• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.211-211
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• 2011

Nanostructures, with a diversity of shapes, built on substrates have been developed within many research areas. Lithography is one powerful, but complex, technique to make structures at the nanometer scale, such as platinum nanowires for studying CO catalytic reactions [1], or aluminum nanodisks for studying the plasmon effect [2]. In this work, we approach a facile method to construct nanostructures using noble metals on a titania thin film by using self-assembled structures as a pattern. Here, a large-scale silica monolayer is transferred to the titania thin film substrates using a Langmuir-Blodgett trough, followed by the deposition of a thin transition metal layer. Owing to the hexagonal close-packed structure of the silica monolayer, we would obtain a metal nanostructure that includes separated metallic triangles (islands) after removing the patterning silica beads. This nanostructure can be employed to investigate the role of metal-oxide interfaces in CO catalytic reactions by changing the patterning silica particles with different sizes or by replacing the oxide support. The morphology and chemical composition of the structure can be characterized by scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. In addition, we modify these islands to a connected island structure by reducing the silica size of the patterning monolayer, which is utilized to generating hot electron flow based on the localized surface plasmon resonance effect of the metal nanostructures.

• Smart Structures and Systems
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• v.24 no.6
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• pp.783-791
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• 2019

Prefabricated reinforced-concrete shear walls are used extensively in building structures because they are convenient to construct and environmentally sustainable. To make large walls easier to transport, they are divided into smaller segments and then assembled at the construction site using a variety of connection methods. The present paper proposes a precast shear wall assembled using steel shear keys, wherein the shear keys are fixed on the embedded steel plates of adjacent wall segments by combined plug and fillet welding. The anchoring strength of shear keys is known to affect the mechanical properties of the wall segments. Loading tests were therefore performed to observe the behavior of precast shear wall specimens with different anchoring components for shear keys. The specimen with insufficient strength of anchoring components was found to have reduced stiffness and lateral resistance. Conversely, an extremely high anchoring strength led to a short-column effect at the base of the wall segments and low deformation ability. Finally, for practical engineering purposes, a design approach involving the safety coefficient of anchoring components for steel shear keys is suggested.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.9
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• pp.1270-1275
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• 2004

Standard positive photoresist techniques were adapted to generate nano-scale patterns of gold substrate using self-assembled monolayers (SAMs) and femtosecond laser. SAMs formed by the adsorption of alkanethiols onto gold substrate are employed as very thin photoresists, Alkanethiolates formed by the adsorption of alkanethiols are oxidized on exposure to UV light in the presence of air to alkylsulfonates. Specifically, it is known that deep UV light of wavelength less than 200nm is necessary for oxidation to occur. In this study, ultrafast laser of wavelength 800nm and pulse width 200fs is applied for photolithography. Results show that ultrafast laser of visible range wavelength can replace deep UV laser source for photo patterning using thin organic films. Femtosecond laser coupled near-field scanning optical microscopy facilitates not only the patterning of surface chemical structure, but also the creation of three-dimensional nano-scale structures by combination with suitable etching methods.

• KIEE International Transactions on Electrophysics and Applications
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• v.5C no.3
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• pp.115-118
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• 2005

Currently, molecular devices are reported utilizing active self-assembled monolayers (SAMs) containing the nitro group as the active component, which has active redox centers [1]. SAMs are ordered molecular structures formed by the adsorption of an active surfactant on a solid surface. The molecules will be spontaneously oriented toward the substrate surface and form an energetically favorable ordered layer. During this process, the surface-active head group of the molecule chemically reacts with and chemisorbs onto the substrate In this paper, the electrical properties of the 4'4- di(ethynylphenyl)-2'-nitro-1-benzenethiolate was confirmed. This material is well known as a conducting molecule having possible application to molecular level negative differential resistance (NDR) device. To deposit the self-assembly monolayers onto the gold electrode, the prefabricated Au(1 l l) substrates were immersed into 0.5[mM/l] self-assembly molecule in THF solution. Then, the electrical properties and surface morphologies of 4' 4-di(ethynylphenyl)-2' -nitro-1-benzenethiolate were measured by using the ultra-high vacuum scanning tunneling microscopy (UHV-STM).

