Search

A material with reversible temperature change capability under an external electric field, known as the electrocaloric effect (ECE), has long been considered as a promising solid-state cooling solution. However, electrocaloric (EC) performance of EC materials generally is not sufficiently high for real cooling applications. As a result, exploring EC materials with high performance is of great interest and importance. Here, we report on the ECE of ferroelectric materials with van der Waals layered structure (CuInP2S6 or CIPS in this work in particular). Over 60% polarization charge change is observed within a temperature change of only 10 K at Curie temperature. Large adiabatic temperature change (|{\Delta}T|) of 3.3 K, isothermal entropy change (|{\Delta}S|) of 5.8 J kg-1 K-1 at |{\Delta}E|=142.0 kV cm-1 at 315 K (above and near room temperature) are achieved, with a large EC strength (|{\Delta}T|/|{\Delta}E|) of 29.5 mK cm kV-1. The ECE of CIPS is also investigated theoretically by numerical simulation and a further EC performance projection is provided., Comment: 32 pages, 10 figures

Molybdenum sulfide (MoS2) has attracted great interest as a promising non-precious-metal catalyst candidate to replace the precious-metal Pt catalysts for the hydrogen evolution reaction (HER). Nevertheless, the catalytic efficiency of MoS2 is significantly restricted by its density of catalytic active sites and inert basal plane. In this work, we have designed a facile one-pot solvothermal method to synthesize porous 1T-MoS2 that is integrated with atomic doping of Cu atoms. The as-prepared Cu@MoS2 sample exhibits enhanced HER performance with a low overpotential of 131 mV at the current density of 10 mA/cm2, a small Tafel slope of 51 mV/dec and as well as a good long-term stability. Enhanced HER performance can be ascribed to the synergistic effect of 1T-MoS2 metallic phase, single atom Cu doping and numerous sulfur vacancies. Theoretical calculations indicates that the adsorption energy of Cu atom on 1T-MoS2 surface (−3.68 eV) is much higher than that on 2H-MoS2 surface (−1.94 eV), moreover, the Cu atom adsorbed on the surface of the 1T-MoS2 has larger charge transfer (−0.38e), which can be contributed to further enhance HER performance of 1T-MoS2.

The mid-infrared spectral band (2–20 μm) is of significant technological importance for thermal imaging, spectroscopic sensing, and free-space communications. Lack of optical materials compatible w...

Two-dimensional (2-D) semiconductors have been intensely explored as alternative channel materials for future generation ultra-scaled transistor technology [1] , [2] , [3] , [4] , [5] , [6] , [7] , [8] . However, significant roadblocks (e.g., poor carrier mobilities [9] , [10] , [11] , instability [4,5,10], and vague potential in scaling-up [10,12–15]) exist that prevent the realization of the current state-of-the-art 2-D materials’ potential for energy-efficient electronics. The emergent solution-grown tellurene exhibits attractive attributes, e.g., high room-temperature mobility, large on-state current density, air-stability, and tunable material properties through a low-cost, scalable process, to tackle these challenges [16]. Nevertheless, the fundamental manufacturing science of the hydrothermal processing for tellurene remains elusive. Here, we report on the first systematic, data-driven learning of the process-structure-property relationship in solution-grown tellurene, revealing the process factors’ effects on tellurene’s production yield, dimensions, and transistor-relevant properties, through a holistic approach integrating both the experimental explorations and data analytics. We further demonstrate the application of such fundamental knowledge for developing tellurene transistors with optimized and reliable performance, which can enable the cost-effective realization of high-speed, energy-efficient electronics.

Smart sensing devices with high stretchability and self-powered characteristics are essential in future generation wearable human-integrated applications. Here we report for the first time scalable synthesis and integration of selenium (Se) nanowires into wearable piezoelectric devices, and explore the feasibility of such devices for self-powered sensing applications, e.g., physiological monitoring. The ultrathin device can be conformably worn onto the human body, effectively converting the imperceptible time-variant mechanical vibration from the human body into distinguishable electrical signals, e.g., gesture, vocal movement, and radial artery pulse, through straining the piezoelectric Se nanowires. Our results suggest the potential of solution-synthesized Se nanowire a new class of piezoelectric nanomaterial for self-powered biomedical devices and opens doors to new technologies in energy, electronics, and sensor applications.

