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In this article, a microcontroller-based high-accuracy dew-point (DP) instrument using a quartz crystal resonance (QCR) sensor is developed. The sensor is a symmetrical double cooled QCR DP sensor, which has the characteristics of efficient cooling and stable oscillation. Based on the proportional—integral—differential control method, the logic level signal and the oscillation amplitude outputted by the drive circuit are used as control feedback to obtain an optimized expert strategy control system, and the automatic DP tracking measurement is realized by the microcontroller. It is proved by experiments that the measurement error of the instrument in the range of 0–15 °C dew point (DP) environment is less than 0.3 °C DP, and it has a good performance of tracking measurement in a dynamic DP environment.

Additive manufacturing, or more commonly known as 3D printing, has been at the forefront of manufacturing research for the past couple decades. Many advances have occurred in the basic printing techniques, materials, and post-processing schemes. In recent years, there have been many critical developments in the field 3D printing, such as the development of volumetric 3D printing to increase the printing speed, composite 3D printing to create piezoelectric devices, and hydrogel structures highly similar to blood vessels. The spectrum of materials that can be printed has also increased, allowing researchers to print a variety of materials including live cells, modulus changing polymers and even spacecraft-grade metals.

Paper-based pressure/strain sensors could have potential wide applications with wearable features in disposable products. In this study, molybdenum carbide-graphene (MCG) composites with porous and stacking micro-structures are fabricated on top of the paper substrate to act as piezo-resistivity strain/pressure sensors. As a strain sensor, this paper-based device can detect not only the amplitude and frequency of applied strain but also the direction as tensile or compressive deformation. The gauge factors are 73 and 43 for tensile and compressive strain, respectively, with demonstration example in detecting and recognizing human body motions. As a pressure sensor, this MCG-based paper device has high sensitivity to weak pressure signals such as sounds by distinguishing the seven piano notes. Our study provides a simple strategy for developing paper-based electronics with unique properties toward practical applications.

Additive manufacturing, or three-dimensional (3D) printing, has garnered significant interest in recent years towards the fabrication of sub-millimeter scale devices for an ever-widening array of chemical, biological and biomedical applications. Conventional 3D printed fluidic systems, however, still necessitate the use of non-portable, high-powered external off-chip sources of fluidic actuation, such as electro-mechanical pumps and complex pressure-driven controllers, thus limiting their scope towards point-of-need applications. This work proposes entirely 3D printed sources of human-powered fluidic actuation which can be directly incorporated into the design of any 3D printable sub-millifluidic or microfluidic system where electrical power-free operation is desired. Multiple modular, single-fluid finger-powered actuator (FPA) designs were fabricated and experimentally characterized. Furthermore, a new 3D fluidic one-way valve concept employing a dynamic bracing mechanism was developed, demonstrating a high diodicity of ∼1117.4 and significant reduction in back-flow from the state-of-the-art. As a result, fabricated FPA prototypes achieved tailorable experimental fluid flow rates from ∼100 to ∼3000 μL min−1 without the use of electricity. Moreover, a portable human-powered two-fluid pulsatile fluidic mixer, capable of generating fully-mixed fluids in 10 seconds, is presented, demonstrating the application of FPAs towards on-chip integration into more complex 3D printed fluidic networks.

In this work, NiCo2O4@TiO2 electrodes based on micro-region heterojunctions were synthesized by a simple one-step hydrothermal method. The material characteristics of resultant samples were characterized by XPS, XRD, SEM, HRTEM and BET. Compared with NiCo2O4 electrodes prepared with the same hydrothermal method, the NiCo2O4@TiO2 electrode shows higher electrochemical performance, cycling stability and lower charge transfer resistance. Specifically, the mass specific capacitances of NiCo2O4 and NiCo2O4@TiO2 electrodes are 564.3 F · g−1 and 1085.7 F · g−1 at current density of 5 A · g−1 and retained 84.4% and 95.5% after 10,000 cycles, while the Rct of NiCo2O4 and NiCo2O4@TiO2 are 1.72 Ω and 0.18 Ω, respectively. For practical applications of NiCo2O4@TiO2 electrode, a NiCo2O4@TiO2//AC two-electrode system was assembled and the performances were tested to achieve 255.9 F · g−1 at current density of 2.5 A · g−1. Additionally, the corresponding energy density and power density were recorded as 91 wh/kg and 4 kw/kg. The superior electrochemical performance and cycle stability of NiCo2O4@TiO2 electrode might be attributed to the higher specific surface and micro-region heterojunctions for enormous future applications.

