1. Nano-Electronics and Nano- technology A course presented by S. Mohajerzadeh, Department of Electrical and Computer Eng, University of Tehran

2. Carbon structures

3. Fullerene C60, a type of carbon arrangement with 60 carbon atoms placed in 1nm lattice separation. C60, a type of carbon arrangement with 60 carbon atoms placed in 1nm lattice separation. Discovery: 1985 by Bukminister Fuller. Discovery: 1985 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 much. Fullerene can be doped (26%) by alkali atoms (sodium) because its empty space is that much.

4. Fullerene Total: 10,000 publications! = 2,000 PhD students?!

5. Multi-wall and single-wall tubes Transmission electron micrograph of single-wall CNT, (bundles of CNT’s) Transmission electron micrograph of single-wall CNT, (bundles of CNT’s) Schematic diagram of single-wall tube Schematic diagram of single-wall tube

6. Multi-wall tubes

8. Physical characteristics Single wall nanotubes: 1 – 5 nm diameter Single wall nanotubes: 1 – 5 nm diameter Types of nanotube formation: Armchair, Zigzag, Chiral Types of nanotube formation: Armchair, Zigzag, Chiral Multi-wall tubes 2-50 nm concentric tubes, ID : 1.5 – 15 nm, OD : 2.5 – 30 nm Multi-wall tubes 2-50 nm concentric tubes, ID : 1.5 – 15 nm, OD : 2.5 – 30 nm 100 times stronger than steel,  1/6 (1.3 – 1.4 g/cm 3 ) 100 times stronger than steel,  1/6 (1.3 – 1.4 g/cm 3 ) Strong, lightweight materials Strong, lightweight materials k CNT = 2000 (Copper 400) W/m.K k CNT = 2000 (Copper 400) W/m.K Transmission of heat is better than diamond Transmission of heat is better than diamond

9. Chirality vector Although the fabrication of nanotubes is not by rolling the graphite sheets, they are modeled by this phenomenon; Although the fabrication of nanotubes is not by rolling the graphite sheets, they are modeled by this phenomenon; “C h ” or Chirality vector or circumferential vector is the translation vector of graphite plane onto nanotube. “C h ” or Chirality vector or circumferential vector is the translation vector of graphite plane onto nanotube. Axis vector is “T” which is perpendicular to chilarity vector “C h ” and shows the tube axis. Axis vector is “T” which is perpendicular to chilarity vector “C h ” and shows the tube axis. C h = na 1 + m a 2 where “a 1 ” and “a 2 ” represent the main constructing vectors of graphite sheet. C h = na 1 + m a 2 where “a 1 ” and “a 2 ” represent the main constructing vectors of graphite sheet.

10. Chirality vectors

11. Electrical properties Semiconductor, metallic behavior Semiconductor, metallic behavior If n-m=3q then metallic Armchair structures, metallic, Armchair structures, metallic, Chiral and Zigzag structures, semiconductor: Chiral and Zigzag structures, semiconductor: Band gap depends on the diameter Band gap depends on the diameter Reducing the diameter leads to higher band gaps. Reducing the diameter leads to higher band gaps.

12. Mechanical 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 stress is S=W/A, If a wire of area A is stressed by a weight “W”, the level of stress is S=W/A, Strain is defined as: ε=ΔL/L and S=E ε Strain is defined as: ε=ΔL/L and S=E ε ε is called: Young’s module and it is 0.21TPa for nanotubes!!, 10 times more than steel! ε is called: Young’s module and it is 0.21TPa for 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 their original status, self-repairing! If we bend the tubes, they act like straws, but come back to their original status, self-repairing! When the tube is severely bent, the “sp 2 ” structure converts onto “sp” orbitals and once the pressure is removed, sp 2 orbitals are reconstructed. When the tube is severely bent, the “sp 2 ” structure converts onto “sp” orbitals and once the pressure is removed, sp 2 orbitals are reconstructed. Tensile strength is the measure of how much force is needed to take apart a material. Tensile strength is the measure of how much force is needed to take apart a material. For nanotubes, tensile strength is 45 billion Pascal (GPa) whereas for steel it is only 2GPa! For nanotubes, tensile strength is 45 billion Pascal (GPa) whereas for steel it is only 2GPa!

