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Powder-based Cu3VS4 photoelectrode with 1.5–1.6 eV of a band gap that was responsive to whole range of visible light was fabricated by a particle transfer method, aiming at enhancement of the photocathodic performance. The particle-transferred Cu3VS4 photoelectrode with a Au-contacting layer (Cu3VS4/Au) showed much higher photocathodic performance for water reduction to produce H2 under simulated sunlight irradiation (AM-1.5 G) than previously reported Cu3VS4/FTO prepared by a conventional drop-casting method. This drastic enhancement is due to the good contact between photocatalyst particles and the Au-contacting layer of the substrate electrode. Loading of a Pt cocatalyst was effective for further enhancement of the photocathodic performance of the Cu3VS4/Au photoelectrode. Pt(1 nm)-loaded Cu3VS4/Au gave about 4 mA cm−2 of the cathodic photocurrent at −0.41 V vs NHE at pH7 that was four times higher than that without a Pt cocatalyst under simulated sunlight irradiation (AM-1.5 G). When Cu3VS4 particles with a small particle size were prepared by a flux method, better durability was obtained compared with a solid-state reaction. Efficient photoelectrodes based on a powdered metal sulfide utilizing whole range of visible light have successfully been developed by a particle transfer method, loading of a Pt cocatalyst, and a flux method on photoelectrochemical performance.

In this study, we investigated the effect of potassium fluoride post-deposition treatment (KF-PDT) on Cu(In 1- x Ga x )Se 2 (CIGS) thin films and solar cells fabricated onto sodalime glass (SLG) substrates. Secondary Ion Mass Spectrometery (SIMS) analysis showed that the K increased in the entire CIGS layer after KF-PDT, however Na seemed no change because of a large amount of K and Na diffused from SLG substrates. X-ray photoelectron spectroscopy (XPS) analysis revealed that the KF-PDT depleted Cu, whereas increased K and Ga at the near surface CIGS layer, before the rinsing process. Removal of native oxides from KF-treated CIGS thin film was observed based on rinsing solutions. Ammonia aqueous solution removed Ga compounds more efficiently from KF-treated CIGS thin film than that of distilled water. Time-resolved photoluminescence (TRPL) revealed that the carrier lifetime and PL intensity greatly increased after KF-PDT, resulting in the reduction of photo-generated carrier recombination. The V oc loss ( E g / q - V oc ) decreased from 0.52 to around 0.44 V for KF-treated CIGS solar cells with band gap (E g ) of 1.06–1.23 eV. Electron beam-induced current (EBIC) analysis indicated that the effective carrier collection of the CIGS solar cells widened toward the Mo back-contact side after KF-PDT. This phenomenon could be attributed to the increase in carrier lifetime. C-V measurements suggested that KF-PDT not only increased hole concentration but also passivated bulk defects.

We investigate on narrow bandgap CIGSe solar cells for tandem application in a spectral splitting devices. Numerical simulations using SCAPS are performed to optimize the Ga content throughout the absorber layer, depending on the illumination condition (AM 1.5 and tandem conditions using two different splitting filters; 620 nm and 880 nm). The simulations show a strong dependence of the efficiency on the minimum bandgap of the absorber, but not on the depth of the narrow bandgap region. Narrow bandgap CIGSe solar cells are experimentally realized and electrically characterized. A similar trend as what was deduced from the simulation is observed on the experiments when the solar cells are characterized in the tandem conditions. For the 880 nm splitting filter, an efficiency of 5.5% is experimentally obtained with a minimum bandgap of 1.05 eV. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A new silicon MEMS process has been proposed utilizing anodic bonding of an extremely thin silicon film (60 m) on a glass substrate, followed by photo lithographically defining micro spring structures on the silicon film and dry etching the silicon film using an inductively coupled plasma (ICP) dry etcher. After that, the underneath glass was selectively etched off using a hydrofluoric (HF) solution to release the micro spring. This technique was successfully applied to a micro vibration detection sensor with the silicon microspring with a cross section of 10 m x 60 m with a length longer than 500 m.

