title: Antenna-mediated back-scattering efficiency in infrared near-field microscopy.
abstract: We evaluate the efficiency of back-scattering, eta(B), from a standard cantilevered AFM probe contacting a flat sample, and also the back-scattering phase. Both quantities are spectroscopically determined over a broad 9-12 mum wavelength range by coherent frequency-comb Fourier-transform spectroscopy (c-FTIR). While Fresnel reflectivity contributes a key factor with the SiC Reststrahlen edge at 975 cm(-1)as previously documented, we observe spectral effects ascribable to antenna resonances involving the shaft, cantilever, and sample. Most conspicuous is strong (eta(B) = 13%), resonant back-scattering at 955 cm(-1), a frequency that suggests the involvement of surface-phonon-polariton excitation, when the tip probes the area near a SiC/Au boundary. The probe's antenna properties are elucidated by numerically simulating the near fields, the fields in the radiation zone, and the far-field scattering distributions. The simulations are performed for a realistic tip/sample configuration with a three-orders-of-magnitude scale variation. The results suggest a standing-surface-plasmon-polariton pattern along the shaft, as well as far-field antenna lobes that change with the sample's dielectric properties.
authors.affiliation: Max-Planck-Institut für Biochemie & Center for NanoScience, Martinsried, München, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Brehm
authors.forename: A
authors.initials: A
authors.lastname: Schliesser
authors.forename: F
authors.initials: F
authors.lastname: Cajko
authors.forename: I
authors.initials: I
authors.lastname: Tsukerman
authors.forename: F
authors.initials: F
authors.lastname: Keilmann
mesh_terms: D003198:Computer Simulation; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007259:Infrared Rays; D008027:Light; D018625:Microscopy, Atomic Force / Q000295:instrumentation* / Q000379:methods*; D008962:Models, Theoretical; D012031:Refractometry / Q000295:instrumentation*; D012542:Scattering, Radiation