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Submillimetre observations of the externally irradiated protostar R CrA IRS7B show that this source has dramatically different chemical abundances in comparison with otherwise similar embedded protostars not subject to external irradiation.
Submillimetre observations of externally irradiated low-mass protostellar envelopes show that the gas temperature in the envelopes is dominated by the external irradiation. Detailed studies of the protostar IRS7B in Corona Australis also show that the chemistry is strongly affected by the irradiation, depleting the abundances of complex organic molecules.
We propose to use Purcell effect emerged at slow light regions in photonic crystal waveguide (PC-WG) modes for controlling the relaxation time of excited carriers in QDs. Straight GaAs PC-WGs including InAs-QDs with various lattice constants of PC were prepared in order to control the wavelength of the slow light in the PC-WG modes. PL measurements of the PC-WGs indicated enhancements of emission from QDs at the localized wavelength of slow light regions due to the Purcell effect. The enhanced emission peak wavelength was continuously shifted with the PC lattice constant. These results suggest that the PC-WG can be utilized to modify the spontaneous emission rate and carrier relaxation time of the embedded QD. This modification can be applied and useful for various QD-based optical devices as well as our proposed all-optical switching device based on PC-WG/QD.
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.
Hydrogenated amorphous carbon (a–C:H) films on stainless steel (AISI430) substrate oxidized in air at 1273 K were prepared from a gas mixture of methane and hydrogen by an rf plasma chemical vapor deposition, and thermally stimulated exoelectron emission (TSEE) was studied for the x-ray irradiated a–C:H films. Glow curves and energy distributions of TSEE from the 80- and 280-nm a–C:H films and from the AISI430 substrate have been measured under ultrahigh vacuum conditions. It was found that the glow curve from the 80-nm a–C:H film was similar to that from the AISI430 substrate, but it was quite different from that from the 280-nm film; the values of the mean energy of exoelectrons at the glow peak temperatures from the 80-nm a–C:H film are almost the same as those from the substrate but are much lower than those of the 280-nm film. The surfaces of 80- and 280-nm a–C:H films are observed with the scanning electron microscope (SEM). Observations by SEM show that the 80-nm film has relatively large-sized clusters of films and the stainless steel substrate still appears in some places, but the surface of the 280-nm film is completely covered by the carbon films. From these results, we propose that TSEE from the 80-nm film originates mainly from the oxide films on the stainless steel substrate and TSEE from the 280-nm film originates from the film itself. Thus, TSEE can be applied to characterize the surface of thin films.
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