Band-Gap Opening in Metallic Single-Walled Carbon Nanotubes by Encapsulation of an Organic Salt

Article abstract of DOI:10.1002/anie.201705258

The encapsulation of viologen derivatives into metallic single-walled carbon nanotubes (SWNTs) results in the opening of a band gap, making the SWNTs semiconducting. Raman spectroscopy, thermogravimetric analysis, and aberration-corrected high-resolution transmission electron microscopy confirm the encapsulation process. Through the fabrication of field-effect transistor devices, the change of the electronic structure of the tubes from metallic to semiconducting upon the encapsulation is confirmed. The opening of a gap in the band structure of the tubes was not detected in supramolecular controls.

Full text of DOI:10.1002/anie.201705258

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
International Edition Chemie
www.angewandte.org
Accepted Article
Title: Band gap opening in metallic single-walled carbon nanotubes by
encapsulation of an organic salt
Authors: Belén Nieto-Ortega, Julia Villalva, Mariano Vera-Hidalgo,
Luisa Ruíz-González, Enrique Burzurí, and Emilio Manuel
Pérez
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201705258
Angew. Chem. 10.1002/ange.201705258
Link to VoR: http://dx.doi.org/10.1002/anie.201705258
http://dx.doi.org/10.1002/ange.201705258

Angewandte Chemie International Edition
10.1002/anie.201705258
COMMUNICATION
Band gap opening in metallic single-walled carbon nanotubes by
encapsulation of an organic salt
[
a]
[a]
[a]
[b]
Belén Nieto-Ortega, Julia Villalva, Mariano Vera-Hidalgo, Luisa Ruiz-González, Enrique
[
a]
[a]
Burzurí* and Emilio M. Pérez*
Abstract We show that the encapsulation of viologen derivatives
Here, we report that the encapsulation of viologen
derivatives into metallic SWNTs results in the opening of a band
gap, making the SWNTs semiconducting. We show that the
endohedral modification is robust enough to survive thorough
into metallic SWNTs results in the opening of a band gap, making
the
SWNTs
semiconducting.
Raman
spectroscopy,
thermogravimetric analysis and aberration corrected high resolution
transmission electron microscopy confirm the encapsulation process, washing of the sample. By using ac-dielectrophoresis, we
and through the fabrication of field-effect transistor devices, we
prove the change of the electronic structure of the tubes from
metallic to semiconductor upon the encapsulation. The opening of a
gap in the band structure of the tubes was not detected in
supramolecular controls.
prepared Field-Effect Transistor (FET) devices and performed
electron transport measurements through the endohedral
derivatives. We show that the electronic band structure of the
initially metallic SWNTs is switched from metallic to a high-
quality, homogeneous and robust semiconductor, in contrast
with adequate supramolecular controls. The resulting FET-like
device displays back-to-back Schottky diode behavior.
Carbon nanotubes (CNTs) are one of the most promising one-
dimensional nanoscale materials with potential applications in
Viologens, which are derived of 1,1'-disubtitued-4,4'-
[
1]
[2]
the fields of nanoelectronics, optoelectronics and medical
bipyridinium, were chosen for their well-known electron transport
[
3]
[4]
[5]
[13]
(
bio)technologies. Interestingly, their optical, electronic and
properties,
and because they have previously been used as
[
6]
mechanical properties can be modulated on demand via
doping agents of carbon-based materials in a supramolecular
[
7]
[14]
controlled chemical modification. Thanks to the versatility of
synthetic chemistry, a broad variety of strategies have been
employed to functionalize carbon nanotubes. Making strong
configuration.
In particular, we synthesized didodecyl-4,4'-
bipyridinium dihexafluorophosphate (Viol in Figure 1a, see SI for
synthetic details). Its low solubility in common organic solvents
facilitates encapsulation inside the SWNTs thanks to
solvophobic effects. Metallic SWNTs with diameter from 1.6 to
[
7a, 8]
covalent bonds to the walls of CNTs
provides remarkable
stability but at the expense of substantial distortion of the
nanotubes’ 1D structure. On the other hand, non-covalent
2.2 nm (length 3−30 µm, 99% purity) were used for the salt
[
9]
[15]
derivatives traditionally mediated via van de Waals interactions
with the outer surface of the SWNTs, preserve the 1D structure
but are typically labile under external manipulation.
encapsulation in this study.
