1. Hydrothermal Synthesis of ZnO, Au2S and CuS Nano/Microstructures and the Characterization of Their Properties 2. Growth of Ultralong and Highly Blue Luminescent Gallium Oxide Nanowires and Nanobelts and Direct Horizontal Nanowire Growth on Substrates

1. 利用水熱法製備氧化鋅、硫化金和硫化銅的奈微米結構與其性質分析 2. 合成超長和具有強藍螢光的氧化鎵奈米線/帶及其於基板上的水平成長

郭啟良(Chi-Liang 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.2008.00324

摘要

本篇論文主要以兩種實驗方法合成奈米或微米結構，一為水熱合成法、一為高溫氣相反應合成。又以水熱法合成氧化鋅、硫化金和硫化銅的奈微米結構，以高溫氣相反應合成氧化鎵奈米線和奈米帶。
氧化鋅微米球於95度下合成，此微米球為一種奈米皺摺結構所組成，外貌像一般俗稱的繡花球結構，若將反應時間從一小時延長到十二小時甚至四十八小時，所有的繡花球結構會轉換成六角柱狀結構。此氧化鋅微米球擁有高的表面積，經過900度高溫退火後可做為光催化的應用。硫化金奈米粒子於175度下合成，此硫化金奈米粒子又可以自組裝成層狀的超級結構。此外界面活性劑CTAB會於反應當中裂解成長碳鏈的分子而促使層狀的超級結構生成。硫化銅奈米盤於90至150度合成，此奈米盤可同時吸收紫外光和紅外光，若將反應溫度提高至220度則可合成微米盤，反應當中必須加入硫酸幫助硫化銅的生成，否則會有不純物的產生。氧化鎵奈米線/帶於750度下管狀高溫爐中合成，其長度可達2微米以上，此為合成金屬氧化物之奈米線難以達成的長度，此外如果將氧化加奈米線以紫外光燈照射會發出強烈的藍色螢光，另外一項重要的發現為氧化鎵奈米線可直接於基板上做水平成長，先將矽基板於900度氧氣的環境下退火生成氧化矽的非結晶薄膜，在拿此退火過的矽基板去成長氧化鎵就可以得到水平成長的奈米線。

關鍵字

氧化鋅 ； 硫化金 ； 硫化銅 ； 氧化鎵

並列摘要

We present the syntheses of ZnO, Au2S and CuS nano/microstructures by using a hydrothermal method. ZnO microstructures were formed by using zinc nitrate hexahydrate (Zn(NO3)2•6H2O), hexamethylenetetramine (HMT, or C6H12N4), and trisodium citrate (TSC) reagents. ZnO microspheres were prepared after 1 h of reaction and are amorphous. By increasing the reaction time, these microspheres gradually dissolved to form short hexagonal microrods with stacked nanoplate or nanosheet structure. The microspheres exhibit an extensive growth of interconnected sheetlike nanostructures and possess high surface areas. These ZnO microspheres can be used in the photodecomposition of phenol under direct sunlight irradiation after heat treatment to 300 °C. Trisodium citrate plays a key role in directing the formation of these microstructures because the ZnO microrods were formed under the influence of trisodium citrate.
Uniform size of 2–4 nm Au2S nanoparticles were formed by using tetrachloroauric acid (HAuCl4) and sodium sulfide (Na2S•9H2O) reagents and CTAB surfactant. These Au2S nanoparticles were found to assemble into a densely packed lamellar phase structure, and the resulting materials display an overall cross-sheet-like morphology. The sheets are 125–250 nm in length and can be suspended in solution. Although some isolated faceted gold nanoparticles were also observed, XRD, TEM, XPS, and EDS characterization of the nanoparticle samples confirmed the composition of the nanoparticles as Au2S. UV–vis absorption spectra also showed only absorption feature from the Au2S nanoparticles. Sufficiently high concentrations of Na2S and CTAB in the reaction mixture were concluded to be necessary to promoting the growth of Au2S nanoparticles, and reducing the production of gold nanocrystals. The growth mechanism of Au2S nanoparticle superstructures is related to the decomposition of CTAB. The thermolysis of CTAB was studied and the results indicate that long alkyl chains interact with the Au2S nanoparticles and direct their assembly into a lamellar phase structure.
The synthesis of hexagonal covellite (CuS) nano/microdisks can be achieved by using a hydrothermal method at 90 to 220 °C. A glass tube with a capacity of 6 mL was used as the reactant container and was sealed by torch. Copper chloride (CuCl2) and Na2S were used as reagents, CTAB was selected as surfactant and sulfuric acid (H2SO4) was chosen as the acid source to maintain an acidic environment during the hydrothermal process. The need of H2SO4 to form CuS crystals is discussed. CuS nanodisks were collected under the reaction temperatures of 90 to 150 °C. The particle size of CuS nanodisks can be controlled by using different reaction temperatures but are usually associated with a large size distribution. CuS nanodisks show two absorption features in the UV□vis and infrared region. CuS microstructures containing hexagonal disks and crisscross disks can be obtained after hydrothermal synthesis at 220 °C. Besides, CuInS2 nanocrystals can be synthesized by using a similar reaction condition.
We have used a vapor phase transport method for the growth of ultralong □-Ga2O3 nanowires and nanobelts on silicon substrates. The growth was carried out in a tube furnace with gallium metal serving as the gallium source and Au-coated Si wafer as the substrate. The nanowires and nanobelts can grow to lengths of hundreds of micrometers and even millimeters, and they display strong blue emission by irradiation with an ultraviolet (UV) lamp. The blue emission shows a band maximum at 470 nm. Their full lengths and strong blue emission have been captured by optical images. Interestingly, horizontal Ga2O3 nanowire growth on the silicon substrates can be observed by annealing the silicon substrates in an oxygen atmosphere to form a thick SiO2 film, and growing Ga2O3 nanowires over the sputtered-gold patterned regions. Their composition has been confirmed by TEM characterization. This represents one of the first examples of direct horizontal growth of oxide nanowires on substrate.

並列關鍵字

ZnO ； Au2S ； CuS ； Ga2O3

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