Weused electron spin resonance (ESR) to analyze several kinds of single-walled carbon nanotubes (SWNTs) synthesized by different methods. We observed that ESR is a sensitive probe that can be used to observe major differences between samples of carbon nanotubes (CNTs), in relation to their proportion of magnetic catalysts, impurities or defects. We analyzed the ESR spectra of CNTs in the usual way, by three overlapping lines. We then, implemented a function to fit the spectra, which gave us the intensity, line width (DHPP), and resonance line position (g factor) of each component line. The asymmetric line, which is assigned to the conduction electrons, could be used as a fingerprint of CNT purity. However, this asymmetric line is not always observed, since the three ESR lines often overlap, particularly when there is a large amount of paramagnetic ions. We studied the ESR spectra for different samples and estimated their purity by comparing the resulting parameters with data obtained by Raman spectroscopy on the same samples.Postprint (published version
Studies of electron spin resonance (ESR) are reported on several types of single-walled carbon nanotubes (SWCNTs) synthesized by different methods. We work both with the obtained samples, which contained randomly distributed semiconducting and metallic SWCNTs, and with selected 99% semiconducting or metallic SWCNTs. Our aim is to use ESR spectroscopy in order to assess the quality of carbon nanotubes. We analyze the temperature dependence of ESR spectra in the range 4-300 K and report the temperature dependence of the linewidth, the intensity and the asymmetry factor (I þ /I À ) of the ESR lines. The ESR response from the arc discharge SWCNTs produced using non-magnetic Pt/Rh catalyst and from the selected semiconducting tubes exhibits an asymmetric line with an intensity that remains almost constant with decreasing temperature, showing a constant linewidth of about 2.9 mT. For selected bucky paper (BP) metallic or semiconducting carbon nanotubes, we also study the ESR signal according to the BP parallel or perpendicular orientation to the magnetic field. The g-factor and the asymmetry factor show a clear anisotropy.
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