Cantilever probes with aperture tips for polarization-sensitive scanning near-field optical microscopy

In this paper we present the application of cantilever based sensors combining scanning force microscopy (SFM) and scanning near-field optical microscopy (SNOM). Microstructure technology processes are employed to fabricate probes with reproducible mechanical and optical properties for both SFM and SNOM applications. The cantilever probe allows simultaneous measurement of the sample topography and the optical transmission of samples with high lateral resolution. The probe consists of a hollow metal tip integrated in a conventional silicon cantilever. The pyramidal tip has at its apex an aperture of sub-wavelength dimensions which is used as a confined light source. Because the tip opening angle is 70.5 degrees the extent of the tapering region is in the order of a quarter wavelength, which improves the optical transmission efficiency and avoids thermal effects. The probes were optically characterized. In particular the polarization properties of the optical aperture have been investigated in the far field as well as the near field. Furthermore, preliminary magneto-optical measurements have been performed on a thin garnet film to demonstrate the usefulness of the probes in view of their application in polarization near-field optical microscopy.