1. Bottom up method for preparing nanostructures: growth of carbon nanotubes Akos Kukovecz Universität Wien 2002

2. 2/30 Talk layout Carbon nanotube basicsCarbon nanotube basics Overview of the synthesis techniquesOverview of the synthesis techniques NT growth theories & modelsNT growth theories & models Application oriented growth – examplesApplication oriented growth – examples PurificationPurification

3. 3/30 Carbon nanotube basics (10,5) SWCNT SWCNT: rolled-up graphene sheet diameter: ~0.7-3 nm, length > 500 nm C(n,m) : chiral vector diameter, electrical properties From the website of Dr. Maruyama. R. Saito et al.: Physical Properties of Carbon Nanotubes, Imperial Press, London, 1999,

4. 4/30 SWCNT morphology Synthesis yields entagled mat of nanotube bundles Science, 273, 483.

5. 5/30 Multi wall carbon nanotubes Co-axial set of increasing diameter SWCNTs Easier synthesis than SWCNTs Easier synthesis than SWCNTs Accurate quality control is even more difficult Accurate quality control is even more difficult

6. 6/30 Talk layout Carbon nanotube basicsCarbon nanotube basics Overview of the synthesis techniquesOverview of the synthesis techniques NT growth theories & modelsNT growth theories & models Application oriented growth – examplesApplication oriented growth – examples PurificationPurification

7. 7/30 Synthesis of multi wall tubes d.c. arc Setup Parameters d.c. arc, 20 V, 100 A d.c. arc, 20 V, 100 A 500 torr He 10 ml/s 500 torr He 10 ml/s electrode distance 1 mm electrode distance 1 mm ~3000 °C in plasma ~3000 °C in plasma Properties No catalyst needed No catalyst needed MWCNT in cathode deposit, MWCNT in cathode deposit, d = 2-25 nm, l  1  m d = 2-25 nm, l  1  m Co/graphite: 100 nm, 60  m Co/graphite: 100 nm, 60  m Co/SiO 2 : 30 nm, 10  m Co/SiO 2 : 30 nm, 10  m Fe: more amorphous carbon Fe: more amorphous carbon Ni, Cu: no nanotubes Ni, Cu: no nanotubes 5-10 % C 2 H 2, C 6 H 6 in N 2, Ar5-10 % C 2 H 2, C 6 H 6 in N 2, Ar Co (Fe, Ni) @ MgO, Al 2 O 3, SiO 2, zeolites, graphite etc. Co (Fe, Ni) @ MgO, Al 2 O 3, SiO 2, zeolites, graphite etc. 700-1100 °C, 1 atm 700-1100 °C, 1 atm Vapor deposition (CVD) APA 67 1.

8. 8/30 SWCNT synthesis Catalyst? no Exotic methods

9. 9/30 Exotic SWCNT synthesis I. TPA is template for AlPO 4 -5 synthesis AlPO 4 -5 is a zeolite analogoue Pyrolysis (550 °C) transforms TPA into SWCNT AlPO 4 -5 Pyrolized APA 69 381.

10. 10/30 Exotic SWCNT synthesis II. Coalescence of C 60 molecules into SWCNT within the nanospace of a larger SWCNT (peapod system). Heating: vacuum, 1000 °C, 14 hours From the website of Dr. Maruyama. CPL 337 48.

11. 11/30 SWCNT synthesis Catalyst? no Exotic methods yes In situ generated? noCVD

12. 12/30 Chemical vapor deposition (CVD) Unique: NT growth location controlled! ParametersCatalystProduct 800-1000 °C CH 4 : 1 dm 3 /min strong metal-support interactionstrong metal-support interaction large surface arealarge surface area large mesopore volumelarge mesopore volume Fe/Mo @ alumina Co @ MgO SWCNT d=1.4 nm, l>10  m NTs grow from the metal clusters. Metal clusters can be positioned by e.g. litography, ink printing, laser etching... APA 67 1.

13. 13/30 SWCNT synthesis Catalyst? no Exotic methods yes In situ generated? noCVD yes Starting phase? solid d.c. arc discharge d.c. arc discharge pulsed laser vaporization (PLV) pulsed laser vaporization (PLV)

14. 14/30 d.c. arc discharge SWCNTs: in soot, collarett. Conditions: as for MWCNT. Anode contains catalyst! Good SWCNT yield: Co, Co/Ni, Co/Fe, Ni/Y, Ni/Fe Product: diameter control not straightforward tubes often covered with amorphous carbon

15. 15/30 Pulsed laser vaporization (PLV) ParametersTargetProduct T = 1200 °C 2 successive pulses Graphite +0.5% catalyst (Ni, Co) SWCNT d=1.4 nm, l>10  m Good diameter control, little amorphous carbon. APA 67 1.

