1. An Introduction to Carbon Nanotubes
John Sinclair

2. Outline History Geometry Electronic Properties Physical Properties
Rollup Vector
Metallicity
Electronic Properties
Field Effect Transistors
Quantum Wires
Physical Properties
Ropes
Separation

3. Introduction High Aspect Ratio Carbon nanomaterial
Family inclues Bucky Balls and Graphene
Single Wall Carbon Nanotubes (SWCNT)
Multiwall Carbon Nanotubes (MWCNT)

4. History 1952 L. V. Radushkevich and V. M. Lukyanovich
50 nm MWCNT Published in Soviet Journal of Physical Chemistry
Cold War hurt impact of discovery
Some work done before 1991 but not a “hot” topic
The Watershed
Iijima discovers MWCNT in arc burned rods Mintmire, Dunlap, and White‘s predict amazing electronic and physical properties
1993 Bethune and Iijima independently discover SWCNT
Add Transition metal to Arc Discharge method (same method as Bucky Balls)

5. Geometry Rollup Vector Chiral Angle Arm Chair (n,n), θ=30 ○
(n,m)
n-m=3d
Chiral Angle
tan(θ) = √3m/(2√(n2+m2+nm))
Arm Chair (n,n), θ=30 ○
Zig-zag (n,0), θ=0 ○
Chiral, 0○< θ<30 ○

6. Field Effect Transistors
FETs work because of applied voltage on gate changes the amount of majority carriers decreasing Source-Drain Current
SWCNT and MWCNT used
Differences will be discussed
Gold Electrodes
Holes main carriers
Positive applied voltage should reduce current

7. SWCNT Transport Properties
Current shape consistent with FET
Bias VSD = 10 mA
G(S) conductance varies by ~5 orders of magnitude
Mobility and Hole concentration determined to be large
Q=CVG,T (VG,T voltage to deplete CNT of holes)
C calculated from physical parameters of CNT
p=Q/eL

8. MWCNT Transport Properties
MWCNT performance is poor without defects
See arrow for twists in collapsed MWCNT
MWCNT has characteristic shape of FET
Hole density similar to SWCNT but Mobility determined to be higher
Determined same as above

9. FET Conclusions Higher carrier density than graphite
Mobility similar to heavily p-doped silicon
Conductance can be modulated by ~5 orders of magnitude in SWCNT
MWCNT FET only possible after structural deformation

10. Quantum Wires SWCNT Armchair tubes SWCNT deposited over two electrodes
Electrode resistance determined with four point probe and found to be ~ 1 MΩ

11. Coulomb Charging Contact Resistance Lower than Rquantum=h/e2~26 kΩ
C very low s.t. EC=e2/2C very large
If EC <<kT, Current only flows when Vbias>EC
Various gate V taken into account
Step-like conductance

12. Quantum Wire Strongly Temperature dependent conduction curve
Occurs when a discrete electron level tunnels resonantly though Ef of electrode
If electron levels of SWCNT where continuous peak would be constant
E levels separated by ΔE
The resonant tunneling implies that the electrons are being transported phase coherently in a single molecular orbital for at least the distance of the electrodes (140 nm)

13. Physical Properties of Ropes
SWCNT rope laid on ultra-filtration membrane
AFM tip applies force to measure Shear Modulus G and Reduced Elastic Modulus Er
Er = Elastic Modulus when Searing is negligible
Displacement of tube/Force was measured and Er and G where calculated

14. Summary of Results Typical Values Gdia ~ 478 GPa Ggla ~ 26.2 GPa
Er-dia ~ 1220 GPa
Er-gla ~ GPa

15. Conclusion On Physical Properties
Shear properties of SWCNT lacking (Even compared to MWCNT ropes)
Elastic properties very promising

16. Synthesis and Seperation
One major reason CNT devices have been so hard to scale up to industry uses is due to the inability to efficiently separate different species of CNT
Different types are produced randomly with 1/3 conducting 2/3 semiconducting
It has now been reported that with the use of structure-discriminating surfactants one can isolate a batch of CNT such that >97% CNT within 0.02 nm diameter

17. Overview of Technique Surfactants change buoyancy properties of CNT
Ultra-centrifugation techniques (which are scale-able) are used to separate different CNT
Effective separation is seen
Separation according to metallicity
Separation according to diameter

18. Conclusion
CNT devices show promise in molecular electronics both as wires and FET
Physical properties are very promising being both strong and light
Separation techniques continue to be developed to allow companies to make CNT devices

19. Sources
M. S. DRESSELHAUS, G. DRESSELHAUS, and R. SAITO. Carbon 33, 7 (1995)
R. Martel, T. Schmidt, H. R. Shea, T. Hertel, and Ph. Avourisa. App. Phys. Lett. 73, 17 (1998)
Sander J. Tans, Michel H. Devoret et al. Nature 386, (1997)
Jean-Paul Salvetat et al. Phys. Rev. Lett. 82, 5 (1999)
MICHAEL S. ARNOLD et al. Nature Nanotechnology 1, (2006)
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