【作者】 陈真英；

【导师】 邓文；

【作者基本信息】 广西大学 ， 理论物理， 2007， 硕士

【摘要】 本文采用正电子湮没技术研究了石墨、纳米碳、金刚石薄膜、C₆₀薄膜四种碳材料的微观结构。结果如下：1、石墨和纳米碳的电子动量分布和微观缺陷（1）石墨晶体中的自由电子动量分布表现出显著的各向异性，偏离[0001]方向越大，自由电子的动量越小；且Doppler展宽谱S参数与cos²θ呈线性关系；而纳米碳中自由电子动量的分布不存在明显的规律性。（2）当温度从25K升至295K时，石墨和纳米碳中缺陷开空间增大，平均自由电子密度降低；纳米碳中自由电子密度与温度变化成线性关系。（3）纳米碳表面层具有活性，可吸附微小杂质氢，导致S参数下降；纳米碳基体内部离表面越远处，吸附杂质氢的量越少。2、未掺杂、掺硼及掺硫金刚石薄膜退火前后的缺陷变化（1）未掺杂金刚石薄膜在600℃以下退火，空位回复；而900℃以上退火会使空位发生移动合并成大的缺陷，导致缺陷开空间增大。（2）在400℃以下退火可减小低掺硼金刚石膜中的缺陷浓度；在600℃以上退火会增加低掺硼金刚石膜的缺陷浓度。（3）高掺硼金刚石膜表面缺陷较容易回复，经不同温度退火后，其S参数降低。（4）掺硫金刚石膜经200至1000℃退火后，样品的S参数保持不变，表明掺硫金刚石膜结构的热稳定性高。（5）掺硫金刚石膜中缺陷浓度大于未掺杂金刚石膜，而掺硼金刚石膜中的缺陷浓度小于未掺杂金刚石膜，掺少量的硼可使金刚石薄膜中空位浓度减少。3、不同离子能量沉积的C₆₀薄膜退火前后样品的缺陷（1）当沉积离子能量低于200ev时，沉积膜中C₆₀分子有序排列、仍保持完整的笼状结构。（2）当沉积离子能量为250ev时，薄膜中C₆₀分子间的结合力增强，形成了C₆₀分子聚合物。（3）薄膜的结构取决于沉积离子能量。当沉积离子能量大于300ev时，一方面，发生C₆₀分子聚合；另一方面，部分C₆₀分子的笼状结构被破坏，形成了无定形碳碎片；而且，高能离子对薄膜的轰击作用加强，致密度加大。薄膜中缺陷开空间大小是这两种因素竞争的结果。（4）不同离子能量沉积膜经600℃退火1h后，膜中无定形碳成分转化为石墨微晶体，同时C₆₀聚合物分解成小的聚合物或单个的C₆₀分子。更多还原

【Abstract】 The microstructure of allotropic carbon materials, such as graphite,nanophase C, diamond films, and C₆₀ films, have been investigated bypositron annihilation techniques. The following experimental results havebeen abtained.1. Microdefects and the distribution of electron momentum ingraphite and nanophase C（1） The remarkable anisotropic distribution of electronic momentumwas found in single crystalline graphite. Furthermore, the S parameter islinear to cos²θ. However, this phenomenon was not found in nanophaseC.（2） With the increase of the temperature from 25K to 295K, the openvolume of defects increase, and the average free electron density decreasein graphite and nanophase C. The electronic density in nanophase C alsohas a linear relationship with temperatures.（3） The defects near to the surface layer of nanophase C may absorbthe hydrogen impurity and gives rise to the decrease of S parameter. The content of hydrogen impurity decreases with the increase of the distantfrom the surface.2. Microdefects in the undoped, B-doped and S-doped diamondfilms before and after annealing（1） The defects in undoped diamond film would recover afterannealing at temperature below 600℃. The open volume of defect willincrease after annealing at temperatures above 900℃due to the thermalvacancies migrating to merge together.（2） The density of defect in low B-doped diamond film will decreaseafter annealing at temperature below 400℃, however it will increaseafter annealing at temperature above 600℃.（3） The defects in high B-doped diamond film are easy to recover.The S parameters of this sample decrease after annealing at defferenttemperature.（4） The S parameters of S-doped diamond film keep unchangedafter annealing at temperature from 200 up to 1000℃, that is, thestructure of this film is quite stable ever at high temperature.（5） The density of defect in the S-doped diamond film is higher thanthat in undoped diamond films. And the density of defect in the B-dopeddiamond film is lower than that of in undoped diamond film. Thus, theaddition of small amount of B atoms will decrease the density of defect inthe film. 3. Microdefects in C₆₀ films deposited at defferent energy before andafter annealing（1） As the deposition energy below 200ev, the C₆₀ film is mainlypristine C₆₀, the C₆₀ molecules maintain their structure and preservemolecular identity.（2） As the deposition energy close to 250ev, the intermolecularcohesion getting stronger. The open volume of defect in C₆₀ filmincreases due to the polymerized fullerenes occuring in the film.（3） The film structure depends on the energy of the incident ions. Asdeposition energy higher than 300ev, the polymerized fullerenes becomelarger, on the other hand, the structure of C₆₀ molecules will be destroyedinto pieces, and the amorphous will form on the film. At meantime, thematerial is more compact at high deposition energy. The open volumedefect in the film depends on the competition between the above twofactors.（4） After the annealing at 600℃for lh, the amorphous carbon willbecome in graphitic clusters, and the polymerized C₆₀ cages aretransformed back to pristine or small polymerized C₆₀.更多还原