Sputtering is a physical vapour deposition technique where the substrate is coated with atoms or molecules from a target material, made possible by the bombardment of energetic particles of plasma or gas onto the target material's surface. Typically, the inert gas argon is introduced to the vacuum chamber and a self-sustaining plasma is established by electrically energising the target material (which is effectively a cathode). In the plasma, the argon atoms lose electrons and become positively charged ions and are accelerated onto the target with enough kinetic energy to dislodge atoms and small molecules. The particles constitute a vapour stream that goes from the target to the substrate to form a thin-film. Sputtering is used in the manufacture of optical coatings, semiconductor devices, and nanotechnology products.