The Relationship Between Water Transmission Rate and Defects on the Film Based on the Defect Analysis Using Fluorescent Calcein Probe.

The most critical issue on flexible electronics such as organic solar cell, OLED, and flexible displays, is the protection of core active materials from the degradation by water and oxygen. The water vapor transmission rate (WVTR), the main characteristics of barrier films, is closely related to defect density in inorganic layers constructed in the film. In this study, a calcein fluorescent probe is used to examine the relationship between the water vapor transmission rate (WVTR) and the defect density of the film coated the inorganic oxide layer. By using the fluorescence characteristics of calcein dye molecules, the calcein can be used for the evaluation of water vapor transmission rate. The result shows that the defect density is linearly increasing with the water vapor transmission rate of barrier films. Furthermore, it is shown that the defect density is inversely proportional to the thickness of the inorganic layer of Al2O3. Based on these results, it is suggested that the defect density measurement of the inorganic layer can predict the water vapor transmission rate of the barrier film.

Phosphine Electrochemical Sensor Using Gold-Deposited Polytetrafluoroethylene Membrane.

Phosphine gas is a toxic and flammable gas, which are useful dopant in the semiconducting industry. OSAH (Occupational Safety and Health Administration) regulates the threshold limit value as 0.3 ppm. To detect phosphine gas, an electrochemical sensor cell using gold as a working electrode is available. In this paper, we prepared Au thin film electrode on porous PTFE (polytetrafluoroethylene) membrane by using d.c. sputtering machine. Au thin film deposited on PTFE membrane for 300 s showed the thickness about 220 nm and electrical resistance between 5 and 10 ohm. We adopted this Au thin film as a working electrode and reference electrode. The sensitivity of the electrochemical cell is about 3000 nA/ppm for phosphine gas. Using Cottrell equation and COMSOL program, we simulated the diffusion coefficient of phosphine gas within the electrochemical cell, which showed the value of 1.21×10-7 m²/s.

Control of Flexibility, Pore Structure and Hydrophobicity of Tetraethylorthosilicate/Methyltriethoxysilane Aerogels by Hybridization.

The flexibility, pore structures and hydrophobicity could be controlled by changing TEOS/MTEOS ratio. A methyl functional group of MTEOS causes the difficulty of hydrolysis and condensation reactions, so that strong basic catalyst needs to be added for the gelation of MTEOS. Therefore, increasing of MTEOS ratio forms larger pore sizes and large primary particles with about one micrometer. MTEOS-based aerogels show the lowest specific area due to macropores with more than one thousand nanometers, although they are very flexible to elongate two times as long as their original sample length. For TEOS/MTEOS hybrid aerogels with 0.4-0.6 of TEOS ratio, they have the large specific surface area and pore volume, a little flexibility and hydrophobicity due to the remaining alkyl functional groups. This research presents the possibility of controlling flexibility, pore structures, hydrophobicity through hybridization of alkoxide and silane. It suggests a way of overcoming weaknesses of silica aerogels like brittleness and hydrophilicity.

Synthesis of One-Dimensional Pillar Arrays by Electrohydrodynamic Jet Printing for Glucose Sensor.

One-dimensional (1-D) Ag arrays were formed by electrohydrodynamic jet-printing (EHD) of polyvinylpyrrolidone (PVP, 1,300 k, Aldrich) solution ink. The 1-D Ag arrays were formed on slide glass by controlling the viscosity and printing conditions such as the tip to the substrate distance, the applied voltage, the flow rate of ink and the velocity. The printed pillars were dried at 80 °C to get rid of the solvent and sintered at 400 °C for 30 min. We found that the arrays of Ag pillars can be fabricated by using the EHD printing method. We could control the diameter of the pillars in the range of 100­200 µm and the length rage between 300 and 700 µm. In order to produce a better performance of glucose sensor, we infiltrated a glucose oxidase as a glucose detector into the Ag pillars previously coated with the mixed solution of multi-walled carbon nanotube (MWCNT, Iljin), Nafion and Pt nanoparticles. In addition, the Ag array electrode with glucose oxidase was used as a working electrode for glucose detection via the three-electrode electrochemical method.

Manipulation of TiO2 Nanotubes in a Transparent Dielectrophoretic Device.

