Platinum thin film with a highly ordered mesostructure by contact plating

Article abstract of DOI:10.1246/cl.2004.1576

By a contact plating technique using a galvanic reaction between Al and Au in the presence of Pt complex, we have for the first time succeeded in the formation of a highly ordered mesostructured Pt film on a Au surface by reduction of Pt ions in the presence of lyotropic liquid crystals. Copyright

Full text of DOI:10.1246/cl.2004.1576

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Chemistry Letters Vol.33, No.12 (2004)
Platinum Thin Film with a Highly Ordered Mesostructure by Contact Plating
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and Kazuyuki Kuroda
Yusuke Yamauchi,
Tokihiko Yokoshima, Toshiyuki Momma,
Tetsuya Osaka,
Department of Applied Chemistry, School of Science and Engineering, Waseda University,
Ohkubo 3-4-1, Shinjuku-ku, Tokyo 169-8555
Major in Nanoscience and Nanoengineering, Graduate School of Science and Engineering, Waseda University
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Kagami Memorial Laboratory for Materials Science and Technology, Waseda University
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CREST, Japan Science and Technology Agency
(Received September 8, 2004; CL-041060)
By a contact plating technique using a galvanic reaction be-
tween Al and Au in the presence of Pt complex, we have for the
first time succeeded in the formation of a highly ordered meso-
structured Pt film on a Au surface by reduction of Pt ions in the
presence of lyotropic liquid crystals.
Nonionic surfactant Brij 76 [C18(EO)10] was used as a for-
mer of lyotropic liquid crystals (LLC). Hydrogen hexachloropla-
tinate (IV) hexahydrate (1.3 g) was dissolved in distilled water
(3.3 g). Brij 76 (9.0 g) was added into the solution, and the con-
centration of the surfactant was adjusted to 65 wt % (surfactant/
ꢁ
water). The mixture was heated to 85 C (higher than the melting
point of Brij 76) and stirred. After the mixture was cooled to
ꢁ
In 1997, Attard et al. reported the first synthesis of mesopo-
rous metal by a chemical reduction of metal ions in the presence
room temperature and aged, it was again heated to 80 C and stir-
red. The thermal/aging procedure was repeated three times to
complete homogeneous mixing. This mixture thus obtained
showed a homogeneous yellow color with a hexagonal meso-
phase (abbreviated as HI–Pt mixture). The formation of a liquid
crystal state was confirmed by a polarizing microscope. A sub-
strate coated with Au was prepared by deposition of titanium
(1 nm) and then gold (10 nm) onto a Si substrate (1:5 ꢂ 1:5
cm) by electron beam evaporation. When the substrate in contact
with an Al wire was immersed in the HI–Pt mixture, the deposi-
tion of Pt was carried out with electrons transferred to the inter-
face between the Au surface and the HI–Pt mixture by dissolving
the Al wire (Figure 1). The deposition was carried out for 30 min
at room temperature, and then the Pt film was soaked in water
and ethanol to remove the surfactants. The mesostructure and
morphology of the film were examined by low-angle X-ray dif-
fraction (XRD), transmission electron microscopy (TEM), and
field emission scanning electron microscopy (FE-SEM).
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of lyotropic liquid crystals (LLC). Since then, this liquid crystal
templating strategy by electrochemical processes has been used
as an approach of direct physical casting to produce mesoporous
metals. Mesoporous metals with high electroconductivity, uni-
formly ordered pore network, and high surface areas have at-
tracted considerate interests in a wide range of electrochemical
reaction media.
The electrochemical method can be utilized to prepare not
only metal films but also metal powders, depending on the oper-
ating conditions. Recently this method has been used in a wide
range of the formation of micro- and nanostructures, such as
functional nanoparticles and microstructure for MEMS (Micro-
Electro Mechanical Systems). Electrodeposition method is a
general approach for the reduction of metal ions. Metal ions
are reduced on substrates by an external power supply, forming
films. By applying this method to LLC systems, several mesopo-
rous metal films with various compositions have been reported
The XRD profiles of the HI–Pt mixture show two peaks in
the range of low angle (Figure 2a, Profile (A)). These d values
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up to date. The electroless deposition method, which utilizes
