二維石墨烯-氮化硼異質結構之熱學與力學性質的分子動力學研究

An Investigation of Thermal and Mechanical Properties of Two Dimensional Graphene-Boron Nitride Heterostructures by Atomistic Simulations

柯郁淳(Yu-Chun Ke)

指導教授 ： 張建成

國立臺灣大學/工學院/應用力學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201703057

摘要

本論文係使用分子動力學模擬方法搭配Tersoff型BCN勢能函數，研究二維石墨烯-氮化硼異質結構的熱學與力學性質。在研究中，定義石墨烯-氮化硼異質奈米帶的組成比例(w_Gr)為石墨烯奈米帶寬度佔其整體寬度之比例。在熱學性質方面，主要研究組成比例、手性角、尺寸、系統溫度與缺陷對於石墨烯-氮化硼異質奈米帶熱傳導係數之影響。首先探討石墨烯-氮化硼異質奈米帶在不同組成比例下的熱傳導係數，結果顯示鋸齒型石墨烯-氮化硼異質奈米帶的熱傳導係數幾乎隨著組成比例上升而單調遞增，而扶手椅型石墨烯-氮化硼異質奈米帶的熱傳導係數則在低組成比例(w_Gr為0.1至0.4)時有小於純氮化硼奈米帶的現象。接著進一步研究額外9個手性角形態的石墨烯-氮化硼異質奈米帶，結果顯示在低組成比例時的熱傳導係數亦小於同手性角的純氮化硼奈米帶。此外，尺寸效應與系統溫度對於石墨烯-氮化硼異質奈米帶的熱傳導係數皆有顯著的影響。再者，亦探討孔洞缺陷與晶界缺陷對於石墨烯-氮化硼異質奈米帶的熱傳導係數有何影響。就孔洞缺陷而言，分別模擬刪除硼、碳與氮原子的情形，結果顯示當石墨烯-氮化硼異質奈米帶具有孔洞缺陷時，其熱傳導係數將會劇烈地下降。在相同的刪除原子濃度下，具有碳原子孔洞缺陷的石墨烯-氮化硼異質奈米帶擁有最小的熱傳導係數，而硼原子孔洞缺陷與氮原子孔洞缺陷對於其熱傳性質的影響則具有相似性。就晶界缺陷而言，石墨烯晶界-氮化硼異質奈米帶會因為晶界的存在與折曲結構的產生，使得其熱傳導係數大幅地下降，因此具有更高的熱調變性。在力學性質方面，針對鋸齒型石墨烯-氮化硼異質異質奈米帶進行分析，發現其楊氏係數隨著組成比例增加而上升，破斷應變大致上具有隨著組成比例增加而下降之趨勢，而破斷強度與組成比例並不存在明顯的關係。

關鍵字

二維材料 ； 石墨烯 ； 氮化硼 ； 異質結構 ； 奈米帶 ； 分子動力學 ； 熱傳導係數 ； 楊氏係數

並列摘要

In this study, we investigate thermal and mechanical properties of two dimensional graphene-boron nitride heterostructures by molecular dynamics simulations with the Tersoff-type BCN potential function. The composition ratio of the hybrid graphene-boron nitride nanoribbon is defined as the width of the graphene nanoribbon divided by the width of the whole hybrid nanoribbon, and it is denoted by w_Gr. In terms of thermal properties, we mainly investigate the effects of composition ratios, chiral orientations, sizes, system temperatures and defects on the thermal conductivity. Firstly, we study the thermal conductivity of hybrid nanoribbons with different composition ratios. The results show that thermal conductivity of zigzag hybrid nanoribbons increases almost monotonically as the composition ratio raises, while the thermal conductivity of armchair ones with small composition ratios (w_Gr is in the range of 0.1 to 0.4) is lower than that of pristine boron nitride nanoribbons. The further study shows that the thermal conductivity of hybrid nanoribbons with small composition ratios in the additional 9 chiral orientations is lower than that of pristine boron nitride nanoribbons as well. In addition, size effects and system temperatures have a significant impact on the thermal conductivity. Besides, we also explore the effects of vacancy defects and grain boundary defects on the thermal conductivity. In the case of vacancy defects, the conditions for deleted boron, carbon and nitrogen atoms are considered respectively. The results show that the thermal conductivity will drop drastically when hybrid nanoribbons have vacancy defects. Under the same concentration of deleted atoms, carbon atom vacancy defects result in the greatest decrease of the thermal conductivity, and the influence of boron atom vacancy defects on thermal properties is similar to nitrogen atom vacancy defects. In the case of grain boundary defects, we investigate thermal properties of the hybrid graphene grain boundary-boron nitride nanoribbon. The thermal conductivity decreases significantly because of the existence of grain boundaries and the generation of folding structures. Hence hybrid graphene grain boundary-boron nitride nanoribbons have the higher thermomutability. In terms of mechanical properties, we analyze zigzag hybrid nanoribbons with different composition ratios. The results reveal that Young's modulus increases as the composition ratio raises, and the fracture strain generally has a tendency to decrease as the composition ratio raises. However, there is no relationship between the fracture strength and the composition ratio.

並列關鍵字

Two Dimensional materials ； Graphene ； Boron nitride ； Nanoribbons ； Heterostructures ； Molecular dynamics ； Thermal conductivity

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