Novel Gas Sensing Approach: ReS2/Ti3C2Tx Heterostructures for NH3 Detection in Humid Environments

Continuous monitoring of ammonia (NH3) in humid environments poses a notable challenge for gas sensing applications because of its effect on sensor sensitivity. The present work investigates the detection of NH3 in a natural humid environment utilizing ReS2/Ti3C2Tx heterostructures as a sensing platform. ReS2 nanosheets were vertically grown on the surface of Ti3C2Tx sheets through a hydrothermal synthetic approach, resulting in the formation of ReS2/Ti3C2Tx heterostructures. The structural, morphological, and optical properties of ReS2/Ti3C2Tx were investigated using various state-of-the-art techniques, including scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, zeta potential, Brunauer-Emmett-Teller technique, and Raman spectroscopy. The heterostructures exhibited 1.3- and 8-fold increases in specific surface area compared with ReS2 and Ti3C2Tx, respectively, potentially enhancing the active gas adsorption sites. The electrical investigations of the ReS2/Ti3C2Tx-based sensor demonstrated enhanced selectivity and superior sensing response ranging from 7.8 to 12.4% toward 10 ppm of NH3 within a relative humidity range of 15-85% at room temperature. These findings highlight the synergistic effect of ReS2 and Ti3C2Tx, offering valuable insights for NH3 sensing in environments with high humidity, and are explained in the gas sensing mechanism.

Recent progress and applications of cellulose and its derivatives-based humidity sensors: A review

Cellulose and its derivatives, which are low-cost, degradable, reproducible and highly hydrophilic, can serve as both substrate and humidity sensitive materials, making them more and more popular as ideal biomimetic materials for humidity sensors. Benefiting from these characteristics, cellulose-based humidity sensors cannot only exhibit high sensitivity, excellent mechanical performance, wide humidity response range, etc., but also can be applied to fields such as human health, medical care and agricultural product safety monitoring. Herein, cellulose-based humidity sensors are first classified according to the different conductive active materials, such as carbon nanotubes, graphene, electrolytes, metal compounds, and polymer materials, based on which the latest research progress is introduced, and the roles of different types of conductive materials in cellulose-based humidity sensors are analyzed and summarized. Besides, the similarities and differences in their working mechanisms are expounded. Finally, the application scenarios of cellulose-based humidity sensors in human movement respiration and skin surface humidity monitoring are discussed, which can make readers quickly familiarize the current preparation method, working mechanism and subsequent development trend of cellulose-based humidity sensors more effectively.

ReS2 on GaN Photodetector Using H+ Ion-Cut Technology

The wafer-scale single-crystal GaN film was transferred from a commercial bulk GaN wafer onto a Si (100) substrate by combining ion-cut and surface-activated bonding. Well-defined, uniformly thick, and large-scale wafer size ReS₂ multilayers were grown on the GaN substrate. Finally, ReS₂ photodetectors were fabricated on GaN and sapphire substrates, respectively, and their performances were compared. Due to the polarization effect of GaN, the ReS₂/GaN photodetector showed better performance. The ReS₂/GaN photodetector has a responsivity of 40.12 A/W, while ReS₂/sapphire has a responsivity of 0.17 A/W. In addition, the ReS₂/GaN photodetector properties have reached an excellent reasonable level, including a photoconductive gain of 447.30, noise-equivalent power of 1.80 × 10^-14 W/Hz^1/2, and detectivity of 1.21 × 10¹⁰ Jones. This study expands the way to enhance the performance of ReS₂ photodetectors.

Fully integrated wearable humidity sensor for respiration monitoring

Respiration monitoring is a promising alternative to medical diagnosis of several diseases. However, current techniques of respiration monitoring often require expensive and cumbersome devices which greatly limit their medical applications. Here, we present a fully integrated wearable device consisting of a flexible LCP-copper interdigital electrode, a sensing layer and a wireless electrochemical analysis system. The developed humidity sensor exhibits a high sensitivity, a good repeatability and a rapid response/recover time. The long-term stability is over 30 days at different relative humidity. By integrating the flexible humidity sensor with miniaturized electrochemical analysis system (0.8 cm × 1.8 cm), response current concerning respiration can be wirelessly transmitted to App-assisted smartphone in real time. Furthermore, the fabricated humidity sensor can realize skin moisture monitoring in a touch-less way. The large-scale production of miniaturized flexible sensor (4 mm × 6 mm) has significantly contributed to commercial deployment.

Analyzing Anisotropy in 2D Rhenium Disulfide Using Dichromatic Polarized Reflectance

In-plane anisotropy in 2D rhenium disulfide (ReS₂ ) offers intriguing opportunities for designing future electronic and optical devices, and toward such applications, it is crucial to identify the crystal orientation in such 2D anisotropic materials. Existing spectroscopy or electron microscopy methods for determining the crystalline orientation often require complicated sample preparing procedures and specialized equipment, which could sometimes limit their application. In this work, a dichromatic polarized reflectance method is demonstrated, which can quickly and accurately resolve the crystal orientation (Re-Re chain) in 2D ReS₂ crystals with different thicknesses. Furthermore, it can be readily extended to multi-chromatic schemes to achieve greater measurement capability and can be easily tailored to work for different 2D materials. The method offers a simple and effective approach for studying anisotropy in 2D materials.

A remarkably ultra-sensitive large area matrix of MXene based multifunctional physical sensors (pressure, strain, and temperature) for mimicking human skin

Electronic skin has attracted a lot of interest in recent years due to its ability to mimic human skin and also its excellent conformability. Even though there are reports on electronic skin, the major issue that still needs to be resolved is achieving multifunctional sensing at the same time as ultra-high sensitivity. Hence, there is an immediate requirement to develop inexpensive, highly sensitive, and superior performance piezoresistive multifunctional sensors that mimic skin. Herein, an as synthesized pure MXene (Ti3C2Tx) colloidal solution was used to deposit a thin film on flexible polyurethane foam, forming a three-dimensional conductive network with an ultra-high sensitivity of ∼34.24 kPa-1 (1.477-3.185 kPa of applied pressure range) and an elevated gauge factor of ∼323.59 (5-20% of applied strain range). Further merits such as reproducibility, low cost, high scalability, and excellent stability after 2500 cycles imply the sturdiness of the fabricated device. The remarkable sensing efficiency can be attributed to the strong interaction of Ti3C2Tx and PU foam, the inherent 3D network of PU coupled with the excellent electrical properties of Ti3C2Tx, and the interconnection of the unconnected branches present in the internal framework of PU-foam, which indicates the existence of more conduction paths. Besides, the fabricated Ti3C2Tx was deposited on cellulose paper to be utilized as a temperature sensor which displayed ∼2.22 × 10-3 °C-1 TCR and 29.43 meV activation energy. Lastly, real time applications for the fabricated device are investigated including detecting an unknown position of an object and human gestures. The successful demonstration of the low-cost, flexible Ti3C2Tx based piezoresistive sensor has shown innovative applications in biomedical, security, educational, and health sectors.

Influence of film-thickness on the ozone detection of perovskite La0.8Pb0.1Ca0.1Fe1−xCoxO3 based sensors

In this study, La_0.8Pb_0.1Ca_0.1Fe_1−xCo_xO₃ (x = 0.10 and x = 0.20) thin films with respective thicknesses of 300 and 600 nm have been prepared by the drop coating technique onto a Si/SiO₂ substrate with platinum interdigitated electrodes.