單晶3C碳化矽於離子輻照下隨溫度變化之膨脹效應

The Swelling Effect of Ion Irradiated Single Crystal 3C-SiC at Various Temperature

林恊弘(Lin, Hsieh Hung)

指導教授 ： 開執中 ； 陳紹文

國立清華大學/原子科學院/核子工程與科學研究所/碩士(2015年)

摘要

碳化矽因具有高熔點、高溫時仍具有良好的機械性質、化學活性低及中子吸收截面小等優點，是未來備受矚目的核能結構材料之一，本實驗結合TEM及XRD分析離子輻照後的單晶3C碳化矽其微結構變化與膨脹效應，本論文中的實驗分為兩部分，一為單晶3C碳化矽於低溫輻照下所產生的點缺陷晶格膨脹效應，另一部分為高溫輻照下所產生之空孔之膨脹，而實驗分為三部分，簡述如下:
　　氦離子單射束實驗使用175、225及275keV的He+於距離表面0.6至0.8μm處形成一輻照劑量為15000或45000 appm的區域，並於800、1000、1200℃進行實驗。利用TEM觀測此區域發現氦氣泡在800℃時率先於材料中原有的疊差處生成，當溫度到達1000℃，除疊差處外於其附近的區域亦開始出現氦氣泡，其略大於800℃的尺寸，且密度明顯增加。當溫度高達1200℃時，氣泡的分部範圍遍佈整個佈植區，且氣泡的尺寸大幅增加，但密度下降。比較45000 appm之結果可發現輻照劑量增加對於氦氣泡的生成機制並無明顯影響，但氣泡密度及大小會隨劑量增加而增加。且經由理論計算得知，在15000appm的實驗中，即使於1200℃的條件下，仍有高達34%的氦原子未進入空缺中形成氦氣泡，而在1000及800℃的條件下有更高比例的氦原子未貢獻入氦氣泡中，此現象推測與打入之氦原子的量大於輻照所產生的缺陷量，因而無法使氦原子完全進入空缺團中形成氦氣泡。
　　矽離子單射束使用2.9 MeV的Si2+離子於距離表面0.6至0.8μm處形成一平均輻照劑量為20 dpa之區域，於40及200℃進行輻照，佈植後發現40℃之樣品有非晶化的現象且經由電子顯微鏡的量測可知若假設為等向性之體膨脹，其體膨脹率為7.7%。而200℃的試片則無非晶化之現象，並利用同步XRD進行各晶面之徑向掃描，量測其膨脹後晶面間距的變化，發現其因薄膜材料的基板箝制效應而為非等向性之膨脹，其體膨脹量僅1.52%。若不考慮基板之效應則應為等向性膨脹，其值為4.04%。此外，於XRD[0 0 2]的徑向掃描結果中亦有觀察到因輻照所產生之沿特定方向排列之缺陷，如C+-C<100>的啞鈴型缺陷(dumbbell)所造成的繞射峰偏移及因輻照缺陷團聚所造成的漫散射駝峰。此外，亦有根據文獻進行理論計算，推出單一一顆缺陷所造成的晶格膨脹量。
　　氦、矽離子雙射束實驗於佈植區的平均劑量為100 appm / 1 dpa，氦離子的能量為201、467、737及1000keV，矽離子能量為5.1MeV，實驗溫度為1000、1200、1350℃，實驗完成後亦利用TEM進行觀察，統計氣泡平均直徑與密度並計算氦氣泡膨脹量，與氦、矽單射束的數據進行統整與比較。由TEM統計結果可發現於相同劑量下，氣泡密度與直徑有隨溫度上升減小與增加，而當劑量增加則密度與尺寸都會略微增加。此外，根據TEM照片可發現於雙射束實驗的條件下，氣泡幾乎是均勻分佈於佈植區，並沒有明顯沿著疊差生成的趨勢，此與氦單射束之結果有很大的不同。最後，利用TEM照片的統計結果計算出單晶3C碳化矽的膨脹量並與其他文獻進行比較，可發現雖然膨脹量略低於前人之結果，但膨脹量隨溫度之變化趨勢是相同的。

