Mutsuyoshi Matsumoto

Micromolding in Capillaries for Calcination-Free Fabrication of Flexible Inorganic Phosphor Films Consisting of Rare-Earth-Ion-Doped Nanoparticles

We discuss the micromolding in capillaries technique for the direct fabrication of calcination-free rare earth ion-doped (RE) phosphor films consisting of RE nanoparticles on plastic sheets. We synthesized two types of RE nanoparticles consisting of Y2O3 matrix doped with Er and Yb ions. Green upconversion luminescence, red upconversion luminescence, and near-infrared fluorescence appeared from the RE nanoparticles under excitation of near-infrared light. Adjusting the channel width and depth of polydimethylsiloxane molds led to control of the density of nanoparticles in the patterned RE nanoparticle films. Adjusting concentration of the RE nanoparticle dispersion and size of the RE nanoparticles allowed for the control of the density of nanoparticles in the patterned RE nanoparticle films. The density of nanoparticles in the patterned RE films on plastic sheets increased with an increase in the number of injection and drying of the RE nanoparticle dispersion. These results demonstrate that this technique enables us to directly fabricate the patterned RE phosphor films on plastic sheets, leading to the fabrication of inorganic flexible devices with small fabrication steps and material consumptions.

Calcination-free micropatterning of rare-earth-ion-doped nanoparticle films on wettability-patterned surfaces of plastic sheets

We demonstrate a patterning technique of rare-earth-ion-doped (RE) nanoparticle films directly on wettability-patterned surfaces fabricated on plastic sheets in one step. Self-assembled monolayers consisting of silane-coupling agent with hydrophobic groups were fabricated on plastic sheets. UV-ozone treatments were performed through a metal mask to selectively remove the self-assembled monolayers in a patterned manner, resulting in the formation of wettability-patterned surfaces on plastic sheets. Using a water dispersion of Er(3+) and Yb(3+)-codoped Y2O3 nanoparticles at a diameter of 100 nm, RE-nanoparticle films were fabricated on the wettability-patterned surfaces by a dip-coating technique. By adjusting the concentration of RE-nanoparticle dispersion, withdrawal speed, and withdrawal angle, amount of RE-nanoparticles, we were able to control the structures of the RE-nanoparticle films. Fluorescence microscope observations demonstrate that visible upconversion luminescence and near-infrared fluorescence were emitted from the RE-nanoparticle films on the wettability-patterned surfaces. This technique allows for the fabrication of flexible emitting devices with long-operating life time with minimized material consumption and few fabrication steps, and for the application to sensors, emitting devices, and displays in electronics, photonics, and bionics in the future.

Soft liquid-phase adsorption for the fabrication of solution processable organic material films on wettability-patterned surfaces.

We discuss a soft liquid-phase adsorption (SLPA) technique for the fabrication of organic films on wettability-patterned templates by using methanol/hexane and toluene/water emulsions. The emulsions are stable for several hours at room temperature, and the diameters of the dispersed phase are estimated to be several micrometers using dynamic light scattering. The templates are fabricated by exposing self-assembled monolayers to an ultraviolet/ozone atmosphere through a shadow mask. Fluorescent dye and semiconductor polymer films are formed selectively on the hydrophilic region of the substrates and the hydrophobic region of the self-assembled monolayer, respectively. The thickness is significantly larger than those of the films fabricated by conventional film-forming techniques such as spin-coating and dip-coating, respectively. These patterned films serve as photoluminescent films. These results demonstrate that the SLPA technique allows for the fabrication of organic films on wettability-patterned templates using solution-processable materials. This technique will find application to the fabrication of electronic and photonic devices with small material consumption and few film-forming processes.

Electron donor and acceptor spatial distribution in structured bulk heterojunction photovoltaic devices induced by periodic photopolymerization.

