Inherent Surface Properties of Adsorbent-Free Ultrathin BiSe Topological Insulator Platelets.

We report on a hydrothermal synthesis of hexagonal ultra-thin BiSe 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 BiSe 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 BiSe 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 BiSe platelets was so clean to enable the occurrence of the localized surface plasmon resonance due to the bulk and topological surface electronic states.