Cs이 흡착된 Si(111)7×7 표면의 초기 산화과정 연구

황찬국,안기석,이득진,장현덕,박종윤 성균관대학교 기초과학연구소 1995 論文集 Vol.46 No.1

X-ray photoelectron spectroscopy를 이용하여 상온에서 Cs이 1ML 흡착된 Si(111)7 × 7 표면의 초기 산화과정에 대하여 연구하였다. 산소의 주입량과 Cs의 흡착량의 변화에 따른 0 1s, Cs 3d_(5/2), 그리고 Si 2p 스펙트럼의 변화를 관측하였다. 이러한 측정결과, 표면에 흡착되는 산소량은 Cs의 임계피복량(약 0.5ML)이상에서 급격한 증가를 보임을 알 수 있다. 따라서 Si(111) 7 × 7-Cs 표면의 산화과정은 non-local mechanism을 따르는 것으로 이해할 수 있다. 또한 0 1s 스펙트럼에 서로 다른 chemical environment를 가진 두 종류의 산소 성분이 존재하는 것을 알수 있다. 이러한 두 종류의 0 1s 성분중 높은 운동에너지 성분의 세기는 Cs 흡착량에 의존하며 낮은 운동에너지 성분은 Cs이 완전히 탈착된 후에도 남아있다. 그리고 산소 주입량이 증가함에 따라 Si 2p peak의 세기는 감소하는 반면 Cs 3d_(5/2) peak의 세기는 거의 일정하다. 이러한 결과로부터 Si(111) 7 × 7 표면에 주입되는 산소원자는 Si-0-Si, Si-0-Cs 두 종류의 결합형태를 가지는 것으로 예상된다. We have studied initial oxidation of Cs-adsorbed Si(111)7×7 surface using X-ray photoelectron spectroscopy at room temperature. It was measured that the changes of 0 1s, Cs 3d_(5/2) and Si 2p spectrum with increasing O_2 exposure and Cs deposition time, respectively. The 0 1s/Si 2p peak intensity ratio rapidly increased at 0.5ML Cs coverage, which means that the non-local mechanism is favored on the Cs-promoted oxidation. The 0 1s peak observed consists of two chemical-shifted components. The 0 1s peak intensity of high kinetic energy component depended on the Cs coverage while low kinetic energy component still remained after complete Cs desorption. The Cs 3d_(5/2) peak intensity was nearly constant, though the Si 2p peak intensity decreased with increasing O_2 exposure. These results suggest that oxygen atoms adsorbed on the Si(111)7×7 surface have two different bond configurations such as Si-O-Si, Si-O-Cs.

Na/Si(111)계의 초기 산화과정에 대한 XPS 연구

이득진,안기석,황찬국,장현덕,박종윤 성균관대학교 기초과학연구소 1995 論文集 Vol.46 No.1

X-선광 전자분광법을 이용하여 Na의 흡착에 의해 형성되는 Si(111)7×7-Na과 Si(111)3×1-Na 표면의 초기 산화과정에 대하여 연구하였다. Si(111)7×7-Na 표면은 깨끗한 Si(111)7×7 표면에 비하여 산화가 더욱 잘 일어나지만, Si(111)3×1-Na의 경우 산소와 거의 반응하지 않음을 알 수 있다. 또한 Si(111)7×7 표면과는 달리, Si(111)7×7-Na 표면에 1 ML의 Na를 흡착시키고 산소를 100L 노출한 경우 0 ls 내각 스펙트럼에 두 종류의 산소성분이 존재를 함을 알 수 있다. 산소의 노출량이 증가함에 따라 낮은 운동에너지 성분의 세기는 계속 증가를 하지만, 높은 운동에너지 쪽의 성분은 초기에 포화되었다. 이러한 0 ls 내각 스펙트럼의 변화와 Na KLL Auger peak intensity 증가로부터 Si(111) 7×7-Na 표면에 흡착되는 산소는 Si-0-Si, 그리고 Si-0-Na 두가지의 결합형태로 존재함을 예상 할 수 있다. 또한, Si(111)7×7-Na 표면에 주입되는 산소 노출량이 증가함에 따른 Na KLL Auger peak intensity가 증가하는 현상에 대하여 논의하였다. The initial oxidation of Si(111)7×7-Na and Si(111)3×1-Na surfaces have been studied by means of X-ray photoelectron spectroscopy(XPS). The Si oxidation rate of Si(111)7×7-Na surface was much enhanced more than that of the clean Si(111)7×7, but the Si(111)3×1-Na surface hardly reacted with oxygen. It shows that 0 1s peak of the Si(111)7×7-Na surfaces for 100L O_2 exposure consists of two components, coming from a different oxygen bonding configuration. From the change in intensity of two component of 0 ls and the increase of Na KLL peak intensity with increasing O_2 exposure, it is found that one component originates from Si-0-Si bonding at the lower kinectic energy and the other component comes from the Si-0-Na bonding at higher kinectic energy. Also, we have discussed a possible interpretation for the abnormally increase of Na KLL peak intensity.

