MIKKEL JUUL JENSEN / SCIENCE PHOTO LIBRARY MIKKEL JUUL JENSEN / SCIENCE PHOTO LIBRARY
Tunnelling current amplifier, computer artwork. Tunnelling current amplifiers are used in scanning tunnelling spectroscopy. This technique is used to provide information about the density of electrons in a sample, as a function of their energy, in order to obtain topographic maps of surfaces. A metal tip (red) is moved over a conducting sample (blue) without making mechanical contact. A bias voltage between the sample and tip allows a current to flow between the tip and the sample even though they are not in contact. This can occur because of quantum mechanical tunnelling, hence the name of the instrument.
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