Biomedical Engineering Reference
In-Depth Information
100
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20
0
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Distance (nm)
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Fig. 7.12. Bending stiffness tests on carbon nanotubes. Top: two individual lateral force-displacement
curves, measured at different points along a tube. The small arrow shows the reproducible buckling
force. Bottom: CNT force constant calculated from curves as shown above. As expected, the force
constant decreases with increasing distance from the fixed tube end, allowing calculation of the
material spring constant. Reproduced with permission from Wong
et al
. [506].
properties such as yield strength of one-dimensional materials can exceed those of the bulk
materials by orders of magnitude [501]. Indeed, it is due to their extremely high mechan-
ical strength and stiffness that carbon nanotubes (CNTs) are the most thoroughly com-
mercially exploited nanomaterial [502-504]. However, making mechanical measurements
of individual nanofibres is extremely difficult, mainly due to the difficulties in locating the
objects and fixing them to the testing devices. AFM is ideal for this task, as it can perform
both imaging and manipulation of the nanostructures. Furthermore the high positioning
accuracy makes it possible to mechanically probe objects having dimensions of less than
10 nm easily [502]. For this reason AFM-based techniques have been widely applied to
mechanical measurements of 1-D nanostructures [482]. For example, carbon nanotubes
[502, 505, 506], many metal oxide nanowires [507], and metal nanowires [508], and other
nanorods [506] have been studied by this technique. Mechanical measurements on 1-D
nanostructures using the AFM can be performed in a number of geometries, making it a
very powerful technique [509, 510]. Just two methods are highlighted below.
An example of the most commonly used approach for testing 1-D nanostructures by
AFM is the direct nanomechanical testing of single CNTs carried out by Wong
et al
. [506]
illustrated in Figure 7.12. Both multiwall carbon nanotubes and silicon carbide nanorods
were deflected, using lateral force microscopy (LFM) while monitoring the deflection of
