Jing Zhang

Using in situ microscopy, thermolysis of an amorphous precursor to form 2D MoS₂ crystals is observed at atomic resolution. Critical steps such as nucleation of nanograins and grain growth through aggregation of nanograins are analyzed using atomic resolution STEM images. The research sheds light on the controlled synthesis of 2D MoS₂ thin films through a thermolysis approach.

Abstract

Understanding and controlling the transformations of transition metal dichalcogenides (TMDs) from amorphous precursors into two‐dimensional (2D) materials is important for guiding synthesis, directing fabrication, and tailoring functional properties. Here, the combined effects of thermal energy and electron beam irradiation are explored on the structural evolution of 2D MoS₂ flakes through the thermal decomposition of a (NH₄)₂MoS₄ precursor inside an ultrahigh vacuum (10⁻⁹ Torr) scanning transmission electron microscope (STEM). The influence of reaction temperature, growth substrate, and the initial precursor morphology on the resulting 2D MoS₂ flake morphology, edge structures, and point defects are explored. Although thermal decomposition occurs extremely fast at elevated temperatures and is difficult to capture using current STEM techniques, electron beam irradiation can induce local transformations at lower temperatures, enabling direct observation and interpretation of critical growth steps including oriented attachment and transition from single‐ to multilayer structures at atomic resolution. An increase in the number of layers of the MoS₂ flakes from island growth is investigated using electron beam irradiation. These findings provide insight into the growth mechanisms and factors that control the synthesis of few‐layer MoS₂ flakes through thermolysis and toward the prospect of atomically precise control and growth of 2D TMDs.

Low-temperature synthesis of two-dimensional (2D) transition metal dichalcogenides (TMDs) is a key challenge for their integration with complementary metal-oxide-semiconductor (CMOS) technology at ‘back-end-of-line (BEOL)’. Most low-temperature synthesis utilizes alkali salts, oxide-based metals, and methyl-group based chalcogen precursors which do not meet current BEOL requirements for contaminant-free manufacturing and process scalability. In this study, we benchmark a carbon and alkali salt-free synthesis of fully coalesced, stoichiometric 2D WSe 2 films on amorphous SiO 2 /Si substrates at BEOL- compatible temperatures (475 °C) via gas-source metal-organic chemical deposition. This work highlights the necessity of a Se-rich environment in a kinetically limited growth regime for successful integration of low-temperature 2D WSe 2 . Atomic-scale characterization reveals that BEOL WSe 2 is polycrystalline with domain size of ~200 nm and band...

We demonstrate that electronic and magnetic properties of graphene can be tuned via proximity of multiferroic substrate. Our first-principles calculations performed both with and without spin–orbit coupling clearly show that by contacting graphene with bismuth ferrite BiFeO 3 (BFO) film, the spin-dependent electronic structure of graphene is strongly impacted both by the magnetic order and by electric polarization in the underlying BFO. Based on extracted Hamiltonian parameters obtained from the graphene band structure, we propose a concept of six-resistance device based on exploring multiferroic proximity effect giving rise to significant proximity electro- (PER), magneto- (PMR), and multiferroic (PMER) resistance effects. This finding paves a way towards multiferroic control of magnetic properties in two dimensional materials.

Superlattice engineering provides the means to reshape the fabric felt by quasiparticles moving in a material. Here we argue that bandstructure engineering with superlattices can be pushed to the extreme limit by stacking gapped van der Waals (vdW) materials on patterned dielectric substrates. Specifically, we find that high quality vdW patterned dielectric superlattices (PDS) realize a series of robust flat bands that can be directly switched on and off by gate voltage in situ . In contrast to existing superlattice platforms, these flat bands are realized without the need for fine tuning. Instead, the bands become flat as the gate voltage increases in magnitude. The characteristics of PDS flatbands are highly tunable: the type of flatband (single non-degenerate or dirac-cone-like), localization length, and interaction energy are sensitive to the applied gate voltage. As a result, electron-electron interactions in the PDS flatbands can become stronger than both the bandwid...

Nature Nanotechnology, Published online: 16 December 2019; doi:10.1038/s41565-019-0585-9

Tellurium thin films thermally evaporated at cryogenic temperatures enable the fabrication of high-performance wafer-scale p-type field-effect transistors and three-dimensional circuits.

