reduce the diffusion from the medium to the work piece or vice versa. For instance, plastic lemonade bottles are frequently coated by anti-diffusion layers to avoid the out-diffusion of CO2, into which carbonic acid decomposes that was introduced into the beverage under high pressure. Another example is represented by thin TiN films in microelectronic chips separating electrically conducting aluminum lines from the embedding insulator SiO2 in order to suppress the formation of Al2O3. Often, thin films serve as protection against abrasion between mechanically moving parts. Examples for the latter application are diamond-like carbon (DLC) layers used in car engines or thin films made of nanocomposites. Electrically operating coatings Thin layers from elemental metals like copper, aluminum, gold or silver etc. and alloys have found numerous applications in electrical devices. Due to their high electrical conductivity they are able to transport electrical currents or supply voltages. Thin metal layers serve in conventional electrical system, for instance, as Cu layers on printed circuit boards, as the outer ground conductor in coaxial cables and various other forms like sensors etc. A major field of application became their use in integrated passive devices and integrated circuits, where the electrical network among active and passive devices like transistors and capacitors etc. is built up from thin Al or Cu layers. These layers dispose of thicknesses in the range of a few 100 nm up to a few µm, and they are often embedded into a few nm thin titanium nitride layers in order to block a chemical reaction with the surrounding dielectric like SiO2. The figure shows a micrograph of a laterally structured TiN/Al/TiN metal stack in a microelectronic chip. Heterostructures of gallium nitride and similar semiconductors can lead to electrons being bound to a sub-nanometric layer, effectively behaving as a two-dimensional electron gas. Quantum effects in such thin films can significantly enhance electron mobility as compared to that of a bulk crystal, which is employed in high-electron-mobility transistors. Biosensors and plasmonic devices Noble metal thin films are used in plasmonic structures such as surface plasmon resonance (SPR) sensors. Surface plasmon polaritons are surface waves in the optical regime that propagate in between metal-dielectric interfaces; in Kretschmann-Raether configuration for the SPR sensors, a prism is coated with a metallic film through evaporation. Due to the poor adhesive characteristics of metallic films, germanium, titanium or chromium films are used as intermediate layers to promote stronger adhesion.