(VS) mechanism8–22 First, the unidirectional motion of the Zn
atom cloud driven by the carrying gas is a key factor in the
preferational 1D growth of the Zn nanobelts. Secondly, the
relatively high-saturated vapor pressure of Zn guarantees the
concentration of this element necessary for the further growth of
the Zn nanobelts. The Zn vapor is generated by the reaction of
eqn. (1) at high temperature (1000 °C):
(1)
(2)
Fig. 2 SEM images of the Zn nanobelts showing their geometrical shapes
and thickness. (a) a low-magnification SEM image of the synthesized Zn
nanobelts. (b) a high-magnification SEM image of a Zn nanobelt, revealing
the shape characteristics of the belt.
ZnS (s) ? Zn (g) + S (g)
C (s) + 2S (g) ? CS2 (g)
The Zn vapor is transported to, and deposited on, the surface of
Si substrate in the relatively low temperature zone to form
nanobelts due to the epitaxial growth of crystals. Meanwhile,
the CS2 vapor [eqn. (2)] is carried away from the furnace by the
flowing Ar.
In conclusion, vapor transport has been employed to
synthesize single crystalline Zn nanobelts with well-defined
morphology distinct from those of metal nanowires and
nanotubes. The synthesis of those single crystalline metal
nanobelts may open up new possibilities for experimental and
theoretical understanding of dimensionally confined transport
phenomena of quasi-1D metal nanomaterials.
single crystalline Zn and suggests that the nanobelt growth
occurs along the < 100 > direction. In addition, Fig. 3c also
shows a lattice-resolved HRTEM image of a Zn nanobelt with
a width of ca. 100 nm; this image clearly reveals the (001) and
(101) atomic planes with separations of 0.4894and 0.2099 nm,
respectively. We have also used EDS to address the composi-
tion of the nanobelts. EDS analysis (Fig. 4) demonstrates that
the nanobelts contain only Zn, and no any other element is
found. The Cu peaks are generated by the copper grid.
The question arises as to how the Zn nanobelts are formed.
There exist several models to explain the growth for crystalline
whiskers including dislocation and vapor–liquid–solid (VLS)
mechanisms.18–21 In the present case, however, none of the
above mechanisms seem suitable to account for the growth of
the Zn nanobelts. This is because first, no evidence of
dislocations was found in our analysis, and second, there were
no nanoparticles observed on any ends of the Zn nanobelts. In
addition, the only source material used in our experiment is pure
ZnS and graphite powder. Therefore, it is likely that the Zn
nanobelts follow a growth mechanism similar to the vapor–solid
Notes and references
1 (a) A. P. Alivisatos, Science, 1996, 271, 937–937; (b) L. Lu, M. L. Sui
and K. Lu, Science, 2000, 287, 1463–1466.
2 (a) C. Dekker, Phys. Today, 1999, 52, 22–28; (b) Y. Cui and C. M.
Lieber, Science, 2001, 291, 851–853.
3 (a) J. Hu, T. W. Odom and C. M. Lieber, Acc. Chem. Res., 1999, 32,
435–445; (b) X. F. Duan, Y. Huang, Y. Cui, J. F. Wang and C. M.
Lieber, Nature, 2001, 409, 66–69.
4 (a) X. F. Duan and C. M. Lieber, Adv. Mater., 2000, 12, 298–302; (b)
P. M. Ajayan, Chem. Rev., 1999, 99, 1787–1799.
5 M. S. Gudiksen and C. M. Lieber, J. Am. Chem. Soc., 2000, 122,
8801–8802.
6 C. C. Chen and C. C. Yeh, Adv. Mater., 2000, 12, 778–741.
7 Y. Y. Wu and P. D. Yang, Chem. Mater., 2000, 12, 605–607.
8 Z. W. Pan, Z. R. Dai and Z. L. Wang, Science, 2001, 291,
1947–1949.
9 (a) N. H. Huang, A. Choudrey and P. D. Yay, Chem. Commun., 2000,
1063–1064; (b) M. Nishizawa, V. P. Menon and C. R. Martin, Science,
1995, 268, 700–702; (c) T. M. Whitney, J. S. Jing, P. C. Searson and C.
L. Chien, Science, 1993, 261, 1316–1319; (d) E. Braun, Y. Eichen, U.
Sivan and G. Ben-Yoseph, Nature, 1998, 391, 775–778.
10 Z. B. Zhang, D. Gekhtman, M. S. Dresselhaus and J. Y. Ying, Chem.
Mater., 1999, 11, 1959–1665.
11 W. K. Hsu, J. Li, H. Terrones, M. Terrones, N. Grobert, Y. Q. Zhu, S.
Trasobares, J. P. Hare, C. J. Pickett, H. W. Kroto and D. R. W. Watton,
Chem. Phys. Lett., 1999, 301, 159–166.
12 B. Nikoobakht, Z. L. Wang and M. A. El-sayed, J. Phys. Chem. B, 2000,
104, 8635–8640.
13 C. J. Brumlik, V. P. Meron and C. R. Martin, J. Mater. Res., 1994, 9,
1174–1183.
14 C. J. Brumlik and C. R. Martin, J. Am. Chem. Soc., 1991, 113,
Fig. 3 TEM and HRTEM images of the Zn nanobelts: (a and b) images of
several straight and twisted Zn nanobelts. (c) HRTEM image of a Zn
nanobelt which shows that the nanobelts are single crystalline and free from
dislocation and defects. (Inset) The corresponding electron diffraction
pattern recorded with the electron beam perpendicular to the long axis of a
belt, showing the growth direction to be < 100 > .
3174–3175.
15 H. Yumoto and R. R. Hasiguti, J. Cryst. Growth, 1986, 75, 289–294.
16 R. K. Willardson and H. L. Goering, Compound Semiconductors,
Reinold, New York, 1962.
17 Powder Diffraction File, Inorganic Vol. No PD1S-SiRB, 4-831 file,
Published by the Joint Committee on Powder Diffraction Stardards
USA, Swarthmere, PA.
18 A. M. Morales and C. M. Lieber, Science, 1998, 279, 208–211.
19 J. D. Holines, K. P. Johnston, R. C. Doty and B. A. Korgel, Science,
2000, 25, 1471–1473.
20 H. Y. Peng, Z. W. Pan, L. Xu, X. H. Fan, N. Wang, C. S. Lee and S. T.
Lee, Adv. Mater., 2001, 13, 317–320.
21 H. Z. Zhang, Y. C. Kong, Y. Z. Wang, X. Du, Z. G. Bai, T. T. Wang, D.
P. Yu, Y. Ping, Q. L. Hang and S. Q. Feng, Solid State Commun., 1999,
109, 677–682.
22 M. Satoh, N. Tanaka, Y. Veda, S. Ohshio and H. Saitoh, Jpn. J. Appl.
Phys., 1999, 38, L586–589.
Fig. 4 EDX spectra recorded at the position of the white dot in Fig. 3b.
Chem. Commun., 2001, 2632–2633
2633