Field Emission: Large Current Densities, Space Charge, and the Vacuum Arc

ABSTRACTA series of tetrahedrally bonded carbon (ta-C) films have been produced using a Filtered Cathodic Vacuum Arc System. The threshold field and current densities achievable have been investigated as a function of sp3/sp2 bonding ratio and nitrogen content. Typical undoped ta-C films have a threshold field of 15–20V/μm and optimally nitrogen doped films exhibit threshold fields as low as ∼ 5 V/μm. Current densities of typically 10-4 A/cm2 at an applied field of 20V/micron were also obtained.

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Electron Transport and Anode Heating Due to Field Emission From Carbon Nanotubes

Heat Transfer, Volume 7 ◽

10.1115/imece2002-32126 ◽

2002 ◽

Author(s):

D. G. Walker ◽

T. S. Fisher

Keyword(s):

Carbon Nanotubes ◽

Field Emission ◽

Anode Surface ◽

Electron Trajectory ◽

Coulomb Interactions ◽

Turn On ◽

Large Current ◽

Ring Diameter ◽

Current Densities ◽

Vacuum Gap

Carbon nanotubes (CNT) are being considered for field emission applications because of their low turn-on voltage and ability to support large current densities. The localization of emission and large currents from CNTs result in significant anode heating. The present work investigates the electron energy distribution at the anode surface through simulation of the field emission process and the trajectory of electrons across the vacuum gap. Field emission is modeled by Fowler-Nordheim-like expressions where the emission site is assumed to be a ring with the diameter of a nanotube. The electron trajectory is determined through a Monte Carlo simulation including Coulomb interactions between electrons. Results indicate that the electron beam spreads due to Coulomb interaction, but that the initial ring is preserved. In fact, the ring diameter at the anode spreads to 3μ per 10μ of vacuum gap in a field of 10 Vμm. This estimate matches well with reported observations. Further, the spreading becomes more significant with increased fields due to the higher current density of field emitted electrons.

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Low Threshold Field Emission From Nanocluster Carbon Films

MRS Proceedings ◽

10.1557/proc-593-207 ◽

1999 ◽

Vol 593 ◽

Author(s):

W.I. Milne ◽

B.S. Satyanarayana ◽

J. Robertson

Keyword(s):

Field Emission ◽

Deposition Process ◽

Carbon Films ◽

Vacuum Arc ◽

Threshold Field ◽

Bonding Ratio ◽

Low Threshold ◽

Current Densities ◽

Vacuum Arc Deposition ◽

Arc Deposition

ABSTRACTCarbon films with variable sp3/sp2 bonding ratio can be deposited on a variety of substrates at room temperature, using the cathodic vacuum arc deposition process. The variation in their surface morphology as a function of He and N2partial pressure during growth have been investigated and it has been shown that the morphology of the films can be varied from the mirror like smooth tetrahedrally bonded carbon (ta-C) films through nanocluster to fibrous type carbon. This paper reviews the work carried out on Field Emission from these various carbon films. Threshold fields as low as 1 V/μm for emission current densities of 1 μA/cm2 and emission site densities of up to 104 -105/cm2 have been obtained.

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Vacuum Arc Cathode Spot Characterization on Graphite Materials Using Field Emission Gun Scanning Electron Microscopy (FEGSEM)

Microscopy and Microanalysis ◽

10.1017/s1431927600013015 ◽

1997 ◽

Vol 3 (S2) ◽

pp. 1225-1226

Author(s):

M. Kandah ◽

J.-L. Meunier ◽

R. Gauvin

Keyword(s):

Heat Flux ◽

Field Emission ◽

Cathode Spot ◽

Ion Beam ◽

Deposition Process ◽

Vacuum Arc ◽

Carbon Ions ◽

Emission Mode ◽

Current Densities ◽

Arc Current

Vacuum arcs on graphite cathodes are currently used as sources of carbon ions for the production of diamond-like films in the arc ion-plating (AIP) deposition process. Emission from these cathode sources is concentrated in very localized “cathode spots” having typically 10 (i.m in diameter for graphite cathodes. These spots carry the totality of the arc current, the remaining of the surface being unaffected by the discharge. For electron emission falling in the thermo-field emission mode, extremely high current densities up to 108 -109 Am-2 are induced generating a high localized heat flux to the surface during the spot lifetime. On metallic electrodes, this strong heat flux generates localized surface melting during the microsecond scale spot lifetime. High localized plasma pressures (>10 Atm in the case of copper) were found to exist in the cathode spot volume, leading to the co-emission of micro-droplets of the liquid metal along with the ion beam.

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Solution for space charge limited field emission current densities with injection velocity and geometric effects corrections

Physics of Plasmas ◽

10.1063/1.2907365 ◽

2008 ◽

Vol 15 (4) ◽

pp. 043301 ◽

Cited By ~ 17

Author(s):

Y. Feng ◽

J. P. Verboncoeur ◽

M. C. Lin

Keyword(s):

Space Charge ◽

Field Emission ◽

Emission Current ◽

Injection Velocity ◽

Field Emission Current ◽

Current Densities ◽

Geometric Effects ◽

Space Charge Limited

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A Stable Field Emission Electron Source

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100077918 ◽

1977 ◽

Vol 35 ◽

pp. 58-59

Author(s):

W.R. Bottoms ◽

G.B. Haydon

Keyword(s):

Field Emission ◽

Signal To Noise Ratio ◽

High Brightness ◽

Electron Sources ◽

Brightness Field ◽

Current Densities ◽

Properties Of Materials ◽

Stable Field ◽

Stable Current ◽

Careful Design

There is great interest in improving the brightness of electron sources and therefore the ability of electron optical instrumentation to probe the properties of materials. Extensive work by Dr. Crew and others has provided extremely high brightness sources for certain kinds of analytical problems but which pose serious difficulties in other problems. These sources cannot survive in conventional system vacuums. If one wishes to gather information from the other signal channels activated by electron beam bombardment it is necessary to provide sufficient current to allow an acceptable signal-to-noise ratio. It is possible through careful design to provide a high brightness field emission source which has the capability of providing high currents as well as high current densities to a specimen. In this paper we describe an electrode to provide long-lived stable current in field emission sources.The source geometry was based upon the results of extensive computer modeling. The design attempted to maximize the total current available at a specimen.

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