Near-field microscopy by elastic light scattering from a tip.
We describe ultraresolution microscopy far beyond the classical Abbe diffraction limit of one half wavelength (lambda/2), and also beyond the practical limit (ca. lambda/10) of aperture-based scanning near-field optical microscopy (SNOM). The 'apertureless' SNOM discussed here uses light scattering from a sharp tip (hence scattering-type or s-SNOM) and has no lambda-related resolution limit. Rather, its resolution is approximately equal to the radius a of the probing tip (for commercial tips, a < 20 nm) so that 10 nm is obtained in the visible (lambda/60). A resolution of lambda/500 has been obtained in the mid-infrared at lambda = 10 microm. The advantage of infrared, terahertz and even microwave illumination is that specific excitations can be exploited to yield specific contrast, e.g. the molecular vibration offering a spectroscopic fingerprint to identify chemical composition. S-SNOM can routinely acquire simultaneous amplitude and phase images to obtain information on refractive and absorptive properties. Plasmon- or phonon-resonant materials can be highlighted by their particularly high near-field signal level. Furthermore, s-SNOM can map the characteristic optical eigenfields of small, optically resonant particles. Lastly, we describe theoretical modelling that explains and predicts s-SNOM contrast on the basis of the local dielectric function.
Keilmann
Fritz
F
Abt. Molekulare Strukturbiologie, Max-Planck-Institut für Biochemie, 82152 Martinsried, München, Germany. keilmann@biochem.mpg.de
Hillenbrand
Rainer
R
D004867:Equipment Design; D007089:Image Enhancement / Q000379:methods; D008027:Light; D020527:Microscopy, Scanning Probe / Q000295:instrumentation* / Q000379:methods*; D008962:Models, Theoretical; D036103:Nanotechnology / Q000295:instrumentation / Q000379:methods; D010316:Particle Size; D020349:Surface Plasmon Resonance / Q000295:instrumentation / Q000379:methods