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Carbon nanotubes can be filled with a high concentration of fullerene molecules to form "peapods". We have investigated such peapods obtained from different sources, and with either C60 or C70 as "peas", under high pressures at room temperature and after various types of high pressure treatment, at room temperature and elevated temperatures. Under some conditions, Raman spectroscopy can be used to detect and study the fullerene molecules inside the nanotubes, both at atmospheric pressure and under high pressures. Such Raman studies show that irradiation by light can induce the formation of covalently bound dimers or short chains inside the tubes. In contrast to most other studies, the conclusion drawn from other measurements is that the interaction between the tube walls and the fullerene molecules inside is equivalent to an effective applied pressure on the fullerene molecules. When using high photon energies, dimerization of the fullerenes is observed. When an external pressure is applied, a similar dimerization is observed at a rather low applied pressure. When the external pressure is increased, the effective pressure on the fullerenes inside increases much slower than the applied pressure, showing that the tube walls to some extent protect the fullerenes inside. Under very-high-pressure conditions, longer polymerized fullerene chains (oligomers) finally form inside the nanotubes. |