Structure and composition studies of chemical vapour-deposited BCN fibre coatings

Abstract

The composition and structure of boron carbonitride (BCN) films were studied. The films were continuously deposited on fibres by atmospheric pressure CVD. The precursors were ammonia, trimethyl borate and toluene. The composition was determined by photoelectron spectra of boron 1s, nitrogen 1s, carbon 1s and oxygen 1s. By fixing the C 1s peak at 285 eV, the position of the B 1s peak and the N 1s peak in the BCN films was equal to BN films. The C content of the films increases from about 6 at% to 60 at%, leaving the stoichiometric boron/nitrogen ratio as well as the oxygen content below 10 at% unchanged. Generally, the carbon content in the films is lower than predicted by the precursor ratios. Obviously, the insertion of carbon into the film is decreased in the presence of ammonia, which is known to etch carbon. With a decreasing ammonia/toluene ratio, the undesired effect in the reaction is suppressed and the carbon deposition becomes considerable. Transmission electron microscopic studies were performed on cross-sections of the coated fibres. High-resolution images generally show a hexagonal turbostratic structure with different orientation preferences of the atomic lamellae similar to hexagonal turbostratic boron nitride and pyrolytic carbon. When a noticeable carbon concentration (20 at%) is reached, the atomic sheets become uniformly distributed in all directions in space.

Formation mechanisms of boron oxide films fabricated by large-area electron beam-induced deposition of trimethyl borate

“…TMB is an alkoxide-based molecule with structural properties similar to those of tetraethyl orthosilicate (TEOS, Si(C 2 H 5 O) 4 ), which has been well characterized as a precursor for EBID of silica films [ 14 ]. TMB has previously been used for boron doping of SiO 2 [ 15 ] and diamond [ 16 ], and the deposition of BCN fibres [ 17 ], BN nanotubes [ 18 ] and BN thin films [ 19 – 20 ]. Thin films were prepared using a novel, large-area deposition system designed for the directed deposition of macroscopic features using the EBID process.…”