Parallel Logic Operations in Electrically Tunable Two-Dimensional Homojunctions.

Two-dimensional materials show great potential for future electronics beyond silicon materials. Here, we report an exotic multiple-port device based on multiple electrically tunable planar p-n homojunctions formed in a two-dimensional (2D) ambipolar semiconductor, tungsten diselenide (WSe). In this device, we prepare multiple gates consisting of a global gate and several local gates, by which electrostatically induced holes and electrons are simultaneously accumulated in a WSe channel, and furthermore, at the boundaries, p-n junctions are formed as directly visualized by Kelvin probe force microscopy.

Dimension-Controlled VO Film for Optoelectronic Logic Gates and Information Encryption.

As the fields of photonics and information technology develop, a lot of novel applications based on VO material, such as optoelectronic computing and information encryption, have been developed. While the performance of these devices was not only closely associated with the VO phase transition properties but also depended on their dimensional characteristics. In the current study, we conducted the dimension-controlled vanadium dioxide (VO) film growth, resulting in the epitaxial 2-dimensional (2D) VO film and well-distributed 3-dimensional (3D) VO crystal film deposition, respectively.

Multifield-Modulated Spintronic Terahertz Emitter Based on a Vanadium Dioxide Phase Transition.

The efficient generation and active modulation of terahertz (THz) waves are strongly required for the development of various THz applications such as THz imaging/spectroscopy and THz communication. In addition, due to the increasing degree of integration for the THz optoelectronic devices, miniaturizing the complex THz system into a compact unit is also important and necessary. Today, integrating the THz source with the modulator to develop a powerful, easy-to-adjust, and scalable or on-chip THz emitter is still a challenge.

Quantum imaging of the reconfigurable VO synaptic electronics for neuromorphic computing.

Neuromorphic computing has shown remarkable capabilities in silicon-based artificial intelligence, which can be optimized by using Mott materials for functional synaptic connections. However, the research efforts focus on two-terminal artificial synapses and envisioned the networks controlled by silicon-based circuits, which is difficult to develop and integrate. Here, we propose a dynamic network with laser-controlled conducting filaments based on electric field-induced local insulator-metal transition of vanadium dioxide.

Liquid-Metal-Assisted Synthesis of Patterned GaN Thin Films for High-Performance UV Photodetectors Array.

GaN's outstanding physical characteristics allow for a wide range of applications in numerous industries. Although individual GaN-based ultraviolet (UV) photodetectors are the subject of in-depth research in recent decades, the demand for photodetectors array is rising as a result of advances in optoelectronic integration technology. However, as a prerequisite for constructing GaN-based photodetectors array, large-area, patterned synthesis of GaN thin films remains a certain challenge.

Multiphysical Field Modulated VO Device for Information Encryption.

In the information explosion society, information security is highly demanded in the practical application, which raised a surge of interest in designing secure and reliable information transmission channels based on the inherent properties of emerging devices. Here, an innovative strategy to achieve the data encryption and reading during the data confidential transmission based on VO device is proposed. Owing to the specific insulator-to-metal transition property of VO , the phase transitions between the insulator and metallic states are modulated by the combination of electric field, temperature, and light radiation.

Ultrahigh Effective Diffusion in Oxide by Engineering the Interfacial Transporter Channels.

Mass storage and removal in solids always play a vital role in technological applications such as modern batteries and neuronal computations. However, they were kinetically limited by the slow diffusional process in the lattice, which made it challenging to fabricate applicable conductors with high electronic and ionic conductivities at room temperature. Here, we proposed an acid solution/WO/ITO sandwich structure and achieved ultrafast H transport in the WO layer by interfacial job-sharing diffusion, which means the spatially separated transport of the H and e in different layers.

Fabrication of a VO-Based Tunable Metasurface by Electric-Field Scanning Probe Lithography with Precise Depth Control.

Vanadium dioxide (VO) is widely employed in developing tunable optoelectronic devices due to its significant changes in optical and electric properties upon phase transition. To fabricate the VO-based functional devices down to the micro/nanoscale, a high-resolution processing technique is in demand. Scanning probe lithography (SPL) on the basis of a tip-induced electric field provides a promising approach for prototyping.

Enhanced Pd/a-WO /VO Hydrogen Gas Sensor Based on VO Phase Transition Layer.

The utilization of clean hydrogen energy is becoming more feasible for the sustainable development of this society. Considering the safety issues in the hydrogen production, storage, and utilization, a sensitive hydrogen sensor for reliable detection is essential and highly important. Though various gas sensor devices are developed based on tin oxide, tungsten trioxide, or other oxides, the relatively high working temperature, unsatisfactory response time, and detection limitation still affect the extensive applications.

Enhanced Contrast of WO-Based Smart Windows by Continuous Li-Ion Insertion and Metal Electroplating.

The electrochromic WO smart window based on an aqueous electrolyte shows an excellent liquid/solid interface and thus can achieve a fast electrochromic response, while the aqueous electrolyte has a limited electrochemical window, which probably induces the H reduction and degrades the practical application. Here, we propose a strategy to modify the traditional Li acidic aqueous electrolyte by adding some selective inert metal ions, which not only improve the electrochromic performance but also avoid the possible production of hydrogen bubbles due to the broadened electrochemical window. Furthermore, reversible electroplating of inert metal ions will occur, leading to an enhanced optical transmission change of up to 77.

