自身模板輔助成長碳化矽奈米結構

Abstract

在本論文裡，我們利用相分離的概念，藉由在氣液或氣固界面的化學反應來成長碳化矽奈米結構。反應過程中，自我生成的無機鹽類氯化鈉，氯化鎂，以及氯化鈣提供了形成奈米碳化矽形貌的模板。 首先，利用不同的氣態有機碳氯矽烷，二氯二甲基矽烷、三氯甲基矽烷、二氯甲基矽烷，和三氯苯基矽烷在523 -723 K下與液態的金屬鈉反應生成碳化矽的前驅物以及副產物氯化鈉。然後經過1273 K的熱處理，生成方形籠狀或圓球型態的碳化矽奈米結構。在利用氣態二氯二甲基矽烷反應時，一開始會生成具可撓曲的線性聚碳矽烷化合物覆著在副產物氯化鈉的表面上。經過熱處理後，可以移除氯化鈉，進而生成方形空心的碳化矽。使用三氯甲基矽烷反應時，則會生成硬性網狀聚碳矽烷化合物與副產物氯化鈉產生相分離，最後移去氯化鈉時，則得到圓球形狀的碳化矽奈米顆粒。然而在使用二氯甲基矽烷時，會因為反應溫度不同而生成不同型態的聚碳矽化合物。在較低溫下會產生硬性聚碳矽烷化合物，進而生成圓球形狀的碳化矽與矽奈米顆粒；而在較高溫度則是生成可撓曲的線性聚碳矽烷化合物，進而生成方形空心的碳化矽。除此之外，如果是具有較多碳的三氯苯基矽烷當前驅物，則會生成類方形碳/碳化矽空心顆粒。 在第二部份，我們利用物理氣相沈積的方法先在矽基材上沈積一層鈣薄膜。然後利用二氯甲基矽烷與鈣金屬在773 – 923 K反應14小時，之後經過1273 K的熱處理，就可以成功的合成出空心長條型態的碳化矽奈米結構。主要的原因是反應一開始副產物氯化鈣會與聚碳矽化合物相分離形成核殼狀的一維型態的產物，而經高溫處理氯化鈣被移除，聚碳矽化合物進而形成空心長條型態碳化矽結構。空心長條型態碳化矽結構可以用於場發射的應用，實驗發現只需要提供相當低的電場2.5 V/ μm 就會有 10□μA/cm2 電流密度的產生。 第三部分，我們再次驗證相分離的概念。藉由二氯甲基矽烷或二氯二甲基矽烷與氫氣電漿處理過後的鎂金屬在823 K或923 K下反應，之後在1273 K高溫熱處理，即可得到藉由自我產生的片狀氯化鎂模板的輔助，得到片狀碳化矽結構。 而在第四部份，我們將相分離的概念延伸到在矽基材上製作孔洞性的碳化矽薄膜。 利用Sn(SiMe3)4 當作化學氣相沈積的前驅物，一開始先在923 K下成長薄膜；此時奈米錫顆粒會與無晶相的矽碳化合物產生相分離，而形成錫奈米顆粒鑲埋在矽碳化合物的薄膜。之後利用HF水溶液或在1423 K的高溫真空下將利用氫氣電漿在薄膜上的錫顆粒移除，即可生成孔洞碳化矽薄膜。我們也利用離子佈值的方式，將磷摻雜到P-type矽基材上的孔洞碳化矽薄膜，使其展現更好的heterojunction diode的性質。 最後，我們也利用錫奈米顆粒鑲埋在矽碳化合物的薄膜當作還原劑。藉由錫顆粒與金氯酸在具有氯化十六烷基三甲基銨鹽(CTAC)的水溶液下，行自發性的賈凡尼置換反應，在矽碳化合物的薄膜表面上生成一維的金奈米線。

In this thesis, we employ phase segregation as the concept to develop diverse SiC nanostructures via vapor-liquid and vapor-solid reactions. Inorganic salts MClx (M=Na, Mg, Ca) act as templates generated in-situ to assist the morphology development. First, cubic shells and spherical nanoparticles of 3C-SiC were produced at 1273 K by processing the ceramic precursors formed from the reactions between vapor of organochlorosilanes, Me2SiCl2, MeSiCl3, MeSiHCl2, and PhSiCl3, and liquid Na at 523 – 723 K. From Me2SiCl2, a flexible linear polycarbosilane precursor was synthesized and covered the NaCl byproduct surface to from a cubic shape. Hollow cubic 3C-SiC shells were produced after the NaCl templates were removed. From MeSiCl3, a rigid cross-linked polycarbosilane was produced and phase segregated from the NaCl byproduct. The precursor was transformed into nanoparticles without special morphology. MeSiHCl2 produced a cross-linked polysilane precursor at low temperatures, which can be converted into a mixture of 3C-SiC and Si nanoparticles. At high temperatures, the polysilane converted to polycarbosilane and produced hollow cubic□□-SiC shells. The carbon-rich PhSiCl3 generated cube-like particles as the final product, which contained 3C-SiC and carbon. In the second section, polycrystalline tubular SiC on Si was prepared by reacting MeSiHCl2 vapor and Ca thin film on Si at 773 - 923 K followed by heat-treatment at 1273 K. The products phase-segregated into a cable-like radial heterostructure composed of a core of CaCl2 and a shell of SiCxHy. After removal of the CaCl2 core, the layer of polycrystalline SiC tubes on Si emitted electrons at a low applied field of 2.5 V/ μm with a current of 10 μA/cm2. In the third section, we also used the phase segregation concept in the reaction of Me2SiCl2 and MeHSiCl2 between and magnesium metal at 823 - 923 K. The product was heat treated at 1273 K under vacuum. It showed pseudo thin plate SiC nanostructure, which was self-templated by MgCl2 generated in situ. In the fourth section, we extended the phase segregation idea to create porous SiC thin film on Si subtrate. Using Sn(SiMe3)4 as the precursor, amorphous SixC1-x thin films with Sn nanoparticles embedded were grown on Si substrates at 923 K by low pressure chemical vapor deposition. After treated under hydrogen plasma at 923 K, the Sn nanoparticles in the films were removed by an HF solution and by evaporation at 1423 K. Following the removal of Sn, high temperature treatments at 1273 - 1423 K converted the amorphous thin films into mesoporous semiconducting 3C-SiC thin films with pore sizes 10 - 100 nm. Finally, one dimensional high aspect ratio Au nanowires were fabricated via galvanic reduction of HAuCl4 solution in the presence of cetyltrimethylammonium chloride (CTAC) by the Sn nanoparticles embedded in amorphous the SixC1-x thin film product.