Growth of ZnO and CdO Nanowires by Vapor Transport. Synthesis of Core-Shell Ga-GaN Nanostructures and GaN Hollow Spheres via Reflux Method

高溫氣相合成高長度氧化鋅與氧化鎘奈米線及其性質探討.低溫迴流合成核-殼 鎵-氮化鎵奈米結構與氮化鎵中空球體

郭子駿(Tz-Jun Kuo)

指導教授 ： 黃暄益

國立清華大學/理學院/化學系/博士(2008年)

https://doi.org/10.6843/NTHU.2008.00332

摘要

1.高長度氧化鋅奈米線的合成與其光催化性質
我們利用高溫氣相沉積以及碳熱還原法合成出長度約100微米的氧化鋅奈米線。這種高徑長比氧化鋅奈米線具有高表面積，應用於光催化分解染料及氯酚分子有很好的效率，在太陽光下亦有相當好的催化效果。此外由於氧化鋅奈米線是成長於矽基板上，因此可以當作一個異相光催化劑並重複使用，根據測試十次催化結果推測氧化鋅奈米線可重複始用數十次以上。

2.氧化鎘奈米線的合成及其性質探討
我們利用碳熱還原法在較低的溫度下合成出氧化鎘奈米線，並且發現在氧氣較充沛的環境下會形成如珍珠項鍊般的奈米線結構。此外我們也偵測到較少被觀察到的氧化鎘發光性質。

3.迴流方式合成鎵-氮化鎵 核-殼結構以及氮化鎵中空球體
我們利用一個簡單的迴流方式在液相合成出鎵-氮化鎵 核-殼結構奈米材料，以酸溶解鎵金屬的核心之後即可得到氮化鎵中空球體結構。在不同溫度以及氮化劑比例作用下，我們可以得到不同殼層厚度以及不同尺寸的鎵-氮化鎵 核-殼結構。同樣方法在較低溫度以及較長反應時間下亦可做出銦-氮化銦的複合材料。

關鍵字

氧化鋅 ； 氧化鎘 ； 奈米線 ； 氣相沉積 ； 核-殼結構 ； 氮化鎵 ； 氮化銦 ； 迴流法

並列摘要

1. Growth of Ultralong ZnO Nanowires on Silicon Substrates by Vapor Transport and Their Use as Recyclable Photocatalysts
We synthesized the growth of ultralong ZnO nanowires on silicon (100) substrates via the gold-catalyzed vapor transport approach. Ample supply of zinc vapor generated through carbothermal reduction of ZnO powder at 917 °C and a suitable amount of oxygen facilitate the rapid growth of nanowires. These ZnO nanowires are extremely long with lengths of 85–100 microns, and exhibit a vertical orientation. The nanowires have largely diameters of 250–400 nm. Crystal structure analysis indicates typical ZnO nanowire growth along the [0001] direction. The band gap of these nanowires was determined to be 3.22 eV. These nanowires show a relatively weak near-band-edge emission peak at 390 nm, and a significant oxygen vacancy-related emission band at 495 nm. Good photocatalytic activity of these nanowires on substrates toward the photodegradation of rhodamine B and 4-chlorophenol was demonstrated. Furthermore, we showed that these nanowires on substrates can serve as effective and convenient recyclable photocatalysts. Only a slight decrease in the photodecomposition rate was observed after 10 cycles of the photocatalysis experiment. The photocatalysts also work well under natural sunlight.

2. Gold-Catalyzed Low-Temperature Growth of Cadmium Oxide Nanowires by Vapor Transport
Uniform and ultralong cadmium oxide nanowires were synthesized in high yield on gold-coated silicon substrates using a vapor transport process. Cadmium vapor generated by the carbothermal reduction of CdO powder in a tube furnace heated to 500 °C was carried to the substrate zone by an argon flow with a trace amount of oxygen. The CdO nanowires grew via a vapor-liquid-solid growth mechanism. The diameters of the nanowires are 80 nm, and can reach lengths of 40 microns. Because the nanowire formation was gold particle-catalyzed, patterned nanowire growth on substrates can be achieved. These nanowires grew along the [111] direction and have slight rough surfaces due to the presence of crystalline CdO shells formed via a vapor-solid deposition process. Interesting CdO nanowires with a necklace-like morphology were also observed in a small region of the substrate, where the oxygen supply may be ample to facilitate the lateral growth of rhombohedral crystals over the pre-formed central wires. Electron diffraction and high-resolution TEM results suggest that the rhombohedral crystals should grow epitaxially from the wire stem. The band gap of the CdO nanowires was determined to be ~2.53 eV. These nanowires exhibit a relatively weak emission band centered at ~550 nm.

3. Synthesis of Self-Templated Core-Shell Ga-GaN Nanostructures and GaN Hollow Spheres via Conventional Reflux Method
Core-shell Ga-GaN nanostructures were synthesized via a simple reflux method. Gallium chloride was reacted with lithium bis(trimethylsilyl)amide in trioctylamine at 380 □C for 24 hours. The core-shell nanostructures are ~500 nm in diameter with a rough surface. After removal of the gallium core by acid, GaN hollow spheres can be obtained. The GaN hollow spheres are composed by GaN nanoparticles with the shell thickness ~25 nm. PXRD and ED pattern show the GaN hollow spheres are zinc blende structure with hexagonal structure less than 10%. By XPS and IR analysis, the GaN nanoparticles are binding by silica to maintain the hollow structure. The growth of Ga-GaN nanostructures were monitored during the increase of temperature and reaction time. Gallium was generated first at lower reaction temperature and followed by GaN deposited on the metal surface. The size and shell thickness of Ga-GaN nanostructures can be varied by changing the amount of lithium bis(trimethylsilyl)amide and reaction temperatures. Furthermore, In-InN nanocomposites also can be synthesized using the same reflux method with a lower reaction temperature and longer reaction time. The InN nanoparticles are wedge-shaped or triangular with a single crystallinity.

並列關鍵字

zinc oxide ； cadmium oxide ； nanowires ； vapor transport ； core-shell structure ； gallium nitride ； indium nitride ； reflux method

參考文獻

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