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Atomically two-dimensional (2D) layered ferroelectric semiconductors, in which the polarization switching process occurs within the channel material itself, offer a new material platform that could drive electronic components towards structural simplification and high-density integration. Here, a room-temperature 2D layered ferroelectric semiconductor, bismuth oxychalcogenides (Bi

Converting vapor precursors to solid nanostructures via a liquid noble-metal seed is a common vapor deposition principle. However, such a noble-metal-seeded process is excluded from the crystalline halide perovskite synthesis, mainly hindered by the growth mechanism shortness. Herein, powered by a spontaneous exothermic nucleation process (Δ

Lead-based halide perovskites (APbX3, where A = organic or inorganic cation, X = Cl, Br, I) are suitable materials for many optoelectronic devices due to their many attractive properties. However, the concern of lead toxicity and the poor ambient and operational stability of the organic cation group greatly limit their practical utilization. Therefore, there has recently been great interest in lead-free, environment-friendly all-inorganic halide perovskites (IHPs). Sb and Sn are common species suggested to replace Pb for Pb-free IHPs. However, the large difference in the melting points of the precursor materials (e.g., CsBr and SbBr3 precursors for Cs3Sb2Br9) makes the chemical vapor deposition (CVD) growth of high-quality Pb-free IHPs a very challenging task. In this work, we developed a two-step CVD method to overcome this challenge and successfully synthesized Pb-free Cs3Sb2Br9 perovskite microplates. Cs3Sb2Br9 microplates ∼25 μm in size with the exciton absorption peak at ∼2.8 eV and a band gap of ∼2.85 eV were obtained. The microplates have a smooth hexagonal morphology and show a large Stokes shift of ∼450 meV and exciton binding energy of ∼200 meV. To demonstrate the applications of these microplates in optoelectronics, simple photoconductive devices were fabricated. These photodetectors exhibit a current on/off ratio of 2.36 × 102, a responsivity of 36.9 mA/W, and a detectivity of 1.0 × 1010 Jones with a fast response of rise and decay time of 61.5 and 24 ms, respectively, upon 450 nm photon irradiation. Finally, the Cs3Sb2Br9 microplates also show good stability in ambient air without encapsulation. These results demonstrate that the 2-step CVD process is an effective approach to synthesize high-quality all-inorganic lead-free Cs3Sb2Br9 perovskite microplates that have the potential for future high-performance optoelectronic device applications.

Hybrid organolead halide perovskites have attracted tremendous attention due to their recent success as high efficiency solar cell materials and their fascinating material properties uniquely suitable for optoelectronic devices. However, the poor ambient and operational stability as well as the concern of lead toxicity greatly hamper their practical utilization. In this work, crystalline, all-inorganic and lead-free Cs3Sb2I9 perovskite microplates are successfully synthesized by a two-step chemical vapor deposition method. As compared with other typical lead-free perovskite materials, the Cs3Sb2I9 microplates demonstrate excellent optoelectronic properties, including substantial enhancements in the Stokes shift, exciton binding energy and electron-phonon coupling. Simple photoconductive devices fabricated using these microplates exhibit an ultra-fast response with the rise and decay time constants down to 96 and 58 µs, respectively. This respectable photoconductor performance can be regarded as a record among all the lead-free perovskite materials. Importantly, these photodetectors show superior thermal stability in a wide temperature range, capable to function reversibly between 80 and 380 K, indicating their robustness to operate under both low and high temperatures. All these results evidently suggest the technological potential of inorganic lead-free Cs3Sb2I9 perovskite microplates for next-generation high-performance optoelectronic devices.

While halide perovskite electronics are rapidly developing, they are greatly limited by the inferior charge transport and poor stability. In this work, effective surface charge transfer doping of vapor-liquid-solid (VLS)-grown single-crystalline cesium lead bromide perovskite (CsPbBr3) nanowires (NWs) via molybdenum trioxide (MoO3) surface functionalization is achieved. Once fabricated into NW devices, due to the efficient interfacial charge transfer and reduced impurity scattering, a 15× increase in the field-effect hole mobility (μh) from 1.5 to 23.3 cm2/(V s) is accomplished after depositing the 10 nm thick MoO3 shell. This enhanced mobility is already better than any mobility value reported for perovskite field-effect transistors (FETs) to date. The photodetection performance of these CsPbBr3/MoO3 core-shell NWs is also investigated to yield a superior responsivity (R) up to 2.36 × 103 A/W and an external quantum efficiency (EQE) of over 5.48 × 105% toward the 532 nm regime. Importantly, the MoO3 shell can provide excellent surface passivation to the CsPbBr3 NW core that minimizes the diffusion of detrimental water and oxygen molecules, improving the air stability of CsPbBr3/MoO3 core-shell NW devices. All these findings evidently demonstrate the surface doping as an enabling technology to realize high-mobility and air-stable low-dimensional halide perovskite devices.