A schematic illustration of Viol
encapsulation in a 1.8 nm-wide metallic carbon nanotube is
shown in Figure 1b.
An interesting alternative is the noncovalent modification to
form rotaxane-like structures, in which macrocycles are clipped
around the SWNTs to yield mechanically interlocked derivatives
[
10]
of SWNTs (MINTs).
MINTs show extreme thermal stability
because the macrocycles cannot be separated from the SWNTs
without breaking a covalent bond. A final possibility is to
introduce molecules inside the cavities of the SWNTs via
endohedral encapsulation, which also results in particularly
[
11]
stable noncovalent derivatives.
In fact, the three distinctive
characteristics of the mechanical bond, namely stability,
topology and dynamic properties are present in endohedral
[
12]
derivatives of carbon nanotubes (X@SWNTs).
As an
additional advantage, the endohedral modification of SWNTs
also keeps the external SWNT surface free for interaction with
the surroundings or even for further chemical modification.
Figure 1. (a) Chemical structure of 1,1'-didodecyl-4,4'-bipyridinium
dihexafluorophosphate (Viol). (b) Model illustration of Viol inside a metallic
6
SWNT of 1.8 nm diameter. The PF anions are drawn inside the nanotube, but
since they are not clearly visible in the AC-HRSTEM images (see below) they
could potentially be outside.
[
a]
b]
Dr. B. Nieto-Ortega, J. Villalva, M. Vera-Hidalgo, Dr. E. Burzurí,
Prof. E. M. Pérez
IMDEA Nanoscience,
Commercial SWNTs are end-closed and therefore need to
be opened as a previous step to encapsulate the organic salt. In
Ciudad Universitaria de Cantoblanco, c/Faraday 9, 28049 Madrid,
Spain
o
short, the SWNTs were opened by heating them in air at 400 C
E-mail: emilio.perez@imdea.org; enrique.burzuri@imdea.org;
for 3 h up to a total weight loss of 20%. Spurious catalytic
nanoparticles were also removed in the process. The powder
[
Prof. L. Ruiz-González
Departamento de Química Inorgánica,
Universidad Complutense de Madrid, Madrid, Spain
o
obtained was annealed at 800 C for 1 hour in vacuum to
remove any functional groups, which can block the SWNT
opened ends. Opened SWNTs are hereafter labelled as
oSWNTs as opposed to pristine, end-closed SWNTs.
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201705258
COMMUNICATION
Encapsulation of the Viol into the oSWNTs was performed
~15% with respect to Viol-SWNT reference sample. This
corresponds to the presence of 1 organic salt molecule every
250-300 carbon atoms of oSWNT.
following the procedure described by Yanagi et al for similar
[
15c, 15d]
molecules.
dissolved in N,N-dimethylformamide (DMF) and the oSWNTs
7 mg) were added to the solution. The mixture was refluxed
overnight under N atmosphere. Thereafter the solution was
Briefly, pure Viol sample (70 mg) was
The Raman spectra of oSWNT, Viol-SWNT and
Viol@oSWNT (λexc = 785 nm) are compared in Figure 2b.
Further Raman characterization is shown in the Supporting
Information. All spectra are very similar with no increase in the
relative intensity of the D band, which confirms that the covalent
structure of the oSWNT is preserved upon functionalization. We
do not observe any significant changes in the wavenumber of
the G band upon the formation of Viol@oSWNT, either, which
suggests that doping of the SWNTs by the encapsulated Viol is
not significant in the ground state. The radial breathing modes
(
2
filtered and washed with DMF several times to remove any non-
encapsulated Viol. We call the complexes produced in this way
Viol@oSWNT (‘@’ refers to filling). A reference sample was
prepared following the same procedure but using raw, end-
closed SWNTs in which the Viol cannot be encapsulated. We
call this reference complex Viol-SWNT.
