Controlled continuous spinning of fibres of single wall carbon nanotubes

Transcription

1 Controlled continuous spinning of fibres of single wall carbon nanotubes Guadalupe Workshop 8-12 April 2011 Krzysztof Koziol and Alan Windle Department of Materials Science and Metallurgy University of Cambridge

2 Catharina Paukner PhD student Lukasz Kurzepa Technician My group Dept of Materials Science) Advanced Carbon Nanostructures Group Agnieszka Lekawa-Raus PhD student Sebastian Pattinson PhD student Rajyashree Sundaram PhD student Jinhu Chen PhD student Jonathan Cormack PhD student Dawid Janas PhD student

3 The required control of matter D L Θ

4 Overview 1. Continuous CVD process for making CNT assemblies, e.g. fibre 2. Process parameters 3. Strategy for the diameter control of single wall nanotube with sulphur 4. Summary 1 5. Strategy for the chiral angle control with nitrogen in multiwalled nanotubes 6. Summary 2

5 Continuous CVD process for making CNT fibre Department of Materials Science and Metallurgy University of Cambridge

6 Challenge in assembly of selected CNTs From single nanotube to fibres, yarns, films single nanotube Inside the reactor bundles fibres, yarns Outside the reactor

7 Continuous CVD process for making CNT fibre Injection system Reactor Fibre collection

8 High Resolution TEM analysis of CNT fibre Individual CNT Bundles Diameter = 4-10 nm Length = mm 80 % double walled 20 % triple walled 10 % single wall nanotubes

9 CNT fibre composition

10 Looking into the reactor Instabilities in the process

11 Collecting carbon nanotube fibres

12 Continuous CVD process for making CNT fibre H 2 Hydrocarbon Catalyst Sulphur Fibre winding rate: (m/min) C C Koziol et al, Science, 318, 1892 (2007) Li, Kinloch, Windle, Science, 304, 276, (2004)

13 The reaction zone Carbon Precursor Methane Catalyst Precursor Ferrocene Sulphur Promoter Temperature profile inside the reactor IN HYDROGEN ATMOSPHERE PYROLYSIS Fe catalyst formation S promoter C availability Reactor height CNT nucleation and growth ⁰C

14 Controlling the Fe catalyst size with the sulphur precursor C x H y Surface diffusion of C C x H y Reactor at 1200 C Fe Fe-S (molten solution, dissolving very little carbon) ~5-10 nm Fast growth of large diameter double wall nanotubes

15 Fibre morphology by SEM Single wall nanotube fibre Predominantly double wall nanotube fibre Carbon disulphide as S source Thiophene as S source

16 Fibre composition by HRTEM Carbon disulphide as S source 10 nm Thiophene as S source

17 Summary 1 1. The direct spinning is quite complicated as it relies on floating catalyst which is highly mobile as well as other dynamic processes taking place in the reactor. 2. FeS eutectic melts just below 1000 ⁰C hence carbon - iron interface is highly mobile and surface diffusion rates greatly enhanced. 3. Sulphur is able to retard the growth of iron catalyst size by collision, so that the particles are of appropriate dimensions for single wall nanotubes at the point where the carbon becomes available for nanotube growth.

18 Control of chiral angles of MW carbon nanotubes with the catalyst Zig-Zag and Arm-chair Multi wall nanotubes: All layers with the same chiral angle Department of Materials Science and Metallurgy University of Cambridge

19 Apparatus and conditions for the synthesis of standard MWNTs Ar 200 ºC 760 ºC quartz reaction tube Solution of ferrocene in toluene Carrier Gas: Argon Carbon source: Toluene Catalyst source: Ferrocene

20 Geometry constraint in MWNTs The circumference of each layer must be a lattice vector (C h ) so only discrete values possible, but it must be larger for each successive tubular layer by 2π(c/2) in order to preserve the correct interlayer spacing. As there is some variation possible in the softer interlayer bonds (in c/2), it does may out. However, it seems that in order to have the greatest choice of lattice vectors to satisfy this restrictive condition, each layer tends to have a different chirality.

21 Control of chiral angles of MW carbon nanotubes with the catalyst The effect of nitrogen Department of Materials Science and Metallurgy University of Cambridge

22 Apparatus and conditions for a different class of MWNTs Ar 200 ºC 760 ºC quartz reaction tube Solution of ferrocene in toluene/pyrazine K. Koziol, M. Shaffer and A. Windle, Adv. Mat. 17, 760 (2005) Carrier Gas: Argon Carbon source: Toluene Catalyst source: Ferrocene Nitrogen source: Pyrazine

23 Ar 200 ºC Apparatus and conditions for a different class of MWNTs 760 ºC quartz reaction Addition of a nitrogen containing heterocyclic compound has a pronounced effect on the formation of carbon nanotubes with significant changes to the morphology and structure Solution of ferrocene in toluene/pyrazine K. Koziol, M. Shaffer and A. Windle, Adv. Mat. 17, 760 (2005) Carrier Gas: Argon Carbon source: Toluene Catalyst source: Ferrocene Nitrogen source: Pyrazine

24 Difference between normal and pyrazine-enhanced MWNTs multiwalled carbon nanotubes top TOP side SIDE top side Pyrazine-enhanced multiwalled carbon nanotubes Straight like a needle

25 Difference between normal and pyrazine-enhanced MWNTs Conical angle could help the graphene layers to get the desired pacing. Webs across core Slight cone angle (0.5 7 deg)

26 Another oddity The catalyst made when heterocyclic nitrogen is part of the feedstock is iron carbide, Fe 3 C, NOT iron, Fe.

