Facile Production of Ordered 3D Platinum Nanowire Networks with “Single Diamond” Bicontinuous Cubic Morphology

Abstract

We report a new method for the production of ordered 3D metal-nanowire network fi lms. The method utilizes a coating of lipid inverse cubic phase as the template for electrodeposition. We have produced platinum fi lms which show a previously unreported "single diamond" nanoarchitecture with Fd3m symmetry and a lattice parameter of approximately 132 Å. Their electrochemically accessible surface area is estimated to be > 40 m 2 g − 1 . The new methodology represents a facile route to 3D cubic nanostructures and thus provides a synthetically attractive route to the preparation of 3D nanostructured devices with diverse potential applications.Nanostructured metals and semiconductors have many important technological uses. They are commonly produced by templating soft materials such as diblock copolymers [ 1 ] or lyotropic liquid-crystal phases that form by amphiphile selfassembly. [ 2 ] These soft templates exhibit a range of different nanostructures that include hexagonal phases, based on simple 2D arrays of cylinders, and the more complex 3D bicontinuous cubic structures, based on mathematical surfaces known as the triply periodic minimal surfaces. Three different symmetries of bicontinuous cubic structure have been reported, based on the gyroid (G), double diamond (D), and primitive (P) minimal surfaces, which correspond to the space groups Ia3d (Q 230 ), Pn3m (Q 224 ), and Im3m (Q 229 ), respectively. In the inverse (Type II) cubic phases whose use as an electrochemical template is described here, the minimal surface lies at the centre of a continuous amphiphile bilayer which separates two continuous, but non-intersecting, water channel networks.Direct electrodeposition of nanostructured materials from normal topology (Type I) lyotropic liquid-crystal phases was fi rst reported by Attard and co-workers in 1997. [ 3 ] The method represents a reliable route to a range of nanostructured materials [ 4 ] under conditions that are suffi ciently mild to preserve the lyotropic mesophase structure during the electrodeposition process. Reported uses of direct electrochemical lyotropic templating using the normal (Type I) hexagonal phase are numerous, but in contrast there is only one reported case involving electrochemical templating from normal topology cubic phases. [ 5 ] There are two main reasons for this: fi rst, the cubic phase typically occupies only a small region of the composition-temperature phase diagram, and second, perhaps more importantly, the bicontinuous cubic phases are much more viscous than their hexagonal counterparts; [ 6 ] the combined result being that electrochemical templating from a cubic phase via the true liquid-crystal templating route is very difficult to achieve in practice.Nonetheless, the production of nanostructured materials with a bicontinuous cubic morphology is highly desirable, and even though the lyotropic liquid-crystal templating route has not been used extensively in this way, some alternative (albeit multi-step) approaches have been reported in the literature. The resulting bicon...

Aligned platinum nanowire networks from surface-oriented lipid cubic phase templates

“…Phytantriol (3,7,11,15-tetramethyl-1,2,3-hexadecanetriol, purity > 98.3 %) was purchased from Adina Cosmetics; chloroplatinic acid (dihydrogen hexachloroplatinate(2-)) solution (8% w/w in water) was purchased from Sigma-Aldrich. Nanostructured platinum films were deposited through films of dip coated phytantriol in a fashion similar to that previously reported by Akbar 18 . Deposition was carried out on gold foil substrates (5 mm × 12.5 µm × 0.5 mm) which were initially cleaned through cycling in 0.5 M H 2 SO 4 at 0.2 V/s between -0.2 and 1.8 V vs. Ag/AgCl until the cyclic voltammogram remained steady.…”

“…However it has also been demonstrated that metals can be templated directly from lyotropic liquid crystal structures. 16,17 Direct liquid crystal templating from type I and II systems has been shown to be a facile, chemically green and cheap method to produce wellordered nanostructures with a variety of morphologies 17 and we have recently shown that this can be extended to bicontinuous cubic lipid systems 18 . The procedure, including template formation and subsequent removal, takes approximately an hour, as compared with over a week for block copolymer 4 or silica 3 templating routes, and does not require harsh chemical or environmental conditions for template removal.…”

“…All three feature a continuous lipid bilayer formed around two discreet water channel networks. We demonstrated templated electrodeposition of platinum through the Q II D phase of the lipid phytantriol 18 , exploiting the fact that type II lipids can form the Q II D phase in excess water conditions 19 which allowed the template to be applied as a thin film. Platinum deposition was found to occur only in a single water network, which was considered to arise from capping of one of the channels at the cubic phase surface; the resulting structure featured a 'single diamond' morphology with Fd3m symmetry, in contrast to the Pn3m symmetry of the 'double diamond' lipid template.…”

A novel route to nanostructured bismuth telluride films by electrodeposition

“…The lipid template was applied by dip coating into a solution of ethanol and phytantriol 1:2(w/w). Once dip coated the substrate was left for no less than 30 minutes to allow the ethanol to evaporate, leaving an estimated 22 ± 1 µm thin film of phytantriol coating [14]. The substrate could then be immersed into the electrolyte and left to equilibrate for no less than 30 minutes prior to deposition.…”

“…In this paper, for example, we describe the deposition of Bi 2 Te 3 nanowires onto electrodes formed from archival DVDs comprising a layer of gold on a backing of polycarbonate, which softens at 145 °C [13], and which therefore require relatively mild deposition conditions. 3D cubic lipid phases offer a promising synthetic route to the production of nanowires with diameters <10nm as illustrated for freestanding nanowire networks of platinum [14,15]. We hypothesise that the application of these templates instead to thermoelectric semiconductors would open up the possibility of producing nanowires with ultralow diameters for efficient thermoelectric generators [1] that would potentially exhibit an increased Seebeck coefficient due to quantum confinement on the electron density of states [3,4].…”