| AVS 55th International Symposium & Exhibition | |
| Tribology Focus Topic | Wednesday Sessions |
| Session TR+MN+NC-WeM |
| Session: | Surfaces and Interfaces in MEMS/NEMS |
| Presenter: | D.A. Hook, North Carolina State University |
| Authors: | D.A. Hook, North Carolina State University B. Vlastakis, North Carolina State University B.P. Miller, North Carolina State University J. Rutledge, University of California, Irvine M.T. Dugger, Sandia National Laboratories J. Krim, North Carolina State University |
| Correspondent: | Click to Email |
Long hydrocarbon and fluorocarbon based monolayers have been widely used in MEMS applications to prevent release related stiction and adhesion. These and similar monolayers, however, have proven ineffective as MEMS lubricants. Indeed, even the most robust of SAM layers fails to protect devices from tribological failure for either normal or sliding cyclic contact.1 Alternate schemes, such as vapor phase lubrication, must therefore be developed if progress is to occur.2 The vapor phase of pentanol has recently been reported by Seong et al to extend the lifetime of a MEMS device in a mixture of dry nitrogen and various concentrations of pentanol. Macroscale friction experiments have meanwhile shown the build up of long carbon chain reaction films in identical conditions.3 In order to probe the effectiveness of pentanol and related alcohols, we have employed a ringdown measurement technique with a specially designed MEMS sidewall tribometer to compare the coefficients of friction of a device before and after introduction of pentanol into a vacuum chamber at one monolayer of coverage. Initial measurements show no change in the coefficient of friction, but subsequent measurements show a progressive decrease. This reflects a formation of a reaction film extremely quickly upon rubbing. Lifetime measurements using the sidewall tribometer were also taken with shorter chain alcohols, namely trifluoroethanol and ethanol, at one monolayer coverage to determine whether amount of carbon present affects the lubricating properties as well as the role of methyl versus trifluoromethyl termination. It has been found that ethanol’s ability to lubricate is dependant upon the initial state of the device whereas trifluoroethanol and pentanol will lubricate a device that has previously failed. Work funded by the AFOSR Extreme Friction MURI #FA9550-04-0381.
1Hook, 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, in press
2Krim, J., Abdelmaksoud, M., “Nanotribology of Vapor-Phase Lubricants” Tribology Issues and Opportunities in MEMS, B. Bhushan, ed. 1998 pp. 273-284
3Asay, D.B., Dugger, M.T., Ohlhausen, J.A., Kim, S.H., “Macro- to Nanoscale Wear Prevention via Molecular Adsorption”, Langmuir 2008, 24, 155-159.