Nature Nanotechnology, Published online: 17 December 2019; doi:10.1038/s41565-019-0621-9

Publisher Correction: Topological frustration induces unconventional magnetism in a nanographene

Lead‐free inorganic high‐k dielectric Ba_xSr_1–xTiO₃ oxides are successfully introduced to support MoS₂ channels in field effect transistors, targeting both extremely low voltage operation and ferroelectric nonvolatile memory function by simply adjusting the composition ratio of Ba and Sr.

Abstract

Coupling between non‐toxic lead‐free high‐k materials and 2D semiconductors is achieved to develop low voltage field effect transistors (FETs) and ferroelectric non‐volatile memory transistors as well. In fact, low voltage switching ferroelectric memory devices are extremely rare in 2D electronics. Now, both low voltage operation and ferroelectric memory function have been successfully demonstrated in 2D‐like thin MoS₂ channel FET with lead‐free high‐k dielectric Ba_xSr_1‐xTiO₃ (BST) oxides. When the BST surface is coated with a 5.5‐nm‐ultrathin poly(methyl methacrylate) (PMMA)‐brush for improved roughness, the MoS₂ FET with BST (x = 0.5) dielectric results in an extremely low voltage operation at 0.5 V. Moreover, the BST with an increased Ba composition (x = 0.8) induces quite good ferroelectric memory properties despite the existence of the ultrathin PMMA layer, well switching the MoS₂ FET channel states in a non‐volatile manner with a ±3 V low voltage pulse. Since the employed high‐k dielectric and ferroelectric oxides are lead‐free in particular, the approaches for applying high‐k BST gate oxide for 2D MoS₂ FET are not only novel but also practical towards future low voltage nanoelectronics and green technology.

Recent progress in understanding the electronic band topology and emergent topological properties encourage us to reconsider the band structure of well-known materials including elemental substances. Controlling such a band topology by external field is of particular interest from both fundamental and technological viewpoints. Here we report possible signatures of the...

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.

Hafnium pentatelluride has heavier molar mass than zirconium pentatelluride, which has ultralow through‐plane thermal conductivity, and thus is expected to have even lower thermal conductivity. However, here, accurate experimental measurements and theoretical calculations together show that the thermal conductivity of hafnium pentatelluride is higher due to weaker anharmonicity. This work can provide guidance for the design of new directional‐heat‐management applications.

Abstract

Hafnium pentatelluride (HfTe₅) has attracted extensive interest due to its exotic electronic, optical, and thermal properties. As a highly anisotropic crystal (layered structure with in‐plane chains), it has highly anisotropic electrical‐transport properties, but the anisotropy of its thermal‐transport properties has not been established. Here, accurate experimental measurements and theoretical calculations are combined to resolve this issue. Time‐domain thermoreflectance measurements find a highly anisotropic thermal conductivity, 28:1:8, with values of 11.3 ± 2.2, 0.41 ± 0.04, and 3.2 ± 2.0 W m^-1 K^-1 along the in‐plane a‐axis, through‐plane b‐axis, and in‐plane c‐axis, respectively. This anisotropy is even larger than what was recently established for ZrTe₅ (12:1:6), but the individual values are somewhat higher, even though Zr has a smaller atomic mass than Hf. Density‐functional‐theory calculations predict thermal conductivities in good agreement with the experimental data, provide comprehensive insights into the results, and reveal the origin of the apparent anomaly of the relative thermal conductivities of the two pentatellurides. These results establish that HfTe₅ and ZrTe₅, and by implication their alloys, have highly anisotropic and ultralow through‐plane thermal conductivities, which can provide guidance for the design of materials for new directional‐heat‐management applications and potentially other thermal functionalities.

The rational design of the interfacial electrocatalyst heterostructure MoS₂ is guided by the kinetics investigation. By optimizing the electronic structure based on the simultaneous modulation of the 3d‐band‐offsets of Ni, Co, and Mo near the interface, superior pH‐universal hydrogen evolution performances are achieved, which opens up a new strategy in the design of highly efficient electrocatalysts.

