Stability and Surface Reconstruction of Topological Insulator Bi₂Se₃ on Exposure to Atmosphere

Abstract

The stability of the surface of vacuum-cleaved topological insulator Bi 2 Se 3 single crystals is investigated with high-resolution synchrotron-based photoelectron spectroscopy. While the surface is stable at room temperature in vacuum, a Bi 2 layer always forms at the surface of Bi 2 Se 3 upon even brief (5 min) exposure to atmosphere. This is accompanied by a depletion of selenium in the near surface region and a 1.4 eV decrease in work function. The Bi 2 surface is found to be stable upon return to ultrahigh vacuum conditions but is unstable with prolonged exposure to air, ultimately resulting in two possible different reconstructed surfaces, explaining previous contradictory results on long-term atmosphere exposure of Bi 2 Se 3 .

Formation of the BiAg2 surface alloy on lattice-mismatched interfaces

“…Irrespective of the (p × √ 3)-Bi traces and the Ag film thickness, their energetic positions are always found at (23.70 ± 0.05) eV and (26.75 ± 0.05) eV, being consistent with the reported values for the well-defined BiAg 2 alloy on Ag(111) [21]. At 340 K, the intensity of BiAg 2 core levels decreases and a new spin-orbit split peak (blue) appears at ∼23.95 eV (Bi-5d 5/2 ), i.e., ∼210 meV shifted towards higher binding energy with respect to the energetic position obtained for the BiAg 2 alloy, being now consistent with the reported value for the elemental bismuth [22,23]. This indicates a partial dealloying and the formation of the (2 × 2) superstructure reported in LEED, Fig.…”

Termination of single-crystal Bi2Se3 surfaces prepared by various methods

“…If a chemical reaction was responsible for the termination change, this would explain why these remained 22 Se-terminated. The detection of oxygen on ex situ cleaved surfaces, as well as data widely found in the literature, indicates the possibility of a surface reaction with air [13,15,39]. In addition, scanning photoelectron microscopy shows that step edges oxidize much faster than the basal planes for Bi 2 Te 2 Se [39], leading to the conclusion that step edge densities will have a profound effect on the rate of oxidation.…”

“…The Bi-Bi metallic bonds that were sometimes observed following ex situ cleaving in refs. [9,15] were not detected. This is not unexpected, however, considering that the probability for an ex situ cleaved sample to be Bi-rich is small and there were only three trials in which XPS spectra were collected here.…”

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

“…As more Cs is deposited, the adatoms do not develop higher order LEED patterns, unlike Cs deposited on other materials [12,[19][20][21][22], but instead the pattern gets blurrier. [23]. The work function is found to be uniform within an approximately 5 mm radius around the sample center.…”