Tham khảo tài liệu 'carbon nanotubes episode 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 88 A. Fonseca el al. a Ả 1 Ả parallel hexagon unit cell 1 for the L 0 tubules perpendicular hexagon unit cell d for the L L tubules a side of die hexagon in graphite 1 width of the hexagon in graphite aV3 Fig. 2. Building blocks for the construction of L 0 and L .L tubules. Connecting a L 0 to a L L tubule by means o f a knee Dunlap describes the connection between L 0 and tubules by means of knees. A knee is formed by the presence of a pentagon on the convex and of a heptagon on the concave side of the knee. An example is illustrated in Fig. 3 a . The 12 0 7 7 knee is chosen for illustration because it connects two tubules whose diameters differ by only 1 . The bent tubule obtained by that connection was called ideal by Dunlap 12 13 . If one attempts to build a second coaxial knee around the ideal 12 0 7 7 knee at an interlayer distance of A the second layer requires a 21 0 12 12 knee. In this case the axis going through the centers of the heptagon and of the pentagon of each tubule are not aligned. Moreover the difference of diameter between the two connected segments of each knee is not the same for the two knees Fig. 3 b . As distinct from the ideal connection of Dunlap we now describe the series of nanotubule knees 9n 0 - 5n 5n with n an integer. We call this series the perfectly graphitizable carbon nanotubules because the difference of diameter between the two connected segments of each knee is constant for all knees of the series Fig. 4 . The two straight tubules connected to form the n 1 knee of that series are directly related to C60 the most perfect fullerenef 15 as shown by the fact that the 9 0 tubule can be closed by 1 2 C6 cut at the equatorial plane perpendicular to its threefold rotation symmetry axis while the tubule can be closed by 1 2 C60 cut at the equatorial plane perpendicular to its fivefold rotation symmetry axis Fig. 5 a . As a general rule any knee of the series 9n 0 5zi 5n can be closed by 1 2 of the fullerene .
