Nano-Electronics and Nano-Nano-Electronics and Nano-

technologytechnology

A course presented by A course presented by S. Mohajerzadeh,S. Mohajerzadeh,

Department of Electrical and Computer Eng,Department of Electrical and Computer Eng,University of TehranUniversity of Tehran

Carbon structuresCarbon structures

FullereneFullerene C60, a type of carbon arrangement with 60 carbon atoms placed in C60, a type of carbon arrangement with 60 carbon atoms placed in 11nm lattice nm lattice

separation.separation. Discovery: Discovery: 19851985 by Bukminister Fuller. by Bukminister Fuller. 12 pentagonal and 20 hexagonal shapes.12 pentagonal and 20 hexagonal shapes. Fullerene can be doped (26%) by alkali atoms (sodium) because its empty space is that Fullerene can be doped (26%) by alkali atoms (sodium) because its empty space is that

much.much.

فولرينفولرين1nm in diameter

Discovery: 1985

C60C70

FullereneTotal: 10,000 publications!

= 2,000 PhD students?!

Multi-wall and single-wall tubesMulti-wall and single-wall tubes

Transmission electron micrograph of single-wall Transmission electron micrograph of single-wall CNT, (bundles of CNT’s)CNT, (bundles of CNT’s)

Schematic diagram of single-wall tubeSchematic diagram of single-wall tube

Multi-wall tubesMulti-wall tubes

Physical characteristicsPhysical characteristics

Single wall nanotubes: Single wall nanotubes: 1 – 5 nm diameter1 – 5 nm diameter

Types of nanotube formation: Armchair, Zigzag, Chiral Types of nanotube formation: Armchair, Zigzag, Chiral

Multi-wall tubes Multi-wall tubes 2-50 nm concentric tubes, 2-50 nm concentric tubes, ID : 1.5 – 15 nm, OD : 2.5 – 30 ID : 1.5 – 15 nm, OD : 2.5 – 30

nmnm

100 times stronger than steel, 100 times stronger than steel, 1/6 (1.3 – 1.4 g/cm 1/6 (1.3 – 1.4 g/cm33) )

Strong, lightweight materialsStrong, lightweight materials

kkCNTCNT = 2000 (Copper 400) W/m.K = 2000 (Copper 400) W/m.K

Transmission of heat is better than diamondTransmission of heat is better than diamond

Chirality vectorChirality vector Although the fabrication of Although the fabrication of

nanotubes is not by rolling nanotubes is not by rolling the graphite sheets, they the graphite sheets, they are modeled by this are modeled by this phenomenon;phenomenon;

““CChh” or Chirality vector or ” or Chirality vector or circumferential vector is the circumferential vector is the translation vector of translation vector of graphite plane onto graphite plane onto nanotube.nanotube.

Axis vector is “T” which is Axis vector is “T” which is perpendicular to chilarity perpendicular to chilarity vector “Cvector “Chh” and shows the ” and shows the tube axis.tube axis.

CChh= na= na11 + m a + m a22 where “a where “a11” ” and “aand “a22” represent the main ” represent the main constructing vectors of constructing vectors of graphite sheet.graphite sheet.

Chirality vectorsChirality vectors

Electrical propertiesElectrical properties Semiconductor, Semiconductor,

metallic behaviormetallic behaviorIf n-m=3q then metallic If n-m=3q then metallic Armchair structures, Armchair structures,

metallic,metallic, Chiral and Zigzag Chiral and Zigzag

structures, structures, semiconductor: semiconductor:

Band gap depends on Band gap depends on the diameterthe diameter

Reducing the diameter Reducing the diameter leads to higher band leads to higher band gaps.gaps.

