Yun-ah Han

Design Optimization of Structural Parameters for Highly Sensitive Photonic Crystal Label-Free Biosensors

The effects of structural design parameters on the performance of nano-replicated photonic crystal (PC) label-free biosensors were examined by the analysis of simulated reflection spectra of PC structures. The grating pitch, duty, scaled grating height and scaled TiO2 layer thickness were selected as the design factors to optimize the PC structure. The peak wavelength value (PWV), full width at half maximum of the peak, figure of merit for the bulk and surface sensitivities, and surface/bulk sensitivity ratio were also selected as the responses to optimize the PC label-free biosensor performance. A parametric study showed that the grating pitch was the dominant factor for PWV, and that it had low interaction effects with other scaled design factors. Therefore, we can isolate the effect of grating pitch using scaled design factors. For the design of PC-label free biosensor, one should consider that: (1) the PWV can be measured by the reflection peak measurement instruments, (2) the grating pitch and duty can be manufactured using conventional lithography systems, and (3) the optimum design is less sensitive to the grating height and TiO2 layer thickness variations in the fabrication process. In this paper, we suggested a design guide for highly sensitive PC biosensor in which one select the grating pitch and duty based on the limitations of the lithography and measurement system, and conduct a multi objective optimization of the grating height and TiO2 layer thickness for maximizing performance and minimizing the influence of parameter variation. Through multi-objective optimization of a PC structure with a fixed grating height of 550 nm and a duty of 50%, we obtained a surface FOM of 66.18 RIU−1 and an S/B ratio of 34.8%, with a grating height of 117 nm and TiO2 height of 210 nm.

Development of low-cost and large-area nanopatterned vitreous carbon stamp for glass nanoreplication

A low-cost and large-area nano-patterning method of vitreous carbon (VC) was proposed for the stamp of glass nanoreplication process. A polymer mold for a VC nano-pattern was replicated by UV imprinting from a silicon master pattern, and a furan precursor with a nano-grating structure with a pitch of 500.5nm and height of 232.4nm was replicated against a polymer mold. By the carbonization of the furan precursor, a VC nanostamp a nanograting cavity with a pitch of 384nm and a height of 151nm was fabricated. Finally, a glass nanograting was fabricated by glass thermal nanoreplication process using the VC mold. To examine the feasibility of the proposed method, the thermal stability of the optical filter composed of glass nanograting and TiO2 layer was analyzed.

Design and Fabrication of Bilayer Wire Grid Polarizer Using Ultraviolet Replicated Nanograting against Nickel Electroformed Nanostamp

A bilayer wire grid polarizer (B-WGP) composed of UV-replicated nanograting and deposited aluminum layer was designed, fabricated, and evaluated as a simpler and less costly reflective polarizer. To design the B-WGP structure, a parametric study of structural design factors on the simulated performance was conducted using rigorous coupled wave analysis. A durable electroformed nickel stamp was fabricated using a lithographed photo resist master pattern having a nanograting with a pitch of 110 nm, a line width of 65 nm, and a height of 80 nm. A polymer grating was fabricated by the UV replication process, and an aluminum layer with a thickness of 50 nm was deposited by electron-beam evaporation. To examine the performance of the fabricated bilayer wire-grid polarizer, the transmission spectra of p- and s-polarized light, and the extinction ratio spectra were measured and compared with the simulated values. The measured transmittance of p-polarized light and the extinction ratio of the fabricated bilayer wire grid polarizer were ~40% and ~103 in whole visible ranges, respectively.

Analysis of urea in human serum using an oblique angle deposited Ag nanorod surface enhanced Raman scattering substrate

We applied surface enhanced Raman spectroscopy (SERS) for the detection of urea in human serum. An oblique angle deposition method was used to prepare SERS-active substrates consisting of Ag nanorods. To maximize the SERS enhancement, the effects of Ag nanorod length on the SERS signal were analyzed. The SERS signals of different concentrations of urea solutions were measured in order to generate a regression model for use in analyzing the amount of urea in body fluid using the SERS substrate. To examine the feasibility of the fabricated SERS substrate, the amount of urea in human serum was measured using the SERS substrate and compared with that determined via conventional blood analysis.

Fabrication of oblique angle deposited Ag nanorods for enhanced fluorescence substrate

Fluorescence is a widely used tool in biology for imaging and sensing biomaterials. Metal-enhanced fluorescence is a powerful technology for improving sensitivity of fluorescence analysis, where the interactions of fluorophores with metallic nanoparticles results in fluorescence enhancement. In this study, we proposed an inexpensive large area fabrication method of Ag nanostructures for enhanced fluorescence substrate using oblique angle deposition. To examine the feasibility of the proposed substrate and maximize the signal enhancement effects, the oblique angle deposited Ag nanorods substrates with different nanorod lengths were prepared and the measured fluorescence signals from the Streptavidin conjugate Cy5 on the Ag nanorods substrates were compared with those on a glass substrate. The enhancement factor is increased by increasing the length of Ag nanorods, because of the higher surface Plasmon resonance effect of high aspect ratio structure. The maximum enhancement factor of ~23 was obtained from the Ag nanorods substrate with a nanorod length of 1000 nm.

Fabrication of bilayer wire grid polarizer using replicated polymer nano grating

A bilayer wire grid polarizer composed of UV-replicated nanograting and deposited aluminum layer was designed, fabricated and evaluated for a simpler and less costly reflective polarizer. An electroformed nickel stamp was fabricated using a lithographed photo resist master pattern having a nanograting with a pitch of 80 nm, a line width of 50 nm, and a height of grating of 100 nm. A polymer grating was fabricated by the UV replication process and an aluminum layer with a thickness of 50 nm was deposited by electron-beam evaporation. To examine the performance of the fabricated bilayer wire-grid polarizer, the transmission spectra of TM- and TE-polarized light, and the extinction ratio spectra were measured and compared with the simulated values obtained from the rigorous coupled wave analysis. The measured TMtransmittance and extinction ratio of the fabricated bilayer wire grid polarizer were ~ 40 % and ~ 103 in whole visible ranges, respectively.