Discovery of a Structure Mediated by a Reconstructed Aluminum Atomic Layer at an AlN/Al₂O₃ Interface

Interfaces often exhibit a variety of unusual physical phenomena. The highly complex atomic arrangements exist at interfaces that crucially affect the properties of a material; however, atom-by-atom pinpointing the structural features always presents a significant challenge. Herein we employed a combination of electron microscopy, calculations, and simulations to investigate the atomic-level structural characteristic of the well-known Al-O-N interface in a large lattice mismatch system. We observed a reconstructed atom layer mediated by Al atoms via aberration-corrected scanning transmission electron microscopy. The presence of Al-O and Al-N chemical bonds was identified at the interfacial region via electron energy loss spectroscopy. Consistent with the result of first-principles calculations, we unambiguously clarified the ratio 1:2 of O/N atoms at the interface, and the reduction in the band gap was primarily attributed to the weakening of Al-O bonds. Our findings provide a vivid case to deepen our understanding of complex interfaces.