Spatial distribution of topological surface state electrons in Bi2Te3 probed by low-energy Na+ ion scattering

Abstract

Bi 2 Se 3 is a topological insulator whose unique properties result from topological surface states (TSS) in the band gap. Low energy ion scattering can determine the properties of the outermost few atomic layers of a solid. The deposition of Cs helps to reveal that the neutralization of Na + is larger when scattered from surface Se than from Bi. This is caused by the spatial redistribution of the conductive charges in the TSS, which are primarily positioned between the first and second atomic layers. This provides direct experimental evidence of the spatial distribution of the TSS electrons.

The growth of bismuth on Bi2Se3 and the stability of the first bilayer

“…The difference in NFs when there is a single BL deposited shows that the chemical environments above the top and bottom Bi atoms in the first bilayer are different. In general, an upward dipole on surface decreases the local work function and thereby increases the measured NF [41,42]. The higher NF in double alignment than in single alignment indicates there are more electrons accumulated under the top Bi atoms in the first bilayer, which is consistent with the calculation in Ref.…”

Cs adsorption on Bi2Se3

“…Se surface vacancies are produced by Ar + ion bombardment, but there is no evidence of any preference for adsorption at these defect sites. In addition, the neutralization of Na + scattered from Cs-adsorbed surfaces confirms that the spatial distribution of the filled TSS in Bi2Se3 is consistent with calculations [5,6] and similar to that of Bi2Te3 [25,26].…”

“…The dipoles formed by the TSS cause an increase in the Se SSP NF and a decrease in that for Bi. This same effect was observed for Na + scattered from clean Bi2Te3 [25], but it is not apparent for clean Bi2Se3 because it has a higher work function that causes the NFs to both be near zero so that any differences are not large enough to be measured above the noise level. After adsorption of Cs, however, the overall work function of the sample is reduced so that the NFs all increase to values that enables the differences in the Bi and Se SSP NFs to be clearly distinguished.…”

“…This property of alkali LEIS has enabled investigations into the inhomogeneity of the LEP for single crystal surfaces that have spatial variations in the valence electron distribution [21] and for surfaces with submonolayer coverages of adsorbates [22][23][24]. Our previous work using neutralization in alkali LEIS successfully verified the inhomogeneous LEP and spatial distribution of the TSS states in Bi2Te3, which is a similar TI material to Bi2Se3 [25].…”

Halogen Adsorption and Reaction with Bi2(Se,Te)3 and Bi/Bi2(Se,Te)3

“…Single crystal Bi2Se3 and Bi2Te3 boules are grown using a multi-step heating method [44] following the procedures described previously [26,45]. The material cleaves easily along the (0001) plane producing approximately 5 mm diameter samples.…”