In Situ Gas Analysis During the Growth of Hexagonal Boron Nitride from Ammonia Borane

Ammonia borane (NH3:BH3) is commonly used as a stoichiometric source of nitrogen and boron for the growth of hexagonal boron nitride (h-BN) by chemical vapour deposition (CVD). We use in situ gas analysis by mass spectrometry to investigate the active chemical components that evolve when an ammonia borane source is heated, and study how these components change after flowing through the CVD growth furnace. This also gives insight into the catalytic effect of copper substrates used for CVD growth of h-BN. We find that in vacuum, even at 40 °C, gaseous amino borane and polyaminoborane fragments are evolved from the solid source; as the temperature of the ammonia borane source increases, the amount of all components increases but proportionally more of the higher mass components are present. Gas phase reactions change the gas composition after flowing through the CVD growth furnace, depending on the temperature of the growth furnace, with increased dehydrogenation at higher furnace temperatures. Further reactions are catalysed by the copper substrate, with decomposition of the higher mass components evident at furnace temperatures $ ?>>900 °C. Direct comparison with CVD h-BN growth suggests that the lower mass components produced by lower ammonia borane source temperatures are preferred for larger island sizes and that furnace temperatures higher than 900 °C are required in order to initiate the catalytic effects of the copper substrate. In situ gas analysis thus gives new insight into the CVD growth of h-BN, and similar methodology could be used to optimise and understand the growth of other two dimensional materials.