Kyeong-Seok Lee

Resolution enhancement in surface plasmon resonance sensor based on waveguide coupled mode by combining a bimetallic approach.

In this study, we present and demonstrate a new route to a great enhancement in resolution of surface plasmon resonance sensors. Basically, our approach combines a waveguide coupled plasmonic mode and a kind of Au/Ag bimetallic enhancement concept. Theoretical modeling was carried out by solving Fresnel equations for the multilayer stack of prism/Ag inner-metal layer/dielectric waveguide/Au outer-metal layer. The inner Ag layer couples incident light to a guided wave and makes more fields effectively concentrated on the outer Au surface. A substantial enhancement in resolution was experimentally verified for the model stack using a ZnS-SiO2 waveguide layer.

Effect of fluorine addition on transparent and conducting Al doped ZnO films

Al doped ZnO (AZO) films with varying fluorine content were prepared by radio frequency magnetron sputtering at a room temperature to investigate doping effects of fluorine on the structural, the optical, and the electrical properties. The small amount of fluorine addition to AZO films resulted in beneficial effect on the electrical conductivity by improving the direct current (dc) Hall mobility, and the minimum specific resistivity was as low as 5.9×10−4Ωcm. With increasing fluorine content in AZO films, the optical absorption loss in the visible range decreased regardless of carrier concentration in the films. X-ray diffraction and scanning electron micrograph analyses showed that the crystallinity of AZO films was deteriorated by addition of fluorine. Small amount of fluorine addition to AZO film resulted in decrease of absorption loss as well as increase in Hall mobility, and the beneficial effects of fluorine addition was deduced to be caused by killing in-grain point defects. From the comparison bet...

Behaviour of Co binder phase during diamond deposition on WCCo substrate

Abstract The movement of the Co-rich binder phase and its interaction with growing diamond particles during deposition were investigated by repeated observations of the same site on a WC-Co substrate surface. Both etched and unetched (as-polished) specimens of WC-5Co were used for deposition. The diamond deposition was carried out using the tungsten filament chemical vapour deposition method. Raman spectra have shown that the quality of the diamond deposited on the etched substrate was better than that on the as-polished substrate. The facet size of the diamond film surface on the as-polished substrate was smaller than that on the etched specimen. These effects were caused by the atomic-scale interaction of Co atoms in the binder phase. A special feature of the diamond film on the as-polished specimen was a very rough diamond film surface. This phenomenon was observed to result from the abnormal movement of the Co-rich binder phase to the deposited diamond particle surface and the subsequent non-uniform growth of particles during deposition. The phenomenological characteristics of the Co-rich binder phase movement were also explained.

Size effects of metal nanoparticles embedded in a buffer layer of organic photovoltaics on plasmonic absorption enhancement

The effects of Au or Ag nanoparticles on optical absorption enhancement of organic photovoltaics based on blended poly(3-hexylthiophene)?:?phyenyl-C61-butyric acid methyl ester (P3HT?:?PCBM) were investigated using a finite-difference-time-domain method. The spherical metal nanoparticles were embedded in a buffer layer of thickness 20?nm and their size was varied from 10 to 50?nm. The metal nanoparticles with diameter 10?20?nm offered negligible absorption enhancement in the active layer. Unlike those short metal nanoparticles, the incorporation of metal nanoparticles taller than the buffer layer led to a significant absorption enhancement by plasmonic resonance especially in the case of Ag nanoparticles. Ag nanoparticles gave broader and stronger absorption enhancement in the active layer than Au nanoparticles. An enhancement of 34% in the optical absorption of the active layer was observed with Ag nanoparticles of 50?nm diameter at 10% coverage. The electric field distributions around metal nanoparticles, their self-absorption and the active layer thickness dependence on the absorption enhancement were studied.

Plasmonic nanograting design for inverted polymer solar cells

Plasmonic nanostructures for effective light trapping in a variety of photovoltaics have been actively studied. Metallic nanograting structures are one of promising architectures. In this study, we investigated numerically absorption enhancement mechanisms in inverted polymer photovoltaics with one dimensional Ag nanograting in backcontact. An optical spacer layer of TiO2, which also may act as an electron transport layer, was introduced between nanograting pillars. Using a finite-difference-time domain method and performing a modal analysis, we explored correlations between absorption enhancements and dimensional parameters of nanograting such as period as well as height and width. The optimal design of nanograting for effective light trapping especially near optical band gap of an active layer was discussed, and 23% of absorption enhancement in a random polarization was demonstrated numerically with the optimally designed nanograting. In addition, the beneficial role of the optical spacer in plasmonic light trapping was also discussed.

