<p>Nucleation underlies the formation of many liquid-phase
synthetic and natural materials with applications in materials chemistry, geochemistry,
biophysics, and structural biology. Most liquid-phase nucleation processes are
heterogeneous, occurring at specific nucleation sites at a solid-liquid
interface; however, the chemical and topographical identity of these nucleation
sites and how nucleation kinetics vary from site-to-site remains mysterious. Here
we utilize <i>in situ</i> liquid cell electron
microscopy to unveil counterintuitive nanoscale non-uniformities in
heterogeneous nucleation kinetics on a macroscopically uniform solid-liquid
interface. Time-resolved <i>in situ</i> electron
microscopy imaging of silver nanoparticle nucleation at a water-silicon nitride
interface showed apparently randomly-located nucleation events at the interface.
However, nanometric maps of local nucleation kinetics uncovered nanoscale interfacial
domains with either slow or rapid nucleation. Interestingly, the interfacial
domains vanished at high supersaturation ratio, giving way to rapid spatially
uniform nucleation kinetics. Atomic force microscopy and nanoparticle labeling
experiments revealed a topographically flat, chemically heterogeneous interface
with nanoscale interfacial domains of functional groups similar in size to those
observed in the nanometric nucleation maps. These results, along with a
semi-quantitative nucleation model, indicate that a chemically non-uniform
interface presenting different free energy barriers to heterogeneous nucleation
underlies our observations of non-uniform nucleation kinetics. Overall, our
results introduce a new imaging modality, nanometric nucleation mapping, and
provide important new insights into the impact of surface chemistry on microscopic
spatial variations in heterogeneous nucleation kinetics that have not been
previously observed.</p>
In Situ Observation of Gold Nanoparticles Self-assembly at the Solid-Liquid Interface Using Liquid-Phase STEM