In the practical work of an engineer, even fairly abstract physical concepts can be of great importance. For example, the electron work function from a metal is a standard value for a developer of electronic systems. Of course, a specialist will need deeper knowledge, depending on what materials you have to work with. This value applies not only to metals, but to any solids, including semiconductors. If a pair of two semiconductors is considered, the Anderson rule is used. But if the mentioned material joins the metal, then the Schottky-Mott rule will come in handy. However, the calculations will be inaccurate, and the main role in this is played by the stabilization
of the Fermi
energy levels .
Definition
In solid state physics, the work function is the minimal thermodynamic action (the same energy) necessary to tear an electron from a solid and place it at a point outside its surface. All generalized calculations are made under the assumption that there is a vacuum around the body. This point is far enough on the scale of the size of the atom, but close enough to be influenced by the electric field in vacuum. The work function is not a characteristic of the composition of the material, but rather the quality of its surface. It is associated with the features of the crystal face and the degree of contamination.
Theoretical formula
The work function will numerically equal the sum of two energies. First, the amount needed to remove an electron from the atomic system. Secondly, the amount of energy needed to place an electron in an atom outside the surface of the solid under investigation.
Caution!
Some physical phenomena are very sensitive to the numerical value of the “work function” indicator. The formula mentioned above is used to build simplified theoretical models, nothing more. In experiments, the values of this indicator can be quite different from the formula calculations obtained without experience. If the surface is not smooth, not homogeneous, then calculating the exact value by itself, before obtaining empirical data, becomes almost impossible.
Measurement Method Groups
The electron work function is calculated by several methods and based on completely different physical phenomena. In total, two groups of experimental methods are distinguished. Absolute use electron emission from a sample, triggered by photoemission, high temperature, field emission, or electron tunneling. Relative methods apply the contact potential difference between the test sample and the reference electrode.
It is quite difficult to predict the magnitude of the work function with high accuracy without an experimental study. But there are certain trends that scientists have identified over the years of working with this phenomenon. Almost always, the value is less for metals with an open crystal lattice. For blunt crystal faces, it is higher than for sharp ones. The explanations of these phenomena are quite obvious. In an open lattice, the electron bonds are weaker, and with acute angle external influences on the atom are easier.