鐵三矽(Fe3Si)為一鐵磁性金屬，居里溫度為840K。由於其與□化鎵(GaAs)之晶格常數十分相近且熱穩定性良好，可得到乾淨的鐵磁金屬-半導體介面，對於自旋注入(spin injection)十分有利。此外，鐵三矽的DO3晶格結構符合Heusler alloy條件，因此有可能為一半金屬(half metal)，使其在自旋電子學上之應用更具潛力。
本研究以點接觸Andreev反射技術(Point-Contact Andreev reflection technique)進行鐵三矽(Fe3Si)單晶薄膜之自旋極化率量測。為達成點接觸，我們製備鉛探針，利用differential screw 機制下針，使探針接觸鐵三矽樣品表面後進行電性量測。由於鐵磁性金屬對Andreev reflection之抑止與介面可能存在之能障 (interface barrier)，在4.2K下，我們得到電導率對電壓值之歸一化曲線於零電壓之值約1.17。以modified Blonder-Tinkham-Klapwijk模型(MBTK model)分析，我們得到不同接點狀況下之自旋率值為38%至46%，並且自旋極化率P隨著界面能障Z呈現減少現象，此可能為界面存在自旋相關之散射所致。經由多次式擬合P-Z曲線，本質自旋極化率(intrinsic spin polarization) 可由外推至Z=0極限得到，為45±5%。
儘管實驗所得之曲線在能隙範圍內與MBTK模型十分吻合，在大電壓處卻有較寬之趨勢。當接點電阻值降低時，曲線傾向更加寬闊，由此推測可能與界面能障相關。我們因此將溫度T作為擬合參數Teff以模擬此一能障之效應，得到與實驗曲線完全符合的擬合曲線，並由此得到不同接點下的自旋極化率由32% 至50 %，也展現出相似之P-Z相依性。由Z=0之外推得到本質自旋極化率為49±5%。
比較以上兩種分析方式所得之自旋極化率，並沒有明顯歧異。

Fe3Si is a ferromagnet with a Curie temperature of 840K. The small lattice mismatch and good thermal stability led to a clean interface between Fe3Si and GaAs. Furthermore, the DO3 structure of Fe3Si can be considered as a Heusler alloy, making it a good candidate of half metals for effective spin injection.
To determine the spin polarization of Fe3Si, Point-contact Andreev reflection (PCAR) spectrum was measured at 4.2K by driving a Pb tip in contact with a gold-capped Fe3Si film using a differential screw mechanism. The conductance-voltage characteristics showed a central peak with a height ratio of 1.17, as attributed to the spin polarization of Fe3Si suppressing the Andreev reflection and the interface barrier.
By fitting the depth of the dip in the central peak with the modified Blonder-Tinkham-Klapwijk (MBTK) model, we extracted spin polarization ranging from 38% to 46% under various contact conditions. Notable decrease of polarization value P with the increasing of interface barrier Z was observed, indicating possible spin-dependent scatterings. The intrinsic polarization P is extracted from the extrapolation in the limit of Z=0 by polynomial fits, and yielded a value of 45±5%.
An unexpected broadening, however, was observed at large bias, which could possibly due to scatterings not accounted for properly by the MBTK theory, since the spectra tends to be broader when the contact resistance is decreased.
To simulate the effect of the unexpected scatterings, we set the temperature T as a fitting parameter Teff and obtained a good agreement between the experimental and theoretical curves. The extracted P ranges from 32% to 50 %, and showed similar P-Z dependence. The intrinsic polarization is 49±5% by extrapolation to Z=0. In both data analyses, we found no substantial discrepancy in the extracted value of spin polarization.

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