Guided growth of horizontal topological insulator Bi₂Se₃ nanowires with controlled orientations on various sapphire surfaces

Topological insulators (TIs) have been in the center of theoretically and experimentally research, and are promising for realizing new physical phenomena (such as braiding Majorana fermions) and developing practical applications (such as dissipationless electronic devices, high mobility devices and room temperature spintronics). In order to make a progress in the TIs field, it is desired to find new TIs or exploit new structures. During the past few years, our group has significantly advanced the guided growth approach to produce horizontal NWs with controlled directions and crystallographic orientations. Here we demonstrate the vapor−liquid−solid growth of guided horizontal topological insulator bismuth selenide (Bi₂Se₃) nanowires on different planes of sapphire. Bi₂Se₃, which is a narrow band gap semiconductor that has been studied also for infrared detection and thermoelectrics, was recently proved to be a 3D TI. Thus, angle-resolve photoemission spectroscopy (ARPES) measurements showed the existence of a single Dirac cone in the bandgap of the bulk material. The growth directions of the grown Bi₂Se₃ nanowires are determined by epitaxial and graphoepitaxial relations between the nanowires and the substrate, and can therefore be employed to build new structures. These relations are here demonstrated and characterized by HRTEM.