Keiko Nishikubo

Flexible piezoelectric pressure sensors using oriented aluminum nitride thin films prepared on polyethylene terephthalate films

We have investigated the high sensitive piezoelectric response of c-axis oriented aluminum nitride (AlN) thin films prepared on polyethylene terephthalate (PET) films. The AlN films were deposited using a radio frequency magnetron sputtering method at temperatures close to room temperature. The c axes of the AlN films were perpendicularly oriented to the PET film surfaces. The sensor consisting of the AlN and PET films is flexible like PET films and the electrical charge is linearly proportional to the stress within a wide range from 0to8.5MPa. The sensor can respond to the frequencies from 0.3 to over 100Hz and measures a clear human pulse wave form by holding the sensor between thumb and middle finger. The resolution of the pulse wave form is comparable to a sphygmomanometer at stress levels of 10kPa. We think that the origin of the high performance of the sensor is the deflection effect, the thin thickness and high elastic modulus of the AlN layer, and the thin thickness and low elastic modulus of the ...

Intense visible light emission from stress-activated SrMgAl6O11:Eu

We have investigated deformation luminescence phenomena and the constituent phases of SrMgAl6O11:Eu. The deformation luminescence is clearly visible to the naked eye in air, and the luminescence intensity is the highest among the materials reported. Using x-ray diffraction the constituent phases of SrMgAl6O11:Eu are determined to be SrAl2O4, SrMgAl10O17, and MgAl2O4. The deformation luminescence center has been identified as the Eu2+ ion from the deformation and photoluminescence studies of the three-phase composite. The thermoluminescence glow curve of the composite indicates the trapping levels around room temperature. This result means that the three-phase structure of the composite influences the high deformation luminescence intensity.

Water-Resistant Surface-Coating on Europium-Doped Strontium Aluminate Nanoparticles

The surface modification reaction was applied to the spherical nanoparticles of an elasticoluminescent material, europium-doped strontium aluminate, to improve the water-resistant property. The superior resistibility of the resulting material against water treatment was proved by scanning electron microscopy, photoluminescence, X-ray diffraction, and Fourier transform infrared measurements. Structure and property of the coating layer was also studied by solid state 31 P magic angle spinning nuclear magnetron resonance, atomic emission spectrometry, and zeta potential measurements.

Sensitivity enhancement in diaphragms made by aluminum nitride thin films prepared on polyimide films

The authors have investigated a combination of high and low modulus materials in diaphragms for high sensitivity response. High and low modulus materials are aluminum nitride (AlN) thin films and polyimide films, respectively. AlN was sputtered deposited. The AlN films consist of columnar crystal grains and indicate c-axis orientation. The diaphragm indicates a high sensitivity response of 37200pC∕N, although the piezoelectric coefficient d33 of the AlN film is 2.6pC∕N. The sensitivity response is fifty times as high as that of diaphragms consisted of AlN films and superalloy foils.

Processing and Properties of SrAl2O4 : Eu Nanoparticles Prepared via Polymer-Coated Precursor

This paper reports a modified reverse micelles process for preparing nanoparticles of europium-doped strontium aluminate, a typical elastico-luminescent material. A polymeric matrix was coated on the surface of the precursor formed in the reverse micelles. The polymeric matrix is considered to prevent particle agglomeration by forming a carbon layer while the precursor is heat-treated. Consequently, the luminescent nanoparticles were obtained after removing the carbon layer and forming luminescent centers in a reducing atmosphere. The processing and properties of the luminescent nanoparticles are discussed.

Electrostrictive Properties of Pr-Doped BaTiO3–CaTiO3 Ceramics

Pr-doped (1-x)BaTiO3–xCaTiO3 (x=0.20–1.0) ceramics were prepared by a solid-state reaction technique. Their structures were found to be a pure tetragonal phase for x≤0.23, coexisting tetragonal and orthorhombic phases for x=0.25 to 0.90, and a pure orthorhombic phase for x≥0.90, respectively. A large electrostrictive strain of 0.265%, 1.76 times that of BaTiO3 ceramics, was obtained near the solubility limit on the side of the composite (x=0.25), which is a diphasic ceramic composed of a ferroelectric tetragonal Ba0.77Ca0.23TiO3:Pr solid solution and a normal dielectric orthorhombic Ba0.1Ca0.9TiO3:Pr solid solution. The enhancement of electrostriction resulted from the doping effect and coupling of the large ionic polarization in Ba0.1Ca0.9TiO3:Pr with the non-180° domains in Ba0.77Ca0.23TiO3:Pr during the external electric field exertion.

