# Annealing Process-Induced Microstructural Variation in NiV/B4C Multilayers
## 3 Results and Discussion
### Transmission Electron Microscope Analysis  
To study the underlying physics of the changes in lateral correlation length and interface roughness, the microstructure of the NiV/B4C multilayer after annealing at 340 \({}^{\circ}\)C for 120 min was characterized by transmission electron microscopy (TEM). As shown in Figure 11, the bright layers were B4C, and the dark layers were NiV. The periodic layered structure of the NiV/B4C multilayers were well-defined through the low magnification images, which confirmed the results found by GIXR and GISAXS. The high-resolution image (Figure 11c-e) showed that the NiV/B4C multilayer had relatively clear interfaces. In Figure 11, the top, middle, and bottom layers of the NiV/B4C multilayer were aligned, and it was found that the thickness of the multilayer layers changed little from the bottom layer to the top layer, indicating that the multilayer was uniform overall after annealing, which was consistent with the GIXR results. After annealing, the interfacial diffusion of the multilayer films was not obvious, which indicated that the interfacial defects were dominated by the interface roughness. The weak crystallization of the NiV/B4C multilayer was not easy to observe with TEM. The NiV/B4C multilayer after annealing was micro-crystalline, and a slight diffraction ring could be seen in the selected electron diffraction in Figure 11b. This was consistent with the XRD results (Figure 6). To study the interface conditions after the annealing of the NiV/B4C multilayer, the one-dimensional projection gray value results of the 2D TEM image were analyzed, and the results are shown in Figure 12. In previous studies [27], the interface width in grayscale maps has typically been defined as the middle portion of the transition region (30-70%). However, we believe this definition lacks sufficient precision. Therefore, we applied an error function to fit the grayscale information [19; 28], which provides for more accurate determination of the interface width, and the interface widths were \(\sigma_{\text{B4C-on-NiV}}=0.35\) nm and \(\sigma_{\text{NiV-on-B4C}}=0.36\) nm, respectively, which were consistent with the GIXR results for \(\sigma_{\text{B4C-on-NiV}}=0.35\) nm and \(\sigma_{\text{NiV-on-B4C}}=0.35\) nm.  
Figure 10: The lateral correlation length (the black line is the result of IMD software, and the red line is the result of GISAXS): (**a**) annealing at different temperatures, (**b**) annealing for different times.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Annealing Parameters** & \(\xi_{\text{//IMD}}\) **(nm)** & \(\xi_{\text{//GISAXS}}\) **(nm)** & \(\Delta\xi_{\text{//}}\) **(nm)** \\ \hline
70 \({}^{\circ}\)C for 60 min & 12.539 & 12.509 & 0.030 \\
140 \({}^{\circ}\)C for 60 min & 12.405 & 12.375 & 0.030 \\
220 \({}^{\circ}\)C for 60 min & 12.263 & 12.236 & 0.027 \\
290 \({}^{\circ}\)C for 60 min & 12.131 & 12.113 & 0.018 \\
340 \({}^{\circ}\)C for 60 min & 12.037 & 12.018 & 0.018 \\ \hline
340 \({}^{\circ}\)C for 10 min & 12.140 & 12.099 & 0.041 \\
340 \({}^{\circ}\)C for 30 min & 12.097 & 12.065 & 0.032 \\
340 \({}^{\circ}\)C for 60 min & 12.037 & 12.018 & 0.018 \\
340 \({}^{\circ}\)C for 120 min & 25.867 & 25.838 & 0.028 \\ \hline \hline \end{tabular}
\end{table}
Table 5: The lateral correlation length of NiV/B4C multilayers after annealing.