摘要
Five-fold symmetric diamond crystals（FSDCs） were synthesized by hot filament chemical vapour deposition（HFCVD） methods. Their surface morphologies and defects were characterised by scanning electron microscopy（SEM）. From the perspective of nucleation-growth, a growth mechanism for icosahedral and other five-fold symmetric diamond crystals was discussed. Computer modelling was also carried out. The results show that the dodecahedrane（C20H20） molecule is proposed as a nucleus for the growth of icosahedral diamond crystals（IDCs）, wherein the 20 {111} surface planes develop orthogonal to the direction of the original 20 C—H bonds by sequential H abstraction and CH3 addition reactions. IDC can be pictured as an assembly of isosceles tetrahedra, with each tetrahedron contributing a {111} plane to the surface of the IDC and the remainder of the tetrahedral surfaces forming twin planes with neighbouring tetrahedra. The small mismatch（1.44°） between the {111} surface dihedral angle of a perfect icosahedron and that of a twinned icosahedron reveals itself via twin planes in the IDC grain. The modelling suggests how the relief of strain induced by this distortion could lead to the formation of defects such as concave pentagonal cavities at vertices and grooves along the grain edges that accord well with those observed experimentally. Similar arguments based on growth from the hexacyclo pentadecane（C15H20） nucleus can also account for the observed formation of star and rod shaped FSDCs, and some of their more obvious morphological defects.
采用热丝化学气相沉积(HFCVD)方法制备五重对称金刚石晶体(FSDCs)。利用扫描电子显微镜(SEM)对其表面形貌和缺陷进行观察。从形核-长大的角度出发,讨论各种五重对称金刚石晶粒的形成机制,并进行计算机模拟。结果表明:正十二面体烷(C20H20)可作为二十面体金刚石晶体(IDC)的晶核,其C—H键垂直于IDC的{111}表面,随着活性H原子和甲基的不断萃取与结合,C20H20中20个C—H键均发展成为与之垂直的20个{111}表面。正二十面体金刚石晶体(IDC)可以看做是由等腰四面体组装而成,其中每个四面体给IDC表面贡献一个{111}晶面,而四面体的其余晶面与其相邻的四面体形成孪晶面。然而,完美二十面体{111}面的二面角与孪晶结构的二面角存在1.44°的差异,该失配导致了IDC的晶格畸变。通过计算模拟讨论晶格失配对IDC长大过程中的能量和稳定性的影响,最终揭示晶格失配所导致的应变如何诱导产生各种缺陷,如顶点处凹五角形腔的形成,以及沿晶粒边缘的凹槽。该计算模型能够较好地解释实验中所观察到的晶体形貌。类似推理可进一步用于解释十五烷(C15H20)作为晶核如何发展成为实验中所观察到的星形和棒形的五重对称结构,以及一些常见缺陷的形成。
基金
Projects(51301211,21271188)supported by the National Natural Science Foundation of China
Project(2012M521540)supported by the China Postdoctoral Science Foundation
Project(2013RS4027)supported by the Postdoctoral Science Foundation of Hunan Province,China
Project(20110933K)supported by the Open Foundation of the State Key Laboratory of Powder Metallurgy,China
Project supported by the Open-End Fund for Valuable and Precision Instruments of Central South University,China
