Near‐field optics on silicon–electrolyte junctions

A technique allowing near‐field photocurrent (PC) mapping of silicon surfaces in contact with an electrolyte is presented. The illumination source is an optical fibre tip with a 100‐nm aperture. A shear force detection system controls the tip–sample distance while scanning the tip across the silicon–electrolyte interface. Topographic and PC images on SiO2/Si mesas both show 300 nm resolution. It is shown that this PC contrast is induced by the tip–topography interaction and hence the PC resolution is limited by the resolution of the topography. Indeed, PC mapping on topography‐less patterned porous‐silicon/silicon samples shows that the lateral resolution is only limited by the aperture size which is of the order of 100 nm.