Nanowires and nanotubes from π-conjugated organic materials fabricated by template wetting

RAPID COMMUNICATION

Nanowires and nanotubes from p-conjugated organic materialsfabricated by template wetting

Kirill Bordo • Manuela Schiek • Horst-Gunter Rubahn

Received: 22 October 2013 / Accepted: 3 January 2014 / Published online: 31 January 2014

� Springer-Verlag Berlin Heidelberg 2014

Abstract 1D nanostructures (nanowires and/or nano-

tubes) from poly(9,9-dioctylfluorene-2,7-diyl) (PF8),

poly(3-hexylthiophene-2,5-diyl) (P3HT), and N,N0-dioctyl-

3,4,9,10-perylenedicarboximide (PTCDI-C8) were suc-

cessfully fabricated by a simple and facile template-based

technique. The technique involved wetting of porous

anodic alumina membranes by solutions and/or melts of

the respective materials. Arrays of 1D nanostructures from

the polymers PF8 and P3HT can be obtained by both

solution- and melt-assisted template wetting. In the case of

PF8, the morphology of the obtained nanostructures

depends on the wetting conditions: for diluted PF8 solu-

tions mostly nanotubes are obtained; while for concen-

trated PF8 solutions and PF8 melts, the formation of

nanowires is dominating. Wetting of the template pores by

P3HT solutions and melts leads to the formation of

nanotubes. For the small-molecule material PTCDI-C8,

arrays of nanowires can only be obtained by melt-assisted

wetting. Wetting of the template pores with PTCDI-C8

solutions does not allow the formation of pronounced 1D

nanostructures. For all three materials, the diameters of

the formed nanowires and nanotubes correspond to those

of the template pores (around 250 nm), while their lengths

range from hundreds of nanometers to tens of microme-

ters. The photoluminescence spectra of the as-prepared

nanostructures show peak shifts and redistribution of the

peak intensities, if compared to unstructured thin films

from the respective materials.

1 Introduction

1D nanostructures from p-conjugated organic molecules

are known to possess interesting optical, electrical and

optoelectronic properties, which are significantly different

from those of the respective bulk materials. In particular,

such nanostructures show emission of light following

electrical or optical excitation, as well as waveguiding and

lasing. They have successfully been used as active layers in

field-effect transistors, light-emitting diodes, full color

displays, organic semiconductor lasers and solar cells [1–

3]. Since the mutual alignment and orientation of such

nanostructures may influence the device performance, it is

important to synthesize well-aligned nanoaggregates in a

controllable manner.

The use of porous anodic aluminas (PAA’s) as templates

is a versatile approach to the preparation of 1D nano- and

microstructures. Wetting of PAA templates with solutions

or melts allows fabrication of nanowires and nanotubes

from a wide variety of materials. The diameters and lengths

of such 1D structures correspond to those of the templates,

which in turn can be readily tuned within a wide range by

adjusting the anodization conditions [4–6].

In the present work, the fabrication of 1D nanostructures

(nanowires and/or nanotubes) from poly(9,9-dioctylfluo-

rene-2,7-diyl) (PF8), poly(3-hexylthiophene-2,5-diyl)

(P3HT), and N,N0-dioctyl-3,4,9,10-perylenedicarboximide

(PTCDI-C8) by means of wetting of PAA templates is

K. Bordo (&)

Section for Materials and Surface Engineering, Department of

Mechanical Engineering, Technical University of Denmark,

2800 Kongens Lyngby, Denmark

e-mail: [email protected]

M. Schiek

Energy and Semiconductor Research Laboratory, Department of

Physics, University of Oldenburg, 26111 Oldenburg, Germany

H.-G. Rubahn

Mads Clausen Institute, University of Southern Denmark,

NanoSYD, 6400 Sønderborg, Denmark

123

Appl. Phys. A (2014) 114:1067–1074

DOI 10.1007/s00339-014-8226-5

considered. The structural formulae of these compounds

are shown in Fig. 1.

