Highlights

TEM Study of Nanoscale Cu-Ni(100) Alloy Oxidation

Scientific Achievement

The metal-oxide interface formed from the nanoscale oxidation Cu-Ni(100) alloys has been investigated by transmission electron microscopy (TEM).  NiO islands with the size of ~ 250nm are observed to form on the alloy surface.  The epitaxial relationship between the NiO islands and the Cu-Ni(100) substrate is identified as NiO(111)//Cu-Ni(100) and NiO(11)//Cu-Ni(010).  The high resolution TEM images reveal that the metal substrate and the oxide islands do not form smooth interface and atomic steps with multiple atomic heights (from two to five atomic layers thick) are present at the metal-oxide interface.  Dislocations are observed to form at the metal-oxide interface. No Cu oxide phase is observed.  However, surprisingly,  many small Cu particles (the particle size varies from 20 to 40 nm) are observed to form on the surface of NiO islands.

Significance

The metal-oxide interface plays a critical role in the mass transport for oxide growth during metal oxidation, but many fundamental questions still remain unresolved regarding the exact atomic structures at the metal-oxide interface and their effect on the transport of atoms between metal substrate and the oxide phase.  Some models have been proposed for such atom transport processes.  For example, Pieraggi and Rapp have proposed that the vacancies that are injected when the metal atoms diffuse into the oxide are annihilated by a dislocation climbing mechanism; however, it is still not verified experimentally.  Our TEM observations of the existence of dislocations at the metal-oxide interface from the Cu-Ni system provide the direct experimental evidence to support this dislocation climbing mechanism.  The formation of nanosized Cu particles on the surface of the NiO islands is an intriguing phenomenon and this may be related to some previously-unnoticed physical processes.  

Performers

G. W. Zhou, J. A. Eastman, D. Fong (Argonne-MSD); L. Wang (UIUC-MSE)