Synthesis and characterization of boron carbon oxynitride films with tunable composition using methane, boric acid and ammonia

Atomically thin films of boron carbon oxynitride (BCNO) are an intriguing new form of thin quaternary semiconducting hybrid films that have recently generated tremendous interest in the scientific community. These films are composition-tunable 2D materials which exhibit rich physical, chemical and electronic properties. Herein, a facile atmospheric pressure chemical vapour deposition (APCVD) synthesis and in-depth characterization of BCNO films with tunable composition, in which methane, ammonia and boric acid were used as precursor materials is reported. The different atomic compositions were achieved by adjusting the vaporization temperature of boric acid by varying the distance (i.e. 2 cm to 12 cm) between the boric acid and the growth substrate. From the XPS survey spectra, the atomic compositions of the BCNO films formed varied as follows: C (48-71 at%), B (2.34-12.8 at%), N (1.98-7.9 at%) and O (33-34 at%). Raman spectral analyses showed that the films exhibited vibrational modes from h-BN, B-C, and graphene domains. XPS data corroborated the Raman analyses by indicating that the films consisted of h-BN, B-O-B, and B2O2 domains embedded within a graphene-rich BCN matrix. Three band gap energies assigned to h-BN (5.87 +/- 0.05-5.66 +/- 0.06 eV), h-BCN (5.76 +/- 0.01-5.22 +/- 0.01 eV) and doped graphene (2.35 + 0.06-1.74 + 0.04 eV) domains were observed from the UV-vis spectra of BCNO films as a function of boric acid distance from the growth substrate. The narrowing optical energies were attributed to an increasing C-content with increasing growth distance, thus leading to C-doping in h-BN and h-BCN as well as in the formation of larger graphene domains. Finally, the in-depth analysis of the samples allowed for a mechanism of the BCNO formation to be proposed and hence provided further understanding of the growth of the BCNO films.