Toshihiko Ooie

A novel approach to prepare zinc oxide films: excimer laser irradiation of sol–gel derived precursor films

Abstract Crystalline zinc oxide films with a c- axis orientation were prepared by a new approach using KrF excimer laser irradiation of sol–gel derived precursor films on glass substrates. The structural characteristics, optical and electrical properties of the laser-irradiated films were investigated and compared with those of heat-treated films. Laser irradiation gives two kinds of crystalline zinc oxide films; irradiation at low energy fluence produces low crystallinity with weak orientation, while irradiation at high energy fluence produces high crystallinity with strong orientation. The differences in crystallinity and orientation are explained in terms of the thermal effect caused by laser irradiation. Laser processing characteristically created oxygen vacancy in contrast to conventional heat-treatment, resulting in a decrease in electrical resistivity of the films. In addition, film irradiated at high energy fluence shows a band structure with indirect band gap, although the other prepared films and a typical ZnO crystal show a band structure with direct band gap.

Observation of sp3 bonding in tetrahedral amorphous carbon using visible Raman spectroscopy

Visible Raman spectroscopy excited at 532 nm was used to characterize the carbon bonding in tetrahedral amorphous carbon (ta-C) films. The vibrational modes of the sp3 bonding in ta-C films were revealed directly. An additional Raman band occurring below 1350 cm−1 was observed. It consisted of two features centered on ∼1270 and ∼1170 cm−1, which were associated with sp3 bond stretching. The observed sp3 related Raman spectrum approached the vibrational density of states of amorphous diamond.

Structural and bonding properties of carbon nitride films synthesized by low energy nitrogen-ion-beam-assisted pulsed laser deposition with different laser fluences

Carbon nitride films were deposited by pulsed Nd:yttrium–aluminum–garnet laser ablation of graphite with assistance of low energy nitrogen-ion-beam bombardment. The nitrogen to carbon (N/C) atomic ratio, surface morphology, bonding state, and microstructure of the deposited carbon nitride films were characterized by x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, micro-Raman spectroscopy, atomic force microscopy (AFM), and x-ray diffraction. The influence of laser fluence on the synthesis of carbon nitride films was investigated. The N/C atomic ratio of the carbon nitride films can reach the maximum at the highest laser fluence. XPS and FTIR analyses indicated that the bonding state between the carbon and nitrogen in the deposited films was significantly influenced by the laser fluence during deposition. The carbon–nitrogen bonding of C–N and C=N were observed in the films. In addition, α and β C3N4 phases were found to coexist in the carbon nitride films with relat...

A Novel Method for the Preparation of Green Photoluminescent Undoped Zinc Oxide Film Involving Excimer Laser Irradiation of a Sol-Gel-Derived Precursor

A green photoluminescent (PL) undoped zinc oxide film was successfully prepared by a novel method involving KrF excimer laser irradiation of a sol-gel-derived precursor. This method requires the appropriate energy fluence (Ef) of 100 mJ/cm2 of the laser, and has the advantage of practical production at a low substrate temperature of 473 K in air. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) observations showed that the green PL film has close-packed columnar crystals in an upper layer, where the green PL centers involving oxygen vacancies are presumed to be present.

Effect of temperature on carbon nitride films synthesized by ion-beam-assisted pulsed laser deposition

Carbon nitride thin films were deposited by pulsed laser deposition with nitrogen ion beam assistance at a substrate temperature varying from room temperature to 800 °C. The effect of the substrate temperature on the nitrogen content, surface morphology, structure, and electrical property of the carbon nitride films was investigated. The deposited films were characterized by atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and four-probe resistance. The nitrogen content of the deposited films reached its maximum value of 25% at a substrate temperature of 400 °C. AFM images revealed that an island structure occurred and developed on the surface of the films deposited at the high substrate temperature. FTIR and XPS spectra showed the existence of sp3C–N and sp2C=N bonds in the deposited films. The deposited carbon nitride films had an amorphous structure with two carbon nitride phases inclusions, which had a stoichiome...

Valence band electronic structure of carbon nitride from x-ray photoelectron spectroscopy

This article reviews the valence band (VB) electronic structure of carbon nitride and reports on results obtained from carbon nitride films prepared by pulsed laser deposition (PLD). In the present work, two series of carbon nitride films have been synthesized by nitrogen-ion-beam-assisted PLD and reactive PLD in nitrogen atmosphere, respectively. X-ray photoelectron spectroscopy (XPS) is applied to determine the VB electronic structures. XPS VB spectra reveal that the electronic structures of the prepared carbon nitride films depend on nitrogen supply manner. In the case of nitrogen-ion-beam-assisted deposition, four bands in the regions ∼0–6.2, ∼6.2–13.7, ∼13.7–20.8, and ∼20.8–30 eV are clearly observed in the VB electronic structure, which stem from C 2p electrons associated with π bonds and sp2N in a planar graphite structure, C 2p and N 2p electrons associated with σ bonds, a mixture of 2s and 2p electrons, and C 2s and N 2s electrons, respectively. For the films deposited by reactive PLD in a nitrog...

Simultaneous immunoassay analysis of plasma IL-6 and TNF-α on a microchip.

