To overcome the intrinsic inefficiency of the von Neumann architecture, neuromorphic devices that perform analog vector-matrix multiplication have been highlighted for achieving power- and time-efficient data processing. In particular, artificial synapses, of which conductance should be programmed to represent the synaptic weights of the artificial neural network, have been intensively researched to realize neuromorphic devices. Here, inspired by excitatory and inhibitory synapses, we develop an artificial optoelectronic synapse that shows both potentiation and depression characteristics triggered only by optical inputs. The design of the artificial optoelectronic synapse, in which excitatory and inhibitory synaptic phototransistors are serially connected, enables these characteristics by spatiotemporally irradiating the phototransistor channels with optical pulses. Furthermore, a negative synaptic weight can be realized without the need for electronic components such as comparators. With such attributes, the artificial optoelectronic synapse is demonstrated to classify three digits with a high recognition rate (98.3%) and perform image preprocessing via analog vector-matrix multiplication.
All solid-state batteries (ASSBs) are the holy grails of rechargeable batteries, where extensive searches are ongoing in the pursuit of ideal solid-state electrolytes. Nevertheless, there is still a long way off to the satisfactorily high (enough) ionic conductivity, long-term stability and especially being able to form compatible interfaces with the solid electrodes. Herein, we have explored ionic transport behavior and high mobility in the sub-nano pore networks in the framework structures. Macroscopically, the frameworked electrolyte behaves as a solid, and however in the (sub)-nano scales, the very limited number of solvent molecules in confinement makes them completely different from that in liquid electrolyte. Differentiated from a liquid-electrolyte counterpart, the interactions between the mobile ions and surrounding molecules are subject to dramatic changes, leading to a high ionic conductivity at room temperature with a low activation energy. Li+ ions in the sub-nano cages of the network structure are highly mobile and diffuse rather independently, where the rate-limiting step of ions crossing cages is driven by the local concentration gradient and the electrostatic interactions between Li+ ions. This new class of frameworked electrolytes (FEs) with both high ionic conductivity and desirable interface with solid electrodes are demonstrated to work with Li-ion batteries, where the ASSB with LiFePO4 shows a highly stable electrochemical performance of over 450 cycles at 2°C at room temperature, with an almost negligible capacity fade of 0.03‰ each cycle. In addition, the FE shows outstanding flexibility and anti-flammability, which are among the key requirements of large-scale applications.
The rapid advancement of AI-enabled applications has resulted in an increasing need for energy-efficient computing hardware. Logic-in-memory is a promising approach for processing the data stored in memory, wherein fast and efficient computations are possible owing to the parallel execution of reconfigurable logic operations. In this study, a dual-logic-in-memory device, which can simultaneously perform two logic operations in four states, is demonstrated using van der Waals ferroelectric field-effect transistors (vdW FeFETs). The proposed dual-logic-in-memory device, which also acts as a two-bit storage device, is a single bidirectional polarization-integrated ferroelectric field-effect transistor (BPI-FeFET). It is fabricated by integrating an in-plane vdW ferroelectric semiconductor SnS and an out-of-plane vdW ferroelectric gate dielectric material—CuInP2S6. Four reliable resistance states with excellent endurance and retention characteristics were achieved. The two-bit storage mechanism in a BPI-FeFET was analyzed from two perspectives: carrier density and carrier injection controls, which originated from the out-of-plane polarization of the gate dielectric and in-plane polarization of the semiconductor, respectively. Unlike conventional multilevel FeFETs, the proposed BPI-FeFET does not require additional pre-examination or erasing steps to switch from/to an intermediate polarization, enabling direct switching between the four memory states. To utilize the fabricated BPI-FeFET as a dual-logic-in-memory device, two logical operations were selected (XOR and AND), and their parallel execution was demonstrated. Different types of logic operations could be implemented by selecting different initial states, demonstrating various types of functions required for numerous neural network operations. The flexibility and efficiency of the proposed dual-logic-in-memory device appear promising in the realization of next-generation low-power computing systems.
The discovery of semiconductor has witnessed remarkable strides toward high performance of photodetectors attributed to its excellent carrier properties. However, semimetal, owning to the high carrier concentration and low carrier mobility compared to those of semiconductor, is generally considered unsuitable for photodetection. Herein, we demonstrate an outstanding photodetection in a layered semimetal titanium diselenide (TiSe2) in Bose-Einstein condensation (BEC) state. High sensitivity of semimetal photodetector is realized in the range of visible, infrared and terahertz bands. The noise equivalent power (NEP) has threefold improvement at the visible and infrared wavebands, and significant decrease by one order of magnitude in the terahertz frequencies via BEC phenomenon, attributed to the electrical parameter variation after condensation. The best NEP value in the terahertz frequency is comparable to that of commercial Si photodetector. Our results show another recipe to fabricate high performance of photodetection via semimetal except for semiconductor and pave the way to exploit macroscopic quantum phenomena for optoelectronics.