A DEP device with a transparent oxide thin film electrode was fabricated by a photolithography process and sputtering deposition with indium tin oxide (ITO). In order to form a fine ITO electrode pattern, we manipulated the negative slope using a photoresist by controlling the intensity of the ultra-violet radiation and the exposure time. In this study, the motions of a 1 microm polystyrene sphere and TiO2 nanotube were observed as a function of the applied voltage and the frequency. The findings confirm that TiO2 nanotubes can be manipulated by a p-DEP force and that they can be effectively aligned under conditions of 10 V(p-p) at 750 Hz.

Alignment of One-Dimensional SnO2 Lines by Electrohydrodynamic Jet Printing.

One-dimensional (1-D) SnO2 line as a representative semiconducting oxide were formed by electro- hydrodynamic jet-printing (EHD) of tin chloride pentahydrate and polyvinylpyrrolidone (PVP, 1,200 k, Aldrich) solution ink. The 1-D polymer lines including Sn precursors were created by controlling the viscosity, that is, polymer/tin precursor ratio, and adjusting printing conditions such as tip to substrate distance, applying voltage, flow rate of ink and velocity. The printed lines were dried at 200 degrees C to get rid of solvent and finally heat-treated at 600 degrees C to burn out PVP and form tin oxide line. We found out that the linearity and shape of the aligned 1-D SnO2 could be controlled by adjusting various parameters such as the viscosity of a precursor solution, the ratio of Sn to PVP polymer in the solution, the shape of a cone, the size of a droplet, the applied voltages, the working distance, the flow rate on the glass slides and the Si wafers with a SiPO2 layer, respectively. It is found out that the heat-treatment for the removal of polymers should be tailored to produce continuous 1-D SnO2 lines due to the drastic volume reduction (>90%) of the aligned fibers in the annealing process. The electrical properties of the 1-D SnO2 aligned on the Si wafers with Au electrode patterns were evaluated.

Low Temperature Synthesis of Fluorine-Doped Tin Oxide Transparent Conducting Thin Film by Spray Pyrolysis Deposition.

Transparent conducting oxide (TCO) is widely used for the application of flat panel display like liquid crystal displays and plasma display panel. It is also applied in the field of touch panel, solar cell electrode, low-emissivity glass, defrost window, and anti-static material. Fluorine-doped tin oxide (FTO) thin films were fabricated by spray pyrolysis of ethanol-added FTO precursor solutions. FTO thin film by spray pyrolysis is very much investigated and normally formed at high temperature, about 500 degrees C. However, these days, flexible electronics draw many attentions in the field of IT industry and the research for flexible transparent conducting thin film is also required. In the industrial field, indium-tin oxide (ITO) film on polymer substrate is widely used for touch panel and displays. In this study, we investigated the possibility of FTO thin film formation at relatively low temperature of 250 degrees C. We found out that the control of volume of input precursor and exhaust gases could make it possible to form FTO thin film with a relatively low electrical resistance, less than 100 Ohm/sq and high optical transmittance about 88%.

Nanostructure Developments of TiO2 Nanocrystals and Aerogels and Their Dye-Sensitized Solar Cell Application.

We synthesized TiO2 nanoparticles (TPs) as a reference via hydrothermal method and also TiO2 aerogels (TAs) via CO2 supercritical drying method. We investigated crystal phase transformation behavior of TPs and TAs with temperature. As-prepared TPs are anatase and rutile phase transformation from anatase starts at 600 °C and was complete at 700 °C. However, TAs are amorphous phase until 300 °C and the crystallization to anatase occurs at 400 °C, and remains anantase phase until 700 °C. At the results of nitrogen adsorption and desorption analyses, TPs with specific surface area of 209 m2/g at 100 °C showed the decrease of the specific surface area and pore volume with increasing temperature and 95% of decrease at 700 °C. TAs showed higher specific surface area, 498 m2/g at 100 °C, and the decreasing trend according to temperature is similar with those of TPs. We prepared three types of photoelectrodes, TPs, TAs, and TATPs (1:1 TAs and TPs composite photoelectrode). After results of DSC photocurrent conversion efficiency measurements of the three type cells, we found that TATPs showed the improved cell efficiency by 1% point, compared with a reference TPs below 15 micrometer thickness. In conclusion, the introduction of nanoporous TAs can improve the photocurrent conversion efficiency due to their high specific surface area for high dye adsorption without degrading of electron transfer.

A low temperature Co-fired ceramic-based dielectrophoretic device for manipulating micro and nanostructure materials.

