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남연식,임종현,이진용 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.1
In this study, we carried out nonadiabatic quantum dynamics simulations to investigate charge carrier dynamics in bulk-like TiO<sub>2</sub> nanoparticles upon different 1) size 2) shape and 3) oxygen vacancy location. We show that the recombination rate was deaccelerated with the increasing particle size. The nanoparticles with both (101) and (001) facets showed longer exciton lifetime compared to nanoparticles with only (101) facets. We also report the strong influence of oxygen vacancy location on charge recombination rate which rationalize the contradictory experimental results for photocatalytic activity: Defects at surface site showed fast recombination, while defects at subsurface (bulk) region or at the tip site showed slow recombination, even slower than in the pristine system. We rationalize the trend in terms of average transition energy, exciton binding energy, and nonadiabatic coupling (NAC). Reference: J. Phys. Chem. Lett. 2019, 10, 2676, J. Mater. Chem. C 2019, 7, 13833.
질소 분극면을 갖는 N형 질화물반도체의 접촉저항 감소를 위한 산소 플라즈마 효과에 관한 연구
남태양,김동호,이완호,김수진,이병규,김태근,조영창,최연식,Nam, T.Y.,Kim, D.H.,Lee, W.H.,Kim, S.J.,Lee, B.G.,Kim, T.G.,Jo, Y.C.,Choi, Y.S. 한국진공학회 2010 Applied Science and Convergence Technology Vol.19 No.1
본 논문은 N-face n-type GaN 표면에 산소 플라즈마 처리에 의해서 오믹전극과 접촉 저항을 낮추기 위한 연구를 하였다. 120초 산소 플라즈마 처리후 Ti (50 nm) / Al (35 nm)을 증착한 결과 오믹 전극을 구현하였으며, $1.25{\times}10^{-3}\;{\Omega}cm^2$의 접촉저항을 보였다. 이는 산소 플라즈마 처리가 기존의 플라즈마 처리와 같이 질소결원이 발생하였기 때문이다. 이를 통해 쇼트키장벽 높이(SBH)이 낮아지게 되었고, 오믹 전극및 플라즈마 처리를 안 한 경우보다 더 낮은 접촉저항의 결과를 획득하였다. We studied the effect of $O_2$ plasma treatments on the electrical property of Ti / Al ohmic contacts to N-face n-type GaN. The surface of N-face, n-type GaN has been treated with $O_2$ plasma for 120 s before the deposition of bilayered electrodes, Ti (50 nm) / Al (35 nm), and its contact resistance was compared with that of the reference sample without $O_2$ plasma. As a result, we found that the ohmic contact was reduced from $4.3\;{\times}\;10^{-1}\;{\Omega}cm^2$ to $1.25\;{\times}\;10^{-3}\;{\Omega}cm^2$ by applying $O_2$ plasma on the surface of n-type GaN, which was attributed to the reduction in the Schottky barrier height (SBH), caused by nitrogen vacancies formed during the $O_2$ plasma process.
Theoretical Approach to Investigate Photocatalytic Acitivity of TiO<sub>2</sub> Nanoparticles
임종현,남연식,이진용 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.1
TiO<sub>2</sub> has been highlighted as eco-friendly energy source due to its photocatalytic activity. However wide band gap of TiO<sub>2</sub> lower photocatalytic performance. There have been a lot of efforts to enhance the activity by modifications such as nanostructuring, oxygen defects, chemical doping. Investigating effects of these modifications on light absorption and charge recombination by experimental method is limited due to inevitable presence of defect and ununiformed particles. In order to overcome this limit, theoretical approaches are needed. The density functional theory (DFT) methods and modeling for analyzing TiO<sub>2</sub> nanoparticles are discussed. Furthermore, chemical modification strategies such as band engineering by controlling structure of TiO<sub>2</sub> nanoparticles and introducing oxygen defects or chemical doping are also discussed. Finally, theoretical studies on excited state dynamics involving charge carrier separation, diffusion, and recombination are discussed.
김경환,남우동,허연식,정구희 대한골절학회 2024 대한골절학회지 Vol.37 No.1
Purpose: The purpose of this study is to analyze the clinical results of patients with basicervical fracture undergoing cephalomedullary nailing (CMN) with an additional cannulated screw fixation compared to only performing CMN. We hypothesized that a difference may exist in the clinical outcomes if an additional screw is fixed with CMN compared to only performing CMN in basicervical fracture. Materials and Methods: A total of 28 consecutive patients who underwent CMN for basicervical fracture were included. In 9 cases, only CMN was conducted, and in 19 cases, an additional cannulated screw fixation was performed with CMN. Bone union, sliding distance, reduction status, and fixation failure were evaluated by postoperative radiography, and ambulatory ability was evaluated by functional results. These findings were compared between a group of CMN and a group of CMN with an additional cannulated screw. Results: There were 4 males and 24 females with a mean age of 84 years (range, 69–100 years). No significant difference was found in postoperative reduction, tip-apex distance, bone union, and walking function recovery after surgery between the two groups, but in the sliding distance of the lag screw, the CMN group demonstrated more sliding (6.2 mm [range, 2.5–13.4 mm] vs 3.5 mm [range, 0.1– 9.2 mm]; p=0.045). Among the two groups, only one case of fixation failure at the postoperative four months was observed in the CMN group (p=0.321), and hemiarthroplasty with nail construct removal was performed. Conclusion: CMN with additional cannulated screw fixation is a safe and reliable surgical option in basicervical fracture. It provided favorable clinical outcomes and may be a good alternative for treating basicervical fracture.
백민현,한지현,김주연,심승혁,나연식,이신화,박정열,김종혁,김용만,김영탁,남주현,김대연 대한산부인과학회 2012 대한산부인과학회 학술대회 Vol.98 No.-
We evaluated the usefulness of pre-operative serum CA-125 and Hormone receptors in the management of women diagnosed with uterine papillary serous carcinoma (UPSC). We hypothesized that elevated pre-operative levels of serum CA-125 and hormone receptor(HR) negative group will correlate with higher disease stage and poorer prognosis. Patients diagnosed with UPSC and treated in our institution were identified from 1989 to 2012, over a period of 23 years. All required information were extracted from EMR(electric medical records). We used Receiver operator characteristic curves (ROC) to find the optimal cut off value and quantify marker performance in UPSC. Disease free survival(DFS) and overall survival(OS) were analyzed using Kaplan-Meier method. Multivariate analyses were performed with a Cox proportional regression method. A total of 67 patients met the study criteria. Mean pre-operative serum CA-125 levels were significantly higher in patients with more advanced stage. CA-125 correlated strongly with stage. On the ROC, a cut-off of 39 IU/mL provided the best sensitivity and specificity (48% vs. 100% respectively) for extra-uterine disease. DFS and OS were longer in patients with CA-12539 U/mL.(P=0.0003) Also DFS and OS were relatively longer in patients with positive HR group but had no statistical significance.(P=0.2851) Pre-operative serum CA-125 levels correlate with stage of disease in patients with UPSC. This may be important for management planning, prognostication and counseling in these women.