Gas Sensing Properties of SnO2-Pd Nanoparticles Thick Film by Applying In Situ Synthesis-Loading Method.

In this study, SnO2-Pd nanoparticles(NPs) were made with an in situ synthesis-loading method. The in situ method is to simultaneously load a catalytic element during the procedure to synthesize SnO2 NPs. SnO2-Pd NPs were synthesized by using the in situ method and were heat-treated at 300 °C. As a result, tetragonal structured SnO2-Pd NPs, having an ultrafine size of less than 10 nm and a uniformly distributed Pd catalyst in the SnO2 lattice, were well made and a gas sensitive thick film with a thickness of c.a. 40 µm was well fabricated by using the NPs. Gas sensing characterization for CH4 gas indicated that the gas sensitivity, R3500/R1000, of the thick film consistent with SnO2-Pd NPs synthesized with the in situ synthesis-loading method, followed by heat-treatment at 500 °C, was enhanced to 0.59. Therefore, the in situ synthesis-loading method is available for synthesis of SnO2-Pd NPs for gas sensitive thick film.

Effect of Polyvinylpolypyrrolidone Surfactant on Characteristics of Iron-Oxide Nanoparticles Synthesized by Using Recycled Waste Permanent Magnets.

In this study, iron oxide nanoparticles (FeOx NPs) were synthesized by using Fe solution recycled from NdFeB permanent magnet scrap. Furthermore, the effect of polyvinylpolypyrrolidone (PVP) as a surfactant on the characteristics of the FeOx NPs was investigated. Firstly, Fe solution was prepared by using 10% H2SO4 solution and Na2SO4 salt. In addition, three reducing agent solutions were prepared by dissolving PVP in 0.5 M NH4OH solution in distilled (D.I.) water with concentrations of 0 wt%, 1 wt%, and 2 wt%, respectively. Each reducing agent solution was added dropwise into the Fe solution to precipitate three precursors of FeOx NPs, and they were heat-treated at 400 °C to prepare three FeOx NPs samples, P0, P1, and P2. In X-ray diffractometer (XRD) analysis, diffraction peaks of P0 sample are consistent with the Fe3O4 with (311) preferred orientation. The XRD peak shifted from Fe3O4 to Fe2O3 structure as PVP concentration increased, and the crystal structure of P2 sample was transformed to Fe2O3 with (104) preferred orientation. Brunauer, Emmett, and Teller (BET) specific surface area increased in proportional to PVP concentration. HRTEM observation also supported the tendency; the particle size of the P0 sample was less than 40 nm, and particle size decreased as PVP concentration increased, leading to the particle size of the P2 sample being less than 20 nm in width. In addition, particle morphology started to be transformed from particle to rod shape as PVP concentration increased and, in the P2 sample, all the morphology of particles was transformed to a rod shape. Magnetic properties analysis revealed that the P0 sample exhibited the highest value of magnetic moment, 65.6 emu/g, and the magnetic moment was lowered in the P1 sample, and the P2 sample exhibited the lowest value of magnetic moment, 2.4 emu/g.

Characterization of Nickel Oxide Nanoparticles Synthesized under Low Temperature.

In this study, ultrafine nickel oxide nanoparticles (NiO NPs) were well synthesized using a simple wet chemical method under low temperature, 300 °C. An Ni(OH)2 precursor was well precipitated by dropping NH4OH into an Ni(Ac)2 solution. TG-DTA showed that the weight of the precipitate decreases until 300 °C; therefore, the precursor was heat-treated at 300 °C. X-ray diffraction (XRD) patterns indicated that hexagonal-structured NiO NPs with (200) preferred orientation was synthesized. In addition, BET specific surface area (SSA) and HRTEM analyses revealed that spherical NiO NPs were formed with SSA and particle size of 60.14 m2/g and ca. 5-15 nm by using the low temperature method. FT-IR spectra of the NiO NPs showed only a sharp vibrating absorption peak at around 550 cm-1 owing to the Ni-O bond. Additionally, in UV-vis absorption spectra, the wavelength for absorption edge and energy band gap of the ultrafine NiO NPs was 290 nm and 3.44 eV.

ITO nanoparticles reused from ITO scraps and their applications to sputtering target for transparent conductive electrode layer.

In this study, ITO nanoparticles (ITO-NPs) were reused from ITO target scraps to synthesize low cost ITO-NPs and to apply to make sputtering target for transparent conductive electrodes (TCEs). By controlling heat-treatment temperature as 980 °C, we achieved reused ITO-NPs having Brunauer, Emmett and Teller specific surface area (BET SSA) and average particle size 8.05 m2/g and 103.8 nm, respectively. The BET SSA decreases along with increasing heat-treatment temperature. The ITO-NPs were grown as round mound shape, and highly crystallized to (222) preferred orientations. Also, applying the reused ITO-NPs, we achieved an ITO target of which density was 99.6%. Using the ITO target, we achieved high quality TCE layer of which sheet resistance and optical transmittance at 550 nm were 29.5 Ω/sq. and 82.3%. Thus, it was confirmed that the reused ITO-NPs was feasible to sputtering target for TCEs layer.