A dielectophoretic (DEP) device fabricated by a conventional low temperature co-fired ceramic (LTCC) process, for manipulating micro and nanostructure materials, such as spherical polystyrene microspheres, titanium dioxide (TiO2) nanotubes, and silver (Ag) nanowires, is described. To generate a non-uniform electric field, a castellated electrode configuration was applied to the LTCC-based DEP device using a screen printing method. The actual motions of the micro and nanostructure materials under both a positive and a negative DEP force were observed in detail and the findings compared with numerical simulation data for the electric field distribution. The performance of the LTCC-based DEP device for separating and trapping was evaluated and potential applications are discussed.

Synthesis and characterisation of polygonal indium tin oxide nanocrystals.

Polygon ITO (Sn-doped In2O3) nanocrystals were synthesised via electrospinning, and their morphology, structural properties, and chemical composition were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). To determine the optimum conditions for the fabrication of polygon ITO nanocrystals, calcination temperature after the electrospinning process was controlled at 500 degrees C, 600 degrees C, 700 degrees C, and 800 degrees C, and the amount of PVP polymer was controlled at 4 wt%, 7 wt%, and 10 wt%. For comparison purposes, single In2O3 nanocrystals were also synthesised via electrospinning and calcination. The results show that ITO nanocrystals fabricated at a calcination temperature of 800 degrees C and with 10 wt% of PVP polymer exhibit clear polygon structure with single-crystallinity, which may be explained in terms of the effect of Sn doping in the In2O3 matrix and the oriented aggregation and Oswald ripening growth during the fusion process of ITO nanocrystals.

Fabrication of electrospun SiC fibers web/phenol resin composites for the application to high thermal conducting substrate.

Polycabosilane (PCS) could be spun to form fiber web by electrospinning PCS solution in 30% dimethylformide (DMF)/toluene solvent at 25 kV. The electrospun web is stabilized at 200 degrees C for 1 hour to connect fibers by softening PCS webs and pyrolysed to synthesize silicon carbide (SiC) webs at 1800 degrees C. The pyrolysis at 1800 degrees C increased the SiC crystal size to 45 nm from 3 nm at 1300 degrees C. However, the pyrolysis at 1800 degrees C forms pores on the surface of SiC fibers due to oxygen evaporation generated during thermals curing. SiC/phenol composite webs could be fabricated by infiltration of phenol resin and hot pressing. The thermal conductivity measurement indicates that higher SiC fibers filler contents increase the thermal conductivity up to 1.9 W/mK for 40% fraction of filler contents from 0.5 W/mK for 20% fraction of filler.

Enhanced performance of TiO2 nanoparticle and aerogel composite electrode for dye sensitized solar cell.

To evaluate the effects of specific surface area to the photocurrent conversion efficiency of dye-sensitized solar cell (DSC), we adopted TiO2 aerogel (TA)/nanoparticle (TP) composite as a photoelectrode. We prepared three types of photoelectrodes, TPs, TAs, and TATPs (1:1 TAs and TPs composite photoelectrode). The performance of TATP composite electrode was compared with that of TP and TAs. TATPs showed the improved cell efficiency, more than 0.5%, compared with a reference TPs below 15 micrometer thickness. Although the introduction of TAs increases the specific surface area for the dye adsorption, DSC composed of only TAs does not show the best efficiency result due to the crack generation. In conclusion, to produce the best photocurrent conversion efficiency, the high specific surface area of TiO2 photoelectrode for high dye adsorption should be balanced with proper control of the good electron transfer path.

Nanosurface-confined anisotropic growth and magnetism of ellipsoidal alpha-Fe nanogranules.

We have investigated the nanosurface-confined anisotropic growth of ordered-ellipsoidal Fe nanogranules when an Fe plume was deposited at a slanting angle onto an anodized aluminum oxide (AAO) film. Layer-by-layer growth was also investigated. This growth is driven by two critical factors: (1) a new rhombic AAO cell and (2) the slanting deposition of the Fe plume. During slanting deposition, the rhombic AAO cell induces strong restrictions in the nucleation site, growth direction, and granular size; therefore, the degree of freedom during growth is restricted. The magnetic dipoles of the ordered Fe nanogranules are placed along the long axis of the ellipsoid at an angle of 180 degrees (antiparallel) due to the demagnetizing field, shape anisotropy, and magnetic dipole-to-dipole interactions.