Search

Exploration of flexible tactile sensors with high sensitivity that can imitate the perception functions (tactile sensing and pain sensing) of human skin is the main force in the realization of electronic skin. The research of electronic skin with the function of pain perception is of great significance in the field of biomimetic robot and treatment of patients losing the pain sensation ability of their skin. Herein, to broaden the application field of traditional electronic skin, we demonstrate a biomimetic and highly sensitive tactile sensor for realization of sensory functionalities of human skin. The structure of our sensor mimics the surface of the tentacles of tentacled snakes, which are strikingly sensitive mechanoreceptors. We design a tentacle-inspired flexible sensor by sandwiching the convex dielectric layer of PDMS/MXene microarrays between two flexible electrodes. It is found that the bioinspired sensor exhibits a high sensitivity of 3.61 kPa−1, a fast response time of 29 ms and a satisfactory stability, ensuring the ability in monitoring physiological signals. Finally, we present the application of the sensor for finger bending, international Morse code detection, and artery pulse detection. By presetting the pain thresholds of different areas of skin in a program, the sensor can identify and distinguish pressure data that exceed the pain threshold, realizing the detection of pain. In addition, it can be further applied on robot skins to assess the risk level of the working environment by monitoring its pressure data.

Acetone commonly exists in daily life and is harmful to human health, therefore the convenient and sensitive monitoring of acetone is highly desired. In addition, flexible sensors have the advantages of light-weight, conformal attachable to irregular shapes, etc. In this study, we fabricated high performance flexible silicon nanowires (SiNWs) sensor for acetone detection by transferring the monocrystalline Si film and metal-assisted chemical etching method on polyethylene terephthalate (PET). The SiNWs sensor enabled detection of gaseous acetone with a concentration as low as 0.1 parts per million (ppm) at flat and bending states. The flexible SiNWs sensor was compatible with the CMOS process and exhibited good sensitivity, selectivity and repeatability for acetone detection at room temperature. The flexible sensor showed performance improvement under mechanical bending condition and the underlying mechanism was discussed. The results demonstrated the good potential of the flexible SiNWs sensor for the applications of wearable devices in environmental safety, food quality, and healthcare.

Layered double hydroxides (LDHs) have recently been revealed to be promising in gas sensor applications due to their compositional flexibility and unique 2D-interlayer channel for gas diffusion and adsorption. This work demonstrates highly porous hierarchical LDHs containing Mg2+ and Al3+ (MgAl-LDHs) for ethanol sensing at room temperature. These MgAl-LDHs, with unique flower-like hierarchical structure and mesoporous interlayer, were synthesized hydrothermally using sodium dodecyl sulfate as soft template as well as intercalating agent. Further modification by discrete Ag nanoparticles (NPs) was achieved via an environmentally friendly glucose-reduction method to improve the gas-sensing response of the LDH-based sensor. It is found that the hierarchical MgAl-LDHs show potential in sensing ethanol gas with rapid dynamic characteristics at room temperature; their response magnitude towards ethanol can be enhanced significantly by Ag NP modification. The gas-response value of the Ag-modified MgAl-LDH sensor is about twice that of pristine MgAl-LDH sensors, towards 5-200 ppm ethanol at room temperature. Meanwhile, rapid response-recovery characteristics are achieved, with response and recovery times shorter than 10 and 50 s, respectively. The satisfactory sensing performance and remarkable response enhancement by Ag NP modification are demonstrated in terms of the unique microstructure of the hierarchical MgAl-LDHs and a constructed conductive effect model of Ag functionalized LDHs.

The limited surface area and compacted configuration of silicon nanowires (SiNWs), which are made by one-step metal-assisted chemical etching (MACE) go against target gas diffusion and adsorbtion for gas sensing application. To harvest suitable gas sensitivity and fast response–recovery characteristics, an aligned, rough SiNW array with loose configuration and high surface area was fabricated by a two-step etching process. The MACE technique was first employed to fabricate a smooth SiNW array, and then a KOH post-etching method was developed to roughen the NW surface further. The influence of the KOH post-etching time on the array density and surface roughness of the SiNWs was investigated, and the H2-sensing properties of the sensor based on the as-fabricated rough SiNW array were evaluated systematically at room temperature. It was revealed that the post-etching of KOH roughens the NW surface effectively, and also decreases the wire diameter and array density considerably. The resulting configuration of the SiNW array with high active surface and loose geometry is favorable for gas sensing. Consequently, the rough SiNW array-based sensor exhibited a linear response to H2 with a wide range of concentrations (50–10 000 ppm) at room temperature. Good stability and selectivity, satisfying response–recovery characteristics were also achieved. However, over-etching of SiNWs by KOH solution results in a considerable decrease in surface roughness and then in the H2-sensing response of the NWs.

