Emission spectra of glows produced by ionic liquid ion sources

Abstract

Electrospray devices, such as ionic liquid ion sources, often exhibit glows during operation in high vacuum facilities. The lack of electron excitation mechanisms during electrospray operation prompts the question: “What causes glow in an electrospray device?” Our optical emission spectroscopy results show that electrospray glow exhibits a broad spectral response between 350 and 800 nm with emission lines corresponding to atomic metal constituents of impinged surfaces, neutral and ionized atomic constituents of the ionic liquid propellant, and molecular line shapes that may also be dissociation products of the ionic liquid. We have previously defined secondary species emission to describe the many complex interfacial phenomena that occur when electrosprayed species impact surfaces downstream of the emitter. Our analysis of the optical emission spectra shows that these glows are only possible in the presence of secondary species emission. Therefore, the answer to the proposed question: high-velocity impacts that generate secondary species are the root cause of glow for electrosprays in high vacuum facilities.

Discharge in electrospraying of highly conductive aqueous solution coated with outer ionic liquid

“…It shows that the ionic liquid meniscus tends to eject nano droplets or ions and the discharge of ionic liquid could be actively controlled through adjusting the applied voltage. Others observed the glow discharge during the operation of ionic liquid electrospray thruster [31][32][33]. The glow discharge is claimed to be caused by the secondary species emission in vacuum, which is different from the corona discharge in air [32,33].…”

“…Others observed the glow discharge during the operation of ionic liquid electrospray thruster [31][32][33]. The glow discharge is claimed to be caused by the secondary species emission in vacuum, which is different from the corona discharge in air [32,33]. Therefore, more studies on ionic liquids with different physical properties and more details on the discharge process (waveform, frequency, amplitude, etc.)…”