It is of great interest to link Raman scattering to the properties of disorders in graphene membranes, which provides an effective characterization method to probe atomic scale defects. The built-in stress effect on the defect densities of substrate-supported monolayer graphene membranes around wells is investigated. First, a modified phenomenological model is developed to depict the relationship between built-in stresses and defect-activated Raman intensities. To validate the rationality of the modified model, Raman spectroscopy is used to characterize stretched graphene membranes on different patterned substrates with micro-scale wells. The experimental data indicate that the intensity ratio of D mode to G mode ID/IG increases with the Raman test point approaching the well edge. According to the modified model, the increase of ID/IG means the rise of defect densities, which originates from the propagation of initial defects in graphene membranes under built-in tension. The underlying mechanism of defect density increasing phenomenon is that the built-in stresses provide the energy for defect propagations in stretched graphene membranes. Theoretical and experimental comparison well validates the rationality of the modified model. The work can provide a theoretical foundation for Raman characterization method of defect propagations in stretched graphene and applications of defective graphene-based nanodevices.

It is desirable and still challenging to develop flexible, breathable and anti-corrosive wearable strain sensors with high stretchability and sensitivity that can realize full range body motions. Here, a superhydrophobic and conductive nanofiber composites (SCNCs) with a hierarchical SiO2/graphene shell and polyurethane (PU) nanofiber core microstructure were fabricated by assembling graphene on PU nanofibers under the assistance of ultrasonication, followed by stretching-induced SiO2 nanoparticles decoration onto the graphene shell. The introduction of graphene and SiO2 nanoparticles improves both Young’s modulus, tensile strength and the elongation at break of PU nanofibrous membrane. The superhydrophobicity and conductivity can be almost maintained after the SCNCs are subject to cyclic stretching or abrasion or even exposed to harsh conditions. When used as strain sensors, the SCNCs show high stretchability, reliability and good durability and can be used in harsh environment including acid and salt conditions. The SCNCs are then assembled to monitor full range body motions including both subtle and large body movements, making it a promising candidate in wearable electronics.

A time- and cost-effective fabrication methodology via a two-mode mechanical cutting process for multilayer stretchable electronics has been developed without using the conventional photolithography-based processes. A commercially available vinyl cutter is used for defining complex patterns on designated material layers by adjusting the applied force and the depth of the cutting blade. Two distinct modes of mechanical cutting can be achieved and employed to establish the basic fabrication procedures for common features in stretchable electronics, such as the metal interconnects, contact pads, and openings by the "tunnel cut" mode, and the flexible overall structure by the "through cut" mode. Three robust and resilient stretchable systems have been demonstrated, including a water-resistant, omnidirectionally stretchable supercapacitor array, a stretchable mesh applicable in sweat extraction and sensing, and a skin-mountable human breathing monitoring patch. Results show excellent electronic performances of these devices made of multilayer functional materials after repetitive large deformations.

The lamellar structure of (Bi,Sb)

The misfit layer compound (SnS)1.2(TiS2)2 is a promising low-cost thermoelectric material because of its low thermal conductivity derived from the superlattice-like structure. However, the strong covalent bonds within each constituent layer highly localize the electrons thereby it is highly challenging to optimize the power factor by doping or alloying. Here, we show that Bi doping at the Sn site markedly breaks the covalent bonds networks and highly delocalizes the electrons. This results in a high charge carrier concentration and enhanced power factor throughout the whole temperature range. It is highly remarkable that Bi doping also significantly reduces the thermal conductivity by suppressing the heat conduction carried by phonons, indicating that it independently modulates phonon and charge transport properties. These effects collectively give rise to a maximum ZT of 0.3 at 720 K. In addition, we apply the single Kane band model and the Debye–Callaway model to clarify the electron and phonon transport mechanisms in the misfit layer compound (SnS)1.2(TiS2)2.

An inexpensive virus detection scheme with high sensitivity and specificity is desirable for broad applications such as the COVID-19 virus. In this article, we introduce the localized surface plasmon resonance (LSPR) principle on the aggregation of antigen-coated gold nanoparticles (GNPs) to detect SARS-CoV-2 Nucleocapsid (N) proteins. Experiments show this technique can produce results observable by the naked eye in 5min with a LOD (Limits of Detection) of 150ng/ml for the N proteins. A comprehensive numerical model of the LSPR effect on the aggregation of GNPs has been developed to identify the key parameters in the reaction processes. The color-changing behaviors can be readily utilized to detect the existence of the virus while the quantitative concentration value is characterized with the assistance of an optical spectrometer. A parameter defined as the ratio of the light absorption intensity at the upper visible band region of 700nm to the light absorption intensity at the peak optical absorption spectrum of the GNPs at 530nm is found to have a linear relationship with respect to the N protein concentrations. As such, this scheme could be utilized as an inexpensive testing methodology for applications in POC (Point-of-Care) diagnostics to combat current and future virus-induced pandemics.

