High-Performance Flexible Humidity Sensor Based on MoO_<i>x</i> Nanoparticle Films for Monitoring Human Respiration and Non-Contact Sensing

Flexible humidity sensors with high sensitivity, fast response time, and outstanding reliability have the potential to revolutionize electronic skin, healthcare, and non-contact sensing. In this study, we employed a straightforward nanocluster deposition technique to fabricate a resistive humidity sensor on a flexible substrate, using molybdenum oxide nanoparticles (MoOx NPs). We systematically evaluated the humidity-sensing behaviors of the MoOx NP film-based sensor and found that it exhibited exceptional sensing capabilities. Specifically, the sensor demonstrated high sensitivity (18.2 near zero humidity), a fast response/recovery time (1.7/2.2 s), and a wide relative humidity (RH) detection range (0–95%). The MoOx NP film, with its closely spaced granular nanostructure and high NP packing density, exhibited insensitivity to mechanical deformation, small hysteresis, good repeatability, and excellent stability. We also observed that the device exhibited distinct sensing kinetics in the range of high and low RH. Specifically, for RH > 43%, the response time showed a linear prolongation with increased RH. This behavior was attributed to two factors: the higher physical adsorption energy of H2O molecules and a multilayer physical adsorption process. In terms of applications, our sensor can be easily attached to a mask and has the potential to monitor human respiration owing to its high sensing performance. Additionally, the sensor was capable of dynamically tracking RH changes surrounding human skin, enabling a non-contact sensing capability. More significantly, we tested an integrated sensor array for its ability to detect moisture distribution in the external environment, demonstrating the potential of our sensor for contactless human–machine interaction. We believe that this innovation is particularly valuable during the COVID-19 epidemic, where cross-infection may be averted by the extensive use of contactless sensing. Overall, our findings demonstrate the tremendous potential of MoOx NP-based humidity sensors for a variety of applications, including healthcare, electronic skin, and non-contact sensing

High-Performance Flexible Humidity Sensor Based on MoO_<i>x</i> Nanoparticle Films for Monitoring Human Respiration and Non-Contact Sensing

Flexible humidity sensors with high sensitivity, fast response time, and outstanding reliability have the potential to revolutionize electronic skin, healthcare, and non-contact sensing. In this study, we employed a straightforward nanocluster deposition technique to fabricate a resistive humidity sensor on a flexible substrate, using molybdenum oxide nanoparticles (MoOx NPs). We systematically evaluated the humidity-sensing behaviors of the MoOx NP film-based sensor and found that it exhibited exceptional sensing capabilities. Specifically, the sensor demonstrated high sensitivity (18.2 near zero humidity), a fast response/recovery time (1.7/2.2 s), and a wide relative humidity (RH) detection range (0–95%). The MoOx NP film, with its closely spaced granular nanostructure and high NP packing density, exhibited insensitivity to mechanical deformation, small hysteresis, good repeatability, and excellent stability. We also observed that the device exhibited distinct sensing kinetics in the range of high and low RH. Specifically, for RH > 43%, the response time showed a linear prolongation with increased RH. This behavior was attributed to two factors: the higher physical adsorption energy of H2O molecules and a multilayer physical adsorption process. In terms of applications, our sensor can be easily attached to a mask and has the potential to monitor human respiration owing to its high sensing performance. Additionally, the sensor was capable of dynamically tracking RH changes surrounding human skin, enabling a non-contact sensing capability. More significantly, we tested an integrated sensor array for its ability to detect moisture distribution in the external environment, demonstrating the potential of our sensor for contactless human–machine interaction. We believe that this innovation is particularly valuable during the COVID-19 epidemic, where cross-infection may be averted by the extensive use of contactless sensing. Overall, our findings demonstrate the tremendous potential of MoOx NP-based humidity sensors for a variety of applications, including healthcare, electronic skin, and non-contact sensing

Response Characteristics of Hydrogen Sensors Based on PMMA-Membrane-Coated Palladium Nanoparticle Films

Coating a polymeric membrane for gas separation is a feasible approach to fabricate gas sensors with selectivity. In this study, poly­(methyl methacrylate)-(PMMA-)­membrane-coated palladium (Pd) nanoparticle (NP) films were fabricated for high-performance hydrogen (H₂) gas sensing by carrying out gas-phase cluster deposition and PMMA spin coating. No changes were induced by the PMMA spin coating in the electrical transport and H₂-sensing mechanisms of the Pd NP films. Measurements of H₂ sensing demonstrated that the devices were capable of detecting H₂ gas within the concentration range 0–10% at room temperature and showed high selectivity to H₂ due to the filtration effect of the PMMA membrane layer. Despite the presence of the PMMA matrix, the lower detection limit of the sensor is less than 50 ppm. A series of PMMA membrane layers with different thicknesses were spin coated onto the surface of Pd NP films for the selective filtration of H₂. It was found that the device sensing kinetics were strongly affected by the thickness of the PMMA layer, with the devices with thicker PMMA membrane layers showing a slower response to H₂ gas. Three mechanisms slowing down the sensing kinetics of the devices were demonstrated to be present: diffusion of H₂ gas in the PMMA matrix, nucleation and growth of the β phase in the α phase matrix of Pd hydride, and stress relaxation at the interface between Pd NPs and the PMMA matrix. The retardation effect caused by these three mechanisms on the sensing kinetics relied on the phase region of Pd hydride during the sensing reaction. Two simple strategies, minimizing the thickness of the PMMA membrane layer and reducing the size of the Pd NPs, were proposed to compensate for retardation of the sensing response

Solvothermal Synthesis of Lateral Heterojunction Sb₂Te₃/Bi₂Te₃ Nanoplates

A lateral heterojunction of topological insulator Sb₂Te₃/Bi₂Te₃ was successfully synthesized using a two-step solvothermal method. The two crystalline components were separated well by a sharp lattice-matched interface when the optimized procedure was used. Inspecting the heterojunction using high-resolution transmission electron microscopy showed that epitaxial growth occurred along the horizontal plane. The semiconducting temperature-resistance curve and crossjunction rectification were observed, which reveal a staggered-gap lateral heterojunction with a small junction voltage. Quantum correction from the weak antilocalization reveals the well-maintained transport of the topological surface state. This is appealing for a platform for spin filters and one-dimensional topological interface states