Although nanocrystal morphology is controllable using conventional colloi
dal synthesis, multiple characterization techniques are typically nee
de
d to
determine key properties like the nucleation rate, in
duction time, growth rate, an
d the resulting morphology. Recently, researchers have
demonstrate
d growth of nanocrystals by
in situ electron beam re
duction, offering
direct observations of single nanocrystals an
d eliminating the nee
d for multiple characterization techniques; however, they foun
d nanocrystal morphologies consistent with two
different growth mechanisms for the same electron beam parameters. Here we show that the electron beam current plays a role analogous to the concentration of re
ducing agent in conventional synthesis, by controlling the growth mechanism an
d final morphology of silver nanocrystals grown via
in situ electron beam re
duction. We
demonstrate that low beam currents encourage reaction limite
d growth that yiel
d nanocrystals with facete
d structures, while higher beam currents encourage
diffusion limite
d growth that yiel
d spherical nanocrystals. By isolating these two growth regimes, we
demonstrate a new level of control over nanocrystal morphology, regulate
d by the fun
damental growth mechanism. We fin
d that the in
duction threshol
d dose for nucleation is in
depen
dent of the beam current, pixel
dwell time, an
d magnification being use
d. Our results in
dicate that
in situ electron microscopy
data can be interprete
d by classical mo
dels an
d that systematic
dose experiments shoul
d be performe
d for all future
in situ liqui
d stu
dies to confirm the exact mechanisms un
derlying observations of nucleation an
d growth.
Keywords:
d="authors" href="http://pubs.acs.org/action/doSearch?action=search&searchText=In+situ+fluid&qsSearchArea=searchText">In situ fluid; d="authors" href="http://pubs.acs.org/action/doSearch?action=search&searchText=STEM&qsSearchArea=searchText">STEM; d="authors" href="http://pubs.acs.org/action/doSearch?action=search&searchText=nanoparticle+growth&qsSearchArea=searchText">nanoparticle growth; d="authors" href="http://pubs.acs.org/action/doSearch?action=search&searchText=silver+nanoparticles&qsSearchArea=searchText">silver nanoparticles; d="authors" href="http://pubs.acs.org/action/doSearch?action=search&searchText=in+situ+electron+microscopy&qsSearchArea=searchText">in situ electron microscopy; d="authors" href="http://pubs.acs.org/action/doSearch?action=search&searchText=classical+nucleation+theory&qsSearchArea=searchText">classical nucleation theory