Visualizing topological insulating Bi2Te3 quintuple layers on SiO2-capped Si substrates and its contrast optimization

TL;DR

This study demonstrates optical visualization of ultrathin Bi2Te3 topological insulator flakes on SiO2/Si substrates, analyzing contrast variations with wavelength and layer thickness, and optimizing conditions for improved imaging.

Contribution

It introduces a contrast optimization method for visualizing thin Bi2Te3 layers using specific illumination wavelengths and models the contrast behavior with Fresnel law-based calculations.

Findings

Maximum contrast at 570nm wavelength.

Contrast reverses below 20 quintuple layers.

Fresnel law-based model accurately describes contrast variations.

Abstract

Thin Bi2Te3 flakes, with as few as 3 quintuple layers, are optically visualized on the SiO2-capped Si substrates. Their optical contrasts vary with the illumination wavelength, flake thickness and capping layers. The maximum contrast appears at the optimized light with the 570nm wavelength. The contrast turns reversed when the flake is reduced to less than 20 quintuple layers. A calculation based on the Fresnel law describes the above observation with the constructions of the layer number-wave length-contrast three-dimensional (3D) diagram and the cap thickness-wavelength-contrast 3D diagram, applicative in the current studies of topological insulating flakes.