Tetsu Oi

Scintillation study of ZnWO4 single crystals

Scintillation characteristics of the Czochralski‐grown ZnWO4 single crystal were studied. This crystal, with light red‐brown color, exhibits a maximum luminescence wavelength of 480 nm under excitation at 254 nm. The total luminescence output under x‐ray excitation at 254 nm. The total luminescence output under x‐ray excitation was found to be 2.3 times larger than that of the best Bi4Ge3O12 at room temperature with small afterglow.

Ionic conductivity of Li2OB2O3 thin films

The ionic conductivity of evaporated Li2OB2O3 thin films has been studied. These thin films were found to show a considerably high ionic conductivity of 1 × 10−7 Ω−1 cm−1 at room temperature. The conductivity increases with increasing Li content and exhibits a maximum value near 3Li2O·B2O3. The structure of these films was determined using infrared absorption and laser Raman scattering spectroscopy. Using the results, the correlation between structure and conductivity is also discussed.

Improvement in the scintillation conversion efficiency of Bi4Ge3O12 single crystals

Abstract Single crystals of Bi4Ge3O12, which are greatly needed as scintillators for positron computed tomography, are grown by the Czochralski technique. Their sensitivity can be brought up to 12% of that of NaI by eliminating voids and purifying the crystals. Radiation damage is also prevented. These crystals provide useful scintillators with high sensitivity and energy resolution.

Electrochromism of WO3/LiAlF4/LiIn thin‐film overlayers

A thin, amorphous LiAlF4 film, with lithium ion conductivity of 1×10−4 S/m at 25 °C, has been prepared by vacuum evaporation. Utilizing this thin film as a solid electrolyte, an ITO/WO3/LiAlF4/LiIn overlayer has been constructed (ITO: indium‐tin‐oxide). For it, the electrochromism of WO3 due to lithium ion injection was observed.

The effects of processing conditions on magnetic properties of amorphous alloys

The effects of processing conditions on the physical properties of Fe40Ni40B20 amorphous alloys produced by a single roll‐casting technique were investigated. These results are discussed in terms of the cooling rate in the casting and the state of disordered structure quenched into the amorphous alloy.

The analysis of casting conditions of amorphous alloys

Processing conditions of Fe40Ni40B20 amorphous ribbon, 10 mm in width, have been investigated by employing a single roll‐casting method. To explore the conditions, the temperature of the melt, the angular velocity of the roll, and the ejection pressure of the melt were varied in turn while holding the other quenching parameters constant. The thickness of the as‐quenched glassy ribbon increases monotonically with increase of ejection pressure and decreases monotonically with increase in roll speed. A mathematical treatment of the conditions for obtaining good‐quality glassy ribbon has been attempted, and shows a good accord with the present experimental data.

Amorphous thin film ionic conductors of mLiF.nAlF3

Abstract The theoretical compound LiAlF 4 (=LiF.AlF 3 ) looks promising as a thin film ionic conductor. This paper describes an experiment to determine the conduction characteristics of that compound. A mixture of LiF and AlF 3 is evaporated under 1 mPa onto glass substrates kept at room temperature. The resulting 0.8 μm thick colorless transparent film is amorphous even after annealing at 600°C as judged by X-ray diffraction. AC conductivity is measured to be 1.0 × 1.0 −4 S/m at room temperature in a nitrogen atmosphere. This conductivity is determined to be principally ionic in nature, from lithium ions and/or protons. Further investigation of the molar ratio, the m and n for each component molecule, reveals that the optimum molar ratio, m/n, for the highest ionic conductivity ranges between 5 3 , corresponding to Li 5 Al 3 F 14 , and 1 1 , corresponding to LiAlF 4 . This conductivity is 10 6 times larger than that of either component material.

Growth of high purity ZnWO4 single crystals

Abstract Zinc tungstate (ZnWO 4 ) single crystals are grown by the Czochralski technique and the influence of growth conditions on impurity concentrations in the crystals are examined. Crystal color is very sensitive to impurities, especially iron. The effective segregation coefficient of iron can be varied by applying an electric field across the growth interface during the growth process. The segregation coefficient can be decreased by using a seed crystal as the anode, thereby yielding high purity, almost colorless ZnWO 4 single crystals.

Noise and electrical transport properties of polycrystalline InSb thin films

Both noise and electrical transport properties of polycrystalline InSb thin films are measured and analyzed for the same potential model. Films are prepared by evaporation upon sputtered SiO2 glass and annealed in an Ar atmosphere. Films are inhomogeneously compensated and show what appears to be p‐ and n‐type conduction at low temperatures. It is found that the n‐type films actually contain p‐n junctions because the measured barrier heights reach the energy of the band gap. Between 150 and 77°K, low conducting sheets along grain boundaries with notch‐type barriers exist. Current noise of 1/f type observed at room temperature is well correlated with this notch‐type barrier. A higher notch‐type barrier leads to lower mobility as well as higher noise voltage. This indicates that the noise originates in the bulk effect of the films.

Ionic conductivity of LiF thin films containing Di- or trivalent metal fluorides

Abstract Evaporated LiF thin films containing M II F 2 (M II =Mg, Ca, Ni, Cu, Zn, Sr) or M III F 3 (M III =Al, Ti, V, Cr, Ga, Y, Ce) of less than 20 mol% are prepared and their electrical conductivity determined. It is found that fluorides of Cu, Ni, Zn, Al, Ti, V, Cr, Ga and Y increase the ionic conductivity of these thin films by up to the order of six, while those of Mg, Ca, Sr and Ce do not. These experimental results are discussed in terms of tendency to form intermediate compounds.