Development of an Atomic Layer Deposition System for Deposition of Alumina as a Hydrogen Permeation Barrier

TL;DR

This study develops and validates an atomic layer deposition system to create alumina thin films that significantly reduce hydrogen isotope permeation, advancing materials for nuclear fusion reactor safety.

Contribution

The paper introduces a custom ALD system for depositing alumina films and demonstrates their effectiveness as hydrogen permeation barriers on copper substrates.

Findings

Al2O3 films achieved growth rates of 1.1 Å/cycle between 100-210°C.

Permeation tests showed over an order of magnitude reduction in deuterium flux.

Distinct transport regimes were identified: diffusion-limited in bare copper, surface-limited in coated samples.

Abstract

Tritium permeation into and through materials poses a critical challenge for the development of nuclear fusion reactors. Minimizing tritium permeation is essential for the safe and efficient use of available fuel supplies. In this work, we present the design, construction, and validation of custom atomic layer deposition (ALD) and deuterium permeation measurement systems aimed at developing thin-film hydrogen permeation barriers. Using the ALD system, we deposited conformal Al2O3 films on copper foil substrates and characterized their growth behavior, morphology, and composition. ALD growth rates of 1.1 angstrom/cycle were achieved for temperatures between 100 degrees C and 210 degrees C. Permeation measurements on bare and ALD-coated copper foils revealed a significant reduction in deuterium flux with the addition of a 10nm Al2O3 layer. While bare copper followed diffusion-limited transport consistent with Sievert's law, the ALD-coated samples exhibited surface-limited, pore-mediated transport with linear pressure dependence. Arrhenius analysis showed distinct differences in activation energy for the two transport regimes, and permeation reduction factors (PRFs) exceeding an order of magnitude were observed. These results demonstrate the potential of ALD-grown Al2O3 films as effective hydrogen isotope barriers and provide a foundation for future studies on film optimization and integration into fusion-relevant components.