Page 62 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin

Chapter 3
insufficient techniques to characterize gas phase products, the quantitative determination of the ferrocene dissociation degree is out of the scope in present work. Figure 3.7(b) is the selected area electron diffraction (SAED) image of nanoparticles produced at the same condition. It brings an additional proof that nanoparticles have polycrystalline structure. The observed rings can either be ascribed to γ-Fe2O3 (3 1 1), (4 0 0) and (4 4 0) planes or to Fe3O4 (3 1 1), (4 0 0) and (4 4 0) planes, indicating the presence of iron oxides in the products. However, since both Fe3O4 and γ-Fe2O3 have same crystalline structure (cubic structure) and almost identical lattice parameter, it is quite difficult to distinguish them.27,28
Figure 3.8 (a) HRTEM image and (b) SAED result of nanoparticles prepared at 1.05 W plasma power 3.3.5 XRD Measurements
The crystalline structure of obtained nanoparticles is further characterized by XRD. Figure 3.9 shows XRD patterns of products prepared at power of 1.05 W and ferrocene concentration of 29.0 ppm. However, we found a broad and significant peak in the 2θ range of 10◦-30◦. To confirm whether it this originates from the specimen itself or from the glass holder covered by Vaseline to load the sample, we carried out an additional comparative XRD measurement by analyzing the background signal from the glass holder with Vaseline. The crystalline nature of produced nanoparticles was confirmed by the results, which is consistent with the HRTEM analysis. Broad peak in the 2θ range of 10◦-30◦ comes from background, while other sharp, less intensive peaks come from our nanoparticles. Peaks at 2θ values of 33.13◦, 40.88◦ and 54.19◦ can be ascribed to the (1 0 4), (1 1 3) and (1 1 6) crystal planes of α-Fe2O3 (JCPDS PDF card #33-0664). Peaks at 2θ values of 30.01◦, 35.60◦, 57.02◦ and 62.66◦ are either ascribed to the (2 2 0), (3 1 1), (5 1 1) and (4 4 0) crystal planes of γ-Fe2O3 (Maghemite, JCPDS PDF card #39-1346) or to the (2 2 0), (3 1 1), (5 1 1) and (4 4 0) crystal planes of Fe3O4 (Magnetite, JCPDS PDF card #19-0629). As it was discussed above, due to the similar crystal structures, we cannot clearly discern between Fe3O4 and γ-Fe2O3 from XRD result. In addition to iron oxide, prominent peaks at 2θ values of 43.25◦, 43.49◦ and 78.46◦ corresponding to the (1 0 3), (0 0 10) and (1 0 14) crystal planes of carbon (JCPDS PDF card #26-1083) are also observed.
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