1. Graphite rod surface coated with C60
Paul Dunk

2. Carbon atoms the hot (10000o) focal point
C60 evapourates unscathed from surrounding warm domain

3. 50% of the C60 converted to higher fullerenes
Desorbed C60
50% of the C60 converted to higher fullerenes
<2% fragmentation of C60
C70
200
400
600
800
1000
C60 on graphite rod – little fragmentation
small Cn species are ingested by C60 forming larger fullerenes

4. MS of C60+n(neven) fullerenes
13C enriched
Carbon + C60
reaction
C64
C66
C68
C70
C72
C74
C76
C78
C80
MS of C60+n(neven) fullerenes

6. Typical desorbed C60 mass spectrum. No growth
C60 coated on a glass rod – just C60

7. Expanded view of larger C60 + Cn fullerenes
The larger fullerenes become increasingly 13C enriched. In agreement with small Cn species inserting into C60 and higher fullerenes to form even higher fullerenes
C64
C66
Note C62 – C68 are not stable
C68
C70
C72
C74
C76
C78
C80
Expanded view of larger C60 + Cn fullerenes

8. Fullerenes grow by ingestion of small carbon species
Cn + C2 → Cn+2 etc

9. The rod translated and rotated by stepper motor
C60 coated
graphite rod
Cluster Source
Helium pulse
C60 reacts with C, C2 exits and undergo supersonic expansion
laser pulse vaporises
rod
The rod translated and rotated by stepper motor

10. Rod coated with 13C enriched amorphous carbon (ca 10%) and pure C60
Pulsed Laser
Pulsed Nozzle
Helium
Rod coated with 13C enriched amorphous carbon (ca 10%) and pure C60

11. Pulsed Laser
Pulsed Nozzle
Helium
Rotating/translating rod coated with 13C enriched amorphous carbon (ca 10%) and pure C60

12. skimmer hole to mass spectrometer Laser and graphite disk
carbon plasma cluster beam
Laser Vapourisation Cluster Beam System - Smalley

14. Supersonic Expansion into the vacuum chamber cools the clusters to very low temperatures
The very sharp edged skimmer skims the expanding pulse into a very narrow beam

15. Skimmer action more slowly

16. Multi stage formation mechanism
Laser fires and produces a ca10,000K plasma of C atoms

17. Multi stage formation mechanism
Laser fires and produces a ca10,000K plasma of C atoms
The atoms at the plasma/He interface cool to form small linear species: C2 C3, C4 etc

18. Multi stage formation mechanism
Laser fires and produces a ca10,000K plasma of C atoms
The atoms at the plasma/He interface cool to form small linear species: C2 C3, C4 etc
Monocylic rings and at least two other families of carbon molecules form

19. Multi stage formation mechanism
Laser fires and produces a ca10,000K plasma of C atoms
The atoms at the plasma/He interface cool to form small linear species: C2 C3, C4 etc
Monocylic rings and at least two other families of carbon molecules form
Small fullerene cages from C28… onwards are created

20. Multi stage formation mechanism
Laser fires and produces a ca10,000K plasma of C atoms
The atoms at the plasma/He interface cool to form small linear species: C2 C3, C4 etc
Monocylic rings and at least two other families of carbon molecules form
Small fullerene cages from C28… onwards are created
Small fullerenes grow into larger cages by ingestion

21. Multi stage formation mechanism
Laser fires and produces a ca10,000K plasma of C atoms
The atoms at the plasma/He interface cool to form small linear species: C2 C3, C4 etc
Monocylic rings and at least two other families of carbon molecules form
Small fullerene cages from C28… onwards are created
Small fullerenes grow into larger cages by ingestion
Final stage condensation to solid product – only Cn n=60, 70 and higher n species survive

22. accumulation octopole
stepper motor
target rod
accumulation octopole
transfer octopole
ICR cell
pulsed valve
skimmer
pulsed valve
source
10-7 torr
diffusion pump
10-7
turbo pump
10-8
turbo pump
10-10
turbo pump

23. C60 reacts with carbon species
supersonic expansion
skimmed into beam
C60 reacts with carbon species

24. The pulses pass across the chamber at about 10 Hz
…and the signal integrated perhaps 100 to a1000 or more times
The University of Sussex machine

25. ions accumulated in octopole
3-10 laser shot accumulated
transferred to the ICR cell

26. C60 reacts with carbon species
supersonic expansion
skimmed into beam
ions accumulated in octopole
3-10 laser shot accumulated
transferred to the ICR cell
C60 reacts with carbon species

27. C60 + amorphous 13C coated on a quartz rod
Desorbed C60
C60 ingests 13C species
C60 + amorphous 13C coated on a quartz rod

28. This study shows unequivocally that fullerenes can grow by ingestion of smaller carbon species
in this case
C60 + Cn → C C C66 C68 C C72 etc
with Paul Dunk and Alan Marshall

