Mizue Mizoshiri

Thin-Film Thermoelectric Modules for Power Generation Using Focused Solar Light

We demonstrated the fabrication of thin-film thermoelectric generators and evaluated their generation properties using solar light as a thermal source. Thin-film elements of Bi0.5Sb1.5Te3 (p-type) and Bi2Te2.7Se0.3 (n-type), which were patterned using the lift-off technique, were deposited on glass substrates using radiofrequency magnetron sputtering. After annealing at 300°C, the average Seebeck coefficients of p- and n-type films were 150xa0μV/K and −104xa0μV/K, respectively, at 50°C to 75°C. A cylindrical lens was used to focus solar light to a line shape onto the hot side of the thin-film thermoelectric module with 15 p–n junctions. The minimum width of line-shaped solar light was 0.8xa0mm with solar concentration of 12.5 suns. We studied the properties of thermoelectric modules with different-sized p–n junctions on the hot side, and obtained maximum open voltage and power values of 140xa0mV and 0.7xa0μW, respectively, for a module with 0.5-mm p–n junctions. The conversion efficiency was 8.75xa0×xa010−4%, which was approximately equal to the value estimated by the finite-element method.

Evaluation of the Thermoelectric Module Consisting of W-Doped Heusler Fe2VAl Alloy

Power generation performance of a thermoelectric module consisting of the Heusler Fe2VAl alloy was evaluated. For construction of the module, W-doped Fe2VAl alloys were prepared using powder metallurgy process. Power generation tests of the module consisting of 18 pairs of p–n junctions were conducted on a heat source of 373–673xa0K in vacuum. The reduction of thermal conductivity and improvement of thermoelectric figure of merit by W-doping enhanced the conversion efficiency and the output power. High output power density of 0.7xa0W/cm2 was obtained by virtue of the high thermoelectric power factor of the Heusler alloy. The module exhibited good durability, and the relatively high output power was maintained after temperature cycling test in air.

Large refractive index changes of a chemically amplified photoresist in femtosecond laser nonlinear lithography

We found that marked increases in refractive index of chemically amplified photoresists induced by highly repetitive femtosecond laser irradiation without post-exposure baking treatment. For laser writing speed less than 30 μm/s, the refractive index change of the nonlinear absorption region was as large as 8 × 10(-3). Moreover, cross-linking reactions of the resists were induced. The refractive index changes can generate optical confinement and subsequent channel propagations of femtosecond laser pulses. The coupling efficiency was estimated as high as 87% using a low numerical aperture objective lens. The peak intensities of the guiding modes exceeded the polymerization threshold of the resist.