氧化鈀奈米片薄膜對丙酮氣體之感測特性研究

Abstract

氧化鈀是 p 型半導體，對於感測還原性氣體(如 CO和 H2)有奇妙的感測特性。丙酮是糖尿病患者重要的揮發性有機呼吸標記物。在本研究我們探討氧化鈀奈米片薄膜在溫度250oC以下對丙酮氣體的感 測機制。氧化鈀感測器是以濺鍍沉積法沉積氧化鈀在SiO2基材上。 此氧化鈀奈米片薄膜提供巨大開放的表面積讓丙酮吸附。氧化鈀感測器在溫度100oC以下感測丙酮響應差，當溫度100oC時，感測電流快速下降，並呈現穩定。在溫度150oC以上，氧化鈀感測丙酮表現出特徵響應。當通入丙酮氣體，量測氧化鈀薄膜之導電率快速下降，接著導電率緩慢上升直至飽和。這具有特徵的響應特性會隨著濃度提高而有不同。此外，導電率衰減在跟高溫是更為明顯的。根據X光光電子能譜儀，在溫度100oC和150oC感測丙酮後會在PdO表面形成羥基，羰基和乙酸根離子等吸附物質。這些吸附物質因在溫度200oC以上近乎不存在，這可能是導致電導率衰減的原因。氧化鈀感測器感測丙酮的機制主要基於電性的變化和XPS分析推論而得。我們也利用濺鍍沉積法修飾白金奈米粒在氧化鈀奈米片薄膜上，探討白金修飾對於氧化鈀感測丙酮的影響。白金修飾可以提高氧化鈀感測丙酮的靈敏度。白金-氧化鈀感測器在溫度25oC和50oC下感測丙酮和在高溫下感測丙酮而有的特徵響應皆和純PdO感測器有不同之處。白金奈米粒修飾之氧化鈀感測行為將在本研究中探討。

PdO is a p-type oxide semiconductor and shows intriguing sensing properties to reducing gases, such as CO and H2. Acetone is an important volatile organic breath marker for diabetic patients. In this thesis, we studied the gas sensing mechanism of PdO toward acetone at temperatures below 250℃. The PdO sensor is a PdO nanoflake thin film sputter-deposited on the SiO2 substrate. The nanoflake feature of the PdO thin film provides a large open surface area for acetone adsorption. The PdO sensor responses poorly to acetone below 100℃, while its conductivity drops rapidly upon acetone exposure at 100℃ and subsequently becomes steady. At temperatures at 150℃ and above, the PdO sensor demonstrates a characteristic sensing response feature toward acetone. Upon the exposure of acetone, the PdO thin film has a prompt conductivity drop, followed by a slow increase and a succeeding decay. The characteristic response feature is more distinct with increasing the acetone concentration. Moreover, the conductivity decay is more obvious at higher sensing temperatures. According to x-ray photoelectron spectroscopy (XPS), hydroxyl, carbonyl and acetate adspecies are formed on the PdO surface after acetone exposure at 100 and 150℃. These adspecies are nearly absent at 200℃ and above, indicating that these adspecies are likely responsible for the conductivity decay. The acetone sensing mechanism of the PdO sensor is proposed on the basis of the sensing response features and the XPS analysis. We also decorated the PdO flake thin film with sputter-deposited Pt nanoparticles to study the influence of Pt on the acetone sensing performance of the PdO sensor. The Pt decoration can greatly enhance the acetone sensing sensitivity of PdO. The Pt-PdO sensor shows apparent response to acetone at 25 and 50℃, and the characteristic response feature observed for the bare PdO sensor becomes unclear at high temperatures. The influence of the acetone sensing behavior of the PdO sensor on Pt nanoparticles is discussed in the thesis.