A variety of autonomous oscillations in nature such as heartbeats and some biochemical reactions have been widely studied and utilized for applications in the fields of bioscience and engineering. Here, we report a unique phenomenon of moisture-induced electrical potential oscillations on polymers, poly([2-(methacryloyloxy)ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide-co-acrylic acid), during the diffusion of water molecules. Chemical reactions are modeled by kinetic simulations while system dynamic equations and the stability matrix are analyzed to show the chaotic nature of the system which oscillates with hidden attractors to induce the autonomous surface potential oscillation. Using moisture in the ambient environment as the activation source, this self-excited chemoelectrical reaction could have broad influences and usages in surface-reaction based devices and systems. As a proof-of-concept demonstration, an energy harvester is constructed and achieved the continuous energy production for more than 15,000 seconds with an energy density of 16.8 mJ/cm2. A 2-Volts output voltage has been produced to power a liquid crystal display toward practical applications with five energy harvesters connected in series., Moisture-induced energy generation is a potential green energy power source. Here, the authors report a moisture-induced autonomous surface potential oscillation phenomenon and apply it to the demonstration of energy harvesters with long persistence time and good energy density

In the last two decades, information technology has been recognized as a modern innovation that influences our private and public life. Technologies made a huge difference in the quality of life. The information technology collects data from different web applications and analyses the reports. The collected information helps in favor of decision-making for management. This research investigates and exposes the structure in an E-commerce business of dynamic data management using blockchain model (DDMS-BCM). The connectivity between Blockchain and modern information technology is made powerful by the ledger. A lightweight security scheme has been suggested for data management on the E-Commerce platform to achieve better results. This paper presents a comprehensive prediction of many literature studies based on the Lightweight Security Scheme for data management in the E-commerce platform. The parameters related to this analysis are carried out by a systemic analysis of data management and business process reports. This analysis found that DDMS-BCMis readily acceptable in e-commerce using Blockchain technologies. A blockchain is an online ledger that uses a data structure to simplify how we transact. It enables users to securely manipulate the ledger without the assistance of a third party. It allows for the development of a free cryptocurrency in a decentralized setting. The number of advantages associated with DDMS is collected with the help of related literature studies. The results extracted from the test have been collected to explain the concept and the role of a data management system in an e-commerce organization using Blockchain technologies. Business companies may store their main records in the blockchain, which provides data immutability and acts as the single source of truth for the enterprises and the supply chain by combining management information systems with private or consortium blockchains. The experimental shows that the overall article activities in various parameters are Data Transaction Ratio is 85.46%, Encryption and Decryption time and the size of access ratio as 86.92%, Accuracy ratio as 80.8%, Storage overhead Ratio is 72.81%, and overall performance ratio is 92.30% is better than the previous research works

Flexible force sensors are of great interest in the fields of healthcare, physiological signals, and aircraft smart skin applications because of their compatibility with curved surfaces. However, the simultaneous detection of multidirectional forces remains an engineering challenge, despite the great progress made in recent years. Herein, we present the development of a flexible capacitive force sensor capable of efficiently distinguishing normal and sliding shear forces. A two-layer electrospun polyimide/graphene oxide (PI/GO) nanofiber membrane is used as the dielectric layer, which is sandwiched between one top electrode and four symmetrically distributed bottom electrodes. This composite membrane has an improved dielectric constant, a reduced friction coefficient, and good compressibility, leading to superior performance that includes high sensitivity over a wide operational range with measured results of 3 MPa−1 for 0–242 kPa (0–2.2 N) and 0.92 MPa−1 for 242–550 kPa (2.2–5 N) in the normal direction; and better than 1 N−1 for 0–3 N in the x- and y-axis directions. The system also has a low detection limit of 10 Pa, fast response and recovery times of 39 ms and 13 ms, respectively, a good cyclic stability of 10,000 cycles at a pressure of 176 kPa, and promising potential for use in high-temperature environments (200 °C). Moreover, a prototype 4 × 4 sensor array has been fabricated and successfully used in a robotic system to grasp objects and operate a wireless toy car. As such, the proposed system could offer superior capabilities in simultaneous multidirectional force sensing for applications such as intelligent robots, human–machine interaction, and smart skin.

