• Journal of Adhesion and Interface
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• v.21 no.3
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• pp.107-112
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• 2020

Recently, the atomically thin transition-metal dichalcogenide (TMD) semiconductors have attracted much attention owing to their remarkable properties such as tunable bandgap with high carrier mobility, flexibility, transparency, etc. However, because these TMD materials have a significant drawback that they are easily degraded in an ambient environment, various attempts have been made to improve chemical stability. In this research article, I report a method to improve the air stability of WSe₂ one of the TMD materials via surface passivation with an h-BN insulator, and its application to field-effect transistors (FETs). With a modified hot pick-up transfer technique, a vertical heterostructure of h-BN/WSe₂ was successfully made, and then the structure was used to fabricate the top-gate bottom-contact FETs. The fabricated WSe₂-based FET exhibited not only excellent air stability, but also high hole mobility of 150 ㎠/Vs at room temperature, on/off current ratios up to 3×10⁶, and 192 mV/decade of subthreshold swing.

• Journal of the korean academy of Pediatric Dentistry
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• v.42 no.1
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• pp.53-61
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• 2015

This study was conducted for the purpose of evaluating the stainless steel crowns on extracted primary molars and thus identifying frequent errors and defects. Visual assessment and micro-computed tomography (micro-CT) image analysis were performed on 97 primary molars for evaluation of the state of marginal adaptation, cement loss, secondary caries, ledge formation, attritive perforation and marginal polishing defect. The results were as follows: In the examination of object teeth by evaluation criteria, cement loss was found most frequently (98%), followed by secondary caries (42.3%), marginal polishing defect (41.2%), ledge formation (29.9%) and attritive perforation (17.5%), in this order. The cement loss at the margins showed a significant relationship with marginal gap and secondary caries: the larger the marginal gap is, the more frequent is the cement loss (p < 0.05). The average marginal gap was $0.31{\pm}0.26mm$ and showed the highest value in the maxillary 2nd primary molars. The location of the crown margin above the cementoenamel junction was found most frequently and it was found that the higher the crown margin is located, the less the marginal gap becomes (p < 0.05). In conclusion, it is thought very desirable to pay closer attention to crown margins and shapes for stainless steel crown restoration in order to minimize the marginal gaps and consequent cement loss.

• Journal of Adhesion and Interface
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• v.14 no.2
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• pp.82-87
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• 2013

Preliminary studies on the synthesis of magnetic nanoparticles including nanoporous carbon materials have been done via a direct carbonization process from resol, ferric nitrate and triblock copolymer F127. The results show that the nanoporous magnetite/carbon ($Fe_3O_4$/carbon) with a low $Fe_3O_4$ content (1 wt%) possesses an ordered 2-D hexagonal (p6mm) structure, uniform nanopores (3.6 nm), high surface areas (up to 635 $m^2/g$) and pore volumes (up to 0.48 $cm^3/g$). Magnetite nanoparticles with a small particle size (10.2 nm) were confined in the matrix of amorphous carbon frameworks with superparamagnetic property (7.7 emu/g). The nanoporous magnetite/carbon showed maximum adsorption amount (995 mg/g) of ibuprofen after 24 h at room temperature. The nanoporous magnetite/carbon was separated from solution easily by using a magnet. The nanoporous magnetite/carbon material is a good adsorbent for hydrophobic organic drug molecules, i.e. ibuprofen.

• Journal of Adhesion and Interface
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• v.15 no.2
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• pp.63-68
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• 2014

Hollow mesoporous carbon nitride material with sphere shape was synthesized using polystyrene sphere as template and cyanamide as nitrogen and carbon atom sources via thermal treatment process. The process of the silica removal is not necessary because silica as template is not in use for the synthesis of hollow mesoporous carbon nitride material and any solvents are also not in use. The size of polystyrene spheres was about 170 nm. Hollow diameter and wall thickness were 82 nm and 13 nm, respectively, in hollow mesoporous carbon nitride sphere. Surface area, mesopore size and pore volume of hollow mesoporous carbon nitride material was $188m^2g^{-1}$, 3.8 nm and $0.35cm^3g^{-1}$, respectively. The wall in hollow sphere has graphitic structure. Hollow mesoporous carbon nitride material has potential applications in the area of fuel cell, catalysis, photocatalysis, electroemmision device, etc.

• Journal of Adhesion and Interface
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• v.22 no.4
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• pp.153-157
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• 2021

Graphene, a two-dimensional carbon allotrope, has outstanding mechanical and electrical properties. In particular, the charge carrier mobility of graphene is known to be about 100 times higher than that of silicon, and it has received attention as a core material for next-generation electronic devices. However, graphene is very sensitive to environmental conditions, especially vulnerable to moisture or oxygen. It becomes a disadvantage in that the stability of the graphene-based electronic device, so various attempts are being made to solve this problem. In this work, we report a method to greatly improve the stability by controlling the surface energy of the polymer layer used for transferring the insulating layer of the graphene field-effect transistor. As the surface energy of the polymer used as the insulating layer was lowered, the stability could be improved by effectively controlling the adsorption of impurities in the atmosphere such as water molecules or oxygen.

