Enhancing the resolution of scanning near-field optical microscopy by a metal tip grown on an aperture probe

We show improvement of the optical and topographical resolution of scanning near-field optical microscopy by introducing a “tip-on-aperture” probe, a metallic tip formed on the aperture of a conventional fiber probe. The tip concentrates the light passing through the aperture. Thus the advantages of aperture and apertureless scanning near-field optical microscopy are combined. Tips are grown by electron beam deposition and then covered with metal. Fluorescent beads are imaged with a resolution down to 25 nm (full width at half maximum) in the optical signal. The near-field appears strongly localized within 5 nm in z direction, thus promising even higher resolution with sharper tips.