The investigation of the formation of 1D nanostructures

from these materials is important, since they are promising

candidates for different electronic device applications. PF8

and other polyfluorenes are typical active materials in blue

light-emitting diodes [7, 8]. P3HT is widely used in BHJ

solar cells [9–11]. PTCDI and perylene-diimide derivatives

are employed in field-effect transistors and other electronic

devices [12–14].

Nanowires (or ‘‘nanohillocks’’) from P3HT were pre-

pared via solution-assisted [15, 16] or melt-assisted [9,

17, 18] wetting of PAA templates, and also by nano-

imprint lithography, using thin PAA films on Si sub-

strates as stamps [11, 19]. The fabrication of PF8

nanowires and nanotubes has also been reported [20–23].

Needle-like nanoaggregates from several different per-

ylene-diimide derivatives were obtained by self-assembly

from solutions [24, 25]. However, this technique only

allowed the formation of randomly oriented ‘‘nanonee-

dles’’ having different lengths and widths. In addition,

nanotube arrays from perylene were fabricated by solu-

tion-assisted template wetting [26] and pyridine-perylene-

diimide nanowires were made by electrophoretic depo-

sition into the pores of a PAA template [27]. In general,

facile and size-controlled preparation of well-defined

nanowires or nanotube arrays from these materials is still

a challenge.

In the present paper, we report on the fabrication of 1D

nanostructures from PF8, P3HT and PTCDI-C8. The

nanostructures were made in a controllable manner by

employing both solution- and melt-assisted wetting of PAA

templates. The solution-assisted wetting by PF8 and P3HT

was studied for two different concentrations of the pre-

cursor solutions. The effects of the preparation conditions

on the morphology of the obtained nanostructures, as well

as their optical properties, are discussed.

2 Experimental section

PF8 (regioregular, semiconductor grade, Sigma-Aldrich),

P3HT (regioregular, semiconductor grade, Rieke Metals)

and PTCDI-C8 (semiconductor grade, Sigma-Aldrich)

were used without further purification.

For the fabrication of nanostructures by means of tem-

plate wetting, mainly commercial membrane filters (Ano-

disc 25, Whatman Ltd.) were used. These membranes had

mean pore diameter of 200 nm and thickness of 60 lm

(according to the manufacturer’s data). The real pore

diameter was found to be 244 ± 48 nm previously [22].

In some of the experiments, lab-made thin-film PAA

templates were employed. Such templates were prepared

by the anodization of thin evaporated Al films on ITO-

coated glass substrates. A detailed description of this pro-

cedure can be found elsewhere [28]. Briefly, the Al films

(thickness 1 lm) were deposited by e-beam evaporation

from a 99.99 % pure Al target in a conventional PVD

machine (Edwards Auto 500). In order to improve the

adhesion of the Al to the substrate, a thin (2 nm) layer of Ti

was applied. The as-prepared thin Al films were anodized

in 0.3 M oxalic acid at 40 V, and the pores of the formed

PAA films were subsequently widened by etching in 5 %

phosphoric acid for 45 min. at room temperature. The

obtained templates had pore diameters of about 80 nm and

thickness of about 1.5 lm.

All three materials were introduced into the pores of the

templates by both solution- and melt-assisted wetting.

For the solution-assisted wetting, two solutions of PF8

in toluene and two solutions of P3HT in chlorobenzene

having different concentrations (a saturated solution and a

1 mg/ml solution for each material) were used. Because of

relatively low solubility of PTCDI-C8, only a saturated

solution of PTCDI-C8 in chloroform was employed. Sat-

urated solutions of the stated materials were prepared by

adding an excess amount of each material to a fixed volume

(about 1 ml) of the corresponding solvent in a glass vial

under constant stirring at room temperature. In the case of

PF8 and P3HT, a drop of a solution was placed on top of a

membrane and the membrane was sandwiched between

two glass slides. The membrane was left clamped between

the glass slides for about 10 h to allow slow evaporation of

the solvent. In the case of PTCDI-C8, the so-called ‘‘dip-

and-dry’’ method was employed. In that technique, the

porous membrane was dipped into the PTCDI-C8 solution

for 2 min. After dipping, the membrane was put on a 50 �C

Fig. 1 Structural formulae of

PF8 (a), P3HT (b) and PTCDI-

C8 (c)

1068 K. Bordo et al.

123

hot plate and the solvent was allowed to evaporate. In total,

20 ‘‘dip-and-dry’’ cycles were conducted.

