顆粒間交互作用對奈米錫顆粒超導參數的影響

Effects of interparticle interaction on superconducting parameters of Sn nanoparticles

鄭佳寧(Chia-ning Cheng)

指導教授 ： 李文献

國立中央大學/理學院/物理學系/碩士(2008年)

摘要

以低真空熱蒸鍍冷凝法製備奈米錫微粒，經X 光繞射及AFM 鑑定粒徑為7 nm，從X 光繞射圖及XRF 判定樣品成份皆為錫。在1.8 K 且零外加磁場環境下，測定7 nm 樣品之交流磁化率，結果顯現超導態。 利用壓合的方式以改變樣品微粒間距，討論微粒間的交互作用對超導參數的影響，發現錫塊材的原子距離不是最佳，藉由調控錫的原子距離，使得錫奈米顆粒的臨界溫度大於塊材錫，塊材錫臨界溫度的公認實驗值為3.722K，且超導抗磁效率為塊材的19 倍。邁斯納效應隨微粒間距的減小而增強，其可能之機制是以穿隧距離相關的直流約瑟夫遜效應為主。此外，樣品具有電子自旋極化的現象，自旋極化效應會與超導抗磁性互相競爭，從實驗數據中發現在高壓合密度時，此樣品的超導抗磁性皆大於自旋極化效應。

關鍵字

奈米粒子 ； 電子自旋極化 ； 超導 ； 錫

並列摘要

A set of Sn nanoparticle powder is fabricated by the thermal evaporation method. The mean particle diameter is determined to be 7 nm by X-ray diffraction profiles and AFM images. The zero field ac magnetic susceptibility
measurements reveal that superconductivity occurs below 3.6 K when the particles are very loosely packed.
Interparticle separation is adjusted by a hydraulic press. The effects of interparticle interactions on the superconducting parameters of Sn nanoparticles are investigated. The critical temperature is found to be sensitive to theinterparticle separation a 7% increase in Tc is revealed at a interparticle separation of 2.2 nm. Recalling the interparticle separation results in a
significant increase in the diamagnetism screening effect. As large as 19 times the bulk screening is also observed at an interparticle separation of 0.03 nm.
We found that the inter-atomic distance in the bulk material is not optimized for the forming of superconducting. The origin of enhanced Meissner effect may
be mainly contributed by DC Josephson effect due to reduction of tunneling
distance.

並列關鍵字

spin polarization ； superconductor ； Sn ； nanoparticle ； tin

參考文獻

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