顆粒間交互作用抑制鋁奈米微粒超導行為; Suppression of superconductivity in Al nanoparticles by interparticle interactions.

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/7620

Title:	顆粒間交互作用抑制鋁奈米微粒超導行為;Suppression of superconductivity in Al nanoparticles by interparticle interactions.
Authors:	陳佳塘;Chia-Tang Chen
Contributors:	物理研究所
Keywords:	庖立順磁;零維超導;奈米;交互作用;抑制;鋁;Pauli paramagnetism;Al;interaction;nanoparticle;suppression;Fluctuation;Zero-dimensional superconductor
Date:	2009-06-22
Issue Date:	2009-09-22 11:00:57 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	使用熱蒸鍍法蒸鍍製作鋁奈米微粒，藉由X-ray Diffraction(XRD)、Scanning Electron Microscopy(SEM)、Atomic Force Microscope(AFM)以及共同體積函數等工具判斷粒徑為7.5 nm，X-ray Fluorescence Spectrometer(XRF)、結構精算軟體(GSAS)分析XRD繞射圖判定樣品成分均為鋁。磁化率量測樣品在低於2.27 K出現超導態，且得到超導溫度比塊材公認值之1.18 K高92%，推測可能是庫倫阻塞效應造成的。本論文使用弱屏蔽模型討論微觀機制。另外在外加小磁場下發現樣品抗磁率變好，與庖立順磁磁化率有關。磁性量測亦觀察到自旋極化效應，與之前論文得到的結果一致。利用壓合工具逐次對樣品壓合改變顆粒間距，探討顆粒與顆粒之間互相影響之效應，發現超導溫度隨顆粒間距縮小而逐漸降低，回到塊材的趨勢，推測可能是由於單電子穿隧效應使得電荷分佈被改變，破壞相位，壓制超導溫度。超導抗磁磁化率也隨著顆粒間距縮小而逐漸變弱，可能是超導屏蔽電流產生的感應磁場互相影響，使的抗磁磁化率變弱。 Al nanoparticles were fabricated by employing the thermal evaporation method.X-ray Diffractio(XRD),Scanning Electron Microscopy(SEM) and Atomic Force Microscope(AFM) were used to determine the pariticle size. The particles size thus determined is 7.5 nm.Profile refinement analysis of the XRD pattern and the XRF experiment indicate that the sample is single phased. The ac magnetic susceptibility were measured by Physical Property Measurement System to explore the superconducting characteristics and the superconducting transitions were observed at 2.27 K.Compared with the bulk value of Tc=1.18 K,Tc increasing 92%.We contribute this increase of Tc to the coulomb blockade effect.We discuss this phenomenon by weak screening model.When applied a small magnetic field,superconducting diamagnetic responses become more effective.Spin polarization that indicates the magnetic nature of the particles has also been observed. To investigate the effect of the interparticle interaction,we changed the interparticle separation by cold press the sample using a hydraulic press,followed by the routine magnetic measurement.A series of samples at different packing fractions is investigated.We found that the Tc decreases with decreasing interparticle separations,and then gradually converges to bulk value. Our observes are discussed by single electron tunneling effect that change the charging distribution,destroy the coherence phase,and depression the superconductivity.Superconducting diamagnetic susceptibility gradually weaked when the interparticle interaction becomes stronger. We use screening current model to explain this phenomenon.
Appears in Collections:	[Graduate Institute of Physics] Electronic Thesis & Dissertation

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