This work presents the attenuation effect due to the surface curvature for the ultrasound pulse-echo detection scheme. The magnitude of attenuation due to the curved surface is simulated and experimentally validated by a piezoelectric micromachined transducer (pMUT) array as a model with 39 × 39 elements and 3 mm × 3mm in size made of 1 µm-thick A1N piezoelectric layer, and 5 urn-thick Si elastic layer. Experimental validations have been conducted to measure the diameter variations of silicone tubes with different diameters in the mineral oil environment to mimic the acoustic properties of the human tissue and blood vessel. Under an applied voltage of 12 V, three sine cycles of 1–10 MHz frequency are emitted and the echo signals from tubes with diameters 2 to 12 mm at a distance of 25 mm are captured. The measured and simulated attenuation is around 7dB for those surfaces to emulate arteries and veins for applications in blood pressure measurements. These results help both the design and analysis of ultrasound detections by pMUTs encountering non-flat surfaces both qualitatively and quantitatively for various applications.

This paper presents an untethered crawling and jumping micro robot via the frequency of the external alternating magnetic field. The prototype micro robot is 8 mm-long made of soft polymeric materials by a 3D printing process. Two permanent magnets are added to be excited by the low-frequency alternative magnetic field source for the crawling operation. A shape memory alloy (SMA) actuator and an aluminum foil to efficiently stimulate induction heating are utilized under the high-frequency alternative magnetic field for the jumping motion. Under a low driving frequency of 60–90 Hz, the prototype robot can crawl with a speed of 5 body length per second via the induced magnetic force. Under a high driving frequency of 30–40 kHz, induction heating is generated to activate the SMA actuator for the jumping action of up to 30 times of the body height of the robot. By exploring other structural designs and manipulation patterns, various forms of robotic actions and locomotion could be realized to execute complex tasks.

We herein present a soft crawling robot based on the design of the magnetic anisotropic actuation to realize untethered crawling movements. With the self-assembled iron filing mesh tuned magnetically and sealed in silicone rubber matrix, we are able to fabricate a large quantity of crawling robots in parallel by a molding process. The magnetic anisotropy is established in the body of the robot to induce the magnetic actuation. Under an alternating magnetic field near the resonant frequency of the robot, the legs of the robot can bend and release repeatedly to achieve a forward moving velocity of ~0.19 cm/s at 2.5 Hz and 46 mT. In addition, the soft crawling robot is robust enough such that even crushed by a 1.8-ton automobile, it can still be fully functional. We envision the magnetic soft robot design and working principle can be further studied for the advancements of micro-robotics research.

We present a light-driven soft robot fabricated by a facile, two-mode laser engraving and cutting process to emulate the crawling motion of inchworm. A porous laser-induced graphene layer is introduced as both a pliable photothermal absorber and a faster heat dissipation material through its high specific surface area. The robot structure is defined and cut via a laser cutting operation, which is very easy to implement to make complex structures. Continuous robot motion of the prototype soft robots under light stimulation has achieved a speed of ∼26 mm/min and a cooling process of 5 s. We envision this fabrication approach and operation principle can be extended as a tool for the advancements of the developing soft robots.

We herein demonstrate micro swimming robots powered by a single-axis magnetic system with controllable mobility and stability. Five distinctive advancements have been achieved: (1) using a single-axis alternating magnetic field to remotely power propeller-style micro swimming robots; (2) controllable moving speed as well as direction for the swimming structure by regulating magnetic field magnitude, frequency, and direction; (3) ultrafast moving speed of 19.1 body length per second under a magnetic field of 1.5 mT; (4) several underwater maneuvering demos including upwards, downwards and stationary motions and movements towards a target location to carry out basic tasks; and (5) attitude stability achieved by the effect of center of pressure over center of mass.

We develop a sensing method based on the double-coffee ring phenomenon for the first time using localized surface plasmon resonance (LSPR) effect in gold nanoparticles (GNPs) to detect SARS-CoV-2 Nucleocapsid proteins with high sensitivity. Testing images are further analyzed via the convolutional neural learning for enhanced accuracy. The circular-shape hydrophilic PTFE porous membrane with a hydrophobic ring barrier is utilized as the sensing platform. When the virus proteins are interacting with antibody coated GNPs solution on the platform, a double-coffee ring image is observed and the convolutional neural network helps the differentiation for the first small protein-GNPs ring at the center and a second non-specific ring at the hydrophobic barrier. We use this double-coffee ring to detect viral infection and quantify the concentration of COVID-19 viruses in 5 ng/ml (LOD), similar to Abbott BinaxNOW® testing kit, to 1000 ng/ml. As such this detection scheme could open up a new class of biomolecular research in the field of micro/nano fluidics.

