Effect of dynamic film debonding on self-assembled monolayers

Self-assembled monolayers (SAMs) provide an enabling platform for molecular tailoring of the chemical and physical properties of an interface in an on-demand fashion. In this work, we systematically vary SAM end-group functionality and investigate the failed interface between a transfer printed gold (Au) film and a SAM-functionalized fused silica substrate. SAMs with two different end groups are investigated: 11-bromo-undecyltrimethoxysilane and 11-mercapto-undecyltrimethoxysilane. The SAM-mediated interfaces are loaded by a non-contact laser-induced spallation method at strain rates in excess of 10⁶ s^-1. A high strain rate test method is selected to facilitate comparison with forthcoming molecular dynamics simulations of the molecular failure process. By making multiple measurements at increasing stress amplitudes (controlled by the laser fluence), the onset of delamination of Au films transfer-printed on different SAM modified substrates are compared. Varying the end-group functionality drastically alters the laser fluence necessary to induce delamination of Au films. We investigate failed interfaces for chemical composition and surface roughness using x-ray photoelectron spectroscopy and atomic force microscopy respectively. We demonstrate that the end group functionality for both 11-mercapto-undecyltrimethoxysilanes and 11-bromo-undecyltrimethoxysilane is expelled from the surface during laser spallation testing.