Physical Vapor Deposition Growth of Topological Insulator Nanostructures

Nanostructures consisting of strong topological insulators are of interest for the fabrication of devices in which surface state transport is dominant. We report Bi$_2$Se$_3$ nanoribbon and nanoplatelet growth using a multi-zone furnace.\footnote{D. Kong \textit {et al.}, Nano Lett. \textbf{10}, 329 (2010).} Nanoribbons are grown by the vapor-liquid-solid method, using Au nanoparticles or Au thin films ($\sim$5 nm) as catalysts, while nanoplatelets are grown on bare silicon. We systematically vary the growth parameters, including the temperatures of the powdered Bi$_2$Se$_3$ precursor and growth substrate, the growth pressure and duration, the rate of the Argon carrier gas flow, size of the gold catalyst, and the quantity of Bi$_2$Se$_3$ source material. Typical nanoribbon growth occurs at 450$^\circ$C and 350 Torr, with the precursor held at 530$^\circ$C in an Argon carrier gas flow rate rate of 140 sccm. Typical platelet growth occurs at lower pressures and temperatures. High resolution transmission electron microscopy, diffraction, and energy dispersive x-ray analysis are used to characterize the synthesized structures.