Lecture 12 February 3, 2014 Formation bucky balls, bucky tubes

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1 Lecture 12 February 3, 2014 Formation bucky balls, bucky tubes Nature of the Chemical Bond with applications to catalysis, materials science, nanotechnology, surface science, bioinorganic chemistry, and energy Course number: Ch120a Hours: 2-3pm Monday, Wednesday, Friday William A. Goddard, III, 316 Beckman Institute, x3093 Charles and Mary Ferkel Professor of Chemistry, Materials Science, and Applied Physics, California Institute of Technology Teaching Assistants:Sijia Dong Samantha Johnson Ch120a- 1 Goddard-

2 C 60 fullerene No broken bonds Just ~11.3 kcal/mol strain at each atom 678 kcal/mol Compare with 832 kcal/ mol for flat sheet Lower in energy than flat sheet by 154 kcal/mol! 2

3 Polyyne chain precursors fullerenes, all even 3

4 4

5 C 540 All fullerens have 12 pentagonal rings 5

6 Mechanism for formation of fullerenes Heath 1991: Fullerene road. Smaller fullerenes and C3 etc add on to pentagonal sites to grow C60 Contradicted by He chromatography and high yield of endohedrals Smalley 1992: Pentagonal road. Graphtic sheets grow and curl into fullerenes by incorporating pentagonal C3 etc add on to pentagonal sites to grow C60 Contradicted by He chromatography Arc environment: mechanism goes through atomic species (isotope scrambling) He chromatography è Go through carbon rings and form fullerenes Has high temperature gradients Ring growth road. Jarrold based on He chromatography 6

7 He chromatography (Jarrold) Relative abundance of the isomers and fragments as a function of injection energy in ion drifting experiments Conversion of bicyclic ring to fullerene when heated 7

8 Energies from QM 8

9 Force Field for sp1 and sp2 carbon clusters 9

10 4n vs 4n+2 for Cn Rings 10

11 Population of various ring and fullerene species with Temperature Based on free energies from QM and FF 11

12 Bring two C30 rings together 12

13 Energetics (ev) for isomerizations converting bicyclic ring to monocyclic or Jarrold intermediates for n = 30, 40, 50 2 rings TS to form tricyclic E tricyclic TS convert E tricyclic C 34 C 60 C 40 TS to Bergman cyclization singlet (leads to Jarrold ring mechanism) 13

14 Energetics (ev) for initial steps of Jarrold Jarrold pathway If get here, then get fullerene Modified Jarrold Number pi bonds 14

15 Downhill race from tricyclic to bucky ball energetics (ev) 30 ev of energy gain as form Fullerene Number sp2 bonded centers 15

16 Structures in Downhill race from tricyclic to bucky ball 16

17 Energy contributions to downhill race to fullerene energetics (ev) Number sp2 bonded centers 17

18 C60 dimer Prefers packing of 6 fold face De = 7.2 kcal/mol Face-face=3.38A 18

19 Crystal structure C60 Expect closest packing: 6 neighbors in plane 3 neighbors above the plane and 3 below But two ways ABCABC face centered cubic ABABAB hexagonal closet packed Predicted crystal structure 3 months before experiment Prediction of Fullerene Packing in C60 and C70 Crystals Y. Guo, N. Karasawa, and W. A. Goddard III Nature 351, 464 (1991) 19

20 C60 is face centered cubic 20

21 C70 is hexagonal closest packed 21

22 Vapor phase grown Carbon fiber, R. T. K. Baker and P. S. Harris, in Chemistry and Physics of Carbon, edited by P. L. Walker, Jr. and A. Thrower (Marcel Dekker, New York, 1978), Vol. 14, pp ; G. G. Tibbetts, Carbon 27, (1989); R. T. K.Baker, Carbon 27, (1989). M. Endo, Chemtech 18, (1988). Formed carbon fiber from 0.1 micron up Xray showed that graphene planes are oriented along axis but perpendicular to the cylindrical normal 22

