• Korean Journal of Materials Research
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• v.21 no.5
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• pp.273-276
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• 2011

Ultraviolet (UV) light emitting diodes (LEDs) were grown on a patterned n-type GaN substrate (PNS) with 200 nm silicon-di-oxide (SiO2) nano pattern diameter to improve the light output efficiency of the diodes. Wet etched self assembled indium tin oxide (ITO) nano clusters serve as a dry etching mask for converting the SiO2 layer grown on the n-GaN template into SiO2 nano patterns by inductively coupled plasma etching. PNS is obtained by n-GaN regrowth on the SiO2 nano patterns and UV-LEDs were fabricated using PNS as a template. Two UV-LEDs, a reference LED without PNS and a 200 nm PNS UV-LEDs were fabricated. Scanning Electron microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Photoluminescence (PL) and Light output intensity- Input current- Voltage (L-I-V) characteristics were used to evaluate the ITO-$SiO_2$ nanopattern surface morphology, threading dislocation propagation, PNS crystalline property, PNS optical property and UVLED device performance respectively. The light out put intensity was enhanced by 1.6times@100mA for the LED grown on PNS compared to the reference LED with out PNS.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.43.2-43.2
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• 2011

Single-walled carbon nanotubes (SWCNT) are transparent in the visible and show conductivity comparable to copper, and are environmentally stable. SWCNT films have high flexibility, conductivity and transparency approaching that indium tin oxide (ITO), and can be prepared inexpensively without vacuum equipment. Transparent conducting Films (TCF) of SWCNTs has the potential to replace conventional transparent conducting oxides (TCO, e.g. ITO) in a wide variety of optoelectronic devices, energy conversion and photovoltaic industry. However, the sheet resistance of SWCNT films is still higher than ITO films. A decreased in the resistivity of SWCNT-TCFs would be beneficial for such an application. We fabricated SWCNT sheet with $KAuBr_4$ on PET substrate. Arc-discharge SWCNTs were dispersed in deionized water by adding sodum dodecyl sulfate (SDS) as surfactant and sonicated, followed by the centrifugation. The dispersed SWCNT was spray-coated on PET substrate and dried on a hotplate at $100^{\circ}C$. When the spray process was terminated, the TCF was immersed into deionized water to remove the surfactant and then it was dried on hotplate. The TCF film was then treated with AuBr4-, rinsed with deionized water and dried. The surface morphology of TCF was characterized by field emission scanning electron microscopy. The sheet resistance and optical transmission properties of the TCF were measured with a four-point probe method and a UV-visible spectrometry, respectively. $HNO_3$ treated SWCNT films with Au nano-particles have the lowest 61 ${\Omega}$/< sheet resistance in the 80% transmittance. Sheet resistance was decreased due to the increase of the hole concentration at the washed SWCNT surface by p-type doping of $AuBr_4{^-}$.

• Korean Journal of Digital Imaging in Medicine
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• v.3 no.1
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• pp.126-132
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• 1997

Purpose : To apply to Program of Auto processor quality control after comparison of Film density variations with amendments to Auto density by using Check density program and Adjust density program of calibration mode into the Laser imager. Methods : Observe Check and Adjust density variations on the Control chart with standard step and value during seven months from December, 1995 to June, 1956 extending twice a week. (1) Measure density value on the steps after printing out 17-step sensitometric pattern of the Check density program. (2) In the same way, measure density values after amending density by using Adjust density program If they are exceeding allowable error limit. Results : In case of Check density program, the exceeding limit rates of Density difference(DD) and Middle density(MD) are: FL-IM3543 DD=75%. MD=72.5%, FL-IMD DD=0%. MD=30.8%(14.5%) After amending density by using Adjust density program, the exceeding limit rates of all both Laser imager were zero percent. The standard deviations are show lower FL-IM D than FL-IM3543 on the Check density control chart, but higher on the Adjust density control chart. Conclusion : (1) Check density variations by printingout sensitometric pattern extending once a week at least for quality control of the Laser imager. (2) In case of a dusty place, check the Laser beam transmission after cleaning Laser optical unit extending once a month. (3) Be sure to measure and check density values by using adjust density program if they are exceeding allowable error limit. (4) Maintain much better film density by performing the adjust density program even if check density values are existed within normal limit.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.12
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• pp.764-770
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• 2014

