A plasma is an ionized gas. It can be created for example thermally or by an electrical field. Flames are a typical thermal plasma. A low pressure plasma can be ignited and sustained by electrons accelerated in an electrical field.
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Low pressure plasma scheme |
The electrons collide with the gas molecules and as a result excited molecules and
ions are formed in primary reaction. In secondary reaction, these species react
with each other, with neutrals, or simply deactivate forming a wide variety of
different species: molecule or fragments, ions and neutral in ground or excited
states, and broad spectrum of radiation ranging from the infrared to the deep
ultraviolet. The energy inside such a plasma is high enough to break any chemical
bond of organic molecules. In this way chemical reactions can be carried out which
run only with very low rates in the framework of traditional organic chemistry. The
temperature of the treated material however remains at room temperatur.
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Energy scale of a low pressure plasma |
Low pressure plasma technology was originally developed for microelectronics
production. Since then it has been adopted in many other industrial fields. This
technique can alter materials surface properties to satisfy the demand of a certain
application. The fine cleaning of parts before adhesive bonding, the surface
activation of plastics in order to improve the adhesion of primers or paints, scratch
resistant or barrier coatings are a few examples of non-electronic industrial
productions that involve low pressure plasmas.