掺雜不同濃度碳的二氧化鈦薄膜之電子結構與磁性研究

Abstract

本研究中，我們利用固態燒結法製備摻雜碳的二氧化鈦粉末，再使用油壓機和箱形爐來對粉末加壓和加熱，使其成為塊材。接著我們使用脈衝雷射鍍膜系統進行鍍膜，並在一系列成長條件下探討碳掺雜對二氧化鈦磁性造成的效應和機制。我們發現摻雜碳的二氧化鈦有明顯的磁滯曲線，顯示碳摻雜確實會形成室溫鐵磁性。本論文藉由C-1s和Ti-2p之XPS量測，發現薄膜中有鈦和碳的鍵結與氧空缺，顯示摻碳二氧化鈦的鐵磁性來源，是由氧空缺與雜質間相互作用所產生。從O-1s的XPS也可以看出，摻雜碳可使氧空缺變多，此可能進而產生更多電子。本實驗也發現隨著碳的掺雜濃度增加，鐵磁性並未維持一直增加的趨勢，甚至反而減弱材料的室溫鐵磁性，本論文亦將對此現象，提出初步的解釋。

Carbon-doped titanium dioxide powders was prepared by solid state sintering at 1200 o C for 24hrs to produce TiO2 bulks with different carbon doping concentrations. The obtained TiO2 bulks were then used to deposit TiO2 thin films by pulsed laser deposition. The effects of carbon doping was investigated via a series of films obtained at various deposition conditions. The results indicate that the carbon-doped titanium dioxide evidently exhibit significant magnetization hysteresis at room temperature, indicating the realization of room-temperature ferromagnetism (RTFM). Further X-ray photoelectron spectroscopy (XPS) analysis on C-1s, O-1s, and Ti-2p electronic states showed the existence of Ti-C bonding and significant amount of oxygen vacancies. These results lend support to the p-p interaction, induced ferromagnetism in these oxides. The observed RTFM, however, did not increase with increasing doping concentration of carbon, presumably due to the excessive free carbon-induced diamagnetism.