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Molecular dynamics study of interfacial bonding strength of self-assembled monolayer-coated Au-epoxy and Au-Au systems |
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| Authors: | Hsien-Chie Cheng Yu-Chen HsuChun-Hung Wu Wen-Hwa Chen |
| Institution: | a Department of Aerospace and Systems Engineering, Feng Chia University, Taichung 40724, Taiwan, ROC b National Center for High-Performance Computing, Hsinchu 30076, Taiwan, ROC c Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan, ROC d National Applied Research Laboratories, Taipei 10622, Taiwan, ROC |
| Abstract: | Interfacial adhesion between metals and organic polymers plays a crucial role in the mechanical properties and reliability performance of multiplayer thin film structures. To improve their interfacial bonding strength and so the reliability, the self-assembled monolayer (SAM) method is considered as an effective means. The present study is devoted to studying the effects of SAM coating on the interfacial bonding strength of the Au-epoxy and the Au-Au bonding structures through molecular dynamics (MD) simulation. Three different types of functionalized alkanethiol SAMs (SH(CH2)nX, X = CH3, OH, NH2) chemisorbed onto two different Au crystal planes, i.e., (1 0 0) and (1 1 1), are considered. The study starts from the characterization of the interfacial bonding strength of both the SAM-coated Au-epoxy and Au-Au systems, followed by the investigation of the dependence of the interfacial bonding strength on the chain lengths and tail groups of the n-alkanethiolates. A comparative study of the effects of the crystal orientation of Au substrate on the bonding strength is reported, and the elastic moduli of these SAMs through uniaxial tensile simulation are also examined. The calculated results are compared with the published experimental data, and also with each other to identify the optimal SAM candidate.Results show that the interfacial bonding strength of the SAM-coated Au-epoxy and Au-Au systems exhibits a strong dependency on the crystal orientation of Au substrate and also on the chain length of the monolayer where it tends to increase with an increasing SAM chain length. In specific, the interfacial bonding strength of the SH(CH2)nCH3 SAM-coated Au-Au joint would reach a maximal value at the chain length n = 8 while that of the SAM/epoxy interface in the SH(CH2)nCH3 SAM-coated Au-epoxy system attains a minimal value at n = 4 and becomes the maximum at n = 10, regardless of the crystal orientation of the Au substrates. Besides, the Au substrate with (1 1 1) crystal orientation would outperform the Au(1 0 0) substrate in the SAM/epoxy interfacial bonding strength of the SAM-coated Au-epoxy system while there is a totally opposite result for that of the SAM-coated Au-Au joint. |
| Keywords: | Self-assembled monolayer Molecular dynamics simulation Bonding strength Au-epoxy bi-material structure Au-Au joint |
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