Amane Mochizuki

SiO2 coating of silver nanoparticles by photoinduced chemical vapor deposition

Gas-phase silver nanoparticles were coated with silicon dioxide (SiO2) by photoinduced chemical vapor deposition (photo-CVD). Silver nanoparticles, produced by inert gas condensation, and a SiO2 precursor, tetraethylorthosilicate (TEOS), were exposed to vacuum ultraviolet (VUV) radiation at atmospheric pressure and varying temperatures. The VUV photons dissociate the TEOS precursor, initiating a chemical reaction that forms SiO2 coatings on the particle surfaces. Coating thicknesses were measured for a variety of operation parameters using tandem differential mobility analysis and transmission electron microscopy. The chemical composition of the particle coatings was analyzed using energy dispersive x-ray spectrometry and Fourier transform infrared spectroscopy. The highest purity films were produced at 300-400 degrees C with low flow rates of additional oxygen. The photo-CVD coating technique was shown to effectively coat nanoparticles and limit core particle agglomeration at concentrations up to 10(7) particles cm(-3).

Electroluminescence from printed stellate polyhedral oligomeric silsesquioxanes

Iridium-based stellate (star-shaped) polyhedral oligomeric silsesquioxane macromolecular dyes were synthesized and an inkjet printing process to deposit inks based on these materials was developed. Polymeric–macromolecular blended light emitting diodes based on these hybrid organic–inorganic dyes were studied. We find peak luminances of ∼10,000 cd/m2 with peak quantum efficiencies of ∼2.5% are possible with the printed layers. White light interferometry measurements suggest that large printed layer thicknesses and interface roughness play a crucial role in limiting device performance. A cumulative coffee-ring effect is considered to be the source of interface roughness.

Organic light emitting diode improves diabetic cutaneous wound healing in rats

A major complication for diabetic patients is chronic wounds due to impaired wound healing. It is well documented that visible red wavelengths can accelerate wound healing in diabetic animal models and patients. In vitro and in vivo diabetic models were used to investigate the effects of organic light emitting diode (OLED) irradiation on cellular function and cutaneous wound healing. Human dermal fibroblasts were cultured in hyperglycemic medium (glucose concentration 180 mM) and irradiated with an OLED (623 nm wavelength peak, range from 560 to 770 nm, power density 7 or 10 mW/cm2 at 0.2, 1, or 5 J/cm2). The OLED significantly increased total adenosine triphosphate concentration, metabolic activity, and cell proliferation compared with untreated controls in most parameters tested. For the in vivo experiment, OLED and laser (635 ± 5 nm wavelength) treatments (10 mW/cm2, 5 J/cm2 daily for a total of seven consecutive days) for cutaneous wound healing were compared using a genetic, diabetic rat model. Both treatments had significantly higher percentage of wound closure on day 6 postinjury and higher total histological scores on day 13 postinjury compared with control. No statistical difference was found between the two treatments. OLED irradiation significantly increased fibroblast growth factor‐2 expression at 36‐hour postinjury and enhanced macrophage activation during initial stages of wound healing. In conclusion, the OLED and laser had comparative effects on enhancing diabetic wound healing.

Self-written waveguide structure in photosensitive polyimide resin fabricated by exposure and thermosetting process

A new fabrication technique of self-written waveguide was developed by using a photosensitive polyimide (PSPI) resin. The PSPI resin enables us to fabricate a solidified cladding portion of the self-written waveguide only by a thermosetting process after writing of the waveguide core. In the PSPI resin, a self-focusing effect of the exposing laser light, induced by difference in refractive index between exposed and unexposed portions, was observed. The coupling loss between two multimode fibers, which were placed with 0.5-mm gap, was decreased to 0.7 dB by insertion of the PSPI all-solid self-written waveguide. This simple fabrication method of the self-written waveguide structure is applicable to a convenient alignment technique of optical components.

Propagation-mode-controlled fabrication of self-written waveguide in photosensitive polyimide for single-mode operation

We have developed a new fabrication method of single-mode self-written waveguide by controlling the propagation mode in an optical fiber. This method is very appropriate for repeatable fabrication of the single-mode self-written waveguide. Since a Gaussian-like near-field pattern is required for the fabrication of a tiny and uniform waveguide core, the propagation mode in a conventional optical communication fiber was controlled by coupling with an optical fiber having 3-/spl mu/m core, which shows a single-mode operation at visible wavelength region. Single-mode propagation at optical communication wavelength was confirmed for the fabricated self-written waveguide. The evaluated core diameter of the self-written waveguide was /spl sim/9.5 /spl mu/m.

