Ligand-structure effect on the formation of one-dimensional nanoscale Cu(II)-schiff base complexes and solvent-mediated shape transformation

Article abstract of DOI:10.1021/cg300372v

We report here a Cu(II)-Schiff base complex that can assemble into one-dimensional (1D) nanoscale fibers, belts, and rods under different synthetic conditions. The ligand-structure effect is investigated by modification of the ligand structure. The format

Full text of DOI:10.1021/cg300372v

Article
pubs.acs.org/crystal
Ligand-Structure Effect on the Formation of One-Dimensional
Nanoscale Cu(II)-Schiff Base Complexes and Solvent-Mediated Shape
Transformation
Wenjing Wang,† Qianhuo Chen,*,†,‡ Qing Li,† Yu Sheng,† Xuanjun Zhang,*,§ and Kajsa Uvdal*,§
†College of Environmental Science and Engineering, Fujian Normal University, Fuzhou 350007, P. R. China
‡Fujian Key Laboratory of Polymer Materials, Fuzhou 350007, P. R. China
§Division of Molecular Surface Physics and Nanoscience, Department of Physics, Chemistry, and Biology (IFM), Linkoping
̈
University, Linkoping 58183 Sweden
̈
S
* Supporting Information
ABSTRACT: We report here a Cu(II)-Schiff base complex that
can assemble into one-dimensional (1D) nanoscale fibers, belts,
and rods under different synthetic conditions. The ligand-structure
effect is investigated by modification of the ligand structure. The
formation of a 1D nanostructure was studied, and the formation of
dimers was revealed as a key factor for 1D assembly. In
dimethylformamide (DMF) medium, this complex represents
one of the rare examples of low-molecular-weight “super-
metallogelators” with a critical gelation concentration of 0.3 wt
% for DMF. The ligand exhibits good selectivity toward different metal ions in terms of gel formation and only the Cu(II)
complex forms gels. It is interesting that this metallogel is a kind of dynamic nanostructure, which can be transformed to rods
with different aspect ratios via a solvent-mediated process under stimulation of ultrasound.
always formed by interfiber interaction that can trap immobilize
solvent molecules, has gained attention until very recen-
tly.2e,12−15 Therefore, development of new synthesis methods
of 1D nanoscale coordination assemblies and understanding the
formation mechanism at the molecular level are significantly
important for the rational design of functional materials for
electronic, optical, and biological applications. We present
herein a molecular approach to metal-containing gels, belts,
fibers, and rods of a Cu(II)-Schiff base coordination complex
(Scheme 1). The metallogel is a dynamic nanostructure, which
exhibits solvent-mediated shape transformation to nanorods
under stimulation of ultrasound.
INTRODUCTION
■
Supramolecular organization of randomly oriented molecules
into long-range ordered nanostructured materials is an
important goal for developing nanodevices, sensors, molecular
circuitry, and machines.1 In particular, coordination-directed
assembly has evolved as an attractive strategy for fabricating
functional materials because the coordination number,
geometry, and oxidation state of the metal centers play
significant roles in controlling the size, shape, and physical
and chemical properties of the final nanomaterials.2 Several
recent studies showed that nanoparticles of metallopolymers
and metal−organic frameworks (MOFs) exhibit promising
functionalities such as ion exchange,3 accelerated guest
adsorption,4 magnetism,5 multimodal bioimaging,6 drug deliv-
ery and sensing,7 field emission,8 encapsulation of functional
guest molecules,9,10 and enhanced fluorescence and/or light
harvesting.10 The properties of these nanomaterials always
depend on the particle sizes and shapes, as well as molecular
arrangements.