Molybdenum disulfide (MoS2 ) has been widely studied as a potential earth-abundant electrocatalyst for the hydrogen-evolution reaction (HER). Defect engineering and heteroelemental doping are effective methods to enhance the catalytic activity in the HER, so exploring an efficient route to simultaneously achieve in-plane vacancy engineering and elemental doping of MoS2 is necessary. In this study, Zinc, a low-cost and moderately active metal, has been used to realize this strategy by generation of sulfur vacancies and zinc doping on MoS2 in one step. Density functional theory calculations reveal that the zinc atoms not only lower the formation energy of S vacancies, but also help to decrease ΔGH of S-vacancy sites near the Zn atoms. At an optimal zinc-reduced MoS2 (Zn@MoS2 ) example, the activated basal planes contribute to the HER activity with an overpotential of -194 mV at 10 mA cm-2 and a low Tafel slope of 78 mV/dec.

Capturing and decoding human motions with textile-based wearables would usher in exciting opportunities for consumer electronics, human–machine interface, and robotics. Transforming textiles into multifunctional materials represents an appealing strategy for implementing human-integrated wearable systems with reconfigurable form factors and designer functions. To this end, significant roadblocks exist primarily due to the challenges in integrating state-of-the-art electronics and power units onto textiles through schemes compatible with the clothing design and processing. Here we present a holistic design and integration of an all-textile triboelectric sensor (ATTS) which is capable of perceiving human motions with a high sensitivity of 1.1 V kPa−1 and a broad pressure-sensitive range from 100 Pa to 400 kPa. The ATTS can be integrated with arbitrary commercial garments. We further demonstrated an ATTS-based smart glove that can capture human gestures for remotely controlling a virtual reality (VR) enabled teleoperated robotic gripper that can dexterously handle delicate objects with a wide range of shapes, sizes, and mechanical properties. Our ATTS technology has the potential for enabling more capable human–machine interfaces and providing dexterity to robots in societally pervasive areas such as teleoperated surgery and advanced manufacturing.

Developing high-capacitance electrode materials with high voltage is always the essential strategy for increasing the energy densities of aqueous supercapacitors. However, it is very difficult to break through the voltage restriction of 2 V due to the narrow electrochemical window of water. Herein, we introduce a double (alkaline–neutral) electrolyte separated with a K+ conductive membrane to assemble a lithium ion capacitor (LIC) with high voltage and high energy density. This electrolyte system adequately exploits the high specific capacitance (256 F g−1) and low potential (−1–0 V vs. Hg/HgO) of nitrogen-rich biomass carbon (NBC) as an anode in alkaline mixed solution, and the large capacitance (440 F g−1) and high redox potential (0–1.2 V vs. SCE) of LiMn2O4 nanorods as a cathode in neutral mixed solution. The as-fabricated NBC//LiMn2O4 LIC realizes a stable working voltage up to 2.3 V and a high energy density of 50 W h kg−1 at 571 W kg−1 as well as excellent rate capability, and is superior to the traditional LIC and many previous carbon-based asymmetric supercapacitors in neutral electrolytes. Moreover, it presents impressive cycling life with 88% capacitance retention after 5000 cycles. These results show that this method has great promise for promoting the electrochemical performance of supercapacitors.

Laser-induced chemical deposition is an economical "grow-in-place" approach to produce functional materials. The lack of precise control over the component density and other properties hinders the development of the method towards an efficient nanomanufacturing technology. In this paper, we provide a mechanism of direct pulsed-laser integration of ZnO nanowire seeding and growth on silicon wafers toward controlled density. Investigation of laser-induced ZnO nucleation directly deposited on a substrate suggested that the coverage percentage of nucleus particles was a function of instantly available area, supplementing the classical nucleation theory for confined area deposition. A processing window was found in which ZnO nanowires only grew from the early deposited nucleated particles as seeds. A study on ZnO nanowire growth showed that the process became transport limited over time, which was important for density-controlled nanowire growth integrated on nucleated seeds. The proposed mechanism provided guidance to integrate nanomaterials using laser-induced chemical deposition with a controlled density and morphology.

The economic production and integration of nanomaterial-based wearable energy storage devices with mechanically-compliable form factors and reliable performance will usher in exciting opportunities in emerging technologies such as consumer electronics, pervasive computing, human–machine interface, robotics, and the Internet of Things. Despite the increased interests and efforts in nanotechnology-enabled flexible energy storage devices, reducing the manufacturing and integration costs while continuously improving the performance at the device and system level remains a major technological challenge. The inkjet printing process has emerged as a potential economic method for nanomanufacturing printed electronics, sensors, and energy devices. Nevertheless, there have been few reports reviewing the scalable nanomanufacturing of inkjet printed wearable energy storage devices. To fill this gap, here we review the recent advances in inkjet printed flexible energy storage technologies. We will provide an in-depth discussion focusing on the materials, manufacturing process integration, and performance issues in designing and implementing the inkjet printing of wearable energy storage devices. We have also compiled a comprehensive list of the reported device technologies with the corresponding processing factors and performance metrics. Finally, we will discuss the challenges and opportunities associated with related topics. The rapid and exciting progress achieved in many emerging and traditional disciplines is expected to lead to more theoretical and experimental advances that would ultimately enable the scalable nanomanufacturing of inkjet printed wearable energy storage devices.