Mechanical propertiesMechanical properties Nanotubes are very strong materials.Nanotubes are very strong materials. If a wire of area A is stressed by a weight “W”, the level of If a wire of area A is stressed by a weight “W”, the level of

stress is S=W/A,stress is S=W/A, Strain is defined as: Strain is defined as: εε==ΔΔL/L and S=E L/L and S=E εε εε is called: Young’s module and it is 0.21TPa for is called: Young’s module and it is 0.21TPa for

nanotubes!!, 10 times more than steel!nanotubes!!, 10 times more than steel! 1 TPa is equivalent to 10millions atmospheric pressure!!1 TPa is equivalent to 10millions atmospheric pressure!! If we bend the tubes, they act like straws, but come back to If we bend the tubes, they act like straws, but come back to

their original status, self-repairing!their original status, self-repairing! When the tube is severely bent, the “spWhen the tube is severely bent, the “sp22” structure ” structure

converts onto “sp” orbitals and once the pressure is converts onto “sp” orbitals and once the pressure is removed, spremoved, sp22 orbitals are reconstructed. orbitals are reconstructed.

Tensile strength is the measure of how much force is Tensile strength is the measure of how much force is needed to take apart a material.needed to take apart a material.

For nanotubes, tensile strength is 45 billion Pascal (GPa) For nanotubes, tensile strength is 45 billion Pascal (GPa) whereas for steel it is only 2GPa!whereas for steel it is only 2GPa!

Characterization methodsCharacterization methods

SEMSEM TEMTEM Raman (interaction of incoming light with solid Raman (interaction of incoming light with solid

vibrations)vibrations) SPM (AFM , STM ,…)SPM (AFM , STM ,…) XRD (X-ray diffraction) similar to electron XRD (X-ray diffraction) similar to electron

diffractiondiffraction TPO, TGA (temperature programmed oxidation) TPO, TGA (temperature programmed oxidation)

and (thermal gravimetric analysis)and (thermal gravimetric analysis) Electrical characterizationElectrical characterization

ApplicationsApplications

ElectronicsElectronics

Hydrogen storage,Hydrogen storage,

Chemical SensorsChemical Sensors

Fuel CellsFuel Cells

Nano-transistors, nano-structuresNano-transistors, nano-structures

Application in STMApplication in STM

Composite materials,Composite materials,

CatalystsCatalysts

4.2, 8, 3004.2, 8, 300 (!) (!)wt% of hydrogen in CNT at 25wt% of hydrogen in CNT at 25ooCC

Nano-wiresNano-wires

Single electron behaviorSingle electron behavior

FET structure at below 1degree Kelvin!FET structure at below 1degree Kelvin! Electron-by-electron transport through the Electron-by-electron transport through the

nanotube, step-wise responsenanotube, step-wise response

Nano-transistorsNano-transistors

Photonic crystalsPhotonic crystals

Similar to atomic periodicity, a structure with matter Similar to atomic periodicity, a structure with matter periodicity is created to form a band-gap for optical periodicity is created to form a band-gap for optical wavelengths.wavelengths.

Only at certain wavelengths, standing waves can be created Only at certain wavelengths, standing waves can be created and at some other wavelengths, transmission is prohibitedand at some other wavelengths, transmission is prohibited

Field emission devicesField emission devices Each sharp tip of Each sharp tip of

nanotube acts as a nanotube acts as a field-emitter device.field-emitter device.

The emitted electrons The emitted electrons hit the top electro-hit the top electro-luminescent material luminescent material (like ZnS).(like ZnS).

Pixels are clusters of Pixels are clusters of nanotubesnanotubes

Standard micro-meter Standard micro-meter photo-lithography,photo-lithography,

Large area applicationsLarge area applications Stable structures are Stable structures are

needed for a reliable needed for a reliable applicationapplication

Hydrogen storageHydrogen storage

Computer simulations of Adsorption of hydrogen ( ) in Computer simulations of Adsorption of hydrogen ( ) in tri-gonal arrays of single-walled carbon nanotubes ( )tri-gonal arrays of single-walled carbon nanotubes ( )

Fabrication (growth) TechniquesFabrication (growth) Techniques

1)1) Direct current arc-discharge Direct current arc-discharge

between carbon electrodes in an between carbon electrodes in an

inert-gas environmentinert-gas environment

2)2) Laser Ablation or Pulsed Laser Laser Ablation or Pulsed Laser

Vaporization (PLV)Vaporization (PLV)

3)3) Plasma Enhanced CVDPlasma Enhanced CVD

4)4) Catalytic Chemical Vapor Catalytic Chemical Vapor

Deposition (CVD) Deposition (CVD)

