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Chang, Min Hui,Kim, Na-Young,Chang, Yun Hee,Lee, Yeunhee,Jeon, Un Seung,Kim, Howon,Kim, Yong-Hyun,Kahng, Se-Jong The Royal Society of Chemistry 2019 Nanoscale Vol.11 No.17
<P>The coordination structure between small molecules and metalloporphyrins plays a crucial role in functional reactions such as bio-oxidation and catalytic activation. Their vertical, tilting, and dynamic structures have been actively studied with diffraction and resonance spectroscopy for the past four decades. Contrastingly, real-space visualization beyond simple protrusion and depression is relatively rare. In this paper, high-resolution scanning tunnelling microscopy (STM) images are presented of di-, tri-, and tetra-atomic small molecules (O2, NO2, and NH3, respectively) coordinated to Co-porphyrin on Au(111). A square ring structure was observed for O2, a rectangular ring structure for NO2, and a bright-center structure for NH3 at 80 K. The symmetries of experimental STM images were reproduced in density functional theory (DFT) calculations, considering the precession motion of the small molecules. Thus, this study shows that the structure of small molecules coordinated to metalloporphyrins can be visualized using high-resolution STM and DFT calculations.</P>
Chang, Yun Hee,Kim, Howon,Kahng, Se-Jong,Kim, Yong-Hyun The Royal Society of Chemistry 2016 Dalton Transactions Vol.45 No.42
<P>Based on density functional theory calculations, we investigated the axial bindings of diatomic molecules (NO, CO, and O-2) to metalloporphyrins and their spin switching behaviors. These binding reactions provide the ways to control molecular states and spins in metalloporphyrin systems that can be used in bio-sensing and spintronic applications. To microscopically understand the non-trivial axial binding structures and spin-switching behaviors of diatomic molecules (NO, CO, and O-2) adsorbed onto Co-tetraphenylporphyrin (CoTPP), we performed spin-polarized density functional theory (DFT) calculations for various CoTPP systems on Au(111), Ag(111), and Cu(111) substrates. We also systematically evaluated the effects of van der Waals and Hubbard U corrections by directly comparing the electronic structure with the results of scanning tunnelling microscopy. From the calculation results, we have found that a NO molecule, almost 60 degrees tilted away from the axial direction, is coordinated with CoTPP with a binding energy of 1.2-1.7 eV depending on substrates, and the spin state of CoTPP is completely switched off due to the charge transfer from NO to CoTPP. On the other hand, CO and O-2 molecules rather weakly interact with a binding energy of 0.4-0.8 eV, and a spin polarization of similar to 1 mu B is still present at CoTPP. A CO molecule is expected to be almost straightly coordinated along the axial direction of CoTPP, but O-2 is tilted similarly to the NO case. Regarding the substrate effects, we have found that there is noticeable charge transfer from Ag(111) and Cu(111) to CoTPP, but no significant charge transfer from Au(111) to CoTPP. These findings of the axial coordination and spin states for NO, CO, and O-2 adsorbed CoTPP systems will be useful for understanding bio-sensing mechanisms and designing molecular spintronic systems.</P>
Kim, Howon,Chang, Yun Hee,Lee, Soon-Hyeong,Kim, Yong-Hyun,Kahng, Se-Jong American Chemical Society 2013 ACS NANO Vol.7 No.10
<P>Controlling and sensing spin states of magnetic molecules at the single-molecule level is essential for spintronic molecular device applications. Here, we demonstrate that spin states of Co–porphyrin on Au(111) can be reversibly switched over by binding and unbinding of the NO molecule and can be sensed using scanning tunneling microscopy and spectroscopy (STM and STS). Before NO exposure, Co–porphryin showed a clear zero-bias peak, a signature of Kondo effect in STS, whereas after NO exposures, it formed a molecular complex, NO–Co–porphyrin, that did not show any zero-bias feature, implying that the Kondo effect was switched off by binding of NO. The Kondo effect could be switched back on by unbinding of NO through single-molecule manipulation or thermal desorption. Our density functional theory calculation results explain the observations with pairing of unpaired spins in d<SUB><I>z</I><SUP>2</SUP></SUB> and ppπ* orbitals of Co–porphyrin and NO, respectively. Our study opens up ways to control molecular spin state and Kondo effect by means of enormous variety of bimolecular binding and unbinding reactions on metallic surfaces.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2013/ancac3.2013.7.issue-10/nn4039595/production/images/medium/nn-2013-039595_0007.gif'></P>
