AVS 52nd International Symposium
    Surface Science Tuesday Sessions
       Session SS2-TuA

Paper SS2-TuA2
Capillary Adhesion and Tribology involving Adventitious Water on SiOx Surfaces

Tuesday, November 1, 2005, 2:20 pm, Room 203

Session: Tribology, Adhesion and Friction
Presenter: J.E. Houston, Sandia National Laboratories
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Thin water films adsorbed on surfaces are very important in interfacial interactions and can be critical in determining the behavior and stability of MEMS and NEMS-type devices, which are dominated by extremely high surface to volume ratios. In this presentation, the results of a study are discussed concerning the interfacial interaction of a silica tip and an O-H terminated SiOx surface as a function of both temperature and relative humidity. The study utilizes Interfacial Force Microscopy (IFM) and involves measurements of the normal and frictional forces as a function of interfacial separation. The results indicate, even at very low humidities, that the force profiles are characteristic of a capillary interaction. In addition, the behavior of the lateral force shows significant levels of friction upon capillary formation, increasing further as the two surfaces approach. Upon separating the surfaces, a small hysteretic behavior is observed but with little indication of the "snap-out" instability normally associated with meniscus rupture. These measurements are repeated as a function of tip speed, relative humidity and temperature in order to gain insight concerning the thickness of the water layers, their viscosities and the rates of capillary condensation and evaporation. These results are contrasted with those from similar experiments involving self-assembled monolayer films terminated by combinations of -CH3 and -COOH end-groups. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.