Nanoscale Mechanical Properties
Mechanical properties such as hardness, elastic modulus, stiffness and
compressibility as well as material behavior such as plastic deformation,
and fracture can be studied with the AFM.
It is possible to study nano-hardness by directly pressing an AFM probe
into a sample's surface; however, it is advantageous to use an instrument
that is optimized for nano-indentation. The primary advantage of the
nano-indenter over an AFM for nano-hardness measurements is that it is
easier to get calibrated measurements with the nano-indenter. It is useful
to use the AFM to measure the three-dimensional topography of indentations
made with a nano-indenter. AFM images allow direct visualization of material
deformation or fracture behavior.
Figure 7: Three-dimensional view of nano-indents in a material surface.
From the AFM image it is possible to see the depth of the indentation
as will as visualizing the material deformation.
Using techniques such as pulsed force mode, the stiffness of a sample at a
matrix of locations is measurable. From this data it is possible to create
a stiffness mapping of a surface. Stiffness maps can only be made on samples
where the stiffness of the surface is lower than the stiffness of the
cantilever. Such stiffness images are routinely measured on polymer samples.
Adding a fixture to the stage of the AFM makes the study of material
behavior such as plastic deformation and fracture possible. The fixture
permits creating forces on a sample while AFM images are being taken.
A variety of materials may be studied with such a technique.
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