A Novel Hollow Graphene/Polydimethylsiloxane Composite for Pressure Sensors with High Sensitivity and Superhydrophobicity.

Flexible pressure sensors have attracted great interest as they play an important role in various fields such as health monitoring and human-machine interactions. The design of the pressure sensors still faces challenges in achieving a high sensitivity for a wide sensing range, and the interference of water restricts the applications of the sensors. Herein, we developed a graphene-polydimethylsiloxane film combining a hierarchical surface with nanowrinkles on it and a hollow structure. The microstructure design of the composite can be facilely controlled to improve the sensing and hydrophobic performance by tailoring the microsphere building units. Attributed to the irregular surface and hollow structure of the sensing layer, the optimized sensor exhibits a superior sensitivity of 1085 kPa-1 in a 50 kPa linear range. For practical applications, the nanowrinkles on the surface of the microspheres and the polymer coating endow the composite with waterproof properties. Inspired by the dual receptors of the skin, two designed microstructured films can simply integrate into one with double-sided microstructures. The sensing performance and the water-repellence property allow the sensor to detect physiological signals under both ambient and underwater conditions. Furthermore, underwater stimuli detection and communication are demonstrated. This method of fabricating a flexible sensor shows great potential in wearable and robotic fields.

SnS2 Quantum Dot-Based Optoelectronic Flexible Sensors for Ultrasensitive Detection of NO2 Down to 1 ppb.

Transition-metal dichalcogenides (TMDs) have gained intense interest for their outstanding optoelectronic and electrochemical characteristics, utilized in versatile applications such as gas sensors and photodetectors. However, TMD-based chemiresistors suffer from poor sensitivity at ppb-level detection, and the experimental detection limit fails to reach 1 ppb. Herein, SnS2 QD/graphene nanoheterostructures as functional flexible sensors are fabricated for NO2 gas and light detection at room temperature. The semiconductor type of the nanohybrids can be shifted between p-type and n-type by adjusting the proportion of the components, both of which exhibit excellent gas-sensing properties. The ppb-level NO2 detection is realized even under room temperature with superior sensitivity (860% to 125 ppb), fast response (114 s), and recovery (166 s). It also demonstrates ultrahigh sensitivity and broadband photodetection in the visible region. The photoresponsivity can reach upto 2.08 × 103 A/W under blue light illumination and under room temperature. Especially, the influence of light illumination of different wavelengths and intensities on gas-sensing performance is studied. Red light (1 mW/cm2) greatly enhances the sensitivity up to 5.1 folds, and the device performs obvious response to NO2 at concentrations as low as 1 ppb. Ab initio density functional theory calculation and band theories are applied to explain the interaction of the components and the effect of the light excitation inducing charge carriers on gas-sensing equilibrium.

High Sensitivity, Humidity-Independent, Flexible NO2 and NH3 Gas Sensors Based on SnS2 Hybrid Functional Graphene Ink.

Here, a high sensitivity gas sensing ink based on sulfonated rGO (S-rGO) decorated with SnS2 is synthesized for room temperature NO2 and NH3 detection. This sensing ink demonstrated an excellent sensitivity to ppb-level NO2 (17% response to 125 ppb) and sub-ppm-level NH3 (11% response to 1 ppm). The unique absorption properties of SnS2 improve the sensitivity of S-rGO 4.2 and 55 times to NO2 and NH3, respectively. Besides, the superhydrophobicity of the SnS2 endows the sensor with exceptional immunity to high relative humidity (RH). Furthermore, the sensors exhibit negligible degradation to NO2 and less than 15% degradation to NH3 in a wide range of RH from 30 (ambient humidity) to 90%. More importantly, the obtained full-written ink can be applied to common substrates, such as glass, clothes, and paper, and maintain excellent performance after being bent and twisted by 180°.

Study on Damage Evaluation and Machinability of UD-CFRP for the Orthogonal Cutting Operation Using Scanning Acoustic Microscopy and the Finite Element Method.

