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Parker Hannifin Powder Characterization Lab. The scanning tunneling microscope takes advantage of the tunneling phenomena observed from quantum mechanics to probe any conductive surface with atomic resolutions. Here is how it works:. Classically, when an electron or for that matter any object is confronted by a potential barrier that it cannot overcome, such as an electric field, it is stopped and deflected by that barrier. In quantum mechanics, however, we find that the wavefunction which is the probability amplitude of the electron can extend into the barrier:.
Figure 1. It is this effect that allows us to precisely scan the tip with angstrom-level control. Lastly, a feedback loop is required, which monitors the tunneling current and coordinates the current and the positioning of the tip.
This is shown schematically below where the tunneling is from tip to surface with the tip rastering with piezoelectric positioning, with the feedback loop maintaining a current setpoint to generate a 3D image of the electronic topography:.
Tunneling is a quantum mechanical effect. However, in the quantum mechanical world, electrons have wavelike properties. If the barrier is thin enough, the probability function may extend into the next region, through the barrier!
Because of the small probability of an electron being on the other side of the barrier, given enough electrons, some will indeed move through and appear on the other side. When an electron moves through the barrier in this fashion, it is called tunneling.
Quantum mechanics tells us that electrons have both wave and particle-like properties. Tunneling is an effect of the wavelike nature. The bottom image shows the scenario if the barrier is quite thin about a nanometer. Part of the wave does get through and therefore some electrons may appear on the other side of the barrier.
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