Variation of chemical reactions of organic molecules on the Si(5 5 12) surface

정석민,정호진,한재량 한국진공학회 2007 한국진공학회 학술발표회초록집 Vol.16 No.1

치아에 대한 치아미백제의 효과에 관한 연구

정석민 광주보건대학 2002 論文集 Vol.27 No.-

This study was purposed to evaluate the effect of commercial home tooth bleaching agent application on the color of tooth. Fifty sound extracted teeth were randomly divided into 5 groups and were evaluated by the color differences between before and after treatment with 5 types of tooth bleaching agents (Nite White Excel, Insta-Brite, Opalescence, Plus White and StarBrite Contrast _(P.M.)). Teeth were treated with 5 types of bleaching agents and the color changes were evaluated. The results were as follows; 1. By 4 weeks bleaching agents treatment, the difference of value (L^(*)) of the tooth were increased as high as 3.61 ∼ 7.75 and the color difference (E^(*)) showed as high as 9 ∼ 14. 2. L^(*) and E^(*) between 2 week treated- and 4 week treated-groups did not show significant changes (p>0.05), except L^(*) and E^(*) in the cases of Plus White and E^(*) in the cases of StarBrite Contrast treated group(p<0.05). 3. Nite White Excel among tested bleaching agents induced greatest L^(*) increase for teeth showing significant changes of L^(*) by 2 weeks bleaching agent treatments and by 4 weeks bleaching agent treatments except in the case of Opalescence (p<0.05). Nite White Excel induced significantly greater E^(*) for teeth by 2 and 4 weeks bleaching agent treatments when comparing to the E^(*) induced by all other tested bleaching agents groups (p<0.05), These results demonstrate that all the commercial tooth bleaching agents have appreciable bleaching effect on teeth.

제26차 학술대회 : 67. 우발적인 표재성 위암

정석민,이중달 대한외과학회 1974 대한외과학회 학술대회자료집 Vol.- No.-

Carbamide peroxide의 함량에 따른 치아미백제의 치아에 대한 효과

정석민,남상용,곽동주,Chung, Suk-Min,Nam, Sang-Yong,Kwak, Dong-Ju 대한치과기공학회 2001 대한치과기공학회지 Vol.23 No.1

The purpose of this study was to evaluate the effects of commercial home-tooth bleaching agents on the color of tooth. Twenty five sound extracted teeth were randomly divided into five groups. The color differences between before and after treatment with five types of tooth bleaching agents (7.5% hydrogen peroxide Nite White $Excel^{(R)}$, 10% carbamide peroxide Nite White $Excel^{(R)}$, 16% carbamide peroxide Nite White $Excel^{(R)}$, 10% carbamide peroxide Insta-BriteTM, 20% carbamide peroxide Insta-$Brite^{TM}$) were evaluated. The results were as follows: 1. By 2 week home tooth bleaching agent applications, the values ($L^*$) of bovine teeth increased as high as 4.38 $\sim$ 8.80 when comparing to those of the samples before treatment, and the color difference (${\Delta}E^*$) showed as high as 10.16 $\sim$ 15.04. 2. 16% carbamide peroxide Nite White Excel induced significantly greater ${\Delta}L^*$ than other test edgroups except for 7.5% hydrogen peroxide Day White Excel, and significantly greater ${\Delta}E^*$ than other tested groups by 2 week bleaching agent treatments (p<0.01). 3. 16% carbamide peroxide Nite White Excel(${\Delta}L^*$=8.80, ${\Delta}E^*$=15.04) induced significantly greater ${\Delta}L^*$ and ${\Delta}E^*$ than 10% carbamide peroxide Nite White Excel(${\Delta}L^*$=5.01, ${\Delta}E^*$=10.16)(p<0.01), but significant difference between 10% carbamide peroxide Insta-Brite(${\Delta}L^*$=4.38, ${\Delta}E^*$=10.51) and 20% carbamide peroxide Insta-Brite(${\Delta}L^*$=5.63, ${\Delta}E^*$=11.23) was not shown in ${\Delta}L^*$ and ${\Delta}E^*$(p>0.01). 4. 16% carbamide peroxide Nite White Excel(${\Delta}L^*$=8.80, ${\Delta}E^*$=15.04) which were applied in night time induced significantly greater ${\Delta}L^*$ and ${\Delta}E^*$ than 7.5% hydrogen peroxide Day White Excel(${\Delta}L^*$=8.47, ${\Delta}E^*$=12.75) which were applied in day time. Conclusions: These results demonstrate that all the commercial home-tooth bleaching agents have appreciable bleaching effect on teeth, and the effects of home-tooth bleaching agents which are used during night time are affected by content of carbamide peroxide. Especially the whitening effect of home tooth bleaching agents that are used through night time is greater than that of short time-applying tooth bleaching agent.

Origin of the Modied Electronic Properties of Au Formed on Pentacene

정석민,허혜은,임규욱,Joung-Real Ahn,송우석,홍준용,박종윤,강태희 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2

A Au lm formed on a pentacene layer, as a model system of a metal contact on a pentacenebased field-effect transistor, has been investigated. Unexpected pentacene derivatives and coarse morphology depending on the Au thickness are suggested as origins of the abnormal electronic structure of the Au film and the poor reproducibility of organic-based devices. The morphology of the Au film shows a strong dependency on the Au coverage. At 600 A of Au, a lift of the pentacene layer is shown as a result of deformation of the cracked Au film induced by a relaxation of the intergranular stresses accumulated during the growth process.