關鍵字

碳化矽 ； 離子輻照 ； 膨脹效應 ； 微結構變化 ； 氦氣泡

並列摘要

Silicon carbide (SiC) is one of the attractive nuclear structure materials in the future, because it has many outstanding properties like high melting point, good mechanical property at high temperature, small cross-section of absorbing neutron, and so on. In this thesis, using transmission electron microscopy (TEM) and synchrotron radiation based X ray diffraction (XRD) to discuss the microstructure change and swelling effect of ion implanted single crystal 3C-SiC. The material is the thin film CVD single crystal 3C-SiC with 1.1μm thickness. The experiment is seperated to 3 parts. The details are as following:
The first part is the single beam irradiation with helium ion (He+). The implanted temperature is 800, 1000 and 1200℃. Using 175, 225 and 275 keV of He+ form a region that has 15000 or 45000 appmHe. This region is at 0.6 - 0.8μm from the sample surface. In the experiment of 15000 appm, the He bubbles will form at the stacking fault region at 800℃. when temperature up to 1000℃, bubbles appear not only at the stacking fault region but also at its near region. The bubble density is higher than the bubble density of 800℃. The bubbles appear in everywhere and the bubble size is increasing obviously at 1200℃. When dose up to 45000 appm, the bubble size and density are increasing, but the bubble appeared region is not affected by dose at the same implanted temperature. Besides, there is only 66% of implanted He atoms diffuse into the bubble at 15000 appm, 1200℃. When the dose increase, the percentage will also increase.However, the percentage of helium atoms diffuse into bubble does not reach 100% at 45000 appm, 1200℃. It suggest that the amount of defects caused by ion irradiation are less than implanted helium ion.
In the second part, the single beam ion implantation up to 20 dpa with 2.9 MeV Si2+ at 40 and 200℃. The sample become amrophous at 40℃, but it is still crystalline at 200℃. The swelling is 7.7% at 40℃. Besides, using synchrotron radiation based XRD radial scanning to get the interplanar information of 200℃. The results find that the swelling is anisotropic, owing to the limitation of Si substrate. Besides, humps are found in Si(002) radial scan result, it may caused by the defect cluster. Also, the swelling which caused by each type of point defect was calculated.
The last part is the dual beam implantation with 201, 467 keV He+ and 5.1MeV Si2+at 1000 - 1350℃. The average dose in implanted area is about 100 appmHe/ 1 dpa. In the statistic, the bubble density decrease, but the bubble size increase as temperature increasing. The increasing dose will cause bubble size and density become lager and denser. Besides, the bubble distribute in the irradiated region homogeneously. This result is defferent from the helium single beam obviously. At the last, compare the experimental statistics with many lectures.

並列關鍵字

silicon carbide ； ion irradiation ； swelling effect ； microstructural change ； helium bubble

參考文獻

[83]胡均輔，「SA-Tyrannohex全纖維碳化矽複合材料於高溫離子輻照下空泡行為與晶粒尺寸之效應」，國立清華大學工程與系統科學所，碩士論文，中華民國一0四年

[86]陳科夆，「應用電子能量損失譜及能量過濾電鏡研究生醫及核能材料之特殊問題」，國立清華大學工程與系統科學所，博士論文，中華民國九十七年

[2] M. Mehregany, C.A. Zorman, "SiC MEMS: opportunities and challenges for applications in harsh environments", Thin Solid Films, pp. 518-524, 1999

[6]林彥儒，「輻照引致單晶3C碳化矽材料的微結構變化與膨脹效應之研究」，國立清華大學先進光源科技學位學程，碩士論文，中華民國一O三年

[7] K.K. Chawla, Composite Materials, 2nd edition, Springer, 1998