Photochemical fabrication of three-dimensional micro- and nano-structured surfaces from a C60 monoadduct

Article abstract of DOI:10.1039/b718888a

Exposure of Langmuir-Blodgett (LB) films of a C₆₀ adduct supported on silicon wafers to UV light leads to cross-linking of the C ₆₀ moieties, which are resistant to removal by solvent exposure, whereas unexposed moieties are readily removed. This process provides a convenient and simple route for the fabrication of highly conjugated surface-attached structures, with dimensions ranging from micrometres (using masks) to a few tens of nanometres using light emitted from a scanning near-field optical microscope (SNOM). The SNOM writing velocity was found to significantly affect the lateral resolution and the height of the three-dimensional nanostructures. Increasing the writing velocity from 0.3 to 2 μm s^-1 resulted in a decrease in the width of the structures from 240 nm to 70 nm (corresponding to the SNOM aperture diameter), respectively, and a reduction in the height from 8 nm (the thickness of the original film) to 3 nm, respectively. This approach provides a simple, direct route to surface-bound nanometre scale assemblies of C₆₀.

Full text of DOI:10.1039/b718888a

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Photochemical fabrication of three-dimensional micro- and nano-structured
surfaces from a C monoadduct
6
0
a
b
c
d
b
a
Parvez Iqbal, Shuqing Sun, Marcus D. Hanwell, David Attwood, Graham J. Leggett,* Jon A. Preece,*
c
Tim H. Richardson and David Tunnicliffe
d
Received 7th December 2007, Accepted 21st February 2008
First published as an Advance Article on the web 6th March 2008
DOI: 10.1039/b718888a
Exposure of Langmuir–Blodgett (LB) films of a C60 adduct supported on silicon wafers to UV light
leads to cross-linking of the C60 moieties, which are resistant to removal by solvent exposure, whereas
unexposed moieties are readily removed. This process provides a convenient and simple route for the
fabrication of highly conjugated surface-attached structures, with dimensions ranging from
micrometres (using masks) to a few tens of nanometres using light emitted from a scanning near-field
optical microscope (SNOM). The SNOM writing velocity was found to significantly affect the
lateral resolution and the height of the three-dimensional nanostructures. Increasing the writing
ꢀ1
velocity from 0.3 to 2 mm s resulted in a decrease in the width of the structures from 240 nm to 70 nm
(
(
corresponding to the SNOM aperture diameter), respectively, and a reduction in the height from 8 nm
the thickness of the original film) to 3 nm, respectively. This approach provides a simple, direct route
to surface-bound nanometre scale assemblies of C .
6
0
1
Introduction
systems. Recently we have begun to explore its application to
other types of photoactive materials, including monolayers of
13
Light is an attractive tool for the fabrication of structures and
devices because of the paradigmatic status of photolithography
in semiconductor device fabrication and the availability of a large
toolkit of synthetic photochemical methodologies. The principal
problem associated with the application of photochemical
methods of fabrication has previously been thought to be the
dominance of the diffraction effects as the Rayleigh limit is
approached. Recently, however, the application of novel optical
phenomena has opened up exciting prospects for photochemical
modification of materials with a resolution significantly superior
to that of conventional approaches. These include the
alkylsilanes. Recently, we reported a simple route to the
fabrication of metal nanowires by utilizing near-field exposure
14
of gold nanoparticles. Langmuir–Schaeffer films (bilayers) of
thiol-stabilized gold nanoparticles were formed on silicon
substrates and selectively exposed to UV light from a near-field
probe. The result was the coagulation of the nanoparticles to
form wires ca. 60 nm in width. Here we report a new route to
the fabrication of C60 structures that utilises a similar simple
methodology. Synthetic modification of the C60 molecules
renders them readily amenable to Langmuir–Blodgett film
15
formation and the photochemical cross-linking yields robust
1–3
exploitation of interferometric methods
and of plasmonic
structures in a single step.
4–7
phenomena, which are currently attracting rapidly growing
interest.
Since C60, or buckminsterfullerene, was first discovered by
16
Kroto et al. in 1985, fullerenes have received a great deal of
One successful approach to the fabrication of nanostructures
has been the exploitation of the near-field optical methods.