Abstract

As a prerequisite for a sustainable energy economy in the future, designing earth‐abundant MoS₂ catalysts with a comparable hydrogen evolution catalytic performance in both acidic and alkaline environments is still an urgent challenge. Decreasing the energy barriers could enhance the catalysts' activity but is not often a strategy for doing so. Here, the first kinetic‐oriented design of the MoS₂‐based heterostructure is presented for pH‐universal hydrogen evolution catalysis by optimizing the electronic structure based on the simultaneous modulation of the 3d‐band‐offsets of Ni, Co, and Mo near the interface. Benefiting from this desirable electronic structure, the obtained MoS₂/CoNi₂S₄ catalyst achieves an ultralow overpotential of 78 and 81 mV at 10 mA cm⁻², and turnover frequency as high as 2.7 and 1.7 s⁻¹ at the overpotential of 200 mV in alkaline and acidic media, respectively. The MoS₂/CoNi₂S₄ catalyst represents one of the best hydrogen evolution reaction performing ones among MoS₂‐based catalysts reported to date in both alkaline and acidic environments, and equally important is the remarkable long‐term stability with negligible activity loss after maintaining at 10 mA cm⁻² for 48 h in both acid and base. This work highlights the potential to deeply understand and rationally design highly efficient pH‐universal electrocatalysts for future energy storage and delivery.

Lead‐free inorganic high‐k dielectric Ba_xSr_1–xTiO₃ oxides are successfully introduced to support MoS₂ channels in field effect transistors, targeting both extremely low voltage operation and ferroelectric nonvolatile memory function by simply adjusting the composition ratio of Ba and Sr.

Abstract

Coupling between non‐toxic lead‐free high‐k materials and 2D semiconductors is achieved to develop low voltage field effect transistors (FETs) and ferroelectric non‐volatile memory transistors as well. In fact, low voltage switching ferroelectric memory devices are extremely rare in 2D electronics. Now, both low voltage operation and ferroelectric memory function have been successfully demonstrated in 2D‐like thin MoS₂ channel FET with lead‐free high‐k dielectric Ba_xSr_1‐xTiO₃ (BST) oxides. When the BST surface is coated with a 5.5‐nm‐ultrathin poly(methyl methacrylate) (PMMA)‐brush for improved roughness, the MoS₂ FET with BST (x = 0.5) dielectric results in an extremely low voltage operation at 0.5 V. Moreover, the BST with an increased Ba composition (x = 0.8) induces quite good ferroelectric memory properties despite the existence of the ultrathin PMMA layer, well switching the MoS₂ FET channel states in a non‐volatile manner with a ±3 V low voltage pulse. Since the employed high‐k dielectric and ferroelectric oxides are lead‐free in particular, the approaches for applying high‐k BST gate oxide for 2D MoS₂ FET are not only novel but also practical towards future low voltage nanoelectronics and green technology.

Nature Nanotechnology, Published online: 09 December 2019; doi:10.1038/s41565-019-0577-9

Topological frustration in the π-electron network of the polycyclic aromatic hydrocarbon C38H18 yields unpaired electrons and a magnetically non-trivial ground state. Here, the authors synthesize this molecule, known as Clar’s goblet, on Au(111) and characterize the antiferromagnetic ground state with scanning tunnelling microscopy.

Nature Nanotechnology, Published online: 09 December 2019; doi:10.1038/s41565-019-0582-z

The fluorination of graphene sheets in bilayer graphene grown by chemical vapour deposition on a single-crystal CuNi(111) surface results in a fluorinated diamond monolayer.

Nature Nanotechnology, Published online: 09 December 2019; doi:10.1038/s41565-019-0601-0

The elusive Clar goblet, a magnetic, bowtie shaped nanographene is now synthesized and its peculiar magnetic ground state is characterized.

The phases occurring on the open‐circuit potential for the lithiation of magnetite are identified through iteration between first‐principles studies and systematic combined refinement with X‐ray absorption spectroscopy (XAS), X‐ray diffraction (XRD), neutron diffraction, and the measured open‐circuit potential. This work is broadly applicable to other nano‐ and mesoscaled systems that exhibit phase change behavior as a function of crystallite size and that have suffered from difficult or crystallite‐size‐dependent phase identification.

