We demonstrated hot-carrier effects in a solar cell containing InAs/GaAs quantum-dots superlattice structure as a light absorber. The bandgap of the host semiconductor plays an important role as an energy-selective barrier for hot carriers created in quantum-dot superlattices. The short circuit current density increases linearly with the excitation photon density, suggesting that two photons absorption or Auger recombination processes can be ignorable. Furthermore, we found that the open circuit voltage of the quantum-dot superlattice solar cell increases drastically in contrast to a solar cell containing conventional quantum dots without a superlattice structure. These results clarify effects of hot carrier population in the one-dimensional energy dispersion of the quantum-dot superlattice.
Light emitting diodes (LEDs) possess advantages to be applied as one of the key medical devices in the field of phototherapy. In this paper, effects of blue light on inducing sleep have been examined based on the experiments for 100 test subjects. Narrow-band (<11 nm in full width of half maximum in the emission spectrum) irradiation was found to be more effective for inducing sleep. It should be noted that the intensity of light employed in this study was far less that that suppressing the secretion of melatonin and obstructing the circadian rhythm, which has recently extended widely. Since a variety of light sources in terms of wavelengths, bandwidths, and intensity are required in the medical applications or light therapy, LEDs are the ideal device and the efforts of developing new LEDs with the materials research of semiconductors are strongly demanded.
A huge attention is given to PEFCs (Polymer Electrolyte Fuel Cells) for eco-friendly engine of automobiles due to their low operating temperature and high output power. However, lack of low-cost materials with high conductivity and corrosion resistance for metal separators in PEFCs interrupts realizing low-cost ones. We have been focusing on tin dioxide (SnO2) as a candidate material. Stainless (SUS) separators coated with SnO2 thin films play important roles to realize low-cost PEFCs. A mist CVD system was employed to fabricate SnO2 thin films aiming to reduce growth costs of thin films. SnO2 thin films were successfully grown on SUS substrates without cracks or pinholes. An obtained PEFC coated with SnO2 thin films achieved the highest output of 0.377 W/cm2 with endurance of more than 750 hours against consecutive power generation. These results indicate SnO2 coated SUS separators are key structures for realization of low-cost PEFCs.
The surface flatness of photo-curable polysilsesquioxane (PSQ) films for gate dielectric layers of pentacene thin film transistors (TFTs) was considerably improved by ultra-violet light (UV)/O3 treatment; the root-mean-squared (RMS) roughness was improved from 0.35 to 0.23 nm after 40-minute treatment. However, the PSQ surfaces became hydrophilic because hydroxyl groups, which degraded transistor performances, replaced the organic functional groups such as methyl groups by the UV/O3 treatment. Therefore, 1,1,1,3,3,3-hexamethyldisilazane (HMDS) treatment was successively performed after the UV/O3 treatment to replace the hydroxyl groups with hydrophobic silyl groups. It was found that four-hour HMDS treatment under dry nitrogen was enough to reduce off current of pentacene TFTs. As a result, the carrier mobility of the pentacene TFT fabricated with UV/O3 and HMDS-treated PSQ layers became 0.59 cm2V-1s-1, which was more than seven times higher than that of the pentacene TFTs with untreated PSQ layers.
The crystallization of GeBiTe (GBT) is faster than that of the well-known phase-change recording material GeSbTe (GST). Therefore, the investigation of GBT structure as well as its crystallization process is attractive. Accordingly, the high-speed crystallization of GBT is due to Bi. Thus, it was necessary to know the local structure around Bi within the amorphous GBT. Note that an interface layer, which is a very thin dielectric film adjacent to recording film, assists the crystallization of phase-change material in the optical recording media. The local structure around Bi in GBT within an actual media was analyzed using XAFS. Bi LIII-edge XAFS spectra of crystalline and amorphous GBT respectively, both with and without interface layer in the media, were obtained. As result of this analysis on GBT, nearest neighbor atom of Bi was found to be Ge. Moreover, within the amorphous GBT, the interatomic distance around Bi is larger than that around Ge. These are the differences between GST and GBT. We speculate that these factors contribute to the improvement of the GBT crystallization speed. On the other hand, the interface layer doesn’t influence the local structure of GBT; however, it does have an electric effect on the recording layer.
In conventional linear ultrasonic flaw detection method, since an ultrasonic wave incident on a steel material is excited at an interface having a difference in acoustic impedance, opening crack can be detected. However, the backscattered waves at ultrasonic spectroscopy method (noise) is the most suitable for detecting and evaluating precursory minute defect size of deterioration damage to equipment along with aging of amine stress corrosion cracking. This approach focuses on power spectrum intensity of a specific frequency band, to grasp precursor behavior by comparing area values of the power spectral intensity is confirmed with an actual device, and thus life expectancy can be predicted.
Multiaxial high cycle fatigue life prediction under constant stress amplitude is proposed. This new criterion, which extends the proposed fatigue limit criterion by the authors in the previous papers, uses the unified equivalent shear stress amplitude. The material properties for the proposed criterion are the axial fatigue limit and the true fracture strength. The multiaxial high cycle fatigue tests for life prediction accuracy verification was carried out with S45C and SCM440. The fatigue tests were conducted under combined axial and torsion stresses with mean stress and phase difference. The criterion error is better than that of the Susmel criterion. The proposed criterion predicted the experimental fatigue life to be within a factor of 3.
It has been known that molybdenum disulfide exists as a monophase in the S/Mo composition ratio range from about 1.94 to 2.25. In this study, sputtered molybdenum disulfide films having S/Mo ratio from 1.96 to 2.25 have been prepared on surface of JIS SUS440C rollers for cross roller bearings by applying the positive voltages ranging from 0 to 60 V to rollers. Friction coefficient and wear life of molybdenum disulfide films have been investigated by friction test conducted in air atmosphere of 10 % relative humidity. It is found that better lubricating performance which means longer wear life and lower friction coefficient was obtained in the films having S/Mo ratio from 2.06 to 2.15 near the center of the S/Mo composition ratio range of molybdenum disulfide. On the other hand, sudden drop of lubricating performance were appeared near both limit values of the composition ratio range.
This paper discusses crack propagation directions of type 304 steel tube specimens in reversed torsion tests. Strain controlled torsion low cycle fatigue tests were performed on type 304 steel tube specimens and the numbers of cycles to failure were obtained. Crack directions were also observed by intermitting the tests. Main-cracks propagated in the maximum shear directions at high strain ranges but in the principal strain directions at low strain ranges. The transition of the main-crack direction from the maximum shear strain direction to the principal direction by lowering strain range was discussed from the observations of micro-crack directions. The main-crack is the crack that directly leaded to the failure of the specimen and the micro-crack is the crack whose length was less than 100μm. Most micro-cracks initiated in the maximum shear directions and they branched in the principal directions as they grew. The critical length at the branching depended on strain range. The critical crack length at high strain ranges was longer than that at low strain ranges, which corresponded well with the main-crack propagation directions. Aspect ratios of the shear and principal cracks were discussed in relation with the main-crack directions and the energy release in the two cracking modes.