The thin intergranular phase in a silicon nitride (Si3N4)ceramic, which has been regarded for decades as having an entirely amorphous morphology, is shown to have a semi-crystalline structure. Using two different but complementary high-resolution electron microscopy methods, the intergranular atomic structure was directly imaged at the atomic level. These high-resolution images show that the atomic arrangement of the dopand element cerium takes very periodic positions not only along the interface between the intergranular phase and the Si3N4 matrix grains, but it arranges in a semi-crystalline structure that spans the entire width of the intergranular phase between two adjacent matrix grains, in principle connecting the two separate matrix grains. The result will have implications on the approach of understanding the materials properties of ceramics, most significantly on the mechanical properties and the associated computational modeling of the atomic structure of the thin intergranular phase in Si3N4 ceramics.

A detailed investigation of the growth mechanism of ultra-thin silicon nitride (Si3N4) films on Si(111) substrates, their structure, morphology and surface chemistry down to atomic scale have been investigated using various surface analytical techniques such as low energy electron diffraction (LEED), scanning tunneling microscopy (STM) and ESCA microscopy. A radio frequency N2 plasma source from Epi Uni-bulb has been used for the nitridation of atomically clean Si(111) surfaces. The substrate temperatures during the nitridation process were ranging from 600,Äì1050¬∞C and the plasma exposure times were varied from 5¬†s for initial nucleation up to 45¬†min for saturation thickness. The initial stage of N nucleation on Si(111), how the structure and morphology of the nitride films depend on thickness and temperature, surface atomic reconstructions and the nitride film chemical composition are discussed here. All findings are explained in terms of thermally activated inter-diffusion of Si and N atoms as well as the surface adatom diffusion/mobility.