金-氧化鎵一維異質結構奈米線的電漿子光學性質與光電性質研究

Plasmonic and Optoelectronic Properties of One-Dimensional Gold-in-Ga2O3 Nanowires

吳宜蓁(Yi-Jen Wu)

指導教授 ： 周立人 ； 陳力俊

國立清華大學/工學院/材料科學工程學系/博士(2011年)

摘要

This dissertation aims to explore fundamental plasmonic and optoelectronic properties and possible photonic applications for one-dimensional gold-in-Ga2O3 peapod and core-shell nanowires. Single-crystalline gold-in-Ga2O3 nanowires have been systematically synthesized by a bottom-up method and a wide range characterized of their peculiar properties. The diameters and interparticle distances of gold peas, core diameters and core lengths of gold rods, were tuned during material growth in a controlled manner. Morphology, microstructure and composition of as-grown nanowires were characterized through scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM) analyses. Light-scattering properties and light-interference phenomena of individual gold-in-Ga2O3 nanowires were investigated by dark-field optical microscopy (OM). Light-emission properties of gold-in-Ga2O3 nanowires were studied by photoluminescence (PL) and electroluminescence (EL) spectroscopy. Surface potential distributions of single gold-in-Ga2O3 nanowires illuminated with a green light source of 532 nm in wavelength were revealed by Kelvin probe force microscopy (KPFM) and optical microscopy under ambient conditions with exceptional spatial and energy resolution.
The major peaks in measured scattering spectra were suggested to result from plasmonic resonance of the gold nanopeas and nanorods embedded in the Ga2O3 nanowires when comparing with simulation data from Mie and Gans calculations. The cladding Ga2O3 dielectric layer was considered as a surrounding medium for localized plasmon resonance on gold nanostructures and played a key role in light-scattering properties. Light-interference spectra of single gold-in-Ga2O3 peapod nanowires excited with a white light source in p-polarization demonstrated their applicability of being plasmonic nano-resonators. During the optical resonance, the Ga2O3 shell provided a wave-guiding medium for surface plasmon wave and scattered light of short propagation length bouncing back and forth within the nanowire. Photoluminescence and electroluminescence studies of gold-in-Ga2O3 nanowires indicated that luminescence of outer single-crystalline Ga2O3 matrix further excites localized plasmon resonance in inner gold nanostructures as the nanowire is properly optically-excited. Surface potential images of single gold-in-Ga2O3 nanowires under the illumination of selective light source presented direct evidence for energy flow from applied electromagnetic wave to gold-in-Ga2O3 complex nanostructures and quantified the induced electric potential fluctuations in the nanowires; which helped depict a detailed profile of the physical mechanism for the nanowires working at plasmon frequencies.
The investigation results of plasmonic and optoelectronic properties of one-dimensional gold-in-Ga2O3 peapod and core-shell nanowires would be applied to the optimum design of related nano-photonic devices and further extend to similar kinds of complex nanowires for enhanced performance, eventually function as an integrated element in optical nano-circuits.

關鍵字

金-氧化鎵異質結構奈米線 ； 侷域性表面電漿子/侷域性表面電漿共振 ； 光學顯微鏡顯微光譜 ； 光激發光譜 ； 克爾文氏力(靜電力)顯微術

並列摘要

這本論文主要探討一維異質氧化鎵包金豆莢結構奈米線與核殼結構奈米線之電漿子光學性質與光電性質，並構思可能的光電應用。單晶型態一維金-氧化鎵異質結構奈米線系統性的由化學合成法製造；其微結構與成分組成由材料檢測分析確認。豆莢結構奈米線內部金顆粒的直徑與顆粒間距；與核殼結構奈米線內部金柱的直徑與長度，在材料成長過程中加以控制。成長出的奈米線其外型、微結構、化學成分組成，經由掃描式電子顯微鏡、X光繞射分析儀、穿透式電子顯微鏡等檢測分析法來確認。進一步利用光學顯微術研究單一金-氧化鎵異質結構奈米線的光散射特性與光干涉特性；利用光激發光以及電激發光量測分析技術研究金-氧化鎵異質結構奈米線的激光特性。最後利用原子力顯微術之克爾文氏力(靜電力)顯微術研究單根金-氧化鎵異質結構奈米線在單色光源綠光照射下奈米線的表面電位分佈變化情況。
量測所得的金-氧化鎵異質結構奈米線的遠場光散射光譜上的主要波峰，對照古典光學理論計算結果，推測是由奈米線內部金奈米結構產生電漿子震盪所造成。奈米線外殼氧化鎵包覆層在金屬奈米結構的電漿子震盪過程中作為外圍介電質環境與反應介面，影響奈米線的光散射性質。由白光激發的豆莢結構奈米線的光干涉光譜展示了利用金-氧化鎵豆莢結構奈米線作為奈米光學共振腔的可能性。高折射係數的氧化鎵外殼提供金屬奈米結構的表面電漿波以及產生的散射光在奈米線內部金屬結構間傳播的介質。金-氧化鎵異質結構奈米線的光激發光譜與電激發光譜顯示單晶態氧化鎵的激光可再次激發奈米線內部金屬奈米結構產生電漿子共振現象。金-氧化鎵異質結構奈米線的表面電位圖則提供了能量由外部施加的單色光源轉換到奈米線內部而相應產生表面電位變化的直接定量證據，幫助理解金屬奈米結構電漿子共振現象以及金-氧化鎵異質結構奈米線光電轉換的物理機制。
對於這些以金-氧化鎵異質結構奈米線為主的光學性質與光電性質的研究成果，將推廣到其他相似異質結構奈米線作更多奈米光電應用。

並列關鍵字

Gold-in-Ga2O3 peapod and core-shell nanowires ； Localized surface plasmons/Localized surface plasmon resonance ； Optical microscopy and spectroscopy ； Photoluminescence ； Kelvin probe force microscopy

參考文獻

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