Catalyst-free Growth of Single Crystalline Bi₂Se₃ Nanostructures for Quantum Transport Studies

Abstract

In this work we report on the growth of single crystalline Bi 2 Se 3 nanostructures (nanoribbons, nanoflakes, and nanowires) by catalyst-free decomposition sublimation in sealed silica ampules. The nanostructures directly grow on Si/ SiO 2 substrates by a vapor−solid growth mechanism and show high degree of crystallinity with dimensions of >10 μm in length and simultaneously <10 nm in height (nanoribbons). In order to optimize the growth process in a reproducible way, thermodynamic calculations were realized. The high quality of as-grown nanostructures was confirmed by transmission electron microscopy including selected area electron diffraction as well as electrical transport measurements. Our electrical transport data are evidence, on the one hand, of the high crystal quality and efficiency of the synthesis by decomposition sublimation. On the other hand, the catalyst-free approach offers the chance to investigate crystals with high purity and to measure surface state properties. ■ INTRODUCTIONRecently, topological insulators (TI) have attracted great interest in the physics community, due to their unique surface states. Topological insulators exhibit a band gap in the bulk but have gapless edge states or metallic states on their surface. The surface states are stable against nonmagnetic disorder and protected by time-reversal symmetry (TRS). Moreover surface states exhibit fascinating electronic properties since they host Dirac Fermions with a locked spin-momentum behavior. These characteristics allow investigation of new physical phenomena which are specific to three-dimensional (3D) TI's surface states. 1−3 TI were theoretically predicted 4−6 and experimentally confirmed for the 3D-TI Bi 2 Se 3 and Bi 2 Te 3 by angle-resolved photoemission spectroscopy (ARPES) 7,8 and electrical transport measurements. 9,10The observation of quantum oscillations known as Shubnikov−de Haas (SdH) 11,12 oscillations allows a quantitative and systematic investigation of the two-dimensional (2D) surface states and bulk states by the precise determination of the Fermi wave vector k F of a given charge carrier population. Nevertheless, crystals with a very high quality are required in order to study quantum oscillations by electrical transport. Nanostructures are preferred for the specific study of the surface states, because they have many advantages compared to their bulk counterpart. Nanostructures of TI materials show a wide variety of morphologies, for instance, nanowires, nanotriangles, and nanoribbons. The large surface-to-volume ratio of nanostructures in comparison to the bulk material allow studies of surface effects 13 as well. The natural doping in Bi 2 Se 3 due to the presence of Se-vacancies leads to a contribution of the bulk carrier density to the conductivity. Therefore, for investigations of the surface states, ultrathin layers of Bi 2 Se 3 must be prepared. 14 Several methods for the fabrication of TI nanostructures are reported, for instance, mechanical exfoliation, 15,16 molecular beam epitaxy (MBE), 17−19 and ...

Weakly-coupled quasi-1D helical modes in disordered 3D topological insulator quantum wires

“…The synthesis of single-crystalline Bi 2 Se 3 and Bi 2 Te 3 nanostructures was realized by catalyst-free vapor transport in a vacuum sealed silica tube with two compartments separated by a bottleneck62. One chamber contains a Bi 2 Se 3 or Bi 2 Te 3 powder (Sigma-Aldrich) and the other a p ++ -Si/SiO x substrate.…”

Surface structure promoted high-yield growth and magnetotransport properties of Bi2Se3 nanoribbons

“…A promising approach to access the surface effects of the TIs is to reduce the size of material down to the nanoscale, thus increasing the surface to volume ratio. Nanostructures prepared by different techniques, such as chemical vapour deposition (CVD) 7 , sonochemical 8 and solvothermal 9 methods, catalysed vapour-liquid-solid 3,10,11 and catalyst-free physical-vapour deposition (PVD) 12–14 have been studied. However, most of the listed techniques have drawbacks associated with surface contamination of the nanostructures due to catalyst residues or low-crystalline structure due to the low process temperatures.…”

Band Bending Inversion in Bi2Se3 Nanostructures

“…This study underlines the importance of controlling the surfaces quality, in addition to solely reducing the bulk residual doping, in order to study only the TSS. The samples studied in this paper are monocrystalline Bi 2 Se 3 nanostructures grown by Chemical Vapor Transport (for growth details see 28 ). Cr/Au contacts were prepared using standard ebeam lithography and metal lift-off, following an in-situ smooth Ar-ion etching to achieve good ohmic contacts.…”