Ah-ha, so that's what the needles are used for.
According to
Bob Wolkow, up in The Great White North(Alberta), quoted in The American Institute of Physics publication,
Physics News Update;
Quote:
The probe tips used in scanning tunneling microscopes (STMs), even though they produce atomic-resolution pictures of atoms sitting on the top layer of a solid material, are not themselves atomically thin. Rather their radius of curvature at the bottom is typically 10 nm or more.
Wolkow (rwolkow@ualberta.ca) says that although a narrower tip will be useful in the construction of STM arrays (you can pack more tips into a small area; and a wide array might even permit movies of atomic motions) the spatial resolution won't improve thereby. The real benefit of the sharp tungsten tips, he believes, will be as superb electron emitters. Being so slender, they would emit electrons in a bright, narrow, stable stream.
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That's the thingy that pdaoust mentioned.