27 Control of chiral angles of MW carbon nanotubes with the catalyst Now for the big surprise Department of Materials Science and Metallurgy University of Cambridge

28 Electron diffraction pattern from standard MWNT Pattern from a control sample synthesised without nitrogen 00n reflections due to interlayer peaks TUBE AXES hk0 reflections form continuous ring(s) because different layers have different chiralities and there is no crystal register between them

29 Electron diffraction pattern from pyrazine-enhanced MWNTs Pattern equivalent to a graphite single crystal pattern rotated about [110] TUBE AXES Pattern implies that all ~ 75 layers have same chirality and are armchair Presence of hkl reflections (e.g.112) indicates abab.. register between layers. K. Koziol, M. Shaffer and A. Windle, Adv. Mat. 17, 760 (2005)

30 Electron diffraction pattern from pyrazine-enhanced MWNTs K. Koziol, M. Shaffer and A. Windle, Adv. Mat. 17, 760 (2005) Pattern implies that all ~ 75 layers have same chirality and are zig-zag TUBE AXES Presence of hkl reflections (e.g.112) indicates abab.. register between layers.

31 High structural order (a) (b) HRTEM image FFT filtered image of the walls of pyrazine enhanced CNTs C. Ducati, K. Koziol, S. Friedrichs, T. Yates, M. Shaffer, P. Midgley, A. Windle, Small, 2, 774 (2006)

32 High structural order (a) (b) HRTEM image FFT filtered image of the walls of pyrazine enhanced CNTs C. Ducati, K. Koziol, S. Friedrichs, T. Yates, M. Shaffer, P. Midgley, A. Windle, Small, 2, 774 (2006)

33 Crystallographic interlayer register (a) HRTEM image of the centre of a pyrazine enhanced CNT (face-on to graphene layers) (b) The corresponding FFT filtered image The arrow in the image indicates the tube axis C. Ducati, K. Koziol, S. Friedrichs, T. Yates, M. Shaffer, P. Midgley, A. Windle, Small, 2, 774 (2006)

34 Standard & pyrazine-enhanced MWNTs Each graphene layer with different chiral angle Each graphene layer has the same chiral angle and there is crystallographic register between them

35 What is going on? What is the role of nitrogen? (needs to be supplied as a heterocylic ring) Where does it end up?

36 EELS studies of individual N-CNTs Nitrogen incorporated in the graphene forming webs as well as N 2 in the core of the tube. No evidence of nitrogen in the walls of the nanotubes Overall there is ~3 %wt of nitrogen (measured by elemental analysis) Caterina Ducati, Krzysztof Koziol, Steffi Friedrichs, Timothy Yates, Milo Shaffer, Paul Midgley, and Alan Windle, Small, 2, 774 (2006)

37 Role of nitrogen It seems that the major role of nitrogen is to stabilise Fe 3 C instead of iron. This behaviour is consistent with the role of nitrogen as a carbide stabiliser in steels and cast irons, where it appears to assist the nucleation of the carbide phase via an FeN x intermediate.

38 Control of chiral angles of MW carbon nanotubes with the catalyst So Far: But why? What is telling the layers to have either arm-chair or zig-zag chirality? Department of Materials Science and Metallurgy University of Cambridge Catalyst is Fe 3 C Small conical angle provides possible answer to geometric restriction No significant nitrogen in walls

39 Electron diffraction of nanotubes and catalyst particles together TUBE AXES Koziol, Ducati and Windle, Chem. Mater., 2010, 22 (17), pp

40 Electron diffraction of nanotubes and catalyst particles together TUBE AXES All carbide particles are oriented the same, with their [100] carbide axes parallel to the CNT tube axes. Also [100] carbide is parallel to either [100] graphene (arm-chair) or [210] graphene (zig-zag) Koziol, Ducati, Windle, Chem. Mater., 2010, 22 (17), pp

41 Lattice imaging of the interface CNT Interface Lets zoom in Steps on the catalyst

42 Epitaxial role of the catalyst CNT Reconstructed surface layer of catalyst 1nm Catalyst Evidence for close packed planes in reconstructed surface region looking very like FCC iron with CP plane parallel to surface But should there be epitaxy?

43 TUBE AXES Surface of carbide reconstructs to fcc with close packed layer parallel to surface

44 The important message Nitrogen is stabilising the formation of iron carbide which has a particular orientation. We found that the [100] carbide axis is parallel to the CNT main axis. This is very important. Furthermore, there are few layers of FCC iron, which are reconstructed on the iron carbide therefore also have orientation. FCC iron is the active surface and it has an epitaxial relationship with graphene so if you can stabilise FCC iron nanoparticle with particular orientation you can produce armchair or zigzag nanotubes. Koziol, Ducati, Windle, Chem. Mater., 2010, 22 (17), pp

45 Summary 2 1. Constant chiral angle tubes easy to make using specific heterocyclic nitrogen containing molecules 2. Crystallographic relationship between carbide catalyst particles and carbon nanotubes observed 3. All catalyst particles oriented with [100] normal to substrate and parallel to tube axis. 4. Surface layers of the carbide providing the epitaxy contact have reconstructed to give a close packed layer of Fe on the surface. 5. Key is that these cp layers form a zone with the tube axis parallel to the zone (tube) axis, unlike in Fe metal where they will be tetrahedrally arranged.

46 Thank You Funding: EPSRC