CCVD CCVD

High-pressure CO conversion High-pressure CO conversion

(HiPCO)(HiPCO)

Carbon Arc-discharge methodCarbon Arc-discharge method Carbon Atoms are evaporated by a plasma of Helium gas Carbon Atoms are evaporated by a plasma of Helium gas

that is ignited by high currents passed through opposing that is ignited by high currents passed through opposing carbon anode and cathodecarbon anode and cathode

Carbon Arc DischargeCarbon Arc Discharge

CNT by Carbon Arc DischargeCNT by Carbon Arc Discharge

Basic ProcessBasic Process

A vacuum chamber is pumped down and back filled with A vacuum chamber is pumped down and back filled with some buffer gas, typically neon or Ar to 500 torrsome buffer gas, typically neon or Ar to 500 torr

A graphite cathode and anode are placed in close proximity A graphite cathode and anode are placed in close proximity to each other. The anode may be filled with metal catalyst to each other. The anode may be filled with metal catalyst particles if growth of single wall nanotubes is required.particles if growth of single wall nanotubes is required.

A voltage is placed across the electrodes, A voltage is placed across the electrodes,

The anode is evaporated and carbon condenses on the The anode is evaporated and carbon condenses on the cathode as CNTcathode as CNT

Pulsed Laser Vaporization /AblationPulsed Laser Vaporization /Ablation

Used for the production of Used for the production of SWNTs SWNTs

Uses laser pulses to ablate Uses laser pulses to ablate (or evaporate) a carbon (or evaporate) a carbon targettarget

Target contains 0.5 atomic Target contains 0.5 atomic percent nickel and/or cobaltpercent nickel and/or cobalt

The target is placed in a The target is placed in a tube-furnacetube-furnace

Flow tube is heated to Flow tube is heated to ~1200°C at 500 Torr~1200°C at 500 Torr

10-200 mg10-200 mg//hr depending on hr depending on the laser power densitythe laser power density

Plasma CVDPlasma CVD

Low temperatureLow temperature

Low PressureLow Pressure

DC, RF:13.56MHzDC, RF:13.56MHz

Microwave:2.47GHzMicrowave:2.47GHz

Reacting gasReacting gas

CHCH4 4 ; C; C22HH4 4 ; C; C22HH6 6 ; C; C22HH2 2 ; CO; CO

Catalytic metal (Fe, Ni, Co)Catalytic metal (Fe, Ni, Co)

Substrate

Gas outlet

Power suplly

Gas inlet

High-pressure CO conversion (HiPCO)High-pressure CO conversion (HiPCO)

New method of growing SWNTNew method of growing SWNT

Primary carbon source is carbon monoxidePrimary carbon source is carbon monoxide Catalytic particles are generated by in-situ thermal Catalytic particles are generated by in-situ thermal

decomposition of iron penta-carbonyl in a reactor heated to 800 - decomposition of iron penta-carbonyl in a reactor heated to 800 -

1200°C1200°C

Process is done at a high pressure to speed up the growth (~10 atm)Process is done at a high pressure to speed up the growth (~10 atm)

Promising method for mass production of SWNTsPromising method for mass production of SWNTs

Chemical Vapor DepositionChemical Vapor Deposition

Involves heating a catalyst material to high temperatures in Involves heating a catalyst material to high temperatures in a tube furnace and flowing a hydrocarbon gas through the a tube furnace and flowing a hydrocarbon gas through the tube reactor.tube reactor.

The materials are grown over the catalyst and are collected The materials are grown over the catalyst and are collected when the system is cooled to room temperature.when the system is cooled to room temperature.

