• Proceedings of the Korea Association of Crystal Growth Conference
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• 1998.09a
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• pp.103-111
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• 1998

Au fine particle dispersed TiO2 film was prepared on silica glass substrate by sol-gel dip and firing process. The films were fabricated from the system of titanium tetraisoproxie-EtOh-HCl_H2O-hydrogen tetrachloroaurate(III) tetrahydrate. The conditions for the formation of the clear solution and dissolving high concentration of Au compound were examined. And a photoreduction process was adopted to control the size of gold metal particles. Phase evolution of matrix TiO2 and variation of Au particle with UV irradiation were investigated by XRDA, SEM, TEM and UV-visible spectrophotometer. And the effect of CPCl(Cetylpyridinium chloride monohydrate) as a dispersion agent was evaluated.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.654-654
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• 2013

One of the most important yet unresolved problems in molecular electronics is the controversy over the number and nature of multiple conductance peaks in single-molecule junctions. Currently, there are three competing explanations of this observation: (1) manifestation of different molecule-electrode contact geometries, (2) formation of gauche defects within the molecular core, (3) involvement of different electrode surface orientations [1]. However, the exact origin of multiple conductance peaks is not yet fully understood, which indicates our incomplete understanding of the scientifically as well as techno-logically important organic-metal contacts. To theoretically resolve this problem, we previously applied a multiscale computational approach that combines force fields molecular dynamics (FF MD), density functional theory (DFT), and matrix Green's function (MGF) calculations [2] to a thermally fluctuating haxanedithiol (C6DT) molecule stretched between flat Au(111) electrodes, but could observe only a single conductance peak [3]. In this presentation, using DFT geometry optimizations and MGF calculations, we consider molecular junctions with more realistic molecule-metal contact conformations and Au(111) electrode surface directions. We also conduct DFT-based molecular dynamics for the highly stretched junction models to confirm our conclusion. We conclude that the S-Au coordination number should be the more dominant factor than the electrode surface orientation.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.150.2-150.2
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• 2013

We elucidate the mechanism of the self-assembled organic layer formation at the organic/metal interface of hexaaza-triphenylene-hexacarbonitrile (HATCN)/Au(111) by first-principles calculations and Lowtemperature scanning tunneling microscope (STM). In this work, we used HATCN to deposit organic material which is well known as an efficient OLED charge generation material. Low-temperature STM measurements revealed that self-assembled hexagonal porous structure is formed at terraces of Au(111). We also found that the hexagonal porous structure has chirality and forms only small (<1000 $nm^2$) phaseseparated chiral domains that can easily change their chiral phase in subsequence STM images at 80 K. To explain the mechanism of these observation, we calculated the molecular-molecular and molecule-surface interaction energies by using density functional theory method. We found that the change of their chiral phase resulted from the competition between the two energies. These results have not only verified our experimental observations, but also revealed the delicate balance between different interactions that caused the self-assembed structures at the surface.

• Korean Journal of Materials Research
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• v.5 no.6
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• pp.673-681
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• 1995

Surface morphology and preferred orientation of 20${\mu}{\textrm}{m}$ gold electrodeposit formed from aqueous solution of the sodium gold sulfite were studied in terms of current density, plating temperature and Au concentration. As the current density changed from 13.0mA/$\textrm{cm}^2$ to 4.6mA/$\textrm{cm}^2$, the solution temperature from 3$0^{\circ}C$ to 6$0^{\circ}C$, pH from 12.0 to 9.0, agitation speed from 0 rpm to 3200rpm and Au concentration from 10g/1 to 14 g/1, local Au concentration near the cathodic surface increased. With increasing the Au concentration, the surface morphology chanced from porous structure to fine-grained structure. Furthermore, it was observed that the preferred orentation of the Au layer changed from (111) to (220) upon the same variation In the Au concentration. The surface morphology and the preferred orientation of the Au layer were found to be closely related to each other.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.111-111
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• 2012

In this talk, we represent a novel approach to investigating intra-nanorod surface plasmon coupling with control over block compositions. The multi-component rod-like nanostructures, which consist of optically active components (Au and Ag) and optically less active component (for example, Ni) in UV-vis-NIR spectral window, showed interesting optical response depending on each block length and the total length of the structure. By controlling the composition and relative lengths of the blocks that comprise these structures, we can tailor the overall optical properties. Depending on the relative fraction of Au and Ag blocks, the intensity of the transverse modes varied without noticeable peak shifts. However, the strong intraparticle surface plasmon coupling resulted in the collective appearance of longitudinal LSP modes, including higher-order modes. The experimental observations were confirmed by theoretical calculation, using a discrete dipole approximation method. In addition, we will briefly discuss how single nanorod solar cells can be synthesized by using by using electrochemical deposition and AAO hard templates.

