Scanning Tunneling Microscopy (STM) uses a thin metal (tungsten) probe that scans a specimen and produces an image revealing the bumps and depressions of the atoms of the surface of the specimen.

The resolving power of an STM is much greater than that of an electron microscope; it can resolve features that are only about 1/100 the size of an atom. Moreover, special prepirations of the specimen for observation is not needed. STMs are used to provide incredibly detailed views of molecules such as DNA.

On a personal note, those are very pricey so I was never lucky enough to use one, thus I cannot give any further details on the subject.

Actually, scanning tunneling microscopes come in quite a wide variety. It's possible to build STMs that operate at room temperature and atmospheric pressure, although only certain, unreactive surfaces can be viewed. However, if you do the work yourself, these can be built very cheaply. (Buying one could cost you a good $10,000.) To do more advanced work, though, you usually have to operate at very low temperatures -- such as that of liquid nitrogen (100 Kelvin) or liquid helium (4.3 K) -- and at ultra-high vaccuum. This is much more difficult.

Besides letting you "view" the electron surface of a material, an STM also lets you do neat things like manipulate individuals atoms or moltecules on a surface -- allowing you to create a quantum corral or the smallest IBM logo in the world.

Other than the obvious benefit of seeing the crystal structure of a material's surface, we can also study the electronic properties of individual atoms or molecules and even carry out chemical reactions one atom at a time.

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