Fully Additively Manufactured, Nanostructured, Miniature Ionic Liquid Electrospray Sources

We report the design, fabrication, and characterization of the first fully additively manufactured ionic liquid electrospray sources in the literature. The devices are diodes composed of an emitting electrode and an extractor electrode: the emitting electrode is a monolithic array of digital light projection (DLP)-printed solid, conical, polymeric needles covered by a conformal layer of hydrothermally grown zinc oxide (ZnO) nanowires as wicking material, while the extractor electrode is a stainless-steel plate with an array of apertures that matches the pattern of the array of needles. Devices with 1, 7, and 19 2.5 mm-long, $\sim 100\ \mu \mathrm{m}$ tip diameter needles (2.1 mm pitch), covered with a forest of $1.2\ \mu \mathrm{m}$ long, 150 nm diameter ZnO nanowires, were designed, fabricated, and characterized in vacuum (∼10⁻⁶ Torr) in a triode configuration (i.e. with an external collector electrode) in the negative polarity. Devices emit up to ∼86% of the current produced by the emitting electrode, and attain peremitter currents as high as $15\ \mu \mathrm{A}$ –a tenfold larger than cleanroom-microfabricated counterparts.