Scanning near-field optical microscopy facilitates the studies on optical properties of nanomaterials beyond the diffraction limit of light. It enables us to reveal the optical properties point by point on the nanomaterials. In this article, we review our recent works on optical properties and their spatial features of localized plasmons in noble metal nanoparticles, revealed by various near-field optical techniques. We show that photonic local density-of-states or optical fields on the nanoparticles are visualized by using near-field linear and non-linear spectroscopic imaging techniques. We also show that the plasmon wavefunction resonant with the incident field is visualized by the near-field methods. Finally, we present spatio-temporal behaviors of the nanoparticles upon the photoexcitation visualized by near-field time-resolved imaging technique. We analyze the origin of the characteristic transient images and discuss energy dissipation processes of the nanoparticles.
We developed a novel method to enhance the light emission efficiencies from solid-state materials by use of surface plasmon (SP). We obtained a 17-fold increase in the luminescence intensity along with a 7-fold increase in the internal quantum efficiency of light emission from InGaN/GaN quantum wells (QWs) when nano-structured silver layers were deposited 10 nm above the QWs. We also observed a 32-fold increase in the spontaneous emission rate of InGaN/GaN at 440 nm probed by time-resolved PL measurements. Electron-hole pairs in the materials couple to electron vibrations at the metal surface and produce SPs instead of photons or phonons. This new path increases the spontaneous emission rate and the internal quantum efficiencies. The SP-emitter coupling technique would lead to super bright and high-speed solid-state light-emitting devices that offer realistic alternatives to conventional fluorescent light sources.
Photoinduced charge separation is possible at interfaces between Au or Ag nanoparticles and TiO2. The charge separation is based on localized surface plasmon resonance of the metal nanoparticles. The Au-TiO2 system can be applied to visible light-responsive photocatalysts and photovoltaic cells. If Ag is used instead of Au, visible light-induced oxidation and UV light-induced re-reduction of Ag nanoparticles are possible. These new photoelectrochemical processes can be applied to multicolor photochromism and photoelectrochemical actuators based on hydrogels.
Micro droplets produced from the introduction of immiscible fluids of organic phase and water phase are useful for a wide range of applications, especially in the field of chemistry and biochemistry. Smaller micro droplets in the microfluidic system increase the efficiencies of chemical reaction and extraction in liquid-liquid interfaces. In order to realize high generation rate of the uniform oil-in-water droplets, we invented the multi-stage divergence system. The droplet generation rate was achieved by the uniform micro fluidic separation up to 16 micro droplets from one droplet. The maximum generation rate was 1760 droplets/s and the deviationof their diameters was smaller than 3%. The generation rate and diameter were well controlled by the flow rates of water phase and organic phase. We also developed the fabrication of nano-porous polymer microcapsules using self-assembly of the block copolymers in the multipahse microfluidic system. The spherical microcapsule was successfully fabricated with the polymer thickness of 0.5∼1.5 μm and nano pores.
Nanobiotechnology was developed for biomolecular and cellular analyses, including DNA, protein, sugar chain, lipoprotein, and cell. The surface conditions of nanopillar device affected the performance of DNA analysis. Surface pretreatments were developed for high performance analysis of protein, sugar chain, and lipoprotein. An importance of surface and interface in the development of new nanobiotechnology was discussed.
Membrane proteins play very important roles in cells. They are also useful in various industrial fields, including drug discovery, and highly sensitive ion-channel-based biosensors. Here, I describe our two approaches toward membrane protein chips: an array of membrane proteins on (1) planar lipid bilayers and (2) giant vesicles. First, a highly reproducible method was developed for planar lipid bilayer reconstitution. Planar lipid bilayers are formed at apertures by flowing lipid organic solution and buffer alternately into an integrated microfluidic channel. Using this technique, multiple lipid bilayers are formed simultaneously, and channel currents through peptide ion channels were recorded. Second, I describe a method for the preparation of lipid vesicles inspired by forming soap bubbles from a soap film. In our “blowing” method, lipid vesicles are blown out of the pre-formed bio-functional planar lipid membrane, directly encapsulating ejected materials. We believe that these devices are useful for an efficient and rapid analysis of singlespecies-specific membrane proteins.
We developed an Encapsulated Production System (EPS) composed of the human space and the product space. The product space is isolated from the human space in protection from penetration of particle and gas in the human space. Concentrations of oxygen, particle, and dissolved oxygen in solutions in the product space are of 5 orders of magnitude lower than those in atmosphere. As an experimental application of the system to the control of semiconductor surface and interface, we formed Schottky barrier diodes of Al/Si(111) interface in the EPS system and investigated diode leakage currents. It was found that electrically-ideal interfaces with no leakage current and no fluctuation of Schottky barrier heights were formed in the system.
We review first-principles theoretical calculations of core level shifts including the final state core hole screening effect. By using pseudopotentials with core holes, it is possible to calculate accurately the shifts of core levels which vary depending on their chemical environments. We point out the validity and limitation of the scheme by showing some examples.