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Front. Mater. | doi: 10.3389/fmats.2018.00071

Elucidating the exceptional passivation effect of 0.8 nm evaporated aluminum on transparent copper films

 Philip Bellchambers1,  Jaemin Lee1, Silvia Varagnolo1, Houari Amari2,  Marc Walker2 and  Ross A. Hatton1*
  • 1Department of Chemistry, Faculty of Science, University of Warwick, United Kingdom
  • 2Department of Physics, Faculty of Science, University of Warwick, United Kingdom

Slab-like copper films with a thickness of 9 nm (~70 atoms) and sheet resistance of ≤ 9 Ω sq-1 are shown to exhibit remarkable long-term stability towards air-oxidation when passivated with an 0.8 nm aluminium layer deposited by simple thermal evaporation. The sheet resistance of 9 nm Cu films passivated in this way, and lithographically patterned with a dense array of ~6 million apertures per cm-2, increases by less than 3.5% after 7000 hrs exposure to ambient air. Using a combination of annular-dark field scanning transmission electron microscopy, nanoscale spatially resolved elemental analysis and atomic force microscopy, we show that this surprising effectiveness of this layer results from spontaneous segregation of the aluminium to grain boundaries in the copper film where it forms a ternary oxide plug at those sites in the metal film most vulnerable to oxidation. Crucially, the heterogeneous distribution of this passivating oxide layer combined with its very low thickness ensures that the underlying metal is not electrically isolated, and so this simple passivation step renders Cu films stable enough to compete with Ag as the base metal for transparent electrode applications in emerging optoelectronic devices.

Keywords: electrode, passivation, lithography, transparent electrode, Copper film, Copper electrode, Window electrode, ultra-thin, Aluminum Oxide

Received: 14 Aug 2018; Accepted: 05 Nov 2018.

Edited by:

Hyung-Ho Park, Yonsei University, South Korea

Reviewed by:

Ho Won Jang, Seoul National University, South Korea
Won Il Park, Hanyang University, South Korea
Hong-Sub Lee, Kangwon National University, South Korea  

Copyright: © 2018 Bellchambers, Lee, Varagnolo, Amari, Walker and Hatton. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Ross A. Hatton, Department of Chemistry, Faculty of Science, University of Warwick, Coventry, CV4 7AL, West Midlands, United Kingdom, ross.hatton@warwick.ac.uk