Characterization of functionalized silicon surfaces and graphenes using synchrotron radiation PES

Chan-Cuk Hwang(황찬국) 한국진공학회 2010 한국진공학회 학술발표회초록집 Vol.38 No.-

Controlling the Electronic Structures of Two-Dimensional Materials for New Functionalities with Synchrotron Radiation based-Photoemission Spectroscopy

Chan-Cuk Hwang 한국진공학회 2018 한국진공학회 학술발표회초록집 Vol.2018 No.2

알칼리금속이 흡착된 Si(111)7×7 계의 초기 산화 과정 연구

황찬국(Chan-Cuk Hwang),안기석(Ki-Seok An),김정선(Jeong-Seon Kim),박래준(Rae-Jun Park),이득진(Deuk-Jin Lee),장현덕(Hyun-Duck Jang),박종윤(Chong-Yun Park),이순보(Soon-Bo Lee) 한국진공학회(ASCT) 1997 Applied Science and Convergence Technology Vol.6 No.2

X-선 광전자 분광법(x-ray photoelectron spectroscopy: XPS)과 반사 고에너지 전자 회절법(reflection high energy electron diffraction: RHEED)을 이용하여 상온과 고온(약 300~500℃)에서 알칼리금속(AM)/Si(111)7×7 표면의 초기 산화 과정에 대하여 연구하였다. 상온에서, Si(111)7×7 표면에 1 monolayer(ML)의 AM을 흡착시키면 Si(111)7×7 표면에 비해 산소의 초기 부착 계수 (initial sticking coefficient)와 산소의 포화량이 증가하는 반면 0.5ML 이하의 AM이 흡착된 경우는 깨끗한 Si(111)7×7 표면에 비하여 초기 부착 계수는 증가하지만 산소의 포화량은 증가하지 않았다. Si(111)7×7-AM 표면에 산소의 주입량을 증가시키면서 측정한 O Is 스펙트럼으로부터 AM이 흡착된 Si(111)7×7 표면에 흡착되는 산소원자는 Si-O, AM-O 두 종류의 결합형태를 가지는 것으로 생각되며 이중에서 AM-O 결합의 산화과정상에서의 역할에 대하여 논의하였다. 상온과는 달리 고온에서는, Si(111)3×1-AM 표면으로 구조가 변화하면서 산소의 흡착이 급격히 떨어지는 것을 관측할 수 있었다. 이때 3×1-AM 표면을 형성시키는 AM 종류의 산화에 대한 의존성을 살펴보았다. We have studied initial oxidation of the alkali metal(AM)/Si(111) surface using X-ray photoelectron spectroscopy(XPS) and reflection high energy electron diffraction(RHEED) at room temperature(RT) and high temperature(HT)(300~500℃). The oxidation of the Si(111)7×7 surface was promoted by the adsorption of 1 monolayer(ML) AM, whereas no promotion occurred for submonolayer(< 0.5 ML) adsorbed Si(111)7×7 surface at RT. 0 Is core level spectra were measured with increasing oxygen exposure. It was found that the oxygen adsorbed on the Si(111)7×7-AM surface have two different bond configurations, Si-O and AM-O, respectively. From these results, we discussed the role of AM-O bonding in the promoted oxidation. At HT(300~500℃), the AM-adsorbed surface became very inactive with the structural transformation to the 3×1-AM. We present the results of the oxidation of the Si(111)3×1-AM(Na, K, Cs) surface.

Angle-Resolved Photoemission Spectroscopy: Momentum-Space Microscope

Hwang, Chan-Cuk Korean Society of Microscopy 2015 Applied microscopy Vol.20 No.1

In this review paper, I'd like to introduce the basics of angle-resolved photoemission spectroscopy (ARPES) and some of my results taken at the Pohang Accelerator Laboratory (PAL), the only synchrotron radiation in South Korea. The results show that ARPES is very useful, in particular, for studying two-dimensional materials. It looks like a microscope in momentum space similar to transmission electron microscope imaging atoms in real space.

Model catalysts of supported Au nanoparticles and mass-selected clusters

Lim, Dong-Chan,Hwang, Chan-Cuk,Gantefö,r, Gerd,Kim, Young Dok Royal Society of Chemistry 2010 Physical chemistry chemical physics Vol.12 No.46

<P>In surface science, much effort has gone into obtaining a deeper understanding of the size-selectivity of nanocatalysts. In this article, electronic and chemical properties of various model catalysts consisting of Au are reported. Au supported by oxide surfaces becomes inert towards chemisorption and oxidation as the particle size became smaller than a critical size (2–3 nm). The inertness of these small Au nanoparticles is due to the electron-deficient nature of smaller Au nanoparticles, which is a result of metal-substrate charge transfer. Properties of Au clusters smaller than ∼20 atoms were shown to be non-scalable, <I>i.e.</I>, every atom can drastically change the chemical properties of the clusters. Moreover, clusters with the same size can show dissimilar properties on various substrates. These recent endeavours show that the activity of a catalyst can be tuned by varying the substrate or by varying the cluster size on an atom-by-atom basis.</P> <P>Graphic Abstract</P><P>The origin of size-selectivity in the chemical properties of nanoparticles and mass-selected clusters consisting of Au has been tackled. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0cp00467g'> </P>

