title: Annealing-Induced Bi Bilayer on Bi2Te3 Investigated via Quasi-Particle-Interference Mapping.
abstract: Topological insulators (TIs) are renowned for their exotic topological surface states (TSSs) that reside in the top atomic layers, and hence, detailed knowledge of the surface top atomic layers is of utmost importance. Here we present the remarkable morphology changes of Bi2Te3 surfaces, which have been freshly cleaved in air, upon subsequent systematic annealing in ultrahigh vacuum and the resulting effects on the local and area-averaging electronic properties of the surface states, which are investigated by combining scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and Auger electron spectroscopy (AES) experiments with density functional theory (DFT) calculations. Our findings demonstrate that the annealing induces the formation of a Bi bilayer atop the Bi2Te3 surface. The adlayer results in n-type doping, and the atomic defects act as scattering centers of the TSS electrons. We also investigated the annealing-induced Bi bilayer surface on Bi2Te3 via voltage-dependent quasi-particle-interference (QPI) mapping of the surface local density of states and via comparison with the calculated constant-energy contours and QPI patterns. We observed closed hexagonal patterns in the Fourier transform of real-space QPI maps with secondary outer spikes. DFT calculations attribute these complex QPI patterns to the appearance of a "second" cone due to the surface charge transfer between the Bi bilayer and the Bi2Te3. Annealing in ultrahigh vacuum offers a facile route for tuning of the topological properties and may yield similar results for other topological materials.
authors: Solid-State Physics and Magnetism Section, KU Leuven , BE-3001 Leuven, Belgium.
authors: Koen
authors: K
authors: Schouteden
authors: EMAT and CMT Group, Department of Physics, Universiteit Antwerpen , B-2020 Antwerpen, Belgium.
authors: Kirsten
authors: K
authors: Govaerts
authors: Department of Materials Engineering, KU Leuven , BE-3001 Leuven, Belgium.
authors: Jolien
authors: J
authors: Debehets
authors: Solid-State Physics and Magnetism Section, KU Leuven , BE-3001 Leuven, Belgium.
authors: Umamahesh
authors: U
authors: Thupakula
authors: Max Planck Institute for Chemical Physics of Solids , D-01187 Dresden, Germany.
authors: Taishi
authors: T
authors: Chen
authors: Solid-State Physics and Magnetism Section, KU Leuven , BE-3001 Leuven, Belgium.
authors: Zhe
authors: Z
authors: Li
authors: Solid-State Physics and Magnetism Section, KU Leuven , BE-3001 Leuven, Belgium.
authors: Asteriona
authors: A
authors: Netsou
authors: National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, and Department of Physics, Nanjing University , Nanjing 210093, China.
authors: Fengqi
authors: F
authors: Song
authors: EMAT and CMT Group, Department of Physics, Universiteit Antwerpen , B-2020 Antwerpen, Belgium.
authors: Dirk
authors: D
authors: Lamoen
authors: Solid-State Physics and Magnetism Section, KU Leuven , BE-3001 Leuven, Belgium.
authors: Chris
authors: C
authors: Van Haesendonck
authors: EMAT and CMT Group, Department of Physics, Universiteit Antwerpen , B-2020 Antwerpen, Belgium.
authors: Bart
authors: B
authors: Partoens
authors: Department of Physics, Virginia Tech , Blacksburg, Virginia 24061, United States.
authors: Kyungwha
authors: K
authors: Park
keywords: Bi bilayer; Bi2Te3; density functional theory; quasi-particle interference; scanning tunneling microscopy; topological insulators