For the melt-assisted wetting, thin films of PF8, P3HT

and PTCDI were formed on microscope glass slides by

drop-casting from the corresponding saturated solutions. A

porous membrane was placed on top of the film and cov-

ered by another glass slide. For each material, such a

‘‘sandwiched’’ structure was heated up slightly above the

respective melting point (to 180 �C for PF8, to 250 �C for

P3HT, to 340 �C for PTCDI-C8) for 15 min. The melting

was carried out on a hotplate placed in a glove box under

constant nitrogen flow. For the sake of comparison, some

of the mentioned drop-casted thin films were left as-pre-

pared, without template-assisted nanostructuring. These

films will be referred to as ‘‘non-structured’’ thin films.

Finally in all of the experiments a sticky carbon pad was

attached to one side of the membrane, while the other side

was cleaned from the excess polymer by scratching with a

scalpel. The nanowire/nanotube arrays were released by

dissolving the membrane in a 2 M NaOH solution.

Optical images of the obtained nanowire/nanotube

arrays were acquired by a fluorescence microscope equip-

ped with a high-pressure Hg lamp (Nikon Eclipse TE 300)

and a CCD camera. Photoluminescence spectra of the

nanostructures were measured on the same microscope

with a fiber spectrometer (Ocean Optics) attached. Scan-

ning electron microscopy (SEM) images of the nanowire/

nanotube arrays were collected using a Hitachi S-4800

instrument operating at beam voltages of 2–3 kV. In order

to facilitate SEM imaging, all the samples were coated with

Au/Pd (2 nm) by magnetron sputtering (Cressington HR

208 sputter coater).

3 Results and discussion

3.1 Morphology of the obtained nanostructures

Fluorescence microscopy reveals arrays of bright blue-emit-

ting 1D nanostructures for PF8 and red-emitting structures for

P3HT and PTCDI-C8 (Fig. 2). It can be seen that the nano-

structures are merged together to form bundles. On the pre-

sented images, the tips of the nanostructures cannot be seen,

since their lengths are bigger than the depth of focus. The

magnification of the microscope is not sufficient to distinguish

between nanowires and nanotubes.

SEM images of PF8 nanostructures prepared by tem-

plate wetting are presented in Fig. 3. Figure 3a shows a

bundle of PF8 nanotubes obtained after the wetting of a

template by a 1 mg/ml PF8 solution. The outer diameter of

the nanotubes follows the pore diameters being around

250 nm. In Fig. 3b, the opening of a single nanotube is

shown. The nanotube wall thickness, as can be roughly

estimated from the picture, is about 50 nm. The observed

morphology of the PF8 nanotubes is in a good agreement

with previously reported results [20–22]. Figure 3c, d

shows arrays of PF8 nanowires obtained by wetting of a

template by a saturated PF8 solution and PF8 melt,

respectively. In these two cases, no nanotubes could be

seen on the SEM images, i.e., the PAA pores were com-

pletely filled by the precursor material.

Notably, for the 1 mg/ml PF8 solution, mostly nano-

tubes are formed, while for the saturated solution and melt

only nanowires can be obtained. This fact can be explained

by the so-called ‘‘precursor wetting’’ mechanism proposed

previously [29–32]. Wetting of the template pores by a

polymer solution involves the formation of a ‘‘precursor

film’’ on the pore walls. If the formed ‘‘precursor film’’ is

kinetically unstable, which probably takes place for PF8,

the pore volume can eventually get completely filled. This

is realized for the wetting with concentrated solutions and

melts of PF8. In that case, the amount of material entering

the pores is much bigger, if compared to a diluted PF8

solution. In principle, a prerequisite for the ‘‘precursor

wetting’’ mechanism is a sufficiently high surface energy

of the pore walls, which is the case for PAA templates.

SEM images of P3HT nanotubes are presented in Fig. 4.

Figure 4a shows a bundle of P3HT nanotubes obtained

after the wetting of a template by 1 mg/ml P3HT solution.

