High-resolution electron microscopy of boron nitride nanotube with yttrium nanowire

Article abstract of DOI:10.1016/j.jpcs.2003.10.026

Boron nitride (BN) nanotubes were investigated by high-resolution electron microscopy (HREM) and image processing. From the HREM image, a BN nanotube encapsulating yttrium nanowire was confirmed by comparing calculated diffraction and a nanostructure model. The present work indicated that yttrium elements could be confined in BN nanotube with large energy gap.

Full text of DOI:10.1016/j.jpcs.2003.10.026

Journal of Physics and Chemistry of Solids 65 (2004) 359–361
www.elsevier.com/locate/jpcs
High-resolution electron microscopy of boron nitride nanotube
with yttrium nanowire
*
Takeo Oku , Ichihito Narita
Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan
Abstract
Boron nitride (BN) nanotubes were investigated by high-resolution electron microscopy (HREM) and image processing. From the HREM
image, a BN nanotube encapsulating yttrium nanowire was confirmed by comparing calculated diffraction and a nanostructure model. The
present work indicated that yttrium elements could be confined in BN nanotube with large energy gap.
q 2003 Elsevier Ltd. All rights reserved.
Keywords: A. Nanostructures; C. Electron microscopy; D. Crystal structure
1. Introduction
introducing a mixed gas of Ar (0.025 MPa) and N2
(0.025 MPa), arc-melting was applied to the samples at
an accelerating voltage of 200 V for 10 s. Arc-melting
was performed with a vacuum arc-melting furnace (NEV-
AD03, Nissin Engineering Co., Ltd).
Since the discovery of carbon nanotubes by Iijima,
new territory of carbon nanomaterials was created [1].
The carbon nanotubes become both a semiconductor and
a metal due to the diameters and chiralities, which are
expected as gas storage materials, single-electron transis-
tors and magnetic refrigeration. Boron nitride (BN)
nanotubes have also been discovered and studied [2–4],
which have a wide band gap (insulator) and are
independent of the tube diameters [5,6]. The BN
nanotubes have a hexagonal ring structure, which is
similar to carbon nanotubes. The BN nanotubes with
metal nanowires are very intriguing for application of
nanocable. The purpose of the present work is to produce
BN nanotubes with metal nanowires inside by arc-
melting method, and to investigate the nanostructures by
high-resolution electron microscopy (HREM) and image
processing [7,8].
Samples for HREM observation were prepared by
dispersing the materials on holey carbon grids. HREM
observation was performed with a 300 kV electron
microscope (JEM-3000F) equipped with side-entry goni-
ometers having a point-to-point resolution of 0.17 nm. To
avoid sample damage by electron irradiation, the electron
beam for HREM observations was minimized by using
smaller spot size. The HREM images recorded on
negative films were digitized by a film scanner, and
the gray scale of digitized images was 256. For image
processing of the observed HREM images, Digital
Micrograph software (Gatan, Inc., California) was used.
The digital image was masked and fast Fourier
transformed. To compare the observed Fourier transform
with simulation, diffraction patterns were produced by
CrystalKit (Total Resolution, CA, USA).
2. Experimental procedures
3. Results and discussion
BN nanotubes were synthesized by arc-melting
method in an Ar/N2 gas mixture from YB6 [9]. YB6
powder (2.0 g, 99.6%, Kojundo Chemical Lab Co., Ltd)
was set on a copper mold in an electric-arc furnace,
which was evacuated down to 1.0 £ 1023 Pa. After
HREM image of a BN nanotube synthesized from
YB6 powder is shown in Fig. 1(a), which was taken
nearly at Scherzer defocus. Fig. 1(b) is an enlarged
image of Fig. 1(a). Number of BN {002} layers is 12,
and lattice fringes are observed in the BN nanotube.
Fourier transform of Fig. 1(b) is shown in Fig. 2(a).
*
Corresponding author. Tel.: þ81-6-6879-8521; fax: þ81-6-6879-8522.
E-mail address: oku@sanken.osaka-u.ac.jp (T. Oku).
0022-3697/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jpcs.2003.10.026

360
T. Oku, I. Narita / Journal of Physics and Chemistry of Solids 65 (2004) 359–361
Fig. 1. (a) HREM image of BN nanotube synthesized from YB6 powder. (b) Enlarged image of (a).
Fig. 2. (a) Fourier transform of Fig. 1(b). (b) Filtered Fourier transform of (a).
Fig. 3. (a) Inverse Fourier transform of Fig. 2(b). (b) Enlarged image of (a).

T. Oku, I. Narita / Journal of Physics and Chemistry of Solids 65 (2004) 359–361
361
Fig. 4. (a) Atomic structure model of yttrium along [101]. (b) Calculated diffraction pattern of (a).
There exists some noise in the Fourier transform, and
noise filtering was carried out, as shown in Fig. 2(b).
Spots of BN 002 are observed as bright spots. In
addition, spots corresponding to yttrium element are
observed and indexed, and the yttrium crystal is observed
along [101].
remain in the BN nanotube. These BN nanotubes with metal
nanowires would be interesting materials for nanodevices.
In conclusion, BN nanotubes encapsulating yttrium
nanowire were produced by an arc-melting method, which
was confirmed by HREM, image processing and diffraction
calculation.
Fig. 3(a) is an inverse Fourier transform of Fig. 2(b).
BN{002} layers are clearly observed in the image. An
enlarged image of Fig. 3(a) is shown in Fig. 3(b), which
indicates lattice fringes at the center of the BN nanotube.
Lattice parameters of yttrium with a hexagonal structure, as
determined by X-ray diffraction analysis [10], were a ¼
0:36474 nm and c ¼ 0:57306 nm; which agrees well with
the present lattice fringes. Dark contrast corresponds to
yttrium atom pairs, as indicated in Fig. 3(b). Based on the
observations, an atomic structure model of yttrium along
[101] was constructed as shown in Fig. 4(a), which indicates
the yttrium atom pairs. Fig. 4(b) is a calculated diffraction
pattern of Fig. 4(a), and agrees well with the observed
Fourier transform of Fig. 2(b).
References
[1] S. Iijima, Nature 354 (1991) 56.
[2] N.G. Chopra, R.J. Luyken, K. Cherrey, V.H. Crespi, M.L. Cohen, S.G.
Louie, A. Zettl, Science 269 (1995) 966.
[3] M. Terauchi, M. Tanaka, T. Matsumoto, Y. Saito, J. Electron Microsc.
47 (1998) 319.
[4] D. Golberg, Y. Bando, O. Stephan, K. Kurashima, Appl. Phys. Lett. 73
(1998) 2441.
[5] A. Rubio, J.L. Corkill, M.L. Cohen, Phys. Rev. B49 (1994) 5081.
[6] T. Oku, M. Kuno, H. Kitahara, I. Narita, Int. J. Inorg. Mater. 3
(2001) 597.
[7] T. Oku, J. Ceram. Soc. Jpn 109 (2001) S17.
[8] T. Oku, Chem. Commun. (2002) 302.
In the present work, the yttrium worked as a good
catalytic element to produce BN nanotubes. Since the YB6
powders formed BN nanotubes, boron atoms were con-
sumed preferentially. As a result, yttrium element would
[9] I. Narita, T. Oku, Diamond Related Mater. 12 (2003) 1146.
[10] F.H. Spedding, A.H. Daane, K.W. Herrmann, Acta Cryst. 9
(1956) 559.