Time dependent models of field-assisted photoemission

Jensen, Kevin L.; Feldman, Donald W.; O’Shea, Patrick G.

doi:doi:10.1116/1.1861047

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Journal of Vacuum Science & Technology B / Volume 23 / Issue 2 / PAPERS FROM THE 17TH INTERNATIONAL VACUUM NANOELECTRONICS CONFERENCE / Theory, Modeling and Simulation of Field Emitters

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J. Vac. Sci. Technol. B 23, 621 (2005); doi:10.1116/1.1861047 (11 pages)

Time dependent models of field-assisted photoemission

Kevin L. Jensen¹, Donald W. Feldman², and Patrick G. O’Shea²

¹Vacuum Electronics Branch, Code 6840, ESTD, 4555 Overlook Avenue, S.W, Naval Research Laboratory, Washington, DC 20375-5347
²Institute for Research In Electronics and Applied Physics, University of Maryland, Maryland

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(Published online 6 April 2005)

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A time-dependent model of photoemission, developed to analyze current from and laser heating of metals and dispenser photocathodes, is here applied to examine the impact of geometrical field enhancement and the contribution of tunneling to the photocurrent from a tungsten needle in terms of temporal response, quantum efficiency, and cathode performance. First, a review is given of an updated Fowler–Dubridge model of quantum efficiency including quantum mechanical effects. Second, a prolate spheroidal model of a tungsten needle is given to determine applied fields and incident angles necessary to evaluate emitted current and laser heating effects. Third, a time-dependent model of laser heating of an electron distribution is given which affects the photoemitted current and (if conditions are right) gives field and thermal components as well. Finally, the methodology is related to the experimental findings of Garcia and Brau [Nucl. Instrum. Methods Phys. Res. A 483, 273 (2002) ], in which an intense laser illuminates a tungsten needle under sufficiently high fields that the photoemitted current contains field and thermal emission components and effects.

Article Outline

INTRODUCTION
MODIFICATIONS TO 1D THEORY
1. Fowler–Dubridge model
2. Modifications due to 1D tunneling theory
3. Quadratic approximation to θ(E)
PROLATE-SPHEROIDAL MODEL OF A NEEDLE CATHODE
1. Potential and field variation
2. Tunneling distance and quadratic potentials
3. Reflectivity
TIME-DEPENDENT ELECTRON AND LATTICE TEMPERATURE EVALUATION
1. Heat diffusion equations
2. Approximations to the time dependence of temperature
3. Post-absorption scattering factor
SIMULATION AND COMPARISON
CONCLUSION
ACKNOWLEDGMENTS

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KEYWORDS and PACS

Keywords

tungsten, photoemission, photocathodes, tunnelling, thermionic emission

PACS

79.60.Bm

Clean metal, semiconductor, and insulator surfaces
85.60.Ha

Photomultipliers; phototubes and photocathodes
79.40.+z

Thermionic emission
73.40.Gk

Tunneling

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History

Received 24 September 2004
Accepted 27 December 2004
Published online 6 April 2005

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http://dx.doi.org/10.1116/1.1861047

PUBLICATION DATA

ISSN:

0734-211X (print)

Publisher:

American Vacuum Society

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