Protective capping of topological surface states of intrinsically insulating Bi2Te3

Abstract

We have identified epitaxially grown elemental Te as a capping material that is suited to protect the topological surface states of intrinsically insulating Bi 2 Te 3 . By using angle-resolved photoemission, we were able to show that the Te overlayer leaves the dispersive bands of the surface states intact and that it does not alter the chemical potential of the Bi 2 Te 3 thin film. From in-situ four-point contact measurements, we observed that the conductivity of the capped film is still mainly determined by the metallic surface states and that the contribution of the capping layer is minor. Moreover, the Te overlayer can be annealed away in vacuum to produce a clean Bi 2 Te 3 surface in its pristine state even after the exposure of the capped film to air. Our findings will facilitate well-defined and reliable ex-situ experiments on the properties of Bi 2 Te 3 surface states with nontrivial topology.

Gate‐Tunable Transport Properties of In Situ Capped Bi2Te3 Topological Insulator Thin Films

“…On the other hand, the Te 3d 5/2 and Te 3d 3/2 peaks are slightly influenced by this capping procedure since their lineshape peak positions are shifted by ∼ 0.8 eV toward higher binding energies upon the deposition of the Te overlayer. This shoulder has been observed previously and was attributed to elemental Te 11,24 . The XPS data on Te capped film are in agreement with recent in-situ ARPES and four-point probe conductivity data on Bi 2 Te 3 films 11 , which revealed that the surface states of the pristine Bi 2 Te 3 samples are not affected by the Te capping, thus suggesting the Te capping method does not cause a doping of the sample.…”

“…Combining different surface-sensitive in-situ characterization tech-niques, we demonstrated that the surface morphology and electronic band structure of Bi 2 Te 3 are not affected by in-vacuo storage and exposure to oxygen, whereas major changes are observed when films are exposed to ambient conditions. Independently, combined in-situ fourpoint probe conductivity and angle resolved photoemission spectroscopy experiments revealed the bulk insulating properties of Bi 2 Te 3 thin films with metallic surface states 10,11 . In the work of Hoefer et al 10 , the authors also demonstrated that short exposure to air causes the bulk conduction band to be filled with electrons and the conductivity is no longer determined by the surface states alone.…”

Spectroscopic perspective on the interplay between electronic and magnetic properties of magnetically doped topological insulators

“…Before taking the samples out of the growth chamber they were capped with a 3 or 5 nm thick Te protective layer. 25 A list of all the studied samples with relevant details is given in LE-µSR experiments were performed at the µE4 beam line of the Paul Scherrer Institute. 26 The samples were glued using silver paint onto Ni-coated sample plates and mounted on the cold finger of a helium flow cryostat.…”

Preservation of pristine Bi2Te3 thin film topological insulator surface after ex situ mechanical removal of Te capping layer

“…18,19 Refinements of this technique have shown that it is possible to restore pristine surfaces after thermal removal of sputtered Se capping on Bi 2 Se 3 , which was exposed to air for a few hours 20 or thermal desorption of ultra-thin Te capping on Bi 2 Te 3 films after exposition to air for 5 min. 21 A third technique applied to layered van der Waals materials consists of cleaving thin films (thicker than 50 nm) inside the UHV chamber to remove the oxidized surface, exposing a new fresh surface to perform the aimed analysis. 17 However, this procedure changes both film thickness and surface morphology, leading to uncontrollable parameters for surface characterization.…”