Inherent Surface Properties of Adsorbent-Free Ultrathin Bi₂Se₃ Topological Insulator Platelets

We report on a hydrothermal synthesis of hexagonal ultra-thin Bi₂Se₃ platelets, which was performed without any organic reactants. The synthesis resulted in the particles with a surface, clean of any organic adsorbents, which was confirmed with a high-resolution transmission electron microscopy, zeta-potential measurements and thermogravimetric measurements coupled with a mass spectroscopy. Due to the absence of the adsorbed organic layer on the Bi₂Se₃ platelet surface, we were able to measure their inherent surface and optical properties. So far this has not been possible as it has been believed that such hexagonal Bi₂Se₃ platelets can only be prepared by a solvothermal synthesis, for which it was unable to avoid the organic surface layer. Here we explain the mechanism behind the successful hydrothermal synthesis and show a striking difference in zeta potential behaviour and UV-vis absorption characteristics caused by the adsorbed layer. The surface of the hydrothermally synthesized Bi₂Se₃ platelets was so clean to enable the occurrence of the localized surface plasmon resonance due to the bulk and topological surface electronic states.