We apply a nanomanipulation technique to assemble pairs of monodispersed octahedral gold nanocrystals (side length, 150 nm) along their major axes with a varying tip-to-tip separation (25-125 nm). These pairs are immobilized onto indium tin oxide coated silica substrates and studied as plasmonic dimers by polarization-selective total internal reflection (TIR) microscopy and spectroscopy. We confirm that the plasmon coupling modes with the scattering polarization along the incident light direction result from the transverse-magnetic-polarized incident light, which induces two near-field-coupled dipole moments oriented normal to the air-substrate interface. In such cases, both in-phase (antibonding) and antiphase (bonding) plasmon coupling modes can be directly observed with the incident light wave vector perpendicular and parallel to the dimer axis, respectively. The observation of antiphase plasmon coupling modes ("dark" plasmons) is made possible by the unique polarization nature of the TIR-generated evanescent field. Furthermore, with decreasing nanocrystal separation, the plasmon coupling modes shift to shorter wavelengths for the incident light perpendicular to the dimer axis, whereas relatively large red shifts of the plasmonic coupling modes are found for the parallel incident light.

Metal nanostructures have the potential to increase photon− molecule interaction efficiency due to their plasmonic antenna effect. However, plasmonic enhancement of the efficiency of photochemical reactions such as photosynthesis is rather difficult because excited molecules are easily quenched near the metal surface. Sphere−plane metal nanostructures have an advantage to reduce such undesirable contribution due to their controllability of metal− molecule interfaces. Here, structural tuning of optical antenna properties, which is indispensable for selective enhancement of photochemical reactions, is demonstrated as plasmonic enhancement of photoinduced electron transfer reactions on porphyrin-based monolayer systems using the sphere−plane nanoantennas. The efficiency of photocurrent generation was substantially enhanced in good agreement with the plasmonic resonance properties of the optical antenna. The contribution of the excited state quenching was also evaluated by comparing the enhancement factor of the photocurrent and the degree of the field enhancement. This result provides useful insights for designing efficient plasmonic photochemical systems.

In this wor 瓦 the themlal stress distribution in ultra 丘n plate − fin stmctUres made of a Ni − based alloy subjected to a macroscopic temperature increment is simulatecl using a homogenization theory for thermoelasticity ． The results show that the stress concentration occurs at joint regions betWeen plates and brazing parts ， and at some parts of 丘ns ， indicating the impOrtance ofthermal stress analysis

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