• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.197-197
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• 2011

In this study, in contrast with cases in which Scanning Tunneling Microscopy (STM) tip-induced reactions were instigated by the tunneling electrons, the local electric field, or the mechanical force between a tip and a surface, we found that the tungsten oxide (WO3) covered tungsten (W) tip of a STM acted as a chemical catalyst for the S-H dissociative adsorption of phenylthiol and 1-octanethiol onto a Ge(100) surface. By varying the distance between the tip and the surface, the degree of the tip-catalyzed adsorption could be controlled. We have found that the thiol head-group is the critical functional group for this catalysis and the catalytic material is the WO3 layer of the tip. After removing the WO3 layer by field emission treatment, the catalytic activity of the tip has been lost. 3-mercapto isobutyric acid is a chiral bi-functional molecule which has two functional groups, carboxylic acid group and thiol group, at each end. 3-Mercapto Isobutyric Acid adsorbs at Ge(100) surface only through carboxylic acid group at room temperature and this adsorption was enhanced by the tunneling electrons between a STM tip and the surface. Using this enhancement, it is possible to make thiol group-terminated surface where we desire. On the other hand, surprisingly, the WO3 covered W tip of STM was found to act as a chemical catalyst to catalyze the adsorption of 3-mercapto isobutyric acid through thiol group at Ge(100) surface. Using this catalysis, it is possible to make carboxylic acid group-terminated surface where we want. This functional group-selective adsorption of bi-functional molecule using the catalysis may be used in positive lithographic methods to produce semiconductor substrate which is terminated by desired functional groups.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.67-72
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• 1999

Scanning probe Microscope(SPM) such as Scanning Tunneling Microscope(STM) and Atomic Force Microscope(AFM) was shown to be the powerful tool for nano-scale characterization of material surfaces Using this technique, surface morphology of the cyclically deformed Cu or Cu-Al single crystal was observed. The surface became proportionately rough as the number of cycles increased, but after some number of cycles no further change was observed. Slip steps with the heights of 100 to 200 nm and the widths of 1000 to 2000 nm were prevailing at the stage. The slipped distance of one slip system at the surface was not uniform. and formation of the extrusions or intrusions was assumed to occur such place. By comparing the morphological change caused by crystallographic orientation, strain amplitude, number of cycles or stacking fault energy, some interesting results which help to clarify the basic mechanism of fatigue damage were obtained. Furthermore, applicability of the scanning tunneling microscopy to fatigue damage is discussed.

• 제어로봇시스템학회:학술대회논문집
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• 1988.10b
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• pp.794-797
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• 1988

G. Binnig and H. Rohrer introduced the Scanning Tunneling Microscope (STM) in 1982 and developed it into a powerful and not to be missed physical tool. Scanning tunneling Microscopy is a real space surface imaging method with the atomic or subatomic resolution in all three dimensions. The tip is scanned over the surface by two piezo translators mounted parallel (X-piezo and Y-piezo) to the surface and perpendicular to each other. The voltage applied to the third piezo (Z-piezo) translator mounted perpendicular to the surface to maintain the tunneling current through the gap at a constant level reflects then the topography of the surface. The feed back control loop for the constant gap current is designed using the automatic control technique. In the designing process of the feed back loop, the identification of the gap dynamics is very complex and has difficulty. In this research, using some suitable test signals, the system dynamics of the gap including the Z-piezo are investigated. Especially, in this paper, a system model is proposed for the gap and Z-piezo series system. Indicial response is used to find out the model. The driving voltage of the Z-piezo and the tunneling current are considered as input and output signals respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.151-151
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• 2000

We have studied the atomic structure of Si(100)-c(4$\times$4) reconstruction using scanning tunneling microscopy(STM). The c(4$\times$4) reconstruction can be formed by annealing the hydrogen exposured surface at temperatures between 850 and 960 K. At this temperature ranges, adsorbed hydrogen atoms are all desorbed. Therefore, the c(4$\times$4) reconstruction is due to the Si dimers on surface. The filled and empty state images of the STM were interpreted in terms of Si dimers in c(4$\times$4) primitive cell forming the reconstruction. Based on the STM images and hydrogen adsorption experiment on c(4$\times$40 surface, we suggest that Si dimers in c(4$\times$40 unit cell are perpendicular ad-dimer to the underlying Si dimer rows.

• Bulletin of the Korean Chemical Society
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• v.22 no.3
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• pp.267-270
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• 2001

The adsorption of chlorine on a Pt(111) surface at 90 K has been studied using scanning tunneling microscopy (STM) in ultra-high vacuum environments. The adsorbed chlorine atoms give rise to two different ordered structures, (3${\times}$3)-Cl and c(4${\times}$2)- Cl, depending on the coverage. It has been determined from the STM image that the absolute coverage of (3${\times}$3)-Cl structure is 0.44, which is not in agreement with coverage calibrated by a low energy electron diffraction technique together with an Auger electron spectrometer and a thermal desorption spectrometer. The Cl atoms bound to on-top sites at the Pt(111)(3${\times}$3)-Cl surface appeared to effectively perturb the density of states of Pt atoms, as compared with that bound to bridging sites. The other ordered structure, c(4${\times}$2)-Cl, with small domain sizes, consists of both on-top and bridge-bonded species with a saturation coverage of 0.5.

