What is plasma

Plasma is a rare state of matter, distinct from the three common states of solid, liquid, and gas in our daily life, hence it is often referred to as the "fourth state of matter". The same substance can exist in all three states, for example, water. Ice is the lowest energy state of water and can be transformed into liquid water by absorbing energy. Liquid water can be transformed into water vapor by absorbing more energy, and water vapor represents the highest energy state among the three states of gas, liquid, and solid. When matter absorbs more energy on the basis of the gas state, it generates plasma. Due to the conservation of electrons and energy, plasma is a neutral substance as a whole. Plasma contains electrons, photons, ions, and neutral particles.

Plasma can be classified into low-temperature and high-temperature plasma according to traditional classification methods, and the difference between them lies mainly in the temperature of plasma, which is defined by the temperatures of electrons and ions. When the temperatures of the two are equal, it is high-temperature plasma, and vice versa for low-temperature plasma. Low-temperature plasma is mainly generated by gas discharge.

Low-temperature plasma contains a large number of high-energy active particles, which can excite, ionize or break molecules of reactants, producing a series of physicochemical reactions such as etching, cross-linking, or polymerization on the surface of materials. In terms of surface modification of materials, low-temperature plasma has good application prospects.

The Fourth State of Matter