Plasmonic Films Can Easily Be Better: Rules and Recipes

Plasmonic Films Can Easily Be Better: Rules and Recipes

| Kevin M. McPeak, Sriharsha V. Jayanti, Stephan J. P. Kress, Stefan Meyer, Stelio Iotti, Aurelio Rossinelli, and David J. Norris
This perspective outlines simple rules and recipes for depositing high-quality plasmonic films of aluminum, copper, gold, and silver using a thermal evaporator. The key factors influencing the optical performance and microstructure of these films include deposition rate, base pressure, substrate temperature, and film thickness. The homologous temperature (T_h), defined as the ratio of the substrate temperature to the metal's melting point, is crucial for controlling film growth and microstructure. Metals with higher standard electrode potentials are more reactive and require faster deposition rates to minimize contamination from residual gases. The optimal deposition conditions depend on the metal's reactivity and the desired optical properties. The study emphasizes the importance of maintaining low base pressures to reduce the impact of residual gases, which can cause grain boundary pinning and reduce film quality. For reactive metals like aluminum, fast deposition rates are necessary to prevent metal-oxide contamination. Less reactive metals, such as gold, can be deposited at slower rates without significant degradation in optical properties. Room-temperature deposition is generally preferred to avoid dewetting, especially for silver, which is highly susceptible to this phenomenon. The optical performance of the films was evaluated using ellipsometry and atomic force microscopy. The results showed that films deposited under optimal conditions exhibit significantly better optical properties compared to those deposited under suboptimal conditions. For example, silver films deposited at 50 Å/sec under a base pressure of 3×10⁻⁸ Torr showed a 160% improvement in the LSPR figure-of-merit and a 200% improvement in the SPP figure-of-merit compared to standard references. Similarly, copper films outperformed gold films in the near-infrared range, and aluminum films deposited at high rates showed improved optical properties and reduced surface roughness. The study provides detailed recipes for depositing each metal under optimal conditions, ensuring high-quality plasmonic films with excellent optical performance. These recipes are based on the principles of surface science and are designed to be easily implemented with commonly available equipment. The results demonstrate that simple thermal evaporator techniques can produce high-quality plasmonic films with performance comparable to or better than those obtained using more complex methods.This perspective outlines simple rules and recipes for depositing high-quality plasmonic films of aluminum, copper, gold, and silver using a thermal evaporator. The key factors influencing the optical performance and microstructure of these films include deposition rate, base pressure, substrate temperature, and film thickness. The homologous temperature (T_h), defined as the ratio of the substrate temperature to the metal's melting point, is crucial for controlling film growth and microstructure. Metals with higher standard electrode potentials are more reactive and require faster deposition rates to minimize contamination from residual gases. The optimal deposition conditions depend on the metal's reactivity and the desired optical properties. The study emphasizes the importance of maintaining low base pressures to reduce the impact of residual gases, which can cause grain boundary pinning and reduce film quality. For reactive metals like aluminum, fast deposition rates are necessary to prevent metal-oxide contamination. Less reactive metals, such as gold, can be deposited at slower rates without significant degradation in optical properties. Room-temperature deposition is generally preferred to avoid dewetting, especially for silver, which is highly susceptible to this phenomenon. The optical performance of the films was evaluated using ellipsometry and atomic force microscopy. The results showed that films deposited under optimal conditions exhibit significantly better optical properties compared to those deposited under suboptimal conditions. For example, silver films deposited at 50 Å/sec under a base pressure of 3×10⁻⁸ Torr showed a 160% improvement in the LSPR figure-of-merit and a 200% improvement in the SPP figure-of-merit compared to standard references. Similarly, copper films outperformed gold films in the near-infrared range, and aluminum films deposited at high rates showed improved optical properties and reduced surface roughness. The study provides detailed recipes for depositing each metal under optimal conditions, ensuring high-quality plasmonic films with excellent optical performance. These recipes are based on the principles of surface science and are designed to be easily implemented with commonly available equipment. The results demonstrate that simple thermal evaporator techniques can produce high-quality plasmonic films with performance comparable to or better than those obtained using more complex methods.
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Understanding Plasmonic Films Can Easily Be Better%3A Rules and Recipes