| 摘要: | 本研究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，成功地在（001）及（111）不同晶面之矽基材上，製備出大面積垂直排列且長度尺寸均一之矽晶奈米線陣列，其寬度約為120 nm。從TEM 影像及其相對應之電子繞射圖形分析鑑定可得知本研究所製備之矽晶奈米柱均為單晶結構，且軸向方向沿著基材晶面方向生成。為了進一步控制所生成矽晶奈米線的外觀，我們利用稀釋的氫氧化鉀溶液，進行溼式蝕刻製程。本實驗中，在20℃下以不同蝕刻時間進行蝕刻，可以對奈米線的寬度及長度進行控制並縮小其尺寸，其奈米線尖端的尺寸可由原本的120 nm 縮小至12 nm。由場發射性質量測所得到的數據可知，和原本的矽晶奈米線相比，經過氫氧化鉀蝕刻後的矽晶奈米線可顯著提升場發射的性質；本實驗中，所量測的最低啟動電場為1.21 V/μm，而場發射增強因子β可以增加至8127。 在氣體量測實驗中，利用平板矽試片、矽晶奈米線以及表面孔洞結構之矽晶奈米線等三種不同條件的試片做成感測器的偵測元件，並於室溫下通入水氣、酒精和丙酮等氣體進行偵測。從量測結果可清楚得知，氣體偵測的靈敏度會隨著通入氣體濃度的提升而增加；而不論是何種通入氣體，表面孔洞結構之矽晶奈米線其靈敏度相比其他兩種試片都是較高的，在11 ppm的低濃度時有著9.7 %的靈敏度，推測是因為其較高的表面積比例，可增加氣體量測性質的靈敏度。In the present study, we have demonstrated that large-area, length-tunable arrays of vertically aligned Si nanowire were successfully produced on (001)Si and (111)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 single-crystalline nature and form along the [001] and/or [111] directions. In order to further modulate the morphologies of the Si nanowires, a post wet etching process with a dilute KOH solution was developed. In this work, the tapering process was performed at 20℃ for various etching time. The length and width of Si nanowires can be controlled and reduced by adjusting the KOH etching duration. After appropriate KOH etching, the diameter of the Si nanowire tips can be reduced from 120 nm to about 12 nm. Field emission measurements showed that the KOH-etched Si nanowires exhibited significantly improved field emission properties compared to the as-produced Si nanowires. In the study, a low turn-on field of 1.21 V/μm was obtained, and the corresponding field enhancement factor, β value, was greatly enhanced to as high as 8127. For the gas sensing experiments, three kinds of samples, blank-Si wafer, Si nanowires, and porous Si nanowires, were prepared and used as the gas sensing in this study. Their gas sensing properties towards water vapor, ethanol, and acetone were investigated at room temperature. The measurement results clearly show that the response magnitudes of the three kinds of sensors improved significantly with increasing the gas concentrations. Whether exposed to water vapor, ethanol, or acetone, the sensitivity of the porous Si nanowires sensor is much higher than that of the blank-Si and Si nanowires sensors. In this work, the sensitivity of the porous Si nanowires sensor reaches as high as 9.7% for 11 ppm acetone. The enhanced sensing performances of the porous Si nanowires sensor can be attributed to its high surface-to-volume ratio. |