Nanoscale one-dimensional (1D) coordination complexes
and polymers such as fibers, belts, rods, and tubes are an
exciting class of materials with excellent potential for nanosized
electronic, mechanical, and medical fields. However, despite the
advances that have been achieved, methods for controlling
particle size and shape of coordination complex/polymers are
still fairly rudimentary.2 1D nanostructured coordination
complexes and polymers are still very scarce.2,11 Metallogels,
a kind of new emerging smart metal-containing nanomaterial
EXPERIMENTAL SECTION
■
Materials and Methods. All of the chemicals were purchased
from Sinopharm Chemical Reagent Co., Ltd. and used without further
purification. UV−visible spectra were recorded on a Varian CARY 50
spectrometer. IR spectra were collected on a Nicolet 5700
spectrometer (using KBr pellets). NMR analysis was performed on
Bruker AVIII-400 instruments. Elemental analysis (C, H, N) was
performed using varioEL III analyzer. Scanning electron microscopy
(SEM) and transmission electron microscopy (TEM) images were
obtained using a JEOL JSM-7500F (field emission scanning electron
microscope) and FEI Tecnai G2 microscope, respectively. X-ray
diffraction (XRD) patterns were recorded on a Panalytical X′Pert
Received: March 20, 2012
Revised: March 28, 2012
Published: April 2, 2012
© 2012 American Chemical Society
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Scheme 1. Molecular Structures of Ligands and Illustration of Shape Control and Transformation of One-Dimensional
Nanostructures
spectrometer using Co Kα radiation (λ = 1.78897 Å) and the data
were converted to Cu Kα data. Ultrasonic reaction was performed with
KQ-250B (40 kHz) ultrasonic cleaning sonicator. Electrospray
ionization (ESI) mass spectra were recorded on BRUKER ESQUIRE
3000 PLUS spectrometer using methanol as the solvent.
DMSO): δ = 162.64, 162.15, 158.00, 148.34, 131.59, 130.08, 125.02,
119.69, 119.14, 116.86, 114.62, 68.22, 31.80, 29.71−28.97, 25.96,
22.58, 14.37. Anal. Calcd (%) for C24H32N2O3: C, 72.7; H, 8.1; N, 7.1.
Found (%): C,72.7, H, 8.0, N, 6.9. MS (m/z) calc. for C24H32N2O3:
396.2; Found: 397.0 [M + H]+.
Synthesis of 1. A flask was charged with a mixture of methyl 4-
hydroxybenzoate (12.78 g, 84 mmol), 1-bromodecane (16.6 mL, 80
mmol), and K2CO3 (30 g, excess). Dimethylformamide (DMF) (120
mL) was added. The flask was degassed by bubbling with nitrogen for
10 min. The mixture was heated at 90 °C with magnetic stirring for
two days. After cooling to room temperature, water (250 mL) and
ethyl acetate (250 mL) were added and stirred for 5 min. The organic
layer was separated, washed with 10% Na2CO3 and water two times,
and dried over anhydrous MgSO4. Then the solid was removed by
filtration, and the filtrate was evaporated to remove ethyl acetate. After
cooling to room temperature, a pale yellow product was obtained.
Scheme 2. Synthesis Route of H2L1
1
Yield: 20.86 g, 89% (based on 1-bromodecane). HNMR (400 MHz,
CDCl3): δ = 7.98 (d, J = 8.9 Hz, 2H, Ar−H), 6.90 (d, J = 8.9 Hz, 2H,
Ar−H), 4.00 (t, J = 6.6 Hz, 2H, -OCH2), 3.88 (s, 3H, -OCH3), 1.77−
1.82 (m, 2H, −CH2), 1.24−1.46 (m, 14H, -C7H14), 0.88 (t, J = 6.5 Hz,
3H, −CH3).
Synthesis of H2L2. A flask was charged with a mixture of
benzhydrazide (2.00 g, 14.7 mmol) and 2-hydroxybenzaldehyde (1.6
mL, 15 mmol). EtOH (30 mL) was added. The flask was degassed by
bubbling with nitrogen for 10 min. The mixture was refluxed at 80 °C
with magnetic stirring for 8 h. After cooling to room temperature, a
yellow precipitate was obtained. The precipitate was collected by
filtration and washed with ethanol three times. The deep yellow
crystals were dried in a vacuum desiccator. Yield: 2.8 g, 80%. 1H NMR
(400 MHz, DMSO): δ = 12.11 (s, 1H, -NH), 11.30 (s, 1H, −OH),
8.66 (s, 1H, -NCH), 7.95 (d, J = 7.3 Hz, 2H, Ar−H), 7.54−7.64 (m,
4H, Ar−H), 7.32 (t, J = 7.3 Hz, 1H, Ar−H), 6.94 (t, J = 8.8 Hz, 2H,
Ar−H). Anal. Calcd (%) for C14H12N2O2: C, 69.99; H, 5.03; N, 11.66.
