Munoz, A.G.; Lewerenz, H.J.: Model experiments on electrochemical formation of nano-dimensioned noble metal-oxide-semiconductor junctions at Si(111) surfaces. Electrochimica Acta 55 (2010), p. 7772-7779

The recently introduced nanoemitter concept allows photovoltaic and photoelectrocatalytic energy conversion. Device functioning is presently based on metallic nanoemitters that are embedded in passivating films on Si absorbers. Model experiments on the electrodeposition of nanoscale noble metal islands onto n-type H:Si(111) are presented. Besides electrochemical methods such as impedance spectroscopy and cyclic voltammetry, atomic force microscopy (AFM), transmission electron microscopy (TEM) and synchrotron radiation photoelectron spectroscopy (SRPES) have been applied to elucidate the surface chemistry and -electronics. The electrodeposition profiles of the reduction current under depletion condition indicate electron exchange via occupied surface states which strongly influence the deposition rate and the surface site selectivity of the nucleation process. SRPES at photon energies adjusted to high surface sensitivity shows formation of an ultrathin silicon dioxide film in the course of the reduction of the noble metal chloride complexes. The presence of this interfacial oxide is confirmed by high-resolution TEM experiments. Step bunching at the Si surface upon electrodeposition is observed by AFM and analyzed in detail using (i) metal-chloride complex containing solutions and (ii) chloride-ion solutions. A model for Si etching in chloride-ion containing solutions is presented that is also based on impedance measurements which show that Cl- is adsorbed at the Si surface. Finally, the successive steps of Pt electrodeposition from the hexachloro complex PtCl62- onto Si(111) are outlined.