A model for the mechanism of field interaction at silicon AFM tips in photon tunneling transfer

Silicon AFM tips are used as infra-red evanescent wave converters over an InP surface under ATR illumination. Transmitted light is observed and measured with a camera as a function of the incident angle θ, the observation angle f and the distance to the surface. From these observation it can be concluded that the usual capture model for infinite dielectric surfaces is satisfactorily obeyed. However, the reference intensity Φo varies with θ much more steeply as expected. This discrepancy is explained by the lateral capture of the tip. A theoretical model is proposed which indicates that the length of the tip involved in the conversion process could be as large as 100 nm for small θ.