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We present a controllable terahertz (THz) metamaterial switch by manipulating toroidal dipolar mode in simulation. The metamaterial switch consists of periodically patterned metallic split rings with photosensitive silicon stripes. The excitation of toroidal dipolar resonance is closely dependent on the transition between the dielectric and conductive phases of photosensitive silicon. The toroidal dipolar mode is exploited to modulate the ON/OFF-switching transmission of THz wave under wide incident angles. The operation mechanism and frequency tunability are discussed.

Ni-rich layered LiNi0·6Co0·2Mn0·2O2 materials have recently drawn much attention for their high specific capacity. However, they still suffer from the cycling instability arising from Li+/Ni2+ ions mixing in crystal structure and harmful side reactions with electrolyte, especially charged at high cut-off voltage to achieve higher energy density. In this study, the Li(Ni0·6Co0·2Mn0.2)O2 (NCM622) cathode materials were prepared by sol-gel method, and Ce4+ modification was utilized to improve cycling stability and rate performance. Through XRD refinement, XPS, SEM and TEM characterization, it was found that in the case of 0.5 at% level, Ce4+ ions not only entered into the crystal lattice to replace transition metal ions, but also produced CeO2 coating on the surface of NCM622 particles. The results of electrochemical performance showed that after 100 cycles at 1 C rate, the capacity retention of NCM-0.5 sample increased by 11.03% compared to pristine sample. Besides, in the case of 5 C, the capacity of NCM-0.5 sample reached to 114.92 mAh·g−1, much higher than that of NCM-0 (91.92 mAh·g−1). The findings indicate that it is the synergistic effect of Ce4+ that endows NCM622 excellent cycling stability and rate performance at high cut-off voltage.

We first report on a stable ReSe2 passively Q-switched Nd:Y3Al5O12 bulk laser near room temperature, which can generate near-repetition rate limit of microsecond pulse output at full depth modulation. A new kind of two-dimensional transition metal dichalcogenide, ReSe2, is exploited as an excellent saturable absorber at 1 . 06 μ m with extremely high rate of loss modulation. The microsecond pulse repetition rate of as high as 274 kHz can be achievable under the pump power of 7.3 W, with the pulsewidth of 1 . 08 μ s and the pulse energy of 2.5 μ J. As the pump power varies from 4.4 to 7.3 W, the pulse repetition rate is tunable from 204 to 274 kHz. The good stability in operation is evaluated with power fluctuation less than 1%. The ultrahigh repetition rate of microsecond pulse source can be suitable for differential absorption lidar of monitoring atmospheric environment, which can meet the specific requirements of adequate interaction duration and sufficient sampling rate to improve the signal-to-noise ratio.

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.

We propose an ultrasensitive tunable terahertz (THz) sensor which consists of single-layer graphene-based gratings integrated with a Fabry–Perot cavity through numerical simulation. The excitation of standing-wave graphene surface plasmon polaritons can make the probing field strongly confined in a gap cavity. This provides an excellent platform for ultrasensitive and high figure-of-merit (FOM) refractive index sensing at the THz band. Our full-wave electromagnetic simulations show a frequency sensitivity as high as 4.2 THz per refractive index unit and an FOM beyond 12.5 at normal incidence in the THz regime. At oblique incidence, the operation angle for effective THz sensing can be maintained as wide as 75° without inducing degeneration of the sensitivity and FOM. The sensing performance can be readily tuned by electrically controlling the chemical potential of graphene. The proposed graphene plasmonic grating scheme is a promising candidate for the development of on-chip integrated THz biochemical sensors.

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.

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.

We report a full telecomband covered half-wave meta-reflectarray for efficient circular polarization conversion at near-infrared frequencies, which is composed of regular Z-shaped antenna array above a conductive ground layer separated with a dielectric spacer. The calculations of polarization conversion spectra demonstrate the ultra-broadband operation at 690 to 2010 nm continuously covering the whole telecom windows, with more than 90% conversion efficiency in full bandwidth. The relative bandwidth of as high as 98% is far higher than those reported previously never exceeding 50%. Sufficiently high conversion efficiencies of beyond 90% can be steadily performed for either left- or right-handed circular polarization incidence. The underlying mechanism is interpreted through the cross-coupling of multiple intrinsic resonances of meta-atoms. The effects of geometry and oblique incidence on the polarization conversion are discussed, showing the acceptable technical tolerance and wide operating angle. The proposed half-wave meta-reflectarray shows promising application in the field of on-chip integrated spin-based logic devices and optical communications.

