Dielectric and fluorescent samples imaged by scanning near-field optical microscopy in reflection

Abstract

Dielectric fluorescent samples are imaged by scanning near-field optical microscopy in reflection. A non-metallized tapered fibre tip is used both as an emitter and a detector. Shear force feedback controls the distance between the tip and the sample and gives simultaneously a topographic image of the surface. A direct correlation with the optical image is obtained. We demonstrate that this reflection setup is suitable for dielectric samples. Images in fluorescence have been obtained on Langmuir-Blodgett films. For fluorescence detection the optical contrast is unambiguous, and consequently we estimate the detecting size of the probe at about 200 nm. Operation in reflection opens new possibilities since it allows the study of metallic, thick, opaque or dielectric sample and can be easily combined with a transmission setup. In this way, biological samples can be imaged optically simultaneously in transmission, reflection and with a shear force control.