Abstract: Introduction With the rapid development of the chemical industry, the emission of the harmful NH 3 has increased significantly, thus the research of high performance NH 3 sensors has attracted extensive attention of the researchers [1]. Over the past decades, the emergence of novel materials has brought opportunities for the development of gas sensors. As a representative of another new family of materials, the 2D transition metal carbides, carbonitrides and nitrides (MXenes) have attracted great attention of the researchers in the field of gas sensors due to their unique chemical and physical properties being recently realized [2] . Taking the well-studied Ti 3 C 2 T x MXene as an example, it has been proved theoretically and experimentally that the Ti 3 C 2 T x has gas sensing properties at room temperature, especially for NH 3 [3]. However, its NH 3 sensing properties still need to be enhanced. In this work, the gas sensor based on TiO 2 /Ti 3 C 2 T x composite film is fabricated by a simple spraying method and its NH 3 sensing properties are investigated at room temperature. Method The 2D Ti 3 C 2 T x nanosheets were prepared through etching Al from Ti 3 AlC 2 in diluted HF and Tetramethylammonium hydroxide (TMAOH) solutions [4]. TiO 2 nanoparticles in water dispersion were purchased from Sigma-Aldrich. The gas sensors were fabricated by a simple spray method. In brief, 0.4 mL diluted TiO 2 nanoparticles solution (5 mg/mL) was sprayed on the polyimide (PI) substrate with seven pairs of Au interdigitated electrodes (electrodes width and distance: 0.2 mm) and dried at 60°C for 10 min for forming the TiO 2 film. Then, 1 mL diluted Ti 3 C 2 T x nanosheets solution (2 mg/mL) was sprayed on the surface of the TiO 2 film for fabricating TiO 2 -supported Ti 3 C 2 T x film gas sensor. For comparison, the gas sensors based on pure TiO 2 nanoparticles (0.4 mL) and Ti 3 C 2 T x nanosheets (1 mL) were prepared by the same approach. The gas sensing properties of the sensors were tested at different NH 3 concentration with 60.8% RH. Results and Conclusions Figure 1a shows the XRD patterns of the three samples, which the diffraction peaks match with the previous reports [5], indicating high purity of the Ti 3 C 2 T x and anatase TiO 2 . From the TEM image of the Ti 3 C 2 T x in Fig. 1b, Ti 3 C 2 T x is of few-layer nanosheet structure, proving that Ti 3 C 2 T x nanosheets is successfully prepared. Figure 1c shows the normalized response-recovery curves of three sensors to 10 ppm NH 3 . As can be seen, there is no NH 3 response for the pure TiO 2 sensor, and the responses of the Ti 3 C 2 T x and TiO 2 /Ti 3 C 2 T x sensors are about 1.9% and 3.1%, respectively. Compare with Ti 3 C 2 T x sensor, the baseline resistance of TiO 2 /Ti 3 C 2 T x sensor is more stable, and the enhanced response of TiO 2 /Ti 3 C 2 T x sensor is 1.63 times than that of pure Ti 3 C 2 T x sensor. Fig. 1d shows the good dynamic response-recovery curve of the TiO 2 / Ti 3 C 2 T x sensor to different concentrations NH 3 and the sensor can even respond to NH 3 as low as 0.5 ppm. In summary, we rationally designed the gas sensor based on based on TiO 2 /Ti 3 C 2 T x bilayer film for enhancing the NH 3 sensing properties of pure 2D Ti 3 C 2 T x nanosheets and the results show that the response value and response/recovery speeds of TiO 2 /Ti 3 C 2 T x sensor are evidently improved. Meanwhile, the enhanced NH 3 sensing response of the TiO 2 /Ti 3 C 2 T x sensor is explained by the model of self-built electric field (space charge layer) regulation. This work demonstrates that Ti 3 C 2 T x nanosheets supported by TiO 2 nanoparticles can be used to enhance the NH 3 sensing response, which is expected to provide useful reference for the development of high performance Ti 3 C 2 T x -based NH 3 sensors. References [1] S. Li, A. Liu, Z. Yang, L. Zhao, J. Wang, F. Liu, R. You, J. He, C. Wang, X. Yan, P. Sun, X. Liang, G. Lu, Design and preparation of the WO 3 hollow spheres@ PANI conducting films for room temperature flexible NH 3 sensing device, Sens. Actuators B Chem. 289 (2019) 252–259. doi:10.1016/j.snb.2019.03.073. [2] Z. Meng, R.M. Stolz, L. Mendecki, K.A. Mirica, Electrically-transduced chemical sensors based on two-dimensional nanomaterials, Chem. Rev. 119 (2019) 478–598. doi:10.1021/acs.chemrev.8b00311. [3] S.J. Kim, H.J. Koh, C.E. Ren, O. Kwon, K. Maleski, S.Y. Cho, B. Anasori, C.K. Kim, Y.K. Choi, J. Kim, Y. Gogotsi, H.T. Jung, Metallic Ti 3 C 2 T x MXene gas sensors with ultrahigh signal-to-noise ratio, ACS Nano, 12 (2018) 986–993. doi:10.1021/acsnano.7b07460. [4] W. Lian, Y. Mai, C. Liu, L. Zhang, S. Li, X. Jie, Two-dimensional Ti 3 C 2 coating as an emerging protective solid-lubricant for tribology, Ceram. Int. 44 (2018) 20154–20162. doi: 10.1016/j.ceramint.2018.07.309. [5] C. Peng, X. Yang, Y. Li, H. Yu, H. Wang, F. Peng, Hybrids of two-dimensional Ti 3 C 2 and TiO 2 exposing {001} facets toward enhanced photocatalytic activity, ACS Appl. Mater. Interfaces 8 (2016) 6051–6060. doi: 10.1021/acsami.5b11973. Figure 1

