Infrared study of large scale h-BN film and graphene/h-BN heterostructure

摘要

We synthesize a series of CVD h-BN films and perform critical infrared spectroscopic characterization. For high-temperature (HT, Temp= 1400 ℃) grown h-BN thin film, only E_(1u)-mode infrared phonon is activated demonstrating highly aligned 2D h-BN planes over large area, whereas low-temperature (LT, Temp = 1000 ℃) grown film shows two phonon peaks, E_(1u) and A_(2u), due to stacking of h-BN plane at tilted angle. For CVD graphene transferred on HT h-BN/SiO_2/Si substrate, interband transition spectrum σ_1 shifts strongly to lower energy compared with that on LT h-BN/ SiO_2/Si and on bare SiO_2/Si substrates, revealing that the residual carrier density n in graphene is suppressed by the use of HT h-BN layer. Also, the interband transition width of σ_1 defined by effective temperature is reduced from 400 K for G/SiO_2/Si to 300 K for HT h-BN/SiO_2/Si. The behaviors of n and effective temperature show that the HT h-BN film can decouple CVD graphene from the impurity and defect of SiO_2 leading to a large scale free-standing like graphene.