• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.209.2-209.2
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• 2015

Two dimensional layered materials, such as transition metal dichalcogenides (TMDs) family have been attracted significant attention due to novel physical and chemical properties. Among them, molybdenum disulfide ($MoS_2$) has novel physical phenomena such as absence of dangling bonds, lack of inversion symmetry, valley degrees of freedom. Previous studies have shown that the interface of metal/$MoS_2$ contacts significantly affects device performance due to presence of a scalable Schottky barrier height at their interface, resulting voltage drops and restricting carrier injection. In this study, we report a new device structure by using few-layer graphene as the bottom interconnections, in order to offer Schottky barrier free contact to bi-layer $MoS_2$. The fabrication of process start with mechanically exfoliates bulk graphite that served as the source/drain electrodes. The semiconducting $MoS_2$ flake was deposited onto a $SiO_2$ (280 nm-thick)/Si substrate in which graphene electrodes were pre-deposited. To evaluate the barrier height of contact, we employed thermionic-emission theory to describe our experimental findings. We demonstrate that, the Schottky barrier height dramatically decreases from 300 to 0 meV as function of gate voltages, and further becomes negative values. Our findings suggested that, few-layer graphene could be able to realize ohmic contact and to provide new opportunities in ohmic formations.

• Biotechnology and Bioprocess Engineering:BBE
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• v.10 no.3
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• pp.212-217
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• 2005

Desorption/ionization on silicon mass spectrometry (DIOS-MS) is a relatively new laser desorption/ionization technique for mass spectrometry without employing an organic matrix. This present study was carried to survey the experimental factors to improve the efficiency of DIOS-MS through electrochemical etching condition in structure and morphological properties of the porous silicon. The porous structure of silicon structure and its properties are crucial for the better performance of DIOS-MS and they can be controlled by the suitable selection of electrochemical conditions. The fabrication of porous silicon and ion signals on DIOS-MS were examined as a function of silicon orientation, etching time, etchant, current flux, irradiation, pore size, and pore depth. We have also examined the effect of pre- and post-etching conditions for their effect on DIOS-MS. Finally, we could optimize the electrochemical conditions for the efficient performance of DIOS-MS in the analysis of small molecule such as amino acid, drug and peptides without any unknown noise or fragmentation.

• Progress in Superconductivity
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• v.11 no.1
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• pp.42-46
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• 2009

With an aim of comparison, single grain Y-Ba-Cu-O (YBCO) bulk superconductors were fabricated using a liquid infiltration growth (LIG) process and a conventional melt growth (MTG) process with top seeding. The MTG process uses an $YBa_2Cu_3O_{7-x}$(Y123) powder as a precursor, while the LIG process uses $Y_2BaCuO_5(Y211)/Ba_3Cu_5O_8(Y035)$ pre-forms. The growth of a single Y123 domain on the top seed was successful in the both processes. Different feature between the two processes is the interior microstructure regarding the critical current density ($J_c$). The LIG-processed YBCO sample showed a lower porosity, more uniform distribution of Y211 particles and the enhanced Y211 refinement compared to the conventional MTG process. The $J_c$ improvement in the LIG process is attributed to the dispersion of finer Y211 particles as well as lower porosity within the Y123 superconducting matrix.

• Transactions of Materials Processing
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• v.24 no.4
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• pp.280-286
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• 2015

Hemming is used to connect two sheet metal components by folding the edge of an outer panel around an inner panel to create a smooth edge. The minimization of hemming defects is critical to the final quality of automobile products because hemming is one of the last operations during fabrication. Designing the hemmed part is not easy and is influenced by the geometry of the bent part. Therefore, the main problem for automotive parts is dimensional accuracy since formed products often deviate geometrically due to large springback. Few numerical approaches using 3-dimensional finite element model have been applied to hemming due to the small element size which is needed to properly capture the bending behavior of the sheet around small die corner and the comparatively big size of automotive opening parts, such as doors, hoods and deck lids. The current study concentrates on the 3-dimensional numerical simulation of hemming for an automotive door. The relationship between the design parameters of the hemming operation and the height difference defect is shown. Quality improvement of the automotive door can be increased through the study of model parameters.

• Macromolecular Research
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• v.15 no.1
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• pp.51-58
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• 2007

The approach studied in the present work produced an exfoliated state of clay layers via confinement of the charged nano-sized polystyrene (PS) beads within the gallery of swollen pristine clay. It was demonstrated that adsorption of the polymer nanobeads dramatically promotes expansion of the clay gallery. A comparative study of incorporation was conducted by employing organo-modified clay along with two different colloid polymer systems: electrostatically stabilized PS nanobeads and cationic monomer-grafted PS nanobeads. The mechanism of adsorption of the monomer-grafted polymer beads onto clay via cationic exchange between the alkyl ammonium group of the polymer nanobeads and the interlayer sodium cation of the layered silicate was verified by using several techniques. As distinct from the polymer nanobeads formed using conventional miniemulsion polymerization method, competitive adsorption of stabilizing surfactant molecules was be prevented by grafting the surface functional groups into the polymer chain, thereby supporting the observed effective adsorption of the polymer beads. The presence of surface functional groups that support the establishment of strong polymer-clay interactions was suggested to improve the compatibility of the clay with the polymer matrix and eventually play a crucial role in the performance of the final nanocomposites.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.53-53
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• 2003

