A uniform array of one-dimensional molecular iodine wires is fabricated by introducing iodine molecules into the channels of AFI zeolite crystals through the vapor phase. The only possible wire structures are formed by linking individual iodine molecules along intramolecular bond axis into a single line. Polarization dependence of Raman intensity at modes of iodine species indicates that the wires are aligned perfectly along the c axis of AFI crystal. Polarized optical absorption as well as resonant Raman scattering reveal two wire species inside the channels of AFI zeolite: In− and (I2)n wires.

The thermal stability of ultrasmall 0.4 nm single-walled carbon nanotubes ͑SWNTs͒ are studied by means of Raman-scattering measurements under a vacuum. The 0.4 nm SWNTs are very stable when they are confined inside the channels of the AlPO 4 -5 zeolite crystal. When these SWNTs are extracted from the channels into free space, however, they become thermally unstable because of the strong curvature effect. The in situ Raman-scattering measurement under 1 ϫ 10 −5 mbar shows all three structures of the 0.4-nm-sized SWNTs are destroyed between 730 to 790 K, a temperature range much lower than that of large-sized SWNTs. The ͑5,0͒ tube is only destroyed after the temperature reaches 790 K and seems slightly more stable than the other two structures: the ͑3,3͒ and ͑4,2͒ tubes. A reference measurement under UHV conditions confirms that the 0.4 nm SWNTs are destroyed after the same thermal treatment indicating that the structural degradation is determined by the curvature effect other than oxidation.