Electron spin resonance from semiconductor-metal separated SWCNTs

Electron spin resonance in the X band is reported for fully metal–semiconductor separated SWCNTs. For the experiments samples were immersed in ethanol or wrapped into a teflon foil. The response from the metallic tubes exhibits a strong asymmetry in the line shape whereas the asymmetry for the semiconducting (SC) tubes is comparatively small. In both cases the line widths are unusual small, of the order of 4G. Particular attention is paid to SC nanotubes which exhibit a much stronger signal as compared to the metallic tubes. The signal intensity is nearly Curie like with a small enhancement beyond 1=T in the low temperature range. The 1=T behavior renders the ESR response unobservable at 300 K. The finite value for the asymmetry parameter in the SC tubes is assumed to originate from charges picked up during exposure to air or to ethanol.