Introduction - Atomic Force Microscopy - page 6

30 Å

Z (Å)

(x10 -10 N)

30
20
10

X (Å)

100 200

Fig. 1.5. The first AFM instrument built by Binnig, Quate and Gerber in the Science Museum,
London (image copyright Science Museum/SSPL), and the first AFM image - reprinted with
permission from 19 . Copyright 1986 by the American Physical Society.

still sensitive to sub-angstrom motions of the cantilever [23, 24]. Furthermore, as sug-
gested by Binnig et al ., oscillating modes have further increased the range of samples that
AFMs can scan, and reduced the chance of sample damage as well.
Due to the high interest in AFM, commercial instruments were soon being produced, the
first available from 1988. Together, AFM and STM are often referred to as scanning probe
microscopy, or SPM. A further explanation of terminology in the SPM field is given in
Chapter 3. Since AFM and STM instruments share several components in common, it is
relatively simple to build an instrument capable of carrying out both kinds of microscopy.
Since together they are referred to as SPM, and because some instruments perform both
STM and AFM, the techniques are often seen as being very similar. However, since its
development, AFM has been modified to measure a huge number of different properties,
and perform lots of additional (non-imaging experiments), and combined with the tech-
niques' greater flexibility in terms of types of samples scanned, means AFM is today much
more widely used than STM. This topic concentrates on AFM, and will not discuss
STM further. For the reader interested in further details of STM, the works [25, 26] are
recommended.

1.2 AFM today

The AFM can be compared to traditional microscopes such as the optical or scanning
electron microscopes for measuring dimensions in the horizontal axis. However, it can
also be compared to mechanical profilers for making measurements in the vertical axis to a
surface. One of the great advantages of the AFM is the ability to magnify in the X , Y and Z
axes. Figure 1.6 shows a comparison between several types of microscopes and profil-
ometers. As shown in Figure 1.6, one of the limiting characteristics of the AFM is that it is