Low-Friction Coatings of Zinc Oxide Synthesized by Optimization of Crystal Preferred Orientation

The crystal preferred orientation of zinc oxide (ZnO) coatings on stainless steel substrates was precisely controlled by a combinatorial sputter-coating system. ZnO coatings were analyzed by X-ray diffraction spectroscopy, and surface and interfacial cutting analysis methods. The frictional properties of the coatings in a vacuum, the atmosphere, oil of n-hexadecane, and oil doped with palmitic acid molecules were observed. Different frictional behaviors of the ZnO coatings were observed by varying the crystal preferred orientation. A low-friction coefficient as less as 0.2 was realized by ZnO coatings with uni- and multi-crystal orientation in all of those conditions. Inverse proportion of the friction coefficient to normal load was observed on ZnO coatings with bi-orientation of (002) and (103) in pure and palmitic acid doped oil.     

Environmental protection: researches in National Institute of Radiological Sciences

Some studies for radiological protection of the environment have been made at the National Institute of Radiological Sciences (NIRS). Transfer of radionuclides and related elements has been investigated for dose estimation of non-human biota. A parameter database and radionuclide transfer models have been also developed for the Japanese environments. Dose (rate)-effect relationships for survival, growth and reproduction have been investigated in conifers, Arabidopsis, fungi, earthworms, springtails, algae, duckweeds, daphnia and medaka. Also genome-wide gene expression analysis has been carried out by high coverage expression profiling (HiCEP). Effects on aquatic microbial communities have been studied in experimental ecosystem models, i.e., microcosms. Some effects were detected at a dose rate of 1 Gy day(-1) and were likely to arise from interspecies interactions. The results obtained at NIRS have been used in development of frameworks for environmental protection by some international bodies, and will contribute to environmental protection in Japan and other Asian countries.     

Rapid erasing of wettability patterns based on TiO2-PDMS composite films

TiO₂-polydimethylsiloxane (TiO₂-PDMS) composite films are prepared using the sol–gel method from a Ti(OBu)₄–benzoylacetone solution containing PDMS. The prepared films are cured by irradiation with ultraviolet (UV) light. Structural changes in the films after UV irradiation are confirmed by UV–vis absorption experiments, which show that an absorption band characteristic of the benzoylacetonate chelate rings disappears. This finding is ascribed to structural changes associated with the dissociation of the chelate rings. The IR spectra of the thin films exhibit a broad absorption band after UV irradiation, indicating that a Ti–O–Ti network forms in the thin film. Contact angles are measured for the TiO₂-PDMS thin films, showing wettability conversion from hydrophobic to superhydrophilic states by irradiation with oxygen plasma for 1 s. This phenomenon is explained by XPS experiments which reveal that the number of carbon atoms decreases, whereas the number of oxygen atoms increases on the surface of the TiO₂-PDMS composite films. Finally, hydrophobic–superhydrophilic patterns are fabricated based on a patterned TiO₂-PDMS composite film. The film displays a rapid change to superhydrophilicity over the whole film surface upon plasma irradiation for 1 s, which means that the wettability patterns are rapidly erasable.     

Scintillation properties of Tm-doped Lu3Al5O12 single crystals

Using the micro-pulling-down (μ-PD) method, Tm-doped Lu₃Al₅O₁₂ (Tm:LuAG) single crystals were grown to examine their scintillation properties. In transmittance spectra, they exhibited about 80% transparency in the wavelengths longer than 320 nm and five absorption lines due to Tm³⁺ 4f–4f transitions were observed. ²⁴¹Am α-ray excited radioluminescence spectra were measured and intense 4f–4f emission peaks were observed with the host emission. When excited by ¹³⁷Cs γ-Ray to obtain pulse height spectra, Tm 1% doped LuAG showed the highest light yield coupled with a photomultiplier (PMT) or a silicon avalanche photodiode (Si-APD). The light yield was estimated to be 5800 and 7300 photons/MeV for PMT and Si-APD, respectively. Decay time profiles consist of two exponential components and the fast and slow components are considered to be attributed to the host and the combination of the host and Tm³⁺ 4f–4f emission, respectively.     