Sandwich enzyme-linked immunosorbant assay (ELISA) using a 96-well plate is frequently employed for clinical diagnosis, but is time-and sample-consuming. To overcome these drawbacks, we performed a sandwich ELISA on a microchip. The microchip was made of cyclic olefin copolymer with 4 straight microchannels. For the construction of the sandwich ELISA for interleukin-6 (IL-6) or tumor necrosis factor-α (TNF-α), we used a piezoelectric inkjet printing system for the deposition and fixation of the 1st anti-IL-6 antibody or 1st anti-TNF-α antibody on the surface of the each microchannel. After the infusion of 2 µl of sample to the microchannel and a 20 min incubation, 2 µl of biotinylated 2nd antibody for either antigen was infused and a 10 min incubation. Then 2 µl of avidin-horseradish peroxidase was infused; and after a 5 min incubation, the substrate for peroxidase was infused, and the luminescence intensity was measured. Calibration curves were obtained between the concentration and luminescence intensity over the range of 0 to 32 pg/ml (IL-6: R2 = 0.9994, TNF-α: R2 = 0.9977), and the detection limit for each protein was 0.28 pg/ml and 0.46 pg/ml, respectively. Blood IL-6 and TNF-α concentrations of 5 subjects estimated from the microchip data were compared with results obtained by the conventional method, good correlations were observed between the methods according to linear regression analysis (IL-6: R2 = 0.9954, TNF-α: R2 = 0.9928). The reproducibility of the presented assay for the determination of the blood IL-6 and TNF-α concentration was comparable to that obtained with the 96-well plate. Simultaneous detection of blood IL-6 and TNF-α was possible by the deposition and fixation of each 1st antibody on the surface of a separate microchannel. This assay enabled us to determine simultaneously blood IL-6 and TNF-α with accuracy, satisfactory sensitivity, time saving ability, and low consumption of sample and reagents, and will be applicable to clinic diagnosis.

Quantitative Analysis of Serum Procollagen Type I C-Terminal Propeptide by Immunoassay on Microchip

Background Sandwich enzyme-linked immunosorbent assay (ELISA) is one of the most frequently employed assays for clinical diagnosis, since this enables the investigator to identify specific protein biomarkers. However, the conventional assay using a 96-well microtitration plate is time- and sample-consuming, and therefore is not suitable for rapid diagnosis. To overcome these drawbacks, we performed a sandwich ELISA on a microchip. Methods and Findings The microchip was made of cyclic olefin copolymer with straight microchannels that were 300 µm wide and 100 µm deep. For the construction of a sandwich ELISA for procollagen type I C-peptide (PICP), a biomarker for bone formation, we used a piezoelectric inkjet printing system for the deposition and fixation of the 1st anti-PICP antibody on the surface of the microchannel. After the infusion of the mixture of 2.0 µl of peroxidase-labeled 2nd anti-PICP antibody and 0.4 µl of sample to the microchannel and a 30-min incubation, the substrate for peroxidase was infused into the microchannel; and the luminescence intensity of each spot of 1st antibody was measured by CCD camera. A linear relationship was observed between PICP concentration and luminescence intensity over the range of 0 to 600 ng/ml (r2 = 0.991), and the detection limit was 4.7 ng/ml. Blood PICP concentrations of 6 subjects estimated from microchip were compared with results obtained by the conventional method. Good correlation was observed between methods according to simple linear regression analysis (R2 = 0.9914). The within-day and between-days reproducibilities were 3.2–7.4 and 4.4–6.8%, respectively. This assay reduced the time for the antigen-antibody reaction to 1/6, and the consumption of samples and reagents to 1/50 compared with the conventional method. Conclusion This assay enabled us to determine serum PICP with accuracy, high sensitivity, time saving ability, and low consumption of sample and reagents, and thus will be applicable to clinic diagnosis.

Irradiation effect of low energy nitrogen-ion beam during pulsed laser deposition process on the structural and bonding properties of carbon–nitride thin films

Carbon–nitride thin films were deposited by pulsed laser ablation of graphite with assistance of low energy nitrogen-ion-beam irradiation. The nitrogen to carbon (N/C) atomic ratio, bonding state, microstructure, surface morphology, and electrical property of the deposited carbon–nitride films were characterized by x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, micro-Raman spectroscopy, x-ray diffraction (XRD), atomic force microscopy, and four-probe resistance. The irradiation effect of low energy nitrogen-ion beam on the synthesis of carbon–nitride films was investigated. The N/C atomic ratio of the carbon–nitride films reached the maximum at the ion energy of ∼200 eV. The energy of ∼200 eV was proposed to promote the desired sp3-hybridized carbon and the C3N4 phase. Electrical resistivity of the deposited films was also influenced by the low energy nitrogen-ion-beam irradiation. However, the low energy irradiation had little effect on the surface morphology of the films. XRD...

Measuring the length distribution of self-assembled lipid nanotubes by orientation control with a high-frequency alternating current electric field in aqueous solutions.

The present work addresses the length distribution of self-assembled lipid nanotubes (LNTs) by controlling the orientation of the LNTs using an alternating current (ac) electric field in aqueous solutions. The effect of the ac field on the orientation and rotation of individual LNTs was examined to evaluate the optimum orientation frequency by visualizing the individual LNTs in real time. By using the high-frequency ac field, we have successfully measured the length distribution for two different types of LNTs and have quantitatively analyzed the maximum occurrences of the length distribution as well as the extension of the longer length region.