Abstract: For a long time, the daily paper and carbon ink have been used for writing and painting. With the development of the electronic technology, they are expected to play new roles in electronic devices. Herein, combining the unique characteristics of the paper (rough surface, hydrophilicity) and carbon ink (conductivity), this work rationally proposed two low-cost, eco-friendly, flexible, multifunctional pressure and humidity sensors. The results show that as-fabricated paper-based (PB) pressure sensor has a good sensitivity of 0.614 kPa −1 in the pressure range of 0–6 kPa. The PB humidity sensor has a large response of ∼2120 (current ratio at 91.5% relative humidity (RH) and 0% RH). The PB pressure sensor is proven to be useful for multiple pressure related contact detections, and the PB humidity sensor can be used for many humidity related non-contact detections. Interestingly, combining the different detecting modes of pressure and humidity sensors, some same detecting functions (e.g. switch, respiratory frequency and speech recognition) are realized from contact to non-contact using PB pressure and humidity sensors, which greatly enhance the wearable comfort. Compared with previous reports, this work demonstrates a much simpler approach without expensive raw materials, toxic reagents and high temperature treatment to achieve outstanding sensing performances of the multifunctional pressure and humidity sensors.

Abstract: The epidermis and dermis of human skin have randomly distributed microstructures, so we can sense external stimuli with high sensitivity and a low detection limit. Herein, a biomimetic microstructure sensor was fabricated using sandpaper as a template. The finite element simulation results show that the strain sensing property of the sensor can be improved by introducing a biomimetic microstructure, which is consistent with the experimental results. The gauge factor of the microstructure sensor (20.64) is 4.81 times that of the planar structure sensor (4.29) in the linear strain range from 0.1% to 1.0%. The microstructure sensor has a very low detection limit (0.1% strain), fast response (53.6 ms), and good cycling durability (3000 cycles). In addition, the microstructure sensor can achieve real-time monitoring of human motion and physiological signals, such as finger bending, knee bending, and breathing frequency. The proposed microstructure sensor is expected to have broad application prospects in motion monitoring and health-care fields.

Abstract: Strain measurement is an important means to study structural strength. Strain gauge measurement method is widely used in different industry area. The strain gauge should be stuck on the surface of the measured object to detect displacement or strain. As the measurement mode is contact measurement, strain gauge can have a certain impact on the measured object itself. So research of strain detection is increasingly moving from contact method to non-contact method. In this paper, we design a digital image correlation non-contact method used for strain detection. The basic principle of image correlation method is introduced. And the image process algorithm is detailed described. A set of laser lighting hardware is especially used for object illumination to get a random distribution light spot instead of sticking target bar on object. The measurement results show that this method can detect strain with good effect and can be applied to non-contact strain detection test.