# Smart Nanocomposites for Nanosecond Signal Control: The Nano4 waves Approach
## 3 Results and Discussion
### Properties of MNPs(Magnetic Nanoparticles)@NCS(Nanocarbon Supports) Nanoinclusions
#### 3.1.1 Morphological Characterization  
In the case of the in-situ deposition of magnetite (Fe\({}_{3}\)O\({}_{4}\)) on GO, abundant precipitation of the MNPs takes place on the graphenic surface. When using the solvothermal route, the particles are homogeneously dispersed on the graphenic sheets. For composites obtained by direct co-precipitation [16], the particles agglomerate in certain areas leaving others almost uncovered (Figure 5).  
A method involving covalent linkage of pre-formed magnetite nanoparticles covered by a silica coating was also tested [16]. For these products, SEM-EDX, TEM, and XPS analyses of the final products confirmed that a series of nanosized objects, presumably individual or slightly agglomerated silica-coated magnetite NPs, were covalently linked via an amide bond to the graphenic sheets (Figure 6).  
Figure 4: Measurement cell for nanopowders (**a**) microstrip configuration (**b**) coplanar configuration. Adapted from [21].  
Figure 3: (**a**) Measurement configuration for nanoinclusions powders (**b**) measurement configuration for absorber thin plates, adapted from [23].  
However, much larger agglomerates, coexisting independently from the synthetized nanocomposites, were also found. In some cases, it seems that graphene sheets are wrapped around these agglomerates (Figure 7). These undesired objects are formed of magnetite @ silica core-shell nanoparticles.  
Figure 5: SEM (**top**) and TEM (**bottom**) images of the GO-supported magnetite Fe\({}_{3}\)O\({}_{4}\) nanocomposites obtained by direct co-precipitation (**left**) and solvothermolysis (**right**) [16], evidencing the differences in distribution of the magnetite NPs over the graphenic surface.  
Figure 6: SEM images of the covalently-linked silica-coated Fe\({}_{3}\)O\({}_{4}\) magnetite nanocomposite. A magnification of the zone indicated by the dashed orange rectangle (**left** image) was made to evidence the presence of a series of nanosized objects (**right** image) considered to be the silica coated MNPs.  
Given these considerations, the covalent or direct co-precipitation routes were considered less suitable than the solvothermal or sol-gel approaches. The performance of the solvothermal method was thoroughly studied in terms of loading ratio, nanoparticle size, shape, and influence of the Fe precursor on these parameters. Also, the magnetic properties of the MNPs deposited on NCS were studied by a superconducting quantum interference device (SQUID), which revealed their superparamagnetic behavior [16]. Indeed, the extensive characterization of the obtained synthetic products proved that Fe\({}_{3}\)O\({}_{4}\) is the only Fe-containing species in the obtained nanocomposites. No zero-valent iron (ZVI) could be obtained given the mild reducing conditions used during the synthesis described therein. We have nonetheless also developed other synthetic procedures to deposit ZVI@\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) core-shell nanoparticles on GO. In those cases, the iron species were determined by Mossbauer spectroscopy [17] and confirmed by SQUID.