Phase Transformation of Alternately Layered Bi/Se Structures to Well-Ordered Single Crystalline Bi₂Se₃ Structures by a Self-Organized Ordering Process

Multilayer films composed of alternating layers of Bi and Se[Bi­(4.55 Å)/Se­(6.82 Å)]_<i>n</i> (Bi4Se6), [Bi­(6.13 Å)/Se(12.26) Å]_<i>n</i> (Bi6Se12), and [Bi­(4.86 Å)/Se­(18.46 Å)]_<i>n</i> (Bi4Se18)were fabricated by controlling the layer thickness at the atomic scale using thermal evaporation techniques. After annealing treatment, the Bi4Se18 alternately layered film shows a single phase of Bi₂Se₃ rhombohedral crystalline structure with the characteristic density of single crystal Bi₂Se₃, whereas the Bi6Se12 and Bi4Se6 films show locally disordered Bi₂Se₃ crystalline structure. The effectively controlled layered structure in the as-grown Bi4Se18 film enhances the Bi–Se chemical bonding state. The formation of a layered crystalline structure during the annealing process increased as the thickness of Se increased. After interdiffusion and the crystallization process, alternately layered Bi4Se18 films become stable Bi₂Se₃ single crystals with a continuous and uniform layered structure. Finally, in the Bi–Se system, atomically controlled multilayers with an optimized ratio of each unit layer can be transformed to a perfect single-crystalline structure on oxidized Si with an amorphous phase through a self-organized ordering process