二维六方氮化硼快重离子辐照损伤的实验和模拟研究

Hexagonal boron nitride (h-BN) is a two-dimensional material which has a similar lattice structure to graphite. It is meaningful to compare the swift heavy ion irradiation-induced effects in h-BN with that in graphite and graphene. However, the evidence of formation of latent ion tracks in h-BN is not observed yet by the experiments, which indicates the lack of the knowledge of swift heavy ion irradiation-induced damage in h-BN. In this project, the experiments of swift heavy ion irradiation of h-BN will be performed on HIRFL. Various kinds of testing tools will be used to characterize the variations of the damage degree and morphology with different irradiation parameters, and to determine the critical threshold for track creation in h-BN. After the calculation of the thermal spike model, the molecular dynamics simulation will be used to model the evolution of the defects generated by swift heavy ion irradiation. The results of the simulations can promote the understanding of the experimental results. The influences of the rapid energy deposition and anisotropy of h-BN on the formation of the defects can be studied. On the basis of our results and previous studies, the different radiation damage induced by swift heavy ions between h-BN and graphite or h-BN and graphene will be studied and the reason will be analyzed, which can help to illustrate the influence of the different electron cloud distributions and other distinct properties on the irradiation-induced damage of two-dimensional materials. The project can provide fundamental data for swift heavy ion irradiation of h-BN.

六方氮化硼(h-BN)是一种二维层状材料，是理想的可与石墨和石墨烯对比研究快重离子辐照效应的对象。但目前实验上还未观察到h-BN中形成潜径迹的证据，其快重离子辐照损伤尚未被系统研究过。本项目借助兰州重离子加速器上产生的多种高能重离子开展h-BN的辐照实验，利用多种微观表征手段揭示其损伤程度和缺陷形貌随辐照条件的变化规律，确定形成潜径迹的电子能损阈值大小。同时基于热峰模型并以分子动力学方法为手段，模拟快重离子辐照下h-BN中微观损伤的时空演化过程，完善对损伤机理的认识。基于实验和模拟的研究结果，了解在高能量密度沉积时各向异性对缺陷形成的影响。通过对比h-BN与石墨、石墨烯在快重离子辐照损伤上的异同，研究材料性质差异对二维材料快重离子辐照效应的影响。本研究为h-BN的快重离子辐照损伤提供基础数据并丰富对二维材料快重离子辐照效应的认识。

六方氮化硼是一种二维层状材料，是理想的可与石墨烯对比研究快重离子辐照效应的对象。但目前其快重离子辐照损伤尚未被系统研究过。因此，本课题已六方氮化硼为研究对象，以分子动力学方法为主要研究手段，模拟快重离子辐照下六方氮化硼中潜径迹形成的条件及其形貌特点和时空演化过程，并与石墨烯的损伤结果进行对比研究。通过不同电子能损条件下的快重离子辐照模拟，发现电子能损小于7.99 keV/nm时，六方氮化硼中出现少量空位缺陷但在长时间演化中可自修复，电子能损大于9.98 keV/nm是产生空洞缺陷的辐照条件，快重离子辐照主要导致形成原子链和溅射原子。通过加速的分子动力学方法，了解了在数百纳秒时间尺度上原子重构和缺陷演化的过程，认识到在被辐照区域趋于形成单个空洞形的缺陷。通过相同条件下石墨烯的快重离子辐照模拟，对两者进行了对比研究，对二维材料性质差异对辐照效应的影响有了进一步的认识。了解到单层六方氮化硼中空洞边缘是以硼原子或者氮原子为边的之字形边缘，而石墨烯中是大量的非六元环的缺陷。认识到导致两者差异的主要原因之一是六方氮化硼中稳定的结构必须由B原子和N原子间隔排列。