We prepared yarned carbon nanotube (CNT) fibers from a CNT forest synthesized on a Si wafer by chemical vapor deposition (CVD). The yarned CNT fibers were thermally annealed to reduce their resistance by removing the amorphous carbonaceous impurities present in the fibers. The resistance of the yarned CNT fiber gradually decreased with an increase in the annealing temperature from 200℃ to 400℃ but increased again above 450℃. We carried out thermogravimetric analysis (TGA) to confirm the burning properties of the amorphous carbonaceous impurities and the crystalline CNTs present in the fibers. The pattern of the mass change of the sample CNT fibers was very similar to that of the resistance change. We conclude that CNT fibers should be thermally annealed at temperatures below 400℃ for reducing and stabilizing their resistance.