Ultrahigh temperature vibration sensors using aluminum nitride thin films and W∕Ru multilayer electrodes

Ultrahigh temperature vibration sensors have been fabricated from highly c-axis-oriented aluminum nitride (AlN) thin films and tungsten/ruthenium (W∕Ru) multilayer bottom electrodes. These films and electrodes were prepared by radio-frequency magnetron sputtering on zirconium oxide (ZrO2) substrates, such as AlN∕W∕Ru∕ZrO2. The vibration sensors resisted the heat treatment of 1450°C for 1h in argon, and after that, peeling and cracks were not observed in the sensor surface. The “tough” behavior of the vibration sensors in the high temperature is probably attributed to the chemical composition change of the W∕Ru multilayer bottom electrodes to Ru60W40 and Ru15W85 solid solutions that prevent chemical reactions and relax thermal stress.

Determination of the Crystal Structure of Spherical Particles of SrAl2 O 4 : Eu Prepared by the Spray Method

The crystal structure of spherical particles of Sr 0.88M Eu 0.12 Al 2 O 4 synthesized by the spray method has been investigated by powder X-ray diffraction measurements. After annealing at 1300°C for 2 h, the spheres of Sr 0.88 Eu 0.12 Al 2 O 4 crystallize in the hexagonal form with a = 5.1160(2) A, c = 8.3722(3)A, V = 189.77(1) A 3 Z = 2, and space group P6 3 22, which is distinct from the structure (monoclinic P2 l ) reported so far. This stable crystal structure was refined by the Rietveld method, and it was found that it consists of a nondistorted stuffed tridymite structure, and the doped Eu 2- ion is located at the same 2h site as the Sr 2+ ion. Furthermore, it is suggested that such an abnormal stabilization of the hexagonal form at ambient temperature is associated with defects of the oxygen ion at the 2d site based on the electron density map from Fourier synthesis.

Synthesis and Electric Property of CeAlO3 Ceramics

Cerium monoaluminate (CeAlO3) ceramics were synthesized at 1350–1500°C in a reducing atmosphere with H3BO3 as flux and characterized of their structural and electric properties. Pellets of such ceramics, sintered at 1400°C or above, showed a perovskite-like tetragonal structure with a density higher than 92% of its theoretical. These ceramic pellets were found to have a large dielectric constant higher than 600 and a small loss tangent lower than 0.04 in the frequency range of 10 kHz to 10 MHz. This sample also showed an electric conductivity of 4.71×10-9 S/cm and an optical bandgap width of 3.29 eV at room temperature.

Determination of Eu Sites in Highly Europium-Doped Strontium Aluminate Phosphor Using Synchrotron X-Ray Powder Diffraction Analysis

Highly europium-doped strontium aluminate phosphor (Sr 0.88 Eu 0.12 Al 2 O 4 ) particles were prepared by microspray pyrolysis. The crystallographic sites of the doped Eu 2+ ions and their local atomic coordinates were determined using a combination of Rietveld refinement and the maximum entropy method (MEM) with high-resolution synchrotron X-ray powder diffraction data. The final Rietveld refinement yielded good R factors of R wp = 2.59% (S = 1.86) and R B = 1.08% with the following lattice parameters: a = 8.44032(7) A, b = 8.81680(8) A, c = 5.15551(5) A, and p = 93.3615(3)°. It was evident that there were two crystallographic sites for doped Eu 2+ ions, namely, Eul and Eu2, which were located far from the Sr sites and had displacements of 0.200(7) and 0.160(8) A, respectively. Comparison of the resulting local atomic coordinates of Eul and Eu2 revealed similar atomic configurations at both Eu sites, indicating that the emission peaks for both appeared at almost the same positions. Electron density distribution was calculated by MEM, and the results clearly showed that all the doped Eu 2+ ions were introduced near Sri and Sr2; no other possible crystallographic sites were found. In addition, a subtle electron density between Sr 2+ /Eu 2+ and O 2- ions was observed, implying the occurrence of charge transfer between Sr 2+ /Eu 2+ and O 2- ions.