Paper MN+IJ+TR-ThA3
Sidewall Tribometer and Quartz Crystal Microbalance Study of a Self-Assembled Monolayer Lubricant Reservoir Effect
Thursday, November 12, 2009, 2:40 pm, Room B3
Long hydrocarbon and fluorocarbon based monolayers have been widely used in MEMS applications to prevent release related stiction and adhesion.[1] These and similar monolayers, however, have proven ineffective as MEMS lubricants alone. Indeed, even the most robust of SAM layers fails to protect devices from tribological failure for either normal or sliding cyclic contact [2]. Alternate schemes, such as vapor phase lubrication, must therefore be developed if progress is to occur. [3] The vapor phase of pentanol has recently been reported by Asay et al to extend the lifetime of a MEMS device in a mixture of dry nitrogen and various concentrations of pentanol. [4] This method of lubrication poses it’s own set of issues in applications where devices need to be operated in native environments outside of lubricating vapors. Namely, does the vapor adsorb onto the surface in such a way that it will continue to lubricate in the native environment. In this study we have used a quartz crystal microbalance (QCM) to measure the adsorption and mobility of ethanol onto a surface coated with a perfluorodecyltrichlorosilane self assembled monolayer and a bare silicone surface. We have also used a MEMS sidewall tribometer to measure lifetimes of a SAM coated and uncoated device dosed with ethanol vapor. QCM measurements show that the self assembled monolayer retains ethanol on the surface once the vapor is removed and the tribometer lasts two orders of magnitude longer with the self assembled monolayer present once the ethanol vapor is removed. This data provides strong evidence that the self assembled monolayer acts as a lubricant reservoir and allows the residual ethanol to flow back into the contact area lubricating for extended periods of time.Work funded by the AFOSR Extreme Friction MURI
1 Srinivasan, U., Houston, M.R., Howe, R.T., Maboudian, R., “Alkyltrichlorosilane-Based Self-assembled Monolayer Films for Stiction Reduction in Silicon Micromachines”, Journal of Microelectromechanical Systems 1998, 7, 252-260
2 Hook, D.A., Timpe, S.J., Dugger, M.T., Krim, J., “Tribological Degradation of Fluorocarbon Coated Silicon Microdevice Surfaces in Normal and Sliding Contact” Journal of Applied Physics, 104, 034303, (2008)
3 Krim, J., Abdelmaksoud, M., “Nanotribology of Vapor-Phase Lubricants” Tribology Issues and Opportunities in MEMS, B. Bhushan, ed. (Kluwer Academic, Dordrecht, 1998), pp. 273-284, invited