23 Multiwall nanotubes "Helical microtubules of graphitic carbon". S. Iijima, Nature (London) 354, (1991). Ebbesen, T. W.; Ajayan, P. M. (1992). "Large-scale synthesis of carbon nanotubes". Nature 358: Outer diameter of MW NT inner diameter of MW NT 23

24 Single wall carbon nanotubes, grown catalytically S. Iijima and T. Ichihashi, "Single-shell carbon nanotubes of 1-nm diameter".nature (London) 363, (1993) used Ni D. S. Bethune, C.-H. Kiang, M. S. de Vries, G. Gorman, R. Savoy, J. Vazquez, and R. Beyers, "Cobalt-catalyzed growth of carbon nanotubes with singleatomic-layer walls".nature (London) 363, (1993). used Co Ching-Hwa Kiang grad student with wag on leave at IBM san Jose 24

25 Single wall carbon nanotubes, grown catalytically S. Iijima and T. Ichihashi, "Single-shell carbon nanotubes of 1-nm diameter".nature (London) 363, (1993) used Ni D. S. Bethune, C.-H. Kiang, M. S. de Vries, G. Gorman, R. Savoy, J. Vazquez, and R. Beyers, "Cobalt-catalyzed growth of carbon nanotubes with singleatomic-layer walls".nature (London) 363, (1993). used Co Ching-Hwa Kiang grad student with wag on leave at IBM san Jose Catalytic Synthesis of Single-Layer Carbon Nanotubes with a Wide Range of Diameters C.- H. Kiang, W. A. Goddard III, R. Beyers, J. R. Salem, D. S. Bethune, J. Phys. Chem. 98, (1994). Catalytic Effects on Heavy Metals on the Growth of Carbon Nanotubes and Nanoparticles C.-H. Kiang, W. A. Goddard III, R. Beyers, J. R. Salem, and D. S. Bethune, J. Phys. Chem. Solids 57, 35 (1995). Effects of Catalyst Promoters on the Growth of Single-Layer Carbon Nanotubes; C.-H. Kiang, W. A. Goddard III, R. Beyers, J. R. Salem, and D. S. Bethune, Mat. Res. Soc. Symp. Proc. 359, 69 (1995) Carbon Nanotubes With Single-Layer Walls," Ching-Hwa Kiang, William A. Goddard III, Robert Beyers and Donald S. Bethune, " Carbon 33, (1995). "Novel structures from arc-vaporized carbon and metals: Single-layer carbon nanotubes and metallofullerenes," Kiang, C-H, van Loosdrecht, P.H.M., Beyers, R., Salem, J.R., and Bethune, D.S., Goddard, W.A. III, Dorn, H.C., Burbank, P., and Stevenson, S., Surf. Rev. Lett. 3, (1996). 25

26 Kiang CNT form

27 Kiang CNT form

28 Distribution of diameters for carbon SWNT, Kiang

29 29

30 Examples Single wall carbon nanotubes 30

31 Some bucky tubes (8,8) armchair (14,0) zig-zag (6,10) chiral 31

32 Contsruction for (6,10) edge

33 13.46A diameter (10,10) armchair carbon SWNT 40 atoms/repeat distance 33

34 (14,0) zig-zag Bucky tube 34

35 13.5A Crystal packing of (10,10) carbon SWNT Density SWNT: 1.33 g/cc Graphite 2.27 g/cc Heat formation Graphite 0 C (10,10) CNT ,7A Ec Young s modulus SWNT 640 GPa Graphite 1093 GPa Ea Young s modulus SWNT 5.2 GPa Graphite 4.1 GPa 35

36 Vibrations in (10,10) armchair CNT 36

37 Carbon fibers and tubes 37

38 Vibrations in (10,10) armchair CNT 38

39 Vibrations in (10,10) armchair CNT 39

40 Mechanism for gas phase CNT formation Polyyne Ring Nucleus Growth Model for Single-Layer Carbon Nanotubes C-H. Kiang and W. A. Goddard III Phys. Rev. Lett. 76, 2515 (1996) 40

