碳纳米管端口的场蒸发

将单根多壁碳纳米管(multi-walled carbon nanotube，MWCNT)组装在W针尖上并送入超高真空场发射/场离子显微镜(Ultrahigh Vacuum Field-emission/Field-Ion microscope，UHV-FEM/FIM)进行场蒸发及场发射研究.结果表明，场蒸发可以降低MWCNT的逸出功，从而增强其场发射能力.估算MWCNT的蒸发场低于1.3×10⁸V·cm^-1，且在此场强下的平均蒸发速率为9.4nm·min^-1.定性讨论了MWCNT的蒸发场大大低于C的理论值的原因.首先，通过场解吸获得的清洁端口上有较多悬挂键，平均每个C原子的配位数较小，所以升华热较低.其次，可能存在于MWCNT中的H原子会在强场下碰撞端口的C原子，使其更易蒸发.以上结果显示了利用场蒸发剪短碳纳米管从而改善其场发射特性的可行性. 关键词： 碳纳米管 场蒸发 场发射

Field evaporation of the end of a carbon nanotube

A single multi-walled carbon nanotube (MWCNT)was assembled onto a W tip and transferred to an ultrahigh vacuum field-emission/field-ion microscope (UHV-FEM/FIM)for the study of field evaporation and field emission. The results showed that the field evaporation lowered the work function of the MWCNT and thus enhanced its field emission. The evaporation field of the MWCNT was estimated to be lower than 1.3×10⁸V·cm^-1 and the evaporation rate under this field was measured to be 9.4nm·min^-1. The physical origin of the fact that the evaporation field of the MWCNT was much lower than the theoretical value for carbon is also qualitatively explained. Firstly，the clean end of the MWCNT，which resulted from field desorption，contained a large number of dangling bonds and the C atoms on it had small coordination number，thus the heat of sublimation of these C atoms was low. Secondly，H atoms that possibly existed in the MWCNT could collide with the C atoms under strong electric field and make the latter evaporate easier. These results indicated an effective approach to obtaining better field emission performance of a carbon nanotube by cutting it short using field evaporation.