RESUMEN
Atomic-force SiN probe tips (atomic-force microscopy) can be conveniently used for scanning-tunnelingoptical-microscopy experiments because of their transparency in the visible domain. They are known to provide a satisfying transmission yield and spatial resolution in spite of their complex structural shape. Nevertheless the photon collection mechanism is not so clearly understood. We give some experimental information on the conversion of the evanescent waves into a propagating mode; we show experimentally (1) that optical coupling satisfactorily obeys a classical global and macroscopic dielectric model, and (2) that the collected photons dominantly follow the photon momentum conservation rule that makes these devices directionally selective.
RESUMEN
Evanescent wave conversion by transparent dielectric nanoprobes has long been achieved in photon scanning tunneling microscopy experiments. Nevertheless, the exact mechanism (i.e., resolution limit) of this optical interaction is not satisfactorily explained theoretically nor evidenced experimentally. We study the ability of doped silicon atomic force microscopy tips to capture infrared near-field waves standing at the flat surface of a semiconductor (semi-insulating InP) material. It is shown that, unlike silicon nitride tips previously studied, the transmitted intensity of these silicon tips does not obey the classical frustrated total internal reflection model but a more complex dependence that involves a resonant tunneling transfer. An explanation is proposed that follows the theoretical predictions for the electromagnetic coupling between subwavelength objects.