an oxidation of reducing agent existing in a solution as the elec-
tron source to reduce metallic ion, was also performed in the
presence of LLC, while only mesoporous noble metal particles
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(
in synthesizing highly ordered mesoporous Ni and mesostruc-
Pt and Pt–Ru alloy ) have been reported. We have succeeded
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tured Ni–Co alloy particles by an autocatalytic electroless plat-
ing using appropriately chosen reducing agents.
In this study, we extended our synthesis methods to contact
plating for the preparation of mesostructured/mesoporous metal
films. This plating method using a galvanic reaction between
metals has been utilized at the initiation of metal deposit in the
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field of surface finishing. Many kinds of metals can easily be de-
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posited on conductive substrates. We can avoid the formation of
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some defects such as holes during electroless deposition. Plati-
num was chosen here because mesoporous Pt-group metals and
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alloy films (e.g. Pt, Pd, Pt–Ru, Pt–Pd ), having their poten-
tials for applications in electrochemistry and catalysis, have re-
cently attracted much attention. Here we report the first example
of the formation of highly ordered mesostructured Pt films on a
Au surface by the contact plating using a galvanic couple be-
tween Al and Au in the presence of LLC including Pt ions.
Figure 1. Schematic mechanism for the preparation of mesostruc-
tured Pt films by the contact plating using a galvanic reaction between
Al and Au in the presence of lyotropic liquid crystals (LLC) including
Pt ions.
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.12 (2004)
1577
Figure 2. a); XRD profiles in the low-angle range. [(A) HI–Pt mixture (The ternary system composed of Brij76, water, and hydrogen hexachloro-
platinate (IV) hexahydrate and (B) mesostrucutured Pt thin film.] b); TEM image of mesostructured Pt film over a wide range. [Inset; Typical
2D-hexagonal arrangement and side view of mesochannels. Underbars are 10 nm.] c) and d); Top-surface SEM image of mesostructured Pt thin
film at c) low and d) high magnifications.
are 7.2 and 3.6 nm, respectively, corresponding to the (100) and
(
single broad diffraction peak (d100 ¼ 7:3 nm) (Profile (B)). The
d spacing of this peak was almost the same as that of the HI–
Pt mixture, indicating that the mesostructure derived from the
mixture was formed on the substrate.
In conclusion, we have for the first time succeeded in pre-
paring Pt thin films with a highly ordered mesostructure by the
contact plating. This approach will be used for a very large
200) diffraction planes. On the other hand, the film showed a
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scaled up reaction cell (in m order), without controlling current
densities and plating bath conditions. This method will be con-
siderably important as a practical and technical approach for
one-step synthesis of mesoporous metal thin films with uniform
thickness and various compositions.
By the TEM observations over a wide range of the film, we
confirmed the formation of a porous nanostructure (Figure 2b).
The clear end-on and side view images (inset) were observed,
showing the presence of the 2D-hexagonal ordered mesostruc-
ture. The pore diameter and wall thickness were roughly estimat-
ed to be ca. 3:9 ꢃ 0:3 nm and ca. 4:3 ꢃ 0:3 nm, respectively.
This observed pore size is comparable to those observed for mes-
oporous Pt–Ru alloy particles obtained from the hexagonal
This work is supported in part by a Grant-in-Aid for Center
of Excellence (COE) Research ‘‘Molecular Nano-Engineering’’,
and the 21st Century COE Program ‘‘Practical Nano-Chemistry’’
and Encouraging Development Strategic Research Centers
Program ‘‘Establishment of Consolidated Research Institute
for Advanced Science and Medical Care’’ from the Ministry of
Education, Culture, Sports, Science and Technology.
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phase of Brij 76. If we assume that the film has a 2D-hexagonal
structure, the distance between the pores, calculated from the
tentatively assigned (100) peak (d100 ¼ 7:3 nm), is 8.4 nm
p
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disruption of a mesostructure.
Published on the web (Advance View) November 13, 2004; DOI 10.1246/cl.2004.1576