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Volum
e 19 | Num
ber 27 | 2009 Journal of M
aterials Chem
istry Pages 4641–4860 0959-9428(2009)19:27;1-P
www.rsc.org/materials Volume 19 | Number 27 | 21 July 2009 | Pages 4641–4860
ISSN 0959-9428COMMUNICATIONShu Yang et al.Direct fabrication of 3D silica-like microstructures from epoxy-functionalized polyhedral oligomeric silsesquioxane (POSS)
FEATURE ARTICLEParas N. Prasad et al.Multifunctional nanoparticles as biocompatible targeted probes for human cancer diagnosis and therapy
As featured in:
see Yuan Zhang, Qun Xiang, Jiaqiang Xu, Pengcheng Xu, Qingyi Pan and Feng Li, J. Mater. Chem., 2009, 19, 4701.
www.rsc.org/materialsRegistered Charity Number 207890
Using self-assembly method, ZnO nanowires have been modified with monodispersed Pd nanoparticles for fabricating H2S chemical sensors with highly enhanced performances. The approach has opened a new pathway for tailoring the functionalities of semiconductor gas sensors.
Title: Self-assemblies of Pd nanoparticles on the surfaces of single crystal ZnO nanowires for chemical sensors with enhanced performances
Showcasing research from the collaborative efforts of Professor Jiaqiang Xu’s group at Laboratory of Functional Materials, College of Science, Shanghai University, China, and Dr. Feng Li at Department of Chemistry, Rice University, Houston, USA.
Volum
e 19 | Num
ber 27 | 2009 Journal of M
aterials Chem
istry Pages 4641–4860 0959-9428(2009)19:27;1-P
www.rsc.org/materials Volume 19 | Number 27 | 21 July 2009 | Pages 4641–4860
ISSN 0959-9428COMMUNICATIONShu Yang et al.Direct fabrication of 3D silica-like microstructures from epoxy-functionalized polyhedral oligomeric silsesquioxane (POSS)
FEATURE ARTICLEParas N. Prasad et al.Multifunctional nanoparticles as biocompatible targeted probes for human cancer diagnosis and therapy
As featured in:
see Yuan Zhang, Qun Xiang, Jiaqiang Xu, Pengcheng Xu, Qingyi Pan and Feng Li, J. Mater. Chem., 2009, 19, 4701.
www.rsc.org/materialsRegistered Charity Number 207890
Using self-assembly method, ZnO nanowires have been modified with monodispersed Pd nanoparticles for fabricating H2S chemical sensors with highly enhanced performances. The approach has opened a new pathway for tailoring the functionalities of semiconductor gas sensors.
Title: Self-assemblies of Pd nanoparticles on the surfaces of single crystal ZnO nanowires for chemical sensors with enhanced performances
Showcasing research from the collaborative efforts of Professor Jiaqiang Xu’s group at Laboratory of Functional Materials, College of Science, Shanghai University, China, and Dr. Feng Li at Department of Chemistry, Rice University, Houston, USA.
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COMMUNICATION www.rsc.org/materials | Journal of Materials Chemistry
Direct fabrication of 3D silica-like microstructuresfrom epoxy-functionalized polyhedral oligomeric silsesquioxane (POSS)†
Jun Hyuk Moon,‡a Jin Seok Seo,‡b Yongan Xub and Shu Yang*b
Received 20th January 2009, Accepted 14th April 2009
First published as an Advance Article on the web 23rd April 2009
DOI: 10.1039/b901226e
We have fabricated 2D and 3D structured organosilcates from
epoxy functionalized polyhedral oligomeric silsesquioxanes (POSS)
cage materials using holographic lithography, which can be conve-
niently converted to silica structures by thermal removal of the
organic moieties.
Three-dimensional (3D) periodic structures offer many unique
properties, including high surface-to-volume ratio, superior
mechanical strength yet low density, and recently, photonic and
phononic bandgap properties.1–7 Among many 3D fabrication tech-
niques,1,2,4,8–16 holographic lithography (HL) is a versatile approach
that can produce periodic structures in micrometre scale defect-free
over a large area (up to a few cm2). It uses the interference pattern of
multiple coherent laser beams in contrast to a photomask in
conventional photolithography processes to create periodic two-
dimensional (2D) and three-dimensional (3D) structures by exposing
a set of interference beams to a photoresist film.2,4 HL allows for
precise control over the size and shape of the resulting structures, and
has the flexibility to access a variety of lattice symmetries through the
proper arrangement of laser beams.5,17–19 Of particular interest is the
fabrication of 3D photonic crystals with controlled symmetries for
large photonic bandgaps (PBGs).
