Yoriko Tominaga

Optical readout of hydrogen storage in films of Au and Pd

For hydrogen sensor and storage applications, films of Au and Pd were (i) co-sputtered at different rates or (ii) deposited in a sequentially alternating fashion to create a layered structure on a cover glass. Peculiarities of hydrogen uptake and release were optically monitored using 1.3 μm wavelength light. Increase of optical transmission was observed for hydrogenated Pd-rich films of 10-30 nm thickness. Up to a three times slower hydrogen release took place as compared with the hydrogen uptake. Compositional ratio of Au:Pd and thermal treatment of films provided control over the optical extinction changes and hydrogen uptake/release time constants. Higher uptake and release rates were observed in the annealed Au:Pd films as compared to those deposited at room temperature and were faster for the Auricher films. Three main parameters relevant for sensors: sensitivity, selectivity, stability (reproducibility) are discussed together with the hydrogenation mechanism in Au:Pd alloys.

Effect of thermal annealing on the crystallization of low-temperature-grown In0.42Ga0.58As on InP substrate

We present the effect of postannealing on the crystallization of low-temperature-grown (LTG) In x Ga1− x As on a (001) InP substrate. LTG In0.42Ga0.58As with a thickness of 1.0 µm was grown directly on the substrate by molecular beam epitaxy at 180 °C. High-resolution X-ray diffraction reciprocal space mapping and cross-sectional transmission electron microscopy (TEM) indicate that the as-grown LTG-In0.42Ga0.58As layer comprises an amorphous layer above the substrate and a columnar crystal layer on top of the amorphous layer. The TEM images indicate that the thermally induced crystallization of the amorphous In0.42Ga0.58As crystal lattice-matched to the InP substrate occurs during annealing above 400 °C.

Coherent effect in nonlinear excitation of low-temperature-grown GaAs by 1.5 μm pulses

The mechanism of the nonlinear photo-carrier generation in low-temperature-grown GaAs by 1.5 μm pulses was investigated by a double pulse experiment. The effect of intermediate excitation on the photo response was distinctly observed. Moreover, the effect was found to be largely coherent, contrary to the proposed model.