開發氮化物寬頻電漿子超穎吸收體於太陽能驅動光化學合成之應用

Abstract

設計與開發能夠涵蓋整個太陽光譜能力的寬頻超穎吸收體在綠能科技中受到廣泛關注。然而，要同時實現高吸收率、化學穩定性與寬頻響應的光吸收體仍具挑戰，特別是對於貴金屬材料，由於其高品質因子（Q-factor），常導致共振吸收峰過於狹窄，頻寬往往小於 100 nm，難以涵蓋整個太陽光譜。為了解決這一問題，本研究採用過渡金屬氮化物（Transition Metal Nitrides, TMNs）作為材料，製備寬頻完美吸收結構。TMNs具備先天較低的Q-factor，能更容易實現寬頻吸收。在本論文的第一章中，我們從電漿子誘導光催化的基本原理出發，說明了金屬與介電常數之間的關係及其對光學響應的影響；第二章則介紹了本研究中所採用的各項光學量測技術，包括橢圓儀與超快瞬態吸收光譜，作為後續實驗佐證的基礎。 在第三章中，我們進行有限時域差分法（FDTD）模擬，設計出以氮化鈮（NbN）為電漿子共振的「鏡上奈米顆粒」（Nanoparticle on Mirror, NPoM）結構，有效侷限電磁場能量。模擬結果顯示，該結構在可見至近紅外光範圍（450至900 nm）內展現平均超過80%的吸收率。此外，我們亦比較 NbN 系統與其他 TMNs（如TiN、HfN）所製作結構的性能差異。在第四章中，我們成功製作出小面積NbN樣品，並結合模擬與實驗結果評估其光學表現與設計準確性。同時也製備了大面積樣品，進行光催化產氨實驗，以驗證其作為電漿子誘導光催化裝置的應用潛力。實驗結果顯示，相較於薄膜的比較組，該結構在氨產率上有明顯提升，增幅達4.5倍，證實其實用性與效能。 此外，為進一步探討其效能提升的物理機制，我們亦在第四章節的後段導入超快瞬態吸收光譜（Ultrafast Transient-Absorption Spectroscopy, TAS）分析載子動力學。結果顯示，熱電子的注入與能量轉移過程發生在數百飛秒的時間尺度內，提供了對於內在載子弛豫路徑如何主導光催化效率的深入理解。本研究所開發之氮化物寬頻電漿子超穎吸收體，提供一種具可持續性的光熱平台，能有效收集熱載子與熱電漿，並對綠能應用之氨生成反應及其他太陽光驅動反應奠定了研究和應用上的基礎。

Broadband metasurface absorbers capable of covering the entire solar spectrum have garnered significant attention in green energy technologies. However, developing light absorbers that simultaneously offer high absorptivity, chemical stability, and a broad bandwidth remains challenging, particularly for noble metals, owing to their high quality (Q) factor, which typically results in narrow resonant peaks with spectral widths often less than 100 nm. To overcome this challenge, we utilize transition metal nitrides (TMNs) to fabricate broadband perfect absorbers. Their intrinsically low Q-factors make it easier to achieve broadband absorption. In Chapter 1, we present the theoretical background of plasmonic photocatalysis and the electromagnetic conditions required for broadband light confinement. Chapter 2 introduces the experimental techniques used throughout this work, including ellipsometry and ultrafast transient absorption spectroscopy. In Chapter 3, we perform Finite-Difference Time-Domain (FDTD) simulations to design a nanoparticle-on-mirror (NPoM) metasurface using niobium nitride (NbN), which supports strong plasmonic resonance modes. The resulting structure achieves over 80% absorption across the visible to near-infrared region (450 to 900 nm). We further compare the optical performance of NbN-based absorbers with those using TiN and HfN. Chapter 4 details the fabrication of both small and large-area NbN metasurfaces. Experimental measurements validate the simulated design, and photocatalytic ammonia production tests reveal a 4.5-fold increase in NH3 yield compared to reference films. These results confirm the structure's effectiveness in enhancing plasmon-induced photocatalytic performance. To further understand the physical origin of this enhancement, ultrafast transient-absorption spectroscopy (TAS) will be employed to study the hot-carrier dynamics in our system, revealing that hot-electron injection and energy transfer occur within a few hundred femtoseconds, which provides valuable insight into how intrinsic relaxation pathways govern photocatalytic efficiency. The successful development of nitride-based broadband plasmonic metasurface absorbers therefore offers a sustainable photothermal platform for harvesting hot carriers and thermal plasmons which can enhance solar-driven chemical reaction rates, and thereby pave the way for sustainable green ammonia production.