|
The spontaneous dissociation of trichloroethylene (TCE) molecules on the Si(111)7x7 and Si(100)2x1 surfaces was investigated using STM. Chlorine atoms were identified by using voltage dependent imaging and by observing voltage dependent tip-induced diffusion. On the (111) surface, at low coverage, we identify one chlorine that dissociates and binds to an adatom, leaving a nearby chlorovinyl group as the other product bound to the surface. Chlorine atoms show strong site selectivity for corner adatoms and some preference for the faulted half of the unit cell. This result differs significantly from previous studies of chlorine on this surface and a site-selective mobile precursor model is used to explain this discrepancy. The observed site-selectivity is consistent with the high electronegativity value for chlorine.
In addition, studies of TCE dissociation on the Si(100)2x1 surface, also at room temperature, will be presented. Again, the observation of tip-induced diffusion is used to identify chlorine atoms. This characterization is helpful in interpreting the rather complex STM images. Based on our STM images and previously reported XPS results, we will propose a number of distinct pathways for TCE dissociation on the (100) surface.
|