Local anodic oxidation (LAO) of Si surfaces deposited with Au nanoislands by electroless plating and Au nanocrystals (∼3 nm) by spin coating has been carried out using a biased AFM tip. Isolated nanoislands and individual nanocrystals exhibited high catalytic activity producing oxide patterns with a height above 13 and 40 nm, respectively, in contrast to 2.5 nm high patterns observed on bare portions of the Si surface. Au nanocrystal aggregates also present on the surface exhibited relatively less activity compared to single nanocrystals. In the case of Au nanocrystal dispersion on the Si surface, etch patterns obtained after a HF wash exhibited depths of 13 and 8 nm with respect to the locations of single nanocrystal and the aggregate, respectively, compared to ∼2 nm trench depth from LAO on the bare surface. Further, nanocrystal-induced etch patterns were much narrower, ∼12 nm. In another experiment, a Au-deposited tip catalytically induced LAO on the bare Si surface with features of ∼6 nm height and the corresponding trenches of ∼2.2 nm. © 2008 American Chemical Society.