Direct, Transfer-Free Growth of Large-Area Hexagonal Boron Nitride Films by Plasma-Enhanced Chemical Film Conversion (PECFC) of Printable, Solution-Processed Ammonia Borane.

Synthesis of large-area hexagonal boron nitride (h-BN) films for two-dimensional (2D) electronic applications typically requires high temperatures (∼1000 °C) and catalytic metal substrates which necessitate transfer. Here, analogous to plasma-enhanced chemical vapor deposition, a nonthermal plasma is employed to create energetic and chemically reactive states such as atomic hydrogen and convert a molecular precursor film to h-BN at temperatures as low as 500 °C directly on metal-free substrates-a process we term plasma-enhanced chemical film conversion (PECFC). Films containing ammonia borane as a precursor are prepared by a variety of solution processing methods including spray deposition, spin coating, and inkjet printing and reacted in a cold-wall reactor with a planar dielectric barrier discharge operated at atmospheric pressure in a background of argon or a mixture of argon and hydrogen. Systematic characterization of the converted h-BN films by micro-Raman spectroscopy shows that the minimum temperature for nucleation on silicon-based substrates can be decreased from 800 to 500 °C by the addition of a plasma. Furthermore, the crystalline domain size, as reflected by the full width at half-maximum, increased by more than 3 times. To demonstrate the potential of the h-BN films as a gate dielectric in 2D electronic devices, molybdenum disulfide field effect transistors were fabricated, and the field effect mobility was found to be improved by up to 4 times over silicon dioxide. Overall, PECFC allows h-BN films to be grown at lower temperatures and with improved crystallinity than CVD, directly on substrates suitable for electronic device fabrication.