立方氮化硼单晶生长界面层的精细结构

Fine Structures in Growth Interface Layer of Cubic Boron Nitride Single Crystal

以Li3N为触媒、六方氮化硼(hBN)为原料,采用静态高温高压法合成立方氮化硼(cBN)单晶。为探讨cBN合成机理,利用扫描电镜观察了cBN单晶生长界面层形貌,利用俄歇电子能谱和X射线光电子能谱对界面层精细结构进行了表征。结果表明,cBN单晶被合成后的触媒粉末所包裹,界面层中B、N元素相对比例基本保持不变,且随着距离cBN单晶越来越近,B、N元素的sp2杂化态逐渐减少,sp3杂化态逐渐增多,这说明hBN含量逐渐减少,而cBN含量逐渐增多。由于Li元素非常活泼,在高温高压体系中的电子结构极不稳定,故可以作为电子转移的桥梁,完成电子由N向B的转移。据此认为在cBN单晶生长界面层中,B、N元素的sp2杂化态逐渐转变成了sp3杂化态。以上结果说明hBN在触媒催化作用下可直接转变为cBN。

Using Li3 N as catalyst,hexagonal boron nitride（ h BN） as raw materials,cubic boron nitride（ c BN） single crystals were synthesized by static high pressure and high temperature method. The morphology of growth interface layer of c BN were observed by scanning electron microscopy,the fine structure of the interface layer for c BN were characterized by Auger electron spectroscopy and X-ray photoelectron spectroscopy. The results indicate that c BN single crystals are coated by catalyst powder after synthesis,the ratio of B and N elements in interface layer is not changed. The sp2 hybridization states of B and N elements decreases with the distance to the c BN single crystal decreasing,but the sp3 hybridization states increases,which show that the contents of h BN reduce and the contents of c BN increase. Li is used as a bridge by which electron can transfer from N to B because of its active chemical properties and instability under high temperature and high pressure. Therefore,the sp2 hybridization states of B and N elements gradually transform into the sp3 hybridization states in the c BN crystal interface layer. These results show that the h BN can directly change into c BN under the catalysis of catalyst.