Pan Caofeng

Controlled synthesis of high-qualitycrystals of monolayer MoS 2 for nanoelectronic device application

Two-dimensional layered materials have attracted significant interest for their potential applications in electronic and optoelectronics devices. Among them, transition metal dichalcogenides (TMDs), especially molybdenum disulfide (MoS2), is extensively studied because of its unique properties. Monolayer MoS2 so far can be obtained by mechanical exfoliation or chemical vapor deposition (CVD). However, controllable synthesis of large area monolayer MoS2 with high quality needs to be improved and their growth mechanism requires more studies. Here we report a systematical study on controlled synthesis of high-quality monolayer MoS2 single crystals using low pressure CVD. Large-size monolayer MoS2 triangles with an edge length up to 405 μm were successfully synthesized. The Raman and photoluminescence spectroscopy studies indicate high homogenous optical characteristic of the synthesized monolayer MoS2 triangles. The transmission electron microscopy results demonstrate that monolayer MoS2 triangles are single crystals. The back-gated field effect transistors (FETs) fabricated using the as-grown monolayer MoS2 show typical n-type semiconductor behaviors with carrier mobility up to 21.8 cm2 V−1 s−1, indicating excellent electronic property comparing with previously reported CVD grown MoS2 monolayer. The MoS2 FETs also show a high photoresponsivity of 7 A W−1, as well as a fast photo-response time of 20 ms. The improved synthesis method recommended here, which makes material preparation much easier, may strongly promote further research and potential applications.摘要二维层状材料由于其在光电器件方面的潜在应用引起了广泛关注, 二硫化钼(MoS2)是其中研究最多的材料之一. 单层二硫化钼可通过机械剥离或者化学气相合成的方法制备, 但是与石墨烯相比, 大面积且高质量的单层二硫化钼单晶的可控合成仍然有待提高. 本文报道了一种可控合成大面积高质量单层MoS2单晶的方法, 合成出了边长达405 μm的单层二硫化钼三角形. 对产物进行了光谱表征, 结果表明其光学性质十分均匀, 透射电镜表征结果表明产物是单晶结构. 基于单层MoS2的场效应晶体管(FET)表现出良好的电学性能, 其载流子迁移率高达21.8 cm2 V−1 s−1,光响应度为7 A W−1, 响应时间仅为20 ms. 此合成方法使单层MoS2的制备更加简易可靠, 可促进其进一步研究及应用.

Self-powered nanosystems based on nanofuelcell

With the rapid progress in researches on nano-materials, a dramatically increasing number of nanoscale functional devices are developed, including nano-biosensors, nano-photoelectric sensors. Most of these nanoscale devices rely on external power supply to work sustainably. Although an energy storage unit is a choice for powering nanodevices, the large dimension of existed power sources has become one limited factor for the miniaturization of independently workable nanodevices. Therefore, a nanoscale power source capable of harvesting energy from the environment is an essential solution for building a “self-powered” nanosystem which is an integration of functional nanodevices and nano- enabled energy scavenging technologies. The successful development of such nanoscale power sources that match with nanodevices is significant for constructing self-powered nanosystems. The self-powered nanosystems will be widely used in industrial fields such as sensors networks, environmental and infrastructural monitoring, portable electronics, and healthcare. Referring to recent vigorously studies on exploiting self-powered nanosystems based on functional nanodevices and nano-batteries, it is obvious that the preparation of nano fuel cell is the key to the establishment of self-powered nanosystems. Fuel cells have many advantages over conventional batteries, such as high energy conversion efficiency, quick startup ability under low temperature, high energy density, and the feature of environmental friendly. What’s more, through the technical route of fuel cells, chemical and biochemical energy, the most abundant energy available in nature or in vivo biosystems, can be converted to electrical energy from fuels such as methanol and glucose, which is meaningful to the development of in vivo implantable nanosystems. Therefore, more and more attentions of the scientific community in fields of nanoenergy and nanosystems have been paid to the researches on micro and even nano scale miniaturization of fuel cells. Our group has done some studies on the proton exchange properties of single perfluorinated sulfonic acid resin (Nafion) nanowire, and on the nano proton exchange membrane fuel cells. We also have built a number of self-powered nanosystems based on such nano fuel cells. In this review article, we begin with the introduction to the proton exchange properties of Nafion nanowires, which is based on the works of our and other research groups. Then we briefly introduce nanofuel, nanobiofuel, hybrid nano biofuel cells, and self-powered nanosystems that are powered by these fuel cells, which represents a new self-powering approach in nanotechnology. We also briefly sum up the state of the art, point out confronting problems, and prospect possible trends in the researches on self-powered nanosystems. This work shows the feasibility of building self-powered nanosystems for biological sciences, environmental monitoring, defense technology and even personal electronics.