Wei Zheng

Bio: Wei Zheng is an academic researcher from Qingdao University. The author has contributed to research in topics: Atomic layer deposition & Materials science. The author has an hindex of 13, co-authored 18 publications receiving 538 citations.

Platinum single atoms on tin oxide ultrathin films for extremely sensitive gas detection

Abstract: Single atom Pt functionalized SnO2 ultrathin films are synthesized by atomic layer deposition (ALD) for application as sensing layers in resistive gas sensors. Here it is shown that the electronic conductivity of the SnO2 ultrathin films is very sensitive to the exposure to triethylamine (TEA), and that the thickness of the SnO2 films (from 4 to 18 nm) has a crucial effect on the sensor response. The 9 nm thick SnO2 film shows the best response to TEA, while a further decrease in the film thickness, i.e., 4 nm, leads to a very weak response due to the two orders of magnitude lower carrier concentration. Single atom Pt catalysts deposited on the 9 nm SnO2 film result in an unexpectedly high enhancement in the sensor response and also a decrease of the sensor working temperature. Consequently, Pt/SnO2 thin film sensors show the highest response of 136.2 to 10 ppm TEA at an optimal temperature of 200 °C (that of a pristine SnO2 film sensor is 260 °C), which is improved by a factor of 9 compared to that of pristine SnO2. Moreover, the Pt/SnO2 sensor exhibits an ultrahigh sensitivity of 8.76 ppm−1 and an extremely low limit of detection (LOD) of 7 ppb, which to our best knowledge are far superior to any previous report. Very fast response and recovery times (3/6 s) are also recorded, thus making our sensor platform highly suitable for highly-demanding applications. Mechanistic investigations reveal that the outstanding sensing performances originate from the synergistic combination of the optimized film thickness comparable to the Debye length of SnO2 and the spillover activation of oxygen by single atom Pt catalysts, as well as the oxygen vacancies in the SnO2 films.

Oxygen Vacancies Enabled Porous SnO2 Thin Films for Highly Sensitive Detection of Triethylamine at Room Temperature.

Abstract: Detection of volatile organic compounds (VOCs) at room temperature (RT) currently remains a challenge for metal oxide semiconductor (MOS) gas sensors. Herein, for the first time, we report on the utilization of porous SnO2 thin films for RT detection of VOCs by defect engineering of oxygen vacancies. The oxygen vacancies in the three-dimensional-ordered SnO2 thin films, prepared by a colloidal template method, can be readily manipulated by thermal annealing at different temperatures. It is found that oxygen vacancies play an important role in the RT sensing performances, which successfully enables the sensor to respond to triethylamine (TEA) with an ultrahigh response, for example, 150.5-10 ppm TEA in a highly selective manner. In addition, the sensor based on oxygen vacancy-rich SnO2 thin films delivers a fast response and recovery speed (53 and 120 s), which can be further shortened to 10 and 36 s by elevating the working temperature to 120 °C. Notably, a low detection limit of 110 ppb has been obtained at RT. The overall performances surpass most previous reports on TEA detection at RT. The outstanding sensing properties can be attributed to the porous structure with abundant oxygen vacancies, which can improve the adsorption of molecules. The oxygen vacancy engineering strategy and the on-chip fabrication of porous MOS thin film sensing layers deliver great potential for creating high-performance RT sensors.

Graphene-MoS2 Hybrid Technology for Large-Scale Two-Dimensional Electronics

Abstract: Two-dimensional (2D) materials have generated great interest in the past few years as a new toolbox for electronics. This family of materials includes, among others, metallic graphene, semiconducting transition metal dichalcogenides (such as MoS2), and insulating boron nitride. These materials and their heterostructures offer excellent mechanical flexibility, optical transparency, and favorable transport properties for realizing electronic, sensing, and optical systems on arbitrary surfaces. In this paper, we demonstrate a novel technology for constructing large-scale electronic systems based on graphene/molybdenum disulfide (MoS2) heterostructures grown by chemical vapor deposition. We have fabricated high-performance devices and circuits based on this heterostructure, where MoS2 is used as the transistor channel and graphene as contact electrodes and circuit interconnects. We provide a systematic comparison of the graphene/MoS2 heterojunction contact to more traditional MoS2-metal junctions, as well as a theoretical investigation, using density functional theory, of the origin of the Schottky barrier height. The tunability of the graphene work function with electrostatic doping significantly improves the ohmic contact to MoS2. These high-performance large-scale devices and circuits based on this 2D heterostructure pave the way for practical flexible transparent electronics.

