Akinobu Yamaguchi

Surface-enhanced Raman spectroscopy using a coffee-ring-type three-dimensional silver nanostructure

We demonstrated surface-enhanced Raman spectroscopy using a coffee-ring-type three-dimensional silver nanostructure (Ag3D). Ag3D has high activity for surface-enhanced Raman scattering (SERS). We fabricated Ag3D using convective self-assembly to form a ‘coffee-ring’ structure that consisted of a mixed solution of silver particles and polystyrene latex beads. The mechanism of the formation of Ag3D is described by the competition among a radial flow, a Marangoni recirculating flow, DVLO interactions and sedimentation. Using Ag3D, measurements of a trace amount of 4,4′-bipyridine (4bpy) in aqueous solution were performed, and typical spectra of 4bpy were observed within 1 min of dropping 4bpy. By optimizing the Ag3D preparation conditions, we could observe the characteristic enhanced Raman spectrum of 1 nM 4bpy solution. In addition, we succeeded in observing chloride activation, which increased the intensity of the Raman spectra by a factor of two to three on addition of sodium chloride to Ag3D. SERS measurements using Ag3D were stable even with passing time, whereas the peak intensity drastically dropped within a few minutes in the case with silver nanoparticles only.

Synthesis of metallic nanoparticles through X-ray radiolysis using synchrotron radiation

The potential to fabricate metallic nanoparticles directly on silicon substrates from liquid solutions is ideal for three-dimensional lithography systems, drug delivery materials, and sensing applications. Here, we report the successful synthesis of Au, Cu, and Fe nanoparticles from the corresponding liquid solutions [gold(I) trisodium disulphite, copper(II) sulfate, and potassium ferricyanide] by synchrotron (SR) X-ray irradiation. The deposition of gold nanoparticles in the gold(I) trisodium disulphite solution was performed by monochromatic X-ray exposure from synchrotron radiation. The use of ethanol as an additive enabled the nucleation and growth of Cu particles, while no Cu particles were produced in the copper sulfate solution without ethanol with polychromatic SR X-ray irradiation. Fe particles were generated by direct polychromatic SR X-ray irradiation. These results demonstrate the behavior of three-dimensional printers, enabling us to build composite material structures with metallic and plastic materials.

One-Step Synthesis of Copper and Cupric Oxide Particles from the Liquid Phase by X-Ray Radiolysis Using Synchrotron Radiation

The deposition of copper Cu and cupric oxide Cu4O3, Cu2O, and CuO particles in an aqueous copper sulfate CuSO4 solution with additive alcohol such as methanol, ethanol, 2-propanol, and ethylene glycol has been studied by X-ray exposure from synchrotron radiation. An attenuated X-ray radiation time of 5u2009min allows for the synthesis of Cu, Cu4O3, Cu2O, and CuO nano/microscale particles and their aggregation into clusters. The morphology and composition of the synthesized Cu/cupric oxide particle clusters were characterized by scanning electron microscopy, scanning transmission electron microscopy, and high-resolution transmission electron microscopy with energy dispersive X-ray spectroscopy. Micro-Raman spectroscopy revealed that the clusters comprised cupric oxide core particles covered with Cu particles. Neither Cu/cupric oxide particles nor their clusters were formed without any alcohol additives. The effect of alcohol additives is attributed to the following sequential steps: photochemical reaction due to X-ray irradiation induces nucleation of the particles accompanying redox reaction and forms a cluster or aggregates by LaMer process and DLVO interactions. The procedure offers a novel route to synthesize the Cu/cupric oxide particles and aggregates. It also provides a novel additive manufacturing process or lithography of composite materials such as metal, oxide, and resin.

Application of gold nanoparticle self-assemblies to unclonable anti-counterfeiting technology

Counterfeits are now world-wide issue. An anti-counterfeit technology with high security level (unclonable), high through-put rate of authentication, and low cost is desirable. Nanotag of plasmonic nanostructure with surface enhanced Raman scattering (SERS) activity is promised for the ideal authentication. The gold nanoparticle (AuNP) self-assemblies were applied to SERS active “stealth nanobeacon” for authentication. Mild deposition of aqueous dispersion of self-assembled AuNP was used. 10 ng AuNP assemblies deposited on a commercial medicine tablet were almost invisible to the eye. Distinguishable SERS signals of reporting molecules was produced by 1s irradiation of 785 nm laser over the nanobeacon, while Raman spectrum of the ingredients was observed on the tablet without the nanobeacon. Rapid authentication of tablets stocked for 60 days was sufficiently carried out. It is considered that the presence of discrete AuNP assemblies allows excellent performances of stealth nanobeacon.

