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|Title:||Surface electronic structure and mechanical characteristics of copper-cobalt oxide thin film coatings: soft X-ray synchrotron radiation spectroscopic analyses and modeling|
|Citation:||The Journal of Physical Chemistry Part C: Nanomaterials and Interfaces, 2013; 117(32):16457-16467|
|Publisher:||American Chemical Society|
|Amun Amri, Zhong-Tao Jiang, Parisa A. Bahri, Chun-Yang Yin, Xiaoli Zhao, Zonghan Xie, Xiaofei Duan, Hantarto Widjaja, M. Mahbubur Rahman, and Trevor Pryor|
|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.|
|Keywords:||Copper concentration; Field emission scanning electron microscopy; Mechanical characteristics; Nanomechanical testing; Near-edge X-ray absorption fine structure spectroscopies; Sol-gel dip-coating method; Surface electronic structures; Synchrotron radiation x-rays|
|Rights:||© 2013 American Chemical Society|
|Appears in Collections:||Mechanical Engineering publications|
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