RESEARCH ARTICLE
Copyright © 2008 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 8, 1–5, 2008
FabricationofGoldNanotubesfrom
RemovableMgONanowiresTemplates
Hyoun Woo Kim
∗
, Jong Woo Lee, Mesfin A. Kebede,
Hyo Sung Kim, Buddhudu Srinivasa, and Chongmu Lee
School of Materials Science and Engineering, Inha University, Incheon 402-751, Republic of Korea
We have prepared MgO/Au core–shell nanowires, subsequently demonstrating the fabrication of
Au nanotubes by using MgO nanowires as a sacrificial template. The samples were characterized
by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and energy-
dispersive X-ray spectroscopy. MgO nanowires were coated with a conformal layer of Au via sputter-
ing. By etching away the MgO core in aqueous (NH
3
)
2
SO
4
solution, hollow nanotube-like structures
of Au were readily obtained. This approach offers a potentially useful route for the fabrication of a
variety of hollow metallic structures.
Keywords: Gold Nanotubes, MgO Nanowires, Templates.
1. INTRODUCTION
Gold (Au) nanostructures have found applications in
biological probes,
1
submicrometer metallic barcodes,
2
surface-enhanced Raman spectroscopy,
3 4
plasmon wave-
guides for optical devices,
5
photonic materials,
6
and chem-
ical sensors.
7
Also, there is currently growing interest in
the fabrication of one-dimensional (1D) materials. One
particularly interesting area of 1D nanostructure research
is core–shell composite nanostructures known as Au nano-
tubes, which have a central nonmetal or hollow core sur-
rounded by an Au wall. Au nanotubes have been used in
various applications, such as molecular sieves,
8 9
sensors,
10
conductors,
11
a liftoff mask in advanced lithography,
12
cat-
alysts for oxidation of CO,
13
and label-free quantification
of DNA sequences.
14
Accordingly, they have been synthe-
sized by a variety of techniques, including irradiation of an
Au film with an electron beam at 150 K
15
and via the use
of template-based electroless plating techniques, where Au
is deposited onto the pore walls of a porous polymetric
membrane.
16–18
In the present study, we suggest a new synthetic
approach where sputtering is used to coat a thin Au shell
onto as-synthesized MgO nanowires. MgO nanowires are
easy to prepare and are suitable for the use of sacrificial
templates. Also, MgO is an important material for such
applications as catalysis, superconductor products, and
oproelectronics.
19–21
The MgO nanowires were removed
by dipping them in a dilute (NH
3
)
2
SO
4
solution to obtain
∗
Author to whom correspondence should be addressed.
hollow Au nanotubes. This simple and low-cost dipping
method in conjunction with an easily controlled sputter-
ing technique presents exciting prospects for the com-
mercial production of metal nanotubes with a variety of
applications.
2. EXPERIMENTALDETAILS
A multi-step process was used to fabricate Au nanotubes.
First, pure MgB
2
powders and Au-coated substrates were
placed on the lower and upper holder, respectively, in the
middle of a quartz tube. The apparatus used in this study
has been illustrated elsewhere.
22
The system consists of a
quartz-tube reactor that is inserted into a horizontal tube
furnace. During the experiment, the furnace was main-
tained at a temperature of 900
C for 1 h. The typical
percentage of O
2
partial pressure was set to approximately
3%, with the O
2
gas in a balance of argon being at a con-
stant total pressure of 2 Torr.
Second, we carried out coating experiments on the as-
prepared MgO nanowires using a turbo sputter coater
(Emitech K575X, Emitech Ltd., Ashford, Kent, UK). The
sputtering target used in the present experiment was a
piece of polished p-type (100) Si wafer, with the distance
between the target and nanowires being about 50 mm.
The sputtering deposition was carried out at a pressure
of 8 × 10
−4
Pa in high purity argon (Ar) gas (99.999%)
with a DC sputtering current of 30 mA, at room temper-
ature. For variation of the thickness of the Au shell layer,
the sputter time was set to 1 min and 3 min, respectively.
Subsequently, in order to selectively remove the MgO core
J. Nanosci. Nanotechnol. 2008, Vol. 8, No. 9 1533-4880/2008/8/001/005 doi:10.1166/jnn.2008.210 1