Formation and atomic-scale characterization of an interfacial β-Si 3 N 4 nanolayer in a C/SiC composite

Abstract β-Si3N4 combines attractive mechanical, thermal, and dielectric properties, yet experimental characterization of its local atomic arrangement and bonding-related electronic structure is often complicated by the sintering additives and intergranular phases present in bulk ceramics. Here, a continuous, sintering-additive-free β-Si3N4 nanolayer was formed at the C/SiC interface through reactive infiltration of molten Si into a nitrogen-containing, glucose-derived carbon framework. The nanolayer exhibits micrometer-scale lateral continuity within the examined interfacial region, with a local thickness on the order of 20 nm, providing a resolvable crystalline interior that remains accessible to site-specific atomic-scale analysis. Correlative HAADF-STEM and iDPC-STEM observations along multiple crystallographic directions resolved both the projected Si framework and the light-element N sublattice, and consistently identified the characteristic ABAB stacking and corner-sharing SiN4 tetrahedral network of β-Si3N4. The N K-edge and Si L2,3-edge electron energy-loss near-edge structures were further examined using reference spectra and density-functional-theory-based simulations. Their principal features were associated with complementary N- and Si-projected components of the hybridized unoccupied states in the tetrahedral Si-N framework. Projected densities of states, charge-density redistribution, and band-structure calculations further revealed N-weighted occupied bonding states, predominantly Si-derived unoccupied states with finite N 2p contributions, partial charge transfer from Si to N, and directional covalent bonding. Together, these results provide correlated atomic-scale structural and bonding-sensitive spectroscopic characterization of the interfacial β-Si3N4 nanolayer, with first-principles calculations supporting the interpretation of the principal ELNES features.