Towards the controlled CVD growth of graphitic B–C–N atomic layer films: The key role of B–C delivery molecular precursor

Graphene-like, ternary system B–C–N atomic layer materials promise highly tunable electronic properties and a plethora of potential applications. However, thus far, experimental synthesis of the B–C–N atomic layers normally yields a microscopic phase-segregated structure consisting of pure C and BN domains. Further, growing the truly ternary B–C–N phase layers with homogenous atomic arrangements has proven to be very challenging. Here, in designing a bettercontrolled process for the chemical vapor deposition (CVD) growth of B–C–N atomic layer films with the minimized C and BN phase segregation, we selected trimethyl borane (TMB), a gaseous organoboron compound with pre-existing B–C bonds, as the molecular precursor to react with ammonia (NH₃) gas that serves as the nitrification agent. The use of this unique B–C delivery precursor allows for the successful synthesis of high-quality and large-area B–C–N atomic layer films. Moreover, the TMB/NH₃ reactant combination can offer a high level of tunability and control of the overall chemical composition of B–C–N atomic layers by regulating the relative partial pressure of two gaseous reactants. Electrical transport measurements show that a finite energy gap can be opened in the as-grown B–C–N atomic layers and its tunability is essentially dependent on the relative C to BN atomic compositions. On the basis of carefully controlled experiments, we show that the pre-existing B–C bonds in the TMB molecular precursor have played a crucial role in effectively reducing the C and BN phase segregation problem, thereby facilitating the formation of truly ternary B–C–N phase atomic layers.