29. Multi stage formation mechanism

30. Multi stage formation mechanism
Refinement of a closed cage growth mechanism proposed by Heath for the fullerenes and Endo and Kroto for nanotube growth

31. Multi stage formation mechanism
Laser fires and produces a ca10000o plasma of C atoms

32. Multi stage formation mechanism
Laser fires and produces a ca10000o plasma of C atoms
The atoms at the plasma/He interface cool to form C2 C3, C4 etc

33. Multi stage formation mechanism
Laser fires and produces a ca10000o plasma of C atoms
The atoms at the plasma/He interface cool to form C2 C3, C4 etc
Monocylic rings (and another family) form

34. Multi stage formation mechanism
Laser fires and produces a ca10000o plasma of C atoms
The atoms at the plasma/He interface cool to form C2 C3, C4 etc
Monocylic rings (and another family) form
Small fullerene cages C28… are created

35. Multi stage formation mechanism
Laser fires and produces a ca10000o plasma of C atoms
The atoms at the plasma/He interface cool to form C2 C3, C4 etc
Monocylic rings (and another family) form
Small fullerene cages C28… are created
Small fullerenes grow into larger cages by ingestion

36. Multi stage formation mechanism
Laser fires and produces a ca10000o plasma of C atoms
The atoms at the plasma/He interface cool to form C2 C3, C4 etc
Monocylic rings (and another family) form
Small fullerene cages C28… are created
Small fullerenes grow into larger cages by ingestion
Final stage – only Cn n=60, 70 and higher n species survive

38. Graphite rod surface coated with C60

40. The pulses pass across the chamber at about 10 Hz
…and the signal integrated perhaps 100 to a1000 or more times
The University of Sussex machine

41. Valve emits a helium pulse
fullerene-coated
graphite target rod
Cluster Source
Valve emits a helium pulse
Fullerenes react with carbon vapor (C, C2) in the “clustering zone”. Then, the gas exits the channel and undergoes a supersonic expansion to create a cooled, molecular beam
laser pulse vaporises
rod
The rod translated and rotated by stepper motor

42. Expanded view of desorbed C60 – normal isotope distribution
12C60 signal
Normal ratio
← 13C12C59 ~ 60% of 12C60 signal
Expanded view of desorbed C60 – normal isotope distribution

43. One strongly held conjecture was that C60 and C70 would be cul-de-sacs and our results indicate that this conjecture is incorrect.

44. One strongly held conjecture was that C60 and C70 would be cul-de-sacs and our results indicate that this conjecture is incorrect. Our results indicate that the primary nascent distribution of fullerenes shows almost no evidence of IPR stabilisation which is a surprise to at least me Requiring a final stage which non IPR cages do not survive

45. One strongly held conjecture was that C60 and C70 would be cul-de-sacs and our results indicate that this conjecture is incorrect. Our results indicate that the primary nascent distribution of fullerenes shows almost no evidence of IPR stabilisation

46. C60 + amorphous 13C on a quartz rod
Desorbed C60
C60 + amorphous 13C on a quartz rod

47. Answer to questions from email.
Q: How many pulses do you need to accumulate?
A: A single laser shot is used vaporize the target during a single Helium pulse. Ten singe laser shot + He pulse are used to accumulate ions.
Q:How do you decide when to transfer them.
A: After the final laser shot, a voltage at the “back” of the accumulation octopole switched, and the ions are transferred to the ICR cell. The switching of the voltage is controlled by the computer program interface.
Q: How many runs do you need in general for an average result?
A: 3 time-domain aquisitions are averaged for when “growing” a preformed fullerene…….the signal is extremely strong.
And 10 time-domain acquisitions are averaged when form endohedrals from a graphite-metal target.
Thus, up to 10 time-domain acquisitions are averaged.

48. Fullerenes react with carbon vapor in the “clustering zone”, then the gas exits the channel and undergoes a supersonic expansion.
As the clusters move from a region of high pressure through a small orifice into a high vacuum, they undergo a supersonic expansion. The random thermal energy of the clusters is converted into a directed motion (creating a cooled, molecular beam in which very few collisions occur) toward the skimmer and the ions subsequently enter the ion optics where they are accumulated and then transferred to the ICR cell for detection.

49. Answer to questions from email.
Q: How do you stop the pulse of ions in the accumulation trap
A: The ions are confined radially by an oscilating radiofrequency within in octopole, and axially by voltages at the ends of the “accumulation octopole:.

