Electronic and field emission properties of boron nitride/carbon nanotube superlattices Page: 48
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48 Appl. Phys. Lett., Vol. 81, No. 1, 1 July 2002
eigenstate of the system. In order to avoid any spurious ef-
fects arising from the periodic calculation, we have deter-
mined that the unit cell should have a vacuum of at least 15
A on both sides of the system along its axis.19 With this
method, we calculated a work function of 5.01 eV for a
(10,10) carbon nanotube, in close agreement with previously
published values.2'021 For the smaller diameter (6,0) carbon
nanotube, we found a considerably larger work function of
6.44 eV. This is primarily due to the mixing of the or and r
valence bands in this highly curved tube.
Turning to the heterostructures, we consider a finite
NB/C (6,0) system consisting of four alternating N and B
layers followed by 8 C layers, giving a total of 96 atoms.
Due to the net polarization field experienced by the electron,
the work function is reduced to 5.04 eV at the C tip and
increased to 7.52 eV at the N tip. The same trend is observed
for the BN/C system, for which the work function at the B
tip is equal to 5.00 eV while it takes a value of 6.45 eV at the
C tip. The work function is therefore decreased by a signifi-
cant 1.40 eV, as compared to the pure carbon system. This is
large enough to lead to significant macroscopic effects. Ac-
cording to the Fowler-Nordheim relationship, the logarithm
of the current density (J) depends upon the work function ob
as In J- -42. It follows that the insertion of BN segments
in C nanotubes will increase the current density by up to two
orders of magnitude as compared to pure carbon nanotube
In summary, we have shown that a wide variety of
nanoscale heterojunctions may be formed with BN/C struc-
tures, with the possibility of band-offset engineering. BN/C
junctions and superlattices are characterized by the presence
of a spontaneous polarization field, whose value is highly
sensitive to the helicity of the underlying nanotubes. The
polarization field can be used to lower the work function of
BN/C nanotube tips, thereby increasing the field emitting
properties over carbon nanotube tips by up to two orders of
The authors would like to thank R. Resta and S. Nakh-
manson for scientific discussions. This work was supported
in part by NASA, DOE, and ONR. We also thank the DOD
and NC Supercomputing Centers for extensive computer
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Meunier, Vincent; Roland, Christopher; Bernholc, Jerry & Buongiorno Nardelli, Marco. Electronic and field emission properties of boron nitride/carbon nanotube superlattices, article, July 1, 2002; [College Park, Maryland]. (https://digital.library.unt.edu/ark:/67531/metadc226889/m1/3/: accessed April 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT College of Arts and Sciences.