Arc discharge synthesized nanoparticles and their applications in thin film coatings

The arc discharge method for nanoparticle production offers all the benefits of gas-phase (aerosol-based) synthesis, including high-throughput production, exceptional purity, continuous operation, and straightforward design. This method is especially effective for synthesizing non-oxide materials, such as metals and ceramics. This work studied the synthesis of metallic copper (Cu) and ceramic titanium nitride (TiN) nanoparticles using an optimized arc discharge reactor, with a focus on how different processing parameters affect the properties of the nanoparticles. Additionally, this research explored the potential applications of these nanoparticles, particularly focusing on Cu nanoparticles for electrically conductive thin films and TiN nanoparticles for protective coatings. Copper nanoparticles (Cu NPs) emerge as cost-effective substitutes for noble metals like silver and gold in conductive inks, due to their superior electrical conductivity and affordability. Through adjusting the reactor process, a steady production rate of 1.2 to 5.5 g/h was achieved, producing Cu nanoparticles with a primary size of less than 100 nm. These nanoparticles were then used to develop copper inks and subsequent thin films on glass substrates. A thermal sintering process eliminated ink residues and reduced copper oxide in the films, achieving a continuous metallic structure within the sintered Cu films. The copper films exhibited low resistivity, three times that of bulk copper, after thermal sintering in a reducing atmosphere. To reduce film porosity, a multilayer sintering technique was developed, enabling the preparation of a denser Cu film through up to four coating and sintering cycles, significantly lowering porosity from 33.6% in single-layered to 3.7% in four-layered sintered films. This reduction in porosity correlates with decreases in electrical resistivity, demonstrating the effectiveness of this multilayer sintering method. Similarly, titanium nitride nanoparticles (TiN NPs), preferred for protective coatings due to their outstanding thermal, mechanical, and chemical stability, were synthesized in an optimized arc discharge reactor. The research explored the effect of parameters like quench gas velocity, composition, and arc current on nanoparticle quality, yield, and size, finding that higher gas velocities led to smaller particles (10-15 nm). It also proposed a mechanism for cathode tip deposit growth, enhancing understanding of the synthesis process and offering optimization insights. Utilizing optimized parameters, the study produced nanostructured thin films through a novel method combining an atmospheric-pressure arc reactor with a magnetron sputter device, achieving nanocrystalline (nc)-TiN/nc-CrN nanocomposite structures. Microstructural analysis confirmed the successful integration of TiN nanoparticles without significant lateral interface defects. However, pores near TiN nanoparticles indicated that external nanoparticles might disrupt the vertical columnar growth of the CrN Matrix. The research also found that increasing TiN nanoparticle content decreased CrN crystallite sizes and increased grain boundaries, indicating the potential for mechanically enhanced thin films.