Preparation Of Two-dimensional Transition Metal Chalcogenides And Their Alloys And Heterostructures By Chemical Vapor Deposition

In recent years,two-dimensional transition metal chalcogenides have received widespread attention due to their peculiar physical,chemical and electrical properties.In particular,alloys and heterostructures represented by MoS2 or WS2,exhibit component-dependent tunable bandgap structures and optoelectronic properties,and have potential applications in next-generation high-performance optoelectronic devices.In order to promote the practical application of these two-dimensional semiconductor materials in future electronic devices,it is one of the core issues in the research field to find a controllable method for high-quality and centimeter-scale two-dimensional semiconductor materials.In this paper,taking MoS2 as the example,large area TMDC and their alloys and heterostructures were prepared.This paper mainly includes the following two aspects:1.Controllable preparation of WS2/MoS2 vertical heterostructure and Mo1-xWxS2 alloyIn the process of preparing two-dimensional alloy and heterostructure by chemical vapor deposition,it is difficult to prepare samples without impure phase simply and effectively due to the inherent difference of the growth temperature of the two kinds of films and the different saturated vapor pressure of the precursor.In this paper,a one-step chemical vapor deposition method is proposed.By introducing different content of low melting point Te powder into W powder,the growth temperature of WS2 is effectively reduced,and the above problems are solved.The WS2/MoS2 vertical heterostructure and the Mo1-xWxS2 alloy were prepared.Raman spectra,photoluminescence spectra,Raman and photoluminescence mapping techniques show that the prepared WS2/MoS2 vertical heterostructure is formed by superimposing a single layer of WS2 and MoS2,and the content of W(x)is 0.83 in the MO1-xWxS2 alloy.2.Controllable preparation of Co-doped large area bilayer MoS2The preparation of the two-dimensional transition metal chalcogenide with large area and thickness control is the key to its industrial application.Taking the MoS2 film as an example,the main factors(growth temperature,sulfur-molybdenum ratio and carrier gas flow rate)affecting the morphology of the MoS2 film were obtained by analyzing the nucleation and growth process of chemical vapor deposition.The three main growth conditions were optimized,and the substrate was subjected to 'oxygen plasma,and then a centimeter-scale Co-doped bilayer MoS2 film was effectively prepared.Raman spectra and atomic force microscopy demonstrated the layer number of the sample is bilayer.Raman and photoluminescence mapping show better uniformity of the sample.Transmission electron microscopy(TEM)and HAADF-STEM techniques show the 2H phase structure of the sample and the presence and position of cobalt atoms in the sample.Magnetic tests show that the saturation magnetization of the sample is increased by 50 times after the introduction of cobalt atoms.