Biomedical Engineering Reference
In-Depth Information
(a)
(b)
38
150
37
36
35
34
33
32
100
50
0
-50
LC phase
LE phase
31
30
-100
0
5
10
15
20
0
5
10
15
20
Piezo movement (nm)
Piezo movement (nm)
(c)
8
6
4
LC phase
LE phase
9 N/m
2
0
-2
-4
-6
-8
-6 nN
-7.5 nN
0246
8 0 2
Rel. distance (nm)
FIGURE 2.15
(a) Spectroscopy curves obtained on the stripes (circles) and the channels
(crosses). The tip-sample interaction is calculated from this amplitude and frequency shift
versus distance curves. (b) Using the numerical procedure described in the text, we calculated
the corresponding tip-sample interaction force and potential. A significant difference between
the curves is observed for distances between 2 and 6 nm.
The local stiffness and adhesion force can be determined from the force curves
plotted in Figure 2.15. Here, we show amplitude and frequency shift versus distance
curves and the resulting tip-sample force measured on the LC- and LE-phase. The
force curves reveal an adhesion force of -6 and -7.5 nN on the stripes and channels,
respectively. However, the local stiffness is about 9 N/m for both positions, and we
could not determine a significant difference in the stiffness between the two phases
of the DPPC monolayers. This outcome can be attributed to the fact that the repul-
sive interaction forces for a thin film depends strongly on its thickness (Domke &
Radmacher, 1998). Therefore, the contact stiffness measured on the two phases of
the DPPC monolayer is dominated by the mica substrate.
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