We report on the succesful fabrication of ZnO nanorod (NR)-based robust piezoelectric nanogenerators(PNGs) by using Cu foil substrate. The ZnO NRs are successfully grown on the Cu foil substrate by using all solutionbased method, a two step hydrothermal synthesis. The ZnO NRs are grown along c-axis well with an average diameterof 75~80 nm and length of 1~1.5 µm. The ZnO NRs showed abnormal photoluminescence specrta which is attributedfrom surface plasmon resonance assistant enhancement at specific wavelength. The PNGs on the SUS substrates showtypical piezoelectric output performance which showing a frequency dependent voltage enhancement and polarity depen-dent charging and discharging characteristics. The output voltage range is 0.79~2.28 V with variation of input strain fre-quency of 1.8~3.9 Hz. The PNG on Cu foil shows reliable output performance even at the operation over 200 timeswithout showing degradation of output voltage. The current output from the PNG is 0.7 µA/cm2 which is a typical out-put range from the ZnO NR-based PNGs. These performance enhancement is attributed from the high flexibility, highelectrical conductivity and excellent heat dissipation properties of the Cu foil as a substrate.

A zinc oxide (ZnO) hybrid structure was successfully fabricated on a glass substrate by metal organic chemical vapor deposition (MOCVD). In-situ growth of a multi-dimensional ZnO hybrid structure was achieved by adjusting the growth temperature to determine the morphologies of either film or nanorods without any catalysts such as Au, Cu, Co, or Sn. The ZnO hybrid structure was composed of one-dimensional (1D) nanorods grown continuously on the two-dimensional (2D) ZnO film. The ZnO film of 2D mode was grown at a relatively low temperature, whereas the ZnO nanorods of 1D mode were grown at a higher temperature. The change of the morphologies of these materials led to improvements of the electrical and optical properties. The ZnO hybrid structure was characterized using various analytical tools. Scanning electron microscopy (SEM) was used to determine the surface morphology of the nanorods, which had grown well on the thin film. The structural characteristics of the polycrystalline ZnO hybrid grown on amorphous glass substrate were investigated by X-ray diffraction (XRD). Hall-effect measurement and a four-point probe were used to characterize the electrical properties. The hybrid structure was shown to be very effective at improving the electrical and the optical properties, decreasing the sheet resistance and the reflectance, and increasing the transmittance via refractive index (RI) engineering. The ZnO hybrid structure grown by MOCVD is very promising for opto-electronic devices as Photoconductive UV Detectors, anti-reflection coatings (ARC), and transparent conductive oxides (TCO).

Transparent conducting oxide (TCO) films are widely used for optoelectronic applications. Among TCO materials,zinc oxide (ZnO) has been studied extensively for its high optical transmission and electrical conduction. In this study, the effectsof O2 plasma pretreatment on the properties of Ga-doped ZnO films (GZO) on polyethylene naphthalate (PEN) substrate werestudied. The O2 plasma pretreatment process was used instead of conventional oxide buffer layers. The O2 plasma treatmentprocess has several merits compared with the oxide buffer layer treatment, especially on a mass production scale. In this process,an additional sputtering system for oxide composition is not needed and the plasma treatment process is easily adopted as anin-line process. GZO films were fabricated by RF magnetron sputtering process. To improve surface energy and adhesionbetween the PEN substrate and the GZO film, the O2 plasma pre-treatment process was used prior to GZO sputtering. As theRF power and the treatment time increased, the contact angle decreased and the RMS surface roughness increased significantly.It is believed that the surface energy and adhesive force of the polymer surfaces increased with the O2 plasma treatment andthat the crystallinity and grain size of the GZO films increased. When the RF power was 100W and the treatment time was120 sec in the O2 plasma pretreatment process, the resistivity of the GZO films on the PEN substrate was 1.05×10-3Ω-cm,which is an appropriate range for most optoelectronic applications.