Two-dimensional (2D) plasmonic oxides represent a new promising type of surface-enhanced Raman spectroscopy (SERS) substrate due to their atomic uniformity and high surface activities. However, current synthesis strategies of 2D structures are largely limited to intrinsically layered compounds, and nonlayered plasmonic oxides are not easy to synthesize as 2D materials, so the development of 2D nanoarchitecture based SERS substrates is seriously hindered. Here, we report a solid–solid surface reaction strategy for the fabrication of 2D nonlayered MoO2 nanosheets with an average thickness of 2–3 unit cells. By using these 2D MoO2 nanosheets as the SERS substrate to detect trace amounts of rhodamine 6G (R6G), the limit of detection concentration can be as low as 10−7 M and the maximum enhancement factor (EF) is up to 104. We anticipate that this strategy would provide beneficial insight for the fabrication of 2D non-layered nanoarchitectures, which would expand the family of 2D plasmonic materials.

Deformable energy devices capable of efficiently scavenging ubiquitous mechanical signals enable the realization of self-powered wearable electronic systems for emerging human-integrated technologies. Triboelectric nanogenerators (TENGs) utilizing soft polymers with embedded additives and engineered dielectric properties emerge as ideal candidates for such applications. However, the use of solid filler materials in the state-of-the-art TENGs limits the devices' mechanical deformability and long-term durability. The current structural design for TENGs faces the dilemma where the enhanced dielectric constant of the TENG's contact layer leads to an undesirable saturation of the surface charge density. Here, we present a novel scheme to address the above issues, by exploring a liquid-metal-inclusion based TENG (LMI-TENG) where inherently deformable core–shell LMIs are incorporated into wearable high-dielectric-constant polymers. Through a holistic approach integrating theoretical and experimental efforts, we identified the parameter space for designing an LMI-TENG with co-optimized output and mechanical deformability. As a proof of concept, we demonstrated an LMI-TENG based wireless media control system for a self-powered user interface. The device architecture and design scheme presented here provide a promising solution towards the realization of self-powered human-integrated technologies.

When uniform strain is applied to noncentrosymmetric semiconductor crystals, which are piezoelectric, static polarization charges are induced at the surface. If the applied strain is not uniform, these charges can even be created inside the crystal. The applied strain affects electronic transport and also photonic processes, and thus can be used to tune the material properties statically or dynamically. As a result, two new fields have emerged, namely piezotronics and piezo-phototronics. This article reviews the history of the two fields and gives a perspective on their applications. The articles in this issue of MRS Bulletin highlight progress in these two fields, and this article places this progress into perspective.

The ability of future electronics to derive operational power from the working environment is attractive for realizing self‐powered unattended electronics. Triboelectric nanogenerator (TENG) effectively harvests the otherwise wasted ubiquitous mechanical energy. Despite the recent advances in the design and development of various triboelectric devices, these devices' output still falls short in meeting the practical needs of directly powering electronics and sensors. Here, we review the recent progress in the design and optimization strategies for improving the TENG output performance, including but not limited to theoretical simulation, materials engineering, device engineering, and power management. The ubiquitous applications of the TENGs in micro/high‐voltage power source, multifunctional intelligence, blue energy harvesting, and self‐powered electrochemical system are also discussed. Finally, we provide our perspectives regarding the challenges and opportunities for the future development of triboelectric devices with engineered high‐performance and designer functionalities.

Tellurium (Te) is a narrow bandgap semiconductor with a unique chiral crystal structure. The topological nature of electrons in the Te conduction band can be studied by realizing n-type doping using atomic layer deposition (ALD) technique on two-dimensional (2D) Te film. In this work, we fabricated and measured the double-gated n-type Te Hall-bar devices, which can operate as two separate or coupled electron layers controlled by the top gate and back gate. Profound Shubnikov-de Haas (SdH) oscillations are observed in both top and bottom electron layers. Landau level hybridization between two layers, compound and charge-transferable bilayer quantum Hall states at filling factor 4, 6, and 8 are analyzed. Our work opens the door for the study of Weyl physics in coupled bilayer systems of 2D materials., Comment: Submitted to Nano Letters

Cost-effective and durable electrocatalysts for the alkaline hydrogen evolution reaction (HER) are urgently required. The slow HER kinetics suppressed by water dissociation hinder the application of catalysts in alkaline media. Herein, we constructed an amorphous heterostructure that combined amorphous-MoO

