Characteristics of Charged Droplet Beams Produced from Vacuum Electrospray

Abstract

  Recently, various cluster ion beam sources have been studied with the aim of improving sensitivity in secondary ion mass spectrometry (SIMS) and achieving damage-free etching in X-ray photoelectron spectroscopy (XPS). Thus, compact gas cluster ion beam guns are now available for commercial SIMS and XPS instruments. The electrospray droplet impact (EDI) method was also developed as a new source for massive cluster beam, in which the charged droplet beams are produced from ambient electrospray and introduced into the vacuum system. The EDI method has been successful in achieving efficient ionization of organic molecules, soft etching of polymers, and nonselective etching of metal oxides. However, the current EDI method lacks adequate beam focusing and brightness for practical use. As a solution for these problems, we have proposed and developed a new method for producing a charged droplet beam and a stable electrospray of aqueous solutions under vacuum. In this study, the characteristics of ambient and vacuum electrospray were investigated with optical microscopy, and the ability of vacuum electrospray as the primary beam source will be discussed.