Johnson Space Center May 18, 2010

Single-walled Carbon Nanotube (SWCNT) Carbon Nanostructures C 60 (Buckminsterfullerene)

taken from 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 / cm 3 Tensile strength:  60 GPa  50 x higher than steel Persistence length:  50  m  very rigid Surface area: > 1000 m 2 / 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 as complex mixtures

van Hove singularities Electronic states of a semiconducting SWCNT E 11 E 22 E 33

Constructing nanotubes from a graphene sheet Roll-up vector Roll-up angle Nanotube axis

E 11 emission E 22 absorption Spectrofluorimetry of semiconducting SWCNTs hole e-e-

Spectral transitions mapped to structures

Application 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, focusing excitation lasers near-IR imager InGaAs 2-D array (82,000 pixels) inverted microscope sample near-IR spectrograph with 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

Emission Intensity Compress Stretch Shift in band gap Compress Stretch Axial deformation changes the nanotube’s electronic structure and causes spectral shifts

Extension Compression Strain jig for microscope stage SWCNTs in PMMA film fused to PMMA bar Strain gauge mounted on sample film

to strain reader resistive strain gauge PMMA beam spin coated nanotube/PMMA film micrometer for pushing swing arm swing arm 2 cm built by Pavel Nikolaev and Sivaram Arepalli PMMA beam stationary pins moving pins side view 4-point bending jig for applying controlled strain

Polarization reveals nanotube orientation

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

2  m 0.6% strain 1% strain 0% strain Spectral shifts vary within a single nanotube in PMMA

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

interrogation laser near-IR imager InGaAs 2-D array (82,000 pixels) Non-invasive sensing of structural strain Spectra near-IR collection optics & spectrometer composite with sorted SWCNTs

(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