Using a scanning near-field optical microscope (SNOM) coupled
to a UV laser, self-assembled monolayers have been patterned
and used as templates for the etching of structures in gold films
attention because of the unique properties of their extended
p-systems, giving rise to potential applications in the bio-
17
logical, electrical and chemical sciences. In 1991, Rao
18
19
20
et al. reported for the first time that C60 was photosensitive.
It was observed that after exposure to UV light, a C60 film
became insoluble in toluene. Evidence from laser desorption
mass spectroscopy, infrared spectroscopy, Raman spectroscopy
and optical absorption spectroscopy gave strong indications
that the C60 had polymerised and the C60 clusters had not been
destroyed during the UV light exposure. In addition, X-ray
diffraction showed that the films became more disordered after
the UV light exposure and the lattice had contracted. Initially,
8–12
with a resolution that may be as good as 9 nm, nearly l/30.
This approach, which we have termed scanning near-field
photolithography (SNP) provides a significant advance in
photolithographic capability. Previously, however, it has
predominantly been applied to the patterning of alkanethiol
a
School of Chemistry, University of Birmingham, Edgbaston, Birmingham,
UK, B15 2TT
20
it was thought that a 2ps + 2ps photochemical cycloaddition
reaction was causing the cross-linking. However, the contraction
seen between neighbouring C60 molecules was smaller than
b
Department of Chemistry, University of Sheffield, Brook Hill, Sheffield,
UK, S3 7HF
c
Department of Physics and Astronomy, University of Sheffield, Hounsfield
Road, Sheffield, UK, S3 7RH
20
expected, and it was then proposed that an ]C]C] allene-
type bridge may have been formed between the C60 moieties to
form C ]C]C]C . After further spectroscopic studies
d
BAE SYSTEMS Advanced Technology Centre, PO Box 5, Filton, Bristol,
UK, BS34 7QW
6
0
58
2
016 | J. Mater. Chem., 2008, 18, 2016–2021
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2
1
performed by members of the same group and theoretical
distribution of the oligomers formed is affected by temperature
24,25
at which the polymerisation is performed.
22
calculations made by Menon et al., the formation of the
allene-type bridge was ruled out and 2ps + 2ps photochemical
cycloaddition was proposed as the most likely mechanism,
whereby two s-bonds are formed between two adjacent C60
cages leading to the formation of a 4-membered ring. Later
The effect of electron beam irradiation on C60 is remarkably
different. Although electron beam irradiation renders C60 and
its methanofullerene derivatives insoluble in toluene compared
28–32
to unirradiated regions,
it is also well documented that the
23–25
24,26,27
experimental studies
and theoretical calculations
electron beam irradiation leads to extensive cage fragmentation
and the formation of disordered networks of graphite-like
concur with the mechanism being 2ps + 2ps photochemical
cycloaddition. The polymerisation is thought to be initiated by
the dimerisation between two adjacent C60 cages followed by
30
particles. In fact, the methanofullerene derivatives have been
shown to have potential as negative tone resists for electron
beam lithography and they are achieving better sensitivity than
some of the commercially available polymers such as
24,25
further 2ps + 2ps cycloadditions to form longer oligomers.
Often, it has been observed that there are a number of oligmers
20,24,27
32
formed with the dimer being the most abundant.
The
poly(methyl-methacrylate) (PMMA).
The clear advantage of a photolithographic patterning process
would thus be that it offers the possibility of cross-linking C60
while causing minimal modification to its molecular structure.
The drawback has previously been the limited resolution
associated with photopatterning techniques. Here we demons-
trate that by using near-field methods it is possible to realise
exceptional resolution during the photochemical fabrication of
C
60 nanostructures.
The process used in the present study is illustrated in Fig. 1.
Langmuir films of the amphiphilic C60 adduct were transferred
on to the Si/SiO2 substrate via the Langmuir–Blodgett (LB)
technique, followed by irradiation with UV light (244 nm) either
in a parallel fashion through a mask or serially with the SNOM.
The irradiation induces the cross-linking in the C60 moieties
rendering the irradiated areas insoluble, such that the unirra-
diated areas of the C60 adduct film may easily be removed by
rinsing with chloroform leaving the insoluble irradiated C60
film intact.
2
Results and discussions
The synthesis of the C60 adduct is shown in Scheme 1. The
0
Fig. 1 The C60 adduct and a schematic diagram (right) showing the
derivatisation was achieved by the reaction of 3,4-dihydro-3 H-
patterning methodology.
pyran (THP) with tetraethylene glycol (1) in the presence of
Scheme 1 Synthesis of the C60 adduct.
