Photo- and thermionic emission from potassium-intercalated carbon nanotube arrays

Westover, Tyler L.; Franklin, Aaron D.; Cola, Baratunde A.; Fisher, Timothy S.; Reifenberger, Ronald G.

doi:doi:10.1116/1.3368466

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Journal of Vacuum Science & Technology B / Volume 28 / Issue 2 / Regular Articles

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J. Vac. Sci. Technol. B 28, 423 (2010); http://dx.doi.org/10.1116/1.3368466 (12 pages)

Photo- and thermionic emission from potassium-intercalated carbon nanotube arrays

Tyler L. Westover, Aaron D. Franklin, Baratunde A. Cola, Timothy S. Fisher, and Ronald G. Reifenberger

Birck Nanotechnology Center, Purdue University, 1205 W. State St. West Lafayette, Indiana 47907

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(Published online 31 March 2010)

Abstract

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Carbon nanotubes (CNTs) are promising candidates to create new thermionic- and photoemission materials. Intercalation of CNTs with alkali metals, such as potassium, greatly reduces their work functions, and the low electron scattering rates of small-diameter CNTs offer the possibility of efficient photoemission. This work uses a Nd:YAG (YAG denotes yttrium aluminum garnet) laser to irradiate single- and multiwalled CNTs intercalated with potassium, and the resultant energy distributions of photo- and thermionic emitted electrons are measured using a hemispherical electron energy analyzer over a wide range of temperatures. For both single- and multiwalled CNTs intercalated with potassium, the authors observe a temperature dependent work function that has a minimum of approximately 2.0 eV at approximately 600 K. At temperatures above 600 K, the measured work function values increase with temperature presumably due to deintercalation of potassium atoms. Laser illumination causes the magnitudes of collected electron energy distributions to increase substantially but in many cases has little effect on their shape. Simple theoretical models are also developed that relate the photo- and thermionic emission processes and indicate that large numbers of photoexcited electrons partially thermalize (i.e., undergo one or more scattering events) before escaping from the emitter surface.

ACKNOWLEDGMENTS

The authors wish to thank the National Science Foundation’s Nanoscale Science and Engineering program under Award No. CTS-0210366 for assistance in funding this project.

Article Outline

INTRODUCTION
THEORETICAL MODELS
1. Thermionic emission
2. Photoemission
3. Laser heating of substrate
4. Energy convolution
EXPERIMENTAL AND SIMULATION RESULTS
1. Sample preparation
2. Experimental setup
3. Tungsten (100) calibration
4. K/SWCNT/PAA sample
5. K/MWCNT sample
CONCLUSIONS

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KEYWORDS and PACS

Keywords

carbon nanotubes, intercalation compounds, laser beam effects, photoemission, photoexcitation, potassium, thermionic electron emission, work function, carbon nanotube, potassium, petrol ether

PACS

79.40.+z

Thermionic emission
79.60.Jv

Interfaces; heterostructures; nanostructures
73.30.+y

Surface double layers, Schottky barriers, and work functions

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History

Received 6 November 2009
Accepted 22 February 2010
Published online 31 March 2010

Digital Object Identifier

http://dx.doi.org/10.1116/1.3368466

PUBLICATION DATA

ISSN

1071-1023 (print)

1520-8567 (online)

Publisher

American Vacuum Society

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