The drive towards nanotechnology has highlighted the need to engineer the properties of surfaces in unprecedented detail. Here, we report the modification of nanocrystalline SnO2 surfaces using the tip of a scanning tunneling microscope (STM) to inject electrons into individual 8 nm SnO2 nanocrystals. The surface displays a characteristic consistent with charge retention within the grains producing dramatic enhancements in the effective height of the nanoparticles, as observed by STM imaging. This allows the production of modified surfaces where patterns can be written onto a surface with a spatial resolution limited by the size of tip and the nanoparticles, 8 nm in this case. It is also possible to selectively erase the features on the surface using the STM tip under reverse bias. The pattern remains for up to three weeks and therefore opens the door to applications such as patterned nanoscale catalysis, molecular docking, and even ultrahigh density analog data storage. (C) 2004 American Vacuum Society.