene, which comes together with a moiré pattern. Based on atomistic simulations and scanning tunneling microscopy/spectroscopy measurements, we argue that such defects are topological in nature and that their core is a stacking fault patch, either in gra...

Two-dimensional layered materials (2DLMs) have attracted great research interest due to their exotic physical properties and potential applications in nanoelectronics and optoelectronics. Device fabrication with 2DLMs is challenging because their ultrathin characteristic makes them extremely sensitive to the external environment, especially to chemical contamination introduced by optical lithography. The shadow mask technique is a clean alternative in lithography-free electrode patterning for emerging nanomaterials. However, shadow mask assisted fabrication over large areas and multilevel alignment of patterns remain challenging for practical applications. In this paper, we report an over wafer scale shadow mask fabrication technique for 2DLMs. Based on successful fabrication of customized silicon shadow masks with micrometer feature sizes, their advantages for fabricating higher mobility and lower interface trapped exfoliated MoS 2 transistors are demonstrated. Meanwh...

Monolayer MoS 2 is a known candidate to replace silicon-based materials for photodetection purposes. Achieving industrial production and application of MoS 2 calls for efficient and economic synthesis of such material. Here, we report a one-step and low-cost chemical vapor deposition method for the controlled synthesis of high quality and uniform wafer-scale (approximately 9.5  ×  4.5 cm) monolayer MoS 2 film on SiO 2 /Si substrates. Using the as-synthesized MoS 2 films, MoS 2 /PbS quantum dot hybrid device arrays are also fabricated. These hybrid devices have broad spectral photoresponse (457–1064 nm), rapid response rate, high responsivity of approximately 1.8  ×  10 4 A W −1 , and ultrahigh detectivity of approximately 7.6  ×  10 13 Jones, which outperforms other pristine two-dimensional as well as commercial Si and InGaAs materials. This low-cost and efficient method of growing wafer-scale...

Spin transistors based on a semiconducting channel attached to ferromagnetic electrodes suffer from fast spin decay and extremely low spin injection/detection efficiencies. Here, we propose an alternative all-in-one spin device whose operation principle relies on electric manipulation of the spin lifetime in two-dimensional (2D) SnTe, in which the sizable spin Hall effect eliminates the need for using ferromagnets. In particular, we explore the persistent spin texture (PST) intrinsically present in the ferroelectric phase which protects the spin from decoherence and supports extraordinarily long spin lifetime. Our first-principles calculations followed by symmetry arguments revealed that such a spin wave mode can be externally detuned by perpendicular electric field, leading to spin randomization and decrease in spin lifetime. We further extend our analysis to ultrathin SnTe films and confirm the emergence of PST as well as a moderate enhancement of intrinsic spin Hall conductiv...

Mild ultraviolet photons are irradiated onto the chemical vapor deposition‐grown molybdenum disulfide (MoS₂) monolayer to selectively generate either sulfur vacancies or oxygen substituents, which are directly verified using atomic‐resolution electron microscopy. The present photon‐assisted defect engineering method allows for the effective modulation of MoS₂ monolayer‐based electronic and optoelectronic device characteristics while preserving the structural integrity.

Abstract

Defect engineering of 2D transition metal dichalcogenides (TMDCs) is essential to modulate their optoelectrical functionalities, but there are only a few reports on defect‐engineered TMDC device arrays. Herein, the atomic vacancy control and elemental substitution in a chemical vapor deposition (CVD)‐grown molybdenum disulfide (MoS₂) monolayer via mild photon irradiation under controlled atmospheres are reported. Raman spectroscopy, photoluminescence, X‐ray, and ultraviolet photoelectron spectroscopy comprehensively demonstrate that the well‐controlled photoactivation delicately modulates the sulfur‐to‐molybdenum ratio as well as the work function of a MoS₂ monolayer. Furthermore, the atomic‐resolution scanning transmission electron microscopy directly confirms that small portions (2–4 at% corresponding to the defect density of 4.6 × 10¹² to 9.2 × 10¹³ cm⁻²) of sulfur vacancies and oxygen substituents are generated in the MoS₂ while the overall atomic‐scale structural integrity is well preserved. Electronic and optoelectronic device arrays are also realized using the defect‐engineered CVD‐grown MoS₂, and it is further confirmed that the well‐defined sulfur vacancies and oxygen substituents effectively give rise to the selective n‐ and p‐doping in the MoS₂, respectively, without the trade‐off in device performance. In particular, low‐percentage oxygen‐doped MoS₂ devices show outstanding optoelectrical performance, achieving a detectivity of ≈10¹³ Jones and rise/decay times of 0.62 and 2.94 s, respectively.

