J. Am. Chem. Soc. 2001, 123, 10397-10398
10397
Metal Nanowire Formation Using Mo3Se3- as
Reducing and Sacrificing Templates
Jae Hee Song, Yiying Wu, Benjamin Messer,
Hannes Kind, and Peidong Yang*
Department of Chemistry, UniVersity of California
Materials Science DiVision, Lawrence Berkeley National
Laboratory, Berkeley, California 94720
ReceiVed August 10, 2001
Figure 1. Schematic illustration of metal nanowire templating reaction
between LiMo Se nanowires and metal ions.
3 3
Recent research in the field of nanometer-scale electronics has
focused on two fundamental issues: the operating principles of
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small-scale devices and schemes that lead to their realization
2
ties of the molecule for the defined buildup of a nanostructure
and installs its electrical functionality by the directed construction
of a metallic wire on the biotemplate. However, the reported 100
nm thick silver wires displayed a nonconducting gap for small
bias voltages.
and eventual integration into useful circuits. The availability of
a nanoscale toolbox is the key for this field of research. Among
the many potential building blocks within this nanoscale toolbox,
nanowires are considered one of the key components because they
can be used as interconnects and other functional devices in
3
3 3 ∞
In this study, we choose [Mo Se molecular chains as our
-]
nanoelectronics. Unfortunately, although several processes have
been developed for the syntheses of semiconductor nanowires,4
few methods have been developed for preparing free-standing,
experimental system for two important reasons. First, these
molecular chains are obtained by dissolution of crystals of quasi-
3 3
Se
in polar solvent.10 Each chain is made of
uniform metal nanowires. Among them, template synthesis (in
1D materials LiMo
3 3
staggered stacks of triangular Mo Se with a diameter of 0.5 nm.
5
porous matrixes such as porous Al
2
O
3
films and mesoporous
6
7
silica ) and step-edge decoration are considered as effective
approaches. The step-edge decoration method was recently
employed to produce Mo nanowires of 100 nm thickness. Metal
nanowires have also been prepared by using DNA and carbon
nanotubes as templates. Herein we report a simple chemical
The molecular chain itself is a reducing agent and can be readily
oxidized. Second, these individual molecular wires form uniform
nanowire bundles with diameters of 2-100 nm in certain polar
solvents such as methanol and DMSO. Hence, these nanowires
possess dual functionalities, being reductive one-dimensional
templates. In fact, the redox chemistry of LiMo Se was previously
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8
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process for synthesizing long, free-standing metal nanowires.
LiMo Se nanowires are used as both reducing agents and
3 3
sacrificial templates in this study to yield continuous metal
3
3
studied by Tarascon, and it was demonstrated that insertion and
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extraction of Li/Mo
To form uniform metal nanowires, a redox reaction is carried
out using LiMo Se nanowires as the reducing agents to reduce
aqueous metal ions (e.g., AuCl
ions are reduced and deposited directly on the nanowire templates,
while the nanowire templates are oxidized into Mo Se and
6 6
Se is reversible.
nanowires. The metal nanowires generally have diameters of 10-
100 nm and lengths of several micrometers. These metal
3
3
nanowires display small ohmic resistances at room temperature,
indicating that these wires could prove useful as interconnects in
nanoelectronic circuits.
-
+
2-
2-
4
, Ag , PdCl
4
, PtCl
4
). Metal
3
3
Previously, DNA has been used as a biotemplate for making
eventually dissolve in water (Figure 1). Consequently, metal
nanowires with diameters of 2-100 nm can be obtained through
this cooperative chemical templating process. Metal nanowires
of Au, Ag, Pt, and Pd can be readily synthesized.
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metallic nanowires, although the continuity of the resulting metal
nanowires has been problematic. Since DNA itself does not
possess any reducing/oxidizing capability, the synthesis generally
is a two-step process, which involves metal activation followed
by chemical reduction. Nevertheless, the construction of electronic
circuits based only on native DNA remains problematic, mainly
due to the high resistance of DNA that limits its potential
applications in this regard. Recently, Braun and co-workers
presented a new approach by fixing DNA between two contacts
and utilizing it as a template for the construction of a silver
3 3
In a typical experiment, a LiMo Se solution was prepared by
dissolving 5 mg of LiMo Se in 20 mL of DMSO. A 2 mL drop
3
3
of metal ion solution (0.005 wt %) was added to this DMSO
solution. Using the Au nanowire system as an example, evidence
of the reaction is apparent immediately after the solution mixing.
The overall solution color develops a pink tint, and a peak at
526 nm appears in the UV-vis absorption spectra, indicating that
Au nanocluster nucleation and growth has occurred.
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nanowire. This technique uses the molecular recognition proper-
(
1) Dekker: C. Phys. Today 1999, 52, 22.
Figure 2 shows transmission electron microscopy images taken
before (a) and after (b-d) the templating reaction for the Au
3 3
nanowire system. Before the reaction, the LiMo Se molecular
chains self-assemble into nanowire bundles of 10-100 nm in
diameter. After the redox reaction, Au nanowires of similar
diameters and morphology are obtained. These Au nanowires are
continuous and polycrystalline. Figure 2d shows a high-resolution
TEM image of an individual Au nanowire with diameter of 15
nm. It can be seen that the Au nanocrystalline domains fuse
together at the interface and form a continuous and robust
(
2) (a) Hu, T.; Odom, W.; Lieber, C. M. Acc. Chem. Res. 1999, 32, 435.
(
b) Collier, C. P.; Wong, E. W.; Behloradsky, M.; Raymo, F. M.; Stoddart, J.
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001. (b) Preston, C. K.; Moskovits, M. J. Phys. Chem. 1993, 97, 8495. (c)
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references therein.
(10) Tarascon, J. M.; DiSalvo, F. J.; Carrol, C. H. J.; Walsh, M.; Rupp, L.
J. Solid State Chem. 1985, 58, 290.
(11) Tarascon, J. M.; Hull, G. W.; DiSalvo, F. J. Mater. Res. Bull. 1984,
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(
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0.1021/ja016818h CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/26/2001