Do-Eok Kim

Variable wavelength surface plasmon resonance (SPR) in biosensing

In this study, we fabricated a novel variable wavelength surface plasmon resonance (SPR) sensor, which detects resonance conditions such as a maximum attenuation wavelength, measuring change of microscopic refractive index. Such a change was measured to detect a salmonella antigen-antibody reaction and a penicillinase-penicillin reaction. Our experiments were performed after immobilizing a salmonella antibody on the sensor chip. We measured the shift in resonant wavelength during the antigen-antibody reaction for 30 min by injecting 5 x 10(7) cells/ml concentration of salmonella antigen solution into the sample chamber. Also, after immobilizing penicillinase on the sensor chip, we measured the shift in resonant wavelength during the reaction. Penicillin solution at 10mM was injected into the sample chamber. The shift of resonant wavelength for each experiment was measured using a white light source, multimode optical fiber, a part of sensor chip and an optical spectrum analyzer. As a result, the resonant wavelength shifted about 0.26 nm/min owing to the salmonella antibody-antigen reaction. Thus, we could detect the change in wavelength (0.8 nm/min) through the interaction of penicillin and penicillinase for 15 min using variable wavelength SPR sensor.

Substrate Heated Spray-Deposition Method for High Efficient Organic Solar Cell: Morphology Inspection

We report a general approach involving the heating of glass substrates for fabricating spray-coated organic photovoltaic cells. We heated a substrate was heated to temperatures of 50, 100, and 150 °C during the spray-coating process and observed different morphology of the active layer. It was found that the morphology influenced the performance of the organic solar cell. The solar cell subjected to spray coating at a substrate temperature of 150 °C showed a power conversion efficiency (PCE) of ~3.84%, an open voltage of ~0.61 V, and a short current density of ~20 mA/cm2. After optimizing post annealing, we obtained the PCE up to 4.3%.

UV-sensitive photofunctional device using evanescent field absorption between SU-8 polymer optical waveguide and photochromic dye

We presented an ultraviolet (UV)-sensitive photofunctional device using a principle of evanescent field coupling occurring between SU-8 waveguide and photochromic dye (spirooxazine). The feasibility as a UV sensor was evaluated. When the 5-mm sensing area was irradiated with UV for 3 s, the absorption and the output intensity of the UV sensor was 0.0396 /spl sim/ 0.114 absorbance/mW and 1 /spl sim/ 10 mW, respectively. The UV sensor had linearity by variation of sensing area. The sensitivity of the proposed sensor was higher than the spectrophotometers method and optical fiber sensors.

Refractive index change by photoinduction of a UV-sensitive SMF-to-PWG coupler

We fabricated a UV-sensitive photofunctional device using evanescent field coupling between a side-polished single-mode optical fiber (SMF) and photochromic dye-dispersed polymer planar waveguide (PWG). PWG was made by diarylethene derivative [1,2-bis(2,5-dimethylthiophen-3-yl) hexafluoro-cyclopentene (DM-BTE)] with a stability and memory effect by photoinduction. The wavelength response characteristic for UV irradiation time was 3.44 nm (UV irradiation time 60 s), and recovery time was 140 s. The optical attenuation characteristic of 1310-nm wavelength was 0.4 dB in 1 wt% concentration of DM-BTE and 1.65 dB at 10 wt% DM-BTE. The refractive index changes of DM-BTE by photoinduction were /spl Delta/n=0.00067 in the condition of 3 wt% of DM-BTE concentration and 5 mW of UV intensity and 70 s of UV irradiation time.

Development of non-invasive optical transcutaneous pCO/sub 2/ gas sensor and analytic equipment

We have studied the development of an optical transcutaneous pCO/sub 2/ gas sensor and analyzer using a non-invasive method. The basic principle of the pCO/sub 2/ measurement adapted Beer-Lamberts law and the embodied system using the NDIR (non dispersive infrared) method. CO/sub 2/ gas reacts with a 4.3 /spl mu/m wavelength, so we selected this wavelength by an optical filter, and used energy decrease by molecule oscillations. We measured the CO/sub 2/ concentration using the MFC (mass flow controller) in basic steps instead of the pCO/sub 2/ gas that can collect by inflicting heat on the outer skin. This measuring system consisted of an IR lamp, an optical filter, an optical reaction chamber, a pyroelectric sensor and a signal processing system. We minimized the volume of the optical reaction chamber in order to make the sensor portable. We made an optical reaction chamber with a Si wafer using MEMS technology and it was shortened to 1 mm. We carried out an experiment in photoreaction length variation from 1 mm to 10 mm. We confirmed the linear graph of CO/sub 2/ concentration variation from 1,000 ppm (parts per million) to 100,000 ppm at 1 mm photoreaction length. The response time of this system was within 2 seconds, which is fairly fast.

