In-situ preparation and characterization of defect-free topological insulator surfaces

Atomically clean and defect-free surface of topological insulators (TI) are essential for reliable quantum application such as the quantum Hall effect, topological superconductivity. We report an alternative and efficient method for preparing clean, defect-free and atomically flat surface of topological insulators compared to conventional in-situ cleaving of single crystals. Scanning tunneling microscopy (STM) measurements reveal that in-vacuo cleaving produces a smooth surface with large terraces but results in atomic native surface defects. Over time, surface contamination roughens the surface and repeated cleaving becomes impractical for thin samples. Argon ion bombardment followed by in-situ e-beam annealing effectively restored a clean surface with fewer defects, eliminating the need of removing the sample from the vacuum for fresh cleaving. Atomic-resolved imaging and spectroscopic measurements revealed detailed surface structures, defect geometries and local density of states for TI (Bi_0.1Sb_0.9)₂Te₃(0001) surface. With further optimization of the e-beam annealing parameters, a completely defect-free pristine surface was obtained as evidenced by spatially resolved differential conductance (dI/dU) measurements. We successfully extended this method to prepare clean defect-free surface of SnTe(001), a pristine topological crystalline insulator. It provides strong evidence to remove surface contaminants and imperfections, thereby ensuring its potential for broad application in the preparation of various 2D materials.