This article reports our recent investigation of the relationship between the density of the active species in nitrogen-oxygen plasma and the degree of isocyanate (R-NCO) functionalization onto multiwalled carbon nanotubes. We first monitored the plasma active species with optical emission spectroscopy focusing on atomic nitrogen and oxygen species, which are the major components to form NCO groups. The optical emission intensity allowed us to find the density of atomic nitrogen and oxygen in plasma through the plasma optical actinometry method. The actinometry result showed that the density of atomic nitrogen and oxygen becomes as close as the nitrogen content in plasma increased to 90%. We then investigated the functionalization ratio with the fluorescent method and Raman spectroscopy to monitor the degree of NCO functionalization. The results suggested that NCO groups on carbon nanotubes should increase as the content ratio of atomic nitrogen and oxygen becomes equal in the plasma.

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