Young Jei Oh

Cu ion ink for a flexible substrate and highly conductive patterning by intensive pulsed light sintering

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).

Enhanced Light Scattering and Trapping Effect of Ag Nanowire Mesh Electrode for High Efficient Flexible Organic Solar Cell

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%).

Preparation of PbTiO3 thin films using an alkoxide-alkanolamine sol-gel system

The stable range of PbTiO3 sol and the processing conditions of uniform thin films were investigated using a solution of titanium isopropoxide, three kinds of alkanolamines (monoethanolamine, diethanolamine, triethanolamine), lead acetate trihydrate and isopropanol. Depending on the sol state with various alkanolamine/alkoxide molar ratios, diethanolamine (DEA) was very effective in preparing uniform and dense oxide films through room-temperature reaction, owing to its superior stability during the hydrolysis and condensation reaction. Perovskite PbTiO3 thin films were obtained on oxidized silicon wafer above 550 °C and completely pure films were obtained at 650 °C using DEA as a complexing agent. The dielectric constant and loss tangent of these thin films fired at 650 °C for 30 min were found to be ∼240 and ∼0.01 at 1 kHz, respectively.

Roll-to-roll slot die production of 300 mm large area silver nanowire mesh films for flexible transparent electrodes

To develop flexible transparent electrodes, an ink fabricated with silver nanowires (AgNWs) was coated on a polyethylene terephthalate substrate using a roll-to-roll slot die machine. The AgNW used in the manufacturing of the transparent electrode is a highly transparent conductive material that is very close to commercialization due to its low sheet resistance, low heat treatment temperature, and high transmittance. An AgNW ink was optimized for the slot die process, which was prepared using the optimized formulation with AgNWs, solvent, and dispersant. As a result, high-quality transparent conductive films were successfully manufactured with 32–94 Ω sq−1 of sheet resistance, 1.3–3.2 of haze and 86.2–92% transmittance with a width of 300 mm. To verify the possibilities in optoelectronic applications, organic solar cells were fabricated with the AgNW mesh transparent electrode and showed a good performance of 7.65% efficiency, which was better than the result obtained using an indium tin oxide-based electrode.

Crystallographic and magnetic properties of CoxFe1−xCr2S4

The mixed series CoxFe1−xCr2S4 has been studied by x‐ray, Mossbauer spectroscopy, and superconducting quantum‐interference device (SQUID) magnetometry. The crystal structure is found to be a cubic spinel, and the lattice constant a0 decreases linearly with increasing cobalt concentration. Mossbauer spectra of CoxFe1−xCr2S4 have been taken at various temperatures ranging from 4.2 to 300 K. The iron ions are ferrous and occupy the tetrahedral sites. The Curie temperature increases linearly with cobalt concentration, suggesting that the superexchange interaction for the Co‐S‐Cr link is stronger than that for the Fe‐S‐Cr link. Magnetic hyperfine and quadrupole interactions in Co0.9Fe0.1Cr2S4 at 4.2 K have been studied, yielding the following results: Hhf=80.8 kOe, 1/2e2qQ(1+1/3η2)1/2=2.65 mm/s, θ=15°, φ=75°, and η=1.0. It is notable that, as the temperature decreases below the Curie temperature, quadrupole splitting increases with decreasing temperature, suggesting the presence of an electric field gradient a...

Influence of Al2O3 buffer layer on the crystalline structure and dielectric property of PbTiO3 thin film by sol-gel processing

Abstracts are not published in this journal

CO Gas Detection of Al-Doped ZnO Nanostructures with Various Shapes

Nanostructure of semiconductor type gas sensors that are high sensitivity, fast response time, inexpensive, and easily fabricated, is suggested. One-dimensional (1D) nanostructures, such as nanorods, and hollow spheres, are attracting particularly great interest because of their large specific surface area and their inherent physical properties. This study combined with ZnCl2 (6.95 g, Sigma-Aldrich), Al(NO3)39H2O (Junsei), NaOH, ethanol, and deionized water (DI) by hydrothermal synthesis to manufacture, spherical, hollow, hierarchical, and nanorod. The same Al-doped ZnO (AZO) were prepared by a colloidal template on a Si wafer to make a 3D igloo structure as well. Sensitivity to carbon monoxide at 50 ppm was tested at 250 °C the compare the sensing properties. Gas sensitivity of the hierarchical structure showed the highest sensitivity at 31.8, a figure 7 times that of the packed spherical sphere, whereas the igloo structure gave the fastest response speed of 32 s. The results of various shapes of the AZO nanostructures demonstrated high sensitivity and quick response time, which is useful in the detection of harmful gases in automobiles and the atmosphere.

Effects of additives on magnetic properties of sheet Sr‐Ba ferrite magnets

Sr0.75Ba0.25Fe12O19 hexagonal ferrite has attracted much attention due to its large (BH)MAX values and workability. We have prepared sheet magnets by the Dr. Blade method. To examine the effects of additives, such as SiO2, TiO2, Al2O3, and Cr2O3, on magnetic properties of sheet magnets, we used VSM magnetometer, x‐ray diffraction, and Mossbauer spectrometer. The crystal structure is found to be a magnetoplumbite of typical M‐type hexagonal ferrite, but the α‐Fe2O3 phase develops with increasing additives concentration. Using our refined computer program, we have analyzed the Mossbauer spectra in the temperature range from 13 to 800 K. The Mossbauer spectra indicate that the line intensity for the 12k site is reduced with increasing SiO2 concentration, which is different from the reports of Fe‐substituted Ba ferrite. This suggests that the developing α‐Fe2O3 phase is related to 12k sites. The isomer shifts show the charge states of Fe ions is ferric. When the additives concentrations increase, the Curie te...

Characterization of the p-type Sn1−xMnxO2 oxide semiconductor nanoparticles by Sol-Gel method

This paper reports the properties of p-type oxide semiconductor Sn1−xMnxO2 (MTO) nanoparticles with a low doping concentration of Mn (0 ≤ x ≤ 0.05) prepared with a sol-gel method. X-ray diffraction (XRD) results show that single-phase rutile MTO was obtained for x up to 0.03. The samples have particle average size of about 100 nm, which was confirmed with scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The compositional changes and electrical properties of the MTO nanoparticles were characterized by using x-ray photoelectron spectroscopy (XPS) and Hall effect measurements. Mn3+ cations are incorporated into the rutile SnO2 lattice. P-type conduction which is arisen from the substitution of Mn3+ to Sn4+ lattice was demonstrate by Hall data. These compositions have hole carrier concentrations in the range 2.26∼8.53 × 1016 cm−3 and exhibit Hall mobilities in the range 0.8∼4.1 cm2/Vs. The mobility of MTO decreases as the Mn content increases due to the doping effect. A transparent, ptype TFT device can be fabricated with this composition.

Preparation and Electrochemical Properties of Carbon Cryogel for Supercapacitor

Electrochemical properties of carbon cryogel electrode for the application of composite electrode materials mixed with metal oxide in supercapacitor have been studied. Carbon cryogels were synthesized by sol-gel polycondensation of resorcinol with formaldehyde, followed by a freeze drying, and then pyrolysis in an inert atmosphere. Physical properties of carbon cryogel were characterized by BET, X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that carbon cryogel is amorphous material. The electrochemical properties of carbon cryogel were measured by cyclic voltammetry as a function of concentration of liquid electrolyte, galvanostatic charge-discharge with different scan rates and electrochemical impedance measurements. The result of cyclic voltammetry indicated that the specific capacitance value of a carbon cryogel electrode was approximately 150.2 F/g (at 5 mV/s in 6 M KOH electrolyte).