| In 2004,the major discovery of graphene was hailed as a "milestone breakthrough" and a "revolutionary push",which immediately aroused an upsurge in the study of two-dimensional(2D)materials by domestic and foreign scholars.Looking back at the development history of 2D materials,it is essentially the exploration history of various novel 2D materials,which has gone from the initial development of graphene to transition metal chalcogenides,black phosphorus,and the recent breakthroughs in intrinsic 2D magnetic materials.The exploration of novel 2D materials and the discovery of novel physical properties have been driving the development of the entire 2D materials field,which has important scientific significance in frontier physics,device applications,and materials science.Among them,the research on trihalide system is also the most worthy of the highlight in the history of the novel 2D materials discovery.The trihalide system generally refers to transition metal trihalides and its derivative oxides.Owing to their unique crystal configuration,electronic band structure,and abundant physical and chemical properties(such as Kitaev quantum spin liquid,intrinsic multiferroicity,etc.),the trihalide system provides an ideal platform for exploring novel physical phenomena.As a novel type of 2D material system,the research of the trihalide system,especially in transition metal oxychlorides,still has a big gap meriting further broad research space.This thesis takes the novel 2D transition metal halide ?-MoCl3 and its derivative oxide MoOCl2 as the main research object,demonstrating the synthesis of novel 2D materials and the characterization of intrinsic properties,focusing on the related electrical,optical,and magnetic transport performance,and further exploring the potential applications in the fields of electronics,optics and spintronics.The research content of this thesis includes the following aspects:(1)Combining the exploration of novel 2D materials and the research needs of related transport properties,we introduced material preparation,sample processing,and related basic characterization and analysis methods in detail,demonstrating a solid theoretical and experimental foundation for subsequent synthesis and characterization of novel 2D materials.In addition,the universal research process of micromechanical exfoliation,device fabrication,transport measurements,and data analysis is further introduced in detail,providing a solid theoretical and experimental foundation for subsequent studies based on the relevant transport properties of novel 2D materials.(2)The preparation of ?-MoCl3 bulk single crystals was explored,and the crystal structure and intrinsic physical properties were fully characterized and analyzed.On that basis,the structural phase transition and in-situ electrical property changes in the layered ?-MoCl3 induced by laser illumination were studied in detail.Laser illumination in a moist atmosphere caused the structural reorganization in layered ?-MoCl3,resulting in hydrogen intercalation reactions and forming a metastable phase of HxMoCl3 in ?-MoCl3.In addition,the effect of laser illumination also induced electronic reorganization in ?-MoCl3,generating additional Mo 3d orbital-polarized electrons,thereby effectively improving the conductivity of ?-MoCl3.Combined with the theoretical analysis based on first-principles calculations,our results shed light on the underlying mechanism of the structural phase transition in ?-MoCl3 under laser illumination.(3)The novel layered material,MoOCl3,was successfully synthesized,and crystal structure and intrinsic physical properties were further fully characterized.On the above basis,the low-temperature transport properties of layered MoOCl2 were systematically studied.We experimentally demonstrated a Landau's Fermi liquid behavior in a wide temperature range of 3?123 K in layered MoOCl2 for the first time.Combining with the specific heat measurement at low temperatures,and further taking into account the carrier density and the effective dimensionality of layered MoOCl2 by modifying the form of Kadowaki-Woods ratio(KWR),we unified the different KWR values for different classes of strongly correlated materials.In addition,a colossal nonsaturating magnetoresistance in MoOCl2 is observed in the magnetotransport measurement,as well as the anisotropic magnetoresistance(AMR)effect.With the help of first-principles calculations,we further shed light on the underlying physical mechanism of electron-electron interaction and colossal magnetoresistance in layered MoOCl2. |
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