Synthesis and characterization of two-dimensional (2D) boron-carbon-nitrogen (BCN) hybrids by chemical vapor deposition (CVD)

Abstract

In recent years, two-dimensional (2D) materials like Graphene and Hexagonal Boron Nitride (h-BN) have been generating considerable interest due to their many outstanding properties. A key difference however, lies in their contrasting band gap; graphene has a band gap of zero (semi-metal) while h-BN has a wide band gap of ~6eV (insulator). A ternary material, Boron-Carbon-Nitride (BCN), presents an excellent solution for its ability to tune its band gap. In this report, five BCN hybrid thin films were synthesized using Chemical Vapor Deposition (CVD) method, with ammonia borane (NH3-BH3) as precursor and methane (CH4) as feedstock for carbon. To investigate its band gap, CVD parameters such as dosage of NH3-BH3 (5 to 50 mg) and temperature of heating the precursor (60 to 120oC) were analyzed. Characterization devices like Scanning Electron Microscopy (SEM), Raman Spectroscopy and Ultraviolet-Visible (UV Vis) Spectroscopy provided verification and analysis. Using Tauc's formulation, results showed that the band gaps of BCN samples were successfully lowered from 6 eV to 4.66 eV when the dosage and/or temperature of heating NH3-BH3 were decreased. While band gap engineering was achieved by the author, there exists a threshold limit. Reduction of precursor dosage or temperature beyond this yielded no significant change. Due to the segregating nature of carbon and Boron Nitride (BN) domains, there exist two band gap values in a single BCN hybrid instead of one. This makes application in switching devices an obstacle. For BCN hybrids to achieve band gap engineering and be applied in electronic switching devices, the formation of a true alloy phase is needed.