|
Vol.
28 No. 2
March-April 2006
Atomic Force Microscopy and Direct Surface Force Measurements (IUPAC Technical Report)
John Ralston, Ian Larson, Mark W. Rutland, Adam A. Feiler, and Mieke Kleijn
Pure and Applied Chemistry
Vol. 77, No. 12, pp. 2149–2170 (2005)
doi:10.1351/pac200577122149
The atomic force microscope (AFM) is designed to provide high
resolution (in the ideal case, atomic) topographical analysis,
applicable to both conducting and nonconducting surfaces.
The basic imaging principle is very simple: a sample attached
to a piezoelectric positioner is rastered beneath a sharp
tip attached to a sensitive cantilever spring. Undulations
in the surface lead to deflection of the spring, which is
monitored optically. Usually, a feedback loop is employed,
which holds the spring deflection constant, and the corresponding
movement of the piezoelectric positioner thus generates the
image.
From this it can be seen that the scanning AFM has all the
attributes necessary for the determination of surface and
adhesion forces; a sensitive spring to determine the force,
a piezoelectric crystal to alter the separation of the tip
and surface, which if sufficiently well calibrated also allows
the relative separation of the
tip and surface to be calculated. One can routinely quantify
both the net surface force (and its separation dependence)
as the probe approaches the sample, and any adhesion (pull-off)
force on retraction.
Interactions in relevant or practical systems may be studied,
and, in such cases, a distinct advantage of the AFM technique
is that a particle of interest can be attached to the end
of the cantilever and the interaction with a sample of choice
can be studied, a method often referred to as colloid probe
microscopy. The AFM, or, more correctly, the scanning probe
microscope, can thus be used to measure surface and frictional
forces, the two foci of this report. There have been a wealth
of force and friction measurements performed between an AFM
tip and a surface, and many of the calibration and analysis
issues are identical to those necessary for colloid probe
work. This report confines itself primarily to elements of
colloid probe measurement using the AFM.
www.iupac.org/publications/pac/2005/7712/7712x2149.html
Page
last modified 10 August 2006.
Copyright © 2003-2006 International Union of Pure and
Applied Chemistry.
Questions regarding the website, please contact [email protected]
|