Study On Electronic Structures Of Several Low-Dimensional Ternary Chalcogenides Single Crystals

In materials with low-dimensional lattice structures,carrier transport behavior is limited by size effect,often leading to novel optical,magnetic and electrical phenomena that are different from their bulk counterparts.These properties can be applied to electrical device manufacturing about microwaves,photons,and to energy conversion fields such as lithium,thermoelectric and photovoltaic.In this thesis,several ternary chalcogenides with low-dimensional lattice structures were selected,and their physical properties such as thermoelectricity,superconductivity and magnetoresistance were studied by first-principles calculation,electrical transport,magnetic measurement,angular resolved photoelectron spectroscopy and scanning tunneling microscopy.A deep understanding of their electronic energy band structure provides some new ideas for the exploration of energy conversion materials.The thesis mainly includes the following experimental contents:1.Quasi-one-dimensionai narrow-bandgap semiconductor,CsBi4Te6 formed by Cs+ion insertion[Bi4Tee6]-slab is a functional material with good low-temperature thermoelectric properties.Deeply comprehending the electronic structure of CsBi4Te6 helps to understand the source and internal mechanism of its thermoelectric and superconducting behavior.In this chapter,angle-resolved photoelectron spectroscopy were used to analyze the electronic structure of CsBi4Te6 in detail.The energy gap at gamma point in Brillouin region is about 0.05-0.1 eV,and the valence and conduction band dispersions near the Fermi level are highly anisotropic.In particular,the k,dispersion is very weak,the conduction band dispersion is ? type and the band width is significantly larger than the calculation result,which means a small effective mass and a high mobility.Revealing the precise electronic structure of CsBi4Te6 helps to find more efficient thermoelectric materials and provides ideas for designing and optimizing their performance.2.Two-dimensional ternary sulfide(SnS)1.17(NbS2)heterostructure is formed by sandwiching two sublayers of NbS2 and SnS in a sandwich form.Comprehending the electronic structures of each sublayer in this kind of natural superlattice materials can provide important guidance for studying the properties of single-layer transition metal disulfides.The authors used angle-resolved photoelectron spectroscopy,scanning tunneling microscopy,electrical transport and magnetic tests to assist with each other systemically,discovering a single-layer NbS2-like electrical behavior in(SnS)1.17(NbS2).This work helps to understand the electronic structural characteristics of heterojunction materials and provides new ideas for studying the properties of transition metal disulfide compounds that are difficult to obtain.3.In the two-dimensional van der Waals ternary telluride crystal FeNbTe2,the author found an intrinsic unsaturated negative magnetoresistance and the magnetoresistance at low temperature deviated from the square relationship with the magnetic field.Through detailed analysis of the electrical and magnetic properties of the material,it is determined that this negative magnetoresistance is derived from the synergistic effect between the Anderson local and spin glass states.The in-depth discussion of the intrinsic microscopic mechanism of negative magnetoresistance in this work will help promote the development of the electronic spin discipline and information storage industry.