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With the in-depth application of quartz crystal microbalance (QCM) sensors in the fields of science and engineering, there is an urgent need for QCM sensors with high mass sensitivity. The mass sensitivity of a QCM is closely related to its resonance frequency, and the high resonance frequency leads to improve its mass sensitivity. However, the resonance frequency of a QCM resonator cannot be increased all the time due to the fragility of quartz wafer and the limits of energy trapping effect. Few studies are associated with mass sensitivity of a QCM resonator under overtone modes. Herein, we propose to make a QCM resonator work in its

Flexible micro-pressure sensors for wearable health monitoring.

Humidity detection has significant and extensive applications in various fields. Herein, a miniaturized integrated relative humidity (RH) sensing system from surface acoustic wave (SAW) sensor to circuits and software is described. Delay-line SAW devices were designed and fabricated to be used as sensor and reference device. Graphene oxide (GO) was deposited on the surface of SAW sensor between interdigitated transducers (IDTs) as ultra-thin and wrinkled sensitive film by the method of drop-cast. The well-matched circuits and software with excellent stability and accuracy were developed to form a miniaturized integrated relative humidity sensing system with SAW sensor. A linear variation of the frequency shift is obtained in an extremely wide detection range from 0 to 97.3 %RH. Besides, the system exhibits a high sensitivity of 3.33 kHz/%RH, rapid response time of 80 s and recovery time of 72 s, good dynamic response and excellent repeatability. These results demonstrate that the SAW sensing system not only realizes humidity detection at system level, but also has excellent performance, which shows great feasibility and tremendous potential for relative humidity measurement applications.

The sensitive detection of low-dose X-ray radiation is essential to many X-ray applications. In this article, the ultrasensitive X-ray detector based on pure Cs2AgBiBr6 all-inorganic lead-free perovskite film is successfully demonstrated and encapsulated using a metal casing with a Be window. The high-quality Cs2AgBiBr6 films are obtained through the low-cost solution process with long electron–hole diffusion length (~700 nm) and long carrier lifetime (~750 ns). Benefiting from the excellent properties of the Cs2AgBiBr6 film and the stable ambient provided by the packaging module, the resulting device exhibits attractive X-ray detection capabilities with a minimum detectable dose rate of 145.2 ${\mathrm {nGy}}_{air}\text{s}^{-1}$ and a detection sensitivity up to $1.8\times 10^{4}\,\,\mu {\mathrm {CGy}}_{air}{}^{-1}$ cm−2, which is about a thousand times higher than the sensitivity achieved with commercial a-Se X-ray detectors. Besides, the encapsulated device maintains superior detection performance after 2 months of storage, indicating the favorable reliability of the encapsulated device. This article demonstrates a possibility to use Cs2 AgBiBr6 perovskite film and Be window for the sensitive X-ray detection, which will inspire further development of radiation electronics by utilizing all-inorganic lead-free perovskite.

Organolead halide perovskites provide tremendous opportunities for ideal radiation detection due to their high atomic numbers, large carrier mobilities, and long lifetimes. Here, we synthesized high-quality single crystal CH3NH3PbBr3 with a high mobility-lifetime product of $\text {4.1} \times \text {10}^{\text {-2}}$ cm2/V by the developed inverse low temperature crystallization method. The sensitive X-ray detector was fabricated by depositing 50 nm of gold on both sides of the perovskite crystal. This device exhibited a high sensitivity up to $259.9~\mu \text{C}$ /Gy $_{\text {air}}$ /cm2 under the 39 keV X-ray exposure at a small electric field of ~0.83 V/mm and yielded a low noise of $\text {3.1} \times \text {10}^{-\text {23}}\,\,\text{A}^{\text {2}}$ /Hz. Additionally, the sensitivity can be further improved by increasing operating voltage. Our results provided a solution for constructing high-performance X-ray detectors.

As a new generation of Zn-ion storage systems, Zn-ion hybrid supercapacitors (ZHSCs) garner tremendous interests recently from researchers due to the perfect integration of batteries and supercapacitors. ZHSCs have excellent integration of high energy density and power density, which seamlessly bridges the gap between batteries and supercapacitors, becoming one of the most viable future options for large-scale equipment and portable electronic devices. However, the currently reported two configurations of ZHSCs and corresponding energy storage mechanisms still lack systematic analyses. Herein, this review will be prudently organized from the perspectives of design strategies, electrode configurations, energy storage mechanisms, recent advances in electrode materials, electrolyte behaviors and further applications (micro or flexible devices) of ZHSCs. The synthesis processes and electrochemical properties of well-designed Zn anodes, capacitor-type electrodes and novel Zn-ion battery-type cathodes are comprehensively discussed. Finally, a brief summary and outlook for the further development of ZHSCs are presented as well. This review will provide timely access for researchers to the recent works regarding ZHSCs.

