Growth of Aligned ZnO Nanowire

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Background ZnO nanowires arrays have broad application in fabricating electronic, optoelectronic, and electromechanical devices. Various methods exist to fabricate these arrays but all suffer from process limitations such as requirements for single crystal substrate, high operating temperatures, ZnO seeding, or an external electric field which complicate and consequently limit the applicability of these manufacturing processes. Technology Zhong Lin Wang, Sheng Xu, and Yaguang Wei from the School of Materials Science and Engineering at Georgia Tech have developed a chemically controlled technique to grow vertical ZnO nanowires on any substrate at low temperatures without an external electric field or ZnO seeding. Following cleaning of a Si (100) wafer using a standard process, a 20 nm layer of Ti followed by a 50 nm layer of Au is deposited on the substrate surface using magnetron plasma sputtering. The Ti acts as a buffer layer to compensate for the lattice mismatch between Si (100) and Au (111). The Au acts as an intermediate layer to assist growth. The substrate is annealed for an hour at 300°C 70°C nutrient solution and then floated face down on a nutrient solution composed of 1:1 ratio of zinc nitrate and hexmethylenetetramine. The substrate floats due to surface tension, and ZnO nanowires grow downward on the lower surface. The hydrothermal reaction that grows the nanowires can be controlled by adjusting the precursor concentration, the growth temperature and the growth time. In general, precursor concentration determines nanowire density, and growth time and temperature control the ZnO nanowire morphology and aspect ratio. For example, by varying the concentration of ZnO, the density of nanowires on the surface first increases and then decreases in a predictable fashion. The use of Au and Ti as intermediate layers allows formation of ZnO arrays on any treated substrate, amorphous or crystalline. Potential Commercial Applications There is a wide range of potential applications of ZnO nanowire arrays including solar cells, ultraviolet lasers, gas sensors, piezoelectric nanogenerators, light emitting diodes, and field emission displays.  Benefits / Advantages A chemical process grows aligned ZnO nanowire arrays without using ZnO seeds or an electrical field to guide growth. Adjusting the concentration of chemical precursors controls the density of ZnO nanowires to within 1 order of magnitude. Use of Au as an intermediate layer allows growth of ZnO nanowires on any substrate, crystalline or amorphous. Growth time and process temperature control the nanowire morphology and aspect ratio.