Sputtering produced by vacuum electrospray droplet ions with different sizes and charges

We have been developing a vacuum electrospray droplet ion (V-EDI) beam technique that uses water droplet ions generated by electrospraying aqueous solutions under vacuum. The V-EDI beam is one of the massive cluster ion beams that have the potential to significantly improve the performance of surface analysis. In order to utilize the V-EDI beams effectively as ionization and sputtering probes in secondary ion mass spectrometry and x-ray photoelectron spectroscopy, it is necessary to optimize the sizes and charge states of the droplet ions included in the V-EDI beams. However, the droplet ions themselves in the V-EDI beams are not well understood. In this study, the V-EDI beams generated from the capillaries with different inner diameters were irradiated on polystyrene film samples under constant electrospray and accelerating voltage conditions, and then their surfaces were analyzed with atomic force microscopy and spectroscopic ellipsometer. The impact trace distributions produced by the droplet ions and the sputtered volumes produced by each droplet ion impact were investigated.