# High-Resolution Printing of Various Electronic Materials by Electrophotography
## 3 Results and Discussion
Figure 3: SEM image of the printed microcircuit pattern with Ag–Ni conductive toner particles. In addition, the main components of the small scattered particles around the printed interdigital pattern are stray toner particles and aggregates. Because some of the low-charged toner particles tend to scatter owing to the movement of the magnetic brush during the printing process, a small number of toner particles stick to the target electrode substrate surface. It is necessary to decrease the toner ratio of the developer to reduce excess toner scattering. A minor component of the scattered particles is a fragment of the carrier particles. Large fragments of carrier particles were removed using a magnet. However, smaller carrier particle fragments have lower magnetic attractive force owing to their smaller volume and are thus difficult to remove. Methods for suppressing or removing particles of small size have yet to be fully developed. Graphene nanoplatelets (GNPs) purchased from Aldrich were expected to be conductive electronic materials that could be developed using electrophotographic printing. The nominal size of the GNP was less than 2 \(\upmu\)m in diameter and a few nanometers in thickness. GNPs are excellent electronic toner materials because of their high fluidity and sufficiently  
Figure 4: Energy dispersive X-ray spectra of the printed Ag–Ni stripe transferred to carbon tape. Due to the atomic ratio calculation, Ag-94.6, Ni:1.8, and Fe:3.6% were obtained. The observed Ni ratio was lower than the nominal Ag-Ni ratio of 5.44:1 in the Ag–Ni toner. Figure 5: Optical micrograph of the interdigital electrode patterns of various electronic materials. (a) Ag NP + Ni NP, (b) Cu NP, (c) ITO NP, (d) ITO NP SEM, (e) C\({}_{8}\)-BTBT, (f) PVP. small particle sizes, producing several \(\upmu\)m patterns. In addition, the electrical resistance of the developed GNPs was sufficiently low, even before the sintering process. In addition, it was confirmed that carbon nanotube powder and other carbon material particles were also developed using the electrophotographic method. Therefore, by combining the proper sintering processes, thin-film printing of carbon materials is possible. These materials could be useful in the development of batteries. Oxide electronic materials such as ITO, ZnO, NiO, and SiO\({}_{2}\) NPs can also be printed using electrophotography. All oxide powders were purchased from Sigma-Aldrich (Burlington, MA, USA) and were used as received. Figure 5c shows the results of high-resolution ITO printing. Because ITO is a transparent electrode material, it is difficult to observe the developed ITO pattern under optical observation conditions. However, a high-resolution interdigital electrode pattern was formed and confirmed via SEM observations (Figure 5d). The SEM result shows that the developed ITO NP pattern was clear-cut and had a dense and uniform distribution. Oxide electronic materials, including ITO, ZnO, and NiO, also have relatively high fluidity and do not spontaneously form aggregates; therefore, they are advantageous for high-resolution electrophotographic printing. These oxide electronic materials are also beneficial for dense and thick pattern formation owing to their low density and high electrical charge. Thus, such materials are useful for fabricating transparent electronics. Organic electronic materials, including C\({}_{8}\)-BTBT, Poly(4-vinylphenol) (PVP), PSS-Octakis (dimethylsilyloxy), and PSS-(2-(trans-3,4-Cyclohexanediol) ethyl)-heptaisobutyl substituted (PSSs), can be electrophotographically printed, as shown in Figure 5e,f. Figure 5e displays the printed C\({}_{8}\)-BTBT toner pattern. The C\({}_{8}\)-BTBT is an organic semiconductor. In the initial stage of this study, we could only obtain a sparse pattern of C\({}_{8}\)-BTBT [86]; however, we can now create a sufficiently dense pattern of C\({}_{8}\)-BTBT toner particles.