Electrochemical tests demonstrate that the as‐prepared phosphorous single‐doped graphite layers exhibit outstanding oxygen and hydrogen evolution activities independently. Experiments and density functional theory calculations reveal that the COP groups are the active species for the high oxygen evolution activity, and the defects derived from the decomposition of C₃P = O species are the active sites for the hydrogen evolution reaction.

Abstract

Advances demonstrate that the incorporation of phosphorous into the network of nitrogen, sulfur, or fluorine‐doped carbon materials can remarkably enhance their oxygen and hydrogen evolution activities. However, the electrocatalytic behaviors of pristine phosphorous single‐doped carbon catalysts toward the oxygen and hydrogen evolution reactions (OER and HER) are rarely investigated and their corresponding active species are not yet explored. To clearly ascertain the effects of phosphorous doping on the OER and HER and identify the active sites, herein, phosphorous unitary‐doped graphite layers with different phosphorous species distributions are prepared and the correlations between the oxygen or hydrogen evolution activity and different phosphorous species are investigated, respectively. Results indicate that phosphorous single‐doped graphite layers show a superior oxygen evolution activity to most of the reported OER catalysts and the commercial IrO₂ in alkaline medium, and comparable hydrogen evolution activity to most reported carbon catalysts in acidic medium. Moreover, the relevancies unveil that the COP species are the main OER active species, and the defects derived from the decomposition of C₃P = O species are the main active sites for HER, as evidenced by density functional theory calculations, showing a new perspective for the design of more effective phosphorous‐containing water‐splitting catalysts.

For the first time, the crystal structure limitation is overcome and the successful structural evolution of 2D ultrathin Sb₂Se₃ flakes (as thin as 1.3 nm), by introducing a sodium‐mediated chemical vapor deposition growth method, is realized. The Sb₂Se₃ flakes‐based photodetector shows a broadband photodetection range from the UV to NIR region, due to the high‐quality single‐crystalline character and 2D morphology of Sb₂Se₃ flakes.

Abstract

As an important member of group VA–VIA semiconductors, 2D Sb₂Se₃ has drawn widespread attention thanks to its outstanding optoelectronic properties as compared to the bulk material. However, due to the intrinsic chain‐like crystal structure, the controllable synthesis of ultrathin 2D planar Sb₂Se₃ nanostructures still remains a huge challenge. Herein, for the first time, the crystal structure limitation is overcome and the successful structural evolution of 2D ultrathin Sb₂Se₃ flakes (as thin as 1.3 nm), by introducing a sodium‐mediated chemical vapor deposition (CVD) growth method, is realized. The formation of 2D planar geometry is mainly attributed to the preferential growth of (010) plane with the lowest formation energy. The thickness‐dependent band structure of 2D Sb₂Se₃ flakes shows a wide absorption band from UV to NIR region (300–1000 nm), suggesting its potential application in broadband photodetection. Strikingly, the Sb₂Se₃ flakes–based photodetector demonstrates excellent performance such as broadband response varying from UV to NIR region, high responsivity of 4320 mA W⁻¹, fast response time (τ_rise ≈ 13.16 ms and τ_decay ≈ 9.61 ms), and strong anisotropic ratio of 2.5@ 532 nm, implying promising potential application in optoelectronics.

A multichannel strain sensor system can precisely realize strain detection of individual fingers of an intelligent robot in real time with an ultrahigh strain resolution of ≈0.1%.

