Effusing source for film deposition of reservoir, comprises hole having hole diameter less than one order of magnitude than mean free path of molecules

The invention relates to an effusing source for film deposition made of a reservoir comprising one hole characterized by the fact that the hole diameter is less than one order of magnitude than the mean free path of the molecules determined by the pressure and its thickness is at least one order of magnitude smaller than the diameter. Preferably the source has several holes.