Herein, abundant and uniform nanopores with sub-3-nm sizes are introduced to 1.5 nm-thick nickel-iron layered double hydroxide (NiFe LDH) ultrathin nanosheets via an etching-aging process, realizing remarkable enhancement in oxygen evolution reaction (OER) performance. Detailed analyses revealed that the NiFe LDH phase around the nanopores can be preferentially oxidized into electroactive Fe:NiOOH phase. In addition, the buffering space provided by the nanopores can effectively avoid structural deformation during repeated redox cycling, leading to better electrochemical stability, which synergistically make the catalyst a promising candidate for commercial water splitting. This work highlights the positive role of porous structure in accelerating the formation of active phases beyond just increment of surface area, which can provide insight in designing advanced catalysts.

Three-dimensional (3D) light fields with spatially inhomogeneous polarization and intensity distributions play an increasingly important role in photonics due to their peculiar optical features and extra degrees of freedom for carrying information. However, it is very challenging to simultaneously control the intensity profile and polarization profile in an arbitrary manner. Here we experimentally demonstrate a metalens that can focus light into an arbitrarily shaped focal curve with a predefined polarization distribution. The efficacy of this approach is exemplified through the demonstration of focused curves in 3D space ranging from simple shapes such as a circle to topologically nontrivial objects such as a 3D knot with controlled local polarization states. This powerful control of the light field would be technically challenging with their conventional counterparts. Our demonstration may find applications in beam engineering and integration optics.

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.

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.

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.

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.

We propose a reflective terahertz (THz) metalens with four focal points for polarization detection of THz beams. The metalens is composed of Z -shaped resonators with spatially variant orientations, a reflective gold layer, and a dielectric spacer between them. The polarization states of the focal points include left circular polarization, right circular polarization, an incident polarization state, and a polarization state whose major axis is rotated π / 4 in comparison with that of the incident polarization. The handedness, ellipticity, and major axis of the polarization state can be determined based on the light intensities of the focal points. The uniqueness of the designed device renders this technique very attractive for applications in compact THz polarization detection and information processing.

The economic production of wearable energy storage devices exhibiting mechanically-compliable form factors and reliable performance enable exciting opportunities in emerging technologies of consumer electronics, human-machine interface, and the Internet of Things. Here we report a hybrid scheme for designing and nanomanufacturing ultralight, high-performance supercapacitor electrodes through the hydrothermal growth of two-dimensional MnO2 on three-dimensional printed graphene aerogel (GA). The derived mixed-dimensional hierarchical macroporous composite electrodes exhibit superior specific capacitance and excellent cycling stability after thousands of cycles. We further explored the integration of a contact mode triboelectric nanogenerator and a mixed-dimensional MnO2/GA based supercapacitor into a self-powered system that is capable of converting mechanical signals into electrical power and further storing such scavenged power. The holistic integration of energy harvesting and storage units promises the implementation of self-powered wearable devices with greater intelligence that can scavenge and store environmental energy through sustainable pathways for ubiquitous electronics in societally-pervasive applications.

Flexible electronic devices involve electronic circuits fabricated onto a flexible (e.g., polymer) substrate, and they have many important applications. However, during their use, they often need to go through repeated deformations (such as bending). This may generate cracks in metallic components that often exist in a flexible electronic device and could obviously affect the device durability and reliability. Carbon nanotubes (CNTs) have a potential to enhance the metal fatigue properties. However, the previous work on the fabrication of CNT–metal composites onto a flexible substrate has been limited. This paper reports the research work on a novel laser-based approach to fabricate CNT–metal composites onto a flexible substrate, where mixtures containing CNTs and metal (silver) nanoparticles (NPs) are deposited onto the substrate through a dispensing device and then laser-sintered into CNT–metal composites. Under the studied conditions and for the tested samples, it has been found that overall the addition of CNTs has significantly enhanced the bending fatigue properties of the laser-sintered material without degrading the material electrical conductivity (which has actually been slightly increased). The laser-based approach has several potential advantages, such as the local, precise, and flexible production of CNT–metal composite patterns with small or little thermal effects to the flexible substrate and other surrounding regions, and without using a mask or vacuum. Future work is certainly still needed on this novel fabrication process.

Recent advances achieved in triboelectric nanogenerators (TENG) focus on boosting power generation and conversion efficiency. Nevertheless, obstacles concerning economical and biocompatible utilization of TENGs continue to prevail. Being an abundant natural biopolymer from marine crustacean shells, chitosan enables exciting opportunities for low-cost, biodegradable TENG applications in related fields. Here, the development of biodegradable and flexible TENGs based on chitosan is presented for the first time. The physical and chemical properties of the chitosan nanocomposites are systematically studied and engineered for optimized triboelectric power generation, transforming the otherwise wasted natural materials into functional energy devices. The feasibility of laser processing of constituent materials is further explored for the first time for engineering the TENG performance. The laser treatment of biopolymer films offers a potentially promising scheme for surface engineering in polymer-based TENGs. The chitosan-based TENGs present efficient energy conversion performance and tunable biodegradation rate. Such a new class of TENGs derived from natural biomaterials may pave the way toward the economically viable and ecologically friendly production of flexible TENGs for self-powered nanosystems in biomedical and environmental applications.

