Rapid Surface Oxidation of Sb₂Te₃ as Indication for a Universal Trend in the Chemical Reactivity of Tetradymite Topological Insulators

Abstract

Within the past few years, topological insulators (TIs) have attracted a lot of interest due to their unique electronic structure with spin-polarized topological surface states (TSSs), which may pave the way for these materials to have a great potential in multiple applications. However, to enable consideration of TIs as building blocks for novel devices, stability of TSSs toward oxidation should be tested. Among the family of TIs with a tetradymite structure, Sb2Te3 is of p-type and appears to be the least explored material since its TSS is unoccupied in the ground state, a property that allows the use of optical excitations to generate spin currents relevant for spintronics. Here, we report relatively fast surface oxidation of Sb2Te3 under ambient conditions. We show that the clean surface reacts rapidly with molecular oxygen and slowly with water, and that humidity plays an important role during oxide layer growth. In humid air, we show that Sb2Te3 oxidizes on a time scale of minutes to hours, and much faster than other tetradymite TIs. The high surface reactivity revealed by our experiments is of critical importance and must be taken into account for the production and exploitation of novel TI-based devices using Sb2Te3 as a working material. Our results contribute to the comprehensive understanding of the universal trend underlying the chemical reactivity of tetradymite TIs.