Fabrication of Organic/Inorganic LED device using nanocrystal quantum dots as active layer

Recently, researches on nanocrystal quantum dot-based LEDs (NQD-based LEDs) have dramatically increased due to their characteristics resulting in pure and saturated colors with a narrow bandwidth. More importantly, colors can be easily tuned by varying the size or the composition of NQDs, and high quantum yields (QY) of NQDs can increase the efficiency greatly. In spite of high fluorescence QY of NQDs, the reported efficiency of QD-LEDs is still low because the carrier transport is not efficient in the fabricated device. We report efficient electroluminescence in quantum dot-based LEDs by enhancing the electronic coupling of NQDs. 2D array of NQDs formed by spin-coating showed enhanced electrical conductivity. They are incorporated into the light emitting device as an active layer. Current-voltage characteristic and electroluminescent spectra of the device are measured. Electroluminescence efficiency of the device is improved, resulting from the facilitated carrier transport between layers by electronic coupling of NQDs.

SPR bio-sensor using white light source and OSA

In this study, we fabricated wavelength type SPR (surface plasmon resonance) sensor to measure microscopic refractive index change in wide band by real time. We measured SPR phenomena according to salmonella antigen-antibody reaction and penicillinase - penicillin reaction to apply in SPR immunosensor. Our experiments used a SAM (self assembled monolayer) method to immobilize Salmonella antibody and penicillinase on each sensor chips. Also, Salmonella antigen and penicillin poured within each antibody immobilized sensor chambers. Concentrations of Salmonella antibody and antigen are 50 µm/ml and 5 × 107 cfu/ml. Concentration of penicillinase and penicillin are 0.5 mg/ml and 10 mM. The shifts of resonance wavelength for each experiment were measured using OSA for 30 minutes. We could know that salmonella antigen-antibody reactions were saturated after 10 minutes and penicillinase - penicillin reactions were saturated after 15 minutes. The shift of resonance wavelength was varied about 0.26 nm/min for Salmonella antigen-antibody reaction and 0.8 nm/min for penicillinase - penicillin reaction.

Fabrication and characteristics of photofunctional polymer waveguide-type UV sensor

Single-mode planar waveguide type UV sensor was fabricated using SU-8 and photochromic dye. Polymer waveguide was fabricated 10 µm width and 2 µm thickness for single-mode operation. The UV sensor had an absorbance with 0.0396~0.114 absorbance/mW respectively when the 5 mm sensing area was irradiated with UV for 3 sec. And sensor had a linear properties by sensing area variation. Proposed single-mode sensor had more excellent properties of UV sensitivity than other UV sensors.

Enhancement of Operating Lifetime and Performance on Polymer Light Emitting Diode by Mg–Zn–F Passivation

Fluorine material MgF2 with Zn has recently been reported to have good encapsulation properties with high optical transmittance. We fabricated a 200 nm Mg–Zn–F passivation film for encapsulation of organic light emitting diodes using a radio frequency magnetron sputter. The water vapor transmission rate of Mg–Zn–F passivation film on poly(ethylene naphthalate) was determined using a calcium degradation test. Heating of the substrate during sputtering enhanced the device performance, and Mg–Zn–F film applied to a polymer light emitting diode device almost doubled its operating lifetime.

Enhancement of PLED lifetime using thin film passivation with amorphous Mg‐Zn‐F

Abstract In this study, a new thin films passivation technique using Zn with high electronegativity and MgF2, a fluorine material with better optical transmittance than the sealing film materials that have thus far been reported was proposed. Targets with various ratios of MgF2 to Zn (5:5, 4:6 and 3:7) were fabricated to control the amount of Zn in the passivation films. The Mg‐Zn‐F films were deposited onto the substrates and Zn was located in the gap between the lattices of MgF2 without chemical metathesis in the Mg‐Zn‐F films. The thickness and optical transmittance of the deposited passivation films were approximately 200 nm and 80%, respectively. It was confirmed via electron dispersive spectroscopy (EDS) analysis that the Zn content of the film that was sputtered using a 4:6 ratio target was 9.84 wt%. The Zn contents of the films made from the 5:5 and 3:7 ratio targets were 2.07 and 5.01 wt%, respectively. The water vapor transmission rate (WVTR) was determined to be 38°C, RH 90–100%. The WVTR of the Mg‐Zn‐F film that was deposited with a 4:6 ratio target nearly reached the limit of the equipment, 1×10‐3 g/m2•day. As the Zn portion increased, the packing density also increased, and it was found that the passivation films effectively prevented the permeation by either oxygen or water vapor. To measure the characteristics of gas barrier, the film was applied to the emitting device to evaluate their lifetime. The lifetime of the applied device with passivation was increased to 25 times that of the PLED device, which was non‐passivated.