16. 16/30 SWCNT synthesis Catalyst? no Exotic methods yes In situ generated? noCVD yes Starting phase? solid d.c. arc discharge d.c. arc discharge pulsed laser vaporization (PLV) pulsed laser vaporization (PLV) gas flame pyrolysis flame pyrolysis gas phase decomposition gas phase decomposition

17. 17/30 NT yield < 1% Mostly SWCNTs Flame pyrolysis Continuous production, familiar plant engineering -> CHEAP! SWCNTs grow in sooting flame: O 2 +fuel+catalyst. Fuel: C 2 H 2, C 6 H 6 1-3 dm 3 /min + x(2-4) O 2 Catalyst: ferrocenes, metallocenes, Fe(NO 3 ) 3 T flame =1200 °C, p=80 Torr, t=250 ms JPC B 104 9615.

18. 18/30 Gas phase catalytic decomposition Continuous production -> low cost! Carbon sources: hexane, benzene, acetylene, CH 4, CO,... Catalyst precursors: metal-carbonyls & metallocenes HiPCO process CO: 10 atm 1 dm 3 /min 1 dm 3 /min Fe(CO) 5 : 5 ppm d = 0.7-1.4 nm l > 1  m Boudouard: 2 CO C + COTreshold: 500 °C C + CO 2 Treshold: 500 °C n Fe(CO) 5 = Fe n + 5n CO Treshold: 250 °C CPL 313 91.

19. 19/30 Talk layout Carbon nanotube basicsCarbon nanotube basics Overview of the synthesis techniquesOverview of the synthesis techniques NT growth theories & modelsNT growth theories & models Application oriented growth – examplesApplication oriented growth – examples PurificationPurification

20. 20/30 Nanotube growth theories Are they really so different? Common points: All go to atomization temperature All go to atomization temperature Hexagonal sp 2 graphite is the most stable form of carbon. Constrain : Constrain : Steric limit / catalyst present Nanotubes instead of graphene sheets!

21. 21/30 Possible growth arrangements Root growth: VLS Tip growth: scooter C C C Growth direction C C C C C C Skullcap

22. 22/30 Tip growth: scooter model Co (Ni) atom cycles: C atoms add to hexagons Co (Ni) atom stops (e.g. gets too large): Co (Ni) atom stops (e.g. gets too large): Dangling bonds make pentagons, close dome. TEM: no metal in NT tip Topics in Appl. Phys. 80 55.

23. 23/30 Root growth: VLS model Vapor-Liquid-Solid (VLS) model Carbon from vapor phase dissolves in liquid metal nanocluster, then segregates on cluster surface to give solid nanotubes. NTs grow radially from Ni-carbid partice. TEM PRL 87 275504.

24. 24/30 Root growth: MD simulation I. Nucleation Red: Co Gray: C 2000 K Homogeneous distr. 1500 K C segregates to surface 25 ps Aromaticrings 1500 K 15 ps 5 new C enter the tube II. Growth PRL 87 275504.

25. 25/30 Skullcap growth: MD simulation Ni cluster (blue): d=1.2 nm Free C atoms come from gas. From the website of Dr. Maruyama. CPL 260 471.

26. 26/30 Talk layout Carbon nanotube basicsCarbon nanotube basics Overview of the synthesis techniquesOverview of the synthesis techniques NT growth theories & modelsNT growth theories & models Application oriented growth – examplesApplication oriented growth – examples PurificationPurification

27. 27/30 Application oriented growth: CVD Electronic industry can not use random NT mats! SWCNT network between Si pillars SWCNT gas sensor 10 ppm range 0.1 % range Field emission displays Field emission displays FET mass production FET mass production APL 81 2261.

28. 28/30 Talk layout Carbon nanotube basicsCarbon nanotube basics Overview of the synthesis techniquesOverview of the synthesis techniques NT growth theories & modelsNT growth theories & models Application oriented growth – examplesApplication oriented growth – examples PurificationPurification

29. 29/30 Nanotube purification I.Contaminants: catalyst metal & amorphous carbon II.Removal: metals by dissolving in acid (HCl, HNO 3 ) carbon by selective oxidation (O 2, wet air, HNO 3, H 2 O 2 etc.) carbon by selective oxidation (O 2, wet air, HNO 3, H 2 O 2 etc.) III.Challanges: NTs not soluble in any solvent sonication can break NTs thin NTs sensitive to oxidation

30. 30/30 Thanks for your attention! Akoska ®