steve cronin university of southern california electrical engineering - electrophysics optical and...
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Steve CroninUniversity of Southern California
Electrical Engineering - Electrophysics
Optical and Electronic Measurements of Individual Carbon Nanotubes
• Imagine rolling a sheet of graphite into a seamless cylindrical tube
Honeycomb Graphite Sheet
• Two integers (n,m) determine all the properties of a carbon nanotube.
• Nanotubes can have metallic or semiconducting electronic structure, if (n-m)/3.
What is a Carbon Nanotube?
Chirality (n,m):
Ch = 4a1 + 2a2 = (4,2)
AFM of Carbon Nanotube and DNA Molecules
Bockrath, et al., Nano Lett., 2, 187 (2002).
Carbon Nanotube
DNA
Why Study Carbon Nanotubes?
• 1nm in diameter, up to 1cm in length, aspect ratio of 107
• 1 defect in 1012 C atoms => ballistic conduction • High melting point ~3800oC • High young’s modulus 1TPa (103 times diamond)• High electronic current carrying capacity (109A/cm2) ~103
times higher than that of the noble metals• Thermal conductivity 6600W/mK at room temperature is
twice the maximum known bulk thermal conductor, isotropically pure diamond = 3320W/mK
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)
Vgate
Gate
NT
Vbias
SiO2doped silicon
0
2
4
6
8
10
12
-10 -5 0 5 10
Gate Voltage (V)
AC
Cu
rren
t (n
A)
on off
1m
Nanotube Field Effect Transistor (NT-FET)
0
0.2
0.4
0.6
0.8
1
1.2
-10 -5 0 5 10
Gate Voltage (V)
AC
Cu
rren
t (n
A)
metallic
semiconducting
Single Nanotube Raman SpectroscopyDespite 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
Semiconducting
Metallic
RBM G-bandJorio, et al., PRL, 86, 1118 (2001)
Raman Spectra of Strained NT
unstrained length =3.8m
strain = 20nm 0.53% 5.3GPa Stress
AFM tip
1m
Cronin, et al., PRL, 93, 167401 (2004).
• D, G, G’ bands are downshifted by 16.1, 14.8 and 27.7cm-1 (5 times bulk)
• Lower phonon frequencies as C-C bond length increases
broken
Raman Spectra of Broken NT
• D, G and G’ downshift by 27, 14 and 40cm-1
• Broken tube resumes original D, G and G’ values.
• Strain deformations are elastic
Cronin, et al., PRL, 93, 167401 (2004).
strain=1.65%
AFM tip
1m
1m
2m
Thank You!
Rajay Kumar, Hao Zhou, Adam Bushmaker (USC)
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)
People:
• NIRT ECS-0210752• NSF Grant Nos. DMR-01-16042 and DMR-02-44441• NSEC Grant No. PHY-01-17795• Dupont-MIT alliance
Grants:
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