以往的熱電轉換裝置皆使用塊材(bulk materials)作為熱電核心，其熱電轉換效率約為8.5% 是傳統發電或致冷裝置的1/3，故效率問題成為熱電轉換應用之一大難題。如今以微觀角度透過調整材料之結構參數便可掌控基本材料性質(如熱傳導係數、電導係數)，可望改善熱電核心之熱電轉換效率約20%。就目前研究顯示奈米技術因奈米超晶格結構之製程成熟，不必再侷限於特定組成，可對奈米超晶格結構在熱電轉換效率上，做整體性的理論分析。鑑此，本研究將建構一套完整的理論模型與電腦模擬方法，以探討熱電轉換效率提升之相關課題。

　　為了提高熱電優值，通常必須降低結構之熱傳導係數或提高電導係數，本文將以分子動力模擬方法配合格林久保定理(Green Kubo formula)以估算結構之熱傳導係數；同時為了得到電導係數以估算熱電優值，故本文考量載子於奈米尺度下之量子效應。首先訂定能障函數並計算載子通過梯形能障之透射係數，再配合藍道定理(Landauer theory) 以估算結構之電導係數，與文獻比對驗證後，再進行晶格結構參數(如晶格週期長度、粒子質量比、與界面粗糙度)之調控以期降低熱傳導係數與提高電導係數。又根據結構參數對熱電優值影響之權重建構設計以車輛廢熱利用與微致冷器熱電核心特性設計等案例加以印證。

　　本文於熱傳導模型中將界面粗糙度納入考量，經模擬後發現熱傳導係數誤差由19%降至7.28%且變異係數亦有效降低，足證實模型在更貼近微觀下的實際情況時模擬結果將更為準確。在此同時，本研究於電導模型中除了考量奈米尺度下載子的穿遂效應，在能障訂定中更依據兩相異元素之組成而使用梯形能障有別以往的矩形能障，驗證後發現誤差可有效地降低。利用本文所建構之理論模型與設計模擬流程進行車輛廢熱利用與微致冷器熱電核心特性設計，其模擬結果皆優於文獻資料足證實本文之理論模型與設計模擬流程具實用性，推測可能原因為實作上有散失的熱能並未能夠納入效率計算中。

　　Traditionally, thermoelectric devices used the bulk materials as the core of conversion, and the thermoelectric conversion efficiency is only 8.5%. Therefore, the efficiency becomes one of the very critical issues for thermoelectric system development. Nowadays, one can control the materials properties such as thermal conductivity, electric conductivity etc… by adjusting the structure parameters in microcosmic. Thus, the thermoelectric conversion efficiency of the system can be expected to improve about 20%. With the advance in manufacture technology for nano-superlattice the upper limit of particular composites can be expected to raise. The analysis of global effect on the thermoelectric conversion efficiency of nano-superlattice can also be estimated. This research intends to construct an intact theory and computer simulation method in an attempt to probe into the subject of enhancing the thermoelectric conversion efficiency based on the development of a nanotechnology-based system.

　　In order to improve the figure of merit (ZT) of thermoelectric materials, one can try to reduce the thermal conductivity or to increase the electrical conductivity. In this study, the molecular dynamics and Green Kubo formula were used to calculate the thermal conductivity of the superlattice. In an attempt to obtain the ZT, electrical conductivity of the structure was estimated. Based on the quantum effect in nano-scale, the energy barrier function of the interface was defined. The carrier transmission probability through the ladder-barrier was estimated. The electrical conductivity of the structure was then derived by using the Landauer theory. The results obtained by using the proposed method were found agree well with the experimental data in literature. Therefore, by reducing the thermal conductivity and increasing the electrical conductivity via adjusting structure parameters (such as lattice period length, mass ratio, interface roughness), the thermoelectric conversion efficiency can thus be improved. According to the weight for the effects of structure parameters on ZT, the proposed method was employed to design for the waste-heat recovery of the hybrid car and microcooler. The thermoelectric character analysis proved that the design procedure based on the proposed theory presented in this study is valuable.

　　By adding the roughness of interface in the thermal conduction model, the thermal conductivity thus obtained was found closer to actual values, and thus the simulation results were more accurate. Moreover, this study employed the MD (molecular dynamics) simulation to obtain the thermal conductivity and other physics quantities, and confirmed that the figure of merit of thermoelectric materials can be actually improved by reducing the thermal conductivity and increasing the electrical conductivity. The design and estimation for the thermoelectric materials can be achieved faster and more precisely by used the implemented theory and computerized simulation package. In this study the ladder-barrier function, that is different from the traditional rectangle-barrier one, was employed to give a more accurate representation for different atoms in superlattice. Finally, it was showed that the proposed theory and computerized simulation procedure are feasible through various case studies, such as the waste-heat recovery of the hybrid car and microcooler thermoelectric character analysis.

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