PROCESSES IN MOS2 GASIFICATION

The gasification of MoS2 by H2 has been studied by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). Two fundamental processes were found upon heating the (0001) surface of MoS2 in H2: first, the surface sulfur layer is removed from some defect sites on the MoS2 basal plane to form monolayer pits, and second, the exposed Mo layer forms small clusters which catalyze the further gasification of the sulfur layer, thus enhancing the number of edge atoms. At low reaction pressures, these two processes remove mainly the top sandwich layer and no Mo particles channel into the top sulfur layer. However, at high pressure or temperature, the gasification is dominated by the motion of the Mo particles which then produce high-density channel structures on the surface. Adding thiophene to H2 retards the gasification of MoS2, suggesting the active catalytic sites are the atoms at the steps on the surface. Ni and Co catalyze the gasification of MoS2 and greatly increase the total number of edge sites. © 1993 Academic Press, Inc.