Abstract

Nanostructured materials can exhibit phase change behavior that deviates from the macroscopic phase behavior. This is exemplified by the ambiguity for the equilibrium phases driving the first open‐circuit voltage (OCV) plateau for the lithiation of Fe₃O₄ nanocrystals. Adding complexity, the relaxed state for Li _x Fe₃O₄ is observed to be a function of electrochemical discharge rate. The phases occurring on the first OCV plateau for the lithiation of Fe₃O₄ nanocrystals have been investigated with density functional theory (DFT) through the evaluation of stable, or hypothesized metastable, reaction pathways. Hypotheses are evaluated through the systematic combined refinement with X‐ray absorption spectroscopy (XAS), X‐ray diffraction (XRD) measurements, neutron‐diffraction measurements, and the measured OCV on samples lithiated to x = 2.0, 3.0, and 4.0 in Li _x Fe₃O₄. In contrast to the Li–Fe–O bulk phase thermodynamic pathway, Fe⁰ is not observed as a product on the first OCV plateau for 10–45 nm nanocrystals. The phase most consistent with the systematic refinement is LiFe₃O₄, showing Li+Fe cation disorder. The observed equilibrium concentration for conversion to Fe⁰ occurs at x = 4.0. These definitive phase identifications rely heavily on the systematic combined refinement approach, which is broadly applicable to other nano‐ and mesoscaled systems that have suffered from difficult or crystallite‐size‐dependent phase identification.

A hybrid photodetector consisting of a 2D semiconductor (MoS₂) integrated with multiple grating metallic stripes (Mo₂C) demonstrates high sensitivity and broad spectral detection of light, overcoming the inherent weakness of conventional 2D photodetectors and opening up possibilities for next‐generation photoelectric device technology by providing new functionalities for high sensitivity and effective broad‐spectrum photodetection.

Abstract

A novel hybrid phototransistor consisting of molybdenum carbide (Mo₂C) and molybdenum disulfide (MoS₂) is proposed. By exploiting the interface properties of MoS₂ and Mo₂C, a highly sensitive and broad‐spectral response photodetector is fabricated. The underlying mechanism of the enhanced performance is the efficient hot carrier injection from Mo₂C to MoS₂. The strong coupling of MoS₂ and Mo₂C at the interface provides the significantly low Schottky barrier height (≈70 meV), which gives rise to the significantly efficient hot carrier transfer from Mo₂C to MoS₂. The grating of metallic Mo₂C produces plasmonic resonance, which provides hot carriers to the MoS₂ channel. By adjusting the grating period of Mo₂C (400–1000 nm), the optimal photoresponse of light can be controlled, from visible to NIR. By integrating various Mo₂C multigrating periods (400–1000 nm) with MoS₂, a novel photodetector is demonstrated with high responsivity (R > 10³ A W⁻¹) and light‐to‐dark current ratio (>10²) over a broad spectral range (405–1310 nm). The proposed novel hybrid photodetector, 2D semiconductors with multigrating 2D metallic stripes, exhibits high sensitivity and broad spectral detection of light and can overcome the inherent weakness of conventional 2D photodetectors, paving the way forward for next‐generation photoelectric devices.

Sn_{1− x} W _x S₂ alloys are synthesized with 1T SnS₂ as the template by adjusting the molar ratios of the precursors. The Sn_0.3W_0.7S₂ alloy shows up to 83% metallic properties and possess a distorted octahedral coordination 1T′ phase structure. Metallic 1T′‐Sn_0.3W_0.7S₂ endows a markedly enhanced hydrogen evolution reaction (HER) performance. The auxiliary of carbon black further effectively improves HER, catalytic performance rarely attenuates, and structure morphology remains stable.

Abstract

Crystal phase control still remains a challenge for the precise synthesis of 2D layered metal dichalcogenide (LMD) materials. The T′ phase structure has profound influences on enhancing electrical conductivity, increasing active sites, and improving intrinsic catalytic activity, which are urgently needed for enhancing hydrogen evolution reaction (HER) activity. Theoretical calculations suggest that metastable T′ phase 2D Sn_{1− x} W _x S₂ alloys can be formed by combining W with 1T tin disulfide (SnS₂) as a template to achieve a semiconductor‐to‐metallic transition. Herein, 2D Sn_{1− x} W _x S₂ alloys with varying x are prepared by adjusting the molar ratio of reactants via hydrothermal synthesis, among which Sn_0.3W_0.7S₂ displays a maximum of concentration of 81% in the metallic phase and features a distorted octahedral‐coordinated metastable 1T′ phase structure. The obtained 1T′‐Sn_0.3W_0.7S₂ has high intrinsic electrical conductivity, lattice distortion, and defects, showing a prominently improved HER catalytic performance. Metallic Sn_0.3W_0.7S₂ coupled with carbon black exhibits at least a 215‐fold improvement compared to pristine SnS₂. It has excellent long‐term durability and HER activity. This work reveals a general phase transition strategy by using T phase materials as templates and merging heteroatoms to achieve synthetic metastable phase 2D LMDs that have a significantly improved HER catalytic performance.

