• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2000년도 제18회 학술발표회 논문개요집
• /
• pp.150-150
• /
• 2000

The adsorption geometry and the electronic property of Mg grown at room temperature on the Si(111)-7$\times$7 surface with various coverages have been studied by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). At low Mg coverage, the Mg atoms preferentially adsorb at the center adatom sites of the faulted half of the Si(111)-7$\times$7 surface. The adsorbed Mg atom acts as nucleophile with respect to Si atoms thus forms a stable ionic bond with the substrate Si atoms. Above 1 Ml, the 7$\times$7 surface starts to be disrupted and an amorphous Mg overlayer is formed. The LEED shows either $\delta$7$\times$7 or 1$\times$1 pattern at this coverage. When more Mg atoms were exposed, a flat and broad {{{{ { 2} over {3 } }}}}{{{{ SQRT { 3} }}}}$\times${{{{ { 2} over {3 } }}}}{{{{ SQRT { 3} }}}}R30$^{\circ}$region evolves. A flat silicide is formed at first and multi-level Mg islands having hexagonal step edges develop with increasing coverage. The scanning tunneling spectroscopy (STS) confirms the electronic properties of these Mg films on the si(111) 7$\times$7 surface at various coverages.

• 접착 및 계면
• /
• 제20권2호
• /
• pp.71-75
• /
• 2019

탄닌산은 식물계에서 가장 많이 발견되는 폴리페놀 중 하나로, 초기 탄닌산 연구는 항산화제 등과 같은 생리학적 기능에 집중되어 있었다. 그러나 최근에는 탄닌산이 단백질, DNA 등 거의 모든 생체고분자와 분자간결합을 하는 것이 밝혀짐에 따라 분자적 접착제로서 많은 관심을 받고 있다. 탄닌산의 다양한 특성들은 표면의 기능, 젖음성을 조절할 뿐 아니라 에너지 저장 및 발생 장치에 기여하고, 의학적 제재로의 다양한 가능성을 보이고 있다. 본 논문에서는 분자적 접착제로서의 탄닌산과 생체고분자와의 결합, 탄닌산을 통한 표면 개질, 의료용 제재로의 활용 등에 대해 다루고자 한다.

• 한국정보디스플레이학회:학술대회논문집
• /
• 한국정보디스플레이학회 2004년도 Asia Display / IMID 04
• /
• pp.766-768
• /
• 2004

Rubbed films of a series of poly(p-phenylene 3,6-bis(4-(n-alkyloxy)phenyloxy)pyromellitimide)s (Cn-PMDA-PDA PIs), which are well-defined brush PIs composed of two aromatic-aliphatic bristles per repeat unit of a fully rodlike backbone, were investigated in detail using atomic force microscopy (AFM), optical retardation analysis and linearly polarized infrared (IR) spectroscopy in order to elucidate their surface morphology and molecular orientation. The liquid crystal (LC) alignment behavior and the anchoring energy of LC molecules on the rubbed films were also determined.

• 한국추진공학회지
• /
• 제19권6호
• /
• pp.54-63
• /
• 2015

본 연구에서는 고온/고압의 연소가스에 의해 야기되는 노즐목 삭마현상의 분자수준 메커니즘을 분자동역학 시뮬레이션을 이용하여 관찰한다. 노즐목은 두 개의 그래핀으로 구성된 그래파이트로 모델링하고 분자동역학 시뮬레이션은 충분한 속도를 가지고 그래파이트에 충돌하는 $H_2O$ 분자와 $CO_2$ 분자가 지속적으로 생성되는 과정과 평형상태의 시뮬레이션으로 구성된다. 반응을 모사할 수 있는 ReaxFF 포텐셜을 사용하며, 충돌에 의해 야기되는 $H_2O$ 및 $CO_2$ 분자의 해리와 화학적 삭마와의 관계에 중점을 두고 관찰하고자 하며, 거시적인 관찰결과들과 비교하고자 한다.

• Bulletin of the Korean Chemical Society
• /
• 제35권1호
• /
• pp.39-44
• /
• 2014

Glass discs functionalized with alkynyl (GDA) terminated monolayers were prepared and incubated in $AgNO_3$ solution (GDA-Ag). The modified functional glass surfaces were characterized by X-ray photoelectron microscopy (XPS). The potential of GDA and GDA-Ag as antimicrobial surfaces was investigated. Anti-microbial efficacies of GDA against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus cereus, and Candida albicans was relatively low ranging from 4.67 to 17.00%. However, the GDA-Ag was very effective and its antimicrobial efficacy ranged from 99.90 to 99.99% against the same set of microbial strains except for C. albicans where it was 95.50%. The durability of the Ag bonded to the terminal alkynyl groups was studied by placing the GDA-Ag in PBS buffer solution (pH 7.4) for two weeks. Initially, the silver release was relatively fast, with 40.05 ppb of silver released in first 24 h followed by a very slow and constant release. To study the potential of GDA-Ag for medical applications, in vitro cytotoxicity of GDA-Ag against Human Embryonic Kidney 293 (HEK293) cell lines was studied using WST-assay. The cytotoxicity of the GDA-Ag was very low (5%) and was almost comparable to the control (blank glass disc) indicating that GDA-Ag has a promising potential for medical applications.