Donor and acceptor spatial distributions were directly formed in a surface relief grating of structured bulk heterojunction (BHJ) photovoltaic devices by simple periodic photopolymerization. Enhanced photocurrents were observed in the structured BHJ photovoltaic devices and formation of the D/A spatial distribution was confirmed by Kelvin probe force microscopy. This technique enables the fabrication of structured BHJ photovoltaic devices with solution-processable organic semiconductors, and has tremendous potential for controlling D/A spatial distribution in organic optoelectronics devices.

Microcrystallization of a Solution-Processable Organic Semiconductor in Capillaries for High-Performance Ambipolar Field-Effect Transistors

We report on the use of microcrystallization in capillaries to fabricate patterned crystalline microstructures of the low-bandgap ambipolar quinoidal quaterthiophene derivative (QQT(CN)4) from a chloroform solution. Aligned needle-shaped QQT(CN)4 crystals were formed in thin film microstructures using either open- or closed- capillaries made of polydimethylsiloxane (PDMS). Their charge transport properties were evaluated in a bottom-gate top-contact transistor configuration. Hole and electron mobilities were found to be as high as 0.17 and 0.083 cm(2) V(-1) s(-1), respectively, approaching the values previously obtained in individual QQT(CN)4 single crystal microneedles. It was possible to control the size of the needle crystals and the microline arrays by adjusting the structure of the PDMS mold and the concentration of QQT(CN)4 solution. These results demonstrate that the microcrystallization in capillaries technique can be used to simultaneously pattern organic needle single crystals and control the microcrystallization processes. Such a simple and versatile method should be promising for the future development of high-performance organic electronic devices.

Calcination-free micromolding in capillaries for nanopatterning of inorganic upconversion luminescent layers on flexible plastic sheets.

We report calcination-free micromolding in capillaries for the nanopatterning of inorganic upconversion luminescent layers on flexible plastic sheets. We prepared Er(3+)- and Yb(3+)-codoped NaYF4 nanoparticles modified with a cationic polymer to improve dispersion stability of aqueous dispersion of the NaYF4 nanoparticles. We controlled the line width and density of nanoparticles in the NaYF4 nanoparticle films on flexible plastic sheets by adjusting the concentrations of the NaYF4 nanoparticle dispersion and the channel sizes of silicone stamps, resulting in the formation of nanopatterned NaYF4 nanoparticle films at the line width of the nanoparticle size (50 nm). Visible upconversion luminescence and near-infrared fluorescence appeared from the NaYF4 nanoparticle films excited with a near-infrared laser beam. These results demonstrate that calcination free micromolding in capillaries using aqueous dispersion of NaYF4 nanoparticles modified with a cationic polymer allows for the nanopatterning of inorganic upconversion luminescent layers on flexible plastic sheets.

Alternate spray-coating for the direct fabrication of hydroxyapatite films without crystal growth step in solution

We discuss an alternate spray-coating technique for the direct fabrication of hydroxyapatite films using metal masks, suction-type spray nozzles and two calcification solutions of calcium hydroxide and phosphoric acid aqueous solutions. Hydroxyapatite films were formed only on the hydrophobic surface of the substrates. Scanning electron microscopy and energy dispersive X-ray spectroscopy showed that the spray-coated films consisted of hydroxyapatite nanoparticles. The Ca/P ratio was estimated to be about 1.26. X-ray diffraction patterns of the spray-coated films almost coincided with those of the hydroxyapatite powders, showing that the spray-coated films consisted of hydroxyapatite nanoparticles. Dot arrays of hydroxyapatite films at a diameter of 100 μm were formed by tuning the concentrations of calcium hydroxide and phosphoric acid aqueous solutions. This technique allows for the direct fabrication of the hydroxyapatite films without crystal growth process in hydroxyapatite precursors, the scaffolds of crystal growth such as biocompatibility SiO2-CaO glasses, or electrophoresis processes. By using this technique, large-area ceramic films with biocompatibility will be micropatterned with minimized material consumption, short fabrication time, and reduced equipment investments.