Hiroshi Tateyama

Flexible pulse-wave sensors from oriented aluminum nitride nanocolumns

Flexible pulse-wave sensors were fabricated from density-packed oriented aluminum nitride nanocolumns prepared on aluminum foils. The nanocolumns were prepared by the rf magnetron sputtering method and were perpendicularly oriented to the aluminum foil surfaces. The sensor structure is laminated, and the structure contributes to avoiding unexpected leakage of an electric charge. The resulting sensor thickness is 50 μm. The sensor is flexible like aluminum foil and can respond to frequencies from 0.1 to over 100 Hz. The sensitivity of the sensor to pressure is proportional to the surface area. The sensor sensitively causes reversible charge signals that correlate with the pulse wave form, which contains significant information on arteriosclerosis and cardiopathy of a man sitting on it.

SMECTITE QUASICRYSTALS IN AQUEOUS SOLUTIONS AS A FUNCTION OF CATIONIC SURFACTANT CONCENTRATION

Quasicrystals of synthetic fluoromagnesian smectite (FMS) in dodecyltrimethylammonium chloride (DTAC) solutions were investigated as a function of the DTAC concentration by wet type X-ray diffraction (XRD) ζ potential measurements, and dispersion and coagulation (DC) tests. The FMS had an electronegative potential and it was dispersed randomly in an aqueous suspension without DTAC. When the DTAC concentration was 0.002 mol/dm3, FMS tactoids started to develop a structure in which the layer thickness was 1.85 nm. At the isoelectric point, the DTAC concentration was 0.012 mol/dm3 and the FMS tactoid formed a regular stacked structure with a 2.25 nm layer thickness. As the ζ potential of FMS changed from negative to positive, the DC test and XRD measurement showed that the FMS association gradually changed from coagulation to dispersion, which indicates that the formation of the bilayer of surfactants on the surface of FMS produces a repulsion between DTA+ adsorbed on the silicate layer of the FMS surfaces. When the equilibrium concentration of DTAC in solution exceeded the critical micelle concentration (CMC), the ζ potential of FMS became greater than the previous values. The XRD analysis of this suspension showed that there were two kinds of rational FMS stackings; one has a layer thickness of 3.20 nm, and the other has a layer thickness of 5.45 nm due to an interstratified structure composed of 3.20 and 2.25 nm layers. The interstratified structure was confirmed by the calculated XRD profiles.

DIFFERENCES IN QUASICRYSTALS OF SMECTITE-CATIONIC SURFACTANT COMPLEXES DUE TO HEAD GROUP STRUCTURE

The organoclay quasicrystals formed by exchange reactions of fluoromagnesian smectite (FMS) and two kinds of cationic surfactants were investigated by X-ray diffraction (XRD) of both aqueous suspensions and dried powders. ζ potential measurements were also carried out. The two cationic surfactants employed in this study, dodecyltriphenylphosphonium bromide (C12PBr) and dodecyltrimethylammonium bromide (C12NBr), have the same alkyl chain length but different head group structures. In aqueous suspensions of C12N/FMS, regular stacking with a basal spacing of 2.28 nm was observed within the range 0.4 to 1.0 of the cation exchange capacity (CEC) of the C12N/FMS ratios. The basal spacing was constant in this range. The most intense diffraction for the C12N/FMS suspension was observed at 0.6 CEC, and a further increase in the C12N/FMS ratio resulted in a decline of the diffraction intensity and a slight increase in the peak width. On the other hand, in C12P/FMS suspensions with the surfactant/FMS ratios <0.6 CEC, only weak, broad XRD peaks were observed. With higher C12P/FMS ratios (0.8 and 1.0 CEC), strong diffraction peaks appeared with a basal spacing of 3.20 nm. The difference in the observed basal spacings of C12N/FMS and C12P/FMS tactoids was ∼0.9 nm, which did not agree with the difference in the estimated height of the two surfactants (∼0.1 nm). These differences of the tactoid structures between C12N/FMS and C12P/FMS suspensions could be explained in terms of the difference in the adsorption manner of the surfactants on the silicate surface and in the size of the surfactant head groups.

Strong blue, green and red light emission at elevated temperatures from Y2SiO5 doped by the rare-earth ions

The temperature dependence of the photoluminescence (PL) of the rare-earth ion activated Y2SiO5 was investigated from room temperature to 573 K. Ion activators such as Eu3+, Ce3+, Sm3+, Tb3+ and some of their combinations were studied in this study. The most efficient blue, green and red phosphors at elevated temperature were found by doping the (Ce3+ + Tb3+), Tb3+ and Eu3+ respectively, in this material system. Meanwhile, the relationship between the structure and the temperature dependence of the PL in RexY2−xSiO5 was also discussed.

Composition, structure and luminescent properties of EuxY2−xSiO5 thin films

Abstract Dense and uniform EuxY2−xSiO5 (EYSO) thin films with an X1–Y2SiO5 structure were prepared by metallorganic decomposition (MOD). The photoluminescence (PL) and triboluminescence of the EYSO thin films were first investigated with relation to structure and composition. The experimental results show that the emission intensity of the PL and triboluminescence of the EYSO films increases with increasing crystallinity. The strongest photoluminescence and triboluminescence were achieved by the EYSO films with the europium contents of 20 and 25 at.%, respectively. In addition, the site selective emission involved within the 5D0→7F1 transitions at room temperature can be observed in the EYSO thin films depending on the position of the europium ions occupied in the lattice.