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Tham khảo tài liệu 'science technology carbon nanotubes part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 10 SWCNT sample has widely been used for the physical-property measurements 40 . 3.1.3 Catalytic synthesis Very recently it has been reported that SWCNT can be synthesized by decomposition of benzene with Fe catalyst 27 . It would be of most importance to establish the controllability of the diameter and the helical pitch in this kind of synthesis of SWCNT toward the development of novel kinds of electronic devices such as single molecule transistor 41 It can be said that this field is full of dream. 3.2 Purification Since SWCNT is easily oxidised compared with MWCNT 42 the purification process such as the burning method cannot be applied to that purpose. Tohji et al. however have succeeded in this by employing the water-heating treatment 43 and furthermore the centrifuge 44 and micro-filtration 39 44 methods can also be employed. It has recently been reported that SWCNT could be purified by size-exclusion chromatography method 45 which made separation according to its length possible. This method looks effective to obtain SWCNT of a high degree of purity. Development of the differentiation method of SWCNT with its diameter is still an open problem. 4 Conclusion MWCNT was first discovered by arc-discharge method of pure carbon and successive discovery of SWCNT was also based on the same method in which carbon is co-evaporated with metallic element. Optimisation of such metallic catalyst has recently been performed. Although these electric arc methods can produce gram quantity of MWCNT and SWCNT the raw product requires rather tedious purification process. The laser-ablation method can produce SWCNT under co-evaporation of metals like in the electric arc-discharge method. As metallic catalyst Fe Co or Ni plays the important role and their combination or addition of the third element such as Y produces SWCNT in an efficient manner. But it is still difficult in the laserablation method to produce gram quantity of SWCNT. Nonetheless remarkable progress in the research
