摘要
本研究以B3LYP/6-311++G**為主，首先計算CF-HHY, CF-HFY, CF-FFY，以研究Y (Y= H, CH3, SiH3, GeH3)或F原子對C-F鍵bond dissociation energies (DE)的取代效應，其次也對C-Cl(CCl-HHY, CCl-HClY, CCl-ClClY)中Y or Cl的取代效應，以穫取比較性的訊息(CF vs CCl)。

我們更對Si-X、Ge-X鍵 De值其取代效應樣是否有一致性的趨勢、有助於我們了解四四複合式半導體中Si-C膜及Si-Ge膜在製作中的反應機制，我們也試著用天然鍵解理論(Natural bond orbital，NBO)來說明C-F鍵、C-Cl鍵在不同的取代效應下，其分子中軌域作用力情形與(DE)是否有一致性的趨勢。當Y=H時C-F鍵隨著F取代增加，鍵能會持續增加，C-Cl隨著Cl取代的增加C-Cl鍵的鍵能減弱，當Y=CH3取代Y=H時C-F鍵與C-Cl鍵與Y=H有一致的趨勢，但鍵能有增強現象產生，如果Y=SiH3或GEeH3取代Y=H時C-F鍵與C-CL鍵也有一致的趨式但鍵能相對的減弱，Y的取代效應對C-F鍵與C-Cl鍵大致為CH3＞H＞GeH3＞SiH3結果顯示，C-F鍵的鹵素取代的增加，鍵能變大，透過NBO的分析方法發現是由於負超共軛lp(F)-*CF作用所超的，相同的結果也發生在Si-F鍵上，但對Ge-F鍵而言，第一個F取代鍵能有上昇的現象，第二個F取代鍵能有減弱的情形，我們更進一步的對第3個取代結果發現(DE)變的最小，對C-Cl鍵的研究，隨著Cl取代增加，鍵減少與F的取代效應不同，此外透過NBO來解釋C-Cl鍵之DE的趨勢失敗，這是值得四四族複合式Si半導體前驅氣體中，鹵素的取代導致很多實驗的程序的要求有很重要的啟發意義。

Abstract

In the current study we have performed B3LYP/6-311++G** calculations on CF-HHY, CF-HFY, CF-FFY three series to study substitution effects of Y (Y= H, CH3, SiH3, GeH3) or halogen (F) on C-F bond dissociation energies (DE). The same investigation is then expanded to C-Cl analogues: CCl-HHY, CCl-HClY, CCl-ClClY . This research is further carried out on silanes and germanes in order to probe manufacturing in Group 4 mixed thin-films, eg, C-Si. The natural bond orbital (NBO) method is also employed to examine its capability of interpreting the substitution effects on CF or CCl dissociation energy through bond nature and orbital interactions.

Both SiH3 and GeH3 substitutions would uniformly reduce the DE of either C-F or C-Cl; However the methyl-substitution (Y=CH3), in general, results in a strengthened C-F bond or C-Cl bond. The results reveal that, for a given Y, the dissociation energy of C-F increases with fluorine substation as expected by the negative hyperconjugation effects, which can be monitored by the extent of lp(F)*CF interaction within the NBO algorithm. Similar results have been observed for SiF. For Ge-F bonds the first F-substitution results in a higher DE but the second F-substitution would lower the value of DE compared to the 1 st substitutions.From the studies advanced on fluoro-gemanes (GeFnH4-n), the third F-substitution would predict a DECF which is even smaller than the magnitude in GeFH3. For the C-Cl studies, Cl substitution would decrease the DE (C -Cl), unlike the fluorine substitution stated above. Moreover, the NBO method fails in accounting the trend of calculated values of DE. It is considerably instructive that, in the preparation of Si-mixed thin-films, halogen-substitution would lead to a more experimentally demanding process

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