Oxygen Vacancies Enabled Porous SnO2 Thin Films for Highly Sensitive Detection of Triethylamine at Room Temperature.

Abstract: Detection of volatile organic compounds (VOCs) at room temperature (RT) currently remains a challenge for metal oxide semiconductor (MOS) gas sensors. Herein, for the first time, we report on the utilization of porous SnO2 thin films for RT detection of VOCs by defect engineering of oxygen vacancies. The oxygen vacancies in the three-dimensional-ordered SnO2 thin films, prepared by a colloidal template method, can be readily manipulated by thermal annealing at different temperatures. It is found that oxygen vacancies play an important role in the RT sensing performances, which successfully enables the sensor to respond to triethylamine (TEA) with an ultrahigh response, for example, 150.5-10 ppm TEA in a highly selective manner. In addition, the sensor based on oxygen vacancy-rich SnO2 thin films delivers a fast response and recovery speed (53 and 120 s), which can be further shortened to 10 and 36 s by elevating the working temperature to 120 °C. Notably, a low detection limit of 110 ppb has been obtained at RT. The overall performances surpass most previous reports on TEA detection at RT. The outstanding sensing properties can be attributed to the porous structure with abundant oxygen vacancies, which can improve the adsorption of molecules. The oxygen vacancy engineering strategy and the on-chip fabrication of porous MOS thin film sensing layers deliver great potential for creating high-performance RT sensors.

Room-Temperature Gas Sensors Under Photoactivation: From Metal Oxides to 2D Materials

Abstract: Room-temperature gas sensors have aroused great attention in current gas sensor technology because of deemed demand of cheap, low power consumption and portable sensors for rapidly growing Internet of things applications. As an important approach, light illumination has been exploited for room-temperature operation with improving gas sensor’s attributes including sensitivity, speed and selectivity. This review provides an overview of the utilization of photoactivated nanomaterials in gas sensing field. First, recent advances in gas sensing of some exciting different nanostructures and hybrids of metal oxide semiconductors under light illumination are highlighted. Later, excellent gas sensing performance of emerging two-dimensional materials-based sensors under light illumination is discussed in details with proposed gas sensing mechanism. Originated impressive features from the interaction of photons with sensing materials are elucidated in the context of modulating sensing characteristics. Finally, the review concludes with key and constructive insights into current and future perspectives in the light-activated nanomaterials for optoelectronic gas sensor applications. Highlights: 1 Operations of metal oxide semiconductors gas sensors at room temperature under photoactivation are discussed.2 Emerging two-dimensional (2D) materials-based gas sensors under light illumination are summarized.3 The advantages and limitations of metal oxides and 2D-materials-based sensors in gas sensing at room temperature under photoactivation are highlighted.

Black Phosphorus Field-effect Transistors

Abstract: Two-dimensional crystals have emerged as a class of materials that may impact future electronic technologies. Experimentally identifying and characterizing new functional two-dimensional materials is challenging, but also potentially rewarding. Here, we fabricate field-effect transistors based on few-layer black phosphorus crystals with thickness down to a few nanometres. Reliable transistor performance is achieved at room temperature in samples thinner than 7.5 nm, with drain current modulation on the order of 10(5) and well-developed current saturation in the I-V characteristics. The charge-carrier mobility is found to be thickness-dependent, with the highest values up to ∼ 1,000 cm(2) V(-1) s(-1) obtained for a thickness of ∼ 10 nm. Our results demonstrate the potential of black phosphorus thin crystals as a new two-dimensional material for applications in nanoelectronic devices.