探討陽極氧化鋁輔助真空壓鑄法製備二氧化錫奈米線及其特性研究

Study on the Properties of Tin Dioxide Nanowires Fabricated via Vacuum Die-Casting Process with Anodic Aluminum Oxide Template

本研究探討過熔點氧化處理對於不同尺度之錫奈米線於電性及氣體感測特性表現之影響。研究中以陽極氧化鋁(anodic aluminum oxide, AAO)作為模板，輔以真空壓鑄法製備出線徑100、250 nm的錫奈米線，接著進行氧化處理以獲得二氧化錫奈米線。由於使用酸液去除AAO模板時會產生氧化層，此氧化層會包覆於奈米線外層，因此在氧化處理的過程中，當氧化溫度高於錫熔點時，奈米線外部會因為氧化層的保護而不會熔化變形，保持原本實心柱狀。本研究所獲得的二氧化錫奈米線經XRD鑑定，其主相為四方晶系，第二相為斜方晶系，此第二相的生成是由於氧化過程中錫奈米線外層氧化殼層將內部錫奈米線包覆住，抑制了體積膨脹而產生內應力從而形成斜方晶結構。而以EDS作成分分析，結果顯示錫及氧之原子比約為1:2，證實錫皆已被氧化成二氧化錫。此外使用ultraviolet-visible (UV–Vis) absorption進行二氧化錫奈米/次微米線光學特性分析，其結果顯示，由於受到量子侷限效應，其吸收光譜會由波長接近400nm偏移至270nm附近，證實奈米線因線徑不同而有藍移現象。另一方面，透過兩點探針分析二氧化錫奈米線之電性及紫外光感性能，結果顯示二氧化錫奈米線顯示良好的歐姆接觸，且經由紫外光照射下，光響應電流可從3nA提升至69nA，因此預期二氧化錫奈米線可拓展氣體感測領域應用的可能性。

In this study, Tin (Sn) nanowires of 90 nm and 250 nm in diameter were prepared by using anodic aluminum oxide (AAO) as the template and vacuum die-casting. Then the Tin dioxide (SnO2) nanowires could further be synthesized after the oxidation treatment. The outer oxide layer was formed during the AAO template removal process by using acid solution. The outer oxide layer could prevent the nanowires from deforming because this oxide layer covered the nanowires even when the oxidation temperature is higher than the melting point of tin. The structure of SnO2 nanowires was identified by XRD as tetragonal and rhombohedral. The generation of rhombohedral phase was formed due to the oxidation process in which the SnO2 nanowires were suppressed the volume expansion, and inner stress was occurred. The composition of SnO2 nanowires was confirmed by EDS, and the results shows the ratio of Sn to O is approximately 1:2. The optical properties of the SnO2 nanowires were analyzed by using UV-Vis absorption, and the results shows that the absorption spectrum was shifted from near 400 nm to 270 nm due to the quantum confinement effect. On the other hand, the electrical properties and the performances of UV light absorption were detected by two-point probe method. The results show that there is good ohmic contact on single SnO2 nanowire, and the current can be increased from 3 nA to 69 nA when they activated by UV light. Overall, this research presents a method to fabricate SnO2 nanowires, in the hopes that it can give rise to alternative methods of producing SnO2 nanowires and expand the possibility of related applications of gas sensor.