Okayama University Acta Medica Okayama 15 2015 Metamaterial absorbers for infrared inspection technologies EN Atsushi Ishikawa No potential conflict of interest relevant to this article was reported.

Nature Publishing Group Acta Medica Okayama 2045-2322 5 2015 Metamaterial Absorbers for Infrared Detection of Molecular Self-Assembled Monolayers 12570 EN Atsushi Ishikawa Takuo Tanaka The emerging field of plasmonic metamaterials has introduced new degree of freedom to manipulate optical field from nano to macroscopic scale, offering an attractive platform for sensing applications. So far, metamaterial sensor concepts, however, have focused on hot-spot engineering to improve the near-field enhancement, rather than fully exploiting tailored material properties. Here, we present a novel spectroscopic technique based on the metamaterial infrared (IR) absorber allowing for a low-background detection scheme as well as significant plasmonic enhancement. Specifically, we experimentally demonstrate the resonant coupling of plasmonic modes of a metamaterial absorber and IR vibrational modes of a molecular self-assembled monolayer. The metamaterial consisting of an array of Au/MgF2/Au structures exhibits an anomalous absorption at ~3000 cm�|1, which spectrally overlaps with C-H stretching vibrational modes. Symmetric/asymmetric C-H stretching modes of a 16-Mercaptohexadecanoic acid monolayer are clearly observed as Fano-like anti-resonance peaks within a broad plasmonic absorption of the metamaterial. Spectral analysis using Fano line-shape fitting reveals the underlying resonant interference in plasmon-molecular coupled systems. Our metamaterial approach achieves the attomole sensitivity with a large signal-to-noise ratio in the far-field measurement, thus may open up new avenues for realizing ultrasensitive IR inspection technologies. No potential conflict of interest relevant to this article was reported.

American Institute of Physics Acta Medica Okayama 0003-6951 111 18 2017 Selective electroless plating of 3D-printed plastic structures for three-dimensional microwave metamaterials 183102 EN Atsushi Ishikawa Department of Electrical and Electronic Engineering, Okayama University Taiki Kato Department of Electrical and Electronic Engineering, Okayama University Nobuyuki Takeyasu Department of Chemistry, Okayama University Kazuhiro Fujimori Department of Electrical and Electronic Engineering, Okayama University Kenji Tsuruta Department of Electrical and Electronic Engineering, Okayama University A technique of selective electroless plating onto PLA-ABS (Polylactic Acid-Acrylonitrile Butadiene Styrene) composite structures fabricated by three-dimensional (3D) printing is demonstrated to construct 3D microwave metamaterials. The reducing activity of the PLA surface is selectively enhanced by the chemical modification involving Sn2+ in a simple wet process, thereby forming a highly conductive Ag-plated membrane only onto the PLA surface. The fabricated metamaterial composed of Ag-plated PLA and non-plated ABS parts is characterized experimentally and numerically to demonstrate the important bi-anisotropic microwave responses arising from the 3D nature of metallodielectric structures. Our approach based on a simple wet chemical process allows for the creation of highly complex 3D metal-insulator structures, thus paving the way toward the sophisticated microwave applications of the 3D printing technology. Published by AIP Publishing. No potential conflict of interest relevant to this article was reported.

American Institute of Physics Acta Medica Okayama 0003-6951 111 24 2017 Robust plasmonic hot-spots in a metamaterial lattice for enhanced sensitivity of infrared molecular detection 243106 EN Atsushi Ishikawa Department of Electrical and Electronic Engineering, Okayama University Shuhei Hara Department of Electrical and Electronic Engineering, Okayama University Takuo Tanaka Metamaterials Laboratory, RIKEN Xiang Zhan NSF Nanoscale Science and Engineering Center, University of California Kenji Tsuruta Department of Electrical and Electronic Engineering, Okayama University High-density and long-lived plasmonic hot-spots are an ideal system for high-sensitive surface-enhanced infrared absorption (SEIRA), but these conditions arc usually incompatible due to unwanted near-field coupling between the adjacent unit structures. Here, by fully controlling plasmonic interference in a metamaterial lattice, we experimentally demonstrate densely packed long-lived quadrupole plasmons for high-sensitive SEIRA. The metamaterial consists of a strongly coupled array of super-and sub-radiant plasmonic elements to exhibit an electromagnetic transparency mode at 1730 cm(-1), which spectrally overlaps with the C=O vibrational mode. In the SEIRA measurement, the C=O mode of poly(methyl methacrylate) molecules is clearly observed as a distinct dip within a transmission peak of the metamaterial. The corresponding numerical simulations reveal that constructive interference uniformly forms coherent quadrupole plasmons over the metamaterial lattice, leading to a stronger molecular signal from the system. Our metamaterial approach provides a robust way to construct ideal hot-spots over the sample, paving the way toward a reliable sensing platform of advanced infrared inspection technologies. Published by AIP Publishing. No potential conflict of interest relevant to this article was reported.