STACKING-FAULTS IN HEXAGONAL AND RHOMBOHEDRAL MOS2 CRYSTALS PRODUCED BY MECHANICAL OPERATION IN RELATION TO LUBRICATION

The crystal structure of synthesized MoS2 was observed by high resolut ion transmission electron microscopy to have a rhombohedral lattice of three sandwich S-Mo-S layers of ABC stacking uniformly spaced through 0.615 nm. An extra half-plane observed in the layer lattice image fro m an ultramicrotomed section of this crystal suggested the appearance of a stacking fault due to a Shockley partial dislocation as in the ca se of h.c.p. MoS2 (molybdenite). The direction of the occurrence of tr ansformation was reversed to that in the h.c.p. MoS2 case (h.c.p.-->rh ombohedral) by missing one layer in the rhombohedral stacking and this transformation leads to the appearance of a stacking fault, slip, twi nning and h.c.p. lattice formation in the slip regions, due to S-S gli de. All these transformations have been observed in the well-determine d orientation [2110BAR] parallel to the electron beam on an atomic sca le. The slip mechanism was interpreted in terms of the fundamental uni t common to f.c.c., h.c.p. and rhombohedral lattices, elucidating the origin of easy glide in the characteristic crystal structure of MoS2. Mo-S glide which entails deformation of the MoS2 trigonal prism was pr oposed to form an S vacancy.