It is expected that the techniques of optical imaging through turbid media enables non-invasive imaging through human skin and biological tissues. In recent years, many researches have shown that imaging through turbid media can be made possible by measuring the transmission matrix (TM) of the turbid medium and utilizing it for image recovery. However, this TM based image recovery requires a huge amount of data acquisition and post signal processing of them. Very recently, there were new results that this problem of huge data acquisition and processing can be resolved by using the compressed sensing (CS) framework. CS is a relatively new signal acquisition and reconstruction framework which makes possible to recover the signal of interest correctly with significantly smaller number of signal measurements. In this paper, the TM-based image recovery in imaging through turbid media is reviewed and the recent progress made by using CS is introduced.

• Journal of Korean Ophthalmic Optics Society
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• v.3 no.1
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• pp.223-228
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• 1998

Glass films of $SiO_2-TiO_2-M_xO_y$ (M = Co, Cr or Cu) have been prepared on soda-lime-silica slide glasses by the chemical solution method using a spin-coating technique. Commercially available tetraethyl orthosilicate, titanium trichloride, and cobalt-, chromium- and copper-nitrates were used as starting materials. No crystalline segregations of $Co_3O_4$, $Cr_2O_3$ and CuO were observed by X-ray diffraction ${\theta}-2{\theta}$ scans. From the optical transmission analysis, cobalt existed as $ Co^{2+}$ in tetrahedral coordination, chromium as $Cr^{6+}$ in tetrahedral symmetry and copper as $Cu^{2+}$ in octahedral coordination. Films with a crack-free and no texture exhibited homogeneous interfaces between the films and the substrates along the cross-section.

• Journal of Sensor Science and Technology
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• v.28 no.6
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• pp.402-406
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• 2019

Recently, semiconducting organic materials have been spotlighted as next-generation electronic materials based on their tunable electrical and optical properties, low-cost process, and flexibility. However, typical organic semiconductor materials are vulnerable to moisture and oxygen. Therefore, an encapsulation layer is essential for application of electronic devices. In this study, SiN_x thin films deposited at process temperatures below 150 ℃ by plasma-enhanced chemical vapor deposition (PECVD) were characterized for application as an encapsulation layer on organic devices. A single structured SiN_x thin film was optimized as an organic light-emitting diode (OLED) encapsulation layer at process temperature of 80 ℃. The optimized SiN_x film exhibited excellent water vapor transmission rate (WVTR) of less than 5 × 10^-5 g/㎡·day and transmittance of over 87.3% on the visible region with thickness of 1 ㎛. Application of the SiN_x thin film on the top-emitting OLED showed that the PECVD process did not degrade the electrical properties of the device, and the OLED with SiN_x exhibited improved operating lifetime

• Advances in nano research
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• v.5 no.3
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• pp.215-230
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• 2017

The development of hybrid systems comprising nanoparticles and polymers is an opening pathway for engineering nanocomposites exhibiting outstanding mechanical, optical, electrical, and magnetic properties. Among inorganic counterpart, iron oxide nanoparticles (IONP) exhibit high magnetization, controllable surface chemistry, spintronic properties, and biological compatibility. These characteristics enable them as a platform for biomedical applications and building blocks for bottom-up approaches, such as the layer-by-layer (LbL). In this regard, the present study is addressed to investigate IONP synthesised through co-precipitation route (average diameter around 7 nm), with either positive or negative surface charges, LbL assembled with sodium sulfonated polystyrene (PSS) or polyaniline (PANI). The surface and internal morphologies, and electrochemical properties of these nanocomposites were probed with atomic force microscopy, UV-vis and Raman spectroscopy, scanning electron microscopy, cross-sectional transmission electron microscopy, and electrochemical measurements. The nanocomposites display a globular morphology with IONP densely packed while surface dressed by polyelectrolytes. The investigation of the effect of thermal annealing (300 up to $600^{\circ}C$) on the oxidation process of IONP assembled with PSS was performed using Raman spectroscopy. Our findings showed that PSS protects IONP from oxidation/phase transformation to hematite up to $400^{\circ}C$. The electrochemical performance of nanocomposite comprising IONP and PANI were investigated in $0.5mol{\times}L^{-1}$ $Na_2SO_4$ electrolyte solution by cyclic voltammetry and chronopotentiometry. Our findings indicate this structure as promising candidate for potential application as electrodes for supercapacitors.