One grand challenge in haptic human-machine interface devices is to electromechanically stimulate sensations on the human skin wirelessly by thin and soft patches under a low driving voltage. Here, we propose a soft haptics-feedback system using highly charged, polymeric electret films with an annulus-shape bump structure to induce mechanical sensations on the fingertip of volunteers under an applied voltage range of 5–20 V. As an application demonstration, a 3 × 3 actuators array is used for transmitting patterned haptic information, such as letters of ‘T’, ‘H’, ‘U’ letters and numbers of ‘0’, ‘1’, ‘2’. Moreover, together with flexible lithium batteries and a flexible circuit board, an untethered stimulation patch is constructed for operations of 1 h. The analytical model, design principle, and performance characterizations can be applicable for the integration of other wearable electronics toward practical applications in the fields of AR (augmented reality), VR (virtual reality) and robotics.

Civilization construction of information society needs a solid industrial foundation, which means that the development of ecological civilization, and improve the level of ecological civilization construction, need to be built on the basis of emerging industries. From the content of ecological civilization construction, the collaborative governance system of ecological civilization construction includes collaborative governance of environmental protection, and collaborative governance of social ecological concept construction. Environmental protection refers to taking protective measures to the fragile ecological environment or the ecological environment that may be damaged, so as to maintain the existing state or develop in a better direction. This paper introduces the related technology of communication optimization theory, and constructs the intelligent system of ecological civilization construction.

In a virtualized system, the virtual machine (VM) scheduler plays a key role to the performance promotion of the virtual machine monitor (VMM), a.k.a. hypervisor. The scheduler is responsible for assigning adequate system resources to each VM according to the demands of the VM tenants, which is quite challenging as VM tenants’ demands are quite dynamic and unpredictable. To this end, CPU pool mechanism has been widely adopted as an adaptive solution. However, the CPU pool mechanism still has defficiency in terms of VM classification model and time-slice allocation strategy, as the two strategies have to be effectively utilized for realizing a high-adaptive VM scheduler. In this paper, we thus explore opportunities to improve the CPU pool mechanism and develop a new VM scheduling solution, called vSimilar, which uses VM multi-classification model to more effectively adaptive to the VMs of running different types of tasks at different time. Moreover, by a dynamic time-slice function, vSimilar manages to provide a more efficient resource allocation. The experimental evaluation shows that vSimilar can significantly improve the performance of a VMM, such as Xen. The improvements include 1) a VM server hosted by Xen with vSimilar can reduce nearly 95% of a client’s Ping round-trip time (Ping RTT), 2) vSimilar can help increase about 40% the TCP throughput, and about 20% the UDP throughput, between a Xen-hosted VM server and a client, and 3) vSimilar also increases the page operation rate by nearly 50% for a Xen-hosted VM Web server.

Server consolidation and virtualization technologies enable multiple end-users to share a single physical server, substantially improving hardware utilization and reducing energy consumption. However, as modern multicore server architectures shift to non-uniform memory access (NUMA), the complex interplay between data access affinity and shared resource overhead continues to pose challenges to consolidation efficiency. In this paper, we first systematically characterize the performance impacts of server consolidation on NUMA systems with various cloud applications. We find that the virtual machine (VM) memory and network I/O access could both affect the cloud applications performance. Moreover, as consolidation density continues to grow, conventional approaches cannot manage the system loads and thus result in overall system performance degradation. Motivated by these two findings, we then propose a load-aware global resource affinity management framework (LG-RAM) that aims to optimize VM consolidation performance on NUMA systems. LG-RAM consists of three components: the VM resource access monitor quantifies the VM resource access behaviors, the shared resource load detector models the load on shared hardware resources, and the VM resource scheduler makes the scheduling decision according to the information from the above two components. Our evaluations on the two different systems indicate that, compared with state-of-the-art approaches, LG-RAM can exhibit an average throughput improvement of 41.5% and 54.2% on Intel and AMD NUMA machines, respectively. Additionally, LG-RAM only incurs an extra CPU usage of no more than 7% on average when consolidating 32 VMs.

