Encapsulation and physical properties of photoactive molecules in SWNTs

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Encapsulation and physical properties of
photoactive molecules in SWNTs
M. A. Loi Zernike Institute for Advanced
Materials University of Groningen, The
Netherlands M.A.Loi_at_rug.nl
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Summary

• Hybrid SWNTs for nanometric optoelectronic
  devices
• nT_at_SWNT
• Synthesis
• Structure
• Optical properties
• Band structure
• Conclusions

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Nano Optoelectronic Device

• Nanometric ambipolar light emitting transistor

J. Chen et al., Science 310, 1171
(2005) Review Ph. Avouris et al., Nature
Nanotechnology 2, 605 (2007)
Ballistic transport - no carrier scattering
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Tunable Nano-Device

• Nano-optoelectronic devices!

Review Ph. Avouris et al., Nature Nanotechnology
2, 605 (2007)
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Tuning the optical properties

• nano-hybrid systems composed of a photoactive
  organic semiconductor (pea)
• and a SWNT (pod)
• hybrid nano-objects with tunable functionality
• towards
• nano-optoelectronics devices

Towards tunable nano-optoelectronic devices
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The peas
Oligothiophene series Quarthiophene
4T, Pentathiophene 5T Sexithiophene 6T
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SWNT purification

• SWNT
• Arc-discharge using Y-Ni catalyst
• Purified and annealed
• Diameter 1.2 1.4 nm

• Purification
• Air oxidation (325C, 420C)
• Acid treatment (HCl)
• Annealing (1100C)

To have open ends
Air oxidation Acid treatment Final annealing
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Thiophenes_at_SWNT

• SWNT sonicated in toluene before encapsulation
  (increases yield)
• Encapsulation through gas phase (sealed tube, T
  gt Mp, 10-3 Torr, 3 days)
• Extensive washings to remove non-encapsulated
  molecules (toluene)
• washing solvent checked with UV VIS
• Control experiment SWNT oligothiophene in
  solution - sonicated

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Thiophenes_at_SWNT
HR-TEM-images
TEM image simulation. Edge-on molecules
TEM image simulation. Flat molecules
pristine tubes
6T_at_SWNT
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Thiophenes_at_SWNT
Raman spectrum of peapods and SWNT exc. 488 nm
New peak
New peak

• Encapsulation
• New peak at 1504 cm-1, 1501 cm-1, 1499 cm-1 for
  4T, 5T, 6T_at_SWNT
• - Control neither shifts nor new peaks

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Thiophenes_at_SWNT
Raman spectra of peapods and SWNT exc. 633 nm

• Good agreement for 2 different kind of SWNT
• Similar results for 2 laser lines (488 and 633
  nm)
• No sign of dimerization inside the SWNT
• No charge transfer (nT in neutral form)
• Shifts due to the confinement 6T
• (698?704 cm-1 CSC deformation,
• 1050 ?1045 cm-1 CH bend, 1459 ?1457 cm-1 CC
  stretch)
• No possible a quantification of 4T, 5T and 6T
  inside SWNT from the Raman because of the change
  of the resonance in the 3 oligomers

CC stretching
CSC
CH bending
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Thiophenes_at_SWNT
RBM of peapods and SWNT exc488 and exc. 633 nm
The RBM shift for both laser lines with the
increasing of the molecule lenght
Radial
Similarly reported by K. Yanagi et al., Adv. Mat.
18, 437 (2006)
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Thiophenes_at_SWNT
Absorption spectra

• Encapsulation
• New band red shifted and broadened
• Absorbance increases with oligothiophene size
• Concentration of oligothiophenes inside SWNT
• C(4T)0.03 M, C(5T) 0.17 M, C(6T) 0.35 M

• Conformation 6T have more trans-form
  (p-conjugation) easier to encapsulate and more
  stabilised inside the SWNT than 4T.

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Thiophenes_at_SWNT
Photoluminescence spectra

• The peapods nT_at_SWNT show an efficient
  photoluminescence emission in the visible
• Shape of the nT_at_SWNT spectra similar to the one
  of the isolated molecules.

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Thiophenes_at_SWNT
Time resolved photoluminescence

• 4T_at_SWNT shows the same photoluminescence lifetime
  than 4T in solution

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Thiophenes_at_SWNT
Time resolved photoluminescence

• Also 5T_at_SWNT has the same photoluminescence
  lifetime than the isolated 5T

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Thiophenes_at_SWNT
Time resolved photoluminescence

• 6T_at_SWNT shows a decay time monoexponential and 80
  ps shorter than the one of the isolated molecule

t813 ps
t734 ps
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Thiophenes_at_SWNT
Calculations Electronic bands
poly-thiophene_at_(n,0)

• The pea and the pod are bound by van Der Waals
  interactions

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Thiophenes_at_SWNT
Calculations

• Electronic bands and optical transitions
  nT_at_(12,0)

2T_at_(12,0)
4T_at_(12,0)
6T_at_(12,0)
poly-T_at_(12,0)
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Thiophenes_at_SWNT
Calculations

• Electronic bands nT_at_(13,0)

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Conclusions

• Successful encapsulation of thiophenes_at_SWNT
• TEM imaging of the nano-hybrids
• Efficient photoluminescence emission in the
  visible spectral range
• New optical transitions allowed
• Van der Waals type bonding between pea and pod
• Interactions depend on the size of the molecule
  and tube diameter

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Aknowledgements
NaPhoD Team Fabrizio Cordella Jia Gao University
of Groningen Pascal Blondeau Enzo
Menna Università di Padova, Italy Barbora
Bártová Feng Tian Cécile Hébert EPFL Lausanne,
Switzerlad
Matus Milko Claudia Ambrosch-Draxl University
of Leoben, Austria
Financial support
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NaPhoD Summer School
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Thank you for your attention