Direct analysis of an organic molecular beam by quadrupole mass spectrometry

The important parameters for the organic molecular beam deposition (OMBD) technique, including the molecular flux and its dependence on the Knudsen-cell (K-cell) temperature, were directly measured by using a high-performance quadrupole mass spectrometer in an ultrahigh vacuum. Functional organic materials such as metal phthalocyanine (M = Cu, Ni, pb, and TiO), tris(8-hydroxyquinolinato) aluminum (Alq3), triphenyl diamine (TPD), and fullerene (C-60), were sublimed from the K-cell using a precisely controlled temperature. The mass spectrum revealed that each molecule was sublimed from the K-cell without significant thermal decomposition. The dependence of the evaporation rate on the K-cell temperature was numerically calibrated for the first time and the enthalpy of sublimation was estimated from the molecular flux.