Controllable Preparation Of Two-dimensional Cr/Mn-based Transition Metal Chalcogenides And Their Optoelectronic And Magnetic Studies

Two-dimensional(2D)transition metal dichalcogenides(TMDs)are the basic materials for the new generation of microelectronics and optoelectronic devices.As an important part of the 2D material family,have become a research hotspot in the past decade due to their unique advantages such as wide band gap tunability and high electron mobility.Researchers have found that it is a special class of materials in the large 2D TMDs family,which have many excellent electrical and photoelectric properties,but also a very novel magnetic property,called magnetic 2D TMDs materials.In recent years,it has been widely concerned because of its great application prospects in spintronics and magnetic memory devices.Therefore,magnetic 2D TMDs materials have become a new research hotspot and the urgent requirements of future industrial development in the fields of low power,high speed and ultra-compact spintronic devices,data storage,information recognition and processing,intelligent sensors and quantum computing applications.However,the choice of existing magnetic 2D TMDs materials is still quite limited,and most of them are unstable in air,which inevitably impedes the exploration and practical application of their intrinsic magnetism.Simultaneously,exploring new kinds of magnetic 2D TMDs materials with better stability,especially the Cr/Mn based magnetic 2D TMDs materials,is still in the initial stage.Which is still facing huge challenges in controllably synthesizing such materials by chemical vapor deposition(CVD)method.So,the controllable synthsis and related properties of novel Cr/Mn based magnetic 2D TMDs materials with better stability will be systematically studied in this paper.Specific research contents are as follows:(1)Controllable synthesis of two-dimensional Cr5Te8 single crystals for ferromagnetism propertiesIn order to solve the issue that 2D CrxTey material is easy to decompose at high temperature and thus causes the uncontrollable components,we have developed a tube-in-tube CVD growth method,which can provide a Te-rich environment during the growth process.Finally,a new magnetic 2D TMDs material Cr5Te8 was successfully prepared for the first time via this approch.By accurately controlling the growth temperature,realizing the controllable synthesis of Cr5Te8 with the thickness from 1.2 nm to 30 nm,and the morphology from triangle to hexagon.XPS,STEM and simulated STEM confirmed the composition and high crystal quality of Cr5Te8.MOKE measurement shows its Tc can up to 160 K,further measurement results also display the excellent air stability and ferromagnetic stability.This work will provide an important reference for precisely controlling the synthesis of 2D ferromagnetic materials and is of great significance for basic research and device applications.(2)CVD growth of semiconductor two-dimensional MnTe for photoelectric propertiesIn this work,2D semiconductor MnTe nanosheets with hexagonal structure were prepared on mica substrates by CVD method.The morphology and thickness of the MnTe nanosheets could be adjusted by accurately controlling the growth temperature.STEM and second harmonic(SHG)measurements show that the as-synthesized 2D MnTe possesses high crystal quality and excellent nonlinear optical properties.Moreover,constructing the field effect transistors and photodetectors based on MnTe nanosheets,showing that the conductive properties change from semiconductor to metal with the thickness increase.(3)Controllable synthesis of nonlayered two-dimensional MnS single crystals for optoelectronic propertiesIn this work,ultra-thin MnS single crystals were successfully synthesized via CVD growth.By precisely adjusting growth parameters,achieving a wide range of adjustable thicknesses from 3.5 nm to 118.8 nm.XPS and STEM confirmed the composition and lattice qualities of as-grown MnS.Notably,a new general transfer method(PS wet assisted transfer)was developed for the unstable MnS in H2O and hydrofluoric acid(HF)solution.Furthermore,orientation analysis of as-grown MnS single crystals on mica substrate shows that the three main orientations,which is attributed to the six-fold symmetrical structure of mica substrate.Field effect transistor device based on 50 nm MnS shows an obvious metallic conductive behavior.This work is expected to realize the potential applications of MnS single crystals in electronic and optoelectronic fields.