Synthesis of topolgical insulators on hexagonal boron nitride

Abstract: Graphene and topological insulators (TIs) have recently become the subject of intense research for their unique band structure which allows for massless Dirac fermions in the material [1]. This allows for the formation of artificial particle quantum dots, an exciting strategy for probing relativistic regime quantum physics [1]. This phenomenon has been studied using Scanning Tunneling Microscopy (STM) in the 2-D material graphene which has similar nontrivial band topology to what is present in the surface states of a 3-D topological insulator [1, 2]. To study these quantum phenomena in the STM on topological insulators, controlled deposition of a TI on hexagonal boron nitride (hBN) is needed for proper gating of the material. Using Molecular Beam Epitaxy (MBE), elements of a TI can be deposited layer by layer to create a thin film version of a material which can be synthesized on hBN. Different strategies to grow good TIs on hBN were considered including which topological material and capping layer material to use. Samples were first grown on Al₂O₃ to ensure that the growth and capping process functioned as expected before moving on to growth on hBN mounted on SiO₂ . Samples with good reflection high energy diffraction (RHEED) patterns were capped with a material in vacuum and then measured using x-ray diffraction (XRD) to determine how the crystallographic structure of the film aligned with the expected values for each material grown. The films were then placed back into the MBE to remove their capping layer and recover the surface of the film. It was found that Bi₂Se₃ is a promising material for the purposes of this sythesis since it can be safely capped with selenium and removed in order to preserve surface states when transferring between the MBE and STM.