Biomedical Engineering Reference
In-Depth Information
1.5
0.6
∆
V
0.3
1
0.0
∆
V
0.5
-0.3
0
-0.6
0
1
2
Distance (nm)
3
4
5
0
100
200
Distance (nm)
300
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
1.2
1.0
OH
0.8
0.6
0.4
CH
3
0.2
0
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
10
20
30
40
50
60
70
80
Load / nN
Cos
q
Fig. 7.8. Measuring friction. Top left: friction loop on a homogeneous material. The value of
˜V
is
characteristic of the materials at a set loading force. Top right: another friction loop acquired on a
crystal surface shows atomic-scale stick-slip behaviour. Bottom left: plot showing variation in the
friction force as a function of the load for a carboxylic acid-terminated tip contacting hydroxyl and
methyl terminated SAMs. From the gradient of these plots, we can obtain
, the coefficient of friction.
Bottom right: the value of
can be compared to other parameters. Here it is plotted versus cos
Ł
, the
water contact angle, which varies as the composition of a mixed SAM is altered. Figures adapted with
permission from [336, 453] (copyright 2000 by the American Physical Society), [334] and [454].
composite polymer materials, wood pulp, integrated circuits, quartz/silicon surfaces and
more. As described in Section 3.2.3.2, phase imaging is sensitive to viscoelastic properties
of the sample and to tip-sample adhesion. This means that many materials can be
differentiated by phase imaging, although it is not always possible to directly identify
the materials based on their phase signals, and the magnitude of the phase signal is hard to
Fig. 7.9 Example of mapping friction changes across a surface to characterize polymer film
heterogeneity. The sample is a Mylar D film, including additive particles at the surface. The images
show (a) left to right LFM image, (b) right to left image and (c) the subtraction of (b) from (a). The
difference in (c) removes topographic effects, and resolves the ambiguity generated by the differ-
ences between (a) and (b); the darker colour of the additive particles in (c) shows they have lower
friction than the film. Adapted with permission from [461].