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RESEARCH PRODUCT

Temperature Dependence of Electronic Transitions of Single-Wall Carbon Nanotubes:  Observation of an Abrupt Blueshift in Near-Infrared Absorption

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Near-infrared (NIR) absorption spectra of single-wall carbon nanotube (SWNT) films are studied between 10 and 293 K. The most prominent effect is the shift of bands with temperature. Some nanotubes show a redshift of transition upon increasing temperature while some show blueshift and others show no shift. The shift is interpreted to originate mainly from the effect of strain induced in the tubes because of interaction with the environment. In particular, at temperatures T = 175−225 K, for some bands, there is an abrupt large blueshift, which is interpreted to originate from interaction of the nanotubes with water. Two models could be considered to explain the effect:  (1) strain induced by a phase transition of water confined inside the nanotubes or (2) adsorption−desorption of water on the surfaces of nanotubes, but the current experimental data does not allow to distinguish unambiguously between the two possibilities. Some evidence of the presence of adsorbed water is obtained from coupled thermogravim...