Polarization properties of fully metal coated scanning near-field optical microscopy probes

We have presented a design of silicon cantilever based scanning near-field optical microscopy (SNOM) probes with aluminum coated quartz tips which have been batch fabricated using micromachining technology. The 12 μm high probe tips are made of SiO₂ and fabricated at the end of silicon cantilevers. A hole in the cantilever, located underneath the tip base, permits light insertion and collection through the cantilever. Transmission electron microscopy reveals a 60 nm thick polycrystalline aluminum layer that covers the tip entirely. Still, far-field measurements show the typical polarization properties of conventional SNOM aperture probes. In order to study the mechanism of light transmission through such a tip, theoretical modelling and several experiments were performed.