풀러린과 2차원 전자기체 표면의 상호작용

정석민 한국진공학회 2008 한국진공학회 학술발표회초록집 Vol.2008 No.8

Dissociation of NO on Si(001) and Incorporation of N into the Subsurface

정석민 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.III

We present our first-principles calculation on NO (nitric oxide) dissociation on the Si(001) surface and subsequent nitrogen incorporation into the subsurface. NO adsorbs on the surface as a molecular form parallel or perpendicular to a Si dimer, but its dissociated structures are much more stable than the molecular forms. In the dissociated configurations, nitrogen or oxygen tends to incorporate into the subsurface to saturate its dangling bonds. Investigation of the elementary processes using a nudged elastic band method reveals that the energy barrier for NO dissociation is nearly absent ($\sim$0.02 eV) for the parallel configuration and is 0.07 eV for the vertical configuration, suggesting that NO can dissociate at very low substrate temperatures. The subsequent stabilization processes lead to the structures with O bridging a Si dimer and subsurface atoms or with N incorporation into the subsurface. The resulting energy barriers are 0.16 eV for both cases. The dissociation across two dimers is also possible. The present findings are consistent with experimental studies reporting low-temperature NO dissociation and N$\equiv$Si$_{3}$ formation.

H Segregation by Adatoms on Hydrogen-Terminated Semiconductor Surfaces

정석민,정호진 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2

We present our first-principles total-energy calculation of the adsorption of various adatoms (the third-row elements and 3d transition metals) and the segregation of H on the hydrogen-terminated Si(111) and Ge(111) surfaces [H/Si(111) and H/Ge(111)]. We find out that the adsorption structures are closely related with the number of the partially-filled valence electrons, n. The Mg and Zn adatoms with filled valence electrons (n = 0) do not interact with the H-terminated surfaces. The adatoms with n = 1, such as Na, Al, Cu and Ag, interact weakly with the surfaces. On the other hand, elements with n ≥ 2, such as group IV ∽ VI and transition metals, show a strong chemical interaction with the surfaces. In these cases, one or more H atoms are segregated from the surface without any energy barrier.

Binding of Ag Adatoms to Dangling Bond Defects on a H-terminated Si(001) Surface

정석민,김규형 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.4

Using a first-principles calculation method, we investigate the binding of Ag adatoms with dangling bond (DB) defects on a H-terminated Si(001) surface and the diffusion of a single Ag adatom near the DB defects. We find that the Ag adatoms saturate DBs with binding energies ~2.0 eV/Ag,much larger that on a perfect H/Si(001) surface. This means that Ag atoms preferentially bind to the DB sites on the surface. The addition energy, which reflects the energy gain when a Ag atom is added from the perfect region (0.35 ~ 1.72 eV), decreases very much when the number of Ag atoms exceeds the number of DBs. This suggests that the Ag atoms cover the DB areas to form Ag nanostructures. The simulated scanning-tunneling microscopy (STM) images of the Ag/H/Si(001)surfaces with the DB defects reproduce the experimental ones well. It is also found that a Ag adatom diffuses anisotropically (along the dimer rows) and that the Schwoebel barriers are small near the DB defects.

Si(001)에 흡착되는 NO에 대한 제일원리 분자동역학 연구

정석민,Jeong Sukmin 한국진공학회 2005 Applied Science and Convergence Technology Vol.14 No.2

제일원리 분자동역학 방법을 이용하여 Si(001) 표면에 NO 분자 흡착을 연구하였다. NO 분자가 Si(001)의 dimer축과 나란히 흡착될 경우에 50K에서도 분해가 일어났다. 이를 에너지 장벽으로 환산해 보면 0.006eV로서 거의 무시해도 좋을 정도이다 만일 NO 분자가 표면에 수직으로 들어오면 이웃에 있는 dimer에 걸쳐서 분해가 일어났다. 이 경우는 에너지 장벽은 0.08eV 정도였으며 여전히 낮은 수준이다. 분해가 된 산소분자는 dimer와 기판 사이의 backbend로 파고들어서 (에너지 장벽 0.007eV) 안정된 구조를 만들었다. 또 dimer에 나란히 흡착된 분자 상태의 경우는 N=Si_3$를 만들기도 하는데 속전자준위분광학(core level spectroscopy) 실험 결과와 일치한다. NO adsorption can be used in synthesizing oxynitride thin films which have potential application in nanodevices. However, it is very difficult to understand the oxynitridation Process since too many factors are involved in it. In this paper, we present our first-principles molecular dynamics calculation of the NO molecule adsorption on the Si(001) surface as the initial stage of the oxynitridation process. The previous first-principles calculation has argued the NO molecule is dissociated with a very small activation barrier, 0.07eV, which acutally corresponds to 1.60eV considering thermodynamics. This is in clear contrast to the observation that NO is dissociated at temperatures as low as 20K From extensive searches of NO on the Si(001) surface, we have found the new dissociation processes that have the much lower activation energies, less than 0.01 eV. We also present the dissociation and penetration processes with the corresponding activation energies and discuss their experimental implications.