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An impact of the vacuum anneal of Al/Ge(111) structure on the Ge segregation has been investigated to get an insight into the precise control of ultrathin Ge crystalline growth. The Al/Ge(111) structure was prepared by thermal evaporation of Al on wet-cleaned Ge(111) and then vacuum annealed without air exposure to promote Ge formation on the Al surface. The Ge formation and its chemical bonding features were evaluated by X-ray photoelectron spectroscopy analysis. In addition, changes in the average Ge thickness depending on annealing temperature and time were crudely estimated. We found that the annealing temperature had a greater effect than time on the control of sub-nanometer scale Ge growth.

We have investigated the formation of an ultrathin Ge crystal layer by vacuum annealing of the Al/Ge(111) structure. An hetero-epitaxial Al layer was found to be grown on a Ge(111) substrate by control of Al thickness and deposition rate during thermal evaporation, which the Al surface becomes the template of crystallographic structure of a segregated Ge layer. Then, surface flattening and Ge segregation of the Al/Ge(111) structure by vacuum annealing were evaluated, and the formation of ultrathin segregated-Ge crystals with a thickness below 1 nm on the hetero-epitaxial Al surface have been demonstrated.

We propose a device which has the same wavelength routing function as a conventional arrayed-waveguide-grating and consists of two planar waveguide spectrographs connected by waveguide array of equal-length. We fabricate the device using compound semiconductor for future integration of many functions. The fabricated device shows a filter width of 1.7 nm and a sidelobe level of -8 dB which is limited by the power distribution in the waveguide array. A device using the whispering gallery mode is also demonstrated. The whispering gallery mode is expected to reduce the phase error. The sidelobe level is reduced by over 5 dB as compared to a device using the conventional channel waveguide. Finally, a design for compensating the effect of the radius of curvature on the propagation constant is proposed.

Two kinds of YBaCuO bulk samples with different densities and sizes of 211 particles were prepared by the melt powder melt growth method. The magnetic field and temperature dependences of critical current density, J c, were measured inductively. Strong dependence of J c on size and density of 211 particles at higher temperatures was observed, while no relationship could be recognized between the two at lower temperatures. This result supports the expectation that nonsuperconducting particles such as the 211 phase act as dominant pinning centers at higher temperatures. A history effect was observed at 4.2 K, suggesting an existence of weak links.