Micropatterning of organic-inorganic hybrid film using photosensitive sol-gel system consisting of double-decker-shaped multifunctional silsesquioxane

Article abstract of DOI:10.1246/cl.2006.1130

The micropatterning of an organic-inorganic hybrid film consisting of a double-decker-shaped multifunctional silses-quioxane was achieved using a photosensitive sol-gel system containing a titanium alkoxide modified with β-diketone. Negative patterns with a high-resolution of ca. 1 μm were obtained by UV-irradiation. Copyright

Full text of DOI:10.1246/cl.2006.1130

1130
Chemistry Letters Vol.35, No.10 (2006)
Micropatterning of Organic–Inorganic Hybrid Film Using Photosensitive Sol–Gel System
Consisting of Double-decker-shaped Multifunctional Silsesquioxane
Akira Watanabe and Tokuji MiyashitaÃ
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University,
Katahira, Aoba-ku, Sendai 980-8577
(Received June 26, 2006; CL-060709; E-mail: miya@tagen.tohoku.ac.jp)
The micropatterning of an organic–inorganic hybrid film
consisting of a double-decker-shaped multifunctional silses-
quioxane was achieved using a photosensitive sol–gel system
containing a titanium alkoxide modified with ꢀ-diketone. Nega-
tive patterns with a high-resolution of ca. 1 mm were obtained by
UV-irradiation.
TMTP/BA chelate in 2-methoxyethanol. The mixed solution
showed no precipitation for several days at room temperature
in contrast to that of DDOH and TMTP without BA. An excess
molar ratio of the isopropoxide group to the silanol group was
employed to reduce the residual silanol group in the hybrid film.
The DDOH/TMTP/BA hybrid film was prepared by spin-coat-
ing of the solution onto a glass substrate (2000 rpm, 30 s) and
post-baked for 1 min at 130 ꢀC on a hotplate. The methacrylate
group of the TMTP is a soft-segment to prevent cracking of
the sol–gel film.
The organic–inorganic hybrid materials have received con-
siderable interest in the past decade because of the prospect of
developing materials with unique microstructures at the nano-
meter scale and properties which cannot be obtained from either
a single material or conventional composites mixed on a micro-
meter scale. The most extensively explored approach to prepar-
ing the organic–inorganic nanohybrids is the incorporation of
metal nanoparticles into a polymer matrix. For example, the hy-
bridization of silica nanoparticles and a polymer matrix yields
unique thermal, mechanical, and chemical properties,1 where in-
organic moieties are prepared by sol–gel technique. Recently,
new approach to nanohybrid materials using polyhedral oligo-
meric silsesquioxane (POSS) as an inorganic moiety has attract-
ed a lot of attention.2 The POSS has a nanometer-sized silica-like
cage structure functionalized with various kinds of organic
groups.3 The POSS as a building block provides elegant designs
and the controllable reaction for organic–inorganic hybrid mate-
rials. The interface between organic and inorganic moieties can
be controlled by the chemical reaction of the functional group of
POSS. By changing the POSS structure, for example, the organic
side chains and the ring structure, we can control the nanostruc-
ture of a hybrid film. In this paper, we report the micropatterning
using a novel photosensitive organic–inorganic hybrid system
consisting of a multifunctional silsesquioxane.
Figure 1 shows the absorption spectra of DDOH, TMTP,
BA, and the hybrid film spin-coated on a quartz substrate. The
Scheme 1. Chemical structures of double-decker-shaped silses-
quioxane silanol (DDOH), titanium methacrylate triisopropox-
ide (TMTP), benzoyl acetone (BA), and ꢀ-diketonato complex
of TMTP (I).
The double-decker-shaped silsesquioxane (DDSQ) is a mul-
tifunctional silsesquioxane with a wide variety of functional
groups.4 The chemical structure of the DDSQ silanol (DDOH)
which has an open-cage structure with four silanol and eight
phenyl (Ph) groups is depicted in Scheme 1. The DDOH was
purchased from Chisso Petrochemical Corporation. The silanol
group has a high reactivity with metal alkoxides and forms a
Si–O–metal bond. The mixing of multifunctional DDOH and ti-
