Piezoresistive Research Articles

Orthogonal Charge Transfer by Precise Positioning of Silver Single Atoms and Clusters on Carbon Nitride for Efficient Piezocatalytic Pure Water Splitting

AbstractDeveloping efficient piezocatalytic systems for two‐electron water splitting (TEWS) with producing H2 and H2O2 shows great promise to meet the industrial demand. Herein, Ag single atoms (SAs) and clusters are co‐anchored on carbon nitride (AgSA+C−CN) to serve as the multifunctional sites for efficient TEWS. The Ag SAs enhance the in‐plane piezoelectric polarization of CN that is intimately modulated by the atomic coordination induced charge redistribution, and Ag clusters afford strong interfacial electric field to remarkably promote the out‐of‐plane migration of piezoelectrons from CN. Moreover, AgSA+C−CN yields a larger piezoresistive effect that elevates carrier mobility under strain. Consequently, a superior H2 and H2O2 evolution rate of 7.90 mmol g−1 h−1 and 5.84 mmol g−1 h−1 is delivered by AgSA+C−CN, respectively, far exceeding that of the previously reported piezocatalysts. This work not only presents the SAs decoration as an available polarization enhancement strategy, but also sheds light on the superiority of multi‐sites engineering in piezocatalysis.

Development and Implementation of Cement-Based Nanocomposite Sensors for Structural Health Monitoring Applications: Laboratory Investigations and Way Forward

Recent advances in material science and self-sensing technology have enabled the development of cement-based nanocomposite sensors that detect the damage on their own by exhibiting piezoelectric properties corresponding to the response of the structures. The present study involves the development and implementation of these sensors in the structural components and monitors the response by correlating the piezoelectric properties of the sensors with the stress-strain response to identify the potential damage. For this purpose, the carbon fiber (CF) and multiwalled carbon nanotubes (MWCNT) are used as nanofiller in the cementitious matrix to develop the self-sensing sensors. These sensors possess high strength, large elastic modulus, and piezo resistivity properties, which make them promising smart sensor materials for structural health monitoring applications. Two example applications involving the beam and column as the structural components are used for the experimentation. After embedding the sensors into the structural components, the response is evaluated in the form of resistance versus load. The self-sensing sensor is capable of detecting the nanostructural cracks during the loading of the system. Based on the severity of loading, the resistivity will indicate the damage state of the structural component which helps in deciding the suitable retrofitting strategies for the maintenance of the structural component to elongate the service life of the structures. The developed sensors also possess good mechanical and electrical properties and hence they have promising characteristics for real-time health monitoring applications.

Orthogonal Charge Transfer by Precise Positioning of Silver Single Atoms and Clusters on Carbon Nitride for Efficient Piezocatalytic Pure Water Splitting.

Developing efficient piezocatalytic systems for two-electron water splitting (TEWS) with producing H2 and H2 O2 shows great promise to meet the industrial demand. Herein, Ag single atoms (SAs) and clusters are co-anchored on carbon nitride (AgSA+C -CN) to serve as the multifunctional sites for efficient TEWS. The Ag SAs enhance the in-plane piezoelectric polarization of CN that is intimately modulated by the atomic coordination induced charge redistribution, and Ag clusters afford strong interfacial electric field to remarkably promote the out-of-plane migration of piezoelectrons from CN. Moreover, AgSA+C -CN yields a larger piezoresistive effect that elevates carrier mobility under strain. Consequently, a superior H2 and H2 O2 evolution rate of 7.90 mmol g-1 h-1 and 5.84 mmol g-1 h-1 is delivered by AgSA+C -CN, respectively, far exceeding that of the previously reported piezocatalysts. This work not only presents the SAs decoration as an available polarization enhancement strategy, but also sheds light on the superiority of multi-sites engineering in piezocatalysis.

