Surface properties of topological insulator Bi₂Se₃ nanoparticles separated by impedance spectroscopy

We have separated the surface and bulk electrical properties of the Bi₂Se₃ nanoparticles by means of impedance spectroscopy. An equivalent circuit analysis of the complex impedance data comprising two separate resistance components, R_B and R_S, and two separate inductance components, L_B and L_S, enabled us to separate the bulk and surface properties of the topological insulator. One of the resistance components, R_S, attributed to the surface, showed no temperature dependence, whereas the other, R_B, attributed to the bulk, showed a weak metallic behavior. With increasing surface-to-bulk ratio by mixing with insulating Al₂O₃ nanoparticles up to the ratio of 1:1, the surface resistivity showed decrease up to ∼70%, whereas the bulk resistivity showed increase up to ∼150%. While the bulk state showed increasing electrical resistivity up to 200% with aging up to 30 days, the surface state resistivity did not show an aging effect.