矽單晶奈米線氧化動力學及其氣體偵測性質研究

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Title:	矽單晶奈米線氧化動力學及其氣體偵測性質研究
Authors:	張尚仁;Chang,Shang-jen
Contributors:	化學工程與材料工程學系
Keywords:	矽晶奈米線;氧化;動力學;氣體偵測;silicon nanowire;oxidation;kinetic;sensor
Date:	2013-08-27
Issue Date:	2013-10-08 15:07:37 (UTC+8)
Publisher:	國立中央大學
Abstract:	??摘要本研究成功利用聚苯乙烯奈米球微影術（Polystyrene Nanosphere Lithography，PSNSL）結合金屬催化化學蝕刻法在（001）晶面之矽晶基材上，製備出垂直於矽晶基材且規則有序排列之矽晶奈米線陣列，其矽晶奈米線寬度約為120 nm。從TEM 影像及其相對應之電子繞射圖形鑑定分析可得知，矽晶奈米線陣列均為單晶結構，且軸向方向沿著[001]方向生成。為了進一步研究矽晶奈米線氧化機制與動力學，我們將120 nm和60 nm之矽晶奈米線進行一系列不同溫度、時間之熱氧化。從TEM影像觀察矽晶奈米線氧化後之形貌即可發現，矽晶奈米線Core-Shell 結構中心半徑會隨著氧化時間及溫度增加而逐漸減少，氧化層厚度則逐漸增厚。由於矽晶奈米線之應力作用，在氧化初期，60 nm之矽晶奈米線的氧化速率會大於矽晶平板基材和120 nm之矽晶奈米線，而其所生成之氧化層厚度與氧化時間呈現一拋物線關係，證明氧化過程為一擴散控制的反應機制。接著利用不同時間對氧化層厚度於不同時間下之生成速率可以得到120 nm矽單晶奈米線和60 nm矽單晶奈米線氧化層之生成反應活化能分別約為65.4 (kJ/mol)、 62.7 (kJ/mol)。在氣體性質量測實驗中，我們利用矽晶基材平板及規則有序排列之矽晶奈米線二種不同的試片做成感測器的偵測元件，並於室溫下通入丙酮、氨水兩種氣體進行偵測。不論通入丙酮或氨水，有結構之矽晶奈米線相對於矽晶平板試片，都具有較高的氣體偵測靈敏度。在660 ppm之丙酮氣體有14%的靈敏度，9 ppm之氨氣則有900%之靈敏度推測原因可能為奈米線結構增加了偵測反應的表面積，使其靈敏度提高。 Abstract In the present study, we have demonstrated that arrays of vertically aligned Si nanowire were successfully produced on (001)Si substrates by using the PS nanosphere lithography combined with the Au-assisted selective chemical etching process. The diameter of the Si nanowire produced was very uniform and observed to be approximately 120 nm. Based on the analyses of the TEM image and the corresponding SAED patterns, it can be concluded that the Si nanowires produced have a single-crystalline nature and formed along the [001] direction. In order to further study the oxidation mechanism of Si nanowires, Si nanowires with diameters of 120 nm and 60 nm of silicon were prepared for a series of different temperature and time on thermal oxidation. The oxidation kinetics of Si nanowires with different diameter were investigated by TEM. The radius core of Si and the thickness of oxide shell were found to decrease and increase with oxidation temperature and time. In addition, the oxidation rate of 60-nm-diameter Si nanowires is faster than that of blank Si and 120-nm-dianeter silicon nanowires due to the stress effects. The thickness of outer SiO2 shell was found to increase parabolically with oxidation time, indicating that the growth of SiO2 shell is diffusion-controlled. By measuring the growth rate of SiO2 shell at different temperatures, the activation energies for the growth of SiO2 shells on 120-nm-diameter and 60-nm-diameter Si nanowires were determined to be about 65.4 kJ/mol, and 62.7 kJ/mol, respectively. For the gas sensing experiments, blank-Si wafer and periodic Si nanowire arrays, were used as the gas sensor in this study. Their gas sensing properties towards acetone and ammonia were investigated at room temperature. Whether exposed to acetone or ammonia the sensitivity of the Si nanowires sensor is much higher than that of the blank-Si sensor. In this study, the gas sensitivity of the Si nanowires sensor reaches as high as 14% for 660 ppm acetone and 900% for 9 ppm ammonia. The enhanced sensing performances of the Si nanowires sensor can be attributed to its high surface-to-volume ratio.
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