Owing to high specific strength and designability, unidirectional carbon fiber reinforced polymer (UD-CFRP) has been utilized in numerous fields to replace conventional metal materials. Post machining processes are always required for UD-CFRP to achieve dimensional tolerance and assembly specifications. Due to inhomogeneity and anisotropy, UD-CFRP differs greatly from metal materials in machining and failure mechanism. To improve the efficiency and avoid machining-induced damage, this paper undertook to study the correlations between cutting parameters, fiber orientation angle, cutting forces, and cutting-induced damage for UD-CFRP laminate. Scanning acoustic microscopy (SAM) was employed and one-/two-dimensional damage factors were then created to quantitatively characterize the damage of the laminate workpieces. According to the 3D Hashin's criteria a numerical model was further proposed in terms of the finite element method (FEM). A good agreement between simulation and experimental results was validated for the prediction and structural optimization of the UD-CFRP.

Calibrating conservative and dissipative response of electrically-driven quartz tuning forks.

Determining sensor parameters is a prerequisite for quantitative force measurement. Here we report a direct, high-precision calibration method for quartz tuning fork (TF) sensors that are popular in the field of nanomechanical measurement. In the method, conservative and dissipative forces with controlled amplitudes are applied to one prong of TF directly to mimic the tip-sample interaction, and the responses of the sensor are measured at the same time to extract sensor parameters. The method, for the first time, allows force gradient and damping coefficient which correspond to the conservative and dissipative interactions to be measured simultaneously. The calibration result shows surprisingly that, unlike cantilevers, the frequency shift for TFs depends on both the conservative and dissipative forces, which may be ascribed to the complex dynamics. The effectiveness of the method is testified by force spectrum measurement with a calibrated TF. The method is generic for all kinds of sensors used for non-contact atomic force microscopy (NC-AFM) and is an important improvement for quantitative nanomechanical measurement.

Biomimic Hairy Skin Tactile Sensor Based on Ferromagnetic Microwires.

We present a multifunctional tactile sensor inspired by human hairy skin structure, in which the sensitive hair sensor and the robust skin sensor are integrated into a single device via a pair of Co-based ferromagnetic microwire arrays in a very simple manner. The sensor possesses a self-tunable effective compliance with respect to the magnitude of the stimulus, allowing a wide range of loading force to be measured. The sensor also exhibits some amazing functions, such as air-flow detection, material property characterization, and excellent damage resistance. The novel sensing mechanism and structure provide a new strategy for designing multifunctional tactile sensors and show great potential applications on intelligent robot and sensing in harsh environments.

Oxidative etching of MoS2/WS2 nanosheets to their QDs by facile UV irradiation.

Oxidative etching has been proved to be an efficient top-down method to prepare quantum dots (QDs) of layered transition-metal dichalcogenides which possess unique properties and have potential applications in various areas. Here, one facile and green oxidative etching method induced by UV irradiation is reported to prepare the QDs of MoS2/WS2 in aqueous solution, respectively. A prominent morphology change occurred to the nanosheets of MoS2/WS2 after irradiation and finally they were etched to ultrasmall nanoparticles which were proved to be the QDs. Insight into the etching mechanism was discussed in detail and hydroxyl free radicals (˙OH) were conclusively demonstrated to play the main role in etching nanosheets. From another point of view, this work also proves the crucial long-term photo instability of MoS2/WS2 since there are increasing photo-related applications of them and points out an easy way to degrade their nanosheets.

Note: Wide band amplifier for quartz tuning fork sensors with digitally controlled stray capacitance compensation.

We presented a preamplifier design for quartz tuning fork (QTF) sensors in which the stray capacitance is digitally compensated. In this design, the manually controlled variable capacitor is replaced by a pair of varicap diodes, whose capacitance could be accurately tuned by a bias voltage. A tuning circuit including a single side low power operational amplifier, a digital-to-analog converter, and a microprocessor is also described, and the tuning process can be conveniently carried out on a personal computer. For the design, the noise level was investigated experimentally.