  We synthesize a series of CVD h-BN films and perform critical infrared
spectroscopic characterization. For high-temperature (HT, Temp = 1400 degrees)
grown h-BN thin film only E1u-mode infrared phonon is activated demonstrating
highly aligned 2D h-BN planes over large area, whereas low-temperature (LT,
Temp = 1000 degrees) grown film shows two phonon peaks, E1u and A2u, due to
stacking of h-BN plane at tilted angle. For CVD graphene transferred on HT
h-BN/SiO2/Si substrate, interband transition spectrum s1 shifts strongly to
lower energy compared with that on LT h-BN/SiO2/Si and on bare SiO2/Si
substrate, revealing that residual carrier density n in graphene is suppressed
by use of HT h-BN layer. Also the interband transition width of s1 defined by
effective temperature is reduced from 400 K for G/SiO2/Si to 300 K for HT
h-BN/SiO2/Si. The behaviors of n and effective temperature show that HT h-BN
film can decouple CVD graphene from the impurity and defect of SiO2 leading to
large scale free-standing like graphene.
