The formation of nanoripples by ultra-low energy ion irradiation reveals the liquidus nature of metallic glass surface

We report an experimental investigation of ion irradiation on metallic glasses (MGs), with extremely low ion energy of 50~225 eV, orders of magnitude lower than that often used in previous studies. Highly periodic ripples with a wavelength of 20 nm and an amplitude of 0.5 nm were developed on MG surfaces under irradiation. With increasing irradiation time, we can identify three regimes: appearance of initial random islands, coarsening of the pattern through annihilation reactions of mobile defects, and finally saturation of the ripples. No change is observed for the devitrified counterparts with the same treatment. These findings reveal the liquidus nature of glass surface even far below the glass transition temperature and provide new clues for surface modification of amorphous materials.