Yaerim Lee

CuO nanowire/microflower/nanowire modified Cu electrode with enhanced electrochemical performance for non-enzymatic glucose sensing

CuO nanowire/microflower structure on Cu foil is synthesized by annealing a Cu(OH)2 nanowire/CuO microflower structure at 250 °C in air. The nanowire/microflower structure with its large surface area leads to an efficient catalysis and charge transfer in glucose detection, achieving a high sensitivity of 1943 μA mM(-1) cm(-2), a wide linear range up to 4 mM and a low detection limit of 4 μM for amperometric glucose sensing in alkaline solution. With a second consecutive growth of CuO nanowires on the microflowers, the sensitivity of the obtained CuO nanowire/microflower/nanowire structure further increases to 2424 μA mM(-1) cm(-2), benefiting from an increased number of electrochemically active sites. The enhanced electrocatalytic performance of the CuO nanowire/microflower/nanowire electrode compared to the CuO nanowire/microflower electrode, CuO nanowire electrode and CuxO film electrode provides evidence for the significant role of available surface area for electrocatalysis. The rational combination of CuO nanowire and microflower nanostructures into a nanowire supporting microflower branching nanowires structure makes it a promising composite nanostructure for use in CuO based electrochemical sensors with promising analytical properties.

Coupling of localized surface plasmons to U-shaped cavities for high-sensitivity and miniaturized detectors

We report numerical analysis of the coupling of localized surface plasmons to the modes of U-shaped cavities. The coupling results in intense resonance for which the electric field is strongly enhanced on the cavity surfaces. As a result, an optical vortex in the power flow is formed in the cavities and a sharp and strong resonance dip is observed in the reflectance spectrum. High sensitivity of the dip wavelength to change in the refractive index of the surrounding medium is reported. The high sensitivity is realized with a small number of cavities, thus enabling miniaturization of detectors based on U-shaped cavities.

Effective light concentration in gold short nanosphere chain on platinum mirror for surface-enhanced Raman scattering

We studied closely spaced gold nanosphere chains on Pt mirrors exhibiting strong plasmon coupling between both horizontally and vertically oriented modes relative to the chain. Resonance modes originating from the plasmon couplings realized effective light concentration around the short nanosphere chain and showed red shifts with decreasing interparticle gap length, revealing the hybrid nature of the two plasmonic modes. Thanks to the effective light concentration, the short nanosphere chain demonstrated strong surface enhanced Raman scattering (SERS) that was not strongly affected by variations in the length of the gaps or when some of the spheres made contact with each other. Even with large gaps, the short nanosphere chain exhibited consistent SERS under a low excitation power of only 0.4 mW/μm2, owing to the geometrical robustness of the nanospheres and Pt plane supporting enhancement of the electric field in the sphere-plane gaps.

A 3D metallic structure array for refractive index sensing with optical vortex

A simple and large-scale fabrication technique for three dimensional structure arrays using a photolithography process was applied to realize an array of high-aspect-ratio metallic fins. The fin array enables light confinement between the high-aspect-ratio fins, thus generating optical vortices. The light confinement between the fins produces sharp dips in the reflection spectrum of the array. We show that the position of the dip wavelength is sensitive to change in the refractive index of the surrounding medium. Sensitivity to change in the refractive index was quantified by optical simulation and experimental measurements.

Triple-walled gold surfaces with small-gaps for nonresonance surface enhanced Raman scattering of rhodamine 6G molecules

To increase the intensity of Raman scattering with surface enhanced Raman scattering (SERS) effect, the authors proposed the triple-walled gold (Au) structures on silicon (Si) substrate. High aspect ratio Au nanowalls with nanogaps were realized by two different techniques. One is layer by layer technique. The other is standing high aspect ratio Au wall fabrication technique. Finally, 50 nm-thick Au standing walls and 50 nm gaps were obtained. Through the comparison of bare Si substrate, Au film, single-walled Au structures, and triple-walled Au structures in SERS intensity with 0.020 wt. % rhodamine 6G molecules, it was revealed that the SERS intensity from triple-walled Au structure was 50 times higher than that from Au film. The enhancement factor (EF) of our proposed SERS chip was estimated as 4.7 × 106. The proposed method will allow us to realize multiwalled Au structure, which can increase EF efficiently.

Localized surface plasmons coupled in U-shaped nano-cavity with high sensitivity

We present simulations of a novel U-shaped cavity supporting the coupling of cavity modes with plasmon resonances. The resonances with optical vortices exhibit strong and sharp reflectance dips having high sensitivity to their environments.