The interesting physical properties of single-walled carbon nanotubes (SWCNT) are strongly related to their structure, which makes structural analyses on nanotubes particularly desirable. However, up to now, X-ray scattering studies have been severely hampered by the poor quality of the available samples, where nanotubes with mixed diameters and helicities are more or less disorientated. In this respect, new samples [1] of SWCNTs synthesised in the parallel channels of AlPO₄-5 zeolite single crystals (typical sizes ~ 10^-1 mm³) appear very promising (Figure 86).

Fig. 86: a) Structure of AlPO4-5 showing the open channels; b) and c) carbon nanotube viewed perpendicular to its long axis and in projection along this axis. Nanotubes are synthesised inside the AlPO4-5 channels.

A diffraction pattern obtained on the ID1 beamline is shown in Figure 87. The SWNTs produce diffuse scattering in the equatorial plane perpendicular to the channel axis, at low wave-vectors (Q < 0.2 Å^-1 in 1/d units). Very small background levels can be reached thanks to the vacuum environment of the beam path. The in-plane localisation of the scattering shows that the nanotubes are very well aligned. The analysis of the scattered intensity enabled us to determine the nanotube diameter which is about 0.4 nm. This value has been confirmed independently by transmission electron microscopy experiments [2]. Such a diameter is exceptionally small; it is attributed to the interactions with the zeolite host during the synthesis.

Fig. 87: Diffraction pattern (crystal and detector fixed) obtained on the ID1 beamline, under vacuum. The axis of the zeolite channels is vertical. A 2-D gas detector was placed at 618 mm from the sample, radiation wavelength was 1.044 Å. The horizontal diffuse scattering streak is characteristic of the nanotubes.

References
[1] Z.K. Tang, H.D. Sun, J. Wang, J . Chen and G. Li, Appl. Phys. Lett., 73, 2287-2289 (1998).
[2] N. Wang, Z.K. Tang, G.D. Li and J.S. Chen, Nature, 408, 50-51 (2000).

Principal Publication and Authors
P. Launois (a), R. Moret (a), D. Le Bolloc'h (b), P.A. Albouy (a), Z.K. Tang (c), G. Li (c) and J. Chen (d), Solid State Comm., 116, 99-103 (2000).
(a) Université Paris Sud (France)
(b) ESRF
(c) Hong Kong University of Science and Technology (China)
(d) Jilin University, Changchun (China)