Aluminum Nanocrystals Form Voids under Their Native Oxide

Aluminum, the most abundant metal in the earth's crust, is protected and stabilized by a native surface oxide layer. Once the oxide is breached, rapid oxidation can occur, igniting Al in particulate form. By slowly heating and cooling Al nanocrystals of well controlled size and shape, we observe a localized void formation under the surface oxide, occurring on specific crystalline facets. These voids form during the slow cooling phase following heating, even for temperatures below the threshold of oxidation, in a manner sensitive to Al nanocrystal size and morphology, surface facet, and the degree of oxide porosity. Because of these sensitivities, this void formation may provide new strategies for modifying Al nanocrystal growth and developing Al nanocrystal-based hybrid materials.