Effective Cleaning of Hexagonal Boron Nitride for Graphene Devices

Hexagonal boron nitride (h-BN) films have attracted, considerable interest as substrates for graphene. (Dean, C. R et al. Nat. Nanotechnol. 2010, 5, 722-6; Wang, H. et al. Electron Device Lett. 2011, 32, 1209-1211; Sanchez-Yamagishi, J. et al. Phys. Rev. Lett, 2012, 108, 1-5.) We study the presence of organic contaminants introduced by standard lithography and substrate transfer processing on h-BN films exfoliated on silicon oxide substrates. Exposure to photoresist processing adds a large broad luminescence peak to the Raman spectrum of the h-BN flake. This signal persists through typical furnace annealing recipes (Ar/H-2). A recipe that successfully removes organic contaminants and results in clean h-BN flakes involves treatment in Ar/O-2 at 500 degrees C.