| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 105 === 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.
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