The influence of capillary condensation and humidity to friction and adhesion properties on a nanometer scale has been studied using a bidirectional force microscope. On a hydrophilic silicon oxide surface strong capillary formation could be observed at high humidities, whereas, on less hydrophilic amorphous carbon films and lubricated silicon oxide surfaces, capillary formation is suppressed. The hydrophilicity of the surface is also found to promote the lubricative effects of adsorbed water.

To simulate the nanotribological effects of adsorbed water molecules and the capillary condensation of water around contacting asperities, we have studied the friction and adhesive forces acting on the tip of a friction force microscope in contact with a flat surface as function of humidity. On the hydrophilic surface of silicon oxide strong capillary formation occurs around the tip. In contrast, on the hydrophobic surface of silicon oxide covered with a perfluoropolyether lubricant, the water capillary formation around the tip is greatly suppressed. Friction and adhesive forces decrease substantially with increasing humidity during sliding of the tip across both sample surfaces, implying that the surfaces are lubricated by adsorbed water.

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We show the simultaneous recording of normal and lateral forces arising in scanning force and friction microscopy on a potential controlled sample immersed in aqueous electrolyte. As a liquid film is present on virtually all solid surfaces under ambient conditions, it is important to control the properties of the solidfliquid interface. In order to obtain reliable information on the friction behaviour of such a surface, a set-up for potentiostatic control of the sample was established. Experiments have been carried out with a stand-alone scanning force and friction microscope (SFFM), combined with an electrochemical cell providing potential control of the sample. First results of simultaneous normal and friction force measurements, obtained on highly oriented pyrolytic graphite (HOPG) immersed in NaCIO,, demonstrate the promising potential of the method.

Electrochemical scanning tunneling microscopy study of the electrochemical behavior of naked and nalkanethiol modified Au (111) surfaces in F− and CN−containing electrolyte solutions Summary Abstract: Dipalmitoylphosphatidylcholine-Langmuir-Blodgett films on various substrates [Si(111), Au, Sn] studied by scanning tunneling microscopy