The Nanoporous Metallisation of Insulating Substrates through Photocatalytically Initiated Electroless Deposition (PIED)
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The Nanoporous Metallisation of Insulating Substrates through Photocatalytically Initiated Electroless Deposition (PIED) Michael A. Bromley and Colin Boxall Lancaster University, Engineering Department, Lancaster LA1 4YR, United Kingdom E-mail addresses: [email protected], [email protected] ABSTRACT We report the novel use of semiconductor photocatalysis for the deposition of metal onto insulating surfaces and the in-process formation of nano-structured porosity within this metal. In the process of Photocatalytically Initiated Electroless Deposition (PIED) we have developed a controllable, spatially selective and versatile metallisation technique with several advantages over traditional, non-photocatalytic techniques such as enhanced controllability and purity of the deposit as well as reduced operational costs and environmental impact. With the addition of a self-assembled, hexagonally close-packed microparticle template to the substrate prior to metal deposition, PIED can be used to fabricate thin metal films with highly ordered porosity on the nano-scale. Nanoporous metallisation in this way is able to produce substrates with potentially wide applications such as membrane and separation technology, energy storage and sensors – especially surface enhanced resonance Raman spectroscopy (SERRS). INTRODUCTION The metallisation of non-conducting materials is typically performed through a process known as electroless plating. This involves the chemical reduction of metal ions from solution in order that they be deposited onto the substrate surface in metallic form [1]. While independent of electrical current, electroless plating does require the catalysis of metal ion reduction by the substrate surface and traditionally involves extensive sensitisation steps with Sn-Pd catalysts before the deposition process can take place. Semiconductor particles, such as TiO2, SnO2, WO3, can act as efficient photocatalysts for a range of processes [2] and, as such, present an alternative means of metal ion reduction which may be employed as part of an electroless plating process, providing a more efficient and cost-effective method for the sensitisation and subsequent metallisation of insulating substrates. Photocatalysis is a multi-step process, initiated by the absorption of ultra-band gap light energy to generate electron-hole pairs. These photogenerated electron-hole pairs may undergo recombination or, given appropriate conditions, can be sufficient to drive redox reactions with species, such as metal ions, on the semiconductor surface or in local solution if the process is thermodynamically viable. We have appropriated these reactions in the development of a novel metallisation technique known as Photocatalytically Initiated Electroless Deposition (PIED), a novel process in which semiconductor photocatalysis is used to nucleate and fully metallise insulating substrate materials via submersion in a typical electroless plating bath [3-5]. The deposition process is initiated photocatalytically by irradiation of the se
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