Rapid Shape Change and Spallation of Isolated Nanoscale Aluminum Cubes, Rods, Pyramids, and Spheres: Implications for Plasmonic and Energetic Materials

Aluminum nanoparticles (Al NPs) are an attractive material for plasmonic and energetic applications. Herein, we investigate the response of spherical and nonspherical (cubes, pyramids, and pentagonal rods) Al NPs to rapid laser heating. Rapid surface diffusion reconfigures the shaped Al NPs toward a spherical geometry. Based on simulations, the surface diffusion occurs below the bulk Al melting temperature. When exposed to sufficient laser flux, Al NPs of all geometries spall. The critical laser flux to induce spallation depends on pulse duration and initial particle geometry. Thermal simulations indicate that complete Al melting occurs in less than 5 ns, with steady state occurring before 20 ns. Experimentally, spallation was observed between 18 and 79 ns. The laser conditions to induce spallation in an oxygen-deprived environment (<200 ppm oxygen) are identical to those in open air, suggesting a thermomechanical spallation mechanism rather than a diffusion-reaction mechanism.