Scandate cathodes ( on W) are important thermionic electron emission materials whose emission mechanism remains unclear. Ab initio modeling is used to investigate the surface properties of both scandate and traditional B-type (Ba–O on W) cathodes. We demonstrate that the Ba–O dipole surface structure believed to be present in active B-type cathodes is not thermodynamically stable, suggesting that a nonequilibrium steady state dominates the active cathode’s surface structure. We identify a stable, low work function surface structure, which may be responsible for some scandate cathode properties and demonstrate that multicomponent surface coatings can lower cathode work functions.
REFERENCES
1.
Y.
Wang
, J.
Wang
, W.
Liu
, K.
Zhang
, and J.
Li
, IEEE Trans. Electron Devices
54
, 1061
(2007
).2.
S.
Taguchi
, T.
Aida
, and S.
Yamamoto
, IEEE Trans. Electron Devices
31
, 900
(1984
).3.
S.
Yamamoto
, T.
Yaguchi
, S.
Sasaki
, and I.
Watanabe
, Jpn. J. Appl. Phys., Part 2
28
, L865
(1989
).4.
J.
Hasker
and C.
Crombeen
, IEEE Trans. Electron Devices
37
, 2589
(1990
).5.
P. M.
Zagwijn
, J. W. M.
Frenken
, U.
van Slooten
, and P. A.
Duine
, Appl. Surf. Sci.
111
, 35
(1997
).6.
W.
Müller
, Appl. Surf. Sci.
111
, 30
(1997
).7.
G.
Lesny
and R.
Forman
, IEEE Trans. Electron Devices
37
, 2595
(1990
).8.
R. S.
Raju
and C. E.
Maloney
, IEEE Trans. Electron Devices
41
, 2460
(1994
).9.
W.
Liu
, K.
Zhang
, Y.
Wang
, K.
Pan
, X.
Gu
, J.
Wang
, J.
Li
, and M.
Zhou
, Appl. Surf. Sci.
251
, 80
(2005
).10.
H.
Yuan
, X.
Gu
, K.
Pan
, Y.
Wang
, W.
Liu
, K.
Zhang
, J.
Wang
, M.
Zhou
, and J.
Li
, Appl. Surf. Sci.
251
, 106
(2005
).11.
G.
Miram
, L.
Ives
, M.
Read
, R.
Wilcox
, M.
Cattelino
, and B.
Stockwell
, Fifth IEEE International Vacuum Electronics Conference Proceedings
, 2004
(unpublished), p. 303
.12.
R.
Forman
, Appl. Surf. Sci.
2
, 258
(1979
).13.
G. A.
Haas
, A.
Shih
, and C. R. K.
Marrian
, Appl. Surf. Sci.
16
, 139
(1983
).14.
A.
Van Oostrom
and L.
Augustus
, Appl. Surf. Sci.
2
, 173
(1979
).15.
S.
Yamamoto
, S.
Sasaki
, S.
Taguchi
, I.
Watanabe
, and N.
Koganezawa
, Appl. Surf. Sci.
33
, 1200
(1988
).16.
G.
Gärtner
, P.
Geittner
, H.
Lydtin
, and A.
Ritz
, Appl. Surf. Sci.
111
, 11
(1997
).17.
P.
Hohenberg
and W.
Kohn
, Phys. Rev.
136
, B864
(1964
).18.
D. M.
Ceperley
and B. J.
Alder
, Phys. Rev. Lett.
45
, 566
(1980
).19.
J. P.
Perdew
, K.
Burke
, and Y.
Wang
, Phys. Rev. B
54
, 16533
(1996
).20.
G.
Kresse
and D.
Joubert
, Phys. Rev. B
59
, 1758
(1999
).21.
G.
Kresse
and J.
Furthmüller
, Comput. Mater. Sci.
6
, 15
(1996
).22.
H. J.
Monkhorst
and J. D.
Pack
, Phys. Rev. B
13
, 5188
(1976
).23.
E.
Heifets
, J.
Ho
, and B.
Merinov
, Phys. Rev. B
75
, 155431
(2007
).24.
P.
Zalm
, in Electronics and Electron Physics
, edited by L.
Marton
(Academic
, New York
, 1968
), Vol. 25
.25.
R.
Forman
, J. Appl. Phys.
47
, 5272
(1976
).© 2009 American Institute of Physics.
2009
American Institute of Physics
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