Cs adsorption on Bi$_2$Se$_3$

TL;DR

This study investigates how cesium atoms adsorb onto Bi$_2$Se$_3$, a topological insulator, revealing their diffusion behavior, effects on work function, and impact on surface electronic states through experimental measurements.

Contribution

It provides new insights into cesium adsorption dynamics, work function variation, and the spatial distribution of topological surface states on Bi$_2$Se$_3$.

Findings

Cesium forms chains at step edges and deposits on terraces.

Work function decreases then slightly increases with Cs coverage.

Adsorbed Cs influences the neutralization of scattered Na$^+$ and surface charge distribution.

Abstract

Bi$_2$Se$_3$ is a topological insulator whose unique properties result from topological surface states (TSS) in the band gap. The adsorption of Cs onto a Bi$_2$Se$_3$ surface is investigated by low energy ion scattering and work function measurements. Much of the deposited Cs quickly diffuses to the step edges forming one-dimensional chains of positively charged adatoms, along with some deposition on the terraces. The work function decreases until a coverage of 0.1 ML is reached, beyond which it increases slightly. The minimum in the work function is due to depolarization of the dipoles induced when the concentration of adatoms in the chains reaches a critical value. A slow diffusion of adsorbed Cs from the terraces to the step edges is also marked by changes in the neutralization of scattered Na$^+$ and work function over time. The spatial distribution of the conductive charges in the TSS, which are primarily positioned between the first and second atomic layers, is confirmed by comparison of the neutralization of Na$^+$ scattered from Bi and Se.