There has been increasing interest in the fabrication of nano-sized structures because of their various advantages and applications. Anodic Aluminum Oxide (AAO) is one of the most successful methods to obtain highly ordered nano pores and channels. Also It can be obtained diverse pore diameter, density and depth through the control of anodization condition. The three types of substrates were used for anodization; sheets of Aluminum on Si wafer and Aluminum on Mo-coated Si wafer. In Aluminum sheet, a highly ordered array of nanoholes was formed by the two step anodization in 0.3M oxalic acid solutions at 10$^{\circ}C$ After the anodization, the remained aluminum was removed in a saturated HgCl$_2$ solution. Subsequently, the barrier layer at the pore bottom was opened by chemical etching in phosphoric acid. Finally, we can obtain the through-channel membrane. In these processes, the effect of various parameters such as anodizing voltage, anodizing time, pore widening time and pre-heat treatment are characterized by FE-SEM (HITACH-4700). The pore size. density and growth rate of membrane are depended on the anodizing voltage and temperature respectively. The pore size is proportional to applied voltage and pore widening time The pore density can be controlled by anodizing temperature and voltage.

• Journal of the Korean Society of Safety
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• v.30 no.3
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• pp.107-113
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• 2015

The goal of this paper is to investigate structural integrity factors of RMI(reflective metal insulation) to confirm the design requirements in nuclear power plant. Currently, a glass wool insulation is using now, but it will gradually be replaced with the reflective metal insulation maded by stainless steel plates. The main function of an insulation is to minimize a heat loss of vessel and pipes in RCS(reactor coolant system). It has to maintain structural a integrity in nuclear power plant life duration. In this study, the structural integrity analysis was carried out both multi-plate and outer shell plate by using a static analysis and experimental test. First, inner multi-plate has a self support structure for being air space. Because the effect of total static weight in multi-layer plate is low, a plate collapse possibility is not high. Considering optimum thin plate pressing process, it has to pre-check the basic physical properties. Second, the outer segment thickness and stiffener shape are verified by the numerical static analysis, and sample test for both type of panel and cylindrical pipe model.

• Progress in Superconductivity
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• v.13 no.2
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• pp.122-126
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• 2011

Superconducting $MgB_2$ thin films were fabricated by using a novel aerosol deposition technique wherein the pre-reacted powder is directly transformed into respective thin film. The formed thin films were characterized by X-ray diffraction technique and FE-SEM to understand its structure and morphology and the superconducting behavior has been characterized with the four probe resistivity measurement. The as-deposited thin films were formed into the frustrated amorphous structure, which were relaxed on the further heat treatment at $900^{\circ}C$ for 3 hrs. The relaxed amorphous $MgB_2$ thin films showed a comparatively high superconducting onset at about 38 K.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1265-1270
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• 2007

Conventional methods for fabricating three-dimensional (3-D) scaffolds have substantial limitations. In this paper, we present 3-D scaffolds that can be made repeatedly with the same dimensions using a microstereolithography system. This system allows the fabrication of a pre-designed internal structure, such as pore size and porosity, by stacking photopolymerized materials. The scaffolds must be manufactured in a material that is biocompatible and biodegradable. In this regard, we synthesized liquid photocurable biodegradable TMC/TMP, followed by acrylation at terminal ends. And also, solidification properties of TMC/TMP polymer are to be obtained through experiments. Cell adhesion to scaffolds significantly affects tissue regeneration. As a typical example, we seeded chondrocytes on two types of 3-D scaffold and compared the adhesion results. Based on these results, the scaffold geometry is one of the most important factors in chondrocyte adhesion. These 3-D scaffolds could be key factors for studying cell behavior in complex environments and eventually lead to the optimum design of scaffolds for the regeneration of various tissues, such as cartilage and bone.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.315-318
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• 1999

Bi$_{2}Sr_{2}CaCu_{2}O_{\delta}$ superconducting films were rapidly fabricated on copper tape by liquid reaction between a Cu-free precursor and Cu tape (LiReac-PreCu) method. Those thick films were well oriented along the c-axis. The precursor was made by melt-quenched technology using twin roller. The melt-quenched films were transparent and glossy yellow in appearance. These films which were the compostion of Bi$_2SrCaO_y$, Bi$_3Sr_2CaO_z$ were placed on copper tape and then heated at various temperatures for several minutes in air. They were analyzed using X-ray powder diffraction, SEM, a DC four-probe method. The mechanism of superconducting phase formation . from the melt-quenched precursor on Cu tape was studied