1. An Introduction to Carbon Nanotubes

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

3. What is Nanotechnology? Switching devices of nanometer (below 100nm, typically 10nm) dimensions define nanotechnology. DNA strands as Bits Molecular orientations as Bits CNFETs SETs Self assembled CNT using DNA Quantum Dots CNT arrays DNA self assembly Logic (Our Focus) Memor y Fabricatio n RTD Molecula r Nano CMOS Molecules in Solution Emerging Nanotechnology Drivers Emerging Nanotechnology Solutions

4. Computing Devices CMOS Devices Solid State Devices Molecular Devices Nano CMOS Quantu m Dot RTD Quantum Devices CNFETSET Electro- mechanical Photoactiv e Quantum Electro- chemical

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

6. 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 1991-1992 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)

7. Carbon nanotubes are long meshed wires of carbon Longest tubes up to 1mm long and few nanometers thick made by IBM.Property Carbon Nanotubes ComparativelySize 0.6-1.8 nm in diameter Si wires at least 50nm thick Strength 45 Billion Pascals Steel alloys have 2 Billion P. Resilience Bent and straightened without damage Metals fracture when bent and restraightened Conductivity Estimated at 10 9 A/cm 2 Cu wires burn at 10 6 A/cm 2 Cost $2500/gram by BuckyUSA in Houston Gold is $15/gram Carbon Nanotubes

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

9. 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

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

11. 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

12. 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

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

14. Coulomb Charging Contact Resistance Lower than R quantum =h/e 2 ~26 kΩ C very low s.t. E C =e 2 /2C very large – If E C E C Various gate V taken into account Step-like conductance

15. Quantum Wire Strongly Temperature dependent conduction curve – Occurs when a discrete electron level tunnels resonantly though E f 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)

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

17. Summary of Results Typical Values – G dia ~ 478 GPa – G gla ~ 26.2 GPa – E r-dia ~ 1220 GPa – E r-gla ~ 65-90 GPa

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

19. 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

20. 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

21. 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

22. CNT-based nanomotor IC integrated CNT CNT-based bio-probe Nanotube oscillator CNT Devices

23. 23 Molecular Electronics Nanowire Arrays (Lieber et al., Harvard) TubeFET (McEuen et al., Berkeley) Nanotube Logic (Avouris et al., IBM Research) Nanotube

24. 24 Length Scale 1 mm 1 m 1 nm MEMS Devices Size of a Microprocessor Nanotube/ Nanowire Diameter 100 nm l (Mean free path at RT) 1 Å Ato m F (Fermi wavelength) L W  l: boundary scattering W  F : quantized effects L  l: ballistic transport - + - W Thin Film Thickness in ICs 10 nm