51. 10-7 turbo pump 10-8 turbo pump 10-10 turbo pump 10-7 torr
After 3-10 single laser shot accumulations, the ions are transferred to the ICR cell, which is located within in the bore of a 9.4 tesla superconducting magnet. Under the influence of the high magnetic field, the ions exhibit cyclotron motion. The ions induce a current on electrodes, which is detected as an “image current” in the time domain, and then the signal is converted to the frequency domain by an FT. Thus, the mass of the ion is detected as a frequency.
Fullerenes react with carbon species in the vapourisation zone, then exit reaction channel
the ions which enter the ion optics, where they are acuumulated in the central octopole segment
…undergo supersonic expansion and are skimmed into beam
10-7
turbo pump
10-8
turbo pump
10-10
turbo pump
10-7 torr
diffusion pump

52. Expanded view of larger C60 + Cn fullerenes
Larger fullerenes increasingly 13C enriched
C64
C66
C68
C70
C72
C74
C76
C78
C80

53. Electron donation stabilizes small fullerenes – prevents addition of small Cn
Empty cage
endohedral
C28
C284-
Less reactive
facile
C30 and higher
C30 and higher
+ C2
+ C2
Added electron density at the triple pentagon junction stabilizes – prevents C2 addition

55. Fullerene Growth Mechanism
“fullerene road” – Small fullerenes are the first to form, and then growth to larger fullerenes occur by uptake of small carbon species such as C2.
There has been no evidence that fullerene growth can actually occur this way…until now!
This growth model accounts for all experimental observations, for endohedrals and empty cages. This is potentially extremely significant if this checks out.

56. C60
C60 has been desorbed many times and analyzed many times by mass spec.
No growth to larger fullerenes occur.
However, most of these experiments are performed in a vacuum under conditions where fullerene growth will not be significant.

57. Bulk C60 coated on a graphite rod
The rod was put in our cluster source
Importantly, the experiment was performed exactly as I would if I were ablating a “clean” carbon rod to produce fullerenes.
Pulse gas, laser timing, etc all known to be the conditions to see fullerenes
The result: Addition of C2 to form larger fullerenes!

58. Small carbon clusters added to C60 to form larger fullerenes
Small carbon clusters added to C60 to form larger fullerenes. The coated C60 did not significantly fragment, but did significantly add carbon to form larger fullerenes.
Desorbed C60
Very minor fragmentation of C60
Significant growth to larger fullerenes
C70

59. Larger clusters are FULLERENES
Larger clusters are FULLERENES. C70 (formed from desorged C60) was SWIFT isolated, and then subjected to collision with He while exciting (SORI).
These larger clusters are clearly fullerenes as C2 fragmentation occurs.
C70
C68
C60

60. C60 coated on a quartz rod
To gain further insight, C60 was coated on a quartz rod
The same experiment was performed to see if fullerene growth occurred.
If no growth occurred, the small carbon species from the graphite were likely adding to C60 in the coated graphite rod experiment.
The result: no growth!

61. C60 + amorphous 13C on quartz rod
C60 was mixed was some amorphous 13C. There was much more C60 than amorphous 13C, approximately 3:1.
This mixture was applied to a quartz rod(from toluene)
Growth to larger fullerene occurred, and they were more 13C enriched with size. This is consistent with small cluster addition to C60

62. U@Cn+ directly formed from U/graphite target U@C28 experimental
simulated
experimental
directly formed from U/graphite target enriched with amorphous 13C
--for a total 13C content of 10%
were probed in the same manner and it is confirmed that titanium endofullerenes are completely assembled bottom-up as well.
There is no doubt that carbon from amorphous 13C in the U/graphite target is completely incorporated even in the smallest fullerene cage, C28.
BOTTOM-UP GROWTH
(9.5% 13C) simulated

63. Growth mechanism and endoherals
It is shown through our experiments that the classical endohedrals of Sc, La, and now Ti, Hf, Zr, U all strongly form endohedral fullerenes. But fullerenes smaller than C60 are most abundant, a clear deviation from the empty cages.
Ionic model – electrons from the metal are transferred to the carbon cage in endohedral fullerenes giving, essentially, an indissociable salt...the cage is negatively charged, the encapsulating metal is positively charged. Our experiments coupled with the theoretical data show this principle applies to small fullerenes too.
Electron transfer from the encapsulating metal to fullerene cage stabilizes the small fullerene from small carbon addition to larger fullerenes. This is why metals that can donate 3-4 electrons to the cage predominately form smaller fullerenes.

64. Growth mechanism and M@C28
Our experiments show that forms first. And then larger clusters are seen under conditions that allow more growth.
The metal nucleates initial growth.
Experiments will need to be performed with coating a rod with an endohedral, I plan to ask Shinohara for a sample to use. This will prove that the “fullerene road” applies to endohedrals as well as the empty cages.
Only a tetravalent metal can stabilize C28 sufficiently to yield a
Our calculations show that the donated electrons reside at the most reactive triple pentagon junction…the end result: C28 does not completely react to larger fullerenes.