Crystal growth and scintillation properties of Nd-doped Lu3Al5O12 single crystals with different Nd concentrations

Nd 0.1%, 0.5%, 1% and 3% doped Lu₃Al₅O₁₂ (Nd:LuAG) single crystals were grown in the nitrogen atmosphere by the micro-pulling down (μ-PD) method. The grown crystals had a single-phase confirmed by powder XRD analysis. In absorption spectra, some weak absorption lines due to Nd³⁺ 4f-4f transitions were observed and their intensity increased with the increase of Nd concentration. When excited by ²⁴¹Am α-ray, a broad emission peak due to defects in the host lattice at 320 nm and some sharp lines due to Nd³⁺ 4f-4f transitions at wavelength longer than 400 nm were observed. The decay time profiles of Nd:LuAG under γ-ray excitation were well approximated by two exponential function of 340-760 ns and 3-5 μs for each sample. By pulse height measurement using ¹³⁷Cs, Nd 0.5%:LuAG showed the highest light yield of 7600 ± 760 photons/MeV.     

Photosensitized hydrogen evolution from water using a single-walled carbon nanotube/fullerodendron/SiO2 coaxial nanohybrid

A coaxial nanohybrid consisting of a single-walled carbon nanotube (SWCNT), fullerodendron, and SiO(2) shows high-efficiency light-driven hydrogen evolution from water. Upon visible light irradiation, SWCNT/fullerodendron/SiO(2) coaxial nanohybrid shows hydrogen evolution activity in the presence of methyl viologen (MV(2+)), benzyldihydronicotinamide (BNAH), and a colloidal polyvinyl alcohol(PVA)-Pt.     

Nano-strip grating lines self-organized by a high speed scanning CW laser

After a laser annealing experiment on Si wafer, we found an asymmetric sheet resistance on the surface of the wafer. Periodic nano-strip grating lines (nano-SGLs) were self-organized along the trace of one-time scanning of the continuous wave (CW) laser. Depending on laser power, the nano-trench formed with a period ranging from 500 to 800 nm with a flat trough between trench structures. This simple method of combining the scanning laser with high scanning speed of 300 m min(-1) promises a large area of nanostructure fabrication with a high output. As a demonstration of the versatile method, concentric circles were drawn on silicon substrate rotated by a personal computer (PC) cooling fan. Even with such a simple system, the nano-SGL showed iridescence from the concentric circles.     

Thin films of Cu(In,Ga)Se2 and ordered vacancy compound prepared by thermal crystallization and their photovoltaic applications

Thin films of Cu–In–Ga–Se alloy system with various composition were prepared by thermal crystallization from In/CuInGaSe/In precursor. Electron probe microanalysis and X-ray diffraction study revealed that these samples were assigned to chalcopyrite Cu(In,Ga)Se₂ or ordered vacancy compound Cu(In,Ga)₂Se_3.5. Solar cell with ZnO:Al/i–ZnO/CdS/Cu(In,Ga)Se₂/Mo/soda-lime glass substrate structure was fabricated by using thermal crystallization technique, and demonstrated a 9.58% efficiency without AR-coating.     

A maximum power point tracking for photovoltaic-SPE system using a maximum current controller

Processes to produce hydrogen from solar photovoltaic (PV)-powered water electrolysis using solid polymer electrolysis (SPE) are reported. An alternative control of maximum power point tracking (MPPT) in the PV-SPE system based on the maximum current searching methods has been designed and implemented.Based on the characteristics of voltage–current and theoretical analysis of SPE, it can be shown that the tracking of the maximum current output of DC–DC converter in SPE side will track the MPPT of photovoltaic panel simultaneously.This method uses a proportional integrator controller to control the duty factor of DC–DC converter with pulse-width modulator (PWM).The MPPT performance and hydrogen production performance of this method have been evaluated and discussed based on the results of the experiment.     

Physicochemical properties and photocatalytic hydrogen evolution of TiO2 films prepared by sol–gel processes

Anatase TiO₂ films were obtained on glass substrates using a sol–gel method using titanium isopropoxide as a precursor. The thickness of the film was about 140 nm for one coating, and the thickness is controlled by the number of coating cycles. The spectra of UV-VIS absorption indicated that the absorption edge of the TiO₂ films is ca. 385 nm, corresponding to the band gap energy of 3.20 eV. We obtained TiO₂ films having a high activity for the hydrogen evolution from photocatalytic water cleavage. By loading with 0.3 wt% Pt rate of hydrogen production increases. No influence of film thickness and calcination temperature on the photocatalytic property is observed.