Optical and Electronic Measurements of Individual Carbon Nanotubes

Optical and Electronic Measurements of Individual Carbon Nanotubes Steve Cronin University of Southern California Electrical Engineering - Electrophysics

What is a Carbon Nanotube? • Imagine rolling a sheet of graphite into a seamless cylindrical tube Honeycomb Graphite Sheet Chirality (n, m): Ch = 4 a 1 + 2 a 2 = (4, 2) • Two integers (n, m) determine all the properties of a carbon nanotube. • Nanotubes can have metallic or semiconducting electronic structure, if (n-m)/3.

AFM of Carbon Nanotube and DNA Molecules Carbon Nanotube DNA Bockrath, et al. , Nano Lett. , 2, 187 (2002).

Why Study Carbon Nanotubes? • • • 1 nm in diameter, up to 1 cm in length, aspect ratio of 107 1 defect in 1012 C atoms => ballistic conduction High melting point ~3800 o. C High young’s modulus 1 TPa (103 times diamond) High electronic current carrying capacity (109 A/cm 2) ~103 times higher than that of the noble metals • Thermal conductivity 6600 W/m. K at room temperature is twice the maximum known bulk thermal conductor, isotropically pure diamond = 3320 W/m. K Despite 18, 000 publications, no large scale commercial applications of nanotubes Li , Yu, Rutherglen, Burke, Nano Lett. , 4 2003 (2004) Fan, Goldsmith, Collins, Nature Materials, 4, 906 (2005)

Nanotube Field Effect Transistor (NT-FET) on Vbias Vgate NT Gate 1 mm Si. O 2 doped silicon semiconducting metallic off

Single Nanotube Raman Spectroscopy Despite the extremely small geometric cross-section the Raman signal from a single isolated nanotube can be observed. Eii • 105 enhancement in scattering cross-section due to singularities in the DOS • Resonance occurs when Elaser=Eii • Only observe nanotubes that are resonant with Elaser Metallic Semiconducting RBM Jorio, et al. , PRL, 86, 1118 (2001) G-band

Strain Nanotubes 1 mm AFM tip unstrained length =3. 8 mm strain = 20 nm 0. 53% 5. 3 GPa Stress

Raman Spectra of Strained NT 1 mm AFM tip unstrained length =3. 8 mm strain = 20 nm 0. 53% 5. 3 GPa Stress • D, G, G’ bands are downshifted by 16. 1, 14. 8 and 27. 7 cm-1 (5 times bulk) • Lower phonon frequencies as C-C bond length increases Cronin, et al. , PRL, 93, 167401 (2004).

Raman Spectra of Broken NT strain=1. 65% broken • D, G and G’ downshift by 27, 14 and 40 cm-1 • Broken tube resumes original D, G and G’ values. • Strain deformations are elastic Cronin, et al. , PRL, 93, 167401 (2004).

Thank You! 2 mm 1 mm AFM tip

Thank You! People: 1 mm Rajay Kumar, Hao Zhou, Adam Bushmaker (USC)2 mm A. Stolyarov, Prof. M. Tinkham (Harvard) R. Barnett, E. Demler (Harvard) Y. Yin, A. Walsh, Prof. A. K. Swan, Prof. B. B. Goldberg (BU) Prof. M. S. Dresselhaus (MIT) Grants: • NIRT ECS-0210752 1 mm • NSF Grant Nos. DMR-01 -16042 and DMR-02 -44441 • NSEC Grant No. PHY-01 -17795 AFM tip • Dupont-MIT alliance