13. Characterization methods SEM SEM TEM TEM Raman (interaction of incoming light with solid vibrations) Raman (interaction of incoming light with solid vibrations) SPM (AFM, STM,…) SPM (AFM, STM,…) XRD (X-ray diffraction) similar to electron diffraction XRD (X-ray diffraction) similar to electron diffraction TPO, TGA (temperature programmed oxidation) and (thermal gravimetric analysis) TPO, TGA (temperature programmed oxidation) and (thermal gravimetric analysis) Electrical characterization Electrical characterization

14. Applications Electronics Hydrogen storage, Chemical Sensors Fuel Cells Nano-transistors, nano-structures Application in STM Composite materials, Catalysts 4.2, 8, 300 (!)wt% of hydrogen in CNT at 25 o C

15. Nano-wires

16. Single electron behavior FET structure at below 1degree Kelvin! FET structure at below 1degree Kelvin! Electron-by-electron transport through the nanotube, step-wise response Electron-by-electron transport through the nanotube, step-wise response

17. Nano-transistors

18. Photonic crystals Similar to atomic periodicity, a structure with matter periodicity is created to form a band-gap for optical wavelengths. Similar to atomic periodicity, a structure with matter periodicity is created to form a band-gap for optical wavelengths. Only at certain wavelengths, standing waves can be created and at some other wavelengths, transmission is prohibited Only at certain wavelengths, standing waves can be created and at some other wavelengths, transmission is prohibited

19. Field emission devices Each sharp tip of nanotube acts as a field-emitter device. Each sharp tip of nanotube acts as a field-emitter device. The emitted electrons hit the top electro- luminescent material (like ZnS). The emitted electrons hit the top electro- luminescent material (like ZnS). Pixels are clusters of nanotubes Pixels are clusters of nanotubes Standard micro-meter photo-lithography, Standard micro-meter photo-lithography, Large area applications Large area applications Stable structures are needed for a reliable application Stable structures are needed for a reliable application

20. Hydrogen storage Computer simulations of Adsorption of hydrogen ( ) in trigonal arrays of single-walled carbon nanotubes ( ) Computer simulations of Adsorption of hydrogen ( ) in trigonal arrays of single-walled carbon nanotubes ( )

21. Fabrication (growth) Techniques 1) Direct current arc-discharge between carbon electrodes in an inert-gas environment 2) Laser Ablation or Pulsed Laser Vaporization (PLV) 3) Plasma Enhanced CVD 4) Catalytic Chemical Vapor Deposition (CVD) CCVD High-pressure CO conversion (HiPCO) CCVD High-pressure CO conversion (HiPCO)

22. Carbon Arc-discharge method  Carbon Atoms are evaporated by a plasma of Helium gas that is ignited by high currents passed through opposing carbon anode and cathode

23. Carbon Arc Discharge

24. CNT by Carbon Arc Discharge Basic Process Basic Process A vacuum chamber is pumped down and back filled with some buffer gas, typically neon or Ar to 500 torr A vacuum chamber is pumped down and back filled with some buffer gas, typically neon or Ar to 500 torr A graphite cathode and anode are placed in close proximity to each other. The anode may be filled with metal catalyst particles if growth of single wall nanotubes is required. A graphite cathode and anode are placed in close proximity to each other. The anode may be filled with metal catalyst 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 cathode as CNT The anode is evaporated and carbon condenses on the cathode as CNT

25. Pulsed Laser Vaporization /Ablation Used for the production of SWNTs Used for the production of SWNTs Uses laser pulses to ablate (or evaporate) a carbon target Uses laser pulses to ablate (or evaporate) a carbon target Target contains 0.5 atomic percent nickel and/or cobalt Target contains 0.5 atomic percent nickel and/or cobalt The target is placed in a tube- furnace The target is placed in a tube- furnace Flow tube is heated to ~1200°C at 500 Torr Flow tube is heated to ~1200°C at 500 Torr 10-200 mg/hr depending on the laser power density 10-200 mg/hr depending on the laser power density