Super long perovskite microwires (PMWs) are in a great demand in many fields such as low-loss microcables and integrated optical waveguide. Despite decades of research into PMWs, single crystal PMWs with several centimeters long have not been obtained. Here, ultralong (up to 7.6 centimeters) monoclinic crystal structure CH3NH3PbI3·DMF PMWs have been synthesized. The high-quality microwire exhibits long carrier lifetime of 1775.7 ns. The as-prepared free-standing PMWs can be integrated to any arbitrary substrate and 808 nm near-infrared photodetectors have been successfully demonstrated. The fabricated device shows a high light on/off ratio of 1.79×106 and an extremely low dark current of 2.5 fA at 1 V bias. This work provides a strategy for the solution growth of ultralong microwires.

MXenes have attracted great attention for their potential applications in electrochemical and electronic devices due to their excellent characteristics. Traditional sound sources based on the thermoacoustic effect demonstrated that a conductor needs to have an extremely low heat capacity and high thermal conductivity. Hence, a thin MXene film with a low heat capacity per unit area (HCPUA) and special layered structure is emerging as a promising candidate to build loudspeakers. However, the use of MXenes in a sound source device has not been explored. Herein, we have successfully prepared sound source devices on an anodic aluminum oxide (AAO) and a flexible polyimide (PI) substrates by using the prepared Ti3C2 MXene nanoflakes. Due to the larger interlayer distance of MXene, the MXene-based sound source device has a higher sound pressure level (SPL) than that of graphene of the same thickness. High-quality Ti3C2 MXene nanoflakes were fabricated by selectively etching the Ti3AlC2 powder. The as-fabricated MXene sound source device on an AAO substrate exhibits a higher SPL of 68.2 dB (f = 15 kHz) and has a very stable sound spectrum output with frequency varying from 100 Hz to 20 kHz. A theoretical model has been built to explain the mechanism of the sound source device on an AAO substrate, matching well with the experimental results. Furthermore, the MXene sound source device based on a flexible PI substrate has been attached to the arms, back of the hand, and fingers, indicating an excellent acoustic wearability. Then, the MXene film is packaged successfully into a commercial earphone case and shows an excellent performance at high frequencies, which is very suitable for human audio equipment.

In this paper, single crystals (SCs) of the Cs2AgBiBr6 double perovskite were grown using the method of crystallization from a supersaturated solution. It was shown that the natural crystal growth surface of the perovskite with perfect crystal quality is along the (111) plane by X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM) analyses. The fabricated high-sensitivity X-ray detector based on the Cs2AgBiBr6 SCs with vertical structure achieved detection sensitivity up to $316~\mu $ CGyair−1 cm−2 under bias voltage of 18 V. Furthermore, the frequency noise characteristics of the device under different posttreatment processes were systematically analyzed, which indicated that the combination of thermal annealing and isopropanol rinsing can suppress field-driven ion migration and surface conduction channel, thereby increasing the resistivity of the perovskite material and reducing the noise current of the device. Our results revealed that the Cs2AgBiBr6 SCs-based X-ray detector with high sensitivity and low cost has a great potential for application in manufacturing lead-free and stable radiation detection electronics in the future.

An ultraviolet (UV) photodetector based on hydrothermally processed ZnO nanorods (ZnO NRs) decorated by gold nanoparticles (Au NPs) was demonstrated to exhibit extraordinary optoelectronic properties. Due the implementation of Au NPs, the UV responsivity and specific detectivity reached 70 A/W and 3.41 $\times$ 1012 cm Hz1/2 W−1, respectively, which were enhanced by approximately four times at an excitation wavelength of 365 nm compared with those of pristine ZnO NRs. Moreover, such photodetector shows good flexibility as well due to the mica substrate, which maintains almost constant performances under different bending radii of curvature and repeatable bending test more than 200 cycles. The photodetector also exhibits good transparency, giving it the potential of integration with other light photodetectors. In addition, a schematic band-diagram and the accompanying finite-difference time-domain analysis were performed to reveal the electron transfer and electric field distribution of ZnO NRs decorated with Au NPs. Our results revealed that the noble metal modified plasmon-enhanced ZnO NRs photodetector with high responsivity, low cost has a great potential for application in manufacturing flexible and transparent integrated optoelectronics.

