Direct Imaging and First Principles Studies of Si$_{3}$N$_{4}$/SiO$_{2}$ Interface*

It is well known that the composition of the integranular films (IGFs) in sintered polycrystalline silicon nitride (Si$_{3}$N$_{4})$ ceramics controls many of their physical and mechanical properties. A considerable effort has been made to characterize these films on the atomic scale using both experimental and theoretical methods. In this talk, we present results from a combined atomic-resolution Z-contrast and annular bright field imaging, electron energy-loss spectroscopy, as well as ab initio studies of the interface between $\beta $-Si$_{3}$N$_{4 }$(10-10) and SiO$_{2}$ intergranular film. Our results show that O replaces N at the interface between the two materials in agreement with our theoretical calculations and that N is present in the SiO$_{2}$ IGF. Moreover, they indicate the presence of atomic columns completing Si$_{3}$N$_{4}$ open rings, which have not been observed experimentally at the recently imaged Si$_{3}$N$_{4}$/rare-earth oxides interfaces, but have been predicted theoretically on bare Si$_{3}$N$_{4}$ surfaces. The structural and electronic variations at the Si$_{3}$N$_{4}$/SiO$_{2}$ interface will be discussed in detail, focusing in particular on bonding characteristics.