Atomic configuration of flat honeycomb lattice structure of bismuthene on Ag(111)

Abstract

Bismuthene, which is the Bi counterpart of graphene, is a promising candidate for the realization of a two-dimensional topological insulator that leads to the development of next-generation spintronic devices. In this study, we examined the atomic configuration of bismuthene grown on an Ag(111) surface at low temperatures using the total-reflection high-energy positron diffraction (TRHEPD) method. Pairs of TRHEPD rocking curves corresponding to the fractional-order spots of bismuthene islands exhibited no substantial differences in their profiles in the low-glancing-angle regions along the [112¯] and [11¯0] azimuths, confirming that bismuthene adopts a flat honeycomb lattice on the Ag(111) surface. Intensity calculations based on dynamical diffraction theory further revealed that the two Bi atoms in the unit cell have equivalent heights (2.48 Å) relative to the underlying Ag(111) layer. The Debye temperatures of bismuthene and Ag in the first layer are 92 and 112 K, respectively, indicating that both atoms experience softening. The structural insights obtained in this study provide a critical foundation for understanding the unique electronic properties of bismuthene and for designing applications in heterostructure devices.