二維奈米平板鑽石之合成及其微結構分析之研究

Abstract

本研究主要是利用微波電漿化學氣相沉積系統中於高溫(大於1100℃)及CH4/H2 =0.667%氣氛中合成二維奈米平板鑽石。 分別依照試片在沉積過程中擺設方式不同，探討合成的條件與溫度效應。 第一種是直立式之基材擺放(基材垂直於基座)，其目的是為了使反應的基材表面與側向電極之間被電漿完全覆蓋。 這個研究除了探討二維奈米平板鑽石的合成，也針對不同基材(Fe/diamond/Si、diamond/Si 及Fe/Si)的影響做比較，最後針對在不同電漿球位置作用下合成碳同素異形體做探討。 合成之後利用掃描式電子顯微鏡及穿透式電子顯微鏡、擇區繞射等來觀察試片表面形態並定義其晶體特徵。 從觀察到的沉積物分布，表面可分成三個不同的區域。 試片表面最上層(靠近電漿球中心較高溫處，> 1100 □C)所觀察到為平板狀物表面形態多為六邊形，其平均厚度約為20-60 nm，邊長從100 nm至500 nm不等，其表面方位大多為<110>鑽石單晶。 中間層(溫度較低處，約1000-1100℃)表面除了可觀察到奈米級平板狀鑽石還可以發現一些奈米碳粒(nano-particle)包覆在純鐵外圍，至於最下層(在電漿邊緣，為最低溫處，約900 □C)則可觀察到奈米鑽石粒、奈米碳管與鐵包覆其中的奈米碳粒。

第二種方式以矽基材(100)為試片平躺於基座上，直接伸入電漿球中心合成二維六方奈米平板鑽石，溫度約在1100 □C 以上。 由SEM 與 TEM 的觀察中可以清楚的看到奈米平板鑽石形成，形狀近似六邊形，其厚度大約在20-30nm，尺寸大約是幾百的奈米。從TEM的分析，發現這些奈米平板單晶鑽石其軸向除了有<110> 外，還有 <111>特徵之平板鑽石。 我們也分析側向結構了解奈米平板鑽石側向生長機制。

Diamond crystallites in 2-dimension nanoplatelet morphology were synthesized in a microwave plasma chemical vapor deposition (MPCVD) system using a CH4/H2 gas mixture with a ratio of 0.667% at relative high temperature (over 1100℃). In this work, we have studied the synthesis conditions of diamond nanoplatelets with the temperature effect using the geometry of specimen positions relative to the plasma during the deposition process.

In the first part of the dissertation, we used substrates in a special position which were standing-up on the holder and allowed it to be entirely embedded within the plasma ball in MPCVD. The influence of various substrates on the deposition of diamond nanoplatelets with the formation of carbon allotrope at different plasma ball deposition was investigated. Surface morphology and crystalline characteristics were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area diffraction (SAD). According to the distribution of the deposits, it can be divided into three distinct areas with respect to different heights on the specimen. The top area of the specimen which is near the center of the plasma ball (temperature > 1100 □C ) is full of diamond nanoplatelets on the surface. These diamond nanoplatelets are hexagonal single crystallites with a thickness of 20-60 nm and side length of several hundred nanometers. TEM examination shows that the diamond nanoplatelets are oriented in <110>. In the middle portion (lower temperature around 1000-1100 □C) it is found that there exist diamond nanoplatelets with some nano-particles which contain Fe and carbon. Three carbon allotrope including nano-diamonds, carbon nano-particles and carbon nano-tubes are coexisted in the lowest area near the edge of plasma ball where the temperature is the lowest, about 900 □C.

In the second part of the dissertation, the substrate in a horizontal position was embedded within the plasma ball close to its center where a high temperature above 1100 □C was reached during the deposition. SEM and TEM observations clearly show that the diamond nanoplatelets exhibit hexagonal-shaped morphologies, and the thickness and the length are measured to be around 20-30 nm and several hundred nanometers, respectively. TEM with selected area electron diffraction shows that each platelet is a single crystalline diamond. In additional to <110> oriented diamond nanoplatelets, it is found another type of diamond platelets which have <111> orientation. Based on TEM observations in a side-view direction, it is understood the lateral growth mechanism of the <111> diamond nanoplatelets.