The nanotube arrays have a characteristic ‘‘coral-like’’

Fig. 2 Fluorescence microscopy images (365-nm excitation) of the fabricated PF8 (a), P3HT (b) and PTCDI-C8 (c) 1D nanostructure arrays

Nanowires and nanotubes 1069

123

shape which originates from the surface features of the

initial PAA membrane. The nanotubes obtained from a

saturated P3HT solution (not shown on the picture) had a

very similar morphology. Figure 4b, c shows P3HT nano-

tubes obtained by melt-assisted wetting. From the high-

magnification image (Fig. 4b) it is seen that an individual

P3HT nanotube has the same diameter as the template

pores (about 250 nm) and the nanotube wall thickness is

about 60–80 nm. In fact it is not possible to see whether all

the tubes really have open tips because of the shapeless

residue covering the nanotube arrays (Fig. 4c). This residue

is probably the unstructured P3HT which got deposited on

Fig. 3 SEM images of PF8

nanotubes obtained by wetting

of a PAA template by PF8

solutions in toluene having

different concentrations [1 mg/

ml (a, b) and saturated solution

(c)] and by PF8 melt (d)

Fig. 4 SEM images of P3HT

nanotubes obtained by wetting

of a commercial PAA template

by a diluted (1 mg/ml) solution

of P3HT in chlorobenzene

(a) and by P3HT melt (b, c);

SEM image of P3HT nanotubes

prepared by melt-assisted

wetting of a lab-made thin-film

PAA template (d)

1070 K. Bordo et al.

123

the top of the PAA membrane during the wetting procedure

and could not be removed completely before the template

dissolution. On the other hand, open nanotube tips can be

clearly seen on the SEM image of a homemade supported

thin-film PAA template wetted by P3HT melt (Fig. 4d). In

that case, the excess of P3HT was completely removed

from the top of the template by carefully wiping it with a

toluene-soaked tissue. Here, the nanotube diameters cor-

respond to those of the thin-film template (60–80 nm) and

the nanotube wall thickness is about 20 nm.

It should be noted that for P3HT both solution- and

melt-assisted wetting lead to the preferential formation of

nanotubes, not nanowires. That can be explained by the

‘‘precursor wetting’’ mechanism which is described above

for PF8. However, in the case of P3HT the ‘‘precursor

film’’, which is formed on the walls of the PAA template, is

kinetically stable. The evaporation of the solvent (in the

case of P3HT solution) and solidification of the polymer

after cooling it below the melting point (in the case of

P3HT melt) leads to the formation of nanotubes in the

pores of the PAA template.

PTCDI-C8 was introduced into the template pores by

means of the so-called ‘‘dip-and-dry’’ method. SEM

imaging of the samples after complete removal of the PAA

did not reveal any pronounced nanostructures. At some

regions, only small PTCDI-C8 nanoaggregates could be

seen. Apparently, the employed number of ‘‘dip-and-dry’’

cycles was not enough to introduce sufficient amount of

material into the template pores and to allow the formation

of long 1D nanostructures. Another technique involved

melting of a PTCDI-C8 thin film formed on top of a PAA

template and filling the pores by the PTCDI-C8 melt, see

Fig. 5. It can be seen that many of the formed nanowires

are more than 20-lm long and their widths are equal to the

PAA pore diameters (about 250 lm). At the same time, a

lot of smaller (a few micrometer long) nanowire fragments

are observed. Such fragments probably appear after

breaking of the nanowires which can happen during the

template dissolution. It might also happen that for some of

the pores the amount of the introduced PTCDI-C8 was not

enough to fill the pores completely. The fact of nanowire

formation, like in the case of PF8 melt, can be explained by

the kinetic instability of the ‘‘precursor film’’ formed dur-

ing the wetting.

The results obtained in the present work for nanostruc-

tures from P3HT, PF8 and PTCDI-C8 are summarized in

Table 1 and compared to the data obtained by other authors

for the same materials or derivatives.