Ultra-thin and smooth transparent electrode for flexible and leakage-free organic light-emitting diodes.

A smooth, ultra-flexible, and transparent electrode was developed from silver nanowires (AgNWs) embedded in a colorless polyimide (cPI) by utilizing an inverted film-processing method. The resulting AgNW-cPI composite electrode had a transparency of >80%, a low sheet resistance of 8 Ω/□, and ultra-smooth surfaces comparable to glass. Leveraging the robust mechanical properties and flexibility of cPI, the thickness of the composite film was reduced to less than 10 µm, which is conducive to extreme flexibility. This film exhibited mechanical durability, for both outward and inward bending tests, up to a bending radius of 30 µm, while maintaining its electrical performance under cyclic bending (bending radius: 500 µm) for 100,000 iterations. Phosphorescent, blue organic light-emitting diodes (OLEDs) were fabricated using these composites as bottom electrodes (anodes). Hole-injection was poor, because AgNWs were largely buried beneath the composite's surface. Thus, we used a simple plasma treatment to remove the thin cPI layer overlaying the nanowires without introducing other conductive materials. As a result, we were able to finely control the flexible OLEDs' electroluminescent properties using the enlarged conductive pathways. The fabricated flexible devices showed only slight performance reductions of <3% even after repeated foldings with a 30 µm bending radius.

Enhancement of Characteristics of a Touch Sensor by Controlling the Multi-Layer Architecture of a Low-Cost Metal Mesh Pattern.

In this study, the characteristics of a metal mesh touch sensor were enhanced by optimizing the multi-layer architecture of the metal mesh pattern. Low-cost metal such as an aluminum (Al) layer was mainly applied to the architectures for practical applications in touch screen panel (TSP) industries. As well, molybdenum (Mo) was added to the architectures in order to minimize the drawbacks of Al. Three types of Mo/Al, Al/Mo and Mo/Al/Mo layers were fabricated by DC sputtering. The thickness of the Al and Mo layer was optimized at 150 and 30 nm, respectively. Low sheet resistance below 0.27 Ω/square was achieved with good adhesion on a glass substrate. Especially, in the case of architectures in which the Al layer was covered with an Mo layer, thermal stability and corrosion resistance was enhanced. The change in resistance of the Mo/Al/Mo architecture was less than 0.056 even after heat-treatment at 260 °C. By using the optimized layer architecture, the mesh pattern with a 4 µm line width showed good optical transmittance (86.7%) and reflectivity (13.1%) at 550 nm, respectively. Also, a touch sensor fabricated by using the Mo/Al/Mo mesh pattern operated well indicating that the mesh pattern is feasible in a TSP application.

Enhancement of Characteristics of Transparent Conductive Electrode on Flexible Substrate by Combination of Solution-Based Oxide and Metallic Layers.

This study investigates solution-processed transparent conductors with hybrid structure consisting of silver nanowires (AgNWs) and indium-tin-oxide nanoparticles (ITO-NPs) layers fabricated on polymeric flexible polyethylene terephthalate (PET) substrate. The transparent conductors had stacked structures of AgNWs/ITO-NPs on 125-µm-thick PET and ITO-NPs/AgNWs/ITO-NPs on 125-µm-thick PET, 188-µm-thick PET, or 700-µm-thick glass substrate, respectively. Successful integrations were possible on the substrates without any deformation or distortion. Sheet resistance of the triple-layered transparent conductor samples exhibits low values ranging from 22.41 Ω/square to 22.99 Ω/squarer. Also, their optical transmittance exhibits high values ranging from 83.78 to 87.29% at 550 nm. The triple-layered transparent conductor showed a good thermal stability in terms of sheet resistance and optical transmittance against the high-temperature environment up to 250 °C. All the double and triple-layered transparent conductors fabricated on PET and glass substrates are so stable against the accelerated thermal aging from 110 °C to 130 °C, that ΔR/R0 and ΔT(550)/T0(550) values exhibit less than 0.068 and 0.049, respectively. Furthermore, the layers are so flexible that ΔR/R0 of the layers on PET substrates is lower than 0.1 even at 4.0-mm bending. Especially, triple-layered transparent conductor on 125-µm-thick PET substrates exhibits ΔR/R0 value of 0.042 even at 4.0 mm bending. Thus, it can be concluded that the hybrid structures have the advantage of both thermal stability and flexibility for electrical and optical properties of transparent conductive electrode; which makes them highly applicable in flexible electronics.

