Boil-off rate

The boil-off rate or evaporation rate describes the amount of evaporated material per unit of time during thermal boil-off or evaporation. In the case of thermal boil-off, a starting material is brought to temperatures close to the boiling point by means of a resistance heater, such as a small vapour deposition vessel or an induction heater, in conjunction with a corresponding heat-resistant ceramic crucible. With this process, the source material evapourates and the atoms or molecules that are released precipitate on the substrate located on the opposite side in the vacuum chamber, forming a thin layer there. The condensation of the material vapour on the substrate is ensured by a substrate that is cooler than the ambient temperature.