ITO and gold substrates were cleaned by sonication in 95% ethanol for 5 minutes, blown dry in a stream of nitrogen, and treated with piranha solution in the case of gold (1 part by volume 30% aqueous hydrogen peroxide to which 3 parts by volume conc. sulfuric acid were added -CAUTION, potent oxidizer and burn hazard) for 5 minutes or by treatment in an argon plasma cleaner for ITO.