Solution-processed silver nanowire/indium-tin-oxide nanoparticle hybrid transparent conductors with high thermal stability.

In this study, solution-processed hybrid structure transparent conductors consisting of silver nanowires (AgNWs) and indium-tin-oxide nanoparticle (ITO-NP) layers are investigated. Fabricated transparent conductors had stacked structures of ITO-NP/AgNW and ITO-NP/AgNW/ITO-NP, and a successful integration was possible on glass substrates. Compared to a single-layered ITO-NP film which has a sheet resistance value of 1.31 k Ω/⟂, a remarkable enhancement in sheet resistance was achieved from the hybrid structures, showing sheet resistance values of 44.74 Ω/⟂ and 28.07 Ω/⟂ for ITO-NP/AgNW and ITO-NP/AgNW/ITO-NP structures, respectively. In addition, the ITO-NP/AgNW/ITO-NP triple-layered transparent conductor showed greatly enhanced thermal stability in terms of sheet resistance and transmittance against a high-temperature environment up to 300 degrees C. Based on these results, it can be suggested that the hybrid structure has advantages of enhancing both electrical properties of ITO-NP layer and thermal stability of AgNW layer, and we believe the hybrid structure transparent conductors can be a suitable option for applications which require high electrical conductivity, transmittance, and thermal stability.

Characteristics of Indium Tin Oxide (ITO) Nanoparticles Recovered by Lift-off Method from TFT-LCD Panel Scraps.

In this study, indium-tin-oxide (ITO) nanoparticles were simply recovered from the thin film transistor-liquid crystal display (TFT-LCD) panel scraps by means of lift-off method. This can be done by dissolving color filter (CF) layer which is located between ITO layer and glass substrate. In this way the ITO layer was easily lifted off the glass substrate of the panel scrap without panel crushing. Over 90% of the ITO on the TFT-LCD panel was recovered by using this method. After separating, the ITO was obtained as particle form and their characteristics were investigated. The recovered product appeared as aggregates of particles less than 100 nm in size. The weight ratio of In/Sn is very close to 91/9. XRD analysis showed that the ITO nanoparticles have well crystallized structures with (222) preferred orientation even after recovery. The method described in this paper could be applied to the industrial recovery business for large size LCD scraps from TV easily without crushing the glass substrate.

Characterization of reliability of printed indium tin oxide thin films.

Recently, decreasing the amount of indium (In) element in the indium tin oxide (ITO) used for transparent conductive oxide (TCO) thin film has become necessary for cost reduction. One possible approach to this problem is using printed ITO thin film instead of sputtered. Previous studies showed potential for printed ITO thin films as the TCO layer. However, nothing has been reported on the reliability of printed ITO thin films. Therefore, in this study, the reliability of printed ITO thin films was characterized. ITO nanoparticle ink was fabricated and printed onto a glass substrate followed by heating at 400 degrees C. After measurement of the initial values of sheet resistance and optical transmittance of the printed ITO thin films, their reliabilities were characterized with an isothermal-isohumidity test for 500 hours at 85 degrees C and 85% RH, a thermal shock test for 1,000 cycles between 125 degrees C and -40 degrees C, and a high temperature storage test for 500 hours at 125 degrees C. The same properties were investigated after the tests. Printed ITO thin films showed stable properties despite extremely thermal and humid conditions. Sheet resistances of the printed ITO thin films changed slightly from 435 omega/square to 735 omega/square 507 omega/square and 442 omega/square after the tests, respectively. Optical transmittances of the printed ITO thin films were slightly changed from 84.74% to 81.86%, 88.03% and 88.26% after the tests, respectively. These test results suggest the stability of printed ITO thin film despite extreme environments.

Microwave annealing of indium tin oxide nanoparticle ink patterned by ink-jet printing.

Indium tin oxide (ITO) is one of the most widely used transparent conducting oxides because of its two chief properties, electrical conductivity and optical transparency, as well as the ease with which it can be deposited as a thin film. In this study, we fabricated the ITO nanoparticles, and dispersed them in an organic mixture of liquid to make a solution for printing. The solution was ink-jet printed on a glass, and we employed microwave heating technology to make the ITO coated layer conductive and transparent. Microwave technology uses electromagnetic waves that pass through material and cause its molecules to oscillate, generating heat. It generates heat within the material and heats the entire volume at about the same rate. The ITO layers could be successfully annealed by the microwave irradiation, which is resulted in the sheet resistance of 365 ohm/sq and the transmittance of 84% within only 15 min of heating.

Application of rapid milling technology for fabrication of SiC nanoparticles.

