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Organic-inorganic perovskites have shown promise as high-performance absorbers in solar cells, first as a coating on a mesoporous metal oxide scaffold and more recently as a solid layer in planar heterojunction architectures. Here, we report transient absorption and photoluminescence-quenching measurements to determine the electron-hole diffusion lengths, diffusion constants, and lifetimes in mixed halide (CH₃NH₃Pbl 3-x Cl x ) and triiodide (CH₃NH₃Pbl₃) perovskite absorbers. We found that the diffusion lengths are greater than 1 micrometer in the mixed halide perovskite, which is an order of magnitude greater than the absorption depth. In contrast, the triiodide absorber has electron-hole diffusion lengths of ~100 nanometers. These results justify the high efficiency of planar heterojunction perovskite solar cells and identify a critical parameter to optimize for future perovskite absorber development.

The CNT-PDMS composite has been widely adopted in flexible devices due to its high elasticity, piezoresistivity, and biocompatibility. In a wide range of applications, CNT-PDMS composite sensors were used for resistive strain measurement. Accordingly, the percolation threshold 2%~4% of the CNT weight ratio in the CNT-PDMS composite was commonly selected, which is expected to achieve the optimized piezoresistive sensitivity. However, the linear range around the percolation threshold weight ratio (2%~4%) limits its application in a stable output of large strain (>20%). Therefore, comprehensive understanding of the electromechanical, mechanical, and electrical properties for the CNT-PDMS composite with different CNT weight ratios was expected. In this paper, a systematic study was conducted on the piezoresistivity, Young’s modulus, conductivity, impedance, and the cross-section morphology of different CNT weight ratios (1 to 10 wt%) of the CNT-PDMS composite material. It was experimentally observed that the piezo-resistive sensitivity of CNT-PDMS negatively correlated with the increase in the CNT weight ratio. However, the electrical conductivity, Young’s modulus, tensile strength, and the linear range of piezoresistive response of the CNT-PDMS composite positively correlated with the increase in CNT weight ratio. Furthermore, the mechanism of these phenomena was analyzed through the cross-section morphology of the CNT-PDMS composite material by using SEM imaging. From this analysis, a guideline was proposed for large strain (40%) measurement applications (e.g., motion monitoring of the human body of the finger, arm, foot, etc.), the CNT weight ratio 8 wt% was suggested to achieve the best piezoresistive sensitivity in the linear range.

Metamaterials and transformation optics play substantial roles in various branches of optical science and engineering by providing schemes to tailor electromagnetic fields into desired spatial patterns. We report a theoretical study showing that by designing and manipulating spatially inhomogeneous, nonuniform conductivity patterns across a flake of graphene, one can have this material as a one-atom-thick platform for infrared metamaterials and transformation optical devices. Varying the graphene chemical potential by using static electric field yields a way to tune the graphene conductivity in the terahertz and infrared frequencies. Such degree of freedom provides the prospect of having different \"patches\" with different conductivities on a single flake of graphene. Numerous photonic functions and metamaterial concepts can be expected to follow from such a platform.

Borophene, as a new material with various configurations, has attracted significant research attention in recent years. In this study, the electronic properties of a series of χ-type borophene nanoribbons (BNRs) are investigated using a first-principles approach. The results show that the width and edge pattern of the nanoribbons can effectively tune their electronic properties. Notably, a super-narrow χ-type BNR is found to be ferromagnetic and exhibits half-metallic properties. Based on these findings, a χ-type borophene nanojunction is proposed, and its spintronic transport properties are investigated using the non-equilibrium Green’s function method combined with density functional theory. The results demonstrate that the nanojunction exhibits excellent spin filtering capabilities under moderate bias voltages when two electrodes are spin parallel. Furthermore, when the spin configurations of the two electrodes are changed from parallel to antiparallel, both the spin-up and spin-down currents demonstrate significant rectifying effects with reversed rectifying directions, and the rectification ratios reach up to 10 5 . Consequently, opposite spin filtering polarizations are obtained for spin-up and spin-down currents. More intriguingly, such bipolar spin filtering and spin rectifying effects can also be achieved by compressing the width of either electrode by 5%, while maintaining the spin parallel configuration of two electrodes. Additionally, the resistance of the device is largely modulated by altering the magnetic configurations of the electrodes or narrowing the width of either electrode, leading to a giant magnetoresistance effect and a piezoresistance effect. These findings open up new avenues for future applications of borophene in spintronic nanodevices.

High accuracy measurement of mechanical strain is critical and broadly practiced in several application areas including structural health monitoring, industrial process control, manufacturing, avionics and the automotive industry, to name a few. Strain sensors, otherwise known as strain gauges, are fueled by various nanomaterials, among which graphene has attracted great interest in recent years, due to its unique electro-mechanical characteristics. Graphene shows not only exceptional physical properties but also has remarkable mechanical properties, such as piezoresistivity, which makes it a perfect candidate for strain sensing applications. In the present review, we provide an in-depth overview of the latest studies focusing on graphene and its strain sensing mechanism along with various applications. We start by providing a description of the fundamental properties, synthesis techniques and characterization methods of graphene, and then build forward to the discussion of numerous types of graphene-based strain sensors with side-by-side tabular comparison in terms of figures-of-merit, including strain range and sensitivity, otherwise referred to as the gauge factor. We demonstrate the material synthesis, device fabrication and integration challenges for researchers to achieve both wide strain range and high sensitivity in graphene-based strain sensors. Last of all, several applications of graphene-based strain sensors for different purposes are described. All in all, the evolutionary process of graphene-based strain sensors in recent years, as well as the upcoming challenges and future directions for emerging studies are highlighted.

