From the overall relative frequency shifts between 0 s and 150 s in Fig. and between 0 s and approximately 100 s in Fig. it is seen that there is in fact no net mass gain. This is expected since the precursor flow was off for the entire time. The recorded relative frequency shifts during Plasma On are likely related to the plasma electron current momentarily disturbing the QCM measurements, although no permanent error in the measurement persists after this phase. This implies that the trend in mass change per unit time is hard to resolve while allowing an electron current to pass through at the initial exposure between 5 W and 20 W during the measurement, as seen in Fig. and Fig. .