title: Atomic structures of a liquid-phase bonded metal/nitride heterointerface.
abstract: Liquid-phase bonding is a technologically important method to fabricate high-performance metal/ceramic heterostructures used for power electronic devices. However, the atomic-scale mechanisms of how these two dissimilar crystals specifically bond at the interfaces are still not well understood. Here we analyse the atomically-resolved structure of a liquid-phase bonded heterointerface between Al alloy and AlN single crystal using aberration corrected scanning transmission electron microscopy (STEM). In addition, energy-dispersive X-ray microanalysis, using dual silicon drift X-ray detectors in STEM, was performed to analyze the local chemistry of the interface. We find that a monolayer of MgO is spontaneously formed on the AlN substrate surface and that a polarity-inverted monolayer of AlN is grown on top of it. Thus, the Al alloy is bonded with the polarity-inverted AlN monolayer, creating a complex atomic-scale layered structure, facilitating the bonding between the two dissimilar crystals during liquid-phase bonding processes. Density-functional-theory calculations confirm that the bonding stability is strongly dependent on the polarity and stacking of AlN and MgO monolayers. Understanding the spontaneous formation of layered transition structures at the heterointerface will be key in fabricating very stable Al alloy/AlN heterointerface required for high reliability power electronic devices.
authors.affiliation: Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan.
authors.forename: Akihito
authors.initials: A
authors.lastname: Kumamoto
authors.affiliation: Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan.
authors.forename: Naoya
authors.initials: N
authors.lastname: Shibata
authors.affiliation: Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan.
authors.forename: Kei-Ichiro
authors.initials: K
authors.lastname: Nayuki
authors.affiliation: Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Tohei
authors.affiliation: Central Research Institute, Mitsubishi Materials Corp., Naka, Ibaraki 311-0102, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Terasaki
authors.affiliation: Central Research Institute, Mitsubishi Materials Corp., Naka, Ibaraki 311-0102, Japan.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Nagatomo
authors.affiliation: Central Research Institute, Mitsubishi Materials Corp., Naka, Ibaraki 311-0102, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Nagase
authors.affiliation: Central Research Institute, Mitsubishi Materials Corp., Naka, Ibaraki 311-0102, Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Akiyama
authors.affiliation: Central Research Institute, Mitsubishi Materials Corp., Naka, Ibaraki 311-0102, Japan.
authors.forename: Yoshirou
authors.initials: Y
authors.lastname: Kuromitsu
authors.affiliation: Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Ikuhara