A novel technique for studying interface abruptness in a STEM

Abstract

The distribution of the electric charges in a solid is such that the volume average of the electrostatic potential, known as the mean inner potential, is positive of the order of a few volts. Incident electrons are accelerated at the surface of the material and noticeable refraction occurs at glancing angles of incidence. At an interface between two materials, a refraction effect may also occur because of the difference in their mean inner potentials. This effect has recently been observed and gives rise to a faint streaking in the spots of a selected area diffraction pattern. Low-angle dark-field images formed with the streak on the undiffracted beam show the interface region as a bright line. We have observed the same effect in a field emission STEM on the interface of polycrystalline Mo and amorphous Si. A preliminary study suggests that this technique can give information on the abruptness of interfaces.