AVS 45th International Symposium
    Nanometer-scale Science and Technology Division Thursday Sessions
       Session NS-ThP

Paper NS-ThP9
Quantitave Surface Force Gradient Measurements Using Atomic Force Microscopy

Thursday, November 5, 1998, 5:30 pm, Room Hall A

Session: Nanometer-Scale Science and Technology Division Poster Session
Presenter: L.A.W. Sanderson, University of Alabama, Huntsville
Authors: L.A.W. Sanderson, University of Alabama, Huntsville
M.A. George, University of Alabama, Huntsville
J.J. Weimer, University of Alabama, Huntsville
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The accepted theory that reconciles attractive and repulsive forces has become known as the Deryaguin-Landau-Verwey-Overbeek (DLVO) theory and may be simply stated as V@sub S@ = V@sub C@ + V@sub A@ + V@sub R@ , where V@sub S@ is the total potential, V@sub C@ is the core repulsive potential due to Pauli exclusion, V@sub A@ is the Van der Waals attractive potential and V-@sub R@ is the double layer repulsive potential. The DLVO theory is widely regarded as a cornerstone for understanding colloidal systems and forces on the molecular scale. The objective of this study is to characterize the forces between two surfaces at the molecular scale using an atomic force microscope (AFM) and to relate the results quantitatively to parameters in DLVO theory. Investigations have been made using an AFM of surface forces present between a standard Si@sub 3@N@sub 4@ AFM tip and mica substrates for water, ethanol, and carbon tetrachloride. Results agree with those previously reported in the literature. Colloidal probes over mica and silica substrates are being used in on going research to provide easier geometries for comparison to the DLVO theory. Variations in surface forces as a function of pH and salt concentrations are being examined. The goal is to obtain a means of characterizing molecular scale forces over thin films such as aminopropyltriethoxysilane and polyethyleneglycol anchored to substrates. From a fundamental side, understanding of these forces is also important in analyzing the behavior of such molecules in solution, and the results can be used to select solutions for improving image resolution with the AFM.