Room-temperature growth of Mg on Si(111): stepwise versus continuous deposition

Lee, Dohyun,Lee, Geunseop,Kim, Sehun,Hwang, Chanyong,Koo, Ja-Yong,Lee, Hangil IOP Pub 2007 Journal of physics, an Institute of Physics journa Vol.19 No.26

<P>Using low-energy electron diffraction and scanning tunnelling microscopy, we studied the formation of Mg silicide and metallic Mg islands on a Si(111)-7 ? 7 surface at room temperature as a function of Mg coverage. We found that the mechanism by which Mg islands grew on the Si(111)-7 ? 7 surface, and the morphology of the islands that formed, depended on whether the Mg deposition was performed in a stepwise or continuous manner. When Mg was deposited in a stepwise manner, with 1?h between deposition events, an amorphous Mg silicide overlayer formed on the Si(111)-7 ? 7 surface during the initial stage of deposition (up to 2.0?ML Mg coverage), as shown by the observation of δ7 ? 7 and 1 ? 1 low-energy electron diffraction patterns. Upon further stepwise Mg deposition, round-shaped Mg islands grew on the amorphous Mg silicide layer, as shown by scanning tunnelling microscopy and the emergence of a 1 ? 1 low-energy electron diffraction pattern. If, on the other hand, the Mg was deposited continuously in a single step, hexagonal Mg islands formed on the flat Mg silicide layers, and a <img SRC='http://ej.iop.org/images/0953-8984/19/26/266004/cm243037ieqn1.gif' ALIGN='MIDDLE' ALT='({{2 \over 3} \sqrt {3}} \times {{2 \over 3} \sqrt {3}})\mathrm {R}30 ^{\circ } '/> and 1 ? 1 mixed phase was observed. Moreover, using scanning tunnelling spectroscopy, we confirmed the semiconducting and metallic nature of the Mg silicide layer and hexagonal Mg islands on the Si(111)-7 ? 7 surface depending on their Mg coverage, respectively. </P>

Surface Spectroscopic Analysis of TiO2 and ZnO Nanoparticles Doped with Noble Metals

Lee, Hangil,Hong, Jung A. Springer-Verlag 2018 Topics in catalysis Vol.61 No.12

Vanadium-induced decrease in the magnetization of a VxCo1−x alloy film on the W(110) surface

Hangil Lee 한국물리학회 2013 Current Applied Physics Vol.13 No.5

The magnetic and structural properties of a series of VxCo1x alloy films prepared in a variety of compositions on a W(110) surface were investigated using spin-resolved photoemission spectroscopy (SRPES) and low-energy electron diffraction (LEED) measurements. The epitaxial structures of the films were preserved over all V concentrations, despite the observation of a structural phase transition (SPT:hcp/bcc at x = 0.38), which was apparent from the LEED images. A magnetic phase transition (MPT) from ferromagnetic to paramagnetic occurred in the Co-rich region at x = 0.38. The SPT (from hcp and bcc)and MPT (from ferromagnetic to paramagnetic) were clearly correlated at x =0.38, possibly due to changes in the electronic and magnetic structures of the valence band, as monitored by SRPES and LEED. The magnetization in the VxCo1-x alloy films on a W(110) surface varied systematically with the V concentration, and correlations between the structural changes and magnetic properties were revealed using SRPES and LEED.

Electronic and Magnetic Properties of 3d Transition Metal Alloy Films on W(110)

Hangil Lee 한국진공학회 2007 한국진공학회 학술발표회초록집 Vol.16 No.2

The Study of Adsorption Structures of 3-Methyl-5-Pyrazolone on the Ge(100) Surface

Lee, Myungjin,Lee, Hangil Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.12

The most stable adsorption structures and energies of four tautomers of 3-methyl-5-pyrazolone (keto-1, enol-1, keto-2, and enol-2) on Ge(100) surfaces were investigated using density functional theory (DFT) calculations. The enol-1, keto-2, and enol-2 tautomers, but not the keto-1 tautomer, were found to exhibit stable adsorption structures on the Ge(100)-$2{\times}1$ surface. Of these three adsorption structures, that of enol-2 is the most stable.

Comparison of the Catalytic Oxidation Reaction on Graphene Oxide and Reduced Graphene Oxide

Lee, Myungjin,Yang, Sena,Kim, Ki-jeong,Kim, Sehun,Lee, Hangil American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.2

<P>The capacities of graphene oxide (GO) and reduced graphene oxide (rGO) films grown on silicon substrate to cause the aniline to azobenzene oxidation reaction were compared by using Raman spectroscopy, high-resolution photoemission spectroscopy (HRPES), and work function measurements as well as scanning electron microscopy (SEM). The oxygen carriers’ existence on GO film, which includes a lot of oxygen carriers, can facilitate the aniline to azobenzene oxidation reaction with slightly partial conversion of aniline to nitrobenzene, as determined by the Raman shifts and core-level spectra resulting from exposure to aniline. The work function of the GO film was found to change dramatically in comparison with rGO film, indicating that aniline exposed to a GO film produced n-type doping characteristics by electron charge transfer from GO to aniline. These results indicate that the oxygen carriers on a GO film oxidize aniline to azobenzene and show that GO film prefers to act as a reaction reagent rather than rGO.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-2/jp411682b/production/images/medium/jp-2013-11682b_0008.gif'></P>

Electronic and Magnetic Structure of Fe/W(100)

