Direct Two-Dimensional Goniometric Steering of Vacuum Electrospray Ion Beams for Angular Time-of-Flight Studies

TL;DR

This paper introduces a dual-axis goniometer system for in-vacuo steering of electrospray ion beams, enabling detailed angular TOF measurements and revealing angular-dependent variations in ion species.

Contribution

The novel dual-axis goniometer allows precise in-vacuo beam steering of electrospray ions, improving angular analysis and signal quality for ESI plume studies.

Findings

Significant angular variations in ion species abundances were observed.

Monomers are minimized at the beam center, while heavy species and fragments peak at certain angles.

Beam steering enhances diagnostic signal-to-noise ratio for ESI plume analysis.

Abstract

Here we present a novel method for two-dimensional steering of vacuum electrospray ionization beams to better understand their angular properties. Utilizing an externally wetted tungsten needle with the ionic liquid 1-Ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF$_4$), we employ a dual-axis goniometer to achieve in-vacuo beam steering in both pitch and yaw. This setup enables detailed angular-dependent time-of-flight (TOF) measurements of molecular species within the ESI plume as a function of plume angle. Our findings reveal significant variations in the relative abundance of monomers, dimers, trimers, and heavy species across different beam angles, with monomers being at a relative minimum and fragments, trimers, and heavy species being at a relative maximum at the beam center. At higher angles, the relative monomer abundance increases, but at the plume extremities heavy species and trimer fragments begin to rise. The ability to accurately aim the ion beam dramatically enhances the signal-to-noise ratio for various diagnostic tools, underscoring the utility of this system for both scientific studies and practical laboratory applications. This two-dimensional steering capability offers a robust framework for future investigations into ESI plume dynamics and composition, enabling more precise characterizations that are critical for optimizing ESI-based propulsion systems and other applications.