不同晶粒大小及氮摻雜鑽石薄膜的拉曼光譜、紅外線光譜及功函數特性研究

Abstract

本實驗利用微波電漿化學汽相沈積法成長鑽石薄膜於矽基板 上,所成長的鑽石薄膜晶粒大小範圍從大約5 奈米(UNCD)至1 微米 (MCD)之間。這些不同晶粒大小的鑽石薄膜是以甲烷/氬氣/氮氣及甲 烷/氫氣的混合氣體,藉著改變氣體的比例、及成長時間等參數來控 制晶粒的成長。並且以電子掃瞄顯微鏡來決定晶粒的半徑大小。 這些成長的鑽石薄膜使用紫外光(325nm)及可見光(514nm) 拉曼光譜進行量測。非結晶SP2 鍵結的碳原子及SP3 鍵結的結晶鑽石 的拉曼散射強度隨著晶粒大小的不同會有強度及拉曼位移上的變化 情形,並且此拉曼強度也與入射光的能量有關。而位於1332cm-1 的 鑽石拉曼訊號與晶粒尺寸大小的關係中可以發現,在微米級的鑽石薄 膜中可以量測出但卻無法在15nm 晶粒以下的鑽石薄膜觀察到。而對 於不同入射光能量的拉曼量測而言,因為可見光光子能量接近π 能 態,所以只可激發SP2 態能階的碳原子。而紫外光光子能量較高,大 於π 能態與σ 能態,而可同時激發SP2 及SP3 鍵結的碳原子,所以 可以得到量測出SP3 鍵結的結晶鑽石訊號。 此外,我們對鑽石薄膜表面進行酸化的處理,使其表面的鍵結改 變。並且進行功函數的量測,發現功函數與表面的SP2 碳原子以及 CHx 的結構相關,這些功函數的變化我們以拉曼光譜與紅外線光譜量 測來探討功函數變化原因,而對於不同摻雜的超奈米結晶鑽石 (UNCD)而言,摻雜量的不同造成結構改變以及CHx 的變化,對於功 函數的影響也在本論文中討論,由這些量測我們發現奈米結晶鑽石 (UNCD)在成長方式以及所呈現出的結構及表面特性方面皆有許多異 於NCD、及MCD 的地方。
Microwave-plasma-chemical-vapor-deposition method was used to diamond films on silicon substrate with the size from 5 nm to 1μm. The different grain size diamond films has been synthesized by microwave plasmas fed with CH4/Ar/N2 and CH4/H2 mixtures by varying the proportion of gas mixtures and the growth time. Scanning electron microscope is used to determine the grain size of the grown diamond film. These diamond films have been examined by using ultraviolet (UV,325 nm) and visible (514nm) micro-Raman spectroscopy. Both the Raman intensity of amorphous sp2-bonded carbon and the strength of the 1332 cm-1 sp3-bonded diamond phonon are found to vary considerably as functions of the grain size of diamond film and the incident photon energy. The 1332 cm-1 diamond peak can be found in micro diamond and cannot be observed for grain size under 500nm in visible Raman spectroscopy. Visible Raman spectroscopy is more sensitive to sp2 sites,as visible photons preferentially excite their π states. UV Raman spectroscopy, with its higher photon energy, excites both the π and the σ states and so is able to probe both the sp2 and sp3 sites, allowing a direct probe of the sp3 bonding. After chemical acid cleaning procedure, oxygen ions were absorbed on the surface of diamond films. The oxygen adsorption caused the surface workfunction of diamond films down bending. The work function also shows a strong correlation with the grain size of diamond films.

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Keywords

鑽石, 拉曼光譜, 紅外線光譜, 功函數, 晶粒大小, diamond, Raman Spectroscopy, FTIR, workfunction, grain size

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