Chemistry Reference
In-Depth Information
be increased further and the tip-sample interaction force has to be reduced in order to
expand the scope of biomolecular processes towhich high-speedAFMcan be applied.
Because high-speed AFM is rather new, its technical issues are not commonly
known while only a few successful imaging experiments have been performed.
Therefore, in this chapter, we focus mainly on the fundamental issues of high-speed
AFM and the various techniques involved, which will, we hope, facilitate the entry of
young researchers to this new
field. In addition, some descriptions on substratum
preparations required for imaging biomolecular processes are given. Examples of
image data are also presented (video images can be seen at http://www.s.kanazawa-u.
ac.jp/phys/biophys/roadmap.htm).
12.2
AFM Set-up and Operation
A general AFM set-up is given in Figure 12.1. AFM forms an image by touching the
sample surface with a sharp tip attached to the free end of a soft cantilever beamwhile
the sample stage is being scanned horizontally in two dimensions. This contact
causes the cantilever to de
ection is often detected by an optical lever
method where a collimated laser beam is focused onto the cantilever and re
ect. The de
ected
back into closely spaced photodiodes whose photocurrents are fed into a differential
ampli
er. The output of the differential ampli
er is proportional to the cantilever
de
ection. During raster scan of the sample stage, the stage ismoved in the z-direction
to maintain a constant de
ection of the cantilever (hence, a constant tip-sample
Figure 12.1 Schematic of tapping mode AFM set-up.
