AlN/Si3N4 multilayers as an interface model system for Al1 - xSixN/Si3N4 nanocomposite thin films

AlN transparent coatings alternated with different thicknesses of Si3N4 layers were epitaxially grown on single-crystalline alpha-Al2O3 (0001) substrates by reactive magnetron sputtering, in order to investigate the possibility of stabilization of a crystalline form of silicon nitride. High resolution transmission electron microscopy study of the cross-sections through these coatings revealed that silicon nitride can be epitaxially stabilized in a crystalline form up to breakdown thickness t(siNy)(epi) of about 0.7-1.0 nm corresponding to similar to 2.5-3.5 monolayers, which is anyway smaller than 1.2 nm (similar to 4 monolayers). For t(siNy) > t(siNy)(epi) amorphous Si3N4 is grown on top of epitaxially stabilized 0.7 nm of crystalline Si3N4 resulting in a mixed growth mode. The influence of the epitaxial stabilization of crystalline Si3N4 on hardness enhancement in the case of the Al-SiN system is compared-to the TiN/Si3N4 system and some issues for extrapolation to nanocomposites are discussed (C) 2014 Elsevier B.V. All rights reserved.