The deposition characteristics and the structural nature of the deposit in the chemical vapour deposition of boron

Abstract

Boron was deposited onto graphite by a chemical vapour deposition (CVD) technique using gaseous mixtures of BCl 3 and hydrogen. The CVD of boron is a thermally activated process with an apparent activation energy of 18.8±0.7 kcal mol -1 at low temperatures and high gas flow rates. At high deposition temperatures and low gas flow rates the deposition rate depends on the gas phase mass transfer. Boron is deposited as an amorphous material below 1250 K, and mainly as the β rhombohedral modification above 1250 K. However, a small amount of β tetragonal boron is deposited together with the β rhombohedral boron. The β rhombohedral boron has a strong (104) preferred orientation at 1500 K. However, the preference for the (104) orientation is reduced as the BCl 3 fraction or the gas flow rate increases.