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Metallic-Enriched Single-Walled Carbon Nanotubes for Electronics Applications. Erik H. Hároz NASA-Rice Nanotechnology Forum May 18, 2010. a 2. Single-Walled Carbon Nanotubes. a 1. ( n , m ) = (4,2). Chiral vector:. C h = n a 1 + m a 2. n – m = 3 M + q. 1) M = q = 0.

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Metallic enriched single walled carbon nanotubes for electronics applications

Metallic-Enriched Single-Walled Carbon Nanotubes for Electronics Applications

Erik H. Hároz

NASA-Rice Nanotechnology Forum

May 18, 2010

Single walled carbon nanotubes

a Electronics Applications2

Single-Walled Carbon Nanotubes


(n,m) = (4,2)

Chiral vector:

Ch = na1 + ma2

n – m = 3M + q

1) M = q = 0

Metal (Armchair)

2) M≠0,q = 0

Narrow Gap Semicond.

3) M≠0,q = ±1



Wide Gap Semicond.

Metallic carbon nanotubes
“Metallic” Carbon Nanotubes Electronics Applications

  • Metallic SWNTs can be divided into two subclasses, identifiable by their chiral indices (n,m):

    • True metallic or “armchair” nanotubes where (n-m)=0 such as the (7,7)

    • Narrow-gap semiconducting nanotubes where (n-m) = integer multiple of 3 such as the (12,6)

  • Are ballistic conductors with electrical conductivity 100x greater than copper and electron mobility 70x that of silicon. Current-carrying capacity 109 A/cm2.

  • Ideal materials for low-loss, high-capacity, power transmission cables and nanometer-sized electronics.

Tans et al., Nature, 386, (1997), 474

  • Problems studying metallic SWNTs:

  • In bulk material, theoretically, 1/3 of all possible chiralities are “metallics”. Outnumbered by semiconductors.

  • In HiPco SWNTs, E22 semiconducting transitions overlap with E11 metallic transitions.

  • Radial breathing mode of armchair SWNTs is very weak in Raman spectra as compared to other chiralities because the electron-phonon coupling being weakest for armchair SWNTs.

Solution: Make samples consisting of all “metallic” SWNTs.

Density gradient ultracentrifugation
Density Gradient Ultracentrifugation Electronics Applications



As-produced SWNTs


HiPco HPR 188.1 SWNTs suspended in 1% sodium deoxycholate (1mg/mL starting conc.)

Sonicated for about 30 min in bath sonicator, 20 hr in tip sonicator, Decant prepared using 1hr centrifugation @ 200,000g

Run in a 40-20% iodixanol gradient in 1.5% sodium dodecyl sulfate, 1.5% sodium cholate

Centrifugated for 18 hrs @ 200,000g

  • Arnold et al., Nature Nanotechnology, 1, (2006), 60

    • -Optical Absoprtion Characterization and sheet conductance measurements

  • Yanagi et al., Applied Physics Express, 1, (2008), 034003

    • -Optical Absorption & Single-line Excitation Raman characterization

  • Iijima, et al., Nano Letters, 8, (2008), 3151

    • - E-beam diffraction TEM chirality assignment of Kataura sample

Absorption spectroscopy
Absorption Spectroscopy Electronics Applications

  • Peaks correspond to absorption of light at energies corresponding to excitonic transitions of specific (n,m) species of SWNTs

  • Transitions are roughly proportional to inverse diameter but also depend on chiral angle and mod # as well.

  • Absorption is most direct optical method to measure (n,m) species populations.

  • Sharpness of features and slope of baseline qualitatively indicate degree of individuality.

  • Sharp, narrow, well-defined peaks with large absorbance in E11M region.

  • Flat, featureless section in E22S & E11S regions.

  • Overlap between E11M & E22S regions eliminated.

  • Absorption features have enhanced peak-to-valley ratios.

  • Decrease in baseline of spectrum indicates increase in degree of individuality.

