石墨和纳米碳中缺陷和电子动量的研究

用正电子湮没技术研究了石墨和纳米碳中的缺陷和电子动量. 结果表明, 纳米碳中缺陷的开空间和缺陷浓度分别大于和高于石墨晶体. 纳米碳中存在开空间小于单空位的自由体积以及开空间相当于约10个空位聚集体的微孔洞. 石墨晶体中的自由电子动量分布表现出显著的各向异性: 沿石墨晶体的\0 001\]晶向的自由电子(即2Pz电子)的动量最大; 偏离该方向越大, 自由电子的动量越小; 垂直于\0 001\]晶向的自由电子的动量最小. 而纳米碳中自由电子动量的分布表现出各向同性. The defects and electronic momenta in graphite and nanocrystalline carbon have been studied by positron annihilation techniques. The results show that the concentration and open volume of defects in nanocrystalline carbon are higher/larger than that in graphite. Two kinds of microdefects were found in the nanocrystalline carbon: free volume (with a size of smaller than that of a monovacancy) and microvoids (with a size of about ten monovacancies). The anisotropic distribution of electronic momentum was found in single crystalline graphite, the momentum of free electron shows a maximum value in \0001\] direction, and decreases with the increase of the angle deviation from \0001\] direction and then reaches a minimum value in the direction perpendicular to \0001\]. However, this phenomenon was not found in nanocrystalline carbon since the distribution of electronic momentum is isotropic.

Studies of Defects and Electronic Momentums in Graphite and Nanocrystalline Carbon

The defects and electronic momenta in graphite and nanocrystalline carbon have been studied by positron annihilation techniques. The results show that the concentration and open volume of defects in nanocrystalline carbon are higher/larger than that in graphite. Two kinds of microdefects were found in the nanocrystalline carbon: free volume (with a size of smaller than that of a monovacancy) and microvoids (with a size of about ten monovacancies). The anisotropic distribution of electronic momentum was found in single crystalline graphite, the momentum of free electron shows a maximum value in \ direction, and decreases with the increase of the angle deviation from \ direction and then reaches a minimum value in the direction perpendicular to \. However, this phenomenon was not found in nanocrystalline carbon since the distribution of electronic momentum is isotropic.