Thin film organic transistors with Si/SiO2 (300 nm)/pentacene (70 nm)/Au and Si/polyimide (320–690 nm)/pentacene (70 nm)/Au structures have been fabricated and their performances have been compared. The evaluated mobility of the holes of the SiO2 transistor was 0.002 cm2/Vs, while those of the polyimide transistors were between 0.026–0.031 cm2/Vs. On the other hand, the threshold voltage of the SiO2 transistor was −15 V, while the threshold voltages of the polyimide transistors were approximately +4 V independent of the polyimide thickness. This apparently strange behavior of the polyimide transistors might be attributed to some more negatively charged species accumulating at the polyimide/pentacene interface as the thickness of the polyimide film increases. The PI films had a significantly low level of the leakage current, and the estimated gate-drain leakage current of the corresponding transistor at the gate voltage of −100 V is estimated to be negligibly small compared with the source-drain current.

We present a post-fabrication treatment that improves thermal conductivity of bulk Gd–Ba–Cu–O magnets for pulsed field magnetization (PFM). A small hole about 1 mm in diameter was artificially drilled into the center of bulk Gd–Ba–Cu–O 25 mm in diameter and 18 mm in thickness. An aluminum wire was inserted into the hole, and then the sample was subjected to the impregnation by using Bi–Sn–Cd alloy. We employed PFM to magnetize Gd–Ba–Cu–O bulk superconductors with and without the alloy impregnation treatment. The temperatures of the samples were monitored with thermocouples, and local magnetic field density was measured with a Hall sensor. It was found that the alloy impregnation was effective in suppressing the temperature rise by 4 K and in increasing the trapped field by 25% at 44 K. The present results show that the alloy impregnation treatment enhanced the thermal conductivity of bulk Gd–Ba–Cu–O, and thereby improved the field trapping ability.

We present a post-fabrication treatment that improves thermal conductivity of bulk Gd-Ba-Cu-O magnets. A small hole about 1 mm in diameter was artificially drilled into the centre of bulk Gd-Ba-Cu-O 25 mm in diameter and 18 mm in thickness. An aluminium wire was inserted into the hole, and then the sample was subjected to the impregnation by using Bi- Su-Cd alloy. A pulsed-field magnetization was performed for Gd-Ba-Cu-O bulk with and without the alloy impregnation treatment. The temperature of samples was monitored with thermocouples and local magnetic field density was measured with a Hall sensor at several positions. The maximum temperature rise was depressed by 4 K and the trapped field was increased by 25 % at 44 K. The result shows that the alloy impregnation is very effective in enhancing the thermal conductivity and thereby improving the field trapping ability.

We investigated magnetic homogeneities of Gd–Ba–Cu–O bulk superconductors by means of a conventional scanning Hall probe (SHP) method and a recently developed magneto-scan method. In the SHP method, we measured the trapped flux density distributions of the superconductors by scanning a Hall sensor above the sample surface. On the other hand, in the magneto-scan method, we scanned a Hall probe sensor together with a permanent magnet, which allowed us to detect the field shielding behavior on the sample surface without applying a strong external field. It was found that the magneto-scan method was more sensitive than the SHP method for the detection of local structures in the flux density distributions.

Pulsed field magnetization (PFM) is a practical method for magnetizing bulk superconductors, but the amount of trapped magnetic flux is usually smaller than that magnetized by the field cooling (FC) method due to the heat generation by the flux motion during pulsed field application. In this study, we magnetized a Y–Ba–Cu–O bulk superconductor grown from a seed which was placed at deviating positions from the centre of the bulk to investigate the effect of inhomogeneous penetration of the flux into the bulk superconductor during the PFM. The maximum trapped field by the PFM was almost the same value as by the FC method. This suggests that the inhomogeneity of the bulk superconductor affects the trapped field on the PFM. The magnetic flux can penetrate into the centre of the bulk even if the applied field is small, which contributes to reducing the extra heat generation due to the flux motion.

We measured the field distribution and the variation of temperature in a large-grain Gd–Ba–Cu–O bulk superconductor during pulse field magnetization. When the applied field was below 3.1 T, the temperature rise due to flux motion was small because the magnetic flux penetrated only the surface thin layer. The trapped field increased with increasing field, although the sample temperature was raised and the trapped field reached 1.6 T for the applied pulse field of 3.1 T. However, when the applied field exceeded 3.1 T, the trapped field suddenly decreased due to an excessive temperature rise in the sample. Thus there is an optimum peak field for the pulse field magnetization process.

In the present study, we modified the simulation method for calculating the trapped field distribution of large bulk Nd–Ba–Cu–O superconductors by taking account of B dependence of J c . First we modeled the J c – B property of Nd–Ba–Cu–O with the secondary peak effect by assuming that the sample has two different J c components: one for normal B dependence and the other with the peak effect. Based on the J c – B results thus determined, we could obtain the trapped field distribution of large grain Nd–Ba–Cu–O, which was in good agreement with the empirical data.

