Scanning Tunneling Electron Microscope Applications
The principle of tunneling microscopy is to make clever use of the tunneling effect and tunneling current in physics. There are a large number of "free" electrons in the metal body, these "free" electrons in the metal body of the energy distribution is concentrated in the vicinity of the Fermi energy level, while in the metal boundary there is a higher energy than the Fermi energy level of the potential barrier. Therefore, from the perspective of classical physics, the "free" electrons within the metal, only the energy higher than the boundary potential barrier of those electrons may escape from the metal to the outside. However, according to quantum mechanics, the free electrons in the metal also have volatility, and when this electron wave propagates towards the metal boundary and encounters the surface potential barrier, there will be some transmission. That is to say, there will be part of the energy below the surface potential barrier of the electron can penetrate the metal surface barrier, the formation of metal surface "electron cloud". This effect is called the tunneling effect. Therefore, when two metals are very close together (below a few nanometres), the electron clouds of the two metals will penetrate each other. When the appropriate voltage is added, even if the two metals are not really in contact, there will be a current flowing from one metal to the other, which is called the tunnel current.
Tunnel current and tunnel resistance with the tunnel gap is very sensitive to changes in the tunnel gap, even if only 0.01nm change, can also cause significant changes in tunnel current.
If a very sharp probe (such as tungsten needle) in the distance from the smooth surface of the sample a few tenths of a nanometre height parallel to the surface in the x, y direction scanning, because each atom has a certain size, and thus in the scanning process tunnel gap will be with the x, y of the different and different, the tunneling current flowing through the probe is also different. Even a height change of a few per cent of a nanometre can be reflected in the tunneling current. The use of a scanning probe with a synchronised recorder, the tunneling current changes will be recorded, you can get the resolution of a few nanometres of the scanning tunneling electron microscope images.
