QUANTITATIVE NANODIFFRACTION FROM CARBON NANOTUBES. J. M. Cowley, Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504, USA.

Electron diffraction patterns obtained with coherent electron beams less than lnm in diameter may now be recorded digitally by use of a CCD detector and quantitative structural analyses may be made of small regions such as portions of the walls of carbon nanotubes. It has been known theoretically for a long time that, for coherent diffraction with a small beam, the diffraction pattern for even very thin specimens should have no center of symmetry unless both the incident beam and the illuminated area of the specimen are symmetric about the same point. However no tests on specimens of known structure have appeared feasible. Carbon nanotubes having an ideal structure with circular cylindrical symmetry are of interest in this connection because their curved walls provide non-symmetric objects of known structure. Measurements of the intensities of diffraction patterns from such walls show asymmetries in good agreement with the calculations made for ideal structures [J. M. Cowley and S. D. Packard, Ultramicroscopy, In Press]. Patterns from the planar regions of walls of those nanotubes having polygonal cross-sections are characteristically different. Observations on diffraction pattern asymmetries may thus be used to deduce information on the curvature of nanotube, or nano-particle, walls in regions where the structure is less obvious such as at the ends of nanotubes and at bends in the walls. Diffraction patterns from single-walled nanotubes and clusters of single-walled tubes are more difficult to record because the scattering is very weak, but can give valuable information on the helicity of the tubes, the regularity of the packing of the clusters and the deformations associated with tube bending.