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p-toluenesulfonic acid monohydrate. The resultant monosubsti-
tuted tetrahydropyranyl ethylene glycol (2) was esterified with
malonyl dichloride in the presence of pyridine, affording the
bis-ester (3). The cyclopropyl fullerene bis-ester (4) was synthe-
the covered and uncovered regions of the substrate, and were
found to be 8 and 12 nm, which are consistent with two and three
bilayers of the C60 adduct, respectively.
To investigate whether the C60 adduct films were photosensi-
tive and stable after UV light irradiation, films consisting of three
bilayers were exposed to UV light through a Cu TEM grid (l ¼
244 nm) for 1 min. Fig. 3a shows an AFM image of the film
before irradiation and Fig. 3b after irradiation. It is clear that
there has been no change in the film topography. However, after
33
sized via the Bingel reaction between the bis-ester (3) and C60
in the presence of base and iodine in the dark. The THP moieties
were removed by TFAA to afford the C60 adduct.
2
ꢀ1
The P–A isotherms for the compression (10 cm min ) and
2
ꢀ1
decompression (10 cm min ) of the C60 adduct Langmuir film
are shown in Fig. 2. Three cycles are shown. The liquid expanded
3
rinsing with CHCl the masked areas of the film were removed,
2
phase (LE) in cycle 1 persists to just below 1 nm . This value is in
2
good agreement with the molecular area of the C60 (0.75 nm ).
while the film exposed to UV light remained on the surface
(Fig. 3c). Well-defined square islands with lateral dimensions
equal to the width of the mask features and a vertical dimension
of ꢁ12 nm were observed.
ꢀ1
The surface pressure rises rapidly to ꢁ20 mN m at an area
2
per molecule of 0.5 nm , at which point a kink in the curve
appears. After the kink the rate of increase in surface pressure
decreases, which suggests possible shearing of the film forming
a partial bilayer. Decompression and recompression (cycles 2
and 3) reveal that the onset of pressure from the liquid expanded
Nanoscale patterns were fabricated by exposing the films of
the C60 adduct with UV light from a near-field probe. Two
bilayers were deposited on a hydrophobic silicon substrate. After
3
exposure, the films were rinsed with CHCl . Again, the resulting
(
LE) phase occurs at increasingly smaller areas per molecule
cross-linked structures were found to be stable, while the
unexposed material was easily removed. A variety of writing
rates were used to examine whether there was an influence on
the resulting feature size. Fig. 4 shows the AFM images of the
samples patterned at SNOM scan velocities of 0.3, 1 and 2 mm
34–36
indicating aggregation and/or bilayer structures.
The C60 adduct Langmuir films were transferred to the
ꢀ1
substrate at a fixed surface pressure of 30 mN m , and a dipping
ꢀ1
velocity of 5 mm min . Samples were prepared by transferring
two/three bilayers using Langmuir–Blodgett deposition tech-
niques. The resulting film structures were characterised by
tapping mode atomic force microscopy (AFM). A representative
image is shown in Fig. 3a. The surface is uniformly covered with
the C60 adduct, and there is no evidence of any defects. The
topography of the films did not change over 3 days suggesting
that they remained stable over this period. The thicknesses of
the films were determined by measuring the step height between
ꢀ1
s . All the images show that well-defined, continuous structures,
which are free from defects, have been formed, with the line
thickness varying with the writing rate. Lines formed with
ꢀ1
writing velocities of 0.3, 1 and 2 mm s exhibited full widths at
Fig. 2 P–A Isotherm of the C60 adduct.
Fig. 4 Representative AFM images and cross-section analysis for the
Fig. 3 AFM images of the C60 adduct films (a) before and (b) after
nanostructures formed after writing onto 2 bilayers of the C60 adduct
ꢀ1
ꢀ
1
LB films with SNOM writing velocities of (a) 0.3 mm s , (b) 1 mm s ,
exposure to UV light for 1 min, and (c) after rinsing with CHCl
2
3
. Image
2
ꢀ1
sizes: (a), (b) are 20 ꢂ 20 mm , and (c) is 100 ꢂ 100 mm .
(c) 2 mm s and rinsing the films with CHCl
3
.
