Fabrication, characterisation, and optical applications of electrochemically deposited nanostructured IrOx films

Abstract

In this work, nanostructured iridium oxide films were fabricated by electrochemical deposition within a template made with polystyrene spheres on gold substrates. SEM pictures show that the nanostructured IrOx films have a very ordered hexagonal structure. To our knowledge, this is the first report of templated deposition of nanostructured IrOx films and only the 2nd of fabrication of templated deposition of nanostructured electrochromic metal oxides.
The deposition solution was carried out under voltammetric control with a solution made from iridium tetrachloride, hydrogen peroxide, oxalic acid and potassium carbonate based on a recipe reported by Yamanaka (Anodically Electrodeposited Iridium Oxide-Films (AEIROF) from Alkaline-Solutions for Electrochromic Display Devices, Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap. 1989, 28, 632). Both non structured and nanostructured IrOx films were grown with the deposition solution. During the voltammetry, the growth of the film was followed by monitoring the cathodic peaks and anodic peaks which reflect redox reactions Ir(?) / Ir(IV) and Ir(IV) / Ir(V) within the IrOx oxide film. During the deposition, the peak currents increase almost linearly with the number of voltammetric cycles thus allowing a fine control of the deposition process. Several attempts were made to estimate the film thickness and establish a relationship between film thickness and deposition cycles. The thickness of the nanostructured films is particularly difficult to measure accurately. Following deposition, the electrochemistry of the nanostructured IrOx films was characterised with cyclic voltammetry in both acid and base solutions.
Optical properties of the nanostructured IrOx films were investigated. The transmittance of a nanostructured IrOx films was measured with transparent ITO substrates. The novel idea of coating a thin layer of IrOx film on a nanostructured gold surface was investigated to test whether the electrochromism of the nanostructured IrOx film could be used to alter the surface plasmons of the nanostructured substrate. The nanostructured IrOx film worked as a surface plasmon modulator when its colours shifted between dark and transparent under potential control. The reflectance of thickness-graded nanostructured IrOx films was measured over a range of incident angles for different potentials. Following very recent publications on the theoretical modelling of light interaction with nanostructured gold films, an attempt was made to analyse the results obtained with the nanostructured IrOx films in terms of the interplay between the localised and delocalised surface plasmons.

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ORCID for Guy Denuault: orcid.org/0000-0002-8630-9492

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