Direct measurements of irradiation-induced creep in micropillars of amorphous Cu₅₆Ti₃₈Ag₆, Zr₅₂Ni₄₈, Si, and SiO₂

We report in situ measurements of irradiation-induced creep on amorphous (a-) Cu₅₆Ti₃₈Ag₆, Zr₅₂Ni₄₈, Si, and SiO₂. Micropillars 1 μm in diameter and 2 μm in height were irradiated with ∼2 MeV heavy ions during uniaxial compression at room temperature. The creep measurements were performed using a custom mechanical testing apparatus utilizing a nanopositioner, a silicon beam transducer, and an interferometric laser displacement sensor. We observed Newtonian flow in all tested materials. For a-Cu₅₆Ti₃₈Ag₆, a-Zr₅₂Ni₄₈, a-Si, and Kr⁺ irradiated a-SiO₂ irradiation-induced fluidities were found to be nearly the same, ≈3 GPa^-1 dpa^-1, whereas for Ne⁺ irradiated a-SiO₂ the fluidity was much higher, 83 GPa^-1 dpa^-1. A fluidity of 3 GPa^-1 dpa^-1 can be explained by point-defect mediated plastic flow induced by nuclear collisions. The fluidity of a-SiO₂ can also be explained by this model when nuclear stopping dominates the energy loss, but when the electronic stopping exceeds 1 keV/nm, stress relaxation in thermal spikes also contributes to the fluidity.