Graphite rod surface coated with C60 Paul Dunk

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

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

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

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

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

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

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

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

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

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

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

Skimmer action more slowly

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

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

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

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

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

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

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

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

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

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

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

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

This study shows unequivocally that fullerenes can grow by ingestion of smaller carbon species in this case C60 + Cn → C62 C64 C66 C68 C70 C72 etc with Paul Dunk and Alan Marshall

Multi stage formation mechanism

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

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

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

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

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

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

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

Graphite rod surface coated with C60

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

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

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

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

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

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

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

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.

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.

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:.

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

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

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

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.

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.

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!

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

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

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!

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

U@Cn+ directly formed from U/graphite target U@C28 experimental U@C28 simulated U@C28 experimental U@Cn+ directly formed from U/graphite target enriched with amorphous 13C --for a total 13C content of 10% U@C28 Ti@Cn 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. U@C44 BOTTOM-UP GROWTH U@C28 (9.5% 13C) simulated U@C36

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.

Growth mechanism and M@C28 Our experiments show that M@C28 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 M4+@C284- 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.