Structure of a Bi/Bi sub(2) Te sub(3) heteroepitaxial film studied by x-ray crystal truncation rod scattering

We studied structure of a Bi(001)/Bi sub(2) Te sub(3) (001) heteroepitaxial film grown on Si(111) by means of surface x-ray diffraction. We revealed that on top of the Bi sub(2) Te sub(3) (001) film the ~ 7-bilayer-thick Bi(001) film is contracted in the surface plane by ~ 3% and is expanded along the vertical direction by ~ 4% compared with the bulk values. The epitaxial strain supports the realization of the topological phase transition of the Bi film [Hirahara et al., Phys. Rev. Lett. 109, 227401 (2012) (http://dx.doi.org/10.1103/PhysRevLett.109.227401)]. We also revealed structural properties of the Bi sub(2) Te sub(3) (001)/Si(111) interface. The electron density profile in the vertical direction, obtained by the combination of the holographic method and phase retrieval methods, exhibits a wetting layer at the interface. It is also indicated that the bottom two Bi sub(2) Te sub(3) layers act as a buffer layer for further growth of the crystalline film.