# Annealing Process-Induced Microstructural Variation in NiV/B4C Multilayers
## 4 Conclusions  
Previously, annealing of NiV/B\({}_{4}\)C multilayers with a periodic thickness of 3 nm has shown that crystallization is the main cause of thickness expansion and greater interface roughness. To further study the microstructure changes in thicker annealed multilayers, NiV/B\({}_{4}\)C multilayers with a period of 8 nm were prepared by the magnetron sputtering method, and two annealing experiments were carried out. The first group of annealing experiments were conducted with varying annealing temperatures at a constant annealing time, while the second involved different annealing times at a fixed annealing temperature. The main objective of this paper is to examine the impact of annealing on the microstructure of thicker NiV/B\({}_{4}\)C multilayers, with the goal of offering insights to enhance the performance of these multilayers. Temperature-dependent experiments show that annealing from 70 \({}^{\circ}\)C to 290 \({}^{\circ}\)C can slightly increase thickness and interface width. High temperature annealing results in significant structural changes. At 340 \({}^{\circ}\)C, the thickness of the film changes significantly, and the average interface width increases by 7%. The time-dependent results showed that most of the microstructure changes occurred mainly after 60 min. GISAXS and X-ray  
Figure 11: TEM data of the multilayers annealed at different parts: (**a**) TEM cross-section images, (**b**) SAED of (**a**), (**c**) TEM image of the upper part of the sample, (**d**) TEM image of the middle part of the sample, (**e**) TEM image of the bottom part of the sample. Figure 12: TEM gray scale image and fitting results: (**a**) grayscale information selection, (**b**) layer profiles and (**c**) fitting curve obtained from the images in the plane of the layer. scattering analysis show that the increase in interface width is mainly due to the increase in interface roughness, and the lateral correlation length is inversely proportional to the interface roughness. However, after annealing at 340 \({}^{\circ}\)C for 120 min, recrystallization and enhanced crystallization led to a significant increase in the transverse correlation length and interface roughness. These results differ slightly from those observed in previous studies on 3 nm multilayers. The XRD results show that the annealed NiV/B\({}_{4}\)C multilayer films showed a microcrystalline structure, and the crystallization caused the change in film thickness and interface roughness, which was the main reason for the change in the microstructure of the multilayer films. AFM results show that after annealing at 340 \({}^{\circ}\)C for 120 min, the surface roughness of the multilayer films increases significantly and the crystalline morphology appeared on the surface, which is consistent with the results of XRD. By TEM test, it was found that the diffusion of the multilayer membrane was not obvious, and the overall state was microcrystalline. The gray value was analyzed by error function, and the interface width was close to the GIXR result. Therefore, we hypothesize that high-temperature annealing causes a substantial increase in the thickness of the multilayer, thereby facilitating the crystallization of the multilayer film. In addition, extending the high-temperature annealing time promotes the crystallization of multilayers. As a result, prolonged high-temperature annealing leads to the recrystallization of the multilayers, which enhances the crystal structure and subsequently increases the interface roughness and lateral correlation length. In view of this phenomenon, we plan to conduct thermal stability studies on multilayers with thicker film layers, aiming to establish a foundation for the development of non-periodic NiV/B\({}_{4}\)C multilayers. Conceptualization, C.C., Z.W. ([PERSON]), Z.Z. ([PERSON]) and Z.Z. ([PERSON]); methodology, C.C., H.J., Z.W. ([PERSON]), Z.Z. ([PERSON]) and Z.Z. ([PERSON]); software, C.C., H.M. and L.J. ; validation, C.C., L.J., [PERSON] ([PERSON]) and [PERSON] ([PERSON]): formal analysis, C.C., H.J. and L.J.