Temperature-dependent permittivity of silver and implications for thermoplasmonics

Silver is an extremely appealing metal for plasmonics due to its very low optical losses in the visible and near-ultraviolet range and its relatively low reactivity. Within the emerging field of thermoplasmonics, where light-metal interactions are exploited to generate heat on the nanometric scale, knowledge of temperature-dependent complex permittivities of plasmonic materials is indispensable. We extracted the temperature-dependent complex permittivity of silver Ag by spectroscopic ellipsometry under high-vacuum conditions. For rising T, we observed an increase of the free-electron contribution to the imaginary part of the permittivity Im[Ag] and a temperature-dependent absorption band splitting off the interband absorption edge in the 320-360-nm range. Around 340 nm the relative increase of Im[Ag] at 600 K with respect to its room-temperature value is around 500%. In order to understand the implications of this behavior on silver thermoplasmonics, we computed the temperature-dependent extinction efficiency of oblate Ag ellipsoids with localized plasmon resonance within the 320-360-nm range. We predict that dramatic damping of the plasmon resonance occurs for increasing temperature, possibly leading to intriguing self-limiting effects in Ag thermoplasmonics.