Quasi-2D halide perovskites, especially the Ruddlesden-Popper perovskites (RPPs), have attracted great attention because of their promising properties for optoelectronics; however, there are still serious drawbacks, such as inefficient charge transport, poor stability, and unsatisfactory mechanical flexibility, restricting further utilization in advanced technologies. Herein, high-quality quasi-2D halide perovskite thin films are successfully synthesized with the introduction of the unique bication ethylenediammonium (EDA) via a one-step spin-coating method. This bication EDA, with short alkyl chain length, can not only substitute the typically bulky and weakly van der Waals-interacted organic bilayer spacer cations forming the novel Dion-Jacobson phase to enhance the mechanical flexibility of the quasi-2D perovskite (e.g., EDA(MA)n-1PbnI3n+1; MA = CH3NH3+) but also serve as a normal cation to achieve the more intact films (e.g., (iBA)2(MA)3-2x(EDA)xPb4I13). When fabricated into photodetectors, these optimized EDA-based perovskites deliver an excellent responsivity of 125 mA/W and a fast response time down to 380 μs under 532 nm irradiation. More importantly, the device with the Dion-Jacobson phase perovskite can be bent down to a radius of 2 mm and processed with 10,000 cycles of the bending test without any noticeable performance degradation because of its superior structure to RPPs. Besides, these films do not exhibit any material deterioration after ambient storage for 30 days. All these performance parameters are already comparable or even better than those of the state-of-the-art RPPs recently reported. This work provides valuable design guidelines of the quasi-2D perovskites to obtain high-performance flexible photodetectors for next-generation optoelectronics.

Electrical manipulation of skyrmions attracts considerable attention for its rich physics and promising applications. To date, such a manipulation is realized mainly via spin-polarized current based on spin-transfer torque or spin-orbital torque effect. However, this scheme is energy-consuming and may produce massive Joule heating. To reduce energy dissipation and risk of heightened temperatures of skyrmion-based devices, an effective solution is to use electric field instead of current as stimulus. Here, we realize an electric-field manipulation of skyrmions in a nanostructured ferromagnetic/ferroelectrical heterostructure at room temperature via an inverse magneto-mechanical effect. Intriguingly, such a manipulation is non-volatile and exhibits a multi-state feature. Numerical simulations indicate that the electric-field manipulation of skyrmions originates from strain-mediated modification of effective magnetic anisotropy and Dzyaloshinskii-Moriya interaction. Our results open a direction for constructing low-energy-dissipation, non-volatile, and multi-state skyrmion-based spintronic devices., Accepted by Nature Communications 11, 3577 (2020)

The strain modulation on the magnetic and electronic transport properties of the ferromagnetic films is one of the hot topics due to the practical applications in flexible and wearable spintronic devices. However, the large strain-induced saturation magnetization and resistance change is not easy to achieve because most of the ferromagnetic films deposited on flexible substrates are polycrystalline or amorphous. Here, the flexible epitaxial γ'-Fe4N/mica films are fabricated by facing-target reactive sputtering. At a tensile strain with a radius of curvature (ROC) of 3 mm, the saturation magnetization (Ms) of the γ'-Fe4N/mica film is tailored significantly with a maximal variation of 210%. Meanwhile, the magnetic anisotropy was broadly tunable at different strains, where the out-of-plane Mr/Ms at a tensile strain of ROC = 2 mm is six times larger than that at the unbent state. Besides, the strain-tailored longitudinal resistance Rxx and anomalous Hall resistivity ρxy appear where the drop of Rxx (ρxy) reaches 5% (22%) at a tensile strain of ROC = 3 mm. The shift of the nitrogen position in the γ'-Fe4N unit cell at different bending strains plays a key role in the strain-tailored magnetic and electronic transport properties. The flexible epitaxial γ'-Fe4N films have the potential applications in magneto- and electromechanical wearable spintronic devices.