Probing Single-Molecule Dissociations from a Bimolecular Complex NO–Co-Porphyrin
Kim, Howon,Chang, Yun Hee,Jang, Won-Jun,Lee, Eui-Sup,Kim, Yong-Hyun,Kahng, Se-Jong American Chemical Society 2015 ACS NANO Vol.9 No.7
<P>Axial coordinations of diatomic NO molecules to metalloporphyrins play key roles in dynamic processes of biological functions such as blood pressure control and immune response. Probing such reactions at the single molecule level is essential to understand their physical mechanisms but has been rarely performed. Here we report on our single molecule dissociation experiments of diatomic NO from NO-Co-porphyrin complexes describing its dissociation mechanisms. Under tunneling junctions of scanning tunneling microscope, both positive and negative energy pulses gave rise to dissociations of NO with threshold voltages, +0.68 and -0.74 V at 0.1 nA tunneling current on Au(111). From the observed power law relations between dissociation rate and tunneling current, we argue that the dissociations were inelastically induced with molecular orbital resonances by stochastically tunneling electrons, which is supported with our density functional theory calculations. Our study shows that single molecule dissociation experiments can be used to probe reaction mechanisms in a variety of axial coordinations between small molecules and metalloporphyrins.</P>
최고 경영자(CEO), 최고 경영진(TMT), 기업 소유구조간의 상호작용이 R&D 투자에 미치는 영향
서정일(Jeongil Seo),장호원(Howon Chang) 한국전략경영학회 2010 전략경영연구 Vol.13 No.1
본 연구는 최고경영자 (CEO)의 의사결정을 설명하는 두 주요이론인 최고 경영층 이론(Upper-Echelons theory)과 대리인 이론 (agency theory)의 통합을 통해, CEO의 인구통계학적 특성이 기업의 연구개발 (R&D)투자에 미치는 영향이 기업의 소유구조 및 최고 경영진 (TMT) 구성원의 인구통계학적 특성에 따라 어떻게 달라지는 가를 살펴보고 있다. 한국의 상장기업 289개를 대상으로 한 연구에서 우리는, (1) CEO의 나이가 증가할수록 기업의 R&D투자는 감소하지만, (2) CEO가 소유경영자인 경우 그렇지 않은 경우보다 R&D 투자의 감소폭이 적게 나타나고 있음을 발견하였다. 또한 우리는, CEO의 인구통계학적 특성과 TMT 구성원들의 인구통계학적 특성 간에 상호 보완적 관계가 나타나고 있음을 발견하였다. 즉, (3) 나이가 많은 CEO가 나이가 어린 TMT 구성원들과 함께 의사결정을 내리는 경우, 그리고 (4) R&D관련 교육배경이 없는 CEO가 R&D 관련 교육배경을 가진 TMT 구성원들과 함께 의사결정을 내리는 경우에, 그렇지 않은 TMT 구성원들과 함께 의사결정을 내리는 경우보다 상대적으로 더 많은 R&D투자를 하고 있음을 발견하였다. 본 연구의 실증결과는, CEO의 의사결정에 대한 보다 정확한 이해를 위해서는, 최고 경영층 이론과 대리인 이론의 통합을 통해 CEO의 인구통계학적 특성과 지배구조상의 지위가 어떻게 상호작용하는지, 그리고 CEO와는 다른 지배구조상의 지위를 가지는 TMT구성원들의 인구통계학적 특성이 CEO의 인구통계학적 특성과 어떻게 상호작용하는지를 살펴볼 필요가 있음을 시사한다. In this paper, we integrate agency theory that emphasizes managers' governance position and Upper-Echelons theory that is interested in managers' demographic characteristics to examine the effects of CEO on firm R&D investment. We investigate the effects of CEO demographic characteristics on firm R&D investment and also examine how TMT demographic characteristics and firm ownership structure moderate the effects of CEO characteristics on firm R&D investment. Using a sample of Korean manufacturing firms listed in 2004. we find that (1) CEO age has a negative effect on firm R&D investment, (2) however, the negative effect is weaker for family CEOs. We also find that (3) old CEOs tend to increase investment in R&D when they work with young top executives and that (4) CEOs who lack R&D-related educational background have a tendency to increase investment in R&D when they work with top executives who have R&D-related educational background. Our findings suggest that CEO decision-making can be better understood when we consider both the effects of CEO‘s demographic characteristics and the effects of CEO's governance positions. Our study also suggests that the demographic characteristics of top executives affect CEO decision-making.
Jong Kwon Lee,Howon Lee,Ung Gi Hong,Yeonshick Yoo,Young-Jin Cho,Jinsuk Lee,Hosik Chang,송인규 한국공업화학회 2012 Journal of Industrial and Engineering Chemistry Vol.18 No.5
X-Mg3(VO4)2/MgO–ZrO2 catalysts were prepared by a wet impregnation method with a variation of vanadium content (X = 2.8, 4.2, 5.6, 9.0, and 11.2 wt%), and they were applied to the oxidative dehydrogenation of n-butane. Effect of oxygen capacity and acidity of Mg3(VO4)2/MgO–ZrO2 catalysts on the catalytic performance in the oxidative dehydrogenation of n-butane was investigated. Experimental results revealed that oxygen capacity and acidity of catalyst were closely related to the catalytic performance in the oxidative dehydrogenation of n-butane. It was found that the catalytic performance of X-Mg3(VO4)2/MgO–ZrO2 catalysts increased with increasing oxygen capacity and with increasing acidity of the catalyst.