(
RBMs), on the other hand, show very interesting changes. The
reference oSWNT sample shows two main RBMs, centered at
-
1
-1
1
12 cm and 144 cm , respectively. The same peaks are
observed in the spectrum of Viol-SWNT, although both are blue-
-
1
shifted by 8 cm . Both peaks are shifted in the same direction
and to the same extent, suggesting that these changes may be
due to a different degree of aggregation in the sample after the
chemical treatment. In contrast, the RBM region of
-
1
-1
Viol@oSWNT, shows three peaks, at 107 cm , 129 cm and
-
1
1
43 cm respectively. The appearance of a new RBM, together
with the redshift of the peak corresponding to the larger diameter
SWNTs, while the peak corresponding to the thinner SWNTs
stays in place, suggests that there is a significant change upon
encapsulation of Viol and that it affects the larger nanotubes to
a greater extent.
o
-1
Figure 2. (a) TGA analysis (N
2
, 10 C min ) of oSWNT (black), Viol-SWNT
blue), Viol@oSWNT (golden) and Viol (green). (b) Raman spectra
exc=785 nm) of oSWNT (black line), Viol-SWNT (blue) and Viol@oSWNT
golden).
(
(
(
λ
Figure 3. (a) Representative AC-HRSTEM image of Viol@oSWNT. Scale bar
is 2 nm. (b) Scanning Electron Microscopy (SEM) image of a Viol@oSWNT
bridging two metallic Au electrodes. Scale bar is 200 nm.
A
first indication of the encapsulation is obtained from
thermogravimetric analysis (TGA). Figure 2a presents the weight
loss curve of Viol@oSWNT sample in comparison with the pure
Viol powder, Viol-SWNT and oSWNTs. The oSWNT sample
Direct evidence for the encapsulation of Viol molecules in
does not decompose under N
sample decomposes completely at ∼470 C. In the
Viol@oSWNT sample, we observe new decomposition
2
atmosphere while the pure Viol
the oSWNTs was provided by aberration corrected high-
o
resolution transmission electron microscopy (AC-HRTEM) (see
a
[16]
SI).
An AC-HRTEM image of Viol@oSWNT is shown in
component not present in oSWNT, that appears at high
temperatures (790 ºC). We tentatively ascribe this step to the
de-encapsulation/decomposition of the Viol, as indicated by the
shift to significantly larger temperatures when compared to bare
Viol, suggesting that the organic salt is protected by the tube.
This analysis is supported by the absence of this step in the
Viol-SWNT supramolecular hybrids. Note that both the
Viol@oSWNT and the Viol-SWNTs samples show a not very
well defined weight-loss that extends from 200 to 500 ºC, which
we attribute to residual DMF and/or adsorbed Viol. The total
Viol mass loss in the Viol@oSWNT sample is around 32%,
Figure 3a. Low energy (60 keV) and dose set were used to
minimize the commonly knock-on damage in molecular
[17]
structures due to the electron beam (e-beam). Imaging at high
magnification reveals that the nanotube cavities are filled with
molecular material. Despite the good quality of the images, we
are not able to elucidate the exact disposition of our molecules
inside the carbon nanotube, due to e-beam induced Brownian
motion of the Viol guests or even to their fast decomposition
[18]
under the e-beam.
The electronic properties of Viol@oSWNT have been
measured in tens of field-effect transistor (FET)-like devices.
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201705258
COMMUNICATION
Series of 400-nm spaced source-drain electrodes are fabricated
around six orders of magnitude and remains below the noise
-
11
by optical lithography and subsequent Au evaporation on Si
level of the electronics (< 10 A). The inset in Figure 4a shows I
in a linear-scale from where Vth is obtained. The hole-carrier
depletion at positive gate voltages is a clear indicative of a p-
doped semiconductor-like behavior of the Viol@oSWNT.
Additional samples are shown in the Supporting Information.
This is in sharp contrast with the metallic transfer characteristic
of bare oSWNT, i.e. without Viol molecules, where only a slight
gate dependence is observed. The encapsulation of Viol
molecules therefore tunes the electronic structure of the tubes
from metallic to semiconductor. In other words, a gap in the
band structure of the tubes is open. A similar effect has been
observed in metallic SWNT doped by boron/nitrogen substitution
substrates coated with 300 nm of SiO
are connected to common Au pad so that tens of
Viol@oSWNT FETs can be electrically probed simultaneously
see scheme of the multielectrode device in the Supporting
2
. Tens of these electrodes
a
(
Information). Viol@oSWNT, Viol-SWNT and oSWNT are
trapped and aligned between the electrodes by ac-field
[
19]
dielectrophoresis.