• Applied Science and Convergence Technology
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• v.25 no.2
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• pp.28-31
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• 2016

The structural and the electronic properties of pentacene on modified Si (001) were investigated using scanning tunneling microscopy (STM), atomic force microscopy (AFM) and ultraviolet photoelectron spectroscopy (UPS). Dodecane was used to modify Si (001) substrates and then pentacene was deposited on dodecane/Si (001). Our STM results show a uniform distribution of aggregated dodecane molecules all over the clean Si (001). The surface structure of pentacene on dodecaene/Si (001) examined by AFM is analogous to that of pentacene on $SiO_2$. The UPS data showed that the work function of pentacene on clean Si (001) and pentacene on modified Si (001) with dodecane was 6.41 and 5.57 eV, respectively. Our results prove that dodecane results in the work function difference between pentacene on clean Si (001) and pentacene on dodecane/Si (001).

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.107-107
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• 2011

Supramolecular structures of anthraquinone molecules on a metallic surface are studied using scanning tunneling microscope (STM) under ultrahigh-vacuum conditions. When we deposited anthraquinone molecules on Au(111) substrate, the molecules formed three different phases (Chevron type, tetragon type and disordered type) on the surface. Based on our STM measurements, we proposed models for the observed molecular structures. Chevrons are consisted of several molecular chains, which make well-ordered two-dimensional islands by some weak interrow interactions and we could observe tetragon structures which make array of (111) metallic surface. each molecular rows in the chevrons are stabilized by two parallel O-H hydrogen bonds and disordered structures are observed 1-dimensional phase with hydrogen bond. First-principles calculations based on density functional theory are performed to reproduce the proposed models. Distances and energy gains for each intermolecular bond are estimated. In this presentation, we explain possible origins of these molecular structures in terms of hydrogen bonds, Van der Waals interactions and molecule-substrate interactions.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.302-302
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• 2011

Fabrications of metal-organic hybrid networks attracted much attention due to possible applications in gas storages, heterogeneous catalyses, information storages, and opto-electronic devices. One way to construct three-dimensional hybrid structures is to make the arrays of planar or linear metal-organic hybrid structures which are linked through electrostatic interactions. As a model study, we fabricated the arrays of one-dimensional hybrid chains and investigated inter-chain interactions between adjacent hybrid chains using scanning tunneling microscopy (STM) and spectroscopy (STS) on Ag(111). Brominated anthracene molecules were used to grow the arrays of hybrid chains on Ag(111). We proposed atomic models for the observed structures. Linear chains are made of repetition of Ag-anthracene units. Br atoms are attached to anthracene molecules through Br-H structures which mediate inter-chain interactions. Two different apparent heights were observed in anthracene molecules. Molecules having a Br-H connection look brighter than those with two connections due to electronic effect. When a chain is laterally manipulated with STM tip, Br atoms move together with the chain implying that Br-H inter-chain interactions are quite strong.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.150-150
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• 2000

The adsorption geometry and the electronic property of Mg grown at room temperature on the Si(111)-7$\times$7 surface with various coverages have been studied by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). At low Mg coverage, the Mg atoms preferentially adsorb at the center adatom sites of the faulted half of the Si(111)-7$\times$7 surface. The adsorbed Mg atom acts as nucleophile with respect to Si atoms thus forms a stable ionic bond with the substrate Si atoms. Above 1 Ml, the 7$\times$7 surface starts to be disrupted and an amorphous Mg overlayer is formed. The LEED shows either $\delta$7$\times$7 or 1$\times$1 pattern at this coverage. When more Mg atoms were exposed, a flat and broad {{{{ { 2} over {3 } }}}}{{{{ SQRT { 3} }}}}$\times${{{{ { 2} over {3 } }}}}{{{{ SQRT { 3} }}}}R30$^{\circ}$region evolves. A flat silicide is formed at first and multi-level Mg islands having hexagonal step edges develop with increasing coverage. The scanning tunneling spectroscopy (STS) confirms the electronic properties of these Mg films on the si(111) 7$\times$7 surface at various coverages.

• Proceedings of the KIEE Conference
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• 2006.10a
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• pp.91-92
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• 2006

The electrical properties of viologen derivatives were studied in terms of the tunneling current characteristics on the length of the viologen derivatives using self-assembling techniques and ultra high vacuum scanning tunneling microscopy (UHV-STM). We fabricated the Au substrate were deposited by thermal evaporation system ($420^{\circ}C$. Self-assembled monolayers (SAMs) were prepared on Au (111), which had been thermally deposited onto freshly cleaved, heated mica. The Au substrate was exposed to a 1 mM solution of viologen derivatives in ethanol for 24 hours to form a monolayer. We measurement of the morphology on the single viologen molecules ($VC_{8}SH$, $VC_{10}SH$, $HSC_{8}VC_{8}SH$, and $HSC_{10}VC_{10}SH$). The current-voltage (I-V) and differential conductance (dl/dV-V) properties were measured while the electrical properties of the formed monolayer were scanned by using a STS. The effective barrier height of viologen derivatives ($VC_{8}SH$, $VC_{10}SH$, $HSC_{8}VC_{8}SH$, and $HSC_{10}VC_{10}SH$) were calculated to be 1.076 eV, 1.56 ${\pm}$ 0.3 eV, 1.85 eV, 2.28 eV, respectively.