OBSERVATION OF ANISOTROPIC MIGRATION OF ADSORBED ORGANIC-SPECIES USING NANOSCALE PATCHWORKS FABRICATED WITH A SCANNING TUNNELING MICROSCOPE

A scanning tunneling microscope (STM) operated under ultrahigh vacuum enabled us to observe the migration of the individual formate ion (DCOO-) adsorbed on a TiO2(110) surface. We could remove off the formate ions in a desired area without damage to the substrate, by rastering the STM tip biased at an appropriate voltage. The patchwork of uncovered substrate was then created in the saturated (2 x 1) monolayer of the formate ions. The residual ions outside diffused into the patches driven by the mutual repulsion in the monolayer. Serial STM images revealed the microkinetics of the migration; the transport of the formate anion along the one-dimensional row of Ti cations was an order of magnitude faster than that across the Ti row. These results demonstrate the potential for application of the scanning tunneling microscopy in tailoring nanometer-sized structures in a distribution far from equilibrium and taking advantage of the reconstruction on the surface in kinetic measurements.