Copper Photodeposition on TiO2 Studied with HREM and EXAFS

The possibility of direct selective surface activation by photodeposition of autocatalytic Cu particles on photosensitive TiO 2 substrates in an alkaline electroless copper solution has been investigated. The nucleation and growth of particles were characterized by transmission electron microscopy (TEM). Ex situ high resolution TEM and in situ extended x‐ray absorption fine structure (EXAFS) spectroscopy were used to determine the oxidation state of photodeposited particles on thin polycrystalline TiO 2 films and suspended TiO 2 powders, respectively. It is shown that in the initial stages of photodeposition small (<3 nm) noncatalytic Cu 2 O particles are formed. Electroactive Cu particles are only observed at relatively long illumination times and/or high light intensities. These results are explained with a model of the illuminated TiO 2 crystallite/electrolyte interface, which considers simple redox reactions involving transfer of TiO 2 photoelectrons to energy levels of the couples between complexed Cu 2+ ions, Cu 2 O and Cu. From this it is concluded that under illumination Cu particles are only formed if deposition of Cu 2 O is limited by either mass transport of complexed Cu 2+ ions or kinetic factors.