Abstract

Flexible strain sensors are an important component for future intelligent robotics. However, the majority of current strain sensors must be electrically connected to a corresponding monitoring system via conducting wires, which increases system complexity and restricts the working environment for monitoring strains. Here, stretchable graphene–polymer nanocomposites that act as strain sensors using a Joule heating effect are reported. When the resistance of the sensor changes in response to a strain, the resulting change in temperature is wirelessly detected in an intelligent robot. By engineering and optimizing the surface structure of graphene–polymer nanocomposites, the fabricated strain sensors exhibit excellent stability when subjected to periodic temperature signals over 400 cycles while being periodically strained and deliver a high strain sensitivity of 7.03 × 10⁻⁴ °C⁻¹ %⁻¹ for strain levels of 0% to 30%. As a wearable electronic device, the approach provides the capability to wirelessly monitor small strains for intelligent robots at a high strain resolution of ≈0.1%. Moreover, when the strain sensing system operates as a multichannel structure, it allows precise strain detection simultaneously, or in sequence, for each finger of an intelligent robot.

In article number https://doi.org/10.1002/adfm.2019061311906131, Gaokuo Zhong, Xiangli Zhong, Jiangyu Li, and co‐workers develop 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, 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.

Free‐standing 2D nanoassemblies are ultrathin nanomembranes or nanosheets constructed from nanoscale building blocks. In this Review, the fabrication methodologies of free‐standing 2D nanoassemblies are summarized, their attributes are highlighted, their properties and applications are discussed, and finally, perspectives on the challenges and future opportunities are shared.

Abstract

Free‐standing 2D nanoassemblies are ultrathin nanomembranes or nanosheets constructed from constituent nanoscale building blocks including metal nanoparticles, quantum dots, and magnetic nanoparticles, typically by a bottom‐up self‐assembly approach. Such free‐standing nanoassemblies are a new class of advanced functional materials that can integrate the unique optoelectronic properties of nanomaterials with thin film mechanics into confined 2D space. This offers attributes such as minimizing substrate effects, facile transfer, and soft devices in comparison to the corresponding substrate‐supported system. This review covers the recent progress in fabrication, characterization, and application of the free‐standing 2D nanoassemblies. To begin with, the attributes of free‐standing 2D nanoassemblies are discussed, followed by the description of fabrication methodologies. Then their novel optical, electronic, mechanical, magnetic, and stimuli responsible properties are covered, and their potential applications in filtration membrane, nanomechanical devices, and chemical sensing are further discussed. Finally, perspectives on the challenges and future opportunities of the free‐standing 2D nanoassemblies are shared.

Nature Nanotechnology, Published online: 27 January 2020; doi:10.1038/s41565-019-0625-5

On two-dimensional layered materials, elemental sulfur can be controllably generated in a supercooled liquid state with enhanced electrochemical figures of merit compared to solid sulfur.

Among the most common few-layers transition metal dichalcogenides (TMDs), WSe 2 is the most challenging material from the lattice dynamics point of view. Indeed, for a long time the main two phonon modes ( A 1g and ##IMG## [http://ej.iop.org/images/2053-1583/7/2/025004/tdmab5decieqn001.gif] ) have been wrongly assigned. In the last few years, these two modes have been properly interpreted, and their quasi-degeneracy in the monolayer has been used for its identification. In this work, we show that this approach has a limited validity and we propose an alternative, more general approach, based on multi-phonon bands. Moreover, we show and interpret all the peaks (about 40) appearing in the Raman spectra of monolayers, bilayers, and trilayers of WSe 2 by combining experimental wavelength- and polarization-dependent Raman studies with density-functional theory calculations providing the phonon dispersions, the polarization-...