Two-dimensional materials are incipient as an innovative class of multifunctional elements with promising attributes for energy and environmental applications. Herein, a novel nanohybrid consisting of Ag-MoS2 loaded mesoporous g-C3N4 (herein ‘m-CN’) with ordered structure was synthesized by a nanocasting method using cubic and ordered mesoporous silica (KIT-6) as a hard template. Due to its unique 3D mesoporous architecture, the as-synthesized Ag-MoS2@m-CN nanohybrid revealed excellent visible-light absorption for enhanced charge separation of photo-induced e−–h+ pairs to improve the degradation performance, high stability, and reusability with respect to Rhodamine B (RhB). The measured very high degradation efficiency is explained by synergistic effects from catalytically active Ag and MoS2 nanoparticles cumulatively decorated on the cubic mesoporous m-CN in form 3D mesoporous architecture. Additionally, the Ag-MoS2@m-CN nanohybrid exhibits high response and selectivity toward n-butanol gas at low-operating temperatures for reliable detection of volatile organic compounds (VOCs). The photocatalysis behavior and VOC sensing response of Ag-MoS2@m-CN nanohybrid material are discussed in detail for possible various application avenues toward environmental purifications and monitoring.

The detection of indoor location based on magnetic fields collected by embedded sensors in smartphones has been progressed rapidly. Most current approaches rely on the particle filter (PF) scheme which combines the pedestrian dead reckoning (PDR) technique with patterns of previously recorded magnetic field intensity. The key challenges include inherent blindness and particle degradation problems. Here, a fusion algorithm combining the extended Kalman filter (EKF) and the PF scheme is proposed to address these issues. EKF is first used to reduce the possible location regions by fusing the PDR and magnetic field intensity results. The particle generation, update, and resampling processes are conducted afterward, and the final position is calculated by using the weighted mean of particles. As such, the blindness and particle degradation problems are alleviated by using particles in the reduced location regions at each processing step. Experiments show a localization accuracy of 1-2m when the user walks smoothly, which is better than those of traditional PF schemes, especially in cases under heavy magnetic distortions by using a reduced number of particles.

For many industrial applications of the methane sensor in a wireless node, the primary requirements are low power consumption and wide detection range. These requirements are considerably challenging as compared to the requirements related with conventional methane sensors. To meet such requirements of Internet of Things (IoT) development for methane monitoring in underground coal mines, we propose a full concentration range methane detector using a micro silicon device with low power consumption. The microheaters are fabricated with a CMOS-compatible SOI (silicon-on-insulator) MEMS (microelectromechanical system) process. Joule heating is utilized to enable micro-local high temperature for methane sensing. To obtain signals with high sensitivity and low heating power under an appropriate supplied current, a working point is determined by means of the maximum voltage variations from the voltage-current characteristics of the microheater. In general, the methane sensitivity of the micro heater increases and the power consumption decreases, as the length of the heater increases. The device has an exponential-decay response in the entire methane concentration range. A typically low power consumption around 27 mW yields an average sensitivity of approximately 20 mV/% CH4 for the methane concentration ranging from 0 to 17%.

Flexible humidity sensors play important roles in wearable devices and consuming electronics which provide a convenient way between digital and physical worlds. This work presents an easy fabricated method for flexible humidity sensors all based on carbon material including electrodes and functional layers. The interdigital electrodes are made by direct laser writing on commercial Kapton tapes and the transferring to flexible Polydimethylsiloxane (PDMS) substrates. The humidity sensing material is reduced graphene oxide (rGO) in nanometer thickness by electrospray. The rGO flakes covered the micro-size laser induced graphite (LIG), forming rGO-graphite balls, dramatically increase surface areas to interact with water molecules. The results show high precision sensitivity and fast response time for adsorption (0.9 s) and desorption (4.5 s). This method provides a novel method for fabricating cost-effective flexible humidity sensors.

Black silicon is a kind of micro-/nanostructure formed on the surface of silicon, which can greatly reduce light reflection. In this review, five main fabrication techniques of black silicon are introduced and these techniques can change the morphology of the surface of crystalline silicon to a certain extent, thus making the preparation of black silicon more feasible and convenient. The utilization of black silicon is then reviewed. Black silicon has originally been used as a bactericidal to eradicate bacteria such as Pseudomonas aeruginosa. It is bound to have more novel applications in the field of sterilization. Black silicon is like a sponge that absorbs light. It can capture almost all sunlight, both visible and infrared light. It also reduces the amount of silicon used in optical sensors, making products cheaper, smaller, and lighter. Due to the above characteristics, black silicon is widely used in Surface Enhanced Raman Scattering detection, biomedical sensing, and infrared device manufacturing. It also has the potential to improve the performance of solar cells. This review is intended to serve as a useful introduction to this novel material and its properties, and provide a general overview of recent progress in its main applications.

