Hexagonal boron nitride (h-BN) is very attractive for many applications, particularly as a protective coating, dielectric layer/substrate, transparent membrane, or deep ultraviolet emitter. In this work, we carried out a detailed investigation of h-BN synthesis on Cu substrate using chemical vapor deposition (CVD) with two heating zones under low pressure (LP). Previous atmospheric pressure (AP) CVD syntheses were able to obtain only a few layers of h-BN without a good control on the number of layers ^{[1] [2]} .  In contrast, under LPCVD growth, monolayer h-BN was synthesized, and time-dependent growth was investigated (Figure 1).  It was also observed that the morphology of the Cu surface affects the location and density of the h-BN nucleation (Figure 2).  Ammonia borane, which is easily accessible and more stable under ambient conditions than borazine, is used as a BN precursor. The h-BN films are characterized by atomic force microscopy, transmission electron microscopy and electron energy loss spectroscopy analyses. Our results suggest that the growth here occurs via surface-mediated growth, which is similar to graphene growth on Cu under LP. These atomically thin layers are particularly attractive for use as atomic membranes or dielectric layers/substrates for graphene devices ^[3] .

1. Y. Shi, C. Hamsen, X. Jia, K. K. Kim, A. Reina, M. Hofmann, A. L. Hsu, K. Zhang, H. Li, Z.-Y. Juang, M. S. Dresselhaus, L.-J. Li, and J. Kong, “Synthesis of few-layer hexagonal boron nitride thin film by chemical vapor deposition,” Nano Letters, vol. 10, pp. 4134-4139, Oct. 2010.
2. L. Song, L. Ci, H. Lu, P. B. Sorokin, C. Jin, J. Ni, A. G. Kvashnin, D. G. Kvashnin, J. Lou, B. I. Yakobson, and P. M. Ajayan, “Large scale growth and characterization of atomic hexagonal boron nitride layers,” Nano Letters, vol. 10, pp. 3209-15, Aug. 2010.
3. K. K. Kim, A. Hsu, X. Jia, S. M. Kim, Y. Shi, M. Hofmann, D. Nezich, J. F. Rodriguez-Nieva, M. Dresselhaus, T. Palacios, and J. Kong, “Synthesis of monolayer hexagonal boron nitride on Cu foil using chemical vapor deposition,” Nano Letters, vol. 12, pp. 161-166, Jan. 2012.