Key parameters are:Key parameters are: CatalystsCatalysts support support active componentactive component Source of carbonSource of carbon Operational conditionOperational condition

simplicity of apparatus

Absolute advantage in

Mass Production

CVD techniqueCVD technique

Catalyst:Catalyst:

Support:Support: Silicon substratesSilicon substrates Quartz substratesQuartz substrates SilicaSilica Zeolites Zeolites MgOMgO AlominaAlomina

Active components :Active components : Transition metals i.e.:Transition metals i.e.:

Co , Fe, Ni / Mo (or oxides of them)Co , Fe, Ni / Mo (or oxides of them)

Nanometric islandsNanometric islands

Catalysts effectCatalysts effect

Sources of carbon:Sources of carbon: Carbon monoxideCarbon monoxide Hydrocarbons:Hydrocarbons: MethaneMethane EthyleneEthylene Acetylene Acetylene propylenepropylene AcetoneAcetone n-pentanen-pentane MethanolMethanol EthanolEthanol BenzeneBenzene Toluene , …Toluene , …

Operational condition:Operational condition:

Temperature: 600-1100 Temperature: 600-1100 ooCC Pressure: 1-10 atmPressure: 1-10 atm Reaction time: 0.5-3 hReaction time: 0.5-3 h Dilutent gas: He, Ar, HDilutent gas: He, Ar, H22 Resident time of gases: Resident time of gases:

Volume fraction ( partial pressure)Volume fraction ( partial pressure)

Flow rate Flow rate

Carbon productsCarbon products

Vertical growth, random growth,Vertical growth, random growth, Wall thickness in the case of multi-wall growthWall thickness in the case of multi-wall growth Single-wall (shell) nanotube (SWNT)Single-wall (shell) nanotube (SWNT) Multi-wall (shell) nanotube (MWNT)Multi-wall (shell) nanotube (MWNT) Graphitic form of carbon Graphitic form of carbon Amorphous form of carbon Amorphous form of carbon

selectivity of SWNT & MWNTselectivity of SWNT & MWNT

Carbon Nanotubes, Production by Carbon Nanotubes, Production by

Catalytic Chemical Vapor Deposition (CCVD)Catalytic Chemical Vapor Deposition (CCVD)

Carbon Nanotubes, Production by Carbon Nanotubes, Production by

Catalytic Chemical Vapor Deposition (CCVD)Catalytic Chemical Vapor Deposition (CCVD)

SWNT-reinforced composites needs tons of CNT per yearSWNT-reinforced composites needs tons of CNT per year

Laser vaporization and arc discharge: g’s/day SWNTLaser vaporization and arc discharge: g’s/day SWNT

Carbon source: CO & HC’s: CHCarbon source: CO & HC’s: CH44 , C , C22HH2-62-6 , C , C66HH66

Conditions: 700-1000 Conditions: 700-1000 ooC, 1-5 atmC, 1-5 atm

Catalyst formulation: Co/Fe/Ni-Mo on SiOCatalyst formulation: Co/Fe/Ni-Mo on SiO22 , zeolite, … , zeolite, …

Quantification of SWNT: SEM , TEM, AFM, Raman, TPOQuantification of SWNT: SEM , TEM, AFM, Raman, TPO

Purification steps:Purification steps:

Caustic to remove silica Caustic to remove silica

Acid to remove metals Acid to remove metals

Carbon NanotubesCarbon Nanotubes Carbon NanotubesCarbon Nanotubes CO deposition on Co-Mo/Silica

Carbon Nanotubes Characterization-QuantificationCarbon Nanotubes Characterization-QuantificationCarbon Nanotubes Characterization-QuantificationCarbon Nanotubes Characterization-Quantification

AFM

Carbon Nanotubes Raman characterizationCarbon Nanotubes Raman characterizationCarbon Nanotubes Raman characterizationCarbon Nanotubes Raman characterization

Graphite

Disordered C

SWNT

1m20 Kx

CCVD CNT Cat. & Reaction Eng. Lab.

Storage of GasesStorage of Gases

Hydrogen storageHydrogen storage

Average storage capacity: at least %8 wt. Average storage capacity: at least %8 wt.

100 km = 1.2 kg H100 km = 1.2 kg H22= 13,500 L= 13,500 L((gaseousgaseous))

For 500 km : 6 kg HFor 500 km : 6 kg H2 2 100 kg CNT100 kg CNT

CNTCNT 1.2 kg/lit 84 lit. CNT 1.2 kg/lit 84 lit. CNT( 3.1 kg !?) (DOE)