We report a near-field optical microscopy experiment at lambda = 10.6 microm, using an apertureless metallic tip functioning simultaneously in the atomic force microscopy tapping mode. The 17-nm optical resolution (lambda/600) that we achieved confirms the validity and the potential of this concept for numerous applications.

Strong electric-field enhancements at the apex of a tungsten tip illuminated by an external light source were recently predicted theoretically. We present an experimental study of the dependence of this effect on the polarization angle of the incident light. It is shown that the intensity of the light scattered by the tungsten tip of an apertureless scanning near-field optical microscope is 2 orders of magnitude higher when the incident light is p polarized than when it is s polarized. This experimental result is in good agreement with theoretical predictions and provides an easy way to test the quality of the tips.

In this letter, we demonstrate the ability of our reflection mode scanning near-field optical microscope functioning in the mid-infrared to reveal infrared dielectric contrast in absence of any topographical contrast. This contrast is induced by local structures prepared by low energy boron implantation in silicon.

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