Found (%): C, 70.15; H, 4.93; N, 11.02. MS (m/z) calc. for
C14H12N2O2: 240.1; Found: 263.76 [M + Na]+.
Synthesis of 2. A flask was charged with a mixture of 1 (20.00 g,
68.5 mmol) and hydrazine hydrate (40 mL, excess). EtOH (100 mL)
was added. The flask was degassed by bubbling with nitrogen for 10
min. The mixture was refluxed at 80 °C with magnetic stirring for two
days. After cooling to room temperature, water (500 mL) was added.
The precipitate was collected by filtration, washed with water four
times and with ethanol/water = 1:4 three times. Then a white product
was dried in a vacuum desiccator. Yield: 17.7 g, 89% (based on 1).
1HNMR (400 MHz, DMSO): δ = 9.61 (s, 1H, -NH), 7.71−7.84 (m,
2H, Ar−H), 6.90−7.03 (m, 2H, Ar−H), 4.53 (broad, 2H, NH2), 4.01
(m, 2H, -OCH2), 1.53−1.86 (m, 2H, −CH2), 1.12−1.49 (m, 14H,
-C7H14), 0.85 (t, J = 6.9 Hz, 3H, −CH3).
Synthesis of H2L1. A flask was charged with a mixture of 2 (2.00 g,
6.8 mmol) and 2-hydroxybenzaldehyde (0.7 mL, 6.8 mmol). EtOH
(40 mL) was added. The flask was degassed by bubbling with nitrogen
for 10 min. The mixture was refluxed at 80 °C with magnetic stirring
for 8 h. After cooling to room temperature, a white precipitate was
obtained. The precipitate was collected by filtration and washed with
ethanol/water = 1:1 three times. The white product was dried in a
vacuum desiccator. Yield: 2.45 g, 91%. 1HNMR(400 MHz, DMSO): δ
= 11.98 (s, 1H, -NH), 11.38 (s, 1H, −OH), 8.62 (s, 1H, -NCH), 7.92
(d, J = 8.5 Hz, 2H, Ar−H), 7.52 (d, J = 7.5 Hz, 1H, Ar−H), 7.30 (t, J =
7.7 Hz, 1H, Ar−H), 7.12−6.81 (m, 4H, Ar−H), 4.05 (t, J = 6.5 Hz,
2H, -OCH2), 1.79−1.60 (m, 2H, −CH2), 1.48−1.12 (m, 14H,
-C7H14), 0.86 (t, J = 6.8 Hz, 3H, −CH3). 13CNMR (100 MHz,
Synthesis of HL3. A flask was charged with a mixture of 2 (2.00 g,
6.8 mmol) and picolinaldehyde (0.7 mL, 6.8 mmol). EtOH (40 mL)
was added. The flask was degassed by bubbling with nitrogen for 10
min. The mixture was refluxed at 80 °C with magnetic stirring for 8 h.
After cooling to room temperature, a white precipitate was obtained.
The precipitate was collected by filtration and washed with ethanol
three times. The white product was dried in a vacuum desiccator.
1
Yield: 2.36 g, 91%. H NMR (400 MHz, DMSO): δ = 11.92 (s, 1H,
-NH), 8.62 (d, J = 4.8 Hz, 1H, pyridine-H), 8.47 (s, 1H, -NCH), 7.84
− 8.03 (m, 4H, pyridine-H, Ar−H), 7.36−7.46 (m, 1H, pyridine-H),
7.06 (d, J = 8.8 Hz, 2H, Ar−H), 4.05 (t, J = 6.5 Hz, 2H, -OCH2), 1.55
− 1.75 (m, 2H, −CH2), 1.15 − 1.52 (m, 14H, -C7H14), 0.86 (t, J = 6.7
Hz, 3H, −CH3). 13CNMR(100 MHz, CDCl3): δ = 162.29, 153.25,
148.99, 136.56, 129.78, 124.65, 124.08, 114.17, 68.17, 31.89, 30.93,
29.34, 25.99, 22.67, 14.11. Anal. Calcd (%) for C23H31N3O2: C, 72.4;
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Figure 1. (a) TEM image of Cu-L1 gels formed in DMF; inset: photoimage of the gels; (b) SEM image of Cu-L1 gels formed in DMF; inset:
enlarged view of nanofiber bundles; (c) SEM image of Cu-L1 nanofibers synthesized from dilute DMF solution by addition of water; (d) SEM image
of Cu-L3 particles.
