Effects of hydrogen and NH(x) species produced by a surface-wave excited Ar/NH(3) plasma on amino group introduction onto a polyurethane surface were studied by comparing the results of optical emission spectroscopy (OES) and primary amino group concentration. For increasing the introduced primary amino group concentration on the surface, the monitoring and control of the concentration of NH(x) species as a precursor and that of atomic hydrogen as an etchant are important. From the results of X-ray photoelectron spectroscopy (XPS) and OES analysis, the primary amino group concentration and the emission intensity of H(beta) reached a minimum and a maximum, respectively, at around 25% NH(3) gas mixture ratio. An excess of atomic hydrogen over nitrogen grafting species might reduce the amino group selectivity and N/C surface density. To increase the concentration of NH(x) species produced in a plasma, the enhancement of NH(x) generation by the Penning effect was examined by adding Ar gas. As a result, the primary amino group concentration increased with the increase in the emission intensity of NH. However, the amino group selectivity became lower than that in the case of pure NH(3) plasma treatment since not only the primary amino group concentration but also the secondary and tertiary amino group concentrations increased with the enhanced decomposition of NH(3) by Ar metastables. (C) 2011 The Japan Society of Applied Physics