Biomedical Engineering Reference
In-Depth Information
100
μ
m
(b)
(a)
20
μ
m
100
μ
m
(c)
(d)
250
μ
m
5
μ
m
5
μ
m
Figure 15.3
Evolution of magnetic force
microscope probes. (a) Optical micrograph of
a Ni cantilever/probe used in early magnetic
force microscopes [38] ; (b) Electron
microscope image of a modern MESP-type
magnetic force microscope tip, displaying the
small fl exible cantilever of about 200 mm
length and the actual tip, which is shown
further magnifi ed within the upper-right
section [39]; (c) SEM image of a single
as - grown carbon - nano - cap (CNC) probe on a
tipless cantilever. Inset: high- magnifi cation
SEM image of the CNC tip [40]; (d) SEM
image of a cross-section of a conical hole
produced by focused ion beam milling with
a nanotube attached inside the hole [41].
Reproduced with permission from Refs
[38 - 41] , as indicated.
15.6.1
Wire Probes
The early magnetic force microscope probes were composed of solid metallic wires
with tapered ends (Figure 15.3a) [38]. For MFM studies in ambient air, Ni wires
have been preferred as Fe wires can become oxidized. Such tips yield a larger tip-
volume and hence a larger tip magnetic moment
m
t
; this in turn will result in a
larger tip-sample interaction signal, but compromise on spatial resolution. Fur-
thermore, each probe must be calibrated individually, and the reproducibility of
an identical probe is diffi cult.
15.6.2
Thin - Film - Coated Si Probes
Due to the widespread use of AFM, cantilevers with integrated sharp tips are
fabricated today in large numbers from silicon-based materials. A typical magnetic
