|Measuring the dimensions of the tip and its lever by Scanning
In order to determine the force out of the beam deflection, the precise optics as well as the
spring constants of the cantilever have to be known.
The calibration procedure is one of the essential parts of
FFM-experiments. Each cantilever should be characterized accurately.
Manufacturer's data are usually not sufficient and can lead to errors
of up to a factor 10. Thus, each cantilever has to be characterized.
One way is to use an electron microscope and to deterimine all the
relevant parameters, such as: Tip radius R; heigth of tip h ;
width, thickness and length of cantilever (w/, t, l) and
position of tip on the cantilever. In addition, elastic constants are
needed: Youngs modulus E, shear modulus G. Having determined all
these parameters, the normal spring constant cB and the torsion
spring constant ct for a rectangular cantilever are given by:
From Scanning Electron Microscopy the dimensions of the cantilever
can be determined in order to compute its spring constant. One can
get more precise results by making use of the resonance frequency
instead of the thickness of the lever, since the thickness is a very
important property which can be determined only with troubles.