41 Mechanism for gas phase CNT formation A two-stage mechanism of bimetallic catalyzed growth of singlewalled carbon nanotubes Deng WQ, Xu X, Goddard WA Nano Letters 4 (12): (2004) 41

42 But mechanism of gas phase C SWNT, no longer important The formation of Carbon SWNT by CVD growth on a metal nanodot on a support is now the preferred mechanism for forming SWNT 42

43 Mechanisms Proposed for Nanotube Growth Stepwise Process Adsorption Dehydrogenation Saturation Diffusion Nucleation Growth 43

44 Vapor-Liquid-Solid (Carbon Filament) Mechanism Vapor carbon feed stock adsorbs unto liquid catalyst particle and dissolves. Dissolved carbon diffuses to a region of lower solubility resulting in supersaturation and precipitation of the solid product. Originally developed to explain the growth of carbon whiskers/filaments. Temperature, concentration or free energy gradient is implicated as the driving force responsible for diffusion. Wagner, R. S.; Ellis, W. C. Appl. Phys. Lett. 1964, 4, 89. Bolton, et al. J. Nanosci. Nanotechnol. 2006, 6,

45 Yarmulke Mechanism Dai, et al. Chem. Phys. Lett. 1996, 260, 471. Raty, et al. Phys. Rev. Lett , Carbon-carbon bonds form on the surface (either before or as a result of super-saturation). Diffusion of carbon to graphene coating can be an important rate limiting step. Coating of more than a complete hemisphere results in poisoning of catalyst. New layers can start beneath the original layer after/as it lifts off the surface resulting in MWNT. 45

46 Experimental Confirmation of a Yarmulke Mechanism Atomic-scale, video-rate environmental transmission microscopy has been used to monitor the nucleation and growth of single walled nanotubes. Hofmann, S. et al. Nano Lett. 2007, 7,

47 Role of the Catalyst Particle in Nanotube Formation Size of catalyst particles is related to the diameter of the nanotubes formed. Catalyst nanoparticles are known to deform (elongate) during nanotube growth. Structural properties of select catalyst surfaces (Ni111, Co111, Fe1-10) exhibit appropriate symmetry and distances to overlap with graphene and allow thermally forbidden C2 addition reaction. Graphene is believed to stabilize the high energy nanoparticle surface. MWNT have been observed growing out of steps, which they stabilize. Hong, S.; et al. Jpn J. Appl. Phys. 2002, 41, Vinciguerra, V.; et al. Nanotechnol. 2003, 14, 655. Hofmann, S. et al. Nano Lett. 2007, 7,

48 Tip vs. Base Growth Mechanisms Same initial reaction step: absorbtion, diffusion and precipitation of carbon species. Strength of interaction between catalyst particle and catalyst support determines whether particles remains on surface or is lifted with growing nanotube. Huang, S.; et al. Nano Lett , Kong, J.; et al. Chem. Phys. Lett. 1998, 292, 567. Images of nanotubes show catalyst particles trapped at the ends of nanotubes in the case of tip growth, or nanotubes bound to catalysts on support in the case of base growth. Alternatively capped nanotube tops show base growth. A kite (tip) growth mechanism has been used to explain the growth of long (order 48 of mm), well III, ordered copyright 2011 William A. Goddard all rights SWNTs. reserved

49 Limiting Steps for Growth Rates Diffusion of reactive species either through the catalyst particle bulk or across its surface can play an important role in determining the rate of nanotube growth. In the case of carbon species which dissociate less readily the rate of carbon supply to the particle can act as the rate limiting step. Vinciguerra, V.; et al. Nanotechnol. 2003, 14, 655. Hofmann, S. et al. Nano Lett. 2007, 7, 602. Hafner, J. H.; et al. Chem. Phys. Lett. 1998, 296, 195. The rate of growth must also take into account a force balance between the friction of the nanotube moving through the surrounding feedstock gas and the driving force for/from the reaction. 49