X-ray Photoelectron Spectroscopy Investigation on the Low-Temperature Degradation of 2 mol% Y2O3-ZrO2 Ceramics

2 mol% Y₂O₃-ZrO₂ polycrystals were annealed in water and under vacuum to highlight the effect of the presence of H₂O on the low-temperature degradation transformation. The specimen surfaces with monoclinic phases transformed during annealing in the different environments were analyzed by X-ray photoelectron spectroscopy with special interest on the electron binding energy change of the constituent ions of the 2 mol% Y₂O₃-ZrO₂ ceramics after the degradation transformation. It was found that no change occurred for the electron-bonding energies of core levels of zirconium ions after the transformation, whereas Y-OH bonds were formed during annealing in water. This result suggested a possibility that the preferred hydration of yttrium took place at the surface of Y₂O₃-partially-stabilized ZrO₂, which is likely to be the reason for the low-temperature degradation accelerated by the presence of H₂O.     

Room temperature pulsed operation of 1.5 μm GaInAsP/InPvertical-cavity surface-emitting laser

Room-temperature pulsed operation of a GaInAsP/InP vertical-cavity surface-emitting laser diode (VCSELD) with an emission wavelength near 1.55 μm is reported. A double heterostructure with a 34-pair GaInAsP (λ_g=1.4 μm)/InP distributed Bragg reflector (DBR) was grown by metalorganic chemical vapor deposition (MOCVD). The measured reflectivity of the semiconductor DBR is over 97% and threshold current is 260 mA for a 40-μmφ device with a 0.88-μm-thick active layer. Threshold current density is as low as 21 kA/cm² at room temperature     

Eight-channel flat spectral response arrayed-waveguide multiplexer with asymmetrical Mach-Zehnder filters

An eight-channel flat spectral response arrayed-waveguide grating (AWG) multiplexer with asymmetrical Mach-Zehnder filters has been fabricated on the planar lightwave circuit (PLC). The monotonic spectral loss characteristics of AWG have been canceled by the opposite spectral response in the asymmetric MZ filter. The 1.5 dB bandwidth of 141 GHz and 3 dB bandwidth of 159 GHz are obtained for the 200 GHz channel spacing. The 1.5 dB bandwidth becomes 1.8 times wider than that of the conventional AWG. Crosstalks to neighboring and all other channels are less than -24 dB and the on-chip insertion losses range from 7.0 to 7.4 dB, respectively.     

Dispersion of ZrO2 particles in aqueous suspensions by ammonium polyacrylate

The effects of poly anionic-electrolyte (ammonium polyacrylate, PAA) as a dispersant on two kinds of ZrO₂ (monoclinic and yttria-doped tetragonal zirconia) aqueous suspensions were examined by the measurements of-potential and viscosity, the sedimentation test and the determination of the wet point and flow point of the powders. Additions above 2.5 wt% PAA to zirconia gave a negative high-potential above –30 mV, and then –45 and –30 mV were obtained for monoclinic and tetragonal zirconia above 5 wt% PAA, respectively. A high negative-potential above –30 mV was retained with 5 wt% PAA for a change in pH over a wider range (pH 6 to 10 for monoclinic ZrO₂, 7 to 9 for tetragonal ZrO₂) in comparison to that of ZrO₂ without dispersant. The increase of the-potential resulted in a decrease in the viscosity. The evaluation of dispersion by the sedimentation test was correlated well with the value of-potential and the viscosity of the suspensions. The presence of native positive charge of monoclinic and tetragonal zirconia powders required an excess amount of PAA to attain dispersion of the suspension. There was a small difference in the least amount of PAA required to attain good dispersion between monoclinic and tetragonal ZrO₂. The difference was also indicated by changes of the flow point on PAA addition. Addition of 0.1% PAA to monoclinic ZrO₂ and 0.25 wt% to tetragonal ZrO₂ gave a maximum value of the flow point, whereas the positive-potential fell to zero. Measurement of the flow point was a simple and useful technique for rapid evaluation of a required amount of dispersant for ZrO₂ suspensions.     

Laser spectroscopic measurement of quenching and doublet mixing rates of the Na(3P(3/2, 1/2)) doublet in a propane-air flame

We have measured the quenching rate of the Na 3P level and the doublet mixing rates of the Na 3P(3/2) and 3P(1/2) levels in a propane-air flame at atmospheric pressure. To obtain these rates, subnanosecond time-resolved fluorescence measurements were made using a mode-locked dye laser and the time-correlated single-photon counting method. Our results are 1.4 x 10(9) s(-1) for the quenching rate and 3.0 x 10(9) s(-1) for the 3P(3/2) --> 3P(1/2) mixing rate.