We report experiments and analysis of field emission from metallic knife-edge cathodes, which are sputter-coated with thin films of lanthanum hexaboride (LaB6), a low-work function material. The emission current is found to depend sensitively on the thickness of the LaB6 layer. We find that films thinner than 10 nm greatly enhance the emitted current. However, cathodes coated with a thicker layer of LaB6 are observed to emit less current than the uncoated metallic cathode. This result is unexpected due to the higher work function of the bare metal cathode. We show, based on numerical calculation of the electrostatic potential throughout the structure, that the external (LaB6/vacuum) barrier is reduced with respect to uncoated samples for both thin and thick coatings. However, this behavior is not exhibited at the internal (metal/LaB6) barrier. In thinly coated samples, electrons tunnel efficiently through both the internal and external barrier, resulting in current enhancement with respect to the uncoated case. In contrast, the thick internal barrier in thickly coated samples suppresses current below the value for uncoated samples in spite of the lowered external barrier. We argue that this coating thickness variation stems from a relatively low (no higher than 1018 cm−3) free carrier density in the sputtered polycrystalline LaB6.
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15 March 2012
Research Article|
March 28 2012
Effect of sputtered lanthanum hexaboride film thickness on field emission from metallic knife edge cathodes
M. P. Kirley;
M. P. Kirley
a)
Department of Electrical and Computer Engineering,
University of Wisconsin-Madison
, Madison, Wisconsin 53706, USA
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B. Novakovic;
B. Novakovic
Department of Electrical and Computer Engineering,
University of Wisconsin-Madison
, Madison, Wisconsin 53706, USA
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N. Sule;
N. Sule
Department of Electrical and Computer Engineering,
University of Wisconsin-Madison
, Madison, Wisconsin 53706, USA
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M. J. Weber;
M. J. Weber
Department of Electrical and Computer Engineering,
University of Wisconsin-Madison
, Madison, Wisconsin 53706, USA
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I. Knezevic;
I. Knezevic
Department of Electrical and Computer Engineering,
University of Wisconsin-Madison
, Madison, Wisconsin 53706, USA
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J. H. Booske
J. H. Booske
Department of Electrical and Computer Engineering,
University of Wisconsin-Madison
, Madison, Wisconsin 53706, USA
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a)
Author to whom correspondence should be addressed. Electronic mail: kirley@wisc.edu.
J. Appl. Phys. 111, 063717 (2012)
Article history
Received:
November 11 2011
Accepted:
February 23 2012
Citation
M. P. Kirley, B. Novakovic, N. Sule, M. J. Weber, I. Knezevic, J. H. Booske; Effect of sputtered lanthanum hexaboride film thickness on field emission from metallic knife edge cathodes. J. Appl. Phys. 15 March 2012; 111 (6): 063717. https://doi.org/10.1063/1.3698281
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