In short, an ac-electric field is applied
tetrachloroethane
between the electrodes immersed in
a
solution containing a dispersion of the nanotubes sample.
Voltage, ac-frequency and time parameters are optimized to
maximize the yield of a single tube per electrode pair (see
Supporting Information). Figure 3b shows a representative
Scanning Electron Microscopy (SEM) image of one of the
devices. The two electrodes are bridged by Viol@oSWNT that is
visible thanks to the enhanced apparent diameter provided by
[
21]
of carbon atoms
and has been proposed for tubes modified
[
22]
with molecules in supramolecular configuration. However, the
first geometry dramatically changes the composition of the tubes
whereas the second is not stable under external manipulation of
the devices. In contrast, note that several Viol@oSWNT (of the
order of 10) are probed simultaneously in the same
multielectrode FET. For the device to be depletable with gate, all
the connected nanotubes must be semiconducting. The
presence of one or several metallic tubes linking a pair of
electrodes would result in a residual current at positive Vg that
would mask the semiconducting behavior. This is actually the
case in a few devices where the spurious metallic nanotubes
could be controllably burned out. The encapsulated geometry is
therefore rather homogeneous (as seen in the TEM images in
Figure 3a), robust to external manipulation like washing, and
keeps the SWNT surface clean for the attachment of functional
molecules for the fabrication of more complex devices.
[
20]
voltage contrast with the substrate.
The analysis of the transfer characteristic in Figure 4a
6
shows an on-off current ratio of around Ion/Ioff = 10 and a FET
2
mobility µ ≈ 600 cm /Vs (See Supporting Information for details).
These values are comparable or better than most reported for
[
23]
semiconducting SWNTs functionalized with molecules,
indicating that the opening of band gap by the ‘soft’
a
encapsulation of molecules preserves the transport properties of
the tubes. The p-doped character of the device could be
2
+
explained by the strong electron affinity of the V molecules but
it could also be associated to the typically lower work functions
[
24]
in graphite-like materials compared to gold. As a sanity check,
the same experimental process, including a thorough cleaning of
the device, has been reproduced for the supramolecular Viol-
SWNT. Only metallic behavior has been observed in the devices
even after controlled burning of some metallic tubes (see Figure
Figure 4. (a) Transfer characteristics of Viol@oSWNT (golden), Viol-SWNT
blue) and bare oSWNT (black) FET devices measured at Vsd = 0.5 V. Clear p-
4
a). The electronic structure of the SWNT is apparently less
(
6
sensitive to supra Viol or, alternatively, the molecules are
washed away in the preparation of the devices.
doped semiconducting behavior with 10 on-off ratio can be observed for
Viol@oSWNT. In contrast, Viol-SWNT and oSWNT FETs show no gate
dependence as expected in metals. The estimated carrier mobility in
Figure 4b shows the I-V characteristics measured in the
2
Viol@oSWNT is µ ≈ 600 cm /(Vs). (b) Current I - Voltage V characteristics
same Viol@oSWNT device at different V
forward bias conditions (Vsd > 0) the current rapidly increases
and saturates at increasingly higher I for increasing V . Under
low reverse bias conditions (-1 < Vsd < 0) the current remains
blocked at |I| ≈ 27 nA. Thereafter |I| abruptly increases and is
modulated by V . This electrical response is characteristic of a
g
around Vth. Under
measured in the same device at different V
g g g
(from V = 0 V (purple) to V = -
1
2.5 V (red) with ΔV =1.25 steps). The electrical response is characteristic of
g
two back to back Schottky diodes generated at the interface between the
metallic electrodes and the Viol@oSWNT. [Inset] Schematic circuit
representing a gold|Viol@oSWNT|gold FET mediated by Schottky barriers.
g
l
g
two back-to-back diodes circuit as sketched in Figure 4b. The
low forward voltage drop (~0.1 V) and the relative high current
Figure 4a shows the transfer characteristics of three multi-
electrode devices made of Viol@oSWNT (golden), Viol-SWNT
l
leakage I point to two Schottky diodes generated at the interface
(
blue) and oSWNT (black). The source-drain current
measured as a function of a gate voltage V applied to the Si
substrate while the source-drain bias voltage is fixed to Vsd
I is
barrier between the metallic Au electrodes and the
semiconducting Viol@oSWNT. The low forward voltage drop is,
in addition, characteristic of p-doped based Schottky diodes, in
agreement with the transfer characteristic in Figure 4(c). This
diode-like behavior is a further proof of the rather homogeneous
g
=
-
5
0
.5 V. The current saturates to almost 10 A at negative V
g
.
