title: Infrared imaging of single nanoparticles via strong field enhancement in a scanning nanogap.
abstract: We demonstrate nanoscale resolved infrared imaging of single nanoparticles employing near-field coupling in the nanoscopic gap between the metal tip of a scattering-type near-field optical microscope and the substrate supporting the particles. Experimental and theoretical evidence is provided that highly reflecting or polariton-resonant substrates strongly enhance the near-field optical particle contrast. Using Si substrates we succeeded in detecting Au particles as small as 8 nm (<lambda/1000) at midinfrared wavelengths of about lambda=10 microm. Our results open the door to infrared spectroscopy of individual nanoparticles, nanocrystals, or macromolecules.
authors.affiliation: Nano-Photonics Group, Max-Planck-Institut für Biochemie, 82152 Martinsried, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Cvitkovic
authors.forename: N
authors.initials: N
authors.lastname: Ocelic
authors.forename: J
authors.initials: J
authors.lastname: Aizpurua
authors.forename: R
authors.initials: R
authors.lastname: Guckenberger
authors.forename: R
authors.initials: R
authors.lastname: Hillenbrand