The goal of this research is to evaluate the potential of single and dual high RF reactors for the treatment of carbon fiber by Raman and FT-IR spectroscopies. Unsized poly-acrylonitrile (PAN) carbon fiber was treated with single high frequency (40.68 MHz) and double radio frequency capacitively coupled plasma (RF-CCP) discharge reactor (40.68/2.1 MHz) using pure nitrogen gas. The changes in the structure of the carbon fiber surfaces due to the variations of the D and G band intensity ratio (I-D/I-G), crystallite size (L-a) and Full-Width-at-Half-Maximum with plasma power, gas pressure, and treatment-time were described. It was found that the disorder of carbon fiber increases (the I-D/I-G ratio increased) with increasing high RF power and the process time. In contrast, the degree of the order (L-a) increases with increasing the gas pressure. It was also observed that the degree of graphitization accrued due to the shift of the D and G bands to the lower wave number. And, from FT-IR result, it was found that the C=C bond disappeared, and only carbon to nitrogen double and triple bonds are available by increasing pressure and RF power. In dual RF reactor, at high pressure and long process time, the disorder values (I-D/I-G) decrease with the increase of low frequency power. Furthermore, this mode has faster effects on the surface of carbon fiber than single RF mode. (C) 2013 Elsevier B.V. All rights reserved.