A high-efficiency surface modification of graphite-encapsulated iron compounds magnetic nanoparticles using an inductively coupled radio-frequency plasma with a pulsed particle explosion technique was studied. A significant increase in N 1s peak intensity in the X-ray photoelectron spectroscopy spectra was obtained by applying a negative pulsed bias voltage of −1 kV to the substrate stage for 15 s or less at a repetition frequency of 1 kHz and a duty ratio of 50% in ammonia plasma. The intensity of the N 1s peak and the N/C ratio of the nanoparticles treated in a pulsed particle explosion system were 3–4 times higher than those of the particles treated without bias. The amino group population of nanoparticles treated using the present technique was determined to be about 8.2 × 104 molecules per nanoparticle, roughly four times higher than that of particles treated without bias. The dispersion of the plasma-treated nanoparticles was significantly improved compared with those of the untreated and treated particles in the nonbiasing system. The surface structure analysis by transmission electron microscopy showed no significant damage on the structure or morphology of the treated nanoparticles, indicating that the present technique is applicable to the high-efficiency surface modification of magnetic nanoparticles.

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In order to enhance the treatment processing for powder of nanoparticle, we developed a modified setup using an inductively coupled radio frequency plasma with a pulsed explosion technique. Applying a negative pulsed bias voltage of -1 kV to the substrate stage in 15 seconds with a repetition frequency of 1 kHz and a duty ratio of 50 % in ammonia plasma, a significant increase of N 1s peak intensity in the X-ray photoelectron spectroscopy spectra was observed. The intensity of N 1s peak treated in the pulsed-biasing system raised both about four times higher than those of the particles treated without bias. After plasma treatment, the amino group was suggested to be covalently functionalized onto the nanoparticle surface and quantitatively examined by chemical derivatization. The amino group population attached onto treated nanoparticles was determined about 8.2 x 104molecules per nanoparticle, roughly four times higher than that of particle without biasing which was about 1.9 x 104molecules per nanoparticle. The surface structure analysis by a high resolution-transmission electron microscopy showed no significant damages were found on the nanoparticles, indicating that the present technique is suitable mainly for surface modification of powder materials without bringing any damages on their structural and morphological surface.

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