晶態氮化矽具備優異的熱穩定性與機械強度，廣泛應用於高溫電子元件、先進封裝與光電系統中，為具發展潛力的奈米熱傳材料。然而，當材料尺度縮小至奈米等級，其熱傳導行為會受到聲子的邊界散射、缺陷與晶向排列等因素影響，這些因素成為探討薄膜熱傳不可忽視的一環。
本研究運用 LAMMPS 分子動力學軟體，以非平衡態分子動力學模擬方法為基礎，針對 α-Si₃N₄ 與 β-Si₃N₄ 兩種晶態氮化矽薄膜，深入探討其熱傳導係數受尺度效應、溫度效應與空位缺陷效應之影響，並藉由聲子狀態密度進行分析，理解上述效應如何改變聲子行為並導致熱傳能力下降。
模擬中建立不同厚度、方向與缺陷率的模型，並使用固定邊界條件與局部熱浴法來穩定建立溫度梯度，再透過傅立葉定律計算出熱傳導係數。研究結果發現在任何條件下 β-Si₃N₄ 的熱傳導係數皆高於 α-Si₃N₄。當薄膜厚度上升時，熱傳導係數會隨之增加，展現由彈道型逐漸轉為擴散型的傳輸行為；當溫度升高時，聲子散射加劇導致熱傳導係數下降；當引入空位缺陷後，晶格週期性被破壞，聲子局域化現象增強，熱傳導效率大幅下滑。
綜合上述，本研究成功建構一套適用於晶態氮化矽薄膜之熱傳模擬流程，釐清不同效應對其熱傳行為的影響機制，並為未來氮化矽薄膜材料設計、熱管理提供理論依據與模擬基準。

This study investigates the thermal transport properties of crystalline silicon nitride thin films (α-Si₃N₄ and β-Si₃N₄) using non-equilibrium molecular dynamics simulations performed with LAMMPS. The objective is to understand how film thickness, temperature, and vacancy defects affect thermal conductivity at the nanoscale, where phonon-boundary scattering, lattice defects, and crystal orientation become significant.
Simulation models with varying thicknesses, crystallographic orientations, and defect concentrations were constructed. Fixed boundary conditions and localized thermostats were applied to create steady temperature gradients. Thermal conductivity was calculated using Fourier’s law, and phonon density of states analyses were conducted to examine phonon behavior.
Results show that β-Si₃N₄ consistently exhibits higher thermal conductivity than α-Si₃N₄ under all conditions. An increase in film thickness leads to higher thermal conductivity, indicating a transition from ballistic to diffusive transport. Thermal conductivity decreases with rising temperature due to enhanced phonon scattering. Vacancy defects significantly reduce thermal transport efficiency by disrupting lattice periodicity and promoting phonon localization.
In summary, this work establishes a robust simulation framework for evaluating thermal transport in silicon nitride thin films. It provides theoretical insight into the mechanisms affecting heat conduction and offers a foundation for the design and thermal management of nitride-based nanoscale materials.

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