In spite of the clear surface-state Dirac cone features in bismuth-based three-dimensional strong topological insulator materials, the Dirac point known as the Kramers point and the topological transport regime are located near the bulk valence band maximum. As a result of a nonisolated Dirac point, the topological transport regime cannot be acquired and there possibly exist scattering channels between surface and bulk states as well. We show that an ideal and isolated Dirac cone is realized in a slab geometry made of Bi2Se3 with appropriate substitutions of surface Se atoms. As an extension of Dirac cone engineering, we also investigate Bi2Se3 ultrathin films with asymmetric or magnetic substitutions of the surface atoms, which can be linked to spintronics applications.
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