An introduction to the scanning tunneling electron microscope
Scanning tunneling electron microscope (STM) is a kind of instrument that uses the tunnelling effect in quantum theory to probe the structure of the surface of matter, using the quantum tunnelling effect of electrons between atoms to convert the arrangement of atoms on the surface of matter into image information.
Introduction
Transmission electron microscopy is useful in observing the overall structure of a substance, but it is more difficult to analyse the surface structure. This is because transmission electron microscopy consists of high-energy electricity passing through the sample to obtain information, reflecting the internal information of the sample substance. Although scanning electron microscopy (SEM) can reveal certain surface conditions, the so-called "surface" analysed is always at a certain depth because incident electrons always have a certain amount of energy and penetrate into the interior of the sample, and the braid rate is also very limited. Field Emission Electron Microscopy (FEM) and Field Ion Microscopy (FIM) can be well used for surface studies, but the samples have to be specially prepared and can only be placed on the tip of a very fine needle, and the samples need to be able to withstand a high electric field, which limits the scope of its application.
Scanning tunnelling electron microscopy (STM) works on a completely different principle. It does not obtain information about the sample material by the action of an electron beam on the sample (e.g. transmission and scanning electron microscopes), nor does it study the sample material by imaging it through the formation of an emitted current (e.g. field emission electron microscopes) by means of a high electric field that gives electrons in the sample more energy than the work of detachment, but by probing a tunneling current on the surface of the sample, which can be used for imaging the surface. It is by detecting the tunneling current on the surface of the sample to image, so as to study the surface of the sample.
Principle
The scanning tunneling microscope is a new type of microscope that can distinguish the surface morphology of a solid by detecting the tunneling currents of electrons in the atoms on the surface of the solid according to the principle of the tunneling effect in quantum mechanics.
Due to the tunneling effect of electrons, the electrons in the metal are not completely confined within the surface boundary, i.e., the density of electrons does not suddenly drop to zero at the surface boundary, but decays exponentially outside the surface; the decay length is about 1 nm, which is the measure of the electron escape from the surface potential barrier. If two metals are close to each other, their electron clouds may overlap; if a small voltage is applied between the two metals, then a current (called a tunneling current) can be observed between them.