Self-adaptive integration of photothermal and radiative cooling for continuous energy harvesting from the sun and outer space.

The sun (∼6,000 K) and outer space (∼3 K) are two significant renewable thermodynamic resources for human beings on Earth. The solar thermal conversion by photothermal (PT) and harvesting the coldness of outer space by radiative cooling (RC) have already attracted tremendous interest. However, most of the PT and RC approaches are static and monofunctional, which can only provide heating or cooling respectively under sunlight or darkness.

Facile Removal of Bulk Oxygen Vacancy Defects in Metal Oxides Driven by Hydrogen-Dopant Evaporation.

Oxygen vacancy is a common defect in metal oxides that causes appreciable damage to material properties and performance. Removing bulk defects of oxygen vacancy (V) typically needs harsh conditions such as high-temperature annealing. Supported by first-principles simulations, we propose an effective strategy of removing V bulk defects in metal oxides by evaporating hydrogen dopants.

Photoassisted Electron-Ion Synergic Doping Induced Phase Transition of n-VO/p-GaN Thin-Film Heterojunction.

As a typical correlated metal oxide, vanadium dioxide (VO) shows specific metal-insulator transition (MIT) properties and demonstrates great potential applications in ultrafast optoelectronic switch, resistive memory, and neuromorphic devices. Effective control of the MIT process is essential for improving the device performance. In the current study, we have first proposed a photoassisted ion-doping method to modulate the phase transition of the VO layer based on the photovoltaic effect and electron-ion synergic doping in acid solution.

Atomic Origin for Hydrogenation Promoted Bulk Oxygen Vacancies Removal in Vanadium Dioxide.

Oxygen vacancies (V), a common type of point defect in metal oxides materials, play important roles in the physical and chemical properties. To obtain stoichiometric oxide crystal, the pre-existing V is always removed via careful post-annealing treatment at high temperature in an air or oxygen atmosphere. However, the annealing conditions are difficult to control, and the removal of V in the bulk phase is restrained because of the high energy barrier of V migration.

Tunable Hydrogen Doping of Metal Oxide Semiconductors with Acid-Metal Treatment at Ambient Conditions.

Hydrogen doping of metal oxide semiconductors is promising for manipulation of their properties toward various applications. Yet it is quite challenging because it requires harsh reaction conditions and expensive metal catalysts. Meanwhile, acids as a cheap source of protons have long been unappreciated.

Electron-Proton Co-doping-Induced Metal-Insulator Transition in VO Film via Surface Self-Assembled l-Ascorbic Acid Molecules.

Charge doping is an effective way to induce the metal-insulator transition (MIT) in correlated materials for many important utilizations, which is however practically limited by problem of low stability. An electron-proton co-doping mechanism is used to achieve pronounced phase modulation of monoclinic vanadium dioxide (VO ) at room temperature. Using l-ascorbic acid (AA) solution to treat VO , the ionized AA species donate electrons to the adsorbed VO surface.

Gate-controlled VO phase transition for high-performance smart windows.

Vanadium dioxide (VO) is a promising material for developing energy-saving "smart windows," owing to its infrared thermochromism induced by metal-insulator transition (MIT). However, its practical application is greatly limited by its relatively high critical temperature (~68°C), low luminous transmittance (<60%), and poor solar energy regulation ability (<15%). Here, we developed a reversible and nonvolatile electric field control of the MIT of a monoclinic VO film.

Temperature-Controlled Asymmetric Transmission of Electromagnetic Waves.

Chiral materials can exhibit different levels of transmission for opposite propagation directions of the same electromagnetic wave. Here we demonstrate thermal switching of asymmetric transmission of linearly polarized terahertz waves. The effect is observed in a terahertz metamaterial containing 3D-chiral metallic inclusions and achiral vanadium dioxide inclusions.

Dynamic Electronic Doping for Correlated Oxides by a Triboelectric Nanogenerator.

The metal-insulator transition of vanadium dioxide (VO ) is exceptionally sensitive to charge density and electron orbital occupancy. Thus three-terminal field-effect transistors with VO channels are widely adopted to control the phase transition by external gating voltage. However, current leakage, electrical breakdown, or interfacial electrochemical reactions may be inevitable if conventional solid dielectrics or ionic-liquid layers are used, which possibly induce Joule heating or doping in the VO layer and make the voltage-controlled phase transition more complex.

Revealing the role of oxygen vacancies on the phase transition of VO film from the optical-constant measurements.

Vanadium dioxide (VO) material shows a distinct metal-insulator transition (MIT) at the critical temperature of ∼340 K. Similar to other correlated oxides, the MIT properties of VO is always sensitive to those crystal defects such as oxygen vacancies. In this study, we investigated the oxygen vacancies related phase transition behavior of VO crystal film and systematically examined the effect of oxygen vacancies from the optical constant measurements.

Non-catalytic hydrogenation of VO in acid solution.

Hydrogenation is an effective way to tune the property of metal oxides. It can conventionally be performed by doping hydrogen into solid materials with noble-metal catalysis, high-temperature/pressure annealing treatment, or high-energy proton implantation in vacuum condition. Acid solution naturally provides a rich proton source, but it should cause corrosion rather than hydrogenation to metal oxides.