Biomedical Engineering Reference
In-Depth Information
(a)
35
MFM probe, polarized sample
MFM probe, shielded sample
AFM probe, polarized sample
30
25
20
15
10
5
0
0
10
20
Lift height (nm)
30
40
50
(b)
30
25
20
15
350 nm
10
5
0
10
20
30
40
50
Lift height (nm)
Figure 15.7
Quantitative analysis of MFM
data [2]. Phase-shift values obtained in MFM
experiments on MNPs as described in Figure
15.6. (a) Phase shift versus lift-height values
for the three experimental conditions, as
indicated. The strength of the probe- sample
interaction (and therefore the phase shift) is
largest when the magnetic force microscope
probe interacts with polarized MNPs (kept in
the presence of an external magnetic fi eld). At
lift heights
∼
20 nm, only the probe with
polarized MNPs shows signifi cant phase-
contrast values, while interaction of the probe
with unpolarized particles is similar to that of
a nonmagnetic probe; (b) Plot of phase-shift
data as a function of lift-height for the
experiment with a magnetic force microscope
probe and polarized MNPs (same as in panel
a) of average height
∼
20.0 nm, corrected for
phase shift due to background interaction
obtained as an average phase shift observed
at a given lift-height in the experiment with
the magnetic force microscope probe on
unpolarized particles. The fi t of these data
(solid line) using Equation 15.11 gives an
effective magnetic moment of the particles
studied as m
s
= 3.7
×
1 0
−
17
A m
2
; (inset in (b))
A TEM image of MNP samples show that the
majority of the particles are clusters or
aggregates of several 10 nm iron oxide
nanoparticles. Reproduced with permission
from Ref. [2] .
