| Transition metal tungsten/molybdenum chalcogenide exist in the bulk form as stacks of strongly bonded layers with weak van der Waals interlayer attraction. They have been the focus of modern advanced materials and advanced device fabrication technology field for decades due to their unique physical structure and novel characteristics. Graphene, with similar structure to transition metal tungsten/molybdenum chalcogenide, was the most widely studied material and famous star of the2D material. It is reported that the electronic band structure of graphene has a linear dispersion near K point, and charge carriers can be described as massless Dirac fermions, providing scientists with an abundance of new physics. Graphene is a unique example of an extremely thin electrical and thermal conductor, with high carrier mobility, and surprising molecular barrier properties However, there is still a long way to achieve the real device applications for graphene, mainly due to its intrinsic small band-gap. Many approaches, such as nanostructuring, chemical functionalization, or applying a high electric field to bilayer graphene, have been reported to engineer the band-gap, but they either are unstable or significantly reduce the carrier mobility. Recently, MoS2/WS2has captured the attention of many scientists because these material not only have similar structure and characteristics as graphene, but also they have band-gap between1.2-2.1eV varied with number of layers. These novel physical phenomena make them the superstart in the filed.However, most of current researches about transition metal tungsten/molybdenum chalcogenide are focused on their single atomic layer. From the point of view of physics, fabrication, and application, it seems that multilayer transition metal tungsten/molybdenum chalcogenide may perform much better than the monolayer one. Therefore, there is a strong desire to investigate multilayer tungsten/molybdenum chalcogenide based device in nanoelectronics and nano-optoelectronics fields.In this paper, we are going to synthesize transition metal tungsten/molybdenum chalcogenide firstly. Need to point out here, when we were trying our best to synthesize tungsten disulfide by hydrothermal method, a new kind material named pyrochlore WO3with microtubes morphology came into being. Because it also possesses a layered structure and has never been reported before, we would also bring it into our research content. After some basic characterization, we would fabricate devices to investigate their photoelectric chararcteristics, the following would be discussed in detail:1%tungsten disulfide microball with2-7μm diameter was successfully synthesized by a bottom-up chemical vapor deposition method, in which WCl6and thiourea reacted in inert gas environment, and the production was collected in low temperature area. Compared with other methods, here it does not need to pass any flammable or explosive gas, such as hydrogen and hydrogen sulfide. In addition, we studied the light response performance of the samples in the light of633nm wavelength. We found the photocurrent rose over eight times after red light irradiation. After scores of cycles, the photocurrent is still changed with turning on/off the red light, which exhibits an excellent stability of our device. At last, we took chance to intercalate NbCl5into WS2samples with two-zone vapor transport process. Based on experiment result, we found36h should be the optimal time for intercalation to realized the p-type doping in it. With the reaction time increasing, intercalate agents will desorb.2、pyrochlore WO3microtubes were successfully synthesized via a hydrothermal method for the first time. In this process, thiourea was employed to overcome the hydrogen bonds on the rim of WO3-0.5H2O and hydroxylamine hydrochloride was used as a viscosity regulator. Field-emission scanning electron microscopy and high-resolution transmission electron microscopy observations revealed that large amounts of uniform single-crystal WO3·0.5H2O microtubes with diameters ranging from100to300nm and length of tens of micrometers were obtained. The thickness of the tube wall was about40nm. A possible rolling mechanism was proposed to explain the formation of the tubular structures and the influence of thiourea and hydroxylamine hydrochloride on the uniform tubular morphology was discussed. The WO3-0.5H2O microtubes showed excellent photocatalytic activity toward the degradation of organic molecules such as RhB, which may find potential applications in the fields of photocatalysts, sensors and transistors.3、Here we use a micrometer-size diametral gold-wire worked as a mask to make the MoS2nanosheet field effect transistor (NSFET) instead of current expensive and fussy photo-etching or electron-beam lithography technology. This method has never been used in MoS2device fabrication and might be more suitable for commercial fabrication process. Moreover, both the experiment and theoretical calculation of the electrical characteristics of MoS2NSFET under air and NH3environment are investigated. The experimental results illustrate that the mobility and the current on/off ratio under air are12.1cm2V-1s-1and1000, respectively, while those under NH3environment are17.3cm2V-1s-1and10. Based on first-principles calculations, we found it is because the adsorbed NH3molecules transfer electrons to the MoS2nanosheet, changing its resistivity. Finally, we also investigate the red light response of our MoS2nanosheet at633nm wavelength and we find the photocurrent rises over three times and settles down to a highly stable and saturated value immediately after red light irradiation. After scores of cycles, the photocurrent is still changed with turning on/off the red light, which is more suitable to use as light detection device. |
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