title: Gold nanoparticle tips for optical field confinement in infrared scattering near-field optical microscopy.
abstract: We report on the implementation of metal nanoparticles as probes for scattering and apertureless near-field optical investigations in the mid-infrared (mid-IR) spectral regime. At these wavelengths, an efficient electric-field confinement is necessary and achieved here through a gold metal nanoparticle of 80 nm in diameter (Au80-MNP) acting as the optical antenna. The Au80-MNP is attached to a standard AFM cantilever used as the spatial manipulator. When approached to a sample surface while being illuminated with an infrared beam, the Au80-MNP produces a considerably improved spatial confinement of the electric field compared to an ordinary scattering AFM tip. We demonstrate here the confinement normal to the sample surface by making use of a sample-induced phonon polariton resonance in a ferroelectric lithium niobate sample. Our experimental findings are in very good agreement with the quasistatic dipole model and show improved optical resolution via well-selected antenna particles.
authors.affiliation: Institute of Applied Photophysics, Technische Universität Dresden, 01062 Dresden, Germany. marc.tobias.wenzel@iapp.de
authors.forename: Marc Tobias
authors.initials: MT
authors.lastname: Wenzel
authors.forename: Thomas
authors.initials: T
authors.lastname: Härtling
authors.forename: Phillip
authors.initials: P
authors.lastname: Olk
authors.forename: Susanne C
authors.initials: SC
authors.lastname: Kehr
authors.forename: Stefan
authors.initials: S
authors.lastname: Grafström
authors.forename: Stephan
authors.initials: S
authors.lastname: Winnerl
authors.forename: Manfred
authors.initials: M
authors.lastname: Helm
authors.forename: Lukas M
authors.initials: LM
authors.lastname: Eng
mesh_terms: D003198:Computer Simulation; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006046:Gold / Q000737:chemistry*; D007089:Image Enhancement / Q000295:instrumentation*; D007259:Infrared Rays; D018625:Microscopy, Atomic Force / Q000295:instrumentation* / Q000379:methods; D008962:Models, Theoretical; D053758:Nanoparticles / Q000737:chemistry*; D012542:Scattering, Radiation; D013055:Spectrophotometry, Infrared / Q000295:instrumentation*; D014159:Transducers
chemical_list: D006046:Gold