The low-temperature electron spin resonance properties of ultra-small (0.45nm) double walled carbon nanotubes (DWCNTs) embedded in zeolite nanochannels were reported. An isotropic ESR signal was observed at gc = 2.00277 with the spin density (S = 1/2) ~ 1019g−1, which was suggested to originate from the carbon-related point defects in the DWCNTs. Measurements of the ESR line width and signal intensity as a function of temperature indicate that the spins were of a localized nature as opposed to the conduction type electrons observed in large diameter CNTs. The results were consistent with the suggestion that electrons were trapped at interstitial defects. The observed linear frequency dependence of the ESR line width of embedded DWCNTs points to 'strain' as the prime source of broadening. By contrast, the study of free-standing DWCNTs shows the presence of a distinctly superlinear frequency dependence of the signal width at low temperatures.

Electron Spin Resonance Investigation of Ultra-Small Double Walled Carbon Nanotubes Embedded in Zeolite Nanochannels. S.S.Rao, A.Stesmans, J.V.Noyen, P.Jacobs, B.Sels: Journal of Physics - Condensed Matter, 2011, 23[45], 455801