In a typical seed-mediated growth synthesis, a seed solution is prepared
by reduction of HAuCl4 in the presence of a surfactant such as
cetyltrimethylammonium bromide (CTAB) with cold sodium borohydride. A
growth solution consisting of HAuCl4 reduced by ascorbic acid, silver nitrate, and
CTAB. Addition of the seed solution to the growth solution provides nucleation
sites for growing nanorods. The mechanism has yet to be fully elucidated, but
one well-known hypothesis is that the surfactant is used as a stabilizer as well as
a capping agent to preferentially attach to the {100} facets of the seeds. This acts
to retard growth in that direction and to permit elongation on the {111} facets at
the ends of the rods1, 17