Most 3D photonic structures fabricated by HL are from conven-
tional organic photoresists, which are originally designed for photo-
lithography in the UV regions. The resists typically possess epoxy
(negative-tone) or (meth)acrylate (positive-tone) functionalities,
allowing for chemically amplified reactions between the functional
groups and photoacid generators (PAGs), therefore, exhibiting high
lithographic resolution (sub-microns), photospeed, and contrast.
However, the organic photoresists also have several unfavorable
characteristics, including low refractive index, high shrinkage, and
low thermal and mechanical stability,3,20,21 to achieve a high quality
photonic crystal with a complete PBG. Thus, the directly fabricated
polymeric 3D structures are often used as sacrificial templates for
conversion to high refractive index inorganic materials (e.g. Si).22–25
The deposition of high refractive index inorganic materials, for
example, through the chemical vapor deposition (CVD) process,
aDepartment of Chemical and Biomolecular Engineering, SogangUniversity, 1 Shinsu-dong, Mapo-gu, Seoul, Korea. E-mail: [email protected]; Fax: +82 2 711 0439; Tel: +82 2 705 8921bMaterials Science and Engineering, University of Pennsylvania, PA19104, USA. E-mail: [email protected]; Fax: +1 215 573 2128;Tel: +1 215 898 9645
† Electronic Supplementary Information (ESI) available:Thermogravimetric analysis of the epoxy-POSS photoresist in air. SeeDOI: 10.1039/b901226e/
‡ These authors contributed equally to this work.
This journal is ª The Royal Society of Chemistry 2009
however, is often accompanied by a high processing temperature
(>400 �C), above which the polymer template is decomposed.22,24
Hence, a double templating procedure via a silica replica of the
polymer template is often utilized for high temperature deposition.
The extra processing steps could complicate the photonic crystal
fabrication, more importantly, our previous studies suggest that it is
nearly impossible to completely fill the HL patterned 3D templates
through conformal coating by CVD process,26 and the double tem-
plating procedure will further aggravate the problem.
Several groups have attempted to use hybrid materials that
combine organic and inorganic components to improve the thermal
and mechanical stability of the 3D structures. For example, the
inorganic nanoparticles, such as silica, have been dispersed in the
photoresist formation as an reinforcement.27 A number of organic–
inorganic hybrid materials have been synthesized for photo-
lithography using sol–gel reactions.15,28–30 Another possibility is a
combination of hard and soft chemistries to assemble thermally
stable 3D opals.31 However, the high loading of inorganic materials
could significantly lower the resist photosensitivity and make the film
crack-prone as film thickness increases. The higher refractive index of
the resists could also cause lattice distortion during the HL fabrica-
tion due to refraction effect at the air–film interface.21 When heated
above the thermal decomposition temperature of the organic
components, cracks often occur due to the residue strain generated
from the large weight loss and film shrinkage, and the brittleness of
pure inorganic materials, which could further degrades the optical
quality of the resulting photonic crystals.
Here, we investigate the direct fabrication of 3D silica-like struc-
tures from epoxy-functionalized polyhedral oligomeric silsesquiox-
anes (POSS) using holographic lithography, their thermal stability
and related chemical nature. The 3D POSS structures can be
conveniently converted to 3D silica structures for infiltration of
a wide range of materials, which can be subsequently removed using
aqueous hydrofluoric acid (HF) solution at room temperature.
Sandhage et al., however, have shown that it is possible to
convert biosilica (diatom) microshells to their ceramic32,33 and Si34
replicas through gas displacement reaction and chemical reduction,
respectively.
POSS is a unique class of hybrid materials, which possess the
structure of cube-octameric frameworks with eight organic corner
groups.35 It has chemical composition of RSiO1.5 with thermal and
mechanical properties intermediate between SiO2 and organic poly-
mers. Unlike SiO2 each POSS molecule contains nonreactive organic
moieties, making it compatible with various polymer systems and
enhancing its crack resistance.35 POSS with various numbers of epoxy
functionalities (n ¼ 1–8), and different organic substituents, R, have
been synthesized and used as nanosized inorganic building blocks to
enhance the thermal and mechanical properties of rubbery epoxy
J. Mater. Chem., 2009, 19, 4687–4691 | 4687
network, based on diglycidyl ether of bisphenol A (DGEBA).36–38
POSS-bearing methacrylate copolymers have been demonstrated to
be positive-tone resists for e-beam lithography, deep UV lithography
and 157 nm lithography.39–41 They show similar lithographic char-
acteristics to conventional photoresists, including high contrast (>10),
high sensitivity (<10 mJ/cm2), and resolution up to sub-100 nm, but
possess higher glass transition temperatures (Tg) and etch resistance.
