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For three-dimensional (3D) topological insulators that have a layered structure, strain was used to control critical physical properties. Here, we show that tensile strain decreases bulk carrier density while accentuating transport of topological surface state using temperature-dependent resistance and magneto-resistance measurements, terahertz-time domain spectroscopy and density functional theory calculations. The induced strain was confirmed by transmittance X-ray scattering measurements. The results show the possibility of reversible topological surface state device control using structural deformation.

In a three-dimensional topological insulator Bi2Se3, a stress control for band gap manipulation was predicted but no systematic investigation has been performed yet due to the requirement of large external stress. We report herein on the strain-dependent results for Bi2Se3 films of various thicknesses that are grown via a self-organized ordering process. Using small angle X-ray scattering and Raman spectroscopy, the changes of d-spacings in the crystal structure and phonon vibration shifts resulted from stress are clearly observed when the film thickness is below ten quintuple layers. From the UV photoemission/inverse photoemission spectroscopy (UPS/IPES) results and ab initio calculations, significant changes of the Fermi level and band gap were observed. The deformed band structure also exhibits a Van Hove singularity at specific energies in the UV absorption experiment and ab initio calculations. Our results, including the synthesis of a strained ultrathin topological insulator, suggest a new direction for electronic and spintronic applications for the future.

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Multilayer films composed of alternating layers of Bi and Se[Bi(4.55 Å)/Se(6.82 Å)] n (Bi4Se6), [Bi(6.13 Å)/Se(12.26) Å] n (Bi6Se12), and [Bi(4.86 Å)/Se(18.46 Å)] n (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.