VISUALIZATION AT THE NANOSCALE
In order to manipulate matter on an atomic scale, we need to see individual atoms and molecules. Although individual molecules have been visualized with the electron microscope, it was the development of scanning probe microscopes that opened up the field of nanotechnology. These instruments all rely on a miniature probe that scans across the surface under investigation.
All scanning probe microscopes work by measuring some property, such as electrical resistance, magnetism, temperature, or light absorption, with a tip positioned extremely close to the sample. The microscope raster-scans the probe over the sample (Fig. 7.2) while measuring the property of interest.
The data are displayed as a raster image similar to that on a television screen.
Unlike traditional microscopes, scanned-probe systems do not use lenses, so the size of the probe rather than diffraction limits their resolution. Some of these instruments can be used to alter samples as well as visualize them.
The first of these instruments was the scanning tunneling microscope (STM), which was developed by Gerd Binnig and Heinrich Rohrer at IBM (see following section). They received the Nobel Prize in 1986. The STM sends electrons, that is, an electric current, through the sample and so measures electrical resistance. The atomic force microscope (AFM) is especially useful in biology and measures the force between the probe tip and the sample.
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