Electrochemistry and electrogenerated chemiluminescence of films of silicon nanoparticles in aqueous solution

Films of octadecyl-capped Si nanoparticles (NPs) (diameter, 3.4 +/- 0.7 nm) prepared by drop-coating on indium tin oxide (ITO) showed electrogenerated chemiluminescence (ECL) for both cathodic and anodic potential sweeps in KOH solutions containing peroxydisulfate. The redox potentials of the Si NPs can be estimated as approximately -0.9 and +0.95 V (versus Ag/AgCl) based on the anodic potential for the onset of ECL minus the ECL peak energy. The ECL exhibits a relatively broad spectrum (FWHM = 160 nm) with a peak wavelength of 670 nm (1.85 eV), similar to the photoluminescence spectra. In electrochemical studies in KOH solution in the absence of peroxydisulfate, an anodic current peak appears at about -1 V (versus Ag/AgCl) following a scan to negative potentials. A similar peak has been observed during the etching of a bulk single crystal Si electrode in alkaline aqueous solution. Unpassivated surface sites of Si NPs seem to be etched at potentials negative of the anodic oxidation peak.