• Architectural research
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• v.18 no.3
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• pp.83-90
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• 2016

Senescent effects are the gradual deterioration of function caused by biological aging. Senescent effects on color vision are not clearly understood even after considerable researches. Part of the reason is that the color vision is a complex phenomenon resulting from various factors such as organic systems, and the physical (neuro-optical) and the psychological (experiential) processes of color perception. We performed a field experiment on color perceptional differences due to aging vision. Our experiment was applied to two different groups in South Korea: an experimental group (46 subjects of over the age of 61 years) and a control group (49 subjects in their twenties). The experimental tools are comprised of (1) six gradual yellowing detector board (40%, 50%, 60%, 70%, 80%, 90%); (2) pairs of vivid-strong, vivid-deep, grayish-deep, deep-dull, and bright-light tones of Blue (B) and Purple (P) colors; (3) Red (R), Yellow (Y), Green (G), Blue (B), and Purple (P) colors of dull-tones and pale-tones; and (4) a questionnaire on the semantic differential scales of the color images and color differences. A diagnosis system of gradual yellow vision, developed by the authors for this study, was adapted to generate the color detecting boards. The results are as follows. (1) There are significant differences between the two groups in detecting colors that simulate 40% and 50% of yellow vision. (2) As to the color difference detecting ability between similar tones, the experimental group shows difficulties in pairs of vivid-strong tones and deep-dull tones of the B color. And (3), the emotional responses to the dull tone and the pale tone are not stable in the red, the yellow, blue, and purple. Thus, we empirically demonstrate the specific differences in color perception between the old and young groups.

• Korean Chemical Engineering Research
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• v.53 no.6
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• pp.798-801
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• 2015

Nanomaterials (NMs) based on cadmium telluride (CdTe) are the theme of numerous research areas due to their unique chemical and physical properties. NM synthesis via a size-controlled procedure has become an intriguing research topic because NMs exhibit novel optical and physical properties depending on their size and shape. In this study, we prepared CdTe nanowires (NWs) via self-assembly from individual Nanoparticles (NPs). Thioglycolic acid (TGA)-to-Cd ion ratio of 1.3 was used instead of the traditional value of 2.4 and the reduced amount of stabilizer resulted in reorganization from individual NPs into NWs consisting of multi-layers of individual NPs. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were performed to characterize NWs. The produced nanowires were straight and long in shape and their length ranged from 500 nm to tens of micrometers.

• Electrical & Electronic Materials
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• v.9 no.5
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• pp.463-469
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• 1996

The double insulating layer consisting of anodic oxide and ZnS was formed for HgCdTe metal insulator semiconductor(MIS) structure. ZnS was evaporated on the anodic oxide grown in H$_{2}$O$_{2}$ electrolyte. Recently, this insulating mechanism for HgCdTe MIS has been deeply studied for improving HgCdTe surface passivation. It was found through TEM observation that an interface layer is formed between ZnS and anodic oxide layers for the first time in the study of this area. EDS analysis of chemical compositions using by electron beam of 20.angs. in diameter and XPS depth composition profile indicated strongly that the new interface is composed of ZnO. Also TEM high resolution image showed that the structure of oxide layer has been changed from the amorphous state to the microsrystalline structure of 100.angs. in diameter after the evaporation of ZnS. The double insulating layer with the resistivity of 10$^{10}$ .ohm.cm was estimated to be proper insulating layer of HgCdTe MIS device. The optical reflectance of about 7% in the region of 5.mu.m showed anti-reflection effect of the insulating layer. The measured C-V curve showed the large shoft of flat band voltage due to the high density of fixed oxide charges about 1.2*10$^{12}$ /cm$^{2}$. The oxygen vacancies and possible cationic state of Zn in the anodic oxide layer are estimated to cause this high density of fixed oxide charges.