Highly Ordered Macroporous Gold Film Formed by CVD Using Monodisperse Polystyrene Spheres as Templates

Abstract

The preparation of ordered macroporous materials composed of metals, [1][2][3] metal alloys, [4] metal oxides, [5][6][7][8] metal chalcogenides, [9] or organic polymers [10][11][12][13] is an emerging field of research in chemistry and materials science. Such macroporous metallic structures exhibit interesting optical properties and thus have potential applications as optical sensors and switching devices. [14] Furthermore, since the pore diameters of these macrostructures are similar to the wavelength of visible light, they can be used to create photonic crystals or photonic mirrors. [6,15] Close-packed arrays of monodisperse spheres (typically polystyrene or silica) are typically chosen as templates for material deposition, and the subsequent removal of the template material yields the ordered macroporous structure. It is known that, using this method, ordered macroporous metals can be deposited by hydrogen reduction of preformed macroporous oxides [5,7,8] and by electroless or electrochemical deposition. [1][2][3][4]14,16,17] CVD has a significant advantage for the deposition of thin, supported films of macroporous materials since no solvent, which can disrupt the highly ordered film structures, is required for the deposition process.This article is a report of the low-temperature CVD of gold on polystyrene and its application for the formation of a highly ordered macroporous gold film. The challenges in using CVD for deposition on polymers are that the process must occur below the softening temperature of the polymer, and that uneven film growth may occur if there is poor adhesion to the polymer. Initial development of a CVD procedure for gold on polymer was carried out using a continuous 1.5 lm thick polystyrene film supported on an aluminum disk. Attempts to achieve direct low-pressure CVD of gold by using the precursor [AuMe(PMe 3 )],[18] 1, with hydrogen as the carrier gas (flow rate of 50 mL min -1), below the softening temperature of polystyrene (ca. 85°C) were unsuccessful and no deposition was observed. Enhancement of the CVD process was therefore investigated and deposition was attempted using catalyst-enhanced (CE)CVD. In this method, either seeding the substrate surface or carrying out co-deposition with a catalytically active metal, usually using a reactive carrier gas such as hydrogen or oxygen, can greatly lower the CVD temperature. [19][20][21][22][23][24][25][26][27] In particular CECVD, with a palladium precursor as the catalyst, is known to reduce the deposition temperatures of CVD.[28] The polystyrene film was primed by transferring catalytic amounts of the 2-methylallylpalladium complex precursor [Pd(g 3 -CH 2 -CMeCH 2 )(fod)], [28] 2, fod = t BuCOCHCOC 3 F 7 , onto the polystyrene surface via sublimation, followed by decomposition of the precursor to palladium metal with a hydrogen carrier gas. In the presence of the pre-deposited palladium catalyst, gold deposition on the polystyrene film was possible, using the above CVD procedure, over the temperature range 65-85°C. When only part o...

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