Preparation And Photoelectric Properties Of Two-Dimensional Molybdenum Disulfide And Their Heterostructures

In the past few years, tremendous attention has been paid to graphene, the thinnest two-dimensional(2D) crystal with exceptional electronical, optical and mechanical properties. And the two-dimensional layered materials have shown great promise for microelectronics and photoelectronics. Driven by the increasing research interest in 2D nanomaterials, atomically thin Mo S2 have been investigated, which exhibited many appealing properties for a wide range of applications, such as transistors, photodetectors, solar cells, and so on. In our study, we systematically investigated the preparation and application of ultrathin Mo S2 and its composites(e.g., hybrid nanostructures and atomically thin van der Waals heterostructures). The main results obtained are as follow. 1. Controllable preparation and mechanism of ultrathin Mo S2.The Mo S2 monolayers are Synthesized via Vapor–Solid–Grown(VSG) method and Chemical Vapor Deposition(CVD). And we found the self-induced intralayer strain was induced in the preparation process of Mo S2 monolayers. High temperature and vacuum are required in the growth conditions of VSG. The Mo S2 single-crystal size is usually less than 100 μm via VSG method. While we can obtain bigger Mo S2 single-crystals(larger than 100 μm) in many substrates via CVD method. The Mo S2 samples have uniform distribution of thickness and element, high crystal quality and excellent optical properties.We report the Mo S2 monolayers with symmetrical van der Waals-stacked interlayer interaction(vd W-SI) by vapor-deposition method. Such a uniaxial strain in the local Mo S2 monolayer is confirmed by Raman study and first-principle calculation. We have discovered and demonstrated self-induced intralayer strain(~0.5%) in the special samples. The PL results indicate that the local vd W-SI can be an effective route to tuning of the band gap of layered Mo S2. This results indicate the finite boundary and interlayer interaction in Mo S2 have great influence on intralayer bonding. The discovery of self-induced intralayer strains by local vd W-SI may create alternative opportunities for strain engineering toward tunable optoelectronic functionalities.2. The composites of ultrathin Mo S2.We study two kinds of composites of ultrathin Mo S2. The first composite is high-quality ternary alloy of Monolayer(ML) Mo(1-x)Wx S2 and ML-Mo S2(1-x)Se2x are synthesized via CVD. We can control doping concentration carefully via change the ratio of source compositions. We also could inverse estimate the compositions by Raman and Photoluminescence(PL) spectra. PL spectra indicated that the band gap of the alloy of ‘Mo S2’ could be tuned precisely between 1.55 e V(ML-Mo Se2) and 1.97 e V(ML-WS2) by changing the ratio of Mo/W/Se compositions.The second composite is a kind of hybrid Mo S2 monolayer containing vertical Zn O nanorods. We coupled Zn O nanorods to vapor–solid–grown Mo S2 monolayers via a flexible and simple hydrothermal route. The results indicated the ML-Mo S2 could be as the seed layer of Zn O nanorods. The excellent geometric structure matching, which enables the coupling of vertical Zn O nanorods to the layered Mo S2 materials. Enhanced PL and Raman emission was observed for the Mo S2 monolayer due to the antenna effect of the Zn O nanorods. Such hybrid nanostructures open alternative pathways for incorporating oxide nanorods on ultrathin 2D materials to promote a wide variety of advanced applications. 3. The atomically thin van der Waals(vd W) heterostructures.In this section, we have demonstrated, for the first time, Mo Te2/Mo S2 vd W monolayer heterostructures via a transfer device of home-built. The DFT simulations and KPFM result indicated the type II band alignment in Mo Te2-Mo S2 heterostructures which agrees with the previous reports. Strong interlayer coupled interactions between Mo Te2 and Mo S2 are observed by Raman and PL spectroscopy. Moreover, the photoinduced charge generation and separation process in Mo Te2-Mo S2 m HS is first clear observed by Kelvin probe force microscopy(KPFM) under illumination. The type II infrared coupled photodetectors based on Mo Te2-Mo S2 m HS is also fabricated. And showed interlayer optical transition for the creation of an infrared(e.g., at ~1.55 μ m) photodetector beyond the limits of the intrinsic band gap of the constituting material( individual Mo Te2 or Mo S2). We believe that our studies will be valuable for better understanding of the interlayer coupling and for fabrication flexible and transparent optoelectronic devices.