Studies of porous silicon before and during ultraviolet excitation were performed using scanning tunneling microscopy. Images taken during ultraviolet excitation compared with images taken immediately prior to ultraviolet excitation show changes in the size of selective surface features. There is an increase in feature height and a decrease in feature width between the images of nonluminescing and luminescing porous silicon. These drastic effects are a consequence of an increase in available charge carriers in porous silicon, namely, in the quantum wires.