In/In2O3奈米顆粒聚合體中的超導性質探討; Superconductivity in In/In2O3 nanoparticle assemblies

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题名:	In/In2O3奈米顆粒聚合體中的超導性質探討;Superconductivity in In/In2O3 nanoparticle assemblies
作者:	吳豐宇;Feng-Yu Wu
贡献者:	物理研究所
关键词:	不可逆行為;超導;約瑟夫陣列;類二類超導體;奈米顆粒;表面氧化;Josephson array;nanoparticle;suerconductivity;type II-like superconductor;irreversible behavior;surface oxidation
日期:	2009-06-20
上传时间:	2009-09-22 11:00:40 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	具有表面氧化銦絕緣層的銦奈米顆粒聚集所構成的奈米顆粒聚合體中的各個銦奈米顆粒之間存在交互作用，而本論文中藉由改變銦顆粒表面的氧化層厚度來探討超導體奈米顆粒間的交互作用。銦奈米顆粒採用熱蒸鍍法製備，且經由不同的曝氧過程在表面滋生氧化層。本實驗所使用一組不同氧化程度的50 nm銦奈米顆粒，以及分別固定氧化物重量比例在90 %、80 %、30 %且粒徑為3.5 nm、7.5 nm、25 nm銦與氧化銦核殼結構的奈米顆粒。並由測量樣品在低溫的磁性而定義樣品的超導性。超導奈米聚合體有兩種不同特徵的超導性質，稱為雙分量的超導行為，藉由改變樣品的氧化程度及外加磁場的強度能夠將此兩種分量區分開來，並提出可能描述超導奈米顆粒聚合體的模型，此兩分量分別來自於獨立的超導顆粒以及經由約瑟夫森界面而連接的超導體陣列所貢獻。此模型能描述超導奈米顆粒聚合體中的各種行為：類似第二類超導體的行為、高臨界磁場、超導抗磁隨溫度轉變以及隨奈米顆粒排列緊密程度不同而改變的行為。 Indium nanoparticles were fabricated by thermal evaporation method and oxidized using different processes. The mean diameter and composition of sample were determined by XRD and AFM. A series of oxidation dependent experiments reveal the influence of oxidation on superconductivity in nanoparticle assembly; critical temperature is lowered after oxidation, and superconducting diamagnetic response is also suppressed substantially. Based on the result of temperature dependent AC magnetic susceptibility measurement, two superconducting components are distinguished: the first SC component, the magnetic response caused from interparticle interaction, shows a smooth transition with high tolerance to magnetic field, and the second SC component more similar to bulk is the contribution of individual nanoparticles. Those two components are separately discovered in rarely oxidized sample and extremely oxidized one. The crossover is corresponding to the behavior of Josephson junction array; surface oxide suppresses supercurrent as insulating layer. We use type II-like superconductor model to describe the system. Type II-like superconductor, not really type II superconductor, is nanoparticle assembly connected by Josephson junction. In this model, magnetic field is allowed to penetrate three dimensional Josephson array, but the vortex current in nanoparticle assembly is still against outer field for maintaining partial system in superconducting state. According to the model, the superconductivity in nanoparticle assembly is very sensitive to the condition of the surface and the structure of cluster.
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