Recently, a ladder-structured methyl silsequioxane (MSQ) presursor
has been used to fabricate thermally stable woodpile structures via
direct laser writing (DLW).15 Despite the success, questions remain
about the resolution and contrast using MSQ as photoresist and its
applicability to HL since the photocrosslinking of MSQ is based on
polycondensation of silanol groups to generate –O–Si–O– bonds
upon exposure to the light and the subsequent post-exposure bake
(PEB). It is known that silanol groups are susceptible to temperature
and environmental effects (e.g. moisture and pH), which could cause
unwanted thermal crosslinking and self-condensing in the unexposed
regions, therefore, lowering the pattern resolution and contrast. It will
be advantageous if we can introduce photocrosslinkable epoxy
groups in POSS resists for high resolution and high contrast
patterning, at the same time build upon the knowledge from 3D
patterning using commercially available, negative-tone SU8 resists to
create thermally stable 3D silica-like structures.
Here, we prepared the negative-tone photoresists for HL from
epoxy cyclohexyl POSS cage mixtures. Since each epoxy-functional-
ized POSS molecule possesses an average of eight epoxy groups,
which can be photocrosslinked through chemically amplified reac-
tions in the same fashion as the SU8 resists, it offers an efficient
molecular building block for high-resolution photopatterning. The
loading of inorganic components can be conveniently controlled by
modification of the corner organic moieties as well as by varying the
degree of crosslinking. By using a single component resist system, we
avoid possible macroscopic separation between inorganic and
organic constituents when mixing epoxy resin and POSS. Three- and
four-beam interference patterns were employed to fabricate 2D
and 3D POSS structures, respectively, which were converted into
silica-like structures when heated above 400 �C (Scheme 1).
We investigated the relative volume, weight, and structural change
in the resultant 2D and 3D patterns at different thermal treatment
temperatures, as well as the related chemical nature, which in turn
influences the thermal and mechanical stability of the film. The 3D
Scheme 1 Photopolymerization reaction of epoxy cyclohexyl
4688 | J. Mater. Chem., 2009, 19, 4687–4691
structure was found well maintained without major cracks when
heated to 400 �C in air even though large volume shrinkage was
suggested according to TGA measurement. SEM image showed
decrease of the thickness of the 3D skeleton, however, the lattice
spacing in the (111) plane remained nearly unchanged. When the
calcination temperature was raised to 500 �C, major cracks occurred
in the film along with additional 21% weight loss.
The epoxy-POSS photoresist was prepared by dissolving epoxy
cyclohexyl POSS cage mixture [EP0408, (C8H13O)n(SiO1.5)n, n¼ 8,10
or 12, FW ¼ 1772.73, from Hybrid Plastics] and 2–4 wt% Irgacure
261 (a UV and visible photoacid generator from Ciba Specialty
Chemicals) in propylene glycol methyl ether acetate (PGMEA) to
obtain a concentration of 50–60 wt%. After soft bake at 65 �C, the
resist film was exposed to three or four interfering beams to fabricate
2D and 3D patterns, respectively, using the same optical assembly for
fabrication of SU8 structures.22,42 During exposure to the interference
beams, photoacids were generated and their diffusion within the
epoxy-POSS photoresist was accelerated when the film was post-
exposure baked at 95 �C, well above its glass transition temperature
to initiate cationic polymerization of the epoxy groups. SEM images
suggested that epoxy-POSS had similar photosensitivity as SU8 with
nearly the same volume fraction of 3D structures in both resist
systems when the concentration of photoacid generators, exposure
time and intensity, and baking conditions were kept the same. The
unexposed film was removed by PGMEA and the resulting pattern
was characterized by AFM and SEM, followed by calcination in
order to remove the organic moieties and form the pure silica
network structure. Since the interference laser beam has a Gaussian
distribution of intensity, for comparison of weight loss and film
shrinkage at different temperatures we kept the characterization in
the same region (e.g. center) of the films.
