Vertically aligned boron nitride nanosheets : Chemical vapor synthesis, ultraviolet light emission, and superhydrophobicity

Boron nitride (BN) is a promising semiconductor with a wide band gap (̃6 eV). Here, we report the synthesis of vertically aligned BN nanosheets (BNNSs) on silicon substrates by microwave plasma chemical vapor deposition from a gas mixture of BF₃-N₂-H₂. The size, shape, thickness, density, and alignment of the BNNSs were wellcontrolled by appropriately changing the growth conditions. With changing the gas flow rates of BF₃ and H₂ as well as their ratio, the BNNSs evolve from three-dimensional with branches to two-dimensional with smooth surface and their thickness changes from 20 to below 5 nm. The growth of the BNNSs rather than uniform granular films is attributed to the particular chemical properties of the gas system, mainly the strong etching effect of fluorine. The alignment of the BNNSs is possibly induced by the electrical field generated in plasma sheath. Strong UV light emission with a broad band ranging from 200 to 400nmand superhydrophobicity with contact angles over 150° were obtained for the vertically aligned BNNSs. The present BNNSs possess the properties complementary to carbon nanosheets such as intrinsically semiconducting, high temperature stability, and high chemical inertness and may find applications in ultraviolet nanoelectronics, catalyst supports, electron field emission, and self-cleaning coatings, etc., especially those working at high temperature and in harsh environments. © 2010 American Chemical Society.