Wuyuan Xie

Temperature-Dependent Abnormal and Tunable p-n Response of Tungsten Oxide–Tin Oxide Based Gas Sensors

We observed the sensing response of temperature-dependent abnormal p-n transitions in WO3-SnO2 hybrid hollow sphere based gas sensors for the first time. The sensors presented a normal n-type response to ethanol at elevated temperatures but abnormal p-type responses in a wide range of operation temperatures (room temperature to about 95 °C). By measuring various reducing gases and applying complex impedance plotting techniques, we demonstrated the abnormal p-type sensing behavior to be a pseudo-response resulting from the reaction between target gas and adsorbed water on the material surface. The temperature-controlled n-p switch is ascribed to the competition of intrinsic and extrinsic sensing behaviors, which resulted from the reaction of target gas with adsorbed oxygen ions and protons from adsorbed water, respectively. The former can modulate the intrinsic conductivity of the sensor by changing the electron concentration of the sensing materials, while the latter can regulate the conduction of the water layer, which contributes to the total conductivity as an external part. The hollow and hybrid nanostructures facilitated the observation of extrinsic sensing behaviors due to its large-area active sites and abundant oxygen vacancies, which could enhance the adsorption of water. This work might give new insight into gas sensing mechanisms and opens up a promising way to develop practical temperature and humidity controllable gas sensors with little power consumption based on the extrinsic properties.

Surrounding Sensitive Electronic Properties of Bi2Te3 Nanoplates-Potential Sensing Applications of Topological Insulators

Significant efforts have been paid to exploring the fundamental properties of topological insulators (TIs) in recent years. However, the investigation of TIs as functional materials for practical device applications is still quite limited. In this work, electronic sensors based on Bi2Te3 nanoplates were fabricated and the sensing performance was investigated. On exposure to different surrounding environments, significant changes in the conducting properties were observed by direct electrical measurements. These results suggest that nanostructured TIs hold great potential for sensing applications.

Enhanced sensitivity of a GHz surface acoustic wave humidity sensor based on Ni(SO4)0.3(OH)1.4 nanobelts and NiO nanoparticles

Ni(SO4)0.3(OH)1.4 nanobelts (NSOH NBs) and NiO nanoparticles (NPs) were used as the sensitive layers for a surface acoustic wave (SAW) humidity sensor. A high frequency SAW resonator up to 1.54 GHz was fabricated on a lithium niobate substrate as the sensing platform. The SAW sensors based on the NSOH NBs and the NiO NPs exhibited significantly decreased resonant frequencies with enhanced relative humidity (RH) from 11% to 85%, and the frequency response was found to be ¬2.95 MHz and ¬5.81 MHz, respectively. Both sensors showed rapid and reversible responses with excellent repeatability and long-term stability. The response and recovery times for NiO NPs were 23 s and 4 s, respectively. The NiO NP based sensor also showed negligible interference with various gases such as hydrogen and methane, demonstrating good cross-selectivity even while working in the GHz range. The high performance could be ascribed to the enhancement of the resonant frequency and the use of hydrophilic nanomaterials with a high surface-to-volume ratio.