| 摘要註: |
本研究分別使用化學氣相沉積法(Chemical Vapor Deposition, CVD)及水熱法合成氧化鋅(ZnO)奈米線/柱，並蒸鍍不同厚度之銅薄膜，於不同氣氛、時間及壓力下退火，以固態擴散的方式合成摻混銅之氧化鋅(Cu doped ZnO, CZO)一維奈米材料。藉此方法可以獨立控制ZnO形貌及銅濃度，並探討銅濃度及熱擴散對ZnO奈米結構及其物理性質之影響。第一部分為使用CVD及熱擴散方式合成CZO，藉由掃描式電子顯微鏡(SEM)及穿透式電子顯微鏡(TEM)可以觀察出此為一沿著<0002>方向成長且富有週期性之CZO奈米結構。當ZnO奈米線直徑小於50奈米時，CZO將形成串珠狀結構；而當ZnO奈米線直徑大於50奈米時，CZO形貌則為一波浪狀結構。高解析度穿透式電子顯微鏡(HRTEM)及X光繞射儀(XRD)可以判斷出摻銅後氧化鋅之(0002)繞射峰皆會往大角度偏移，即(0002)面間距會下降。X光光電子能譜儀(XPS)顯示Cu2+為主要的摻雜離子，因為Cu2+離子的半徑較Zn2+小，所以此結果與TEM和XRD的觀察吻合。從螢光光譜儀(FL)及陰極發光光譜儀(CL)之結果發現，摻銅後之ZnO其近能隙發光有紅移的現象，且發出強烈且寬頻的可見光，波長範圍涵蓋紫光到黃橘光。此CZO週期性結構之成長機制，是由一種應變輔助的機制所主導，由於其可激發強烈且寬頻之可見光，在光電元件之應用極有潛力。第二部分為先以水熱法合成ZnO奈米柱，鍍薄層銅後施以不同的退火處理。從SEM可觀察出隨著鍍銅薄層厚度增加，CZO表面將會有許多塊狀產生。由XRD可以發現，隨著退火壓力或銅薄層厚度增加時，氧化銅繞射峰值之訊號將增強，但仍以氧化鋅的繞射峰為最主要的強度。而當退火時間為4小時，隨著銅薄層厚度上升，ZnO奈米柱(0002)繞射峰將會先往小角度偏移再產生一回復情形，但回復以後角度仍小於未摻雜之ZnO奈米柱之角度，此結果與CVD所製備的完全相反，因為Cu+離子的半徑較Zn2+大，固推測主要的摻雜離子為Cu+。由XPS的分析顯示Cu+離子為主要攙雜的離子，此結果與XRD 的分析與推論相符。此外，若控制退火壓力為0.1 torr，且退火時間從4小時提升至12小時，則氧化銅繞射峰值之訊號將會消失，顯示Cu 可完全地摻雜入氧化鋅晶格中。CL 的分析顯示，摻銅之後氧化鋅奈米柱的近能隙發光消失，且可見光的發光由黃光變為藍光。本研究以不同方式合成CZO一維奈米材料，使用CVD-ZnO和銅擴散製程製備之CZO奈米線，主要摻雜為二價銅離子；使用水熱-ZnO和銅擴散製程製備之CZO奈米柱，主要摻雜為一價銅離子。由CL 的缺陷發光可以判斷，造成此差異的原因可能為CVD-ZnO與水熱-ZnO奈米材料其原本的本質缺陷不同，與銅離子產生不同的反應。本研究可藉此控制氧化鋅內銅的價數，影響其物理性質。 In this study, we prepared ZnO NRs (NRs) and NWs (NWs) by chemical vapor depositions (CVD) or hydrothermal method first, respectively, then coated Cu nanoshells with various thicknesses, and followed by annealing treatments with different atmosphere, duration, and pressure. We independently controlled Cu concentration and diameter of Cu doped ZnO (CZO) nanostructures by using the solid state diffusion methods and investigated the physical properties of CZO nanostructures. In the first part, we prepared CZO nanostructures (NSs) by CVD grown ZnO NWs and thermal diffusion of Cu. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show the bead-like Cu: ZnO NWs grow along the <0002> direction and the average diameter of neck and bead parts are 5 and 25 nm, respectively. When the diameters of ZnO NWs are smaller than 50 nm, the CZO nanostructures will become the periodic bead-like structures after the annealing treatment. High resolution TEM and XRD (X-ray diffraction) show the d-spacing of (0002) planes decreases and the diffraction peaks of (0002) plane shift to higher angle after the Cu diffusion. XPS (X-ray photoelectron spectrum) shows the main ions doped in ZnO is Cu2+, consistent with the data of XRD and TEM since radius of Cu2+ is smaller than Zn2+. PL (photoluminescence) and CL (cathodoluminescence) measurements show that CZO nanostructures exhibit strong and broad band visible light convoluted with purple, blue, green, and yellow emissions. Besudes, the near-edge emission red shifted after the annealing compared with undoped ZnO NWs. In the work, we propose a strain-assisted growth mechanism of the CZO periodic nanostructures. The prepared Cu doped ZnO NSs show strong and broad band visible emission, which are promising for optoelectronic applications. In the second part, we prepared ZnO NRs by hydrothermal routes, coated Cu nanoshells with various thicknesses, and followed by annealing treatments in different conditions. SEM images show there are many bulks generated on the surface of NRs, which increased with the thicknesses of Cu nanoshells. XRD patterns show the signal of CuO increase with pressure or thickness of Cu, but (0002) planes of ZnO are still the main diffraction peaks of the sample. Besides, the (0002) diffraction peaks of CZO NRs shift to lower angles and then finally recover with the increasing the Cu thickness, but that is still lower than angle of undoped ZnO NWs. Notably, this shift direction of (0002) diffraction peak is just opposite to those prepared by CVD grown ZnO NWs. XPS shows the main ions doped in ZnO is Cu+, consistent with the decrease of d-spacing, obtained from XRD and TEM. In addition, the diffraction peaks of CuO disappear in a pressure of 1.1 torr when annealing time increase from 4 to 12 hours, which exhibits the Cu ions can be completely doped in ZnO in suitable condition. CL measurements show the near band edge emission disappears after the doping of Cu, and the visible emission shifts from yellow to blue light. In this research, we synthesize CZO nanostructures by two different methods. The main dopants in CZO nanostructures prepared by CVD-ZnO/Cu diffusion and hydrothermal-ZnO/Cu diffusion processes are Cu2+ and Cu+, respectively. The different valences of Cu in ZnO are ascribed to distinct original intrinsic defects in the CVD-ZnO and hydrothermal-ZnO nanostructures. The valence of Cu ions can be controlled by the two integrated routes, which can change the physical properties of the CZO nanostructures. |