We have studied the effect of geometry on the trapped magnetic field in bulk Y–Ba–Cu–O superconductors by varying the thickness. The trapped field first increased with increasing thickness of the bulk superconductor, and then saturated when the thickness reached a certain value. We have also performed simulation studies based on the sand-pile model and the Biot–Savart law, which were in fairly good agreement with the experimental results.

We estimated Jc-B characteristics based on the sand-pile model from the magnetic field distribution on large disk samples with dimensions of 10×10×1 mm3. Such thin disks show a large demagnetizing effect. Thus simple estimates of Jc from the field distribution failed to determine correct values, and a large discrepancy was observed with Jc values determined from magnetization loops of small specimens. Jc-B characteristics obtained from the sand-pile model were in good agreement with those obtained from small specimens.

We have performed a comparative study of the magnetization behavior with applying pulse fields for Y–Ba–Cu–O and Sm–Ba–Cu–O, which exhibit the different field dependence of critical current densities (Jc’s). Time variation of the field was monitored with the Hall probe sensor which is attached to the sample surface by varying the maximum field values from 0 to 2 T. In a low field region, the trapped magnetic field of Sm–Ba–Cu–O was slightly smaller than that of Y–Ba–Cu–O, however, it exceeded the value of Y–Ba–Cu–O in a high field region. The results reflect the Jc–B characteristic of Sm–Ba–Cu–O, in which the Jc values show the secondary peak effect and high field Jc values are higher than those of Y–Ba–Cu–O.

Near-field radiation that has a high intensity of electric field was applied to enhance conversion from thermal energy to electricity in a wavelength range less than 1.1 μm or 1.8 μm. A commercial Si-photovoltaic cell and a thermophotovoltaic cell made of GaSb semiconductors were used to confirm that the near-field radiation effect (the evanescent wave effect) can be applied to enhance generation of electricity. As a result, an increase in output power generation of electricity by the evanescent wave effect was detected and the short-circuit current density increased about 1.3 times for the Si-PV cell and 3.0 times for the GaSb-TPV cell as larger than those obtained by the conventional propagating-wave radiation.Copyright © 2011 by ASME

We performed numerical simulation of the trapped magnetic field by varying the thickness and the side length of the bulk superconductor, based on the sand-pile model and Biot–Savart law. It was found that the trapped magnetic field density at the center of the sample saturated when the sample thickness exceeds a certain value. Such thickness dependence is explained in terms of the geometrical effect or de-magnetizing effect.

It is known that melt processed RE-Ba-Cu-O (RE: rare earth elements) superconductors can trap magnetic field over 1T at liquid nitrogen temperature (77K). The trapped field is dependent on the critical current density (J c ). J c -B characteristic of oxygen-controlled-melt-growth (OCMG) processed Sm-Ba-Cu-O superconductors are different from that of Y-Ba-Cu-O. Therefore, we investigated the J c effect on pulsed field magnetization at various maximum applied field values of 0 – 2T for Sm-Ba-Cu-O grown by the OCMG method.

We have investigated how the critical current densities (J c ’s) affect the magnetization behavior with pulse fields by varying the maximum values from 0 to 2 T in Y-Ba-Cu-O and Sm-Ba-Cu-O superconductors. In a low field region, the trapped magnetic field of Sm-Ba-Cu-O was slightly smaller than that of Y-Ba-Cu-O, however, it exceeded the value of Y-Ba-Cu-O in a high field region. The results reflect the J c -B characteristic of Sm-Ba-Cu-O, in which the J c values show the secondary peak effect and high field J c values are higher than those of Y-Ba-Cu-O.

We fabricated pentacene OTFTs with chemically modified SiO2 surface by phenyltrichlorosilane (PTS), and studied the molecular ordering of the pentacene films and electrical characteristics of the OTFTs. The molecular ordering of the pentacene thin film was improved by PTS treatment. We also fabricated organic thin film transistors with phenyltrichlorosilane treatment. The carrier mobility of the transistor with PTS treatment was 3.7 × 10−2 cm2/Vs, it was larger than that of the transistor without PTS treatment (2.0 × 10−2 cm2/Vs). We believe that this improvement of the μ value was due to improvement of the molecular ordering by PTS treatment.