2
018 | J. Mater. Chem., 2008, 18, 2016–2021
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half maximum height (FWHM) of ꢁ240, ꢁ100, ꢁ70 nm,
was purchased from the Mer Corporation and was used as
received. Solvents were either used as received or dried; DCM
respectively. The line lateral thickness observed with writing
ꢀ1
velocity of 2 mm s is comparative to the diameter of the
aperture of the SNOM probe (ꢁ70 nm), and hence indicates
that the polymerisation of the film has not spread outside the
area illuminated by the probe, whereas, at the slower velocities,
from CaH , THF and PhMe were distilled from Na–benzo-
2
2
phenone ketyl under a N atmosphere. Thin-layer chromato-
graphy (TLC) was carried out on aluminium plates coated
with silica gel 60 F254 (Merck 5554). The TLC plates were
air-dried and analysed under a short wave UV lamp (254 nm)
ꢀ1
0
.3 and 1 mm s , some polymerisation has extended laterally
through the film. It is known that the electric field associated
with a near-field excitation diverges reasonably rapidly through
a dielectric medium, and the most likely explanation for the
observation of structures larger than the aperture diameter
here is the effective spreading of the excitation through the finite
depth of the resist medium (ca. 8 nm for two bilayers of C60
adduct). Nevertheless, the resolutions exhibited by the structures
in Fig. 4 are extremely good.
2
or by developing the TLC plates in an I chamber. Column
chromatography separations were performed on silica gel 120
˚
(ICN Chrom 32–63, 60 A).
4
.2 Synthesis of C60 adduct
2-(2-{2-[2-(Tetrahydropyran-2-yloxy)ethoxy]ethoxy}ethoxy)-
ethanol (2). A solution of 3, 4-dihydro-2H-pyran (3.27 ml,
35.9 mmol) in dry DCM (50 ml) was added dropwise to a stirred,
ice cold solution of tetraethylene glycol (1) (18.6 ml, 107.7 mmol)
and p-toluenesulfonic acid monohydrate (0.137 g, 0.719 mmol)
in dry DCM (500 ml) under a N2 atmosphere. The solution
was allowed to warm to room temperature and was stirred
overnight. The DCM was removed in vacuo and the resulting
oil purified by flash column chromatography (eluent; EtOAc–
hexane–MeOH, 8 : 1 : 1). The solvent was removed in vacuo to
The height of the structures formed with writing velocity of
ꢀ
1
0
.3, 1 and 2 mm s are observed as ꢁ8, ꢁ3 and ꢁ3 nm, respec-
tively. The height of the structure obtained with writing velocity
ꢀ1
of 0.3 mm s is comparable to the C60 adduct LB film (ꢁ8 nm,
determined from AFM), whereas at the faster velocities the
structures are less than half of the initial LB film thickness
(
before irradiation). This observation suggests that incomplete
polymerisation occurs at faster writing times (i.e. lower dwell
times), and the C60 adducts are not fully polymerised and may
be rinsed away.
ꢀ1
afford a pale yellow oil (6.98 g, 71%). nmax/cm (film): 3491
m,br (O–H), 2940 m (C–H), 2871 m (C–H), 1119 m (THP, C–
O–C), 1072 (C–O–C); dH (300 MHz; CDCl ; Me Si) 4.57–4.60
In some images, narrow, discontinuous lines may be observed
that extend diagonally between the main features created
lithographically. These are thought to be artifacts resulting
from the minimal exposure of the samples as the probe moved
3
4
(1 H, br, m, THP), 3.77–3.86 (2 H, br, m, THP), 3.42–3.51 (1 H,
br, m, THP), 3.54–3.72 (15 H, br, m, HO(CH CH O) CH –,
2
2
3
2
THP), 2.82 (1 H, br, s, –OH), 1.45–1.85 (6 H, br, m, THP); dC
ꢀ1
rapidly (35 mm s ) from the end of one line to the beginning
of the next structure to be written. It appears even at this
much reduced exposure the C60 adduct film is still partially
polymerised, leading to even thinner (but incomplete) lines.
(75 MHz; CDCl ; Me Si) 98.8, 77.7, 73.1, 70.8, 70.7, 70.2, 66.9,
4
3
+
62.4, 61.8, 30.8, 30.7, 25.6, 19.7; m/z (ESMS): 301 ([M + Na] ,
100%); m/z (HRMS): found 301.1617. Calc. mass for
C H O Na: 301.1627.
