Reactive chemical doping of the $Bi_2 Se_3$ topological insulator

TL;DR

This study investigates how water vapor exposure alters the surface electronic structure of the topological insulator Bi2Se3, revealing surface reactions, band bending, and quantum well states while confirming the protection of the topological state.

Contribution

It demonstrates that water vapor induces chemical reactions on Bi2Se3 surfaces, causing band bending and quantum well states, and explains aging effects in the material's electronic properties.

Findings

Water vapor causes band bending and quantum well states in Bi2Se3.

Surface reactions involve Se-abstraction, creating vacancies.

Topological surface states remain protected despite surface chemistry changes.

Abstract

Using angle resolved photoemission spectroscopy we studied the evolution of the surface electronic structure of the topological insulator $\text{Bi}_2\text{Se}_3$ as a function of water vapor exposure. We find that a surface reaction with water induces a band bending shifting the Dirac point deep into the occupied states and creating quantum well states with a strong Rashba-type splitting. The surface is thus not chemically inert, but the topological state remains protected. The band bending is traced back to Se-abstraction leaving positively charged vacancies at the surface. Due to the presence of water vapor, a similar effect takes place when $\text{Bi}_2\text{Se}_3$ crystals are left in vacuum or cleaved in air, which likely explains the aging effect observed in the $\text{Bi}_2\text{Se}_3$ band structure.