• Journal of the Korean Ceramic Society
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• v.40 no.11
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• pp.1113-1119
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• 2003

We used isopropanol which has low boiling point to prepare thin films at low temperature and changed mole concentration of zinc acetate from 0.3 to 1.3 mol/l. The structural, optical and electrical properties of ZnO thin films with Zn content were investigated. ZnO thin films highly oriented along the c-axis were obtained at Zn concentration of 0.7 mol/l. ZnO thin films with Zn concentration of 0.7 mol/l showed a homogeneous surface layer of nano structure. The transmittance of ZnO thin films by UV-vis. measurement was about 87% under the Zn concentration of 0.7 mol/l, but rapidly decreased over the 1.0 mol/l. The optical band gap energy was obtained from 3.07 to 3.22 eV which is very close to the band gap of bulk ZnO (3.2 eV). The electrical resistivity of ZnO thin films was about 150 $\Omega$-cm that shows little difference with Zn concentration. I-V curves of ZnO thin films exhibited typical ohmic contact properties.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2021.05a
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• pp.374-376
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• 2021

For the diagnosis of cancer-related diseases in clinical practice, pathological examination using biopsy is essential after basic diagnosis using imaging equipment. In order to proceed with such a biopsy, the assistance of an oncologist, clinical pathologist, etc. with specialized knowledge and the minimum required time are essential for confirmation. In recent years, research related to the establishment of a system capable of automatic classification of cancer cells using artificial intelligence is being actively conducted. However, previous studies show limitations in the type and accuracy of cells based on a limited algorithm. In this study, we propose a method to identify a total of 4 cancer cells through a convolutional neural network, a kind of deep learning. The optical images obtained through cell culture were learned through EfficientNet after performing pre-processing such as identification of the location of cells and image segmentation using OpenCV. The model used various hyper parameters based on EfficientNet, and trained InceptionV3 to compare and analyze the performance. As a result, cells were classified with a high accuracy of 96.8%, and this analysis method is expected to be helpful in confirming cancer.

• Korean Journal of Optics and Photonics
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• v.34 no.6
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• pp.261-268
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• 2023

We propose a compact differential interference contrast microscopic module, which enables snapshot measurements for quantitative phase imaging. The proposed module adopts the lateral shearing interferometric principle, which can obtain self-interference without a reference. Due to the absence of the reference, the system is more stable than the typical interferometric systems. It uses a polarization grating to generate two laterally shifted wavefronts based on its birefringence and polarizing beam-splitting characteristics. Furthermore, the use of a polarization camera does not require sequential measurements for the phase extraction. In the experiments, we observe and measure the timely varying changes of various specimens to verify the system performance with the bright field images and phase contrast images. Because the proposed microscopic module also has the merit of being adaptable to typical microscopy instead of using an imaging camera, it can conveniently replace conventional contrast microscopy.

• Applied Chemistry for Engineering
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• v.10 no.1
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• pp.148-153
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• 1999

In situ composites containing a thermotropic liquid crystalline polymer were prepared by polycondensation of 1,4-bis(p-hydroxy-benzoyloxy)butane with 2-bromoterephthaloyl chloride in a poly(methyl methacrylate) solution. Morphology and mechanical, thermal properties of the composites were examined by differential scanning calorimeter(DSC), dynamic mechanical thermal analyser(DMTA), optical microscope and scanning electron microscope(SEM). The TLCP domains showed nematic phase. The glass transition temperature($T_g$) and mechanical properties of the PMMA in the composites increased with increasing the content of TLCP. The TLCP domains were finely dispersed in the PMMA matrix. The 20 wt % TLCP/PMMA composite prepared by in situ polymerization showed more improved mechanical property with finely well dispersed morphology compared with that prepared by solution blending of the same composition.

