(350g) Spot Welding Though a Molecular Boundary Layer Due to Repetitive Contact

Micro-switches are becoming increasingly present in modern electronic devices; however, their unreliable performance and limited useful lifetimes are still an issue. Low force repetitive cycling of a gold micro-contact (simulated by an Interfacial Force Microscope probe tip) provides a unique insight into the root cause of failure in these devices. Self assembling monolayers (SAMs), in addition to controlling the contamination present on the switching surfaces, lower the surface energy of the gold, reducing adhesion between the surfaces (a common reason for failure in MEMS) and enable us to consider the formation of a nano-scopic sharp spike on an initially smooth contact. Although SAMs have proven to be robust in single cycle events, such as nano-indentation, repetitive contact degrades the monolayer to the point where localized penetration causes the formation of a metallic spot weld. Feedback stablized withdrawal of the tip with minimal current flow allow us to generate nano-scale changes in topography, transforming an initially electrochemically smooth surface into a roughened one with drastically different resistance characteristics. Additionally, the presence of a SAM appears to enhance the formation of localized arcs as we break electrical contact.