Helium-Plasma-Induced Nanostructures on Metals: Fundamentals, Properties, and Applications

Helium plasma irradiation is a unique surface modification technique that can induce various surface textures, including self-organized nanostructures, porosity, defects, and compositional changes, on a wide variety of materials. Initially investigated on tungsten mainly in the context of plasma-material interaction for fusion applications, helium-plasma-induced nanostructuring has recently attracted increasing attention as a versatile route for functional surface engineering. In particular, the resulting nanostructured and porous surfaces exhibit strongly altered optical, physicochemical, and electrochemical properties, enabling emerging applications in broadband optical absorbers, light diffusers, photocatalysis, photoelectrochemical water splitting, electrocatalysis, gas sensing, and energy-storage electrodes. This topical review summarizes the fundamentals of helium plasma treatment, including irradiation conditions, morphology evolution, and associated changes in material properties, and then surveys recent progress in application-oriented studies.