In this paper, porous silicon/V2O5 nanorod composites are prepared by a heating process of as-sputtered V film on porous silicon (PS) at 600 °C for different times (15, 30, and 45 min) in air. The morphologies and crystal structures of the samples are investigated by field emission scanning electron microscope (FESEM), x-ray diffractometer (XRD), x-ray photoelectron spectroscopy (XPS), and Raman spectrum (RS). An improved understanding of the growth process of V2O5 nanorods on PS is presented. The gas sensing properties of samples are measured for NO2 gas of 0.25 ppm~3 ppm at 25 °C. We investigate the effects of the annealing time on the NO2-sensing performances of the samples. The sample obtained at 600 °C for 30 min exhibits a very strong response and fast response-recovery rate to ppm level NO2, indicating a p-type semiconducting behavior. The XPS analysis reveals that the heating process for 30 min produces the biggest number of oxygen vacancies in the nanorods, which is highly beneficial to gas sensing. The significant NO2 sensing performance of the sample obtained at 600 °C for 30 min probably is due to the strong amplification effect of the heterojunction between PS and V2O5 and a large number of oxygen vacancies in the nanorods.

Here we present research on an ultra-luminous X-ray source (ULX) candidate 2XMM J140229.91+542118.8. The X-ray light curves of this ULX candidate in M101 exhibit features of a flare star. More importantly, the Chandra light curve displays unusual X-ray double flares, which is comprised of two close peaks. The X-ray (0.3–11.0 keV) flux of the first peak was derived from the two-temperature APEC model as ~ 1.1 ± 0.1 × 10 −12 erg cm −2 s −1 . The observed flux at its first peak increased by about two orders of magnitude in X-ray as compared to quiescence. The slope of the second fast decay phase is steeper than the slope of the first fast decay phase, indicating that the appearance of a second flare accelerated the cooling of the first flare in a way we do not understand yet. We also observed its optical counterpart using a 2.16 m telescope administered by National Astronomical Observatories, Chinese Academy of Sciences. By optical spectral fitting, it is confirmed to be a late type dMe2.5 star. According to the spectral type and apparent magnitude of its optical counterpart, we estimate the photometric distance to be ~133.4 ± 14.2 pc. According to the X-ray spectral fitting, a possible explanation is provided. However, more similar close double flares are needed to confirm whether this accelerated cooling event is a unique coincidence or a common physical process during double flaring.

The effects of reoxidation annealing on the electrical properties and the positive temperature coefficient of resistance (PTCR) effects of multilayer Ba1.005(Ti1−x Nb x )O3 (BTN) ceramics sintered at different temperatures from 1100 to 1160 °C for 2 h in a reducing atmosphere and reoxidized at various temperatures in the range 500–900 °C were investigated. The results indicated that the room-temperature (RT) resistance of the BTN ceramics reoxidized at different temperatures first increased slowly and then quickly with the increase in the reoxidation temperature. Meanwhile, the resistance jump of the samples increased first and then decreased with the increase in the reoxidation temperature. In addition, the PTCR effect could be improved by prolonging the reoxidation time. Finally, the samples reoxidized at a low temperature of 600 °C after sintering at 1160 °C in a reducing atmosphere exhibited a significant PTCR effect, with a resistance jump of 3.5 orders of magnitude, along with a low RT resistance of 0.38 Ω. Additionally, the influences of the reoxidation temperature and time on the grain resistance and grain-boundary resistance were investigated using complex-impedance spectroscopy.

Density functional theory (DFT) calculations are conducted to explore the interaction of H2 with pure and Ti-doped WO3 (002) surfaces. Four top adsorption models of H2 on pure and Ti-doped WO3 (002) surfaces are investigated respectively, they are adsorption on bridging oxygen O1c, absorption on plane oxygen O2c, absorption on 5-fold W5c (Ti), and absorption on 6-fold W6c. The most stable and H2 possible adsorption structure in the pure surface is H-end oriented to the surface plane oxygen O2c site, while the favourable adsorption sites for H2 in a Ti-doped surface is not only an O2c site but also a W6c site. The adsorption energy, the Fermi energy level EF, and the electronic population are investigated and the H2-sensing mechanism of a pure-doped WO3 (002) surface is revealed theoretically: the theoretical results are in good accordance with our existing experimental results. By comparing the above three terms, it is found that Ti doping can obviously enhance the adsorption of H2. It can be predicted that the method of Ti-doped into a WO3 thin film is an effective way to improve WO3 sensor sensitivity to H2 gas.