Abstract
We have developed the low-temperature conformal ZnO nanowire fabrication on flexible plastic substrates by utilizing the solution-processible metal seed-assisted hydrothermal ZnO crystallization. Structural evolution of ZnO nanowires controlled by major parameters involving growth temperature, growth time, and seed coating condition, has been systematically investigated towards uniform and large-area growth of conformal ZnO nanowires. Direct ZnO nanowire growth on flexible plastics without undergoing the high-temperature seed sintering has been realized by developing the low-temperature Ag-seeded hydrothermal ZnO nanowire growth. The nanoporous Ag layer favorable for ZnO crystal nucleation and continued nanowire growth can be reduced from the Ag ion solution coating at the temperature as low as 130 °C. This tactfully enables the selective hydrothermal growth of ZnO nanowires on the Ag patterns on flexible plastics. Such an all-solution-processible low-temperature fabrication protocol may provide an essential and practical solution to develop many diverse applications including wearable and transparent electronics, sensors, and photocatalytic devices. As one example, we demonstrate that a transparent UV sensor can be devised based on the ZNW growth on the Ag micromesh electrode.
Highlights
Possessing wide band gap (~ 3.37 eV), large exciton binding energy (~ 60 meV), non-central symmetric wurtzite crystal structure (a = 0.3249 nm, c = 0.5205 nm), and biocompatibility, zinc oxide (ZnO) has been one of the most versatile metal oxide materials [1, 2]
We show one example that Zinc oxide nanowire (ZNW) are selectively grown on the metal micromesh pattern, which can be directly applied for transparent UV sensors
3.1.1 Effect of growth temperature Figure 2 shows the results of hydrothermal ZNW growths at different temperatures with the growth time of 150 min and other conditions fixed
Summary
We demonstrate that the nanoporous metal (e.g. Ag) layer reduced from the ionic solution coating at much lower temperature (< 130 °C) can work as an alternative seed for hydrothermal ZNW growth This realizes direct ZNW growth on the common plastic substrates without resort to high-temperature seed sintering. Such a metalseeded low-temperature ZNW growth allows scalable fabrication of flexible ZNW-based electronic devices by the selective ZNW growth on the designed metal patterns. For the metal-seeded ZNW growth, the isopropyl alcohol (IPA)-based Ag-ion solution ink (TEC-CO-011, InkTec Co., Ltd.; ‘Ag ink’ hereafter) was diluted in IPA with 1:1 volume ratio by sonication This Ag ink was spin-coated onto the target substrate (i.e. glass, PC, and polyimide (PI)) typically at 2000 rpm for 20 s. The photocurrent generated upon UV illumination with controlled power density was measured at the applied bias of 0.1 V
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