LOCALIZATION OF ELECTRODE-REACTIONS BY A FOCUSED LASER-BEAM

The localization of electrode reactions in a focused laser beam is com pared to other localization techniques such as photolithography or the application of catalysis and inhibition. The geometric resolution of the reactions is given by primary effects of the laser spot and second ary effects of the system (light scattering, thermal and electronic co nductivity). A combination of several localization methods is favourab le. Tests with natural (Ti) and artificially simulated (Ti/TiN) grain boundaries show a resolution of some mum, close to the theoretical res olution, as long as low power densities are used. Some progress has be en achieved by full coordination of observation with localized laser r adiation. Most of the localized reactions studied are based on photo-e lectrochemical processes at thin n-type semiconducting films, but loca lized photochemical copper deposition onto quartz is also presented. Q uantitative investigations are carried out with laser-induced Ag-depos ition onto anodic TiO2 layers as an example. Experiments with point ar rays as well as velodynamic experiments prove that optically visible s pots can be obtained after a minimum consumption of some 10(17) e cm-2 . With increasing power density the reaction becomes delocalized by se condary effects. Depending on the illumination time, i.e. the number o f photons absorbed, competition between laser-induced oxide growth and metal deposition was observed on Nb2O5 layers. Substrate influences a re demonstrated by various examples. Long-range effects are caused by charge-carrier migration. Furthermore, crystallization is induced far away from the laser spot.