Figure 2. IR data of H2L1, Cu-L1, HL3, and Cu-L3.
H, 8.2; N, 11.0. Found (%): C, 72.2; H, 8.1; N, 10.4. MS (m/z) cacl.
for C23H31N3O2: 382.2; Found: 382.0 [M + H]+.
precipitate was collected by centrifugation and washed with ethanol
three times. Yield: 87%. Anal. Calcd (%) for (C14H10CuN2O2): C,
55.72; H, 3.34; N, 9.28. Found(%): C, 55.80; H, 3.31; N, 8.76.
Synthesis of Cu-L3. HL3 (0.01 mmol, 3.8 mg) was dissolved in
DMF (1 mL), Cu(OAc)2·H2O (0.01 mmol, 2 mg) in DMF (0.5 mL)
was added. The mixture was stirred for 30 min at room temperature
and the powder was collected by centrifugation and washed with
ethanol three times. Yield: 51%. Anal. Calcd (%) for C25H33CuN3O4:
C, 59.70; H, 6.57; N, 8.36. Found (%): C, 59.75; H, 6.50; N, 7.73.
Synthesis of Cu-L1. A DMF solution of Cu(OAc)2·H2O (0.02
mmol, 0.5 mL) was added into a solution of H2L1 (0.01 M, 1 mL) in
DMF under stirring at room temperature for 30 min and green gels
were obtained. The nanofibers were washed with ethanol three times
and redispersed in ethanol for SEM and TEM analysis. For elemental
analysis (C, H, N), the powder was dried in a vacuum desiccator for
three days before measurement. Yield: 67%. Anal. Calcd (%) for
C24H30CuN2O3: C, 62.95; H, 6.56; N, 6.12. Found (%): C, 62.91; H,
6.49; N, 5.61. Long and short nanorods of Cu-L1 were obtained by
ultrasonication of as-prepared Cu-L1 gel in DMF for 15 and 60 min,
respectively. The nanorods were collected by centrifugation and
washed with ethanol and dried in a vacuum.
RESULTS AND DISCUSSION
■
As shown in Scheme 1, H2L1 is a three dentate chelating ligand.
The addition of long alkyl chains is expected to promote cross-
linking between molecular stacks and thus effectively modulate
the final morphologies.2e,10g Addition of an DMF solution of
Cu(OAc)2 (0.02 M, 0.5 mL) into a solution of H2L1 in DMF
(0.01 M, 1 mL) resulted in green precipitate in 10 min, which
Synthesis of Cu-L2. H2L2 (0.02 mmol, 4.8 mg) was dissolved in
ethanol (5 mL) and a solution of Cu(OAc)2·H2O (0.02 mmol, 4.0
mg) in ethanol (5 mL) was added dropwise under stirring. The
mixture was further stirred for 30 min and the resulting green
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Figure 3. (a) UV−vis absorption of H2L1 and Cu-L1. (b) XRD data of Cu-L1 fibers, rods, and belts, Cu-L2 nanofibers, and Cu-L3 particles. (c)
Photoimage of H2L1 after the addition of different metal ions, from left to right: Cu2+, Zn2+, Co2+, Cd2+, Mn2+, Ni2+, Li+.
forms gels after further stirring for 30 min at room temperature.
The gel formation can be promoted by increasing the precursor
concentrations. For example, gels can be obtained within 4 min
when the concentrations of Cu(OAc)2 and H2L1 are increased
to 0.04 and 0.02 M, respectively. TEM and SEM analyses reveal
that the gels consist of aligned nanofibers with widths of 80 nm
and lengths up to hundreds of micrometers (Figures 1a,b and
S1, Supporting Information). In fact, Cu-L1 acts as a “super-
gelators”12,13 with critical gelation concentration of 0.3 wt % for
DMF, which represents one of the rare examples of
metallogelators with low molecular weight.
When the precursor solution is dilute, no precipitate is
observed. For example, mixing of H2L1 (2 × 10−3 M, 1 mL)
and Cu(OAc)2 (4 × 10−3 M, 0.5 mL) leads to a clear solution.