1
3
26
6
Malonic acid bis-2-(2-{2-[2-(tetrahydropyran-2-yloxy)ethoxy]e-
3
Conclusion
thoxy}ethoxy) ester (3). A solution of malonyl dichloride
In summary, it is clear that near-field optical methods provide
a simple route to the fabrication of surface-bound nano-
structures composed of C60 building blocks. This methodology
may have widespread utility in the fabrication of functional
molecular nanostructures. The relatively small perturbation of
the molecular structure of the C60 moieties via (i) the attachment
of the hydrophilic glycol chain in the formation of the C60
adduct, and (ii) the subsequent photochemical cross-linking in
the LB films, coupled to the small inter C60 moiety separation
in the nanowires lends itself to the exciting possibility that these
nanowires may very well be electrically conductive as a result of
overlap of the p-frameworks from neighbouring molecules.
Currently we are examining this aspect further. The integration
of novel nanolithographic methodologies that can induce specific
chemical reactions in nanomaterials presents a new paradigm
for the fabrication of nanostructured surfaces with three-
dimensional form and potential function.
(
0.70 ml, 7.19 mmol) in dry DCM (30 ml) was added dropwise
to a stirred, ice cold solution of tetrahydropyranyl ether (2)
4.00 g, 14.40 mmol) and dry pyridine (1.45 ml, 18.00 mmol) in
dry DCM (150 ml) under a N atmosphere. The dark red
(
2
coloured reaction mixture was allowed to warm to room
temperature and stirred overnight. Followed by plug filtration
(
silica gel) washing first with DCM (200 ml) and secondly with
EtOAc (300 ml) to elute the product. The EtOAc was removed
in vacuo and the crude oil purified by flash chromatography
(
gradient elution: 70 to 100% EtOAc in hexane, increasing in
increments of 5% EtOAc per 100 ml of eluent). The solvent
was removed in vacuo to yield a yellow oil (2.24 g, 50%). d
300 MHz; CDCl ; Me Si) 4.58–4.63 (2 H, br, m, THP), 4.23–
.28 (4 H, br, m, 2(–CH CH CO CH CH )), 3.78–3.89 (4 H,
br, m, THP), 3.54–3.71 (26 H, br, m, (–CH O(CH CH
CH O–), THP), 3.40–3.51 (4 H, br, m, –O CCH CO –, THP),
.41–1.85 (12 H, br, m, THP), dC (75 MHz; CDCl ; Me Si)
H
(
3
4
4
2
2
2
2
2
2
2
2
O)3-
2
2
2
2
1
1
3
4
66.5, 99.9, 71.7, 69.9, 67.7, 65.6, 63.2, 42.3, 31.6, 26.5, 20.5;
+
4
Experimental
m/z (ESMS): 647 ([M + Na] , 100%); m/z (HRMS): calc. mass
for C H O Na 647.3255, found 647.3245.
2
9
52 14
4
.1 Chemicals
0 0
h
3 H-Cyclopropa[1,9][5,6]fullerene-C60-I -3,3 -carboxylic-2-(2-
Unless otherwise stated, all commercially available chemicals
were purchased from Aldrich and were used as received. C60
{2-[2-(tetrahydropyran-2-yloxy)ethoxy]ethoxy}ethoxy) ester (4).
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A
solution of 1,8-diazabicyclo(5.4.0)undec-7-ene (64 mg,
2.55 mmol) in dry PhMe (50 ml) was added dropwise to a stirred,
ice cold solution of C60 (300 mg, 417 mmol), iodine (53 mg,
09 mmol) and bis-tetramalonate ester (3) (130 mg, 208 mmol)
in dry PhMe (100 ml). The reaction was covered with aluminium
foil and stirred overnight at room temperature under a N
4.3.2 Mass spectrometry (MS). Electron impact mass
spectroscopy (EIMS) was performed on VG Prospec. Low and
high resolution electrospray mass spectrometry was performed
on a micromass time of flight (TOF) instrument using methanol
as the mobile phase. The matrix assisted laser desorption ioniza-
tion–time of flight mass spectroscopy (MALDI–TOF MS) was
performed on a Bruker Biflex. The samples were prepared by
mixing the dissolved compounds with a matrix (sinapinic acid)
and then allowing the solvent to evaporate to leave crystals as
the samples.