Due to the excellent electrical and optical properties, small bandgap III–V nanowire (NW) materials hold great promise for future electronics and optoelectronics. In particular, InAs1−xSbx, the ternary alloy of InAs and InSb, is one of the most studied III–V nanomaterial systems; however, the As-rich InAs1−xSbx NWs are usually obtained with significant crystal phase mixing and high density of planar defects, limiting their electrical transport characteristics. In this work, unusual phase-pure zinc blende and highly-crystalline As-rich InAs1−xSbx NWs with x < 0.2 are successfully achieved using solid-source chemical vapor deposition, and this excellent phase-purity and crystallinity has not been reported elsewhere. By simply controlling the precursor powder mixing ratio between InAs and InSb, the morphology and composition of NWs can be controlled reliably. When these InAs1−xSbx NWs are fabricated into field-effect transistors, they exhibit a superior device performance, especially a high electron mobility. Specifically, the average peak mobility of the InAs0.948Sb0.052 NW device can be improved up to 3160 cm2 V−1 s−1, which is substantially better than that of the pure InAs NW counterparts (2030 cm2 V−1 s−1). This mobility enhancement can be attributed to the Sb-alloyed-induced electron effective mass reduction. Also, there exists a surface charge accumulation layer on the NWs as confirmed by the decrease of device transconductance measured under vacuum, indicating future possibilities to manipulate the NW surface for enhanced functionality. All these results evidently indicate the potential of these phase-pure zinc blende As-rich InAs1−xSbx NWs for high-mobility devices.

Defects exist ubiquitously in crystal materials, and usually exhibit a very different nature from the bulk matrix. Hence, their presence can have significant impacts on the properties of devices. Although it is well accepted that the properties of defects are determined by their unique atomic environments, the precise knowledge of such relationships is far from clear for most oxides because of the complexity of defects and difficulties in characterization. Here, we fabricate a 36.8° SrRuO3 grain boundary of which the transport measurements show a spin-valve magnetoresistance. We identify its atomic arrangement, including oxygen, using scanning transmission electron microscopy and spectroscopy. Based on the as-obtained atomic structure, the density functional theory calculations suggest that the spin-valve magnetoresistance occurs because of dramatically reduced magnetic moments at the boundary. The ability to manipulate magnetic properties at the nanometer scale via defect control allows new strategies to design magnetic/electronic devices with low-dimensional magnetic order., We manipulate the local magnetic properties of SrRuO3 at a grain boundary, providing new strategies to design atomic-sized magnetic/electronic devices with low-dimensional magnetic order via defect engineering.

Lead-based halide perovskites (APbX

Electric-field control of magnetization is imperatively desired in spintronic devices with high speed, low energy exhaust and small size. Herein, electric-field control of magnetization and the ferromagnetic resonance field was achieved in the epitaxial γ′-Fe4N/PMN-PT [Pb(Mg1/3Nb2/3)0.7Ti0.3O3(011)] heterostructures. At an electric field of +10 kV cm−1, remanent magnetization with a change as large as ∼900 emu cm−3 was observed, together with a tunable ferromagnetic resonance field of 700 Oe. Moreover, nonvolatile control of magnetic anisotropy was also realized. The magnetoelectric coupling (MEC) achieved in this study can be ascribed to the spin-dependent screening effect. In addition, remarkable negative damping appears in the high-frequency measurement. These results provide a new platform for greatly enhancing the MEC in properly designed FM/FE heterostructures.

2D metal phosphide loop-sheet heterostructures are controllably synthesized by edge-topological regulation, where Ni2 P nanosheets are edge-confined by the N-doped carbon loop, containing ultrafine NiFeP nanocrystals (denoted as NiFeP@NC/Ni2 P). This loop-sheet feature with lifted-edges prevents the stacking of nanosheets and induces accessible open channels for catalytic site exposure and gas bubble release. Importantly, these NiFeP@NC/Ni2 P hybrids exhibit a remarkable oxygen evolution activity with an overpotential of 223 mV at 20 mA cm-2 and a Tafel slope of 46.1 mV dec-1 , constituting the record-high performance among reported metal phosphide electrocatalysts. The NiFeP@NC/Ni2 P hybrids are also employed as both anode and cathode to achieve an alkaline electrolyzer for overall water splitting, delivering a current density of 10 mA cm-2 with a voltage of 1.57 V, comparable to that of the commercial Pt/C||RuO2 couple (1.56 V). Moreover, a photovoltaic-electrolysis coupling system can as well be effectively established for robust overall water splitting. Evidently, this ingenious protocol would expand the toolbox for designing efficient 2D nanomaterials for practical applications.

A high-spin ruthenate phase is achieved at the SrRuO${}_{3}$/SrTiO${}_{3}$ interface via a solid ionic chemical junction, which benefits from the distinct formation energies and diffusion barriers of oxygen vacancies across the heterostructure. This high-spin SrRuO${}_{3}$ phase can be reversibly switched by electric field in a solid-state ionic gating device, providing a framework for atomic design of controllable functionalities in strongly correlated oxides using solid-chemistry tools.

