Controllable Synthesis And Correlated Physical Performances Of Two Dimensional Transition Metal Magnetic Materials

Two-dimensional?2D?materials have been under spotlight due to their perfectly preserved atomic crystals,abundant energy band structures and emerged quantum properties at atomic thickness.2D materials are thus been expected to be the cornerstone for the next generation integrated electronics and optoelectronics devices.Nevertheless,the development of 2D materials is now faced with critical challenges,including the lack of materials system,the difficulty in synthesizing high-quality single crystals,and the lack of theoretical basis about the collective excited electrons,photons,and phonons at the 2D limits.Specifically,the practical application of spintronics and valleytronics have long been impeded due to the thermal fluctuation destabilized long range magnetic orders at the 2D limit.In this thesis,the 2D magnetism has been stabilized with enhanced magnetic anisotropy based on the designation of 2D CrX₂ family,and demonstrate the magnetic behaviors in correspondence.By introducing vd W substrates and gaseous sources,these materials are synthesized with their growth dynamics and coppesponding physical behaviors investigated.The specific research contents are listed as follows:1.The quasi layered two-dimensional magnetic CrX_i system,including Cr2S3,Cr Se,and Cu Cr S2,is designed on the anisotropic CrX₂ structure.For Cr₂S₃,ferrimagnetism is introduced between the competing ferromagnetic and antiferromagnetic orders due to the exchange interaction of intercalated Cr and intralayered Cr atoms.For Cr Se,ferromagnetism is introduced due to the ferromagnetic exchange interaction of Cr³⁺and Cr²⁺at the 2D limit.While in Cu Cr S₂,antiferromagnetism is intralayer localized due to the substitution of intercalated Cr through Cu atoms.2.The growth dynamics of the APCVD process have been studied:mica was introduced as vd W substrate to realize the vd W epitaxial growth of non-layered 2D materials.By regulating the concentration of precursor in the gaseous source,the stoichiometric ratio of metal:sulfide elements is designed,and the epitaxial growth of 2D non-layered materials with cellular thickness was realized.For Cr₂S₃,the final nanosheet size is close to 200?m,with a thickness of 1.78 nm,maintaining satisfying unit-cell characteristics.The obtained nanosheets with domain size of 40?m is achieved in a large range.For Cr Se,a maximum of 150?m single-domain nanosheet growth is realized,and the coverage of nanosheets on mica could be regulated to obtain continuous thin film samples.For Cu Cr S₂,unit-cell resolved growth was realized by introducing the limited space.The nanosheets possess uniform thickness distribution,and their anisotropy is demonstrated by Raman characterization.3.The magnetism of the obtained non-layered materials is investigated.The ferrimagnetic Néel temperature around 120 K and ferromagnetic Curie temperature of290 K have been revealed in Cr₂S₃ and Cr Se nanosheets,respectively.Our works demonstrate the great potential of Cr family into future spintronics and valleytronics applications.4.By introducing sleeved quartz tube as reactor,the precursors with relatively low melting points could be localized with enhanced abundance,through which stoichiometric Ni PS₃ nanosheets with a minimum thickness down to 3.5 nm have been obtained.Further,the Ni PS₃ nanosheets based devices demonstrated ultrafast solar-blind ultraviolet detection??3 ms?with high detectivity(1.22×10¹² Jones)and ultralow dark current?f A level?.