Fluorine-doped tin oxide (FTO) has been used as a representative transparent conductive oxide (TCO) in various optoelectronic applications, including light emitting diodes, solar cells, photo-detectors, and electrochromic devices. The FTO plays an important role in providing electron transfer between active layers and external circuits while maintaining high transmittance in the devices. Herein, we report the effects of substrate rotation speed on the electrical and optical properties of FTO films during ultrasonic spray pyrolysis deposition (USPD). The substrate rotation speeds were adjusted to 2, 6, 10, and 14 rpm. As the substrate rotation speed increased from 2 to 14 rpm, the FTO films exhibited different film morphologies, including crystallite size, surface roughness, crystal texture, and film thickness. This FTO film engineering can be attributed to the variable nucleation and growth behaviors of FTO crystallites according to substrate rotation speeds during USPD. Among the FTO films with different substrate rotation speeds, the FTO film fabricated at 6 rpm showed the best optimized TCO characteristics when considering both electrical (sheet resistance of 13.73 Ω/□) and optical (average transmittance of 86.76 % at 400~700 nm) properties with a figure of merit (0.018 Ω-1).

Copper oxide thin films are deposited using an ultrasonic-assisted spray pyrolysis deposition (SPD) system. To investigate the effect of substrate temperature and incorporation of a chelating agent on the growth of copper oxide thin films, the structural and optical properites of the copper oxide thin films are analyzed by X-ray diffraction (XRD), field-emssion scanning electron microscopy (FE-SEM), and UV-Vis spectrophotometry. At a temperature of less than 350 ℃, threedimensional structures consisting of cube-shaped Cu2O are formed, while spherical small particles of the CuO phase are formed at a temperature higher than 400 ℃ due to a Volmer-Weber growth mode on the silicon substrate. As a chelating agent was added to the source solutions, two-dimensional Cu2O thin films are preferentially deposited at a temperature less than 300 ℃, and the CuO thin film is formed even at a temperature less than 350 ℃. Therefore the structure and crystalline phase of the copper oxide is shown to be controllable.

Li-incorporated ZnO thin films were deposited by using ultrasonic-assisted spray pyrolysis deposition (SPD) system. To investigate the effect of Li-incorporation on the performance of ZnO thin films, the structural, electrical, and optical properites of the ZnO thin films were analyzed by means of X-ray diffraction (XRD), field-emssion scanning electron microscopy (FE-SEM), Hall effect measurement, and UV-Vis spectrophotometry with variation of the Li concentraion in the ZnO sources. Without incorporation of Li element, the ZnO surface showed large spiral domains. As the Li content increases, the size of spiral domains decreased gradually, and finally formed mixed small grain and one-dimensional nanorod-like structures on the surface. This morphological evolution was explained based on an anti-surfactant effect of Li atoms on the ZnO growth surface. In addition, the Li-incorporation changed the optical and electrical properties of the ZnO thin films by modifying the crystalline defect structures by doping effects.

We investigated a Leidenfrost effect in the growth of ZnO nanostructures on silicon substrates by ultrasonic-assisted spray pyrolysis deposition(SPD). Structural and optical properties of the ZnO nanostructures grown by varying the growth parameters, such as substrate temperature, source concentration, and suction rate of the mist in the chambers, were investigated using field-emission scanning electron microscopy, X-ray diffraction, and photoluminescence spectrum analysis. Structural investigations of the ZnO nanostructures showed abnormal evolution of the morphologies with variation of the substrate temperatures. The shape of the ZnO nanostructures transformed from nanoplate, nanorod, nanopencil, and nanoprism shapes with increasing of the substrate temperature from 250 to 450 °C; these shapes were significantly different from those seen for the conventional growth mechanisms in SPD. The observed growth behavior showed that a Leidenfrost effect dominantly affected the growth mechanism of the ZnO nanostructures.

Fluorine-doped tin oxide (FTO) coated NiCrAl alloy foam is fabricated using ultrasonic spray pyrolysis deposition (USPD). To confirm the influence of the FTO layer on the NiCrAl alloy foam, we investigated the structural, chemical, and morphological properties and chemical resistance by using USPD to adjust the FTO coating time (12, 18, and 24 min). As a result, when an FTO layer was coated for 24 min on NiCrAl alloy foam, it was found to have an enhanced chemical resistance compared to those of the other samples. This improvement in the chemical resistance of using USPD NiAlCr alloy foam can be the result of the existence of an FTO layer, which can act as a protection layer between the NiAlCr alloy foam and the electrolyte and also the result of the increased thickness of the FTO layer, which enhances the diffusion length of the metal ion.