Sequential infiltration synthesis (SIS) is a novel technique for fabricating organic–inorganic hybrid materials and porous inorganic materials by leveraging the diffusion of gas-phase precursors into a polymer matrix and chemical reactions between the precursors to synthesize inorganic materials therein. This study aims to obtain a fundamental understanding of the physicochemical mechanisms behind SIS, from which the SIS processing conditions are rationally designed to obtain precise control over the distribution of metal oxides. Herein, in situ FTIR spectroscopy was correlated with various ex situ characterization techniques to study a model system involving the growth of aluminum oxides in poly(methyl methacrylate) using trimethyl aluminum (TMA) and water as the metal precursor and co-reactant, respectively. We identified the prominent chemical states of the sorbed TMA precursors: (1) freely diffusing precursors, (2) weakly bound precursors, and (3) precursors strongly bonded to pre-existing oxide clusters and studied how their relative contributions to oxide formation vary in relation to the changes in the rate-limiting step under different growth conditions. Finally, we demonstrate that uniform incorporation of metal oxide is realized by a rational design of processing conditions, by which the major chemical species contributing to oxide formation is modulated.

The decoration of the TCO electrode surface with chemical species serving as a charge transfer mediator, electrochemical tag, or electrocatalyst is a widely employed strategy to realize desirable electrochemical properties in electrodes. [11][12][13] Recent progress in the fabrication of porous TCO electrodes has rendered the surface modification scheme more successful by maximizing the loading of the functional redox species onto the porous electrodes with a high surface area. [14,15] Given that the mass transport of the electrolyte species to the electrode is not restricted, surfacemodified porous electrodes will enable more efficient electron transfer, thereby increasing the efficiency of electrochemical and bioelectrochemical devices. [11][12][13] In addition, the high surface area of porous electrodes is anticipated to facilitate the miniaturization of devices owing to their increased implantable capability. [16,17] Numerous approaches have been proposed for the fabrication of porous transparent electrodes, including nanoparticle casting, [18,19] salt precursor deposition, [20,21] etching, [19,22] and electrospinning. [23] Casting a nanoparticle via dip coating or spin coating is a low-cost, simple method to prepare porous TCOs. However, it cannot easily achieve precise control over the pore morphology, such as the pore size and size distribution. [10] TCOs of organized structures with a controlled morphology can be realized via template deposition methods, which exploit the self-assembly of soft templates, such as molecular cationic surfactant templates [24,25] or block copolymers, [20,26] with a solution of soft templates containing precursor salts for oxide formation. In this study, we employed sequential infiltration synthesis (SIS) as a new approach to fabricate porous TCO electrodes. SIS has recently emerged as a novel and attractive approach for the fabrication of inorganic-organic hybrid films and porous templated films.SIS is similar to template deposition methods in that both methods require polymer films spun on a substrate. However, the growth mechanisms of SIS differ from those of soft template deposition methods. The key mechanisms involved in SIS are as follows: 1) Infiltration of gas-phase precursor molecules into the polymer matrix, 2) coordination of the precursor molecules with a specific functional group of the polymer, and 3) a chemical reaction between the infiltrated precursor molecules Sequential infiltration synthesis (SIS) is an emerging technique for producinginorganic-organic hybrid materials and templated inorganic nanomaterials. The application space for SIS is expanding rapidly in areas such as litho graphy, filtration, photovoltaics, antireflection, and triboelectricity, but not in the field of electrochemistry. This study performs SIS for the fabrication of porous, transparent, and electrically conductive films of indium zinc oxide (IZO) to evaluate their potential as an electrode for electrochemistry. The elec trochemical activity of IZOcoated electrodes is evaluated when th...

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We demonstrate the growth of polymer–Al–O(−R) hybrid thin films via a sequential infiltration synthesis (SIS). SIS using an organic coreactant resulted in the expansion of the hybrid thin films with a highly uniform distribution of the chemical composition. This behavior stems from the large free volumes created by the long and flexible chains of the organic coreactant, enabling the continued incorporation of SIS precursors into the structures. The proposed method will be a valuable addition to vacuum deposition techniques for both organic–inorganic hybrid thin films and porous inorganic films with tunable porosity, pore morphology, and film thickness.

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