We have developed a selective-area-growth (SAG) method of self-assembled InAs quantum dots (QDs) using a metal-mask (MM) combined with molecular beam epitaxy for realizing photonic crystal (PC) based ultra-small and ultra-fast all-optical devices (PC-SMZ and PC-FF). Successful SAG of QDs was confirmed by atomic-force-microscopy observations and photoluminescence (PL) measurements. High density and high uniformity comparable to those of conventional QDs grown without the MM were achieved; the QD density was 4 × 1010cm-2 and a linewidth of the PL peak was around 30meV at room temperature. In addition, insertion of a strain-reducing layer on the grown QD was effective for varying the PL peak wavelength of the QD from 1240nm to 1320nm without any extra optical degradation. The MM method reported here is promising for achieving the all optical devices, PC-SMZ and PC-FF, which require SAG of QDs and a QD ensemble with a different absorption-peak wavelength in a different area.

We made accelerator mass spectrometry (AMS) 14C measurements on terrestrial macrofossils from the Late Pleistocene/Holocene of the annually laminated sediments of Lake Suigetsu (central Japan). The AMS 14C dates of terrestrial macrofossils showed agreement between varve counting years and calibrated ages (tree rings and U/Th on coral) in the interval of 10.5 and ca. 11.5 ka cal bp. Beyond 11.5 ka cal bp, the age difference between 14C and varve counting years gradually diminish, contradicting published data on corals dated by U/Th and 14C.