Si Nanostructure on Graphene

Yong Han,Heeseob Kim,Chan-Cuk Hwang,Hangil Lee,Bongsoo Kim,Ki-jeong Kim 한국진공학회 2014 한국진공학회 학술발표회초록집 Vol.2014 No.2

백서의 피부 및 뇌혈류에 미치는 고려홍삼 사포닌 및 비사포닌의 영향

김신희(Shin Hee Kim),김국성(Cuk Seong Kim),박진봉(Jin Bong Park),한찬수(Chan Soo Han),김광진(Kwang-Jin Kim),김신혜(Shin Hye Kim),김세훈(Se Hoon Kim),남기열(Ki Yeul Nam),전병화(Byeong Hwa Jeon) 고려인삼학회 2002 Journal of Ginseng Research Vol.26 No.3

본 연구에서는 혈류량의 변화를 실시간으로 측정할 수 있는 레이져 도플러 혈류량측정장치를 이용하여 피부혈류 및 뇌혈류량에 미치는 고려홍삼의 사포닌과 비사포닌의 효능을 연구하고자 고려홍삼의 정맥내 복강내 및 구강내로 주입하고 혈류의 변화를 관찰하여 다음과 같은 결론을 얻었다. 고려 홍삼<br/> 의 사포닌 성분은 피부혈류량에는 영향을 주지 않으나 뇌혈류량을 증가시키는 효능이 있다. 고려 홍삼의 비사포닌 성분은 피부혈류량 및 뇌혈류량에 거의 영향을 주지 않았다. 고려홍삼 사포닌에 의한 뇌혈류량의 증가는 복강내 및 경구로 투여할 경우는 관찰할 수 있으나 정맥내로 직접 투여할 경우는<br/> 관찰되지 않았다.이상의결과를종합해볼때고려홍삼의 사포닌 성분은 뇌혈류량을 증가시키는 혈류개선작용이 있는 것으로 사료된다. To study the effect of Korea red ginseng (KRG) on the skin and cerebral blood flow, we evaluated the change of skin perfusion rate and cerebral perfusion rate after the intravenous, intraperitoneal, and oral administration of crude saponin (CS) and saponin-free fraction (SFF) of KRG in the rats. The change of skin perfusion rate and cerebral perfusion rate was measured laser doppler flowmetry. The intravenous injections of CS or SFF of KRG and intraperitoneal injection of SFF of KRG did not change the relative skin and cerebral blood flow in the rats. When the rats were treated by the<br/> intraperitoneal injection of CS of KRG, relative cerebral blood flow was significantly increased with a time-dependent manner, however, relative skin blood flow was not influenced by the them. Oral administration of CS of KRG slightly increased skin blood flow in the rats. Also, the change of cerebral blood flow by transient bilateral carotid arterial clamp in the CS-treated rats was significantly decreased, compared with control groups. From the above results, it was suggested that Korea red ginseng have a increasing property of cerebral blood flow in the rats.<br/> Key words : Korea Red Ginseng, Cerebral blood flow, Skin blood flow, Laser Doppler flowmeter.

Adsorption of Benzenethiol and 1,4-Benzenedithiol on the Si(111)-7 X 7 Surface

Jaeyoon Baik,박종윤,Bongsoo Kim,Chan-Cuk Hwang,Han-Na Hwang,Jong Yeol Ahn,Jungwoon Park,Ki-Seok An,Minkook Kim 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.3

Benzenethiol- and 1,4-benzenedithiol-adsorbed Si(111)-7~$\times$~7 surfaces were studied by using scanning tunneling microscopy and synchrotron radiation photoemission spectroscopy, which showed that benzenethiol molecules were adsorbed on Si adatoms with upright structures and 1,4-benzenedithiol molecules on two adjacent Si adatoms with a bridging structure. At the initial stage, the adsorptions can be understood by a dissociative process between sulfur and hydrogen on the Si atoms. Here, sulfur bonds to the electrophilic adatoms while hydrogen bonds to neighboring nucleophilic restatoms. On the other hand, this adsorption mechanism during the initial stage does not apply at higher exposures of molecules, as is noticed from the photoemission spectra. Benzenethiol- and 1,4-benzenedithiol-adsorbed Si(111)-7~$\times$~7 surfaces were studied by using scanning tunneling microscopy and synchrotron radiation photoemission spectroscopy, which showed that benzenethiol molecules were adsorbed on Si adatoms with upright structures and 1,4-benzenedithiol molecules on two adjacent Si adatoms with a bridging structure. At the initial stage, the adsorptions can be understood by a dissociative process between sulfur and hydrogen on the Si atoms. Here, sulfur bonds to the electrophilic adatoms while hydrogen bonds to neighboring nucleophilic restatoms. On the other hand, this adsorption mechanism during the initial stage does not apply at higher exposures of molecules, as is noticed from the photoemission spectra.