A review of field emission cathode technologies for electric propulsion systems and instruments

Marrese, Colleen M.

doi:10.1109/aero.2000.878369

Cited by 16 publications

(9 citation statements)

References 37 publications

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“…The nanoscale or microscale features are fragile, and when the features become damaged, the electron source loses functionality. Researchers have found some ways to minimize damage to the emitters [10], and they have also found more sputterresistant longer-life emitter materials [8,[11][12][13]. However, all electron field emitters become damaged over time [14,15]; it is just a matter of how much time it will take.…”

Section: Introductionmentioning

confidence: 99%

Regenerable Field Emission Cathodes: Surface Morphology and Performance

Makela

Washeleski

King

2011

Journal of Propulsion and Power

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This paper reports on a field-emission cathode for use in electric propulsion that has the potential for very long lifetime due to its ability to be regenerated when the emitter tip(s) become damaged. The field-emitting tips were formed by applying an ion-extracting electric potential to a heated indium-coated tungsten needle, known as a liquidmetal ion source. The liquid-metal ion source was then cooled, freezing in a solid nanotip at the apex. When the modified emitter was then subjected to electron-extracting potentials, stable and long-lived electron emission was observed. The first goal of this investigation was to operate and quench a liquid-metal ion source at ion emission currents from 1 to 30 A to acquire micrographs of the surface morphology as a function of the ion emission current at quench. Micrographs of the quenched emitter tips revealed Taylor-cone-shaped structures. Some of the quenched emitters exhibited multiple nanoprotrusions on the tapered surface of the microscale Taylor cone, which were capable of electron field emission. The second goal of this investigation was to compare regenerable field emitters with single-needle tungsten field emitters. Each type of emitter was used to obtain electron emission at a vacuum chamber pressure of 10 8 Torr, and then the emitters were exposed to increased pressure, up to 10 5 Torr, to observe how long they could sustain emission. In all cases, emission from the regenerable emitters lasted 10s of hours longer at increased pressure, and it was demonstrated that the tungsten emitters would eventually permanently fail, whereas the regenerable emitters could be repaired when they became damaged. Nomenclature a = Fowler-Nordheim empirical relation b 0 = Empirical relation between tip radius and gap spacing k = Fowler-Nordheim field-voltage proportionality factor m = slope r t = emitter tip radius s m = standard error t e = elapsed time = Fowler-Nordheim image-correction factor ' = work function

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Section: Introductionmentioning

confidence: 99%

Regenerable Field Emission Cathodes: Surface Morphology and Performance

Makela

Washeleski

King

2011

Journal of Propulsion and Power

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“…It then becomes possible to use the emitter tip to obtain FowlerNordheim emission of electrons by reversing the polarity of the LMIS extraction electrode. The sharp protrusions are ideal due to the fact they only require extraction voltages of tens to thousands of volts to obtain field emission [6]. The protrusions can then be used as field emission electron sources until the point in time when the tip becomes damaged, causing their performance to degrade.…”

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confidence: 99%

“…Field emission cathodes are used as neutralizers for space propulsion devices and as electron sources for flat-panel displays, focused electron beams for electron microscopy, and neutralization for spacecraft mass spectrometry [6][7][8][9]. The motivation for the research reported here is the limited lifetime of many current microfabricated field emitters, with the exception of carbon nanotube cathodes, which have demonstrated impressive life tests [10].…”

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confidence: 99%

“…1 [5]. Because the local electric field is inversely proportional to the electrode tip radius, the sharper the emitter tip, the lower the electric potential needed to obtain electron field emission [6]. A tungsten single-needle field emitter typically has a tip radius on the order of tens of nanometers to a few microns and can produce up to 100 A of electron emission current [5].…”

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Regenerable Field Emission Cathode for Spacecraft Neutralization

Makela

Washeleski

King

2009

Journal of Propulsion and Power

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This research investigates the discharge characteristics of a field emission cathode for use in electric propulsion that has the ability to be regenerated when the emitter tip becomes damaged. Emitter tip regeneration is achieved by taking advantage of Taylor cone formation from an operating liquid-metal ion source. Tip formation is accomplished by solidifying, or quenching, the ion-emitting cone to preserve the sharp protrusion so that it can then be used for electron emission. Electron emission I-V curves were taken after tips were formed by quenching the liquid-metal ion source at ion discharge currents ranging from 1 to 25 A. Fowler-Nordheim modeling was then used to estimate the emitter tip radii of each quenched liquid-metal ion source. 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 15-22 nm when quenched at 25 A.

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“…The field electron emitter is particularly attractive as an electron source, due to its suitable emission properties and simple operating principle . Tungsten is still one of the materials that are most frequently used for manufacturing field emitter tips (Latham, 1981;Marrese, 2000;Marulanda, 2010). Theoretically, cold field electron emission is the regime where (i) the electrons in the emitting region are effectively in local thermodynamic equilibrium (Mousa et al, 2012), and (ii) most electrons escape by deep tunneling from states close to the emitter's Fermi level .…”

Section: Introductionmentioning

confidence: 99%

Relationship of the Distribution Thickness of Dielectric Layer on the Nano-Tip Apex and Distribution of Emitted Electrons 

Al-Qudah

Mousa

2016

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This paper analyses the relationship between the distribution of a dielectric layer on the apex of a metal field electron emitter and the distribution of electron emission. Emitters were prepared by coating a tungsten emitter with a layer of epoxylite resin. A highresolution scanning electron microscope was used to monitor the emitter profile and measure the coating thickness. Field electron microscope studies of the emission current distribution from these composite emitters (Tungsten-Clark Electromedical Instruments Epoxylite resin [Tungsten/CEI-resin emitter]) have been carried out. Two forms of image have been observed: bright single-spot images, thought to be associated with a smooth substrate and a uniform dielectric layer; and multi-spot images, though to be associated with irregularity in the substrate or the dielectric layer.

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A review of field emission cathode technologies for electric propulsion systems and instruments

Cited by 16 publications

References 37 publications

Regenerable Field Emission Cathodes: Surface Morphology and Performance

Regenerable Field Emission Cathodes: Surface Morphology and Performance

Regenerable Field Emission Cathode for Spacecraft Neutralization

Relationship of the Distribution Thickness of Dielectric Layer on the Nano-Tip Apex and Distribution of Emitted Electrons

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A review of field emission cathode technologies for electric propulsion systems and instruments

Cited by 16 publications

References 37 publications

Regenerable Field Emission Cathodes: Surface Morphology and Performance

Regenerable Field Emission Cathodes: Surface Morphology and Performance

Regenerable Field Emission Cathode for Spacecraft Neutralization

Relationship of the Distribution Thickness of Dielectric Layer on the Nano-Tip Apex and Distribution of Emitted Electrons&nbsp;

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Relationship of the Distribution Thickness of Dielectric Layer on the Nano-Tip Apex and Distribution of Emitted Electrons