Copper Photodeposition on TiO2 Studied with HREM and EXAFS

Abstract

The possibility of direct selective surface activation by photodeposition of autocatalytic Cu particles on photosensitive TiO2 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 extendedx-ray absorption fine structure (EXAFS) spectroscopy were used to determine the oxidation state of photodeposited particles on thin polycrystalline TiO2 films and suspended TiO2 powders, respectively. It is shown that in the initial stages of photodeposition small (<3 nm) noncatalytic Cu20 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 TiO2 crystallite/electrolyte interface, which considers simple redox reactions involving transfer of TiO2 photoelectrons to energy levels of the couples between complexed Cu 2+ ions, Cu20 and Cu. From this it is concluded that under illumination Cu particles are only formed if deposition of Cu20 is limited by either mass transport of complexed Cu 2+ ions or kinetic factors.In the last few years patterned electroless metal deposition has gained increasing attention for potential application in the fabrication of microelectronic devices (1-5). Basically, electroless metal deposition involves a heterogeneous catalytic electron-transfer reaction, in which electrons are transferred from a reducing agent to metal ions. It can be carried out selectively on patterned electroactive areas on the substrate, since deposition is autocatalytic and requires an electrocatalytic surface to start. In most cases, the active areas are obtained by the application of electrocatalytic metal nuclei on the substrate, for example by photoselective activation procedures (6, 7). A disadvantage of this procedure is that metallization involves at least two steps: activation and electroless metal deposition. Furthermore, reducible species, e.g., adsorbedPd ions, may be left behind at undesirable places on the substrate after the activation step. When these are reduced to electrocatalytic species in the electroless solution, the latter may cause uncontrolled, nonselective electroless metal deposition. Therefore, it seemed worthwhile to study the possibility of direct selective surface activation in an electroless solution.In the work described in this paper, which is a continuation of earlier reports on different aspects of the initiation of electroless metal deposition (8-10), direct laser-induced copper deposition from an electroless copper solution on TiO2 substrates is investigated. It was exPected that photochemically deposited metallic Cu nuclei from an electroless solution on photosensitive TiO2 films would show autocatalytic behavior. This means that prenucleated areas on the TiO2 film should be intensified by subsequent electroless copper deposition in the dark. Preliminary experiments, however, showed that this...

On the Origin of Enhanced Photocatalytic Activity of Copper-Modified Titania in the Oxidative Reaction Systems

“…The first papers about Cu/TiO 2 systems were mainly connected with photodeposition of copper on titania surface as the efficient method for Cu removal from water environments [29][30][31][32]. Cu II ions were reduced to metallic copper with the participation of photogenerated electrons (e − ) and holes (h + ) according to the following Reactions (1) …”

“…However, Jacobs et al showed that photodeposition of zero-valent Cu particles was possible and was preceded by photodeposition of Cu 2 O particles [32].…”

Enhanced photocatalytic reduction of toxic Cr(VI) with Cu modified ZnO nanoparticles in presence of EDTA under UV illumination

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“…[141][142] Photodeposition has been utilized for removal of metal ions from aqueous environments with semiconducting WO 3 or TiO 2 as photoactive substrates. 48,50,[143][144][145][146] In addition to environmental remediation, photo-assisted deposition can also function as a potentially facile, low-temperature method to modify photoactive surfaces such as TiO 2…”