some arrangmentsof carbon types of swnt
TRANSCRIPT
15-398 lecture 5
© 2004 Seth Copen Goldstein 1
lecture 8 15-398 © 2004 Seth Copen Goldstein 1
Carbon Nanotubes
Seth Copen [email protected]
CMU
15-398 Introduction to Nanotechnology
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Basics
CNTs come in two basic flavorsSingle walledMulti-walled
CNTs are basically rolled up Graphite
http://www.photon.t.u-tokyo.ac.jp/~maruyama/agallery/agallery.html
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Some Arrangments of Carbon
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Types of SWNT
Carbon Nanotubes
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A Graphene Sheet
http://ipn2.epfl.ch/CHBU/NTbasics1.htmlecture 8 15-398 © 2004 Seth Copen Goldstein 6
An Armchair nanotube (10,10)
http://www.photon.t.u-tokyo.ac.jp/~maruyama/agallery/agallery.html
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A chiral nanotube (10,5)
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Geometries
Length: can be > 1 mDiameter:
down to 1nm (SWNT)Upto 50nm (MWNT)
Tubes formed from hexagonsEnds from pentagons and hexagons(1/2 a fullerene)Open and closedBranching possible
http://ipn2.epfl.ch/CHBU/NTbasics1.htm
The Wondrous World of Carbon Nanotubes
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Calculating Diameter of SWNT
SWNT structure can be 1. (n,m) Armchair2. (n,m) Zigzag3. (n,m) ChiralWhere (n,m) are found with:
R = na1 + ma2
The diameter is found with:d = (n2 + m2 + nm)1/20.0783nm
Dai, H. Dai, H. Acc. Chem. ResAcc. Chem. Res. . 20022002, , 3535, 1035, 1035--1044.1044.
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Basic Properties
ChemicalConductors and semiconductorsStiffFlexibleThermal conduction
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Manufacturing
Many methods (covered last time)Ball millingLaser ablationPlasma arcEtc.
Result is a messPurification necessary
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Purification: WhySoot has many contaminants:
Catalyst particlesCarbon clustersSmaller fullerenes: C60 / C70
Even the NTs are mixedConducting, semiconductinSNT and MWNTDiameters, lengths
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Purification: HowRemoval of catalyst:
Acidic treatment (+ sonication)Thermal oxidationMagnetic separation (Fe)
Removal of small fullerenesMicro filtrationExtraction with CS2
Removal of other carbonaceous impuritiesThermal oxidationSelective functionalisation of nanotubesAnnealing
Main issuesNot to damage or modify the CNTsEconomics
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Conductance
Conducting or semiconducting?(n-m)/3 = 0 mod 3 -> conductingOtherwise -> semiconducting
Method of conduction?Not the same as bulk metalBallistic (Fermi-liquid)
Current Densities109A/cm2! 1000x better than copper!What does this mean when diam = 2nm?
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Mechanical Properties
Young s modulos in GigaPascals!
J.-P. Salvetat et al., Adv. Mater. 11, 161 (99).lecture 8 15-398 © 2004 Seth Copen Goldstein 16
Some Applications
Electronic NanotechnologyField-Effect DisplaysCompositesSensorsEnergy StorageSupercapacitorsAFM tips
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Single nanotubes
Pull-out and release of MWNT Van der WaalsforceWorld s smallest balance
Weighing a 22 fg particleScience 283, 1513(1999)Applying hf voltage got frequency for resonance
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Hydrogen Storage
Can CNTs can be used to store hydrogen?Why?
Zero emissions
Why not?Compare Energy density3 MJ/l (5000 psi H2) vs. 32 MJ/l (gasoline)
Use: Fuel container (e.g., fuel cell) to replace use of hydrocarbons (e.g., oil)DOE minimum: 6.5% of Weight
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Two Basic Methods
Gas phase (physisorption)Van der walls bonds Room TemperatureHigher %wt (between 0-14?)
Electrochemical adsorptionElectrically dissassociate H2 from OH2 adsorbs into C
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Field-effect displays
Generates large fieldsLarge aspect ratioLarge current densities
Use as electron source in Flat-panel
Schematic structure of nanotube flat panel display.(Choi et al.)Samsung display 1999
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CNTs for interconnect
High current densitiesLow resistance (6.2K ohm)Ballistic behaviorHowever,
InductanceContact resistanceassembly
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Measuring the resistance
Note quantization of conductance
Bachtold
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MWNT resistance
Frank et al., Science 280, 1744 (1998)
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off
on
On - off state controlled by nanotube contactHysteresis in both states
Off - Elastic restoring forceOn - van der Waals attractive force
Crosstalk and addressing are still problems
C. Lieber, et al., Science 2000, 289, 94.
SWCN Crosspoint Memory
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Nanotube transistor
S.J. Tans et al., Nature 393, 49 (1998).lecture 8 15-398 © 2004 Seth Copen Goldstein 26
Carbon Nanotube FETs
IBM Nanoletters
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Using CNTs in circuits
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CNT Sensors
J. Kong et al., Science 287, 622 (2000).
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Next Time
Lets pop up a levelNanocomputing
Paper will be posted on the web
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