Fabrication And Characterization Of Low Dimensional Quantum Structures In Tellurium And Telluride Films

Since the discovering of the quantum Hall effect of two-dimensional free electron gas and the successful preparation of graphene,the research of low-dimensional condensed matter physics has attracted more and more attention from scientists.With the enrichment of material systems,many novel quantum states have been found in low-dimensional materials and structures which don't exist in the bulk ones.These quantum states of matter are expected to be used in future functional devices.Many studies have been conducted on the macroscopic properties on two-dimensional materials.However,the study of constructing one/zero-dimensional quantum states in two-dimensional materials is still in its infancy.The boundary and defects of two-dimensional materials are natural one-dimensional and zero-dimensional systems.Scientists pursue to realize the controllable preparation and controlling the physical properties of edge states or defects states.There are several reasons that there are still few breakthroughs in this field:First,there are not enough low-dimensional materials,it is still difficult to prepare stable and controllable one-dimensional quantum states.Second,one-dimensional and zero-dimensional quantum states require atomic-scale characterization and regulation means,the technical barriers still exist at present.Third,the electronic properties in the low dimensional material system are in a wide range.Different systems often have different behaviors,so it is difficult to have a unified theory.Among these low-dimensional systems,two dimensional elemental materials and transition metal chalcogenides are two systems with broad research prospects.Research on the controllable preparation and tuning of their physical properties are necessary for promoting their application.In this dissertation,we studied the fabrication of monolayers of elemental tellurium and transition metal ditelluride and their low-dimensional quantum structure using molecular beam epitaxy and scanning tunneling microscopy.Firstly,we used scanning tunneling microscope(STM)to distinguish the chirality of ultra-thin elemental tellurium nanoribbons,which laid a foundation for the future study of chirality related physics in elemental tellurium single crystal and its nanostructures.Then we combined STM and density functional theory calculations to determine the structure of the quasi-periodic edge defects on the tellurium nanoribbon introduced by the substrate effect from graphene/Si C.Scanning tunneling spectroscopy(STS)was used to characterize the one-dimensional modulation of the electronic states induced by quasi-periodic defects at the edge of tellurium nanoribbons.It is proposed that a series of quantum well states were formed by such edge defects.We provide an idea for the preparation of low dimensional quantum states in tellurium nanostructures.Then,based on the controlled preparation of tellurium nanoribbon and thin film,we explored the regulation of on the physical properties of tellurium nanoribbon by selenium doping.Then,we achieved the construction of the elemental selenium nanostructure using tellurium thin film as an auxiliary layer.In addition to the study of the nanostructures of elemental tellurium and selenium,we have also studied the preparation of monolayers of transition metal tellurides and investigated their electronic properties.The charge density modulation and periodic lattice distortion caused by(4×4)and(4×1)charge density wave states in a monolayer VTe₂ film have been detected in real space.Then,the transition temperature of charge density wave was determined to be 192 K by temperature-dependent low energy electron diffraction(LEED)experiments.After a careful analysis of the STM results,we revealed the breaking of the rotational and mirror symmetries in the(4×4)charge density wave states of monolayers of vanadium ditelluride.Based on the method of selenium doping in elemental tellurium nanostructures,we doped monolayer vanadium ditelluride with selenium.The modulation effect of doping on charge density wave states in vanadium ditelluride is characterized by STM.Finally,we explored the growth of other transition metal tellurides.Monolayer chromium ditelluride was successfully prepared.The electronic properties of this possible two-dimensional magnetic material were studied.