Graphene-based photodetectors have received widespread attention because of the superior characteristics. However, most of previous research focused on improving the performance of the detector. Herein, an angle-sensitive photodetector, which fabricated via vertically standing layered graphene (VSG) grown on $\mathrm{n}$ -type silicon substrate, is demonstrated. Due to the vertical structure of the VSG, the current change rate can reach up to 188.6% when the incident angle is 55 degree, which demonstrates promising applications for omnidirectional detection.

Recently, soft electrothermal actuators have attracted tremendous attentions. Large deformation under low driving voltage has long been the design concerns for scholars. However, in practice, apart from larger deformation, higher requirements are put forward for higher deformation speed in repeated cycles to achieve efficient and agile actuation. Herein, a soft electrothermal actuator is fabricated based on laser reduced graphene oxide and silver nanowire composite with polydimethylsiloxane substrate, which completely realizes the above required advantages. Besides, a concept of periodic curvature rate is proposed to accurately evaluate the deformation speed, which is more normalized than time alone to reflect before. The soft electrothermal actuator here can achieve a large curvature of 2.5 cm-1 with a high periodic curvature rate of up to 8.93×10-2 cm-1/s under low power density input of 0.8W•cm-2 (driving voltage of 28V), which shows obvious advantages in both deformation quantity and speed compared with most reported electrothermal actuators till now. Finally, a bionic hand consisting of five U-shaped electrothermal actuators is demonstrated to achieve gesture following and restoring, showing its promising prospects in the emerging bionics field.

Single-crystal (SC) perovskite is currently a promising material due to its high quantum efficiency and long diffusion length. However, the reported perovskite photodetection range ( 10 μs) are still limited. Here, to promote the development of perovskite-integrated optoelectronic devices, this work demonstrates wider photodetection range and shorter response time perovskite photodetector by integrating the SC CH3NH3PbBr3 (MAPbBr3) perovskite on silicon (Si). The Si/MAPbBr3 heterojunction photodetector with an improved interface exhibits high-speed, broad-spectrum, and long-term stability performances. To the best of our knowledge, the measured detectable spectrum (405-1064 nm) largely expands the widest response range reported in previous perovskite-based photodetectors. In addition, the rise time is as fast as 520 ns, which is comparable to that of commercial germanium photodetectors. Moreover, the Si/MAPbBr3 device can maintain excellent photocurrent performance for up to 3 months. Furthermore, typical gray scale face imaging is realized by scanning the Si/MAPbBr3 single-pixel photodetector. This work using an ultrafast photodetector by directly integrating perovskite on Si can promote advances in next-generation integrated optoelectronic technology.

Here, we demonstrate a novel 2-D–3-D graphene (Gr)/MoS2/Si nanowires Schottky-NP bipolar van der Waals heterostructure, which allows the combination of the unique properties of 2-D layered materials with the proven merits of well-developed silicon technologies. Significantly, the resultant devices exhibit an ultrahigh response speed of 17 ns with a broad spectral response characteristic, which represents most fast response for 2-D transition metal dichalcogenide (TMD)-based photodetectors and is comparable to that of commercial Si photodetectors. A high responsivity of 0.6 A $\text{W}^{-{1}}$ and a detectivity of ${8}\times {10}^{{12}}$ Jones are also achieved. This result suggests a pathway for the fabrication of high-speed photodetectors based on TMDs.

Due to its excellent flexibility, graphene has an important application prospect in epidermal electronic sensors. However, there are drawbacks in current devices, such as sensitivity, range, lamination, and artistry. In this work, we have demonstrated a multilayer graphene epidermal electronic skin based on laser scribing graphene, whose patterns are programmable. A process has been developed to remove the unreduced graphene oxide. This method makes the epidermal electronic skin not only transferable to butterflies, human bodies, and any other objects inseparably and elegantly, merely with the assistance of water, but also have better sensitivity and stability. Therefore, pattern electronic skin could attach to every object like artwork. When packed in Ecoflex, electronic skin exhibits excellent performance, including ultrahigh sensitivity (gauge factor up to 673), large strain range (as high as 10%), and long-term stability. Therefore, many subtle physiological signals can be detected based on epidermal electronic skin with a single graphene line. Electronic skin with multiple graphene lines is employed to detect large-range human motion. To provide a deeper understanding of the resistance variation mechanism, a physical model is established to explain the relationship between the crack directions and electrical characteristics. These results show that graphene epidermal electronic skin has huge potential in health care and intelligent systems.

