High-resolution constant-height imaging with apertured silicon cantilever probes

We present high-resolution aperture probes based on noncontact silicon atom ic force microscopy (AFM) cantilevers for simultaneous APM and near-infrare d scanning near-field optical microscopy (SNOM). For use in near-field opti cal microscopy, conventional AFM cantilevers are modified by covering their tip side with an opaque aluminium layer. To fabricate an aperture, this me tal layer is opened at the end of the polyhedral probe using focused ion be ams (FIB). Here we show that apertures of less than 50 nm can be obtained u sing this technique, which actually yield a resolution of about 50 nm, corr esponding to lambda /20 at the wavelength used. To exclude artefacts induce d by distance control, we work in constant-height mode. Our attention is pa rticularly focused on the distance dependence of resolution and to the infl uence of slight cantilever bending on the optical images when scanning at s uch low scan heights, where first small attractive forces exerted on the ca ntilever become detectable.