The photopolymerization was monitored by comparing the FT-IR
spectra of epoxy POSS before and after laser exposure. As shown in
Fig. 1, the decrease of the absorption peak around 830 cm�1 (epoxy
ring vibration) and the increase of the peak around 937 cm�1 (C–O–C
stretching) and 3450 cm�1 (hydroxyl group stretching) can be
attributed to the ring-opening polymerization of cycloaliphatic
epoxide.43 The absorption at 2853 cm�1–2988 cm�1 can be attributed
to the C–H stretching of the cyclohexane ring,43,44
Fig. 2 shows typical SEM and AFM images of 2D hexagonal
cylinders by three-beam interference pattern. The calcination was
POSS cage mixture and its subsequent thermal treatment.
This journal is ª The Royal Society of Chemistry 2009
Fig. 1 FT-IR spectra of epoxy cyclohexyl POSS films before and after
photocrosslinking and calcination at various temperatures in air for 1 h.
Fig. 2 SEM (a) and AFM (b) images of a typical 2D holo-
graphic pattern. Scale bar in SEM ¼ 5 mm. Distance to dotted line in
AFM ¼ 1.6 mm.
carried out at 400 �C, 500 �C, and 600 �C in air for 1 h. Thermog-
ravimetric analysis (TGA) was conducted in air to quantify the
weight loss of epoxy-POSS during the heat treatment (Fig. S1†). The
crosslinked epoxy-POSS was found thermally stable up to 350 �C in
air,45 above which the organic moieties started to be decomposed,
showing linear weight loss vs. temperature (Table 1). The initial
weight loss presumably is due to the residual solvent in the film. The
neat POSS film showed no weight loss below 300 �C in air. At 600 �C,
however, only 30 wt% residue remained, close to the inorganic
fraction of the epoxy-POSS, 27 wt%. On the basis of the relative
weight loss from TGA measurement and the relative volume change
from AFM study of 2D patterns (Table 1), we estimated the relative
density of the film at different temperatures. Up to 400 �C, the
volume and weight of epoxy-POSS decreased by the same rate,
therefore, less then 10% relative change of density was observed. In
contrast, film densification below 300 �C occurs in MSQ films due to
Table 1 Relative weight, volume and density of the matrix of 2Dpatterns at various heat-treatment temperatures
Temp/�CRelativeweight (%)
Relativevolume (%)a
RelativeDensity b
25 100.0 100 1.0400 72.0 63–67 1.1500 51.0 30–35 1.5–1.7600 32.0 16–18 1.8–2.0
a The 2D patterns were considered as cylinders, whose diameter andheight were measured by SEM and AFM, respectively, and averaged toestimate the volume. b Relative density was calculated by the ratio ofrelative weight to relative volume.
This journal is ª The Royal Society of Chemistry 2009
condensation of unreacted silanol groups after photo-
polymerization.15 The relative film density of epoxy-POSS was found
increased more than 50% at 500 �C, which could be attributed to
removal of the organic moieties and collapse of the POSS cage to
denser SiO2-like network.
The FT-IR spectra of crosslinked epoxy-POSS treated at different
calcination temperatures were measured and compared to that of
photocrosslinked film to monitor the change of chemical structure
(Fig. 1). It is clearly seen that the C–H stretching peak was highly
intact at 300 �C, however, nearly disappeared above 400 �C. Because
of the broad hydroxyl peak (3000–3700 cm�1) appeared in the same
region, it is difficult to draw a conclusion whether all organic
components are completely decomposed above 400 �C or not. The
peak at 1054 cm�1 was attributed to O–Si–O long chain vibration due
to the presence of cage structure of POSS, which gradually dis-
appeared at higher temperatures. The absorption at�1165 cm�1 (O–
Si–O ladder structure or short chain vibration) broadened, suggesting
the collapse of the silica cage structure.44,46 This result is consistent to
the above analysis of relative film density. The absorption at 1232–
1252 cm�1 (Si–C stretching) appeared in all films, indicating the
existence of residual carbon in the film after calcinations in air. In
addition, absorption at 1630–1720 cm�1 (C]O stretching) appeared
after heating the film above 300 �C, indicating the formation of acid
and/or acid anhydride due to oxidation of the organic contents in air.
In comparison to the IR spectrum of SiO2 as a reference,44 it seems
that all films contain carbon content to a certain extent. To further
investigate the chemical nature of the POSS films treated above
400 �C, we performed compositional analysis using energy dispersive
X-ray (EDX) spectroscopy mapping technique. The film was trans-
ferred to Si wafers before EDS mapping. While there were substantial
carbons left in the film treated at 400 �C and below, it was clear that
residual carbon remained in the film after heated at 500 �C in air (see
Table 2). Meanwhile, there is a deviation from the theoretical value of
compositional weight ratio between Si and O (Si : O ¼ 41.2 : 58.8) if
the POSS film is fully oxidized at 500 �C. It is likely that a surface
oxide is formed in air, which passivates against further oxidation
below the surface, leaving residual carbon trapped.
