LPCVD AND CHARACTERIZATION OF BORON-CONTAINING PYROCARBON MATERIALS

Pyrocarbon materials containing various amounts of boron have been pre pared by LPCVD from BCl3-C3H8-H-2 precursor mixtures. By increasing th e BCl3/(C3H8 + BCl3) ratio up to 85%, the incorporation of boron can r each 33 at.%. A small amount of boron (e.g. 8 at.%) highly enhances th e structural anisotropy of pyrocarbon, as evidenced by optical microsc opy, X-ray diffraction and transmission electron microscopy (selected area diffraction and lattice fringes techniques). X-ray photoelectron spectroscopy has shown that a large fraction of the boron atoms are in cluded by substitution in the carbon layers; the remaining boron atoms belong to a boron-rich amorphous part of the material. As the boron c ontent increases beyond 8 at.%, the structural anisotropy of the boron -rich pyrocarbon decreases, due to the limited growth and stacking of the carbon layers. Also, amorphous boron-rich regions are more and mor e abundant as the total amount of boron increases. The oxidation resis tance of the C(B) materials is better than that of pure pyrocarbon. Th is is mainly due to the improvement of the structural organization for the low boron content materials and to the coating of the whole mater ial with a stable boron oxide for materials with a higher boron conten t. Copyright (C) 1996 Elsevier Science Ltd