Scanning nonlinear optical microscopy, at a resolution of similar to 2 mu m
, was utilized to examine monolayers of alkylthiol-passivated silver nanocr
ystals. Selected regions of the monolayers were irradiated with a pulse tra
in of picosecond 1064 nm laser pulses, and then the second harmonic generat
ion(SHG) response of those monolayers was recorded in a second scan. Two li
thographic processes-one leading to a negative contrast SHG image (observed
for particles <4 nm diameter) and a second leading to a positive contrast
SH G image (observed for larger particles)-were found. These processes are
explained within the context of literature models that account for particle
size dependent energy partitioning.