Ptfe

Polyyne-containing carbon side Damaged polyyne side

Polyyne-containing carbon side Damaged polyyne side

CNTs

Polyyne-containing carbon side Damaged polyyne side

Figure 4. Illustration of process of heating and synthesis of CNTs under an electron radiation: melting of the PTFE film occurs at 350 °C and growth of aligned CNTs starts on the nondamaged polyyne side at 800 °C.

Figure 4. Illustration of process of heating and synthesis of CNTs under an electron radiation: melting of the PTFE film occurs at 350 °C and growth of aligned CNTs starts on the nondamaged polyyne side at 800 °C.

Metal core Carbon micro-graphenes

Figure 5. Formation process of carbon nanocapsules and nanoparticles upon the evaporation of magnesium metal core particles under both thermal heating and electron radiation.

differential growth of CNTs from CNCs and CNPs. Under the investigated conditions, CNTs are always grown on the inside of the carbonized layer while CNCs and CNPs are grown on the outside where the magnesium metal particles are supposed to be richer based on the incorporation mechanism during the electrochemical reduction. These metal particles may act as growth cores to form the CNCs and CNPs. Compared to those in the inner layer, polyyne-containing carbons in the outside layer are more oxidized (or more damaged), and thus more wettable on the metal particles owing to easy cross-linking. The cross-linking increases the viscosity of the melted carbons, prohibiting the formation of long carbon rods (1D). It has been known that the CNTs are formed from the rod-like carbons after graphitization. Therefore, through this in-situ TEM investigation, selective solid-state formations of CNTs and CNCs/CNPs can be explained thoroughly with direct experimental evidences, especially with the degree of graphitization of graphene sheets for all these nanocarbons at various formation stages [72a].

Apart from the selective growth study, the same group of researchers has recently observed the graphitization mechanism during the CNT formation based on the in-situ HRTEM investigation [72b]. Their study shows that micrographenes exist from the beginning of the formation process and later change to highly ordered graphene layers through fusion and rearrangement of premature layers. These processes are also accompanied by evaporation of micro-graphenes. In their latest investigation [72c], these researchers found that the CNTs prepared under TEM environment are formed in two steps: rapid formation of rod-like carbons, and slow formation of hollow cavity in parallel with graphitization. In particular, the length and the diameter of the CNTs are defined in the first step, and are not varied any further during the second step, that is, the hollow inner cavity formation.

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