Fabrication of self-written waveguide in photosensitive polyimide resin by controlling photochemical reaction of photosensitizer

We have investigated optical properties of photosensitive polyimide appropriating for long self-written waveguide fabrication. From systematic measurements of absorption properties, it was found that photochemical reaction of photosensitizer dissolved in the photosensitive polyimide resins relates to transparency after the exposure, which limits the length of the fabricated self-written waveguide. By controlling the photochemical reaction, in which the photosensitive polyimide resin has sufficient transparency during exposure, four times longer self-written waveguide core was fabricated.

Fabrication of low-loss optical waveguides using a novel photosensitive polyimide

Fabrication of optical waveguides by a simple patterning process using photosensitive polyimide (PSPI) is described. Light waveguide based on PSPI was fabricated by photolithographic processing without use of dry etching process. The PSPI varnish is comprised of polyamic acid (PAA) which was made from fluorinated diamine and fluorinated tetracarboxylic dianhydride, and photosensitizer. The PSPI has the following characteristics: glass transition temperature (Tg) of 330 °C, coefficient of thermal expansion of 40 ppm/K. Moreover the PSPI is colorless, and posses low absorption at 1 .3 and 1 .55im. The sidewalls and the surfaces ofthe fabricated waveguide are very smooth, which is essential for the low loss optical mode propagation and lower scattering of the mode due to the imperfections. Single and multimode buried ridge waveguides on quartz glass substrate were fabricated and tested. Optical propagation losses were measured by standard cut back method and found to be as low as 0.4 dB/cm @ 1.55 jim. This fabrication process would be expected to contribute to low cost production for high performance opto-electronic devices.

Bright Inkjet Printed Macromolecular Organic Light emitting Diodes on Flexible Substrates

We present results of printing solution-processable organic light emitting diodes (OLEDs) based on electrophosphorescent Ir(III) stellate polyhedral oligomeric silsesquioxane (POSS) macromolecules. The macromolecules are doped into a polymer-based ink containing a hole transporting polymer, poly(9-vinylcarbazole) (PVK) and an electron transporting material, 2-4-biphenylyl-5-4-tertbutyl-phenyl-1,3,4-oxadiazole (PBD), and the resulting ink is printed on a layer of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) spin-coated on indium tin oxide (ITO). An exciton-blocking layer consisting of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) is thermally evaporated onto the printed ink layers, followed by a LiF/Al cathode. While the photoluminescence (PL) spectrum of printed ink on glass indicates a significant contribution from the PVK:PBD exciplex, electroluminescence measurements (EL) suggest a much smaller effect of these states, which implies significant charge trapping at dopant molecular sites. Our latest experiments with devices printed on PEDOT:PSS/ITO/glass indicate that the devices exhibit high luminances (∼ 13,000 cd/m 2 at 70 mA/cm 2 ) and a fairly consistent quantum efficiency (∼ 2.5%) across a wide range of luminances. The corresponding figures for spin-coated devices are expectedly higher, with efficiencies ∼ 4.5% at similar levels of brightness. We use white light interferometry as a non-contact technique to quantify surface roughness and thickness of printed layers. Our current results thus indicate that inkjet printing of macromolecular phosphor doped polymer inks is suitable for fabrication of OLEDs with high brightness, in spite of the low glass transition temperature of some of the species. Our initial work with these devices on flexible ITO-coated plastic substrates shows devices with moderately high luminance values (∼ 2,500 cd/m 2 at 35 mA/cm 2 ). Our more recent devices show higher brightnesses (∼ 9, 600 cd/m 2 ). We are working on the development of inkjet printing materials and processes for pure macromolecular OLEDs that are not performance and reliability limited by the presence of the PVK:PBD matrix with low glass transition temperatures. This requires the development of macromolecules that subsume all the functions of the host matrix and have high enough T g to be usable in high concentrations needed. In conjunction with the inkjet printing technology demonstrated in this work, this has the potential to yield low-cost manufacturing of these devices.

New waveguide technique using photosensitive polyimide for integrated optics

New fabrication methods of optical waveguide and light-induced self-written waveguide were developed by using photosensitive polyimide resin. This resin will enable to reduce cost of optical devices and modules by a simpler fabrication process.

17.3: Control of the Refractive Index and the Birefringence of Side‐Chain Liquid Crystalline Copolymers

The refractive index(no) and the birefringence(Δn) of side-chain liquid-crystalline copolymers (LCPs) are investigated. Introduction of the second fragment to a cyanobiphenyl derivative unit conducted LCPs to a wide range of optical properties. This technology is expected to be usable on a variety of optical devices.