Laser-induced, in situ, nanoparticle shell synthesis in polymer matrix nanocomposites

This work investigates processes involved in the patterning and production of structured nanoparticles in polymer matrix nanocomposites using femtosecond laser irradiation. An in situ, chemical vapor deposition process was used to synthesize silver nanoparticles in the bulk of an optically transparent polytetrafluoroethylene-co-hexafluoropropylene polymer matrix. The strong optical absorption at the surface plasmon resonance frequency was used to selectively irradiate and photothermally heat the material near particles using femtosecond laser pulses. Having species for chemical vapor deposition in the near-particle environment allows for localized decomposition of the precursor species via unimolecular reactions. Decomposition products can subsequently participate in the production of a variety of core-shell nanostructures. The overall process is demonstrated using femtosecond, photothermal heating of silver nanoparticles to decompose tungsten hexacarbonyl in the polymer matrix leading to the formation of tungsten oxide shells surrounding the silver. For this system, a 40 nm red shift of the surface plasmon resonance was measured. Control of the spatial and temporal characteristics of the excitation source allows for synthesis of nanocomposites with a high degree of control over the location, composition and size of nanoparticles in a polymer matrix resulting in patterned materials with continuously variable properties.