Research announcements:
In this research, we work to uncover a more fundamental understanding of friction using the Atomic Force Microscope (AFM).
A schematic drawing of the AFM is shown at left. A tip, with typically 10-100 nm radius of curvature, which is attached to a compliant cantilever spring, is brought into contact with nominally flat surface. At low applied loads, the tip can form a nanometer-scale single contact point (an “asperity”) with the sample surfaces, thus providing, in principle, a well-defined interface. In practice, careful measurement of the tip shape is needed since substantial variations in tip size and shape are common for commercial AFM cantilevers. The cantilever’s deflections are recorded using, most commonly, a reflected optical beam. These deflections are converted to forces by using Hooke’s Law. The normal and lateral forces can be measured with sub-nanoNewton precision, provided that appropriate calibration methods are used. The tip is rastered over the surface with sub-Ångstrom displacement precision in x, y, and z using piezoelectric scanning tubes.
Additional information on how the AFM works.
A brand new state-of-the-art AFM was installed this fall in the nanotribology research lab. This system is designed and manufactured by Veeco Instruments in Santa Barbara, CA. This AFM, as pictured below, is a MultiMode V Nanoscope V AFM.
AFM tip deconvolution methods: "Pursuing improved atomic force microscope tip shape quantification methods at Luther College", Isaac White, Summer 2007 - Spring 2008
An important aspect of friction research is characterization of both sides of the tribological interface. For nanotribology studies usingthe AFM, it is crucial to determine the physical and chemical properties of both the surface and the AFM tip. Often the tip can be received from the manufacturer in unacceptable condition, with a tip apex that is broken or blunt. Techniques to determine tip geometry include direct imaging with a Scanning Electron Microscope or Transmission Electron Microscope (TEM), and indirect
methods.
Tip deconvolution is an indirect method to determine tip geometry. Imaging sharp features on a sample surface with an AFM tip results in an inverse image of the tip itself. If the surface feature is not infinitely sharp (which no real surface can be), mathematical methods must be used to extract an upper bound to the tip geometry.
The goal of this project is to compare TEM tip imaging with the indirect tip deconvolution method to quantify both techniques, as well as to determine the pros and cons of both methods. This information is important for future nanotribology research at Luther, as well as for the AFM community as a whole.
This research was recently presented at the MidStates Consortium Undergraduate Reseach Symposium at the University of Chicago (Nov 2007).
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Last updated 12/20/07