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Dynamic Surface Force Measurement. 2. Friction and the Atomic Force Microscope

Summary: Dynamic Surface Force Measurement. 2. Friction and the
Atomic Force Microscope
Phil Attard*
Ian Wark Research Institute, University of South Australia,
The Levels, South Australia 5095, Australia
Archie Carambassis and Mark W. Rutland
School of Chemistry F11, University of Sydney, New South Wales, 2006, Australia
Received July 8, 1998. In Final Form: November 2, 1998
The mechanism and geometry of force measurement with the atomic force microscope are analyzed in
detail. The effective spring constant to be used in force measurement is given in terms of the cantilever
spring constant. Particular attention is paid to possible dynamic effects. Theoretical calculations show that
inertial effects may be neglected in most regimes, the exception being when relatively large colloidal probes
are used. Model calculations of the effects of friction show that it can cause hysteresis in the constant
compliance region and a shift in the zero of separation. Most surprising, friction can cause a significant
diminution of the measured precontact force, and, if it actually pins the surfaces, it can change the sign
of the calibration factor for the cantilever deflection, which would cause a precontact attraction to appear
as a repulsion. Measurements are made of the van der Waals force between a silicon tip and a glass
substrate in air. The evidence for friction and other dynamic effects is discussed. Interferometry is used
to characterize the performance of the piezoelectric drive motor and position detector used in the atomic
force microscope. It is shown that hysteresis in the former, and backlash in the latter, preclude a quantitative


Source: Attard, Phil - School of Chemistry, University of Sydney


Collections: Chemistry