二維氮化碳硼之力學與熱學性質的分子動力學研究

Abstract

二維材料被視為是下一代半導體元件的材料。自石墨烯被發現後， 其優異的電學性質已經使科學家對它提出了許多構想，而後氮化硼問 世後，類似絕緣體的性質也使二維材料有了更多的應用。氮化硼碳與 石墨烯與氮化硼同樣結構，而其性質隨著內部原子比例不同而改變， 因此具有許多的可調變性，對於其中熱傳的特性為本論文深入探討的主題。 本論文使用非平衡分子動力學計算氮化碳硼的熱學以及力學性質， 除了計算隨原子比例改變後材料的熱傳性質之外，在奈米尺度下尺寸 效應也會使熱傳導係數改變，越長或越寬的奈米帶會使得熱傳導係數 上升，而最終會趨於一定值。改變手性角結構發現熱傳導係數在手性 角為 0 度時最高，而手性角介於 8 度到 10 度間與 20 到 25 度間其熱傳 導係數會最低，並分析其邊緣粗糙度發現其與手性角與熱傳導係數的變化有很大的關係，邊緣粗糙度對於手性角的曲線與熱傳導係數對於手性角的曲線非常接近。 模擬結果分析了摻雜、溫度、尺寸、手性角與邊緣對於熱傳的影 響，發現摻雜對於熱傳導率的調變性非常大。在摻雜後可以降低其熱 傳導，在石墨烯中摻雜 10% 的硼氮分子對，其熱傳導係數可以降低達 76%，這樣的性質可以拿來應用於熱電材料上，使其熱電優值提升。

2D-Materials are considered to play an important role in next-generation semiconductor devices. These materials may have outstanding properties in such as electron mobility and mechanical flexibility. Boron carbon nitride (BCN), with the same structures of graphene and boron nitride but totally different properties depending on the interior atomic contents, may give various tunable properties. In this study, we investigate the mechanical and thermal properties of BCN ribbons by applying the Non-Equilibrium Molecular Dynamics (Muller-Plathe method and directly measure method). At the scales of nanometers, the thermal property may change significantly with varying the size (width by length) of the ribbon. Hence, besides varying the composition, issues involved with nanoribbon structures such as the width, length as well as the chiral angle and edge roughness are addressed. By increasing the width of nanoribbon, the heat conductivity rises up as well and reaches a fix value finally. The roughness is an important factor of decreasing heat conductivity by rotating the chiral angle, and we found that the conductivity-chiral angel curve is similar to the edge roughness-chiral angel curve. In particular, by replacing 10% of carbon atoms with boron & nitrides in graphene, the thermal conductivity can reduce by 76%. The BCN has the highest thermal conductivity at zero chiral angle, whilst having the lowest at the angles between 8 & 10 and 20 & 25. The findings provide direction/useful information for better design of thermoelectric materials.