CVD金刚石薄膜孪晶形成的原子机理分析

采用X射线衍射技术、电子背散射衍射技术和扫描电镜分别观察了不同甲烷浓度条件下沉积的CVD自支撑金刚石薄膜的宏观织构、晶界分布和表面形貌. 研究了一阶孪晶在金刚石晶体{111}面生长的原子堆垛过程. 结果表明，由于一阶孪晶〈111〉60°的取向差关系以及{111}面的原子堆垛结构，使{111}面上容易借助碳原子的偏转沉积产生一阶孪晶. 低甲烷浓度时，碳原子倾向于在表面能较低的{111}面沉积，为孪晶的形成提供了便利，且高频率孪晶使薄膜织构强度减弱. 甲烷浓度升高使生长激活能较小的{001}面成为主要前沿生长面，因而只有〈001〉晶向平行薄膜法向的晶粒能够不断长大，因此孪晶形核概率明显减小. 另外，在薄膜中发现二阶孪晶，并对二阶孪晶的形成进行了分析. 关键词：金刚石薄膜孪晶原子机理取向差

Atomic mechanism of twin formation in CVD diamond films

The macro-texture, grain boundary distribution and surface morphology in CVD free standing diamond films deposited with different methane concentrations were observed by X ray diffraction, electron backscatter diffraction and SEM. The atom stacking process of twins on {111} planes of diamond crystal were studied. It is shown that the twins form easily on {111} planes because of the 〈111〉 60° orientation relationship of first order twin and the stacking structure of {111} planes. At low methane concentration, carbon atoms tend to deposit on {111} planes with lower surface energy, which facilitates the formation of twins by means of rotating deposition of carbon atoms, while the high twinning frequency weakens the texture. With increasing methane concentration the {001} planes with lower growing activation energy become the main frontal growth fronts, and only those grains with 〈001〉 crystal direction which is parallel to the surface normal can continuously grow, so that the probability of twin nucleation decreases. In addition, second_order twins were found in diamond film, and their formation mechanism was analyzed.