Stearic acid films have been deposited on single crystalline TiO2 (1 1 0) substrates by vacuum evaporation. No changes are seen in AFM topographic images of the stearic acid films after the scan at a bias voltage of - 10 to 10 V in the dark. Similarly, ultraviolet irradiation at a bias voltage < 0.0 V brings about no changes of the AFM topographic images. In contrast, a rectangular hole with the size of 200 nm x 200 nm is formed in the stearic acid film after the scan at 10 V under ultraviolet irradiation. No current flows on the stearic acid film, whereas an appreciable current flows at -2.0 Vat the rectangular hole. The formation of the rectangular hole results from the field-assisted photocatalytic decomposition of the stearic acid film by AFM. (c) 2004 Elsevier B.V. All rights reserved.