Direct printing techniques that utilize nanoparticles to mitigate environmental pollution and reduce the processing time of the routing and formation of electrodes have received much attention lately. In particular, copper (Cu) nanoink using Cu nanoparticles offers high conductivity and can be prepared at low cost. However, it is difficult to produce homogeneous nanoparticles and ensure good dispersion within the ink. Moreover, Cu particles require a sintering process over an extended time at a high temperature due to high melting temperature of Cu. During this process, the nanoparticles oxidize quickly in air. To address these problems, the authors developed a Cu ion ink that is free of Cu particles or any other impurities. It consequently does not require separate dispersion stability. In addition, the developed ink is environmentally friendly and can be sintered even at low temperatures. The Cu ion ink was sintered on a flexible substrate using intense pulsed light (IPL), which facilitates large-area, high-speed calcination at room temperature and at atmospheric pressures. As the applied light energy increases, the Cu2O phase diminishes, leaving only the Cu phase. This is attributed to the influence of formic acid (HCOOH) on the Cu ion ink. Only the Cu phase was observed above 40 J cm(-2). The Cu-patterned film after sintering showed outstanding electrical resistivity in a range of 3.21-5.27 μΩ·cm at an IPL energy of 40-60 J cm(-2). A spiral-type micropattern with a line width of 160 μm on a PI substrate was formed without line bulges or coffee ring effects. The electrical resistivity was 5.27 μΩ·cm at an energy level of 40.6 J cm(-2).

It is of critical importance to improve toughness, strength, and wear-resistance together for the development of advanced structural materials. Herein, we report on the synthesis of unoxidized graphene/alumina composite materials having enhanced toughness, strength, and wear-resistance by a low-cost and environmentally benign pressure-less-sintering process. The wear resistance of the composites was increased by one order of magnitude even under high normal load condition (25 N) as a result of a tribological effect of graphene along with enhanced fracture toughness (KIC) and flexural strength (σf) of the composites by ~75% (5.60 MPa·m1/2) and ~25% (430 MPa), respectively, compared with those of pure Al2O3. Furthermore, we found that only a small fraction of ultra-thin graphene (0.25–0.5 vol%, platelet thickness of 2–5 nm) was enough to reinforce the composite. In contrast to unoxidized graphene, graphene oxide (G-O) and reduced graphene oxide (rG-O) showed little or less enhancement of fracture toughness due to the degraded mechanical strength of rG-O and the structural defects of the G-O composites.

Thin films with cobalt ferrite layers on thermally oxidized silicon wafers were fabricated by a sol-gel method. Magnetic and structural properties of the films were investigated with an x-ray diffractometer, a vibrating sample magnetometer and atomic force microscopy. The crystallization temperature for Co ferrite thin films was determined by using Mössbauer spectroscopy. Co ferrite films annealed at and above 450 °C have only a single phase spinel structure without any preferred crystallite orientation. Their rms surface roughness is less than 3 nm and the size of grains is about 30 nm for annealing temperatures greater than 650 °C. Films fired at and above 550 °C have moderate saturation magnetization and there is no significant difference of their magnetic properties for external fields applied parallel and perpendicular to their planes. The coercivity shows a strong dependence on the annealing temperature.

The electrical, optical, thermal, chemical, mechanical and tribological characteristics of a highly flexible transparent conductive electrode (HFTCE) coating based on reduced graphene oxide (rGO), carbon nanotubes (CNTs) and silver nanowires (AgNWs) were investigated under various conditions. The motivation was to develop a highly durable and flexible film for transparent conductive electrode applications. The overall characteristics of multilayers based on rGO, CNTs and AgNWs were found to be much better than those of the single-layer AgNW coating. The rGO and CNT layers served to protect the AgNW layer from damage due to bending and contact sliding motions. The contact pressure and bending stress were effectively distributed by the CNT layer deposited on top of the AgNW layer due to its spring-like behavior. In addition, the shear force from the friction force was reduced by the rGO top layer, which acted as a solid lubricant. Furthermore, the excellent performance of an HFTCE heater based on the rGO/CNT/AgNW coating was demonstrated by the results of a defrosting test. NPG Asia Materials (2017) 9, e438; doi:10.1038/am.2017.177; published online 13 October 2017 INTRODUCTIONIn recent decades, various transparent conductive films electrodes have been widely used in electronic devices such as solar cells, displays, memories and batteries. 1 In particular, indium tin oxide (ITO) has attracted considerable attention as a transparent conductive electrode because of its excellent optical and electrical properties. 2 However, indium, which is the main raw material used in ITO, has some disadvantages in terms of production and cost. Moreover, ITO application in flexible devices is limited by its brittleness. 3 To replace ITO in flexible devices, several types of conductive polymers, such as poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-butyric acid methyl ester have been suggested. 4,5 However, the electrical efficiency of these conductive polymers is much lower than that of ITO. Moreover, the mechanical properties of these conductive polymers are very weak despite their flexibility. Therefore, it is necessary to combine these conductive polymers with other electrodes to improve efficiency.Many studies using other types of conductive materials, such as graphene and carbon nanotubes (CNTs), have been conducted. [6][7][8][9][10][11][12] While carbon-based nanosheets and nanowires are known as materials with excellent mechanical and electrical properties, the sheet resistance of the coatings based on carbon is higher. Li et al. 6 demonstrated that the number of graphene layers deposited on the surface had a significant effect on their conductivity and transmittance. They found

Ag nanowire (NW) mesh is used as transparent conducting electrode for high efficient flexible organic solar cells (OSCs). The Ag NW mesh electrode facilitates light scattering and trapping, allowing enhancement of light absorption in the active layer. OSCs incorporating Ag NW mesh electrode exhibit maximum power conversion efficiency (PCE) of 4.47%, 25%, higher than that of OSCs with a conventional ITO electrode (3.63%).

Microstructure developments under fluorine plasma have been investigated in the Al2O3 ceramics containing artificial pores with controlled purity. The erosion behaviors by fluorine plasma consisted of a uniform erosion throughout the specimen surface and local erosions around the artificial pores and defects such as intrinsic irregular pores and damages formed during the grinding and polishing steps. The effects of the pores on the microstructure development were more distinct in the low purity Al2O3 specimen. The erosions around the pores, in the beginning, showed polygonal or flower-like microstructures in high or low purity Al2O3, respectively, indicating a weak grain boundary of glassy phase under the fluorine plasma. The extended plasma treatment resulted in loose structures around the pores in the low purity specimen, possibly producing contamination particles. In contrast to the polycrystalline Al2O3, single crystalline Al2O3 showed only uniform erosion. Although the microstructure developments were completely different depending on purity, porosity and polycrystallinity, etch depths did not appear so different, implying that the etch depths might not properly represent the plasma resistance of the materials.

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We have prepared oxides having various yttrium to aluminum ratios and exposed them to fluorine-based plasma. The etch rate of the aluminum oxide decreased abruptly with the addition of yttrium oxide and then slowly with further addition. The yttrium oxide had a more fluorinated surface than the aluminum oxide, indicating that the etch rate was not determined by the surface fluorination, contrary to the etching of Si-based materials. From the X-ray photoelectron spectroscopy (XPS) analysis of a multication YAlO 3 single crystal, a similar tendency was observed, showing a higher ratio of Y-F to Y-O bonding than the ratio of Al-F to Al-O. Angle resolved XPS and depth profiling analysis revealed the presence of a fluorinated layer of a few nanometer thick under a roughly 1 nm carboneous top layer. The etching behavior and surface chemical status of these oxides were discussed in terms of thermodynamic aspects of aluminum and yttrium fluoride.