26. Plasma CVD Low temperature Low Pressure  DC, RF:13.56MHz  Microwave:2.47GHz  Reactiing gas  CH 4 ; C 2 H 4 ; C 2 H 6 ; C 2 H 2 ; CO  Catalytic metal (Fe, Ni, Co) Substrate Gas outlet Power suplly Gas inlet

27. High-pressure CO conversion (HiPCO) New method of growing SWNT New method of growing SWNT Primary carbon source is carbon monoxide Primary 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 - 1200°C decomposition of iron penta-carbonyl in a reactor heated to 800 - 1200°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 SWNTs Promising method for mass production of SWNTs

28. Chemical Vapor Deposition Involves heating a catalyst material to high temperatures in a tube furnace and flowing a hydrocarbon gas through the tube reactor. Involves heating a catalyst material to high temperatures in a tube furnace and flowing a hydrocarbon gas through the tube reactor. The materials are grown over the catalyst and are collected when the system is cooled to room temperature. The materials are grown over the catalyst and are collected when the system is cooled to room temperature. Key parameters are: Key parameters are:  Catalysts support support active component active component  Source of carbon  Operational condition simplicity of apparatus Absolute advantage in Mass Production

29. CVD technique

30. Catalyst: Support: Support: Silicon substrates Silicon substrates Quartz substrates Quartz substrates Silica Silica Zeolites Zeolites MgO MgO Alomina Alomina Active components : Active components : Transition metals i.e.: Transition metals i.e.: Co, Fe, Ni / Mo (or oxides of them)

31. Nanometric islands

32. Catalysts effect

33. Sources of carbon: Carbon monoxide Carbon monoxide  Hydrocarbons: Methane Methane Ethylene Ethylene Acetylene Acetylene propylene propylene Acetone Acetone n-pentane n-pentane Methanol Methanol Ethanol Ethanol Benzene Benzene Toluene, … Toluene, …

34. Operational condition: Temperature: 600-1100 o C Temperature: 600-1100 o C Pressure: 1-10 atm Pressure: 1-10 atm Reaction time: 0.5-3 h Reaction time: 0.5-3 h Dilutent gas: He, Ar, H 2 Dilutent gas: He, Ar, H 2 Resident time of gases: Resident time of gases: Volume fraction ( partial pressure) Volume fraction ( partial pressure) Flow rate Flow rate

35. Carbon products Vertical growth, random growth, Vertical growth, random growth, Wall thickness in the case of multi-wall growth Wall 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 & MWNT selectivity of SWNT & MWNT

36. Carbon Nanotubes, Production by Catalytic Chemical Vapor Deposition (CCVD) SWNT-reinforced composites needs tons of CNT per year SWNT-reinforced composites needs tons of CNT per year Laser vaporization and arc discharge: g’s/day SWNT Laser vaporization and arc discharge: g’s/day SWNT Carbon source: CO & HC’s: CH 4, C 2 H 2-6, C 6 H 6 Carbon source: CO & HC’s: CH 4, C 2 H 2-6, C 6 H 6 Conditions: 700-1000 o C, 1-5 atm Conditions: 700-1000 o C, 1-5 atm Catalyst formulation: Co/Fe/Ni-Mo on SiO 2, zeolite, … Catalyst formulation: Co/Fe/Ni-Mo on SiO 2, zeolite, … Quantification of SWNT: SEM, TEM, AFM, Raman, TPO Quantification 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

37. Carbon Nanotubes CO deposition on Co-Mo/Silica

38. Carbon Nanotubes Characterization-Quantification AFM

39. Carbon Nanotubes Raman characterization Graphite Disordered C SWNT

40. 1m1m 20 Kx CCVD CNT Cat. & Reaction Eng. Lab.

41. Storage of Gases Hydrogen storage Hydrogen storage Average storage capacity: at least %8 wt. Average storage capacity: at least %8 wt. 100 km = 1.2 kg H 2 = 13,500 L (gaseous) 100 km = 1.2 kg H 2 = 13,500 L (gaseous) For 500 km : 6 kg H 2 100 kg CNT For 500 km : 6 kg H 2 100 kg CNT  CNT  1.2 kg/lit 84 lit. CNT  CNT  1.2 kg/lit 84 lit. CNT ( 3.1 kg !?) (DOE)