Interestingly, nanofibers can also be obtained after addition of
water into this precursor solution (Figure 1c). Commonly,
spherical amorphous particles precipitate after addition of
nonsolvents such as water or ether into a precursor solution
containing ligands and metal ions.2 The formation of nanofibers
after addition of water in this system indicates that the
unidirectional intermolecular forces are strong enough to
overcome the rapid and random aggregation of coordination
complexes and effectively modulate the final morphology.
Infrared spectrum (Figure 2) of Cu-L1 dried powder does
not play the amide CO (1642 cm−1) stretch and peak for
NH at 3247 cm−1. The intensity increase at 390 nm in the UV−
vis absorption spectrum of Cu-L1 indicates the extension of π−
conjugation in the whole ligand (Figure 3a). These results
indicate that H2L1 is deprotonated to coordinate with Cu(II)
in the enolate form. Elemental analysis revealed the ratio
between ligand and Cu(II) is 1:1. XRD analysis revealed that
the nanofibers exhibit sharp diffraction peaks, indicative of high
crystallinity (Figure 3b). The ligand exhibits good selectivity
toward different metal ions in term of metallogel formation. As
shown in Figure 3c, after the addition of different metal acetate
salts (Cu2+, Zn2+, Co2+, Cd2+, Mn2+, Ni2+, Li+), only Cu-L1 gel
was observed.
the first stage. To study the mechanism of 1D assembly, we
further synthesized ligands H2L2 and HL3. H2L2 has the same
chelating moiety with that of H2L1 but it has no alkyl chain.
Addition of an ethanol solution of Cu(OAc)2 into a solution of
H2L2 in ethanol resulted in green precipitate. SEM analysis
revealed that the Cu-L2 particles are also nanofibers with
diameters of 90 nm and lengths up to hundreds of micrometers
(Supporting Information, Figure S2). No precipitation was
observed when DMF was used as the solvent due to the good
solubility in this solvent. Interestingly, nanofibers were also
obtained by the addition of water into a DMF solution of the
precursors. This result reveals that the chelating moiety plays a
key role in the coordination-induced assembly of the 1D
nanostructure.
To investigate this mechanism at the molecular level,
electrospray ionization (ESI) mass spectrometry was per-
formed. Figure 4 shows the ESI data of Cu-L2 measured using
methanol as the solvent. The main peak at 602.9 (m/z) can be
assigned to Cu2(L2)2, which indicates that there are dimers
formed even in the dilute solution. Similarly, the dimer
formation was also observed from the ESI data of the Cu-L1
complex. On the basis of the experimental results, the
formation of the 1D nanostructure was proposed. As shown
in Scheme 1 and Figure 5, H2L1 is a tridentate chelating ligand,
which can form a neutral complex with Cu(II) ions in a molar
ratio of 1:1. However, this ligand could not saturate the
coordination numbers if they formed a neutral mononuclear
complex. As a result, the complexes may form dimers, which
then assemble into supramolecular structures by sharing some
coordinating atoms (or linked by sharing coordinating atoms of
solvent molecules) to saturate the coordination of Cu(II).
To further investigate this formation mechanism, comparison
ligand HL3 was synthesized. HL3 is also a tridentate ligand.
The difference is that L3 is a negatively charged monovalent
ligand when coordinated with Cu(II). Under the same
preparation condition with that of Cu-L1, microscale block
crystals of Cu-L3 were obtained (Figure 1d). Elemental analysis
and IR data revealed that Cu-L3 has a formula of
Cu(CH3COO)L3. Because L3 is a monovalent tridentate
chelating ligand, an acetate anion further binds to Cu(II) (via
As revealed from our experiment results, the formation of
gels is about 30 min later than nanofibers, which indicates that
the growth along the 1D direction is fast and predominant in
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possibility for the Cu atom to further share coordinating atoms
with neighboring molecules to form polymeric structures.
Another comparison experiment (Cu-L1) was performed in
DMF in the presence of pyridine. Because excess pyridine can
easily saturate the coordination number of Cu atom in the Cu-
L1 monomer, it is unnecessary for Cu atom to form dimers and
further share coordinating atoms with neighboring molecules,
and therefore no 1D nanostructure is expected. In our
experiment, three drops of pyridine was premixed with H2L1
(0.02 M, 1 mL) before addition of Cu(OAc)2 (0.04 M, 0.5
mL). Experimental results showed that neither precipitate nor
gels were formed, which again supports the proposed
mechanism.
