  Light-based nanowelding of metallic nanoparticles is of particular interest
because it provides convenient and controlled means for the conversion of
nanoparticles into microstructures and fabrication of nanodevices. Here, we
demonstrated the wavelength dependence of laser-induced nanowelded shapes of
silver nanoparticles (AgNPs). We observed that the nanowelded microstructures
illuminated by the 405 nm laser only were more branched than those formed with
illumination of both the 405 nm and 532 nm lasers. We quantified this
observation by several compactness descriptors and examined the dependence of
the power of the 532 nm laser. More importantly, to understand the experimental
observations, we formulated and tested a hypothesis by calculating the
wavelength-dependent electric field enhancement due to surface plasmon
resonance of the AgNPs and nanowelded microstructures when illuminated with
lights at the two wavelengths. Based on the different patterns of "hot spots"
for welding AgNPs from these calculations, numerical simulations successfully
"reproduced" the different shapes of nanowelded microstructures, supporting our
hypothesis. This work suggests the possibility of light-based controlling the
shapes of laser-induced nanowelded microstructures of metallic nanoparticles.
This work is expected to facilitate the development of better nanowelding
strategies of metallic nanoparticles for broader applications.
