Borane–Aluminum Surface Interactions: Enhanced Fracturing and Generation of Boron–Aluminum Core–Shell Nanoparticles

We present an experimental and theoretical study of borane–aluminum surface interactions that lead to rapid production of aluminum nanoparticles when Al balls are milled in the presence of diborane or pentaborane. Mass spectrometry was used to probe reactions of the boranes with aluminum fracture surfaces produced by milling collisions, which also generate local, transient high temperatures. Density functional theory was used to examine the interactions between a model aluminum surface and diborane and pentaborane, providing insight into the energetics of the first steps in the process that ultimately enables nanoparticle production. Further insight into the surface chemistry was obtained by analyzing the nanoparticles with X-ray photoelectron spectroscopy, scanning transmission electron microscopy with both electron-energy-loss and energy-dispersive X-ray spectroscopies, and dynamic light scattering. Particles were found to have fcc aluminum cores, capped by a ∼2-nm-thick shell, rich in both boron and hy...