Halogen adsorption and reaction with Bi$_2$(Se,Te)$_3$ and Bi/Bi$_2$(Se,Te)$_3$

TL;DR

This study investigates how halogens interact with Bi$_2$Se$_3$ and Bi$_2$Te$_3$ surfaces, revealing their potential to modify surface termination through chemisorption, dissociative adsorption, and etching processes.

Contribution

It provides new insights into halogen-induced surface modifications of topological insulator materials using surface-sensitive techniques.

Findings

Br$_2$ weakly chemisorbs and can be removed by annealing.

Halogens dissociatively adsorb on Bi-covered surfaces, causing p-doping.

Annealing removes halogens and etches Bi, restoring original surface termination.

Abstract

Bi$_2$Se$_3$ and Bi$_2$Te$_3$, and these same surfaces covered with Bi films, are exposed to Br$_2$ and Cl$_2$ in ultra-high vacuum. Low energy electron diffraction (LEED) and low energy ion scattering (LEIS) are used to investigate the surface composition before and after halogen exposure. It is found that Br$_2$ weakly chemisorbs to the Se- or Te-terminated clean surfaces and light annealing removes the adsorbates restoring the intact surfaces. In contrast, halogens dissociatively adsorb onto surfaces covered with an additional bilayer of Bi, having a p-doping effect. Annealing these halogen-covered surfaces at 130{\deg}C causes Bi atoms to be chemically etched away and the surface reverts to a Se- or Te-termination. This work shows how halogen adsorption and reaction can be used to modify the surface termination of such materials.