Accurate and fast breath monitoring is of great importance for various healthcare applications, for example, medical diagnoses, studying sleep apnea, and early detection of physiological disorders. Devices meant for such applications tend to be uncomfortable for the subject (patient) and pricey. Therefore, there is a need for a cost-effective, lightweight, small-dimensional, and non-invasive device whose presence does not interfere with the observed signals. This paper reports on the fabrication of a highly sensitive human respiratory sensor based on silicon nanowires (SiNWs) fabricated by a top-down method of metal-assisted chemical-etching (MACE). Besides other important factors, reducing the final cost of the sensor is of paramount importance. One of the factors that increases the final price of the sensors is using gold (Au) electrodes. Herein, we investigate the sensor’s response using aluminum (Al) electrodes as a cost-effective alternative, considering the fact that the electrode’s work function is crucial in electronic device design, impacting device electronic properties and electron transport efficiency at the electrode–semiconductor interface. Therefore a comparison is made between SiNWs breath sensors made from both p-type and n-type silicon to investigate the effect of the dopant and electrode type on the SiNWs respiratory sensing functionality. A distinct directional variation was observed in the sample’s response with Au and Al electrodes. Finally, performing a qualitative study revealed that the electrical resistance across the SiNWs renders greater sensitivity to breath than to dry air pressure. No definitive research demonstrating the mechanism behind these effects exists, thus prompting our study to investigate the underlying process.

A force plate is mainly used in biomechanics; it aims to measure the ground reaction force in a person’s walking or standing position. In this study, a large-area force mat of the piezoresistance sensing type was developed, and a deep-learning-based weight measurement calibration method was applied to solve the problem in which measurements are not normalized because of physical limitations in hardware and signal processing. The test set was composed of the values measured at each point by weight and the value of the center of the pressure variable, and the measured value was predicted using a deep neural network (DNN) regression model. The calibration verification results show that the average weight errors range from a minimum of 0.06% to a maximum of 3.334%. This is simpler than the previous method, which directly measures the ratio of the resistance value to the measured weight of each sensor and derives an equation.

In this study, polydimethylsiloxane (PDMS) and conductive carbon nanoparticles were combined to fabricate a conductive elastomer PDMS (CPDMS). A high sensitive and flexible CPDMS strain sensor is fabricated by using stamping-process based micro patterning. Compared with conventional sensors, flexible strain sensors are more suitable for medical applications but are usually fabricated by photolithography, which suffers from a large number of steps and difficult mass production. Hence, we fabricated flexible strain sensors using a stamping-process with fewer processes than photolithography. The piezoresistive coefficient and sensitivity of the flexible strain sensor were improved by sensor pattern design and thickness change. Micro-patterning is used to fabricate various CPDMS microstructure patterns. The effect of gauge pattern was evaluated with ANSYS simulations. The piezoresistance of the strain gauges was measured and the gauge factor determined. Experimental results show that the piezoresistive coefficient of CPDMS is approximately linear. Gauge factor measurement results show that the gauge factor of a 140.0 μm thick strain gauge with five grids is the highest.

his paper presents a complete study of the impactof mechanical stress on the performance of SOI MOSFETs.This investigation includes dc, analog and RF characteristics.Parameters of a small-signal equivalent circuit are also ex-tracted as a function of applied mechanical stress. Piezore-sistance coefficient is shown to be a key element in describingthe enhancement in the characteristics of the device due tomechanical stress.

The piezoresistance of carbon nanotube (CNT)-coated microfibers is examined using diametric compression. Diverse CNT forest morphologies were studied by changing the CNT length, diameter, and areal density via synthesis time and fiber surface treatment prior to CNT synthesis. Large-diameter (30–60 nm) and relatively low-density CNTs were synthesized on as-received glass fibers. Small-diameter (5–30 nm) and-high density CNTs were synthesized on glass fibers coated with 10 nm of alumina. The CNT length was controlled by adjusting synthesis time. Electromechanical compression was performed by measuring the electrical resistance in the axial direction during diametric compression. Gauge factors exceeding three were measured for small-diameter (<25 μm) coated fibers, corresponding to as much as 35% resistance change per micrometer of compression. The gauge factor for high-density, small-diameter CNT forests was generally greater than those for low-density, large-diameter forests. A finite element simulation shows that the piezoresistive response originates from both the contact resistance and intrinsic resistance of the forest itself. The change in contact and intrinsic resistance are balanced for relatively short CNT forests, while the response is dominated by CNT electrode contact resistance for taller CNT forests. These results are expected to guide the design of piezoresistive flow and tactile sensors.