氧化鈀奈米片薄膜對一氧化碳氣體感測特性研究

CO Gas Sensing by PdO Nanoflake Thin Film

施博翔(Bo-Siang Shih) ； 江昱儒(Yu-Ju Chiang) ； 林心弘(Hsin-Hung Lin) ； 潘扶民(Fu-Ming Pan)

《真空科技》 24卷4期 (2011/12) Pp. 30-36

https://doi.org/10.29808/JVSROC.201112.0005

摘要

本研究以活性濺鍍法沉積氧化鈀（PdO）奈米片薄膜，探討PdO 對一氧化碳（CO）氣體感測的電性響應。PdO奈米片厚度僅十數奈米，表面因氣體吸附伴隨之電荷轉移會在薄片形成大範圍之空間電荷區，使薄膜電性發生顯著變化，同時該薄膜具有巨大表面積可吸附大量CO分子，提昇感測靈敏度。研究發現，PdO薄膜在 200℃時，對CO感測有最佳的響應速率與靈敏度，薄膜吸附CO分子後，電阻值升高，顯示奈米片內產生電荷空乏區，而PdO為p型半導體，此現象似乎為吸附之CO傳輸負電荷至薄膜，降低主載子電洞密度。XPS分析顯示在200℃感測環境下，PdO表面被還原成金屬Pd，因感測於真空中進行，缺乏氧氣氧化被還原之金屬Pd，因此薄膜對CO感測的靈敏度為CO吸附在PdO或Pd金屬表面仍有待於大氣中感測來釐清。

關鍵字

氧化鈀 ； 奈米片 ； 一氧化碳 ； 氣體感測 ； 活性濺鍍沉積法

並列摘要

This study deposited PdO nanoflake thin films on the SiO2/Si substrates by reactive sputter deposition, and investigated CO sensing properties of the PdO thin film. The nanoflake has a single crystalline structure after thermal anneal at temperatures ＞200oC. As CO adsorption occurs on the nanoflake, the space charge region, which results from charge transfer between CO adsorbates and the PdO thin film, will occupy most volume of the ultrathin nanoflake, thereby dramatically changing electrical properties of the thin film. Moreover, the nanoflake thin film can adsorb a large amount of CO molecules as a result of the large surface area and, therefore, the PdO nanoflake thin film should have a high sensitivity toward CO gas sensing. According to our study, the PdO thin film has the best CO sensing performance at 200oC, including a fast response time (＜10 sec), a high sensitivity and a good reproducibility. Because PdO is a p-type semiconductor, the electrical resistivity of the PdO thin film increases upon CO adsorption, indicating that the depletion region is formed in the nanoflake. This observation suggests that negative charges transfer from the CO adsorbate to the PdO nanoflake, inducing the reduction in the majority carrier density. X-ray photoelectron spectroscopy analysis shows that the PdO surface is reduced to metallic Pd at 200oC. Because our experiments were carried out under a vacuum condition of 1x10^(-2) torr, re-oxidation of metallic Pd during experiment was unlikely. To clarify whether the change in the electrical property of the PdO thin film is a result of CO adsorption on the PdO or the Pd surface, we have been undertaking the CO sensing experiment under the dry air condition.

並列關鍵字

PdO ； Nanoflake ； CO ； Gas Sensor ； Reactive Sputter Deposition