Surface electronic structure and mechanical characteristics of copper-cobalt oxide thin film coatings: Soft X-ray synchrotron radiation spectroscopic analyses and modeling

Document Type

Journal Article

Publisher

American Chemical Society

Faculty

Faculty of Health, Engineering and Science

School

School of Engineering

RAS ID

15907

Comments

This article was originally published as: Amri, A., Jiang, Z., Bahri, P., Yin, C., Zhao, X. , Xie, Z. , Duan, X., & Widjaja, H., Rahman, M., Pryor, T. (2013). Surface Electronic Structure and Mechanical Characteristics of Copper-Cobalt Oxide Thin Film Coatings: Soft X-ray Synchrotron Radiation Spectroscopic Analyses and Modeling. The Journal of Physical Chemistry C, 117(32), 16457-16467.

This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/jp404841m

Abstract

Novel copper-cobalt oxide thin films with different copper/cobalt molar ratios, namely, [Cu]/[Co] = 0.5, 1, and 2, have been successfully coated on aluminum substrates via a simple and cost-effective sol-gel dip-coating method. Coatings were characterized using high resolution synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy, in combination with nanomechanical testing and field emission scanning electron microscopy (FESEM). The surfaces of both [Cu]/[Co] = 0.5 and 1 samples consisted primarily of fine granular nanoparticles, whereas the [Cu]/[Co] = 2 has a smoother surface. The analyses reveal that the increase of copper concentration in the synthesis process tends to promote the formation of octahedral Cu2+ which minimizes the development of octahedral Cu+, and these octahedral Cu2+ ions substitute the Co2+ site in cobalt structure host. The local coordinations of Co, Cu and O are not substantially influenced by the change in the copper to cobalt concentration ratios except for the [Cu]/[Co] = 2 coating where the local coordination appears to slightly change due to the loss of octahedral Cu+. The present film coatings are expected to exhibit good wear resistance especially for the [Cu]/[Co] = 1.0 sample due to its high hardness/elastic modulus (H/E) ratio. Finite element modeling (FEM) indicated that, under spherical loading conditions, the high stress and the plastic deformation were predominantly concentrated within the coating layer, without spreading into the substrate.

DOI

10.1021/jp404841m

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