Ultrathin transition metal carbides with high capacity, high surface area, and high conductivity are a promising family of materials for applications from energy storage to catalysis. However, large-scale, cost-effective, and precursor-free methods to prepare ultrathin carbides are lacking. Here, we demonstrate a direct pattern method to manufacture ultrathin carbides (MoCx, WCx, and CoCx) on versatile substrates using a CO2 laser. The laser-sculptured polycrystalline carbides (macroporous, ~10–20 nm wall thickness, ~10 nm crystallinity) show high energy storage capability, hierarchical porous structure, and higher thermal resilience than MXenes and other laser-ablated carbon materials. A flexible supercapacitor made of MoCx demonstrates a wide temperature range (−50 to 300 °C). Furthermore, the sculptured microstructures endow the carbide network with enhanced visible light absorption, providing high solar energy harvesting efficiency (~72 %) for steam generation. The laser-based, scalable, resilient, and low-cost manufacturing process presents an approach for construction of carbides and their subsequent applications., Nature Communications, 10, ISSN:2041-1723

Flexible and wearable devices with the capabilities of both detecting and generating mechanical stimulations are critical for applications in human-machine interfaces, such as augmented reality (AR) and virtual reality (VR). Herein, a flexible patch based on a sandwiched piezoelectret structure is demonstrated to have a high equivalent piezoelectric coefficient of d33 at 4050 pC/N to selectively perform either the actuating or sensing function. As an actuator, mechanical vibrations with a peak output force of more than 20 mN have been produced, similar to those from the vibration mode of a modern cell phone, and can be easily sensed by human skin. As a sensor, both the pressure detection limit of 1.84 Pa for sensing resolution and excellent stability of less than 1% variations in 6000 cycles have been achieved. The design principle together with the sensing and driving characteristics can be further developed and extended to other soft matters and flexible devices.

Quantum-dot (QD) white light-emitting diodes (LEDs) are promising for illumination and display applications due to their excellent color quality. Although they have a high quantum yield close to unity, the reabsorption of QD light leads to high conversion loss, significantly reducing the luminous efficacy and stability of QD white LEDs. In this report, SBA-15 mesoporous particles (MPs) with two-dimensional hexagonal pore structures (2D-HPS) are utilized to largely enhance the luminous efficacy and color-conversion efficiency of QD white LEDs in excess of 50%. The reduction in conversion loss also helps QD white LEDs to achieve a lifetime 1.9 times longer than that of LEDs using QD-only composites at harsh aging conditions. Simulation and testing results suggest that the waveguide effect of 2D-HPS helps in reducing the reabsorption loss by constraining the QD light inside the wall of 2D-HPS, decreasing the probability of being captured by QDs inside the hole of 2D-HPS. As such, materials and mechanisms like SBA-15 MPs with 2D-HPS could provide a new path to improve the photon management of QD light, comprehensively enhancing the performances of QD white LEDs.

External tactile force/pressure sensing, as a vital function of electronic skins, is very important to robots in non-structured environments, intelligent prosthesis of the disabilities for baby care or daily life and medical cares, etc. Despite of great advance of pressure sensors for medium pressure (10–100 kPa), to achieve high sensitivity, good pressure resolution and fast response in electronic skins for applications in biomedicine, artificial prosthetics, personal health monitoring and robotics remains challengeable. Here we direct-wrote graphene nanoplatelets (GNPs) using Weissenberg effect on a PDMS substrate to fabricate a flexible pressure sensor with high pressure sensitivities about 6.56 MPa−1 and 0.335 kPa−1 respectively under the pressure less than 65 kPa and around 100 kPa. Minimum pressure change of ca. 14 Pa to the placement or removal of a tiny item can be detected. It is characterized to be of faster response/recovery speed (ca. 171 ms/110 ms), better repeatability and cycling stability, compared with most reported flexible medium-pressure sensor. The pressure electronic skin demonstrates good performance in its applications including pulse sensing on wrist and fingertip grabbing, indicating its greatly potential sensor candidate for electronic skins.

