Kenneth Jarefors, Mats Hedlund, Jonas Zinders, 3M Svenska AB, Gagnef, Sweden
Achieving high-quality ultrathin silver coatings is challenging due to silver's tendency to form clusters during deposition, resulting in inhomogeneous layers with pinholes and rough surfaces. These issues limit the overall quality and the minimum achievable thickness of usable silver layers. A literature review revealed that recent studies have reported improved quality of ultrathin silver layers by incorporating small amounts of dopant materials, which help silver atoms distribute more evenly across the surface. Various dopant materials and deposition processes have been explored in these studies. In our research, we utilized copper as the dopant material and employed Thermal Evaporation Physical Vapor Deposition (PVD) as the deposition process. This approach resulted in significantly improved homogeneity and smoother surfaces with fewer geometric anomalies. The spectral transmittance of the doped silver layers was closer to the calculated ideal, and light scattering was reduced. Consequently, the minimum usable layer thickness was successfully decreased to approximately 11 nm while maintaining high quality. Less thin layers, in the range 12 nm – 25 nm showed improved performance. In addition, the resulting performance was less sensitive to deposition rate during the coating process.