• Journal of Adhesion and Interface
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• v.23 no.3
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• pp.75-79
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• 2022

Graphene is a two-dimensional carbon allotrope composed of honeycomb sp² hybrid orbital bonds. It shows excellent electrical and mechanical properties and has been spotlighted as a core material for next-generation electronic devices. However, it exhibits low environmental stability due to the easy penetration or adsorption of external impurities from the formation of an unstable interface between the materials in the electronic devices. Therefore, this work aims to improve and investigate the low environmental stability of graphene-based field-effect transistors through direct growth using solid hydrocarbons as a precursor of graphene. Graphene synthesized from direct growth shows high electrical stability through reduction of change in charge mobility and Dirac voltage. Through this, a new approach to utilize graphene as a core material for next-generation electronic devices is presented.

• Journal of Adhesion and Interface
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• v.24 no.2
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• pp.60-63
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• 2023

The AlGaN/GaN heterostructure has high electron mobility due to the two-dimensional electron gas (2-DEG) layer, and has the characteristic of high breakdown voltage at high temperature due to its wide bandgap, making it a promising candidate for high-power and high-frequency electronic devices. Despite these advantages, there are factors that affect the reliability of various device properties such as current collapse. To address this issue, this paper used metal-organic chemical vapor deposition to continuously deposit AlGaN/GaN heterostructure and SiN passivation layer. Material and electrical properties of GaN HEMTs with/without SiN cap layer were analyzed, and based on the results, low-frequency noise characteristics of GaN HEMTs were measured to analyze the conduction mechanism model and the cause of defects within the channel.

• The Korean Journal of Zoology
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• v.39 no.4
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• pp.410-418
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• 1996

Gangilosides are ubiquitous membrane components in mammalian cells and are suggested to play essential roles in cellular phenomena such as cell-cell interadion, differentiation, and signal transduction. Rat ovary contained GM3 as major gangiloside. Nn order to study GM3 distribution in the atretic follicles and its possible changes during follicular development, frozen sections were stained with spedfic monocional antibodies against eleven gangilo-series gangliosides including GM3. In the atretic follicles, Glf3 was expressed in a spatlo-temporally different manner during foilicular development, but GM1 and other gangliosides were not immunohistochemicaily detected. in atretic follicle from primary follicle stage, GM3 was expressed in all the theca cells and some granulosa cells adjacent to oocyte. In atretic follicle from secondary follicle stage, GM3 were expressed in all theca cells and granulosa cells. in atretic follicles from developing Graaflan follicle stages, GM3 was similarly expressed as in secondary follicle stage.

• Economic and Environmental Geology
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• v.35 no.4
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• pp.355-368
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• 2002

The multi-storied Daewonsa stone pagoda (Treasure No. 1112) in the Sancheong, Korea was studied on the basis of deterioration and geological safety diagnosis. The stone pagoda is composed mainly of granitic gneiss, partly fine-grained granitic gneiss, leucocratic gneiss, biotite granite and ceramics. Each rock of the pagoda is highly exfoliated and fractured along the edges. Some fractures in the main body and roof stones are treated by cement mortar. This pagoda is strongly covered with yellowish to reddish brown tarnish due to the amorphous precipitates of iron hydroxides. Dark grey crust by manganese hydroxides occur Partly, and some Part coated with white grey gypsum and calcite aggregates from the reaction of cement mortar and rain. As the main body, roof and upper part of the pagoda, the rocks are developed into the radial and linear cracks. Surface of this pagoda shows partly yellowish brown, blue and green patchs because of contamination by algae, lichen, moss and bracken. Besides, wall-rocks of the Daewonsa temple and rock aggregates in the Daewonsa valley are changed reddish brown color with the same as those of the pagoda color. It suggests that the rocks around the Daewonsa temple are highly in iron and manganese concentrations compared with the normal granitic gneiss which color change is natural phenomena owing to the oxidation reaction by rain or surface water with rocks. Therefore, for the attenuation of secondary contamination, whitening and reddishness, the possible conservation treatments are needed. Consisting rocks of the pagoda would be epoxy to reinforce the fracture systems for the structural stability on the basements.

• Journal of Adhesion and Interface
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• v.18 no.2
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• pp.75-81
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• 2017

In this study, we synthesized mesoporous carbon (Carbonized Ni-FDU-15) containing nanoporous structures and magnetic nanoparticles. Carbonized Ni-FDU-15 was synthesized via evaporation-induced self-assembly (EISA) and direct carbonization by using a triblock copolymer (F127) as a structure-directing agent, a resol precursor as a carbon-pore wall forming material, and nickel (II) nitrate as a metal ion source. The mesoporous carbon has a well-ordered two-dimensional hexagonal structure. Meanwhile, nickel (Ni) metal and nickel oxide (NiO) were produced in the magnetic nanoparticles in the pore wall. The size of the nanoparticles was about 37 nm. The surface area, pore size and pore volume of Carbonized Ni-FDU-15 were $558m^2g^{-1}$, $22.5{\AA}$ and $0.5cm^3g^{-1}$, respectively. Carbonized Ni-FDU-15 was found to move in the direction of magnetic force when magnetic force was externally applied. The magnetic nanoparticle-bearing mesoporous carbons are expected to have high applicability in a wide variety of applications such as adsorption/separation, magnetic storage media, ferrofluid, magnetic resonance imaging (MRI) and drug targeting, etc.