AFM University Introduction to Atomic Force Microscopy by Paul West

« Cover
« Foreward
« Chapter 1
 
1.1. History
1.2. Comparison
1.3. Enabling Nanotechnology
 « Chapter 2
 « Chapter 3
 « Chapter 4
 « Chapter 5
 « Chapter 6
 « Chapter 7
« Appendix A
« Appendix B
« Appendix C
« Appendix D
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Chapter 1
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The force sensor in an atomic force microscope is typically constructed from a light lever, see Figure 1-3. In the light lever, the output from a laser is focused on the backside of a cantilever and reflected into a photo-detector with two sections. The output of each of the photo-detector sections is compared in a differential amplifier. When the probe at the end of the cantilever interacts with the surface, the cantilever bends, and the light path changes causing the amount of light in the two photo-detector sections to change. Thus the electronic output of the light lever force sensor, So, is proportional to the force between the probe and sample.

FIGURE 1-3 Illustration of the light lever force sensor (left). An AFM SEM image of the cantilever/probe used in an AFM force sensor (right).

Although the AFM is capable of extreme magnification, it is not a large instrument. An AFM that is capable of resolving features as small as a few nanometers can be easily installed in a laboratory on a desk top. The greatest deterrent to high magnification with the AFM is often environmental vibrations that cause the probe to have unwanted vibrations.
Although the AFM is an amazing instrument for visualizing and measuring nanometer scale features, it has several characteristics that make it unique. They are:
a)
Built-in, Atomic-scale Sensitivity - Most measuring instruments become larger when greater sensitivity is required. With an AFM the sensitivity is built-in at the nanometer or atomic scale. Thus to make the instrument more sensitive, there is no need to make it larger.
b)
Fabrication Technology – An AFM may be used for rapidly making changes in surface structures at the nanometer scale. Such changes can be made for the fraction of the amount it would cost with traditional technologies such as e-beam or photolithography.

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