SiC nanoparticles were successfully fabricated by a high energy ball milling method, so that can be used in the printed electronics to make SiC thin film patterns. Here we utilized the waste of Si sludge for making the SiC nanoparticles. In order to achieve uniform thin film from the nanoparticle ink, fine sized SiC nanoparticles less than 100 nm has to be uniformly dispersed. In this study, we employed the ultra apex milling (UAM) system for particle comminution and dispersion. We investigated the effects of milling parameters, e.g., size of ZrO2 bead and milling time. The size of the SiC particles reached about 103 nm after 4 hours of UAM, when the ZrO2 beads of 50 microm were used. Then SiC ink was formulated with organic solvents and a dispersing agent. A specially designed pattern was printed by an ink-jet printer for evaluating the feasibility of the SiC nanoparticle inks.

Synthesis of Ag nanowires for the fabrication of transparent conductive electrode.

Recently, advances in nano-materials research have opened the door for various transparent conductive materials, which include CNTs, graphene, Ag and Cu nanowires, and printable metal grids. Among them, Ag nanowires are particularly interesting to synthesize because bulk Ag exhibits the highest electrical conductivity among all metals. We tried to synthesize the Ag nanowires with a small diameter and long length, resulting in large aspect ratios. For the synthesis of the Ag nanowires, effects of various experimental parameters, i.e., the reaction time for synthesis, molar ratio of Ag source to surfactant, and molar weight of the surfactant were investigated with the physical shape of synthesized products. The Ag nanowire suspensions were formulated with the synthesized Ag nanowires, and a bar coating method with a Meyer rod was used to fabricate the transparent and conductive film on a glass substrate. For the thinnest wet coating, the transparent conductive layer of 90.6% transmittance at 550 nm of light wavelength and 66 ohm/sq sheet resistance could be obtained, while 13 ohm/sq was achieved at the transmittance of 76%.

Fabrication of SiC nanoparticles by physical milling for ink-jet printing.

Here we tried to show the possibility of mechanical milling method for fabrication of SiC nanoparticles and ink-jet printing method to make SiC patterns for use as several applications, e.g., micro hotplates. Planetary milling was employed to fabricate the nano-scale SiC particles from coarse powders. After 100 hours of milling, the size of the SiC particles decreased to about 100 nm, which was sufficient for the formulation of ink for ink-jet printing. The SiC particles were dispersed in an ink system consisted of ethylene glycol and ethanol with a small amount of additives. The ink with SiC nanoparticles could be successfully printed on an alumina substrate by the ink-jet printing method.

Fabrication and ink-jet patterning of copper nanoparticles with improved dispersion stability.

Copper (Cu) nanoparticles as the metal nanoparticles in the conductive ink were synthesized using electrochemical reaction. This method is characterized as the synthesis process without any metal salts and the post-treatment of washing and drying. It means that it does not need to consider about oxidized and agglomerated metal nanoparticles during the extra treatments. The Cu nanoparticles were synthesized in the various conditions of electrolyte to investigate the mechanism of the synthesis reaction of Cu nanoparticles. And also, the synthesized Cu nanoparticles were controlled the dispersion stability with the addition of dispersion agent such as PVP and Dextran. Finally, it was achieved the ink-jet printed Cu patterns using the synthesized Cu nanoparticles, and examined the morphology of the patterns.

Growth factors for silver nanoplates formed in a simple solvothermal process.

We synthesized both big and ultra-small silver nanoplates through a simple solvothermal process in a common autoclave. Using this approach, we achieved the reduction of silver nitrate in DMF or ethanol in the presence of PVP as a capping agent. The reduction capacity of PVP was also investigated. Growth factors such as the concentration of silver precursor, quantity of capping agent, reaction time, and temperature have been shown to play important roles in the formation of different sizes and shapes of silver nanoplates. The big plates, over 100 nm in edge length, were found mainly in the shape of a connected triangular. Single triangle plates, truncated triangular plates, and hexangular plates were also found under different reaction conditions. The ultra-small silver nanoplates, 20-100 nm in edge length, were successfully extracted from the solution under different centrifugation conditions. The UV-vis spectrum exhibited intense in-plane dipole absorption peaks varying from 470-630 nm, as reflected by the gradual color change of the solution from orange to red, and finally to blue.

The synthesis and characterization of metal nanoparticles using a modified electrolysis method for conductive ink in ink-jet printing technology.

In the ink-jet patterning process, conductive ink composed of metal nanoparticles and solutions, is an important factor for improving properties of printed patterns and processes. In this study, metal (Cu) nanoparticles in conductive ink were synthesized using a modified electrolysis method that extracted to metal nanoparticles from bulk metal plates. The Cu nanoparticles were prepared with a narrow size distribution. The dispersion stability and oxidation properties in conductive inks were also studied. Cu nanoparticles were homogeneous and had a diameter of 15 approximately 20 nm. By addition of PVP, the dispersion and oxidation stability of the metal nanoparticles, which were not oxidized after 2 month, were improved.