To grow the ZnO NRAs on silica microspheres, we layered aluminum-doped ZnO (AZO) as a seed layer over the surface of microspheres by radio-frequency magnetron sputtering. Using a hydrothermal technique, we aligned the ZnO nanorods vertically on the surface of the seed layer in line with the c-axis direction of growth in wurtzite crystal structures. The urchin aggregation-shaped ZnO architectures then formed on the transparent substrate. For these nanostructures on silica microspheres, we also observed enhanced UV photoluminescence (PL) intensity and their hydrophobic surface properties.5 We noted high UV PL emission intensity, owing to the increased intensity of the ZnO NRAs on silica spheres. In comparison with the ZnO NRAs without the spheres, the UV PL emission intensity was 4.26 times greater. Additionally, the modified surface of the urchin aggregation-shaped ZnO architectures changed the contact angle () from 36.65 to 90.51°.
Piezoelectric charge generation occurs when the ZnO NRAs are deformed by an external influence.
use they are bent with a large radius. We observed that output current density was enhanced 1.54 times in the piezoelectric NG with a very rough gold top electrode.
Figure 3. Schematic diagram and beam pattern of the fabricated aluminum-doped subwavelength nanostructure arrays (AZO SNAs) on gallium nitride (GaN)-based green LEDs. CW: Continuous wave.
In summary, the unique optical and morphological properties of wide-bandgap metal oxide nanostructures used in multifunctional materials are advantageous for optoelectronic and energy device applications. For example, urchin aggregation-shaped ZnO architectures induce diffuse light scattering while keeping a high total transmittance, which is promising for improving the light-trapping properties of thin-film silicon solar cells. The novel surface morphology of ZnO SMRAs is favorable for forming a highly rough top electrode, which bends the ZnO nanorods of piezoelectric NGs and leads to an increase in output current density. Furthermore, AZO SNAs can be employed as a top layer for LEDs to increase light-extraction efficiency.
In future work, we will develop a fabrication method for integrating the ZnO nanostructures onto textile or polymer substrates for use in wearable, flexible, or stretchable optoelectronic and energy devices. We will also extend the studies on the wide-bandgap semiconductor nanostructures by incorporating TiO2, tin dioxide, and cerium(IV) oxide.
Financial support for this work came from the Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT, and Future Planning (2013-010037) and a grant from the Ministry of Knowledge Economy of the Republic of Korea, under project 10039151.
