Local modification of self-assembled monolayers by a photocatalytic probe

We demonstrate a novel nanolithography method based on the photocatalytic decomposition of the self-assembled monolayer (SAM) near a TiO2-coated probe. The TiO2 film was deposited on Ti-Pt coated Si probes by plasma sputtering. After annealing at 500 degrees C in air for 2 hr, the film was in the anatase phase, according to examination by Raman and X-ray diffraction spectra. Island-structured octadecyltrichlorosilane (OTS) partial monolayers on glass were used as the substrates. When the photocatalytic probe was illuminated by ultra-violet light, the modification occurred on the near OTS SAM islands. No change was observed on the exposed oxide surface between OTS islands. Without UV illumination, no modification occurred on OTS. Thus, the modification of the OTS surface is related to the photocatalytic reaction. A line width as small as 60 nm was achieved and observed by lateral force microscopy (LFM). The diffusion of reactive oxygen species were also observed from the remote photodecomposition of the OTS monolayer. These results should be beneficial to the development of hierarchically constructed nanolithography.