Growth studies of sp(2)-hybridized boron nitride (BN) phases by thermal chemical vapor deposition (CVD) are presented; of particular interest is the presence of oxygen and water during growth. While Fourier transform infrared spectroscopy reveals the presence of B-N bonds and elemental analysis by elastic recoil detection analysis shows that the films are close to stoichiometric, although containing a few atomic percent oxygen and hydrogen, X-ray diffraction measurements show no indications for nucleation of any crystalline BN phases, despite change in N/B-ratio and/or process temperature. Thermodynamic modeling suggests that this is due to formation of strong B-O bonds already in the gas phase in the presence of water or oxygen during growth. This growth behavior is believed to be caused by an uncontrolled release of water and/or oxygen in the deposition chamber and highlights the sensitivity of the BN CVD process towards oxygen and water. (C) 2012 Elsevier B.V. All rights reserved.