Above a threshold voltage Vth = -3 V, the current abruptly drops
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201705258
COMMUNICATION
semiconducting behavior of the Viol@oSWNT when compared
with the linear and symmetric I-V curves obtained in oSWNT and
Viol-SWNT junctions, as expected for metal-metal contacts (see
Figure S4 in the Supporting Information).
[4]
a)H. Kataura, Y. Kumazawa, Y. Maniwa, I. Umezu, S. Suzuki,
Y. Ohtsuka, Y. Achiba, Synth. Met. 1999, 103, 2555-2558;
b)M. S. Dresselhaus, G. Dresselhaus, R. Saito, A. Jorio, Phys.
Rep 2005, 409, 47-99.
a)R. Saito, A. R. T. Nugraha, E. H. Hasdeo, N. T. Hung, W.
Izumida, Top. Curr. Chem. 2017, 375, 7; b)T. W. Odom, J.-L.
Huang, P. Kim, C. M. Lieber, Nature 1998, 391, 62-64; c)C. N.
R. Rao, B. C. Satishkumar, A. Govindaraj, M. Nath,
ChemPhysChem 2001, 2, 78-105; d)E. Bekyarova, M. E. Itkis,
N. Cabrera, B. Zhao, A. Yu, J. Gao, R. C. Haddon, J. Am.
Chem. Soc. 2005, 127, 5990-5995.
[
5]
Several mechanisms may contribute to the band gap
opening. One could be the local field induced by the cation, or
alternatively the partial hybridization of the molecular orbitals
[
25]
with the band structure of the tube.
Additionally, mechanical
deformations induced by molecules in SWNTs could modify their
electronic bands. To understand the role of the charges, we
synthesized a neutral structural analogue of Viol featuring
alkylated biphenyl moieties, Biphenyl@oSWNT system. The
preliminary electronic characterization (see Supporting
Information) indicates that although certain semiconducting-like
behavior is observed, the on/off ratios are drastically reduced
pointing to an important role of the cation charge. A more
[
[
6]
7]
a)G. Guanghua, Ç. Tahir, A. G. William, III, Nanotechnology
1
998, 9, 184; b)N. Khandoker, S. C. Hawkins, R. Ibrahim, C.
P. Huynh, F. Deng, Procedia Eng. 2011, 10, 2572-2578.
a)P. Singh, S. Campidelli, S. Giordani, D. Bonifazi, A. Bianco,
M. Prato, Chem. Soc. Rev. 2009, 38, 2214-2230; b)A. Hirsch,
Angew. Chem. Int. Ed. 2002, 41, 1853-1859.
J. L. Bahr, J. M. Tour, J. Mater. Chem. 2002, 12, 1952-1958.
a)Y.-L. Zhao, J. F. Stoddart, Acc. Chem. Res. 2009, 42, 1161-
[
[
8]
9]
1
171; b)G. Gavrel, B. Jousselme, A. Filoramo, S. Campidelli,
thorough study will be the subject of
manuscript.
a future follow-up
in Making and Exploiting Fullerenes, Graphene, and Carbon
Nanotubes (Eds.: M. Marcaccio, F. Paolucci), Springer Berlin
Heidelberg, Berlin, Heidelberg, 2014, pp. 95-126.
In conclusion, Viol molecules were successfully
encapsulated in SWNTs. The filling of the carbon nanotubes
was confirmed by TGA, Raman spectroscopy, and crucially by
AC-HRTEM. The encapsulation tunes the electronic properties
of the nanotube-based FET devices, from metallic to high-quality
semiconductor. Such tuning is not observed in analogous
supramolecular derivatives. The resulting back-to-back diode
circuits could be exploited as tunable rectifiers or current limiters
to protect more complex SWNT or molecule-based electronic
circuits.
[
[
10] a)S. Leret, Y. Pouillon, S. Casado, C. Navio, A. Rubio, E. M.
