Atomic Layer Deposition on Porous Substrates

Atomic Layer Deposition on Porous Substrates: From General Formulation to Fibrous Substrates and Scaling Laws

Szmyt, Wojciech (University of Applied Sciences and Arts Northwestern Switzerland; University of Basel)
Guerra-Nuñez, Carlos (Swiss Federal Laboratories for Materials Science and Technology (Empa))
Huber, Lukas (Swiss Federal Laboratories for Materials Science and Technology (Empa))
Dransfeld, C.A. (TU Delft Aerospace Manufacturing Technologies)
Utke, Ivo (Swiss Federal Laboratories for Materials Science and Technology (Empa))

2021

Atomic layer deposition (ALD) is a technique of choice for a uniform, conformal coating of substrates of complex geometries, owing to its characteristic self-limiting surface reactions upon sequential exposure to precursor vapors. In order to achieve a uniform coating, sufficient gas exposure needs to be provided. This requirement becomes particularly relevant for highly porous and high aspect-ratio substrates, where the gas transport into the substrate structure is limited by diffusion (diffusion-limited regime), or for ALD precursor systems exhibiting a low surface reaction rate (reaction-limited regime). This work reports how the distinction between diffusion- and reaction-limited ALD regimes is directly quantitatively related to the width of the reaction front and the profile of chemisorption coverage in a single-cycle ALD, all of them being determined by the natural length unit of the system. We introduce a new parametrization of the system based on its natural system of units, dictated by the scales of the physical phenomena governing the process. We present a range of scaling laws valid for a general porous substrate, which scale intuitively with the natural units of the system. The scaling laws describe (i) the coating depth in a diffusion-limited regime with respect to the gas exposure, (ii) the chemisorption coverage in a reaction-limited regime with respect to the gas exposure, and (iii) the width of the reaction zone in the diffusion-limited regime. For the first time, the distinction between diffusion- and reaction-limited ALD regimes is directly quantitatively related to the width of the reaction zone and the profile of chemisorption coverage in a single-cycle ALD. The model system for the multicycle diffusion-limited coating of random fibrous mats was validated with an experiment of ALD on a forest of tortuous carbon nanotubes.

http://resolver.tudelft.nl/uuid:52c56c8e-c725-4e3e-b319-48090eadb706

https://doi.org/10.1021/acs.chemmater.1c03164

2023-01-01

0897-4756

Chemistry of Materials, 34 (1), 203-216

Institutional Repository

journal article

© 2021 Wojciech Szmyt, Carlos Guerra-Nuñez, Lukas Huber, C.A. Dransfeld, Ivo Utke