Effects of the temperature of a protic ionic liquid on ion beam production by vacuum electrospray

Abstract

Ionic liquid ion sources generate ion beams from ionic liquids by vacuum electrospray. Electrospray characteristics generally depend on the physical properties of the liquids used. A key factor affecting physical properties is temperature. In this study, ion beam production was investigated using a protic ionic liquid, propylammonium nitrate (PAN), at temperatures ranging from 22 to 60 °C. An ion beam was produced using a needle emitter equipped with a cartridge heater, thermocouple, and sharpened glass rod externally wetted with PAN. The experimental results showed that the heating of the emitter increased the ion beam current. This will be due to an increase in the conductivity and a decrease in the viscosity of PAN with increasing temperature. Furthermore, the abundance of larger cluster ions increased, whereas that of smaller cluster ions decreased with increasing temperature. It turned out, however, that higher heating of the emitter stopped ion beam production. Two hypotheses for the beam stop are proposed and discussed.