In addition to net mass gain and surface saturation, the QCM can be useful as a tool to unveil the surface reactions when combined with e.g., mass spectrometry. Through this approach, we can both study the adsorption of the precursor but also the reaction by-products. The use of the biased QCM system together with a time-resolved CVD approach shows the potential of the QCM system to unveil details of the surface chemistry of this new CVD method in combination with other in situ techniques.