Construction Of In-situ Mutual Inductance System And Scanning Probe Microscopes,and STM Studies Of Cr₂Ge₂Te₆ Ferromagnetic Semiconductor

The development of sophisticated experimental technology and its application in the study of the physical properties of exotic materials are important driving forces for the development of experimental condensed matter physics.The research work of this dissertation focuses on the establishment and optimization of in-situ experimental measurement technology and its application in ferromagnetic semiconductor materials.The main contents include the construction of the in-situ mutual inductance measurement device,the optimization of various scanning probe microscopes,and the use of scanning tunneling microscopy to study the electronic structure of ferromagnetic semiconductors.The in-situ measurement techniques allow people to measure the physical properties of a sample while keeping it clean,avoiding sample contamination and degradation caused by the transfer process,and therefore plays an important role in the study of condensed matter physics.The thesis describes how to design and build a dual-coil in-situ mutual-magnetic measurement device that operates in an ultra-high vacuum environment.The device can be used for in-situ calibration of superconducting thin films grown in ultra-high vacuum by molecular beam epitaxy technology.Much effort have been put in improving compatibility and thus it can be integrated with a variety of ultra-high vacuum sample growth systems as a plug and play device.Scanning probe microscopy is an important method in experimental condensed matter physics.One can study the fine structure of electrical,magnetic,and optical properties of non-uniform samples by taking advantage of spatial resolution.In this paper,the working principles and practical designs of three types of scanning probe devices are introduced,including scanning tunneling microscopes,a non-contact atomic force microscope,and a scanning microwave impedance microscope.Based on the experience of the construction process,detailed analysis on how to improve the performance of the scanning probe devices is presented.Scanning tunneling microscopy is a powerful experimental method for studying the electronic structure of new low-dimensional materials because of its capability of measuring electronic tunneling spectrum at atomic-scale.In recent years,the ferromagnetic semiconductor Cr₂Ge₂Te₆ of layered structure has attracted widespread attention because it is a representative quasi-two-dimensional magnetic system and can be combined with a large number of two-dimensional materials discovered recently to make various kinds of electronics and spintronics devices.However,there are fewer experimental results for microscopic electronic structure and mechanism of ferromagnetic order of this material.In this paper,we use the scanning tunneling microscope to perform detailed measurements on the topography,electronic structure,defect type,and impurity electronic state of Cr₂Ge₂Te₆.With the help of density functional theory calculations,our experimental results reveal the close relations between the microscopic electronic structure and the magnetic order,and provide new clues for the application of the ferromagnetic semiconductor in spintronics.