A piezoelectret pulse sensor combined with the approximate entropy (ApEn) analysis is utilized to detect human pulses to reveal health conditions. Inspired by the traditional Chinese medicine (TCM) with a foundation of more than 2500 years, human pulses are helpful in the diagnostics of illness as the body's vital energy circulates through blood vessels with branches connected to organs. A flexible cellular polypropylene (PP) piezoelectret film with a wooden cylinder substrate is used to emulate the pulse taking process in TCM to record the pulse characteristics. A group of 26 volunteers have been successfully diagnosed by the wearable sensing system and the approximate entropy analysis has been implemented to analyze the data. Results show a threshold approximate entropy value of 0.1 as the separation point between the volunteers of normal and abnormal health conditions.

Conductive polymer composite based strain sensors have promising applications in the fields of artificial skin, wearable health-care device, etc. However, fabrication of strain sensors with good stretchability, anti-corrosion, excellent durability and reliability remains challenging. In this work, a superhydrophobic strain sensor based on conductive thermoplastic polyurethane/carbon nanotubes/polydimethylsiloxane (TPU/CNTs/PDMS) was prepared by ultrasonication induced CNTs decoration onto the electrospun TPU nanofiber surface, followed by the PDMS modification. Uniformly dispersed CNTs on the nanofiber surface with a hierarchical structure construct the conductive network. The PDMS layer with a low surface energy endows the nanofiber composite with superhydrophobicity thus anti-corrosion property. The introduction of CNTs/PDMS improves both the Young's modulus, tensile strength and the elongation at break. The superhydrophobicity and conductivity can be maintained after the cyclic stretching-releasing test, displaying excellent durability. When used as a wearable strain sensor, the nanofiber composite is capable of detecting body motion and could work even under harsh conditions (moisture, acid and alkaline environment), showing promising application in wearable electronics.

The influences of temperature, humidity, and O2 to the gas sensing characteristics of graphene field effect transistors (FETs) have been studied as these environmental factors are often encountered in practical gas sensing applications. Both empirical results and theoretical analyses are characterized for heated graphene FET gas sensors from room temperature to 100 °C under a wide range of applied gate voltages. It is found that at a constant applied gate voltage of −20 V with respect to the gate voltage at the neutrality point, the sensitivity of the device to humidity decreases; while the sensitivity to O2 decreases first, and increases afterwards as the operation temperature increases. These phenomena are explained by using the physisorption and chemisorption models between gases and the graphene surface. Furthermore, devices operate in the hole regime (the majority carrier is hole in the prototype devices) result in lower sensitivity to humidity and O2 as compared to those results of gas sensors operating in the electron regime due to the p-type doping effects of moisture and O2. As such, this work provides good foundations for graphene-based FET gas sensors in practical application environments under the influences of ambient air, temperature, and humidity.

Metal-based materials have been widely used for the electromagnetic interference (EMI) shielding due to their excellent intrinsic conductivity. However, their high density, poor corrosion resistance, and poor flexibility limit their further application in aerospace and flexible electronics. Here, we reported a facile means to prepare lightweight, mechanically durable, superhydrophobic and conductive polymer fabric composites (CPFCs) with excellent electromagnetic shielding performance. The CPFC could be fabricated by three steps: (1) the polypropylene (PP) fabric was coated by a polydopamine (PDA) layer; (2) PP/PDA adsorbed the Ag precursor that was then chemically reduced to Ag nanoparticles (AgNPs); (3) PP/PDA/AgNPs fabrics were modified by one layer of polydimethylsiloxane (PDMS). The contact angle (CA) of the CPFCs could reach ∼152.3° while the sliding angle (SA) was as low as ∼1.5°, endowing the materials with excellent self-cleaning performance. Thanks to the extremely high conductivity of 81.2 S/cm and the unique porous structure of the fabric, the CPFC possessed outstanding EMI shielding performance with the maximum shielding effectiveness (SE) of 71.2 dB and the specific shielding effectiveness (SSE) of 270.7 dB cm

Graphene quantum dots (GQDs) have been explored in recent years for electrochemical applications with considerable potentials. Here, we present GQD-doped CuCo2S4 nanocomposites through two-step hydrothermal process for supercapacitor electrodes. The surface of CuCo2S4 nanosheets changes from smooth to particles-accumulative shape, which assists the electrochemical cycling processes as well as the ion diffusion and charge transfer kinetics for improved supercapacitor performances. As a result, GQD/CuCo2S4 electrodes demonstrate a specific capacitance of 1725 F g−1 under a current density of 0.5 A g−1 and a cycling life of 10,000 cycles by retaining 90% of the energy storage capability. As such, this work extends the potential of GQDs in electrochemical applications by means of morphology change of CuCo2S4 nanosheets.