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Atomic Force Microscope
Atomic Force Microscope (AFM)
As the newest in high-tech microscopy with ultra-fine resolution, the Atomic Force Microscope (AFM) holds the title as the world's best microscope that does not require a vacuum chamber. Its design was closely influenced by the invention of the Scanning Tunneling Microscope in the early 1980's by Binnig et al over at IBM's Zurich research center. A few years after their successful demonstration of the STM as the only microscope to clearly visualize atoms, they launched their second version to the amazement of the scientific world. The year was 1986, and it would be a fateful year for Binnig and his team. That was the year they unveiled the AFM and received a Nobel Prize for their work on the STM. If it were not for Binnig and IBM's funding of his work, nanotechnology would not be possible.
The atomic force microscope works like the scanning tunneling microscope in terms of the 'scanning' portion of the microscopy. A piezoelectric sample position manipulator can move the specimen in three dimensions with precision in angstroms. The difference with the AFM and the STM is in the mode of information. Instead of tunneling electrons jumping across an air gap, this time a sharp probe (usually only an atom-wide at the tip) comes into contact with the surface. The probe is shaped like a cantilever, with the probe tip at the end of it. As the specimen moves underneath the tip, it flexes up and down accordingly. These scant motions are monitored by a laser that reflects off the top of the tip and into a photodiode that can accurately detect the subtle movements.
The result is a topographical image of the surface of the specimen in true 3D. In an interesting spin on the idea, scientists have found that the tip is also very useful for investigating the material properties of a sample by tapping it with the probe or using lateral dragging movements. While this sort of behavior will cause some damage to the surface, it extends the usefulness of the microscope quiet a bit.
Researchers at IBM have even taken it one step further. They think that a hard drive based on an AFM tip could store more information on a single substrate than is currently imaginable. Though it is still in the preliminary research stages, such innovative use of a microscopy technique is worth mention.
The reason why AFMs are so popular these days is not only due to its great precision. It is currently the only microscope that does not require a vacuum or extensive sample calculations. The only drawbacks are its relatively small scanning area, poor depth resolution, slow scanning speed, and the need for constant human monitoring.