Synthesis of Two-Dimensional Single Crystalline Silver Nanosheets for Low-Temperature Sintering

Recently, there has been a growing interest in flexible electronic devices within the electronics industry. Consequently, some electronic components based on polymer substrates such as Polyethylene Terephthalate (PET), Polyimide (PI), and Polyethylene Naphthalate (PEN), as well as organic groups or nanoscale building blocks, are being applied. However, these components cannot maintain their functionality and stability at high temperatures above a certain threshold. Therefore, research on metal filler materials that can be sintered at low temperatures below 200 °C is necessary. Silver (Ag) nanoparticles are readily sintered, facilitating easy bonding at the interfaces between metals such as copper (Cu) [1]. This allows for the formation of sintered metals with bulk melting temperatures, making them more useful than solder over a wide temperature range [2]. However, research has primarily focused on using Ag nanoparticle paste to bond with other metals and organic materials.<br/>In this study, we propose synthesizing Ag nanoparticle-decorated Ag nanosheets, which enhance electrical performance through sintering under conditions below 200 °C, focusing on the low-temperature performance of submicron-sized particles. We synthesized large silver nanosheets at room temperature and atmospheric pressure by mixing silver nitrate, poly (vinyl pyrrolidone), sodium chloride, hydrogen peroxide, and ammonium hydroxide. The silver nanosheets exhibited shapes such as triangles, truncated triangles, hexagons, or polygons, with edge sizes ranging from 1 μm to approximately 50 μm and thicknesses proportional to their size, ranging from 10 to 100 nm. During this process, we controlled the reduction rate of Ag⁺ ions to Ag⁰ using hydrogen peroxide (H₂O₂). This allowed us to regulate the formation and growth rate of Ag clusters into Ag nanosheets, thereby controlling the size and surface morphology of the nanosheets. Synthesis with a high concentration of H₂O₂ resulted in smooth-surfaced Ag nanosheets, while synthesis with a low concentration of H₂O₂ produced Ag nanosheets decorated with Ag nanoparticles.<br/>The Ag nanoparticle-decorated Ag nanosheets synthesized under these conditions had an edge size of approximately 5 μm, a thickness of about 30 nm, and the decorated Ag nanoparticles had a diameter of roughly 70 nm. Films fabricated using these nanosheets demonstrated successful sintering, with the sheet resistance decreasing from 25.5 Ω/sq to 4.4 Ω/sq after 30 minutes at a low temperature of 100 °C. Films fabricated using these nanosheets demonstrated successful sintering, with the sheet resistance decreasing from 25.5 Ω/sq to 4.4 Ω/sq after 30 minutes at a low temperature of 100 °C. This represented a two-fold reduction in resistance compared to films made with Ag nanosheets lacking nanoparticles. Thus, we confirmed that we could control the size, thickness, and surface morphology of micron-sized large silver nanosheets. These findings suggest that such nanosheets can be effectively utilized as 2D metal nanofilms and as efficient metal fillers.