Spatially controlled plasmon-induced photopolymerization at the apex of gold nanobipyramids: paving the way for 3D nanofabrication.

In this study, we investigate near-field photopolymerization at the tips of gold nanobipyramids (AuNBPs) under linearly polarized irradiation conditions with femtosecond pulses in the near infrared region. TEM was used to visualize the localisation and spatial extend of the polymer resulting from the near-field photopolymerization. The single-tilt mode in TEM provides 3D information of the position of the nanoparticle on the substrate and the polymer lobes. In particular, we demonstrate that photopolymerization is localized mainly at the tips of AuNBPs, in line with the electromagnetic field distribution expected by simulations. We observed experimentally that when AuNBPs lie on the substrate a facet, asymmetrical polymerization occurred: while polymerization is constrained by the substrate on the side in contact with the surface, we showed the possibility of fabricating a nano-sized polymer volume in 3D near-field photopolymerization. These results illustrate the great control of photopolymerization at the nanoscale and represent a major step towards 3D fabrication at nanometer resolution.