Nanoscale domain formation of liquid-like aluminum emerging from sapphire through electron-beam heating

초록

Electron irradiation has long been used to induce structural modifications in nanoscale materials; nonetheless, the principles behind these changes are not well understood. This study examined sapphire (alpha-Al2O3) as a model system to elucidate the origin of localized melting induced by electron-beam exposure in transmission electron microscopy (TEM). In situ TEM revealed rounded aluminum (Al) liquid-like nanodomains (in projection) averaging similar to 3 nm in diameter along the specimen edge, indicating local temperatures approached melting-point depression values for nanoscale Al. During irradiation, the nanodomains exhibited liquid-like behavior, and occasionally solidified. Traditional models which rely exclusively on the energy loss of incident electrons fail to explain the observed heating. In this study, we hypothesized Auger excitation as the mechanism of beam heating because of its large cross section and capacity for highly localized energy deposition. We conducted thermal analyses by combining finite element analysis (FEA) with Monte Carlo simulations under this assumption. The results suggest that Al nanoclusters formed at the specimen edge can be heated by several hundred kelvin-conditions favorable for forming liquid-like nanodomains. These findings definitively advance the understanding of electron-matter interactions at the nanoscale and establish a beam-assisted approach to fabricate amorphous metal coatings under ambient-temperature conditions by using rapid, localized heating and cooling.

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