CEAC06, Zürich 11.07.2006 Achim Hartschuh, Nano-Optics München 1 High-Resolution Near-Field Optical Spectroscopy of Carbon Nanotubes Achim Hartschuh, Huihong Qian Tobias Gokus, Department Chemie und Biochemie, University of München Neil Anderson, Lukas Novotny The Institute of Optics, University of Rochester, Rochester, NY Alfred J. Meixner Institute of Physical and Theoretical Chemistry, University of Tübingen
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CEAC06, Zürich 11.07.2006 Achim Hartschuh, Nano-Optics München 1
High-Resolution Near-Field Optical
Spectroscopy of Carbon Nanotubes Achim Hartschuh, Huihong Qian
Tobias Gokus,Department Chemie und Biochemie,
University of München
Neil Anderson, Lukas NovotnyThe Institute of Optics, University of Rochester,
Rochester, NY
Alfred J. MeixnerInstitute of Physical and Theoretical Chemistry,
University of Tübingen
CEAC06, Zürich 11.07.2006 Achim Hartschuh, Nano-Optics München 2
Single-walled Carbon Nanotubes
Graphene sheet + roll up single-walled carbon nanotube
1D crystal:
• Diameter ~ 0.5-3 nm
• Length up to mm
• Different structures (Diameter, chirality) (n,m)
• Structure determines properties (n-m) mod 3 = 0
metallic else semicond.
S. Maruyama, http://chishiki.t.u-okyo.ac.jp/~maruyama/index.html
CEAC06, Zürich 11.07.2006 Achim Hartschuh, Nano-Optics München 26
Signal Enhancement
Senhanced ~ f2
Raman enhancement
500 nm
Far-field Raman ~ 2000 counts/s
Near-field Raman ~ 4000 counts/s
Raman-enhancement ~ 6000 / 2000
= 3
Senhanced ~ f4
PL enhancement
500 nm
No far-field PL < 200 counts/s
Near-field PL ~17000 counts/s
PL-enhancement >17000 / 200
= 85
PL quantum yield must be increased by tip (SEF)
CEAC06, Zürich 11.07.2006 Achim Hartschuh, Nano-Optics München 27
Near-field Interactions
Uncertainty relation:Diffraction limit for propagating waves:
2ΔkΔx x 10.01nmλ
2πk
k-vectors of tip enhanced fields extend through BZ !
selection rules for optical transitions?
1x 1nm10nm5
2πΔx
2πΔk
High resolution provided by evanescent fields that have higher k-vectors:
Nanotubes:
1
t
r|| 1nm
d3
2dk
CEAC06, Zürich 11.07.2006 Achim Hartschuh, Nano-Optics München 28
Summary
High-resolution optical microscopy of carbon High-resolution optical microscopy of carbon nanotubes using a sharp laser-illuminated metal tipnanotubes using a sharp laser-illuminated metal tip
• PL and Raman spectroscoy and imaging• Spatial resolution < 15 nm• Signal enhancement
ResultsResults• Resolved RBM variations (IMJ) on the nanoscale• Non-uniform emission energies that result from local
variations of dielectric environment• Strongly confined emission signals bound excitons?• PL-Quantum yield can be enhanced by metal structures
CEAC06, Zürich 11.07.2006 Achim Hartschuh, Nano-Optics München 29