The capability of sensor systems to efficiently scavenge their operational power from stray, weak environmental energies through sustainable pathways could enable viable schemes for self-powered health diagnostics and therapeutics. Triboelectric nanogenerators (TENG) can effectively transform the otherwise wasted environmental, mechanical energy into electrical power. Recent advances in TENGs have resulted in a significant boost in output performance. However, obstacles hindering the development of efficient triboelectric devices based on biocompatible materials continue to prevail. Being one of the most widely used polymers for biomedical applications, polyvinyl alcohol (PVA) presents exciting opportunities for biocompatible, wearable TENGs. Here, the holistic engineering and systematic characterization of the impact of molecular and ionic fillers on PVA blends' triboelectric performance is presented for the first time. Triboelectric devices built with optimized PVA-gelatin composite films exhibit stable and robust triboelectricity outputs. Such wearable devices can detect the imperceptible skin deformation induced by the human pulse and capture the cardiovascular information encoded in the pulse signals with high fidelity. The gained fundamental understanding and demonstrated capabilities enable the rational design and holistic engineering of novel materials for more capable biocompatible triboelectric devices that can continuously monitor vital physiological signals for self-powered health diagnostics and therapeutics.

Atomically thin materials, leveraging their low-dimensional geometries and superior mechanical properties, are amenable to exquisite strain manipulation with a broad tunability inaccessible to bulk or thin-film materials. Such capability offers unexplored possibilities for probing intriguing physics and materials science in the 2D limit as well as enabling unprecedented device applications. Here, the strain-engineered anisotropic optical and electrical properties in solution-grown, sub-millimeter-size 2D Te are systematically investigated through designing and introducing a controlled buckled geometry in its intriguing chiral-chain lattice. The observed Raman spectra reveal anisotropic lattice vibrations under the corresponding straining conditions. The feasibility of using buckled 2D Te for ultrastretchable strain sensors with a high gauge factor (≈380) is further explored. 2D Te is an emerging material boasting attractive characteristics for electronics, sensors, quantum devices, and optoelectronics. The results suggest the potential of 2D Te as a promising candidate for designing and implementing flexible and stretchable devices with strain-engineered functionalities.

New narrow-gap two-dimensional (2-D) semiconductors exemplified by black phosphorus and tellurene are promising material candidates for mid-IR optoelectronic devices. In particular, tellurene, atomically thin crystals of elemental tellurium, is an emerging narrow-gap 2-D semiconductor amenable to scalable solution-based synthesis and large-area deposition. It uniquely combines tunable bandgap energies, high carrier mobility, exceptionally large electro-optic activity, and superior chemical stability, making it a promising and versatile material platform for mid-infrared photonics. Here we discuss the design and experimental realization of integrated photonic devices based on tellurene and other 2-D semiconductors specifically for the mid-IR spectral regime based on a chalcogenide glass (ChG) photonic platform.

Flexible optoelectronic devices have attracted considerable attention due to their low weight, portability, and ease of integration with other devices. However, major issues still exist: they are subject to repeated stresses, which often leads to damage; and the current fabrication methods such as photolithography and nano-imprint lithography can be very time-consuming or costly. This work aims to develop a novel cost-effective and time-efficient laser metasurface fabrication (LMF) technique for production of flexible optoelectronic devices. The experimental results have shown that the laser patterned flexible surfaces exhibit high visible transmittance, low sheet resistance, and extraordinary mechanical durability under repeated bending cycles. The laser patterned flexible surfaces have also demonstrated the potential to be utilized as heaters, which renders them new de-icing or de-fogging applications. This innovative laser patterning method will provide a new avenue for fabrication of multifunctional optoelectronic devices.

Dirac and Weyl nodal materials can host low-energy relativistic quasiparticles. Under strong magnetic fields, the topological properties of Dirac/Weyl materials can directly be observed through quantum Hall states. However, most Dirac/Weyl nodes generically exist in semimetals without exploitable band gaps due to their accidental band-crossing origin. Here, we report the first experimental observation of Weyl fermions in a semiconductor. Tellurene, the two-dimensional form of tellurium, possesses a chiral crystal structure which induces unconventional Weyl nodes with a hedgehog-like radial spin texture near the conduction band edge. We synthesize high-quality n-type tellurene by a hydrothermal method with subsequent dielectric doping and detect a topologically non-trivial π Berry phase in quantum Hall sequences. Our work expands the spectrum of Weyl matter into semiconductors and offers a new platform to design novel quantum devices by marrying the advantages of topological materials to versatile semiconductors.