From the presented data, it can be seen that the tech-

nique of template wetting allows facile and controllable

fabrication of 1D nanostructures from PF8, P3HT and

PTCDI-C8 having high aspect ratios. The overall mor-

phology of the obtained nanostructures strongly depends on

the nature of the precursor material, as well as on the

fabrication conditions, i.e., on the template pore dimen-

sions, the method of fabrication (solution- or melt-assisted

wetting), the concentration of the solution (for the case of

solution-assisted wetting with PF8).

In general, the morphologies of the template-fabricated

P3HT and PF8 nanostructures, observed in the present

work, are in a good agreement with those reported by other

authors. The P3HT nanostructures observed in the case of

melt-assisted wetting were referred to as ‘‘nanohillocks’’ or

‘‘nanopillars’’ [9, 17, 18]. The results obtained for P3HT in

the present work clearly show the formation of nanotubes

(i.e., hollow nanostructures) for the wetting of PAA pores

with a P3HT melt.

It should be noted that nanowire arrays from PTCDI-C8

were obtained for the first time using the mentioned tech-

nique. If compared to the previously reported fabrication of

pyridine-perylene-diimide nanowires via electrophoretic

deposition [27], the procedure used in the present work is

quite facile and does not require any sophisticated

equipment.

3.2 Optical properties of the obtained nanostructures

The as-fabricated 1D nanostructures from PF8, P3HT and

PTCDI-C8 were characterized by PL spectroscopy. The

intensity-normalized PL spectra of the obtained nanostructures

Fig. 5 SEM images of PTCDI-

C8 nanowires obtained by

wetting of a PAA template by a

PTCDI-C8 melt

Nanowires and nanotubes 1071

123

as well as the respective ‘‘non-structured’’ thin films are pre-

sented in Fig. 6.

In the PL spectra of the ‘‘non-structured’’ thin films

before and after heat treatment, no changes were observed.

Therefore, it was assumed that the employed heat treatment

did not cause any change in the chemical composition of

the studied materials.

For the determination of the peak positions, each spec-

trum was fit with a set of Gaussian curves. The spectrum of

a spin-coated PF8 film (Fig. 6a) exhibits a vibronic pro-

gression with peaks at 441, 465 and 501 nm, corresponding

to 0–0, 0–1 and 0–2 vibronic transitions, respectively. A

broad peak at around 540 nm can also be seen. The PL

spectra of the PF8 nanotubes and nanowires are slightly

shifted to the blue with respect to that of PF8 thin film. The

broad featureless band centered around 540 nm can be

attributed to the on-chain chemical defects probably

associated with oxidatively generated fluorenone units [7,

8, 33–36]. The relative intensity of this band is maximal for

the PF8 nanowires, being significantly lower for the PF8

nanotubes and the thin film.

It can be seen that the relative intensities of the 0–0 and

0–1 vibronic peaks are significantly changed for the PF8

nanowires and nanotubes, compared to PF8 thin film. In

particular, the relative intensity of the 0–0 peak decreases

for the PF8 nanowires and increases for the PF8 nanotubes.

The relative intensity of the 0–1 peak exhibits the opposite

trend. It should be noted, however, that PF8 nanostructures

of both morphologies (nanowires and nanotubes) can be

present on the observed areas of the samples simulta-

neously. Thus, the observed PL spectra might be a super-

position of the spectra for both nanowires and nanotubes.

Therefore, it is difficult to attribute the observed spectral

features to any particular form of PF8 nanostructures.

Table 1 1D nanostructures from PF8, P3HT and perylene derivatives fabricated via template-based techniques

