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<p>Adhesion layers play a crucial yet often overlooked role in determining the optical performance of plasmonic nanostructures. In this work, a three-dimensional finite-element modeling framework is employed to systematically quantify how adhesion-layer material and thickness influence nanofocusing efficiency in tapered metal–insulator–metal (MIM) waveguides. Titanium (Ti), chromium (Cr), germanium (Ge), and self-assembled monolayers (SAMs) are compared over a thickness range of 1–10&#xa0;nm under identical geometrical and excitation conditions, enabling direct isolation of adhesion-layer-induced optical losses. The simulations show that even ultrathin metallic adhesion layers (1–3&#xa0;nm) introduce severe absorption losses, reducing coupling efficiency by more than 50% and approaching 90% at 10&#xa0;nm. In contrast, SAMs preserve high throughput and strong field confinement due to negligible absorption and improved impedance matching, while Ge exhibits intermediate behavior and serves as a comparative optical case. These results establish a predictive, fabrication-relevant framework for understanding interfacial optical losses in plasmonic MIM nanofocusing structures and provide quantitative design guidelines for selecting low-loss adhesion strategies in nanophotonic, sensing, and data-storage applications.</p>

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Numerical investigation of adhesion-layer-induced optical losses in tapered plasmonic MIM waveguides

  • 期刊论文

  • 发表日期：

    2026年2月5日

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  • Kruawan Wongpanya,
  • Wanchai Pijitrojana

摘要

Adhesion layers play a crucial yet often overlooked role in determining the optical performance of plasmonic nanostructures. In this work, a three-dimensional finite-element modeling framework is employed to systematically quantify how adhesion-layer material and thickness influence nanofocusing efficiency in tapered metal–insulator–metal (MIM) waveguides. Titanium (Ti), chromium (Cr), germanium (Ge), and self-assembled monolayers (SAMs) are compared over a thickness range of 1–10 nm under identical geometrical and excitation conditions, enabling direct isolation of adhesion-layer-induced optical losses. The simulations show that even ultrathin metallic adhesion layers (1–3 nm) introduce severe absorption losses, reducing coupling efficiency by more than 50% and approaching 90% at 10 nm. In contrast, SAMs preserve high throughput and strong field confinement due to negligible absorption and improved impedance matching, while Ge exhibits intermediate behavior and serves as a comparative optical case. These results establish a predictive, fabrication-relevant framework for understanding interfacial optical losses in plasmonic MIM nanofocusing structures and provide quantitative design guidelines for selecting low-loss adhesion strategies in nanophotonic, sensing, and data-storage applications.