In this work, both the zT and critical voltage are simultaneously optimized in Cu₂Se via tailoring chemical compositions at multiple atomic positions, i.e., introducing Cu deficiency at the Cu‐sites to lower Cu ion chemical potential and alloying sulfur at the Se‐sites to reduce carrier concentration. This study greatly accelerates the real application of Cu₂Se‐based liquid‐like materials.

Abstract

Liquid‐like thermoelectric (TE) materials have the advantages of ultrahigh performance, low cost, and environment friendly, but their stability is greatly limited by the possible Cu/Ag deposition under a large current and/or temperature gradient. The pratical application based on liquid‐like TE materials requires both a high TE figure of merit (zT) for high energy conversion efficiency and large critical voltage for good stability, but they are very difficult to be simultaneously achieved in one material. In this work, both the zT and critical voltage are simultaneously optimized in Cu₂Se via tailoring chemical compositions at multiple atomic positions, i.e., introducing Cu deficiency at the Cu‐sites to lower Cu ion chemical potential and alloying sulfur at the Se‐sites to reduce carrier concentrations. A maximum zT of 2.0 at 1000 K has been successfully achieved for Cu_1.96Se_0.8S_0.2, about a 30% improvement over that for Cu₂Se. More importantly, Cu_1.96Se_0.8S_0.2 demonstrates a much higher critical voltage than Cu₂Se, yielding a greatly enhanced service stability under the conditions with/without a temperature gradient. An Ni/Mo/Cu_1.96Se_0.8S_0.2 TE unileg is successfully fabricated with a stable power output even after 400 thermal cycles between 473 and 873 K. This study greatly accelerates the real application of Cu₂Se‐based liquid‐like materials.

A new strategy for enhancing thermoelectric performance for eco‐friendly SnSe₂ is demonstrated. Simultaneous Cu intercalation into a van der Waals gap and Br doping into a SnSe₂ lattice electrically bridges otherwise isolated SnSe₂ layers, leading to a record high electron mobility, power factor, and engineering ZT for SnSe₂. Its highly unusual temperature‐independent power factor is crucially important in stable thermoelectric power generation.

Abstract

Due to its single conduction band nature, it is highly challenging to enhance the power factor of SnSe₂ by band convergence. Here, it is reported that simultaneous Cu intercalation and Br doping induce strong Cu–Br interaction to connect SnSe₂ layers, otherwise isolated, via “electrical bridges.” Atom probe tomography analysis confirms a strong attraction between Cu intercalants and Br dopants in the SnSe₂ lattice. Density functional theory calculations reveal that this interaction delocalizes electrons confined around SnSe covalent bonds and enhances charge transfer across the SnSe₂ slabs. These effects dramatically increase electron mobility and concentration. Polycrystalline SnCu_0.005Se_1.98Br_0.02 shows even higher electron mobility than pristine SnSe₂ single crystal and the theoretical expectation. This results in significantly improved electrical conductivity without reducing effective mass and Seebeck coefficient, thereby leading to the highest power factor of ≈12 µW cm⁻¹ K⁻² to date for polycrystalline SnSe₂ and SnSe. It even surpasses the value for the state‐of‐the‐art n‐type SnSe_0.985Br_0.015 single crystal at elevated temperatures. Surprisingly, the achieved power factor is nearly independent of temperature ranging from 300 to 773 K. The engineering thermoelectric figure of merit ZT_eng for SnCu_0.005Se_1.98Br_0.02 is ≈0.25 between 773 and 300 K, the highest ZT_eng ever reported for any form of SnSe₂‐based thermoelectric materials.