6
2
2
atmosphere. Followed by plug filtration (silica gel) washing first
with PhMe (200 ml) to remove the excess C60 and secondly with
5
% MeOH in DCM (200 ml) to elute the product. The solvent
was removed from the second fraction in vacuo and purified by
flash chromatography (gradient elution: 0 to 3% MeOH in
DCM; increasing in increments of 0.5% MeOH per 100 ml of
eluent). The solvent was removed to yield a dark brown tar
4.3.3 Infrared spectroscopy (IR). The IR spectra were
recorded as thin solid films on NaCl discs or KBr discs using
a Perkin Elmer 1600 FT-IR. The solids were mixed with nujol
to form a paste that was spread between the NaCl discs to
form a thin film.
ꢀ1
(
140 mg, 49%). nmax/cm (nujol): 2939 m (C–H), 2871s (C–H),
119s (THP, C–O–C), 1072s (C–O–C); d (300 MHz; CDCl
Me Si) 4.58–4.63 (6 H, br, m, (–CH CO CH
.53–3.88 (30 H, br, m, 2(–CH O(CH CH
1
H
3
;
4
2
2
2
CO
2
CH
2
–), THP)
3
2
2
2
O)
3 2
CH O–) +
THP), 3.42–3.51 (2 H, br, m, THP), 1.42–1.84 (12 H, br, m,
THP); d (75 MHz; CDCl ; Me Si) 163.5, 145.2, 145.1, 144.8,
43.1, 143.0, 142.9, 142.2, 141.8, 140.9, 139.0, 98.9, 70.6, 70.5,
8.7, 66.6, 62.2, 30.5, 25.4, 19.5; m/z (MALDI-TOF MS): 1368
4.3.4 Elemental analysis. Elemental analysis was carried out
C
3
4
on a Carlo Erba EA 1110 (C H N) instrument.
1
6
4.3.5 High performance liquid chromatography (HPLC).
HPLC were recorded on a Dionex Summit System with Chrome-
leon Software, using a Summit UVD 170s UV/vis multi-channel
detector with analytical flow cell. The analytical HPLC runs were
+
(
[M + 2H] , 35%).
0
H-Cyclopropa[1,9][5,6]fullerene-C -I -3,3 -carboxylic-2-(2-{2-
60 h
[
2-(tetrahydropyran-2-yloxy)ethoxy]ethoxy}ethoxy)alcohol (C60
performed on a Luna (Phenomenex), C , 250 ꢂ 4.6 mm ID, with
18
adduct). TFAA (113 mg, 538 mmol) was added dropwise at
room temperature to a solution of 4 (75 mg, 55 mmol) in a 1 : 1
mixture of DCM–MeOH (7 ml) followed by heating the reaction
10 mm pore size column using a gradient of MeCN–H
4.4 Surface pressure-area (P–A) isotherm studies
2
O.
ꢃ
mixture at 50 C for 2 h. The reaction mixture was allowed to
The P–A isotherm studies were performed using a Nima 611
cool to room temperature and the solvent was removed in vacuo.
The crude solid was purified by flash chromatography (gradient
elution: 0 to 2% MeOH in DCM, increasing in increments of
trough with Wilhelmy type balance. Prior to use, the trough
3 2
was cleaned with CHCl , IPA and 3 times with 15 MU H O.
The subphase used to form the Langmuir film was 15 MU
H O. The C adduct (2.4 mg) was dissolved in CHCl (5 ml)
0
.5% per 100 ml of eluent) and solvent removed in vacuo to yield
2
60
3
a brown solid (53 mg, 82%). HPLC run in 50% MeCN and 50%
and 50 ml of the prepared solution was spread over the H O
2
H O showed compound was 97% pure (retention time: 13 min).
2
subphase at room temperature. The CHCl3 was allowed to
evaporate for 10 min before the isotherm studies were
performed. The surface pressure was increased by reducing the
surface area via controlling the closure of the barrier at a rate
Elemental analysis found: C, 80.51%; H, 2.84%. Calc.
