Plasmonic Behaviors of Metallic AZO Nanostructures
|摘要:||電漿光學是奈米光學的一個分支，因可操控光場於奈米尺度下而受到許多關注。目前，電漿元件多傳統金屬材料(如金或銀)所構成，其主要原因在於金屬本身富含自由電子。然而，金屬材料在光學頻率下，因載子能帶躍遷而產生較大的光學損耗，這些損耗將嚴重導致電漿元件特性變差進而限制其可行性。透明導電的氧化物材料在近紅外光波段下，可取代傳統金屬作為低損耗的電漿材料。本研究中，我們製作出不同特性的氧化鋁鋅(aluminum-doped zinc oxide, AZO)薄膜，並驗證其在近紅外光波段是否具備金屬性與低損耗之特徵。我們分別從薄膜的結構性、電性及光性，去探討不同退火條件與不同厚度下之薄膜特質，結果顯示AZO在近紅外光波段可成為低損耗的電漿材料，同時透過適當的製程改變可使材料之電漿行為具高度可調性。此外，我們研究AZO奈米盤結構之光學行為，透過有限元素分析法之模擬計算與實驗分析，顯示奈米盤結構隨著結構退火參數變化(退火溫度、退火氣體)及尺寸變化(直徑、厚度)，可在近紅外光區域清楚地觀察到侷域性表面電漿共振(localized surface plasmon resonance， LSPR)，並且發現其電漿共振行為與結構尺寸及退火條件高度相關。最後，我們進行AZO奈米盤在不同折射率環境下之感測能力，並依序在實驗與模擬中觀察到874.31 nm/RIU和1019.27 nm/RIU的高靈敏度。藉由新穎AZO 電漿材料之優勢，期許發展出更適合的圖樣化AZO奈米結構朝前瞻性光學奈米感測器邁進。|
Plasmonics is a subfield of nanophotonics and is concerned primarily on enabling the manipulation of light at the nanoscale. Currently, plasmonic devices are made of metals such Au or Ag due to the fact that metals can support an abundance of free electrons. However, metals suffer from large losses in optical frequencies because of their interband transitions. These losses lead to the weak performance of the plasmonic devices. Transparent conducting oxides (TCOs) are suitable candidate for low-loss plasmonic materials in near-infrared (NIR) region. In this study, we fabricated aluminum-doped Zinc oxide (AZO) thin films and examined their suitability as plasmonic materials in NIR region. AZO films with different thickness and annealing conditions were grown by radio frequency (RF) magnetron sputtering system to observe the structural, electric, and optical properties. From the results, we successfully demonstrated that AZO material possessed metal-like and low optical loss properties and were highly tunable plasmonic materials at various annealing conditions. Furthermore, AZO nanodisk arrays with various sizes under different annealing temperatures and atmospheres were fabricated in experiment while AZO nanodisk structures were simulated by finite element method (FEM) to compare with experimental results. Based on the results of experiment and simulation showed that localized surface plasmon resonance (LSPR) behaviors were clearly observed in the NIR region, and plasmonic resonances highly depended on annealing conditions and structural dimension. In the end, the refractive index sensing of AZO nanodisk structures was implemented, and high sensitivity of 874.31 nm/RIU and 1019.27 nm/RIU were observed in experiment and simulation, respectively. Taking the advantages from AZO plasmonic materials, we expect that AZO materials integrated into the suitable patterned nanostructures have the potential to develop the novel optical nanosensors.