What+is+STM

//__ What exactly does the __////__ STM __////__ do with a sample to scan it? __// The answer depends on some basic ideas from electricity, as well as the somewhat complicated phenomenon of quantum tunneling. Simply put, the STM scans its tip above the sample surface at the incredibly small distance of only a few nanometers and maintains a current between the sample and the tip as it moves. As the tip encounters changes in the contour of the surface, the current changes (an explanation for this follows) and the STM moves the tip up or down until the current reaches its original strength. The change in height of the tip is then mapped in the computer software. As mentioned above, the STM depends on electric current flow between the tip and the sample. This occurs even though there is no physical contact because, by the laws of quantum mechanics, some electrons flow between the tip and surface by "tunneling" through the air between them. The microscope is very sensitive to changes in height because the strength of a tunneling current changes exponentially with distance.

The action described above occurs when the STM works in "constant current" mode. It also has the capability to operate in "constant height" mode, in which the STM does not adjust the height of the tip as it scans. Instead, it relays information about changes in the current to the computer program, and this information is mapped as the image. In theory, both modes give the same representation of the surface.

//__ What can be scanned with an __////__ STM __////__ ? __// The answer is that almost any conducting material with a (relatively) smooth surface can be scanned. The biggest obstacle to overcome is figuring out how to mount a sample, especially one that has not been specially prepared for use on the STM. Different materials may require different mounting methods; outside help will most likely be necessary with this process.



https://sjhsrc.wikispaces.com/STM []

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