An ultrahigh vacuum coevaporator equipped with three sources for preparation of Y–BaF2 –Cu–O thin films is described. Evaporation rates of Y, BaF2, and Cu were controlled using a quadrupole mass spectrometer operating in a multiplexed mode. To evaluate the method depositions have been performed using different source configurations and evaporation rates. Utilizing Rutherford backscattering spectrometry absolute values of the actual evaporation rates were determined. It was observed that the mass‐spectrometer sensitivity is highest for Y, followed by BaF2 (BaF+ is the measured ion) and Cu. A partial pressure of oxygen during evaporation of Y, BaF2, and Cu affected mainly the rate of Y. It is shown that the mass spectrometer can be utilized to precisely control the film composition.

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