Figure 1.
(a) Schematic representation of the interaction volume for in situ nanoparticle growth. The interaction volume is dictated by both the viewing area size and the fluid path length. At low nominal magnification the scan area is large, yielding a large interaction volume, while at higher magnification and identical fluid path length the scan area is relatively small, yielding a smaller interaction volume. (b) Schematic representation of the concentration of aqueous electrons in the interaction volume after a single STEM scan, showing the effect of pixel dwell time and beam current on radical production, while holding the interaction volume constant. (c) Time lapsed series of (cropped) BF-STEM images showing nucleation of silver nanocrystals from 1.0 mM AgNO3. The red outlines indicate particles that are detected by image analysis, while undetected particles are still below the detection threshold. The magnification is M = 100,000x, the frame rate is .33 fps, the dwell time is 5 μs, and the current density if ie = 40 pA, yielding an electron dose rate of 3.37 electrons/Å2 s. The scale bar is 100 nm. (d) The total number of particles (left axis) and the cumulative electron dose (right axis) as a function of time for the images in (c). The vertical dashed line marks the median nucleation induction time, while the horizontal dashed line marks the corresponding median induction dose.