A centimeter‐scale, visible wavelength light‐emitting display is demonstrated utilizing a tungsten disulfide monolayer synthesized via chemical vapor deposition. Operated in the transient mode, the device exhibits bright red emission from an emission layer measuring 0.7 nm in thickness. This work highlights the potential use of monolayer semiconductors in ultrathin displays, taking advantage of their high luminescence quantum yields.

Abstract

Monolayer 2D transition metal dichalcogenides (TMDCs) have shown great promise for optoelectronic applications due to their direct bandgaps and unique physical properties. In particular, they can possess photoluminescence quantum yields (PL QY) approaching unity at the ultimate thickness limit, making their application in light‐emitting devices highly promising. Here, large‐area WS₂ grown via chemical vapor deposition is synthesized and characterized for visible (red) light‐emitting devices. Detail optical characterization of the synthesized films is performed, which show peak PL QY as high as 12%. Electrically pumped emission from the synthetic WS₂ is achieved utilizing a transient‐mode electroluminescence device structure, which consists of a single metal–semiconductor contact and alternating gate fields to achieve bipolar emission. Utilizing this aforementioned structure, a centimeter‐scale (≈0.5 cm²) visible (640 nm) display is demonstrated, fabricated using TMDCs to showcase the potential of this material system for display applications.

Advanced Functional Materials, Volume 29, Issue 49, December 5, 2019.

Tri‐component materials comprised of an ambipolar diketopyrrolopyrrole‐based semiconducting polymer combined with two different photochromic diarylethene molecules are used to develop organic field‐effect transistors, in which the transport of both holes and electrons can be photo‐modulated. A fully reversible lightswitching process is demonstrated, with a light‐controlled 100‐fold modulation of p‐type charge transport and a tenfold modulation of n‐type charge transport.

Abstract

One of the grand challenges in organic electronics is to develop multicomponent materials wherein each component imparts a different and independently addressable property to the hybrid system. In this way, the combination of the pristine properties of each component is not only preserved but also combined with unprecedented properties emerging from the mutual interaction between the components. Here for the first time, that tri‐component materials comprised of an ambipolar diketopyrrolopyrrole‐based semiconducting polymer combined with two different photochromic diarylethene molecules possessing ad hoc energy levels can be used to develop organic field‐effect transistors, in which the transport of both, holes and electrons, can be photo‐modulated. A fully reversible light‐switching process is demonstrated, with a light‐controlled 100‐fold modulation of p‐type charge transport and a tenfold modulation of n‐type charge transport. These findings pave the way for photo‐tunable inverters and ultimately for completely re‐addressable high‐performance circuits comprising optical storage units and ambipolar field‐effect transistors.

Nature Nanotechnology, Published online: 04 December 2019; doi:10.1038/s41565-019-0592-x

The magnetic phase diagram of thin-layered antiferromagnets is revealed experimentally by investigating the tunnelling conductance as a function of magnetic field. A rich magnetic behaviour in CrCl3 is uncovered, from which relevant magnetic information is extracted that is not easily available with other approaches.

Machine learning is applied to study atomic mechanisms for the Si impurity dynamics in graphene from scanning transmission electron microscopy movies. Specifically, deep learning is used to extract atomic features from noisy data, which is followed by a Gaussian mixture model to create a library of the structural descriptors. Then, a Markov model is used to analyze the transition probabilities.

Abstract

The dynamic behavior of e‐beam irradiated Si atoms in the bulk and at the edges of single‐layer graphene is examined using scanning transmission electron microscopy (STEM). A deep learning network is used to convert experimental STEM movies into coordinates of individual Si and carbon atoms. A Gaussian mixture model is further used to establish the elementary atomic configurations of the Si atoms, defining the bonding geometries and chemical species and accounting for the discrete rotational symmetry of the host lattice. The frequencies and Markov transition probabilities between these states are determined. This analysis enables insight into the defect populations and chemical transformation networks from the atomically resolved STEM data. Here, a clear tendency is observed for the formation of a 1D Si crystal along zigzag direction of graphene edges and for the Si impurity coupling to topological defects in bulk graphene.