Two-dimensional (2D) semiconductors have been extensively explored as a new class of materials with great potential. In particular, black phosphorus (BP) has been considered to be a strong candidate for applications such as high-performance infrared photodetectors. However, the scalability of BP thin film is still a challenge, and its poor stability in the air has hampered the progress of the commercialization of BP devices. Herein, we report the use of hydrothermal-synthesized and air-stable 2D tellurene nanoflakes for broadband and ultrasensitive photodetection. The tellurene nanoflakes show high hole mobilities up to 458 cm2/V·s at ambient conditions, and the tellurene photodetector presents peak extrinsic responsivity of 383 A/W, 19.2 mA/W, and 18.9 mA/W at 520 nm, 1.55 μm, and 3.39 μm light wavelength, respectively. Because of the photogating effect, high gains up to 1.9 × 103 and 3.15 × 104 are obtained at 520 nm and 3.39 μm wavelength, respectively. At the communication wavelength of 1.55 μm, the tellurene photodetector exhibits an exceptionally high anisotropic behavior, and a large bandwidth of 37 MHz is obtained. The photodetection performance at different wavelength is further supported by the corresponding quantum molecular dynamics (QMD) simulations. Our approach has demonstrated the air-stable tellurene photodetectors that fully cover the short-wave infrared band with ultrafast photoresponse.

As a promising non-precious metal photoelectrochemical (PEC) catalyst, MoS2 exhibits high electrocatalytic activity and stability, while the weak light absorption efficiency and low photoresponse current limit its practical application. Herein, a facile co-assembly approach is proposed to construct porphyrin-MoS2 composite photoelectrocatalysts. The as-prepared photoelectrocatalysts show a significantly enhanced photocurrent response as high as 16 μA cm-2 , which is about 2 times higher than that of bare MoS2 . Furthermore, the obtained porphyrin-MoS2 catalysts exhibit excellent durability when tested for 23000 s, thus providing a useful strategy for the design of highly efficient dye-sensitized PEC catalysts.

Tellurium (Te) has a trigonal crystal lattice with inherent structural anisotropy. Te is multifunctional, e.g., semiconducting, photoconductive, thermoelectric, piezoelectric, etc., for applications in electronics, sensors, optoelectronics, and energy devices. Due to the inherent structural anisotropy, previously reported synthetic methods predominantly yield one-dimensional (1D) Te nanostructures. Much less is known about 2D Te nanostructures, their processing schemes, and their material properties. This review focuses on the synthesis and morphology control of emerging 2D tellurene and summarizes the latest developments in understanding the fundamental properties of monolayer and few-layer tellurene, as well as the recent advances in demonstrating prototypical tellurene devices. Finally, the prospects for future research and application opportunities as well as the accompanying challenges of 2D tellurene are summarized and highlighted.

Finding catalysts and mechanisms for efficient electroreduction of N2 into NH3 remains of great challenge, due to the limitation of the scaling relations and competing HER. Here we report that N2 can be dissociated and dynamically hydrogenized on a peculiar sub-monolayer MoS2-x structure. Different with conventional surface-binding paradigms of the reaction intermediates, such a dynamic surface-binding paradigm can selectively stabilize the nitrogen intermediates and enable the circumvention of the inherent scaling relations in electrocatalysis of N2 to NH3. Atomic resolution AC-STEM and DFT calculations confirm the atomic arrangement and a ∼3% compressive strain in the large area of in-plane S-vacancies of sub-monolayer MoS2-x structure. Further experimental and theoretical results demonstrate that the as-designed surface tune their catalytic properties through adjusting their surface-binding to nitrogen intermediates with tunable nitrogen affinity, leading to outstanding electrocatalytic NRR performance at ultra-low overpotential (−0.2 V. vs. RHE).

Piezoelectricity provides an ideal electromechanical mechanism with emerging applications in wearable devices due to its simplicity and self-powered nature. However, the 3D printing of piezoelectric devices still faces many challenges, including material printability, high energy poling process, and low dimensional accuracy. This study demonstrates, for the first time, a tellurium nanowire-based piezoelectric device fabricated by a hybrid printing method integrating highly complementary aerosol jet printing and extrusion printing in a single printing platform. The aerosol-jet-printed tellurium nanowire demonstrates piezoelectric properties without the need for any poling processing due to the unique properties of the tellurium nanowires. The silver nanowire electrodes printed by aerosol jet printing demonstrate excellent conductivity and stretchability without the need for sintering. An extrusion method is employed to print the silicone films, which serve as the stretchable substrate and the electrical insulation layers between the printed tellurium and silver. The printed wearable piezoelectric devices were attached to a human wrist to detect different hand gestures and to a human neck to detect heartbeat without using an external power source. The fully printed, sintering-free and poling-free, and stretchable piezoelectric device opens enormous opportunities for facile integration with a broad range of printed electronics and wearable devices.

