The addition of energy into matter modifies electromagnetic forces, binding atoms together. The state of matter evolves from solid to liquid, then from liquid to gas. Adding even more energy dissociates molecular bonds and may lead to ionization. Gas molecules are split into charged particles, ions and free electrons.
Plasma is often called "the fourth state of matter".
Low pressure technologies allow to deposit far more performant coatings like metallic alloys, diamond like carbons, nitrides, carbides with astonishing mechanical, optical or thermal properties. Ionics is specialized in the treatment of powders, fibers and loose parts.