Organometal halide perovskite materials are outstanding candidates not only for solar cells but also for photo-detection. In this work, we develop a well-controlled lower temperature ( 0.1 cm2) without external power supply. Remarkably, the perovskite photovoltaic detectors demonstrate an excellent air-exposure stability for more than two months without particular encapsulation. These excellent performances are attributed to a well-controlled expansive gas–solid reaction and formation of perovskite crystallites that collide and pinch off the pinhole leakage paths at the grain boundaries. More importantly, the accumulated strain at the colliding grain boundaries leads to a selective evaporation of MAI during post-growth annealing, and thus passivate the local defects by the remnant PbI2 layer. These results highlight the potential of LFCVD perovskite materials in developing ultra-fast and self-driven photovoltaic detectors with outstanding stability and scalability.

MoS2, the classical representative of layered structure transition metal dichalcogenides (TMDCs), has been widely used as an ideal n-type semiconductor, offering an interesting opportunity to construct heterostructures with other 2D layered or 3D bulk materials for ultrafast optoelectronic applications. In this work, we report the synthesis of ultrathin MoS2 nanopetals via a solution-processable route, and the solution assembly of a 2D MoS2 nanopetal/GaAs n–n homotype heterojunction using graphene as the carrier collector. The fabricated devices have excellent photoresponse characteristics including a good detectivity of ∼2.28 × 1011 Jones, a noise current approaching 0.015 pA Hz−1/2 at zero bias and notably a very fast response speed, up to ∼1.87/3.53 μs with a broad photoresponse range. More interestingly, the device could respond to fast pulsed illumination up to 1 MHz, far exceeding the performance of many current congeneric 2D nanostructured and solution-processable photodetectors reported. These results suggest that our devices, together with the solution assembly methodology of the device described herein, can be utilized to give large-scale integration of low-cost, high-performance photodetectors, thus opening up new possibilities for 2D layered material-based photovoltaic and optoelectronic applications in the future.

Organic–inorganic hybrid perovskites have exhibited unprecedented advantages for x-ray photon detection due to their exotic properties. Their high-crystalline quality has a great impact for high-detection sensitivity under a low electric field, especially related to the synthesis method. In this work, we analyze the capability of CH3NH3PbI3 (MAPbI3) perovskites as an x-ray detection material and propose to control the temperature gradient (TG) during the synthesis of MAPbI3 single crystal perovskites for device fabrication. Our results show that the decreasing TG can effectively reduce the trap density and improve the crystal quality, which could lead to a boosted sensitivity of 1471.7 μC/Gyair/cm2 under a low electric field of 3.3 V/mm. In addition, a higher detection sensitivity can be achieved by increasing the electric field. Our work presents a strategy to construct high-performance direct x-ray detectors.

Advances in the photocurrent conversion of two-dimensional (2D) transition metal dichalcogenides have enabled the realization and application of ultrasensitive and broad-spectral photodetectors. The requirements of previous devices constantly drive for complex technological implementation, resulting in limits in scale and complexity. Furthermore, the development of large-area and low-cost photodetectors would be beneficial for applications. Therefore, we demonstrate a novel design of a heterojunction photodetector based on solution-processed ultrathin MoSe2 nanosheets to satisfy the requirements of its application. The photodetector exhibits a high sensitivity to visible–near infrared light, with a linear dynamic range over 124 decibels (dB), a detectivity of ~1.2 × 1012 Jones, and noise current approaching 0.1 pA·Hz–1/2 at zero bias. Significantly, the device shows an ultra-high response speed up to 30 ns with a 3-dB predicted bandwidth over 32 MHz, which is far better than that of most of the 2D nanostructured and solution-processable photodetectors reported thus far and is comparable to that of commercial Si photodetectors. Combining our results with material-preparation methods, together with the methodology of device fabrication presented herein, can provide a pathway for the large-area integration of low-cost, high-speed photodetectors.