Ga and Ti co-doped In2O3 films for flexible amorphous transparent conducting oxides

We designed Ga and Ti co-doped In₂O₃ (IGTO) films to use as a flexible and transparent amorphous conducting oxide electrode in thin film heaters (TFHs) and flexible touch screen panels (FTSPs) for automobiles. The properties of the IGTO electrodes deposited on cyclic olefin copolymer (COP) at room temperature were investigated as a function of the O₂/(Ar + O₂) flow ratio, to confirm the best sputtering condition for transparent and flexible electrode. Depending on the oxygen flow ratio, the IGTO/COP electrodes showed sheet resistance of (39.3 – 1.57) × 10⁴ Ohm/sq, an average transmittance of (84.90 – 87.12) % at visible wavelength area, and a surface roughness of (0.95 – 3.23) nm. In addition, IGTO/COP samples exhibited good mechanical flexibility with critical bending radius of 3 mm, which is enough to be used as FTSPs. From the previously mentioned results, we found the amorphous IGTO/COP to be a promising flexible and transparent electrode for curved TFHs and FTSPs. The flexible IGTO/COP TFHs demonstrated a saturated temperature of 78.6 °C when applied with low operating direct current (DC) of 8 V, due to its low sheet resistance. In addition, the IGTO/COP FTSPs showed very stable touch sensitivity, even at a bent state. We found that the optimized IGTO/COP is a promising flexible and transparent electrode for next-generation automobiles.     

Electroless deposition of transparent conducting and 〈0 0 0 1〉-oriented ZnO films from aqueous solutions

Electroless ZnO deposition on a glass substrate from dissolved oxygen-free aqueous solutions containing Zn(NO₃)₂ and dimethylamineborane (DMAB) was examined to yield ZnO films applicable to a transparent conducting oxide (TCO). Concentration of Zn(NO₃)₂ was optimized in terms of crystal growth orientation and surface morphology using XRD and AFM, and that ranging from 0.065 to 0.075 M was found to provide well 〈0 0 0 1〉-oriented dense ZnO films. The polycrystalline ZnO films deposited with Zn(NO₃)₂ concentration of 0.07 M had a preferred 〈0 0 0 1〉 growth orientation and exhibited high visible transparency. Top-view and cross-sectional FE-SEM images revealed that hexagonal columnar ZnO grains with 200 nm in diameter and 290 nm in length grew almost vertically from a glass substrate. Heat treatment at 723 K under a reductive atmosphere was performed to increase the intrinsic carrier concentration in the ZnO film, and Hall effect measurements revealed low electrical resistivity of 4.7 × 10⁻³ Ω cm.     

Enhanced response of the photoactive gas sensor on formaldehyde using porous SnO2@TiO2 heterostructure driven by gas-flow thermal evaporation and atomic layer deposition

Nanoporous SnO₂@TiO₂ heterostructure was synthesized by a facile two-step dry process, modified thermal evaporation followed by atomic layer deposition (ALD). The introduction of inert gas, Ar, with a pressure of 0.2 Torr during thermal evaporation of SnO, enabled the formation of the nanoporous 3D structure by inducing the collision and loss of kinetic energy during deposition. A photocatalytic material, TiO₂, was grown on the porous structure of SnO₂ to detect target gas, formaldehyde, under UV irradiation selectively. Microstructural and elemental analysis with a transmission electron microscope and X-ray photoelectron spectroscopy confirmed the porous structure of SnO₂ induced by our evaporation process as well as the conformal coating of TiO₂ on the porous structure. The sensing capabilities of a photoactive sensor on the formaldehyde were assessed in terms of the film porosity, irradiated UV power, and thickness of photoactive materials at room temperature. As a result, the SnO₂@TiO₂ heterostructure, with an optimum thickness of TiO₂ exhibited low detection limit, down to 0.1 ppm, good linearity to the concentration of formaldehyde in the range of 0.1–10 ppm, and high response of 15% in the HCHO 0.1 ppm. This core-shell porous structure developed by modified thermal evaporation combined with ALD paved the way for 3D architectures to explore various applications, such as biosensors, photocatalysts, and optoelectronic devices.