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Hexagonal boron nitride (h-BN) is a promising two-dimensional insulator witha large band gap and low density of charged impurities that is isostructuraland isoelectronic with graphene. Here we report the chemical and atomic-scalestructure of CVD-grown wafer-scale (~25 cm2) h-BN sheets ranging in thicknessfrom 1-20 monolayers. Atomic-scale images of h-BN on Au and graphene/Ausubstrates obtained by scanning tunneling microscopy (STM) reveal high h-BNcrystalline quality in monolayer samples. Further characterization of 1-20monolayer samples indicates uniform thickness for wafer-scale areas; thisthickness control is a result of precise control of the precursor flow rate,deposition temperature and pressure. Raman and infrared spectroscopy indicatethe presence of B-N bonds and reveal a linear dependence of thickness withgrowth time. X-ray photoelectron spectroscopy (XPS) shows the filmstoichiometry, and the B/N atom ratio in our films is 1 + 0.6% across the rangeof thicknesses. Electrical current transport in metal/insulator/metal(Au/h-BN/Au) heterostructures indicates that our CVD-grown h-BN films can actas excellent tunnel barriers with a high hard-breakdown field strength. Ourresults suggest that large-area h-BN films are structurally, chemically andelectronically uniform over the wafer scale, opening the door to pervasiveapplication as a dielectric in layered nanoelectronic and nanophotonicheterostructures.

Atomic-scale Structural and Chemical Characterization of Hexagonal Boron  Nitride Layers Synthesized at the Wafer-Scale with Monolayer Thickness  Control