Hiroyasu Sato

Rhopaladins A ∼ D, new indole alkaloids from marine tunicate Rhopalaea sp

Abstract Four new bis(indole) alkaloids, rhopaladins A ∼ D ( 1 ∼ 4 ), have been isolated from the Okinawan marine tunicate Rhopalaea sp. and the structures were elucidated on the basis of spectroscopic data. The presence of two rotational isomers ( 3a and 3b ) of 3 was deduced from NOESY data and molecular calculation using Macromodel program.

Brasiliquinones A–C, new cytotoxic benz[a]anthraquinones with an ethyl group at C-3 from actinomycete Nocardia brasiliensis

Three new cytotoxic benz[a]anthraquinones with an ethyl group at C-3, brasiliquinones A–C 1–3, have been isolated from the actinomycete Nocardia brasiliensis IFM 0089, and their structures elucidated on the basis of spectroscopic data and by chemical means. Brasiliquinone A 1 is the first benz[a]anthraquinone possessing ristosamine as an O-glycoside moiety, while brasiliquinones B 2 and C 3 correspond to the aglycone of 1 and the 8-O-methyl derivative of 2, respectively.

Precise slit-width control of niobium apertures for superconducting LEDs

We introduce a novel three-step procedure for precise niobium (Nb)-etching on the nanometer-scale, including the design of high contrast resist patterning and sacrifice layer formation under high radio frequency (RF) power. We present the results of precise slit fabrication using this technique and discuss its application for the production of superconducting devices, such as superconductor-semiconductor-superconductor (S-Sm-S) Josephson junctions. For the reactive ion etching (RIE) of Nb, we selected CF(4) as etchant gas and a positive tone resist to form the etching mask. We found that the combination of resist usage and RIE process allows for etching of thicker Nb layers when utilizing the opposite dependence of the etching rate (ER) on the CF(4) pressure in the case of Nb as compared to the resist. Precise slit-width control of 80 and 200 nm thick Nb apertures was performed with three kinds of ER control, for the resist, the Nb, and the underlying layer. S-Sm-S Josephson junctions were fabricated with lengths as small as 80 nm, which can be considered clean and short and thus exhibit critical currents as high as 50 µA. Moreover, possible further applications, such as for apertures of superconducting light emitting diodes (SC LEDs), are addressed.

High photon extraction efficiency from GaAs pillar with InAs quantum dots embedded in Niobium

We studied the novel structure for improving the emission properties of semiconductor light sources both theoretically and experimentally. The proposed structure is a semiconductor pillar buried in a metal except for one end surface of the pillar. Photons are extracted only from the air-exposed surface. The structure consists of the GaAs nanopillar structures embedded in metal and is analyzed by the finite-difference-time-domain method. InAs quantum dots buried in a GaAs pillar are assumed to be the photon emitters. Simulations are performed on GaAs pillars with different diameters buried in Niobium. Consequently, the simulation showed 75% light extraction efficiency from the pillar to air with the optimization of the structure. In addition, we experimentally measured photoluminescence intensities of up to 40 times enhancement in embedded structures compared to normal pillar structure. These are promising for future applications to overcome single photon sources.