Regensburg 2004 – scientific programme

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O: Oberflächenphysik

O 23: Rastersondentechniken II

O 23.8: Talk

Tuesday, March 9, 2004, 17:30–17:45, H36

Apertureless SNOM with vibrating AFM probes — •Ralf Vogelgesang, Ruben Esteban, Alpan Bek, and Klaus Kern — MPI für Festkörperforschung, 70569 Stuttgart

In the so called apertureless Scanning Near Field Optical Microscopy (a-SNOM), strongly localized enhancement of the near fields at the apex of a conical tip probe excited by external radiation is used to achieve spatial resolution of optical surface properties in the range ∼ 10 nm at infrared or visible frequencies.

We use Multiple Multipole (MMP) simulations to quantitatively understand the interaction between the tip and substrate. We study the variations due to changing tip sample distance in the near field and consequently in the scattered far field, i.e., the measurable physical magnitude. For a better understanding of the level of sophistication necessary, different models are considered, ranging from a point dipole in the static case to spheres or a conical tip with spherical apex including retardation. In general two different regions are observed, slowly varying field strengths for distances of several hundred nm or more and rapid increases in field strengths for less than 10 nm. This strongly nonlinear dependence translates into generation of higher harmonics in the scattered far field intensity when the tip-sample distance is varied sinusoidally. Detecting the intensity and phase of these harmonics allows to obtain images of the localized near field interactions essentially free of parasitic linear scattering signatures from the surrounding area. The consideration of different tip and substrate materials is important to interpret and optimize experiments.