Atomic force microscopy silicon tips as photon tunneling sensors: a resonant evanescent coupling experiment.

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.