We note that the mass gain during precursor exposure is high in the early stage of the precursor pulse, indicating formation of a monolayer 9,10 (Fig. ). This is followed by a slower mass gain after about 5 s, suggesting formation of multilayers of the precursor. Keep in mind that the QCM sensor was maintained at 50 °C, meaning that some condensation likely occurs as the Cu(hfac)2 was evaporated at 40 °C. We also note from the mass evolution trace that the mass decreased to the level of the expected monolayer during the argon purge (Fig. ), suggesting that the precursor multilayer can be purged away with long enough argon purge.