In this work, we report on the ability to write features less than 15 nm in size on nanocrystalline SnO2 by applying negative voltage pulses onto an STM tip. The fact that these features can be erased by scanning with a positive tip bias, and the strong dependence of the apparent height of the features with scanning bias after writing seems to indicate that a degree of charge confinement within the 8 nm nano-crystals is involved. (C) 2004 Elsevier B.V. All rights reserved.