[en] ZnO is an attractive material for use in various technological products such as phosphors, gas sensors, and transparent conductors. Recently, aluminum-doped zinc oxide has received attention as a potential replacement for indium tin oxide, which is one of the transparent conductive oxides used in flat panel displays, organic light-emitting diodes, and organic solar cells. In this study, the characteristics of ZnO films deposited on polycarbonate (PC) substrates by atomic layer deposition (ALD) are investigated for various process temperatures. The growth mechanism of these films was investigated at low process temperatures using x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). XRD and XPS were used to determine the preferred orientation and chemical composition of the films, respectively. Furthermore, the difference of the deposition mechanisms on an amorphous organic material, i.e., PC substrate and an inorganic material such as silicon was discussed from the viewpoint of the diffusion and deposition of precursors. The structure of the films was also investigated by chemical analysis in order to determine the effect of growth temperature on the films deposited by ALD

[en] This work reports the atomic layer deposition (ALD) of tin oxide-phosphate films using tetrakis(dimethylamino)tin and trimethyl phosphate as precursors. The growth rates were 1.23–1.84 Å/cycle depending upon the deposition temperature and precursor combination. The ionic conductivity of the ALD tin oxide-phosphate films was evaluated by cross-plane impedance measurements in the temperature range of 50–300 °C under atmospheric air, with the highest conductivity measured as 1.92 × 10"−"5 S cm"−"1 at 300 °C. Furthermore, high-resolution x-ray photoelectron spectroscopy exhibited two O1s peaks that were classified as two subpeaks of hydroxyl ions and oxygen ions, revealing that the quantity of hydroxyl ions in the ALD tin oxide-phosphate films influences their ionic conductivity

[en] Single-walled carbon nanotubes (SWCNTs) are promising materials as active channels for flexible transistors owing to their excellent electrical and mechanical properties. However, flexible SWCNT transistors have never been realized on paper substrates, which are widely used, inexpensive, and recyclable. In this study, we fabricated SWCNT thin-film transistors on photo paper substrates. The devices exhibited a high on/off current ratio of more than 10⁶ and a field-effect mobility of approximately 3 cm²/V·s. The proof-of-concept demonstration indicates that SWCNT transistors on flexible paper substrates could be applied as low-cost and recyclable flexible electronics

[en] We evaluated the performance of solid oxide fuel cells (SOFCs) with a 50 nm thin silver (Ag) cathode surface treated with cerium oxide (CeO_x) by atomic layer deposition (ALD). The performances of bare and ALD-treated Ag cathodes were evaluated on gadolinia-doped ceria (GDC) electrolyte supporting cells with a platinum (Pt) anode over 300 °C–450 °C. Our work confirms that ALD CeO_x treatment enhances cathodic performance and thermal stability of the Ag cathode. The performance difference between cells using a Ag cathode optimally treated with an ALD CeO_x surface and a reference Pt cathode is about 50% at 450 °C in terms of fuel cell power output in our experiment. The bare Ag cathode completely agglomerated into islands during fuel cell operation at 450 °C, while the ALD CeO_x treatment effectively protects the porosity of the cathode. We also discuss the long-term stability of ALD CeO_x-treated Ag cathodes related to the microstructure of the layers. (paper)

[en] The fabrication of nanostructures having diameters of sub-5 nm is very a important issue for bottom-up nanofabrication of nanoscale devices. In this work, we report a highly controllable method to create sub-5 nm nano-trenches and nanowires by combining area-selective atomic layer deposition (ALD) with single-walled carbon nanotubes (SWNTs) as templates. Alumina nano-trenches having a depth of 2.6 ∼ 3.0 nm and SiO₂ nano-trenches having a depth of 1.9 ∼ 2.2 nm fully guided by the SWNTs have been formed on SiO₂/Si substrate. Through infilling ZnO material by ALD in alumina nano-trenches, well-defined ZnO nanowires having a thickness of 3.1 ∼ 3.3 nm have been fabricated. In order to improve the electrical properties of ZnO nanowires, as-fabricated ZnO nanowires by ALD were annealed at 350 °C in air for 60 min. As a result, we successfully demonstrated that as-synthesized ZnO nanowire using a specific template can be made for various high-density resistive components in the nanoelectronics industry. (paper)

[en] In this study, we successfully fabricated an yttria-stabilized zirconia (YSZ) aerogel using the sol-gel method and CO₂ supercritical drying. We confirmed the successful thermal insulation function as a thermal barrier coating (TBC) on a high-temperature gas turbine surface. In order to evaluate the performance of the YSZ aerogel, the thermal conductivity and temperature profile were measured in addition to microstructure observation by scanning electron microscopy. The thermal conductivity of the YSZ aerogel was 0.212 W/m·K at 1000 °C, which is significantly lower than the reference values of YSZ materials. The low heat conduction is attributed to heat insulation by the fine pores and low heat conduction through the nanopore spaces in the aerogel structure. The heat insulation of the YSZ aerogel as the TBC was evaluated on a gas turbine blade material by monitoring surface temperature profiles on a heater at 300–700 °C. The heat-blocking performance of the YSZ aerogel coating was superior to that of a conventional YSZ TBC (by 30–50%). By comparison with a numerical calculation, the thermal conductivity of the YSZ aerogel coating was estimated to be 0.05 W/m·K, which is significantly lower (30–40 times) than that of the YSZ TBC used for commercial gas turbines. The porous structure of the aerogel was well preserved even after the high-temperature test confirming the good thermal stability. This study demonstrated that the YSZ aerogel is promising as a gas turbine TBC material.

