Quantifying the Efficiency of Plasmonic Materials for Near-Field Enhancement and Photothermal Conversion

Following recent advances in nanoplasmonics related to high-temperature applications, hot-electron processes, nanochemistry, sensing, and active plasmonics, new materials have been introduced, reducing the supremacy of gold and silver in plasmonics. The variety of possible materials in nanoplasmonics is now so wide that selecting the best material for a specific application at a specific wavelength may become a difficult task. In this context, we introduce in this Article two dimensionless parameters acting as figures of merit to simply compare the plasmonic capabilities of different materials. These numbers, which we named Faraday and Joule numbers, aim at quantifying the ability of a nanoparticle to respectively enhance the optical near field and produce heat. The benefit of these numbers compared to previously defined figures of merit is that (i) they possess simple close-form expressions and can be simply calculated without numerical simulations, (ii) they give quantitative estimations in the nonretarded regime, and (iii) they take into account the nature of the surrounding medium. Within this Article, we address a wide variety of materials, namely, gold, silver, aluminum, copper, cobalt, chromium, iron, molybdenum, manganese, nickel, palladium, platinum, rhodium, tantalum, titanium, titanium nitride, tungsten, and zirconium nitride.