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1178-AA06-38

Hydrothermal Synthesis of Zinc Oxide Nanowires on Kevlar using ALD and Sputtered ZnO Seed Layers Ashley D. Mason1, Todd J. Waggoner1, Sean W. Smith1, John F. Conley Jr.1, Brady J. Gibbons2 David Price3 and Derryl Allman3 1 Electrical Engineering and Computer Science, 2Mechanical, Industrial and Manufacturing Engineering, Oregon State University, Corvallis, OR 97331, U.S.A. 3 ON Semiconductor, Gresham OR 97030, U.S.A. ABSTRACT Low temperature hydrothermal methods allow for growth of nanowires on novel substrates. We examine the impact of variations in chemical concentration, time, temperature, and seed layer on nanowire (NW) growth and crystallite formation. The majority of growth (NWs and crystallites) was found to occur within the first two hours. Lower Zn(NO3)2 concentrations produced a reduction in the undesired large crystallites, whereas hexamethylene tetramine (HMT) concentration did not largely impact crystallite density or nanowire morphology. Growth temperature appeared to impact NW diameter variation. Nanowires grow only on the ZnO seed layer and crystallites seem to attach preferentially to the bare Kevlar surface. INTRODUCTION Recent work by Wang, et al. showed that ZnO nanowire (NW) coated Kevlar fibers can be mechanically actuated to produce small amounts of current, suggesting the possibility nano-piezo energy harvesting [1 – 9]. This application requires the uniform growth of NWs on novel substrates such as Kevlar. Due to the low decomposition temperature of Kevlar (~ 400 C), potential growth processes are limited to low temperature hydrothermal methods [10, 11]. To achieve selective growth of ZnO NWs on Kevlar, we used a uniform coating of ZnO to seed growth [12, 13], rather than the more widely used metal catalyst method [14]. An initial investigation of hydrothermally grown ZnO NWs on atomic layer deposition (ALD) and RF sputtered seed layers revealed the formation of large crystallites that could degrade the performance and reliability of piezoelectric nanogenerators. Since these large crystallites could not be removed easily without damaging the substrate or nanowires, the impact of growth parameter variation on prevention of large crystallite nucleation and growth was investigated. EXPERIMENTAL DETAILS The growth substrate used in these experiments is Kevlar 129, an aramid synthetic fiber. Two or more NW coated Kevlar fibers can be wound together as described in [1] so that if fibers are mechanically actuated, the NW coating may produce a piezoelectric current. Since the substrate is cylindrical, deposition of a uniform seed layer is more difficult than with a flat substrate. Because of its inherent high conformality, ALD was chosen as a seed deposition method. As an alternative, RF sputtering was also investigated; however, rotation of the fiber would be required for complete radial coverage. ALD seed layers were deposited using (C2H5)2Zn and H2O at 170 C. RF sputtering was performed using a ZnO target at 75 W and

10 mTorr. With both methods the target thickness of the seed lay