MECHANICS OF ADHESION - Nanoindentation with Biological Applications - page 99

Figure 4-11. The variations in the net force (solid line) with tip position for combined
Mie (M) and harmonic (S) interactions (dotted lines) between a probe tip and a surface as
an actuator moves the probe towards the surface. The probe spring stiffness is sub-critical
such that stable equilibrium positions of the tip are possible only for limited domains of
imposed probe position. The domains are separated by a non-equilibrium “snap-on”
configuration. The values are normalized using the characteristic values ( Eqs. 4-22 and
4-25) .

surface) from the instability point. As in the super-critical case, further
decrease in s through s / z 0 = 2.5 leads to almost invariant tip position
as z ∗ / z 0 → 1 , until at s / z 0 = 1.0, z ∗ / z 0 = 1 and the probe and surface are
at the quiescent point. Further decreases in s beyond this point lead to an
indentation interaction as before.
Figure 4-12 displays the retraction segment that leads to a pull-off
instability and separation and begins with the system at the quiescent
point of s / z 0 = 1.0, z ∗ / z 0 = 1. As s is increased to s / z 0 = 2.5 the tip