Atomic layer deposition of alumina films on reduced-activation ferritic-martensitic steel for nuclear fusion applications

One of the critical challenges facing the fusion energy community is effective handling of tritium fuel. Tritium permeation barrier coatings have been extensively studied as a means of preventing tritium ingress into structural materials. Atomic layer deposition (ALD) is a method of applying such coatings, with advantages including precise control over the thickness and uniformity. Here, it is used to apply thin-film coatings of alumina on reduced-activation ferritic-martensitic (RAFM) steel substrates using a custom-built ALD reactor. X-ray photoelectron spectroscopy was used to characterize the films’ composition. Optical models were developed for spectroscopic ellipsometry and x-ray reflectivity to measure their thicknesses. By optimizing the reactor growth conditions, alumina growth rates of 1.2 Å/cycle were achieved on the RAFM substrates. Experiments revealed that ALD alumina films on the order of 10 nm can reduce D2 permeation through the RAFM by more than one order of magnitude. The work presented here demonstrates the applicability of ALD to fusion-relevant substrates and provides detailed methodologies with which similar thin-film characterization can be performed in future studies.