Sensing performance of engineered cementitious composites in different application forms

The method of application of self-sensing composites in structural health monitoring is urgent to be determined before real application. In this paper, the mechanical and sensing properties of self-sensing engineered cementitious composites (ECC) under monotonic and variable amplitude cyclic tension and compression were analyzed. With the consideration of different application forms such as sensor, coating and bulk types, three kinds of concrete samples were prepared. For each sample, the sensing properties and applicability of piezoresistive effect were analyzed and compared. The results demonstrate that the developed self-sensing ECC guarantees desirable sensing performances and high ductility with a tensile strain of above 6.0%. The gauge factor (GF), signal-to-noise ratio (SNR) and repeatability are 165.48, 53.07 and 4.19%, respectively in compression, while they are 14.71, 25.05 and 7.16%, respectively in tension. It was verified that the sample strain could be constantly monitored by self-sensing ECC, especially when the strain is less than 0.005 %. Compared with coating and bulk types, the sensor type could significantly improve the sensitivity, SNR and repeatability. Besides, the sensor type could eliminate the zero drift greatly and has little negative effect on the mechanical properties of samples.

Surface-potential-modulated piezoresistive effect of core–shell 3C-SiC nanowires

The effect of surface potential on the carrier mobility and piezoresistance of core–shell silicon carbide nanowires (SiC NWs) was investigated to realize small and sensitive SiC-microelectromechanical systems sensors. The p-type cubic crystalline SiC (3C-SiC) NWs were synthesized via the vapor–liquid–solid method and coated with silicon dioxide (SiO2) or aluminum oxide (Al2O3) dielectric shells to form core–shell structured NWs with different surface potentials. Four-point bending devices (FBDs) with a field-effect transistor (FET) configuration integrating a single core–shell 3C-SiC NW as the FET channel were fabricated to apply an additional electric field and strain to the core–shell 3C-SiC NWs. The fixed oxide charge densities of the SiO2 and Al2O3 shells showed positive and negative values, respectively, which were equivalent to electric fields of the order of several hundred thousand volt per centimeter in absolute values. In the core–shell 3C-SiC NWs with originally low impurity concentrations, the electric field induced by the fixed oxide charge of the shells can determine not only the electrical conduction but also the charge carriers in the NWs. Bending tests using the FBDs showed that the piezoresistive effect of the SiO2-coated NW was almost the same as that of the as-grown 3C-SiC NW reported previously, regardless of the gate voltage, whereas that of the Al2O3-coated NW was considerably enhanced at negative gate voltages. The enhancement of the piezoresistive effect was attributed to the piezo-pinch effect, which was more pronounced in the NW, where the carrier density at the core–shell interface is enhanced by the electric field of the dielectric.

Self-Powered Resilient Porous Sensors with Thermoelectric Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) and Carbon Nanotubes for Sensitive Temperature and Pressure Dual-Mode Sensing.

Portable and wearable dual-mode sensors that can simultaneously detect multiple stimuli are essential for emerging artificial intelligence applications, and most efforts are devoted to exploring pressure-sensing devices. It is still challenging to integrate temperature and pressure-sensing functions into one sensor without the requirement for complex decoupling processes. Herein, we develop a self-powered and multifunctional dual-mode sensor by dip-coating melamine sponge with both poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and carboxylated single-walled carbon nanotubes (CNTs). By integrating thermoelectric and conductive PEDOT:PSS/CNT components with the hydrophilic and resilient porous sponge, the resultant sensor is efficient in independently detecting temperature and pressure changes. The temperature and pressure stimuli can be independently converted to voltage and electrical resistance signals on the basis of the Seebeck and piezoresistive effects, respectively. The sensor exhibits a high Seebeck coefficient of 35.9 μV K-1 with a minimum temperature detection limit of 0.4 K and a pressure sensitivity of -3.35% kPa-1 with a minimum pressure detection limit of 4 Pa. Interestingly, the sensor can also be self-powered upon illumination. These multi-functionalities make the sensor a promising tool for applications in electronic skin, soft robots, solar energy conversion, and personal health monitoring.

