Department of Physics and the William Mong Institute of Nano Science and Technology, the Hong Kong University of Science and Technology, Hong Kong, China

We developed a carbon-assisted physical-vapor-deposition method for the growth of highly aligned ZnO nanowire arrays on any flat substrates in large area. Amorphous carbon (a-C) films acted as the preferential nucleation sites to facilitate the growth of high-quality ZnO nanowire array patterns. The ultrathin a-C films can effectively retard the inclined growth of ZnO nanowires at the edge of the a-C patterns. The investigations of the nanowire structures, photoluminescence and electrical transport properties have shown that the ZnO nanowires were well crystallized and the formation of defects in the nanowires was largely suppressed.


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Comments on the manuscript’s significance:

 1)      We have developed a novel route for fabricating and patterning high-quality ZnO nanowire arrays using amorphous carbon films. The fabrication process is free of catalysts, carrier gases and complex operation.  

 2)      The excellent vertical growth of ZnO nanowires in our work is independent of the substrates. Larger area aligned ZnO nanowire arrays have been demonstrated grown on Si wafer (2 inch) and FTO glass instead of expensive lattice-matched substrates such as sapphire, SiC and GaN etc., which are required in most methods for vertical growth of ZnO nanowires.

 3)      The catalyst-free synthesis process and high deposition temperature ensure highly pure ZnO nanowires with excellent crystal quality, optical and electrical properties, as confirmed by our TEM, PL and FET studies. No crystalline defects are found and no green emission related point defects are revealed. The average electron mobility of as-fabricated single nanowires is μ_e=34.7 cm²V^-1s^-1, which about three times higher than that of high-quality ZnO NWs grown by the traditional carbon thermal method using Au as the catalysts (10.2 cm²V^-1s^-1 in ref.10 and 12 cm²V^-1s^-1 in ref. 5).

 4)      Different from most traditional carbon thermal methods, the a-C films acted as the preferential nucleate sites and efficiently lowered the deposition temperature. The ultrathin a-C films can effectively retard the inclined growth of ZnO NWs at the edge of the a-C patterns, which is inevitable at the thick edges of patterned photoresist or other thick carbon films.