The reliable production of two-dimensional (2D) crystals is essential for the development of new technologies based on 2D materials. However, current synthesis methods suffer from a variety of drawbacks, including limitations in crystal size and stability. Here, we report the fabrication of large-area, high-quality 2D tellurium (tellurene) using a substrate-free solution process. Our approach can create crystals with process-tunable thickness, from a monolayer to tens of nanometres, and with lateral sizes of up to 100 µm. The chiral-chain van der Waals structure of tellurene gives rise to strong in-plane anisotropic properties and large thickness-dependent shifts in Raman vibrational modes, which is not observed in other 2D layered materials. We also fabricate tellurene field-effect transistors, which exhibit air-stable performance at room temperature for over two months, on/off ratios on the order of 106, and field-effect mobilities of about 700 cm^2 V^(−1) s^(−1). Furthermore, by scaling down the channel length and integrating with high-k dielectrics, transistors with a significant on-state current density of 1 A mm^(−1) are demonstrated.

An etching-intralayered Ostwald ripening process is proposed, which leads to the formation of a β-Ni(OH)2 ultrathin nanomesh with abundant and uniformly distributed nanopores of 3-4 nm. The nanomesh catalyst exhibits outstanding oxygen evolution reaction performance, with high catalytic current density and superior long-term stability, making this Earth-abundant nanomesh catalyst a promising candidate for commercial water splitting.

We report a compact triple-band tunable perfect terahertz metamaterial absorber (TMA) at the subwavelength scale of thickness, which is composed of a planar metallic disk resonator array above a conductive ground plane separated with liquid crystal (LC) mixture. The calculations of terahertz absorption spectra demonstrate triple near-unity absorption bands in the gap plasmonic resonance coupling regime. Three resonance frequencies of the absorber exhibit continuous linear-tunability as changing the refractive index of LC. Remarkably, each peak absorbance of the triple bands maintains at a level of beyond 99% in the whole tuning operation, and the absorbance can remain more than 90% over a wide range of incident angles. Our work suggests that the LC tunable absorber scheme has the potential to overcome the basic difficulty to perform simultaneously multiband spectral tuning and near-unity absorbance with wide angle of incidence and weak polarization dependence. The proposed LC-tunable multiband perfect TMA is promising in the application of biomolecular spectra-selective terahertz imaging and sensing.

Emerging technologies in wearable systems demand that functional devices can adaptively interact with the human body, where mechanical stimuli are ubiquitous and abundant. However, the electrical manipulation of charge carriers underpins the operations of state-of-the-art devices, and the effective control of interfacial energetics for charge carriers by the dynamic mechanical stimuli is still a relatively unexplored degree of freedom for semiconductor nanodevices. Piezotronic effect in nanostructured piezoelectric semiconductors offers exciting opportunities in addressing the above challenges. Here we report the first experimental exploration of piezotronic effect in 1D van der Waals solid of p-type tellurium nanobelt and systematically investigate the strain-gated charge carriers transport properties. The strain-induced polarization charges at the surfaces of Te nanobelt can modulate the electronic transport through the interfacial effect on the Schottky contacts and the volumetric effect on the conducting channel. The competing phenomenon between interfacial and volumetric effects has been studied for the first time in piezotronics. Our research allows the access to a broad range of characterization and application of Te nanomaterials for piezotronics and could guide the future study of piezotronic effect in other materials. This progress in piezotronics, together with emerging methods for deterministic production and assembly of nanomaterials, leads to compelling opportunities for research from basic studies of piezoelectricity and semiconductor properties in functional nanomaterials to the development of 'smarter' electronics and optoelectronics.

Ongoing research in triboelectric nanogenerators (TENGs) focuses on increasing power generation, but obstacles concerning economical and eco-friendly utilization of TENGs continue to prevail. Being the second most abundant biopolymer on earth, lignin offers a valuable opportunity for low-cost TENG applications in biomedical devices, benefitting from its biodegradability and biocompatibility. Here, we develop for the first time a lignin biopolymer based TENGs for harvesting mechanical energy in the environment, which shows great potential for self-powered biomedical devices among other applications and opens doors to new technologies that utilize otherwise wasted materials for economically feasible and ecologically friendly production of energy devices.