Multifunctional Ti3C2Tx MXene/Poly(Styrene‐Methacrylic Acid)@Polypyrrole Nanospheres/Thermoplastic Polyurethane Electrospinning Membrane for High Sensitivity Pressure Sensing and Pressure‐Electrothermal

AbstractThe introduction of superior conductive materials on flexible substrates with surface‐built microstructures has proven to be an effective solution for enhancing the sensitivity of pressure sensor. Thermoplastic polyurethane electrospun membrane (TPUEM) with multi‐void structure is used as substrate, and poly(styrene‐methacrylic acid)@polypyrrole nanospheres (PPNs) are pumped into the TPUEM by vacuum filtration to form a microstructure on the surface of thermoplastic polyurethane (TPU) electrospun fibers. The MXene dispersion is sprayed on the surface of PPNs/TPUEM. As it is gradually infiltrated into the material, a conductive network is formed. When the MXene/PPNs/TPUEM is subjected to pressure, its resistance decreases significantly due to the close contact between MXene and PPNs. The assembled pressure sensor shows superior sensitivity (16.72 kPa−1), broad sensing range (0–32.1 kPa), and rapid response (145 ms). The pressure sensor demonstrates the ability to detect human health signals and activities, including human pulse, breathing, and joint movements, etc. Benefiting from its excellent negative piezoresistive effect, the pressure sensor shows a significant pressure‐electrothermal function at 2.0 V and the local temperature is 48.08 °C. The MXene/PPNs/TPUEM has potential applications in human physiological signal monitoring, motion monitoring, and energy saving electric heating mats.

Ultrasensitive piezoresistive behavior of silicon carbonitride thin films by optimizing nanomorphologies

Silicon carbonitride (SiCN)-containing amorphous carbon network is a promising piezoresistive material for pressure sensor due to superior high temperature stability and strong piezoresistive properties. However, current works mainly concerned on bulk SiCN that is unable to satisfy rapid development of large area electronics, and the mechanism of the superior piezoresistive characteristics is still not clear. In this work, SiCN thin films with various carbon concentrations are prepared by magnetron sputtering, and first principles approach is applied to reveal the piezoresistive mechanism of SiCN. The SiCN sample with moderate carbon content features ultrahigh gauge factors range of 1713–7290 under varied stress, which are significantly larger than those of existing piezoresistive thin films. By combining with first principles calculations, it is concluded that the distance between carbon clusters is crucial for piezoresistive effect of SiCN, and a distance of 1.8 Å is optimal for generating tunneling effect and obtaining outstanding piezoresistive performance. Moreover, the influence of carbon concentration on resistance change in experiments is nicely predicted by the bandgap change calculated by first principles, which can be applied to evaluate the nanostructure–property relationship for piezoresistive materials.

A MEMS Device Integrating Multiple Cantilever Displacement Sensors to Evaluate Flat Machined Surfaces

Multi-point scanning measurement, which is effective in eliminating motion errors of the stage in on-machine profile measurement, requires multiple displacement sensors of equal pitch to measure displacements simultaneously. However, it is not easy to arrange small sensors with high alignment accuracy when applying the multi-point method at a narrow pitch. In addition, if many sensors can be arranged in parallel, improvement in measurement accuracy can be expected. Therefore, a new micro electro mechanical system (MEMS) device for straightness measurement, one that integrates 10 cantilever displacement sensors, has been proposed. This device can be expected to solve the problem involved in the multi-point method because of the characteristics of MEMS, as the semiconductor processing method can make mechanical structures with high accuracy and it can easily make the device with many identical structures. The device is designed to measure waviness less than 100 μm in height. Ten cantilevers of 11 mm length are fabricated in parallel with 1.8 mm pitch on a side of a base substrate 20 mm square. The strain induced by a displacement of the probe placed near the front edge of the cantilever is detected as a change in the resistance of the piezo resistor at the foot of the cantilever. In the fabrication process of this device, crystal anisotropic etching is performed for 12 hours to form probes 250 μm high. A new fabrication process is also proposed in which a protective process is added to prevent damage to the circuits already formed during the etching. A prototype is investigated, and it is found that the resistance value increases about 0.45% in proportion to the displacement of 100 μm. It is therefore confirmed that this device has the basic ability to detect displacement.

