Uniform Large-Area Free-Standing Silver Nanowire Arrays on Transparent Conducting Substrates

Abstract

Arrays of silver nanowires have received increasing attention in a variety of applications such as surface-enhanced Raman scattering (SERS), plasmonic biosensing and electrode for photoelectric devices. However, until now, large scale fabrication of device-suitable silver nanowire arrays on supporting substrates has seen very limited success. Here we show the synthesis of free-standing silver nanowire arrays on indium-tin oxide (ITO) coated glass by pulsed electrodeposition into anodic aluminum oxide (AAO) templates. We use an in situ oxygen plasma cleaning process and a sputtered Ti layer to enhance the adhesion between the template and ITO glass. An ultrathin gold layer (2 nm) is deposited as a nucleation layer for the electrodeposition of silver. An unprecedented high level of uniformity and control of the nanowire diameter, spacing and length has been achieved. In photovoltaics nanowire arrays are of particular interest for costeffective organic and hybrid solar cells, whose near-optimal architecture is proposed to consist of arrays of nanostructures (approximately 200 nm long).12,13 The major advantage to using nanowire arrays is the enhancement of the charge collection due to the high charge carrier mobility in the metallic and some semiconductor nanowires. 13,14 However, due to the huge junction area, most semiconductor nanowire solar cells face limitations in device performance due to charge recombination across material interfaces, 13,14 leading to poor solar cell performance. Many research groups have tried to address this issue by developing metal oxide core-shell nanowire arrays. [15][16][17] In this work, a conductive metal oxide core (e.g. ZnO) is coated with a shell layer with an offset conduction band (e.g. TiO 2 , Al 2 O 3 ) in order to further increase distance between electron-hole pairs while simultaneously promoting charge extraction along the axis of the nanowire. This phenomenon was further employed in doped TiO 2 core-shell wires to amplify the electron mobility in the core of the wire without forming a recombination center along the internal interface.18 However, to ultimately enhance the performance of organic solar cells, a hybrid core-shell nanostructure with enhanced charge mobilities could provide an optimal electrode, e.g. a Ag nanowire with an inorganic shell layer. Additionally, these wires promote field amplification via plasmonic resonance as well as acting as a light scatterer, 19 leading to an increase in absorption in the surrounding active layers of the organic solar cells.For our approach, we use an industrially-applicable method for producing silver nanowires on a large area via filling anodic aluminum oxide (AAO) templates using electrodeposition. AAO was first introduced as a self-organizing mesoporous structure by Keller et al. in 1953. 20 Much research was later conducted to improve the formation and to fabricate AAO pores with various pore distances and diameters using thick (∼ mm) bulk Al foils. 21 Recently, it has been shown that the production of AAO templates ...

Giant polarization anisotropic optical response from anodic aluminum oxide templates embedded with plasmonic metamaterials

“…The substrate is comprised of a thick ITO-coated glass slide with a 5 nm thick adhesive layer of Ti and a 2 nm thick Au layer. The highly uniform, large-area, quasi-hexagonal AAO template was produced by anodization in oxalic acid at 40 V. A thorough description of AAO can be found in our previous work [46]. The resulting nano-inverted conical Au assembly is strongly anisotropic, as shown in the scanning electron microscopic images in Figs.…”

Uniform arrays of gold nanoelectrodes with tuneable recess depth

“…Thus, an increase in the fraction of active nanoelectrodes could be achieved under kinetic control of electrodeposition process, which requires lower overpotentials [ 24 , 26 ] and/or lower electrolyte temperatures [ 30 – 31 ]. Moreover, thin AAO templates with highly ordered porous structure (and, as a consequence, small quantity of the branched pores) can be used [ 27 , 32 – 33 ]. One more useful approach that can be applied for the increase in the number of contacting nanowires is planarization of the nanocomposite surface using mechanical polishing or ion etching and subsequent re-deposition of the current collector.…”

An Overview of Anodic Oxides Derived Advanced Nanocomposites Substrate for Surface Enhance Raman Spectroscopy

“…Because of the advantages of using AAO in nanostructure fabrication (like low cost, facile, and recurrent), a lot of research groups study the possibility of utilizing these materials in SERS substrate production. An ultrathin AAO membrane (up to 100 nm thick) was used to produce nanodots, nanowires, or metallic nanowires with plasmonic properties, and samples prepared in this way were used as SERS substrates [72][73][74][75][76][77][78][79]. Successful attempts were also made to produce SERS flexible substrates using AAO matrices [20,80,81].…”