Tuning surface porosity on vanadium surface by low energy He⁺ ion irradiation

Highlights: • Surface nanostructuring on vanadium surface using novel He⁺ ion irradiation process. • Tuning surface-porosity using high-flux, low-energy He⁺ ion irradiation at constant elevated sample temperature (823–173 K). • Presented top-down approach guarantees good contact between different crystallites. • Sequential significant enhancement in surface-pore edge size (and corresponding reduction in surface-pore density) with increasing sample temperature. - Abstract: In the present study, we report on tuning the surface porosity on vanadium surfaces using high-flux, low-energy He⁺ ion irradiation as function of sample temperature. Polished, mirror-finished vanadium samples were irradiated with 100 eV He⁺ ions at a constant ion-flux of 7.2 × 10²⁰ ions m⁻² s⁻¹ for 1 h duration at constant sample temperatures in the wide range of 823–1173 K. Our results show that the surface porosity of V₂O₅ (naturally oxidized vanadium porous structure, after taking out from UHV) is strongly correlated to the sample temperature and is highly tunable. In fact, the surface porosity significantly increases with reducing sample temperature and reaches up to ∼87%. Optical reflectivity on these highly porous V₂O₅ surfaces show ∼0% optical reflectivity at 670 nm wavelength, which is very similar to that of "black metal". Combined with the naturally high melting point of V₂O₅, this very low optical reflectivity suggests potential application in solar power concentration technology. Additionally, this top-down approach guarantees relatively good contact between the different crystallites and avoids electrical conductivity limitations (if required). Since V₂O₅ is naturally a potential photocatalytic material, the resulting sub-micron-sized cube-shaped porous structures could be used in solar water splitting for hydrogen production in energy applications.