Plasmon-Induced Grafting in the Gap of Gold Nanoparticle Dimers for Plasmonic Molecular Junctions

Gold nanoparticle (NP) dimers of various shapes have been fabricated on indium tin oxide (ITO) by electron-beam lithography. The gap separating two NPs was set to 30–50 nm. Oligo(bisthienylbenzene) was then grafted onto these substrates by plasmon-induced diazonium salt reduction. We show that this organic semiconductor can be selectively grafted onto these NPs and that growth is strongly affected by light polarization. When light is polarized in the direction perpendicular to the dimer axis, a 15 nm thick layer of oligo(bisthienylbenzene) is observed on each NP with minimal grafting between them. On the contrary, when light is polarized in the direction of the dimer axis, oligomer deposition occurs mainly between the gold NPs and completely fills the 30–50 nm gap. As a consequence, plasmonic molecular junctions are obtained in a few minutes in a massively parallel process.