Structure determination of flat honeycomb Bi grown on Ag(111) by low-energy electron diffraction

<p>Bismuthene is a two-dimensional material with a honeycomb structure of Bi. Because Bi is heavy element(Z=83) with a strong spin-orbit coupling (SOC), bismuthene is considered to be a two-dimensional topological insulator possessing a huge nontrivial gap [1], [2], [3].</p><p></p><p>Recently, a honeycomb structure of bismuthene grown on Ag(111) has been reported [1], where Bi was deposited at low temperatures. The atomic structure and topological edge states of the synthesized ultraflat bismuthene are observed at the atomic scale using STM/STS. This experiment reported that the honeycomb structure is completely flat with a lattice constant of around 5.7 Å [1]. The electronic structure of this flat bismuthene with honeycomb structure on Ag(111) was elucidated by angle-resolved photoemission spectroscopy using synchrotron radiation [4]. However, the structure determination of the honeycomb bismuthene has not been performed yet. </p><p></p><p>We examined the atomic structure of the honeycomb bismuthene using dynamical low-energy electron diffraction (LEED) analysis. Intensity-voltage I(V) curves have been measured on (2×2)-Bi grown on Ag(111) at about 180 K. We have found that the flat honeycomb structure of Bi shown in Fig.1 reproduces the experimental IV curves well, and that two Bi in the unit cell lay on the same plane within an experimental error. The layer distance between Bi and Ag is 2.43 Å, shorter than that for Bi/SiC (2.75 Å) [3]. The short layer distance in Bi/Ag would account for the strong interference between Bi p-states and Ag substrate.</p><p></p><p>[1] S. Sun et al., ACS Nano, 16, 1436, (2022).</p><p>[2] M. Zhou et al., Proc. Natl. Acad. Sci. U.S.A., 111, 14378, (2014).</p><p>[3] F. Reis et al., Science, 357, 287, (2017).</p><p>[4] K. Takahashi et al., Phys Rev B, 108, L161407, (2023).</p>