No abstract

Observation of aftershocks of the 2003 Tokachi-Oki earthquake was conducted in the southern part of the Tokachi basin in Hokkaido, Japan for estimation of local site effects. We installed accelerographs at 12 sites in Chokubetsu, Toyokoro, and Taiki areas, where large strong motion records were obtained during the main shock at stations of the K-NET and KiK-net. The stations of the aftershock observation are situated with different geological conditions and some of the sites were installed on Pleistocene layers as reference sites. The site amplifications are investigated using spectral ratio of S-waves from the aftershocks. The S-wave amplification factor is dominant at a period of about 1 second at the site near the KiK-net site in Toyokoro. This amplification fits well with calculated 1D amplification of S-wave in alluvial layers with a thickness of 50 meters. In addition to the site effects, we detected nonlinear amplification of the soft soils only during the main shock. The site effects at the strong motion site of the K-NET at Chokubetsu have a dominate peak at a period of 0.4 seconds. This amplification is due to soft soils having a thickness of about 13 meters. Contrary to the results at the two areas, site effects are not significantly different at the stations in the Taiki area, because of similarity on surface geological conditions.

A Cu 2 ZnSnS 4 (CZTS) thin film was fabricated by co-evaporation of its constituents (Cu, Zn, Sn, and S) and subsequent annealing in S-flux using molecular beam epitaxy system. Two Sn crucible temperatures were considered, 1,010 and 1,020°C. The Raman spectrum of the sample exhibited the main peaks at 336 cm %1 attributed to CZTS and 472 cm %1 attributed to Cu 2%x S. The annealing temperature that yielded CZTS with a lower amount of Cu 2%x S was in the range of 380-420°C. The peaks of the Cu 2%x S phase were not observed in the sample fabricated at the Sn crucible temperature of 1,020°C and annealed at 420°C. The suppression of the Cu segregation near the surface, yielded a suppression of the Cu 2%x S phase, as revealed by the Raman spectra. The increase of the Sn ratio, achieved by increasing the crucible temperature, contributed to the suppression of the Cu 2%x S phase and improvement of the CZTS crystalline quality.

Cu2ZnSnS4 (CZTS) thin films are highly suitable as the light-absorbing layer in solar cells. In this study, Cu, Zn, Sn, and S are co-evaporated on the Mo/soda-lime glass (SLG) surface at 320 °C and then annealed in sulfur flux at temperatures of 320–450 °C within the same molecular beam epitaxy system (one-stop process). The Raman spectroscopy of the coated surfaces shows that CZTS is formed with a secondary Cu2−xS phase, where the relative concentrations of the phases strongly depend on the annealing temperature. With an increase in the annealing temperature above around 400 °C, the fraction of CZTS decreases and that of Cu2−xS increases. The depth profile analysis shows that Cu segregates to the surface and Cu2−xS is formed on the film. The solar cells fabricated on these samples show that photovoltaic performance is limited by the surface Cu2−xS. The observed external quantum efficiency behavior is consistent with the degradation of carriers collected in the solar cell formed on the CZTS film owing to the presence of the secondary Cu2−xS phase.