Abstract
To preserve the high quality topological surface state after air exposure without degradation, it is crucial to identify an effective capping layer. In this study, we report an effective capping layer obtained by crystallizing Se. Upon extended exposure to ultrahigh vacuum or humid air, we show by using x-ray photoemission spectroscopy that the stability and resistance to oxidation of crystalline Se capping layers are superior to those of the amorphous Se capping layer, which has been commonly used by current communities. Furthermore, time-dependent Hall measurements showed that crystalline Se capping layers had a much stronger ability to sustain the intrinsic transport properties of Bi2Se3.
Highlights
Topological insulators (TIs), a new form of quantum matter, attract much attention in recent years because of the unique surface states protected by the time-reversal symmetry.[1,2] Many exciting physics are realized, for example, a magnetically doped TI film opens an energy gap at the Dirac point, leading to the emergence of massive Dirac fermions displaying extraordinary phenomena such as the quantized anomalous Hall effect,[3] axion electrodynamics, and an image magnetic monopole.[4]
Because of the very low sublimation temperature of selenium, a method that involves amorphous selenium capping and thermal de-capping has been used to protect the films of selenides such as ZnSe and Bi2Se3.9,10 This method is used for the fabrication of TI-based devices for spintronics
In the Py/Bi2Se3 hetero-structure for spin-torque ferromagnetic resonance, the critical topological surface state of Bi2Se3 is preserved by the amorphous selenium capping layer before depositing Py.[11]
Summary
Topological insulators (TIs), a new form of quantum matter, attract much attention in recent years because of the unique surface states protected by the time-reversal symmetry.[1,2] Many exciting physics are realized, for example, a magnetically doped TI film opens an energy gap at the Dirac point, leading to the emergence of massive Dirac fermions displaying extraordinary phenomena such as the quantized anomalous Hall effect,[3] axion electrodynamics, and an image magnetic monopole.[4]. After observing the special rod-like surfaces of c-Se layers on Bi2Se3 films, we further used the HR-XRD and HR-TEM to study the crystal structure of these bilayer samples. A small signal in the patterns of 30 nm a-Se/Bi2Se3 sample stored in an UHV chamber for (e) 7 days; (f) 14 days; (g) time-dependent peak area ratio between Bi–Se bonding and Se–Se bonding; (h) STM spectrum of Bi2Se3 after the removal of the c-Se layer via heating to 100 ◦C for 20 min.
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