Synthesis and Characterization of Uniform Nanowires of Trigonal Selenium

This article describes a soft, solution-phase approach to the large-scale synthesis of uniform nanowires of trigonal selenium (t-Se) with lateral dimensions controllable in the range of ∼10 to ∼800 nm, and lengths up to hundreds of micrometers. These highly anisotropic, one-dimensional (1D) nanostructures were directly nucleated and grown from aqueous solutions without the help of any physical templates, such as channel-like structures etched in porous materials, or scaffolds assembled from surfactants or block-copolymers. The 1D morphology of the product was solely determined by the linear characteristics of the building blocks—i.e., the extended, helical chains of atoms contained in the crystalline lattice of t-Se. A blue shift was observed for the bandgap and interchain transition of these nanowires when their diameters were reduced from ∼32 to ∼10 nm. The photoconductivity of individual nanowires has also been measured using the four-probe method, and an increase by ∼150 times was found when the sample was taken from the dark and exposed with ∼3 μW μm–2 tungsten light. Since no exotic seeds were involved in this synthetic process, every nanowire (including both ends) should be made entirely of pure selenium, crystallized in the trigonal phase. We believe the protocol described here can be scaled up for the high-volume production of t-Se nanowires that can subsequently serve as the physical or chemical templates to generate 1D nanostructures of various kinds of functional materials. The synthetic strategy itself, may also be extendable to other systems containing chain-like building blocks. The single crystallinity and absence of kinks and other related defects in these nanowires should make them particularly useful in fabricating nanoscale electronic, optical, or mechanical nanodevices.