Integrated acoustic resonators in commercial fin field-effect transistor technology

In radio communication, the growth of beamforming and multiple-input–multiple-output technologies, which increase transceiver complexity, have led to a drive to reduce the size, weight and power of radio components by integrating them into a single system on chip. One approach is to integrate the frequency references of acoustic microelectromechanical systems (MEMS) with complementary metal–oxide–semiconductor processes, typically through a MEMS-first or MEMS-last approach that requires process customization. Here we report unreleased acoustic resonators that are fabricated in 14 nm fin field-effect transistor technology and operate in the X-band frequency range (8–12 GHz). The devices use phononic waveguides for acoustic confinement and exploit metal–oxide–semiconductor capacitors and transistors to electromechanically drive and sense acoustic vibrations. Fifteen device variations are analysed across 30 bias points, quantifying the importance of phononic confinement on resonator performance and demonstrating the velocity-saturated piezoresistive effect in active resonant transistors. Our results illustrate the feasibility of integrating acoustic devices directly into standard complementary metal–oxide–semiconductor processes.

Bioinspired two-in-one nanotransistor sensor for the simultaneous measurements of electrical and mechanical cellular responses.

The excitation-contraction dynamics in cardiac tissue are the most important physiological parameters for assessing developmental state. We demonstrate integrated nanoelectronic sensors capable of simultaneously probing electrical and mechanical cellular responses. The sensor is configured from a three-dimensional nanotransistor with its conduction channel protruding out of the plane. The structure promotes not only a tight seal with the cell for detecting action potential via field effect but also a close mechanical coupling for detecting cellular force via piezoresistive effect. Arrays of nanotransistors are integrated to realize label-free, submillisecond, and scalable interrogation of correlated cell dynamics, showing advantages in tracking and differentiating cell states in drug studies. The sensor can further decode vector information in cellular motion beyond typical scalar information acquired at the tissue level, hence offering an improved tool for cell mechanics studies. The sensor enables not only improved bioelectronic detections but also reduced invasiveness through the two-in-one converging integration.

An Automated System for Strain Engineering and Straintronics of 2D Materials

AbstractThis work presents an automated three‐point bending apparatus that can be used to study strain engineering and straintronics in 2D materials. This work benchmarks the system by reporting reproducible strain tuned micro‐reflectance, Raman, and photoluminescence spectra for monolayer molybdenum disulfide (MoS2). These results are in good agreement with reported literature using conventional bending apparatus. This work further utilizes the system to automate strain investigations of straintronic devices by measuring the piezoresistive effect and the strain effect on photoresponse in an MoS2 electrical device. The details of the construction of the straightforward system are given and it is anticipated that it can be easily implemented for study of strain engineering and straintronics in a wide variety of 2D material systems.

Piezoresistance Characterization of Silicon Nanowires in Uniaxial and Isostatic Pressure Variation.

Silicon nanowires (SiNWs) are known to exhibit a large piezoresistance (PZR) effect, making them suitable for various sensing applications. Here, we report the results of a PZR investigation on randomly distributed and interconnected vertical silicon nanowire arrays as a pressure sensor. The samples were produced from p-type (100) Si wafers using a silver catalyzed top-down etching process. The piezoresistance response of these SiNW arrays was analyzed by measuring their I-V characteristics under applied uniaxial as well as isostatic pressure. The interconnected SiNWs exhibit increased mechanical stability in comparison with separated or periodic nanowires. The repeatability of the fabrication process and statistical distribution of measurements were also tested on several samples from different batches. A sensing resolution down to roughly 1 pressure was observed with uniaxial force application, and more than two orders of magnitude resistance variation were determined for isostatic pressure below atmospheric pressure.

