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標題: | 以分子動力學模擬研究矽鍺材料之介面穿透率 An investigation into the transmissivity of the Si-Ge interfaces in use of molecular dynamics simulation |
作者: | Jiun-Sung Huang 黃鈞淞 |
指導教授: | 黃美嬌(Mei-Jiau Huang) |
關鍵字: | 分子動力學模擬,聲子色散關係,矽鍺介面,介面熱阻,穿透率, Molecular dynamics,Phonon dispersion relation,Si-Ge interface,Thermal boundary resistance,Transmissivity, |
出版年 : | 2018 |
學位: | 碩士 |
摘要: | 本論文之重點可分為兩部分,其中一部分為利用分子動力學模擬數值工具求得矽鍺聲子色散關係,而後進行波包實驗探討單介面及雙介面之穿透率;另一部分為推導理論模型,採用應力應變梯度模型推導出色散關係,並且利用此模型提出新的SGSG-AMM單介面穿透率模型,於雙介面中則與干涉理論之雙介面穿透率預測相比較。
在此研究中,矽及鍺原子間作用力是採用兼具二體及三體勢能的Stillnger-Weber勢能函數。利用晶格動力學於模擬中求得聲子色散關係,探討波向量 的聲子振動模態,發現縱波聲頻支原子振動方向皆為同一平面波;橫波聲頻支並非單純的SH波或SV波,而是兩者混合波,且不同的原子種類會有不同的平面波形,並且互不干擾的傳遞於晶格中。 在單介面波包實驗中波包由矽穿透至鍺區域,研究發現入射波之頻率為一分布範圍,不論縱波或橫波穿透過介面時皆為彈性散射(頻率範圍皆重疊),且穿透率隨著頻率增加而緩緩降低,在接近鍺德拜頻率時穿透率急遽下降,最後入射頻率分布範圍完全超過鍺德拜頻率時穿透率才為零。縱波在入射頻率超過鍺聲頻支德拜頻率時,出現聲頻支轉變為光頻支的極化改變;橫波則發現不同的偏振方向會影響著穿透率,因與介面處原子鍵結方向有關(當偏振方向與鍵結方向相同時則會有較大的穿透率)。 雙介面是由夾於矽材中間的鍺薄膜左右兩邊界所形成,探討的參數包括薄膜厚度及入射波數,發現穿透率會因薄膜厚度及入射的波數不同而有上下震盪,原因是因為穿透波干涉現象所造成,當干涉現象為建設性干涉則穿透率會較大,反之,破壞性干涉則會讓穿透率變小。干涉理論預測值在波數小時有不錯的準確度,但波數大時預測並不佳。 There are two parts in this study. The first part is about molecular dynamics simulation for the sake of obtaining the phonon dispersion relations of silicon and germanium based on the lattice dynamics and exploring numerically the transmissivity associated with a single Si-Ge interface and double Si-Ge interfaces. The second part is about theoretical models for predicting the dispersion relations and the transmissivity. The stress-gradient-strain gradient (SGSG) model is employed to describe the relation between the stress and the strain. The wave interference is employed to explain the observed transmissivity in the double-interfaces experiments. The Stillnger-Weber potential function including two-body potential and three-body potential is employed in this study to describe the interatomic force. The phonon vibration modes along the direction are calculated. The found vibration mode associated with the acoustic longitudinal wave is a perfect plane wave. That of the transverse waves however is neither a simple shear horizontal wave (SH) nor a shear vertical wave (SV) but a mixed one; besides the vibration mode can be divided into two different plane waves that are travelling in the crystal independently. On the other hand, although the SGSG-AMM gives a better prediction of the transmissivity than the traditional AMM at frequencies near the Debye frequency, it fails to predict accurately the transmissivity at intermediate frequencies. The AMM model with the wave interference phenomenon can explain well why the transmissivity associated with the double interfaces varies and oscillates with the incident wave number and with the spacing distance of the two interfaces. However the quantitative accuracy of the AMM predictions is acceptable only for small wave numbers. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/71904 |
DOI: | 10.6342/NTU201804133 |
全文授權: | 有償授權 |
顯示於系所單位: | 機械工程學系 |
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