• Journal of Korean Ophthalmic Optics Society
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• v.8 no.2
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• pp.129-134
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• 2003

A wide variety of unsaturated vinyl derivatives can be induced to undergo free-radical chain polymerization. The capability to carry out a thermodynamically feasible polymerization relies on its kinetic feasibility on whether the proceeds at a reasonable rate under a given set of reaction conditions. Initiator or promoter is often required to achieve the kinetic feasibility. Only a few unsaturated monomers including methyl methacrylate(MMA) are known to absorb light between 250 and 500 nm which is the most convenient wavelength range. Also, the polysilanes with unusual optical and electronic properties have been used as ceramic precursors, deep UV photoresists, photoconductors. The hydrosilation has been used to make many interesting types of silicon containing polymers such as copolymer, dendrimers. Bulk polymerization of monomers with different molar radio of hydrosilanes(9:1 through 1:9) were performed. A quartz test tube charged with monomer and hydrosilane was degassed and irradiated with 250 nm UV for 6 hours. The polymer was taken in toluene, precipitated in hexane, filtered off, and dried. It was found that the initiators appeared to competitively and concurrently function as both chain initiation and transfer agents in the polymerization of vinyl monomers.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.21-21
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• 2006

21세기 정보통신 및 관련 소재의 연구방향은 새로운 기능성 확보, 극한적 제어성, 복합 및 융합이라는 경향으로 발전해 가고 있다. 반도체 기술 분야에서 현재의 공정적 한계를 극복하고 새로운 기능성을 부여하기 위해 나노 합성과 배열을 기본으로 하여 bottom-up 방식의 나노소자 구현이 큰 주목을 받고 있다. 나노선의 경우 나노 스케일의 dimension, 양자 제한 효과, 우수한 결정성, self-assembly, internal stress 등 기존 벌크형 소재에서 발견할 수 없는 새로운 기능성이 나타나고 있어 바이오, 에너지, 구조, 전자, 센서 등의 분야에서의 활용이 가능하다. 현재 국내외적으로 반도체 나노선으로 널리 연구되고 있는 재료는 ZnO, $SnO_2$, SiC 등이 중심이 되고 있다. 이중 ZnO 나 노선의 합성을 위해서는 thermal CVD, MOCVD, PLD, wet-chemical 등 다양한 방법이 사용되고 있다. 특히 MOCVD 방법에 의해 수직 정렬된 ZnO 나노막대를 성장할 수 있다. 이러한 나노막대는 MO 원료 및 산소 공급량을 적절히 제어함으로서 수직 배향 및 나노선의 구경 제어가 가능하며, 나노 막대의 크기 제어와 관련해서는 반응 관내의 DEZn 와 $O_2$의 양을 변화시켜 구조체의 크기를 수 십 ~ 수 백 나노미터의 크기로 제어할 수 있다. 본 연구는 이러한 ZnO 나노선의 성장과정에서 $210^{\circ}C$ 이하의 저온에서 성장한 ZnO 버퍼층을 이용해 나노구조의 형상을 제어하고자 하였다. 특히 ZnO 저온 버퍼층의 두께에 따라 나노막대의 직경변화, 수직배향성, 형상변화의 제어가 가능하였다. 나노막대의 특성 평가는 TEM, SEM, PL, XRD 등을 이용하여 구조적, 결정학적, 광학적 특성을 분석하였다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.1
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• pp.12-16
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• 2004

In this study, we have investigated the development of the crystal growth stability and reproducibility for large and high-quality DAST. DAST crystal were grown from a saturated methanol solution by a slow cooling method and DAST was synthesized by the condensation of 4-methyl-n-methyl pyridinum tosylate, which was prepared from 4-pocoline and methyl toluenesulponate and 4-N-dimethyl amino-bezaldehyde in the presence of piperidine. We had synthesized DAST crystals in dry Argon atmosphere in order to avoid the formation of hydride organge co-crystals, DAST$.$$H_2O$. Since DAST molecules crystallize in a humid atmosphere, crystal structure become centrosymmetric, and then second order NLO (nonlinear optical) properties would be disappeared. We fixed the growth orientation of DAST crystal (001) surface. The crystal growth was proceeded at a cooling rate of $H_2O$/day and the cooling period is for 4 days. The dimensions of seed crystal was $2.5\times 3.6\times0.4\textrm{mm}^3$ and we have obtained a DAST crystal with the dimension of $10\times 10.5\times3.0\textrm{mm}^3$. The color of grown DAST crystal is red and it's surface appears to be metallic green.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2958-2965
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• 2015

The PLGA(Poly lactide-co-glycolide) Copolymer have been actively applied to the medical implant material as biomaterials. PLGA membrane was able to alveoloplasty with osteotomy for favorable degradation characteristics and possibilities for sustained drug delivery. In this study, PLGA membrane was prepared using phase inversion method, and examined to optical method analysis(NMR, IR), mechanical property measurement (tearing strength) and thermal characteristic analysis(DSC). In addition, the biodegradation characteristics of the PLGA membrane filled with a PBS(Phosphate Buffered Solution) of the water bath ($60^{\circ}C$) according to the degree of surface degradation in the degradation time, the pH change of the solution and change of the mass of the membrane were measured.

