In the flow: a finely controlled approach to catalyzed nanowire growth

A breakthrough in semiconductor nanowire synthesis that allows fine control over axial heterostructuring was recently advanced by Hollingsworth and co-workers.1 The report also reveals fascinating mechanistic aspects of catalyzed nanowire growth. Catalyzed wire or whisker growth was discovered by Wagner and Ellis in 1964.2 They found that gold droplets on a silicon substrate catalyze silicon wire growth under chemical-vapor-deposition conditions. Gaseous precursors react at the gold-droplet surfaces, depositing silicon into solution within the gold droplets. The droplets become supersaturated, inducing precipitation of crystalline silicon upon the substrate. As precipitation occurs only at the droplet–silicon interfaces, the silicon crystallites acquire pseudo-cylindrical wire morphologies as they grow upward from the substrate. The gold-catalyst droplets rise elevator-like from the substrate, riding upon the tips of the growing wires. Wagner and Ellis2 named this method ‘vapor-liquid-solid’ or ‘VLS’ growth after the three participating phases: the vaporous precursors, liquid catalyst droplets and solid silicon wires.