Johnson Space Center May 18, 2010

Single-walled Carbon Nanotube(SWCNT)

Carbon Nanostructures

C60

(Buckminsterfullerene)

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

van Hovesingularities

Electronic states of a semiconducting SWCNT

E11 E22 E33

Constructing nanotubes from a graphene sheet

Roll-up vector

Roll-up angle

Nan

otu

be

axis

E11

emissionE22

absorption

Spectrofluorimetry of semiconducting SWCNTs

hole

e-

Spectral transitions mapped to structures

ApplicationApplication

SWCNT Composites

• 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

Fluorescence from a Single Nanotube

(7,5)

160 m field

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

Polarization reveals nanotube orientation

(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

Peak position shifts linearly as host is strained

Spectral shifts agree with simple theory

Spectral shift is linear until …

it splits into 2 peaks!

Part of one nanotube slipping

Strain data for a single SWCNT in Epon 862 epoxy

(10,2) nanotube in PFO

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

References

O’Connell et al., Science 297, 593 (2002)Bachilo et al., Science 298, 2361 (2002)Bachilo and Weisman, Nano Letters 3, 1235 (2003)Tsyboulski et al., Nano Letters 5, 975 (2005)Leeuw et al. Nano Letters 8, 826 (2008)Ghosh et al., Nature Nanotechnology, web-posted May 9, 2010