An Introduction to Carbon NanotubesJohn Sinclair

OutlineHistoryGeometryRollup VectorMetallicityElectronic PropertiesField Effect TransistorsQuantum WiresPhysical PropertiesRopesSeparation

IntroductionHigh Aspect Ratio Carbon nanomaterialFamily inclues Bucky Balls and GrapheneSingle Wall Carbon Nanotubes (SWCNT)Multiwall Carbon Nanotubes (MWCNT)

History1952 L. V. Radushkevich and V. M. Lukyanovich50 nm MWCNT Published in Soviet Journal of Physical ChemistryCold War hurt impact of discoverySome work done before 1991 but not a hot topic1991-1992 The WatershedIijima discovers MWCNT in arc burned rods Mintmire, Dunlap, and Whites predict amazing electronic and physical properties1993 Bethune and Iijima independently discover SWCNTAdd Transition metal to Arc Discharge method (same method as Bucky Balls)

GeometryRollup Vector(n,m)n-m=3dChiral Angletan() = 3m/(2(n2+m2+nm))Arm Chair (n,n), =30 Zig-zag (n,0), =0 Chiral, 0<

Field Effect TransistorsFETs work because of applied voltage on gate changes the amount of majority carriers decreasing Source-Drain CurrentSWCNT and MWCNT usedDifferences will be discussedGold ElectrodesHoles main carriersPositive applied voltage should reduce current

SWCNT Transport PropertiesCurrent shape consistent with FETBias VSD = 10 mAG(S) conductance varies by ~5 orders of magnitudeMobility and Hole concentration determined to be largeQ=CVG,T (VG,T voltage to deplete CNT of holes)C calculated from physical parameters of CNTp=Q/eL

MWCNT Transport PropertiesMWCNT performance is poor without defectsSee arrow for twists in collapsed MWCNTMWCNT has characteristic shape of FETHole density similar to SWCNT but Mobility determined to be higher Determined same as above

FET ConclusionsHigher carrier density than graphiteMobility similar to heavily p-doped siliconConductance can be modulated by ~5 orders of magnitude in SWCNTMWCNT FET only possible after structural deformation

Quantum WiresSWCNT Armchair tubesSWCNT deposited over two electrodesElectrode resistance determined with four point probe and found to be ~ 1 M

Coulomb ChargingContact Resistance Lower than Rquantum=h/e2~26 kC very low s.t. EC=e2/2C very largeIf EC

Quantum WireStrongly Temperature dependent conduction curveOccurs when a discrete electron level tunnels resonantly though Ef of electrodeIf electron levels of SWCNT where continuous peak would be constantE levels separated by EThe 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)

Physical Properties of RopesSWCNT rope laid on ultra-filtration membraneAFM tip applies force to measure Shear Modulus G and Reduced Elastic Modulus ErEr = Elastic Modulus when Searing is negligible Displacement of tube/Force was measured and Er and G where calculated

Summary of ResultsTypical ValuesGdia ~ 478 GPaGgla ~ 26.2 GPaEr-dia ~ 1220 GPaEr-gla ~ 65-90 GPa

Conclusion On Physical PropertiesShear properties of SWCNT lacking (Even compared to MWCNT ropes)Elastic properties very promising

Synthesis and SeperationOne 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 CNTDifferent types are produced randomly with 1/3 conducting 2/3 semiconductingIt 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

Overview of TechniqueSurfactants change buoyancy properties of CNT Ultra-centrifugation techniques (which are scale-able) are used to separate different CNTEffective separation is seenSeparation according to metallicity Separation according to diameter

ConclusionCNT devices show promise in molecular electronics both as wires and FETPhysical properties are very promising being both strong and lightSeparation techniques continue to be developed to allow companies to make CNT devices

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