Адгезійні плівки на електричних контактах

Abstract

ADHESION FILMS FOR ELECTRICAL CONTACTS
A. M.Mrachkovskyy, M. Khomyak
The surface of the solid body can’t be perfectly smooth and if even contacts made of solid material perfectly, the touch is not more than three points. Since the real material is deformed, flatten and place contact surfaces are small, and they formed contact spots. The sum of all these spots is the surface on which under the influence of various factors formed film.
In the electrical contacts can be formed following types of films: films browning (oxidation or sulfide), adhesive film, passivation film, boundary lubrication film.
Oxide and sulphide films are semiconductors with high resistivity that occurs in violation of their lattice. As such violations density varies from point to point, which partly depends on the structure of the metal lattice, which is located under the film, resistivity oxides will also vary from point to point. In addition, the thickness of the film darkening depends on crystal faces that appeared this film. It all together leads to the conclusion that any darkening of the film on the polycrystalline metal surface is heterogeneous.
Established that the metal surface have extremely high heterogeneity and consist of alternating areas with low and very high resistance and the phenomenon is observed even in precious metals.
Visible eye film, unless they are destroyed by electrical breakdown, are practically isolated hard surfaces and greatly complicate the work of electrical contacts. The most famous adhesive film consists of oxygen. In tungsten are two layers of oxygen atoms has the first heat of adsorption for about 4 eV, and the second - about 2 eV and the two layers of contact with the surface of the metal. Consequently physically connected film can withstand mechanical loads visible, but it is poorly resists abrasion. These very thin films characterized nuclear tunneling conductivity and resistivity at different metals has almost the same amount as in tungsten. This implies that oxygen layers are formed on different metals.
Usually oxygen atoms long exist as electronic affinity of oxygen leads to eject electrons from the metal and oxygen atoms are converted into negative adiony. Then they form negative layer on the metal, which prevents evaporation of electrons, that increases the work function φ. If pure tungsten φ is within 4,2-5,5 eV, in the presence of oxygen adionov it could rise to 6.6 eV. The work function depends on the atoms, as their electronic exchange with the metal surface leads to the fact that for some time they may be negatively charged. However, this alternating effect is negligible.
The fact of the formation of oxide films darkening means that oxygen atoms or ions are also able to extract the metal atoms and bind them to the grid oxide or attach them and form oxide depending on which of these processes requires less energy consumption. Thus, if the heat of evaporation of electrons (work function) is less than the heat of evaporation of metal atoms, it is formed adionov.
In micro contacts where efforts are a few milligrams, even the thinnest adhesive film creates a noticeable resistance, since the contact area in this case is very small.
The tunneling resistance only chemisorbed layer on the order of less than the total resistance of both layers. This is great sensitivity tunneling to small changes in the thickness of the film.