The seamless and adaptive interactions between functional devices and their environment (e.g., the human body) are critical for advancing emerging technologies, e.g., wearable devices, consumer electronics, and human-machine interface. The state-of-the-art technologies, however, require a complex integration of heterogeneous components to interface the environmental mechanical stimulus, which is ubiquitous and abundant in the above applications. Moreover, all existing technologies require a power source, which complicates the system design and limits operation schemes. I will discuss our recent progress in developing self-powered human-integrated nanodevices through the hybrid nanomanufacturing of heterostructured nanodevices with hierarchical architectures. This new class of wearable devices are conformable to human skins and can sustainably perform non-invasive functions, e.g., physiological monitoring and gesture recognition, by harvesting the operation power from the human body. This research is expected to have a positive impact and immediate relevance to many societally pervasive areas, e.g., biomedical monitoring, consumer electronics, and intelligent robotics.

Wearable Joule heating devices have received tremendous attention from researchers due to their applications in personal thermal management systems, like thermal management cloth, and healthcare application, such as wearable thermotherapy. Permeability, stretchability, dynamic stability, and conductivity are essential factors for electrothermal heating devices. Wearable devices usually work under cyclic loading of low stain, so fatigue, mechanical failure induced by cyclic loading at low strain level, is a common disease for metal electrodes. Fatigue-free materials are of great importance to ensure robustness for long-term application. Stretchable electrodes, such as noble metal nano mesh, conductive fillers-based elastomer and metal nanowires have been used to fabricate wearable heater. Liquid metal (LM) has also attracted lots of attention due to its high conductivity and fluidity at room temperature. Such fluidity not only makes LM attractive materials for flexible devices, but also render LM fatigue-free attribute. Many manufacturing methods, such as direct ink writing, screen printing and spray coating have been applied to fabricate LM based electrodes for flexible devices. Recently, electrospun technique have also been applied to fabricate LM particles doped polymer fibers, but LM based conductive fiber electrodes have not yet been fabricated using electrospun process. Here, a LM particles embedded fibers network electrode is fabricated using electrospun method, followed by wrapping a polymer layer on the fiber surface. The LM particles embedded in the electrospun fibers form interconnected network, which exhibits excellent electrical conductivity, high mechanical stretchability, and good fatigue performance. Such network electrode could be directly used as a Joule heater, which is permeable, stretchable and fatigue-free. High conductivity of the electrodes ensures low driving voltage for this electrothermal heating devices. High stretchability of the electrode ensures good Joule heating performance at high strain level. In addition, the uniform fibers size could induce large-scale uniform heating. The LM fiber electrodes could be cut into various patterns to fit curvilinear surface of human skin. Also, the ultrathin and compliant nature of the LM fiber electrode enable seamless attachment with human skin, which could ensure high thermal transfer efficiency. The combination of good electrical and mechanical performances of the LM fiber-based Joule heater enable long-term wearable thermotherapy.

Piezoelectric nanogenerators have attracted intensive interest in harvesting the stray mechanical energy in the environment to power miniaturized electronics and sensors. However, their efficient integration into systems and compatibility with existing technologies for practical applications remains challenging. Here, we report for the first time the systematic, data-driven learning of the process-property-performance relation in ZnO nanowires piezoelectric nanogenerators that are synthesized and integrated through a laser-induced chemical process. An experiment-derived behavioral model was established to reveal the apparent connections between the production parameters and the output performance of the ZnO piezoelectric nanogenerator. We further demonstrated the application of such knowledge for integrating the optimized ZnO nanowires piezoelectric nanogenerator with a photosensor into a self-powered sensor system, exhibiting the potential for future system-level improvements.

Amorphous MoO3-x with enhanced LSPR has been fabricated successfully by introducing Mo atoms into the interlayers of MoO3 nanosheets via a hydrothermal method. The inserted Mo atom could bond with inherent Mo atoms and further form a distorted atomic configuration structure. Thus, the amorphous MoO3-x possesses a relatively excellent photothermal conversion efficiency of 61.79%.

Several materials studied intensively in their bulk forms several decades ago have re-emerged in recent years in their thin film and monolayer manifestations. Tellurium, like black phosphorus, is one such elemental two-dimensional material with promising semiconducting properties for electronic and optoelectronic applications. To study fundamental carrier properties such as hot carrier relaxation and recombination, we performed ultrafast femtosecond pump-probe spectroscopy on thin flakes of solution-grown tellurium. To access the low band gap of tellurium, we used infrared, near-band-gap and below-band-gap probes to monitor the relaxation processes. Sweeping the probing wavelengths across the band gap helps to shed light on the anisotropic band structure of the material. We find that relaxation in flakes of 60--160 nm thickness is on the order of 100 s of picoseconds. Thinner flakes (10--20 nm), on the other hand, exhibit fast relaxation times of sub-20 ps. Radiative recombination is identified as the relaxation mechanism in thick flakes, whereas midgap trap states arising from surface defects and impurities are responsible for the fast relaxation in thin flakes. A diffusion-recombination model accounting for the surface defect and radiative recombinations explains the experimental data well.

