Controlled Growth Of Topological Insulator Nanostructures And Their Surface Properties

As a new state of quantum matter, topological insulators have attracted muchmore attention in recent years. Topological insulator is a gapped insulator in the bulkbut possessing metallic surface states, which is different from a conventional metal ora semiconductor. These metallic surface states are determined by the specialtopological electronic structure, which is independent of the detailed structure of thematerial and protected by time-reversal symmetry. These unique properties maketopological insulators have promising applications in the fields of spin devices,quantum computation as well as micro-nano electronic devices. Controlled growth oftopological insulators is essential for the study of new quantum states and thefabrication of corresponding electronic devices. In this dissertation, we have achievedthe controlled growth of high quality bismuth telluride, bismuth selenide, antimonytelluride as well as ternary topological insulator nanoplates by thermal evaporationmethod. The surface potentials and charge distributions of topological insulatornanoplates have been systematically investigated by Kelvin probe force microscopy.The major results are summarized as follows:1. Bismuth telluride and bismuth selenide nanoplates exhibiting a variety ofmorphologies with triangular, truncated triangular and hexagonal shapes have beenfabricated by vapor phase deposition method. We have systematically investigated theinfluence of growth time, growth pressure as well as the placement direction ofsubstrates on the evolution of nanostructures.2. The surface potentials of bismuth telluride and bismuth selenide grown onSiO2substrate are studied by Kelvin probe force microscopy. Uniform surfacepotential distributions can help to further understand the properties of topologicalinsulator-based electronic devices. The surface potentials of bismuth telluride andbismuth selenide grown on n-doped and p-doped silicon substrates are simultaneouslyinvestigated. Experimental results indicate that the substrate has a doping effect on thenanoplate, which provides a new route to tune the topological insulator surface states.3. High quality of antimony telluride nanoplates on various substrates have beenfabricated by vapor phase deposition method. The surface potential distributions ofantimony telluride nanoplates grown on highly oriented graphite are uniform and thework function of the nanoplates is determined to be~5.016eV. The spiral growth mode on the antimony telluride nanoplate surface is investigated.4. High quality ternary Bi2(SexTe1-x)3topological insulator nanoplates have beenfabricated and the morphologies and microstructures have been systematicallyinvestigated. Through the variation of Se/Te composition ratio, the Fermi level of thenanoplate can be tuned up to0.23eV and the work functions for Bi2(SexTe1-x)3nanoplates have been determined.5. Graphene with different layers has been obtained by micromechanicalcleavage method. We found that the surface potentials increase with the graphenelayers both under ambient air and high vacuum environment. The surface potentialreaches to the bulk value after five layers and the surface potential has a shiftmeasured under high vacuum environment compared to that obtained in ambient air.Few-layer molybdenum disulfide films have been simultaneously fabricated by usingmicromechanical cleavage method and the surface potentials have been systematicallyexplored by Kelvin probe force microscopy. We foud that the film edges, defect grainboundaries as well as folded area have lower surface potential distributions comparedto the sample surface. The bismuth telluride nanoplates have been successfully grownon graphene, molybdenum disulfide thin films. The surface potentials of the obtainedheterostructures have been systematically studied. The Fermi level shift is up to~80meV for ultra-thin Bi2Te3NPs.