Simulation of the electron field emission characteristics of a flat panel x-ray source

Posada, Chrystian M.; Castaño, Carlos H.; Grant, Edwin J.; Lee, Hyoung K.

doi:doi:10.1116/1.3680112

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Journal of Vacuum Science & Technology B / Volume 30 / Issue 2 / Microelectronic & Nanoelectronic Devices

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J. Vac. Sci. Technol. B 30, 022201 (2012); http://dx.doi.org/10.1116/1.3680112 (9 pages)

Simulation of the electron field emission characteristics of a flat panel x-ray source

Chrystian M. Posada¹, Carlos H. Castaño², Edwin J. Grant³, and Hyoung K. Lee⁴

¹Missouri University of Science and Technology, Department of Mining and Nuclear Engineering, 230 Fulton Hall, Rolla, Missouri 65401
²Missouri University of Science and Technology, Department of Mining and Nuclear Engineering, 224 Fulton Hall, Rolla, Missouri 65401
³ Missouri University of Science and Technology, Department of Mining and Nuclear Engineering, 230 Fulton Hall, Rolla, Missouri 65401
⁴ Missouri University of Science and Technology, Department of Mining and Nuclear Engineering, 219 Fulton Hall, Rolla, Missouri 65401

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(Published online 6 February 2012)

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A distributed flat panel x ray source is designed as an alternative for medical and industrial imaging fields. The distributed x ray source corresponds to a two dimensional array of micro (93 μm) x ray cells similar in format to a field emission display. In this paper the field electron emission characteristics of a single micro x ray cell are presented. The field electron emission from a carbon-nanotube- (CNT-) based cold cathode is simulated using the particle-in-cell code oopic pro. The electron source is simulated as a triode structure, composed of an emitting cathode, extracting grid and anode. The possibility of using focusing lenses to control the trajectory of emitted electrons is also evaluated. The layer of CNT emitters is modeled as Fowler–Nordheim emitters. The field emission characteristics were analyzed for extracting voltages between 20 and 70 V and accelerating voltages between 30 and 120 kV. Under these conditions, J_FN-V curves, energy, and electron distributions at the anode surface were determined. Electron trajectories were determined as well. When no focusing structures were employed, electron trajectories were found to be divergent. When focusing lenses were included in the triode structure, the emitted electrons could be made to converge at the anode. In the cases where focusing structures were used, a dependency between the focal spot size and the extracting grid voltage was found. Results indicated an early feasibility of the proposed device to be employed as an electron source in the distributed flat panel x ray source.

ACKNOWLEDGMENTS

This work was possible due to support from NRC Grant No. HR-FN208-NED02 and Missouri S&T Research Board Award.

Article Outline

INTRODUCTION
SIMULATION PROCEDURE
1. Electron field emission
2. Triode structure
3. OOPIC Pro model
RESULTS AND DISCUSSION
1. Total number of particles and convergence
2. Electron trajectories
3. Current density versus extracting voltage ( J _FN -V curves)
4. Current density: Space charge limitation effects
5. Energy distribution of electrons at the anode
6. Focal spot size versus grid voltage
SUMMARY AND CONCLUSIONS

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KEYWORDS and PACS

Keywords

carbon, carbon nanotubes, electron field emission, electron lenses, electron sources, field emission displays, flat panel displays, microdisplays, optical focusing, triodes, X-ray imaging

PACS

07.85.-m

X- and γ-ray instruments
85.45.Fd

Field emission displays (FEDs)

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History

Received 15 June 2011
Accepted 31 December 2011
Published online 6 February 2012

Digital Object Identifier

http://dx.doi.org/10.1116/1.3680112

PUBLICATION DATA

ISSN

1071-1023 (print)

1520-8567 (online)

Publisher

American Vacuum Society

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