Material Reference Method of

fabrication

Fabrication conditions Morphology of the

nanostructures

Length/outer diameter of

the nanostructures

P3HT [15] SAW 2 mg/ml P3HT in chloroform Nanotubes 200/65 nm

[16] SAW 0.5 % P3HT in chloroform Nanotubes 100-nm outer diameter

[9] MAW 250 �C, 30 min., in air Nanopillars 295/269 nm

[17] MAW 250 �C, 30 min., in air Nanopillars 500/52 nm

[18] MAW 250 �C, vacuum Nanohillocks 800/100 nm

[11] NIL 230 �C, 10 min., vacuum Nanopillars 200/50 nm

[19] NIL with PAA film

on Si as a stamp

125 �C Nanohillocks 450/80 nm

Present

work

SAW 1 mg/ml P3HT in chlorobenzene Nanotubes Tens of lm/250 nm

Present

work

SAW Saturated solution of P3HT in

chlorobenzene

Nanotubes Tens of lm/250 nm

MAW 250 �C, 15 min., N2 flow Nanotubes Tens of lm/250 nm

MAW 250 �C, 15 min., N2 flow Nanotubes 1.5 lm/60–80 nm

PF8 [20] SAW 60 mg/ml PF8 in THF Nanowires Not stated

[21] SAW 60 mg/ml PF8 in THF Nanowires 46 lm/232 nm

[22] SAW 40 mg/ml PF8 in THF Nanotubes Diameter: 257 nm

[23] MAW 250 �C, 2 h, vacuum Nanowires Not stated

Present

work

SAW 1 mg/ml PF8 in THF Nanotubes Tens of lm/250 nm

SAW Saturated solution of PF8 in THF Nanowires Tens of lm/250 nm

MAW 180 �C, 15 min., N2 flow Nanowires Tens of lm/250 nm

Perylene [26] MAW 240 �C 10 h, N2 flow Nanotubes 60 lm/200 nm

Pyridine-perylene-

diimide

[27] ED into PAA

template

CF3COOH as protonating agent Nanowires 20 lm/80 nm

Other perylene-

diimide

derivatives

[24, 25] Self-assembly from

solutions

– Nanowires or

‘‘nanoneedles’’

Up to 500 lm/ca.

200 nm

PTCDI-C8 Present

work

SAW Saturated solution of PTCDI-C8 in

chloroform, ‘‘drip-and-dry’’

None Hundreds of nm

MAW 340 �C, 15 min., N2 flow Nanowires Tens of lm/250 nm

MAW melt-assisted wetting, SAW solution-assisted wetting, NIL nanoimprint lithography, ED electrophoretic deposition

1072 K. Bordo et al.

123

The fitting of the PL spectrum of a thin spin-coated

P3HT film (Fig. 6b) reveals three peaks at 650, 730 and

810 nm. The spectrum of P3HT nanotubes is blue-shifted

with respect to the spectrum of the P3HT thin film. Like in

the case of PF8, a redistribution of peak intensities is

observed. The relative intensity of the 0–0 peak decreases

for the P3HT nanotubes, while the relative intensity of the

0–1 peak increases.

The PL spectrum of a drop-casted PTCDI-C8 film

(Fig. 6c) shows the main peak at 680 nm and a shoulder at

around 640 nm. In the spectrum of PTCDI-C8 nanowires,

the main peak is red-shifted compared to that of the thin

film and an additional shoulder appears at around 800 nm.

Peak shifts and redistribution of peak intensities in PL

spectra have been observed previously for 1D nanostruc-

tures from different p-conjugated organic materials [20–22,

37–43].

For the polymers, PF8 and P3HT, such spectral features

can be explained by phase transitions or changes in the

molecular alignment occurring during the template pore

filling. In particular, the presence of large amount of b-

phase was shown for PF8 nanowires prepared by solution-

assisted wetting [20–22]. The observed phase transition

was attributed to the mechanical stresses arising within a

polymer material during the pore filling and solvent

evaporation.

In general, the observed changes in the PL spectra can

also be explained by surface effects associated with 1D

nanostructures [37, 42]. In nanowires and nanotubes, the

fraction of molecules existing on the surface of these

nanostructures is significantly higher than in the respective

bulk materials or drop-casted thin films. The energy states

and energetic coupling of these molecules are different

when compared to those located in the bulk. That leads to

the changes in the overall structure of absorption and

emission spectra observed for the nanowires and

nanotubes.

In order to determine the particular mechanisms

responsible for the observed spectral changes, more

detailed spectroscopic studies (including, e.g., temperature-

dependent photoluminescence and polarization measure-

ments) are required.