ꢀ
1
for C79
m (O–H), 3054 m (C–H), 2923 m (C–H), 1746s (C]O),
072s (C–O–C); d (300 MHz; CDCl ; Me Si) 4.67–4.63 (4
H, br, m, (–CH CO CCO CH –)), 4.23–4.28 (4 H, br, m,
)), 3.53–3.88 (24 H, br, m, 2(–CH O(CH CH O)
(75 MHz; CDCl ; Me Si) 163.5, 147.0, 146.9, 146.4,
34
H O12: C, 80.75%; H, 2.92%; nmax/cm (DCM) 3458
1
H
3
4
2
ꢀ1
2
of 10 cm min from 200 to 20 cm during the isotherm studies.
2
2
2
2
2
(–CO
2
CH
2
CH
2
2
2
2
3
4
.5 Preparation of the C60 adduct Langmuir films
CH O–); d
2
C
3
4
1
7
1
46.3, 145.6, 144.8, 144.7, 143.9, 143.6, 142.7, 140.8, 75.2, 75.2,
+
3.3, 73.0, 71.5, 69.0, 64.4; m/z (ESMS): 1197 ([M + Na] ,
The Langmuir films were prepared using a Nima 611 trough.
Prior to the use, the trough was cleaned with CHCl , IPA and
3
00%); m/z (HRMS): found 1197.1967. Calc. mass for
3
times with 15 MU H O. The solution of the C adduct
2 60
C H O Na: 1197.1948.
34 12
7
9
(
50 mL, 0.41 mM) in CHCl
3
was spread over the H
2
O subphase,
left for 10 min for the solvent to evaporate and compressed at
2
ꢀ1
4
.3 Compound characterisation
a rate of 10 cm min .
.6 Preparation of the C60 adduct Langmuir–Blodgett film
The LB bilayer films were formed on hydrophobic Si/SiO
1
.3.1 NMR. H nuclear magnetic resonance (NMR) spectra
4
4
were recorded on a Bruker AC 300 (300.13 MHz) spectrometer.
13
C NMR spectra were recorded on a Bruker AV 300 (75.5 MHz)
2
using Pendant pulse sequences. All chemical shifts are quoted in
substrates. The substrates were cleaned prior to use by immersing
ppm to higher frequency from Me Si using deuterated chloro-
4
in IPA, which was distilled before use. The Si/SiO substrates were
2
form (CDCl ) as the lock and the residual solvent as the internal
3
hydrophobised with hexamethyldisilazane by placing the
standard. The coupling constants are expressed in Hertz
substrates in a chamber containing hexamethyldisilazane
(
Hz) with multiplicities abbreviated as follows; s ¼ singlet, d ¼
ensuring that the meniscus of the silazane was just below the upper
surface of the substrate. The substrates were left for 24 h in the
doublet, dd ¼ double doublet, t ¼ triplet, q ¼ quartet and
m ¼ multiplet.
chamber followed by sonication in CHCl
3
, IPA and 15 MU
2
020 | J. Mater. Chem., 2008, 18, 2016–2021
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H O for 1 min each and dried with N after each sonication. The
2
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hydrophobic Si/SiO2 substrates were lowered into and raised
1
6 H. W. Kroto, J. R. Heath, S. C. O’Brien, R. F. Curl and
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ꢀ1
from the Langmuir film (P ¼ 30 nN m ) at a velocity of
mm min to afford the 2 or 3 bilayer LB films. Finally the
LBFs were dried with N
ꢀ1
5
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Photopatterning was conducted using light from a frequency
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a square grid mask consisting of 40 ꢂ 40 mm square openings
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0
6
LBF and the sample was irradiated with power of 100 mW.
The irradiation time was 1 min, and the area of illumination
2
was typically 0.2–0.4 cm . The surface was then rinsed
1
3 2
thoroughly with CHCl and dried with N . For the scanning
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Microscopes Aurora III near-field scanning optical microscope
fitted with a fused silica fiber probe (Veeco). The aperture
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for each probe velocity. The irradiated samples were rinsed
thoroughly with CHCl and dried with N .
2
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Acknowledgements
JAP, DA and DT would like to thank the European Community
FP6, Contract No. NMP4-CT-2005-014006 NANO3D) and
(
JAP would like to thank the Engineering and Physical Sciences
Research Council (EPSRC, Adventurous Chemistry Scheme
EP/C5238571) for financial support. GJL thanks RCUK (Grant
EP/C523857/1), the RSC Analytical Chemistry Trust Fund and
the EPSRC for their support.
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