We report optical properties of the smallest single-walled carbon nanotubes (SWNTs) with a diameter of only 3 A. These ultrasmall SWNTs are fabricated in the elliptical nanochannels of an AlPO-11 (AEL) single crystal. Polarized and resonant Raman scattering unambiguously revealed that these 0.3 nm SWNTs are of (2,2) armchair symmetry. Interestingly, the (2,2) armchair tube has two metastable ground states corresponding to two slightly different lattice constants in the axial direction: one state is metallic and the other is semiconducting.

Well-aligned iodine molecular wires were synthesized by means of loading iodine molecules in the elliptical nanometer-scale channels of AlPO(4)-11 (AEL) single crystals. Polarized Raman spectra reveal that the iodine molecular wires are oriented along the crystal channel direction by lining iodine molecules on the yz plane, where y and z represent the channel direction and the major-axial direction of the elliptical rings, respectively. Natural iodine wires are unstable, but they are very stable in the AEL channels. The template technique offers us an ideal platform to study the novel properties of these molecular wires.

No abstract