Jinkai Chen

Fast Response and High Sensitivity ZnO/glass Surface Acoustic Wave Humidity Sensors Using Graphene Oxide Sensing Layer

We report ZnO/glass surface acoustic wave (SAW) humidity sensors with high sensitivity and fast response using graphene oxide sensing layer. The frequency shift of the sensors is exponentially correlated to the humidity change, induced mainly by mass loading effect rather than the complex impedance change of the sensing layer. The SAW sensors show high sensitivity at a broad humidity range from 0.5%RH to 85%RH with < 1 sec rise time. The simple design and excellent stability of our GO-based SAW humidity sensors, complemented with full humidity range measurement, highlights their potential in a wide range of applications.

Bendable transparent ZnO thin film surface acoustic wave strain sensors on ultra-thin flexible glass substrates

Flexible and transparent (FT) ZnO thin film based surface acoustic wave (SAW) devices using indium tin oxide (ITO) electrodes were fabricated on ultrathin flexible glass substrates. The influence of the annealing process and ITO thickness on the optical properties and acoustic wave power transmission properties of the devices was investigated. The performance of the devices improved significantly when the annealing temperature was raised up to 300 °C. The flexible glass based SAW devices exhibited similar power transmission performance, but have a better optical transmittance than those on rigid glass. These FT strain sensors worked well under various applied strains up to ±3000 μe with fast response time, and showed excellent linearity of resonant frequency with the change of strain with a sensitivity of ∼34 Hz μe−1. The strain sensors demonstrated excellent stability and reliability under cyclic bending. The results demonstrated great potential of applications of the FT-SAW device based strain sensors on flexible glass substrates.

Thermal annealing effect on ZnO surface acoustic wave-based ultraviolet light sensors on glass substrates

Surface acoustic wave (SAW) based ultraviolet (UV) light sensors have a high sensitivity and have been extensively studied and explored for application. However, all of them were made of piezoelectric (PE) bulk materials or PE thin films on crystalline substrates such as Si and sapphire. This paper reports the fabrication of ZnO thin film SAW UV-light sensors on glass substrates and the effect of post-deposition thermal annealing on the sensing performance. It was found that annealing at temperatures higher than 300 °C can improve the properties of ZnO films and the sensing performance of the UV-sensors remarkably. When the ZnO film annealed at 400 °C was used for sensors, the UV light induced resonant frequency shift increased more than 20 times with the response speed reduced to less than 2.4 s, much better than those made on ZnO films with lower temperature annealing.

Bendable ZnO thin film surface acoustic wave devices on polyethylene terephthalate substrate

Bendable surface acoustic wave (SAW) devices were fabricated using high quality c-axis orientation ZnO films deposited on flexible polyethylene terephthalate substrates at 120 °C. Dual resonance modes, namely, the zero order pseudo asymmetric (A0) and symmetric (S0) Lamb wave modes, have been obtained from the SAW devices. The SAW devices perform well even after repeated flexion up to 2500 μe for 100 times, demonstrating its suitability for flexible electronics application. The SAW devices are also highly sensitive to compressive and tensile strains, exhibiting excellent anti-strain deterioration property, thus, they are particularly suitable for sensing large strains.

Rapid Determination of Phenylalanine by Micro-chip Based Field Asymmetric Waveform Ion Mobility Spectrometry Technology

Abstract The microchip field asymmetric ion mobility spectrometry (FAIMS) technology was used for rapid analysis of phenylalanine (PHE) using the metal diffusion tube-microchip μ-FAIMS system. The test pressure was set at 0.25 MPa, and the temperature of the gas generator for the diffusion tube was at 190 °C. The ion characteristic spectra were acquired under the optimized conditions with a gas flow rate of 2000 mL min −1 , a dispersion voltage of 152.8 V and a compensation voltage of −0.62 V for phenylalanine in positive mode. Phenylalanine gas samples with different concentrations were analyzed in detail by FAIMS. The results showed that the ion intensity was linearly correlated with phenylalanine concentration in the range from 6 mg L −1 to 20 mg L −1 , with the detection limit of 5.93 mg L −1 for phenylalanine. This investigation shows the feasibility of FAIMS technique for rapid detection of phenylalanine. The FAIMS instrument is simple, and has high sensitivity and fast response, and shows great potential for rapid detection of phenylalanine.