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.

Evidence for Magnetic Skyrmions at the Interface of Ferromagnet/Topological-Insulator Heterostructures

“…This is consistent with our recent observation that the black-phosphorus-like bismuth (BP-Bi) nanosheets embedded in the CT lattice plays the crucial role in the formation of magnetic skyrmions . The Bi bilayer has been demonstrated very robust in many material systems. − With an atomic number of 83, Bi atoms host a strong SOC, which is the prerequisite for a significant DM interaction. The hybridization of Bi p-orbitals and Cr d-orbitals can greatly enhance the DM interaction, which is also confirmed by atomistic spin-dynamics simulations based on Landau–Lifshitz–Gilbert (LLG) equation to study the stability of the skyrmions formed in these systems. − Moreover, two additional features will be underlined: (1) The majority carrier type can be tuned from n to p by manipulating the thickness of each film, which means the Fermi level can sweep the entire gap of the material.…”

“…The surface morphological evolution of CT characterized by STM could provide more information on the growth process as well as atomic environment of the interface. The step height measured on the BT surface after annealing in Figure a matches that of the hexagonal Bi(111) bilayer, i.e., 0.4 nm, , clearly different from that of Bi 2 Te 3 (∼1 nm). Cr and Te were then deposited on such a surface.…”

“…The BT/CT interface shown in Figure c is sharp and of quasi-vdW type. The STEM image of the CT/BT interface atomic structures is displayed in Figure d. , In contrast to the BT/CT interface, the Bi bilayer nanosheets have been observed at such interface. The color scale corresponds to the intensity, which is related to the scattering power of the elements, which can unambiguously illustrate that an intercalation Bi bilayer nanosheet exists between the upper CT and lower BT layers.…”

Anti-site defect effect on the electronic structure of a Bi2Te3 topological insulator

“…The reduction of Te fraction at T g >390 C can be attributed to the desorption of Te from the surface. 29 Nevertheless, a shi of E F away from the DP at T g > 390 C indicates a redistribution of the Bi Te /Te Bi ratio at the elevated growth temperatures. Detailed studies regarding the antisite defects dependent on growth temperature enable a quantitative analysis with EXAFS in the following.…”

Spin-resolved band structure of heterojunction Bi-bilayer/3D topological insulator in the quantum dimension regime in annealed Bi2Te2.4Se0.6

“…It allows to grow the epitaxial 2D/3D TIs heterostructures and electronic and spin properties of MBE grown Bi bilayer on 3D TIs have been investigated10111213222324. For the fabrication purposes, the relatively easier way to produce the Bi bilayer film on bismuth chalcogenides by the sample annealing have recently been developed in refs 25 and 26. By means of STM authors have measured detailed surface morphology and local density of states and revealed the Bi bilayer formation at the surface of Bi 2 Te 3 as a result of annealing.…”