Fabrication of ZnO nanoflower arrays by lift-off technique on patterned sapphire substrates

本論文利用舉離(lift-off)技術製作奈米點陣列 圖案之氧化鋅種子層，再以水熱法成長氧化鋅奈米柱，使結構成奈米花狀，並以改變鋁犧牲層的厚度、氧化鋅奈米柱的成長時間及醋酸鋅溶液的濃度，觀察氧化鋅種子層的結構特性、氧化鋅奈米柱成長機制及光學特性。在犧牲層厚度效應上，經由蝕刻時間及蝕刻率的計算，可以得知 120 nm的鋁犧牲層所花費的蝕刻時間最少，蝕刻率最快。由 XRD 分析可得知經由舉離轉印的種子層，為纖鋅礦結構，在成長方向上沒有特定在(002)方向且結構較差。由 SEM 和 EDS 分析得知較厚的犧牲層所花費的蝕刻時間較長，將造成較多的由鋁形成的雜質沉積在種子層上，影響種子層外觀結構及阻礙奈米柱生長。 在不同的奈米柱生長時間上，由 XRD 分析可得知氧化鋅的 5 個生長方 向的峰值隨著時間增強，表示奈米柱生長不完全垂直於基板。由 SEM 及 FIB可得知在相同濃度下，三種犧牲層厚度轉印的種子層，成長奈米柱的長度、寬度、高寬比和總表面積將隨生長時間增加，且可發現 120 nm 轉印的種子層生長效率最高。由 PL 分析可得知隨著時間的增加，紫外光會隨之變強，而綠光則因缺陷的減少而變弱，且鋅缺陷會隨著生長時間增加而轉變為氧缺陷。奈米柱生長在不同濃度的醋酸鋅溶液中，由 XRD 分析可得知峰值將隨著濃度增加而變強。由 SEM 分析可得知隨著濃度增加，奈米柱直徑的成長率將大幅增加，將會降低高寬比及奈米柱密度。由 PL 分析可得知隨濃度增加，在 0.02 M 紫外光將會最強，而缺陷將隨濃度增加而降低。This study uses a hydrothermal method to fabricate nanoflower-like ZnO nanorods on patterned zinc-oxide (ZnO) seed layer arrays by lift-off technique. The structural properties of the ZnO seed layer and the growth mechanism and optical properties of the ZnO nanorods were explored under various process parameters including the thickness of the aluminum sacrificial layer, growth time of ZnO nanorods, and the concentration of the zinc acetate solution. As to effects of the sacrificial layer thickness, the 120 nm-thick aluminum sacrificial layer of 120nm had the shortest etching time and etching rate. XRD analysis found that the ZnO seed layer after lift-off was wurtzite structure and had a poor (002) orientation. SEM and EDS analyses showed that the longer etching time resulted from the thicker sacrificial layer and caused more impurities (aluminum) formed on the seed layer, thus hindering the growth of nanorods. As to effects of the growth time of nanorods, XRD results showed five peaks of the ZnO nanorods increased as the time increased, indicating that the nanorods did not grow perfectly perpendicular to the substrate. SEM and FIB analyses found that the length, width, aspect ratio and total surface area of the nanorods all increased with the growth time. Moreover, the transferred seed layer in 120nm had the highest efficiency of growth. In PL analysis, the intensity of UV light increased with the increasing of the time, and the intensity of green light became weaker as the defects reduced. The zinc defects would result in oxygen defects with the growth of time. As to effects of the concentration of the zinc acetate solution, it was also found that the peaks increased as the concentration of zinc acetate solution increased. The growth rate of the diameter of nanorods significantly increased with the increase of concentration, and it also led to the decrease of the aspect ratio and nanorods density. In PL analysis, the highest intensity of the UV peak was found from the sample with 0.02 M concentration, and the defects decreased with the increase of concentration.誌謝 ................................ i 摘要 ................................... ii Abstract.....................................iii 目錄 ...............................v 第一章 緒論 .......................................... 1 1.1 前言 ........................................... 1 1.2 研究動機與目的 ............................................... 2 第二章 文獻回顧與基礎理論 ............................ 4 2.1 氧化鋅晶體結構與特性 ............................. 4 2.2 氧化鋅光學特性 ..............................6 2.3 氧化鋅的成長機制 ....................................8 2.4 溶膠-凝膠法(Sol-Gel Method)........................ 11 2.5 溶膠-凝膠的製備方法 ............................... 14 2.6 舉離(Lift-off)技術................................15 2.7 高寬比及表面積與體積比 .............................15 第三章 實驗流程與步驟 ..................................17 3.1 實驗流程 .......................................17 3.1.1 實驗流程圖................................17 3.1.2 氧化鋅奈米花陣列製作示意圖 ......................18 3.2 化學藥品與實驗用品 ................................19 3.2.1 化學藥品...............................19 3.2.2 基板材料..............................19 3.3 實驗儀器介紹 ...............................21 3.3.1 熱蒸鍍機...............................21 3.3.2 X光繞射分析儀..............................22 3.3.3 FE-SEM場發射掃描電子顯微鏡 ........................22 3.3.4 多功能聚焦離子束系統 .............................23 3.3.5 光激發螢光分析儀 ..................................24 3.4 基板清洗 ........................................25 3.5 種子層製備 .....................................26 3.6 種子層轉印 .......................................29 3.7 水熱法成長氧化鋅奈米柱陣列 ..........................32 第四章 結果與討論 ......................................33 4.1 平面氧化鋅種子層與奈米柱陣列之形貌與晶體分析 ........................ 33 4.1.1 氧化鋅種子層XRD分析 ........................................33 4.1.2 氧化鋅種子層SEM分析 ..................................... 34 4.1.3 氧化鋅種子層EDS分析 .........................................35 4.1.4 氧化鋅奈米柱陣列XRD分析 ...................................................... 35 4.1.5 氧化鋅奈米柱陣列SEM分析 ...................................................... 37 4.1.6 氧化鋅奈米柱陣列室溫螢光光譜分析 ...................................... 43 4.2 犧牲層蝕刻研討 .......................................... 46 4.3 點陣列氧化鋅種子層與奈米花陣列之形貌與晶體分析 .................... 50 4.3.1 點陣列氧化鋅種子層XRD分析 .................................................. 50 4.3.2 點陣列氧化鋅種層子SEM與FIB分析 ........................................ 51 4.3.3 點陣氧化鋅種子層EDS分析 ....................................................... 53 4.3.4 氧化鋅奈米花XRD分析 ............................................ 54 4.3.5 氧化鋅奈米花陣列SEM與FIB分析 ............................................ 57 4.3.6 氧化鋅奈米花室溫螢光光譜分析 .............................................. 63 第五章 結論 .......................................... 69 參考文獻 ............................................. 7