High-performance MoS2phototransistors with Hf1-xAlxO back-gate dielectric layer grown by plasma enhanced atomic layer deposition.

Molybdenum sulfide (MoS2) as an emerging optoelectronic material, shows great potential for phototransistors owing to its atomic thickness, adjustable band gap, and low cost. However, the phototransistors based on MoS2have been shown to have some issues such as large gate leakage current, and interfacial scattering, resulting in suboptimal optoelectronic performance. Thus, Al-doped hafnium oxide (Hf1-xAlx) is proposed to be a dielectric layer of the MoS2-based phototransistor to solve this problem because of the relatively higher crystallization temperature and dielectric constant. Here, a high-performance MoS2phototransistor with Hf1-xAlxO gate dielectric layer grown by plasma-enhanced atomic layer deposition has been fabricated and studied. The results show that the phototransistor exhibits a high responsivity of 2.2 × 104A W-1, a large detectivity of 1.7 × 1017Jones, a great photo-to-dark current ratio of 2.2 × 106%, and a high external quantum efficiency of 4.4 × 106%. The energy band alignment and operating mechanism were further used to clarify the reason for the enhanced MoS2phototransistor. The suggested MoS2phototransistors could provide promising strategies in further optoelectronic applications.

Advances in Noble Metal-Decorated Metal Oxide Nanomaterials for Chemiresistive Gas Sensors: Overview.

Highly sensitive gas sensors with remarkably low detection limits are attractive for diverse practical application fields including real-time environmental monitoring, exhaled breath diagnosis, and food freshness analysis. Among various chemiresistive sensing materials, noble metal-decorated semiconducting metal oxides (SMOs) have currently aroused extensive attention by virtue of the unique electronic and catalytic properties of noble metals. This review highlights the research progress on the designs and applications of different noble metal-decorated SMOs with diverse nanostructures (e.g., nanoparticles, nanowires, nanorods, nanosheets, nanoflowers, and microspheres) for high-performance gas sensors with higher response, faster response/recovery speed, lower operating temperature, and ultra-low detection limits. The key topics include Pt, Pd, Au, other noble metals (e.g., Ag, Ru, and Rh.), and bimetals-decorated SMOs containing ZnO, SnO2, WO3, other SMOs (e.g., In2O3, Fe2O3, and CuO), and heterostructured SMOs. In addition to conventional devices, the innovative applications like photo-assisted room temperature gas sensors and mechanically flexible smart wearable devices are also discussed. Moreover, the relevant mechanisms for the sensing performance improvement caused by noble metal decoration, including the electronic sensitization effect and the chemical sensitization effect, have also been summarized in detail. Finally, major challenges and future perspectives towards noble metal-decorated SMOs-based chemiresistive gas sensors are proposed.

Heterostructured α-Fe2 O3 @ZnO@ZIF-8 Core-Shell Nanowires for a Highly Selective MEMS-Based ppb-Level H2 S Gas Sensor System.

Highly selective and sensitive H2 S sensors are in high demand in various fields closely related to human life. However, metal oxide semiconductors (MOSs) suffer from poor selectivity and single MOS@metal organic framework (MOF) core-shell nanocomposites are greatly limited due to the intrinsic low sensitivity of MOF shells. To simultaneously improve both selectivity and sensitivity, heterostructured α-Fe2 O3 @ZnO@ZIF-8 core-shell nanowires (NWs) are meticulously synthesized with the assistance of atomic layer deposition. The ZIF-8 shell with regular pores and special surface functional groups is attractive for excellent selectivity and the heterostructured α-Fe2 O3 @ZnO core with an additional electron depletion layer is promising with enhanced sensitivity compared to a single MOS core. As a result, the heterostructured α-Fe2 O3 @ZnO@ZIF-8 core-shell NWs achieve remarkable H2 S sensing performance with a high response (Rair /Rgas  = 32.2 to 10 ppm H2 S), superior selectivity, fast response/recovery speed (18.0/31.8 s), excellent long-term stability (at least over 3 months), and relatively low limit of detection (down to 200 ppb) at low operating temperature of 200 °C, far beyond α-Fe2 O3 @ZIF-8 or α-Fe2 O3 @ZnO core-shell NWs. Furthermore, a micro-electromechanical system-based H2 S gas sensor system with low power consumption is developed, holding great application potential in smart cities.

Recent Progress on Flexible Room-Temperature Gas Sensors Based on Metal Oxide Semiconductor.

With the rapid development of the Internet of Things, there is a great demand for portable gas sensors. Metal oxide semiconductors (MOS) are one of the most traditional and well-studied gas sensing materials and have been widely used to prepare various commercial gas sensors. However, it is limited by high operating temperature. The current research works are directed towards fabricating high-performance flexible room-temperature (FRT) gas sensors, which are effective in simplifying the structure of MOS-based sensors, reducing power consumption, and expanding the application of portable devices. This article presents the recent research progress of MOS-based FRT gas sensors in terms of sensing mechanism, performance, flexibility characteristics, and applications. This review comprehensively summarizes and discusses five types of MOS-based FRT gas sensors, including pristine MOS, noble metal nanoparticles modified MOS, organic polymers modified MOS, carbon-based materials (carbon nanotubes and graphene derivatives) modified MOS, and two-dimensional transition metal dichalcogenides materials modified MOS. The effect of light-illuminated to improve gas sensing performance is further discussed. Furthermore, the applications and future perspectives of FRT gas sensors are also discussed.