Athermal glass work at the nanoscale: Engineered electron-beam-induced viscoplasticity for mechanical shaping of brittle amorphous silica

Room Temperature Viscous Flow of Amorphous Silica Induced by Electron Beam Irradiation

“…It has been stated in the literature that this observation cannot be correlated to electron beam heating. [ 4,26 ] Nevertheless, the electron beam heating for the highest irradiation dose applied in this study has roughly been estimated to ΔT ≈ 32 K for an electron range of 6 µm as determined earlier. [ 23,46 ] This value is too low to attribute the observed softening to thermal influences especially as this value is expected to be even lower in SEM scanning mode.…”

“…This observation agrees well with Kang's findings on amorphous silica nanospheres, who found the electron beam‐induced defect generation to be most efficient for beam parameters where the electron interaction volume is of comparable size to the amorphous silica nanospheres. [ 26 ] In other words, the electron acceleration voltage defines the electron range in the material and must be selected according to the test volume for a most efficient electron distribution. It can therefore be assumed that experiments under acceleration voltages in the 200 kV region as reached in TEM or modern electron beam welding or sintering machines may allow for viscous flow in test volumes of several ten or hundred micrometers in size (Figure 8b).…”

“…[4,18,21,28] According to Kang et al, the viscoplastic deformation of amorphous silica strongly depends on the electron range, i.e., the volume of the region where electron-matter interaction occurs. [26] Hence, the electron range has been analyzed for different acceleration voltages using the Win X-ray Monte Carlo software. [44] The resulting electron trajectories are visualized in Figure 8a with the micropillar geometry sketched around them.…”

“…In those studies, the examined geometries range from 30 nm (nanowire) to 500 nm (nanosphere) in diameter. [4,26,28,29] On the micron scale, however, there is to the best of the authors knowledge no such data available. In a recent study fracture enhancement of 200% and beyond was reported in pillar-splitting experiments on micron-scale amorphous silica (Ø ≈ 5 μm) once the experiment was performed under running electron beam condition.…”

“…[4,24,25] Latter process is expected to take place at high acceleration voltages in the range of 200 kV as found in TEM while the first process is expected to occur at acceleration voltages below 30 kV as found in conventional SEM. [4,26] Those defects induce additional degrees of freedom which reduce the flow stress and mediate very large ductility, the authors term as superplastic. [4] Recently, the first attempts to use this effect productively for shaping have been described.…”