Near-field observation of selective photomodification in fractal aggregates

Summary form only given. Optical properties of metal fractal nanocomposites consisting of monomers with high polarizability are determined to a large extent by the localized dipolar modes with high Q-factors. The localized optical modes ("hot spots") of silver colloid aggregates were directly observed with the help of photon scanning tunneling microscope (PSTM). These modes arise because of light-induced interactions between monomers in fractals, and the most important is interaction between closely located monomers. There are many different local configurations of monomers in a fractal, so eigenmodes cover a broad spectral range. We report the first observation as well, as computer simulations of changes in the near-field images of fractal nanocomposites that occur through selective photomodification. Fractal aggregates were synthesized both from a controlled precipitation from silver colloidal solution and laser evaporation of a silver target in a buffer gas. Electron microscopic study of these samples showed that fractal clusters consist of hundreds of 2030 nm diameter monomers.