Template synthesis of novel monolayer B4C ultrathin film

The excellent physical and chemical properties of two-dimensional (2D) ultrathin film of boron carbide (B₄C) make it suitable for various applications. Nonetheless, the related fabrication strategies have not been well established yet. In this paper, the branches of dendritic magnesium oxide (MgO) nanofibers have been firstly used to serve as the template for synthesis of high-quality monolayer B₄C ultrathin film. As a thermal source, DC arc-discharge plasma was adopted to co-evaporate the raw mixture target comprising of boron, graphite and magnesium oxide species. In the evaporation and subsequent condensation processes, the scaffolds of crossed MgO nanofibers were built at higher temperature prior to heterogeneous nucleation of B₄C nanosheets on them. It is indicated that the kneaded B₄C films can wrap MgO nanofibers into a round-shaped sphere and were entirely stretched out by removal of MgO scaffolds through a simple water-washing purification. The monolayer B₄C ultrathin film is about 1.5?nm in thickness and several micrometers in length. UV–vis diffuse reflectance spectra reveal that the band gap of B₄C films is ~1.37?eV, which is around 50% higher than that of normal B₄C films. This work describes the formation mechanism of such monolayer B₄C ultrathin film in aspect of nucleation/growth processes under the high-temperature plasma conditions.