In this tutorial, you have learned that when the total energy of the electron is high enough (although lower than the potential energy of the barrier) there is some probability for an electron to be detected on the right side of a thin foil after approaching the foil from the left, even when the electron's total energy is less than its potential energy inside the foil.
This phenomenon is called quantum tunneling, because
it appears that the electron passes through the foil to get to
the other side.
In reality we do not know and cannot say whether the electron
really "passes through" the region where the total energy
of the electron is less than the potential energy in the barrier.
According to the wave function description of the electron, however,
there is a small, but non-zero, probability that the electron
appears on the other side.
The Kanji character for "atom" - created by placing iron atoms on a copper surface
The phenomenon in which an electron appears to pass through a solid object is called tunneling because the situation appears similar to one in which an object drills a hole through a barrier to appear on the other side. The electron does not physically bore a hole for its own passage, but it merely has a probability of appearing on the other side.
Tunneling is a purely quantum mechanical effect and can be explained only when we describe an electron as a wave. It is the mechanism by which electrons can be transferred from the sample's surface to the probe tip of a scanning tunneling microscope. We will now examine how the tunneling phenomenon is applied to a scanning tunneling microscope.