[en] We compared the ionic properties of yttria-stabilized zirconia (YSZ) thin films prepared by atomic layer deposition (ALD) using various oxidants including water, oxygen, and ozone. Cross-plane conductivity measurements were performed at low temperature (50 °C) and high temperature (450 °C) using AC impedance spectroscopy. As a result, we have confirmed that the conductivity of ALD YSZ films below 300 °C is greater by several orders of magnitude compared to the nano-scale YSZ thin films synthesized by other conventional techniques. Among the ALD YSZ samples, ALD YSZ fabricated using water showed the highest conductivity while ALD YSZ fabricated using ozone showed the lowest. We have analyzed this result in relation with grain morphology characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM), and the chemical binding states measured by X-ray photoelectron spectroscopy (XPS). - Highlights: • YSZ is prepared by atomic layer deposition (ALD) with H_2O, O_2, and O_3 as oxidants. • Grain size of ALD YSZ membranes deposited using H_2O is the smallest. • Conductivity of ALD YSZ made with H_2O shows the highest value below 300 °C. • Conductivity trends coincide with the hydroxyl group content measured by XPS

[en] Highlights: • Ag cathode surface-coated with nano-YSZ is prepared by sputtering. • Ag-YSZ cathode outperforms Ag and Pt in terms of fuel cell performance. • GDC pellet cells with Ag-YSZ achieves over 100 mW/cm² at 450 °C. • YSZ surface-coating helps enhancement of electrochemical surface kinetics. Herein we propose silver surface-coated with nano-scale yttria-stabilized zirconia (YSZ) as a high-performance cathode for use in low-temperature solid oxide fuel cells (LT-SOFCs). YSZ was coated on the Ag cathode surface by sputtering of Y/Zr alloy films followed by thermal annealing for oxidation of YSZ. An electrolyte-support type SOFC was fabricated on 350-μm-thick gadolinium-doped ceria (GDC) pellets. The yttrium concentration and sputtering time for obtaining the YSZ coating layer was varied to optimize the cathode composition. It was determined that the GDC SOFCs with optimized Ag-YSZ cathodes significantly outperform cells with bare silver or platinum cathodes, which are considered to be the best-performing catalysts at low temperatures. The peak power density obtained using cells with Ag-YSZ cathodes was as high as ∼100 mW/cm² at 450 °C, 3–4 times greater than the performance of cells with Ag or Pt cathodes. Electrochemical impedance spectroscopy was performed during fuel cell testing to compare polarization and charge transport performances of the Ag-YSZ cathodes. The long-term stability of the Ag-YSZ cathode was evaluated by monitoring the change in cathode morphology compared to the bare Ag and Pt cathodes.

[en] To quantify the effect of high voltage on the electrochemical properties of high-potential spinel ordered-LiNi_0.5Mn_1.5O₄, it was intentionally exposed to 5.3 V for 100 h that can ensure the decomposition of electrolyte. After this treatment, the bulk structure did not change, but electrochemical properties of the sample were severely degraded; polarization became large and capacity loss was substantial. Polarization was caused by formation of a thick insulating passivation layer on the surface of the sample that was measured by impedance spectroscopy. The capacity loss can be partially caused by incomplete phase transformation during discharging as a result of loss of electrical contact due to the presence of the thick passivation layer on the surface of particles. This indicates that the phase transformation depends on the applied current. The other cause for the capacity loss can be from the inactiveness of transition metals in the surface that was measured by XPS. Thick passivation layer on the surface can have inactive transition metals leading to permanent capacity fading. Hence, to control the electrode stability in high voltage spinel LiNi_0.5Mn_1.5O₄, a bare LNMO sample coated with Al₂O₃ by Atomic Layer Deposition (ALD) were prepared, then exposed to 5.3 V for 100 h. After this surface treatment, the Al₂O₃-coated sample showed much better electrochemical performance than the bare sample. During the exposure, the bare sample underwent intensive surface reactions with very large generated current density and large charge-transfer resistance. In contrast, the coated sample experienced much weaker surface reactions with low charge-transfer resistance even though the applied potential, 5.3 V was much higher than the stable upper voltage limit (∼4.5 V) of conventional electrolyte. The coating effectively protects the surface of the material from surface reactions such as oxidation of the electrolyte; therefore Al₂O₃-coated LNMO shows reasonable electrochemical properties after exposing at 5.3 V for 100 h. This finding demonstrates that detrimental effects of the exposure at high potential on the electrochemical properties strongly depends on surface characteristics. This understanding can be used to stabilize high-voltage positive electrode materials.

[en] The effects of A-site non-stoichiometry and crystallinity on the proton conductivity of anhydrous proton conducting yttria-doped barium zirconate (BYZ) thin film were investigated. The membranes were fabricated by atomic layer deposition (ALD) as it allows tailoring and varying the concentration of barium. Electrochemical impedance spectroscopy was conducted to investigate the ionic conductivity according to the stoichiometry and crystallinity of the ALD BYZ thin films. - Highlights: • Atomic layer deposition (ALD) of yttrium barium zirconate thin films. • Controlled ALD process for various cation concentrations. • Proton conducting ceramic electrolyte. • Controlling the degree of crystallinity of yttrium doped barium zirconate ALD thin films. • Electrochemical impedance spectroscopy for proton conductivity characterization