• Nuclear Engineering and Technology
• /
• 제54권7호
• /
• pp.2592-2598
• /
• 2022

Research groups in the field of PET instrumentation are studying time-of-flight(TOF) technology to improve the signal-to-noise ratio of PET images. Scintillation light transport and collection plays an important role in improving the coincidence resolving time(CRT) of PET detector based on a pixelated crystal array. Four crystal arrays were designed by the different optical reflection configuration such as external reflectors and surface treatment on the CRT and compared with the light output, energy resolution and CRT. The design proposed in the study was composed of 8 × 8 LYSO crystal array consisted of 3 × 3 × 15 mm³ pixels. The entrance side was roughened while the other five surfaces were polished. Four sides of all crystal pixels were wrapped with ESR-film, and the entrance surface was covered by Teflon-tape. The design provided an excellent timing resolution of 210 ps and improved the CRT by 16% compared to the conventional method using a polishing treatment and ESR-film. This study provided a method for improving the light output and CRT of a pixelated scintillation crystal-based brain TOF PET detector. The proposed configuration might be an attractive detector design for TOF brain PET requiring fast timing performance with high cost-effectiveness.

• Macromolecular Research
• /
• 제16권5호
• /
• pp.473-480
• /
• 2008

In this study we investigated bacterial and cell adhesion to poly(propylene carbonate) (PPC) films, that had been synthesized by the copolymerization of carbon dioxide (a global warming chemical) with propylene oxide. We also assessed the biocompatibility and biodegradability of the films in vivo, and their oxidative degradation in vitro. The bacteria adhered to the smooth, hydrophobic PPC surface after 4 h incubation. Pseudomonas aeruginosa and Enterococcus faecalis had the highest levels of adhesion, Escherichia coli and Staphylococcus aureus had the lowest levels, and Staphylococcus epidermidis was intermediate. In contrast, there was no adhesion of human cells (cell line HEp-2) to the PPC films, due to the hydrophobicity and dimensional instability of the surface. On the other hand, the PPC films exhibited good biocompatibility in the mouse subcutaneous environment. Moreover, contrary to expectation the PPC films degraded in the mouse subcutaneous environment. This is the first experimental confirmation that PPC can undergo surface erosion biodegradation in vivo. The observed biodegradability of PPC may have resulted from enzymatic hydrolysis and oxidative degradation processes. In contrast, the PPC films showed resistance to oxidative degradation in vitro. Overall, PPC revealed high affinity to bioorganisms and also good bio-degradability.

• 접착 및 계면
• /
• 제5권4호
• /
• pp.17-23
• /
• 2004

본 연구에서는 무정형의 폴리카보네이트를 bisphenol-A 및 disphenyl carbonate를 원료로 하여 융용중합방법에 의해 분자량 별로 합성하고 표면처리에 의한 결정화 거동을 살펴보았다. 사용된 결정화 방법으로는 용매 결정화 방법이 사용되었다. 용매의 종류 및 혼합용매의 조성, 온도, 분자량 등에 따른 결정도 및 용융온도의 차이를 DSC, XRD, SEM 등을 이용하여 관찰하였다. 폴리카보네이트의 분자량이 낮음에 따라, 용매 결정화 온도가 높아짐에 따라 용매 결정화에 의한 결정화도가 증가함을 확인할 수 있었으며, 용매 결정화 온도 및 농도가 높아짐에 따라 상대적으로 균일한 결정이 얻어짐을 확인하였다. 또한 혼합용매를 사용함으로써 원하는 표면적을 지닌 결정성 폴리카보네이트를 제조할 수 있었으며, 용매/비용매 비율이 10/90인 혼합용매를 사용한 경우 표면적이 큰 폴리카보네이트를 얻을 수 있었다.

• 대한기계학회논문집A
• /
• 제24권4호
• /
• pp.830-838
• /
• 2000

The paper addresses an application of molecular dynamics technique for fracture mechanics. Molecular dynamics simulation is an atomistic approach, while typical numerical methods such as finite element methods are macroscopic. Using the potential functions, which express the energy of a molecular system, a virtual specimen with molecules is set up and the trajectory of every molecule can be calculated by Newton's equation of motion. Several three-dimensional models with various types of cracks are considered. The stress intensity factors, the sizes of plastic zone as well as the dislocation emission are sought to be compared with the analytical solutions, which result in good agreement.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 추계학술대회
• /
• pp.410-415
• /
• 2004

Molecular dynamics simulations of nanoimprint lithography in which a stamp with patterns is pressed onto amorphous poly-(methylmethacrylate) (PMMA) surface are performed to study the deformation of polymer. Force fields including bond, angle, torsion, inversion, van der Waals and electrostatic potential are used to describe the intermolecular and intramolecular force of PMMA molecules and stamp. Periodic boundary condition is used in horizontal direction and $Nos\acute{e}$-Hoover thermostat is used to control the system temperature. As the simulation results, the adhesion forces between stamp and polymer are calculated and the mechanism of deformation are investigated. The effects of the adhesion force and friction force on the polymer deformation are also studied to analyze the pattern transfer in nanoimprint lithography. The mechanism of polymer deformation is investigated by means of inspecting the indentation process, molecular configurational properties, and molecular configurational energies.