In the case of 3D patterning, the umbrella-like 4-beam interfer-
ence pattern was transferred onto the epoxy-POSS resist film. In
Fig. 3a and 3b, the SEM images show 3D face-centered cubic
(FCC) lattice structure in POSS with a facing (111) plane. The
average period in the (111) surface is�1 mm according to SEM. The
3D POSS structures were then heated at 400 �C and 500 �C in air for
1 h, respectively, to study their thermomechanical stability. As seen
in Fig. 3c, the 3D network was surprisingly well-maintained
without major cracks during the heat treatment at 400 �C even
though large volume shrinkage occurred due to the weight loss,
�30 wt%, according to the TGA measurement from the isolated
2D patterns (see Table 1). A closer investigation of the SEM image
(inset of Fig. 3c) in comparison to non-calcined POSS structure
(inset of Fig. 3b) suggests that the thickness of shell connecting unit
atoms did shrink by �23%, however, in the (111) plane only �5%
shrinkage of the lattice spacing was observed at 400 �C. Such
skeleton structure has been reported,47 during backfilling of poly-
styrene opal template with titania precursor, followed by calcina-
tion. The authors note that it is possible to achieve two photonic
bandgaps simultaneously by varying the radius of cylinders.
In our system, when the calcination temperature was raised to
500 �C, major cracks occurred in the film (Fig. 3d), which could be
J. Mater. Chem., 2009, 19, 4687–4691 | 4689
Table 2 Elemental analysis of epoxy POSS films treated at different temperatures in air for 1 h
ElementBare filma If fully oxidized
At 400 �C At 500 �C
Relative weight (%) Relative weight (%) Relative weight (%) Relative atomic (%) Relative weight (%) Relative atomic (%)
C 58.5 0 20.31 27.59 2.28 3.45O 24.4 58.8 59.44 60.64 67.74 77.11Si 17.0 41.2 20.26 11.77 29.98 19.44Total 100.0 100.0 100.00 100.00 100.00 100.00
a The composition was calculated based on chemical fomulation of epoxy POSS provided by Hybrid Plastics, (C8H13O)n(SiO1.5)n.
Fig. 3 (a) A tilted SEM image of 3D patterns and a simulated image
(inset). Top-view SEM images of the central area in 3D patterns before
(b) and after heat-treatment at 400 �C (c) and 500 �C (d) in air for 1 h.
Insets in (b) and (c) show high-magnification images. (Scale bar ¼ 2 mm.)
attributed to the tensile stress within the 3D network since the film was
attached to the substrate and undergoing large weight loss and volume
shrinkage at 500 �C. The results agree well with the TGA, FTIR and
EDS studies, confirming that above a critical temperature, here 400�C, the removal of carbon is large enough to cause collapse of O–Si–O
network, leading to the formation of cracks in the films. Currently we
investigate different film treatment conditions to maintain certain
carbon content in the film without major crack formation.
We have demonstrated the direct patterning of 2D and 3D orga-
nosilcates from epoxy-POSS cage materials using holographic
lithography. The patterned epoxy-POSS structures can be conve-
niently converted to silica structures by thermal removal of organic
moieties above 400 �C. In order to investigate the fidelity (both
structural and compositional) of the epoxy-POSS structures during
the heat-treatment, we measured FT-IR and estimated the variation
of relative density by using the TGA and AFM measurements.
