Observation of 'hidden' planar defects in boron carbide nanowires and identification of their orientations.
Observation of 'hidden' planar defects in boron carbide nanowires and identification of their orientations.
复制标题
DOI：
10.1186/1556-276x-9-30
复制
发表时间：
2014-01-15
影响因子：
--
通讯作者：
Xu TT
中科院分区：
文献类型：
--
作者：
Guan Z;Cao B;Yang Y;Jiang Y;Li D;Xu TT
纳米结构的物理性能在很大程度上取决于其结构，尤其是平面缺陷会显著影响纳米线的性能。本文利用透射电子显微镜对碳化硼纳米线中的平面缺陷（孪晶或层错）进行了广泛的研究。结果表明，这些缺陷很容易被看不见，即在高分辨率TEM图像中不存在调制对比度和衍射图中的条纹等特征缺陷特征。这种不可见性的简化原因是TEM检查时的观察方向与（001）型平面缺陷不平行。由于碳化硼独特的菱形结构，只有当观察方向沿轴向或短对角线方向（[100],[010]，或）在（001）平面内（区内条件）时，平面缺陷才明显。然而，在大多数情况下，当碳化硼纳米线在TEM网格上随机分散时，这三个特征方向并不平行于观察方向。为了识别TEM未显示平面缺陷的纳米线的断层方向（横向断层或轴向断层），提出了一种基于预测的纳米线优选生长方向与（001）平面外（离区条件下）沿轴向或短对角线方向记录的特定衍射斑之间的几何分析的新方法。该方法大大减轻了纳米线繁琐的透射电镜检查，有助于建立可靠的结构-性能关系。我们的研究提醒研究人员在用透射电镜研究具有潜在平面缺陷的纳米线时要格外小心。了解平面缺陷的真正本质，是通过操纵这些纳米结构来调整其特性的必要条件。
The physical properties of nanostructures strongly depend on their structures, and planar defects in particular could significantly affect the behavior of the nanowires. In this work, planar defects (twins or stacking faults) in boron carbide nanowires are extensively studied by transmission electron microscopy (TEM). Results show that these defects can easily be invisible, i.e., no presence of characteristic defect features like modulated contrast in high-resolution TEM images and streaks in diffraction patterns. The simplified reason of this invisibility is that the viewing direction during TEM examination is not parallel to the (001)-type planar defects. Due to the unique rhombohedral structure of boron carbide, planar defects are only distinctive when the viewing direction is along the axial or short diagonal directions ([100], [010], or ) within the (001) plane (in-zone condition). However, in most cases, these three characteristic directions are not parallel to the viewing direction when boron carbide nanowires are randomly dispersed on TEM grids. To identify fault orientations (transverse faults or axial faults) of those nanowires whose planar defects are not revealed by TEM, a new approach is developed based on the geometrical analysis between the projected preferred growth direction of a nanowire and specific diffraction spots from diffraction patterns recorded along the axial or short diagonal directions out of the (001) plane (off-zone condition). The approach greatly alleviates tedious TEM examination of the nanowire and helps to establish the reliable structure–property relations. Our study calls attention to researchers to be extremely careful when studying nanowires with potential planar defects by TEM. Understanding the true nature of planar defects is essential in tuning the properties of these nanostructures through manipulating their structures.