AES, XPS AND TEM CHARACTERIZATION OF BORON NITRIDE DEPOSITED UNDER CHEMICAL VAPOR INFILTRATION (CVI) CONDITIONS

BN-films deposited, from BF3-NH3 mixtures under CVI-conditions, either within porous SiC fiber preforms or on plan sintered SiC substrates, have been characterized, at a submicron scale, by XRD, AES, XPS and TEM. The deposits are non-stoichiometric with an excess of boron (N:B at. = 0.6 - 0.8) and contain a significant amount of oxygen. The basic structural unit is an almost perfect hexagonal ring. The stacking of the hexagonal layers is turbostratic (d002 = 3.64 A ; Lc = 28 A). The BN layers are randomly orientated in the bulk of the deposit but tend to be aligned parallel to the interface near the substrate surface. The deposit contains numerous submicroscopic pores. It has a low density (1.6 - 1.9 g.cm-3) and a significant nanoporosity (8 - 22 %). The main features of the microstructure are similar to those of pyrocarbon deposits.