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 better- controlled 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.