In situHV TEM observation of the tip shape of lead liquid metal ion sources

Abstract

Lead liquid metal ion sources (LMISs) were operated using a special specimen holder in situ in a 1 MeV TEM. The dynamics of the tip shape have been observed as a function of the ion emission current. At currents there was a jet-like protrusion on the vertex of the Taylor cone. Linear dependences were found for the decrease of the cone half-angle and the increase of the jet length l as functions of increase in ion emission current. Microdroplet emission was observed at the shank of the Taylor cone over time intervals of 0.1 s and more. The diameter of these microdroplets varied between 40 and 340 nm. This work has improved our understanding of the ion and microdroplet emission processes from the Pb LMIS.

Regenerable Field Emission Cathodes: Surface Morphology and Performance

“…The LMIS was constructed of an electrochemically etched tungsten emitter that was coated with a thin layer of the low-melting-temperature metal indium. Ion emission was established and simultaneous formation of a Taylor cone structure, by heating the emitter tip and applying an ion-extracting field between the emitter tip and an extraction electrode [19]. By cooling the LMIS during ion emission, Makela and King [16] were able to solidify the metal Taylor cone into a permanent solid structure.…”

Regenerable Field Emission Cathode for Spacecraft Neutralization

“…Results of the Fowler-Nordheim modeling were promising, showing the ability to regenerate tips and to control the features of the resulting tips by varying the ion current during the quench process. The set of experiments that are reported demonstrated the regeneration process of emitter tip radii ranging from approximately 30-45 nm from a tip quenched at 2 A down to tip radii of [15][16][17][18][19][20][21][22] NTEREST in the miniaturization of space propulsion has been growing over the past 10 to 15 years. The Darwin infrared space interferometer and the Laser Interferometer Space Antenna (LISA) [1] are examples of missions that require technology capable of producing 0.1 to 1000 N of thrust with low thrust noise and high thrust precision.…”

“…In an LMIS or FEEP thruster, an intense electric field is created near the surface of a low-melting-temperature liquid metal, such as indium, by a downstream electrode. A balance between the liquid surface tension and the electrostatic force between the liquefied metal and the downstream electrode causes a structure known as a Taylor cone to form in the liquid, as shown in a micrograph taken from Driesel et al's work [16] in Fig. 2.…”

In situ study of ionic liquid Taylor cones using electron microscopy

“…While it is challenging to operate an electrospray source within an electron microscope, several groups overcame this challenge, and have been able to produce Taylor cone/jet emission in the specimen chamber of a TEM using liquid metal ion sources (LMIS). This allowed these groups to capture in-situ visualizations of an operating Taylor cone using gold, 33 lead, 34 tin, 35 gallium, 36 indium, 37 gold-germanium alloy, 38 and cobalt-germanium alloy 39 ion sources. Such direct observation enabled researchers to verify the fundamental structure of the cone/jet emitter; specifically, cone-angle, jet length, and jet angle were measured at varying levels of emission current of the ion source.…”