Degradation of ultra-thin boron films in air

Abstract Corrosion of B films in air can limit their practical applications. Here, we study the evolution of the elemental composition, thickness, and morphology of 10 – 100 -nm-thick amorphous B films sputter-deposited onto glassy carbon substrates and stored under different conditions. Results show that films with thicknesses of ≳ 55 nm have expected excellent corrosion resistance during storage in laboratory air at room temperature over several months. In contrast, ≲ 45 -nm-thick films exhibit pronounced degradation upon air exposure, starting with a change in the composition to ∼ 30 and ∼ 50 at.% of O and H, respectively. After such an O and H uptake, the degradation proceeds via mass loss with a characteristic time constant of ∼ 5 days in air at room temperature. A post-deposition annealing at 1000 ° C in an inert atmosphere makes all the films corrosion resistant.