The plethora of potential applications associated with carbon nanotubes (CNTs) has triggered intense research on their synthesis and characterization. Their electronic properties range from semiconducting to metallic, depending on their chiral angle and diameter. However, tailoring their electronic properties by controlling their chiral angle and/or diameter is non-trivial, moreover, bundling during synthesis appears as a technological difficulty for obtaining their dispersion in matrixes. Instead, one uses post-growth treatments such as grafting molecules or metal clusters to the tube sidewall. Hence, understanding the effect of post-treatments is essential in terms of assessing process controllability, CNT stability and eventual integration. The question to be addressed in this work is: How does the grafting of nitrogen atoms at the tube surface influence on CNT electronic structure and dispersion characteristics?

In this study, multi-wall CNTs (MWCNTs) were exposed to atomic nitrogen formed in a microwave Ar + N₂ plasma. Their electronic structure was thereafter investigated using X-ray and UV photoelectron spectroscopy (at beamlines BW2 and Flipper II at Hasylab), showing that plasma treatment induces the formation of nitrogen chemical groups at the CNT surface altering the density of electronic states. The modification of the relative intensities of photoemission near 3.5 eV (assigned to 2p-π states), and around 5.5 eV (top of 2p-σ states) suggests that the groups introduced by nitrogen-plasma promote the 2p-σ states.

Dispersion characteristics found for plasma-functionalized-MWCNTs will be discussed in terms of reduction in the π-π interaction between tubes due to the promotion of 2p-σ states.

This work is financially supported by the Belgian Program on Interuniversity Attraction Pole (PAI 6/1), by Nano²Hybrids (EC-STREP-033311), and by DESY and the European Commission under contract RII3-CT 2004-506008 (IASFS). JG is research associate of NFSR (Belgium).

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