抄録
Bi2Se3 has a layered structure with a unit of -Se-Bi-Se-Bi-Se- five layers (one quintuple layer (QL)) and the QLs are weakly bound together by van der Waals forces. Bi2Se3 is one of the typical three-dimensional topological insulators, which have a bulk band gap with protected surface states on their surface due to the spin-orbit interaction and time-reversal symmetry. There exist spin-momentum-locked surface states, which constrain the spin orientation perpendicular to the electron momentum. When a spin current flows through the surface state, the spin current is converted into an electric current, which is known as the inverse Edelstein effect and is expected to have applications in spintronics. We have developed a spin-polarized atomic hydrogen beam [1] that can select a single electron spin state. This beam is expected to enable directly inject spin currents on topological insulator surfaces without a ferromagnetic interface as in spin pumping.
First, we conducted the analyses of structural changes and hydrogen desorption characteristics of atomic hydrogen exposed Bi2Se3 thin films. Bi2Se3 thin films with a thickness of about 100 nm were epitaxially grown on Si(111) substrates by MBE [2] and exposed to atomic hydrogen at 300 K and 90 K. LEED results showed that the intensity of the spots decreased after atomic hydrogen exposure, which indicated that the crystallinity decreased. By annealing at around 570K, the crystallinity was restored. LEED I-V and the spot-to-spot distance showed no interlayer and intralayer relaxation in the Bi2Se3 thin film. The TDS spectrum of Bi2Se3 films after the atomic hydrogen exposure showed desorption peaks of hydrogen selenide and a small amount of bismuth (hydride) in addition to hydrogen. The results indicated that exposure to atomic hydrogen caused the etching of the Bi2Se3 thin film. In the case of atomic hydrogen exposure at 295 K, one desorption peak was observed, whereas at 90 K, an additional peak appeared on the low temperature side. Based on the LEED and TDS results and the previous theoretical study [2], it is suggested that atomic hydrogen exposure to Bi2Se3 at 295 K results in hydrogen adsorption only on the surface, while at 90 K, hydrogen intercalation between the QLs occurred in addition to hydrogen adsorption. Finally, we report on the results of spin injection into Bi2Se3 thin films using a spin-polarized hydrogen atom beam.
References
[1] Y. Nagaya, et. al., J. Chem. Phys. 155, 194201 (2021).
[2] Lee, K.W, Lee, C.E. Sci Rep 10, 14504 (2020).
