Studies On Microstructure And Properties Of Antiferromagnetic Transition Metal Phosphorus Trisulfide NiPS₃ And MnPS₃

Two-dimensional semiconductor materials exhibit special lattice structure,controllable thickness and excellent physical,chemical and optoelectronic properties,which are benifical for their promising application in the next generation of high-performance nanoelectronics and optoelectronic devices.This family have attracted the interest of the majority of scientific researchers.However,currently the studies on how to maintain the good performance of two-dimensional material electronic devices in the working environment are still very limited.Based on this situation,this thesis mainly studies the microstructure,optical and stability of two-dimensional van der Waals antiferromagnetic materials NiPS₃ and MnPS₃,in order to explore the future application of these materials in the field of two-dimensional electronic devices.The following are the main results of this thesis:1.The microstructure and properties of NiPS₃ single crystal were characterized,the air stability of the few-layer NiPS₃ was studied.The NiPS₃ single crystals were prepared by chemical vapor transprt method.A series microstructure characterization methods have been jointly used such as X-ray diffraction spectroscopy,transmission electron microscope,scanning electron microscope,energy dispersive X-ray spectroscopy and Raman spectroscopy,which domentstrate that high-quality NiPS₃single crystals have been obtained.NiPS₃ exhibits paramagnetism to anferromantiesm transition at about 154 K.Raman spectroscopy shows that the peaks below 200 cm^-1 come from the vibration of metal atoms,while the higher frequency peaks come from[P₂S₆]^4-.Temperature dependent Raman spectra measurements show that as the temperature decreases,Raman peaks have the slight blue shift that is mainly caused by the shrinkage of the crystal lattice.Using atomic force microscope to accurately measure NiPS₃ nanosheets with different thicknesses,and according to the color change under the optical microscope,the thickness of the nanosheets can be accurately estimated,which provides a reference for studying the stability of multilayer NiPS₃ nanosheets.It is found that under normal enviroment conditions,NiPS₃ has a complex oxidation process caused by oxygen and atmospheric humidity.It is shown that a single layer of NiPS₃ can remain stable within 3 days.This provide the reference for future preparation of van der Waals heterostructure based on single layer of NiPS₃.2.The microstructure and properties of MnPS₃ single crystal were characterized,the Raman spectrum of few-layer MnPS₃ changed with thickness,and the change of Raman spectrum of few-layer MnPS₃ when covered with graphite flakes under environmental conditions was analyzed.The MnPS₃ single crystals were prepared using the chemical vapor transport method,and a series of characterization methods such as X-ray diffraction spectroscopy and transmission electron microscope were used to verify the structure and performance of crystals.The real part of the AC susceptibility of bulk MnPS₃ measured at different frequencies does not shift with temperature,thus eliminating the phenomenon of spin freezing transition.Thickness-dependent Raman spectra found that as the number of layers decreases,the Raman phonon mode frequency remains almost unchanged.This shows that the interlayer coupling of MnPS₃ is very weak compared to other two dimensional layered materials.At the same time,the graphite flakes are transferred on the MnPS₃ flakes by dry transfer method for Raman comparative analysis,and it is found that the MnPS₃ flakes can be maintained for a week in a normal environment,The MnPS₃ flakes covered with graphite flakes can remain stable for 20 days.3.Use the Castep module to calculate the band structure and density of states of bulk MnPS₃and the band structure of single-layer MnPS₃.When calculating the MnPS₃ crystals,the LDA+U method is used.The strucutrue of MnPS₃ crystals is gradually optimized to obtain the smallest energy model,and then its energy band and density of states are calculated,and the final calculated band gap is 2.882 e V,it was close to the experimental value of 3.0 e V.The density of states of MnPS₃ can be decomposed into 8 sub-bands.When calculating single-layer MnPS₃,by comparing the band gap calculated by LDA+U and PBE+U algorithms and combining with previous research,it is found that corresponding results by PBE+U is more consistent with the experimental data.