Silicene: an excellent material for flexible electronics

The outstanding properties of graphene have laid the foundation for exploring graphene-like 2D systems, commonly referred to as 2D-Xenes. Among them, silicene is a front-runner due to its compatibility with current silicon fabrication technologies. Recent works on silicene have unveiled its useful electronic and mechanical properties. The rapid miniaturization of silicon devices and the useful electro-mechanical properties of silicene necessitate the exploration of potential applications of silicene flexible electronics in nano electro-mechanical systems. Using a theoretical model derived from the integration of ab initio density-functional theory and quantum transport theory, we investigate the piezoresistance effect of silicene in the nanoscale regime. As with graphene, we obtain a small value of the piezoresistance gauge factor (GF) of silicene, which is sinusoidally dependent on the transport angle. The small GF of silicene is attributed to its robust Dirac cone and strain-independent valley degeneracy. Based on the obtained results, we propose to use silicene as an interconnect in flexible electronic devices and as a reference piezoresistor in strain sensors. This work will hence pave the way for exploring flexible electronics applications in other 2D-Xene materials.

Piezoresistive behavior of electric arc furnace slag and graphene nanoplatelets asphalt mixtures for self-sensing pavements

Self-sensing road pavements can autonomously monitor their stress/strain and damage states without the need for embedded sensors. This kind of multifunctional pavements could be used for the realisation of autonomous structural health monitoring (SHM) systems. Moreover, it would permit to collect important traffic data for traffic-monitoring analysis and the development of Vehicle to Infrastructure Communication (V2I) tools, hence contributing to the digitalisation of the transport sector. The sensing mechanism is based on the piezoresistive effect, consisting of a change in the electrical response of the road material when subjected to stress/strain or damage. This paper aims to investigate the piezoresistive behavior of conductive asphalt mixtures with electric arc furnace slag (EAFS) and graphene nanoplatelets (GNPs) for self-sensing application. The results showed that asphalt mixtures with EAFS as fine aggregate and 7 wt% of GNPs exhibited excellent self-sensing properties for both traffic monitoring and SHM systems.

A novel eco- and user-friendly graphene/leather-based composite for real-time mechano-monitoring of human motion

Up to now, flexible wearable sensors have played a significant role in mimicking the comprehensive functions of human sensing as an essential part of the realization of human-machine interactions and artificial intelligence. However, most electronic devices are made of polymer-based materials, which have poor biodegradability and are harmful to the environment. Inspired by natural hair squama structure, a high conductivity, biodegradable, and biocompatible flexible sensor was designed for detecting human physiological signals. The graphene/leather-based composite was leeched onto oil-tanned leather prepared without the involvement of chromium ions, then scalable adsorption assisted coating was used to construct a piezoresistive sensor. With the micro-to-nano hierarchical three-dimensional structure of natural leather, the novel conductive oil-tanned leather (COL) exhibited a high specific surface area for a piezoresistive effect and excellent conductivity (80 kΩ·sq−1), high sensitivity (28.96 kPa−1 under compressing condition and 52.10 under stretch condition). Meanwhile, favorable biodegradability and biocompatibility could be achieved. Moreover, the relatively mature and fully integrated commercial wearable sensors are mostly wired transmission and expensive. The piezoresistive COL sensor can not only be used to monitor physiological signals, but can also be connected to a wireless module to obtain real-time monitoring data of plantar pressure. Furthermore, the sensor can control the light of LED to achieve human-machine interaction. This wearable intelligent sensor can not only solve the problem that traditional sensors are toxic to the environment but also has broad applications in health-monitoring technology.