4 Conclusions

In the present work, facile and controllable template-based

fabrication of 1D nanostructures from PF8, P3HT and

PTCDI-C8 is reported. Nanostructures from the polymers

P3HT and PF8 can be obtained by both solution- and melt-

assisted template wetting. For these materials, the so-called

‘‘precursor wetting’’ is realized. For P3HT, the ‘‘precursor

film’’ formed on the pore walls is kinetically stable, and

therefore this material can only form nanotubes––for wet-

ting with both solutions and melts. For PF8, the formed

‘‘precursor film’’ is not stable and the morphology of the

obtained nanostructures depends on the amount of material

introduced into the pores. For solutions with lower

Fig. 6 Intensity-normalized photoluminescence spectra of the fab-

ricated nanostructures and the respective ‘‘non-structured’’ thin films:

PF8 (a), P3HT (b) and PTCDI-C8 (c)

Nanowires and nanotubes 1073

123

concentrations, mostly nanotubes are obtained. For highly

concentrated solutions and melts, the pore volume can be

filled completely, and the formation of nanowires is dom-

inating. The small-molecule material PTCDI-C8 can be

introduced into a PAA template by wetting it with a melt.

Even a big number of ‘‘dip-and-dry’’ cycles in solution-

assisted wetting do not allow the formation of pronounced

1D nanostructures.

The photoluminescence spectra of the as-prepared

nanostructures show peak shifts and redistribution of the

peak intensities, compared to unstructured thin films from

the respective materials.

As can be seen from the obtained results, the method of

template wetting provides an effective and reliable general

route for the preparation of 1D nanostructures from prac-

tically important organic polymers and small molecules.

The fabrication of supported PF8, P3HT and PTCDI-C8

nanowire and/or nanotube arrays by wetting of thin-film

PAA templates would be the next step in the realization of

highly efficient electronic devices based on these materials.

Acknowledgments The authors are grateful to the Danish research

agency as well as the Danish Advanced Technologies Trust for sup-

porting this work by various grants.

References

1. F.S. Kim, G. Ren, S.A. Jenekhe, Chem. Mater. 23, 682 (2011)

2. S.B. Jo, W.H. Lee, L. Qiu, K. Cho, J. Mater. Chem. 22, 4244

(2012)

3. A.L. Briseno, S.C.B. Mannsfeld, S.A. Jenekhe, Z. Bao, Y.N. Xia,

Mater. Today 11, 38 (2008)

4. C.R. Martin, Chem. Mater. 8, 1739 (1996)

5. G. Cao, D. Liu, Adv. Coll. Interf. Sci. 136, 45 (2008)

6. R.O. Al-Kaysi, T.H. Ghaddar, G. Guirado, J. Nanomat. 2009, 1

(2009)

7. J.M. Lupton, J. Klein, Synth. Met. 138, 233 (2003)

8. W. Zhao, T. Cao, J.M. White, Adv. Funct. Mater. 14, 783 (2004)

9. A. Santos, P. Formentin, J. Pallares, J. Ferre-Borrull, L.F. Marsal,

Sol. Energ. Mat. Sol. C. 94, 1247 (2010)

10. M.T. Dang, L. Hirsch, G. Wantz, Adv. Mater. 23, 3597 (2011)

11. D. Chen, W. Zhao, T.P. Russell, ACS Nano 6, 1479 (2012)

12. A.L. Briseno, S.C.B. Mannsfeld, C. Reese, J.M. Hancock, Y.

Xiong, S.A. Jenekhe, Z. Bao, Y. Xia, Nano Lett. 7, 2847 (2007)

13. J.H. Oh, H.W. Lee, S. Mannsfeld, R.M. Stoltenberg, E. Jung,

Y.W. Jin, J.M. Kim, J.-B. Yoo, Z. Bao, PNAS 106, 6065 (2009)

14. H. Yu, Z. Bao, J.H. Oh, Adv. Funct. Mater. 23, 629 (2013)

15. J.P. Cannon, S.D. Bearden, S.A. Gold, Compos. A 41, 836 (2010)

16. J. Byun, Y. Kim, G. Jeon, J.K. Kim, Macromolecules 44, 8558

(2011)

17. A. Santos, P. Formentin, J. Pallares, J. Ferre-Borrull, L.F. Marsal,

Mat. Lett. 64, 371 (2010)

18. J.S. Kim, Y. Park, D.Y. Lee, J.H. Lee, J.H. Park, J.K. Kim, K.

Cho, Adv. Funct. Mater. 20, 540 (2010)

19. W. Wiedermann, L. Sims, A. Abdelilah, A. Exner, R. Meier, K.P.

Musselman, J.L. MacManus-Driscoll, P. Muller-Buschbaum, G.

