靜電紡絲技術製備鍺奈米結構於熱電效應與表面增強拉曼散射之應用研究

Thermoelectric and Surface Enhanced Raman scattering property of Ge Nanostructures fabricated by electrospinning

牛翊凡(Yi-Fan Niu)

指導教授 ： 李勝偉

國立中央大學/工學院/材料科學與工程研究所/碩士(2014年)

摘要

本實驗利用靜電紡絲法 (Electrospinning method) 搭配電子槍蒸鍍系統 (Electron beam evaporation system) 鍍上鍺薄膜，製備出可以控制直徑的鍺一維奈米結構，並探討其熱電性質 (Thermoelectric properties) 和表面增強拉曼散射效應 (Surface-enhanced Raman scattering effect)。由於靜電紡絲法製備的奈米纖維直徑可以藉由電紡前驅液濃度加以控制，因此鍍上鍺薄膜並移除 PVP 奈米纖維後即得到對應直徑之鍺一維奈米結構，其形貌為溝渠狀的薄膜。
在熱電性質方面，鍺具有與矽為基礎的半導體製程做整合的潛力，相較於矽有較高的電子及電洞遷移率以及較低的熱導率，且容易產生量子侷限效應，在製備成一維奈米結構後其直徑小於聲子的平均自由徑，可以有效阻礙聲子的傳導降低熱導值。根據實驗結果，直徑175 nm的鍺奈米溝渠熱導率為2.2－2.6 W/m-k相較於塊材鍺低了25倍，ZT值在600 K時達0.67。
在表面增強拉曼散射效應的探討，本實驗在不同直徑的鍺奈米溝渠表面鍍銀並退火形成銀奈米粒子，發現較小直徑的銀鍺複合奈米溝渠有較好的SERS 效果，因為其溝渠內曲率較大造成晶粒成長受到應力和空間的限制使的銀奈米粒子直徑較小，較密集，其侷域性表面電漿共振效應 (Localized surface plasmon resonance, LSPR) 的熱點數目較多增強效果較強。本實驗進一步將銀鍺複合奈米溝渠捲成螺旋結構，增加其機械強度和應用性，並縮短了溝渠間的距離到足以形成熱點，使的銀鍺複合螺旋結構有更優異的 SERS 效果。

關鍵字

鍺 ； 一維奈米結構 ； 靜電紡絲 ； 熱電效應 ； 表面增強拉曼散射

並列摘要

This work utilized electrospinning method and electron beam evaporation system to fabricated one-dimensional germanium nanostructure which diameter can be controlled, also studied thermoelectric properties and surface-enhanced Raman scattering effect. Because the diameter of nanofibers fabricated by electrospinning method can be controlled by concentration of precursor, the diameter of curled germanium thin film coated on Polyvinylpyrrolidone (PVP) nanofibers are also controlled by concentration of PVP precursor. When the PVP nanofibers are removed, the remaining one-dimensional germanium nanostructures have a groove like cross-section.
In thermoelectric properties, germanium has the potential to integrate with traditional silicon based technology and has high carrier mobility, low thermal conductivity and good quantum confinement effect. When diameter of one-dimensional germanium nanostructure is less than the phonon mean free path, the surface boundary scattering will hinder the transportation of phonons and result in the lower thermal conductivity. In this experiment, the Ge nanotrough with diameter of 175 nm has the lowest thermal conductivity of 2.2－2.6 W/m-k which is a factor of 25 lower than bulk Ge. The ZT value reaches 0.67 at 600 K. In surface-enhanced Raman scattering effect, the as-prepared Ge nanotroughs with different diameters were coated silver thin film and annealed to form nanoparticles. The nanotrough with smaller diameter has better SERS effect. Because it has bigger curvature, silver nanoparticles would lack of space and subject to stress during grain growth stage. Silver nanoparticles become smaller and closer. This means it has more hot spots on the nanotrough. This experiment further twisted nanotroughs to form helix structure. The helix structure has better mechanical strength for practical applications. Because junctions of wires which have SERS effect possess better enhancement, the helix structure has better SERS effect than single nanotrough.

並列關鍵字

germanium ； one-dimensional nanostructures ； electrospinning ； thermoelectric ； SERS

參考文獻

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