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  • 學位論文

一維矽、鍺材料之製作及其場發射性能

One-dimensional Silicon and Germanium Materials: Fabrications and Their Electron Field Emission Properties

指導教授 : 李紫原 裘性天
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摘要


One-dimensional (1D) structures are regarded as ideal electric field emission (EFE) sources owing to their high aspect ratio. In previous studies, the strong screening effect of the crowded silicon wall-like arrays that are formed by EMD (electrolessmetaldeposition) degrades the performance of EFE. In this thesis, free standing and vertically aligned silicon rice-straw like array emitters were fabricated by modified-EMD, using HFH2O2 as an etching solution to reduce the emitter density and to make the emitter end of the formed silicon rice-straw arrays shaper than those formed by conventional EMD. These silicon rice-straw array emitters can be turned on at 4.7 V/μm, yielding a field enhancement factor b of 1406 and an EFE current density of 139μA/cm2 in an applied field of 12.8 V/μm. For a long-term modified etching, highly porous, individually separated, and vertically aligned rough silicon rods (r-SiRs) were formed. r-SiRs, to be a silicon-based template, were decorated with two kinds of field emitters (carbon nanotubes, CNTs, and zinc oxide nanowires, ZnO NWs) to form a heterojunction nano/microstructure and have better EFE properties than emitters grown on flat silicon substrates. For CNT/r-SiRs has a turn-on field of 2.3 V/um, a β value of 1384, and a current density of 3.7 mA/cm2 at applied field of 5.1 V/um; and for ZnO NWs/rSiRs has a turn-on field of 2.9 V/um, a β value of 1311, and a current density of 900 uA/cm2 at applied field 8.6 V/m. Furthermore, 1D germanium (Ge) nanostructures were synthesized by reduction of GeO2 in H2 atmosphere at various temperatures. Entangled and straight Ge nanowires with oxide shell were grown at high temperatures. Ge nanowires with various amounts of nodules were obtained at low temperature. Ge nanowires without nodules exhibited remarkable field emission properties with turn-on field of 4.6 V/μm, field enhancement factor of 1242. and a current density of 910 uA/cm2 at applied field 10.9 V/um.

並列摘要


由於一維材料擁有極高的深寬比,因此被視為是場發射體中理想的材料來源。在過去的研究中指出,藉由「無電極金屬沉積法」所製造出來的一維矽陣列,由於該陣列的排列分佈過於擁擠,進而影響到其場發射特性的表現,因此在本論文中,我們使用了含有氫氟酸及過氧化氫的酒精溶液當作蝕刻溶液來改變前述過於密集排列的一維矽陣列結構。經由再一次的蝕刻後,矽陣列的形貌由初始相交連結的牆狀轉變成各自獨立存在的稻草堆形貌。擁有稻草堆外貌的一維矽陣列其場發射量測出來的起始電壓約為 4.7 V/μm,且在外加電場 12.8 V/μm 時,可以得到場加強因子1406和電流密度139 μA/cm2,此一結果顯示其場發射效能優於初始的牆狀矽陣列。 若將初始的牆狀矽陣列長時間置於前述蝕刻液中,則會得到崎嶇外表的一維矽柱陣列。利用此崎嶇外表的矽柱彼此間擁有較大間距的特點,期望能減少場發射應用中常見的「遮蔽效應」。故,以此矽柱陣列為基板,將奈米碳管及氧化鋅奈米線分別成長於矽柱上。經由量測結果顯示,藉由矽柱陣列為基板所形成的場發射體其性能表現優於場發射體成長於平坦矽基板上的場發射表現。成長於矽柱陣列上的奈米碳管,其起始電場為2.3 V/um,場加強因子為1384,且可以在外加電場5.1 V/um時得到 3.7 mA/cm2的電流密度;而成長於矽柱陣列上的氧化鋅奈米線,其起始電場為2.9 V/um,場加強因子為1311,且可以在外加電場8.6 V/um時得到 900 uA/cm2的電流密度。 另外,我們合成「鍺」的一維奈米材料。藉由二氧化鍺在氫氣的高溫環境下進行還原反應,而在低溫的地方可以得到不同性貌的一維鍺奈米結構。在低溫區較高溫度的區域可以得到長度較短且帶有較厚氧化層的奈米線,其形貌有二種:糾纏彎曲以及筆直;而在低溫區較低溫度的地方則可以得到長度較長且氧化層較薄的奈米線,另外,此區域所得到的奈米線根據成長溫度的不同而會有不同數量的結狀物成長於側。經由場發射量測所顯示出來的結果表示:在低溫區所形成無側向成長結狀物的鍺奈米線擁有較佳的場發射性能,其起始電場約為 4.6 V/um、場增強因子為1242,且可以在外加電場10.9 V/um時得到 910 uA/cm2的電流密度。

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