Ultrasound and solvents can effectively tune the particle sizes
and aspect ratio of the 1D nanostructure. When the experiment
was performed in THF, belt-shaped crystals were obtained. As
shown in Figure 6a, the particles exhibit an average width 0.5
μm, thickness of 80 nm, and lengths up to hundreds of
micrometers. Compared with those in DMF and THF, the
formation of nanofibers in an ethyl acetate system is much
faster and the width of fibers is much thinner (ca. 40 nm). This
probably results from the low solubility of Cu-L1 in ethyl
acetate, which induces the unidirectional growth rapidly (Figure
6b).
Cu-L1 gels here are a dynamic nanostructure, which exhibit
shape transformation under stimulation of ultrasound. For
example, 15 min of ultrasonication of the gels in DMF leads to
long nanorods with a width of 80 nm and average lengths of 4
μm as revealed by SEM measurement (Figure 6c). Longer time
of ultrasonication leads to further shorter rods. Figure 6d shows
the SEM image of nanorods obtained after 1 h of ultra-
sonication, which have an average width of ∼85 nm and lengths
of 1−1.5 μm. XRD analysis revealed that both of the nanowires
and nanorods exhibit sharp and very similar diffraction peaks,
indicative of high crystallinity (Figure 3b). It is interesting that
the nanobelts synthesized in THF also exhibit this shape
transformation upon stimulation of ultrasound. The aspect ratio
of nanofibers prepared from ethyl acetate and that precipitated
from DMF dilute solution by the addition of water do not show
any change after ultrasonication. When these nanofibers
(collected by centrifugation) were dispersed in DMF or
THF, they exhibited shape transformation under stimulation
of ultrasound. The effect of DMF and THF is probably owing
to the relatively better solubility of Cu-L1 in DMF and THF
than those in ethyl acetate and water, which may facilitate this
solvent-mediated shape transformation.
Figure 4. ESI-MS data of Cu-L1 and Cu-L2 showing the dimer
formation in dilute solution.
monodentate coordination mode, νas − νs = 239 cm−1, Figure
2) to saturate the coordination number of Cu(II) and also
balance the charge of the complex. Therefore, there is less
In conclusion, we have demonstrated a supramolecular
approach to nanoscale metal-containing gels, fibers, belts, and
rods. The ligand-structure effect and mechanism of 1D growth
of nanofibers have been studied. In this system, dimer
formation was found to be a key factor for the 1D
supramolecular assemblies. Cu-L1 acts as “super-gelators”
representing one of the rare examples of metallogelators with
low molecular weight. The dynamic metal-containing gels and
nanofibers formed by supramolecular assembly exhibit solvent-
mediated shape transformation by stimulation of ultrasound.
The shape control and the study of the structure effect at the
molecular level in this work will certainly expand the synthesis
of 1D metal-containing nanostructure in the development of
new functional materials.
Figure 5. Proposed 1D supramolecular structure and schematic
illustration of gel formation.
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Figure 6. SEM images of Cu-L1 prepared under different conditions: (a) in THF with ultrasonication for 7 min; (b) in ethyl acetate with stirring for
15 min; (c) in DMF under ultrasonication for 15 min; (d) in DMF under ultrasonication for 1 h.
(2) See recent reviews: (a) Leong, W. L.; Vittal, J. J. Chem. Rev. 2011,
ASSOCIATED CONTENT
■
111, 688−764. (b) Lin, W.; Rieter, W. J.; Taylor, K. M. L.
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* Supporting Information
SEM images. This material is available free of charge via the
Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
■
Chem. Soc. Rev. 2011, 40, 291−305. (g) Whittell, G. R.; Hager, M. D.;
Schubert, U. S.; Manners, I. Nat. Mater. 2011, 10, 176−188.
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Corresponding Author
*E-mail: qhchen@fjnu.edu.cn (Q.C.); xuazh@ifm.liu.se (X.Z.);
kajsa@ifm.liu.se (K.U.).
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
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The authors are indebted to the financial support of Natural
Scientific Foundation of Fujian Province of China (No.
A0710001); the Education Department of the Fujian Province
of China (No. JB10010); the Swedish Foundation for Strategic
Research (SSF) within the Nano-X program (Grant No. SSF
[A3 05:204]), and Swedish government strategic faculty grant
in material science (SFO, MATLIU) in Advanced Functional
Materials (AFM).
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