Nanoscale mechanical tailoring of interfaces using self-assembled monolayers

Functional groups in self-assembled monolayers (SAMs) provide a way to tailor the structural, thermal and electrical properties of interfaces, as the interaction between SAMs and target surfaces can range from weakly bonded to strong bonding. The present study focuses on evaluating the interfacial mechanical properties of SAMs with different affinities to a gold film. We use molecular dynamics (MD) with the ReaxFF potential to evaluate the spallation response of the SAM-gold interface characteristics for two SAMs, namely dodecyltriethoxysilane (DTES) and 11-mercapto-undecyltrimethoxysilane (MUTMS), which respectively have weak and strong bonding with gold. MD simulations predict the MUTMS-gold interface to be four times stronger than the DTES-gold interface. Laser spallation experiments performed to evaluate the cohesive strength of the two SAMs show a similar ratio of cohesive strength; however MD results are about 50 times higher than experimental observations. AFM surface analyses of interacting interfaces demonstrate that surface roughness values are of the same order as atomistic interactions. The role played by surface roughness is then incorporated in a simple continuum model.