Controlling synthesis of carbon nanostructures by plasma means in arc discharge

1. Controlling synthesis of carbon nanostructures by plasma means in arc discharge Olga Volotskova1, Alexei Shashurin1, Michael Keidar1, Yevgeny Raitses2, Jeffrey Fagan3, Ji Yeon Huh3, Jon Torrey1 1GWU MNPL, 2PPPL, 3NIST APS DPP, November 2009

2. Experimental setup

3. Region of SWNTs formation Typical temperature evolution in the system After experiment Before experiment • SWNT mat : • catalyst C:Ni:Y=56:4:1 • P= 500 Torr of helium • arc current ~ 55 A 2m 2m Experimental setup

4. Tmin ≈ 620 K and Tcr ≈650 K SWNT mat before ignition SWNT mat during ignition Destruction started at T ≈650K Dependence of resistance (normalized) on temperature. Experiment was conducted in the air and p≈760torr TGA measurements in SWNT sample under the pressure of about 760Torr Region of SWNTs formation

5. Destruction time of SWNT Dtdist <10 ms Flight time in plasma column Dtflight >1 ms Thus SWNT produced by an anodic arc discharge and collected in the web area outside the arc plasma most likely originate from the arc discharge peripheral region Minimum temperature (Tmin ) Critical temperature (Tcr) Temperature difference ΔT=Tcr-Tmin Region of SWNTs formation

6. Magnetic field t 1 Cathode 2-D simulation of B-field flux Plasma t 2 Helium Magnet Anode t 3 Experimental setup t 4

7. Magnetic field effects • New way of few layers graphene synthesis • Change of composition of • SWNTs: • Increase of length of SWNTs • Shift of SWNTs diameter to a smaller side that is also implying change of SWNTs charality 1 M. Keidar et al. Appl. Phys. Lett 92 (2008)

8. Few layers graphene 1µm SEM AFM Magnetic field effects

9. Few layers graphene 1210 0110 1120 1100 1010 50nm TEM (HV 100kV) Diffraction Pattern Magnetic field effects

10. Few layers graphene G Graphenefeatures2,3,4 2D Magnet area D ~ 1324cm-1 G ~ 1583cm-1 2D ~ 2652cm-1 2D-shift D Cathode deposit D ~ 1340cm-1 G ~ 1571cm-1 2D ~ 2685cm-1 Chamber walls D ~ 1333cm-1 G ~ 1581cm-1 2D ~ 2668cm-1 A.Gupta et al, Nano Letters, 6, 12, 2667 (2006) D. Graf et al., Nano Letters 7, 2, 238 (2007) D.Wei Nano Lett., 9, 5, 2009

11. Diameter S33 M11 S22 S11 B=1.2kG B=2kG B=0.2kG B=0.6kG No field UV-vis-NIR measurements shows that diameter distribution is shifted to smaller diameters (although there is still a broad mixture) Magnetic field effects

12. Diameter (10,5) (9,4) (8,6) (8,7) (8,6) (8,7) (7,5) (7,6) (7,6) (10,3) B=0.2kG B=0.6kG (9,2) (11,3) (10,5) (9,7) (10,5) (9,7) (11,3) (9,4) (8,6) (8,7) (8,6) (8,7) (9,4) (10,3) (10,3) (7,5) (7,6) (7,6) B=1.2kG B=2kG (7,5) (9,2) S. Bachilo et al., Science 298 (2002) (reference for assigned optical spectra)

13. Length UV-vis-NIR spectrum of length separated purified SWNTs, with no filed applied Fraction NF 4 Ave rage length of SWNTs in NF 4 ~ 1m Magnetic field effects

14. Length UV-vis-NIR spectrum of length separated purified SWNTs, with B=1.2kG applied Fraction B 5 Ave rage length of SWNTs in B 5 ~ 3m Magnetic field effects

15. Semiconducting/Metallic Ratio Before separation Before separation No filed B=1.2kG Me Semi Mixture After separation After separation Magnetic field effects

16. Conclusions • SWNTs origin of SWNTs formation in arc discharge is at the peripheral region • Application of the magnetic field resulting in: new way of few layers graphene synthesis and change of SWNTs composition may caused by: • Non-uniformities which are desirable for creation of various conditions inside arc • Increasing of plasma density (increase of carbon flux toward SWNT surface and increase of heating flux) • Interaction with catalyst • Arc reshaping • Acknowledgment: PPPL University support program sponsored by DOE US. Department of Energy