Advanced atomic tracking techniques play a critical role in characterizing structural evolution, elucidating fundamental mechanisms of exotic phenomena and tailoring delicate properties. Thermally driven structural modulation in 2D crystals, such as the charge density wave (CDW), often leads to intriguing quantum properties, making them a valuable platform for exploring fundamental physics and potential device applications. However, despite their significance, experimental studies addressing atomic tracking of thermally-driven structural evolution in 2D crystals have been limited. Herein, we utilize high-accuracy variable-temperature atomic tracking measurements with scanning tunneling microscopy (STM) to directly observe a series of structural transitions in a model 2D crystal, namely NbSe2. With the atomic tracking technique, we confirm the existence of the universal thermally-driven CDW transition hysteresis between the heating and cooling cycles. This transition hysteresis, characterized by a constant temperature offset, represents a new phenomenon of structural evolution. Our findings provide a feasible method to track CDW transitions at the atomic scale in 2D crystals, significantly contributing to a better understanding and the potential modulation of these materials' functions in nanodevices.
The crystal-structure symmetry in real space can be inherited in the reciprocal space, making high-symmetry materials the top candidates for thermoelectrics due to their potential for significant electronic band degeneracy. A practical indicator that can quantitatively describe structural changes would help facilitate the advanced thermoelectric material design. In face-centered cubic structures, the spatial environment of the same crystallographic plane family is isotropic, such that the distances between the close-packed layers can be derived from the atomic distances within the layers. Inspired by this, the relationship between inter- and intra-layer geometric information can be used to compare crystal structures with their desired cubic symmetry. The close-packed layer spacing was found to be a practical guideline of crystal structure symmetry in IV-VI chalcogenides and I-V-VI2 ternary semiconductors, both of which are historically important thermoelectrics. The continuous structural evolution toward high symmetry can be described by the layer spacing when temperature or/and composition change, which is demonstrated by a series of pristine and alloyed thermoelectric materials in this work. The layer-spacing-based guideline provides a quantitative pathway for manipulating crystal structures to improve the electrical and thermal properties of thermoelectric materials.
Solar-blind ultraviolet (UV) photodetectors based on p-organic/n-Ga2O3 hybrid heterojunctions have attracted extensive attention recently. Herein, the multifunctional solar-blind photodetector based on p-type poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT)/n-type amorphous Ga2O3 (a-Ga2O3) is fabricated and investigated, which can work in the phototransistor mode coupling with self-powered mode. With the introduction of PCDTBT, the dark current of such the a-Ga2O3-based photodetector is decreased to 0.48 pA. Meanwhile, the photoresponse parameters of the a-Ga2O3-based photodetector in the phototransistor mode to solar-blind UV light are further increased, that is, responsivity (R), photo-detectivity (D*), and external quantum efficiency (EQE) enhanced to 187 A W-1, 1.3 × 1016 Jones and 9.1 × 104 % under the weak light intensity of 11 μW cm-2, respectively. Thanks to the formation of the built-in field in the p-PCDTBT/n-Ga2O3 type-II heterojunction, the PCDTBT/Ga2O3 multifunctional photodetector shows self-powered behavior. The responsivity of p-PCDTBT/n-Ga2O3 multifunctional photodetector is 57.5 mA W-1 at zero bias. Such multifunctional p-n hybrid heterojunction-based photodetectors set the stage for realizing high-performance amorphous Ga2O3 heterojunction-based photodetectors.
Electrohydrodynamic (EHD) printing technique, which deposits micro/nanostructures through high electric force, has recently attracted significant research interest owing to their fascinating characteristics in high resolution (<1 μm), wide material applicability (ink viscosity 1-10 000 cps), tunable printing modes (electrospray, electrospinning, and EHD jet printing), and compatibility with flexible/wearable applications. Since the laboratory level of the EHD printed electronics' resolution and efficiency is gradually approaching the commercial application level, an urgent need for developing EHD technique from laboratory into industrialization have been put forward. Herein, we first discuss the EHD printing technique, including the ink design, droplet formation, and key technologies for promoting printing efficiency/accuracy. Then we summarize the recent progress of EHD printing in fabrication of displays, organic field-effect transistors (OFETs), transparent electrodes, and sensors and actuators. Finally, a brief summary and the outlook for future research effort are presented.
High-voltage nickel (Ni)-rich layered oxide-based lithium metal batteries (LMBs) exhibit a great potential in advanced batteries due to the ultra-high energy density. However, it is still necessary to deal with the challenges in poor cyclic and thermal stability before realizing practical application where cycling life is considered. Among many improved strategies, mechanical and chemical stability for the electrode electrolyte interface plays a key role in addressing these challenges. Therefore, extensive effort has been made to address the challenges of electrode-electrolyte interface. In this progress, the failure mechanism of Ni-rich cathode, lithium metal anode and electrolytes are reviewed, and the latest breakthrough in stabilizing electrode-electrolyte interface is also summarized. Finally, the challenges and future research directions of Ni-rich LMBs are put forward.
Solid-state batteries that employ solid-state electrolytes (SSEs) to replace routine liquid electrolytes are considered to be one of the most promising solutions for achieving high-safety lithium metal batteries. SSEs with high mechanical modulus, thermal stability, and non-flammability can not only inhibit the growth of lithium dendrites but also enhance the safety of lithium metal batteries. However, several internal materials/electrodes-related thermal hazards demonstrated by recent works show that solid-state lithium metal batteries (SSLMBs) are not impenetrable. Therefore, understanding the potential thermal hazards of SSLMBs is critical for their more secure and widespread applications. In this contribution, we provide a comprehensive overview of the thermal failure mechanism of SSLMBs from materials to devices. Also, strategies to improve the thermal safety performance of SSLMBs are included from the view of material enhancement, battery design, and external management. Consequently, the future directions are further provided. We hope that this work can shed bright insights into the path of constructing energy storage devices with high energy density and safety.