Wearable gas sensors have received lots of attention for diagnostic and monitoring applications, and two-dimensional (2D) materials can provide a promising platform for fabricating gas sensors that can operate at room temperature. In the present study, the room temperature gas-sensing performance of TiCT nanosheets was investigated. 2D TiCT (MXene) sheets were synthesized by removal of Al atoms from TiAlC (MAX phases) and were integrated on flexible polyimide platforms with a simple solution casting method. The TiCT sensors successfully measured ethanol, methanol, acetone, and ammonia gas at room temperature and showed a p-type sensing behavior. The fabricated sensors showed their highest and lowest response toward ammonia and acetone gas, respectively. The limit of detection of acetone gas was theoretically calculated to be about 9.27 ppm, presenting better performance compared to other 2D material-based sensors. The sensing mechanism was proposed in terms of the interactions between the majority charge carriers of TiCT and gas species.

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The fracture strength of ultrananocrystalline diamond (UNCD) has been investigated using tensile testing of freestanding submicron films. Specifically, the fracture strength of UNCD membranes, grown by microwave plasma chemical vapor deposition (MPCVD), was measured using the membrane deflection experiment developed by Espinosa and co-workers. The data show that fracture strength follows a Weibull distribution. Furthermore, we show that the Weibull parameters are highly dependent on the seeding process used in the growth of the films. When seeding was performed with microsized diamond particles, using mechanical polishing, the stress resulting in a probability of failure of 63% was found to be 1.74 GPa, and the Weibull modulus was 5.74. By contrast, when seeding was performed with nanosized diamond particles, using ultrasonic agitation, the stress resulting in a probability of failure of 63%, increased to 4.13 GPa, and the Weibull modulus was 10.76. The tests also provided the elastic modulus of UNCD, which was found to vary from 940 to 970 GPa for both micro- and nanoseeding. The investigation highlights the role of microfabrication defects on material properties and reliability, as a function of seeding technique, when identical MPCVD chemistry is employed. The parameters identified in this study are expected to aid the designer of microelectromechanical systems devices employing UNCD films.

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A sonochemical technique was developed to infuse Cloisite clay nanoparticles into phenolic foam materials. Phenolic resin solution (Part A) was mixed with clay particles, and irradiated using a high intensity ultrasonic liquid processor. In the next step, the modified phenolic resin solution containing clay particles was mixed with Part B (containing phenol sulfonic acid, catalyst) through a highspeed mechanical stirrer. The reaction mixture was then cast into rectangular molds to make nanophased foam panels. Test coupons were cut precisely from the panels to carry out thermal, morphological, and mechanical characterizations. The as-prepared foam samples were characterized by scanning electron microscopy (SEM), X-ray diffraction, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The SEM studies have shown that the particles are well dispersed over the entire volume of the matrix with minimal agglomeration. The foam cells structures are wellordered and uniform in size and shape. The TGA and DSC analyses show that the nanophased foams are thermally more stable than the corresponding neat system. Quasistatic compression tests have been carried out for both nanophased and neat foams systems. The test results show that there is a significant increase (approximately in the range of 150-180%) in the compressive strength and modulus of the nanophased foams over the neat system. This improvement in compressive properties has been noted repeatedly for multiple batches and with a minimum of three specimens tested from each batch. Details of the synthesis, thermal and mechanical characterization are presented in this paper.

A study of coupled flexural-longitudinal wave motion in a periodic dual-beam structure with transverse connection

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