A technique allowing near-field photocurrent (PC) mapping of silicon surfac
es 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 sho
w 300 nm resolution. It is shown that this PC contrast is induced by the ti
p-topography interaction and hence the PC resolution is limited by the reso
lution of the topography. Indeed, PC mapping on topography-less patterned p
orous-silicon/silicon samples shows that the lateral resolution is only lim
ited by the aperture size which is of the order of 100 nm.