• 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.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.326-329
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• 2005

As a flexible method to fabricate sub-micrometer patterns, Focused Ion Beam (FIB) instrument and Self-Assembled Monolayer (SAM) resist are introduced in this work. FIB instrument is known to be a very precise processing machine that is able to fabricate micro-scale structures or patterns, and SAM is known as a good etch resistance resist material. If SAM is applied as a resist in FIB processing fur fabricating nano-scale patterns, there will be much benefit. For instance, low energy ion beam is only needed for machining SAM material selectively, since ultra thin SAM is very sensitive to $Ga^+$ ion beam irradiation. Also, minimized beam spot radius (sub-tens nanometer) can be applied to FIB processing. With the ultimate goal of optimizing nano-scale pattern fabrication process, interaction between SAM coated specimen and $Ga^+$ ion dose during FIB processing was observed. From the experimental results, adequate ion dose for machining SAM material was identified.

• Steel and Composite Structures
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• v.39 no.2
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• pp.201-213
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• 2021

Currently, there is a lack of research in the design approach to avoid column wall failure in the concrete filled double skin steel tubular (CFDST) column-beam connections. In this paper, a finite element model has been developed and verified by available experimental data to analyze the failure mechanism of CFDST column-beam connections. Various finite element models with different column hollow ratios (χ) were established. The simulation result revealed that with increasing χ the failure mode gradually changed from yielding of end plate, to local failure of the column wall. Detailed parametric analyses were performed to study the failure mechanism of column wall for the CFDST column-beam connection, in which the strength of sandwiched concrete and steel tube and thickness of steel tube were incorporated. An analytical model was proposed to predict the moment resistance of the assembled connection considering the failure of column wall. The simulation results indicate that the proposed analytical model can provided a conservative prediction of the moment resistance. Finally, an upper bound value of χ was recommend to avoid column wall failure for CFDST column-beam connections.

• International conference on construction engineering and project management
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• 2022.06a
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• pp.1252-1252
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• 2022

Temporary work that utilizes temporary equipment (e.g., system scaffold and system pipe support) in construction work is one of the most vulnerable work from a safety perspective in South Korea. Typically, temporary equipment is reused at construction sites. The Korea Occupational Safety and Health Agency announced guidelines regarding the performance standards for reusable temporary equipment to prevent the accidental collapse of temporary facilities. Nevertheless, temporary facilities' collapse still occurs, which could be attributed to a degradation in the performance due to the reuse of temporary equipment. Therefore, this study investigated the performance of simple temporary structures assembled with new and reused equipment. To this end, an experimental module was designed based on previous research cases, and two experimental models were constructed, in which one was assembled using new equipment (Model A), and the other was built using reused equipment (Model B). To determine the performance of each model, a load test was conducted to measure the maximum load that each model could withstand. The experimental results revealed that the maximum load of Model B was 15% lower than that of Model A. This indicates that there is a meaningful performance difference between those two models. Based on this result, the authors decided to perform additional tests with more realistic models than previous ones. The new experimental module was designed to ensure compliance with the Korean design guidelines. In this presentation, the authors show details of the first tests and their results and plan for the additional test.

• Korean Journal of Construction Engineering and Management
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• v.23 no.5
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• pp.43-55
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• 2022

Since assembled temporary equipment is widely used for construction work that should be carried out before this construction begins, it is essential to secure quality during assembly and prevent safety accidents caused by assembled temporary equipment after installation. However, it was investigated that most construction site managers are not aware of its importance, such as recognizing the quality management of assembled temporary equipment as a task of managing temporary structures that are dismantled after installation for this construction. The quality management work of assembled temporary equipment at the construction site is carried out in different ways for each construction site because there is no formalized procedure and the subject of performing. In addition, it is analyzed that the manager of the general construction company inspects and reflects the parts that need to be inspected without evidence, so transparency is not guaranteed and the result leads to a serious disaster. Therefore, the purpose of this study is to establish a document preparation-oriented system that provides systematic quality evaluation and management procedures for securing the quality of assembled temporary equipment, develops a checklist for quality evaluation and management, and supports history management on the web.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.22-22
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• 2003

Studies on the optical properties related to the built-in internal field and the carrier localization present in various GaN-based structures are essential not only for the physical interest but in designing practical visible and ultraviolet light emitting device applications with better performance and quantum efficiency. We report on the optical characteristics of various dimensional GaN-based structures such as (i) GaN self-assembled quantum dots grown in Stranski-Krastanov mode (OD), vertically-aligned GaN nanorods (1D), graded-In-content InGaN quantum wells (2D), laterally-overgrown GaN pyramids (3D), and GaN epilayers grown on various substrates. We used a wide variety of optical techniques, such as photoluminescence (PL), PL excitation, micro-PL, cathodoluminescence, optically-pumped stimulated emission, and time-resolved PL spectroscopy. An overview and comparison of the optical characteristics of the above GaN-based structures will be given.