taken from http://www.photon.t.u-tokyo.ac.jp/~maruyama/wrapping.files/frame.html
Rolling up graphene to make a SWCNT
armchair ( = 30°)
zigzag ( = 0°)
intermediate (0 30°)
zigzag
Many SWCNT structures exist( different diameters and angles )
Typical diameter: 0.6 – 3 nm
Typical lengths: 100 – 10,000 nm large aspect ratios
Density: 1.4 g / cm3
Tensile strength: 60 GPa 50 x higher than steel
Persistence length: 50 m very rigid
Surface area: > 1000 m2 / g (every atom on surface)
Electrical transport: metallic or semiconducting
Optical spectra: intense -* bands, direct band-gap semiconductors
SWCNT Properties
Even pure single-walled samples contain:
• many diameters
• many chiral angles
• many lengths (no effect on electronic structure)
• bundles of tubes bound by van der Waals forces
Nanotubes are produced ascomplex mixtures
• Add small amounts of SWCNTs to polymers to make composites with improved mechanical strength, thermal conductivity, and/or electrical conductivity
• SWCNTs can retain their near-IR fluorescence in the composite. This allows in situ monitoring of:
dispersion (fluorescence microscopy) orientations (polarized fluor. microscopy)
axial strains (spectral shifts)
The Basic Idea
polarization control, focusingexcitation lasers
near-IR imager InGaAs 2-D array
(82,000 pixels)
inverted microscope
sample
near-IR spectrographwith InGaAs 1-D array
Apparatus for near-IR fluorescence microscopy
Tsyboulski, et al. Nano Lett. 5, 975 (2005)
Images Spectra
Em
issi
on I
nten
sity
Compress
Stretch
Shift in band gap
Compress
Stretch
Axial deformation changes the nanotube’selectronic structure and causes spectral shifts
Extension Compression
Strain jig for microscope stage
SWCNTs in PMMA film fused to PMMA barStrain gauge mounted on sample film
to strain reader
resistive strain gauge
PMMAbeam
spin coatednanotube/PMMA filmmicrometer
for pushing swing arm
swing arm2 cm
built by Pavel Nikolaev and Sivaram Arepalli
PMMAbeam
stationary pins
moving pins
side view
4-point bending jig for applying controlled strain
(8,7)
Wavenumbers (cm-1)
7600 7800 8000 8200
Nor
m. e
mis
sion
inte
nsity
0.0
0.2
0.4
0.6
0.8
1.0
1.2 0.8%0.0%-0.8% strain
Single SWCNT spectra
(8,7) nanotube
• are linear with strain
• reverse sign for mod 1 and mod 2 species
• depend on projection of strain along nanotube axis
• depend on nanotube roll-up angle
Theory predicts that shifts in SWCNT emission peaks
0.6% strain
Wavelength (nm)
900 1000 1100 1200 1300
Nor
mal
ized
Em
issi
on I
nten
sity
-0.2
0.0
0.2
0.4
0.6
0.8
1.0 End 1MiddleEnd 2
2 m
0.6%strain
1% strain
0%strain
Spectral shifts vary within a single nanotube
in PMMA
Strain (%)
0.0 0.2 0.4 0.6 0.8 1.0 1.2
E11
(cm
-1)
-1000
-800
-600
-400
-200
0 End 1MiddleEnd 2
Middle shows linear behavior
Ends slip
Ends slip while the middle adheres
Copyright © 2007 Applied NanoFluorescence, LLC
Quantitatively deduce nanotube strain from spectral shifts
Measure the limits beyond which nanotube loses adhesion to surrounding polymer host
For long nanotubes, observe slipping of ends while center remains adherent
Method should provide important insights into interfacial load transfer at the molecular level
Single-SWCNT strain studies
Goals
• Further refine methods for monitoring nanotube dispersion, orientation, and load transfer from host
• Use near-IR fluorescence spectroscopy to study load transfer in single nanotubes and variations within and among tubes
• Develop a remote spectroscopic monitoring system to measure strain in structural components made from SWCNT composites
interrogationlaser
near-IR imager InGaAs 2-D array
(82,000 pixels)
Non-invasive sensing of structural strain
near-IR collection optics & spectrometer
composite with sorted SWCNTs
Den
sity
(g/
mL)
1 .0 6
1 .0 7
1 .0 8
1 .0 9
1 .1 0
1 .1 1
7 ,3
6 ,5
8 ,3
7 ,5
7 ,6
U n s o rte d H iP c o
a b c d6 ,4
W a v e le n g th (n m )9 0 0 1 0 0 0 1 1 0 0 1 2 0 0
Nor
mal
ized
em
issi
on in
tens
ity
0 .0
0 .2
0 .4
0 .6
0 .8
1 .0
1 .2
7 ,36 ,58 ,3 7 ,5 7 ,66 ,4 9 ,1
6 ,4
6 ,5
8 ,3
7 ,57 ,6
N a n o tu b e d ia m e te r (n m )0 .7 0 .8 0 .9 1 .0
Refractive index
1 .3 5 2
1 .3 5 6
1 .3 6 0
1 .3 6 4
1 .3 6 8
7 ,3
8 ,7
e
1 0 ,2
W a v e le n g th (n m )1 0 0 0 1 2 0 0 1 4 0 0
Absorbance (a.u.)
9 ,28 ,4
D e p th in c e n trifu g e tu b e (m m )
5 1 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5 5 0
Refractive index
1 .3 4
1 .3 6
1 .3 8
1 .4 0
1 .4 2
P o s t N o n lin e a r D G U
P o s t L in e a r D G U
Den
sity
(g/
mL)
1 .0 0
1 .0 5
1 .1 0
1 .1 5
1 .2 0
1 .2 5
1 .3 0
fN a n o tu b e e n a n tio m e rs
(n,m) sorting of SWCNTs by nonlinear density gradient ultracentrifugation
Separated fractions contain robust near-IR fluorophores with distinct emission peaks
Ghosh, Bachilo, and Weisman, Nature Nanotechnology, published online May 9, 2010