Negligible Surface Reactivity of Topological Insulators Bi₂Se₃ and Bi₂Te₃ towards Oxygen and Water

Abstract

The long-term stability of functional properties of topological insulator materials is crucial for the operation of future topological insulator based devices. Water and oxygen have been reported to be the main sources of surface deterioration by chemical reactions. In the present work, we investigate the behavior of the topological surface states on Bi2X3 (X = Se, Te) by valence-band and core level photoemission in a wide range of water and oxygen pressures both in situ (from 10(-8) to 0.1 mbar) and ex situ (at 1 bar). We find that no chemical reactions occur in pure oxygen and in pure water. Water itself does not chemically react with both Bi2Se3 and Bi2Te3 surfaces and only leads to slight p-doping. In dry air, the oxidation of the Bi2Te3 surface occurs on the time scale of months, in the case of Bi2Se3 surface of cleaved crystal, not even on the time scale of years. The presence of water, however, promotes the oxidation in air, and we suggest the underlying reactions supported by density functional calculations. All in all, the surface reactivity is found to be negligible, which allows expanding the acceptable ranges of conditions for preparation, handling and operation of future Bi2X3-based devices.

Rapid Surface Oxidation of Sb2Te3 as Indication for a Universal Trend in the Chemical Reactivity of Tetradymite Topological Insulators

“…This behavior raises the question of what is the mechanism underlying the fast surface oxidation observed in our experiments, which we discuss below. The fast oxidation observed in the present work distinguishes Sb 2 Te 3 from Bi 2 Te 3, and Bi 2 Se 3 , which we studied earlier 23 . Generally, the oxidation proceeds in several steps, which are:…”

“…Moreover, nanoscale mapping under ambient conditions reveals a 10−100x current enhancement at step-edges as compared to that on terraces 25 . On the other hand, scanning probe microscopy data evidence very similar behavior in the absence of morphology features upon oxidation, resulting in the formation of a flat and uniform oxide layer 23,26 .…”

“…Therefore, we may conclude that CO 2 plays no role in the surface degradation. [23][24][25][26][27] . By analogy with Sb 2 Te 3 the scattering and differences between the published experimental data can be attributed to the fact that the induction period is huge due to the low probability of the elementary chemical reaction event, which occurs on a time scale comparable with or faster than the time scale of experimental exposures.…”

Communication: Surface stability and topological surface states of cleaved Bi2Se3: First-principles studies

“…As a result, their naturally cleaved surfaces are expected to be terminated with the Se or Te with extremely low surface activity toward adsorbates and, subsequently, their TPSS should be highly stable. [6][7][8] However, a time-dependent band bending [9][10][11] and new surface states were observed after cleavage by using angle-resolved photoemission spectroscopy (ARPES). [12][13][14] This "aging effect" was typically assigned to the existence of surface vacancies or impurities, or to slow interlayer relaxations.…”

Surface and interface states of Bi2Se3 thin films investigated by optical second-harmonic generation and terahertz emission

“…All the samples were kept in the air for more than one week before the measurement so that the surface state of Bi 2 Se 3 could interact sufficiently with an atmospheric environment. [20][21][22] We used an 800-nm wavelength wave (x) as fundamental light and detected 400-nm wavelength SH light (2x) in a specular-reflection geometry in which the incident and detection angles (h in and h out , respectively) were 45 from the surface normal, as shown in Fig. 1…”