Copper migration and surface oxidation of $\text{Cu}_{x}\text{Bi}_2\text{Se}_3$ in ambient pressure environments

TL;DR

This study reveals that copper atoms migrate and the surface of Cu_xBi_2Se_3 oxidizes over time when exposed to ambient conditions, significantly altering its surface chemistry and composition.

Contribution

It demonstrates the time-dependent copper migration and surface oxidation in Cu_xBi_2Se_3 under ambient pressure, highlighting the importance of environmental effects on intercalated topological insulators.

Findings

Copper migration occurs over hours to days after cleaving.

Surface oxidation correlates with increased near-surface copper.

A composition gradient develops near the surface with oxygen exposure.

Abstract

Chemical modifications such as intercalation can be used to modify surface properties or to further functionalize the surface states of topological insulators. Using ambient pressure X-ray photoelectron spectroscopy, we report copper migration in $\text{Cu}_{x}\text{Bi}_2\text{Se}_3$, which occurs on a timescale of hours to days after initial surface cleaving. The increase in near-surface copper proceeds along with the oxidation of the sample surface and large changes in the selenium content. These complex changes are further modelled with core-level spectroscopy simulations, which suggest a composition gradient near the surface which develops with oxygen exposure. Our results shed light on a new phenomenon that must be considered for intercalated topological insulators$\unicode{x2014}$and intercalated materials in general$\unicode{x2014}$that surface chemical composition can change when specimens are exposed to ambient conditions.