The gallop of artificial intelligence ignites urgent demand on information processing systems with ultralow power consumption, reliable multi-parameter control and high operation efficiency. Here, the poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) wrapped InGaAs nanowire (NW) artificial synapses capable to operate with record-low subfemtojoule power consumption are presented. The essential synaptic behaviors are mimicked and modulated effectively by adjusting the thickness of top modulation gate P(VDF-TrFE) films. Moreover, the long-term depression is realized by applying visible light (450 nm) because of the negative photoconductivity of InGaAs nanowires. Combined with optimal P(VDF-TrFE) films, the synaptic devices have the more linear long-term potentiation/depression characteristics and the faster supervised learning process simulated by hardware neural networks. The Pavlovian conditioning is also performed by combining electrical and infrared stimuli. Evidently, these ultralow-operating-power synapses are demonstrated with the brain-like behaviors, effective function modulation, and more importantly, the synergistic photoelectric modulation, which illustrates the promising potentials for neuromorphic computing systems.

Although there are recent advances in many areas of quasi-2D halide perovskites, photodetectors based on these materials still cannot achieve satisfactory performance for practical applications where high responsivity, fast response, self-powered nature, and excellent mechanical flexibility are urgently desired. Herein, utilizing one-step spin-coating method, self-assemble quasi-2D perovskite films with graded phase distribution in the order of increasing number of metal halide octahedral layers are successfully prepared. Gradient type-II band alignments along the out-of-plane direction of perovskites with spontaneous separation of photo-generated electrons and holes are obtained and then employed to construct self-powered vertical-structure photodetectors for the first time. Without any driving voltage, the device exhibits impressive performance with the responsivity up to 444 mA W-1 and ultrashort response time down to 52 µs. With a bias voltage of 1.5 V, the device responsivity becomes 3463 mA W-1 with the response speed as fast as 24 µs. Importantly, the device's mechanical flexibility is greatly enhanced since the photocurrent prefers flowing through the metal halide octahedral layers between the top and bottom contact electrodes in the vertical device structure, being more tolerant to film damage. These results evidently indicate the potential of graded quasi-2D perovskite phases for next-generation optoelectronic devices.

The structure, magnetic and electronic transport properties of the facing-target reactively sputtered polycrystalline CuFe3N films have been investigated systematically. The CuFe3N film has a cubic antiperovskite structure. The saturation magnetization satisfied the modified Bloch's spin wave theory. At 300 K, the saturation magnetization of the 80 nm-thick CuFe3N films is 402 emu/cm3, which is smaller than 800 emu/cm3 of the 80 nm-thick polycrystalline Fe4N films. The CuFe3N films are metallic. The anomalous Hall effect in the “dirty region” of σxx

Epitaxial γ′-Fe4N films with different thicknesses were fabricated on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) substrates by facing-target reactive sputtering. The magnetoelectric coupling (MEC) in the samples was systematically investigated. Firstly, the magnetization along different in-plane directions is tunable by the electric field. It was found that MEC in the films on PMN-PT(011) is stronger than that on PMN-PT(001) due to the different in-plane magnetic anisotropy. Moreover, the magnetoelectric coupling is strongly related to the γ′-Fe4N film thickness, which can be ascribed to the competition between the strain and spin-dependent screening effect induced MEC. Additionally, the electric-field tailored remanent magnetization of the samples gradually increases with temperature due to the thermal agitation. Besides, the electric-field effect on the out-of-plane magnetic hysteresis loops is consistent with the in-plane cases. The results are of benefit to the development of the electric-field controlled spintronic devices.

The microstructure and high frequency properties of facing-target sputtered epitaxial γ'-Fe4N films were investigated in detail. It was found that the eddy current in ultrathin γ'-Fe4N films is too small to influence the ferromagnetic resonance (FMR) linewidth, where the linewidth is mostly determined by intrinsic damping and the two-magnon scattering (TMS) process. In relatively thick films, the TMS process can significantly affect the linewidth due to the roughness on the sample surface. However, the TMS process in a thin film is quite weak because of its smooth surface. The Gilbert damping constant of about 0.0135 in our γ'-Fe4N films is smaller than the experimental value in the previous work. Moreover, substrates can also influence the FMR linewidth of the γ'-Fe4N films by the TMS process. Besides, the resonance field of polycrystalline γ'-Fe4N film is larger than the epitaxial ones because of the lack of a magnetic anisotropic field, but the linewidth of the polycrystalline γ'-Fe4N film is smaller.