Furthermore, we showed that the 3D POSS FCC structures could be
maintained without global volume shrinkage during the heat treat-
ment (up to 400 �C) by thinning the struts that connect atoms. The
study of the thermal and mechanical integrity of the POSS 3D
structures at different temperatures will offer important insights to
the design of ultrastrong yet light-weight engineering materials. The
direct conversion to 3D silica or silica-like structures will allow us to
simplify the backfilling procedure for high refractive index 3D
4690 | J. Mater. Chem., 2009, 19, 4687–4691
photonic crystals, therefore, minimizing problems such as incomplete
filling. We are especially encouraged by a recent report of creating 3D
silicon photonic crystals from a colloidal template by backfilling
silane at 325 �C through CVD process,48 suggesting that possibility of
directly backfilling silicon into our POSS 3D structures without
compromising the structural integrity may exist. The ability to
remove the template at room temperature using aqueous HF solution
will enable infiltration of a broader range of materials (e.g. inorganic,
polymers, nanoparticles) for many other applications. We believe
that our POSS resists can be easily adapted to other 3D fabrication
processes, such as multi-photon polymerization. Along the lines, the
ability to fabricate 3D structures from hybrid materials will broaden
the range of materials for study of nano- micromechanical properties
in 3D.3,49 Further, it will be intriguing to see whether structure
collapse or any pattern transformation could be observed during
backfilling or other surface functionalization of the POSS templates
in comparison to backfilled glassy polymeric structures.50
Experimental
Preparation of epoxy-POSS photoresists
Epoxy cyclohexyl POSS cage mixture [(C8H13O2)n(SiO1.5)n, n¼ 8,10
or 12] and Irgacure 261 (a visible photoacid generator, 2–4 wt%) were
dissolved in propylene glycol methyl ether acetate (PGMEA, 50–60
wt%). By varying the spin coating speed from 4000 to 6000 rpm, we
obtained film thickness ranging from 2 to 5 mm. After soft baking at
65 �C for 3 min and 95 �C for 3 min, respectively, the resist film was
exposed to three- or four-interfering beams.
Fabrication of 2D and 3D structures by holographic lithography
A laser beam source (Nd:YVO4 laser, l ¼ 532 nm) was expanded
by achromatic lens pair. For 2D holographic patterns, the three
beams possess wave vectors of 2p=a�12
ffiffiffi3p
=20�, 2p=a
�12
ffiffiffi3p
=20�
and 2p/a[1 0 0]. The polarization vectors of three-beams are equal
to each other to produce circular cylinders with hexagonal
symmetry. In the case of 3D patterns, the central beam was circu-
larly polarized with normal incidence to the photoresist film, while
the other three surrounding beams were linearly polarized and
oblique at 39� relative to the central one. The wave vector of each
beam is p/a[333], p/a [511], p/a [151], and p/a [115], respectively.
The polarization vectors of the obliqued beams are [�0.250 0.345
0.905], [0.905 �0.250 0.345], and [0.345 0.905 �0.250], respectively.
The intensity ratio was 1.8 : 1 : 1 : 1. The circular polarization of the
central beam distributes the intensity equally to the surrounding
beams. The exposure dose of interference pattern was 0.2–0.5 J/cm2
This journal is ª The Royal Society of Chemistry 2009
for 2D and 0.1–0.3 J/cm2 for 3D. After the exposure to the epoxy-
POSS photoresist, the film was baked at 95 �C. The unexposed film
was removed by PGMEA.
Characterizations
The Fourier Transform Infrared (FT-IR) spectra were acquired using
Nicolet 8700 equipped with a Nicolet Continuum Infrared Micro-
scope. The samples were measured in a reflection mode with a MCT
detector, and the aperture size used was�80 mm� 80 mm. All epoxy-
POSS films were heated in air for 1 h at a specific temperature.
For thermogravimetric analysis (TGA, TA Instruments), the
photoresist film was lifted off from the substrate, and ground to
powder. The relative weight was measured when the sample was
heated in air up to 700 �C at a heating rate of 10 �C/min. For the
measurement of the volume and morphology in 2D and 3D patterns,
we only scanned the central part of each samples by AFM (Digital
instrument Dimension 3000) and SEM (FEI Strata). This is because
the volume fraction decreases from centre to the sample boundary
due to the Gaussian laser beam profile.
EDX analysis was performed on a high resolution field emission
SEM (JEOL 7500F) coupled to an Oxford Si/Li detector and INCA
software to study the overall chemical composition and the distri-
bution of the chemical elements of interest in the POSS films treated
at different temperatures. The spectra were acquired and collected at
an acceleration voltage 15 keV.
Acknowledgements
This research is supported in part by the Office of Naval Research
(ONR), Grant # N00014-05-0303, and Air Force of Scientific
Research (AFOSR), Grant # FA9550-06-1-0228. JHM thanks the
Manpower Development Program for Energy & Resources of the
Ministry of Knowledge and Economy (2008-E-AP-HM-P-23-0000)
and the Korea Research Foundation Grant funded by the Korean
Government (KRF-2008-313-D00295). We thank Prof. Chris Mur-
ray for helping with the access to the FT-IR instrument. We also
acknowledge the Penn Regional Nanotechnology Facility (PRNF)
and Korea Basic Science Institute (KBSI) for access to SEM, EDX,
and AFM analysis.
Notes and references
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