• Bulletin of the Korean Chemical Society
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• v.26 no.4
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• pp.553-557
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• 2005

The formation of striped phases of unsymmetric hexyl octadecyl disulfide ($CH_3(CH_2)_5SS(CH_2)_{17}CH_3$, HOD) and 1-hydroxyundecyl octadecyl disulfide ($CH_3(CH_2)_{17}SS(CH_2)_{11}$OH, HUOD) on Au(111) and graphite has been investigated by scanning tunneling microscopy (STM) to understand the self-assembly processes of dialkyl disulfides. STM imaging clearly shows the formation of striped phases having corrugation periodicities that are nearly consistent with the molecular length of alkanethiolate moieties formed after the S-S bond cleavage of dialkyl disulfide on a gold surface. On the other hand, self-assembled monolayers (SAMs) of dialkyl disulfides on a graphite surface displayed long-range, well-ordered monolayers with one striped pattern that shows periodicity as a function of molecular length via nondissociative adsorption. From a nonoscopic viewpoint, we have clearly demonstrated that dialkyl disulfide SAMs on gold form via S-S bond cleavage of disulfide.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.191.1-191.1
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• 2014

Crystallization has become the most popular technique for the separation of enantiomers since the Pasteur's discovery. To investigate mechanism of crystallization of chiral molecules, it is necessary to study self-assembled structures on two-dimensional surface. Here, we have studied two-dimensional self-assembled structures of an unnatural amino acid, (S)-${\beta}$-methyl naphthalen-1-${\gamma}$-aminobutyric acid (${\gamma}^2$-1-naphthylalanine) on Au(111) surface at 150 K using scanning tunneling microscopy (STM). At initial stage, we found two chiral honeycomb structures which are counter-clockwise and clockwise configurations in one domain. The molecules are arranged around molecular vacancies, dark hole. By further increasing the amounts of adsorbed ${\gamma}^2$-1-naphthylalanine, a well-ordered square packed structure was observed. In addition, we found the other structure that molecules were trapped in the pore of the hexagonal molecular assembly.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.130-130
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• 2012

Axial bindings of diatomic molecules to metalloporphyrins involve in the dynamic processes of biological functions such as respiration, neurotransmission, and photosynthesis. The binding reactions are also useful in sensor applications and in control of molecular spins in metalloporphyrins for spintronic applications. Here, we present the binding structures of diatomic molecules to surface- supported Co-porphyrins studied using scanning tunneling microscopy. Upon gasexposure, three-lobed structures of Co-porphyrins transformed to bright ring shapes on Au(111), whereas H2-porphyrins of dark rings remained intact. The bright rings are explained by the structures of reaction complexes where a diatomic ligand, tilted away from the axis normal to the porphyrin plane, is under precession. Our results are consistent with previous bulk experiments using X-ray diffraction and nuclear magnetic resonance spectroscopy.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.460-460
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• 2013

본 연구는 Si (111) 기판위에 Ga 분자선량을 변화시켜 GaN 박막을 molecular beam epitaxy 법으로 성장하고, Schottky 장벽 다이오드를 제작한 후에 deep level transient spectroscopy (DLTS) 법을 통하여 깊은 준위 결함에 대하여 조사하였다. 성장 시 Ga 분자선량은, 그리고 Torr로 달리하여 V/III 비율을 변화시켰고, Schottky 장벽 다이오드 제작을 위하여 e-beam evaporator를 사용하여 metal을 증착하였다. Schottky 접촉에는 Ni (20 nm)/Au (100 nm)를 증착하였고, ohmic 접촉에는 Ti (20 nm)/Au (100 nm)를 증착하고 I-V, C-V 그리고 DLTS를 측정하였다. DLTS 신호를 통해 GaN 박막 성장 과정에서 형성되는 깊은 결함의 종류를 확인하였으며, 열처리 등의 처리 및 측정 조건변화에 따른 결함의 거동과 종류 및 원인에 대하여 분석 설명하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.389-389
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• 2010

우리 연구그룹에서는 분자 소자에서의 소자 구조와 전도도 간의 상관관계를 알아보기 위해서 분자동역학 전산모사와 전자밀도범함수이론 계산 및 전하수송성 계산을 자동으로 수행할 수 있는 소프트웨어를 개발하고 이를 적용해 다양한 나노소자를 연구하고 있다. 본 발표에서는 hexanedithiolate 단일 분자가 Au(111) 전극 사이에서 다양한 S-Au 접점 구조를 가지고 구성된 소자 모델에서 열적 진동이 소자 전도도에 끼치는 효과를 통계적으로 분석하여 단분자 소자 실험에서 제기된 여러 개의 conductance peak의 측정에 대한 논란에 대해 이론적인 규명을 시도할 것이다.