AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS2-MoA

Paper SS2-MoA10
Degradation of Self-Assembled Monolayer in Humid Environments

Monday, November 3, 2003, 5:00 pm, Room 327

Session: Tribology, Adhesion, and Friction
Presenter: B.-I. Kim, Sandia National Laboratories
Authors: B.-I. Kim, Sandia National Laboratories
T.M. Mayer, Sandia National Laboratories
M.G. Hankins, Sandia National Laboratories
M.P. de Boer, Sandia National Laboratories
B.C. Bunker, Sandia National Laboratories
Correspondent: Click to Email
Self-assembled monolayers (SAMS) are used extensively to control friction and stiction in micromachines. While as-prepared coatings are effective at minimizing adhesion, coating performance can deteriorate with time in humid environments. We are using the interfacial force microscope (IFM) to monitor the aging behavior of SAMS as a function of temperature, humidity, time, SAM composition, and fabrication procedures. The IFM provides force-distance curves between functionalized scanning probe tips and substrate surfaces while avoiding the "snap-to-contact" problems associated with conventional atomic force microscopy(AFM). We have simultaneously measured both normal and friction forces between a tip and SAM coated surfaces as a function of separation distance. Together with topographic images taken with AFM, we can correlate adhesion and friction with structural information. Our results indicate that adsorbed water can disrupt hydrogen bonds at the SAM-substrate interface, reorganizing the coating to create bare patches that promote adhesion. To date, coatings that have been tested include standard octadecyl trichlorosilane (OTS), tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS), octadecene (reacted with surface Si-H bonds), dichlorodimethylsilane(DDMS), and an octadecyl coupling agent attached to the surface using amine functional groups. At all humidities and temperatures tested, it appears that FOTS coating that have been annealed to promote condensation reactions with surface silanols are most effective at resisting degradation in hot, humid environments. @FootnoteText@ Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.