• Polymer(Korea)
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• v.25 no.2
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• pp.279-292
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• 2001

Two kinds of (hydroxypropyl)cellulose(HPCs) with different molar substitution (MS) and three types of derivatives based on the HPCs: (acetoxypropyl)celluloses, (ethoxypropyl)celluloses, and (cyanoethoxyprofyl)celluloses were synthesized, and their thermal and mesomorphic properties were investigated. All samples, which exhibit cholesteric reflection colours at room temperature, formed right-handed helicoidal structures whose optical pitches (λ$_{ms}$ ) increase with temperature. However, the isotropization ($T_{i}$) and glass temperatures, the magnitude of λ$_{m}$ of the mesophase at the same temperature, and the temperature dependence of λ$_{m}$ of the investigated derivatives highly depended on MS and the length and structure of the side chain introduced in HPC. The results were discussed in terms of the difference in the polarity and flexibility of the substituents and the distance between the main chains. For all derivatives, Am values approached infinity at temperatures above the $T_{i}$, of the mesophase, and no reversal in the sense of the pitch with temperature was detected.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.655-655
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• 2013

그래핀은 높은 전자 이동도, 열전도도, 기계적 강도, 유연성 등의 고유한 특성으로 다양한 분야에 응용하기 위한 연구가 수행되고 있으며, 특히 전자 소자에의 적용에 관한 연구가 활발히 이루어지고 있다. 전자 소자에 적용하기 위해서는 성장 및 물성에 관한 규명, 응용 소자에 따른 특성 평가가 필요하다. 이러한 소자 특성은 그래핀 물성에 의한 영향이 기본적이지만 에칭, 전사 등의 공정 중 발생하는 오염, 표면 특성, 잔여물 등에 의한 물성 변화 또한 분석 및 제어에 관한 연구가 필요하다. 열화학증착법(thermal chemical vapor deposition)을 이용한 그래핀 합성은 구리 기판을 사용하며, 합성된 그래핀의 에칭, 박리 및 전사 공정이 있다. 이러한 공정 중 발생하는 오염 입자가 그래핀 표면에 흡착되거나, 제거되지 않은 PMMA 잔여물이 그래핀의 특성에 영향을 미치게 된다. 따라서 본 연구에서는 $CO_2$ 클러스터의 표면 충돌을 이용하여 이러한 오염 물질 및 잔여물을 제거하고 그래핀 표면을 평탄화하는 것에 관한 연구를 수행하였다. 가스 클러스터란 작동기체의 분자가 수십에서 수백 개 뭉쳐 있는 형태를 뜻하며 이렇게 형성된 클러스터는 수 nm 크기를 형성하게 된다. 그리고 짧은 시간의 응축에 의해 수십 nm 크기 까지 성장 하게 된다. 클러스터를 이용한 표면 처리는 충돌에 의한 제거에 기반 한다. 따라서 생성 및 가속되는 클러스터로부터 대상으로 전달되는 운동량의 정도가 세정 특성에 영향을 미치며 이는 생성되는 클러스터의 크기에 종속적이다. 생성 클러스터의 크기 분포는 분사거리, 유량, 분사 각도, 노즐 냉각 온도 등의 변수에 관한 함수이다. 본 연구에서는 이러한 변수들을 제어하여 클러스터를 이용한 그래핀 표면 처리 실험을 수행하였다. 평가는 클러스터 표면 처리 전과 후의 특성 비교에 기반 하였으며, 광학 현미경을 이용한 표면 형상 측정, 라만분광 분석, AFM을 이용한 표면 조도 측정, 그래핀 면저항 측정 결과를 비교하였다. 평가 결과를 통하여 표면 처리를 하지 않은 그래핀에 비하여 면저항과 표면 조도가 낮아지는 것을 확인 할 수 있었다. 또한 클러스터 세정은 300 mm 웨이퍼 크기 이상의 대면적을 짧은 시간에 건식으로 세정할 수 있다는 장점이 있어 향후 최적화를 통해 그래핀 양산 시 특성 향상을 위한 후처리 방법으로 사용될 수 있음을 확인하였다.