# Temperature Estimation during Pulsed Laser Sintering of Silver Nanoparticles
## 4 Results and Discussion  
Ag NPs printed lines were sintered to find the effect of laser parameters on the surface morphology and electrical properties. Beam duration of a CW laser was modulated into milliseconds and microseconds with appropriate repetition rates. In Figure 3 the resistivities of Ag NPs lines are presented with various scanning speeds of 14, 27, 81, 135, and 189 \(\mu\)m/s. The pulse durations of 10 and 100 ms with corresponding repetition rates of 10 and 1 Hz at 276 mW were tested to find the combinations that can produce low Ag NPs line resistivity. A minimum resistivity of about 3 \(\mu\Omega\cdot\)cm was obtained with 100 ms and 1 Hz at the scanning speed of 135 \(\mu\)m/s, which corresponded to 50% of pulse overlapping. With 95% overlapping at 14 \(\mu\)m/s with 100 ms and 1 Hz, the resistivity of approximately 3.7 \(\mu\Omega\cdot\)cm was obtained. However, 95% overlapping at 14 \(\mu\)m/s is impractical to be applied since the total scanning times reaches to 500 s to cover the 7 mm-long sample. The laser parameters of 100 ms, 1 Hz, and 135 \(\mu\)m/s were adopted for the numerical calculation since the lowest resistivity was obtained at this combination. The obtained minimum resistivity is an improved result compared with those from previous laser sintering studies [35] and conventional oven sintering at much higher temperatures and longer processing times [36; 37]. Using similar Ag NPs ink composition, [PERSON] et al. [38] were able to produce 5.8 \(\mu\Omega\cdot\)cm via furnace sintering at 250 \({}^{\circ}\)C for 30 min. Moreover, the obtained minimum resistivity of approximately 3 \(\mu\Omega\cdot\)cm with 100 ms, and laser parameters of 1 Hz, 276 mW, and 135 \(\mu\)m/s is lower than the reported values from several other sintering methods [18; 39]. The discrepancies among the resistivity values in Figure 3 have been found to be caused by several parameters such as surface  
Figure 3: Resistivity against various scanning speeds for 100 ms and 10 ms pulse durations at 1 Hz and 10 Hz repetition rates. morphology [40], laser wavelength effect [35; 40], properties of the organic additives used in the NPs ink [16; 41], the size of NPs [36; 42], laser power, and scanning speed [14; 35; 43]. The periodic temperature fluctuations caused by the pulse interaction and relaxation periods are depicted in Figure 4. The position where the maximum temperature appears coincides with the center of the irradiated laser beam at the specified moment. The 7000 \(\upmu\)m-long Ag NPs line is completely covered in approximately 52 s with a scanning speed of 135 \(\upmu\)m/s. The maximum recorded temperature was around 204.4 \({}^{\circ}\)C. As mentioned before, 5.8 \(\upmu\)\(\Omega\)-cm were obtained via furnace sintering at 250 \({}^{\circ}\)C for 30 min. However, the lower resistivity of 3 \(\upmu\Omega\)-cm was produced at 204.4 \({}^{\circ}\)C in scanning pulsed laser sintering. The drop in the temperature profile after attaining the maximum local temperature at the end of each pulse is due to the pulse relaxation (0.9 s pulse relaxation period). During the laser interaction period of 0.1 s, the energy is absorbed by the NPs and subsequently conducted to the surrounding NPs. The laser energy absorption and the subsequent heat loss from the NPs to their surroundings occur in less than 1 ns [44; 45]. Therefore, the 0.1 s laser beam interaction period with the Ag NPs is long enough to cause a continuous rise in the process temperature. The rise and fall of the temperature in the plot depict the corresponding laser excitation and relaxation periods. During the simulation, the starting position of the laser scan was at the boundary of the Ag NPs pad and Ag NPs line such that half of the laser beam irradiated on the pad and half on the Ag NPs line. From the plot we notice that the temperature rise is instantaneous as the pulse interacts with the NPs without any time delay.