二氧化鈰摻雜過渡金屬奈米粒子之軟X光吸收能譜研究

Soft X-ray Absorption of Transition-Metal Doped Cerium Oxide

顏榕峻(Jung-Chun Yen)

指導教授 ： 黃迪靖

國立清華大學/理學院/物理學系/碩士(2012年)

https://doi.org/10.6843/NTHU.2012.00388

摘要

自旋電子學為目前電子元件材料的熱門領域，稀磁半導體是在半導體中摻雜過渡金屬，不會影響半導體本身的電子特性，反而會使材料同時具有鐵磁性。很多研究提出稀磁半導體的磁性來源與其電子結構及材料的奈米效應有相關關係，因此我們利用軟X光吸收光譜探討稀磁性半導體材料-二氧化鈰摻雜鈷或銅奈米粒子的電子結構與其奈米效應，控制前驅物達到調整摻雜物的種類及濃度。

軟X光吸收光譜為研究二氧化鈰摻雜鈷有效的工具，分別可以提供我們鈷的L-edge、氧的K-edge以及鈰的M-edge吸收現象。從鈷的L-edge，可以發現Co2+以高自旋態存在。當摻雜濃度增加，會加強2p核電洞和3d電子的庫倫交互作用及交換交互作用。氧的K-edge，可以發現當粒子趨近奈米尺度時，氧的2p電子較為反局域性(delocalized)，與鈰的混成效應較強。鈰的M-edge，則得知CeO2奈米粒子為Ce3+和Ce4+共存，當粒子縮小奈米尺度時，Ce3+的強度將會增加。當摻雜的濃度增加時，會使得Ce3+強度被壓抑。

關鍵字

軟X ； 二氧化鈰 ； 奈米粒子 ； 稀磁半導體 ； 電子結構

並列摘要

Dilute magnetic semiconductors (DMS) are materials in which a semiconductor is doped with a small amount of transition-metal atoms to induce magnetic properties necessary for spintronics and no deteriorate the optical and electronic properties. Recent research works indicate that the magnetic properties concerned with the electronic structure and the nanoscale effect are interesting and important. We used soft X-ray absorption to probe the electronic structure and the nanoscale effect of material-CeO2(Co).

Soft X-ray absorption (XAS) is a powerful tool for studying DMS. In this thesis, we studied XAS of CeO2(Co) with the X-ray energy tuned about Co L-edge,O K-edge, and Ce M-edge. The Co2+ ions doped in CeO2 exhibit a high spin state. Our XAS results indicate that the Coulomb interaction of Co core holes and electrons increases with the increase of concentration of Co. The hybridization between Ce and O will be enhanced as the particle size is in the nano scale regime. We also found that the Ce3+ and Ce4+ coexist in CeO2(Co) and the formation of Ce3+ is suppressed by increase of Co concentration.

參考文獻

[1.26] P. Hohenberg and W. Kohn, Physical Review, 136, B864 (1964).

[1.29] Sugano, Tanabe, & Kaimura, Multiplets of transition-metal ion in crystal (2010).

[3.23] L. H. Tjeng, C. T. Chen, and S.-W. Cheong, Phys. Rev. B 45, 8205 (1992).

[3.24] L. H. Tjeng, C. T. Chen, and S.-W. Cheong, Phys. Rev. B 45, 8205 (1992).

[3.27] H. Eskes, L. H. Tjeng, and G. A. Sawatzky, Phys. Rev. B. 41 288 (1990).