A material with reversible temperature change capability under an external electric field, known as the electrocaloric effect (ECE), has long been considered as a promising solid-state cooling solution. However, electrocaloric (EC) performance of EC materials generally is not sufficiently high for real cooling applications. As a result, exploring EC materials with high performance is of great interest and importance. Here, we report on the ECE of ferroelectric materials with van der Waals layered structure (CuInP

Two-dimensional (2-D) materials of atomic thickness have attracted considerable interest due to their excellent electrical, optoelectronic, mechanical, and thermal properties, which make them attractive for electronic devices, sensors, and energy systems. Scavenging the otherwise wasted energy from the ambient environment into electrical power holds promise to address the emerging energy needs, in particular for the portable and wearable devices. The versatile properties of 2-D materials together with their atomically thin body create diverse possibilities for the conversion of ambient energy. The present review focuses on the recent key advances in emerging energy-harvesting devices based on monolayer 2-D materials through various mechanisms such as photovoltaic, thermoelectric, piezoelectric, triboelectric, and hydrovoltaic devices, as well as progress for harvesting the osmotic pressure and Wi-Fi wireless energy. The representative achievements regarding the monolayer heterostructures and hybrid devices are also discussed. Finally, we provide a discussion of the challenges and opportunities for 2-D monolayer material-based energy-harvesting devices in the development of self-powered electronics and wearable technologies.

Introducing anion vacancies on two-dimensional transition-metal dichalcogenides (TMDs) would significantly improve their catalytic activity. In this work, we proposed a solid-phase reduction (SPR) strategy to simultaneously achieve efficient exfoliation and controlled generation of chalcogen vacancies on TMDs. Consecutive sulfur vacancies were successfully created on the basal plane of the bulk MoS2 and WS2, and their interlamellar distances were distinctly expanded after the SPR treatment (about 16%), which can be conveniently exfoliated by only gentle shaking. The S-vacancy significantly increases the hydrogen-evolution reaction activity of the MoS2 and WS2 nanosheets, with overpotential of -238 and -241 mV at 10 mA cm-2, respectively. We anticipate that our SPR strategy will supply a general platform for the development of TMD-based electrocatalysts for industrial water splitting and hydrogen production in the near future.

Synthesizing high-performance electrode materials plays a vital role in fabricating advanced supercapacitors. Heteroatom doping has been proved to be effective in enhancing the electrochemical properties of carbon-based electrodes. Herein, we report an O, P co-doped porous carbon (PC) originated from waste biomaterials, cicada sloughs. The PC possesses meso-/microporous structure with a large specific surface area (1945 m2·g−1) and a high O, P co-doping ratio of 18 wt.%. These superior factors together enable it to deliver high specific capacitance (295 F·g−1 in 6 M KOH and 291 F·g−1 in 1 M H2SO4), good cycling stability (100% capacitance retention after 10000 cycles in 1 M H2SO4) and rate performance. Therefore, from the respects of environment friendliness and cost effectivity, obtaining heteroatom doped carbons from the nature might be better compared to pyrolyzing heteroatom-containing chemicals.

Tellurium (Te) is an intrinsically p-type doped narrow bandgap semiconductor with excellent electrical conductivity and low thermal conductivity. Bulk trigonal Te has been theoretically predicted and experimentally demonstrated to be an outstanding thermoelectric material with high value of thermoelectric figure-of-merit ZT. In view of the recent progress in developing synthesis route of two-dimensional (2D) tellurium thin films as well as the growing trend of exploiting nanostructures as thermoelectric devices, here for the first time we report excellent thermoelectric performance of tellurium nanofilms, with room temperature power factor of 31.7 {\mu}Wcm-1K-2 and ZT value of 0.63. To further enhance the efficiency of harvesting thermoelectric power in nanofilm devices, thermoelectrical current mapping was performed with a laser as a heating source, and we found high work function metals such as palladium can form rare accumulation-type metal-to-semiconductor contacts to 2D Te, which allows thermoelectrically generated carriers to be collected more efficiently. High-performance thermoelectric 2D Te devices have broad applications as energy harvesting devices or nanoscale Peltier coolers in microsystems., Comment: manuscript+SI, 30 pages

Tellurium (Te) has attracted great research interest due to its unique crystal structure since the 1970s. However, the conduction band of Te is rarely studied experimentally because of the $p$-type accumulation layer at the surface of Te. By the atomic layer deposited dielectric doping technique, we are able to access the conduction-band transport properties of Te in a controlled fashion. In this paper, we report on a systematic study of the weak-anti-localization (WAL) effect in $n$-type two-dimensional (2D) Te films. We find that WAL agrees well with Iordanskii, Lyanda-Geller, and Pikus theory. The gate and temperature-dependent WAL reveal that the D'yakonov-Perel mechanism, dominant for spin relaxation and phase relaxation, is governed by electron-electron interaction. A large phase-coherence length near 600 nm at $T=1\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ is obtained together with gate-tunable spin-orbit interaction (SOI). Transition from weak-localization to WAL depending on gate bias is also observed. These results demonstrate that newly developed solution-based synthesized Te films provide a new controllable strong SOI 2D semiconductor with high potential for spintronic applications.