Perez, Chem. Sci. 2017, 1927-1935; b)A. de Juan, M. Mar
Bernal, E. M. Pérez, ChemPlusChem 2015, 80, 1153-1157;
c)A. de Juan, Y. Pouillon, L. Ruiz-González, A. Torres-Pardo,
S. Casado, N. Martín, Á. Rubio, E. M. Pérez, Angew. Chem.
Int. Ed. 2014, 53, 5394-5400; d)A. Lopez-Moreno, E. M.
Perez, Chem. Comm. 2015, 51, 5421-5424.
11] a)D. A. Britz, A. N. Khlobystov, Chem. Soc. Rev. 2006, 35,
6
37-659; b)J. Campo, Y. Piao, S. Lam, C. M. Stafford, J. K.
Streit, J. R. Simpson, A. R. Hight Walker, J. A. Fagan,
Nanoscale 2016, 1, 317-324; c)R. Kitaura, N. Imazu, K.
Kobayashi, H. Shinohara, Nano Letters 2008, 8, 693-699; d)M.
Hart, E. R. White, J. Chen, C. M. McGilvery, C. J. Pickard, A.
Michaelides, A. Sella, M. Shaffer, C. G. Salzmann, Angew.
Chem. Int. Ed., n/a-n/a.
Acknowledgements
[
[
12] A. de Juan, E. M. Perez, Nanoscale 2013, 5, 7141-7148.
13] a)C. L. Bird, A. T. Kuhn, Chem. Soc. Rev. 1981, 10, 49-82;
b)M. Suzuki, N. D. Morris, T. E. Mallouk, Chem. Comm. 2002,
1534-1535; c)P. M. S. Monk, The viologens: physicochemical
properties, synthesis, and applications of the salts of 4,4'-
bipyridine, Wiley, England, 1998.
We thank Dr. Andrés Castellanos-Gómez (Instituto de Ciencia
de Materiales de Madrid) for fruitful discussions. We thank Dr.
Daniel Granados and Dr. Manuel Rodriguez for the help with the
nanofabrication. We thank Dr. Prabhash Mishra for initial studies
on dielectrophoresis. The research leading to these results has
received funding from the European Research Council under the
European Union’s Seventh Framework Programme (FP/2007-
[
[
14] S. M. Kim, J. H. Jang, K. K. Kim, H. K. Park, J. J. Bae, W. J.
Yu, I. H. Lee, G. Kim, D. D. Loc, U. J. Kim, E.-H. Lee, H.-J.
Shin, J.-Y. Choi, Y. H. Lee, J. Am. Chem. Soc. 2009, 131,
327-331.
15] a)S. Cambré, J. Campo, C. Beirnaert, C. Verlackt, P. Cool, W.
Wenseleers, Nat Nano 2015, 10, 248-252; b)P. Horn, M.
Kertesz, J. Phys. Chem. C. 2010, 114, 12139-12144; c)K.
Yanagi, K. Iakoubovskii, H. Matsui, H. Matsuzaki, H. Okamoto,
Y. Miyata, Y. Maniwa, S. Kazaoui, N. Minami, H. Kataura, J.
Am. Chem. Soc. 2007, 129, 4992-4997; d)K. Yanagi, Y.
Miyata, H. Kataura, Adv. Mater. 2006, 18, 437-441.
2
013)/ERC Grant Agreements No. 307609 (ERC Starting Grant
MINT“). We thank the Ministerio de Economía, Industria y
Competitividad (Spain) (CTQ2014-60541-P and JdC-2015-
3531). E.B. thanks the AMAROUT-II fellowship (Marie Curie
“
2
Action, FP7-PEOPLE-2011-COFUND). We thank National
Centre for Electron Microscopy (ICTS-CNME, Universidad
Complutense) for aberration corrected electron microscopy
facilities
[
16] a)T. Zoberbier, T. W. Chamberlain, J. Biskupek, N.
Kuganathan, S. Eyhusen, E. Bichoutskaia, U. Kaiser, A. N.
Khlobystov, J. Am. Chem. Soc. 2012, 134, 3073-3079; b)T. W.
Chamberlain, J. C. Meyer, J. Biskupek, J. Leschner, A.
Santana, N. A. Besley, E. Bichoutskaia, U. Kaiser, A. N.