In this work, a novel Schottky barrier height tuning method is proposed, which realizes the reversible conversion between Schottky contact and Ohmic contact by the treatment of triboelectric nanogenerator. By this method, a Schottky to Ohmic reversible (SOR) biosensor is developed for achieving highly sensitive detection of a neurotransmitter and neural electric impulse in a physiological environment.

Abstract

Schottky and Ohmic contacts–based electronics play an important role in highly sensitive detection of biomolecules and neural electric impulses, respectively. The reversible conversion between these two contacts appears especially important for multifunctional sensing by just one biosensor. Here, Schottky barrier height (SBH) is successfully tuned by triboelectric nanogenerator (TENG) and the same device is made to achieve reversible conversion between Schottky contact and Ohmic contact. In the same Schottky to Ohmic reversible (SOR) biosensor, highly sensitive detections of biomolecule (i.e., neurotransmitter) and neural electric signal are achieved at different contact states. The SOR biosensor reveals the feasibility of using one device to realize multifunctional detection. This work proposes a simple and significant method to achieve reversible tuning between the Schottky contact and Ohmic contact on one device by TENG, which exhibits great potential in developing multifunctional and high‐sensitivity biosensors, rectifiers, and other functional electronic devices.

The discovery of high-temperature (Tc) superconductivity in monolayer FeSe on SrTiO3 raised a fundamental question: Whether high Tc is commonly realized in monolayer iron-based superconductors. Tetragonal FeS is a key material to resolve this issue because bulk FeS is a superconductor with Tc comparable to that of isostructural FeSe. However,...

Nature Nanotechnology, Published online: 25 November 2019; doi:10.1038/s41565-019-0590-z

Author Correction: Rapid gate-based spin read-out in silicon using an on-chip resonator

The phases occurring on the open‐circuit potential for the lithiation of magnetite are identified through iteration between first‐principles studies and systematic combined refinement with X‐ray absorption spectroscopy (XAS), X‐ray diffraction (XRD), neutron diffraction, and the measured open‐circuit potential. This work is broadly applicable to other nano‐ and mesoscaled systems that exhibit phase change behavior as a function of crystallite size and that have suffered from difficult or crystallite‐size‐dependent phase identification.

Abstract

Nanostructured materials can exhibit phase change behavior that deviates from the macroscopic phase behavior. This is exemplified by the ambiguity for the equilibrium phases driving the first open‐circuit voltage (OCV) plateau for the lithiation of Fe₃O₄ nanocrystals. Adding complexity, the relaxed state for Li _x Fe₃O₄ is observed to be a function of electrochemical discharge rate. The phases occurring on the first OCV plateau for the lithiation of Fe₃O₄ nanocrystals have been investigated with density functional theory (DFT) through the evaluation of stable, or hypothesized metastable, reaction pathways. Hypotheses are evaluated through the systematic combined refinement with X‐ray absorption spectroscopy (XAS), X‐ray diffraction (XRD) measurements, neutron‐diffraction measurements, and the measured OCV on samples lithiated to x = 2.0, 3.0, and 4.0 in Li _x Fe₃O₄. In contrast to the Li–Fe–O bulk phase thermodynamic pathway, Fe⁰ is not observed as a product on the first OCV plateau for 10–45 nm nanocrystals. The phase most consistent with the systematic refinement is LiFe₃O₄, showing Li+Fe cation disorder. The observed equilibrium concentration for conversion to Fe⁰ occurs at x = 4.0. These definitive phase identifications rely heavily on the systematic combined refinement approach, which is broadly applicable to other nano‐ and mesoscaled systems that have suffered from difficult or crystallite‐size‐dependent phase identification.

Raman spectroscopy is a precious tool for the characterization of van der Waals materials, e.g. for the determination of the layer number in thin exfoliated flakes. For sensitive materials, however, this method can be dramatically invasive. In particular, the light intensity required to obtain a significant Raman signal is sufficient to immediately photo-oxidize few-layer thick metallic van der Waals materials. In this work we investigated the impact of the environment on Raman characterization of thin NbSe 2 crystals. We show that in ambient conditions the flake is locally oxidized even for very low illumination intensity. Based on this extreme sensitivity to the presence of light and oxygen, we could study the air-tightness of the hBN encapsulation method, the most common passivation method for a wide range of 2D material-based devices. We find that only fully encapsulated devices are reliably air-tight. On the contrary, a simple hBN cover from the top does not preve...