Scarpa, P. Lugli, L. Schmidt-Mende, Appl. Phys. Lett. 96,

263109 (2010)

20. D. O’Carrol, G. Redmond, Chem. Mater. 20, 6501 (2008)

21. D. O’Carrol, D. Iacopino, A. O’Riordan, P. Lovera, E. O’Connor,

G.A. O’Brien, G. Redmond, Adv. Mater. 20, 42 (2008)

22. S. Moynihan, D. Iacopino, D. O’Carrol, P. Lovera, G. Redmond,

Chem. Mater. 20, 996 (2008)

23. D. O’Carrol, I. Lieberwirth, G. Redmond, Small 3, 1178 (2007)

24. Y. Che, A. Datar, K. Balakrishnan, L. Zang, J. Am. Chem. Soc.

129, 7234 (2007)

25. Y. Che, X. Yang, K. Balakrishnan, J. Zuo, L. Zang, Chem. Mater.

21, 2930 (2009)

26. L. Zhao, W. Yang, Y. Ma, J. Yao, Y. Li, H. Liu, Chem. Commun.

19, 2442 (2003)

27. R. Bai, M. Ouyang, R.-J. Zhou, M.-M. Shi, M. Wang, H.-Z.

Chen, Nanotechnology 19, 1 (2008)

28. K. Bordo, Nanoporous thin film templates for the fabrication of

nanowires and nanotubes (Ph.D. thesis, University of Southern

Denmark, Sønderborg, 2011)

29. http://www.mpi-halle.mpg.de. Accessed 16 Dec 2012

30. M. Steinhart, R.B. Wehrspohn, U. Gosele, J.H. Wendorff, An-

gew. Chem. Int. Ed. 43, 1334 (2004)

31. M. Steinhart, J.H. Wendorff, A. Greiner, R.B. Wehrspohn, K.

Nielsch, J. Schilling, J. Choi, U. Gosele, Science 296, 1997

(2002)

32. S. Schlitt, A. Greiner, J.H. Wendorff, Macromolecules 41, 3228

(2008)

33. A.C. Grimsdale, K.L. Chan, R.E. Martin, P.G. Jokisz, A.B.

Holmes, Chem. Rev. 109, 897 (2009)

34. A.C. Grimsdale, K. Mullen, Adv. Polym. Sci. 199, 1 (2006)

35. A.C. Grimsdale, K. Mullen, Macromol. Rapid Commun. 28, 1676

(2007)

36. A.C. Grimsdale, K. Mullen, Adv. Polym. Sci. 212, 1 (2008)

37. J.-K. Lee, W.-K. Koh, W.-S. Chae, Y.-R. Kim, Chem. Commun.

2, 138 (2002)

38. S. Guha, J.D. Rice, Y.T. Yau, C.M. Martin, M. Chandrasekhar,

H.R. Chandrasekhar, R. Guentner, P. Scanduicci de Freitas, U.

Scherf, Phys. Rev. B 67, 125204 (2003)

39. J. Beermann, S.I. Bozhevolnyi, V.G. Bordo, H.-G. Rubahn, Opt.

Commun. 237, 423 (2004)

40. J. Beermann, S.I. Bozhevolnyi, F. Balzer, H.-G. Rubahn, Laser

Phys. Lett. 2, 480 (2005)

41. F. Balzer, A. Pogantsch, H.-G. Rubahn, J. Lumin. 129, 784

(2009)

42. X.-P. Shen, G. Yin, C. Gao, Z. Xu, Mat. Chem. Phys. 113, 202

(2009)

43. K. Bordo, M. Schiek, A. Ghazal, I. Wallmann, A. Lutzen, F.

Balzer, H.-G. Rubahn, J. Phys. Chem. C 115, 20882 (2011)

1074 K. Bordo et al.

123