We studied the effects of thermal annealing (in air and in ultra-high vacuum from room temperature up to 300 °C) of mechanically exfoliated mono-layer and few layer MoS 2 onto 270 nm SiO 2 /Si(1 0 0). The experiments were performed with optical microscopy, atomic force microscopy, non resonant Raman spectroscopy, and photoluminescence (PL) spectroscopy on the mono-layer flakes. We demonstrate the presence of a nano-confined water layer at the interface with the silicon substrate. The thickness of this water layer can be increased by immersing the exfoliated samples in water for one hour, or decreased by post exfoliation annealing. Then, we directly demonstrate the sublimation with annealing of the bottom layer at the interface with SiO 2 . PL experiments performed on the mono-layers in the 250 °C–300 °C annealing range, together with previous x-ray photoemission experiments, demonstrate the direct correlation of the PL integrated spectral intensity wi...

Due to unique properties arising from its 2D nature, molybdenum disulfide (MoS 2 ) has been studied widely toward its application for biosensing. While MoS 2 field effect transistor has been utilized for electrical detection of biological events in many studies, photoluminescence (PL) characteristics of MoS 2 have been poorly employed. MoS 2 PL can provide not only information of interactions between biological moieties and the surface, but also their spatial distribution. In this work, we utilized PL of single-layer MoS 2 as a label-free bioimaging sensor. To fabricate the imaging device, we synthesized MoS 2 by chemical vapor deposition and transferred it on a glass substrate with patterned electrodes. We employed Lactobacillus known as a probiotic microorganism to demonstrate the ability of bioimaging. We found that the MoS 2 PL can be modulated by the concentration of lactic acid. Finally, we succeed...

In article number https://doi.org/10.1002/adfm.2019061311906131, Gaokuo Zhong, Xiangli Zhong, Jiangyu Li, and co‐workers develop 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, 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.

The grain size effect on the thermal transport properties of hexagonal boron nitride (h-BN) thin films was experimentally investigated using the opto-thermal Raman technique. High-quality monolayer h-BN with mean grain sizes ranging from ~7 µ m to ~19 nm were successfully synthesized on Pt foil by chemical vapor deposition (CVD). The thermal conductivity ( κ ) of the single-crystalline h-BN was measured to be ~545 Wm −1 K −1 at 315K, well above the bulk value, and more than a factor of four higher than the value of poly-crystalline h-BN with mean grain size of ~19 nm. The very low thermal boundary conductance (deduced to be ~9.6 GW m −2 K −1 ) accounts for the significant reduction of κ for h-BN with small grain size. Molecular dynamics (MD) simulations reveal that due to the disordered vibrations of atoms along/near GB, the phonon scattering in poly-crystalline h-BN is greatly enhanced compared to large-grained or single-...

Laminar MoS 2 membranes show outstanding potential for practical applications in energy conversion/storage, sensing, and as nanofluidic devices. The re-stacking of exfoliated MoS 2 creates nanocapillaries between the layers of MoS 2 nanosheets. These MoS 2 membranes have been shown to possess a unique combination of ionic rejection properties, high water permeation rates, and long-term solvent stability, with no significant swelling when exposed to aqueous or organic solvents. Chemical modification of MoS 2 membranes has been shown to improve their ionic rejection properties, however the mechanism behind this improvement is not well understood. In this work, we elucidate the ion-sieving mechanism by the study of potential-dependent ion transport through functionalized MoS 2 membranes. The ionic permeability of the MoS 2 membrane is transformed by chemical functionalization with a simple naphthalene sulfonate d...

Engineering 2D material heterostructures by combining the best of different materials in one ultimate unit can offer a plethora of opportunities in condensed matter physics. Here, in the van der Waals heterostructures of the ferromagnetic insulator Cr 2 Ge 2 Te 6 and graphene, our observations indicate an out-of-plane proximity-induced ferromagnetic exchange interaction in graphene. The perpendicular magnetic anisotropy of Cr 2 Ge 2 Te 6 results in significant modification of the spin transport and precession in graphene, which can be ascribed to the proximity-induced exchange interaction. Furthermore, the observation of a larger lifetime for perpendicular spins in comparison to the in-plane counterpart suggests the creation of a proximity-induced anisotropic spin texture in graphene. Our experimental results and density functional theory calculations open up opportunities for the realization of proximity-induced magnetic i...