Yasushi Nakata

Strong resonant luminescence from Ge quantum dots in photonic crystal microcavity at room temperature

Freestanding hexagonal two-dimensional photonic crystal (PhC) microcavities with Ge self-assembled quantum dots were fabricated on silicon-on-insulator substrates. Strong photoluminescence associated with Ge quantum dots was observed in the wavelength region of 1.2–1.6μm at room temperature. Sharp peaks dominated the spectrum, showing strong optical resonance inside the cavity. A resonant peak with a quality factor of 560 was observed at 1.58μm along with a significant enhancement of the luminescence in the microphotoluminescence spectrum. The peaks were also observed to reasonably shift when the structural parameter of PhC was changed.

Effects of pyrenebutyrate on the translocation of arginine-rich cell-penetrating peptides through artificial membranes: Recruiting peptides to the membranes, dissipating liquid-ordered phases, and inducing curvature

Arginine-rich cell-penetrating peptides, including octaarginine (R8) and HIV-1 TAT peptides, have the ability to translocate through cell membranes and transport exogenous bioactive molecules into cells. Hydrophobic counteranions such as pyrenebutyrate (PyB) have been reported to markedly promote the membrane translocation of these peptides. In this study, using model membranes having liquid-ordered (Lo) and liquid-disordered (Ld) phases, we explored the effects of PyB on the promotion of R8 translocation. Confocal microscopic observations of giant unilamellar vesicles (GUVs) showed that PyB significantly accelerated the accumulation of R8 on membranes containing negatively charged lipids, leading to the internalization of R8 without collapse of the GUV structures. PyB displayed an alternative activity, increasing the fluidity of the negatively charged membranes, which diminished the distinct Lo/Ld phase separation on GUVs. This was supported by the decrease in fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH). Additionally, PyB induced membrane curvature, which has been suggested as a possible mechanism of membrane translocation for R8. Taken together, our results indicate that PyB may have multiple effects that promote R8 translocation through cell membranes.

Side-illuminated tip-enhanced Raman study of edge phonon in graphene at the electrical breakdown limit

Nanoscale integration of graphene into a circuit requires a stable performance under high current density. However, the effects of the current density that approach the electronic breakdown limit of graphene are not well understood. We explored the effects of a high current density, close to the electronic breakdown limit of 10 A/cm (∼3.0 × 108 A/cm2), on graphene, using tip-enhanced Raman scattering. The results showed that the high current density induces Raman bands at 1456 and 1530 cm−1, which were assigned to edge-phonon modes originating from zigzag and armchair edges. This led us to conclude that C–C bonds are cleaved due to the high current density, leaving edge structures behind, which were detected through the observation of localized phonons.

Enhanced Light-emission from Crystalline Silicon in Microdisk Resonators

Microdisks were fabricated on silicon-on-insulator. Sharp resonant luminescent peaks, corresponding to the whispering-gallery modes, were observed in the disks. Integral photoluminescence intensity from crystalline silicon was significantly enhanced due to the microdisks.