Hangil Lee,J. Y. Lee,B. G. Park,S. Kim,C. C. Hwang,J.-Y. Kim,J.-H. Park,Changyong Hwang 한국자기학회 2007 한국자기학회 학술연구발표회 논문개요집 Vol.- No.-

Photo-oxidation activities on Pd-doped TiO₂ nanoparticles: critical PdO formation effect

Lee, Hangil,Shin, Minjeong,Lee, Myungjin,Hwang, Yun Jeong Elsevier 2015 Applied Catalysis B Vol.165 No.-

<P><B>Abstract</B></P> <P>The catalytic activities of three distinct Pd-doped TiO<SUB>2</SUB> (PdTiO<SUB>2</SUB>) nanoparticle samples, post-annealed (at 700, 800, and 900°C) after fabrication on silicon substrates, were analyzed with respect to the photo-oxidation of aniline and 2-thiophenecarboxaldehyde. Through a combination of Raman spectroscopy and high-resolution photoemission spectroscopy (HRPES), we demonstrated that the photocatalytic oxidation occurred only when the PdTiO<SUB>2</SUB> nanoparticles were annealed at temperatures above 800°C, that is, when PdO and Ti<SUP>3+</SUP> had partially formed on the PdTiO<SUB>2</SUB> nanoparticles, which indicates that the presence of PdO and Ti<SUP>3+</SUP> is critical for the photocatalytic oxidation. Additionally, we determined the decrease in the band gaps to visible region with PdTiO<SUB>2</SUB> nanoparticles annealed above 800°C from their valence-band spectra, which resulted in photocatalytic activities even under visible light, <I>λ</I> =540nm.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Enhanced photocatalytic oxidation activity of PdTiO<SUB>2</SUB> nanoparticles with existence of PdO. </LI> <LI> PdO formation in PdTiO<SUB>2</SUB> nanoparticles by thermal annealing above 800°C. </LI> <LI> Capability for photo-oxidation of aniline and 2-thiophenecarboxaldehyde under visible light. </LI> <LI> Decrease of PdTiO<SUB>2</SUB> band gap to visible region (1.92eV) by thermal annealing at 900°C. </LI> </UL> </P>

Magnetic Linear Dichroism Studies of the 3p Core Level in Fe-based Alloy Films on W(110)

Hangil Lee 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2

We used X-ray magnetic linear dichroism to investigate the correlation between variations in the magnetic properties and structural changes in Fe-based alloy ¯lms grown on a W(110) surface. Three systems were analyzed: Fe1¡xNix, Fe1¡xCox, and Fe1¡xVx. By examining values of the WMLD (the peak-to-peak asymmetry width) and the AMLD (peak-to-peak asymmetry amplitude) between the mj = +3/2 and {3/2 orbitals of core electronic states obtained from the spectral analysis, we validated that the local magnetic moment is not related to structural changes in these systems and that the surface magnetic moment depends on the crystallographic anisotropy. Moreover, we con¯rmed that the collapse of the magnetic moment for Fe1¡xVx originates from antiferromagnetic coupling between the local magnetic moment of the V atoms and that of the Fe atoms. We used X-ray magnetic linear dichroism to investigate the correlation between variations in the magnetic properties and structural changes in Fe-based alloy ¯lms grown on a W(110) surface. Three systems were analyzed: Fe1¡xNix, Fe1¡xCox, and Fe1¡xVx. By examining values of the WMLD (the peak-to-peak asymmetry width) and the AMLD (peak-to-peak asymmetry amplitude) between the mj = +3/2 and {3/2 orbitals of core electronic states obtained from the spectral analysis, we validated that the local magnetic moment is not related to structural changes in these systems and that the surface magnetic moment depends on the crystallographic anisotropy. Moreover, we con¯rmed that the collapse of the magnetic moment for Fe1¡xVx originates from antiferromagnetic coupling between the local magnetic moment of the V atoms and that of the Fe atoms.

The aniline-to-azobenzene oxidation reaction on monolayer graphene or graphene oxide surfaces fabricated by benzoic acid

Lee, Myungjin,Kim, Kijeong,Lee, Hangil Springer 2013 NANOSCALE RESEARCH LETTERS Vol.8 No.1

<P>The oxidation of aniline to azobenzene was conducted in the presence of either monolayer graphene (EG) or graphene-oxide-like surface, such as GOx, under ultra-high vacuum conditions maintaining a 365-nm UV light exposure to enhance the oxidation reaction. The surface-bound products were investigated using micro Raman spectroscopy, high-resolution photoemission spectroscopy, and work function measurements. The oxygen carriers present on the GOx surfaces, but not on the EG surfaces, acted as reaction reagents to facilitate the oxidation reaction from aniline to azobenzene. Increasing the aniline concentration at 300 K confirmed that the exchange ratio from the aniline to the azobenzene was enhanced, as determined by the intensity ratio between the aniline- and azobenzene-induced N 1 <I>s</I> core-level spectra. The work function changed dramatically as the aniline concentration increased, indicating that the aniline on the GOx surface conveyed <I>n</I>-type doping characteristics at a low coverage level. A higher aniline concentration increased the <I>p</I>-type doping character by increasing the azobenzene concentration on the GOx surface. A comparison of the oxidation reactivity of aniline molecules on the EG or GOx surfaces revealed the role of the oxygen carriers on the GOx surfaces in the context of catalytic oxidation.</P>