Interface effect for EPES sampling depth for overlayer/substrate systems

We found that the interface effects for the sampling depth of elastic peak electron spectroscopy (EPES) for the overlayer/substrate system, first noticed by Zommer and Jablonski for the Rh/Al and Au/Ni systems, differ profoundly in their magnitude and dependence on the overlayer thickness when the overlayer and substrate materials are swapped. Monte Carlo calculations performed for the Al/Rh and Ni/Au systems show that their sampling depths, in contrary to the Rh/Al and Au/Ni, can be substantially greater than those of the elements constituting the respective system. The magnitude of the interface effect increases with the energy of the primary electron beam. It is interesting to mention that the sampling depth can be equivocal for a system with overlayer.