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Chemistry Letters Vol.34, No.4 (2005)
Wet Chemical Synthesis of Ag Nanowires Array at Room Temperature
Ju Weigang,y;yy Zhang Xiaohong,ꢀy and Wu Shikangy
yNano-organic Photoelectronic Laboratory, Technical Institute Physics and Chemistry,
Chinese Academy of Science, Beijing 100101, P. R. China
yyGraduate School of Chinese Academy of Science, Beijing 100039, P. R. China
(Received December 22, 2004; CL-041581)
This letter describes a new simple method to prepare silver
nanowires array in solution phase by direct chemical reduction at
room temperature. In the process no seeds and no stabilizers are
needed.
One-dimentional (1D) nanostructures (wires, tubes, and
rods) are expected to play an siganificant role in fabricating
nanoscale devices. Metal nanowires have been the focus of many
recent studies because of their potential use as active compo-
nents or interconnects in fabricating electronic, photonic and
sensing devices.1,2 Bulk silver has excellent electronic and ther-
mal conductivities among all the metals. As a result, the synthe-
sis and characterization of silver nanowires recently attracted
great attention from a broad range of researchers. Silver nano-
rods and nanowires have been prepared by ultraviolet irradia-
tion–photoreduction, solid–liquid phase arc discharge,3 a pulsed
sonochemical method.4 Several direct solution-phase ap-
proaches to silver nanowires by chemical reduction in the pres-
ence of functional polymers5–7 or surfactants8 and other ‘‘soft
templates’’9–12 have been explored. However, these methods
are often characterized by adscititious seeds and stabilizers or
elevated temperature (>100 ꢁC).5,13 Moreover, silver nanowire
arrays have not been obtained directly by chemical reduction
in solution phase. Highly ordered arrays of metallic nanowires
are expected to play an essential role for interconnects and
high-density magnetic storage devices because of their unique
electrical and magnetic properties.14,15 One promising technique
for the intergration of nanowires into well-defined architectures
is their deposition into ordered templates. But most of the metal-
lic nanowires (cobalt, copper, iron, etc.) were synthesized by
electrodeposition in porous templates.16 The diameters of the
rod or wire-shaped nanoparticles can be varied by using template
membranes with different pore diameters. Piao and Kim success-
fully synthesized AgI nanowires17 by the ion reaction between
Agþ and Iꢂ in anodic alumina oxide (AAO) membrane, and
the diameter of the wires can be controlled by the diameters of
the used template. Herein, we developed a relatively new and
simple method to prepare Ag nanowires array through chemical
reduction of Agþ by BH4ꢂ in AAO template (Agþ is reduced by
BH4ꢂ rapidly and Ag deposited in the pores.). Different from the
above methods stated, no seeds and stabilizer are needed. Fur-
thermore, the synthesis was conducted at room temperature.
Anodic alumina oxide (AAO) membrane (thickness 60 mm)
was purchased from Whatman Corp. The diameter of the pore is
200 nm averagely. The membranes were cleaned for 10 min in an
ultrasonic water bath. AgNO3 (analytical reagent) and NaBH4
(analytical reagent) were purchased from Beijing chemical fac-
tory and used without further purification. An apparatus shown
in Figure 1 was constructed and manufactured using PTFE for
Figure 1. The apparatus constructed for the synthesis of Ag
nanowires array.
the synthesis of Ag nanowires array.
In a typical synthesis, 0.02 mol/L of AgNO3 and 0.02 mol/L
of NaBH4 aqueous solutions of the same volume were poured in-
to the glass tubes from different sides, respectively. AAO was
placed in the center of the equipment and its edge was sealed
by two rubber gaskets, which can keep the two different solu-
tions from blending by leaking out through the clearance. Then,
ꢂ
both ions Agþ and BH4 diffused into the pore of AAO mem-
brane from different direction owing to the presence of concen-
tration difference of solutions, which aꢂpplied as a driving force
for the ionic diffusion. Agþ and BH4 would enter and meet
ꢂ
in the pore of the AAO membrane. Agþ was reduced by BH4
rapidly in situ, and Ag was obtained. Thus each pore of AAO
membrane served as a reaction vessel. In this process, Ag ob-
tained in the initial stage formed nanoparticles, and the nanopar-
ticles grew up gradually and connected each other with the reac-
tion going along, which can be rectified by SEM images at dif-
ferent stages. After completion of the reaction, the Ag/AAO
composite was thoroughly washed with deionized water. Then
the resulting composite was immersed in 10 wt % H3PO4 for
4 h at room temperature to remove the alumina membrane, and
the bare bundles of nanowires were cleaned by a large amount
of distilled water and ethanol. When the concentration of the so-
lution was changed to 0.06 mol/L and 0.08 mol/L, the similar
results were obtained.
Field emission scanning electron microscopic (FE-SEM, S-
4300FEG equipped with Energy dispersive X-ray) images of the
prepared Ag nanoparticles at different stages are shown in
Figure 2. In the short reaction time (1.5 h), only small nanopar-
ticles of Ag were found (Figure 2a). It was attached on the wall
of AAO separately. When the process continued to 12 h, nano-
rods can be observed (Figure 2b). After 24 h, silver nanowires
can be obtained (shown in Figure 2c). The diameter of the nano-
wires was approximately 200–250 nm, equal to the pore diame-
ter of the alumina membrane, and the length was about 60 mm.
Besides that, the AAO template with an average pore diameter
of 100 nm (100 ꢃ 40 nm) was also used to prepare Ag nano-
wires. For the obtained Ag nanowires, their diameters were
about 100 nm. And the morphologies had no obvious difference.
The composition of as-prepared Ag nanowires was charac-
terized by energy dispersive X-ray spectroscope (EDX). The
Copyright ꢀ 2005 The Chemical Society of Japan
Weigang, Ju