Colossal piezoresistance in narrow-gap Eu5In2Sb6

A remarkably large reduction in the electrical resistivity of the quantum material Eu${}_{5}$In${}_{2}$Sb${}_{6}$ is discovered as a function of applied uniaxial pressure. This phenomenon, called colossal piezoresistance, is linked to a colossal magnetoresistance effect previously observed in this material. There is a common origin for the two phenomena, namely the interaction-driven formation of magnetic metallic clusters in semiconducting Eu${}_{5}$In${}_{2}$Sb${}_{6}$. These results will aid our understanding of colossal magnetoresistance and piezoresistance effects in a broad set of quantum materials.

Piezo displacement sensors for a compact high-speed x–y nanopositioner in differential actuation mode

An emerging actuation technique in piezo driven nanopositioners is differential actuation, where each axis has two opposing actuators that operate differentially and provide bilateral motion. It has simultaneous benefits of improving linearity and range of displacement. However, few methods for displacement sensing employing in-situ transducers have been considered for this kind of nanopositioners. We address a novel application of PZT piezoelectric chips for direct displacement sensing in differentially driven nanopositioners. First, an electromechanical force analysis is performed in order to increase the PZT sensor sensitivity through the structural design of the nanopositioner. Secondly, the sensing performances of the proposed in-situ PZT sensor are compared with those from an alternative built-in piezoresistive (PZR) strain gauge sensor under equal circumstances, in different sensing and actuation configurations. While the PZR sensor has a larger sensing bandwidth than the PZT one and performs better if the actuation frequency is smaller than 30 Hz, the PZT sensors provides better accuracy when the actuation is well within its sensing bandwidth. The accuracy of the differential sensors and the input-displacement linearity are improved when the mechanical preload force magnitudes on the opposing actuators are balanced. The differential PZT sensor can provide accurate measurements even in a non-differential mode after recalibration.

Smart structures with embedded flexible sensors fabricated by fused deposition modeling-based multimaterial 3D printing

ABSTRACT Smart structures have the advantages of high system integrity and diverse sensing capabilities. However, the labor-intensive and time-consuming fabrication process hinders the large-scale adoption of smart structures. Despite recent attempts to develop sensor-embedded structures using 3D printing technologies, the reported smart structures generally suffer from the complex fabrication process, constrained part size, and limited sensing modality. Herein, we propose a workflow to design and fabricate novel smart structures via multimaterial fused deposition modeling (FDM)-based 3D printing. More specifically, conductive filaments with tailorable mechanical and electrical properties, e.g. piezoresistive effects, were developed. Additionally, the printing process was optimized for processing soft filaments with Young’s modulus around 2 MPa, resolving the issue of filament buckling. Furthermore, the potential applications of the proposed workflow were showcased using three design cases, i.e. biaxial strain sensor, smart tire, and cable-driven soft finger with multiple sensing capabilities. This workflow provides a cost-effective and rapid solution for developing novel smart structures with soft materials.

The stretchable carbon black-based strain fiber with a remarkable linearity in a wide sensing range

ABSTRACT Ascribed to its wide sensing range, high sensitivity, and low stiffness to match target objects with complex 3D shapes, the stretchable strain sensor has shown its promising applications in various fields, ranging from healthcare, bodynet, and intelligent traffic system, to the robotic system. This paper presents a low-cost and straightforward fabrication technology for the stretchable strain fiber with the combined attributes of a wide sensing range, exceptional linearity, and high durability. The hybrid composite consisting of carbon black and silicone is utilized as the functional material to respond to the external mechanical deformation due to the piezoresistive effect. To address the remarkable hysteresis of the CB-silicone composites, the latex tubes with excellent mechanical robustness and a considerable accessible tensile strain are introduced as the outer supporting components. After injecting the conductive CB-silicone composite into these tubes, the stretchable strain fibers are successfully prepared. Notably, the stretchable strain sensor exhibits linearity (R2 = 0.9854) in a wide sensing range (0–400%) and remarkable durability even after the 2500 cycles under 100% tension. Additionally, the potential of this stretchable strain fiber as the wearable strain sensor and the real-time feedback is demonstrated by detecting the body motion and the expansion devices.