Silicon nanodisk array design for effective light trapping in ultrathin c-Si

The use of ultrathin c-Si (crystalline silicon) wafers thinner than 20 μm for solar cells is a very promising approach to realize dramatic reduction in cell cost. However, the ultrathin c-Si requires highly effective light trapping to compensate optical absorption reduction. Conventional texturing in micron scale is hardly applicable to the ultrathin c-Si wafers; thus, nano scale texturing is demanded. In general, nanotexturing is inevitably accompanied by surface area enlargements, which must be minimized in order to suppress surface recombination of minority carriers. In this study, we demonstrate using optical simulations that periodic c-Si nanodisk arrays of short heights less than 200 nm and optimal periods are very useful in terms of light trapping in the ultrathin c-Si wafers while low surface area enlargements are maintained. Double side texturing with the nanodisk arrays leads to over 90% of the Lambertian absorption limit while the surface area enlargement is kept below 1.5.

Pump-probe optical switching in prism-coupled Au:SiO2 nanocomposite waveguide film

The resonance properties due to the surface plasmon excitation of metal nanoparticles make the nanocomposite films promising for various applications such as optical switching devices. In spite of the well-known ultrasensitive operation of optical switches based on a guided wave, the application of nanocomposite film has inherent limitation originating from the excessive optical loss related to the surface plasmon resonance. In this study, we address this problem and present the experimental and theoretical analyses on the pump-probe optical switching in prism-coupled Au(1vol%):SiO2 nanocomposite waveguide film.

Fabrication of Plasmonic Nanodiscs by Photonic Nanojet Lithography

In this study, we present and demonstrate a new route to the fabrication of plasmonic nanostructures with a controlled size and shape using photonic nanojet lithography. Through the approach of dual-layer lift-off, the achievable size was remarkably reduced to a sub-100 nm scale and the introduction of an engineered diffuser was proved to give a facile and precise way of controlling the anisotropy in shape without a process burden even when the spherical focusing beads are used.

A method of determining the elastic properties of diamond-like carbon films

The elastic properties of diamond-like carbon (DLC ) films were measured by a simple method using DLC bridges which are free from the mechanical constraints of the substrate. The DLC films were deposited on a Si wafer by radio frequency (RF ) glow discharge at a deposition pressure of 1.33 Pa. Because of the high residual compressive stress of the film, the bridge exhibited a sinusoidal displacement on removing the substrate constraint. By measuring the amplitude with a known bridge length, we could determine the strain of the film which occurred by stress relaxation. Combined with independent stress measurement using the laser reflection method, this method allows the calculation of the biaxial elastic modulus, E/(1’n), where E is the elastic modulus and n is Poisson’s ratio of the DLC film. The biaxial elastic modulus increased from 10 to 150 GPa with increasing negative bias voltage from 100 to 550 V. By comparing the biaxial elastic modulus with the plane‐strain modulus, E/(1’n2), measured by nano-indentation, we could further determine the elastic modulus and Poisson’s ratio, independently. The elastic modulus, E, ranged from 16 to 133 GPa in this range of the negative bias voltage. However, large errors were incorporated in the calculation of Poisson’s ratio due to the pile up of errors in the measurements of the elastic properties and the residual compressive stress.

Detection of Amyloid-β42 Using a Waveguide-Coupled Bimetallic Surface Plasmon Resonance Sensor Chip in the Intensity Measurement Mode

The waveguide-coupled bimetallic (WcBiM) surface plasmon resonance (SPR) chip had been utilized in the intensity interrogation detection mode to detect amyloid-β42 (Aβ42), a biomarker of the Alzheimer disease. The SPR reflectance curve of the WcBiM chip has the narrower full-width-at-half-maximum (FWHM) compared with the SPR reflectance curve of the conventional gold (Au) chip, resulting in the steeper gradient. For the enhancement of resolution, the light source was fixed at an angle where the slope of the reflectance curve is the steepest, and the change in the reflectance was monitored. For the detection of Aβ42, the antibody of Aβ42 (anti-Aβ42) was immobilized on the WcBiM SPR chip using the self-assembled monolayer. The SPR responses, the average changes in the reflectance to the Aβ42 at the concentrations of 100 pg/ml, 250 pg/ml, 500 pg/ml, 750 pg/ml, 1,000 pg/ml, and 2,000 pg/ml were 0.0111%, 0.0305%, 0.0867%, 0.1712%, 0.3021%, and 0.5577%, respectively, for the three replicates. From linear regression analysis, the calibration curve indicated that the SPR response had a linear relation with Aβ42 with the concentration in the range of 100 pg/ml to 2,000 pg/ml. A control experiment showed the anti-Aβ42-modified surface of the WcBiM chip had a high specificity to Aβ42. Thus, the enhanced resolution by utilizing the WcBiM SPR chip in the intensity interrogation detection mode aids the diagnosis of the Alzheimer disease by detecting the Aβ42 around the criteria concentration (500 pg/ml) without any labeling.