# High-Resolution Printing of Various Electronic Materials by Electrophotography
## 3 Results and Discussion
A small number of C\({}_{8}\)-BTBT toner particles was sufficient to fabricate a thin-film transistor because the volume of the toner particles was sufficient to fill a thin layer of less than several dozen nm [86]. PVP is a polymeric insulator material expected to act as a gate insulator in organic thin-film transistors. The melting point of PVP is 360 \({}^{\circ}\)C, which may be too high to fix PVP particles on the PET film thermally. PSS group polymers are alternative insulating polymers, with melting points ranging from 120 \({}^{\circ}\)C to 350 \({}^{\circ}\)C. However, as the melting point decreases, ball milling of these materials becomes difficult, the fluidity of nano/micro-particles decreases. Their fluidity can be adjusted with the addition of inert nanoparticles, including SiO\({}_{2}\) NPs. After the electrophotographic development of the electronic materials, the materials had to be fixed because the toner particles are individual, not forming a thin film. As previously investigated, materials with lower melting points, such as organic semiconductors, can be thermally fixed [86; 99; 100]. Application of ultrasonic vibration produces a thermal effect that is also useful for melting the organic semiconductor [87], as well as a mechanical effect that is effective for fixing metals such as Au and Ag. In this study, IPL sintering was performed to sinter metallic materials. Figure 6a shows the printed Ag stripe patterns before and after IPL sintering. The left half of the figure shows the powdery Ag pattern on the PET film, and the right half shows the IPL applied region. Before sintering, the surface of the printed Ag stripe exhibited a dark gray color and no gloss. Conversely, the IPL applied surface has a white-silver color and is glossy, specific to the bulk Ag surface. This change in appearance is achieved after applying several pulsed light flashes. SEM micrographs of the printed Ag pattern surfaces before and after IPL sintering are displayed in Figure 6b,c, respectively. The surface of the developed Ag stripe comprised individual Ag particles densely packed within the stripe pattern. However, after IPL sintering, the boundaries of the Ag particles became unclear because the surfaces of the Ag nanoparticles melted slightly and formed connections with them. No individual particles are observed on the IPL-sintered surface in the SEM images, and the features of the original piled particles are retained. In addition, a glossy silver color was observed in the macroscopic image. This indicates that the developed Ag particles formed continuous Ag thin films after IPL sintering. Figure 7 presents the printed Ag-Ni stripe pattern used for the four-probe electrical resistance measurement. A steady electrical current flow was applied between the two Ag paste pads, reinforcing the ohmic electrical contact by securing a sufficient contact area. The two probes touched the Ag paste, and an electrical current flowed through the sample. In addition, two other probes were used to measure the electrical voltage difference by directly touching the sintered Ag-Ni striped surface. Because the printed Ag-Ni stripe is thin, direct contact of the probes with the Ag-Ni stripe surface carries the risk of damaging the stripe. Therefore, we used a contact probe with a tip radius of 50 \(\upmu\)m to touch the Ag surface carefully. The two-terminal electrical resistance was greater than 75 M\(\Omega\) before sintering; however, it decreased to 84.9 \(\Omega\) after IPL sintering. We obtained 3.07 \(\Omega\) using four-probe electrical-resistance measurements.