過渡金屬矽化物最近被廣泛運用於CMOS元件、表面塗層、塊材、電熱元件、光伏元件、熱電材料、自旋電子元件中。其中半導體性矽化物可被用在矽基的光電元件中，如LED與紅外線偵測器。對於CrSi2、β-FeSi2、MnSi1.8和 ReSi1.75這些窄能隙材料而言，由於其為穩定且不昂貴的材料，因此被廣泛應用於熱電材料及光伏元件。其中β-FeSi2為富矽相矽化物，具有斜方晶 (Orthohombic)結構，其直接能隙的特性已被運用於發光二極體元件。而鐵矽化物另一相ε-FeSi為金屬性，為立方晶結構 (Cubic)，其特殊的磁性質引起大家廣泛討論。
使用雙前驅物FeCl3和SiO並利用氧化物輔助生長方式成長β-FeSi2與ε-FeSi奈米線，其外層會包覆一層較厚的二氧化矽層。不像一般VLS法成長機制，OAG沒有金屬催化劑故沒有金屬球頭形成於奈米線頂端。奈米線的表面形貌及結構我們利用XRD、SEM、TEM進行觀測。由SEM我們可以看出，奈米線的直徑均小於100nm，長度均大於10μm。XRD指出在不同溫度下可形成混相或單相的形式。ESCA指出奈米線表層有一層厚的SiO2層。最後，TEM指出奈米線的成長方向均往低指數面方向生長。
我們利用兩點探針測量β-FeSi2和ε-FeSi奈米線電性，平均為2000μΩ．cm和250μΩ．cm。在半導體奈米線中，當導線直徑接近於費米波長，電子傳遞將從散射方式轉換成彈射方式，電阻率將隨著奈米線直徑減小而下降。
就本實驗，我們利用OAG法成功合成單晶β-FeSi2和ε-FeSi奈米線，這些材料將在未來奈米科技會有很大助益。

Transition metal silicide nanowires compose a highly broad set of refractory materials that are promising materials that are currently used for many applications including CMOS devices, thin film coatings, bulk structural components, electrical heating elements, photovoltaics, thermoelectric and spintronics. Semiconducting silicides have been extensively investigated for silicon-based optoelectronics such as LEDs and IR detectors. The narrow bandgap semiconducting silicides, in particular CrSi2, β-FeSi2, MnSi1.8, and ReSi1.75, have been targeted and used for robust, stable, and inexpensive thermoelectric materials, and have shown potential for photovoltaic applications. β-FeSi2 is a silicon-rich phase with a orthorhombic structure (space group Cmca) that has direct-bandgap . It allows for making light-emitting devices which operate at 1.5mm that incorporate β-FeSi2 into a conventional silicon bipolar junction. ε-FeSi is a metallic material with a cubic structure (space group P213) that has been classified as a Kondo insulator. It has attracted interest for over half a century, mainly because of its unusual magnetic behavior.
β-FeSi2 and ε-FeSi nanowires were produced on silicon substrates covered with a thick layer of silicon oxide through the decomposition of the double-source precursor FeCl3 and SiO in a Oxygen Assisted Growth (OAG) process. Unlike typical Vapor-Liquid-Solid (VLS) NWs growth, The NWs form without the addition of metal catalysts had no catalyst tips. The morphologies and structure of NWs were confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). SEM shows that the diameter of the NWs is below 100nm and the length of NWs is tens of micrometers. XRD reveals that samples can grow in single phase or in double phase NWs depending on the growth temperature. Energy spectroscopy for chemical analysis (ESCA) shows the NWs are covered a thick SiO2 layer. TEM results indicate that the NWs growth is along the low index plane.
We also have fabricated two-terminal electrical devices of β-FeSi2 and ε-FeSi NWs, and they exhibited average resistivity about 2000μΩ．cm and 250μΩ．cm. We found that the resistivity decreases stepwise as the NWs is thinned in semiconducting nanowires.
In conclusion, we have successfully synthesized freestanding single-crystalline nanowires of β-FeSi2 and ε-FeSi by OAG method. This shows that semiconducting and metallic NWs will prove to be promising materials in future nanotechnology.

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