In typical critical and industrial cleaning applications, liquid is used to remove particulate and thin film contamination from solid objects. Solid media, alone or in combination with a liquid may also be used for cleaning. The gas phase, as in vapor degreasing, may be used to minimize cleaning agent contamination.
What is sometimes overlooked is that a fourth state of matter, plasma, has important applications in critical cleaning and contamination control. Many applications also involve surface modification. Plasmas are all around us; in fact we couldn’t exist without one object that consists of a plasma, the sun. The stars and most of the mass in interstellar space consist of plasma. The light emitted by fluorescent lights, neon signs, lightning, and visible flames is due to plasmas.