Sequential control of catalyst alloying and oxygen-mediated nucleation for continuous synthesis of SnO nanowires floating in the gas phase

Abstract

In floating catalyst chemical vapour deposition (FCCVD), nanotubes or nanowires grow suspended in a gas stream using a catalyst aerosol as they travel through a tubular reactor and are collected at the outlet as macroscopic paper-like networks. The method is continuous, removes the need for substrates and reduces reaction times to seconds. We demonstrate fast growth of SnO nanowires with high selectivity through sequential injection of precursors and carrier gases in order to separately control the stages of precursor decomposition, alloying of Au and Sn, and nucleation and growth as a nanowire of SnO instead of alloy encapsulation by SnOx, all occuring within 10 seconds under continuous flow at atmospheric pressure. Reaction selectivity is monitored in-situ through measurement of nanoparticle mobility in the gas phase to discrimintate undesired homogenous precursor decomposition as quasi-spherical particles from heterogeneous nanowire growth via the vapour-liquid-solid route, offering a tool to accelerate synthesis of new nanowires by FCCVD. The nanowires have a log-normal diameter and length distributions, with means of 11.4 nm and 257 nm, respectively. A mean growth rate of 40 nm/s (max. 107 nm/s) is obtained, substantially times higher than for substrate growth, and limited by precursor incorporation into the catalyst.