Tunable Atomic Layer Deposition into Ultra-High-Aspect-Ratio (>60000:1) Aerogel Monoliths Enabled by Transport Modeling

Atomic layer deposition (ALD) modification of ultra-high-aspect-ratio structures (>10000:1) is a powerful platform with applications in catalysis, filtration, and energy conversion. However, the deposition of conformal and tunable ALD coatings at these aspect ratios remains challenging, resulting in empirical trade-offs between the precursor utilization and reaction time. Here, we demonstrate tunable control of the ALD infiltration depth into an aerogel monolith (AM) and develop a reaction-diffusion model to accurately describe the coating process. Specifically, we investigate the ALD exposure time and precursor dose needed to conformally coat a silica AM with pore sizes of similar to 20 nm, a monolith thickness of similar to 2.5 mm, and aspect ratios exceeding 60000:1. We demonstrate complete infiltration into the AM, which is quantified by elemental mapping. A reaction-diffusion model is developed, which accounts for multiple doses and the precursor depletion in the ALD chamber during an exposure step. The experimentally validated model enables the prediction and tuning of infiltration depth into a tortuous, high-aspect-ratio structure such as an AM, allowing for the synthesis of rationally designed material architectures. Additionally, the model allows for co-optimization of the total deposition time and percentage of unreacted precursor, which are important for the manufacturability and sustainability of ALD processing. Lastly, we demonstrate that ultrathin ALD Al2O3 coatings can be used to stabilize silica AMs against structural degradation under high-temperature annealing conditions (700-800 degrees C) by limiting changes in the surface area and monolith volume. This improved high-temperature stability has implications for numerous aerogel applications, including catalysis and thermal insulation.

Automated summary

ALD modification of ultra-high-aspect-ratio structures presents challenges in conformal and tunable coating. This study demonstrates tunable control of ALD infiltration depth and develops a reaction-diffusion model for accurate coating description. The experimentally validated model enables prediction and tuning of infiltration depth into high-aspect-ratio structures, allowing for rationally designed material architectures.