JMM 2006 Abstract
Contact Scanning Mode AFM for Nanomechanical Testing of Free Standing
A technique for performing nanomechanical testing of free standing structures using
contact scanning mode atomic force microscopy (AFM) has been developed and implemented.
The technique consists of performing a contact mode scan of an area of a cantilever test
structure as well as of an area that does not deform. The use of two different values
of the force during the scan allows the effect of the topography of the test structure
to be eliminated. Also note that in this constant force scan, the bending moment in the
test cantilever changes continuously with the position of the applied force, allowing
both the stress and strain to change even though the force remains constant. With the
dimensions of the structure known, material properties (i.e. the elastic modulus) can
be determined from the relationship between the applied force and the structural
deflection. This method is not susceptible to nonlinearities in the AFM photodetector
and allows for piezo drift during testing to be quantified and corrected for.
P.J. Ryan, G.G. Adams, N.E. McGruer, N.E., and S. Müftü
Fifty nanometer thick chromium cantilever structures were fabricated for testing using
electron-beam lithography. The determination of the elastic modulus gave consistent
results as the AFM tip was scanned along the cantilever. As is the case with AFM fixed
position force-displacement measurements, the accuracy of the results are affected by
uncertainties in the measured AFM cantilever stiffness and by uncertainties in the test
structure dimensions. This testing method can be performed by any AFM capable of
scanning in the contact mode without requiring specialized software. Fabrication of the
cantilevers requires only a single mask process.