What is a plasma?

Plasmas are said to be the fourth state of matter and are among the most widely studied subjects in modern science. Stated simply, a plasma is an ionized gas that conducts electricity.

Plasmas come in many forms, ranging from a welding torch to a fluorescent light bulb. As show in Fig. 01, they may be identified by their relationship between the neutral gas temperature and the electron temperature in the plasma (1 eV ~11,000 ºC). In a torch, an arc forms between the electrodes resulting in complete ionization of the gas and a temperature rise >4,000 ºC. Atmospheric plasma spray guns take advantage of the high temperatures found in arcs. These devices are able to vaporize many materials, and coat them at high speed onto surfaces.

The fluorescent light bulb, by contrast, contains a low pressure glow discharge. The vacuum inside the bulb is essential, because it allows the gas to be weakly ionized with low power input. Such weakly ionized plasmas are not at thermal equilibrium, i.e., the neutral molecules are close to 25 ºC, while the free electrons are above 10,000 ºC. The high-energy electrons collide with the neutral molecules, dissociating them into atoms and radicals, thereby yielding a reactive gas mixture. Most plasmas used for materials processing at low temperature are weakly ionized and produced in a vacuum.

Using plasmas for materials processing requires expertise in chemistry. The Atomflo™ atmospheric plasma is a source of atoms and radicals that are carefully selected for surface treatment, cleaning, etching, or depositing thin coatings. For example, a hydrogen plasma may be used to cure polymer films, whereas a nitrogen plasma may be combined with silane to deposit a silicon nitride plasma coating. The key in all these applications is combining the right hardware with the right chemistry to achieve the desired results.

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