矽化鈦奈米結構之成長及其鑑定

Abstract

金屬矽化物奈米線具有低電阻、良好的熱穩定度等優異的特性。近年來，製備各種金屬矽化物奈米線成為重要的研究議題。本研究中我們提出利用化學氣相沉積法以四氯化鈦與鈦金屬為反應前驅物，並且在不使用模版或金屬催化劑的條件下成長矽化鈦奈米線、二維奈米片狀產物及薄膜。此外本研究也對矽化鈦奈米材料的成長機制以及電子場發射性質作了詳細的探討。 首先，我們利用在1173 K由四氯化鈦與鈦金屬生成的TiClx (x=1-3)與在低溫區 (723 – 1073 K) 的矽基材反應後可以得到各種矽化鈦奈米線。本研究中所得矽化鈦奈米線具有兩種不同的結晶型態，分別為三矽化五鈦(Ti5Si3)以及矽化鈦(TiSi)。矽化鈦奈米線的直徑分布大約為20 – 80 奈米，線長可長達數個微米。Ti5Si3及TiSi奈米線的成長方向經過鑑定分別為[001]以及[010]方向。在奈米線以及其下方的矽化鈦薄膜之間可以觀察到一層非晶相矽化鈦薄膜，此半液相薄膜在奈米線的成長裡扮演了相當重要的角色。 利用相同的反應，在TiCl4前驅物的蒸氣壓於相對低的條件下，可以得到C49二矽化鈦二維奈米結構。經過分析，此二維結構傾向展露出(010)晶面，此一特性源自C49二矽化鈦本身的層狀晶體結構。由此二矽化鈦二維奈米結構及前述奈米線的結果可知本論文中提及奈米結構的非等向性成長與材料本身的晶體結構排列有相當大的關聯。 經由探討矽化鈦樣品的電子場發射性質，顯示出樣品的形貌及結晶性與其場發射特性具相當的關聯性。可知矽化鈦奈米線具有很高長寬比使得其場發射特性具有很好的表現。結果顯示Ti5Si3與TiSi 奈米線具有很低的起始電場 Eo 分別為5.4 與 5.25 V/um，以及優異的場增強因子beta 可達到816與876。從研究結果顯示矽化鈦奈米線在未來的場發射元件上具有相當大的潛力。

Recently, synthesis of various metal silicide nanowires (NWs) has raised many attentions due to their excellent physical properties. In this work, we demonstrate the synthesis of titanium silicide nanowires, nanoplates, and thin films via a unique chemical vapor deposition process, using TiCl4 and Ti powder as the precursors, without the usage of template and catalysts. Field emission properties, growth mechanism of these titanium silicide samples were also investigated. Titanium silicide NWs, including single crystalline Ti5Si3 NWs and crystalline TiSi NWs, were prepared by reacting titanium subchlorides TiClx (x = 1-3), generated by the reaction between TiCl4(g) and Ti metal in the high temperature zone at 1173 K initially, and the Si substrates in the lower temperature zone at 723 - 1073 K. The diameters of the nanowires are 20 - 80 nm, and the lengths are several micrometers. The growth directions of the Ti5Si3 and TiSi NWs are determined to be along the [001] and [010] axes, respectively. An amorphous titanium silicide interlayer was observed between the NWs and the C54-TiSi2 film. This interlayer, probably existed as a quasi-liquid thin film during the growth, appears to be the key factor to assist the NW development. The C49 TiSi2 nanoplates on Si substrate were obtained at a low TiCl4 vapor pressure condition. The preferred basal plane of the C49-TiSi2 nanoplates was determined to be parallel to the (010) plane. This could be attributed to the anisotropic crystal structure nature of the C49-TiSi2. The characterization and the growth mechanism of the two-dimensional nanostructure will be discussed below. Comparing with preferred growth direction the titanium silicide NWs, [001] and [010] for Ti5Si3 NWs and TiSi NWs, respectively. The crystal structure nature takes an important role on the growth of anisotropic nanostructures. The field emission properties of the titanium silicides samples have been studied. The results show that the field emission performances are highly dependent on the morphology and crystal structures of the NWs and thin films. The high aspect ratio nature of the NWs has improved the performance of field emission properties. The field emission property obtained from Ti5Si3 and TiSi NWs on C54 -TiSi2 thin film demonstrates low turn-on fields Eo of 5.4 and 5.25 V/micrometer and high field enhancement factor beta of 816 and 876, respectively. These remarkable results suggest that titanium silicide nanoemitters could serve as promising candidates for future field emission devices.