Coexisting Bi and Se surface terminations of cleaved Bi2Se3 single crystals

Abstract

Evidence for the coexistence of both Bi and Se terminations of the topological insulator Bi2Se3 is presented that is connected with details of sample storage and cleaving procedures. X-ray photoelectron spectroscopy of the Bi 4f core levels show a lower binding energy component indicative of metallic Bi near the sample surface. Single crystals stored and cleaved in high vacuum predominantly show the usual Se surface termination while those stored in air for long periods of time have a high probability for Bi termination. The different terminations have very different electronic structures as measured by angle resolved photoelectron spectroscopy. Our photoemission studies show the Se-terminated electronic structure can be recovered after annealing at 400 °C.

Termination of single-crystal Bi2Se3 surfaces prepared by various methods

“…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.…”

“…An intact QL would be terminated with Se atoms and have Bi in the second layer. Such a Se-termination has been widely demonstrated for samples cleaved in situ under vacuum [9][10][11]. A previous study from our group had found a Bi-termination, however, and included density functional theory (DFT) calculations which showed that termination by a complete Bi bilayer is energetically more favorable than the Se-termination [12].…”

“…used x-ray photoelectron spectroscopy (XPS) to show that metallic Bi forms at the surface after a 5 min exposure to air, but the surface would either oxidize or revert back to a Se-termination after extended exposure [15]. Hewitt, et al found that both Bi-rich and Se-terminated surfaces are possible after ex situ cleaving with carbon tape, and that the probability for obtaining a Bi-rich surface is 48%, but drops to 25% if the sample is stored in vacuum [9]. Note that a sample with metallic Bi at the surface is labeled here as Bi-rich, instead of Bi-terminated, as it's not always clear if the excess Bi forms an epitaxial overlayer, amorphous film or isolated metallic islands.…”

Surface structure of in situ cleaved single crystal Bi2Se3 measured by low energy ion scattering

“…The QLs are held together by a weak van der Waals force, so that Bi 2 Se 3 is expected to naturally cleave between QL's to reveal a Se-terminated surface. There are, however, different terminations reported in the literature following cleaving, including Se-termination [6][7][8][9], Bi-termination [10,11], oxidized surface [11,12], coexisting Seand Bi-terminations, either Se-termination or Bi-rich surfaces [6], and evolving surfaces [11].…”

Efficient charge-spin conversion and magnetization switching through the Rashba effect at topological-insulator/Ag interfaces

“…An energetically favored heterostructure, Bi2Se3 (1×1)/Ag (1×1), with the selenium termination is adopted [37][38][39]. The ion-electron, electron-electron and van der Waals (vdW) interactions between Ag and Bi2Se3 are included in our model implemented in the Vienna ab initio simulation package (VASP) [24,40,41].…”