QCM response to variable energy electrospray plume

This paper presents the frequency response of a 6 MHz quartz crystal microbalance (QCM) when bombarded by ionic liquid ion source electrospray plumes of various energies using EMI-BF $$_4$$ . Time of flight mass spectrometry (ToF-MS) measurements confirm ion mode emission from the single, externally wetted tungsten emitter ion source and a retarding potential analyzer (RPA) was used to record the energy profile of the plume. The frequency change of the QCM is positively correlated with plume energy, with the most energetic plume (1900 eV) yielding the largest (positive) frequency change, and the lowest energy (30 eV) yielding a decrease in frequency. These measurements indicate removal of material on the quartz crystal surface at high energies, and deposition of propellant at low energies. X-ray photoelectron spectroscopy (XPS) was used to measure the equivalent homogeneous composition of the surface of each quartz crystal, which revealed traces of propellant across all samples and showed greater deposition rates when exposed to a low energy plume.