Experimental and theoretical studies of microstructural instabilities in WS2 undergoing electron irradiation

In this article, we report the study of WS2 crystals after being irradiated with a high dose of electrons. A 2 MeV Van de Graaff acelerator was used to irradiate the sample at the following conditions: 1.3 MeV voltage, 5 mu A current, dose rate 25 kGy/min, total dosage 1000 kGy. The samples were examined in a high resolution transmission electron microscope. Three distinct structures were observed: onions layers with fullerene like structure, randomly oriented worm-like structures with their planes rotated with respect of each other by well-defined angles, and nanotube like structures. We present calculations showing that relative rotations of the sulphur layers by 2 degrees, 4 degrees, 5 degrees, 8 degrees and 16 degrees basically have the same average energy and average energy/atom as the unrotated structure. Therefore, rotations of the layers through those angles will be favorable. Instabilities on the structure produced by the irradiation will induce rotations as well as other capricious structures resembling a knot formation.