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.

Fabrication and Characterization of the Barrier Film Having Excellent Moisture Barrier Characteristics Using Polysilazane.

Organic solar cell and OLED display devices are very sensitive to moisture, which leading to a fast degradation by the exposure to moisture and oxygen in the air. Therefore, in order to enhance the stability of the devices, a barrier film having WVTR (Water Vapor Transmission Rate) of 10-4 to 10-6 g/m²/day is required. In order to prepare the barrier film with excellent moisture blocking characteristics, perhydro polysilazane (PHPS) is used, which is developed to prepare an insulating film for semiconductors. Also a catalyst is added to lower the curing temperature to 100 °C or less. The result shows that the polysilazane is cured and converted to SiO2 under 100 °C in 30 min. WVTR of the polysilazane coated film is estimated to be 2.1×10-2 g/m²/day. In addition, when the inorganic layer such as SiO2 and Al2O3 is deposited on the planarization layer, the film shows excellent moisture blocking characteristics having WVTR to be 7.9×10-5 g/m²/day.

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.

Ultrasensitive FRET-based DNA sensor using PNA/DNA hybridization.

In the diagnosis of genetic diseases, rapid and highly sensitive DNA detection is crucial. Therefore, many strategies for detecting target DNA have been developed, including electrical, optical, and mechanical methods. Herein, a highly sensitive FRET based sensor was developed by using PNA (Peptide Nucleic Acid) probe and QD, in which red color QDs are hybridized with capture probes, reporter probes and target DNAs by EDC-NHS coupling. The hybridized probe with target DNA gives off fluorescent signal due to the energy transfer from QD to Cy5 dye in the reporter probe. Compared to the conventional DNA sensor using DNA probes, the DNA sensor using PNA probes shows higher FRET factor and efficiency due to the higher reactivity between PNA and target DNA. In addition, to elicit the effect of the distance between the donor and the acceptor, we have investigated two types of the reporter probes having Cy5 dyes attached at the different positions of the reporter probes. Results show that the shorter the distance between QDs and Cy5s, the stronger the signal intensity. Furthermore, based on the fluorescence microscopy images using microcapillary chips, the FRET signal is enhanced to be up to 276% times stronger than the signal obtained using the cuvette by the fluorescence spectrometer. These results suggest that the PNA probe system conjugated with QDs can be used as ultrasensitive DNA nanosensors.

A "turn-on" fluorescent microbead sensor for detecting nitric oxide.

Nitric oxide (NO) is a messenger molecule involved in numerous physical and pathological processes in biological systems. Therefore, the development of a highly sensitive material able to detect NO in vivo is a key step in treating cardiovascular and a number of types of cancer-related diseases, as well as neurological dysfunction. Here we describe the development of a fluorescent probe using microbeads to enhance the fluorescence signal. Microbeads are infused with the fluorophore, dansyl-piperazine (Ds-pip), and quenched when the fluorophore is coordinated with a rhodium (Rh)-complex, ie, Rh2(AcO(-))4(Ds-pip). In contrast, they are able to fluoresce when the transition-metal complex is replaced by NO. To confirm the "on/off" mechanism for detecting NO, we investigated the structural molecular properties using the Fritz Haber Institute ab initio molecular simulations (FHI-AIMS) package. According to the binding energy calculation, NO molecules bind more strongly and rapidly with the Rh-core of the Rh-complex than with Ds-pip. This suggests that NO can bond strongly with the Rh-core and replace Ds-pip, even though Ds-pip is already near the Rh-core. However, the recovery process takes longer than the quenching process because the recovery process needs to overcome the energy barrier for formation of the transition state complex, ie, NO-(AcO(-))4-(Ds-pip). Further, we confirm that the Rh-complex with the Ds-pip structure has too small an energy gap to give off visible light from the highest unoccupied molecular orbital/lowest unoccupied molecular orbital energy level.

Silver nanoparticles are assembled only on the two facets of the rod template.

Although the focus of nano-research appears to be shifting to the creation of the secondary structures using primary nanoparticle (NP) building blocks, very complex preparation routes to assemble NPs have been reported so far. In this work, for the first time, we demonstrate that silver NPs can be organized to assemble on the two facets of the 1-dimensional rod template via facile one-step process. This method could potentially be used to prepare assembly of diverse metal, semiconductor, or metal oxide NPs in the one dimensional material form.

Robust, functionalizable, nanometer-thick poly(acrylic acid) films spontaneously assembled on oxidized aluminum substrates: structures and chemical properties.

Immersion of oxidized aluminum substrates in ethanol solutions of poly(acrylic acid) (PAA), followed by extensive solvent immersion, results in tenaciously chemisorbed, nanometer scale, controllable thickness films for a wide range of solution concentrations and molecular weights. Atomic force microscope images reveal isolated polymer globules from adsorption in low-concentration solutions with crossover to conformal, highly uniform, nanometer-thickness films at higher concentrations, an indication that the chemisorbing chains start to overlap and trap underlying segments to form planar chemisorbed films only two or three chains in thickness. Quantitative IR reflection spectroscopy in combination with chemical derivitization on a standard set of 1.0(±0.2) nm thick films reveals a film structure with 5.5(±1) chemisorbed -CO(-)(2) groups/nm(2) and 6.3 unattached -CO(2)H groups/nm(2), with up to ∼3.6/nm(2) available for chemical derivitization, a comparable number to typical self-assembled monolayer coverages of ∼4-5 molecules/nm(2). Thermal treatment of the ∼1 nm chemisorbed films, at even extreme temperatures of ∼150 °C, results in almost no anhydride formation via adjacent -CO(2)H condensation, in strong contrast to bulk PAA, a clear indication that the films have a frozen glass structure with effectively no segment and side group mobility. Overall, these results demonstrate that these limiting thickness nanometer films provide a model surface for understanding the behavior of strongly bound polymer chains at substrates and show potential as a path to creating highly stable, chemically functionalized inorganic substrates with highly variable surface properties.