Real-space observation of magnetic vortex core gyration in a magnetic disc both with and without a pair tag

We demonstrate the time-resolved real-space observation of vortex gyration in a magnetic circular disc by X-ray magnetic circular dichroism photoemission microscopy at the SPring-8 beamline BL25SU, both with and without an additional structure called a pair tag, which serves to control the magnetic curling direction. By comparing the gyration orbits of the vortices, we found that the gyration properties are dependent on the presence of the additional structure in spite of the discs having the same diameter. Furthermore, we reproduced the vortex gyration by micromagnetic simulation. The confinement potential of the vortex can be controlled by the additional structure.

Ferromagnetic resonance of Ni wires fabricated on ferroelectric LiNbO3 substrate for studying magnetic anisotropy induced by the heterojunction

The electrical ferromagnetic resonance of micro-scale Ni wires with magnetic anisotropy induced by the heterojunction between the Ni layer and ferroelectric single crystalline LiNbO3 substrate was demonstrated by using rectifying effect. The two resonance modes were observed in the Ni wire aligned parallel to the applied magnetic field in plane. The lower resonance frequency mode is considered to correspond to the normal resonance mode with domain resonance, while the higher resonance mode is attributed to the mode which is contributed by the heterojunction between the Ni layer and LiNbO3 substrate. Our results manifest that the rectifying electrical detections are very useful for understating and evaluating the magnetic properties induced by the heterojunction.

Synthesis and immobilization of cupric oxide particles using X-ray raiolysis

We demonstrated synthesis and immobilization of cupric oxide particles using X-ray radiolysis directly from a liquid solution. The X-ray radiolysis of CuSO4 and Cu(CH3COO)2 solutions was observed to produce higher-order microstructures consisting of cupric oxide (CuO, Cu2O, Cu4O3) particles and Cu particles. The sizes of the particles depended on the ratio of ethanol in the stock solution and the surface of the substrate. The results indicate that there are several routes and reaction processes for these particles and aggregation to be synthesized. The technique of X-ray radiolysis enables us to achieve the rapid and easy synthesis of higher-order structures consisting of cupric oxide and copper particles.

Fabrication of higher order nanostructure for molecular sensing

We demonstrate fabrication of higher-order nanostructure for molecular sensing using dielectrophoresis-induced aggregation of Au-nanoparticles-decorated polystyrene beads (AuNPs/PS). We are also able to add the specific linker bridges which bind a target molecule. We achieved the in situ highly sensitive surface enhanced Raman Scattering using the higher-order nanostructure.

Fabrication of waveguide butler matrix for short millimeter-wave using X-ray lithography

The microfabrication technique based on X-ray lithography has recently been applied to construct PTFE-based microstructures. This paper attempts to fabricate an integrated waveguide Butler matrix for short millimeter-wave using X-ray lithography. First, a cruciform 3-dB directional coupler and an intersection circuit are designed at 180 GHz. Then, a 4×4 butler matrix with horn antennas is designed and fabricated. Finally, the measured radiation patterns of the Butler matrix are shown.

Control of Domain Structure in Artificial Ni Wires Fabricated on an LiNbO 3 Substrate

We demonstrated control of magnetic domain structure formation within micro-scale polycrystalline Ni wires fabricated on a single crystalline LiNbO3 substrate. We observed the domain structures using X-ray magnetic circular dichroism-photoemission electron microscopy at SPring-8 BL25SU and BL17SU. Both zebra-stripe domain and ordinary single domain structures can be formed in the Ni wire in control of alignment of the wire onto the substrate. The result suggests that magnetoelastic effects from pizoelectristic substrates can strongly influence the magnetization alignment, overwhelming their shape magnetic anisotropy. The formation of zebra-stripe domain structure can be qualitatively explained by the micromagnetic simulation under the assumption of the magnetic anisotropy perpendicular to the longitudinal axis of wire. Our finding provides a way to control the domain structure and magnetization reversal using the combination of shape magnetic anisotropy and strain-induced anisotropy.