The electrical performance of SiC-based microelectronic devices is strongly affected by the densities of interfacial traps introduced by the chemical and structural changes at the SiO2∕SiC interface during processing. We analyzed the structure and chemistry of this interface for the thermally grown SiO2∕4H-SiC heterostructure using high-resolution transmission electron microscopy (TEM), Z-contrast scanning TEM, and spatially resolved electron energy-loss spectroscopy. The analyses revealed the presence of distinct layers, several nanometers thick, on each side of the interface; additionally, partial amorphization of the top SiC surface was observed. These interfacial layers were attributed to the formation of a ternary Si–C–O phase during thermal oxidation.

Sodium phosphosilicate glasses exhibit unique properties with mixed network formers, and have various potential applications. However, proper understanding on the network structures and property-oriented methodology based on compositional changes are lacking. In this study, we have developed an extended topological constraint theory and applied it successfully to analyze the composition dependence of glass transition temperature (Tg) and hardness of sodium phosphosilicate glasses. It was found that the hardness and Tg of glasses do not always increase with the content of SiO2, and there exist maximum hardness and Tg at a certain content of SiO2. In particular, a unique glass (20Na2O-17SiO2-63P2O5) exhibits a low glass transition temperature (589 K) but still has relatively high hardness (4.42 GPa) mainly due to the high fraction of highly coordinated network former Si((6)). Because of its convenient forming and manufacturing, such kind of phosphosilicate glasses has a lot of valuable applications in optical fibers, optical amplifiers, biomaterials, and fuel cells. Also, such methodology can be applied to other types of phosphosilicate glasses with similar structures.

Lateral-polarity heterostructures of GaN on c sapphire were prepared by deposition and patterning of a thin low-temperature AlN nucleation layer. Adjacent macroscopic domains were found to have opposite polarity; domains grown on the AlN nucleation layer were Ga polar while those grown on the nitrided sapphire were N polar, as confirmed by convergent-beam electron diffraction and Z-contrast images. We directly determined the atomic interface structure between the AlN and c sapphire with an aberration-corrected scanning transmission electron microscope at ∼1.0Å resolution. This is the direct experimental evidence for the origin of the polarity control in III nitrides. This understanding is an important step toward manipulating polarity in these semiconductors.

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