This article was published in an Elsevier journal. The attached copy
is furnished to the author for non-commercial research and
education use, including for instruction at the author’s institution,
sharing with colleagues and providing to institution administration.
Other uses, including reproduction and distribution, or selling or
licensing copies, or posting to personal, institutional or third party
websites are prohibited.
In most cases authors are permitted to post their version of the
article (e.g. in Word or Tex form) to their personal website or
institutional repository. Authors requiring further information
regarding Elsevier’s archiving and manuscript policies are
encouraged to visit:
http://www.elsevier.com/copyright
Author's personal copy
Available online at www.sciencedirect.com
Electrochemistry Communications 10 (2008) 222–224
www.elsevier.com/locate/elecom
Electric field-directed assembly of gold and platinum nanowires
from an electrolysis process
Yanqing Lu, Hai-Feng Ji *
Institute for Micromanufacturing, Louisiana Tech University, Ruston, LA 71272, USA
Received 23 October 2007; received in revised form 21 November 2007; accepted 22 November 2007
Available online 3 December 2007
Abstract
Gold and platinum nanowires have been grown on a silicon dioxide surface between two microfabricated electrodes from an electrolysis process under an AC signal with a DC offset. In the process, the anode electrode acted as a sacrificing layer and oxidized to metal
ions. The metal ions were reduced to particles and aligned along the electric field forming nanowires connected with the cathode. Greater
than 10 V and 12 V DC offset were required for growing gold and platinum nanowires, respectively. Other factors affecting the growth of
the nanowires include frequency of applied bias and gap between the electrodes.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Nanowires; Electrolysis process; Electrode; Electric field assisted assembly
1. Introduction
Metallic nanowires are one-dimensional, conductive
nanostructures. They are expected to play an important
role as interconnections and functional units in electronic
and mechanical devices with nanoscale dimensions. In
general, patterned metallic nanowires on surfaces are prepared from three approaches. The traditional lithography
approach includes UV lithography, e-beam [1,2], focusedion-beam [3], proximal probe writing [4,5], and deep ultraviolet [6,7] etc.; the second approach is the alignment of
metallic nanowires prepared from template-assisted process [8–11]; self-assembly is the third approach, which has
been generally explored as a bottom-up approach for generating complex nanostructures. Nanowires have been
assembled from a colloidal system of metallic nanoparticles
suspended in water [12] or ionic solutions of the targeted
metals [13].
In this paper, we report another direct, self-assembled
approach to grow nanowire on a surface using an electrol*
Corresponding author. Tel.: +1 318 257 5125; fax: +1 318 257 5104.
E-mail address: hji@chem.latech.edu (H.-F. Ji).
1388-2481/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.elecom.2007.11.030
ysis process. Gold and platinum nanowires were produced
between two microfabricated electrodes.
2. Experimental
In our design, two 150-nm-thick gold electrodes were
fabricated using standard UV lithography and lift-off techniques. Electrodes with different gap at 5 lm, 10 lm,
20 lm, 40 lm, and 120 lm were tested. Fig. 1 shows the
schematic diagram of the electrodes used in this work.
Two pads on both ends of the electrodes were designed
for wiring. The scanning electron microscopic (SEM)
images and energy dispersive spectrometry (EDS) analysis
were done using a Hitachi FESEM S4800. The voltage
applied on the two electrodes was provided by a function
generator (FG2, Beckman Industrial Corp. Fullerton, CA).
3. Results and discussion
In these experiments, the two electrodes were immersed
into ethanol. By applying a sinusoidal signal to the electrodes and adjusting the amplitude and the frequency of
the function generator, nanowires were generated between
Author's personal copy
Y. Lu, H.-F. Ji / Electrochemistry Communications 10 (2008) 222–224
223
Fig. 1. A schematic diagram of the gold electrodes. The electrodes were
made on a Si wafer covered by a 300-nm-thick SiO2.
the two electrodes within 2–3 min (Fig. 2). Typically, when
the electrical signal was applied, the cathode remained
intact while the anode was gradually oxidized and irregularly etched away from the cathode. During the process,
nanowires formed between the two electrodes. The nanowires were distributed along the cathode (Fig. 2a) with
10–40 lm distance between two neighboring nanowires.
The diameters of the nanowires were from 200 nm to
3 lm (Fig. 2a and b). Growth of the nanowires was directed by the electric field and was nearly perpendicular to the
cathode edge, but spread to dendrites near the irregular
anode (Fig. 2). The gold composition of the nanowires
was confirmed by EDS analysis (Fig. 3). It is noteworthy
that the Si and O elements in Fig. 3 were from the SiO2
background (the teal areas in Fig. 2a).
The growth of the gold nanowires was affected by gaps
between the two electrodes, frequency of the AC signal,
and voltage of the applied DC offset.
3.1. Effects of gaps between the two electrodes
Shorter gaps between the two electrodes facilitated
the growth of the nanowires. Nanowires appeared in
approximately 2 min at the 5 lm gap and 4 min at the
10 lm gaps. However, no nanowires were observed
between two electrodes when the gap was greater than
20 lm. The 5 lm gap was then used in the following
experiments.
Fig. 3. EDS analysis of the components of the gold nanowires and the
adjacent SiO2 surface.
