Tree-like nanostructured gamma-Al2O3 tends to form at the interface of Al/glass during anodic bonding. The gamma-Al2O3 trees possess a distorted lattice and contain crystallographic defects including grain boundaries, twins, stacking faults, dislocation loops, and edge dislocations. They grow into the glass to a much greater degree than into the aluminum. Between the trees are aluminum-enriched amorphous regions. The Al/gamma-Al2O3 interface is sharp and is free of an amorphous layer. The diffusion of aluminum into the glass does not lead to gamma-Al2O3 trees if low voltages or short bonding durations are employed. (c) 2007 Elsevier B.V. All rights reserved.