Spallation of Isolated Aluminum Nanoparticles by Rapid Photothermal Heating

The spallation of isolated aluminum (Al) nanoparticles (NPs) is initiated using rapid photothermal heating. The Al NPs exhibited a nominal diameter of 120 nm, with an average oxide shell thickness of 3.8 nm. Photothermal heating was achieved by coupling a focused laser (446 nm wavelength) to an optical grating substrate and to the plasmonic resonance of the Al NPs themselves. These factors enhanced the absorption cross section by a factor of 8-18 compared to no substrate and generated an Al NP heating rate on the order of 10(7) -10(8) K/s. Observations indicate that molten Al is ejected from the heated NP, indicating that melting of the Al core is required for spallation. A graphene layer atop the grating substrate encouraged the formation of discrete particles of ejected Al, while irregular elongated filament products were observed without the graphene layer. Numerical simulations indicate that laser-heated Al NPs reach temperatures between approximately 1000 and 1500 K. These observations and experimental conditions are consistent with those anticipated for the melt dispersion mechanism, a thermomechanical reaction mechanism that has not previously been clearly demonstrated. Activating and controlling this mechanism is anticipated to enhance applications ranging from biological phototherapy to energetic materials.

Automated summary

This study investigates the spallation of isolated aluminum nanoparticles induced by rapid photothermal heating. By coupling a focused laser to an optical grating substrate and plasmonic resonance of the nanoparticles, the absorption cross section and heating rate are enhanced. The melting of the aluminum core is found to be necessary for the spallation process, and the presence of a graphene layer promotes the formation of discrete particles.