# Exploring Surface-Driven Mechanisms for Low-Temperature Sintering of Nanoscale Copper
## 3 Results and Discussion
### Sintering of Multiple Copper Nanoparticles
#### 3.1.3 Surface-Driven Atomic Migration
In the early stages of nanoparticle contact, there exists a significant number of interconnected voids, where the connecting regions are densely populated with jumping atoms. These jumping atoms facilitate the further evolution of the  
Figure 5: The graph illustrating the relationship between the number of atomic jumps and the sintering temperature highlights the step occurring between 500 and 600 K with a red dashed line. Figure 6: (**a–f**) The distribution of jumping atoms within the sintering system from 0.1 ns to 2.0 ns. (**g**) The pore volume and (**h**) the internal surface area changes with time during the sintering. voids and assist in establishing connections between voids that have yet to interconnect. As illustrated in Figure 6g-h, this rapid fusion process occurs within the initial 50 ns, followed by a stabilization phase. During the rapid fusion process, variations in particle positioning lead to fluctuations in the initial void volume and surface area. However, once the system transitions into the stabilization phase, the increased temperature persistently induces smaller values in void volume and surface area. The enlarged view of Figure 6b highlights two void connection regions that are on the verge of merging. In the vicinity of these two interconnected regions, there is a substantial presence of jumping atoms, with the atomic jumping directions concentrated around the narrowest areas of the connection, as illustrated in Figure 7a. These atoms undergo a gradual centripetal circular displacement around the connecting region, facilitating the exchange and structural rearrangement of atoms in the vicinity of that area. Concurrently, a distinct collective motion pattern emerges among these atoms, characterized by a head-to-tail connection, suggesting that the rapid dynamic state of surface atoms significantly enhances the low-temperature sintering process. Figure 7b shows the distribution of crystal structures, providing additional insights into the effects of different sintering temperatures on the low-temperature sintering process. The percentage of atoms identified as FCC structure and their post-slip configurations within the final sintered samples formed at different sintering temperatures. The black (FCC) curve suggests that the proportion of FCC components in the simulated system significantly increases at 600 K, compared to the range of 300-500 K. Additionally, higher sintering temperatures contribute to a greater presence of FCC components in the final samples. The red curve, corresponding to the structure after slips, reveals intriguing information, particularly a noticeable decline after 700 K. The slip planes in the simulated system revert to a perfect FCC structure through further sliding and twisting, suggesting a marked reduction in defects within the system at elevated sintering temperatures. Generally, fewer defects can enhance the mechanical strength of the sintered samples, although it is also possible that samples with a higher number of slip defects may develop stronger structures during tensile and compressive processes due to the continued sliding of the slip planes. Overall, as illustrated in Figure 7b, once the sintering temperature exceeds 600 K, the system undergoes substantial adjustments, transforming the originally amorphous components into crystalline phases. Through sliding and twisting, the initially imperfect FCC crystalline components are converted into perfect crystals, further enhancing the strength of the sintered samples. In the following section, the mechanical strength of  
Figure 7: **(a)** The circular atomic motion occurring around the connected regions that are about to merge. (b) The percentage of FCC structure and the post-slip structure relative to the total number of atoms in samples formed at the same sintering temperature. different samples is measured, and related elastic constants of the sintered samples are used to further elucidate the mechanisms by which sintering temperature influences the low-temperature sintering process.