Hiroaki Matsui

By Hiroaki Matsui and Hitoshi Tabata

Part of the book: Nanowires

By Hiroaki Matsui and Hitoshi Tabata

We introduce excitonic polarized photoluminescence (PL) of nonpolar ZnO layers and related quantum well (QW) structures in terms of crystal symmetries and lattice distortions. Polarized PL characters are attributed to in-plane anisotropic strains in the host, which are fully demonstrated on A-plane ZnO. Theoretical evaluations propose that in-plane compressive strains induced in ZnO layers play an important role in obtaining highly polarized optical properties. We experimentally achieve polarized PL responses in strain-controlled A-plane ZnO layers. Furthermore, we find interesting relationship between polarization degree of PL and in-plane anisotropic strains. Finally, highly polarized PL at room temperature is obtained by controlling well width in Cd0.06ZnO0.94O/ZnO QWs as a consequence of change in crystal symmetry from C6v to C2v at interfaces between Cd0.06Zn0.94O well and ZnO barrier layers in the QW samples.

Part of the book: Luminescence

By Hiroaki Matsui and Hitoshi Tabata

This chapter describes plasmonic responses in In2O3:Sn nanoparticles (ITO NPs) and their assembled ITO NP sheets in the infrared (IR) range. ITO NPs clearly provide resonance peaks related to local surface plasmon resonances (LSPRs) in the near-IR range, which are dependent on electron density in the NPs. In particular, electron-impurity scattering plays an important role in determining carrier-dependent plasmon damping, which is needed for the design of plasmonic materials based on ITO. ITO NPs are mainly dominated by light absorption. However, a high light reflection is observed in the near- and mid-IR range when using assembled NP sheets. This phenomenon is due to the fact that the introduction of surface modifications to the NPs can facilitate the production of electric-field (E-field) coupling between the NPs. The three-dimensional (3D) E-field coupling allows for resonant splitting of plasmon excitations to the quadrupole and dipole modes, thereby obtaining selective high reflections in the IR range. The high reflective performances from the assembled NP sheets were attributed to the plasmon interactions at the internanoparticle gaps. This work provides important insights for harnessing IR optical responses based on plasmonic technology toward the fabrications of IR solar thermal-shielding applications.

Part of the book: Nanoplasmonics

By Hiroaki Matsui

The chapter reports photoluminescence (PL) and an energy transfer dynamic in a hybrid heterostructure consisting of an Ag nanoparticle (NP) layer and Cd0.08Zn0.92O/ZnO quantum well (QW). The observed PL quenching was closely related to electronic states of excitons confined in the QW. The PL quenching of the QW emission was only observed at low temperatures which excited carriers were radiatively recombined due to excitonic localization derived from fluctuated energy potentials in the QW. In contrast, delocalization of excitons from the QW with increasing temperature resulted in disappearance of the PL quenching. Time-resolved PL measurements revealed a decay rate of PL from the QW emission through the presence of energy transfer from the QW to Ag NP layer. The temperature-dependent energy-transfer rate was similar to that of the radiative recombination rate. The Ag NP layer surface showed a visible light absorption caused by localized surface plasmons (LSPs), which was very close to the PL peak energy of the QW. These results indicated that the excitonic recombination energy in the QW was nonradiatively transferred to Ag NP layer owing to energy resonance between the LSP and the QW. These phenomena could be explained by a surface energy transfer mechanism.

Part of the book: Noble and Precious Metals

By Hiroaki Matsui

Oxide semiconductors have received much attention for potential use in optoelectronic applications such as transparent electrodes, transistors, and emitting devices. Recently, new functionalities of oxide semiconductors have been discovered such as localized surface plasmon resonances (LSPRs), which show high-efficiency plasmon excitations in the infrared (IR) range using different structures such as nanorods, nanoparticles (NPs), and nanodots. In this chapter, we introduce optical properties of carrier- and size-dependent LSPRs in oxide semiconductor NPs based on In2O3: Sn (ITO). In particular, systematic examinations of carrier- and size-dependent LSPRs reveal the damping mechanisms on LSPR excitations of ITO NPs, which play an important role in determining excitation efficiency of LSPRs. Additionally, the control of carrier and size in the ITO NPs contribute toward improving solar-thermal shielding in the IR range. The high IR reflectance of assembled films of ITO NPs is due to three-dimensional plasmon coupling between the NPs, which is related to electron carriers and particle size of ITO NPs. This chapter provides new information concerning structural design when fabricating thermal-shielding materials based on LSPRs in oxide semiconductor NPs.

Part of the book: Nanocrystalline Materials

By Hiroaki Matsui

We report on plasmonic resonances on VO2 nanodot arrays and associated optical dynamics. The plasmon excitations based on electric field interactions lead to red shifts of the plasmon resonances to lower photon energy with increasing nanodot size. The spectral linewidths of plasmon peaks gradually become narrow with increasing nanodot size. This is related to a reduction in plasmon damping with respect to the electronic band structure of VO2. This specific band structure of VO2 affects the optical dynamics of plasmon resonances at the sub-picosecond scale. The optical excitations of VO2 comprise intraband and interband transitions. The existence of plasmon bands induces long-lived lifetimes on decay processes. Intraband transitions in the conduction band (C.B.) play an important role in producing long lifetimes, attributing to free carriers in the C.B. By contrast, interband transitions related to bound electrons contribute to plasmon damping. The dynamic optical responses are closely related to the electronic band structures of VO2.

Part of the book: Novel Imaging and Spectroscopy

By Hiroaki Matsui

Biological detection based on surface plasmon resonances (SPRs) on metallic Ga-doped zinc oxide (ZnO: Ga) film surfaces is introduced as one of the interesting functionalities of ZnO. SPRs on ZnO: Ga films (ZnO-SPRs) have attracted much attention as alternative plasmonic materials in the infrared (IR) range. This chapter focuses on the structure and optical properties of ZnO-SPR with different layer structure from experimental and theoretical approaches. First, the plasmonic properties of single ZnO: Ga films excited by Kretschmann-type SPRs were investigated. Second, an insulator–metal–insulator structure with a ZnO: Ga film applied as a metal layer is introduced. Finally, hybrid layer structures with the capping of thin dielectric layers to ZnO-SPR (dielectric-assisted ZnO-SPR) were fabricated to enhance SPR properties in the IR range. The biological sensing on ZnO-SPR is experimentally demonstrated by measuring biological interactions. This work provides new insights for fabricating biological sensing platforms on ZnO materials.

Part of the book: Biosignal Processing