Page 94 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin

Chapter 5
Figure 5.2 A representative OES spectrum recorded from discharge operated at plasma power of 3.4 W, with Ni(cp)2 concentrations of 35 ppm.
Moreover, to investigate the influence of the plasma power on the dissociation process, spectra recorded from discharges operated at conditions 1-3 are shown in Supplementary Material Figure S1 a-c. It is clearly observed that the line intensities of the Ni(cp)2 originated fragments and their ratios relative to the argon lines increase with the discharge power, indicating concentration growth of the corresponding excited species. This is probably due to an increased electron density at higher power which, in turn, results in a higher precursor dissociation rate and deeper fragmentation. In addition to the plasma power variation, spectra corresponding to different Ni(cp)2 concentrations are also recorded to study the effect of variation in precursor flow. As shown in Supplementary Material Figure S1 d-f, for the discharge with a Ni(cp)2 concentration of 11.7 ppm, only barely distinguishable spectral features of Ni(cp)2 fragments are detected. By contrast, their intensities are found to increase significantly with the Ni(cp)2 concentration. This is probably because a higher Ni(cp)2 concentration results in an improved production rate of radiating fragments. Therefore, in the described setup, the precursor dissociation rate can be controlled by tuning the discharge power or by the variation in Ni(cp)2 mass flow.
Ex-situ materials characterization starts with SEM analysis to give a general overview of product morphology. Representative images of products synthesized at 1.3 W and 3.4 W with 35 ppm Ni(cp)2 vapors are shown in Figure 5.3 to study the influence of plasma power. Meanwhile, typical images of products obtained at 2.0 W and 2.7 W with the same Ni(cp)2 concentration are also provided in Supplementary Material Figure S2 for complementary information. It is indicated that the products prepared at 1.3 W are clustered as spherical
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