tanium methacrylate triisopropoxide (TMTP) in 2-methoxyetha-
nol gave white precipitates immediately. This result suggests the
reaction of the silanol group of DDOH with isopropoxide group
of TMTP. The reaction rate can be controlled by the chelate
formation of the metal alkoxide with a ꢀ-diketone because the
chelate ring is in general durable against hydrolysis.5 In the case
of the TMTP combined with benzoyl acetone (BA) as a chelate
agent, the chemical structure (I) as depicted in Scheme 1 is
expected for the modified metal-alkoxide. A clear yellow solu-
tion was prepared by mixing a 0.025 M DDOH and a 0.1 M
Figure 1. Absorption spectra of (a) DDOH, (b) TMTP, (c) BA
in 2-methoxyethanol, and (d) DDOH/TMTP/BA hybrid film.
Copyright ꢀ 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.10 (2006)
1131
Figure 2. Changes in optical absorption spectra under UV-irra-
diation for DDOH/TMTP/BA hybrid film.
absorption band of the DDOH at 263 nm is assigned to the phen-
yl group substituted to the silsesquioxane cage. The broad ab-
sorption band of the TMTP in the UV region is attributable to
the methacrylate group. The BA showed strong absorption band
at 309 nm, which completely disappeared in the absorption spec-
trum of the DDOH/TMTP/BA hybrid film and new bands were
observed at 365 and 269 nm as shown in Figure 1d. These ab-
sorption bands can be attributed to the chelate ring as depicted
in Scheme 1.5 Figure 2 shows the changes in optical absorption
spectra of the DDOH/TMTP/BA hybrid film under UV-irradia-
tion. The UV-irradiation using a high-pressure mercury lamp
(360 mW/cm2) brought about the decrease of the intensity of
both absorption bands. The absorption bands at 365 and 269
nm almost disappeared and the film became transparent after
the UV-irradiation for 10 min. The monochromatic UV irradia-
tion at the wavelength of 365 nm using a mercury-xenon lamp
with an interference filter also caused the uniform photobleach-
ing of both the bands at 365 and 269 nm. After the UV irradiation
using the high-pressure mercury lamp, the decrease of the film
thickness from 211 to 177 nm was observed.
The photosensitive sol–gel system was applied to fabricate
the micropatterns of the organic–inorganic hybrid film consist-
ing of DDOH. By photodecomposition of the chelate ring, the
reaction between DDOH and TMTP can be initiated, which in-
duces the characteristics of a negative resist. Figure 3a shows
an optical micrograph of the micropatterns of the hybrid film
obtained by UV-irradiation using a high-pressure mercury lamp
for 10 min through a photomask, where unirradiated area was
removed by development using toluene as an eluent. A high-
resolution line and space pattern with 1 mm period is seen in
the micrograph. Such micropatterns showed a high thermal
stability up to 300 ꢀC. Figure 3b is the micropattern prepared
by laser-direct drawing technique using the 248.6-nm line of
a Ne–Cu laser, where the laser beam was focused on the
DDOH/TMTP/BA hybrid film using an objective lens and the
focal point was scanned by a computer-controlled xyz stage.
An optically transparent micropattern with various shapes can
be prepared freely using such a laser direct drawing technique.
In conclusion, the micropatterning of an organic–inorganic
film consisting of a multifunctional silsesquioxane was achieved
using a photosensitive sol–gel system. New application possibil-
ities of organic–inorganic nanohybrid materials in optoelectron-
ic technology must be opened by the patternable characteristics
in combination with the optically transparent and thermally
Figure 3. Optical micrographs of micropatterns of the DDOH/
TMTP/BA hybrid film prepared by (a) UV-irradiation through
photomask and (b) laser-direct drawing using the 248.6-nm line
of a Ne–Cu laser.
stable properties of silsesquioxanes. The hybridization method
using ꢀ-diketonate complexes of metal alkoxides also makes it
possible to incorporate various kinds of metals into silsesquiox-
ane hybrid film and to modify the optoelectronic properties.
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Published on the web (Advance View) September 9, 2006; doi:10.1246/cl.2006.1130