*2.2. Microstructural Characterization of the Ni-Fe-TiO<sup>2</sup> Nanocomposites*

The microstructure of the Ni-Fe-5 wt.% TiO<sup>2</sup> nanocomposite is shown in Figure 1. The formation of a nanocrystalline Ni-Fe matrix with irregularly shaped TiO<sup>2</sup> particles (as indicated by black arrows) can be clearly seen. The TiO<sup>2</sup> particles were evenly dispersed in the Ni-Fe matrix. Chemical compositions of the Ni-Fe-5 wt.% TiO<sup>2</sup> nanocomposite are illustrated in Figure 2. Based on the analysis by EDS, only the presence of Ni, Fe, Ti, and O elements can be seen in the matrix. No other contaminants or impurity substances were formed in the matrix during the electrodeposition. Similar microstructural characteristics and chemical compositions could also be found in the other two nanocomposites. The average size of grain in the Ni-Fe matrix was measured using the Scherrer method [11]. It was found that the average size of the grain is between 15 nm~20 nm. One thing to consider during the analysis is that the Scherrer method used in this study might not provide accurate grain sizes because of some effects; for example, the presence of stacking faults and broadening of the diffracted beam caused by microstrains. Thus, TEM was also employed to determine the grain size for the investigated nanocomposites. Figure 3 shows the microstructures and grain sizes of the as-deposited Ni-Fe-5 wt.%

TiO2. Grain size is calculated from a plan-view of TEM micrograph. Apparently, the as-deposited Ni-Fe matrix was a polycrystalline structure with a grain size of ~50 nm (Figure 3a). The Ni-Fe matrix belongs to the FeNi3 phase with a face-centered cubic crystalline structure. Moreover, a diffraction ring pattern (Figure 3a) and numerous white nanocrystalline structures (Figure 3b) were seen in the matrix indicating that the TiO<sup>2</sup> nanoparticles were successfully deposited in the nanocomposite matrix. According to the camera length and *d*-spacings from the selected-area diffraction pattern, the deposited TiO<sup>2</sup> belongs to the anatase with a tetragonal crystalline structure. Hence, the microstructure of the electrodeposited Ni-Fe-5 wt.% TiO<sup>2</sup> nanocomposite was FeNi3 phase containing anatase nano-TiO2. These features were also discovered in the Ni-Fe-10 wt.% TiO<sup>2</sup> and Ni-Fe-20 wt.% TiO<sup>2</sup> nanocomposites. Figures 4 and 5 present a car-like shape model fabricated with Ni-Fe-5 wt.% TiO<sup>2</sup> nanocomposite through an optimal UV-LIGA method. Clearly, the micro-scale car-like shape model with a smooth surface and structural integrity could be fabricated via this potential method. calculated from a plan-view of TEM micrograph. Apparently, the as-deposited Ni-Fe matrix was a polycrystalline structure with a grain size of ~50 nm (Figure 3a). The Ni-Fe matrix belongs to the FeNi3 phase with a face-centered cubic crystalline structure. Moreover, a diffraction ring pattern (Figure 3a) and numerous white nanocrystalline structures (Figure 3b) were seen in the matrix indicating that the TiO2 nanoparticles were successfully deposited in the nanocomposite matrix. According to the camera length and *d*-spacings from the selected-area diffraction pattern, the deposited TiO2 belongs to the anatase with a tetragonal crystalline structure. Hence, the microstructure of the electrodeposited Ni-Fe-5 wt.% TiO2 nanocomposite was FeNi3 phase containing anatase nano-TiO2. These features were also discovered in the Ni-Fe-10 wt.% TiO2 and Ni-Fe-20 wt.% TiO2 nanocomposites. Figures 4 and 5 present a car-like shape model fabricated with Ni-Fe-5 wt.% TiO2 nanocomposite through an optimal UV-LIGA method. Clearly, the micro-scale car-like shape model with a smooth surface and structural integrity could be fabricated via this potential method. calculated from a plan-view of TEM micrograph. Apparently, the as-deposited Ni-Fe matrix was a polycrystalline structure with a grain size of ~50 nm (Figure 3a). The Ni-Fe matrix belongs to the FeNi3 phase with a face-centered cubic crystalline structure. Moreover, a diffraction ring pattern (Figure 3a) and numerous white nanocrystalline structures (Figure 3b) were seen in the matrix indicating that the TiO2 nanoparticles were successfully deposited in the nanocomposite matrix. According to the camera length and *d*-spacings from the selected-area diffraction pattern, the deposited TiO2 belongs to the anatase with a tetragonal crystalline structure. Hence, the microstructure of the electrodeposited Ni-Fe-5 wt.% TiO2 nanocomposite was FeNi3 phase containing anatase nano-TiO2. These features were also discovered in the Ni-Fe-10 wt.% TiO2 and Ni-Fe-20 wt.% TiO2 nanocomposites. Figures 4 and 5 present a car-like shape model fabricated with Ni-Fe-5 wt.% TiO2 nanocomposite through an optimal UV-LIGA method. Clearly, the micro-scale car-like shape model with a smooth surface and structural integrity could be fabricated via this potential method.