3.2. Effects of frequency of the AC signal
When only DC current was applied, gold particles were
uniformly deposited onto the cathode to form a uniform
film. The nanowires would grow between the electrodes
only when both AC and DC were applied. The growth of
nanowires was dependent on the DC voltage, but independent of the AC frequency. The AC frequency from 1 Hz to
1 MHz did not cause any significant differences in nanowire
formation.
3.3. Effects of applied DC voltage
When the applied DC offset was lower than 1.5 V, no
reaction was observed and no nanowires appeared between
the electrodes. This can be readily explained since the
reduction potentials of Au3+/Au is 1.53 V. When the
applied DC offsets were between 1.5 V and 10 V, the anode
was oxidized and gold particles were uniformly deposited
on the cathode, however no nanowires formed. The anode
oxidation/cathode reduction is a well known electrolysis
process [14]. During the oxidation–reduction process, the
Fig. 2. (a) Optical; (b) SEM images of the gold nanowires grown from a electrolysis process under an AC signal of 7 Vrms and 1 MHz with a DC offset of
10 V. The original gap between the two gold electrodes was 5 lm.
Author's personal copy
224
Y. Lu, H.-F. Ji / Electrochemistry Communications 10 (2008) 222–224
Fig. 4. SEM images of the platinum nanowires grown from the electrolysis process under an AC signal of 9 Vrms and 10 Hz with a DC offset of 13 V.
platinum nanowires. Instead of relatively clean surface on
the gold cathode (Fig. 2), platinum particles were widely
observed on the platinum cathode after the oxidation–
reduction process (Fig. 4).
In summary, we demonstrated the formation of gold
and platinum nanowires on silicon dioxide surfaces during
an electrolysis process. The phenomena might be used to
grow nanowires directly from metal ions. We are currently
investigating quantitative explanations and the feasibility
and conditions to growing nanowires directly from the gold
and platinum metal ions in solutions.
Acknowledgements
This work was partially supported by NSF Sensor and
Sensor Network ECS-0428263.
Fig. 5. EDS component analysis of the Pt nanowires.
References
+
3+
gold on the anode was firstly oxidized to Au and Au ,
and these ions were then reduced to gold particles on the
cathode. When the DC offset is greater than 10 V, nanowires appeared on the silicon surface in less than 1 min
after the bias was applied, indicating that stronger electric
field is required to direct the growth of nanowires. In general, it takes relatively shorter time to form the nanowires
when higher DC offset is applied. However, no quantitatively work has been done in this work due to the limitation
of the Function Generator (up to 13 V only) used in these
studies. Under the relatively stronger electric field, the
reduction of gold ions to particles was localized on the
tip of growing nanowires along the direction of the electric
field [15–17]. The different observations under DC offset
below and above 10 V could be attributed to competition
of reduction rate at nanowire tips and diffusion rate of gold
ions under different electric fields. This is under investigation and will be published in due courses.
It was expected that similar results could be found on
other metallic electrodes. Fig. 4 shows platinum nanowires
produced under similar conditions. EDS analysis confirmed the platinum component of the nanowire (Fig. 5).
A minimum of 12 V DC offset was required for growing
[1] F. Cerrina, C. Marrian, Solid State Commun. 129 (2004) 681–
685.
[2] J.M. Gibson, Phys. Today 50 (1997) 56–61.
[3] S. Matsui, Y. Ochiai, Nanotechnology 7 (1996) 247–258.
[4] S.H. Hong, J. Zhu, C.A. Mirkin, Science 286 (1999) 523–525.
[5] J.A. Dagata, Science 270 (1995) 1625–1626.
[6] M.D. Levenson, Solid State Technol. 38 (1995) 81–98.
[7] S. Goolaup, A.O. Adeyeye, N. Singh, Thin Solid Films 505 (2006) 29–
34.
[8] Z. Liu, P.C. Searson, J. Phys. Chem. B 110 (2006) 4318–4322.
[9] B. Nikoobakht, Z.L. Wang, M.A. El-Sayed, J. Phys. Chem. B 104
(2000) 8635–8640.
[10] C.J. Murphy, A.M. Gole, S.E. Hunyadi, C.J. Orendorff, Inorg. Chem.
45 (2006) 7544–7554.
[11] Y.Y. Yu, S.S. Chang, C.H.L. Lee, C.R.H. Wang, J. Phys. Chem. B.
101 (1997) 6661–6664.
[12] K.D. Hermanson, S.O. Lumsdon, J.P. Williams, E.W. Kaler, O.D.
Velev, Science 294 (2001) 1082–1086.
[13] C. Cheng, R.K. Gonela, Q. Gu, D.T. Haynie, Nano Lett. 5 (2004)
175–178.
[14] J. Rodriguez-Fernandez, J. Perez-Juste, P. Mulaney, L.M. LizMarzan, J. Phys. Chem. B. 109 (2005) 14257–14261.
[15] Y.J. Yuan, M.K. Andrews, B.K. Marlow, Appl. Phys. Lett. 85 (2004)
130–132.
[16] K.H. Bhatt, O.D. Velev, Langmuir 20 (2004) 467–476.
[17] A. Ramos, H. Morgan, N.G. Green, A.J. Castellanos, Phys. D: Appl.
Phys. 31 (1998) 2338–2353.