Real-space characterization of reactivity towards water at Bi2Te3(111) surface

TL;DR

This study uses scanning tunneling microscopy to reveal that only the top layer of Bi2Te3(111) reacts with water, forming passivating Bi layers, with implications for understanding its surface chemistry in ambient conditions.

Contribution

It provides the first direct real-space evidence that water reacts intrinsically with Bi2Te3(111), specifically at the top quintuple layer, revealing a new reaction mechanism.

Findings

Only the top quintuple layer reacts with water.

Reaction results in hydrated Bi bilayer and Bi islands.

Water reaction is intrinsic, not defect-dependent.

Abstract

Surface reactivity is important in modifying the physical and chemical properties of surface sensitive materials, such as the topological insulators (TIs). Even though many studies addressing the reactivity of TIs towards external gases have been reported, it is still under heavy debate whether and how the topological insulators react with H$_2$O. Here, we employ scanning tunneling microscopy (STM) to directly probe the surface reaction of Bi$_2$Te$_3$ towards H$_2$O. Surprisingly, it is found that only the top quintuple layer is reactive to H$_2$O, resulting in a hydrated Bi bilayer as well as some Bi islands, which passivate the surface and prevent from the subsequent reaction. A reaction mechanism is proposed with H$_2$Te and hydrated Bi as the products. Unexpectedly, our study indicates the reaction with water is intrinsic and not dependent on any surface defects. Since water inevitably exists, these findings provide key information when considering the reactions of Bi$_2$Te$_3$ with residual gases or atmosphere.