Zongbiao Ye

Ammonia gas sensors based on poly (3-hexylthiophene)-molybdenum disulfide film transistors

In this work, in order to enhance the recovery performance of organic thin film transistors (OTFTs) ammonia (NH3) sensors, poly (3-hexylthiophene) (P3HT) and molybdenum disulfide (MoS2) were combined as sensitive materials. Different sensitive film structures as active layers of OTFTs, i.e., P3HT-MoS2 composite film, P3HT/MoS2 bilayer film and MoS2/P3HT bilayer film were fabricated by spray technology. OTFT gas sensors based on P3HT-MoS2 composite film showed a shorter recovery time than others when the ammonia concentration changed from 4 to 20 ppm. Specifically, x-ray diffraction (XRD), Raman and UV-visible absorption were employed to explore the interface properties between P3HT and single-layer MoS2. Through the complementary characterization, a mechanism based on charge transfer is proposed to explain the physical originality of these OTFT gas sensors: closer interlayer d-spacing and better π-π stacking of the P3HT chains in composite film have ensured a short recovery time of OTFT gas sensors. Moreover, sensing mechanisms of OTFTs were further studied by comparing the device performance in the presence of nitrogen or dry air as a carrier gas. This work not only strengthens the fundamental understanding of the sensing mechanism, but provides a promising approach to optimizing the OTFT gas sensors.

The Investigation of Reduced Graphene Oxide/P3HT Composite Films for Ammonia Detection

In this paper, single reduced graphene oxide (rGO) and rGO/Poly (3-hexylthiophene) (P3HT) composite films were prepared by the spray process, which were deposited on the interdigitated transducers for preparing the resistive ammonia (NH3) sensor. The morphology of sensitive films was characterized by scanning electron microscopy (SEM). The gas-sensing properties of GO/P3HT film sensor were tested and analyzed. The results showed that rGO/P3HT composite film sensor exhibited better sensing properties and restorability than that rGO film sensor, which maybe was ascribed to π-π interaction between rGO and P3HT and the superior surface morphology of composite films.

Reduced graphene oxide–polyethylene oxide hybrid films for toluene sensing at room temperature

A reduced graphene oxide (RGO)–polyethylene oxide (PEO) hybrid film was constructed with composite and bilayer film structures for effective ambient toluene detection. The morphology and chemical properties of the fabricated RGO–PEO hybrid materials were characterized by SEM, and Raman and FTIR spectroscopies, respectively. Sensitive properties of real-time response, sensitivity, repeatability and selectivity to toluene vapor were studied as well at room temperature. The experimental data show that the gas sensors based on composite film have a higher sensitivity than the ones based on bilayer film and pure RGO film at toluene concentrations from 80 ppm to 140 ppm. In addition, the effect of PEO volume fraction and humidity on the sensing performance was also studied. The sensor with a PEO volume fraction of 50% has a better sensitivity and faster response/recovery than others. With respect to selectivity, the gas response of the prepared sensors to toluene was at least 2-fold higher than those to other vapor species, including acetone, ethanol, hydrogen, water and formaldehyde. Furthermore, the sensing mechanism of the fabricated sensors was investigated by comparing the device performance in the presence of dry air or nitrogen as carrier gas.

Wind energy harvesting and self-powered flow rate sensor enabled by contact electrification

We have developed a free-standing-mode based triboelectric nanogenerator (F-TENG) that consists of indium tin oxide (ITO) foils and a polytetrafluoroethylene (PTFE) thin film. By utilizing the wind-induced resonance vibration of a PTFE film between two ITO electrodes, the F-TENG delivers an open-circuit voltage up to 37 V and a short-circuit current of 6.2 μA, which can be used as a sustainable power source to simultaneously and continuously light up tens of light emitting diodes (LEDs) and charge capacitors. Moreover, uniform division of the electrode into several parallel units efficiently suppresses the inner counteracting effect of undulating film and leads to an enhancement of output current by 95%. The F-TENG holds prominent durability and an excellent linear relationship between output current and flow rate, revealing its feasibility as a self-powered sensor for detecting wind speed. This work demonstrates potential applications of the triboelectric generator in gas flow harvesters, self-powered air navigation, self-powered gas sensors and wind vector sensors.

The investigation of reduced graphene oxide/titanium dioxide-based sensor for formaldehyde detection at room temperature

Reduced graphene oxide/titanium dioxide (rGO/TiO2) layered film was firstly utilized through simple spray method for trace detection of formaldehyde (HCHO) at room temperature. A remarkable sensitivity of layered film (0.8 ppm-1) was identified in the concentration range of 0.1 ppm to 0.5 ppm, which was higher than that of rGO-based sensor (0.5 ppm-1). It was worth noting that an interesting abruption behavior of rGO sheets during the thermal reduction process was observed. However, the collapse of rGO honeycomb network during temperature-rise period could be prevented due to the introduction of TiO2 nanoparticles. Furthermore, a novel mechanism based on àie combination of catalytic reactions and supporting function of TiO2 nanoparticles was introduced to explain the enhanced sensing performance of rGO/TiO2 layered film in contrast to bare rGO film.

Enhancement humidity sensing properties of graphene oxide/Poly(ethyleneimine) film QCM sensors

In this work, a novel graphene oxide (GO)/Poly(ethyleneimine) (PEI) layered film was prepared on the quartz crystal microbalance (QCM) by feasible spray process for the humidity detection. The morphology of sensitive film was analyzed by field emission scanning electron microscopy (FESEM). it was worth mentioning that a chemical bonding could be formed at the interface between PEI and GO sheets due to the acylation reaction, which was proved by the Fourier transform infrared (FTIR) transmission spectrum characterization. The humidity-sensing results showed that the frequency shift of sensors exhibited the excellent response and reproducibility, which might be partly ascribed to the effective interaction between PEI and GO. Meanwhile, an instant recovery time (5s) and negligible humidity hysteresis (less than 1%RH) were achieved. Furthermore, the mechanism of performance enhancement of layered film sensors was analyzed.

Piezo-phototronic UV photosensing with ZnO nanowires array

Here a promising approach is proposed to enhance the responsivity of a ZnO nanowires array based photodetector with metal-semiconductor-metal structure through piezo-phototronic effect. The ZnO nanowires arrays were synthesized on the surface of ZnO seedlayer via hydrothermal method. Using polarization charges created at metal-ZnO interface under strain to modulate the local Schottky barrier height (SBH), the responsivity of the prepared photon sensor was increased by as much as 107% when the device was subjected to a -0.67% compressive strain. This work not only strengthens the fundamental understanding of piezo-phototronic effect on photodetectors but also provides an efficient means for optimization/improvement of piezoelectric semiconductor nanowires based optoelectronic devices.

Thin film transistors gas sensors based on poly(3-hexylthiophene)/Zinc oxide-nanorods composite film for nitrogen dioxide detection

A new approach was proposed to evaluate the performance of organic thin film transistors (OTFTs) gas sensors. Back-gated OTFTs gas sensors with poly (3-hexylthiophene) (P3HT)/Zinc oxide (ZnO) nanorods composite film as the active layers and gas sensing layers were prepared for nitrogen dioxide (NO2) detection. Electrical parameters of OTFTs based on pure P3HT film and P3HT/ZnO-nanorods composite film were calculated and analyzed. Response characteristics of gas sensors to NO2 were studied. It can be found that responses of OTFTs gas sensors were inaccurate according to conventional definition. The slope of fitting line (ΔI versus log t) was proposed as a new method to evaluation gas properties of OTFTs sensors. The calculate results illustrated that the sensitivity can be increased 40.2% due to appropriate amount of ZnO-nanorods doping.