AVS 47th International Symposium
    MEMS Thursday Sessions
       Session MM-ThA

Paper MM-ThA10
Viewing a Moving Surface Contact: An STM-QCM Study of Vapor Deposited Films on Metal Surfaces

Thursday, October 5, 2000, 5:00 pm, Room 309

Session: Material Science of MEMS
Presenter: B. Borovsky, North Carolina State University
Authors: B. Borovsky, North Carolina State University
M. Abdelmaksoud, North Carolina State University
J. Krim, North Carolina State University
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With the emergence of MEMS technology and the problems of high friction and mechanical failure encountered in the operation of such devices, new experimental techniques are needed which are able to probe nanometer scale contacts under sliding conditions relevant to MEMS. By combining a Scanning Tunneling Microscope (STM) with a Quartz Crystal Microbalance (QCM), we have constructed a nanotribological test set-up in which a single asperity contact is subject to contact pressures and sliding speeds relevant to both MEMS and macroscopic devices. We have applied STM-QCM to the study of vapor phase lubricants, which may prove to be an effective, and perhaps exclusive, means of lubricating MEMS devices. The STM allows direct imaging of the surface contact under both stationary and vibrating conditions, and is able to track changes in the conductivity and mobility of molecularly thin lubricant films. Surprisingly, the amplitude and speed of the sliding contact may be directly measured using STM images of the vibrating QCM surface. We show that the QCM achieves sliding speeds over 1 m/s and senses changes in sliding friction as a function of normal load upon application of a lubricant film to a bare metal surface. Together, our nanometer scale STM-QCM results are highly suggestive of the known macroscopic lubricant properties of the applied films. By performing rubbing-and-imaging experiments with this combined apparatus, dramatic changes in the properties of the contact are observed which are highly localized to the region of rubbing. Such investigations provide evidence of possible tribochemical effects, the observation of which is associated with the realistic sliding conditions attained with the STM-QCM. Research supported by the NSF and the AFOSR.