鐵鉑合金奈米顆粒之X光散射及吸收光譜研究

X-ray scattering and absorption spectroscopy study of FePt nanoparticles

黃子文(Tzu-Wen Huang)

指導教授 ： 李志浩

國立清華大學/原子科學院/工程與系統科學系/博士(2006年)

摘要

本論文利用X光散射與X光吸收光譜技術研究鐵鉑合金奈米顆粒在3-5奈米尺寸高溫退火下之相轉變與磁轉變現象。除了利用略角X光繞射發現自組裝的面心堆積形式的鐵鉑顆粒現象外，利用X光吸收光譜，我們更近一步的証實鐵鉑奈米顆粒的表面化學型態，在退火過程中佔有舉足輕重的腳色。 而一開始在合成顆粒時，原先披附在顆粒表面的介面活性分子會於退火過程中轉變成碳質的材料附著在顆粒表面。 搭配X光繞射與散射的觀察下，發現這些碳質的存在會阻礙奈米顆粒在退火中聚集或是晶粒成長的行為。 此現象的觀察發現實得我們進一步提出使用異質、非互融的異質材料，能夠阻絕奈米顆粒在退火中不必要的聚集，並保持原先的顆粒尺寸。 進一步我們使用非磁性的金薄膜沈積在單層鐵鉑奈米顆粒之上，再加溫退火過後，為了證實金膜的可行性，我們利用X光異常略角小角度散射的分析來證實並得知鐵鉑奈米顆粒在退火過程中的確仍保有其完整特性，此發現可進一步的證實並提共金膜在未來使用鐵鉑奈米顆粒在硬式磁碟的應用上，將會是有效並重要的製程環節。

關鍵字

鐵鉑合金 ； 奈米顆粒 ； 異常略角小角度散射 ； X光 ； 吸收光譜 ； 散射

並列摘要

In this thesis the phase and magnetic transition of 3-5 nm FePt nanoparticles surface and monolayer system were studied using X-ray scattering and absorption techniques. A self-assembled structure was verified as a face center cubic packing structure by grazing incident X-ray diffraction. However, this self-assembled structure was easily destroyed when the surfactant on the particles surface were decomposed at the annealing temperatures more than 400 oC. Besides, the grain sizes also didn’t change enormously, even at the temperature up to 640 oC. The remaining carbons which burned out from the surfactant were investigated by X-ray absorption spectroscopy. The evidence shows that those remaining heterogeneous materials, such as carbon or silicon, on the particles surface might be useful to preventing aggregation during the post-annealing.
In order to keep those particles intact during the annealing, we also use a layer of non-magnetic material, gold, as an overlayer material coating on FePt monolayer particles. Unfortunately, due to the high electron density of Au on the surface, it is difficult to define the particles sizes and distribution by the traditional X-ray scattering during the annealing process. Thus, the anomalous grazing incident small angle x-ray scattering (anomalous GISAXS) has been developed successfully to measure the morphology of FePt monolayer with Au overlayer system. Based on the anomalous GISAXS results, we proved that the Au is an effectively cover layer to prevent those FePt nanoparticles from collapsing together even at the annealing temperatures up to 800 oC for 1 h. In addition, by measuring the diffraction anomalous fine structure spectrum in the near edge region, the ordering FePt L10 phase was observed. According to this approach, the particle size of monolayer FePt nanoparticles can remain small to fit the ultrahigh density demand for the next generation magnetic disk.

並列關鍵字

FePt alloy ； nanoparticles ； anmalous grazing incident SAXS ； X-ray ； absorption spectrum ； scattering

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