Topological Insulator Nanowires and Nanoribbons

Abstract

Recent theoretical calculations and photoemission spectroscopy measurements on the bulk Bi 2 Se 3 material show that it is a three-dimensional topological insulator possessing conductive surface states with nondegenerate spins, attractive for dissipationless electronics and spintronics applications. Nanoscale topological insulator materials have a large surface-to-volume ratio that can manifest the conductive surface states and are promising candidates for devices. Here we report the synthesis and characterization of high quality single crystalline Bi 2 Se 3 nanomaterials with a variety of morphologies. The synthesis of Bi 2 Se 3 nanowires and nanoribbons employs Au-catalyzed vapor-liquid-solid (VLS) mechanism. Nanowires, which exhibit rough surfaces, are formed by stacking nanoplatelets along the axial direction of the wires. Nanoribbons are grown along [11][12][13][14][15][16][17][18][19][20] direction with a rectangular crosssection and have diverse morphologies, including quasi-one-dimensional, sheetlike, zigzag and sawtooth shapes. Scanning tunneling microscopy (STM) studies on nanoribbons show atomically smooth surfaces with 1 nm step edges, indicating single Se-Bi-Se-Bi-Se quintuple layers. STM measurements reveal a honeycomb atomic lattice, suggesting that the STM tip couples not only to the top Se atomic layer, but also to the Bi atomic layer underneath, which opens up the possibility to investigate the contribution of different atomic orbitals to the topological surface states. Transport measurements of a single nanoribbon device (four terminal resistance and Hall resistance) show great promise for nanoribbons as candidates to study topological surface states.Bi 2 Se 3 is a narrow gap semiconductor, previously studied for infrared detectors and thermoelectric applications. 1 Recently, research on Bi2Se3 and related compounds (Bi2Te3 and Sb2Te3) has attracted much interest because they are predicted to be three-dimensional (3D) topological insulators (TIs), a new class of quantum matter possessing conducting surface states with nondegenerate spins. 2 In TIs, the strong spin-orbit coupling dictates robust, nontrivial surface states, which are topologically protected against back scattering from time-reversal invariant defects and impurities. Angleresolved photoemission spectroscopy (ARPES) measurements on bulk single crystals of BixSb1-x, Bi2Se3, and Bi2Te3 have verified the existence of the 3D TI phase. [3][4][5][6][7] In particular, the surface states of Bi2Se3 forms a single Dirac cone inside a large bulk band gap of 0.3 eV, thus being suggested as the reference material for the 3D TIs. 2,4,8 The unique properties of the Bi2Se3 TI may pave the way for dissipationless quantum electronics and room temperature spintronics applications.1 To date, the surface properties of the 3D TIs have been mainly investigated by ARPES measurements on the cleaved surface of bulk crystals. [3][4][5][6][7] Single crystalline nanostructure, on the other hand, offers an attractive alternative system to study the surface sta...

Two-dimensional surface charge transport in topological insulators

“…Following that, the same group used spin-resolved ARPES to measure the spin polarization of the surface states, demonstrating the correlation between spin and momentum. 54 58 and experiments have begun to investigate the transition between the three-and two-dimensional phases in this material. 59 Bi 2 Se 3 has also been studied in a magnetic field, revealing a magnetoelectric coupling 60 and an oscillatory angular dependence of the magnetoresistance.…”

Zigzag GaN/Ga2O3 heterogeneous nanowires: Synthesis, optical and gas sensing properties

“…6-8, 24, 25 Zigzag nanowires (NWs) and nanoribbons can be used as highly electronic and optoelectronic devices. [9][10][11] By contrast, investigations on using zigzag nitrogen oxide NWs for NO gas sensing are few. [26][27][28] Moreover, to the best of our knowledge, the evolution of zigzag GaN/Ga 2 O 3 heterogeneous NWs from changes caused by the on/off frequency process has not been reported thus far.…”

Review of 3D topological insulator thin‐film growth by molecular beam epitaxy and potential applications

“…This review will focus on the recent progress in reference to exploration of new properties of topological insulators. At the current stage, the experimental realizations of TI materials are mainly by chemical vapor deposition (CVD) [15][16][17], bulk Bridgman growth [18][19][20], wet chemical synthesis [9,21], Thin films of V-VI compound semiconductors (Bi 2 Se 3 , Bi 2 Te 3 and Sb 2 Te 3 ) have been synthesized recently as threedimensional topological insulators (TIs). Although these materials have been used as thermoelectric materials for many years, for future studies and applications of the topological surface states, a major bottleneck remains the lack of highquality bulk materials that have very few defects and the Fermi level can be moved to inside the bulk bandgap.…”