  • Based on absorption peak areas, sample is 98% metallic.

x 0.1

x 2

Photoluminescence excitation spectroscopy
Photoluminescence Excitation Spectroscopy Electronics Applications

Starting SWNT material

Metallic-enriched SWNTs

  • Only individualized, wide-gap semiconducting SWNTs fluoresce in the

  • near-infrared via visible excitation.

  • Individualized, narrow-gap semiconducting SWNTs, armchair SWNTs,

  • and bundles of SWNTs containing metallics do not fluoresce.

Resonant raman spectroscopy
Resonant Raman Spectroscopy Electronics Applications

  • Resonant Raman scattering with a tunable excitation source is the only optical method able to identify all chiralities present, including the armchairs (n,n).

  • Using excitation sources including:

    • CW Ti:Sapphire laser (695-850 nm)

    • Kiton red laser dye (610-685 nm),

    • Rhodamine 6G+B laser dye (562-615 nm),

    • Ar+ laser (514.5, 501.7, 496.5, 488, 476.5, & 457.8 nm)

    • doubled CW Ti:Sapphire (500-440 nm)

    • 5 weeks and 230 spectra later….

Raman 562 670 nm
Raman (562-670 nm) Electronics Applications

Metallic-enriched HiPco

As-produced HiPco

Raman 440 500 nm
Raman (440-500 nm) Electronics Applications

Metallic-enriched HiPco

As-produced HiPco

Enrichment of armchair nanotubes
Enrichment of Armchair Nanotubes Electronics Applications

  • Probing further using Raman scattering, we find not only did we enrich in metallic nanotubes but…

  • Of those metallic species, a large majority (~50%) are armchairs (n,n).

Results summarized in Hároz et al., ACS Nano4, 1955 (2010).

Absorption of films uv vis nir
Absorption of Films: UV-vis-NIR Electronics Applications

  • 100% SWNT films produced by vacuum filtration from DGU-enriched solutions.

  • Sharp, narrow, well-defined peaks with large absorbance in E11M region.

  • Metallic features remain relatively unperturbed in film form probably due to screening.

  • Broadened, redshifted peaks in E22S & E11S regions.

Rbm raman of dgu films
RBM Raman of DGU Films Electronics Applications


514 nm excitation

Very little iodixanol

  • Enrichment results in suppression of (8,5), (9,3) & (8,2) leaves behind mostly (7,7).

  • Very little density gradient medium left.




Absorption of films terahertz
Absorption of Films: Terahertz Electronics Applications

  • THz examines optical conductivity.

  • Response thought to be due to concentration of metallic SWNTs (i.e. THz absorbance proportional to conductivity).

  • Although metallic films have lower overall optical absorption, they possess greater more metallic nanotubes.

How can these materials be used in research
How can these materials be used in research? Electronics Applications

  • In the Kono group, we are using these enriched materials to look at

    • Temp. dependent DC magneto-transport

    • Optical spectroscopy

    • Electron spin resonance

    • Ultrafast spectroscopy

      • Terahertz conductivity

      • Pump-probe

  • We are also looking at ways to scale separations using column chromatography

Armchair quantum wire program
Armchair Quantum Wire Program Electronics Applications

  • More broadly at Rice, we are engaged in trying to create macroscopic structures (films and wires) comprised of armchair nanotubes.

    • Primary question to answer:

      • While individual armchair SWNTs are excellent ballistic conductors, how about in macrostructures?

        • What dominates, tunneling barriers (i.e. variable range hopping)? Can this be overcome?

Acknowledgements Electronics Applications

  • Prof. JunichiroKono (Rice, advisor)

  • Prof. R. Bruce Weisman (Rice)

  • Dr. Stephen K. Doorn (LANL)

  • Dr. Robert H. Hauge (Rice)

  • Mr. William D. Rice (Rice)

  • Mr. SaunabGhosh (Rice)

  • Mr. Benjamin Y. Lu (Rice)

  • Mr. Budihpta Dan (Rice)

  • Mr. Lei Ren (Rice)

  • Funding provided by DOE, AFRL, NSF, LANL LDRD program, and Welch Foundation.