Long-wave-infrared near-field microscopy

We have extended scanning near-field optical microscopy to work at long wavelengths with sub-Gun resolution. This allows to exploit the rich spectroscopic signatures of vibrations and other low-energy excitations for nano-scale imaging. The experiment uses an "apertureless" metal probe tip which at the same time serves as force and tunneling probe tip to acquire the surface topography. The applied microwave or infrared wave generates an enhanced longitudinal field at the tip apex. The tip scattering is recorded with a resolution of about 100 nm, a limit given by the tip diameter. Surface-enhanced infrared absorption contrast is observed as predicted by a model which treats the combined scattering of the tip dipole together with its mirror dipole in the sample.