was found that the average size of the grain is between 15 nm~20 nm. One thing to consider during the analysis is that the Scherrer method used in this study might not provide accurate grain sizes because of some effects; for example, the presence of stacking faults and broadening of the diffracted beam caused by microstrains. Thus, TEM was also employed to determine the grain size for the investigated nanocomposites. Figure 3 shows the microstructures and grain sizes of the as-deposited Ni-Fe-5 wt.% TiO2. Grain size is

was found that the average size of the grain is between 15 nm~20 nm. One thing to consider during the analysis is that the Scherrer method used in this study might not provide accurate grain sizes because of some effects; for example, the presence of stacking faults and broadening of the diffracted beam caused by microstrains. Thus, TEM was also employed to determine the grain size for the investigated nanocomposites. Figure 3 shows the microstructures and grain sizes of the as-deposited Ni-Fe-5 wt.% TiO2. Grain size is

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*Inorganics* **2022**, *10*, x FOR PEER REVIEW 3 of 11

**Figure 1.** The FE-SEM micrographs of the Ni-Fe-5 wt.% TiO2 nanocomposite: (**a**) irregular shaped TiO2 particles are embedded in a nanocrystalline Ni-Fe matrix and (**b**) a higher magnification image taken from the Ni-Fe matrix (marked as the black circular area) in (**a**). **Figure 1.** The FE-SEM micrographs of the Ni-Fe-5 wt.% TiO<sup>2</sup> nanocomposite: (**a**) irregular shaped TiO<sup>2</sup> particles are embedded in a nanocrystalline Ni-Fe matrix and (**b**) a higher magnification image taken from the Ni-Fe matrix (marked as the black circular area) in (**a**). **Figure 1.** The FE-SEM micrographs of the Ni-Fe-5 wt.% TiO2 nanocomposite: (**a**) irregular shaped TiO2 particles are embedded in a nanocrystalline Ni-Fe matrix and (**b**) a higher magnification image taken from the Ni-Fe matrix (marked as the black circular area) in (**a**).

**Figure 2.** *Cont.*

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**Figure 2.** The chemical compositions of the Ni-Fe-5 wt.%TiO2 nanocomposite: (**a**) a higher magnification FE-SEM micrograph for EDS analysis and (**b**) an EDS spectrum taken from the matrix with TiO2 particles (marked as the black circular area) in (**a**). **Figure 2.** The chemical compositions of the Ni-Fe-5 wt.%TiO<sup>2</sup> nanocomposite: (**a**) a higher magnification FE-SEM micrograph for EDS analysis and (**b**) an EDS spectrum taken from the matrix with TiO<sup>2</sup> particles (marked as the black circular area) in (**a**). **Figure 2.** The chemical compositions of the Ni-Fe-5 wt.%TiO2 nanocomposite: (**a**) a higher magnification FE-SEM micrograph for EDS analysis and (**b**) an EDS spectrum taken from the matrix with TiO2 particles (marked as the black circular area) in (**a**).

**Figure 3.** The TEM micrographs of the Ni-Fe-5 wt.%TiO2 nanocomposite: (**a**) bright-field image showing the polycrystalline structure in the Ni-Fe matrix and (**b**) dark-field image indicating the TiO2 nanocrystallization formation. **Figure 3.** The TEM micrographs of the Ni-Fe-5 wt.%TiO2 nanocomposite: (**a**) bright-field image showing the polycrystalline structure in the Ni-Fe matrix and (**b**) dark-field image indicating the TiO2 nanocrystallization formation. **Figure 3.** The TEM micrographs of the Ni-Fe-5 wt.%TiO<sup>2</sup> nanocomposite: (**a**) bright-field image showing the polycrystalline structure in the Ni-Fe matrix and (**b**) dark-field image indicating the TiO<sup>2</sup> nanocrystallization formation.
