Jonghyun Ju

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.

Fabrication of All Glass Bifurcation Microfluidic Chip for Blood Plasma Separation

An all-glass bifurcation microfluidic chip for blood plasma separation was fabricated by a cost-effective glass molding process using an amorphous carbon (AC) mold, which in turn was fabricated by the carbonization of a replicated furan precursor. To compensate for the shrinkage during AC mold fabrication, an enlarged photoresist pattern master was designed, and an AC mold with a dimensional error of 2.9% was achieved; the dimensional error of the master pattern was 1.6%. In the glass molding process, a glass microchannel plate with negligible shape errors (~1.5%) compared to AC mold was replicated. Finally, an all-glass bifurcation microfluidic chip was realized by micro drilling and thermal fusion bonding processes. A separation efficiency of 74% was obtained using the fabricated all-glass bifurcation microfluidic chip.

Fabrication of Glass Microchannel via Glass Imprinting using a Vitreous Carbon Stamp for Flow Focusing Droplet Generator

This study reports a cost-effective method of replicating glass microfluidic chips using a vitreous carbon (VC) stamp. A glass replica with the required microfluidic microstructures was synthesized without etching. The replication method uses a VC stamp fabricated by combining thermal replication using a furan-based, thermally-curable polymer with carbonization. To test the feasibility of this method, a flow focusing droplet generator with flow-focusing and channel widths of 50 µm and 100 µm, respectively, was successfully fabricated in a soda-lime glass substrate. Deviation between the geometries of the initial shape and the vitreous carbon mold occurred because of shrinkage during the carbonization process, however this effect could be predicted and compensated for. Finally, the monodispersity of the droplets generated by the fabricated microfluidic device was evaluated.

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.

Fabrication and characterization of glancing angle deposited nanostructured surfaces for enhanced boiling heat transfer

Glancing angle deposition (GLAD) process has been regarded as an efficient method to fabricate nanostructured surfaces for enhanced boiling heat transfer because of its simplicity and variety of material selection. In this study, the effects of structural parameters (particularly the orientation and length of GLAD nanostructures) on boiling heat transfer were analyzed. The boiling heat transfer characteristics of Ag GLAD nanorods on a silicon substrate were examined using pool boiling experiments with deionized water. The vertical nanorod provided better performance than a slanted one, and a length of 200 nm was selected as the optimal length for maximizing the boiling heat transfer. A pool boiling critical heat flux of 20.6 W/cm2 was obtained for a 200 nm tall Ag-vertical nanostructure, and 13.6 W/cm2 was obtained for plain Ni-Ag layer on Si substrate. A 420% enhancement in the heat transfer coefficient was successfully achieved on a nanostructured surface compared to a plain Ni-Ag layer.

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.

Fabrication of single crystal silicon nanowires by metal assisted chemical etching with nanoimprinted barrier pattern

Study of the combined effects of strong electronic correlations with spin-orbit coupling (SOC) represents a central issue in quantum materials research. Predicting emergent properties represents a huge theoretical problem since the presence of SOC implies that the spin is not a good quantum number. Existing theories propose the emergence of a multitude of exotic quantum phases, distinguishable by either local point symmetry breaking or local spin expectation values, even in materials with simple cubic crystal structure such as Ba

Silver nanorod structures for metal enhanced fluorescence

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

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Fabrication of oblique angle deposited Ag nanorods for enhanced fluorescence substrate

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