Accurate measurement of the chirality of WS 2 nanotubes.

We describe the structural parameters and atomic positions of a single-walled WS2 nanotube. The structure factor is calculated in detail using analytic expressions for both single-walled and multi-walled WS2 nanotubes. A zoning scheme has been developed to obtain the ratio m/n from the electron diffraction patterns. The procedure for determination of the chiral indices of both single-walled and multi-walled WS2 nanotubes and the tilt angle is illustrated in detail for either normal incidence or inclined incidence. As an example of application, the determination of the chiral indices of a five-shell WS2 nanotube was carried out and the tilt angle was obtained as 17.7°. The method developed here is useful and valid to determine the atomic structure of WS2 nanotubes.