(Fig. 5, Supporting Info Figure S4). In order to achieve a high
yield of nanowires, the ratio of molecular precursor to catalyst
was optimized.
For both materials, concentrations used to form high nanowire
yields were typically higher than those used for the growth
of the non-catalyzed nanostructures. At the optimized concentrations,
well-faceted nanowires with a high degree of branching
are grown on the substrates. In the case of PbS, we observe the
presence of a catalyst droplet at the tips of all nanowires
(Fig. 5B), however, such spherical droplets were not observed on
the Cu2S. In previous work on SLS mechanism growth, the
persistence or disappearance of a catalyst droplet has been shown
to vary. For example, even within the same material system
CdSe-Bi, Bi catalyst tips may or may not be found on the
nanowire product depending on cooling conditions.27 In our
studies, at the precursor concentration used to form the Cu2S
via SLS, nanowires with 90 branched morphology do not form
without the presence of a Bi thin film. This is strong evidence for
the SLS mechanism in the formation of the Cu2S branched
structures, even without the presence of a catalyst droplet on the
final product.