Trigonal tellurium (Te) is a chiral semiconductor that lacks both mirror and inversion symmetries, resulting in complex band structures with Weyl crossings and unique spin textures. Detailed time-resolved polarized reflectance spectroscopy is used to investigate its band structure and carrier dynamics. The polarized transient spectra reveal optical transitions between the uppermost spin-split H4 and H5 and the degenerate H6 valence bands (VB) and the lowest degenerate H6 conduction band (CB) as well as a higher energy transition at the L-point. Surprisingly, the degeneracy of the H6 CB (a proposed Weyl node) is lifted and the spin-split VB gap is reduced upon photoexcitation before relaxing to equilibrium as the carriers decay. Using ab initio density functional theory (DFT) calculations, we conclude that the dynamic band structure is caused by a photoinduced shear strain in the Te film that breaks the screw symmetry of the crystal. The band-edge anisotropy is also reflected in the hot carrier decay rate, which is a factor of two slower along the c-axis than perpendicular to it. The majority of photoexcited carriers near the band-edge are seen to recombine within 30 ps while higher lying transitions observed near 1.2 eV appear to have substantially longer lifetimes, potentially due to contributions of intervalley processes in the recombination rate. These new findings shed light on the strong correlation between photoinduced carriers and electronic structure in anisotropic crystals, which opens a potential pathway for designing novel Te-based devices that take advantage of the topological structures as well as strong spin-related properties., The complex band structure and carrier decay response upon photoexcitation of the chiral semiconductor tellurium remain to be unveiled. Here, the authors report unusual dynamic band modifications in Te near band-edge structure due to photoinduced symmetry breaking and strong anisotropy in carrier decay dynamics.

Tellurene—the 2D form of elemental tellurium—provides an attractive alternative to conventional 2D semiconductors due to its high bipolar mobilities, facile solution processing, and the possibility of dopant intercalation into its 1D van der Waals lattice. Here, we study the microscopic origin of transport anisotropy in lithographically defined four-terminal tellurene devices using spatially resolved near-field scanning microwave microscopy (SMM). Our conductivity- and carrier type-sensitive SMM imaging reveals that the overall p-type transport measured between adjacent and opposite terminals originates from strong p-type character at the device edges. Despite using an atomic layer deposition-grown conformal overcoat that n-dopes the device interior, we observe only weak n-type transport along the main device channel at positive backgate voltages. This weak n-type transport along the device channel is shown to arise from local p-doping within a few micrometers of the electrodes, which produces a transport barrier from the n-type interior to the electrodes. These results reveal how the backgate-dependent conduction anisotropy could be leveraged to weigh different inputs for non-von Neumann architectures.

The seamless and adaptive interactions between functional devices and their environment (e.g., the human body) are critical for advancing emerging technologies, e.g., wearable devices, consumer electronics, and human-machine interface. The state-of-the-art technologies, however, require a complex integration of heterogeneous components to interface the environmental, mechanical stimulus, which is ubiquitous and abundant in the above applications. These limitations have severely hampered the advancement and broader utilization of related technologies. Moreover, all existing technologies require a power source, which complicates the system design and limits operation schemes. In this talk, I will discuss our recent progress in developing self-powered human-integrated nanodevices through the hybrid nanomanufacturing of heterostructured nanodevices. This new class of wearable devices are conformable to human skins and can sustainably perform self-powered, non-invasive functions, e.g., physiological monitoring and gesture recognition, by harvesting the operation power from the human body. Such an operation scheme is fundamentally hinged on the polarization induced current term in Maxwell’s displacement current. This research is expected to have a positive impact and immediate relevance to many societally pervasive areas, e.g., biomedical monitoring, consumer electronics, and intelligent robotics.

Strain-gated flexible optoelectronics are reported based on monolayer MoS2 . Utilizing the piezoelectric polarization created at the metal-MoS2 interface to modulate the separation/transport of photogenerated carriers, the piezophototronic effect is applied to implement atomic-layer-thick phototransistor. Coupling between piezoelectricity and photogenerated carriers may enable the development of novel optoelectronics.