AVS 69 Session TF-ThM: Creating Organic-Inorganic Hybrid Materials

Robust and efficient process for synthesis of various composition inorganic coatings with controlled nanoporosity and structure is highly desirable for design of efficient catalytic, purification, and detection systems. Recently, infiltration of a nanoporous polymer template with inorganic precursors using sequential infiltration synthesis with inorganic vapor precursors followed by oxidative annealing was proposed as a new and efficient approach to create porous inorganic structures with tunable porosity and composition. The major limitations of the original water-based thermal sequential infiltration synthesis, though, are the thickness of the patterned structure being limited by vapor penetration depth of the precursors into the polymer template and the resulting material selection being restricted by the availability of high vapor pressure precursors. Here, we propose a swelling-based modification to the polymer infiltration process that allows to overcome these limitations. We summarize the basics of the multi-step infiltration approach, the structure and properties of the resulting materials, and their functional potential for practical applications. We report ultra-high accessibility of the pores when porous films are prepared via the polymer swelling-based infiltration synthesis (SBI). Using a quartz crystal microbalance (QCM) technique, we demonstrate increased solvent absorbing capabilities of highly porous ceramic films as a result of high interconnectivity of the pores in such structures. Our results show that the approach can be been extended toward preparing conformal coatings, freestanding membranes, and powders consisting of metal or metal oxide nanoparticles embedded in a porous oxide matrix.

Polymer templates infiltration synthesis of all-inorganic metal oxide architectures provides control over their thickness, porosity, and composition. In this study, we provide insights into the synthesis of nanoporous zinc oxide films as a model system via infiltration of polymers such as polymer of intrinsic microporosity (PIM-1) and representative of the block-copolymers family (polystyrene-polyvinyl pyridine block copolymer) that have different mechanisms of interaction with metal oxide precursors. We investigated the polymer infiltration process with both gas (diethyl zinc, DEZ, and water vapors) and solution (zinc acetylacetonate, Zn(acac)2, dissolved in ethanol) phase precursors. We systematically studied the effect of polymer template and the form of the metal oxide precursors on the properties of synthesized metal oxide thin coatings using the quartz crystal microbalance (QCM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses. Our study prove that the infiltration of polymer templates can be efficiently achieved using both gas phase and solution phase precursors. Furthermore, we show that the crystallinity of the synthesized ZnO films is mainly affected by the state of the precursor (gas or solution phase) and is independent of the polymer template type. In turn, the polymer type affects the surface termination of ZnO films. In addition, our findings demonstrate that the surface of porous ZnO coatings synthesized with BCP (here PS-P4VP) is more accessible than the surface of ZnO synthesized with PIM; however, despite the lower surface accessibility for ethanol molecules, ZnO synthesized via infiltration of PIM-1 with solution-phase precursors demonstrates the largest change in resistivity upon its exposure to ethanol vapor at room temperature.

Vapor phase infiltration (VPI) is a post-processing modification technique used to imbue inorganic materials into polymers to create organic-inorganic hybrid materials with new properties. In VPI, inorganic material can become entrapped by reaction with the polymer functional group, by reacting with a co-reactant or by physical entrapment due to loss of volatility. While several VPI precursor-polymer chemistries have been explored and their chemical mechanisms have been noted, a lack of chemical intuition remains for fully understanding the chemical mechanisms that govern VPI processes. This study seeks to continue to build this knowledge by examining the chemical reaction mechanisms that occur during TiCl₄ infiltration into esters namely PMMA and PLA. In this research, the poly-methyl methacrylate / TiO_xand poly-lactic acid / TiO_x hybrid materials are prepared using VPI. The chemical states of the atoms in the polymerspre &post infiltration are studied using x-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy. The chemical mechanism of infiltration appears to occur via an acid catalyzed SN2-alkylation reaction. As infiltration occurs in PMMA, there is an increase loss of methyl groups in the PMMA ester, whereas, in PLA there is an observed cleavage of the main chain at the methoxy bond, resulting in degradation of the polymer. The kinetics of this reaction and consequently the TiCl₄ infiltration increases with both VPI process temperature and TiCl₄ exposure time. Interestingly, the resulting hybrid materials offer new properties due to the reaction with TiCl₄. Increased titanium loading leads to up to 100% chemical stability in PMMA. Additionally, films infiltrated with up to 6% Ti have a 50 % and 70 % reduction in coefficients of thermal expansion (CTE) below and above T_g respectively. CTE continually reduces with increased titanium loading. In this talk, we will discuss how these chemical and physical changes could be used for various applications.

This project is supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Vapor-phase infiltration (VPI) is a post-polymerization chemical modification technique that exposes organic polymers to gas-phase inorganic precursors that sorb and become entrapped within the polymer to create organic-inorganic hybrid materials. The process kinetics for VPI are a complicated convolution of sorption, non-Fickian diffusion, and reaction processes. We recently introduced a reaction-diffusion model to capture many of the VPI process kinetics phenomena, and recent experimental work has demonstrated the validity of this model’s process predictions. This talk will introduce our publication of this model on Google Colab, a free, web-based environment for running Python codes without any need for installing or configuring a Python platform on your personal computer. This web-based platform makes it free and simple for anyone to now run our reaction-diffusion VPI process simulation model. This talk will include how to access and run these simulations, defining the important model variables as well as how they relate to physical process parameters. Example simulations will be run and then compared to experimental data we and others have published to demonstrate how this reaction-diffusion model can be used to interpret and help predict VPI process phenomena.

Here, we present a high-throughput multi-chamber MLD reactor that can quickly screen hybrid MLD processes for their EUV compatibility. In the reactor, films are deposited with one shared inorganic reactant and six independent counter-reactants in parallel, simultaneously producing multiple potential resist materials. In this work, inorganic reactants consisted of highly and non-highly EUV absorbing metals, like diethyl zinc, trimethylaluminum, and tin(IV) t-butoxide, while the organic counter-reactants included ethylene glycol, 1,2,4-trihydroxybenzene, 1,5-hexadiene-3,4-diol, 2-butyne-1,4-diol, cis-2-butene, and 2-methylenepropane-1,3-diol. The resulting films were tested for solvent, developer, and etchant stability before and after exposure to deep UV, electron beam, or X-rays. Promising resists were further characterized and could be used for patterning. Results showed that the inorganic and organic linkers exhibited a range of stabilities and light sensitivities, which could be used to optimize the performance of thin film EUV resists. In addition, this method provides a much faster screening process for potential photoresist materials in a scalable system, allowing for the continued improvement of processor efficiency and progress.