矽化鈷及矽鍺化鈷奈米結構之合成、結構鑑定及特性之研究

Cobalt Silicide and Cobalt Germanosilicde Nanostructures: Synthesis, Characterization, and Properties

蔡純怡(Chun-I Tsai)

指導教授 ： 陳力俊

國立清華大學/工學院/材料科學工程學系/博士(2011年)

https://doi.org/10.6843/NTHU.2011.00336

摘要

One dimensional metal silicide nanostructures have attracted much attention for their potential applications in electronic and spintronic nanodevices. In the present work, synthesis and characterizations of cobalt silicide and cobalt germanosilicide nanostructures have been investigated. In addition, the physical properties, including electrical, magnetic, and field emission properties, of the nanostructures were examined.
Cobalt silicide nanostructures have been synthesized by a spontaneous chemical vapor transport and reaction method. The temperature and the vapor flow rate were shown to critically influence the growth of nanostructures. The effects of nanowires (NWs) growth by two main parameters were discussed. Various phases (CoSi, Co2Si) and morphologies, such as single-stem NWs, three-dimensional (3D) nanowire networks, and aloe-like NWs, have been synthesized. Very low turn-on field (1.42 V/m) and good conductance in field-emission and electrical property measurements indicate that CoSi NWs are potentially useful for electronics.
The effects of partial substitution of Ge for Si in cobalt germanosilicde (CoSi1-xGex and Co2Si1-xGex) NWs on the electrical transport, magnetic properties and magnetoresistance (MR) have been investigated. Cobalt germanosilicide NWs were synthesized by a spontaneous chemical vapor transport (CVT) growth method. The Ge concentration can be selectively controlled from 0-15% and 0-50% for CoSi1-xGex and Co2Si1-xGex NWs, respectively, by varying the reaction temperature. Electrical measurements showed that the resistivities of CoSi1-xGex NWs are 90, 60, 30, and 23 Ω-cm for x = 0, 0.01, 0.05 and 0.15, respectively. Therefore, the electrical resistivity of CoSi1-xGex NWs was found to decrease significantly with an increasing Ge concentration which is believed to be a result of the band gap narrowing. On the other hand, the Co2Si1-xGex NWs exhibited ferromagnetism at 300 K, which is attributed to the uncoordinated Co atoms on the NW surface and spin glass behavior at low temperature, which is induced by the Co2Ge compound. The highest MR response of Co2Si1-xGex NWs occurred at x = 0.5, where a MR ratio of 11.7% can be obtained at 25 K with a magnetic field of 8 T. The enhanced physical properties of cobalt germanosilcide NWs with Ge substitution will lead to promising application in the fabrication of nanodevices, including spintronics and serving as the gate and interconnect material.

一維金屬矽化物之奈米結構由於在奈米電子元件及自旋電子元件的應用中深具潛力，近年來，受到學界矚目及廣泛的被討論。本研究中，以合成矽化鈷及矽鍺化鈷之奈米結構為主題，並針對其奈米結構作分析鑑定與成長機制的探討，以及進行材料之電性、磁性和場發射等物理特性的量測與奈米元件之製作。
本研究利用化學氣相傳輸法合成矽化鈷奈米結構，在此合成方法中，反應溫度及反應氣體流量為影響奈米結構成長的兩個重要因素。除了深入探討此兩變因對生成奈米結構具體的影響外，利用調控此二成長變因，成功合成出多元矽化鈷奈米結構，包含: 高密度奈米線(CoSi、Co2Si)、三維奈米網狀結構(CoSi)及奈米蘆薈花(Co2Si)。從場發射性質的量測結果，矽化鈷奈米結構擁有低啟動電場及低臨界值電壓，其中以高密度奈米線結構的表現為最佳。電性量測的結果顯示，矽化鈷奈米線的電阻率優於其塊狀材料，且電阻率隨著奈米線的尺寸減小而下降。
進一步將鍺元素參雜至矽化鈷奈米線中，並探討在矽鍺化鈷奈米線中鍺濃度對於電性、磁性及磁阻變化的影響。在CoSi1-xGex奈米線中，鍺取代矽原子位置將縮小材料帶狀間隙距離，使得CoSi1-xGex奈米線在電性的表現有所提升。另一方面，磁性量測結果觀察到Co2Si1-xGex奈米線擁有室溫鐵磁與低溫自旋玻璃特性，室溫鐵磁性來自於表面未鍵結鈷原子，而自旋玻璃性質來自於奈米線中鍺化鈷化合物。此磁特性使Co2Si1-xGex奈米線擁有高磁阻變化，顯示此材料在奈米自旋電子元件中有潛在的應用性。

關鍵字

cobalt silicide ； naowires

參考文獻

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