Low-Temperature Growth Improves Metal/Polymer Interfaces: Vapor-Deposited Ca on PMMA

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• 作者：Huanxin Ju ; Yifan Ye ; Xuefei Feng ; Haibin Pan ; Junfa Zhu ; Nancy Ruzycki ; Charles T. Campbell
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：March 27, 2014
• 年：2014
• 卷：118
• 期：12
• 页码：6352-6358
• 全文大小：400K
• 年卷期：v.118,no.12(March 27, 2014)
• ISSN：1932-7455

文摘

The controllable design of interfacial structures is of great importance in the applications of metal/polymer interfaces in a variety of technologies. The vapor deposition of Ca films on poly(methyl methacrylate) (PMMA) was studied as a prototype system to investigate the effects of substrate temperature on metal/polymer interfacial structure, using Ca adsorption microcalorimetry, sticking probability measurements, and X-ray photoemission spectroscopy. Earlier studies showed that when Ca vapor is deposited at room temperature, Ca atoms preferentially diffuse subsurface and react with the ester groups of PMMA at low coverage, leading to the formation of polymeric Ca carboxylates. As Ca coverage increases, the depth of the reacted polymer increases, so that diffusion of Ca through it to find unreacted esters gets slower, leading to an increase in the probability that Ca instead grows 3D Ca(s) particles on the surface, which eventually grow together into a continuous surface film. By deposition of metal vapor onto the polymer substrate at 90 K, the subsurface reaction is suppressed and a sharp Ca(s)/PMMA interface is instead obtained, essentially eliminating the intermediate layer of polymeric Ca carboxylate that forms at 300 K. The thickness of this intermediate layer is estimated to be <0.3 nm (0.6 layers of reacted PMMA) at 90 K, in contrast to 2.5 nm (5.4 layers of reacted PMMA) at 300 K. Thus, a cleaner and more abrupt Ca/PMMA interface is achieved by metal deposition at low substrate temperature, due to less competition from subsurface diffusion of the Ca atoms.