## 2 Materials and Methods  
This research is aimed to investigate the laser sintering processes of silver NP arrays synthesized by electrical erosion in a spark discharge between silver electrodes in an argon flow atmosphere and deposited on a substrate. The setup for the micron-sized elements formation from such NPs is schematically presented in Figure 1a. NPs with an average size of around 10 nm were synthesized in a spark discharge chamber. Further an aerosol of those particles with the high-purity argon flow entered the focusing aerodynamic system in the form of the nozzle, described earlier in [14; 27]. The design of the nozzle provides an additional external compressing gas stream, which allows to control the cross-section of the aerosol stream by adjusting its parameters [28; 29]. In addition, the experimental setup enables to control the distance between the nozzle and the substrate within its change up to 4 mm, which makes printing on a curved surface possible. Silver NP arrays in the form of lines were deposited on polished silicon substrates 540 \(\upmu\)m thick placed on a precision movable coordinate table. To demonstrate the applicability of the proposed approach for the formation of silver NP arrays on heat-sensitive substrates, we conducted similar experiments on the deposition of silver NP arrays by dry aerosol printing and their subsequent sintering by pulsed laser radiation on the polyamide substrates 140 \(\upmu\)m thick. These lines had cross-sections in the form of a Gaussian distribution with the FWHM parameter in the range of 40-80 \(\upmu\)m and a height parameter of 10-20 \(\upmu\)m (Figure 2b). The lines were formed between two prefabricated silver contact pads about 5 \(\upmu\)m thick spaced 5 mm apart (Figure 2a). Contact pads were used to measure the conductivity of the sintered lines by a two-contact method. They were formed by an AMT AJ 15 XE aerosol printer (Neotech, Nuremberg, Germany) by depositing microdrops of silver NP ink and then sintered in a conventional resistive furnace at 250 \({}^{\circ}\)C for 20 min. The ink used for printing was a mixture of PG-007 MOP \(\upmu\)PG007-EG (PARU Co., Ltd., Sunchon, Republic of Korea) in a volume ratio of 3:1, with a mass concentration and an average nanoparticle size 46% and 18 nm, respectively. The method described provides a high conductivity of the material for  
Figure 1: The sketches of (**a**) the setup for the formation of silver NP arrays and (**b**) the setup for local laser sintering of deposited silver NP arrays. the contact pads, equal to the half of the specific conductivity for bulk silver [30]. This peculiarity is important for voltage drop minimization on contact pads while measuring the conductivity of the studied lines. The sintering process of the resulting silver NP arrays in the form of lines was done under the influence of a laser radiation with wavelengths 527, 980 and 1054 nm. The characteristics of the lasers used are given in Table 1. Four types of CW and pulsed laser sources were installed alternately on the laser position into optical stand being combined with the aerosol printing setup. The optical setup is schematically presented in Figure 1b. The use of the same coordinate table in the time-spaced processes of printing and subsequent sintering made it possible to continuously form and sinter NP lines. Sintering processes under the influence of laser radiation were controlled by adjusting the power and diameter of the laser beam, and the speed of movement both of the substrate and the sample. Pulsed laser sources were additionally characterized by a pulse repetition rate, chosen equal to 4 kHz for the research, and a pulse duration equal to 20 ns.