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采用60Coγ射线辐照纯净的多壁碳纳米管,用高分辨透射电镜和拉曼光谱,研究了多壁碳纳米管由石墨结构向无定形结构转变的演化过程.发现在γ射线辐照下,碳纳米管的外部石墨层逐渐失去最初的有序结构而向无定形结构转变.而且,随着γ射线辐照剂量的增加,无定形结构不断推进,而石墨层结构则不断减小,直至使整个碳纳米管变为一个中空的无定形纳米线结构.用原子位移理论和溅射机理对这种转变过程进行了分析.γ射线轰击碳纳米管击出碳原子,碳原子停留在晶格的间隙位置上产生间隙原子,在它原来的平衡位置则留下一个空位.当轰击粒子动能足够大时导致碰撞级联效应,无序结构增加.多数空位和间隙原子可能相互复合而彼此退火,但仍有少数原子作为间隙原子而造成晶格进一步缺陷.辐射也可以引起碳原子的溅射,溅射出来的碳原子沉积在碳纳米管的外壁上形成一层无定形碳结构.
The evolution of multiwalled carbon nanotubes (MWCNTs) from amorphous graphite to amorphous structures was investigated by high resolution transmission electron microscopy and Raman spectroscopy using 60Coγ-ray irradiation of pure multi-walled carbon nanotubes. It was found that under the γ-ray irradiation, The external graphite layer of carbon nanotubes gradually lost the original ordered structure and transformed to the amorphous structure.Also, with the increase of γ-ray irradiation dose, the amorphous structure was continuously advanced while the graphite layer structure was continuously reduced until The entire carbon nanotube turns into a hollow amorphous nanowire structure.The atomic shift theory and the sputtering mechanism are used to analyze the transformation process.The γ-ray bombardment of the carbon nanotubes breaks out carbon atoms and the carbon atoms remain in the lattice Gap atoms are generated at the gap sites, leaving a vacancy at its original equilibrium position. When the kinetic energy of the bombardment particles is large enough, the collision cascade effect is caused and the disordered structure increases. Most of the vacancy and interstitial atoms may anneal to each other, There are still a few atoms as interstitial atoms causing further lattice defects.Radiation can also cause the sputtering of carbon atoms, sputtered carbon atoms deposited on the outer wall of the carbon nanotubes Form a layer of amorphous carbon structure.