Multiscale design of Au-based alloys for improved plasmon delivery and nanoheating in near-field transducers

Plasmonic near-field transducers (NFTs) play a key role in administering nanoscale heating for a number of applications ranging from medical devices to next generation data processing technology. We present a novel multi-scale approach, combining quantum many-body perturbation theory with finite-element modeling, to predict the electric and thermal material parameters of various Au-based, noble metal (M) alloys. In particular, we focus on modeling their performance within an NFT designed to focus high-intensity, sub-diffracted light for technologies such as nanoscale etching, manipulation, sensing, and heat-assisted magnetic recording. Elemental Au is the long-standing general-purpose NFT medium due its excellent plasmonic performance at relevant wavelengths. However, elemental Au is a soft, ductile material that tends to extrude and deform in response to extreme temperature gradients. Therefore, alloying Au with other noble metals, such as Ag, Cu, Pd, or Pt, has attracted considerable interest for improved mechanical and thermal robustness while reaching threshold plasmonic generation at standard optoelectronics operating wavelengths (e.g., ≈830 nm) and approximate high-power NFT temperatures (≈400 K). We predict that certain Au–Ag alloys may offer improved thermal stability as whole-NFT media compared to elemental Au, alongside plasmonic figures of merit comparable with that of Au. Simulations of certain solid solution Au–Pd/Pt alloys enable us to predict significantly enhanced thermal conductivity. We predict that alloying with Pd at low concentrations ∼10% may preserve the NFT performance of Au, while offering the benefits of improved thermal and mechanical stability.