Growth And Etching Of Two-dimensional Hexagonal Boron Nitride

Hexagonal boron nitride,referred as "white graphene",is composed of alternating boron and nitrogen atoms in a two-dimensional honeycomb plane.It has attracted intense research interests owing to its unique atomic structure,outstanding physical/chemical properties,and broad application prospects.Currently,various techniques have been explored to synthesize h-BN,including mechanical cleavage,liquid phase exfoliation,chemical vapor deposition(including vapor phase epitaxy and non-vapor phase epitaxy),ion beam sputtering deposition etc.However,high-quality h-BN films can be achieved only through mechanical cleaving from the bulk h-BN crystals with small size and low yield.The h-BN film grown by other techniques has much lower quality than that of the exfoliated materials.The production of high quality,large area h-BN with controllable thickness is still a big challenge to date.Therefore,it is an urgent need to develop the novel approach to prepare large-scale and high-quality h-BN for further applications.Chemical vapor deposition(CVD)has been a great success in the preparation of large-scale and high-quality graphene films,and has become an effective technique for the growth of other two-dimensional thin film materials.In this thesis,the growth and etching of h-BN were studied through CVD method.The atmospheric and low pressure CVD techniques were both applied to synthesis h-BN films on copper substrate.Optical microscopy,Raman spectroscopy,scanning electron microscopy and X-ray photoelectron spectroscopy have been performed to further characterize the as-grown films.The effect of various growth parameters(growth temperature,precursor temperature,substrate polishing,etc.)on the growth of h-BN crystals were systematically investigated by atmospheric pressure CVD.Large area,high quality monolayer h-BN film was finally achieved through the optimized growth parameters.On the other hand,the effect of growth factors on the growth of h-BN was investigated by low pressure CVD.The role of hydrogen pressure on the growth and etching of h-BN domains was further studied.A hydrogen pressure induced structural phase transition point was observed during the growth and etching of h-BN domains,which were further explained by the structural phase diagram curve calculated by the first principle simulation.The kinetic process of hydrogen etching were revealed by morphology evolution of h-BN domains with increasing etching time as well as the AES mapping technique.Combined with the growth and etching process,the growth dynamic of complex h-BN domain structure were further explored.