Khlobystov, Nat. Chem. 2011, 3, 732-737; c)J. H. Warner, Y.
Ito, M. H. Rümmeli, B. Büchner, H. Shinohara, G. A. D. Briggs,
ACS Nano 2009, 3, 3037-3044.
Keywords: nanotubes • viologen • encapsulation • electronic
band gap • FET
[
[
17] R. F. Egerton, P. Li, M. Malac, Micron 2004, 35, 399-409.
18] T. W. Chamberlain, J. Biskupek, S. T. Skowron, P. A. Bayliss,
E. Bichoutskaia, U. Kaiser, A. N. Khlobystov, Small 2015, 11,
[
[
1]
2]
a)R. H. Baughman, A. A. Zakhidov, W. A. de Heer, Science
002, 297, 787-792; b)Z. Liu, L. Jiao, Y. Yao, X. Xian, J.
Zhang, Adv. Mater. 2010, 22, 2285-2310.
2
6
22-629.
a)Y. He, H. Jin, S. Qiu, Q. Li, Chem. Comm. 2017, 53, 2934-
[
19] a)X. Q. Chen, T. Saito, H. Yamada, K. Matsushige, Appl.
Phys. Lett. 2001, 78, 3714-3716; b)L. A. Nagahara, I. Amlani,
J. Lewenstein, R. K. Tsui, Appl. Phys. Lett. 2002, 80, 3826-
2
937; b)C. Chen, C. Song, J. Yang, D. Chen, W. Zhu, C. Liao,
X. Dong, X. Liu, L. Wei, N. Hu, R. He, Y. Zhang, Nano Energy
017, 32, 280-286; c)J. Wan, Y. Xu, B. Ozdemir, L. Xu, A. B.
2
3
828; c)K. Yamamoto, S. Akita, Y. Nakayama, J. Phys. D:
Sushkov, Z. Yang, B. Yang, D. Drew, V. Barone, L. Hu, ACS
Nano 2017, 11, 788-796.
Appl. Phys. 1998, 31, L34-L36.
[
[
20] T. Brintlinger, Y.-F. Chen, T. Dürkop, E. Cobas, M. S. Fuhrer,
J. D. Barry, J. Melngailis, Appl. Phys. Lett. 2002, 81, 2454-
[
3]
a)E. K. Wujcik, C. N. Monty, Wiley Interdiscip. Rev. Nanomed.
Nanobiotechnol. 2013, 5, 233-249; b)G. Bardi, in
Nanomedicine and the Nervous System, Science Publishers,
2
456.
21] Z. Xu, W. Lu, W. Wang, C. Gu, K. Liu, X. Bai, E. Wang, H.
2
012, pp. 3-16.
Dai, Adv. Mater. 2008, 20, 3615-3619.
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201705258
COMMUNICATION
[
[
22] A. K. Manna, S. K. Pati, Nanoscale 2010, 2, 1190-1195.
23] a)V. Derenskyi, W. Gomulya, W. Talsma, J. M. Salazar-Rios,
M. Fritsch, P. Nirmalraj, H. Riel, S. Allard, U. Scherf, M. A. Loi,
Adv. Mater. 2017, 1606757; b)C. Biswas, S. Y. Lee, T. H. Ly,
A. Ghosh, Q. N. Dang, Y. H. Lee, ACS Nano 2011, 5, 9817-
9
823.
24] S. J. Tans, A. R. M. Verschueren, C. Dekker, Nature 1998,
93, 49-52.
25] O. O. Ogunro, C. I. Nicolas, E. A. Mintz, X.-Q. Wang, ACS
Macro Lett. 2012, 1, 524-528.
[
[
3
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201705258
COMMUNICATION
Entry for the Table of Contents
Layout 2:
COMMUNICATION
B. Nieto-Ortega J. Villalva, M. Vera-
Hidalgo, L. Ruiz-González, E. Burzurí*
and E. M. Pérez*
Page No. – Page No.
Band gap opening in metallic single-
walled
carbon
nanotubes
by
encapsulation of an organic salt
Bandgap, be opened! The encapsulation of viologen salts within the tube tunes the electronic band gap
of the tube from metallic to a high-quality semiconductor.
This article is protected by copyright. All rights reserved.