Surface Electronic Structure and Mechanical Characteristics of Copper鈥揅obalt Oxide Thin Film Coatings: Soft X-ray Synchrotron Radiation Spectroscopic Analyses and Modeling

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• 作者：Amun Amri ; Zhong-Tao Jiang ; Parisa A. Bahri ; Chun-Yang Yin ; Xiaoli Zhao ; Zonghan Xie ; Xiaofei Duan ; Hantarto Widjaja ; M. Mahbubur Rahman ; Trevor Pryor
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：August 15, 2013
• 年：2013
• 卷：117
• 期：32
• 页码：16457-16467
• 全文大小：673K
• 年卷期：v.117,no.32(August 15, 2013)
• ISSN：1932-7455

文摘

Novel copper鈥揷obalt 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鈥揼el 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.