Structure characterization of CVD amorphous Si3N4 by pulsed neutron total scattering

The structure factor S(Q) of chemically vapor-deposited (CVD) amorphous Si₃N₄ has been measured by pulsed neutron diffraction over the range of the scattering vector Q from 1–330 nm^?1. The oscillatory behavior in the S(Q) persists up to Q = 300 nm^?1 and there is appreciable small angle scattering intensity. The SiN bond length is l_SiN = 0.1729 nm, and its coordination numbers n_SiN and n_NSi are 3.70 and 2.78 respectively. The bond angles around a Si and a N atom are found to be 109.8 and 121°. Analysis of the small angle scattering intensity shows the existence of voids with an average diameter of about 1 nm and a volume fraction of about 4%, which may stabilize the amorphous structure of Si₃N₄ having rigid covalent bonds due to relaxing the strain energy accumulated in the matrix.