以第一原理理論計算調控過渡金屬氮化物之電漿子特性

Abstract

電漿子學為凝態物理學中的先進概念，其探討的是表面電漿共振——受光激發的金屬和介電質界面之電子密度波。在新穎光子元件的開發中，過渡金屬氮化物（TMNs）為極具潛力的材料。由於表面電漿子與材料特性的相關，使半導體、金屬、以及存在量子侷限效應的二維材料等皆擁有不同的電漿效應。而利用不同的化學組成造成電漿性質的變化能夠使TMNs有更卓越的特性。在本論文中，我們從理論計算與實驗的角度來研究過渡金屬氮化物的電子能帶結構與光學特性。利用第一原理計算作為分析材料介電性質的理論方法，Drude-Lorentz模型使我們得以用直觀的角度研電漿子方面的應用。透過介電常數與品質因數的計算，以及50奈米厚TMNs薄膜在藍寶石基板上的量測，我們發現TMNs的特性可以良好地被其元素組成調控。其中Ti0.25Hf0.75N與Ti0.50Zr0.50N在金屬和介電質之界面展現優於二元TMNs的介電響應。在近紅外光波段，Ti0.50Hf0.50N則具有在高能量吸收率與更強的調變應用中的潛力。因此，三元化合物的形式使TMNs在可見光及近紅外光波段的電漿子特性可以有所變化，研究成果可應用在針對頻率調控的積體光子元件。

Plasmonics, an advanced concept in condensed matter physics, studies surface plasmon resonance - the collective electron oscillations at the dielectric-metal interface, revealing significant plasmonic properties when interacting with light. Transition metal nitrides (TMNs) are promising materials for developing next-generation photonic devices. Surface plasmons are influenced by nanomaterial characteristics, resulting in distinct plasmonic effects in semiconductors, metals, and 2D nanomaterials due to their unique confinement properties. A practical way toward high-performance TMNs is to tune their plasmonic properties through different compositions. Here, we investigate the electronic structures and optical properties of TMNs (Ti1-xZrxN and Ti1-xHfxN, x = 0, 0.25, 0.50, 0.75, and 1) computationally and experimentally. The Drude-Lorentz model which gives a theoretical insight into a material and can be employed in plasmonic applications is an intuitive way to study the underlying dielectric characteristics of solids. Our calculated dielectric permittivities and quality factors suggest that the overall performance of TMNs is well-tuned by their compositions, supported by our measured data obtained from the 50-nm thick TMN films deposited on sapphire (0001). Particularly, at the dielectric-metallic interface, Ti0.25Hf0.75N (ENZ of 401 nm) and Ti0.50Zr0.50N (ENZ of 406 nm) show a better dielectric response than the binary TMNs. Ti0.50Hf0.50N (ENZ of 457 nm) holds promise for applications requiring efficient energy absorption and enhanced wave manipulation in the near-infrared range. Using mixed ternary TMNs to tune plasmonic properties in the visible and near-infrared regions can thus achieve frequency-targeting photonics applications.